ENote-Practical Considerations for Converting Boiler to Burn Natural Gas

8/10/2019 ENote-Practical Considerations for Converting Boiler to Burn Natural Gas

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PracticalConsiderationsforConvertingBoilerstoBurnNaturalGas

NathanielS.

Schindler

All en Adri an i

Combustion Components Associates, Inc.

ABSTRACT

Pulp and paper mill engineers and operations managers will benefit from the practical guidance provided to assesstheir facility to use low cost natural gas in their boilers. Basic principles of burning natural gas are discussed alongwith impacts on the current equipment. The differences associated with converting major power boiler types --package boilers and field-erected wall and t-fired units are reviewed. Other boilers biomass and coal stokers,recovery boilers, and fluidized bed boilers -- can utilize natural gas as an auxiliary fuel for startup or load carryingcapacity. The paper includes options and limitations related to keeping your current fuel for use during emergenciesor in the event of market changes. Standards for safety and controls are reviewed. Emission control methodsassociated with natural gas are also discussed. Meeting NOxpermit limitations can be a significant factor in the costof converting a boiler to burn natural gas. Any calculation of the return on investment and determination of thefeasibility of converting to natural gas must incorporate NOxemissions and associated control technologies to beaccurate.

1 INTRODUCTION:

Conversion to natural gas is an important opportunity in the pulp and paper industry today. Energy costs represent asignificant portion of fixed costs for pulp and paper mills and the reduced cost and complexity of firing natural gascan add to the mills profit. Returns on investment of 1 year are not uncommon, making natural gas conversionsattractive, even in these times of lean capital expenditures. But not all projects are equal. Mills have been seekingfeasibility studies to determine the practicality and cost considerations of switching to natural gas. This paperpresents some of the technical considerations of implementing a natural gas conversion.

Comparison of natural gas combustion properties;

Natural gas emissions fundamentals; Common uses for natural gas at a pulp and paper mill;

Basic requirements of all natural gas conversion projects;


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q g p j ;

the superheater. Boiler tube modifications may be required to maintain existing steaming capacity. Assess thisearly in the project so that capital costs of modifications and steam capacity limits can be accurately assessed.

2.2

Fuels

Many different types of fuels can be burned inside a boiler. Biomass, coal, oil and gas are among the common fuels.Table 1 compares natural gas to these fuels. NFPA 85 defines natural gas as a gaseous fuel that is comprised of

methane, propane, ethane and butane with a heating value of between 700

and 1000

.

Table 1: Typical Fuel Combustion Properties

Fuel

Type

HHV

BTU/LBm

Mass Air to

Mass Fuel

% Excess

Air

Typical

BoilerEfficiency

Natural

Gas

21,000 17.23 10-15 82-84%

#6 Oil 18,100 10.63 10-15 85-88%

Coal 11,000-13,000 10.7 25-30 84-86%

Biomass 7,300-9,000 4.8 25-32 84-86%

2.3 EmissionsFormationFundamentals

Boiler emissions have, during the last thirty years, come under the scrutiny of not only the U.S. EPA but also localand state governments. Solid and liquid fuels typically are highly regulated for a variety of emissions, includingopacity, particulate, oxides of sulfur (SOx), mercury, nickel, carbon monoxide (CO), volatile organic compounds(VOCs), and NOx. Many of these pollutants are a result of components in the fuel or difficulties with combustion.

Modern natural gas supplies have very few contaminants that cause pollution. Modern natural gas burners are welladapted to burn cleanly and completely. The primary pollutant of concern is NOx. CO and opacity are typicallyregulated because NOxreduction techniques, as discussed below, focus on reducing the flame temperature and can

result in elevated CO or opacity. Opacity is typically not an issue with gas. When burning gas, VOC and particulaterates can often be higher at the FD fan inlet then at the boiler outlet.

2 3 1 Thermal NO By reducing combustion temperature the production of NOx can be reduced NOx


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1 2 1 2 2

2 3 3

d Nk O N k NO N k N O

dt

k NO O k N OH k NO H

(0.5)

The forward and reverse rate constants are denoted as kn. At lower temperatures there is less activation energy inthe mixture and thereby the rate of NOx formation is reduced. Temperature, molecular surface area andconcentration all influence the activation energy level (Kuo, 2005). Since the physical surface area of the moleculecannot be changed, temperature and concentration become the controlling factors to reduce NO and NO2.

