Lessons Learned 

from Natural Gas STAR Partners 

Replacing Glycol Dehydrators With 

Desiccant Dehydrators 

Executive Summary 

There are approximately 30,000 high-pressure, onshore 

gas wells producing 4 trillion cubic feet (Tcf) of natural gas

annually in the United States. About 700 of these wells 

have conventional glycol dehydrators, emitting an 

estimated 1 billion cubic feet (Bcf) of methane per year to 

the atmosphere. Glycol dehydrators vent methane, 

volatile organic compounds (VOCs), and hazardous air

pollutants (HAPs) to the atmosphere from the glycol 

regenerator and also bleed natural gas from pneumatic

control devices. This process wastes gas, costs money, and 

contributes to local air quality problems as well as global

climate change. 

Natural Gas STAR Partners have found that replacing 

glycol dehydrators with desiccant dehydrators reduces

methane, VOC, and HAP emissions by 99 percent and also 

reduces operating and maintenance costs. In a desiccant 

dehydrator, wet gas passes through a drying bed of 

desiccant tablets. The tablets pull moisture from the gas

and gradually dissolve in the process. Since the unit is 

fully enclosed, gas emissions occur only when the vessel is

opened, such as when new desiccant tablets are added. 

Economic analyses demonstrate that replacing a glycol

dehydrator processing 1 million cubic feet per day (MMcfd)

of gas with a desiccant dehydrator can save up to $9,232

per year in fuel gas, vented gas, and operation and 

maintenance (O&M) costs and reduce methane emissions

by 444 thousand cubic feet (Mcf) per year. This Lessons 

Learned study describes how Partners can identify areas 

where desiccant dehydrators can be implemented and

determine their economic and environmental benefits. 

Technology Background 

Produced natural gas is normally saturated with water. If 

not removed, the water can condense and/or freeze in 

gathering, transmission, and distribution piping causing 

plugging, pressure surges, and corrosion. To avoid these 

problems, the produced gas is typically sent through a

dehydrator where it contacts a dewatering agent such as 

triethylene glycol (TEG), diethylene glycol (DEG), or 

propylene carbonate. In the most common process, glycol

dehydration, the TEG absorbs water from the gas along 

with methane, VOCs, and HAPs. The absorbed water and 

hydrocarbons are then boiled off in a reboiler/regenerator

and vented to the atmosphere. (See EPA’s Lessons 

Learned: Optimize Glycol Circulation and Install Flash 

Tank Separators in Glycol Dehydrators.) 

Natural Gas STAR Partners have reported success using 

an alternative method for drying gas: desiccant 

dehydrators. These dehydrators use moisture- absorbing

salts to remove water from the gas without emitting large 

quantities of methane, VOCs, or HAPs. 

Method for 

Reducing Natural 

Gas Lossesa 

Methane 

Emissions 

Savings 

(Mcf/year)b 

Volume of 

Natural Gas 

Savings 

(Mcf/year)c 

Value of Natural Gas 

Savings ($/year) Implementation 

Cost ($)d 

Other 

Costs 

($/ 

year)e 

Payback (Months) 

$3 per 

Mcf 

$5 per 

Mcf 

$7 per 

Mcf 

$3 per 

Mcf 

$5 per 

Mcf 

$7 per 

Mcf 

Replacing a Glycol 

Dehydrator with a 

Desiccant 

Dehydrator 

444 1,063 $3,189 $5,315 $7,441 $15,787 $(1,791) 38 27 

General Assumptions: 

a Based on a 1 MMcfd dehydrator operating at 450 psig and 47°F. b Difference between methane vented from the glycol and desiccant dehydrators. c Sum of net gas emissions reductions and fuel gas savings. 

d Installed cost of desiccant dehydrator minus surplus equipment value for the replaced glycol dehydrator. e Difference between glycol and desiccant dehydrators O&M costs. 

21 

Economic and Environmental Benefits 

1 
 

 

 

 

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

Desiccants 

Deliquescent salts, such as calcium, potassium and lithium

chlorides, have been used by the oil and gas industries to

dehydrate petroleum products for more than 70 years. 

These salts naturally attract and absorb moisture 

(hygroscopic), gradually dissolving to form a brine solution.

The amount of moisture that can be removed from 

hydrocarbon gas depends on the type of desiccant as well

as the temperature and pressure of the gas. Calcium 

chloride, the most common and least expensive desiccant, 

can achieve pipeline-quality moisture contents at 

temperatures below 59oF and pressures above 250 psig. 

Lithium chloride, which is more expensive, has a wider 

operating range: up to 70oF and above 100 psig. Appendix 

A provides equilibrium moisture contents of natural gas 

dehydrated by commercially available calcium and lithium

chloride salts. 

Process Description 

A desiccant dehydrator is a very simple device; it has no

moving parts and needs no external power supply; 

therefore, it is ideal for remote sites. 

As shown in Exhibit 1, wet natural gas enters near the 

bottom of the dehydrator vessel, below the desiccant 

support grid. The support grid and ceramic ball pre-bed 

prevent the desiccant tablets from dropping down into the 

brine sump (claim area). The wet gas flows upward

through the drying bed. When the gas comes into contact 

with the surface of the tablets, the desiccant salts remove 

water vapor from the gas (hydrate). As the desiccant 

continues to remove water vapor from the gas, droplets of 

brine form and drip down through the drying bed to the 

brine collection sump (claim area) at the bottom of the

vessel. This brine formation process gradually dissolves 

the desiccant. 

Brine collected in the claim area can be periodically

drained to either a brine (or produced water) storage tank,

or (where permitted) to an evaporation pond. Produced 

water and brine may be deep-well injected near the site, or

periodically picked up for disposal offsite. 

