Oil and Gas - Petroleum refineries

These activities include the production of petroleum and a variety of petroleum-based products, gasolines, lubricants and petrochemicals. Petroleum refining comprises the following steps:

a) fractioning of crudes by boiling point,

b) conversion, c) removal of impurities, especially
sulphur, d) blending and mixing in additives.

Refinery facilities can pollute the quality of air as a result of their emissions (sulphuric gases, nitrogen oxides, greenhouse gases, volatile organic compounds). They can also generate wastewater which is heavily laden with organic chemicals. Lastly, the risk of soil and water pollution following hydrocarbon spillage must also be taken into account.

Nevertheless, it should be noted that refineries have made considerable efforts in the past few years to focus production activities on products that pollute less. This has had a positive impact on atmospheric pollution and particularly on vehicle-generated pollution levels.

of these factors are analysed by Coface. In case the goods or services in question only play a minor role with respect to the overall project, this situation is nonetheless taken into account in the conclusions of the environmental review.

Main impact factors

The main impact factors building new facilities are:

to consider when

atmospheric emissions (excluding CO2);

use of natural resources and greenhouse gas emissions;

water supply and wastewater;

noise generated by facility operations;

 

• waste and management of toxic or hazardous
substances;

• location;

• construction of new secondary infrastructures
(roads, storage facilities, oil and gas pipelines,
etc.);

• safety and industrial risk management.

Whatever the goods or services exported, all of these factors are analysed by Coface. In case the goods or services in question only play a minor role with respect to the overall project, this situation is nonetheless taken into account in the conclusions of the environmental review.

Factor 1: Atmospheric emissions (under normal operating conditions and excluding

Most countries have adopted regulations which aim to limit atmospheric emissions from refineries. Compliance with these local standards and regulations is required.

In addition, Coface bases its analysis of a given project's impact in terms of atmospheric emissions on a benchmark with the maximum emission levels defined in the guidelines set out by the World Bank for all new refinery projects¹. For all significant pollutants not regulated by the World Bank, Coface refers to the maximum emission levels set by French standards (Order of February 2nd 1998). These levels are presented in Table 1.

Projects are required to comply with the maximum emission levels defined in the World Bank guidelines (reference criteria). Compliance with the maximum emission levels set by French legislation for pollutants which do not fall within the scope of World Bank regulations (VOCs and NH3) is recommended (target criteria).

It should be noted that these maximum levels apply only to processing plants. Energy production plants, where applicable, are subject to the guidelines governing thermal power plants.

 

Fugitive volatile organic compound (VOC) emissions must be assessed and minimised whenever possible (vapour recovery system, joints, pump fittings, etc.). It is best practice to avoid burning gases in flaring stacks and to recover these gases whenever feasible.

Coface would like to encourage the use of the Best Available Techniques as laid down in EU Directive 96/61/EC on Integrated Pollution Prevention and Control.

These techniques are described in the document "Best Available Techniques Reference Document for Mineral Oil and Gas Refineries", European Commission, December 2001, and can be accessed at the following Internet address: http://eippcb.jrc.es/.

Table 2 presents the main pollutants concerned, the emission factors identified, the main emission sources and the measures and Best Available Techniques available to reduce atmospheric emissions.

Regular monitoring of the emissions of the entire facility's main pollutants is required in order to ensure that maximum emission levels are respected.

are

Lastly, it is advisable that projects comply with the yearly averages in terms of maximum concentration levels recommended by the WHO and the World Bank (background pollution) and with the recommended hourly or daily averages, including peaks, in terms of maximum concentration levels for at least 95% of the time. These maximum air concentration levels presented in Tables 3 and 4 (targer criteria).

Table 1: Benchmark and recommended maximum emission levels (VOCs, NH₃)

Pollutant	Maximum emission level (in mg/Nm3 to 15% dry O2)
SO2	5001 150 for desulphurisation equipment
NOx (expressed as NO2)	460
Particulate matter	50
VOCs except methane	1502
NH3	502
Nickel and vanadium	2

¹ This level can be adapted to local conditions, provided it is justified by a risk analysis in the impact review.

² Level defined in the Order of February 2nd 1998, governing ICPEs (classified installations for the protection of the
environment) which are regulated.