When the reaction rate is reduced by temperature, the first mechanism reduces the concentration of NO and N. This

reduces the potential reactants in the second mechanism. Therefore, a reduction of temperature for the first reactionintroduces a limiting factor for NOxemissions. For that reason, the objective of the technology to be applied is toreduce thermal NOxby lowering the reaction temperature.

CO emission is effected by combustion temperature and excess air. When combustion temperature is too low, COwill not burnout reducing boiler efficiency. When excess air is insufficient, the CO emissions will increase becauseO2is insufficient to complete the reaction of CO to CO2. There is a range of excess air that is optimal to minimizeboth CO and NOxemissions.

2.3.2 PromptNOx. Ultra low NOxis not merely a name change from low NOx. Ultra low NOxis usually definedas less than 10 ppm NOx corrected to 3% O2. The important difference is that below 10 ppm, prompt NOxmechanisms, not thermal NOxmechanisms, dominate the formation of NOx. Prompt NOxis formed by the reactionof nitrogen from the combustion air with combustion radicals formed at the outset of the combustion process in thefuel rich zones. Prompt NOx occurs almost instantaneously and cannot be controlled by reducing peak flametemperature, hence the apt name prompt.

NOxemissions lower than 10 ppm are not achievable through the use of staged fuel and air low-NO xburner designs.A complete change in the burner concept is required to reduce or eliminate prompt NO x. Ultra low NOxburners thatrely on high volumes of flue gas recirculation (FGR) (typically recirculating 30% of the flue gas mass or more) have

been developed for single burner boilers or two burner unison fired boilers. Selective catalytic reduction (SCR) canbe a cost-effective alternative to Ultra-Low NOxburners because of technical and control limitations on multi-burnerboilers with pre-heated air.


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Package units typically burneither natural gas or fuel oil.Other liquid and gaseous fuelscan be burned in packageburners as waste fuels orauxiliary fuels. Package boilerburners are relativelystandardized in designs for fueloil and natural gas. A newburner or burner modificationcan be relatively easilyimplemented. New fuel and air

staged burners can be longer, sowindbox modifications or newwindboxes are often required fornew burners. Most oil burnerscan be modified with a

replacement fuel gas assembly in place of the oil burner. Low NOxburner modifications can include a low NOxgasmanifold that also retains the capability to fire oil. (Figure 1.)

Natural gas combustion is slightly less efficient than oil combustion because of the latent heat in the exhaust gas.

However, the oil combustion air supply is often sufficient for gas firing because oil burners require a higher excessair level to complete combustion and reduce opacity than gas.

If the package unit is designed to burn #6 fuel oil, consideration should be given to converting to #2 fuel oil as abackup fuel. A gallon of #2 fuel oil is more expensive than a gallon of #6 fuel oil; however, the overall costs ofhandling #2 fuel oil as a backup fuel can be lower. #2 fuel oil is easier to handle, burns better in the tight furnace ofa package unit, and does not require heating. If the oil is expected to be burned only rarely, the high heat valuecomponents of #6 fuel oil can volatilize leaving a viscous slurry that is difficult to burn when needed. Low NOx#6fuel oil (~0.25 lb/mmBtu) and low NOx#2 fuel oil (~0.1 lb/mmBtu) atomizers are available. Because of the highsulfur content and other fuel components, #6 fuel oil is not compatible with ultra low NOxburners.

3.2 FieldErectedUnits

Figure1:LowNOxGasManifold


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Multi-burner boilers are typically arranged in two ways, wall-fired and tangent or corner-fired. Burners on wall-fired units are arranged in rows and columns on one or more walls of the boiler. The burners are designed to createand maintain their own flame. Tangent fired units are designed with burners located in each of four corners on asingle level. All four burners on a level are designed to fire together and create a swirl zone in the center of thefurnace with a single stable flame.

3.2.1 Wallfiredfielderectedboilers.Wall-fired burners are typically round. They can be fired from a singlewall or opposed fired. They can be arranged on a single level or multiple levels. Wall-fired burners have integratedregisters or dampers to balance air to each burner and isolate burners that are not firing. These mechanisms help toensure that each burner has a good fuel to air ratio under avariety of operating conditions. Typical natural gaspressures at the burner are 12 to 15 psig. The existing

burners can often be modified to accept a low NOx naturalgas burner manifold in the center. This permits reuse ofdampers and actuators and reduces installation cost and time.Even when the register must be replaced, burner throatpressure parts are not usually required to convert a coal or oilburner to natural gas. Low-NOx gas burner retrofits capableof burning coal and oil are available. (Figure 2.)