With a drying bed of sufficient depth, the gas reaches

equilibrium moisture content with the desiccant before it

reaches the top of the drying bed. Excess salt, above the 

minimum depth needed to achieve equilibrium moisture

content, is referred to as the “working salt bed.” This 

working inventory is refilled periodically. To avoid halting

gas production or bypassing wet gas to a sales line when 

refilling the desiccant dehydrator, most installations use a 

Exhibit 1: Schematic of Single Vessel 

Desiccant Dehydrator 

minimum of two vessels: one in drying service while the

other is being refilled with salt. 

Operating Requirements 

To protect their pipelines, producers dry gas to a dew point 

below the minimum temperature expected in the pipeline.

If the gas is not dried appropriately, water and other free 

liquids can precipitate as the gas cools which can lead to

pipeline blockage or corrosion. To avoid this, producers 

normally dehydrate gas to a pipeline moisture specification

between 4 and 7 pounds of water per MMcf of gas. 

Desiccant performance curves show the temperature and 

pressure combinations that will result in gas meeting

pipeline moisture standards. Exhibit 2, derived from the 

moisture content table in Appendix A, shows the gas

temperature and pressure combinations that would result 

in 7 pounds of water per MMcf of gas for two of the most 

common desiccants. The shaded region above the 

saturation line in Exhibit 2 represents a “safe operating 

region” for calcium chloride dehydrators where the gas will 

be at or below pipeline moisture specification. Operators 

use these curves to determine the minimum gas pressure

required to ensure a given moisture content. In this 

example, an inlet gas at 47oF passing through a calcium 

chloride desiccant dehydrator must be pressurized to at

least 450 psig to meet the 7 pounds of water per MMcf 

standard. Curves for both calcium and lithium chloride 

are shown, although lithium chloride is rarely used 

because of its cost. 

2 
 

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

Exhibit 2: Desiccant Performance Curves at 

Maximum Pipeline Moisture Content 

Requirement (7 lb. of water/MMscf) 

Refilling Desiccants and Draining Brine 

As the desiccant tablets absorb moisture from the gas, the

depth of the desiccant tablets in the drying bed slowly 

decreases. Some manufacturers place a “window” (sightglass) on the vessel (see Exhibit 1) at the minimum

desiccant level. When the top of the desiccant reaches the 

sight-glass, the operator needs to refill the desiccant up to

the maximum level. Refilling the working bed is a manual 

operation that involves switching gas flow to another 

dehydration vessel, shutting valves to isolate the “empty” 

vessel, venting gas pressure to the atmosphere, opening

the top filler hatch, and pouring desiccant pellets into the 

vessel. This requires the operator to dump one or more 30

to 50 pound bags of salt into the vessel, depending on

dehydrator design. Because this procedure needs to be

performed more frequently the higher the gas throughput,

desiccant dehydrators are usually used when the volume of 

gas to be dried is 5 MMcfd or less. 

The brine in the claim area is sometimes drained manually 

(desiccant dehydrators typically accumulate from 10 to 50 

gallons of brine a week). Draining to an evaporation pond 

is best done after the vessel is depressurized, while 

draining to a produced water tank can be done before the 

vessel is depressurized—taking advantage of the gas 

pressure to push the brine into the tank. On rare 

occasions brine may be pumped into a tank truck using a 

pneumatic “duplex-type” pump. 

Economic and Environmental Benefits 

Using desiccant dehydrators as alternatives to glycol 

dehydrators can yield significant economic and 

environmental benefits, including: 

Reduced capital cost—The capital costs of 

desiccant dehydrators are low compared to the 

capital costs of glycol dehydrators. A desiccant 

dehydrator does not use a circulation pump,

pneumatic controls, a gas heater, or a fired reboiler/ 

regenerator. 

Reduced operation and maintenance cost— 

Glycol dehydrators burn a significant amount of 

produced gas for fuel in a gas heater and glycol 

regenerator. If the brine drain valve is automatic, 

the only O&M cost for a desiccant dehydrator is for 

refilling the desiccant bed. 

Minimal methane, VOC, and HAP emissions— 

Glycol dehydrators continuously vent gas to the 

atmosphere from pneumatic devices and the TEG 

regenerator vent. The only gas emissions from 

desiccant dehydrators occur during desiccant vessel 

depressurizing for salt refilling, typically one vesselvolume per week. Brine is produced in small 

quantities and absorbs little hydrocarbon. 

Decision Process 

Partners can evaluate potential locations and economics

for replacing existing glycol dehydrators with desiccant

dehydrators using the following five steps. 

Step 1: Identify appropriate locations. 

Desiccant dehydrators are an economic choice under 

certain operating conditions. Their applicability is 

determined primarily by gas throughput and produced gas

temperature and pressure. Desiccant dehydrators work

best when the volume to be dried is 5 MMcfd or less, and 

absorb moisture down to pipeline specifications when the 

wellhead gas temperature is low and the pressure is high. 

Five Steps for Evaluating a Desiccant Dehydrator: 

 Step 1: Identify appropriate locations.
 

 Step 2: Determine dehydrator capacity. 

 Step 3: Estimate the capital and operating costs.
 

 Step 4: Estimate savings.
 

 Step 5: Conduct economic analysis.
 

3 
 

 

 

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

If the inlet temperature of the gas is too high, desiccants

can form hydrates that precipitate from the solution and

cause caking and brine drainage problems. While it is 

possible to cool or compress the produced gas in order to 

use desiccant dehydrators, these measures increase system

complexity and typically are cost prohibitive. 

In contrast, glycol dehydrators are a better choice for 

higher producing well sites and work best for higher 

temperature gas at any pressure. If the produced gas 

temperature is too low for the TEG process, however,

operators will need to heat the gas prior to entering the

dehydrator. Since heating the gas requires more product 

to be burned as fuel, these situations are likely to be good 

candidates for desiccant dehydrators. Exhibit 3 shows 

which gas drying systems work best under various 

operating conditions. 