 

Table 2: Pollutants, emission factors, sources and best available techniques

Pollutant	Emission factors	Main sources	Measures andBAT to reduce emissions
SO2	Sulphur content in crude and combustibles	Furnaces, boilers, gas turbines (~60%) Fluidised Catalytic Cracking (FCC) (~14%) CO boiler Sulphur recovery unit (~11%) Flaring stacks (~5%) Incinerators	quantification of the contribution of the various units in order to determine the main sources; increase in the energy efficiency of the refinery, heat recovery, vapour management, change of combustibles; for FCCs, reduction in emissions through feedstock desulphurisation, use of low-SOx2 catalyst, desulphurisation of combustion gases; use of crude containing less sulphur.
Particulate matter	Catalyst regeneration, combustion conditions	Furnaces, boilers, Fluidised Catalytic Cracking (FCC) regenerator, coking plants, incinerators	quantification of the contribution of the various units; electrostatic filters, (multi) hydrocyclones, wet filters, etc.; reduction in particulate matter emissions from solid wastes (catalysts, sludges, etc.).
NOx	Nitrogen and hydrogen content in combustibles. Operating conditions and equipment design	Furnaces, boilers, gas turbines, Fluidised Catalytic Cracking (FCC) regenerator, CO boiler, coke calcination, incinerators, flaring stacks	quantification of the contribution of the various units; use of low-NOx burners; for FCCs: optimisation of CO/NOx ratios, Selective or Non-Selective Catalytic Reduction, thermal low-NOx removal, water/steam injection.
VOCs	Storage, handling, leaks	Storage loading and unloading areas, gas-liquid separation units, oil/water separation system, fugitive emissions (valve leaks, etc.), flaring stacks	quantification of the contribution of the various units; vapour recovery systems, (internal) floating roof tanks; adapted pumps and gate valves, limited number of joints and flanges in the design; covered separation basins (e.g. for wastewater treatment).

Table 3: Maximum concentration levels defined by WHO guidelines

Pollutant	Maximum level [µg/m3]	Average over:
CO	100,000	15 minutes
60,000	30 minutes
30,000	1 hour
10,000	8 hours
NOx	200	1 hour
40	1 year
Ozone	120	8 hours
SO2	500	10 minutes
125	24 hours
50	1 year

 

Table 4: Maximum concentration levels defined by World Bank guidelines

Pollutant	Maximum level [µg/m3]	Average over:
Particulate matter	50	1 year
70	1 day
NOx	150	1 day

Impact factor 1 - Atmospheric emissions - Summary table

Reference criteria

Compliance with maximum emission levels defined in the World Bank guidelines.

Assessment of fugitive VOC emissions in order to minimise them whenever feasible.

Regular monitoring of the emissions of main pollutants.

Target criteria

Compliance with maximum emission levels set by French legislation for VOCs and NH₃.

Modelling survey of impact on air quality.

Compliance with maximum air concentration levels set by the WHO and the World Bank.

Best practice criteria

Compliance with the following specific flows³:

SO₂< 0.2 kg/t of crude NOx < 0.15 kg/t of crude

Avoidance of burning in flaring stacks and recovery of gases when possible.

Factor 2: Use of natural resources and greenhouse gas emissions

Refineries are major energy consumers. They have a significant impact on the conditions for sustained development, notably due to the fact that they deplete natural resources which cannot be renewed (by man) and through their greenhouse gas emissions.

It is therefore advisable to implement an energy
production/consumption management

programme for the entire refinery and to ensure that the consumption of combustibles used for energy production does not exceed approximately:

• 3.5% of the quantity of crude treated for simple or category 1 refineries (distillation, catalytic reforming, desulphurisation);

 

• 5 to 7% for category 2 refineries (category 1
plus catalytic and/or thermal cracking and/or
hydrocracking) or category 3 refineries
(category 1 or 2 and/or vapour cracking unit
and/or oil unit);

• and less than 10% for category 4 refineries
(i.e. category 1, 2 or 3 with a deep conversion
or desulphurisation unit).

There is no national or international standard

which defines the maximum CO2 emission levels

(in mg/Nm³ or in g/t produced).

Given current technologies and those being

developed, specific emissions of less than 100 kg

of CO2 per tonne of crude are considered best

practice.

Impact factor 2 - Greenhouse gases - Summary table

Reference criteria	Target criteria	Best practice criteria
	Rational energy management programme throughout the refinery.	Specific emissions less than 100 kg of CO2 per tonne of crude.

