Odour Assessment Methodology for Petrochemical Industry.

Scentroid, A division of IDES Canada Inc.431 Alden Rd. #3 Markham, ON, L3R 3L4

T: 416.479.0078 or 1.888.988.IDES (4337) www.Scentroid.com

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Contents

1. Introduction ............................................................................................................................................. 3

2. A Hybrid Approach ................................................................................................................................... 4

3. Implementation........................................................................................................................................ 5

3.1 Phase 1 Description of the Field Odour Patrol ..................................................................................... 5

3.2 Selecting Points for Monitoring (Inside and Outside of Plant Boundary): .......................................... 6

3.3 Data gathered at each survey location ............................................................................................... 7

3.4 Selecting and Training the Odour Patrollers ....................................................................................... 8

3.5 Equipment used for Odour Patrol ....................................................................................................... 9

3.5 When each location should be surveyed: ........................................................................................... 9

3.6 Phase 2: Source sampling and olfactometric analysis ....................................................................... 10

3.7 Reverse Modeling .............................................................................................................................. 11

3.8 Predictive Modeling .......................................................................................................................... 12

4. Analyzing the Results and the Deliverables ........................................................................................... 13



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1. Introduction This article will describe an approach to address odours at a gas/petroleum/oil refinery plant from a

practical perspective. Using traditional methods of source sampling and modeling for refineries has been

shown to be ineffective due to the vast number of sources within the plant. While stacks and lagoons can

be easily identified and the odour emission quantified, fugitive sources such as leaks, holding tank

openings, overpressure relief valves, flaring, and residual liquids can all significantly contribute to the total

odour emission from the plant. The odours from these processes will travel differently and will often have

adverse impact on residence up to hundreds of kilometers away.

This article will describe a new and innovative approach to odour emission assessment of petrochemical

refineries. This approach takes into account all sources both from stacks as well as from all fugitive sources.

The objective is to determine not only the impact of the plant but also to identify the most significant

sources to be targeted for remediation. The result of the study can also be used to implement electronic

continuous odour monitoring and complaint management system.



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2. A Hybrid Approach Odour assessment of a refinery plant must utilize 3 main phases and technologies:

1. Field Odour Patrol using personal olfactometery and portable gas analyzers.

2. Source sampling and olfactometric laboratory analysis

3. Dispersion modeling

The addition of Odour Patrol using personal olfactometery is a critical step and differentiates this

methodology from all previous attempts using classical odour assessment. The classical approach of

source sampling, olfactometric analysis, and dispersion modeling was developed decades ago for dealing

with waste water treatment plants. This approach is not suited to a refinery without the use of an odour

patrol as way to tie real field measurements with predicted impact.

Field Odour Patrol is used for:

1. Source identification: determining the sources that need to be sampled and measured using

olfactometric laboratories

2. Baseline Study: assess the plants emission at the boundary and at the sensitive receptors (neighboring

residents)

3. Contribution Study: assess the impact of other nearby refineries or odour causing industries

4. Quality Assurance: assess the accuracy of predicted impact from dispersion model and source sampling

by comparing the results to real measured field data.

5. Determine the effect of certain process events (e.g. flaring) on odour impact of the plant.

Source sampling, olfactometric laboratory analysis and dispersion modeling are not used in this method

to assess the impact but rather to determine the contribution of each odour source to the total odour

impact of the plant. The ranking of odour sources are first based on contribution followed by ease/cost of

mitigation technology allowing the company to maximize their odour impact reduction with minimal

investment. Source testing also allows the plant to determine the mitigation efficiency of any solution that

is implemented.



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3. Implementation

3.1 Phase 1 Description of the Field Odour Patrol The first step in conducting a thorough odour survey is to select the locations that will be patrolled by the

field odour survey technicians. To conduct a full and comprehensive survey the odour patrol must cover

both inside and outside of the plant boundary.

Within the plan the ambient odour monitoring is done by measuring upwind and downwind of significant

sources in order to determine if the source is contributing to the total odour emissions. While individual

sources cannot be separated and easily identified in all cases, this method works well when sources are

considered in groups. For example in a natural gas refinery, each LNG train (liquefaction and purification

facility) can be considered as one group initially. Off‐spec ponds, holding tanks, and other visible sources

can be considered separate sources.