Exhibit 3: Optimum Operating Conditions for 

Dehydration Technologies 

Low Pressure 

(<100 psig) 

High Pressure 

(>100 psig) 

Low Temperature 

(<70°F) Desiccant/Glycola Desiccant 

High Temperature 

(>70°F) Glycol Glycol/Desiccantb 

a The gas may need to be heated to use a glycol dehydrator, or the gas may need to be compressed to 

use a desiccant dehydrator. 

b The gas may need to be cooled to use a desiccant dehydrator. 

Step 2: Determine dehydrator capacity. 

The first step in estimating the size of a desiccant 

dehydrator is to determine the inlet and outlet moisture

content of the gas. This is required to calculate the 

quantity of desiccant needed, and from that the size of the 

vessel. Operators use a natural gas water vapor content 

graph (example shown in Appendix B), a moisture content

table, or a sizing program such as the Hanover Company’s 

Quick Size program, found at <www.hanover-co.com/home/

products/index.html>, to estimate the water content in the 

gas stream. For this analysis, we will assume the 

dehydrator is being designed to handle a 1 MMscf/day gas 

stream at 47oF and 450 psig. For this scenario, using any

of these methods yields the same results—the natural gas

stream contains 21 pounds of water per MMcf. 

In order to meet a pipeline

moisture specification of 7 

pounds per MMcf, calcium 

chloride desiccant must 

remove 14 pounds of water 

Vendor’s Rule-of-Thumb 

One pound of desiccant removes three 

pounds of moisture from the gas. 

Nelson Price Indexes 

In order to account for inflation in equipment and 

operating & maintenance costs, Nelson-Farrar 

Quarterly Cost Indexes (available in the first issue of 

each quarter in the Oil and Gas Journal) are used to 

update costs in the Lessons Learned documents. 

The “Refinery Operation Index” is used to revise

operating costs while the “Machinery: Oilfield Itemized 

Refining Cost Index” is used to update equipment 

costs. 

To use these indexes in the future, simply look up the 

most current Nelson-Farrar index number, divide by 

the February 2006 Nelson-Farrar index number, and, 

finally multiply by the appropriate costs in the Lessons 

Learned. 

per MMcf of gas. For a 1 MMcfd dehydrator, and using a

vendor’s rule-of-thumb that 1 pound of desiccant removes 3

pounds of water, 4.7 pounds of calcium chloride will be

dissolved per day. Exhibit 4 summarizes this calculation. 

Exhibit 4: Determine the Daily 

Consumption of Desiccant 

Where: 

D 

F 

I 

O 

B 

= Daily consumption of desiccant (lb/day) 

= Gas flow rate (MMcf/day) 

= Inlet water content (lb/MMcf) 

= Outlet water content (lb/MMcf) 

= Desiccant-to-water ratio (lb desiccant/lb water) 

Given: 

F 

I 

O 

B 

= 1 MMcf/day of production gas at 47°F and 450 psig 

= 21 lb/MMcf 

= 7 lb/MMcf (pipeline moisture requirement) 

= 1 lb desiccant/3 lb water (vendor rule-of-thumb) 

Calculate: 

D = F * (I-O) * B 

= 1 * (21-7) * 1/3 

= 4.7 lb desiccant/day 

The next step is to size the vessel. Vendors supply 

desiccant dehydrator vessels in standard sizes, usually 

specified by outside diameter and maximum gas

throughput at various operating pressures, as shown in 

Exhibit 6. The bed dimensions are fixed to achieve 

equilibrium gas moisture content. This includes a 

standard size working bed depth: 5 inches for this vendor. 

4 
 

 

 

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

Exhibit 5: Determine the Size of 

the Desiccant Dehydrator 

Where: 

ID 

D 

H 

T 

B 

= Inside diameter of the desiccant vessel (in) 

= Daily desiccant consumption (lb/day) 

= Working salt bed height (in) 

= Time between refilling (days) 

= Bulk density (lb/ft3

) 

Given: 

D 

H 

T 

B 

= 4.7 lb/day (Exhibit 4) 

= 5 in (vendor rule-of-thumb) 

= 7 days (operator’s choice) 

= 55 lb/ft3

 (vendor’s data) 

Calculate: 

ID = 12 * 

= 12 * 

= 16.2 in 

Select standard vessel size from Exhibit 6: 

 Select next larger size than ID = 20 in 

BPH

TD



4  12

555 

1274.74 





P

Partners can select the desiccant vessel size from the 

vendor’s table or calculate the size using the equations in 

Exhibit 5. For the 1 MMcfd dehydrator example above,

using Exhibit 5 gives a vessel with a 16.2 inch inside

diameter (about 17 inch outside diameter with a 3/8 inch 

wall thickness). To use Exhibit 6, follow the 450-psig 

column down to the throughput capacity equal to or 

greater than what is needed; in this example, 1,344 Mcfd

(1.344 MMcfd). Following this row to the left yields an

outside diameter of 20 inches. 

Step 3: Estimate the capital and operating costs. 

Capital costs for single vessel desiccant dehydrators 

suitable for gas production rates from 0.1 to 5 MMcf per

day (including the initial fill of desiccant) range between

$3,500 and $21,000. After determining the necessary 

vessel size (Step 2), Partners can use Exhibit 6 to 

determine the capital costs of a desiccant dehydrator. For 

the example given in Step 2, the capital cost of a 20-inch, 

single vessel desiccant dehydrator is $8,048. For a twovessel dehydrator, the cost would be $16,096. 

Installation costs typically range from 50 to 75 percent of

the equipment cost. Using an installation factor of 75 

percent of the equipment cost, the single vessel desiccant

dehydrator described above would cost $6,036 to install.

The two-vessel dehydrator would cost $12,072 to install. 