 

Factor 3: Water supply and wastewater

The main impacts associated with this factor are:

	Potential impact	Measures to limit impact
Net quantity of water used (incoming — outgoing)	Adjustment to hydrological flow, and therefore ecosystems and use.	Reduction in water requirements, e.g. by the implementation of closed circuits.
Pollution discharged into the environment through effluents	Damage to the quality of the water. Changes in ecosystems and use.	Appropriate treatment of effluents before discharge. Optimisation of the use of reactives that are compatible with maximum discharge levels.

Keeping water consumption and therefore wastewater production to a minimum through the implementation of water conservation measures is recommended whenever feasible.

If effluents are discharged into surface waters or the natural environment, their physico-chemical characteristics, after any treatment, must comply with the maximum levels defined in the World Bank guidelines⁴ (reference criteria). In addition, it is advised that specific flows of effluents per tonne of crude comply with the acceptable levels, also indicated in the guidelines (target criteria). These levels are presented in Table 5.

 

Table 5: Maximum discharge levels defined by World Bank guidelines

Parameter	Maximum level on an average daily basis, without dilution [in mg/l, except pH and temperature]	Specific flow (in g/ t of crude treated)
Outflow of effluents (process water, cooling and sanitary wastewaters)		0.4 (m3/t)
pH	6-9	-
BOD5	30	6
COB	150	50
TSS total solid suspension	30	10
Hydrocarbons (Oils and grease)	10	2
Total chromium	0.5	-
Chromium VI	0.1	-
Lead	0.1	-
Phenol compounds	0.5	-
Benzene	0.05	-
Benzo(a)pyrene	0.05	-
Nitrogen (total)	10	-
Sulphide	1	-
Temperature	Increase of < 3 °C at the edge of the zone where initial mixing and dilution take place	-

 

Rainwater runoff onto parking lots, roads and roofs also represents a pollution risk.

It is therefore advisable to develop a rainwater collection system which drains into tanks with the necessary capacity to contain surface rainwater runoff. It is also recommended that the quality of rainwater collected in this manner be controlled and, if necessary, treated prior to discharge.

When wastewater is discharged into surface water used for a specific purpose (irrigation, fishing, shellfish beds, recreational or domestic use), it is advised to ensure that the quality of the environment, with regard to this purpose, is not compromised.

Pollutant concentration levels in the environment (based on measurement or a dispersion study) can be checked against quality criteria, according to the use of the resource, as defined by WHO and European regulations.

Impact factor 3 - Effluents - Summary table

Regular monitoring of the discharge of main pollutants is required to ensure that maximum levels are respected. Periodic measurement of the concentration of pollutants in the natural environment is considered best practice.

Lastly, Coface would like to encourage the use of the Best Available Techniques as laid down in EU Directive 96/61/EC on Integrated Pollution Prevention and Control.

These techniques are described in the document "Best Available Techniques Reference Document for Mineral Oil and Gas Refineries", European Commission, December 2001.

 

Reference criteria	Target criteria	Best practice criteria
Compliance of effluents	Compliance of specific flows with the	Regular measurement of
with the maximum levels	acceptable levels set by the World Bank.	pollutant concentration levels in
defined in the World Bank		the environment.
guidelines.	Implementation of closed water circuits
	whenever feasible.	Discharge levels comparable
Regular monitoring of the		with those obtained by using the
discharge of main	Collection and, if necessary, treatment of	best available techniques (BAT).
pollutants.	runoff waters.
	Avoidance of damage to the
	environment with regard to its specific
	purpose.

 

Factor 4: Noise generated by facility operations

The maximum acceptable noise levels recorded on receptors on the edges of the property boundary and on an average hourly basis, as defined in the World Bank guidelines, are presented in Table 6 (opposite). Compliance with these noise levels is required (reference criteria).

Table 6: maximum noise levels

Day______ Night

Residential, educational or institutional area

Industrial or commercial area

 

Impact factor 4 - Noise - Summary table

Reference criteria	Target criteria	Best practice criteria
Compliance with maximum levels recommended by the World Bank.

