Partner Reported Opportunities (PROs) 

### PRO Fact Sheet No. 206 for Reducing Methane Emissions



# Zero Emissions Dehydrators

Technology/Practice Overview

Description Produced natural gas is saturated with water, which must be removed in preparation for transmission. The oil and gas industry relies heavily upon glycol dehydrators using triethylene glycol (TEG) to remove water from gas. Dehydrators can produce significant methane emissions from the venting of still column vapors, as well as leaks from gas-driven glycol circulation pumps and pneumatic controls. Some of these emissions include methane, volatile organic compounds (VOCs) and hazardous air pollutants (HAPs).

Zero emissions de hydrators combine several technologies to virtually eliminate methane emissions. This equipment includes flash tanks, electric pumps and electric control valves, which reduce emissions by avoiding use of pneumatic gas. Zero emissions dehydrators are also designed to collect all condensable components from the still column vapor and use the remaining non-condensable still vapor (methaneand ethane) as fuel for the glycol reboiler.

A water exhauster removes water from the wet glycol stream and yields high glycol concentrations without the use of a gas stripper. Electric circulation equipment are used instead of gas driven pumps to eliminate gas emissions from natural gas-driven diaphragm pumps. Another option is to replace methane with compressed air as the operating gas for pneumatic controls . This eliminates significant methan e emissions from valves and controllers.

Estimated Gas Price Annual
Methane Savings Value of
Annual Gas Savings* EstimatedImplementation Cost Incremental Operating Cost Payback (months)

$7.00/Mcf 33,900 — 37,300 Mcf $253,000 —$278,000 $22,065—$63,300 $165—$6,500 <1 — 4 Months

$5.00/Mcf 33,900 — 37,300 Mcf $180,500 —$199,000 $22,065—$63,300 $165—$6,500 1 — 5 Months

$3.00/Mcf 33,900 — 37,300 Mcf $108,300 —$119,200 $22,065—$63,300 $165—$6,500 2 — 8 Months 

### Economic and Environmental Benefits

Economic Evaluation

 Reduced maintenance costs

 Reduced fuel cost for the re-boiler Additional Benefits: Estimated annual methane emission reductions 31,400 Mcf per average application Natural Gas and Methane Savings

* Whole gas savings are calculated using a conversion fa ctor of 94% methane in pipe line quality natural gas. Compressors/Engines

Dehydrators

Directed Inspection & Maintenance

Pipelines

Pneumatics/Controls

Tanks

Valves

Wells

Other

Applicable Sector(s)

Production

Processing

Transmission

Distribution

Other Related Documents:

Reroute Glycol Skimmer Gas, PRO No. 201

Convert Natural Gas-Driven Chemical Pumps, PRO No. 202

Pipe Glycol Dehydrator to Vapor Recovery Unit, PRO No. 203

Portable Desiccant Dehydrators, PRO No. 207

Convert Pneumatics to Mechani

cal Controls, PRO No. 301PRO Fact Sheet No. 206 Continued 

# Zero Emissions Dehydrators (Cont’d)

Operating RequirementsGlycol dehydrators require electric utilities or an enginegenerator set to achieve zero emissions. A five kW generator set for electric al power will allow the conversion of all gas fueled pumps to electric as well as the use of electric controllers. An electric compressed air system with storage vessels for fuel air can also be used to actuate various controls throughout the system.

Flash tank separators capture methane that flashes or evaporates from rich glycol (water wet glycol) in an energy-exchange pump. Flas h tank separators recover about 90 percent of methane emissions and reduce VOCs by 10 to 40 percent. These installations require an outlet for low pressure gas such as a vapor recovery unit, compressor suction or fuel line.

Some partner companies install glycol still column condensers to comply with current regulation of HAP emissions. Still column condensers require routing of the non-condensable methane and ethane to a low pressure fuel line, VRU or flare. Desiccant dehydrators can be used in place of glycol dehydrators. Desiccant dehydrators eliminate the use of glycol in the process which also eliminates most of the methane emissions associated with dehydrator s. Refer to the Lessons Learned paper, Replacing Glycol Dehydrators with Desiccant Dehydrators. The water content of produced gas that can be removed by desiccant dehydrators depends upon the temperature and pressure of the gas and the type of desiccant. Desiccant dehydrators are most effective for higher pressure, lower temperature conditions and comparatively low flow rates.

