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Article # 0028

Air Quality Permit Application Considerations for Skid-Mounted Amine Regeneration and Glycol Dehydration Units

by Jack Bullard, P.E.
 

 

INTRODUCTION

 

This report describes typical considerations when preparing an air quality permit application for a small (less than two long-tons of sulfur produced per day) Amine Regeneration and Glycol Dehydration Unit to be located in the State of Texas.  It evaluates typical state-level environmental regulatory requirements; Federal environmental requirements are not addressed.  This report provides a project description, discussion of emission sources, and important design characteristics to reduce the unit’s environmental impact. This report covers a hypothetical company known as the ABC Company.

 

PROJECT SUMMARY

ABC Company is “permitting” the construction and operation of a skid-mounted amine regeneration and glycol dehydration unit(s).  The units or “facility” will service gas well(s) by removing sour gas components from field gas through amine contact (sweetening) and by removal of moisture by glycol dehydration. The site is proposed for location in Texas. 

Emission sources addressed in this report include small heaters/reboilers, gas flare, and a glycol dehydration unit process vent.  Other emission sources that may be associated with such units include storage tanks to hold any crude or liquids separated from the gas and minor process equipment leaks that create gaseous fugitive emissions. 

The amine unit’s process vent will be routed to the flare for destruction of H2S.   An analysis of raw gas from the land lease where the wells to be serviced are located indicate no detectable levels of non-methane, non-ethane volatile organic compounds (VOC) so the glycol dehydrator will be vented to the atmosphere at a height of 40 feet or greater to disperse any residual H2S or entrained hydrocarbons.  Also, the heaters/reboilers will be fired with pipeline-quality (sweet) natural gas.  All emission sources are greater than one mile from the nearest resident or sensitive receptor.

 

 

PROCESS DESCRIPTION

 

ABC Company is registering the construction and operation of skid-mounted amine regeneration and glycol dehydration units to service gas wells.  The units or “facility” will be used to remove the sour gas components H2S and CO2 from field gas through amine contact.

The gas flows in the following order: Inlet Separator, Filter Separator, Amine Plant, and Dehydration Unit.  The field gas is produced at the wellhead.  The gas (mainly methane and ethane) may contain moisture as well as trace amounts of H2S and CO2.  The inlet gas and any entrained liquids are separated and the gas is sent to the amine unit to remove CO2 and H2S to obtain a saleable (maximum H2S concentration of 5 ppmV) product. The amine regeneration unit removes the sour gas components from the gas by extraction with amine solution.  The vent gas from the unit is routed to a flare to destruct the H2S, CO2 and any VOC.  The flare stack will be at least 40 feet tall.  An amine heater/reboiler will generate process heat for the unit and will be fired using pipeline quality natural gas.

 

The sweetened and wet field gas is sent to the glycol dehydration unit wherein entrained water is removed from the gas.  The dehydration unit will utilize a heater - to be fired with pipeline quality (sweet) natural gas - to supply process heat for removal of the water.  The glycol dehydration unit has a process vent that will be exhausted to the atmosphere at a height of 40 feet or greater.  The gas chromatographic analysis of indicates that the field gas to be processed is composed mainly of methane and ethane (both non-VOC) with no measurable amount of volatile organic compounds (VOC.  The maximum concentration of H2S in the gas exhausted from the process vent is estimated at 5 ppmV which is the maximum H2S concentration specified for the product gas.  The dry and sweetened product gas is sent off-site for sale by a metered pipeline. 

 

 

EMISSIONS DATA AND CALCULATIONS

 

The emissions from this facility include products of combustion (NOx, CO, SO2, PM) and non-combusted VOC from the two small gas-fired heaters and a flare.  Also, emissions of volatile organic compounds (VOC) and H2S may result from process equipment fugitives (leaks), process vents, and storage tank standing and breathing losses.

 

The maximum design daily wet gas flow rate of the facility (amine/glycol process units) is 0.5 million standard cubic feet per day (MM scf/day).  Field gas from the lease indicates H2S is present at 175 grains H2S per 100 scf of gas.  The facility will produce less than one long ton of sulfur per day at its maximum design capacity:

(500,000 scf gas/day)(175 grains total sulfur/100 scf of gas)(1 lb/7000 grains)(1 long ton/2,240 lb) = 0.06 long ton sulfur/day

 

Sulfur Dioxide (SO2) emission rate calculations were performed using industry accepted emission calculation methodology from the Environmental Protection Agencies (EPA’s) Compilation of Air Pollutant Emission Factors (also known as AP-42).  The result of the calculations was estimates of SO2 air emission rates of 1.0 and 0.5 (pounds per hour) lb/hr at maximum design and typical operating capacities respectively.  Hydrogen sulfide emissions were estimated using industry accepted methodology at 0.25 lb/hr.