Low NOxnatural gas burners rely on fuel and air staging to

reduce peak flame temperature. Therefore, low NOxnaturalgas flames tend to be longer and wider than older coal or oilflames with the same heat input. Burner flame length can bereduced by increasing pressure drop through the burner. TheFD fans on most coal boilers have sufficient capacity for anatural gas burner, even with a higher pressure loss. However, this should also be evaluated during the feasibilityinvestigation.

On the other hand, low NOx natural gas burners offer significantly higher turndowns than coal or oil burners.Natural gas burners are capable of 10:1 turndown, while oil burners are limited to approximately 6:1 and coalburners are limited to 3:1. Therefore, if the plant is eliminating coal, the total number of burners can sometimes bereduced. The cycling of burners in and out as load swings can also be reduced. Also, for two burner multi-burnerunits unison firing should be considered The safety system and controls become much less complicated reducing

Figure2:WallFiredMultiFuelBurner


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considered a priority because of the low cost of modifying the burners and the high cost of oil. Modifications to thecirculation system to reach full load firing gas are not uncommon. However, incorporating natural gas bucketsrequires minimal modification to the existing corner buckets. The current coal buckets and oil burners can beretained often with no changes. On tangent fired coal units, oil igniters providing 10% of the heat input are typical.These igniters can be used to warm up the boiler and support combustion of the coal. Replacing these igniters withnatural gas igniters can provide a significant return on investment. During low demand periods, low-cost natural gasigniters are often a cost-effective means of keeping the boiler warm. When firing natural gas alone, the mill canshut down the coal mills, feeders and other coal equipment, saving energy and operating costs.

Low NOxgas and coal modifications are possible by incorporating current generation swirlers to stabilize a coreflame and enhance fuel staging. We are not aware of any commercially available ultra low NOxburners for tangentfired units.

3.3 AuxiliaryFuelBoilers

Paper mills often have hog fuel or coal stokers, fluidized bed boilers, and liquor recovery boilers. Many of theseboilers have oil igniters or starting guns that can be modified to burn natural gas. These boilers also have the abilityto supplement load capacity through upper level natural gas burners, maximizing the uptime of these units. Whenthese boilers have existing auxiliary burners capable of oil firing, it is generally straightforward to convert andfollow many of the same principles as multi-burner boilers, discussed above.

3.3.1

Stokerunits.

Stoker units burn solid fuel on a grate. Typically, the solid fuel is hog fuel (a biomass

product) or coal. As part of the combustion air system for the grate fire, over-fire air is incorporated above the grateto complete combustion and reduce CO emissions. The grate over-fire air is not to be confused with over-fire air forNOx emissions control. Auxiliary fuel burners capable of burning oil or gas can be installed above the grate. Theburners can be arranged as tangent fired units or wall units. A significant difference between stoker units and multi-burner units is that the grate must always be kept cool with undergrate air. When burning fuel in the auxiliaryburners, the undergrate air impacts the fuel to air ratio and total excess air. Air to the grate must be controlled whilefiring natural gas to keep NOx emissions low while ensuring complete combustion. Emissions from auxiliaryburners on stoker units tend to be higher than similar sized multi-burner units because of the higher excess air

requirement to keep the grate cool. FGR can sometimes be used to cool the grate when firing natural gas. Naturalgas burners on stoker units usually will not be able to supply the same steam output as the solid fuels due to thereduced radiant heat transfer in the lower furnace. Auxiliary heat input above approximately 50% of design heatinput will likely require modifications of the superheater and circulation system so a boiler study is necessary If


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ambient air combustion supply. Load burners can be installed as wall burners or tangent burners. Most of the time,existing port openings and registers for oil burners can be reused. Recovery boilers without existing load burnersusually have sufficient height to incorporate new load burners. These are often designed for about 50% of boilerdesign steam output. Heat transfer from the load burners to the lower furnace will be limited by the high elevationof the burner in the boiler and the limited luminosity of the gas flame reducing heat transfer to the lower furnace.

Class I igniters are typical for startup and load burners, which scan the igniter only as more repeatable in thedynamic furnace environment of a recovery boiler. Flame detection of the igniter is also less susceptible tointerference from slag from the liquor process. Class 1 igniters can also be utilized to verify combustion of wastegases in the auxiliary burners.

