DESIGN PRACTICES

ExxonMobil Proprietary

AIR POLLUTION CONTROL Section Page

GUIDELINES FOR SELECTION OF XVIII-A 1 of 27

DESIGN PRACTICES AIR POLLUTION CONTROL EQUIPMENT December, 2000

ExxonMobil Research and Engineering Company � Fairfax, VA

CONTENTSSection Page

SCOPE ............................................................................................................................................................3

REFERENCES ................................................................................................................................................3

DEFINITIONS ..................................................................................................................................................4

BACKGROUND ..............................................................................................................................................5

AIR POLLUTANTS OF INTEREST.........................................................................................................5

SOURCES OF AIR POLLUTION ............................................................................................................6

EFFECTS OF AIR POLLUTANTS ..........................................................................................................6

AIR POLLUTION REGULATIONS ..........................................................................................................8

STEPS IN SELECTING CONTROL SYSTEMS ..............................................................................................8

EMISSIONS INVENTORIES ...........................................................................................................................9

REASONS FOR CONDUCTING AN EMISSIONS INVENTORY ............................................................9

INVENTORY FOCUS..............................................................................................................................9

CONDUCTING AN EMISSIONS INVENTORY - OVERVIEW...............................................................10

PREPARING FOR AN INVENTORY - METHODOLOGY SELECTION ................................................10

PREPARING FOR AN INVENTORY - DATA COLLECTION ................................................................10

ESTIMATING EMISSIONS ...................................................................................................................11

IMPACT ANALYSIS / AIR DISPERSION MODELING .................................................................................11

MODEL SELECTION ............................................................................................................................12

DATA REQUIREMENTS.......................................................................................................................12

HYDROCARBON, VOC, AND AIR TOXICS EMISSIONS CONTROL..........................................................13

CONTROLLING FUGITIVE EMISSIONS..............................................................................................15

CONTROLLING TANK EMISSIONS.....................................................................................................15

CONTROLLING LOADING EMISSIONS ..............................................................................................16

CONTROLLING WASTEWATER TREATING AIR EMISSIONS...........................................................16

COMBUSTION EMISSIONS CONTROL.......................................................................................................16

CONTROL OF NOX EMISSIONS FROM FUEL BURNING EQUIPMENT............................................17NOx Control for Fired Heaters and Boilers.........................................................................................17NOx Control for Gas Turbines............................................................................................................18Control of NOx Emissions for Stationary Internal Combustion Engines .............................................19NOx Control for Process Combustors ................................................................................................20

CONTROL OF SOx EMISSIONS FROM FUEL BURNING EQUIPMENT ............................................20Control of SOx Emissions From Fired Heaters and Boilers................................................................20Control of SOx Emissions From Process Combustors .......................................................................20

CONTROL OF PARTICULATE EMISSIONS FROM FUEL BURNING EQUIPMENT...........................21

Changes shown by ➧


Section Page AIR POLLUTION CONTROL

XVIII-A 2 of 27 GUIDELINES FOR SELECTION OFDecember, 2000 AIR POLLUTION CONTROL EQUIPMENT DESIGN PRACTICES


CONTENTS (Cont)Section Page

AIR PERMITTING ......................................................................................................................................... 23

THE PERMIT APPLICATION ............................................................................................................... 23

COST ANALYSIS OF CONTROL OPTIONS................................................................................................ 26

TOTAL COST INVESTMENT ............................................................................................................... 26

AVERAGE COST EFFECTIVENESS ................................................................................................... 27

INCREMENTAL COST EFFECTIVENESS........................................................................................... 27

TABLESTable 1 Related Air Pollution Control DP Sections ............................................................................... 3Table 2 Air Pollutants of Interest to Refineries and Chemical Plants .................................................... 5Table 3 Approximate Relative Emissions of Anthropogenic Pollutant Source Types in the

United States, 1998 (From US EPA Annual Emission Report, Ref. 5) ..................................... 7Table 4 Steps in Selecting Air Pollution Control Systems ..................................................................... 9Table 5 Major Sources of Hydrocarbons to the Air from Process Plants............................................. 13Table 6 Control Options for Hydrocarbon and Air Toxics Emissions................................................... 14Table 7 Relative Distribution of Combustion Emissions to the Air from a Complex Refinery Without

Emission Controls .................................................................................................................. 17Table 8 Controls for NOx Emissions from Fired Heaters and Boilers.................................................. 18Table 9 Controls for NOx Emissions from Gas Turbines..................................................................... 18Table 10 Controls for NOx Emissions for Stationary IC Engines .......................................................... 19Table 11 Controls for SOx Emissions from Fired Heaters and Boilers.................................................. 20Table 12 Controls for SOx Emissions from FCCU Regenerators.......................................................... 20Table 13 Controls for Particulate Emissions ......................................................................................... 21Table 14 Advantages and Disadvantages of Control Equipment for Particulate Emissions.................. 22

Revision Memo

12/00 Design Practices format updated to Word document. Table of Contents expandedto include additional subsections and tables.Minor editorial revisions completed. References updated. Control of particulateemissions section expanded.






SCOPE

➧ This section of Design Practices discusses overall air pollution control technology and serves as an introduction to the otherDesign Practice sections on air pollution control. It provides background on sources of air pollution and the methodologiesused to achieve compliance with regulations.

For the topics of IMPACT ANALYSIS / AIR DISPERSION MODELING, HYDROCARBON AND AIR TOXICS EMISSIONSCONTROL, and COMBUSTION EMISSIONS CONTROL, this section introduces more detailed guidance contained inSections XVIII-A1 through A6, A8, and B1. Table 1 shows where to find more detailed information in the other Air PollutionControl DPs.

This introductory section also contains a description of the procedures for conducting an Emissions Inventory and for preparingan Air Permit application. Additional details on these two topics are available in the references or from the Air, Water &Solid/Hazardous Waste Section of ExxonMobil Engineering.

➧ TABLE 1RELATED AIR POLLUTION CONTROL DP SECTIONS

HYDROCARBONS ANDAIR TOXICS COMBUSTION EMISSIONS

IMPACT ANALYSIS / AIRDISPERSION MODELING INDUSTRIAL HYGIENE

• Fugitives: XVIII-A2

• Tanks: XVIII-A2

• Loading: XVIII-A2

• Wastewater: XVIII-A2

• Odors: XVIII-A2

• Exposure Limits: XVIII-B1

• Toxic Effects: XVIII-B1

• Cyclones: XVIII-A3

• Fabric Filters: XVIII-A4

• Wet Gas Scrubbers: XVIII-A5

• Electrostatic Precipitators: XVIII-A6

• Nitrogen Oxides: XVIII-A8

• Dispersion Modeling: XVIII-A1 • Guidelines: XVIII-B

• Exposure Limits: XVIII-B1

• Toxic Effects: XVIII-B1

➧ REFERENCES

1. Emission Estimating Guide, EMRE Technical Manual TMEE-046.

2. Compilation of Air Pollutant Emission Factors, AP-42, United States Environmental Protection Agency, Fifth Edition, 1995.

3. Godish, Thad, Air Quality, Lewis Publishers, 1991.

4. Buonicore, A. J., and Davis, W. T., Eds., Air Pollution Engineering Manual, Van Nostrand Reinhold, 1992.

5. National Air Pollutant Emissions Trends, 1900-1998. U.S. EPA and the States: Working Together for Cleaner Air, EPA-454/R-00-002, March 2000.

6. Rethinking the Ozone Problem in Urban and Regional Air Pollution, National Research Council, National Academy Press,1991.

7. Lipfert, Frederick W., Air Pollution and Community Health, Van Nostrand Reinhold, 1994.

8. Patrick, David R., Ed., Toxic Air Pollution Handbook, Van Nostrand Reinhold, 1994.

9. William, M., Estimating Costs of Air Pollution Control, Lewis Publishers, 1990.

10. EMRE Process Data and Economics Guide (PDEG), EEPD-0005.

11. New Source Review Workshop Manual, Prevention of Significant Deterioration and Nonattainment Area Permitting, (Draft),United States Environmental Protection Agency, 1990.





REFERENCES (Cont)

12. Protocol for Equipment Leak Emission Estimates, EPA 435-R-95-017, United States Environmental Protection Agency,November 1995.

13. ATMYS Study of Refinery Fugitive Emissions from Equipment Leaks, American Petroleum Institute Publication 4613, April1994.

14. ATMYS Development of Fugitive Emission Factors and Emission Profiles for Petroleum Marking Terminals, AmericanPetroleum Institute Publication 4588, May 1993.

15. Atmospheric Hydrocarbon Emissions from Marine Vessel Transfer Operations, American Petroleum Institute Publication2514A, Second Edition, September 1981.

16. Turner, D. B., Workbook of Atmospheric Dispersion Estimates, EPA Ref. AP-26 (NTIS PB191-482), United StatesEnvironmental Protection Agency, 1970.

17. Zanneti, P., Air Pollution Modeling, Theories, Computational Methods and Available Software, Van Nostrand, Reinhold,1990.

18. Screening Procedures for Estimating the Air Quality Impact of Stationary Sources, (Revised). EPA-454/R-92-019, UnitedStates Environmental Protection Agency, 1992.

19. Workbook of Screening Techniques for Assessing Impacts of Toxic Air Pollutants, EPA-450/R-92-024, United StatesEnvironmental Protection Agency, 1992.

20. Manual of Petroleum Measurement Standards, Chapter 19 - Evaporative Loss Measurement, Section 1 - Evaporative Lossfrom Fixed-Roof Tanks, American Petroleum Institute Publication 2518, Second Edition, October 1991.

21. Manual of Petroleum Measurement Standards, Chapter 19 - Evaporative Loss Measurement, Section 2 - Evaporative Lossfrom Floating-Roof Tanks, American Petroleum Institute, First Edition, April 1997.

22. EMRE Leak Detection and Repair (LDAR) Manual, TMEE 061.

DEFINITIONS

Air Pollutant - Any substance in ambient air that is present above its normally occurring standard concentration. This pollutantmay or may not be harmful and can include naturally occurring substances such as volcanic dust. Air pollutants generallyinclude the emissions from industrial and agricultural activities; from transportation sources such as cars, buses, trains andships; and from the treatment of human and animal wastes. Almost any human or animal activity, or any natural occurrence,can cause the generation of an air pollutant. Many regulatory agencies have developed lists of specific air pollutants, whichthey have the authority to control.

Ambient Air Quality - A measure of the concentration of a pollutant in air compared to a concentration limit, which may havean adverse effect on humans, animals, vegetation, materials, structures, visibility, or the quality of life. Many regulatoryagencies have developed concentration limits for specific air pollutants. These limits are often different for indoor and outdoorair as well as for worker and community exposure. There may also be more than one limit based on the adverse effect beingconsidered.