 

 

TYPICAL ENVIRONMENTAL PERMIT REQUIREMENTS

 AND PROPOSED METHODS OF COMPLIANCE

 

 

Sample environmental permit requirements or conditions that the amine (gas sweetening) and glycol dehydration units may be required to comply with are listed below in bold text.  The proposed method of compliance with the requirement directly follows, that is, after each underlined “ABC Company” heading.  Note that the requirements listed below are not an exhaustive list of requirements for obtaining a permit in Texas, but are some of the major design criteria for meeting the requirements of a simplified permit known as a “Permit-by-Rule”.  The current rules and regulations of the state environmental agency, Texas Commission on Environmental Quality, should be contacted to identify all pertinent requirements.

 

Any oil or gas production facility, carbon dioxide separation facility, or oil or gas pipeline facility consisting of one or more tanks, separators, dehydration units, free water knockouts, gunbarrels, heater treaters, natural gas liquids recovery units, or gas sweetening and other gas conditioning facilities, including sulfur recovery units at facilities conditioning produced gas containing less than two long tons per day of sulfur compounds as sulfur are permitted by rule, provided that the following conditions of this section are met.  This section applies only to those facilities named which handle gases and liquids associated with the production, conditioning, processing, and pipeline transfer of fluids found in geologic formations beneath the earth’s surface.

 

ABC Company

This facility will produce 0.06 long tons of sulfur per day from the field gas that is processed which is less than the 2 tons allowed.

 

 (1) Compressors and flares shall meet the requirements described below:

 

ABC Company

The ABC Company facility will not operate any compressors.  A flare will be constructed to destruct sour gas components vented from the amine unit and will meet the requirements and specifications described below: 

 

(A) The flare shall be equipped with a flare tip designed to provide good mixing with air, flame stability, and a tip velocity less than 60 feet per second (ft/sec) for gases having a lower heating value less than 1,000 British thermal units per cubic foot (Btu/ft3 ) or a tip velocity less than 400 ft/sec for gases having a lower heating value greater than 1,000 Btu/ft3 .

 

ABC Company

The ABC Company’s flare (including flare tip) will be designed to meet the specifications described above.

 

(B) The flare shall be equipped with a continuously burning pilot or other automatic ignition system that assures gas ignition and provides immediate notification of appropriate personnel when the ignition system ceases to function.

 

ABC Company

The ABC Company’s flare will be equipped with an automatic ignition system that assures gas ignition and provides immediate notification of appropriate personnel when the ignition system ceases to function. 

 

(C) A flare which burns gases containing more than 24 parts per million by volume (ppmv) of sulfur, chlorine, or compounds containing either element shall be located at least 1/4 mile from any recreational area or residence or other structure not occupied or used solely by the owner or operator of the flare or the owner of the property upon which the flare is located.

 

ABC Company

The flare will not emit HCL as no chlorine containing compounds will be present in the gas to be flared.  Nevertheless the flare will be located one mile from any recreational area or residence or other structure not occupied or used solely by the owner or operator of the flare or the owner of the property upon which the flare is located

 

(D) The heat release of a flare which emits sulfur dioxide (SO2) or hydrogen chloride (HCl) shall be greater than or equal to the value Q:

 

Q = 53,000 X lb/hr SO2 Emission Rate

 

Where:

Q = heat release in Btu per hour based on lower heating value of gas combusted

SO2 = SO2 emission rate in lb/hr

 

ABC Company

Average heat value of gas to be destructed will range between 200 and 1000 Btu/scf.  Supplemental fuel will be added as necessary to meet the flares minimum heat release requirement calculated as Q below.  Approximately 500,000 scf gas/day will be processed by the facility.  The minimum heat released by the flare is estimated as 500,000 scf gas/day X 200 Btu/scf gas X 1 day/24 hr = 4,200,000 Btu/hr which exceeds the heat release requirements estimated below: 

 

At maximum design capacity (0.5 MM scf wet gas/day) of facility:

Q = 53,000 X SO2 Emission Rate = 53,000 X 1.0 lb/hr = 53,000 Btu/hr

 

At typical operating capacity (80% of maximum design) of facility:

Q = 53,000 X SO2 Emission Rate = 53,000 X 0.5 lb/hr = 26,000 Btu/hr

 

 

(2) Operational conditions.

 

(A) The flare shall burn a combustible mixture of gases containing only carbon, hydrogen, nitrogen, oxygen, sulfur, chlorine, or compounds derived from these elements. When the gas stream to be burned has a net or lower heating value of more than 200 Btu/ft3 prior to the addition of air, it may be considered combustible.

