Natural Gas Dehydration

Lessons Learned
from Natural Gas STAR

Producers and Processors

Technology Transfer Workshop

Western Gas Resources and

EPAs Natural Gas STAR Program
Gillette and Rock Springs, WY
May 9 & 11, 2006

Natural Gas Dehydration: Agenda

Methane Losses

Methane Recovery

Is Recovery Profitable?

Industry Experience

Discussion Questions

1
Methane Losses from Dehydrators

Dehydrators and pumps account for:

17 Bcf of methane emissions in the production, gathering, and
boosting sector
1 Bcf of methane emissions in the processing sector
Other Sources
Storage Tank 21 Bcf
Venting
9 Bcf
Meters and Pneumatic
Devices
Pipeline Leaks
61 Bcf
10 Bcf
Gas Engine
Exhaust
12 Bcf Inventory of U.S. Greenhouse
Dehydrators and Well Venting
Gas Emissions and Sinks
Pumps and Flaring 1990 - 2003
17 Bcf 18 Bcf

What is the Problem?

Produced gas is saturated with water, which must be

removed for gas processing and transmission
Glycol dehydrators are the most common equipment
to remove water from gas
32,000 dehydration systems in natural gas
production, gathering, and boosting
Most use triethylene glycol (TEG)
Glycol dehydrators create emissions
Methane, VOCs, HAPs from reboiler vent
Methane from pneumatic controllers
Source: www.prideofthehill.com

2
Basic Glycol Dehydrator System
Process Diagram
Dry Sales Gas

Glycol
Contactor

Water/Methane/VOCs/HAPs
Inlet Wet Gas To Atmosphere

Driver

Gas Rich TEG

Glycol
Bypass
Energy
Exchange
Pump Glycol Reboiler/
Regenerator Fuel Gas
Lean TEG
Pump

Methane Recovery: Five Options

Optimize glycol circulation rates
Flash tank separator (FTS) installation
Electric pump installation
Zero emission dehydrator
Replace glycol unit with desiccant dehydrator
Flare (no recovery)

3
Optimizing Glycol Circulation Rate
Gas wells initial production rate decreases over its
lifespan
Glycol circulation rates designed for initial, highest
production rate

Operators tend to set it and forget it

Glycol overcirculation results in more methane

emissions and fuel gas consumption without

significant reduction in gas moisture content

Partners found circulation rates two to three times higher

than necessary
Methane emissions and fuel gas consumption are directly
proportional to circulation rate

Installing Flash Tank Separator (FTS)

Flashed methane can be captured using an FTS
Many units are not using an FTS

100
80
Percent

60 With FTS
40
Without FTS
20
0
<1 1-5 >5
MMcfd processed
Source: API

4
Methane Recovery
Recovers ~ 90% of methane emissions

Reduces VOCs by 10 to 90%

Must have an outlet for low pressure gas

Fuel

Gas
Compressor suction
Recovery
Vapor recovery
Reduced
unit Flash Emissions
Tank

Low Capital Cost/Quick Payback

Flash Tank Costs

Lessons Learned study provides guidelines for

scoping costs, savings and economics
Capital and installation costs:

Capital costs range from $5,000 to $10,000 per flash tank

Installation costs range from $2,400 to $4,300 per flash

tank

Negligible O&M costs

5
Installing Electric Pump
Dry Sales Gas

Glycol
Contactor

Water/Methane/VOCs/HAPs
Inlet Wet Gas To Atmosphere
Gas
Driver

Rich TEG
Electric
Motor
Driven
Pump Glycol Reboiler/
Regenerator Fuel Gas
Lean TEG
Pump

Overall Benefits
Financial return on investment through gas savings
Increased operational efficiency
Reduced O&M costs
Reduced compliance costs (HAPs, BTEX)
Similar footprint as gas assist pump
Limitation: must have electric power source

6
Is Recovery Profitable?
Three Options for Minimizing Glycol Dehydrator Emissions

Capital Annual O&M Emissions Payback

Option
Costs Costs Savings Period1
Optimize
130 13,133
Circulation Negligible Negligible Immediate
Mcf/year
Rate

Install Flash $5,000 236 7,098 2 months

Negligible
Tank $10,000 Mcf/year 6 years

Install < 1 month

$4,200 360 36,000
Electric $3,600 several
$23,400 Mcf/year
Pump years
1 Gas price of $7/Mcf

