Natalie Smith

Paper #2

Energy, Resources & Public Policy

 

Landfill Gas

Abstract:         This paper examines the use of landfill gas for electricity generation. Landfill gas is comprised mostly of methane, so it can be used in ways similar to natural gas. Landfills also emit nonmethane organic compounds (NMOC), which include volatile organic compounds (VOC) that contribute to ozone formation and hazardous air pollutants (HAP) that can affect human health when exposed. However, combustion of landfill gas (for flaring or electricity generation) significantly reduces emissions of methane and NMOC. Landfill gas can be collected and used for electricity generation through a variety of methods, which differ in their cost, efficiency and emissions. Electricity derived from landfill gas has many environmental advantages (reduced emissions, offsetting of fossil fuel use, etc.), but some drawbacks as well (continued reliance on consumer waste, offsetting of cleaner renewable energy sources, etc.). These impacts affect the landfill’s local community as well as the global community. Landfill gas electricity also faces economic barriers (expensive technology, competitive market, etc.) but still shows economic promise (including subsidies, tax incentives and rising fossil fuel costs).

 

 

 

There are many types of biomass used for electricity generation today, including wood and agricultural products, solid waste, landfill gas, and alcohol fuels. Landfill gas (LFG) is increasingly being used in the U.S. to produce electricity, but can also be used for direct-use in boilers and greenhouses, for cogeneration (electricity and thermal energy using steam) and for alternative fuels such as compressed natural gas. The focus of this paper, however, is landfill gas as an electricity source. Since landfill gas is generated continuously it provides a reliable fuel for electric power generation. (www.mtpc.org/cleanenergy/other) The U.S. “landfill gas to energy” industry has experienced about a 10% growth per year since 1990. (www.mswmanagement.com/-msw_0003_database) See Figure 1 for a chart of annual and cumulative growth of landfill gas projects. As of December 2004, there are approximately 380 operational LFG energy projects in the United States and more than 600 landfills that are good candidates for LFG projects. (www.epa.gov/lmop/overview.htm) See Figure 2 for a map of current and potential LFG energy projects in the United States.

According to the Massachusetts Technology Collaborative, “Landfill gas is created when food, wood, and other organic waste in a landfill decomposes under anaerobic conditions.” (www.mtpc.org/cleanenergy/other.htm) Landfill gas is roughly 50% methane. The remainder of landfill gas is mostly carbon dioxide (roughly 45%) with varying amounts of nitrogen, oxygen and assorted contaminants known as "non-methane organic compounds" (NMOCs). NMOCs usually make up less than 1% of landfill gas, but consist of certain hazardous air pollutants (HAP) and volatile organic compounds (VOC) such as benzene, toluene, chloroform, vinyl chloride, carbon tetrachloride, and 1,1,1 trichloroethane. Emissions of VOC contribute to ground-level ozone formation (smog). Ozone is capable of reducing or damaging vegetation growth as well as causing respiratory problems in humans. Finally, exposure to HAP can cause a variety of health problems such as cancerous illnesses, respiratory irritation, and central nervous system damage.  (http://www.energyjustice .net/lfg/ and www.eia.doe.gov/cneaf/solar.renewables/ -renewable.energy.annual/chap10.html) Municipal solid waste landfills are the largest source of human-related methane emissions in the United States, accounting for about 34 % of these emissions. (www.epa.gov/lmop/overview)