Anthropogenic Emissions - These are emissions of pollutant(s) from �man-made" sources or activities. They includeindustry, manufacturing, transportation, agriculture, waste treatment and all other sources that are not naturally occurring.

➧ Biogenic Emissions - These are emissions of pollutant(s) from natural sources. They include vegetation and volcanoes.

Dispersion - The transport and dilution of emissions due to natural atmospheric phenomena such as wind and turbulence.

Ozone (Tropospheric or Ground Level) - A substance, O3, that is a principal component of smog and can be formed in theatmosphere from the reaction of volatile organic compounds and nitrogen oxides in the presence of sunlight.

Primary Air Pollutant - An air pollutant that is in the same form as when it was released. The concentration of the pollutantwill be changed, but the chemical species of the pollutant is the same as when it was emitted. Sometimes referred to asnon-reactive pollutants.

Secondary Air Pollutant - An air pollutant that is present in a form other than when it was released. Secondary Air Pollutantsare formed in the atmosphere by the reaction of one or more Primary Air Pollutants.

Volatile Organic Compound (VOC) - Compounds containing carbon that react with nitrogen oxides in the presence of sunlightto form ozone.






BACKGROUND

Decisions on the design of air pollution control systems require information on plant emissions, comparison of these emissionsand resulting air concentrations to standards, and cost comparison of potential control alternatives. Emissions to the air fromrefineries and chemical plants include products of combustion, volatile organics, air toxics, and particulate matter. Anemissions inventory lists the types, quantities, and sources of air pollutants that are released. These emissions may becompared to regulatory limits or may be used in impact analysis modeling to predict community or worker exposure levels.Regulatory agencies may require some type of permit application, which describes the facility, its predicted emissions, and anycontrol equipment that will be employed. In most cases, there is a choice among alternative technologies or methods that canachieve emissions reduction. An economic analysis is recommended in order to identify the most cost effective emissionsreduction options.

It is often more cost effective to prevent an emission than to add control equipment to remove it. This is the focus of �pollutionprevention." Many controls tend to convert one pollutant to another (e.g., incineration of sulfur-containing waste streamsproduces SOx, NOx, CO2, etc.) or move the pollutant from one media to another (e.g., particulate scrubber). Pollutionprevention focuses on reducing or eliminating the need for the �add on," �end-of-pipe" control by modifying the process designor operation.

AIR POLLUTANTS OF INTEREST

Table 2 lists the principal Air Pollutants of interest to refineries and chemical plants as well as their potential emission sources.Process plants usually have many combustion units such as fired heaters and boilers that emit SOx, NOx, CO, CO2, andparticulates, as well as trace quantities of unburned fuel, metals, and other organic compounds.

Since refineries and chemical plants handle large quantities of volatile organic compounds, they will usually have emissions ofthese compounds. The largest sources of VOCs are valves, flanges, pumps, compressors and other �piping" components.VOC emissions also come from storage tanks, loading operations, and wastewater treating. VOCs and other air pollutants arealso of interest due to their potential to cause annoying odors in the communities surrounding process plants.

➧ The policy debate continues over concern that humans may need to limit emissions of greenhouse gasses, especially CO2,CH4, and N2O, to reduce the threat of climate change. The Framework Convention on Climate Change, which took effect in1995, requires nations to prepare and publish inventories of greenhouse gas emissions. The Kyoto Protocol, an internationaltreaty that has not entered into force, contains targets and timetables to restrict greenhouse gas emissions in developedcountries. The targets, that would take effect in the period 2008-2012, would require emissions reductions of approximately30% from projected levels in 2010. While the Protocol may not enter into force, most nations have implemented someprograms to limit emissions. These include voluntary agreements, energy efficiency standards, and taxes. The issue of publicpolicy on climate change will continue to evolve for decades.

➧ TABLE 2AIR POLLUTANTS OF INTEREST TO REFINERIES AND CHEMICAL PLANTS

AIR POLLUTANT EXAMPLE POTENTIAL EMISSION SOURCE

Sulfur Oxides SO2, SO3 Combustion

Nitrogen Oxides NO, NO2 Combustion

Carbon Oxides CO, CO2 Combustion

Particulates FCCU Catalyst Fines Combustion, construction, catalyst handling, landfarming, unpaved roads

Volatile Organic Compounds Hydrocarbons, Alcohols Equipment leaks (fugitives), tanks, loading, wastewatercollection and treating, relief/safety valves, combustion

Air Toxics Benzene, H2S

1,3 - Butadiene, Formaldehyde

Equipment leaks (fugitives), tanks, loading, wastewatercollection and treating, relief/safety valves, combustion

Ozone (ground level) O3 Formed in the atmosphere from the reaction of nitrogenoxides, volatile organic compounds, and sunlight

Metals Pb, Cr, As Combustion, Land farms, Catalyst fines

Chloroflorocarbons Freons Refrigeration, Fire-suppression systems

�Greenhouse" Gases CO2, CH4, N2O Combustion, equipment leaks, production operations





BACKGROUND (Cont)

SOURCES OF AIR POLLUTION

Air pollutants can generally be classified as either anthropogenic (�man-made") or biogenic (naturally occurring). In manylocations, the contribution from biogenic sources can be substantial. These natural sources include vegetation as an emitter ofVOCs and volcanoes as intermittent emitters of SO2 and particulates. In some areas of high ozone levels, VOC emissionsfrom natural vegetation have been found to be a major contributor to local air pollution.

Anthropogenic emissions come from industrial, manufacturing, transportation, and most other activities of man. The majorsources of regulated air pollutants are combustion sources, evaporation, leaks, spills, and vehicles. As previously mentioned,combustion processes are usually sources of sulfur oxides, nitrogen oxides, and particulates. Industrial facilities using organiccompounds are sources of emissions from evaporation as well as leaking equipment, spills, and venting. Many consumerproducts such as paints and polishes contain volatile organics that evaporate during use. Some local regulatory agencies haveeven identified sources as small as gasoline powered lawnmowers, boat engines, and motorcycles as significant emitters of airpollutants.

The two largest sources of air pollutants in many locations are power generation and transportation. The quantity of emissionsfrom power plants depends on the fuel type, with coal having the highest emissions, oil being lower, and gas being lower still.Combustion of oil or gas results in about 100 times less particulate emissions as compared to coal. While sulfur oxideemissions are usually much lower for oil (depending on the amount of sulfur in the fuel) as compared to coal, sulfur oxideemissions from gas-fired units is usually the lowest among the different fuels.

The air pollutants emitted from transportation include the products of combustion, and evaporative losses during use, fueling,and delivery and storage of the fuel. Due to the large number of these individual sources, as well as the potential effect on thelife style of the entire population, significant control of vehicular emissions has been difficult to achieve in many locations.Recent controls include more fuel efficient vehicles and changes in the composition of the fuels (e.g., lower volatility, removal oflead as an octane booster, decreases in the concentration of benzene, and reductions in fuel sulfur levels). A single, poorlyperforming automobile can contribute more emissions than many newer, well performing models.

Table 3 provides approximate relative emissions of various air pollutants by anthropogenic source types in the United States in1998 (Ref. 5). With the exception of volatile organic compounds, the petroleum and petrochemical industries are not asignificant source of air pollutants. In most cases the larger sources of SOx and NOx are utilities. CO emissions are primarilydue to mobile sources (cars, trucks, etc.). These percentages are likely to be different in other countries since they depend onthe extent of industrialization, the fuels used to generate electrical power, the climate, and the modes of transportation.

EFFECTS OF AIR POLLUTANTS

There are many potential effects from the exposure to air pollutants including those to humans, animals, vegetation, materials,structures, visibility, and the quality of life. This section contains a general description of the atmospheric, health, and othereffects from exposure. For a more detailed discussion on the specific health effects of air pollutants see Section XVIII-B1.The effects described here may occur where the ambient concentration of an air pollutant is above a specified concentration.In many cases, however, there is considerable controversy regarding the value of this concentration. For the latest acceptedexposure limits, contact your local Industrial Hygienist or ExxonMobil Biomedical Sciences in Clinton, N.J.

Atmospheric effects of air pollutants include visibility reduction, acid precipitation, stratospheric ozone depletion, and potentially,climate change. Reduced visibility is one of the most noticed effects of air pollution and is primarily due to the presence ofparticulates and aerosols. Sulfur oxides and nitrogen oxides react with moisture in the atmosphere and are converted intoacids, which can precipitate in the form of rain, snow, or mist. Chloroflorocarbons and certain other compounds (e.g., CCl4,CHCl3) are reported to decrease the protective stratospheric ozone layer.

➧ Basic understanding of the influence of air pollutants on atmospheric radiation suggests that the ongoing accumulation ofgreenhouse gases could lead to global warming and associated climate changes over the next century. Potential impacts of airpollutants include global warming; rising sea levels; changes in hydrology; shifts in the distribution of ecological systems,ranges of agricultural crops, pests and some diseases; changes in air quality; and changes in climate variability including thefrequency and intensity of severe storms and drought. The issue is controversial because uncertainty and ignorance aboutcritical aspects of the science and about future human behavior limit our ability to project both future emissions and theirimpacts through climate change. Much of what we project must be evaluated in large computational models. While thesemodels are the best tools available today to make forecasts, they are known to be incomplete and unconfirmed, and they arelikely to remain so for decades. Little understood natural climate variability complicates the problem of identifying a humaninduced component of climate change against a backdrop of significant natural climate variability.






BACKGROUND (Cont)

Health effects due to exposure to air pollutants above certain concentrations include irritation of the eyes, nose, throat, andskin, and respiratory and cardiovascular distress. Different effects may result from either short or long term exposures. Inaddition, certain segments of the population, such as smokers, are much more susceptible to the effects of ambient airpollutants.

Other effects of air pollutants are those on vegetation, animals, structures, and the effect of odors on the �quality of life." Inmost cases these effects have received much less attention than the health effects. Sulfur oxides and ozone have beenreported to cause significant injury to vegetation. Gaseous and particulate pollutants are known to effect metals, carbonatebuilding stones, paints, textiles, rubber, leather, and paper.

➧ TABLE 3APPROXIMATE RELATIVE EMISSIONS OF ANTHROPOGENIC POLLUTANT

SOURCE TYPES IN THE UNITED STATES, 1998(FROM US EPA ANNUAL EMISSION REPORT, REF. 5)

SOx85% Stationary Source Combustion (Utilities, Industrial/Residential Furnaces/Boilers)

8% Industrial Processes (Ore Processing, Petroleum/Chemicals, Paints, Agriculture)

7% Transportation (Cars, Trucks, Buses, Aircraft, Ships, Trains, Motorcycles)

NOx54% Transportation (Cars, Trucks, Buses, Aircraft, Ships, Trains, Motorcycles)

42% Stationary Source Combustion (Utilities, Industrial/Residential Furnaces/Boilers)


1% Other Combustion (Forest Fires, etc.)

