# Presentation: 186927

## Replacing Glycol Dehydrators with Desiccant Dehydrators

**Lessons Learned **
**from Natural Gas STAR Partners**
**Small and Medium Sized Producer Technology Transfer Workshop**
**Bill Barrett Corporation, Evergreen Resources Inc,**
**Southern Gas Association and**
**EPA’s Natural Gas STAR Program**
**June 29, 2004**

**Notes:**
Pneumatic devices are used throughout the gas industry to open and close valves automatically.  “Pneumatic” refers to gas pressure used as an energy source to exert power and carry signals.

In the natural gas industry, clean, inexpensive, readily available natural gas has served almost exclusively as the pneumatic gas source.  Because of the low relative cost of natural gas, the design of pneumatic devices allows significant amounts of gas to vent (or “bleed”) to the atmosphere.

These older devices are called “high-bleed” pneumatic devices.  This presentation discusses newer designs and practices for pneumatic devices that bleed considerably less gas to the atmosphere, thereby saving you money.

## Desiccant Dehydrators: Agenda

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

## 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**
**CO****2**** from reboiler fuel**
**CO****2**** from wet gas heater**

- 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.

## Dehydrator Schematic

**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**

## Methane Recovery Alternative

- Desiccant Dehydrator
**Very simple process**
**No moving parts**
- Moisture removed depends on
**Type of desiccant (salt)**
**Gas temperature and pressure**
- Desiccants gradually dissolves into brine

| 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 lb 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***

## Economic and Environmental Benefits

- Reduce capital cost
**Only capital cost is the vessel **
**Desiccant dehydrators do not use pumps or fired reboiler/regenetador**
- Reduce maintenance costs
- Less methane, VOCs and HAPs emissions
**Desiccant tablets only absorb water**
**No hydrocarbons vented to atmosphere by brine**

* *

- Desiccant Dehydrator Unit
- Source: GasTech

## Five Steps for Implementing a Desiccant Dehydrator

**IDENTIFY possible locations for desiccant dehydrators**

**ESTIMATE capital and operating costs**

**ESTIMATE savings**

**CONDUCT economic analysis**

**DETERMINE dehydrator capacity**

**Notes:**
In summary, the decision process follows five steps.
Step 1:  Locate and inventory all high-bleed pneumatic devices.
Step 2:  Whenever practical, use a measuring device, such as a Hi-Flow Sampler, to measure and record bleed rates.  Alternatively, use vendor specification, recognizing that they are often understated.  EPA defaults can also be used.
Step 3:  Establish the technical feasibility of alternatives.  Vender or in-house expert advice may be necessary for determining the feasibility of certain alternatives.
Step 4:  Evaluate the economics of alternatives.
Step 5:  Develop a plan for the most cost-effective implementation.  This may include procuring replacement, retrofit, and repair equipment in time for major maintenance events.

## Optimum Operating Conditions

- Works best in high pressure and low temperature conditions

|  | Low Pressure
(<300 psig) | High Pressure
(>300 psig) |
| --- | --- | --- |
| Low Temperature 
(<70 oF) | Desiccant/
Glycol1 | 
Desiccant |
| High Temperature 
(>70 oF) | 
Glycol | Glycol/
Desiccant2 |

- 1 The gas needs to be heated to apply glycol dehydrators or the gas has to be compressed to apply desiccant dehydrators.
- 2The gas needs to be cooled to apply desiccant dehydrator.