Because landfill gas is about 50 % methane, it can be used as a source of energy similar to natural gas (which is about 90% methane). “Instead of allowing LFG to escape into the air, it can be captured, converted, and used for electricity generation.” (www.epa.gov/lmop/overview) Landfill gas is extracted from landfills using a series of wells and a blower/flare (or vacuum) system. To see how an LFG well works, see Figure 3. This system directs the collected gas to a central point where it can be processed and treated (cleaned to remove particulates and moisture) depending upon the ultimate use for the gas. From this point, the gas can be simply flared or used to generate electricity. If a landfill does not use the gas for electricity, it still needs to be managed because the gas is potentially explosive if it is allowed to accumulate. In fact, as of 1996, federal law requires landfill operators to control landfill gases by either burning it or utilizing it for electricity. The legislation requires that sites containing more than 2.5 million megagrams (Mg) and 2.5 million m3 or more of waste must collect and control landfill gas if their estimated emissions of NMOCs are 50 Mg or more per year. It was calculated that by the year 2000, this regulation would result in a reduction of around 6 million mt/year of carbon released into the atmosphere. The associated greenhouse gas reduction is equivalent to taking 4 million cars off the road. (www.mswmanagement.com/msw_0003_database.html)

According to the Environmental Protection Agency, “The generation of electricity from landfill gas makes up about two-thirds of the currently operational projects in the U.S.. Electricity for on-site use or sale to the grid can be generated using a variety of different technologies, including internal combustion engines, turbines, microturbines, Stirling engines (external combustion engine), Organic Rankine Cycle engines, and fuel cells. The vast majority of projects use internal combustion (reciprocating) engines or turbines, with microturbine technology being used at smaller landfills and in niche applications. Certain technologies such as the Stirling and Organic Rankine Cycle engines and fuel cells are still in the development phase.” (www.epa.gov/lmop/overview.htm) Fuel cells are being considered as the preferred technology for LFG utilization because of their higher energy efficiency compared to conventional technology and minimal environmental impact. (www.mswmanagement.com/msw- _0003_database.html) In today’s market, internal combustion engines are most economical where the supply of LFG is enough to produce 1 to 3 megawatthours (small and medium size plants). Turbines are most economical at sites with output of over 3 megawatthours (large plants). (www.eia.doe.gov/cneaf/solar.renewables/renewable.energy.annual/chap10.html)

In Fairfax County, Virginia the I-95 Sanitary Landfill collects 3.3 million cubic feet per day of landfill gas and uses 8 internal combustion engines to generate 6 megawatts of electricity. In Los Angeles, California the Mountaingate Landfill control and recovery plant collects 5 million cubic feet of landfill gas per day. The facility processes the gas on site to remove impurities and pipes the purified gas to the University of California at Los Angeles (UCLA), about 4.5 miles away. UCLA in turn compresses the gas to approximately 500 pounds and blends it with natural gas. The blend is used to fuel two 14.5-megawatt combustion turbine generators that provide power for the UCLA campus. (www.eia.doe.gov/cneaf/solar.-renewables/renewable.energy.annual/apph.html) These are just two examples of how landfill gas is helping to power American homes and businesses.

Using landfill gas for electricity generation has many positive environmental and public health impacts. The combustion of raw landfill gas in an engine or a turbine dramatically reduces the overall toxicity of the gas, which benefits the surrounding environment and population. The collection, cleaning and combustion of landfill gas associated with electricity generation dramatically reduces its global warming impacts and toxicity. The Natural Resources Defense Council’s analysis of the inhalation cancer-risk factor suggests that the overall toxicity of LFG combustion is 23 times less than that of raw LFG.(www.nrdc.org/air/energy/lfg/execsum.asp) The combustion of landfill gas converts the methane to carbon dioxide, which while still a heat-trapping gas, is dramatically less powerful. Methane has 21 times the global warming potential of carbon dioxide. (www.thegreenpowergroup.org/landfillgas.html) Collecting landfill gas to produce electricity also improves the air quality of the surrounding community by reducing landfill odors. Burning landfill gas to produce electricity also destroys most of the non-methane organic compounds that are present at low concentrations in uncontrolled landfill gas, thereby reducing possible health risks from these compounds. Gas collection can also improve safety by reducing explosion hazards from gas accumulation in structures on or near the landfill. (www.epa.gov/lmop/benefits.htm)