CO





1% Solid Waste Disposal (Materials Handling, Incineration)

VOLATILE ORGANIC COMPOUNDS


30% Solvent Utilization (Degreasing, Graphic Arts, Dry Cleaning, Surface Coating)

8% Industrial Processes (Ore Processing, Agriculture, Petroleum/Chemicals, Paints)

7% Storage and Transport (Storage Tanks, Loading, Service Stations)




PARTICULATES (PM10)

85% Fugitive Dust (Unpaved Roads, Paved Roads, Construction)






PARTICULATES (PM2.5)

56% Fugitive Dust (Unpaved Roads, Paved Roads, Construction)










BACKGROUND (Cont)

AIR POLLUTION REGULATIONS

Regulations to control air pollution may require the application of specific control equipment or practices, limitations on theemission rates of specific chemicals, and/or the assessment of risk. It is important to determine which regulations apply in eachsituation before selecting any air pollution controls. Contact the plant environmental coordinator for the most recent applicableregulations.

Some regulatory agencies set a standard for the maximum allowable concentration of a pollutant in ambient air at ground level.This concentration is designed to be what most individuals may be exposed to without harm. An emission source will usuallybe required to apply controls such that it does not cause concentrations that exceed the regulatory standard. Comparison tothe standard can be determined using either ambient air monitoring or dispersion modeling. Monitoring to determine the impactof new facilities not yet built is clearly impossible. One of the difficulties with the modeling approach, however, is that there aremany sources that may need to be included in the analysis in order to accurately predict the resultant concentration.

Regulations that limit emission rates may be based on total flow or on the concentration of a particular species. Some areapplied to an entire plant (�bubble" approach) rather than to each individual emission source. Source testing may be requiredto demonstrate compliance with some regulations.

When specific equipment or practices are required, it is often possible to substitute options that result in an equivalent effect onthe quality of the ambient air. In most cases, these options include alternative equipment on a specific emission source or anearby source of the same pollutant. More recently, emissions trading between different companies and even differentpollutants has been utilized. Check with the local regulatory agency to determine if these alternatives are an option.

The most recent regulatory approach for controlling the emissions of air pollutants is risk assessment. In one type of thisanalysis, the total emissions of a plant are included and, using sophisticated population models, concentrations of manyspecies are compared to long term exposure limits. In another approach, various leak and/or spill scenarios are analyzed todetermine the potential effects on the surrounding communities in the event of a major, accidental release of toxic chemicals.

It is clear that many regulatory agencies intend to apply more stringent regulations to control air pollution than are currently inplace. These regulations tend to be copied from those locations where standards have already been applied. In this manner,requirements that may not always be the best technological solution to reducing air pollution are implemented. Early interactionwith local regulatory agencies is recommended in order to ensure that the most appropriate solutions to reducing air pollutionare considered.

STEPS IN SELECTING CONTROL SYSTEMS

Table 4 provides a step-by-step procedure for selecting air pollution control systems when emissions reductions are needed.Not all of these steps are required for all projects and only those that are applicable need be included. The first step is toidentify the need for applying the air pollution control equipment. This is done by identifying the applicable regulations that mayset limits on the emissions of specific pollutants by either rate or concentration. For new projects, it is important to considerfuture as well as current regulations so that the plant can continue to remain in compliance as the new regulations becomeeffective and are enforced. This may also serve as a good opportunity to review all regulations covering the plant air emissionsto ensure compliance.

In addition to meeting the applicable environmental regulations, a check should be made to ensure that potential exposurelevels for plant personnel are within allowable limits. In some cases there may be a need to apply more restrictive controls onemissions of potentially toxic materials.

To determine the need for air pollution control equipment, it is necessary to compare the current emissions to the regulatorylimits. In order to do this, an emissions inventory is required. An inventory lists all the individual sources of each air pollutant inthe plant and the quantity of the emissions. Various emissions estimating methods may be utilized and, in some cases,emissions measurements may be required. These results are then compared to the allowable emission limits and any requiredreductions are noted.

The results of the emissions inventory can be used in the next step, dispersion modeling, to predict the ground level ambientconcentration of the pollutants for the area surrounding the plant. There are often limits on the ambient concentration of eachpollutant in the local air, and this step will allow comparison of the predicted concentration to those limits and determine theneed for emissions controls to achieve compliance.

➧ The final step in selecting an air pollution control system is to identify the potential control options that may be used to comeinto compliance and to evaluate their cost. Cost effectiveness is a concept that regulators use. Project teams focus on capitalcost and, to a lesser extent, O&M costs.






STEPS IN SELECTING CONTROL SYSTEMS (Cont)

TABLE 4STEPS IN SELECTING AIR POLLUTION CONTROL SYSTEMS

STEP 1 Identify current and future applicable regulations which may limit emission rates and/or concentrations or specifyspecific control equipment. Include all air pollution regulations that may impact operations.

STEP 2 Determine the sources and emissions rates of each air pollutant using estimating methods or by actualmeasurements if appropriate. Include new, planned, and existing sources (also those outside the facility) whichmay have an impact on meeting regulatory or health limits. Determine potential exposure levels for plantpersonnel and the need for more restrictive controls.

STEP 3 For each pollutant, predict the impact on ground level ambient air concentrations for the area surrounding theplant and compare these to the appropriate regulatory or health standards. Determine the area impacted byreleases from the plant.

STEP 4 From comparisons of the estimated emissions and predicted ambient concentrations to the regulatoryrequirements, determine the required emissions reductions, if any.

STEP 5 Identify the potential control options for reducing emissions of each pollutant. Analyze the technical feasibilityand cost effectiveness of each option.

EMISSIONS INVENTORIES

An emissions inventory is an estimate of the emissions from a facility, or part of one, over a fixed period of time, usually oneyear. This section contains a general description of why an inventory might be required and provides guidance in how toconduct an emissions inventory. For specific instructions in estimating emissions from various sources, reference is made to anumber of ExxonMobil technical manuals.

REASONS FOR CONDUCTING AN EMISSIONS INVENTORY

The scope and purpose of the emissions inventory will largely determine the methodology employed to generate the emissionsestimate. An inventory can be a very detailed assessment of the emissions from the facility using measurement data or can bean approximation based upon simple emission estimating factors. Most inventories will fall somewhere between these twoextremes. The resources and effort required to produce an inventory are closely related to the level of accuracy required.Thus, a primary step in any inventory process is to determine the intended use of the emission estimates.

The most common reasons for conducting an emissions inventory are:

• Regulations - National or local regulations may require an emissions inventory. Guidance on the extent of the inventoryand acceptable approaches may be available from the regulatory agency.

• Company Policy or Initiative - Company initiatives to track emissions may require regular inventories even where noneare required by local regulations.

• Permitting and Health Risk Assessments - Emission estimates for the entire or affected parts of the facility or aproposed facility, are often required in permit applications and health risk assessments.

• Determining Baseline Emissions - The relative magnitude of the types and sources of emissions can help prioritizeemissions reduction projects. Also, the inventory can be used as a baseline to allow emissions reduction progress to bemonitored.

The level of accuracy depends on the purpose of the inventory.

INVENTORY FOCUS

An emissions inventory is often focused on a specific compound or type of emission such as benzene, volatile organiccompounds, or products of combustion. The inventory focus may be emissions to a single media, such as air, or multi-media,including emissions to the air, water, and land (waste disposal). Potential emission sources to air include tanks, stacks andflares, piping components, cooling towers, and waste water treatment equipment. A detailed list of potential sources can befound in the EMRE Emission Estimating Guide (Ref. 1).





EMISSIONS INVENTORIES (Cont)

Although routine emissions are often the focus of an inventory, non-routine emissions should also be included. These non-routine emissions (e.g., from turnarounds, etc.) can be significant.

CONDUCTING AN EMISSIONS INVENTORY - OVERVIEW

There are two main steps in conducting an emissions inventory. The first step is preparation, including selection of theestimating methodology to be used and collection of the data required. This step is commonly the most time consuming part ofthe inventory process. The choice of estimating methodology can be iterative and often runs in parallel with data collection, asthe method chosen generally depends upon the information available.

An important part of preparation for an inventory is communication of the aim of the inventory to those responsible for providingthe data. In a busy operating environment, communication is needed to stress the importance of the data. It is useful to havesomeone familiar with the facility operation involved in the data collection process to provide an ongoing reasonableness checkof the data as it is collected.

The second step of the inventory process is the actual estimation of the facility's emissions.

PREPARING FOR AN INVENTORY - METHODOLOGY SELECTION

The appropriate emission estimating techniques will depend upon the purpose of the estimate and the data and resourcesavailable. The most realistic emissions estimate would be one based upon data that has been collected continuously or over acomplete range of operating conditions. However, measurement data for an emission source, if available at all, is often over ashort time frame or �snapshot" of the operation. If data is unavailable, an emission factor may be used. These factors predictthe emissions based on some generally known operating variable. Common variables include time, flowrate, volume, and fuelused. An emissions factor is usually derived from measurements made at one or more source types and can be unit specific oran industry average.

In many cases, several different factors are available to estimate emissions from a source. Generally, the more informationrequired to use the factor the more representative the estimated emission. However, the factor may have been developed fromdifferent equipment types or conditions, and may not be representative of your operation. For some types of emission sources,computer programs are available that estimate emissions using site specific input data. Default values are generally provided ifsite specific data is not available. Details on many of the available estimating techniques and selection guidance are providedin the EMRE Emission Estimating Guide.

PREPARING FOR AN INVENTORY - DATA COLLECTION

Collection of the data, especially for the first inventory, is the most time-consuming part of the inventory. The data may not becentrally located, and in some cases, not readily available. A suggested data collection method is to compile a list of theinformation (based upon the selected method) and have the operations supervisor or similar person forward the data request tothe person most likely to have the information or who knows where it may be found. In some cases where the data is unknownor would take a great deal of time to find, it may be appropriate to use engineering judgment to estimate the value. Alternately,the referenced emission estimating guides may contain typical values.

Depending upon the scope of the inventory, the amount of data collected can be voluminous. To save time later, document thesource of each item of information, including the physical location and the person providing this information. In the event thedata proves insufficient, this can save a great deal of time and effort. For similar reasons, a consistent filing system (e.g., acomputerized database) should be developed.

The data to estimate emissions depend upon the estimating technique selected. Some of the data for a multi-media facilityinventory include the following:

• Crude (or feed stock) throughput and product throughput from production records.

• Storage tanks: type of seals and fittings for each tank, tank dimensions and color, product stored, tank throughput, andstorage temperature.

• Loading: type of containers used, loading procedures, products loaded, volume loaded, and previous cargo.

