# Presentation: 698709

## Reducing Emissions from Compressor Seals

**Lessons Learned**
**from Natural Gas STAR**
**Transmission Technology Transfer Workshop**
**Duke Energy Gas Transmission**
**Interstate Natural Gas Association of America (INGAA) and**
**EPA’s Natural Gas STAR Program**
**September 22, 2004**

## Compressor Seals: Agenda

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

## Methane Losses from Transmission and Storage

- Transmission and storage sector responsible for 96 billion cubic feet (Bcf) in methane emissions

**Trans & Storage **
**96 Bcf **

**Production   **
**149 Bcf**

**Processing  **
**36 Bcf **

**Distribution **
**77 Bcf**

**26 Bcf**

**5 Bcf**

**20 Bcf**

**1 Bcf**

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

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

**Notes:**
Emissions from 2002 inventory of natural gas systems and petroleum systems.
iSTAR reductions data taken in September 2004.

## Methane Losses from Compressor Seals

**Methane Losses from ****Compressor Seals**

- Compressor seals contribute 50% of transmission and storage emissions
**40 Bcf from reciprocating compressors**
**8 Bcf from centrifugal compressors**

**Pneumatic Devices**
**11 Bcf**

**Centrifugal Compressors**
**8 Bcf**

**Pipeline Leaks**
**7 Bcf  **

**Gas Engine Exhaust**
**11 Bcf**

**Reciprocating**
**Compressors **
**40 Bcf**

**Station Venting**
**7 Bcf**

**Other Sources **
**5 Bcf**

**Station Fugitives**
**7 Bcf**

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

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

## Compressor SealsWhat is the problem?

- Compressor seals account for 13% of natural gas industry emissions
**Over 45,000 compressors in the natural gas industry**
**Over 8,500 compressors in gas transmission sector**

**Notes:**
Compressors are found throughout the natural gas industry.
 At the well-head of gas and crude oil with associated gas production where the well-head flowing pressure has declined
 There are about 25,000 production compressors in the U.S.
 Gathering/booster stations pick-up the gas from several wells and boost it into gas processing plants.
 Most of the gas processing operations are carried out at elevated pressures to induce condensation of gas liquids at ambient temperatures
 Residue gas, primarily methane with some ethane, is compressed for delivery to the transmission cross-country transmission systems
 There are about 5,000 methane compressors in the U.S. processing sector 
Transmission pipelines re-compress the gas every few hundred miles as it is economically transported from remote production regions to industrial, commercial and residential centers for consumption
 Gas is sometimes stored in underground caverns or depleted reservoirs near the consumer locations, for re-production during peak demands
 There are about 8,500 transmission and storage compressors
 The distribution systems do not usually operate compressors, but rather control the pressure reduction and delivery up to the consumer’s meter.

## Methane Losses from Reciprocating Compressors

- Reciprocating compressor rod packing leaks some gas by design
**Newly installed packing may leak 60 cubic feet per hour (cf/h)**
**Worn packing has been reported to leak up to 900 cf/h**

**Notes:**
Numbers from Rod Packing LL

## Reciprocating Compressor Rod Packing

- A series of flexible rings fit around the shaft to prevent leakage
- Leakage still occurs through nose gasket, between packing cups, around the rings and between rings and shaft

## Gas STAR Partners Reduce Emission with Economic Rod Packing Replacement

- Compare current leak rate to initial leak rateto determine leak reduction expected

- Monitor and record baseline packing leakage and piston rod wear

- Assess costs of replacements

- Determine economic replacement threshold

- Replace packing and rods where cost-effective

- Decision Process

## Methane Recovery Through Economic Rod Packing Replacement

- Step 1: Monitor and record baseline leakage and rod wear
**Establishing baseline leak rates and monitoring rod wear can help to track leakage and evaluate economics**
- Step 2: Compare current leak rate to initial leak rate to determine leak reduction expected
**Leak Reduction Expected (LRE) = Current Leak Rate (CL) – Initial Leak Rate (IL)**
**Example: The current leak rate is measured as 100 cf/h, the same component leaked 11.5 cf/h when first installed**
**	****	****	****	****LRE = 100 cf/h – 11.5 cf/h****	****	****	****LRE = 88.5 cf/h**

**Notes:**
Example from Rod Packing LL

## Methane Recovery Through Economic Rod Packing Replacement

- Step 3: Assess costs of replacements
**A set of rings:****	****	****$  500****	****   to ****	****$  800****	****(with cups and case)****	****$1500****	****   to ****	****$2500**
**Rods:****	****	****	****	****$1800****	****   to****	****$3500**
- Step 4: Determine economic replacement threshold
**Partners can determine economic threshold for all replacements**