According to the Environmental Protection Agency, the greenhouse gas reduction benefits of a typical 4 megawatt LFG project equate to planting over 60,000 acres of forest per year or removing the annual carbon dioxide emissions from over 45,000 cars. This amount of energy would also offset the use of 1,000 railcars of coal or prevent the use of almost 500,000 barrels of oil. This concept of offsetting the use of other energy sources is also an important environmental impact of LFG electricity. Producing energy from landfill gas avoids the need to use non-renewable resources such as coal, oil, or natural gas to produce the same amount of energy. LFG electricity’s offsetting of fossil fuel derived energy can avoid gas end-user and power plant emissions of CO2 and pollutants such as sulfur dioxide (which is a major contributor to acid rain), particulate matter (a respiratory health concern), nitrogen oxides (NOx), and trace hazardous air pollutants. (www.epa.gov/lmop/benefits.htm) See Figure 4 for a comparison of LFG electricity plant emissions and coal electricity plant emissions.

There are criticisms of landfill gas as a source of electricity. For example, there has been concern about the dioxin levels of landfill gas emissions. Critics say that no energy source that emits dioxin should be considered “green”, especially considering there are renewable energy sources that have zero emissions. Dioxin levels are hard to predict and report, though, because the levels vary depending on the contents of the landfill. According to the Energy Justice Network, “when chemicals such as chlorine, fluorine, and bromine (which make a small part of landfill gas) are combusted in the presence of hydrocarbons, they can recombine into highly toxic compounds such as dioxins and furans. Burning at high temperatures doesn't solve the problem as dioxins are formed at low temperatures and can be formed as the gases are cooling down after the combustion process.” (www.energyjustice.net/lfg/) Some environmentalists worry that LFG electricity will offset more environmentally friendly technologies such as new natural gas plants, wind power and solar power.

Critics also say that since the cost-effectiveness of recycling programs is directly linked to the cost of alternative waste-management options, LFG energy subsidies could possibly reduce the competitiveness of recycling programs (by enabling landfill operators to charge lower tipping fees), and encourage landfilling instead of recycling. On a related note, use of landfill gas for electricity has been criticized as not addressing the more important environmental issues of waste reduction and management (i.e. recycling over landfilling). Because landfills contribute to groundwater and air pollution, critics argue they should be avoided- not perpetuated through energy subsidies. According to the Natural Resources Defense Council, “Burying garbage in landfills results in the release of more heat-trapping gases than any other waste-management option. The best way to combat landfill gas is to avoid landfilling biomass. This is true regardless of how much landfill gas is collected and used for energy. The best strategies [for combating the release of heat-trapping gasses] are resource reduction and recycling.” (www.nrdc.org/air/energy/lfg/execsum.asp)

There are many economic and logistical barriers to the recovery and conversion of landfill gas for electricity. Older landfills and small landfills (less than 500,000 metric tons) are usually not economically capable of developing or supporting LFG electricity systems (www.thegreenpowergroup.org/landfillgas) and relatively low oil and gas prices make LFG electricity not easily competitive in today’s energy market (although this is changing). Currently, electricity generated from landfill gas can cost anywhere between 3.4 cents per kilowatt hour to 10 cents per kilowatt hour.  Another barrier is that LFG electricity projects require expensive new, sometimes untested, technology (e.g., fuel cells) and are associated with high transportation costs (for example, dedicated pipelines have to be built for relatively small supplies of gas). The tax credits that support LFG electricity projects have been inconsistent since the mid 1990’s, and obtaining third-party project financing at reasonable cost is difficult, time-consuming, and proportionately more costly for small projects than for large ones. There is even taxation on LFG extraction and energy conversion facilities by some states such as California. These barriers are compounded with logistical barriers such as difficulties obtaining air permits, especially for projects located in ozone, nitrogen oxide, and carbon monoxide non-attainment areas, because air boards and utilities often have lengthy permit processes and contract negotiation. In addition, LFG electricity projects often have difficulty negotiating power contracts with local utilities because the utility companies are primarily interested in purchasing low-cost power without considering environmental externalities. (www.thegreenpowergroup.org/landfillgas.html)