Factor 5: Waste and management of toxic or hazardous substances

The main impacts associated with this factor are:

	Potential impact	Measures to limit impact
Storage of hydrocarbons and other hazardous products	Contamination of soil and water. Accidental discharge into the environment.	Storage in accordance with appropriate safety and sealing directives.
Hydrocarbon waste: barrel deposits, oily sludges, contaminated soil, filters, etc.	Treatment of oily sludges (settling, centrifuging, etc.) stabilisation, etc.
Catalyst waste	Recovery, recycling, treatment, storage.
Barrels and other containers	Recovery, recycling, treatment, storage.

Any waste generated by a facility requires appropriate treatment in order to ensure that its disposal will only have a very limited impact on the environment.

The risk of soil and water contamination as a result of waste and the different toxic or hazardous substances stored on-site must be controlled. More specifically:

• tank truck loading and unloading areas must
be sealed and linked to containment areas;

• hazardous substance storage areas must be
contained and, when possible, covered to
avoid any pollution through runoff;

• wastewater and chemical drainage systems
must undergo regular inspection for leaks;

• chemical drainage systems inside the facility
and storage tanks must be above ground,
unless otherwise recommended for reasons of
hygiene or safety.

It is recommended that a monitoring programme be implemented to check underground water for any spill-over. This programme should also define the necessary measures, in the event of water table pollution, to contain this pollution within the boundaries of the site.

Moreover, in line with World Bank guidelines governing the use and storage of certain hazardous substances, the use of asbestos in new facilities and the installation of PCB transformers are prohibited.

Previously installed equipment containing these substances must be gradually phased out in compliance with national legislation and international best practices.

As stated in the Montreal Protocol on substances that deplete the ozone layer, the implementation of procedures or equipment which use the substances targeted by the agreement (including CFCs, 1,1,1-trichloroethane, HCFCs, HBFCs and methyl bromide) is prohibited, unless it is proven that no other alternative is currently available.

Lastly, it is best practice that all necessary measures be taken in the design and operation of the facility to ensure proper waste treatment through the definition of procedures which aim to:

• limit the quantity and toxicity of waste at
source;

• sort, recycle and reuse manufacturing sub-
products;

• ensure the treatment or pre-treatment of toxic
waste;

• ensure the storage of final waste in the best
possible conditions.

Impact factor 5 - Waste and management of toxic substances - Summary table

Reference criteria	Target criteria	Best practice criteria
Appropriate treatment of waste prior to disposal. Control of contamination risks linked to the storage of toxic or hazardous waste: waterproofing and installation of containment systems for loading and unloading areas; installation of chemical storage areas which are linked to containment systems and, if possible, covered; avoidance of chemical and storage tank drainage systems installed underground; regular inspection of wastewater and chemical drainage systems to ensure that they are fully watertight.	Regular monitoring of the quality of the water table to check for any spill-over. Measures to limit water table pollution. Implementation of containment tanks with a capacity that is at least equal to the greater of the two following values: 100% of the capacity of the largest tank or 50% of the capacity of all tanks in the containment system.	Minimisation of production. Sorting, recycling, reuse. Treatment or pre-treatment of toxic waste.
The use of asbestos, PCBs and other substances targeted by the Montreal protocol is prohibited.

Factor 6: Location

The main impacts associated with the project location are:

	Potential impact	Measures to limit impact
Project location in or near an	Damage to or disappearance of	Choice of site location.
environmentally sensitive area	biotopes. Impoverishment of	Rehabilitation of site after
(nature reserve, specific use,	biodiversity and landscapes.	construction work.
purpose in the balance of the		Consideration of the site's future at
ecosystem, etc.)	Change in the lifestyle of local	the end of the refinery's useful life.
	populations.	Consideration of the site's uses.
		Compensatory measures.

The rather localised nature and character of the impacts that may be caused by the transformation of the project site depend heavily on its uses and functions, in terms of both human activity and the balance of the ecosystem. This impact factor must be taken into account in the project design.

It is advised to avoid building the project facility in or near an environmentally sensitive area.

An environment is considered sensitive if:

• it is protected by international agreements (e.g. RAMSAR wetlands);

it is protected by national or regional

legislation and regulations, or is listed as an

IUCN-protected site;

it is listed as a world heritage site by

UNESCO;

it is located in a biosphere reserve listed by

UNESCO, or has a vast biodiversity (primary

forests, coral reefs, mangroves, etc.);

it is a particularly important site for

endangered animal or plant species on the

IUCN red list;

it has a special significance for ethnic groups,

particularly for people in the scope of the

World Bank Operational Directive 4.20.