Within the plant boundary along the perimeter, a comprehensive odour survey using field patrollers can

determine odour levels at the property line caused from plant processes and distinguish it from those

entering from neighboring plants/sources. This distinction between what is produced by the plant

versus what odours enter the plant can have significant regulatory implications as well as considerable

impact on the investment required by the plant in mitigation technology. It is useful to not think of the

odour issues as the result of operation of any one plant, but rather the contribution of all odour causing

processes in a region. Odours often mix from various plants to produce a new, unique, and perhaps much

more foul odour. Unfortunately the mixture of odours with a refinery tends to have characteristics with

strong resemblance to the original odours emitted by the refinery; however the odour concentration can

be much higher because of the mixture of odours from neighboring processes. Therefore, while the

refinery is blamed and identified as the sole cause of the odour emissions, they are often one of the many



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Scontributors to the issue. Proper boundary patrol can help the plant identify how much of the total odour

impact they are responsible for.

In addition to odour survey conducted within the plant boundary, additional measurement points must

be considered in the surrounding area around plant especially where sensitive receptors are located.

This survey allows the team to identify locations of possible complaints such as a residential community

impacted by the odour emissions. Field odour survey outside the plant can also provide valuable data for

validating dispersion models created in the source sampling and laboratory olfactometery phase.

3.2 Selecting Points for Monitoring (Inside and Outside of Plant Boundary): The points selected for odour survey within the plant boundary will be based on plant layout, interviewing

field process engineers, and interviewing environmental officers. Outside of the plant boundary, the team

must rely on meteorological data, recorded complaint locations, and location of the sensitive receptors to

determine effective and practical survey points.

An initial assessment of the plant is the first and most critical step. This is where a sampling plan is

determined. The key to a successful odour monitoring program is to select areas where odour is

potentially or usually present. The engineer conducting survey may have a plant map, wind roses and

discussions with senior management and operators during an initial site visit for an assessment. A

valuable source of information during this initial assessment is to speak to field operators, who have

excellent knowledge into where odours may be present. Speaking to as many of these people will help

develop an effective plan from the beginning. Odour technicians in the initial days of measurement

should also engage field operators and covey any important information to the senior engineer to update

the sampling plan.

The selection of a point during the site visit and after reviewing the plant map may result in what appears

like a good point, yet may prove not as worthy. For example, selecting an elevated point on top of a tank

at a downwind distance of 300m of several process may appear a good option, but may actually yield

very few odour readings. Selecting these ambient monitoring points may require some ‘hunt and try.’

Since wind is a transporter of odour, wind roses are used to help pick ambient monitoring points in and

outside of the property line. A general wind direction can be determined and upwind and downwind

points be determined. Wind direction and speed change is influenced by season/month and time of day.

Depending on process and wind speed and direction, odours may move slightly in location of an area.

Although they may disappear, technicians may be able to capture readings with some frequency. For

example, on one side of road odours may be strong, yet on the other side no odour can be detected.



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It is tempting to use initial air dispersion modelling to predict potential points of highest odour. However

due to the large number of unforeseen odour sources at this stage of the project, any dispersion modeling

will be too simplified to yield any useful information on odour impact locations.

Once a complete list of survey points is created the team will validate the points by collecting odour

concentration measurement at each location for up to 30 days. The validation period will allow the team

to gather base levels for each location and discard locations that have less than 5% frequency of perceived

odour. Additional survey points may also be added during the validation period based on observation

and experience the team gains while conducting the odour patrols.

3.3 Data gathered at each survey location At each data location, the odour patrol team records: date, time of measurement, GPS coordinate, odour

concentration based on personal olfactometery, description of the characteristic perceived odour, local

wind speed and direction, and optionally additional chemical readings (such as H2S or VOC) using portable

sensors such as the Scentroid OdoTracker. The team will encounter two types of odour, those that are

constantly present and those that are perceived intermittently. Intermittent drafts are usually due to wind

dusts and calm conditions below 1 m/s wind speeds. The drafts typically last between 20 to 60 seconds.

If drafts are below 20 seconds but repeat every few minutes, it is recommended to use a lung sampler to

capture a 10 min sample and analyze the sample using SM100 personal olfactometer at site. The team

will stay at the location and take an SM100 readings every 3 minutes for total duration of 10 minutes. This

will result in 3 readings over the 10 minute duration. The results are then used to determine the 10 min

average of the odours perceived. This will ensure any drafts are captured and also helps to correlate

with the 10 min interval in dispersion modelling. Technicians should face the wind direction when taking

odour measurements and avoid having nearby objects or structures upwind.

Significant odour readings that were not typical to a point were conveyed back to the process in order to

determine if a process event was responsible.

Tracer compounds can be measured, such as H2S and VOC’s, during ambient and source sampling to

determine if rises in specific compounds could be correlated to increases in odour. This information can

be used to implement a continuous total odour monitoring solution. H2S generally does not appear to

have a direct correlation with most refinery processes. Initial study shows total VOC to have some

correlation that could be used as part of continuous odour monitoring.