- @ interest *i*

**Notes:**
Numbers from Rod Packing LL

## Is Recovery Profitable?

- Step 5: Replace packing and rods when cost-effective
**Example:**

**Rod and Rings**
- Rings:		$1,200
- Rod:		$7,000
- Gas:		$3/Mcf
- Operating:	8,000 hrs/yr

**Rings Only**
- Rings:		$1,200
- Rod:		$0
- Gas:		$3/Mcf
- Operating:	8,000 hrs/yr

- Based on 10% interest rate
- Mcf = thousand cubic feet, scfh = standard cubic feet per hour

**Notes:**
Numbers from Rod Packing LL

## Industry Experience

- One partner reported replacing worn rod packing rings on 15 compressor units
- Estimated gas savings of 7,000 Mcf or $21,000 @ $3/Mcf
- Cost including materials and labor of $17,000
- Payback period of less than one year

**Notes:**
Partner experience from Rod Packing LL

## Methane Losses from Centrifugal Compressors

- Centrifugal compressor wet seals leak little gas at the seal face
**Seal oil degassing may vent 40 to 200 cubic feet per minute (cf/m) to the atmosphere**
**A Natural Gas STAR partner reported wet seal emissions of 75 Mcf/day (52 cf/m)**

**Shaft****Seal**

**Notes:**
Numbers from Wet/Dry Seal LL

## Centrifugal Compressor Wet Seals

- High pressure seal oil is circulates between rings around the compressor shaft
- Gas absorbs in the oil on the inboard side
- Little gas leaks through the oil seal
- Seal oil degassingvents methane to                                                      the atmosphere

## Gas STAR Partners Reduce Emissions with Dry Seals

- Dry seal springs press the stationary ring in the seal housing against the rotating ring when the compressor is not rotating
- At high rotation speed, gas is pumped between the seal rings creating a high pressure barrier to leakage
- Only a very smallamount of gas escapes through                                                           the gap
- 2 seals are often used in tandem

## Methane Recovery with Dry Seals

- Dry seals typically leak at a rate of only 0.5 to 3 cf/m
**Significantly less than the 40 to 200 cf/m emissions from wet seals**
- These savings translate to approximately $48,960 to                                              $279,360                                                         in annual gas                                                  value

**Notes:**
Numbers from Wet/Dry Seal LL

## Other Benefits with Dry Seals

- Aside from gas savings and reduced emissions, dry seals also:
**Lower operating cost**
**Dry seals do not require seal oil make-up**
**Reduced power consumption**
**Wet seals require 50 to 100 kiloWatt hours (kW/hr) for ancillary equipment while dry seals need only 5 kW/hr**
**Improve reliability**
**More compressor downtime is due to wet seals**
**Eliminate seal oil leakage into the pipelines**
**Dry seals lower drag in pipelines (and horsepower to overcome)**

**Notes:**
Numbers from Wet/Dry Seal LL

## Gas STAR Partners Reduce Emissions with Dry Seal Replacement

- Estimate savings of dry seal retrofit

- Identify candidates for wet seal replacement

- Determine costs for conversion to dry seals

- Compare costs to savings

- Decision Process

## Decision Process to Replace Seals

- Step 1: Identify candidates for replacement
**Dry seals are routinely used for compressors operating up to 1,500 pounds per square inch (psi), up to 400o Fahrenheit**
- Step 2: Estimate savings from a dry seal
**Gas savings between 34 to 196 cf/m**
**Other dry seal benefits ≈ $63,000/yr**

**Notes:**
Numbers from Wet/Dry Seal LL

## Decision Process to Replace Seals

- Step 3: Determine dry seal conversion costs
**Dry seals cost $5,000 to $6,000 per inch of shaft diameter or $8,000 to $10,000 for tandem seals**
**Beam compressors require two seals, one at each end**
**Overhung compressors require one seal at the inboard end**

**Notes:**
Numbers from Wet/Dry Seal LL

## Decision Process to Replace Seals

- Step 4: Compare costs and savings for a     6-inch shaft beam compressor

**Flowserve Corporation**

**Notes:**
Numbers from Wet/Dry Seal LL

## Is Recovery Profitable?

- Replacing wet seals in a 6 inch shaft beam compressor operating 8,000 hr/yr
**Net Present Value = $531,940**
**Assuming a 10% discount over 5 years**
**Internal Rate of Return = 86%**
**Payback Period = 14 months**
**Ranges from 8 to 24 months based on wet seal leakage rate**
- Economics are better for new installations
**Vendors report that 90% of compressors sold to the natural gas industry are centrifugal with dry seals**

**Notes:**
Numbers from Wet/Dry Seal LL

## Industry Experience

- One Gas STAR partner replaced a wet seal with a dry seal and reduced emissions by 97%
- Dry seal leaked 2 Mcf/d versus wet seal emissions of 75 Mcf/d

**Notes:**
Numbers from Wet/Dry Seal LL

## Discussion Questions

- To what extent have you replaced rod packing or seals in your reciprocating and centrifugal compressors?
- How can the Lessons Learned study 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?