In the event of potentially significant impacts on ecosystems or local populations, a management plan must be developed in order to adequately mitigate and/or compensate for these impacts.

In the event of expropriation and/or the involuntary displacement of local populations, adequate compensation, particularly indemnities and/or rehousing, must be offered promptly and in the best possible conditions.

In such case, a compensation / resettlement plan, established in accordance with the provisions laid down in the World Bank Operational Directive 4.30 / Operational Procedure 4.12 must be developed.

The site should be reinstated once construction is complete.

Impact factor 6 - Location - Summary table

Reference criteria

Analysis of the environmental sensitivity of the plant site and its surroundings (assessment of use and functions, quality of animal and plant life, etc.).

Appropriate mitigation and compensatory measures in the event of a significant impact on ecosystems or local populations.

If necessary, a plan to compensate / resettle
project affected people, in accordance with
World Bank Operational Directive 4.30 /
Operational Procedure 4.12._________

Target criteria

Avoidance of environmentally

sensitive sites.

Reinstatement of the site after construction.

Best practice criteria

Definition, in

collaboration with the authorities and local populations, of how the project can best be integrated within the long-term development of the site (including the future of the site at the end of the project).

Factor 7: Construction of new secondary infrastructures

The main impacts associated with this factor are:

Civil engineering works for the different connections needed for the smooth running of the project (roads, gas or oil pipelines, storage, etc.).

Potential impact

Cut-off effects: impoverishment of

biodiversity and landscapes.

Change in the lifestyle of local

populations.

Risk of induced effects (parcelling out

of land, etc.) on protected natural sites.

Measures to limit impact

Integration of the project within existing infrastructures, and strengthening of these infrastructures if necessary.

As for the preceding impact factor, the impacts potentially generated by secondary infrastructures in the design of the project, as well as the related abatement and compensatory measures, must be taken into account. It is recommended to avoid developing these infrastructures in environmentally sensitive areas.

Impact factor 7: Secondary infrastructures - Summary table

Reference criteria	Target criteria	Best practice criteria
Analysis of the environmental sensitivity of sites affected by the new infrastructures (assessment of their use and functions, the quality of the animal and plant life, etc.). Appropriate mitigation and compensatory measures in the event of a significant impact on ecosystems or local populations.	Integration of the project within existing infrastructures wherever possible, and the strengthening of these infrastructures if necessary. Avoidance of cutting off sensitive natural environments. Avoidance of the transport of hazardous substances across urban areas. Site reinstatement after construction.

Factor 8: Safety and industrial risk management

A detailed risk assessment is required. It must identify and analyse any risk, assess the extent and scope of the consequences of potential accidents (scenarios) and justify the technical parameters and equipment installed or to be installed in order to minimise the risk for local populations and the environment. It can also define zones in which urban planning control is necessary for the area around the facility.

An emergency plan must also be drawn up, if possible in collaboration with the local authorities. This plan must specify all of the necessary measures to be taken and potentially necessary resources for each risk scenario. In particular, it defines all emergency procedures and outlines the information and protection measures to be put in place for the surrounding populations (warning systems, evacuation plans, etc.).

The local populations must be informed of the procedures defined in the emergency and assistance plans.

Moreover, if the plant is classed as a high-risk facility, as defined by the Seveso II directive 96/82 of December 9th 1996 (or is classified AS, as defined by French regulations), it is advisable that a document outlining all safety management aspects, as specifically defined by the Seveso II directive (controlled set of required organisational measures to minimise the risk of major accidents and limit their consequences), be included in the risk assessment.

Impact factor 8 - Safety and industrial risk management - Summary table

Reference criteria	Target criteria	Best practice criteria
Completion of a risk assessment. Draw up an emergency plan to be communicated to the local populations.	Define a safety management system as defined by the Seveso II directive.

APPENDIX D—DEFINITION OF A SOUR ENVIRONMENT (REPRINTED FROM NACE STANDARD MR0175-94: STANDARD MATERIAL REQUIREMENTS SULFIDE STRESS CRACKING RESISTANT METALLIC MATERIALS FOR OILFIELD EQUIPMENT2")

Sour Environments

D.1.1 Sour Environments are defined as fluids containing water as a liquid and hydrogen sulfide exceeding the limits defined in Pars. D.I. 1.1 and D.I. 1.2; these environments may cause sulfide stress cracking (SSC) of susceptible materials.