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3.4 Selecting and Training the Odour Patrollers A properly trained technician is critical since they produce the crucial data of the odour survey. Odour

patrollers use the same technology used in olfactometric laboratories that conduct odour concentration

measurements to EN13725; meaning that they act as a panelist and use their olfactory sense with the

personal olfactometer to determine ambient odour concentration. Technicians need to be certified by n‐

butanol following the international odour standard EN13725. They should avoid smoking, alcohol, coffee,

gum, or other nerve stimulating chemicals. They need to have basic theory and practice (or training) on

odour perception and sampling methods. This will make them aware of issues such as odour fatigue which

can affect accurate recordings.

The ideal odour patrol consists of three technicians. Two technicians (panelists) are equipped with

SM100 personal olfactometers, and one ‘spotter’ whom performs initial survey and data collection. The

spotted will instruct the panelists when to start their measurement and will record other parameters such

as wind speed, direction, GPS coordinates, chemical readings, and odour characteristic. If panelists are

using the SM100i intelligent personal olfactometer, the unit will automatically record chemical levels,

odour concentration, GPS position, and wind speed/direction and therefore it may be possible to avoid

the use of the spotter.

The use of two panelists allows the for greater data reliability. Panelists should obtain results within a

maximum of 20% difference when conducting measurements at the same location and at the same time.

Results should be communicated to the spotter technician in private, so as not to influence the other

technician’s results, if not using the SM100i. Psychology plays a role in this matter and must be noted.



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3.5 Equipment used for Odour Patrol Equipment used for ambient odour concentration measurement can be the SM100 or the SM100i. Both

devices work on the same principle of olfactometry as used in an olfactometric laboratory. Clean diluting

air is provided from a micro‐tank and is used to draw a sample and mix it at exact dilutions starting from

30,000 all the way to 2 times. The panelists breathe the mixture of ambient and diluting air and determine

at which concentration the odour becomes perceivable. The main difference between the two devices is

that the SM100i automatically controls the dilutions while the SM100 the panelist must manually decrease

the dilution if no odour is perceived.

Chemical sensors in the form of portable analyzers such as Scentroid OdoTracker or GC based portable

instruments can be used. The important characteristic that must be considered for any type of handheld

analyzer is the lower detection threshold. Certain chemicals such as H2S have an extremely low odour

detection threshold (e.g. H2S is 0.5 ppb). This means that at 0.5 ppb H2S has a perceived odour; therefore

sensors measuring H2S in ppm level are not useful for odour survey applications.

3.5 When each location should be surveyed:

The main objective when scheduling odour patrol shifts is

to ensure each location has data recorded at varying times

during the day over the survey period. It is recommended

to have two odour patrol teams: one for the locations

inside the plant and one team to survey the external

locations. The teams must measure concurrently to be able

to get as much correlated data as possible. The teams must

work on rotating shifts of day and night each lasting 10 to

12 hours. For example both teams would be on day shift

surveying locations from 7 am to 11 am and then again

from 2 pm to 6 pm. This shift schedule would last for 4

days then after a 2 day rest they would be switched to

night shift from 7 pm to 6 am. The order in which locations

are surveyed must also be changed every shift to ensure

odour concentration data is gathered from each location at

all hours of the day. Typical duration of the odour patrol

phase is a minimum of 30 days repeated once in summer season and once in the winter season to capture

different wind patterns.



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3.6 Phase 2: Source sampling and olfactometric analysis The data collected by the odour patrol is then used to identify the odour sources within the plant. Some

of these sources may be practical to sample (e.g. off spec pond, holding tanks, stacks) and others may not

be practical to sample (in process leaks, over pressure relief valves, emission from liquid spilled on the

ground), referred to as fugitive sources.

For the point and area sources, the sampling team will use common sampling techniques as dictated by

the international odour standard EN13725. This includes flux chamber emission measurements for all area

sources both on land and on a liquid surface. Typical stacks in a refinery have high moisture and

temperature content and therefore must be properly pre‐diluted while sampling. A dilution probe with

capability to pre‐dilute up to 100 times is generally required to sample refinery stacks in accordance to

EN13725. All samples collected must be stored in PTFE bags as most compounds found in refineries (e.g.

benzene) escape easily from Nalophan and Tedlar bags. Samples of extremely high odour concentration

(over 10,000 OU) should be pre‐diluted at the source to avoid contamination of the olfactometer and to

minimize sample degradation.