4 SAFETY,CONTROLS,ANDEMISSIONS

Natural gas safety systems are specialized to avoid boiler explosions by controlling when fuel can be let into thefurnace. Controlling the fuel and air ratio properly is also essential to avoid boiler explosions, increase efficiency,and meet emission requirements. If your state has NOxlimits of 0.1 lb/mmBtu or less, NOxcontrol technologies willprobably be required for preheated combustion air units to meet permit requirements. Implementing NOx controltechnologies are often similar in cost to modifying the burners. If NO xemission levels less than 0.04 lb/mmBtu isrequired, emission controls can double the cost of the project.

4.1 Safety

Natural gas safety standards have been well developed of the years by the National Fire Protection Association(NFPA), Factory Mutual (FM) and BLRBAC. NFPA 85 is an industry standard for the burner management systemof single burner and multi-burner gas and oil burners, duct burners, pulverized coal burners and fluidized bedburners. In many states, NFPA requirements have been adopted as regulatory or legal requirements. NFPA 85 wascompletely revamped around 2000 and has been updated a few times since then. Adding natural gas burners willrequire modifications to the existing burner management system to incorporate the necessary interlocks and startupsequence for gas firing. On older systems, a completely new burner management system may be required along withupgrades to the oil, biomass or coal safety systems. In addition, NFPA 54 provides standards for natural gas piping

design. At some point in the project the insurance carrier must be involved to insure a smooth project and eliminaterework.

FM has many standards and general requirements that apply to natural gas burner and piping systems for single and


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pulverized coal is still expected to be used, then dust tight electrical enclosures may be required.

4.2 Controls

Control systems for natural gas firing vary based on boiler type and emission control requirements. For most papermills, air and fuel will be controlled independently through a fully metered control system driven by a DCS.Combustion air, FGR, and over-fire air flow rate, furnace exit oxygen, furnace exit CO, combustion air oxygen, andnatural gas flow are common measurements, depending on the emissions control technology implemented.Implementing natural gas burners with the ability to co-fire with the biomass or other primary fuel require separateair measurement to the natural gas burners and the grate. Individual burner airflow measurement is also used forsome co-firing applications. If cofiring more than one fuel in a burner is contemplated, the controls become muchmore complex.

4.3 EmissionsControls

There are several technologies on the market today to control NO xformation in natural gas fired boilers. Low NOxtechnologies include: FGR, overfire air (OFA), low NOx burners, burners out of service (BOOS), selective non-catalytic reduction (SNCR), and water injection. Typical NOxemissions from low NOxgas burners in a packageunit firing natural gas are 0.1 lb/mmBtu without additional control technology. Typical uncontrolled NOxfrom lowNOxfield erected natural gas boilers range from 0.12 to 0.3 lb/mmBtu depending on boiler type and furnace design.Depending on the requirements of the project, these technologies can be layered to maximize NO xreductions and

minimize costs. Emissions controls to meet permitting levels for natural gas burners can be a significant percentageof the conversion project cost. Early discussions with your state regulators on an adhoc basis can sometimes befruitful for a smooth project.

NOx control technologies can be added in various combinations to reduce NOxemissions from gas fired boilers toapproximately 0.04 lb/mmBtu. Ultra low NOxburners and SCR are the only methods for reaching emissions of lessthan 0.01 lb/mmBtu. Table 2 lists emission reduction technologies considered. The table shows each technologyindividually and compares the potential decrease in NOx emissions on boilers between these technologies.

Table 2: Comparison of NOxTechnologies

Reduction MethodDecrease in NOx, % Compared to

Conventional Gas BurnersAnnualize $/TonNOx Removed


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4.3.2 Flue gas recirculation. FGR is the recirculation of flue gases into the combustion air stream to theburner. FGR is a common emission control technology for gas and oil units. FGR reduces thermal NOx byincreasing the specific heat of the combustion mixture to reduce the flame temperature (Agrawal, 2004). AddingFGR also lowers the concentration of O2available in the combustion zone, slowing combustion and reducing theavailable oxygen for reaction with free nitrogen.

FGR can be provided to the burners through a couple of methods. The easiest and least costly method is byinducing FGR into the existing FD fan. This method has several advantages:

Ducting runs from flue gas outlet to FD fan inlet are typically short;

Existing FD fan often provides sufficient pressure and flow characteristics to induce 10% FGR whenconverting from coal without upgrading the fan or motor; and

Tipping the fan, upgrading the motor, and increasing fan speeds are low cost options of increasing fancapacity.

Induced FGR; however, typically cannot be used with #6 fuel oil or coal because sulfuric acid tends to condense inthe FD fan when mixed with cold combustion air, causing major damage to the fan wheel and housing. In addition,SOFA, discussed below, is incompatible with induced FGR.