• Fugitive emissions: number and type of piping components, some details on the stream condition, (liquid, gaseous etc.),any monitoring data available from Inspection and Maintenance (I & M) programs.






EMISSIONS INVENTORIES (Cont)

• Secondary emissions: wastewater treatment facilities - water temperature, oil concentration in the water, types ofcollection and treatment equipment, water throughput.

• Combustion units: fuel specifications, fuel-firing records, pollution controls, manufacturers� specifications, and continuousemission monitoring data if available.

• Spill records.

• Facility specific information such as ambient temperature ranges and wind speed.

• Product and intermediate information: molecular weight, vapor pressure, and composition (if a specific compound, ratherthan total VOC emissions is the focus).

• Waste records and any analysis of the waste.

• Turnaround and shutdown or down time information for process units: whether the unit was degassed and cleaned.

• Materials Safety Data Sheets (MSDS) for details on compositions of chemicals used.

• The removal efficiency of any installed control equipment.

The referenced technical manuals provide full details of the information based upon the method chosen and some guidance asto where the information may be found.

ESTIMATING EMISSIONS

➧ Detailed instructions on estimating emissions are available from the EMRE Emission Estimating Guide (TMEE-046). Themanual discusses the different estimating methods and their advantages. The manual and its background documents areincluded in the list of references.

To complete emission inventories, clearly document the source of the method selected, the reason why it was appropriate, andALL the assumptions. Where computer programs are used to speed the estimating process, annotations are helpful.Whatever the original driving force for completing a facility inventory, it is likely that the data will be used for many otherreasons. Ensuring that clear documentation accompanies the estimated emission value will facilitate answering questions onthis inventory and the completion of future inventories.

The following sections of this section provide an overview of the technology in each area, general guidance for controlling airpollutants, and the locations in other DP sections to find more detailed information.

➧ IMPACT ANALYSIS / AIR DISPERSION MODELING

Regulations often require a plant to show that emissions from a new or modified facility will not cause ambient air quality toviolate local standards. Also, it may be required to show that emissions during normal shut down and turnarounds will be incompliance with standards. Since it is not possible to make measurements of air quality for a facility that has not yet beenconstructed or operated at new conditions, air quality dispersion modeling is used to predict the impact. Dispersion modelingconsiders the atmospheric influences on a pollutant stream emitted into the atmosphere and predicts the concentrations atdownwind distances. Dispersion modeling is used to model continuous releases, as well as episodic releases of hazardous ortoxic materials.

Dispersion modeling takes into account the atmospheric diffusion and transport, which mixes and dilutes the emissions as theplume travels away from the point of release. The following mechanisms are usually included:

• Plume rise.

• Atmospheric transport and diffusion.

• Aerodynamic downwash effects of nearby structures and terrain.

• Chemical and photochemical reactions.

• Particle deposition.





IMPACT ANALYSIS / AIR DISPERSION MODELING (Cont)

MODEL SELECTION

➧ Selection of a particular dispersion model depends on: 1) the type of pollutant (chemically reactive or non-reactive, gaseous orparticulate, and lighter or denser-than-air), 2) the type of emission source (point, line, area or volume source, and continuousemission versus instantaneous release), 3) the meteorological (land or water) and topographic complexities of the area (flatterrain or hilly [complex] terrain), 4) the level of detail and accuracy needed for the analysis (screening or detailed modeling), 5)the detail and accuracy of the data base (i.e., emission inventory, and meteorological data), and 6) the transport distance tosurrounding areas of concern. The greater the detail with which a model considers the spatial and temporal variations inemissions, meteorological conditions and site characteristics, the greater the ability to evaluate the source impact and todistinguish the effects of various control strategies.

There are two levels of sophistication for modeling methods. The first level consists of general, relatively simple estimationtechniques that provide conservative estimates of the air quality impact of an emission source. These are screeningtechniques. The purpose of such techniques is to eliminate the need for more detailed modeling of those sources that clearlywill not contribute to ambient concentrations in excess of the standards. If the screening dispersion modeling predicts that theconcentration contributed by the source exceeds the standards, then the second level of more sophisticated models should beapplied.

The second level consists of those analytical techniques that provide more detailed treatment of emission sourcecharacteristics, meteorological conditions, site/receptor conditions, and physical and chemical atmospheric processes. Thislevel of dispersion modeling requires more detailed input data and provides more accurate concentration estimates. These arereferred to as refined dispersion models.

There are three general types of dispersion models: 1) conventional (Gaussian models), 2) denser-than-air modeling, and 3)reactive modeling (i.e., photochemical smog). Gaussian models are the most widely used techniques for estimating the impactof non-reactive pollutants.

The Gaussian model is based on a normal distribution (the bell-shaped distribution) that describes a concentration profilegenerated by a pollutant emission source. The Gaussian model uses several assumptions: continuous emissions that are notvariable over time, conservation of mass, and steady-state meteorological conditions. Predicted concentrations depend onthree factors: 1) the emission source conditions (i.e., release characteristics, emission rate), 2) the meteorological conditions(i.e., wind speed/direction, atmospheric stability), and 3) the receptor (i.e., location and terrain).

DATA REQUIREMENTS

The data inputs for dispersion modeling include information on the emission sources, the meteorological conditions and thelocations at which concentrations are to be predicted. The emissions sources are generally categorized into four basic types ofsources: point, line, area, and volume. Point sources are stacks and vents. Line sources may be rail lines, roads or buildingedges. Area sources may be storage piles, lagoons, and land farms. Volume sources may be buildings or process fugitiveemissions. Information required to model emissions from point sources includes: 1) stack height, 2) inside stack diameter, 3)exit velocity, 4) gas temperature, 5) emission rate, and 6) coordinates of all the sources to be modeled. If the source is a line,area or volume source, some additional information may be required. If plumes from stacks are affected by aerodynamicwakes and eddies produced by nearby buildings or other structures, this needs to be accounted for also.

As pollutants are released into the atmosphere, turbulence disperses the pollutants vertically and horizontally. Thisatmospheric turbulence is caused by both mechanical and thermal effects. Wind moving past vegetation or structures createsmechanical turbulence. The stronger the wind or the more uneven the surface, the greater the degree of mechanicalturbulence generated. The heating or cooling of air near the earth's surface generates buoyant or thermal turbulence. Heatingfrom the sun creates an upward heat flux at the ground surface and this heats the air in the lower layers. With heating,convective eddies generate upward-rising thermals that may extend vertically on the order of 1000 to 1500 m.

Meteorological data required for dispersion modeling include wind speed and direction, atmospheric stability, ambienttemperature, and mixing heights. Atmospheric stability categories are indicators of atmospheric turbulence. The stabilitycategory at any given time will depend upon thermal turbulence (caused by heating of the air at ground level), and mechanicalturbulence (a function of wind speed and surface roughness). The most commonly used method to classify atmosphericstability includes six stability classes (A through F): strongly unstable, A; moderately unstable, B; slightly unstable, C; neutralconditions, D; slightly stable, E; and moderately stable, F.

For screening quality dispersion modeling, or when the local meteorology is unknown, a range of 33 stability and wind speedconditions is used to identify the potential worst case (maximum) ambient concentration. Refined dispersion modeling requireshourly meteorological observations. Data may be obtained either by installing on-site meteorological equipment and measuringconditions or by obtaining data from nearby airports, military installations or weather stations.






IMPACT ANALYSIS / AIR DISPERSION MODELING (Cont)

The Gaussian dispersion model used for estimating ambient concentrations of pollutants is representative of a 1-hourconcentration averaging time. The averaging time accounts for variations in the ambient concentration due to changes in themeteorological conditions from the mean values. For concentration averaging times greater than 1-hour, the concentration willbe less than the 1-hour value and for averaging times less than 1-hour the concentration will be higher. This is due to theincreased variation of wind direction over longer periods of time causing greater horizontal dispersion and lower concentrations.

Concentrations predicted by dispersion models also depend on the surface roughness. The surface roughness establishes theextent of the vertical wind gradient. One method used to establish surface roughness is to classify the area surrounding thesource as either �rural" or �urban." �Urban" areas with buildings and manufacturing facilities typically have greater surfaceroughness than �rural" areas and atmospheric dispersion is greater than for �rural" areas. Land use classification has beenbased on either population density or land use. More sophisticated methods based on actual surface roughness are currentlybeing developed.

Plumes from stacks that are affected by nearby buildings or structures require more sophisticated modeling. If the height ofrelease is below or just above a roof, then the plume is likely to become caught in the turbulent wake of the building. Theconcentrations in such a wake are usually several times higher than they would be in the absence of wake effects. The stackheight necessary to ensure that the plume escapes the building wake effects is referred to as the �Good Engineering Practice"(GEP) stack height:

HGEP = Hb + 1.5 L

where: HGEP = GEP stack heightHb = Structure heightL = Lesser of structure height or width

Stacks should be analyzed to determine whether their proximity to �nearby" buildings or structures could cause turbulent wakeeffects. �Nearby" includes structures within a distance of five times the lesser of the height or width of the structure, but notgreater than 2625 ft (0.8 km).

Additional information on dispersion modeling procedures can be found in Section XVIII-A1.

HYDROCARBON, VOC, AND AIR TOXICS EMISSIONS CONTROL

Emissions of hydrocarbons and air toxics have become increasingly regulated. Many hydrocarbons are VOCs and contribute,with NOx, to the formation of ozone. In addition, concerns about the risk of both short and long term exposure to chemicalshave led to a focus on emissions of �toxic" chemicals. This section describes the sources of these emissions and outlinesapplicable controls. A more detailed discussion of the subject and control recommendations is contained in Section XVIII-A2.

Table 5 shows the major sources of hydrocarbon emissions to the air from process plants. The relative percents varydepending on the specific processes employed and the type of emission controls installed. In almost all cases, fugitiveemissions are the largest source of hydrocarbons and air toxics. In those locations with large uncontrolled marine or productloading facilities, loading emissions may also be high. In locations that have implemented a fugitives control program, andhave large but uncontrolled loading emissions, the contribution from loading may even exceed that from fugitives. Airemissions from tanks and wastewater treating are usually much smaller than those from fugitives and loading.

The most applicable and economic control system will depend on the specific emission source, the level of controls already inplace, and the target emission level. The costs can vary widely. Table 6 lists options for controlling emissions of hydrocarbonsand air toxics. These are discussed in the remainder of this section.

➧ TABLE 5MAJOR SOURCES OF HYDROCARBONS TO THE AIR FROM PROCESS PLANTS

SOURCE TYPICAL PERCENTAGES*Fugitive Equipment Leaks

Loading

Wastewater Treating

Storage Tanks

Process Vents

50 - 60

20 - 30

10 - 15

10 - 15

Site specific

Note:

* Actual values vary based on plant configuration and existing controls.





