REQUEST FOR PROPOSALS

Methane Reduction – Introduction

 

Methane is emitted from a variety of both human-related (anthropogenic) and natural sources. Human-related activities include fossil fuel production, animal husbandry (enteric fermentation in livestock and manure management), rice cultivation, biomass burning, and waste management. These activities release significant quantities of methane to the atmosphere. It is estimated that 60% of global methane emissions are related to human-related activities (IPCC, 2001c). Natural sources of methane include wetlands, gas hydrates, permafrost, termites, oceans, freshwater bodies, non-wetland soils, and other sources such as wildfires.

When released to the atmosphere, methane is a potent greenhouse gas with a Global Warming Potential (GWP) 23 times that of CO2. Methane emissions account for approximately nine percent of total U.S. anthropogenic greenhouse gas (GHG) emissions, second only to carbon dioxide. At the global level, methane emissions are an even higher fraction of total GHG emissions.

Reducing methane emissions can also produce substantial economic and environmental benefits. Further, studies by U.S. Environmental Protection Agency (EPA) indicate that there are many actions that can be taken to reduce methane emissions at little or no cost.

The five primary sources of methane emissions - landfills, livestock management, natural gas systems, coal mining, and manure management - together account for about 90 percent of U.S. methane emissions. However, the relative emissions from each type of methane source reflects the extent of the activity and the associated technologies and controls. In different countries the ranking of methane sources will likely differ from the U.S. experience.

While the IUEP is interested in all types of methane reduction projects, we are particularly interested in those that also result in the recovery of methane for use as a fuel, such as the following activities:

  • Landfills
  • Natural Gas Systems
  • Coal Mine Methane

The following sections offer some background on each of these three methane sources.

Landfills

 

Landfill methane is produced when organic materials (such as yard waste, household waste, food waste, and paper) are decomposed by bacteria under anaerobic conditions (i.e., in the absence of oxygen). Landfills are one of the largest sources of U.S. anthropogenic methane emissions.

Methane production varies greatly from landfill to landfill depending on site-specific characteristics such as waste in place, waste composition, moisture content, landfill design and operating practices, and climate. Unless captured first by a gas recovery system, methane generated by the landfill is emitted when it migrates through the landfill cover. During this process, the soil oxidizes a small portion (approximately ten percent) of the methane generated, and the remaining 90 percent is emitted.

Landfill methane emissions can be reduced by flaring or through methane recovery and use projects. Because landfill gas has a high methane concentration (typically 40 to 60 percent), it can also be a fuel source, presenting landfill owners with an opportunity to reduce compliance costs by converting methane into energy. The principal technologies for reducing emissions from landfills involve collecting methane and using it as fuel for electric power generation or for sale to nearby industrial users.

Gas collection, by vertical wells and horizontal trenches, typically begins after a portion of a landfill (a "cell") is closed. Vertical wells are most commonly used for gas collection, while trenches are sometimes used in deeper landfills, and may be used in areas of active filling. The collected gas is routed through lateral piping to a main collection header.

Natural Gas Systems

 

Methane is the major component of natural gas, comprising about 95 percent of the processed gas. Methane emissions from natural gas systems are generally process-related, mostly stemming from normal operations, routine maintenance, and system upsets. Emissions from normal operations include exhaust from natural gas combustion engines and turbines, bleed and discharge emissions from pneumatic devices, and fugitive emissions from various system components. Routine maintenance emissions can occur during repair and maintenance activities on pipeline, equipment, and wells. Pressure surge relief systems and accidents can lead to system upset emissions. Since natural gas is often found in conjunction with petroleum, crude petroleum gathering and storage systems are also a source of methane emissions.

Leaks in the natural gas system can also be characterized by the stage of activity from initial production to delivery to the end-user. Significant emissions occur from each of the four components, with different factors affecting each one. Most of the leaks occur from the production, transmission, and distribution stages, with lesser leakage from the processing and storage stages:

  • Field Production. In this stage, wells extract the gas from underground formations. In the U.S., there are hundreds of thousands of wells and their associated piping and treatment and processing equipment. Some amount of initial gas processing occurs in the field before gas is piped to centralized processing facilities. The majority of emissions from field production are fugitive emissions from well-associated equipment (separators, meters and dehydrators) and gathering lines, and releases from pneumatic (i.e., gas-powered) control devices.
     
  • Processing. Processing plants ensure that gas meets the quality standards for transmission. Before gas is injected into the transmission system, it is processed to remove condensate, particulates, and other compounds. Fugitive emissions from compressors are the source of the majority of processing-related methane emissions, with fugitive emissions from piping and releases from pneumatic devices also significant.
     
  • Transmission and Storage. High pressure, large diameter pipelines are used to transport gas from production, processing and storage facilities to large gas consumers and distribution networks. Pressure in the system is maintained by compressor stations. These stations, along with metering and regulating stations, account for the majority of methane emissions in the transmission stage. Storage facilities, which are underground formations into which gas is injected and kept during times of low demand, produce emissions mainly from compressors and dehydrators.
     
  • Distribution. Distribution includes lower pressure pipelines delivering gas from the transmission network to consumers. In the U.S., this system is made up of over one million miles of low-pressure iron, steel, and plastic piping that supplies gas customers. Emissions from this system mainly occur at metering and regulation stations and from pipeline leaks, primarily in older iron and unprotected steel mains and service pipes.