FGR can also be provided through a separate FGR fan. This method is called boosted FGR. Boosted FGR is moreexpensive than induced FGR, in that an additional fan is required and the ductwork is typically longer and more

complicated. The additional costs can be offset by corresponding benefits, including higher FGR levels,compatibility with #6 fuel oil and SOFA, discussed below, and reuse of the existing FD fan if its capacity is limited.

FGR increases mass flow through the furnace and the boiler back pass. The increased velocity increases heattransfer to the superheater. In some boilers, particularly those constructed for coal only, boiler circulation andsuperheater attemperation capacity will be even more important at high FGR rates.

4.3.3 Waterinjection. Similar to adding FGR, injecting water into the flame is an effective means of reducingthermal NOxand is known as water injection. By targeting the hot spots in the flame, Combustion tempering can

reduce NOx25% with just 1 gal/min per 100 mmBtu/hr heat input. It is often used as a topping technology whereNOxreduction is only required at full load and not used at lower loads. Unlike FGR, water injection has minimalimpact on combustion air or flue gas flow. Fans are typically not impacted. Heat transfer in the superheater is only

i i ll i t d d th i l t ti t b l


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increases the percentage of FGR through the burner without increasing the total mass flow of FGR. This techniquemaximizes the benefits of FGR and OFA and provides combined emissions reductions of approximately 75% onnatural gas.

4.3.6 UltralowNOxburners.Ultra-low NOxgas burners in package units are capable of achieving less than0.01 lb/mmBtu with 30% FGR. In contrast, low NOx burners in field erected units are typically 0.12 to 0.3lb/mmBtu without additional control technology. Ultra low NOxburners are not proven below 0.01 lb/mmBtu onpreheated air units. Ultra-low NOxburners vary from low- NOxburners in several ways:

Ultra-low NOxburners are longer and have a larger throat diameter;

Ultra-low NOxburners require approximately 30% FGR; and

Ultra-low NOxburners require a high pressure drop (10-12 in w.c.);

Ultra-low NOxburners cannot be combined with #6 fuel oil or coal.

These differences can double the cost of converting versus a low NO xburner retrofit. The windbox often will needto be replaced or extended to accommodate the longer burner. New burner pressure part openings may be required toaccommodate the larger burner throats. The high FGR rate impacts both the FD and ID fans. An existing FD fanusually cannot accommodate a 30% increase in FGR flow. 30% FGR may raise the temperature at the FD fan inletabove its design temperature. Existing FD fans also cannot usually provide sufficient static pressure to overcome theincrease in burner pressure drop from 5-6 in w.c. typical for standard burners to 10-12 in w.c. typical for utra-lowNOxburners. A separate FGR fan or tipping the FD fan may be options to reuse the existing equipment. The FGR

increases the flue gas exit temperature, which can exceed the design temperature of the ID fan.

Ultra low NOx burners are not compatible with burning #6 fuel oil because of the high sulfur content and othercontaminants in the flue gas, which can damage the burner. They are not compatible with burning coal.

4.3.7 Postcombustiontreatment. SNCR systems can be effective to reduce NOxwhile firing natural gas, buthas not been shown to reduce emissions below approximately 0.05 lb/mmBtu. SNCR is worth considering if theunit has already implemented or is planning to implement SNCR for NO xcontrol of coal or oil emissions. However,it is not generally as cost-effective as other comparable low NOxtechnologies. In addition, placement of the SNCR

injection system at the proper temperature is critical for maximum NOx reduction with minimal ammonia slip. Theexisting SNCR injectors would need to be evaluated to determine if the injector location is appropriate for naturalgas firing. Determining whether the existing SNCR system can be reused and predicting the performance ofteni l CFD d li


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Borman G., and Ragland K,. Combustion Engineering, McGraw-Hill Inc., 1998.

Heywood, J.B., Internal Combustion Engines, McGraw-Hill Inc., 1988.

Kou, K., Principles of Combustion, Second Edition, Wiley, 2005.


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COMBUSTION COMPONENTS ASSOCIATES, INC.

884 Main Street, Monroe, Connecticut 06468

Tel: (203) 268-3139 Fax: (203) 261-7697www.cca-inc.net

Presented to

TAPPI-PEERS

October 2012

Savannah, GA

Presented byNathan Schindler

PracticalGuide to Converting to Natural Gas

2012 PEERS Conference Page 2310


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Introduction

Comparison of combustion properties; Emission fundamentals;

Basic requirements of conversion projects;

Special considerations with respect to boilerconfigurations;

Safety, controls, and NOx reduction

techniques.