HYDROCARBON, VOC, AND AIR TOXICS EMISSIONS CONTROL (Cont)

➧ TABLE 6CONTROL OPTIONS FOR HYDROCARBON AND AIR TOXICS EMISSIONS

FUGITIVE EMISSIONS

Initiate a leak detection and repair program.

Install new packing sets in block and control valves.

Upgrade pumps seals to multi-seal designs.

�On-Line" valve repair.

Route pressure relief valves to flare system.

TANK EMISSIONS

Fixed Roof Tanks

• Install vapor balance system.

• Install vapor recovery/destruction.

• Install internal floating roof.

External Floating Roof Tanks

• Check condition of existing seals and repair if needed.

• Replace vapor-mounted primary with liquid-mounted primary seal.

• Control losses from roof fittings.

• Install sleeve on slotted guidepole.

• Install secondary rim seal.

• Convert tank to internal floating roof design.


Internal Floating Roof

• Check condition of existing seals and repair if needed.

• Replace vapor-mounted primary seal with liquid-mounted seal.

• Control losses from roof fittings.

• Install secondary rim seal.


WASTEWATER TREATING EMISSIONS

Decrease wastewater volume and organic concentrations.

Optimize stripper operation.

Install sewer system emission suppression.

Reduce air/water contact area (covering, nitrogen blanketing, etc.).

Replace API separator with covered corrugated plate interceptor.

LOADING EMISSIONS

Use �submerged" loading in place of �splash" loading.

Use vapor balancing during loading.

Install vapor recovery/destruction system.







CONTROLLING FUGITIVE EMISSIONS

Fugitive emissions, also know as �equipment leaks," are those emissions from valves, flanges, pump and compressor seals,pressure relief valves, and other �piping components" located throughout any process plant. Although these emissions aresometimes visually detected, they are most often located with sensitive gas detection instruments placed adjacent to the leakpoint. When environmental engineers refer to levels of fugitive emissions, they typically use ppm values measured with theseinstruments.

Although fugitive emissions from a single piping component are in most cases extremely small, there are a very large numberof components throughout a process plant. It is for this reason that fugitive emissions are usually the largest source ofhydrocarbons and air toxics. Approximately half of the fugitive emissions are from valves. The next largest contributors tofugitive emissions are flanges and connectors. As locations continue to reduce valve emissions through monitoring and betterequipment, flanges may become a much larger percentage of the total fugitive emissions.

The most cost effective control measure to reduce fugitive emissions is to initiate an inspection and maintenance (I&M)program (also known as Leak Detection and Repair - LDAR or monitoring and maintenance - M&M). For those locationswithout any current controls, instituting an annual I&M program may in some cases reduce oil losses by an amount exceedingthe cost of the program. Actual emission reductions depend on the current condition of the components, with reductions of atleast 50 to 75 percent being typically achieved compared to average factor emission estimates. These programs can beoptimized by more frequent inspection of those components found to be leaking more frequently.

An I&M program uses a sensitive gas detection instrument to sample each piping component individually to determine theconcentration of hydrocarbons adjacent to a potential leak point (e.g., the packing gland on valves or the seal on pumps). If theinstrument detects hydrocarbons above a predetermined �leak" level, the equipment is repaired. A typical definition of �leak"level depends on local regulations, although 10,000 ppm is a widely accepted leak level. In some United States locations,however, new regulations set the �leak" definition as low as 100 ppm.

➧ New techniques are under development to focus LDAR efforts on the few piping components that leak the most. This practicehas been termed "Smart LDAR". Technology that allows "visualization" of hydrocarbon plumes is being developed which willallow easier identification of those components needing repair.

On-line repairs for valves include tightening the packing gland to further compress the packing. (The packing gland should notbe so over tightened that it prevents movement of the valve stem.) If this is not successful, then, when the valve is next out ofservice, the packing may need to be replaced with a �low emission" packing design. In cases where the valve stem is corrodedor there are other mechanical problems, the valve may need to be replaced during the next turnaround. Pump emissions maybe reduced by using a multi-seal design with a fluid barrier or essentially eliminated by the use of �canned" or magnetic drivedesigns.

CONTROLLING TANK EMISSIONS

Emissions from atmospheric storage tanks are the result of addition and removal of stock, temperature and pressure changes,and wind passing over the tank. The particular emission mechanisms and their contribution to total emissions depend on thetank construction, material stored, and local meteorology. There are three types of tank designs used for the atmosphericstorage of petroleum liquids: fixed roof; external floating roof; and internal floating roof.

Fixed roof tanks consist of a cylindrical shell and are covered with a stationary roof. There is a volume of gas above the liquidstored in a fixed roof tank. The major mechanism for emissions from a fixed roof tank is from hydrocarbon saturated vaporsthat are expelled as liquid is added. Another, although usually smaller, emission mechanism is from changes in thetemperature and pressure causing volume changes in the vapor space of the tank. During these changes, air may flow into thetank, become saturated with hydrocarbons, and then be expelled.

Emission controls for fixed roof tanks include vapor balancing, conversion to an internal floating roof tank, and the installation ofa vapor recovery or destruction system. Vapor balancing involves transferring the vapor that would have been expelled duringtank filling to the source of the liquid. The installation of a floating roof converts the fixed roof tank into an internal floating roofdesign. Collection of the vapors for recovery or destruction is the most effective, although usually the most costly, control forfixed roof tank designs.

Floating roof tanks consist of a cylindrical shell with a roof that floats on top of the liquid and rises and falls as the liquid level inthe tank changes. In an internal floating roof tank, there is also a stationary roof on top of the tank. The major mechanism foremissions from a floating roof tank is from evaporation through openings in the floating roof (roof fittings) and the spacesbetween the rim seal and tank wall. Another, although usually smaller, mechanism is from evaporation of the liquid coating thetank walls and poles as the roof is lowered.






➧ The first step in controlling emissions from floating roof tanks is to inspect the condition of the primary rim seal for excessivespace at the tank wall and repair or replace if required. Other emissions controls include the installation of a secondary rimseal, replacing a vapor-mounted primary rim seal with a liquid-mounted seal, and controlling the losses from roof fittings.External floating roof tanks can be converted to internal floating roof tanks to reduce wind-induced emissions. Roof fittingcontrols include adding gaskets to guide pole wells, gauge hatches, and access hatches as well as bolting the hatches. If aslotted guide pole is used, installation of a sleeve surrounding the pole can substantially reduce tank emissions because an�uncontrolled" slotted guide pole is a relatively large emissions source. Pole floats are not recommended since they caninterfere with tank gauging.

CONTROLLING LOADING EMISSIONS

Emissions from the loading of ships, barges, rail cars, and tank trucks are caused by the displacement of a volume of vapordue to the addition of a similar volume of liquid. In some respects it is similar to emissions from the filling of a fixed roof tank.The quantity and composition of the vapor displaced will depend upon the previous material contained, any cleaning prior toloading, the new material being loaded, the method of loading, and the use of any vapor collection or control devices. Thevapors displaced during loading operations consist of two components. Initially, they are predominantly the vapors formed bythe evaporation of the previous product (unless the holding vessel or compartment was cleaned after discharge). Later in theloading process, the emissions are predominantly those vapors generated during loading of the new liquid.

Significant emissions control for loading operations will result from a reduction in the amount of turbulence created when theliquid is introduced. This can be done by using bottom or submerged loading rather than splash loading. With splash loading,liquid is introduced at the top of the container and there is significant turbulence and potential entrainment of liquid droplets inthe displaced vapor. Using bottom or submerged loading significantly reduces the turbulence, lowering the vapor generation.

Other emission controls for loading operations include vapor balancing and the installation of vapor recovery or destructiondevices. Vapor balancing is only an option when the source of the liquid can eventually collect or dispose of the returnedvapor. Vapor recovery devices include condensation, absorption, and adsorption. Vapor destruction devices includeincineration, flares, and biofilters.

CONTROLLING WASTEWATER TREATING AIR EMISSIONS

The wastewater collection and treating system includes drains, manholes, sewers, junction boxes, primary oil/water separators,air flotation units, and biological treatment units. Emissions are the result of evaporation from an organic containing wastewaterflowing through or being treated in this equipment. Organics enter the water either through direct or indirect contact. Directcontact sources include processes that use water for washing (e.g., desalter), sour water stripping and steam used in jeteductors to produce vacuum. Indirect sources include leaks from heat exchangers, condensers and leaking pumps.

The most cost-effective way to reduce organic emissions from wastewater is to minimize the quantity of hydrocarbons enteringthe system. The use of drains and sumps as routine organic collection systems should be minimized. Another pollutionprevention option is to improve the performance of steam or gas strippers so that the organic concentration of water that entersthe system is lowered. During unit shut-downs, in preparation for turnarounds, all liquid should be collected and not allowed tobe discharged into the sewer system.

Once the flow has entered the wastewater system, most emission control opportunities are focused on reducing the contactthat the water has with the ambient air. Sewer system suppression includes installing traps in drains, and covering and sealingsewers, junction boxes, and manholes. Emissions from separators and treaters can be reduced by covering the unit, andrecovering the emissions in a safe manner.

COMBUSTION EMISSIONS CONTROL

This section describes the typical emissions and applicable controls for many of the combustion sources found in refineries andchemical plants. The sources covered include fired heaters and steam boilers, gas turbines, stationary internal combustionengines and process combustors.

The principal air pollutants from combustion sources are sulfur oxides (SOx), consisting of SO2 and SO3; oxides of nitrogen(NOx), consisting primarily of NO and NO2; and particulate matter. Carbon monoxide (CO) is also produced, although energyefficiency considerations normally result in low emissions of this pollutant. Depending on the chemical composition of the fuelsused, heavy metals can also be present as, or on, particulates. Trace amounts of uncombusted hydrocarbons, partially burnedhydrocarbons (for example, aldehydes), and condensation products (for example poly-cyclic organic matter) can also beproduced, with the quantity depending on the fuel composition and combustion conditions. Carbon dioxide (CO2) is receivinggrowing attention because of its contribution to global warming.






COMBUSTION EMISSIONS CONTROL (Cont)

Table 7 shows the relative distribution of combustion emissions to the air from a complex refinery without emission controls.While the emission level and the distribution of emissions among the sources is obviously site and fuel specific, the table doesillustrate the widespread distribution of NOx across the refinery and the concentration of SOx and particulate in the processcombustors (e.g., the catalytic cracker regenerator and the coke burners). Modern emission control technologies can usuallyreduce any of the principal combustion emissions by up to 90%.