Zero Emission Dehydrator

Combines many emission saving technologies into
one unit
Still gas is vaporized from the rich glycol when it
passes through the glycol reboiler
Condenses the still gas and separates the skimmer
gas from the condensate using an eductor
Skimmer gas is rerouted back to reboiler for use as
fuel

7
Overall Benefits
Still gas is condensable (heavier hydrocarbons and
water) and can be removed from the non-
condensable components using a still condenser
The condensed liquid will be a mixture of water and
hydrocarbons and can be further separated
Hydrocarbons (mostly methane) are valuable and
can be recovered as fuel or product
By collecting the still column vent gas emissions are
greatly reduced

Replace Glycol Unit with Desiccant

Dehydrator
Desiccant Dehydrator

Wet gasses pass through drying bed of desiccant tablets

Tablets absorb moisture from gas and dissolve

Moisture removal depends on:

Type of desiccant (salt)

Gas temperature and pressure

Hygroscopic Typical T and P Cost

Salts for Pipeline Spec
Calcium chloride 47oF 440 psig Least expensive
Lithium chloride 60oF 250 psig More expensive

8
Desiccant Performance
Desiccant Performance Curves at Maximum
Pipeline Moisture Spec (7 pounds water / MMcf)

Max Spec Line

for CaCl2
Max Spec Line
for LiCl2

Desiccant Dehydrator Schematic

Filler Hatch
Maximum

Desiccant Level

Dry Sales Gas

Minimum

Desiccant Level

Desiccant
Tablets
Drying Bed
Support
Grid
Inlet Wet Gas

Brine

Drain Valve

9
Estimate Capital Costs

Determine amount of desiccant needed to remove

water
Determine diameter of vessel
Costs for single vessel desiccant dehydrator
Capital cost varies between $3,000 and $17,000
Gas flow rates from 1 to 20 MMcf/day
Capital cost for 20-inch vessel with 1 MMcf/day gas flow is $6,500
Installation cost assumed to be 75% of capital cost
Normally installed in pairs
One drying, one refilled for standby
Note:

MMcf = Million Cubic Feet

How Much Desiccant Is Needed?

Example: Where:
D=? D = Amount of desiccant needed (pounds/day)
F = 1 MMcf/day F = Gas flow rate (MMcf/day)
I = 21 pounds/MMcf I = Inlet water content (pounds/MMcf)
O = 7 pounds/MMcf O = Outlet water content (pounds/MMcf)
B = 1/3 B = Desiccant/water ratio vendor rule
of thumb

Calculate:
D = F * (I - O) * B
D = 1 *(21 - 7) * 1/3
D = 4.7 pounds desiccant/day

Note:
MMcf = Million Cubic Feet Source: Van Air

10
Calculate Vessel Diameter
Example: Where:
ID = ? ID = Inside diameter of the vessel (inch)
D = 4.7 pounds/day D = Amount of desiccant needed (pounds/day)
T = 7 days T = Assumed refilling frequency (days)
B = 55 pounds/cf B = Desiccant density (pounds/cf)
H = 5 inch H = Height between minimum and
maximum bed level (inch)

Calculate:

ID = 12* 4*D*T*12 = 16.2 inch

H*B*

Standard ID available = 20 inch

Note:
cf = Cubic Feet Source: Van Air

Operating Costs
Operating costs
Desiccant: $2,059/year for 1 MMcf/day example
$1.20/pound desiccant cost
Brine Disposal: Negligible
$1/bbl brine or $14/year
Labor: $1,560/year for 1 MMcf/day example
$30/hour
Total: ~$3,633/year

11
Savings
Gas savings

Gas vented from glycol dehydrator

Gas vented from pneumatic controllers

Gas burner for fuel in glycol reboiler

Gas burner for fuel in gas heater

Less gas vented from desiccant dehydrator

Methane emission savings calculation
Glycol vent + Pneumatics vents Desiccant vents
Operation and maintenance savings
Glycol O&M + Glycol fuel Desiccant O&M

Gas Vented from Glycol Dehydrator

Example: Where:
GV = ? GV= Gas vented annually (Mcf/year)
F = 1 MMcf/day F = Gas flow rate (MMcf/day)
W = 21-7 pounds H2O/MMcf W = Inlet-outlet H2O content (pounds/MMcf)
R = 3 gallons/pound R = Glycol/water ratio (rule of thumb)
OC = 150% OC = Percent over-circulation
G = 3 cf/gallon G = Methane entrainment (rule of thumb)