Applicability New dehydrators can be designed to eliminate methane, VOC, and HAP emissions. In addition, existing glycol The average methane content of na tural gas varies by natural gas industry sector. The Natural Gas STAR Program assumes thefollowing methane content of natural gas when estimating methane savings for Partner Reported Opportunities.

Production 79 %

Processing 87 %

Transmission and Distribution 94 % 

### Methane Content of Natural Gas

dehydrators can be retrofitted with zero emissions technology through modifications of the gas stream piping, valves, pumps, and controllers, as well as modification of the fuel used, and/or the dehydrating media. Partners can apply zero emission dehydrator technologies to various onshore and offshore production, processing and gas transportation settings.



### Methane Emissions

The reductions in natural gas losses are calculated assuming a conventional dehydrator processing 28 MMcf/day (million cubic feet per day) with a glycol circulation rate of 4 gpm (gallons per minute). The zero emissions dehydrator eliminates emissions from glycol circulation pumps, gas stripp ers, and most of the still column effluent.



### Economic Analysis

Basis for Costs and Savings A conventional dehydrator of similar size (processing 28 MMcf/day) shows losses of 5.95 scf (standard cubic feet)



### Table 1. Zero Emission Dehydr ator Technology Examples; Partner-Reported Costs and Savings

Option Capital Costs Annual O&M Cost Annual Methane Emission Savings

Install Flash Tank $6,500 - $18,800 Negligible 1,191 – 10,717 Mcf

Install Electric Pump $1,400 - $13,000 $165 - $6,500 360 – 36,000 Mcf

Glycol Still Column Condenser $14,000 - $25,000 not reported 400 – 5,033

TOTAL $21,900 - $56,800 $165 - $6,500 1,951 – 51,750

2PRO Fact Sheet No. 206 Continued 

# Zero Emissions Dehydrators (Cont’d)

per gallon of glycol that is circulated with a Kimray pump at 4 gpm. The conventional dehydrator also has gas losses of 4 scf per gallon of glycol that is circulated through the gas stripper. A zero emissions dehydrator avoids these gas losses by eliminating Kimray pumps and gas strippers. Condensate is also recovered from the still column vapor at 2.88 gal/hr (gallons per hour) whilethe non-condensable vapor is used to fuel the glycol reboiler in the zero emissions dehydrator. Two to four cubic feet per minute of gas venting is eliminated by replacing gas pneumatic controllers with electric controls. Examples of Natural Gas STAR Partner reported emissions savi ngs and corresponding implementation costs for different zero emission dehydrator technologies are provided in Table 1.

Discussion Installation costs for a zero emissions dehydrator are similar to those for a conventional dehydrator with a thermal oxidizer. Electric motors and controllers offer several benefits as compared to gas-powered devices; they are more reliable and efficient and provide lower operating and maintenance costs. The cost of electric

Conventional Glycol Dehydrator System power is generally offset by increased methane and condensate production sales. Overall benefits of zero emission dehydrators include:

 Rapid return on investme nt through gas savings,

 Increased operational efficiency

 Reduced O&M costs

 Reduced Compliance Cost for HAPs and BTEX

EPA provides the suggested methane emi ssions estimating methods contained in this document as a tool to develop basic methane emissions estimates only. As regulatory reporting demands a higher-level of accuracy, the methane emis

sion estimating methods and terminology contained in this document may not conform to the Greenhouse Gas Reporting Rule, 40 CFR Part 98, Subpart W methods or those in other EPA regulations.

Source: U.S. EPA, Envi ronmental Technology Ve rification (ETV) Program (CO, CO 2 , NO x )

3PRO Fact Sheet No. 206 Continued 

# Zero Emissions Dehydrators (Cont’d)

Quantum Leap Dehydrator System (A Zero Emissions Dehydrator)

(CO, CO 2 , NO

x )

Source: U.S. EPA, Envi ronmental Technology Ve rification (ETV) Program

2011

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