 

(B) Under no circumstances shall liquids be burned in the flare.

 

 

(3) Total emissions, including process fugitives, combustion unit stacks, separator, or other process vents, tank vents, and loading emissions from all such facilities constructed at a site under this section shall not exceed 25 tons per year (tpy) each of sulfur dioxide (SO2), all other sulfur compounds combined, or all volatile organic compounds (VOC) combined; and 250 tpy each of nitrogen oxide and carbon monoxide. Emissions of VOC and sulfur compounds other than SO2 must include gas lost by equilibrium flash as well as gas lost by conventional evaporation.

 

ABC Company

The units will comply with the operational conditions described in (2) above and total emissions estimated from all sources at this site are less than the levels listed in (3) above.

 

 

(4) Any facility handling sour gas shall be located at least 1/4 mile from any recreational area or residence or other structure not occupied or used solely by the owner or operator of the facility or the owner of the property upon which the facility is located.

 

ABC Company

This facility handles sour gas which is a gas that contains H2S and CO2.  All potential sources of emissions will be located at least one mile from any recreational area or residence or other structure not occupied or used solely by the owner or operator of the facility or the owner of the property upon which the facility is located. 

 

 

(5) Total emissions of sulfur compounds, excluding sulfur oxides, from all vents shall not exceed 4.0 pounds per hour (lb/hr) and the height of each vent emitting sulfur compounds shall meet the following requirements, except in no case shall the height be less than 20 feet:

 

Total as

Hydrogen Sulfide, lb/hr

Minimum

 vent height, feet

 

0.27

20

0.60

30

1.94

50

3.00

60

4.00

68

 

ABC Company

Total hourly emissions of hydrogen sulfide (H2S) from all facility sources were estimated at 0.25 lb/hr.  The glycol dehydrator process vent will release at a height of at least 40 feet above ground level.  The amine process vent is routed to the flare which releases at 40 feet above ground level.  The total emissions vented are less than 0.27 lb/hr; therefore the minimum vent height allowed is 20 feet.  The vents are proposed to be constructed at a height of 40 feet which exceeds the minimum height of 20 feet.

Article # 0028         TEST QUESTIONS:

1.   Removing sour gas components from field gas through amine contact is called ___.

  1. filtering

  2. glycol dehydration

  3. sweetening

  4. None of the above

2.   Which of the below is the correct order of gas flow through the plant?

  1. Inlet Separator, Filter Separator, Dehydration Unit, Amine Plant

  2. Filter Separator, Amine Plant, Dehydration Unit, Polishing Separator

  3. Inlet Separator, Filter Separator, Amine Plant, Dehydration Unit

  4. Filter Separator, Amine Plant, Dehydration Unit, Outlet Separator

3.   At the time of this paper, what is the name of the Texas state environmental agency?

  1. Texas Environmental Protection Agency

  2. Texas Commission on Environmental Quality

  3. Texas Natural Resource Conservation Commission

  4. Texas Air Quality Board

4.   What is done with the vent gas containing H2S, CO2 and any VOC  from the amine plant?

  1. It is pumped back down the well.

  2. It is used to fire the heaters/reboilers.

  3. It is compressed and trucked offsite for disposal.

  4. None of the above

5.   In this example, what is the maximum allowable (saleable) H2S concentration in the treated gas?

  1. 0.5 ppmV

  2. 5 ppmV

  3. 50 ppmV

  4. 500 ppmV

6.   In this example, the glycol dehydrator process vent will be ______.

  1. sent to the flare at a height of at least 40 feet

  2. catalytically scrubbed to allowable (by permit) levels

  3. vented to atmosphere at a height of at least 40 feet

  4. All of the above

7.   At the time of this paper, what is the permissible flare tip velocity for gasses having a lower heating value less than 1,000 British thermal units per cubic foot (Btu/ft3)?

  1. Less than 60 feet per second (ft/sec).

  2. More than 60 feet per second (ft/sec).

  3. More than 400 feet per second (ft/sec).

  4. None of the above.

8.   At the time of this paper, what is the minimum lower heating value, prior to the addition of air, for a gas to be considered combustible?

  1. 200 Btu/ft3

  2. 400 Btu/ft3

  3. 600 Btu/ft3

  4. 1000 Btu/ft3

 

9.   At the time of this paper, a facility handling sour gas must be how far from any recreational area?

  1. At least 100 yards.

  2. At least 1/4 mile.

  3. At least 1000 yards.

  4. At least 1 parsec.

10.   In this example, what is the minimum height of a vent emitting sulfur compounds?

  1. 10 feet

  2. 20 feet

  3. 40 feet

  4. 68 feet

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