The operating cost of using a desiccant dehydrator

includes the costs of desiccant replacement and brine 

disposal. Because the desiccant tablets dissolve as they

remove moisture from the gas, the working salt bed will 

need to be replenished periodically. The resulting brine 

also requires removal and treatment or disposal. 

Exhibit 7 shows the operating cost calculations for the 1 

MMcfd dehydrator example. Depending on the vendor, the 

Exhibit 6: Cost and Maximum Throughput Capacity (Mcfd) of Desiccant Dehydrators 

Outside 

Diameter 

(inches) 

Cost ($)a,b 100 psig 200 psig 300 psig 350 psig 400 psig 450 psig 500 psig 

10 3,529 95 177 260 301 342 383 424 

12 4,674 132 247 362 419 476 533 590 

16 7,262 214 400 587 680 773 866 959 

20 8,048 311 620 909 1,054 1,199 1,344 1,489 

24 11,014 481 900 1,319 1,528 1,738 1,948 2,158 

30 15,911 760 1,422 2,085 2,416 2,747 3,078 3,409 

36 21,092 1,196 2,230 3,270 3,789 4,308 4,827 5,346 

a The capital cost is for pressure ratings up to 500 psig, including one vessel with vessel supports, valves, piping, all appurtenances and the initial fill of calcium chloride desiccant tablets. b Dehydrator cost includes all appurtenances: vessel, support structure, valves, and piping. 

Source: Van Air, updated to 2006 equipment costs. 

5 
 

 

 

 

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

cost of calcium chloride can range from $0.80 to $1.49 per 

pound. Using $1.49 per pound for the cost of calcium 

chloride, the total cost for refilling 4.7 pounds per day 

(from Exhibit 4) is $2,556 per year. In the example given

in Exhibit 4, very little brine is produced removing

moisture from gas to achieve the desired pipeline moisture

specification (i.e., 7 pounds per MMcf): 4.7 pounds per day 

of salt plus the 14 pounds of water per day removed from 

the gas, or 18.7 pounds of brine per day—a little over 2

gallons per day. 

Exhibit 7: Determine the Operating Cost 

of a Desiccant Dehydrator 

Where: 

TO 

CD 

CB 

I 

O 

F 

P 

D 

S 

BD 

LC 

LT 

LR 

= Total operating cost ($/year) 

= Cost of desiccant ($/year) 

= Cost of brine disposal ($/year) 

= Inlet water content (lb/MMcf) 

= Outlet water content (lb/MMcf) 

= Gas flow rate (MMcf/day) 

= Price of the desiccant ($/lb) 

= Daily desiccant consumption (lb/day) 

= Density of CaCl2 brine (lb/bbl) 

= Cost of brine disposal ($/bbl) 

= Labor cost ($) 

= Labor time for operator to refill with desiccant (hr) 

= Labor rate for operator ($/hr) 

Given: 

F 

P 

D 

S 

BD 

LT 

LR 

= 1 MMcf/day of production gas at 47°F and 450 psig 

= $1.49/lb of calcium chloride (vendor data) 

= 4.7 lb desiccant/day (Exhibit 4) 

= 490 lb/bbl 

= $1.40/bbla 

= 1 hr/week 

= $40/hr 

Calculate: 

CD 

CB 

LC 

TO 

= D*P*365 day/yr 

= 4.7*1.49*365 

= $2,556/yr 

= 

= 

= $20/yr 

= LT*LR*52 weeks/yr 

= 1*40*52 

= $2,080/yr 

= CD+CB+LC 

= $2,556+$20+$2,080 

= $4,656/yr 

a GRI Atlas of Gas-Related Produced Water for 1990, May 1995, updated to 2006 costs. 

S

BDDFOI  days/365]))[(( yr

490 

[((21 7) 1) 4.7] 1.4 365 

Step 4: Determine economic replacement threshold. 

Replacing a glycol dehydrator with a desiccant dehydrator

significantly saves gas and reduces operation and 

maintenance costs. 

Determining Net Gas Savings 

The amount of gas saved can be determined by comparing 

the gas emissions and usage for the existing glycol

dehydrator to the gas vented from a desiccant dehydrator.

Partners can determine the gas savings by determining 

the following five factors. 

Estimate the gas vented from glycol 

dehydrator—The amount of gas vented from the 

glycol regenerator/reboiler is equal to the gas

entrained in the TEG. To determine this, Partners 

will need to know the gas flow rate, the inlet and 

outlet water content, the glycol-to-water ratio, the 

percent over-circulation, and the methane 

entrainment rate. Exhibit 8 demonstrates this 

calculation for the 1 MMcfd dehydrator example. In 

this example, an energy exchange pump without a 

flash tank separator is assumed. Using rules-of

thumb from EPA’s Lessons Learned: Optimize Glycol 

Circulation and Install Flash Tank Separators in 

Glycol Dehydrators, methane gas emissions of 69 Mcf

per year is calculated. 

Estimate the gas vented from pneumatic 

controllers—Pneumatic controllers are commonly

used to monitor and regulate gas and liquid flows, 

temperature, and pressure in glycol dehydrator units. 