CAUTION: It should be noted that highly susceptible mate­rials may fail in less severe environments. The SSC phe­nomenon is affected by complex interactions of parameters including:

a. chemical composition, strength, heat treatment, and mi-
crostructure of the material;

b. hydrogen ion concentration (pH) of the environment;
с hydrogen sulfide concentration and total pressure;

d. total tensile stress (applied plus residual);

e. temperature; and

f. time.

The user shall determine whether the environmental con­ditions fall within the scope of this standard. (Editorial Com­ment: The critical hydrogen sulfide levels in D.I.1.1 and D.I.I .2 and Figures D-l and D-2 were developed from data derived from low alloy steel.)

Sour Gas

Materials shall be selected to be resistant to SSC or the en­vironment should be controlled if the gas being handled is at a total pressure of 0.4 MPa (65 psia) or greater and if the par­tial pressure of hydrogen sulfide in the gas is greater than 0.0003 MPa (0.05 psia). Systems operating below 0.4 MPa (65 psia) total pressure or below 0.0003 MPa (0.05 psia) hy­drogen sulfide partial pressure are outside the scope of this standard. Partial pressure is determined by multiplying the mole fraction (mol % + 100) of hydrogen sulfide in the gas by the total system pressure. Figure D-l provides a conve­nient method for determining whether the partial pressure of

hydrogen sulfide in a sour environment exceeds 0.0003 MPa (0.05 psia). A few examples are provided:

a. partial pressure of hydrogen sulfide in a system contain­
ing 0.01 mol % hydrogen sulfide (100 ppm or 6.7 grains per
100 standard cubic feet [SCF]) at a total pressure of 7 MPa
(1,000 psia) exceeds 0.0003 MPa (0.05 psia) (Point A on
Figure D-l).

b. partial pressure of hydrogen sulfide in a system contain­
ing 0.005 mol % hydrogen sulfide (50 ppm or 3.3 grains per
100 SCF) at a total pressure of 1.4 Mpa (200 psia) does not
exceed 0.0003 Mpa (0.05 psia) (Point В on Figure D-l).

Sour Oil and Multiphases

Sour crude oil systems that have operated satisfactorily us­ing standard equipment are outside the scope of this standard when the fluids being handled are either crude oil, or two- or three-phase crude, water, and gas when:

a. the maximum gas:oil ratio is 5000 SCF:bbl (barrel of oil);

b. the gas phase contains a maximum of 15% hydrogen sul­
fide;

c. the partial pressure of hydrogen sulfide in the gas phases
is a maximum of 0.07 MPa (10 psia);

d. the surface operating pressure is a maximum of 1.8 MPa
(265 psia) (see Figure D-2); and

e. when pressure exceeds 1.8 MPa (265 psia), refer back to

The satisfactory service of the standard equipment in these low-pressure systems is believed to be a result of the in-hibitive effect of the oil and the low stresses encountered un­der the low-pressure conditions.

Descriptions of Gaussian and Puff Dispersion Models

Descriptions of Gaussian and Puff Dispersion Models

INTRODUCTION

The emergency response Gaussian and Puff screening models are designed to predict the downwind dispersion (plume-centerline, ground-level concentration and maximum ground-level plume width as a function of downwind dis­tance) of a neutrally-buoyant, steady-state point source gaseous release under steady-state meteorological condi­tions. Classical EPA-approved Gaussian dispersion theory is applied in the models. The programs are in BASIC and are designed for use on personal computers. The models are de­scribed below. The program listings and runs should use the IDLH, ERPG-2, and TLV and STEL levels as the concentra­tions of interest because they usually are the concentration values of concern. Both models can be run for other concen­trations by substituting the values of interest in place of the

values for IDLH, ERPG-2, and TLV and STEL in the com­puter programs. Copies of the example program listings and computer runs are available on request from American Petroleum Institute, Exploration & Production Department, 700 North Pearl Street, Suite 1840, Dallas, Texas 75201-2845.