A number of technologies and practices have been identified for reducing methane emissions from natural gas systems. In the U.S., EPA and the natural gas industry, through the Natural Gas STAR Program, have identified several Best Management Practices (BMPs) that are cost-effective in reducing methane emissions. The Natural Gas STAR Program has sponsored a series of Lessons Learned Studies of these BMPs and several other practices. In addition, companies that are Natural Gas STAR Partners have identified other practices that reduce methane emissions.

EPA has analyzed the cost and emissions reduction potential of over 100 emissions reduction options. Many appear to be economic at gas prices below current and forecasted levels. Some of the more economic options that also represent relatively large opportunities for incremental emissions reductions (e.g., over 0.5 MMTCE per year) include (1) practicing enhanced directed inspection and maintenance at gate stations and surface facilities; (2) installing fuel gas retrofit systems on compressors to capture otherwise vented fuel when compressors are taken off-line; (3) replacing high-bleed pneumatic devices with low-bleed pneumatic devices; (4) reducing glycol circulation rates in dehydrators; (5) practicing enhanced directed inspection and maintenance at gate stations and surface facilities; and (6) installing dry seals on reciprocating compressors.

Coal Mining

 

In the geological process known as coalification, methane and coal are formed together. Depending upon the geologic conditions, the methane can be trapped within the coal seams and/or the surrounding rock strata. As the coal mining reduces the geologic pressure, the methane is released to the air.

The amount of methane formed generally correlates with the rank of the coal and the geologic pressure. Higher-ranked coals, such as low-volatile and mid-volatile bituminous coals, have had more of the original volatile matter squeezed out from the coal over time, and much of the methane formed adsorbs onto the coal or into the surrounding rock strata. Lower-ranked coals, such as subbituminous coal, still have most of the volatile matter in the solid coal structure itself, and typically have low methane contents. Geologic pressure, typically greater at greater depths, also correlates with methane concentrations. In the U.S., the gassiest mines are the very deep, low-volatile and mid-volatile bituminous coal mines, most notably in Alabama’s Warrior Basin and in the western part of Virginia. In contrast, surface subbituminous coal mines are typically very low in methane content.

Because methane is explosive in low concentrations, it is hazardous to mines and miners. A required safety practice at underground mines is to install ventilation systems to dilute the methane to a low concentration and then vent it directly to the atmosphere.

Methane is released during mining and post-mining activities. Methane emissions are typically divided into the following categories:

  • Underground Mining. In underground mining, methane is released into the mine workings during mining. Mining regulations require methane to be diluted in the ventilation air, and then vented to the atmosphere. Mines can also remove methane before and during mining by using degasification systems. The gas can be vented, flared, or recovered for its energy content. Emissions are reduced if recovered gas is flared or beneficially used. Up to 50 to 60 percent of methane can typically be recovered with degasification; the remainder is released in the ventilation air.
     
  • Surface Mining. During surface mining, methane is released directly to the atmosphere as the overlying rock strata are removed. No emissions mitigation options are being used at this time. In theory, some pre-mining degasification and recovery could occur at gassy surface mines. However, the low gas content of surface mines relative to that of underground mines makes it unlikely that significant recovery would be technically feasible, let alone cost-effective.
     
  • Post-Mining Activities. Some methane remains in the coal after mining and is released during subsequent processing and transportation of coal. No proven mitigation options exist at this time.
     
  • Abandoned Mines. Methane emissions from closed or abandoned mines are not quantified and not included in U.S. inventory estimates, but may be significant. In some cases, degasification techniques can, and have been used to, remove methane from abandoned underground mines. There is uncertainty as to whether and at what rate the methane present in these mines would have been emitted.

Most coal mine methane recovery in the U.S. is at active underground mines, with the remainder from inactive or abandoned underground mines. Because the distribution of gassiness among underground mines is so skewed, a small number of the very gassy mines have offered the greatest need to degasify as well as the greatest economic opportunities to use the gas. Some coal mines, particularly the very gassy ones, already employ a range of technologies for recovering methane. These methods have been developed primarily for safety reasons, as a supplement to ventilation systems. The major degasification techniques used at U.S. coal mines are vertical wells, long-hole and short-hole horizontal boreholes, and gob wells. Vertical wells and in-mine horizontal boreholes, which recover methane in advance of mining, produce nearly pure methane. In contrast, gob wells, which recover post-mining methane, may recover methane that has been mixed with mine air.

Over 30 of the gassier underground mines employ additional techniques to remove some of the methane before, during, and after mining; some of these also recover the gas for beneficial use. Degasification systems, which are wells or boreholes drilled into the coal seam, can remove up to 50 to 60 percent of methane before and during mining. At its simplest, a degasification system will simply vent the methane directly to the atmosphere before it can enter into the mine ventilation air. But with a gathering system attached, methane can be recovered for energy use.

The quality of the gas determines how it may be used. Methane recovered from degasification can be used for pipeline injection, power generation, on-site use in a thermal coal drying facility, or sale to nearby commercial or industrial facilities. At present, most recovered coal mine methane in the U.S. is sold through natural gas pipelines.

Even where degasification systems are used, mines can still emit significant quantities of methane via ventilation systems. Currently, technologies are in development that would catalytically oxidize the low concentrations of methane in ventilation air, producing usable thermal heat as a by-product.