## 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/d**
**Capital cost for 20-inch vessel with 1 MMcf/d gas flow is $6,500**
**Installation cost assumed to be 75% of capital cost**

## How Much Desiccant Is Needed?

**Example:****	****	****   Where:**
- D = ?	 	   D = Amount of desiccant needed (lb/d)
- F = 1 MMcf/d 	   F = Gas flow rate (MMcf/d)
- I = 21 lb/MMcf 	   I = Inlet water content (lb/MMcf)
- O = 7 lb/MMcf 	   O = Outlet water content (lb/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 lb desiccant/d

- Source: Van Air

## Calculate Vessel Inside Diameter

**Example:****	****	****   Where:**
- ID = ?		   ID =  Inside diameter of the vessel (in)
- D = 4.7 lb/d  	   D = Amount of desiccant needed (lb/d)
- T = 7 days 	                T = Assumed refilling frequency (days)
- B = 55 lb/cf 	   	   B = Desiccant density  (lb/cf)
- H = 5 in	                H = Height between minimum and 		                                    maximum bed level (in)
**Calculate:**
- ID = 12*   _4*D*T*12_   =  16.2 in
-                 H*B*
-               Commercially ID available = 20 in.

- Source: Van Air

## Operating Costs

- Operating costs
**Desiccant: $2,059/yr for 1 MMcf/d example**
**$1.20/lb desiccant cost**
**Brine Disposal: negligible**
**$1/bbl brine or $14/yr**
**Labor: $1,560/yr for 1 MMcf/d example**
**$30/hr**
- Total: ~$3,633/yr

## 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/yr)
- F = 1 MMcf/d  		F = Gas flow rate (MMcf/d)
- W = 21 – 7 lb water/MMcf	W = Inlet – outlet water content (lb/MMcf)
- R = 3 gal/lb			R = Glycol/water ratio (rule of thumb)
- OC = 150%			OC = Percent over-circulation
- G = 3 cf/gal 	   		G = Methane entrainment (rule of thumb)
-    **Calculate:**
- GV = _(F * W * R * OC * G * 365 days/yr)_
-           1,000 cf/Mcf
- GV = 69 Mcf/yr

- Glycol Dehydrator Unit
- Source: GasTech

## Gas Vented from Pneumatic Controllers

**Example:****	****	****	****Where:**
- GE= ?			GE = Annual gas emissions (Mcf/yr)
- PD= 4 		    	PD = Number of pneumatic devices per 				     	         dehydrator
- EF = 126 Mcf/device/yr    	EF = Emission factor
- 				         (Mcf natural gas leakage/
- 				         pneumatic devices per year)
**Calculate:**
- GE = EF * PD
- GE= 504 Mcf/yr

- Source: www.norriseal.com

- Norriseal         Pneumatic Liquid Level Controller

## Gas Lost from Desiccant  Dehydrator

- GLD = ?		GLD = Desiccant dehydrator gas loss (Mcf/yr)
- ID = 20 in (1.7 ft)	ID = Inside Diameter (ft)
- H = 76.75 in (6.4 ft)   	H = Vessel height  by vendor specification (ft)
- %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__ *   * P__2__ * %G * 365 days/yr_
-             4 * P1 * T * 1,000 cf/Mcf
- GLD = 10 Mcf.yr

**Gas Lost from Desiccant  Dehydrator**

- Desiccant Dehydrator Unit
- Source:www.usedcompressors.com

## Desiccant Dehydrator and Glycol Dehydrator Cost Comparison

- Gas savings for 1 MMcf/d example
**Glycol: 69 Mcf/yr vented + 504 Mcf/yr pneumatics**
**Desiccant: 10 Mcf/yr**
**563 Mcf/yr savings, or $2,292/yr gas savings**
**Glycol: fuel gas savings of 500 Mcf/yr**
**500 Mcf/yr savings, or $2,000/yr fuel savings**
**Total gas savings: ~ $4,252/yr**
- Based on $4/Mcf

## Desiccant Dehydrator - Lessons Learned

- Example calculations of gas savings
**Glycol dehydration vent**
**Glycol dehydration pneumatic bleed**
**Glycol dehydration reboiler fuel gas**
**Gas heater fuel for glycol dehydration**
- Other savings
**Make-up glycol**
**Glycol dehydration O&M**
**Glycol dehydrator surplus equipment value**

## Discussion Questions

- To what extent are you implementing this BMP?
- How can this BMP be improved upon or altered for use in your operation(s)?
- What are the barriers (technological, economic, lack of information, regulatory, etc.) that are preventing you from implementing this technology?