Specifically, the controllers regulate gas and liquid

flows in dehydrators and separators, temperature in 

dehydrator regenerators, and pressure in flash tanks 

(when in use). In this example, the glycol dehydrator

unit with a gas heater is assumed to have four

bleeding pneumatic controllers—level controllers on 

the contactor and reboiler and temperature

controllers on the 

reboiler and gas 

Determine the Net Gas Savings: heater. It does not 

have a flash tank Add Savings from eliminating: separator. Pneumatic  Gas vented from glycol dehydrator. devices are assumed to

 Gas vented from pneumatic controllers. be a typical mix of  Gas burned as fuel in glycol reboiler. high bleed and low  Gas burned as fuel in a gas heater. bleed (i.e., they bleed

Subtract: in excess of 50 Mcf of 

 Gas vented from desiccant dehydrator. gas per year during

operation). Based on 

6 
 

 

 

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

Exhibit 8: Gas Vented from the 

Glycol Dehydrator 

Where: 

GV 

F 

W 

R 

OC 

G 

= Amount of gas vented annually (Mcf/yr) 

= Gas flow rate (MMcf/day) 

= Inlet-outlet water content (lb/MMcf) 

= Glycol-to-water ratio (gal/lb)a 

= Percent over-circulation 

= Methane entrainment rate (ft3

/gal)a 

Given: 

F 

W 

R 

G 

OC 

= 1 MMcfd of gas at 47°F and 450 psig 

= 21 - 7 = 14 lb water/MMcf (Exhibit 4) 

= 3 gal/lb (rule-of-thumb)a 

= 3 ft3

/gal for energy exchange pumps (rule-of-thumb)a 

= 150% 

Calculate: 

GV = 

= 

= 69 Mcf/yr 

a From EPA’s Lessons Learned: Optimize Glycol Circulation and Install Flash Tank Separators in Glycol 

Dehydrators. 

Mcfcf

WF R OC G days yr

/1,000 

(  )/365

1,000 

(1 14  365)33 1.5

the GRI/EPA study, Methane Emissions From the 

Natural Gas Industry, Volume 12–Pneumatic Devices, 

the annual emission factor for an average bleed 

pneumatic device is estimated to be 126 Mcf per year.

Therefore, the four pneumatic devices will contribute 

504 Mcf of the methane emissions annually. Exhibit 

9 summarizes this example. 

Exhibit 9: Gas Vented from 

Pneumatic Controllers 

Where: 

GB 

EF 

PD 

= Gas bleed (Mcf/yr) 

= Emission factor (Mcf natural gas bleed/pneumatic device per 

year)a 

= Number of pneumatic devices 

Given: 

EF 

PD 

= 126 Mcf/device/yr 

= 4 pneumatic devices/glycol dehydrators 

Calculate: 

GB = EF * PD 

= 126 * 4 

= 504 Mcf/yr 

a GRI/EPA study, Methane Emissions from the Natural Gas Industry, Volume 12. 

Estimate the gas burned for fuel in glycol 

reboiler—The glycol dehydrator uses natural gas in 

the reboiler/regenerator to boil-off water from the 

rich glycol. Assuming that the heat duty of the 

reboiler is 1,124 Btu per gallon of TEG, the gas used 

by the reboiler is 17 Mcf per year. Exhibit 10 

summarizes this calculation. 

Exhibit 10: Gas Burned for Fuel 

in Glycol Reboiler 

Where: 

FGR 

F 

W 

Qr 

Hv 

R 

= Fuel gas for reboiler (Mcf/yr) 

= Gas flow rate (MMcfd) 

= Inlet-outlet water content (lb/MMcf) 

= Heat duty of reboiler (Btu/gal TEG)a 

= Heating value of natural gas (Btu/scf)b 

= Glycol-to-water ratio (gal TEG/lb water)c 

Given: 

F 

W 

Qr 

Hv 

R 

= 1 MMcfd 

= 21 - 7 = 14 lb water/MMcf 

= 1,124 Btu/gal TEG 

= 1,027 Btu/scf 

= 3 gal TEG/lb water removed 

Calculate: 

FGR = 

= 

= 17 Mcf/yr 

a Based on calculation in Engineering Data Book, Volume II, 11th edition, Gas Processors Supply 

Association, 1998, Section 20-Dehydration. b Energy Information Administration (EIA), Monthly Engineering Review, Table A4. c From EPA’s Lessons Learned: Optimize Glycol Circulation and Install Flash Tank Separators in Glycol 

Dehydrators. 

Hv Mcfcf

RQrWF yrdays

/1,000 

( )/365



   

1,027 1,000

365 )31,12414(1 



   

Estimate the gas burned for fuel in a gas 

heater—TEG does not perform well on low 

temperature gas. As a result, the gas is typically 

heated prior to entering the dehydrator unit. 

Natural gas is used to fuel the gas heater. The 

amount of fuel gas used to heat 1 MMcfd of produced 

gas from 47oF to (assumed) 90oF is 483 Mcf per year. 

Exhibit 11 shows this calculation. 

Estimate the gas loss from desiccant 

dehydrator—The gas loss from a desiccant 

dehydrator is determined by calculating the amount

of gas vented from the vessel every time it is 

depressurized for the refilling process. To determine 

the volume of gas vented, Partners will need to 

determine the volume of the dehydrator vessel and

what percentage of this volume is occupied by gas. 

The 20-inch OD vessel in Exhibit 6 would have an 

7 
 

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

Exhibit 11: Amount of Fuel Gas 

Used to Heat the Gas 

Where: 

FGH 

Hv 

Cv 

D 

DT 

F 

E 

= Fuel gas used in heater (Mcf/yr) 

= Heating value of natural gas (Btu/cf) 

= Specific heat of natural gas (Btu/lb°F) 

= Density of natural gas (lb/cf) 

= (T2 - T1) change in temperature (°F) 

= Flow rate (MMcf/d) 

= Efficiency 

Given: 

Hv 

Cv 

D 

DT 

F 

E 

= 1,027 Btu/cf 

= 0.441 Btu/lb°F 

= 0.0502 lb/cf 

= 43°F (90 - 47)°F 

= 1 MMcf/d 

= 70% 

Calculate: 

FGH = 

= 

= 483 Mcf/yr 

)( 

( )/1,000/365

EHv

DTCvDF days yr MMcfMcf



 

0.7)(1,027 

0.0502(1 430.441 365 1,000)





Exhibit 12: Gas Lost from 

the Desiccant Dehydrator 

Where: 

GLD 

H 

D 

P1 

P2 

P 

%G 

T 

= Gas loss from desiccant dehydrator (scf/yr) 

= Height of the dehydrator vessel (ft) 

= Inside diameter of the vessel (ft) 

= Atmospheric pressure (psia) 

= Pressure of the gas (psig) 

= pi 

= Percent of packed vessel volume that is gas 

= Time between refilling (days) 

Given: 

H 

D 

P1 

P2 

P 

%G 

T 

= 76.75 in (6.40 ft)a 

= 19.25 in (1.6 ft) 

= 14.7 psia 

= 450 psig + 14.7 (464.7 psig) 

= 3.14 

= 45% (vendor’s rule-of-thumb)a 

= 7 days 

Calculate: 

GLD = 

= 

= 10 Mcf/yr 

a Based on product data provided by Van Air. 