Gaussian Model

This model calculates the plume-centerline, ground-level concentration, and maximum ground-level plume width for a single, steady-state, continuous-point release at user-spec­ified, steady-state meteorological conditions and downwind distances. The model uses standard Gaussian dispersion modeling with Pasquill-Gifford dispersion coefficients. The user inputs the release rate, effective release height (release height plus plume rise), nominal wind speed, incremental downwind distance for which calculations are to be made, type of material released, and the stability class. A total of eight compounds are currently accepted by this model. Ad­ditional compounds can be entered by replacing compounds presently in the model. The model uses a default D Stability Class; but, can be run with any of the standard six Pasquill-Gifford Stability Classes (A, B, C, D, E, or F—with A being the most unstable and F being the most stable).

Puff Model

This model calculates the plume-centerline, ground-level concentration, and maximum ground-level plume width for a single, instantaneous-point release at user-specified, steady-state meteorological conditions and downwind distances. The model uses standard Gaussian dispersion theory for an instantaneous (puff) release with Slade dispersion coeffi­cients. User inputs to the model are the same as those used in the Gaussian model except that the total amount of material released is entered rather than the rate of release. Three val­ues are accepted for the Stability Class (A, B, or С—with A being unstable, В being neutral, and С being stable).

Radius of Exposure (ROE) Calculation

Using the values of coefficients "A" and "B" in Table C-1, the radius of exposure (ROE) for various hydrogen sul­fide release rates (H₂S) can be mathematically predicted us­ing the following equation:

ROE - Antilog [A X log (H₂S) + B]

For a continuous release, enter the hydrogen sulfide re­lease rate (H₂S) in standard cubic feet per hour (SCFH). For a puff (instantaneous) release, enter the quantity of hydrogen sulfide (H₂S) released in standard cubic feet (SCF).

C.9 Sample Calculation—Continuous Release (Daylight)

Determine the ROE_{IOO ppm} for a continuous release of 100 percent hydrogen sulfide gas at a rate of 11,170 SCFH in daylight (PG D stability) conditions and 5 mph wind speed. Using Table C-1, the coefficients applicable to this scenario are: A - 0.58; В - 0.45. Using the equation in Par. C.8:

ROE_100ppm - Antilog [0.58 x log (11,170) + 0.45] - 628 feet.

C.10 Sample Calculation—Continuous Release (Nighttime)

Determine the ROE_)00p()in for a continuous release of 100 percent hydrogen sulfide gas at a rate of 11,170 SCFH in nighttime (PG F stability) conditions and 2.2 mph wind speed. Using Table C-1, the coefficients applicable to this scenario are: A - 0.66; В - 0.69. Using the equation in Par. C.8:

Antilog [0.66 x log (11,170) + 0.69] - 2,300 feet

 

C.11 Sample Calculation—

Instantaneous Release (Daylight)

Determine the ROE,,,^^ for an instantaneous release of 100 percent hydrogen sulfide gas of 1,117 SCF in daylight (Slade A stability) conditions and 5 mph wind speed. Using Table C-l, the coefficients applicable to this scenario are: A - 0.39; В - 1.91. Using the equation in Par. C.8:

ROE_100ppm - Antilog [0.39 x log (1,117) + 1.91] - 1,255 feet.

C.12 Sample Calculation—

Instantaneous Release (Nighttime)

Determine the ROE_l00p(m for an instantaneous release of 100 percent hydrogen sulfide gas of 1,117 SCF in nighttime (Slade В stability) conditions and 2.2 mph wind speed. From Table C-l, the coefficients applicable to this scenario are: A - 0.40; В - 2.40. Using the equation in Par. C.8:

. Antilog [0.40 x log (1,117) + 2.40] - 4,161 feet.

ROE

lOOppm'

Sample Calculations for Figures C-1 through C-4

The following calculations may be used to estimate vol­ume and mass of hydrogen sulfide when total gas volume and its hydrogen sulfide content are known:

Continuous Release.

Assume: Release of 5,000,000 SCFD of natural gas con­taining 8,000 ppm (by volume) of hydrogen sulfide.

Note: The user must know both the volume (or flow rate) of natural gas and its hydrogen sulfide concentration so that Figures C-I through C-4 can be effectively used.

To determine standard cubic feet per hour (SCFH) of hy­drogen sulfide released, the following calculations should be performed using appropriate values for the conditions being evaluated:

5,000,000 SCFD x 8,000 ppm H₂S

24,000,000 - 1,667 SCFH of H₂S released.