Calculate:
GV = (F * W * R * OC * G * 365 days/year)
1,000 cf/Mcf

GV = 69 Mcf/year

Glycol Dehydrator Unit

Source: GasTech

12
Gas Vented from Pneumatic Controllers
Example: Where:
GE = ? GE = Annual gas emissions (Mcf/year)
PD = 4 PD = Number of pneumatic devices per
dehydrator
EF = 126 Mcf/device/year EF = Emission factor
(Mcf natural gas bleed/
pneumatic devices per year)

Calculate:
GE = EF * PD Norriseal
GE = 504 Mcf/year Pneumatic Liquid
Level Controller

Source: norriseal.com

Gas Lost from Desiccant Dehydrator

Example: Where:
GLD = ? GLD = Desiccant dehydrator gas loss (Mcf/year)
ID = 20 inch (1.7 feet) ID = Inside Diameter (feet)
H = 76.75 inch (6.4 feet) H = Vessel height by vendor specification (feet)
%G = 45% %G = Percentage of gas volume in the vessel
P1 = 15 Psia P1 = Atmospheric pressure (Psia)
P2 = 450 Psig P2 = Gas pressure (Psig)
T = 7 days T = Time between refilling (days)

Calculate:
GLD = H * ID2 * * P2 * %G * 365 days/year
4 * P1 * T * 1,000 cf/Mcf
GLD = 10 Mcf/year

Desiccant Dehydrator Unit

Source: usedcompressors.com

13
Desiccant Dehydrator and Glycol
Dehydrator Cost Comparison
Type of Costs and Savings Desiccant Glycol
($/yr) ($/yr)
Implementation Costs
Capital Costs
Desiccant (includes the initial fill) 13,000
Glycol 20,000
Other costs (installation and engineering) 9,750 15,000
Total Implementation Costs: 22,750 35,000
Annual Operating and Maintenance Costs
Desiccant
Cost of desiccant refill ($1.20/pound) 2,059
Cost of brine disposal 14
Labor cost 1,560
Glycol
Cost of glycol refill ($4.50/gallon) 167
Material and labor cost 4,680
Total Annual Operation and Maintenance Costs: 3,633 4,847

Based on 1 MMcfd natural gas operating at 450 psig and 47F

Installation costs assumed at 75% of the equipment cost

Desiccant Dehydrator Economics

NPV= $18,236 IRR= 62% Payback= 18 months

Type of Costs
and Savings Year 0 Year 1 Year 2 Year 3 Year 4 Year 5
Capital costs -$22,750
Avoided O&M
costs $4,847 $4,847 $4,847 $4,847 $4,847
O&M costs
Desiccant -$3,633 -$3,633 -$3,633 -$3,633 -$3,633
Value of gas
saved 1 $7,441 $7,441 $7,441 $7,441 $7,441
Glycol dehy.
salvage value 2 $10,000
Total -$12,750 $8,655 $8,655 $8,655 $8,655 $8,655
1 Gas price = $7/Mcf, Based on 563 Mcf/yr of gas venting savings and 500 Mcf/yr of fuel gas savings
2 Salvage value estimated as 50% of glycol dehydrator capital cost

14
Partner Experience
One partner routes glycol gas from FTS to fuel gas
system, saving 24 Mcf/day (8,760 Mcf/year) at each
dehydrator unit
Texaco has installed FTS
Recovered 98% of methane from the glycol
Reduced emissions from 1,232 - 1,706 Mcf/year to <47
Mcf/year

Lessons Learned

Optimizing glycol circulation rates increase gas savings,

reduce emissions

Negligible cost and effort

FTS reduces methane emissions by ~ 90 percent

Require a low pressure gas outlet

Electric pumps reduce O&M costs, reduce emissions,

increase efficiency

Require electrical power source

Zero emission dehydrator can virtually eliminate emissions

Requires electrical power source

Desiccant dehydrator reduce O&M costs and reduce

emissions compared to glycol

Best for cold gas

15
Discussion Questions
To what extent are you implementing these

technologies?

How can the Lessons Learned studies be improved

upon or altered for use in your operation(s)?

What are the barriers (technological, economic, lack

of information, regulatory, focus, manpower, etc.)

that are preventing you from implementing this

technology?

16