# Presentation: 010661

## Efficient Pigging of Gathering Lines

**Lessons Learned from Natural Gas STAR**
**Processors Technology Transfer Workshop**
**Gas Processors Association,**
**Devon Energy, Enogex**
**Dynegy Midstream Services, and**
**EPA’s Natural Gas STAR Program**
**April 22, 2005**

## Agenda

- Methane Losses from Pipeline Pigging
- Methane Recovery
- Industry Experience
- Is Recovery Profitable?
- Discussion Questions

## Natural Gas and Petroleum Industry Emissions

**Natural Gas and Petroleum Industry Emissions**

- Processing plants responsible for 36 Bcf of methane emissions annually, and gathering/ booster stations contribute >22 Bcf

**Transmission & Storage **
**98 Bcf **

**Production/ Gathering/ Booster   **
**150 Bcf**

**Processing  **
**36 Bcf **

**Distribution 73 Bcf**

**25 Bcf**

**10 Bcf**

**18 Bcf**

**1 Bcf**

**Oil Downstream  **
**2 Bcf **

- Inventory of U.S. Greenhouse Gas Emissions and  Sinks 1990 - 2002*** ***

**Notes:**
To arrive at Gathering/Booster emissions, went into the 2002 inventory and identified gathering sources within the production sector. This was 22.2Bcf

FYI: The DI&M Lessons Learned says Processing plants AND Booster stations emit a total of 36 Bcf...this is out dated.

## Pigging Gathering Lines

- Hydrocarbons and water condense inside wet gas gathering lines, causing pressure drop and reducing gas flow
- Periodic line pigging removes liquids and debris to improve gas flow
- Efficient pigging:
**Keeps pipeline running continuously**
**Keeps pipeline near maximum            throughput by removing debris**
**Minimizes product losses during              launch/capture**

## Pigging Applications

- Pipeline pigs come in a variety of shapes and sizes for different applications
**Cleaning pigs **
**Have brushes or blades to help remove debris**
**Sealing pigs**
**Make tight seal for removing ****liquids from the pipe**
**Inspection pigs**
**Specialized pigs outfitted with****instruments to monitor the ****pipeline integrity**

- www.westernfilterco.com

## Pigging and Methane Losses

- Gas lost when launching and receiving a pig
- Fugitive emissions from pig launcher/receiver valves
- Gas lost from storage tanks receiving condensate removed by pigging
- Gas vented from pipeline blowdowns

## How Does Pigging Vent Methane?

- Gathering lines have built-in pig launchers
- Pig launchers have isolation valves for loading pigs, pressurizing pigs, and launching pigs with gas bypassed from the pipeline
- Launcher pressuring/depressuring loses methane out the vent valve

- Gas Flow

- Gas Flow

**Pig Launcher**

**Vent Valve**

- http://www.girardind.com/

## Pigging Vents Methane Twice!

- Methane lost through vent valve on the launcher and again through vent valve on the receiver
**Once receiver is isolated from the line, it must be depressured to remove the pig**
**Liquids ahead of the pig drain to a vessel or tank**
- Isolation valve leaks                                      cause excessive                                         venting to depressure

- http://www.girardind.com/

**Notes:**
Depending on the company practices, a launcher will remain pressurized or they will depressurize it. Fugitives should be a lot less in the latter case.

## Estimating Pigging Vents

- E = P * V / 14.7 * n * f
- 	where:	E    = methane emissions (cubic feet)
- 		P = Gathering line pressure (psia)
- 		V   = Launcher and receiver volume (cubic feet)
- 		n   = % methane
- 		f    = number of piggings
- Pig trap isolation valve leakage increases this minimum amount of gas venting

**Notes:**
P is more of a factor than T, so omitted T as a variable as to simplify for the audience

## Estimating Emissions from Pigging

- Estimating V
- Estimating P
**Default: 315 psia**

| Line Diameter (inches) | V (cf) |
| --- | --- |
| 6 | 0.9 |
| 12 | 4.6 |
| 18 | 11.5 |
| 26 | 27.7 |
| 34 | 65.2 |
| 48 | 170.7 |

- Adapted from http://www.pigsunlimited.com

- Estimating n
**Default: 78.8**

## Gas Recovery from Pipeline Condensate Storage Tanks

- Pressurized condensate collected from pigging is sometimes stored in atmospheric tanks
- Gas released during atmospheric flashing can be recovered using a vapor recovery unit (VRU) rather than venting the gas
- Facilities with existing pigging and liquid storage capabilities can install an electric or gas powered VRU compressor to recover flashed gasses

## Industry Experience

- One partner pigged gathering lines 30 to 40 times per year, collecting several thousand barrels of condensate per application
- Partner reported saving 21,400 Mcf/yr from recovering flash gases
- Dedicated VRU was installed with an electric compressor

## Is Recovery Profitable?

- Partner reported installation cost of $24,000 for electric VRU compressor
- Annual operating cost of $40,000 mostly electricity
- Large gas savings and increasing gas prices will offset costs

## Use Inert Gases and Pigs to Perform Pipeline Purges

- Pipeline maintenance requires pipe section blowdown before work can begin
- Gas in pipeline is usually vented to the atmosphere
- Inert gas can be used to drive a pig down the section of pipe to be serviced, displacing the natural gas to a product line rather than venting
- Inert gas is then blown down to the atmosphere, avoiding methane loss

## Inert Gas Setup

- Existing pig launcher can be used, set up to work with inert gases
- Portable nitrogen supply connected to the pig launcher vent
- Close valve on the main pipeline, pressurize launcher with inert gas, open launcher tomain pipeline
- Supply nitrogen                                             until pig reaches                                           receiver

- http://www.girardind.com/

## Industry Experience

- One partner reported using inert gas to purge six pipelines for maintenance
- Gas savings from these applications was 538 Mcf
- These savings correspond to a typical application of:
**2 miles of 10” diameter pipeline**
**Nitrogen at 280 psi**

## Is Recovery Profitable?

- No capital costs with existing pigging facilities
- Labor costs are estimated at eight hours for two operators
- Nitrogen costs are roughly $8/Mcf
- Increased safety is the primary benefit of this opportunity
- Gas savings are a secondary benefit, as the labor and nitrogen costs outweigh the gas value

## Discussion Questions

- What opportunities do you have to reduce methane emissions from your pigging operations?
- How can this presentation be made more useful to help you identify and evaluate opportunities?
- What are the barriers to your implementing the technologies and practices in this presentation?