In evaluating landfill gas, questions arise concerning sustainability and future use. Although using landfill gas for electricity does reduce its negative environmental impacts, the inherit problems of landfills such as groundwater pollution and the unavoidable emissions of LFG energy projects must be addressed. The concept of landfills as acceptable methods of waste management is good for LFG electricity projects, but overall might not be helping to combat issues of global climate change and pollution. For the foreseeable future, though, landfills will probably remain the primary source for municipal waste. For this reason, the EPA should move towards requiring all landfills that accept biomass to collect landfill gas for energy use, and pass stricter emissions standards for landfill gas plants. In addition, more attention should be paid to the containment and treatment of highly toxic chemicals. As the Energy Justice Network suggests, “gas should be filtered so that the [highly toxic chemical compounds] are segregated. Once filtered out, these compounds should not be combusted (as that doesn't tend to improve the situation, but may make it worse). They should be handled as hazardous waste and isolated from the environment as best as is possible until there is a proven technology which can neutralize them.” (http://www.energyjustice.net/lfg/) It might make sense to segregate organic wastes from other wastes by placing them in different cells of a landfill. Source separation would concentrate the methane generation in an area where many of the toxic compounds would not be present (which is not to imply that yard waste and such is not contaminated by toxins), and therefore the filtering and control of landfill gas could be applied more appropriately.

In order to best utilize landfill gas for electricity, more attention and funding must be concentrated on developing fuel cell technology. Future subsidies should favor the cleanest methods of landfill gas electricity generation (like fuel cells) over the more dirty methods (such as internal combustion engines). In addition, future legislation should involve incentives that allocate subsidies competitively, so that landfill gas energy projects do not offset greener and renewable energy projects. All in all, electricity generation from landfill gas is an innovative way to deal with our current municipal waste challenges, but must be further developed with concurrently increased financial support.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

APPENDIXES

 

Figure 1. Source: http://www.mswmanagement.com/msw_0003_database.html

 

 

Figure 2. Source: http://www.epa.gov/lmop/overview.htm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3. Source: http://www.epa.gov/lmop/over-photos.htm#6

 

 

 

 

 

 

 

Figure 4. Source: http://www.nrdc.org/air/energy/lfg/lfg.pdf

 

Comparison of Average Emissions for Coal and Landfill Gas (LFG) Electric Plants

Emissions Source

NOx

SOx

VOC

Particulate Matter

CO2

All Coal Power Plants

4.81

11.05

.032

.24

2210

LFG internal combustion plants

3

.024

1.6

.5

0

LFG turbine plants

2

.03

.12

.3

938

(all data is in lbs./MWh)

All data collected by the NRDC, Published 2003

Bibliography:

 

                Chen, Cliff and Green, Nathaneal. “Is Landfill Gas Green Energy?”. March 2003.

Natural Resources Defense Council, http://www.nrdc.org/air/energy/lfg/lfg.pdf

 

Energy Justice Network, Primer on Landfill Gas as ‘Green’ Energy, www.energyjustice.net/lfg/

 

Green Power Market Development Group, www.thegreenpowergroup.org/landfillgas.html

 

Massachusetts Technology Collaborative, www.mtpc.org/cleanenergy/other.htm

 

MSW Management, Database of Landfill-Gas-to Energy Projects in the United States

www.mswmanagement.com/msw_0003_database.html

 

Natural Resources Defense Council, http://www.nrdc.org/air/energy/lfg/execsum.asp

 

U.S. Department of Energy, Energy Information Administration, Office of Coal, Nuclear, Electric and Alternate Fuels (CNEAF)

www.eia.doe.gov/cneaf/solar.renewables/renewable.energy.annual/chap10.html and www.eia.doe.gov/cneaf/solar.renewables/renewable.energy.annual/apph.html

 

U.S. Environmental Protection Agency, Landfill Methane Outreach Program (LMOP)

www.epa.gov/lmop/overview.htm and www.epa.gov/lmop/benefits.htm