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Emission Reductions Can Be Cost Effective.

Although the Enron Gas Pipeline Group's (Enron) domestic natural gas pipeline compressor stations have less methane emissions than the industry average, Enron has developed a proactive program using new measurement technology to further reduce methane emissions from its compressor stations. This has important benefits in that methane is the primary component in natural gas, and any reduction in emissions means more natural gas is available to market to Enron customers. In addition, methane is a "greenhouse gas," and Enron believes voluntary programs are an important component in the overall strategy to cost-effectively reduce greenhouse gas emissions. There is the possibility that the properly documented reductions may be sold as emission credits when a greenhouse gas emission trading system is developed.

The new measurement technology that Enron is using is the Hi-Flow Sampler[TM], which was developed by the Gas Research Institute (GRI). This measurement technology is unique because it measures actual emission rates from sources that traditionally were not easily measured. As a result, Enron personnel can make informed decisions on the reductions that are cost-effective to perform, and then focus their time and efforts on reducing emission sources with the greatest payback.

The Enron Gas Pipeline Group is composed primarily of four interstate natural gas pipelines and two intrastate pipelines. Northern Natural Gas with 16,463 miles of pipeline serves the upper Midwest market. The 2,487-mile Transwestern Pipeline transports gas east and west between markets in California and the Texas and Oklahoma region. Florida Gas Transmission Company, a 4,795-mile system owned 50 percent by Enron Corp, moves natural gas from Texas across the Gulf Coast states and into Florida. The 1,214-mile Northern Border Pipeline, 12 percent owned by Enron through a limited partnership, is one of the largest transporters of natural gas from Canada to the United States Houston Pipe Line Company is a Texas intrastate pipeline which includes 5,269 mile of mainline and gathering systems. Louisiana Resources Pipeline Company (LRC) is an intrastate pipeline company in Louisiana with 540 miles of pipeline.

An Enron entity known as Enron Transportation and Storage (ET&S) operates the Northern Natural Gas and Transwestern gas pipelines. Another Enron entity known as Gulf Coast Operations (GCO) operates the Houston Pipeline, Louisiana Resources and Florida Gas Transmission pipelines. Northern Border Pipeline is operated by an Enron affiliate Northern Plains Natural Gas Company (Northern Plains). The ET&S, GCO and Northern Plains operating companies developed independent approaches to successful programs to reduce methane emissions.

The Natural Gas STAR Program

Enron is an active participant in the Natural Gas STAR Program, one of several successful "Green Program" partnerships initiated by the U.S. Environmental Protection Agency to reduce methane emissions. A voluntary agency/industry partnership, this program is designed to accomplish environmental protection through cost-effective measures without regulation. Enron joined the STAR program in 1994 and has been an active participant since then.

One of the Best Management Practices under the STAR program is a leak detection and repair program at compressor stations. Beginning in 1994, Enron used "sniffer" type instruments, such as Organic Vapor Analyzers (OVA), at compressor stations to measure leak concentrations in parts per million. By using correlation equations developed by EPA, the concentration measurement can be converted to leak rate. However, the variability in the leak rate is 3 to 4 orders of magnitude. GRI has shown that because of this variability, a cost effective leak detection and repair program cannot be developed using this approach, and Enron's experience supports this conclusion. Using this methodology from 1994 through 1996, Enron spent $55,957 on methane emission surveys, $41,223 to repair the larger leaks, but only saved $9,452 worth of natural gas (based on an annualized emission rate at $2 Mcf). Obviously this program was not cost effective. Also, the inability to accurately determine the leak rate from a concentration measurement means that the true emissions from the facility and the amount of gas actually saved will never be known. There was not much current benefit in pursuing the program during this period.

Enron's Methane Survey Program

Two events occurred in 1996 and 1997 that would change Enron's methane survey program. GRI asked Enron to participate in a study financed by GRI and the Pipeline Research Committee (PRCI) to measure fugitive methane emissions using the Hi-Flow Sampler. Enron volunteered one of its compressor stations in Sunray, TX, and began the study in August 1996. Operations personnel at the station participated in the study and quickly saw the value of the Hi-Flow Sampler. They could determine the sources of the greatest emissions and make informed decisions about where to focus their efforts to reduce emissions and make repairs.

The second event was that ET&S management was given the objective of reducing the "unaccounted for" gas in their pipeline system. As the process to reduce the unaccounted for gas unfolded, it became apparent that the Sampler could be an important tool in documenting and reducing emissions not previously accounted for by Enron. The combined impact of the buy-in from operations and the use of the Sampler to satisfy an important management objective resulted in its extensive use at ET&S compressor stations.

In 1997-98, Enron spent $233,000 on emission surveys using the Hi-Flow Sampler, and $363,000 on emission reduction projects and repairs. As a result, Enron reduced emissions by 879,000 Mcf of methane annually. At $2 Mcf, this gas is valued at almost $1,758,000 and the potential net savings is over $1,160,000 the first year. Assuming that emissions from the repaired components are small the next year, the additional savings from the program for the second year could be as much as $1,758,000. It should be noted that the. value of the gas saved in this program goes generally to Enron's bottom line in three of the Enron pipeline companies, and in the other three companies is basically used to reduce the rate charged to Enron's customers. There does not appear to be a correlation between the success of the survey and emission reduction program and whether the gains are realized directly by Enron, or are passed on to its customers.

ET&S has surveyed over 100 compressor stations with the Hi-Flow Sampler. The company chose to use its own personnel to perform most of the emission surveys and make the repairs and reductions. Each of the regions within ET&S had personnel to perform the surveys. Before performing surveys, ET&S personnel received eight hours of training that included classroom theory and hands-on training at a compressor station. They learned how to use a Bascom Turner Instruments meter for screening purposes and the Hi-Flow Sampler for quantitative measurements. They also learned where to look for methane emission sources.

