Partner Reported Opportunities (PROs) 

### PRO Fact Sheet No. 104 for Reducing Methane Emissions



# Install Automated Air/Fuel Ratio
Controls

Technology/Practice Overview

Description Natural gas-fueled internal combustion engines can provide continuous duty operations over a set range of air to fuel ratios (AFR). Low air to fuel mixtures (rich burn) are used when greater horsepower is needed; high air to fuel mixtures (lean burn) are used when lower horsepower and greater fuel efficiency are the goals. Rich conditions
result in more unburned fuel emissions (primarily methane), more CO emissions, and fewer NO

x emissions. Lean conditions produce lower methane and CO emissions, but more NO

x emissions. Manufacturer performance curves for standard rich burn engines
indicate that when AFRs exceed a value of 18:1 (the stoichiometric AFR is approximately 16:1), temperature, power
and NO

x emissions start to decrease. Such engines, equipped with conventional controls that continuously monitor oxygen levels in the exhaust gas with a single sensor, cannot operate for extended periods with AFRs in excess of

20:1. Typically, specially configured lean burn engines (AFRs 20:1 to 50:1) with turbo chargers or pre-combustion
chambers are used where low NO

x emissions is the goal.

Natural Gas STAR Partners have achieved significant fuel savings, and reduced associated emissions, by installing automated AFR control systems to automatically adjust and optimize the operating parameters for their natural gas-fired internal combustion engines. Such parameters

Estimated

Gas Price Annual

Fuel Gas Savings Value of Annual Fuel Gas Savings EstimatedImplementation Cost Payback 1

$7.00/Mcf 28,470 Mcf $199,290 $138,000 8 Months

$5.00/Mcf 28,470 Mcf $142,350 $138,000 11.6 Months

$3.00/Mcf 28,470 Mcf $85,410 $138,000 1.6 Years

1 The payback is calculated based on th e value of annual fuel gas savings and the estimated implementation cost. The value of the methane savings is assumed to be included in the valu e of annual fuel gas savings due to the fact that the methane savings are a direct result of avoided fuel consumption. Annual

Methane Savings

913—12,175 Mcf

913—12,175 Mcf

913—12,175 Mcf 

### Economic and Environmental Benefits

Economic Evaluation (based on fuel gas savings per engine installation)

 Reduced engine fuel consumption

 Lower maintenance costs  Reduced emissions of CO 2 and criteria air pollutants

 Improved engine reliability and safety Additional Benefits: Estimated annual methane emission reductions 913—12,175 Mcf per engine

Estimated fuel gas savings 78 Mcf per engine per day, or 28,470 Mcf per year Methane and Fuel Gas Savings Compressors/Engines

Dehydrators

Directed Inspection &

Maintenance

Pipelines

Pneumatics/Controls

Tanks

Valves

Wells

Other

Applicable Sector(s)

Production

Processing

Transmission

Distribution

Other Related Documents:

Reduce Natural Gas Venting from Fewer Compressor Engine Startups & Improve Engine Ignition, PRO No. 102

Convert Engine Starting to Air or Nitrogen, PRO No. 101PRO Fact Sheet No. 104 Continued



### Install Automated Air/Fuel Ratio Controls (Cont’d)

include air manifold pressure and temperature, and fuel delivery to the combustion chambers. Alarm or shutdown triggers can be set to react to various real-time engine operating parameters, which reduces the risk of catastrophic engine failure. Other benefits from optimizing engine operation with AFR control systems include fewer false starts, lower combustion temperature, longer engine life, lower maintenance and fuel costs, and greater safety. Also, according to one vendor, using gas from an area with fugitive hydrocarbon emissions could lead to additional fuel savings as the AFR control system adjusts the fuel intake to account for the additional hydrocarbons in the

air intake.



### Operating Requirements

AFR control technology can be configured as a stand

alone system, or to interface with most existing electronic control and telemetry systems.