To determine the pounds of hydrogen sulfide released per hour, the following calculations should be performed using appropriate values for the conditions being evaluated:

5,000,000 SCFD x 8,000 ppm H₂S

267,605,634 - 150 lb/hr of H₂S released.

Instantaneous Release.

Assume: Release of 100,000 SCF of natural gas contain­ing 8,000 ppm (by volume) of hydrogen sulfide. Also, as­sume this example is a daytime release, 5 miles per hour

wind speed (refer to Figure C-3).

To determine the volume (SCF) of hydrogen sulfide re­leased, the following calculations should be performed using appropriate values for the conditions being evaluated:

100,000 SCF x 8,000 ppm H2S

1,000,000 - 800 SCF of H₂S released

After applying the appropriate calculations and using known factors to arrive at either hydrogen sulfide release rate or quantity of hydrogen sulfide released, refer to the appro­priate chart (Figs. C-1 through C-4) or the equation in Par. C.8 (example calculations in Pars. C.9 through С12) for ob­taining radius of exposure (ROE) information.

The following equation can be used to convert percent hy­drogen sulfide to parts per million on a volume basis:

Percent H₂S x 10,000 - ppm H₂S

Publicly-available Models

Note: Users should carefully evaluate applicability of these models to pre­vailing conditions.

A list of some publicly-available models that can be used to address special site-specific scenarios follows:

DEGADIS—(\5. S. Coast Guard): DEGADIS, the Dense Gas Dispersion Model, is designed to simulate dispersion of heavier-than-air gas releases. It can handle both evaporative emissions from liquid spills and jet emissions. It is basically steady-state but simulates transient conditions by a series of steady-state calculations. Vapor generation rate, spill area, and meteorological parameters are important inputs to the

model. Information available through National Technical In­formation Service (NTIS), U. S. Department of Commerce, Springfield, VA 22161.

HEGADAS—(Shell Research B.V.): HEGADAS is a dis­persion model for neutrally-buoyant and dense gases. The basic model components are solutions to the advection/diffu-sion equations and are in the standard form of Gaussian dis­persion models. The model can handle a wide variety of source types, including transient horizontal jets. Information available through National Technical Information Service, U. S. Department of Commerce, Springfield, VA 22161.

SLAB—(Lawrence Livermore National Laboratory): SLAB is designed for application to dense gases that are emitted from liquid spills. The model considers the concen­tration integrated over a cross-section perpendicular to the plume centerline. The downwind variation of the integrated concentration is calculated. The size and emission rate of the liquid spill are required inputs to the model. Information available through Lawrence Livermore National Laboratory, Box 808, Livermore, CA 94550, or contact American Petroleum Institute, Health & Environmental Sciences De­partment, 1220 L Street, NW, Washington, D.C. 20005.

Proprietary Dispersion Models

Note: Users should carefully evaluate applicability of these models to pre­vailing conditions.

A list of some proprietary models that can be used to ad­dress special site-specific scenarios follows:

CHARM—(Radian Corporation): CHARM is a Gaussian puff model for continuous and instantaneous releases of gases or liquids. The model is configured to handle chemi­cals that are buoyant, neutrally buoyant, and heavier than air. Heavy gas dispersion is estimated using the Eidsvik model. Source components in the model include a modified version of Shell Oil Company's SPILLS Model. (Radian Corp., 850 MOPAC Blvd., Austin, TX 78759.)

FOCUS—(Quest Consultants, Inc.): FOCUS is a model­ing package that includes both emission rate models (two-phase discharges, pool evaporation, jet vapor releases, etc.) and dispersion models for both neutrally-buoyant and dense-gas plumes. The models can be run separately or in a linked mode. (Quest Consultants, Inc., 908 26th Avenue, NW, Suite 103, Norman, OK 73069-6216.)

TRACE—(Dupont): TRACE uses a multiple Lagrangian Wall dispersion model to handle both puff and continuous releases. Wind channeling can be incorporated. Liquid evap­oration and buoyancy effects are considered also. (E. I. Dupont de Nemours & Company, 5700 Corea Avenue, West-lake Village, CA 91362.)

WHAZAN—(Technica International): WHAZAN is a package of dispersion models for both neutrally-buoyant and dense-gas plumes. Submodels are included to handle two-phase discharges, evaporation, and vapor dispersion as a free jet. The model can be run both individually and in a linked mode. (Technica International Associates, Inc., Box 187, Woodstock, GA 30128-4420.)