If areas of the plant are identified by the odour survey to be of high odour impact but has no identifiable

point or area source then the odour is caused by fugitive odours. If an area has only fugitive sources, a

reverse modelling technique is required to quantify the emissions from the area to be used in dispersion

modeling. This technique assumes the entire area as a volume source and relies on measurements

collected during patrolling upwind and downwind of the location to determine the total odour emission.

Olfactometric analysis should be performed within 6 hours sampling in accordance to the VDI3880. Care

should be taken to ensure panelist are not exposed to full concentration of the odour as temporary

olfactory “blindness” is very common when exposed to contaminants found in refineries such as H2S and

Benzene.

Scentroid, A division of IDES Canada Inc

431 Alden Rd. #3 Markham, ON, L3R 3L4

T: 416.479.0078 or 1.888.988.IDES (4337)

www.Scentroid.com

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3.7 Reverse Modeling

Reverse modeling is used in two stages within the odour impact assessment of a refinery. In the first stage, the entire data

collected by the odour patrol is used to conduct reverse modeling of the plant as a whole. In this model, the plant is

assumed to be a large volume source and data collected over the patrol period along with the associated metrological

data is then used to determine the total odour emission of the plant. Scentroid has developed automation tools to make

the reverse modeling more efficient and cost effective.

Reverse modeling can also be used to determine total odour emission from a small portion of the plant, in which the

odour survey was identified as a high impact area containing only fugitive odours. The reverse modeling and total odour

emission is then used in a predictive model to determine the exact impact of the specific area on the total odour impact

of the plant. This result can be used to rank the odour sources (both fugitive and source) based on their impact for more

efficient and economically feasible odour abatement implementation.



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3.8 Predictive Modeling

The predictive model can be

created once all odour sources

are identified and their total

odour emission is measured. As

mentioned previously, all fugitive

odour sources must have a total

odour emission based on reverse

modeling. The predictive model is

created to determine how much

each source contributes to the

odour levels perceived at

different locations. While some

odours may have a high total

odour emission, their impact on

the sensitive receptors may be insignificant. Generally, odours from low level sources (e.g. off‐spec pond)

close to the ground travel less than odour from high level sources (e.g. tall stacks). Certain odours travel

more due to their temperature or their flow velocity from the source.

The predictive model allows us to create a list of sources with their odour contribution as a percentage of

the total odour perceived at the sensitive receptor. Those with highest impact should be targeted for

remediation if the total odours are to be reduced. Sources must also be ranked based on the cost of

remediation to ensure a feasible and economically efficient remediation plan is created.

The predictive model can also be used as a validation of the sampling and olfactometric process. Predictive

model can be executed for meteorological conditions during surveying and the theoretically predicted

odour levels can be compared to those obtained in the field. While some errors may be expected due to

omission of certain odour sources, uncertainty in measurement in the field and in the laboratory, a strong

correlation should be observed. This correlation will validate that the process of the predictive model was

correctly performed and matches the actual readings.



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4. Analyzing the Results and the Deliverables One of the key deliverables from the odour impact assessment will be the effect of process events on total

odour impact. During the odour patrol, field odour concentration is collected and compared with any

irregular process events. Results from each data point is analyzed to find instances where odour

concentration exceeded the 90th percentile. For each of those instances, the plant log book is studies to

determine if any potentially odour causing event had occurred. If there is correlation found between the

events and the change in odour impact, the plant can be notified to change the process or if possible, to

schedule the event to minimize the odour impact. The scheduling can be based on meteorological

conditions (when wind speeds exceed certain velocity or are not blowing to the sensitive receptors or

certain ambient temperatures), or based on time of day (late night when the odour impact may not be

noticed). The knowledge of odour impact of each process event can play a significant role in reducing the

odour nuisance of a plant.

The odour survey will also produce graphs showing frequency, duration, concentration and offensiveness

of the odour at each location. The maps and graphs will clearly show the impact of the plant and can be

used as a comprehensive baseline study. Repetition of the survey after mitigation technologies have been

implemented, can show the effectiveness of these solutions and demonstrate due diligence. The graphs

can also be used to determine when and how often the plant can expect to impact the neighbouring

residents.

The odour impact through survey can be combined with results from predictive and reverse modeling

to show using exactly the impact of the plant as a percentage of the total odour impact. The data can also

be used to determine where other external odour emitters are located and quantify their contribution.

At the end of the study the plant will have exact knowledge of their own odour impact, what events and

processes cause the adverse effects, and what may be done to reduce their odour emission.

Odour Assessment Methodology for Petrochemical Industry.

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Transcript of Odour Assessment Methodology for Petrochemical Industry.