# Presentation: 796975

## Natural Gas Dehydration

**Lessons Learned**
**from Natural Gas STAR**
**Producers Technology Transfer Workshop**
**Devon Energy and**
**EPA’s Natural Gas STAR Program**
**Casper, Wyoming**
**August 30, 2005**

## Natural Gas Dehydration: Agenda

- Methane Losses
- Methane Recovery
- Is Recovery Profitable?
- Industry Experience
- Discussion Questions

## Methane Losses from Production

**Methane Losses from Production**

- 1990-2004 Partners reported saving ~ 12.5 Bcf (Billion cubic feet) from dehydrators

**Pneumatic Devices**
**61 Bcf**

**Storage Tank **
**Venting**
**9 Bcf**

**Other Sources **
**21 Bcf**

- Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990 - 2003

**Meters and**
**Pipeline Leaks**
**10 Bcf**

**Gas Engine**
**Exhaust**
**12 Bcf**

**Dehydrators and**
**Pumps**
**17 Bcf**

**Well Venting **
**and Flaring**
**18 Bcf**

**Notes:**
2002 reporting year methane emissions from natural gas systems

## What is the Problem?

- Produced gas is saturated with water, which must be removed for gas transmission
- Glycol dehydrators are the most-common equipment to remove water from gas
**38,000 dehydration systems in the natural gas production sector**
**Most use triethylene glycol (TEG)**
- Glycol dehydrators create emissions
**Methane, VOCs, HAPs from reboiler vent**
**Methane from pneumatic controllers**

- Source: www.prideofthehill.com

**Notes:**
The major sources of methane loss from natural gas facilities include the following:1
Compressor seals;
Valve/piping connectors;
Vents; and
Pneumatic controllers.

Of all of these sources, pneumatic devices contribute the largest methane loss:
Most natural gas industry sites use natural gas;
Refineries, chemical plants, and some gas processing plants use compressed air;
There are over 250,000 such devices in the production sector;
There are between 90,000 and 130,000 in the transmission sector.

## Basic Glycol Dehydrator System Process Diagram

**Basic Glycol Dehydrator System Process Diagram**

**Glycol Contactor**

***Dry Sales Gas***

***Inlet Wet Gas***

***Lean TEG***

**Pump**

**Driver**

***Water/Methane/VOCs/HAPs***
***To Atmosphere***

***Rich TEG***

***Fuel Gas***

**Glycol Reboiler/ Regenerator**

**Gas Bypass**

**Glycol Energy Exchange Pump**

**Notes:**
GMAQS study indicates that the reboiler often uses electric heater or waste heat

## Methane Recovery:  Four Options

- Optimized glycol circulation rates
- Flash tank separator (FTS) installation
- Electric pump installation
- Replace glycol unit with desiccant dehydrator

## Optimizing Glycol Circulation Rate

- Gas well’s 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 without significant reduction in gas moisture content
**Partners found circulation rates two to three times higher than necessary**
**Methane emissions are directly proportional to circulation rate**

## Installing Flash Tank Separator

- Flashed methane can be captured using an FTS
- Many units are _not_ using an FTS

## Methane Recovery

- Recovers ~ 90% of methane emissions
- Reduces VOCs by 10 to 90%
- Must have an outlet for low pressure gas

- Flash Tank

**Gas Recovery**

**Reduced Emissions**

**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

## Installing Electric Pump

**Glycol Contactor**

***Dry Sales Gas***

***Inlet Wet Gas***

***Lean TEG***

**Pump**

**Driver**

***Water/Methane/VOCs/HAPs***
***To Atmosphere***

***Rich TEG***

***Fuel Gas***

**Glycol Reboiler/ Regenerator**

**Electric **
**Motor**
**Driven**
**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

## Is Recovery Profitable?

**Three Options for Minimizing Glycol Dehydrator Emissions**

| Option | Capital Costs | Annual O&M Costs | Emissions Savings | Payback Period |
| --- | --- | --- | --- | --- |
| Optimize Circulation Rate | Negligible | Negligible | 130 – 13,133 Mcf/year | Immediate |
| Install Flash Tank | $5,000 - $10,000 | Negligible | 236 – 7,098 Mcf/year | 5 months – 17 months |
| Install Electric Pump | $4,200 - $23,400 | $3,600 | 360 – 36,000 Mcf/year | < 2 months – several years |

## 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 Salts | Typical T and P for Pipeline Spec | Cost  |
| --- | --- | --- |
| Calcium chloride | 47oF    440 psig | Least expensive |
| Lithium chloride | 60oF    250 psig | More expensive |

## Desiccant Performance

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

**Max Spec Line for CaCl****2**

**Max Spec Line for*** ***LiCl****2**

## Desiccant Dehydrator Schematic 

**Drain Valve**

**Support Grid**

**Minimum Desiccant Level**

**Maximum Desiccant Level**

**Brine**

**Desiccant Tablets**

**Desiccant Dehydrator Schematic **

**Drying Bed**

***Inlet Wet Gas***

***Dry Sales Gas***

## Estimate Capital Costs

- Determine amount of desiccant needed to remove water
- Determine inside 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**

- 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

- Source: Van Air

- Note:
- MMcf = Million Cubic Feet

**Notes:**
TENTATIVE SLIDES can be removed if not necessary

## Calculate Vessel Inside Diameter

- 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*π
-               Commercially ID available = 20 inch

**Calculate Vessel Inside Diameter**

- Source: Van Air

- Note:
- cf = Cubic Feet

**Notes:**
TENTATIVE SLIDES can be removed if not necessary

## 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

## 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

**Notes:**
TENTATIVE SLIDES can be removed if not necessary

## 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 leakage/
- 				         pneumatic devices per year)
**Calculate:**
- GE = EF * PD
- GE= 504 Mcf/year

- Source: norriseal.com

- Norriseal         Pneumatic Liquid Level Controller

**Notes:**
TENTATIVE SLIDES can be removed if not necessary

## Gas Lost from Desiccant  Dehydrator

- 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 * ID__2__ * __π__ * P__2__ * %G * 365 days/year_
-                    4 * P1 * T * 1,000 cf/Mcf
- GLD = 10 Mcf/year

**Gas Lost from Desiccant  Dehydrator**

- Desiccant Dehydrator Unit
- Source: usedcompressors.com

**Notes:**
TENTATIVE SLIDES can be removed if not necessary

## Desiccant Dehydrator and Glycol Dehydrator Cost Comparison

- Based on 1 MMcfd natural gas operating at 450 psig and 47°F
- Installation costs assumed at 75% of the equipment cost

**Desiccant **

**($/yr)**

**Glycol **

**($/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**

**Type of Costs and Savings**

## Partner Reported Experience

- Partners report cumulative methane reduction of 12.5 Bcf since 1990
- Past emission reduction estimates for U.S offshore is 500 MMcf/year or $1.5 million/year

**Notes:**
Reduction – 12,542,226,886 cf = 12.5 Bcf  for glycol recirculation, installing flash tanks, and installing electric pumps
Adding reductions from desiccant dehydrators (iStar – PRO Detail Report) Reduction – 62,340,000 cf
Total Reductions – 12,542,226,886 cf + 62,340,000 cf = 12.6 Bcf
DESICCANT DATA ONLY BACK UNTIL 1999

## Case Study

- 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
**Recovers 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 gas sink and platform space**
- Electric pumps reduce O&M costs, reduce emissions, increase efficiency
**Require electrical power source**
- Desiccant dehydrator reduce O&M costs and reduce emissions compared to glycol
**Best for cold gas**

**Notes:**
LESSONS LEARNED REVISED TO REFLECT DESICCANT

## 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?