➧ TABLE 7RELATIVE DISTRIBUTION OF COMBUSTION EMISSIONS TO THE AIR

FROM A COMPLEX REFINERY WITHOUT EMISSION CONTROLS*

SOURCE NOx SOx PARTICULATES

Fired Heaters and Boilers Medium Medium Low

Gas Turbines Medium Low Low

Stationary Internal Combustion Engines High Low Medium

Process Combustors (Regenerators and Coke Burners) Medium High High

Note:

* Refinery is assumed to burn mixture of natural gas and nitrogen-containing fuel oil.

CONTROL OF NOX EMISSIONS FROM FUEL BURNING EQUIPMENT

A wide variety of NOx emission control technologies have been developed which have a wide range of NOx reductionperformance. They provide numerous options to control NOx emissions through changes before the combustor (pre-combustion), in the combustion process (in-situ), or after the combustor (post-combustion). The wide variety of technologiesthat can be applied to NOx control, the many factors that determine the effectiveness of these technologies, the range of NOxreductions required, and the performance and cost variations among the technologies, make generalizations on how to controlNOx difficult. While this section provides general guidelines for selecting control options, a more detailed discussion can befound in Section XVIII-A8.

➧ NOx is formed by three mechanisms: 1) the oxidation of molecular nitrogen in the combustion air (thermal NOx), 2) theoxidation of chemically bound nitrogen in the fuel (fuel NOx), and 3) reactions of molecular nitrogen with hydrocarbon fragmentsunder rich combustion conditions (prompt NOx). Accordingly, NOx control techniques depending on changes in the combustionprocess must, as a minimum, consider the flame temperature, the oxygen concentration and the fuel nitrogen content. NOxformation is also strongly influenced by the physical characteristics of the units in which the combustion reaction is occurring.For example, the type of fuel: gas, liquid, or solid; and the specific process application: boiler, fired heater, gas turbine, etc.,also play a part in determining the capability and effectiveness of a particular NOx emission control technique.

As mentioned above, many sources of NOx contribute to the problem, each having its own specific NOx emission intensity andadaptability to control requirements. For example, the internal combustion engines and gas turbines often contributeconsiderably more NOx per unit of fuel fired than other sources. Some sources are easier and less costly to control thanothers. Thus, if a facility-wide NOx emission control level (often referred to as a �bubble") is allowed, a systematic considerationof the design and integration of all NOx emitting units in the facility can help determine where to place the NOx reduction effortto achieve the lowest emission at the minimum cost.

NOx Control for Fired Heaters and Boilers

There are many fired heaters and boilers in a refinery or chemical plant. Collectively, they account for a substantial portion ofthe NOx emissions.

The pre-combustion changes depend on fuel selection to limit either the temperature of the flame or the concentration of fuelnitrogen, thereby reducing the oxidation rate of nitrogen.

In-situ combustion modifications are all based on reducing the temperature or the oxygen concentration in the flame, therebyreducing the reaction rate for NOx formation. Some of the modifications, for example, steam injection or flue gas recirculation(FGR), are directly applicable to existing units. Others, like Low NOx Burners (LNB), require replacement of existing hardware.LNBs incorporate within the burner design the air staging and FGR techniques found to be effective in controlling the NOxreaction rate.






➧ The post-combustion techniques usually use ammonia or urea to promote the nitrogen (N2) forming reaction between NHspecies and NOx. Both catalytic and non-catalytic technologies for selective NOx removal have been developed. The non-catalytic approach (Selective Non-Catalytic Reduction, SNCR) is normally applied at flue gas temperatures between 1600°F(871°C) and 2200°F (1204°C). With added reagents, such as H2, the range can be extended as low as 1300°F (704°C). Thereare two SNCR processes: 1) ExxonMobil's THERMAL DENOx which uses ammonia as the reagent, and 2) those that use urealike reagents. The catalytic approach (Selective Catalytic Reduction, SCR) can be applied at flue gas temperatures between350°F (176°C), and 1100°F (593°C). However, at lower temperatures [< 550°F (288°C)] this process is sensitive to pluggingfrom condensates and particulates.

Table 8 presents options for NOx control for fired heaters and boilers. The most cost-effective option is unit specific anddepends on fuel gas composition, individual burner firing rates, equipment type, firebox temperatures, and burner type.

Low NOx Burners (LNBs), SNCR and SCR are the three most frequently considered options. LNBs have been the mostfrequently applied. Other options are limited in applicability or in the NOx reduction achievable and are not as cost effective.Some are applied, however, on a temporary basis to solve short term high NOx conditions (e.g., reducing air preheat).

TABLE 8CONTROLS FOR NOx EMISSIONS FROM FIRED HEATERS AND BOILERS

Pre-Combustion Options • Switch to lower H2 content fuel

• Switch to lower N content fuel

In-Situ Combustion Modifications • Reduce air preheat

• Reduce excess air level

• Reduce load, if operating above design capacity

• Install flue gas recirculation (FGR)

• Install steam injection

• Install Low NOx Burners (LNB)

Post-Combustion Clean-up • Install Selective Non-Catalytic Reduction (SNCR), e.g., THERMAL DENOx

• Install Selective Catalytic Reduction (SCR)

NOx Control for Gas Turbines

The gas turbine, used for electric or motive power at the facility, is a special case of the more generic combustion source.Therefore, it is not surprising that NOx reduction techniques are similar to those encountered for fired heaters and boilers.

Steam or water injection, a method to reduce the temperature of the flame, is the simplest technology for NOx reduction. LowNOx combustors (staged-air combustion devices, similar, in principle, to LNBs for fired heaters and boilers) are now included innew gas turbines and are becoming available for retrofit of existing turbines. Selective Catalytic Reduction (SCR), using NH3as the reductant, often in combination with steam injection, has been used to achieve emissions as low as 9 ppmv (corrected to15% O2, dry basis).

As with fired heaters and boilers, gas turbine NOx emissions tend to increase when high H2 content refinery gases are burned.Using a fuel containing less hydrogen will reduce the flame temperature, and hence the NOx emission level.

The following table summarizes options for NOx reduction from gas turbines.

TABLE 9CONTROLS FOR NOx EMISSIONS FROM GAS TURBINES

Pre-Combustion Option • Switch to low H2 content fuels

In-situ Combustion Modifications • Increase power augmentation steam

• Install steam or water injection

• Install low NOx combustor

Post-Combustion Clean-up • Install Selective Catalytic Reduction

Combinations • Install steam injection and SCR







Control of NOx Emissions for Stationary Internal Combustion Engines

Stationary reciprocating Internal Combustion (IC) engines are used in the petroleum and petrochemical operations wheremechanical work is performed using shaft power. These engines operate on the same principles as automotive engines. Twomethods of igniting the fuel-air mixture are used in IC engines: Spark Ignition (SI) and Compression Ignition (CI). The ignitionmethod is related to the type of fuel used and the thermodynamic cycle involved. All gasoline or natural gas engines are SIengines. All diesel-fueled engines are CI engines. The SI engines used in the petroleum industry are typically large boreengines, with multiple cylinders of 8 to 18 in. bore, and 400 to 13,000 hp (300 to 9,700 kW) output. These engines tend to befueled with natural gas and are used in applications requiring continuous operations, such as electric power generation, oil andgas pipeline transmission, oil and gas production, and refinery and chemical plant drives. Diesel engines, with power ratings ofabout 350 hp (260 kW) are used extensively in on-land and off-shore drilling. Engines produce significant CO, hydrocarbon,particulates, and NOx emissions per unit of fuel fired.

The NOx, CO, particulates and hydrocarbon emissions are interrelated and depend on the relative amount of fuel and oxidant.This concentration ratio, the Air-to-Fuel ratio (A/F), is expressed in weight of air to weight of fuel. Normal operation of the ICengine differs among manufacturers and can be at A/F ratios slightly lower (fuel-rich combustion or rich-burn) or slightly higher(fuel-lean combustion or lean-burn) than stoichiometric. Since the formation rate of NOx increases with increases incombustion temperature and oxygen concentration, the maximum NOx occurs when the A/F is slightly above stoichiometric.Changes in the A/F ratio on either side of stoichiometric will reduce NOx. Fuel-lean operations reduce the combustiontemperature because of additional air. Fuel-rich operations reduce the oxygen concentration.

CO and hydrocarbon emissions increase slightly at fuel rich A/F due to the lack of oxygen to fully oxidize the carbon. This isone of many examples in air pollution control where control of the emissions of one pollutant is often at the expense ofincreased emissions of another pollutant.

By delaying, or retarding, the timing of ignition, the combustion process occurs later in the downward power stroke. Thiseffectively increases the combustion chamber volume, which reduces pressure in the cylinder and lowers combustiontemperature. The lower combustion temperature, in turn, results in lower NOx emissions. Emissions of CO and hydrocarbonsare not significantly affected by timing retard, except when misfiring occurs.

The Pre-Stratified Charge (PSC) control system is an add-on control device for rich-burn, naturally aspirated or turbo-charged,carburetor equipped, 4-cycle engines. In PSC, air is injected into the intake manifold in a layered, or stratified charge,arrangement. This stratified charge allows a leaner A/F to be burned without increasing the possibility of misfire due to lowflammability limits.

Fuel composition also plays a role in determining NOx emissions. As with fired heaters and boilers, fuel molecular hydrogencontent has an effect on the formation of thermal NOx and fuel-bound nitrogen has an effect on the formation of fuel NOx.Hence, fuel selection is a pre-combustion option to reduce NOx emissions. The post combustion NOx reduction options basedon ammonia can also be used, although they are only cost effective for the very large stationary engines.

TABLE 10CONTROLS FOR NOx EMISSIONS FOR STATIONARY IC ENGINES

Pre-Combustion Option • Switch to low H2 and N content fuels

In-situ Combustion Modifications • Reduce A/F ratio (i.e., run fuel-rich)

• Retard ignition timing

• Install Pre-Stratified Charge system (limited to SI, 4-cycle, carbureted engine)

Post-Combustion Clean-Up • Install SNCR or SCR






NOx Control for Process Combustors

Fluid catalytic cracking (FCC) regenerators and coker burners are combustors in which coke deposited on a particulatesubstrate (catalyst or seed coke) is contacted with air or oxygen to regenerate the catalyst or generate process heat. ThermalNOx is generally not a major contributor to NOx emissions since the combustion temperature is considerably cooler than thatexperienced in the flame of fired heaters or boilers. However, levels of nitrogen in the coke can produce significant emissionsof fuel NOx. Also, use of CO promoters and SOx reduction catalysts have increased NOx from FCC regenerators. If NOxemission reduction is required, process unit feed denitrogenation or the post-combustion clean-up options, namely, SNCR andSCR are available. Post-combustion options have been demonstrated on fluid catalytic cracker regenerators, but not on cokeburners.

CONTROL OF SOx EMISSIONS FROM FUEL BURNING EQUIPMENT

Sulfur oxide (SOx) formation is solely determined by the sulfur content of the feed. The SOx reduction options are thus limitedto removing the sulfur from the fuel prior to combustion or treating the flue gas after combustion.