(4 )/1,000

( )/365%

1 

2 

2 

McfcfTP

GPPDH yrdays





1,000 )714.7(4 

3.141.6(6.4 464 .7 365 )0.45 2 





approximately 19.25-inch ID (assuming a 3/8 inch

wall thickness). The vessel has an overall length of 

76.75 inches with 45 percent of its volume filled with 

gas. Using Boyle’s Law, the amount of gas vented to 

the atmosphere during depressurizing of the vessel is 

10 Mcf per year. Exhibit 12 summarizes this 

calculation. 

Estimate the total gas savings—The total gas 

savings is the total avoided emissions and gas use of

the glycol dehydrator minus the gas lost from venting

of the desiccant dehydrator when replacing the 

desiccant. In this example, total gas savings are 

1,063 Mcf per year. Using a gas price of $7.00 per 

Mcf, the gas value saved is $7,441 per year. Nonassociated natural gas contains 78.8 percent

methane. Therefore, the total methane emission 

savings is 78.8 percent of the difference between the 

gas emitted by the glycol dehydrator and its 

pneumatic controllers (Exhibits 8 and 9 respectively), 

and the desiccant dehydrator (Exhibit 12); in this 

case, 507 Mcf per year. Exhibit 13 summarizes this 

example. 

Exhibit 13: Total Gas Savings 

Calculate: 

TGS 

Savings 

= Total Gas Savings (Mcf/yr) 

= Exhibit 8 + Exhibit 9 + Exhibit 10 + Exhibit 11 - Exhibit 12 

= 69 + 504 + 17 + 483 - 10 

= 1,063 Mcf/yr 

= 1,063 Mcf/yr * $7/Mcf 

= $7,441/yr 

Methane Emissions Reduction 

TMER 

TMER 

= Total methane emissions reduction 

= 78.8% * (Exhibit 8 + Exhibit 9 - Exhibit 12) 

= 0.788 * (69 + 504 - 10) 

= 444 Mcf/yr 

Determining Operations and Maintenance Savings 

Other savings include the difference between the operating 

and maintenance cost (labor cost) of a desiccant dehydrator

and a glycol dehydrator. 

The operation cost of a desiccant dehydrator includes the 

8 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

The average methane content of natural gas varies by natural gas 

industry sector. The Natural Gas STAR Program assumes the 

following 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 

refill cost of the desiccant, disposal of the brine, and labor 

costs. Since a desiccant dehydrator has no moving parts

and does not require power to operate, maintenance costs

are negligible. The refill and brine disposal costs

previously calculated in Exhibit 7 are $2,556 and $20 per 

year, respectively. Labor costs assume one hour per week

for the operator to refill the desiccant dehydrator. At $40 

per hour, this would cost about $2,080 per year. 

Operating cost for a glycol dehydrator includes topping-up

the glycol sump to maintain glycol levels. Maintenance 

and labor include inspecting and cleaning the mechanical 

systems, periodically repairing the circulation pump and 

pneumatic controls, and annually cleaning the fire-tubes of 

the reboiler and gas heater. Glycol costs $5.57 per gallon,

and a typical make-up rate is 0.1 gallons per MMcf of gas

processed. For this example, this works out to about 37

gallons of glycol per year, or $206 per year. Labor costs 

assume operators spend an average of two hours per week 

maintaining and repairing the unit. At $40 per hour this 

amounts to about $4,160 per year. Spare parts are

estimated at half the labor cost, or $2,080 per year. Based 

on this, total operation, maintenance, and labor costs for 

our example glycol dehydrator system is $6,446 per year. 

Step 5: Conduct economic analysis. 

The final step is to compare the implementation and

annual operating and maintenance costs of each option 

and the value of gas saved or used/lost by each unit.

Exhibit 14 provides a comparison of the implementation

and operating and maintenance costs of a desiccant 

dehydrator and a glycol dehydrator (dehydrating 1 MMcfd

natural gas at 450 psig pressure and 47oF temperature). 

Exhibit 15 compares the amount and the value of gas used

and lost by each system. 

Exhibit 16 shows the savings a Natural Gas STAR Partner

could expect over a 5-year period by replacing an existing

glycol dehydrator of 1 MMcfd at 450 psig and 47oF gas

with a desiccant dehydrator. 

Exhibit 14: Cost Comparison of Desiccant 

Dehydrator and Glycol Dehydrator 

1 MMcfd natural gas at operating 450 psig and 47°F 

Type of Costs and Savings Desiccant 

($/yr) 

Glycol 

($/yr)

Implementation Costs 

Capital Costs 

 Desiccanta

 (includes the initial fill) 16,097 

 Glycol 24,764 

 Other costs (installation and engineering)b 12,073 18,573 

Total Implementation Costs: 28,169 43,337 

Annual Operating and Maintenance Costs 

Desiccant 

 Cost of desiccant refillc

 ($1.20/lb) 2,556 

 Cost of brine disposalc 20 

Glycol 

 Labor costd 2,080 

 Cost of glycol refilld

 ($5.57/gal) 206 

 Material and labor costd 6,240 

Total Annual Operation and Maintenance Costs: 4,656 6,446 

a Based on two desiccant vessels used alternatively. See Exhibit 5. 

b Installation costs assumed at 75% of the equipment cost. 

c Values are from Exhibit 7. 

d See Step 4, Estimate Savings. 