Conversely, the Gulf Coast Operations (GCO) company decided on a different approach to its methane survey program. Rather than use Enron employees for the methane emission surveys, GRI's contractor, Indaco Air Quality Services headed by Touche Howard conducted the Hi-Flow measurements. Enron crews in each operational region assisted in the screening process to reduce survey costs, but Indaco performed the Hi-Flow measurements at over 50 GCO stations. Indaco started the surveys in March of 1998 and completed them the following April.

Analysis of !be Emissions Data

Enron and GRI analyzed the results of the surveys to determine if there is a relationship between total emissions from a station and size of the facility (i.e., the number of engines) and/or a relationship between emissions per engine and the age of a compressor station. Figures 1 and 2 are a plot of total station emissions versus the number of engines for ET&S and GCO, respectively.


As anticipated, there seems to be a trend toward increasing station emissions with the increasing numbers of engines in the facility. On a per station, (or per engine basis) the measured emissions from the GCO stations are larger than the measured emissions from the ET&S facilities.

However, the success of the Enron program is not directly related to measured emissions but is calculated by comparing the value of the actual emission reductions to the cost of the surveys and the cost to perform the reduction/repairs. Using these criteria the ET&S and GCO programs are comparable.

Figures 3 and 4 depict the emissions per engine divided by the average value for the system versus age of the station for facilities with reciprocating engines. In previous studies GRI has seen a difference in emissions from stations with turbines as opposed to reciprocating engines. Therefore only data from facilities with reciprocating engines were used.


Considering the different histories, geographical regions, and survey methods used at ET&S and GCO, one might not expect the graphs to be as similar as they are. It is apparent that the newer stations have low emission rates on average. The older stations have a great range of emission rates from low to high. One could speculate that this greater range indicates that the older stations have a tendency to leak more with age, but that the maintenance practices at a station can greatly reduce this rate. Further study is required to verify this assumption.

The Northern Border pipeline is unique as compared to the other Enron pipeline companies since it was built in the 1980's and has one turbine at each compressor station. Rather than survey all of the stations, one representative station was selected to perform a methane emissions survey in 1997. It was suspected that there would be a low methane emission rate from their respective stations. This was confirmed when, with the exception of the emissions from the seal oil-degassing vent, the station emissions rate was determined to be only 52 Mcf of methane. Since the survey was concluded, there has been an expansion of this pipeline system and the wet gas seals were replaced with dry gas seals on all new and existing turbines. Although follow-up measurements have not been taken, it is anticipated that the emissions from the seal vent were reduced after the installation of the dry gas seals, based on EPA emission factors.

Emission Reduction Success Stories

There are a number of success stories that describe the efforts that were made to reduce emissions. These examples are important because in addition to illustrating how profits can be increased, they also illustrate how morale and job satisfaction are increased. It is very rewarding for people to realize that in a few hours--sometimes minutes--they can save a substantial amount of money. These are just a few examples:

* A cylinder head was tightened that reduced the annualized emissions rate from 63,989 Mcf to 3,255 Mcf. This resulted in annualized savings of $121,468 worth of gas at $2 per Mcf. It took 9 man-hours to perform the repair work;

* A 1/2-inch tube fitting was leaking 4,121 Mcf of gas per year. Five minutes of repair work reduced the emission rate to 10 Mcf per year resulting in an annualized savings of $8,222;

* A one-inch fuel and gas pressure relief valve was emitting 36,774 Mcf of gas per year. Five man-hours of work and $125 of materials eliminated the emissions, resulting in an annualized savings of $73,548; and a station blowdown valve was emitting 14,483 Mcf of gas per year. Rather than replace this expensive valve, personnel spent just $720 on labor and materials to reduce the emissions rate to 104 Mcf per year resulting in annualized savings of $28,758 worth of gas.

The EPA recognized the Enron Gas Pipeline Group for its efforts by honoring it as the Natural Gas STAR Transmission Partner of the Year in 1997 and 1998. Enron also received the Climate Protection Award from EPA in 1998 for the work done with the Hi-Flow Sampler.

Marc Phillips is the Manager of Regulatory Technical Analysis within the Enron Gas Pipeline Group. Phillips' job duties of overseeing the regulations and legislation that impact Enron include managing the Natural Gas STAR Program. He has been with Enron for nine years and has over twenty years of experience in the environmental field. Phillips has a B.S. and M.S. in the sciences, a M.S. in environmental engineering, and is a registered professional engineer in the state of Texas.

Robert Lott is the Manager of Air Quality Services for the Gas Research Institute and has managed programs in the areas of global climate change, methane emission&, atmospheric chemistry, hazardous air pollutants (HAPs), NOx control and emissions from compressor engines. Lott managed the project co-funded with EPA for determining methane emissions from the U.S. gas industry and is currently focusing on developing methods for reducing operating cost for the gas industry by reducing emissions. He has a B.S. and M.S. degree in Engineering and over 25 years experience managing environmental research projects in both the natural gas and electric utility industries.

By Marc Phillips, Manager of Regulatory Analysis, Enron Gas Pipeline Group, Houston, TX, and Robert Lott, Manager of Air Quality Services, Gas Research Institute, Chicago, IL
COPYRIGHT 1999 Oildom Publishing Company of Texas, Inc.
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Author:Phillips, Marc; Lott, Robert
Publication:Pipeline & Gas Journal
Date:Oct 1, 1999
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