Applicability Any natural gas fired engine over 1,000 horsepower can benefit from AFR control and optimization systems. Partners report that the greatest opportunities for significant system and efficiency improvements are for rich burn, high-speed, turbocharged engines ranging in size from 1,000 hp to 3,000 hp.

One Partner reduced fuel consumption and methane emissions by installing an automated AFR control system called REMVue, marketed by REM Technology
Inc. REMVue controllers monitor several engine parameters and optimize air-fuel mixtures through a combination of electronic controls, use of a high-energy long duration spark to ensure reliable ignition, and other mechanical modifications to the engine. Another Partner purchased and installed new compressor units of 1340 hp and larger that are equipped with Caterpillar ADEM 3 AFR control systems.



### Methane Emissions

Unburned fuel from the exhaust stream is a source of methane emissions from natural gas-fueled internal combustion engines. Such emissions are generally estimated using commonly accepted emission factors based on engine type, size, and operating conditions. The Natural Gas STAR Program typically uses 0.24 scf methane per horsepower-hour, based on Volume 11 of the 1996 EPA/GRI Study. The average methane content of na tural gas varies by natural gas industry sector. The Natural Gas STAR Program assumes thefollowing methane content of natural gas when estimating methane savings for Partner Reported Opportunities.

Production 79 %

Processing 87 %

Transmission and Distribution 94 % 

### Methane Content of Natural Gas

Partners report annual methane emission reductions of 913 Mcf and 12,175 Mcf per unit after installing AFR control systems for compressors. Another Partner reduced fuel consumption by 18 to 24 percent after installing automated AFR controls on 51 new compressor engines in its Gulf of Mexico operations. By reducing the engines’ fuel consumption, the Partner estimates average annual methane emissions reductions of 128 Mcf per unit based on AP-42 emission factors 1 . For the 51 engines, the total estimated annual emissions reductions are estimated as 6,528 Mcf.



### Economic Analysis

Basis for Costs and Savings The Partner-reported REMVue installation reduced total fuel consumption for 51 en gines by 2,900 million cubic feet (MMcf) during a two-year period. Average fuel gas savings were 78 Mcf per day per engine when adjusted for load (28,470 Mcf per year per engine). This represents a 39 percent increase in estimated fuel savings (based upon a sample inventory, which yielded a pre-job fuel savings estimate of 56 Mcf per day). The total reported implementation cost for the 51 engines was $7.04 million. Capital costs to install an AFR control system on existing engines ranged from $98,000 to $161,000 per unit, with the average cost being $138,000 per installation. At a nominal value of $5 per Mcf, the total reported fuel savings for 51 engines was more than $7.25 million, yielding a ca lculated payback of 11.6
months.

Discussion The economics are based solely on the value of the avoided fuel losses and the capital cost to install an AFR control system on 51 engines. The value of other reported benefits including fewer misfires, easier engine starting, more reliable operatio n, and longer engine life are not captured in this report. The Partner found that

2PRO Fact Sheet No. 104 Continued



### Install Automated Air/Fuel Ratio Controls (Cont’d)

the additional cost of operating the REMVue systems was offset by reduced engine maintenance costs. A postaudit conducted on 20 percent of the installed base reviewed pre-, post- and post-post-values for fuel consumption, emissions redu ctions, availability, and economics based on a normalized gas price. The study
results show that while NO x emissions were unchanged, significant improvements in air quality management were achieved since unburned hydrocarbons were down 3,549 tons per year (TPY), CO 2 emissions were down 2,309 TPY, and CO emissions were down 83,300 TPY.

1 ‘AP 42’ refers to publication AP 42, Compilation of Air Pollutant Emission Factors, Volume 1: Stationary , Point and Area Sour ce, available online from the U.S. EPA Technology Transfer Network Clearinghouse for Inv entories & Emissions Fact ors (www.epa.gov/ttn/chief/ap42/ index.html)

2 All costs presented are in 2010 dollars.

3 2011