Exhibit 15: Gas Use/Loss and Value Comparison 

1 MMcfd natural gas at operating 450 psig and 47°F 

Type of Loss/Use 

Desiccant Glycol 

Mcf/yr $/yra Mcf/yr $/yra 

Gas Use 

 Fuel (Exhibits 10 and 11) — — 500 3,500 

Gas Loss 

 Pneumatic devices (Exhibit 9) — — 504 3,528

 Vents (Exhibits 8 and 12) 10 70 69 483 

Total: 

Methane Emissionsb

: 

10 

8 

70 

— 

1,073 

452 

7,511 

— 

a Gas price based on $7/Mcf. 

b Values are from Exhibit 12 and Exhibit 13. 

9 
 

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

Exhibit 16: Economics of Replacing a Glycol Dehydration System 

with a Two-Vessel Desiccant Dehydrator System 

Types of Costs and Savingsa Year 0 ($/yr) Year 1 ($/yr) Year 2 ($/yr) Year 3 ($/yr) Year 4 ($/yr) Year 5 ($/yr) 

Capital costs (28,169) 

Avoided O&M costs 6,446 6,446 6,446 6,446 6,446 

O&M costs - Desiccant ($/yr) (4,656) (4,656) (4,656) (4,656) (4,656) 

Value of gas saved 7,441 7,441 7,441 7,441 7,441 

Surplus equipment value 12,382b 

Total ($) (15,787) 9,232 9,232 9,232 9,232 9,232 

NPV (Net Present Value)c

 = $19,208 

IRR (Internal Rate of Return)d

 = 51% 

Payback Period (months) = 21 

a All cost values are obtained from Exhibits 14 and 15. The gas price is assumed to be $7/Mcf. b Based on a 50% of the capital cost of glycol dehydrator. 

c The NPV is calculated based on 10% discount over 5 years. d The IRR is calculated based on 5 years. 

When considering replacing glycol dehydrators with 

desiccant dehydrators, natural gas price may influence the

decision making process. Exhibit 17 shows an economic 

analysis of installing a 1 MMcfd desiccant dehydrator that

operates at 450 psig and 47o F at different natural gas 

prices. 

Exhibit 17: Gas Price Impact on 

Economic Analysis 

$3/Mcf $5/Mcf $7/Mcf $8/Mcf $10/Mcf 

Value of Gas 

Saved $3,189 $5,315 $7,441 $8,504 $10,630 

Payback Period 

(months) 39 27 21 19 16 

Internal Rate of 

Return (IRR) 17% 35% 51% 59% 74% 

Net Present 

Value (i=10%) $3,089 $11,148 $19,208 $23,237 $31,296 

Lessons Learned 

Desiccant dehydrators can cost-effectively reduce methane

emissions for gas dehydration. Partner experience offers 

the following lessons learned: 

Desiccant dehydrators can provide significant 

economic benefits, such as increased operating

efficiency and decreased capital and maintenance 

costs for low flow rate gas at higher pressures and 

lower temperature conditions. 

Make-up (replacement) cost of the desiccant is 

slightly higher than the glycol because the desiccants 

dissolve in water and must be replaced regularly,

while the glycol is recirculated. 

Desiccant dehydrators are an effective method for 

eliminating methane, VOC, and HAP emissions, 

resulting in both economic and environmental 

benefits. 

Include methane emissions reductions attributable to 

replacing glycol dehydrators with desiccant 

dehydrators in Natural Gas STAR Program annual 

reports. 

References 

Acor, Lori G. and David Mirdadian. Benefits of Using Deliquescing 

Desiccants for Gas Dehydration. Society of Petroleum Engineers 

(SPE82138), 2003. 

Bowman, Bob. Benefits of Using Deliquescing Desiccants for Gas 

Dehydration. Society of Petroleum Engineers (SPE 60170), 2000. 

10 
Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

Dow Chemical Company, product literature. Gas Dehydration with 

PELADOW DG Calcium Chloride. 

Energy Information Administration. Monthly Energy Review, 2002, Table 

A4. 

Eskrigge, Charles. Air and Vacuum Process Inc. (Van Air), personal 

contact. 

Gas Processors Supply Association. Engineering Data Book, Volume II, 

11th edition, 1998, Section 20-Dehydration. 

Gas Research Institute. Atlas of Gas-Related Produced Water for 1990. 

(GRI-95/0016, May 1995). 

Gas Research Institute. Methane Emissions From the Natural Gas 

Industry, 1996, Volume 12 (GRI-94/0257.29). June 1996. 

Murray, Curt. Practical Methods of Drying Natural Gas. Pride of the Hills 

MFG., Inc. 

Murray, Curt. Pride of the Hills Mfg., Inc., personal contact. 

Smith, Reid. BP, personal contact. 

The Hanover Compressor Company. personal contact. 

Tingley, Kevin. U.S. EPA Natural Gas STAR Program, personal contact. 

U.S. Environmental Protection Agency. Lessons Learned: Optimize Glycol 

Circulation and Install Flash Tank Separators in Glycol Dehydrators 

(EPA430-B-03-013, May 2003). 

U.S. Environmental Protection Agency. Lessons Learned: Replacing Gas— 

Assisted Glycol Pumps with Electric Pumps (EPA430-B-03-014, May 

2003). 

Vavro, Matthew E. Minimizing Natural Gas Dehydration Costs with Proper 

Selection of Dry Bed Desiccants and New Dryer Technology. Society 

of Petroleum Engineers (SPE37348), 1996. 

Zavadil, Duane. Williams Production, personal contact. 