Control of SOx Emissions From Fired Heaters and Boilers

The use of low sulfur containing fuels is the first choice for reducing SOx emissions from small refinery combustion sources.

The post-combustion flue gas desulfurization systems (FGDS) are used for large boilers and process combustors.

There are a wide variety of FGDS options and the choice will often depend on the type of secondary emission that isacceptable. Some of the FGDS, known as �throwaway" or single-use systems, produce liquid or solid waste for disposal.Other FGDS systems are �regenerable," that is, they recover the sulfur content of the gas streams in a useable form and reusethe scrubbing chemicals, thereby reducing the amount of secondary waste to be disposed.

TABLE 11CONTROLS FOR SOx EMISSIONS FROM FIRED HEATERS AND BOILERS

Pre-Combustion Option Use low sulfur fuel

Post-Combustion Clean-Up Use flue gas desulfurization (FGDS)

Control of SOx Emissions From Process Combustors

Feed sulfur control is an expensive, although effective option for reducing SOx emissions from FCC regenerators and cokeburners. Options include feed hydrodesulfurization, which is never justified solely on environmental grounds, and purchase oflower sulfur crudes.

The FCCU, involving both a reactor vessel that operates under reducing conditions and a regenerator vessel that can operateunder oxidizing conditions, offers a unique stage for operating a self-contained regenerative flue gas desulfurization process.DeSOx agents provide the basis for such a process. A metal-oxide that picks-up SO3 at the regenerator conditions circulateswith the cat-cracking catalyst, and forms a metal sulfate which is then converted to the metal sulfide when it recirculates to theFCCU reactor. From the reactor, the cracking catalyst and the agent pass into the stripper used to separate hydrocarbons fromthe cracking catalyst. The stripper steam reduces the metal sulfide to form hydrogen sulfide and regenerates the metal oxide.The H2S formed is incremental to the H2S that is normally formed in the FCCU reactor and goes with the latter to the sulfurrecovery plant for capture as elemental sulfur. The metal oxide is returned to the regenerator to repeat the cycle.

The use of FGDS and, more specifically, the ExxonMobil Wet Gas Scrubber (WGS) are options for post-combustion clean up ofemissions from the catalytic cracking regenerator or the coker burners.

TABLE 12CONTROLS FOR SOx EMISSIONS FROM FCCU REGENERATORS

Pre-Combustion Option • Use feed sulfur control

In-situ Modifications • Use DeSOx catalyst

Post-Combustion Clean-Up • Use flue gas desulfurization (FGDS)

• Use ExxonMobil Wet Gas Scrubber (WGS)







CONTROL OF PARTICULATE EMISSIONS FROM FUEL BURNING EQUIPMENT

Particulate formation depends very much on the fuel used. Gaseous and distillate fuels generate essentially no particulatesand control technology is generally not required for these fuels. The combustion of heavy fuel oils, steam cracker tars and solidfuels, including petroleum cokes, generate sufficient particulates to require control.

Particulate size and physical characteristics are important characteristics affecting particulate emission control. Controlequipment collection efficiency typically decreases as particle size decreases. The performance of electrostatic precipitators(ESPs) depends on the resistivity of the particulates. Wet or caking particulates may blind bag filters.

Particulate removal equipment is sized to the flow rate of the gas stream to be cleaned. This sets the physical size of thecontrol equipment and can make for a very high capital cost per ton of particulates removed from the gas stream.

The electrostatic precipitator (ESP) is the most practical control device for reducing particulate loading from combustors firedwith residual oil or steam cracker tars. ESPs remove particles greater than one-half micron in size. Cyclones, or mechanicalcollectors, are the most effective for removing high loadings of larger particles (generally particles greater than 5 microns indiameter). Fabric filters are generally more effective than the other technologies for removing fine particles (less than onemicron). However, fabric filters are susceptible to blinding by the oil and are not used with liquid fuels. Venturi scrubbers areparticularly suitable if, in addition to particulates, SOx has to be removed. This makes the ExxonMobil WGS an ideal controldevice for emissions from FCCU regenerators. Table 13 shows the pre-combustion and post-combustion controls forparticulate emissions. Advantages and disadvantages of the control equipment are listed in Table 14.

Further details on the control of particulate emissions can be found in Sections XVIII-A3 (Cyclones), A4 (Fabric Filters), A5(Wet Gas Scrubbers), and A6 (Electrostatic Precipitators).

TABLE 13CONTROLS FOR PARTICULATE EMISSIONS

Pre-Combustion Option • Switch to cleaner (low particulate) fuels, such as natural gas or distillate

Post-Combustion Clean-up • Use a cyclone (mechanical collector)

(limited to large particles)

• Use an electrostatic precipitator (ESP)

• Use a venturi scrubber

• Use a fabric filter





➧ TABLE 14ADVANTAGES AND DISADVANTAGES OF CONTROL EQUIPMENT FOR PARTICULATE EMISSIONS

CONTROLEQUIPMENT

ADVANTAGES DISADVANTAGES

Cyclone • Low construction costs.

• Small space requirements.

• Minimum maintenance requirements.

• Dry collection and disposal.

• Minimal corrosion and rusting.

• Low pressure drop, typically 2-6 in. (50-150 mm) wg.

• Pressure and temperature limitations imposed only by materials of construction.

• Wet collection is difficult.

• Low removal efficiencies for fine particles.

• Particulate buildup may be an explosion hazard.

ElectrostaticPrecipitator

(ESP)

• Low operating costs.

• Minimum maintenance requirements.

• Dry collection and disposal.


• Low pressure drop, typically < 0.5 in. (13 mm) wg.

• High removal efficiencies for coarse and fine particles.

• Operates under high pressures [up to 150 psi (1.03 MPa)] or vacuum conditions and high temperatures [up to 1300oF (700°C)].

• High capital costs.

• Large space requirements.

• Low removal efficiencies for particles with very high/low resistivities.


• Particulate buildup may reduce unit performance.

• Sensitive to fluctuations in gas stream conditions.

• Special safety precautions required around high-voltage equipment.

• Wastewater treatment required for wet ESPs.

Wet GasScrubber

(WGS)

• Low capital costs.

• Small space requirements.

• Removes gases and particles.

• Handles high-temperature and high-humidity gas streams.

• High horsepower requirements (high pressure gas streams can reduce power costs).

• Wet collection and disposal.

• Wastewater treatment required.

• Corrosion and rusting.

• High pressure drop.

• Particulate buildup at wet/dry interface may be a problem.

• Steam plume opacity may be objectionable.

Fabric Filter • Dry collection and disposal.


• High removal efficiencies for coarse and fine (submicron) particles.

• Selected fibrous or granular filter aids promote high-efficiency removal of submicron smokes and gaseous contaminants.

• Efficiency and pressure drop are relatively unaffected by large fluctuations in inlet dust loadings for continuously cleaned filters.

• Recirculated filter air can conserve energy.

• High filter costs for temperatures > 550oF (288°C).

• High maintenance requirements.

• Fabric treatments may be required.

• Medium pressure drop requirements, typically 4-10 in. (100-250 mm) wg.







AIR PERMITTING

Most countries in which ExxonMobil operates have laws governing air pollution. In many cases these require obtaining apermit from a government body prior to constructing, modifying or changing the method of operating equipment, if it is asignificant source of air pollutants. Depending upon the regulatory structure involved, the government body authorized to granta permit may have national, regional or local jurisdiction. In some cases, permits may need to be obtained from agenciesrepresenting all three jurisdictions.

Air permitting can sometimes be a two-step process. First, a �permit to construct" is issued. After startup of equipment, this isfollowed by issuance of a �permit to operate." Historically, the greater challenge has been to obtain the �permit to construct."This often involves significant review of data by government agencies and, in many instances, citizen groups (if the laws requirepublic hearings). Therefore, the emphasis of this section will be on the �permit to construct."

A successful permitting effort achieves the following:

• Compliance with applicable laws.

• Permission to build facilities as planned by the applicant without expensive and time-consuming add-ons which thereviewing agency may desire.

• No impact on the overall project schedule desired by the applicant.

• Avoidance of unnecessary engineering studies.

The key to achieving this result is submitting a timely application which contains all of the information required by the reviewingagency. Clearly, the application also needs to demonstrate that standards, emission limits and other requirements applicableto the equipment will be met.

The remainder of this section will summarize the major steps involved in preparing a permit application. To ensurecomprehensive coverage, it will be assumed that the application is for a significant grass-roots or revamp project and that theregulatory environment is severe. For minor projects or perhaps all projects in a more flexible regulatory environment, asignificant number of these steps may not be necessary.

THE PERMIT APPLICATION

1. Planning/Scheduling the Application

One of the greatest challenges in permitting is to fit the schedule for obtaining the permit into the overall project schedule,so that the project is not adversely affected. Many agencies have explicit standards on how far a project may beprogressed prior to permit issuance. Unfortunately, it is rare for regulatory agencies to be under a deadline as to howquickly they must review and issue a permit. The elapsed time can vary from a few months to many months and theapplicant usually has very limited capability to expedite this part of the process. The project planning and permittingfunctions of any ExxonMobil unit should be alert to this. A useful �rule of thumb" is that if permitting has not been initiatedby completion of the DBM, some impact on the project schedule may be expected.

2. Defining the Reviewing Agency's Requirements

An essential early step in preparing the application is to review all pertinent laws and regulations and any permittinghandbooks or other guidance which have been issued by the reviewing agency. Consultation with other ExxonMobil unitsoperating within the same jurisdiction to discuss their recent permitting experience can also be useful.

A further step, which is highly recommended for all except the simplest permits, is the pre-application meeting with thereviewing agency. This is not only a useful cross-check against missing a requirement, but also provides opportunity toclarify pertinent regulatory language as well as to obtain insight into which aspects the reviewer may emphasize and vice�versa.

Many agencies are guided by internal policies (often unpublished and ever-changing) as much as by the published statutesand regulations. Such policies, while lacking the direct force of law, can add complications and requirements beyondthose set forth in the regulations. Thus, the pre-application meeting can also be viewed as the first round of negotiationleading to eventual agreement on what the actual requirements of the permit will be. Even in the most comprehensiveregulatory environment, negotiation is as basic a component of permitting as in those jurisdictions where �negotiated limits"are the rule. It follows that the lead �negotiator" for the applicant should preferably be someone with experience innegotiating permits with the agency involved. If local staff does not have this experience, hiring an external counsel orconsultant with the requisite credentials should be considered.





AIR PERMITTING (Cont)

3. Basic Components of the Application

• Project Description

This can obviously vary depending upon size, complexity and other aspects of the project, but areas normally coveredare:

- A narrative description of the equipment, purpose, capacity, cost/benefit.