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0 5 10 15 20 25 30

FuelFlow Rate - gpm/burner

0.0

0.1

0.2

0.3

0.4

0.5

AtomizingMassRatio-Ms/Mf

0 psid

10 psid

20 psid

30 psid

Atomizing Steam Differential

Map-aof

Atomizing Steam Mass Ratio with Fuel Flow and Atomizing Differential

140 psi fuel at 12.5 gpm15 psi Differential

10.5% Steam Mass ratio5.0 inwc Windbox Differential

Natural Gas Properties

Combustion Properties

Impacts to Existing EquipmentFormation of Emissions



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Fuel TypeHHV

BTU/LBmMass Air toMass Fuel

% ExcessAir

Typical BoilerEfficiency

Natural Gas 21,000 17.23 10-15 82-84%

#6 Oil 18,100 10.63 10-15 85-88%

Coal11,000-

13,00010.7 25-30 84-86%

Biomass7,300-

9,0004.8 25-32 84-86%

Fuel Properties



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Impacts to Existing Equipment

FD and ID Fans Stoichiometry

combustion air requirements

total combustion products Boiler

Combustion product temperature, quantity, and

composition affect the velocities and heat

absorption within the boiler, superheater and

economizer



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Thermal NOx

NOxformation is a function of temperature. By reducing combustion temperature, the

production of NOxcan be reduced.

The higher the combustion temperature, thegreater the NOxproduced.

Dominant mechanism of NOx formation for

low NOx gas burners.



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NOx (ppm) Production vs. Temperature (F)



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Prompt NOx

Dominant mechanism of NOx formation forultra-low NOx

Formed by the reaction of nitrogen from air

with combustion radicals formed in fuel richzones

Occurs almost instantaneously and cannot

be controlled by reducing peak flame

temperature



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0 5 10 15 20 25 30


0.0

0.1

0.2

0.3

0.4

0.5


0 psid

10 psid

20 psid

30 psid


Map-aof




Package BoilersField Erected Boilers

Auxiliary Fuel Boilers

Boiler Type Specific Modifications



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Package Units

Ambient Combustion Air Lower efficiency

Gas/oil

Relatively easy to convert Lower NOx

Firetube/Watertube



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Low-NOx Gas Injectors

Flame

Stabilizer

Gas Retrofit



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Field Erected Units

Multi-burner Preheated Combustion Air

Higher Efficiency

Higher NOx

Gas/Oil/Coal/Biomass

Wall-Fired/T-Fired



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Gas Retrofit to Coal Circular Burners

Retain Coal Pipe - Retrofit Gas Manifold and Poker

Assembly Around Coal Pipe

Gas Pokers

Gas Manifold

Coal Pipe

(Existing



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Retrofit Low-NOx Gas Injectors Above & Below Coal

Retrofit GasInjectors

Behind

Bucket

Flame

Stabilizer

Low-NOx Gas

Injectors

Gas Retrofit to Coal T-Fired Burners



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Auxiliary Fuel Boilers

Stoker Units Auxiliary Oil Burners

Fluidized Bed Boilers

Duct Burners Startup Lances

Recovery Boilers

Startup Burners Load Burners



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0 5 10 15 20 25 30


0.0

0.1

0.2

0.3

0.4

0.5


0 psid

10 psid

20 psid

30 psid


Map-aof




Natural Gas Safety, Controls, &Emissions Reduction Technologies



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Main Gas Valve Train



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Overview of Emission Technologies

Typical Multi-Burner Boiler



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Comparison of NOx Technologies

Reduction Method NOx, % Reduction

Annualized Cost

Factor

NOx Removal

Low NOx Burner 25% Low

OFA/BOOS 25% Low

Water Injection 25-35% Low

FGR 25-75% Moderate

SOFA & FGR 50-80%Moderate

Ultra Low NOx

Burners90% High

SCR 90% High



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Low-NOx Circular Burner



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Gas FlameHigh FGR

21



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Water Injection Skid



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SCR vs. SNCR

SCR Requires Catalyst

90% or more NOx

reduction for Ultra-

Low NOx

Multi-fuel operation

presents special

problems for catalystdesign

SNCR No Catalyst Required

30-50% NOx reduction

Low NOx only

Multi-fuel operation

possible but

performance highly

dependent ontemperature profile at

injection location



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Conclusions



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Questions

Nathan Schindler

203-268-3139 ext 137

[email protected]

www.cca-inc.net

ENote-Practical Considerations for Converting Boiler to Burn Natural Gas

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