11 
             

                                                      

                                                              

                                                             

                                                                 

                                                             

                                                             

                                                             

                                                             

                                                         

                                                         

                                                             

                                                             

                                                             

                                                                     

           

                                                  

                                                              

                                                           

                                                             

                                                           

                                                           

                                                           

                                                       

                                                   

                                                   

                                                       

                                                       

                                                       

                                                           

Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

Appendix A 

Moisture Content of Natural Gas in Equilibrium with Desiccants (lb water/MMcf of natural gas) 

Type Calcium Chloride Deliquescent Desiccant Tablets

10

PSIG

25

PSIG

50

PSIG

75

PSIG

100

PSIG

125

PSIG

150

PSIG

175

PSIG

200

PSIG

225

PSIG

250

PSIG

275

PSIG

300

PSIG

350

PSIG

400

PSIG

500

PSIG

750

PSIG

1000

PSIG

80oF 344 219 13 98 77 64 55 48 43 39 35 33 30 27 23.6 19.7 14.3 11.6

75oF 292 186 113 83 65 54 46 41 36 33 30 28 26 22.5 20.1 16.8 12.2 9.9

70oF 246 157 96 70 55 46 39 43 31 27 25 23.4 21.7 19.1 17.1 14.3 10.4 8.5

65oF 207 132 81 59 47 39 33 29 26 23.5 21.4 19.8 18.4 16.2 14.5 12.1 8.9 7.3

60oF 174 111 68 50 39 33 29 24.5 21.9 19.8 18.1 16.8 15.5 13.7 12.3 10.3 7.6 6.2

58oF 162 103 63 46 36 31 26 22.8 20.3 18.4 16.8 15.6 14.4 12.9 11.4 9.6 7 5.8

56oF 150 96 59 43 34 29 24.1 21.2 18.9 17.1 15.7 14.5 13.4 11.8 10.6 8.9 6.6 5.4

54oF 140 89 55 40 32 26 22.5 19.8 17.6 16 14.6 13.5 12.6 11.1 9.9 8.3 6.2 5.1

52oF 130 83 51 37 29 24.5 21 18.4 16.4 14.9 14.4 12.6 11.7 10.3 9.3 7.8 5.8 4.7

50oF 121 77 47 35 27 22.8 19.5 17.1 15.3 13.9 12.7 11.7 10.9 9.6 8.6 7.2 5.4 4.4

45oF 100 64 39 29 22.7 18.9 16.2 14.3 12.7 11.5 10.6 9.8 9.1 8 7.2 6.1 4.5 3.7

40oF 83 53 32 24 18.8 15.6 13.4 11.8 10.5 9.6 8.8 8.1 7.5 6.7 6 5 3.8 3.1

35oF 68 44 27 19.6 15.5 13 11.1 9.8 8.7 7.9 7.2 6.7 6.2 5.5 5 4.2 3.1 2.6

Type Lithium Chloride Deliquescent Desiccant Tablets

10

PSIG

25

PSIG

50

PSIG

75

PSIG

100

PSIG

125

PSIG

150

PSIG

175

PSIG

200

PSIG

225

PSIG

250

PSIG

275

PSIG

300

PSIG

350

PSIG

400

PSIG

500

PSIG

750

PSIG

1000

PSIG

80oF 128 81 50 36 29 23.7 20.2 17.8 15.8 14.3 13 12 11.1 9.8 8.7 7.3 5.3 4.3

75oF 108 69 42 31 24.2 20 17.2 15.1 13.4 12.1 11.1 10.2 9.5 8.3 7.4 6.2 4.5 3.7

70oF 91 59 36 26 20.4 17 14.5 12.7 11.3 10.3 9.4 8.7 8 7.1 6.3 5.3 3.8 3.1

65oF 77 49 30 21.9 17.2 14.3 12.2 10.8 9.6 8.7 7.9 7.3 6.8 6 5.4 4.5 3.3 2.7

60oF 65 41 25 18.4 14.5 12.1 10.3 9.1 8.1 7.4 6.7 6.2 5.7 5 4.5 3.8 2.8 2.3

58oF 60 38 23.4 17.1 13.5 11.2 9.6 8.4 7.5 6.8 6.2 5.7 5.3 4.7 4.2 3.5 2.6 2.1

56oF 56 37 21.7 15.9 12.5 10.5 8.9 7.8 7 6.3 5.8 5.4 5 4.4 3.9 3.3 2.4 2

54oF 52 33 20.3 14.8 11.7 9.7 8.3 7.3 6.5 5.9 5.4 5 4.6 4.1 3.7 3.1 2.3 1.8

52oF 48 31 18.9 13.8 10.9 9 7.7 6.8 6.1 5.5 5 4.7 4.3 3.8 3.4 2.9 2.1 1.7

50oF 45 29 17.5 12.8 10.1 8.4 7.2 6.4 5.8 5.1 4.7 4.4 4 3.5 3.2 2.7 2 1.6

45oF 37 23.8 14.5 10.7 8.4 7 6. 5.3 4.7 4.3 3.9 3.6 3.3 2.9 2.6 2.2 1.6 1.3

40oF 30 19.6 12 8.7 6.8 5.8 4.9 4.4 3.8 3.6 3.2 3 2.8 2.4 2.2 1.8 1.4 1.1

35oF 25 16.1 9.9 7.2 5.7 4.8 4.1 3.6 3.2 2.9 2.7 2.5 2.3 2 1.8 1.5 1.1 0.9

Source: Van Air 

12 
Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

Appendix B 

Water Vapor Content of Natural Gas at Saturation 

Source: Smith Industries, Inc., Houston, Texas 

13 
Replacing Glycol Dehydrators With Desiccant Dehydrators 

(Cont’d) 

United States 

Environmental Protection Agency 

Air and Radiation (6202J) 

1200 Pennsylvania Ave., NW 

Washington, DC 20460 

October 2006 

EPA provides the suggested methane emissions 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 emission 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. 

14