- Simplified process flow plans and plot plans.

- Construction schedule.

- Changes in feedstock/product movements and modes of transport.

- Information on new chemicals (e.g., hazard data sheets).

- Other data - depending upon local interests/concerns this can include utilities consumption, staffing, traffic issuesduring construction and post-startup, environmental effects concerning other media (e.g., noise, wastewater andsolid waste disposal), visual impacts (e.g., tall stacks), etc.

• Emissions Source Data

Depending on the type of equipment involved, the following data on emissions sources may need to be compiled:

- Quantity and type of components which are potential sources of fugitive emissions, e.g., valves, flanges, pumps,compressors, safety valves, sampling systems, drains, etc.

- Parameters for stacks/process vents, such as height, diameter, temperature, exhaust gas flow rate, etc.

- Firing rates and fuel quality, e.g., heating value, sulfur, nitrogen and ash content.

- Storage tank data, e.g., type, size, throughput, temperature, etc.

- Information on other sources such as wastewater treatment systems, product loading/unloading, etc.

- Emission control equipment, including data on demonstrated control efficiency.

- Speciation of process streams (for calculation of speciated estimates of fugitive and tank emissions) andstack/process vent exhaust.

If the permit approval process is expected to be lengthy, the project schedule may require that an application besubmitted at an early stage of project development (e.g., DBM). In such a situation, compiling the above source datais a difficult task, since design details are usually lacking. The best approach is to work as much as possible from thedetailed design of prior similar projects and to be conservative in estimating equipment counts, operating rates, etc.This may tend to over-estimate the emissions, as compared to the final project. However, if an emission estimate hasto be revised at a late stage in the permitting process, it is much easier to avoid schedule impact if the emissions havedeclined relative to the initial application.

• Emissions Estimate

The above information on emission sources needs to be translated into an estimate of emissions from the equipmentto be permitted. For most locations, emissions of common pollutants, such as SOx, NOx, CO, particulates andhydrocarbons will need to be estimated. In some locations, all chemical species emitted theoretically have to beaccounted for. In the most extreme case, this can extend to estimating the emissions of �toxics" generated by fuelcombustion. The major concern here is the emission of Polynuclear Aromatic Hydrocarbons (PAH), some of whichare known human carcinogens, e.g., benzo(a)pyrene. However, benzene, formaldehyde and certain metals (e.g.,chromium VI) also may be considered to be important �combustion toxics."

Routine emissions are commonly classified by reviewing agencies into the following types:

- Process vent.

- Combustion stack.

- Storage tanks.

- Transfer/loading.

- Fugitive equipment leaks.

- Secondary (e.g., emissions from wastewater treating, cooling tower, etc.).







There is always some degree of variability in those sources for which the operating rate is a determinant of theemissions rate. It is very important to agree with operations management on both the maximum short term emissionsrate (e.g., pounds per hour) and average long term rate (e.g., tons per year) at which such equipment should bepermitted. If possible, any restriction on future operating flexibility should be avoided.

In some jurisdictions, particularly for large grass-roots projects, the reviewing agency may require that �one-time"emissions, such as those generated during construction, and/or periodic emissions, such as those from turnaroundsand flaring, be estimated.

Further detail on methods of estimating emissions can be found in the EMRE Emission Estimating Guide, TMEE-046.

Essentially all of the emission estimating methods use factors. Published emission factors exist for all of the emissionsources mentioned above. Variants of most of them have been developed by agencies, trade associations and evenby individual companies and plants. Some agencies require use of �approved factors." It is essential that theapplicant obtain a list of the factors �approved" by the regulatory agency at an early stage in the emissions estimatingprocess.

Since �approved" factors tend to be generalized, and therefore conservative, they should be reviewed by the applicantto determine whether they fairly represent the equipment and operations involved in the application. A first stepshould always be to determine whether the application can succeed if they are used, regardless of how conservativethey are. If not, the applicant should enter into a dialogue with the agency, with the hope of arriving at �negotiatedfactors" which can be approved, at least for the present application. The applicant should understand, however, thatsuch negotiations can be time-consuming and are not guaranteed to be successful.

• Control Technologies or Other Mitigations Proposed

In many jurisdictions, the laws prescribe the application of some level of control technology, or other means ofemissions mitigation, particularly for new equipment. These can be classified as follows:

- Basic equipment design features (e.g., floating roofs on tanks, dual seals on pumps, etc.).

- Add-on control technology (e.g., scrubbers, filters, absorbers, etc.).

- Fuel/feedstock switching.

- Work practices (e.g., monitoring for/repair of leaks).

- Emission offsets (e.g., shutdown or control of emissions from an existing source to �make room for" the emissionsfrom the new source).

- Other (e.g., acceptance of limitations on operating rates).

Even if the local laws address few of these aspects explicitly, it is likely that equipment designed to ExxonMobil'sstandards will incorporate features, which limit emissions as compared to �uncontrolled" designs. It is good publicrelations to explain these features.

4. Additional Components - the �Advanced" Application

Some ExxonMobil units have encountered the following as requirements for permit issuance:

• Compliance Demonstration

- Demonstration that equipment installed and/or fuel fired will meet applicable technology standards.

- Demonstration that off-property pollutant concentrations will meet applicable air quality standards. This typicallyinvolves use of air dispersion modeling. Normally, the reviewing agency has prescribed procedures which needto be observed. A common requirement is that a modeling protocol be submitted to the agency for approvalbefore any modeling is done. For more details on dispersion modeling techniques see the IMPACT ANALYSIS /AIR DISPERSION MODELING section of this DP or Section XVIII-A1.

- Demonstration, or at least a statement, of compliance with other pertinent regulations governing air pollution, e.g.,prohibition against creating nuisance odors, etc.






• Emissions Monitoring

Regulations may require that emissions monitoring systems be addressed, or, if public hearings are to be held, it maybe known that the local community is interested in their use to mitigate potential environmental impact. The types ofmonitoring systems which may be considered are:

- Stack - Continuous Emissions Monitoring Systems (CEMS).

- Process - Predictive Emissions Monitoring Systems (PEMS).

- Fugitive Emissions - Leak Detection and Repair Procedures (LDAR).

- Ambient Air Quality - Fence line or Community Monitoring (this can be done by fixed systems which periodicallysample the air, open-path detection systems which can continuously monitor the plant boundary, or by portablesampling equipment used at some agreed frequency).

• Community Exposure Analysis

A synonym for this activity is Risk Assessment and it is often encountered when a project is of sufficient size towarrant an Environmental Impact Review or Assessment (EIR or EIA). Two different types of assessments may beneeded:

- Health Risk Assessment (HRA), which in the U.S., usually attempts to calculate increased health risk (cancer risk)to the community by assuming a 70 year exposure to routine emissions on the part of the Maximally ExposedIndividual (MEI) within the community.

➧ • Temporary Emissions Reduction Plans

- Plans to reduce plant emissions if requested by local regulatory authorities during a period of ambient air qualityexceeding standards (e.g. high ground level ozone alerts).

➧ • Emergency Response Plans

- Plans to respond to episodic releases of hazardous materials.

- Quantitative Risk Assessment (QRA), which looks at acute risks posed by such events as fires/explosions andmajor chemical releases. Transportation risks may be included. As its name suggests, this type of study extendsthe scope of the HAZOP type reviews, which ExxonMobil routinely conducts, by requiring the estimation ofmathematical probabilities that certain events will occur.

Both the HRA and QRA usually involve dispersion modeling of either routine emissions or identified accidental releasescenarios. The following need to be agreed with the reviewing agency before either can be carried out:

- Characterization of emission sources or release scenarios.

- Identification of nearby sensitive population centers and/or ecologies.

- Representative topographic/meteorological data.

- Dispersion modeling protocol.

- Risk evaluation protocol.

- Effects of planned mitigation procedures.

COST ANALYSIS OF CONTROL OPTIONS

Choosing among various pollution control options will likely require some type of efficiency and cost comparisons of themethods being considered. Among the possibilities for control are pollution prevention, conversion of the pollutant to analternative form, dilution of the stream, and collection and treatment of the emission. When selecting air pollution controlequipment, there are often several technology options which should be considered. The options are first narrowed bydetermining their technical feasibility and their capability to meet the regulatory limit. After this screening, the remaining optionsshould be analyzed to determine their cost.

The cost analysis for air pollution control equipment should be as comprehensive as the one done for any new plantinvestment. The analysis should consider two criteria. One is the total capital investment required. Frequently a plant mayhave a limit on available capital. The second criteria is the cost effectiveness. This criteria is used to assess pollutant removalat the least cost and has the units of cost/ton of pollutant removed.

TOTAL COST INVESTMENT

The Total Capital Investment (TCI), also Total Erected Cost (TEC), includes direct material and labor and indirect costs (fieldlabor overheads and erection fees, contractor's engineering and engineering fee, EMRE services, and project contingency).






COST ANALYSIS OF CONTROL OPTIONS (Cont)

AVERAGE COST EFFECTIVENESS

Cost effectiveness is generally the average cost effectiveness which is defined as:

tons/yr rate),emissionsoptionControlrateemissions(Baseline

CostAnnualizedTotalOptionControlessEffectivenCost

−=

The Total Annualized Cost (TAC) is the sum of three elements. These are the Direct Annual Costs (DAC), the Indirect AnnualCosts (IAC), and the Recovery Credits (RC).

)yr/($RCIACDACTAC −+=

These costs are defined as follows:

DACs comprise the annual operating costs and include items such as utilities (e.g., steam, water, fuel), operating labor,maintenance materials, maintenance labor, chemicals (e.g., ammonia, caustic).

IACs are associated with the TCI and include capital recovery, property taxes, insurance and administrative charges.Generally, the dominant cost is the capital recovery and the IAC can frequently be approximated as:

)TCI()CRF(IAC =

where CRF is the Capital Recovery Factor.

RCs are credits associated with the control options and include annual savings in energy and materials, for example.

INCREMENTAL COST EFFECTIVENESS

Sometimes there is also a need to consider the incremental cost effectiveness. This occurs when a regulatory agency hasestablished guidelines for a reasonable average cost effectiveness for a pollutant control and several options are within theguideline. In such cases examining the incremental cost effectiveness can provide a justification for eliminating an option. Theincremental cost effectiveness (cost per incremental ton removed) is defined as:

Incremental Cost Effectiveness =

rate)emission1Optionrateemissionoption(Next

option)nextofcostannualizedTotal1optionofcostannualized(Total

−−

Besides being useful for deciding between different control options, the incremental cost effectiveness can also be useful inevaluating a specific control over a range of effectiveness. Total and incremental costs may vary significantly over theoperating range of a control device.

DESIGN PRACTICES

Documents

Transcript of DESIGN PRACTICES