Electric power and medium Btu gas projects historically have been the most common uses for landfill gas (LFG), but recent economic changes and market limitations have stimulated the industry to look for alternative ways to use LFG profitably.
A significant drop in power rates in recent years due to regulatory, technical and economic changes sweeping the electric industry has caused a decline in the marketability of LFG produced as electric power. Medium Btu gas, used as a substitute for natural gas, has fared well in spite of depressed natural gas prices, but projects only can be developed when a suitable end user is located reasonably close to the landfill.
These obstacles have opened the door for the development of pipeline quality gas, vehicle fuel, fuel cells, and hydrogen and methanol production. Here is a look at how those uses can be applied and their advantages and disadvantages.
Pipeline Quality Gas Pipeline quality gas production has seen a decade hiatus since the successful development of several products in the late 1980s. However, even at today's depressed natural gas prices, it now appears that LFG projects can compete effectively with natural gas in the pipeline market.
Prior to selling LFG to natural gas distribution pipeline operators, it must be processed to double the LFG's Btu content and to ensure that it meets strict standards for hydrogen sulfide, moisture, carbon dioxide, oxygen and volatile organic compounds (VOCs). Removing carbon dioxide is the principal step to increase the Btu content.
Developing pipeline quality gas from LFG requires near zero air infiltration into the landfill gas well field. Air reduces the Btu content and can cause the gas to exceed oxygen content limits. Zero air infiltration typically requires supply by wells located in the core of the landfill.
One concern for landfill owners is the contradiction between the need to produce zero air infiltration to support the processing plant's requirements and the desire for surface emissions and gas migration control. This is because pulling some air in reduces surface emissions and gas migration, but it conflicts with the need for zero air in pipeline quality gas production.
Selexol, Kryosol, molecular sieve-based technology and membrane processing all are used to process LFG into pipeline gas.
The Selexol process requires LFG compression and removal of: hydrogen sulfide in a solid media bed, VOCs in a primary Selexol absorber and carbon dioxide in a secondary Selexol absorber.
Kryosol technology is similar to the Selexol process, but it requires a different proprietary solution.
A molecular sieve-based plant uses the same compression, moisture removal and hydrogen sulfide removal steps as Kryosol and Selexol, but it relies on vapor phase activated carbon for VOC removal and a molecular sieve for carbon dioxide removal.
Membrane technology has been used in large-scale natural gas production for many years to remove carbon dioxide from natural gas using polymeric membranes. Though somewhat unproven on LFG, the technology appears feasible as long as LFG is pretreated to protect the membranes.
The main uncertainty with this process is membrane life, which affects operating cost. The construction costs for a membrane plant processing 5 million standard cubic feet per day (mmscfd) of raw landfill gas is approximately $7 million. Net production costs would be approximately $1.60 per thousand cubic feet (mcf) of natural gas equivalent after incorporating Section 29 tax credits.
Vehicle Fuel While gasoline and diesel fuel have been preferred energy sources for vehicles since the turn of the century, the nation's heavy dependence on imported oil and the problem of air emissions recently have prompted a growing interest in alternative fuel vehicles (AFVs), including those powered by compressed natural gas (CNG).
Though AFVs face an uphill battle to replace gasoline and diesel-fueled vehicles, CNG-powered vehicles have begun to penetrate the market in the form of public transit vehicles, taxis, delivery trucks, etc.
LFG, which can be used to produce a compressed biogas (CBG) fuel, has its hat in the ring because CBG is interchangeable with CNG. To do so, CBG must satisfy CNG's fuel quality standards, which are set by state agencies such as the California Air Resources Control Board (CARB), Sacramento, Calif., or by independent organizations such as the Society of Automotive Engineers (SAE), Warrendale, Pa.
CBG is a high-Btu application using the same production technologies as pipeline quality gas. However, CBG projects generally are smaller than pipeline quality projects, making membrane technology preferable.
Similar to pipeline quality gas production, converting LFG to CBG requires reducing carbon dioxide, moisture, nitrogen and oxygen.
Although there are projects under development, the Los Angeles County Sanitation District (LACSD) owns the only operating CBG facility in the United States. Located at the Puente Hills landfill, the LACSD facility has been operating for more than five years, and has a capacity of about 1,000 gallons of gasoline equivalent (GGE) per day.
The CBG facility's construction cost five years ago is equivalent to $1.2 million dollars today. LACSD estimates that CBG production costs can range from 40 cents to 85 cents per GGE, depending on plant size. Applying Section 29 tax credits against the cost of production would lower the net cost of production by 22 cents per GGE, putting it well below the market price of gasoline. However, the market price of gasoline is the "at the pump" price with distribution and retailing costs considered, while the LACSD's CBG prices only include production costs.
CBG's real competitor is CNG, which already is priced below the cost of gasoline and diesel fuel in most regional markets, retailing at 60 percent to 100 percent of gasoline's cost on a dollar per GGE basis.
CBG faces two additional problems general marketing and financing. A reasonably sized CBG facility must market a large fuel volume to what currently is a relatively small and geographically disbursed customer base.
Also, most LFG projects are developed with a combination of equity and/or secured debt and unsecured debt. With a volatile market, it may be difficult for a landfill owner to acquire unsecured debt for a CBG landfill gas project.
Fuel Cells The public was introduced to fuel cells in the 1960s when they were used to power manned spacecraft. Today, utilities, environmental and federal agencies, and private manufacturers are funding research to broaden their use.
Fuel cells, which have high fuel efficiency and low emissions, chemically convert hydrogen and oxygen to electricity while emitting water vapor and carbon dioxide. There are several fuel cell technologies available or under development: Phosphoric acid, molten carbonate, solid oxide and polymer-membrane cells.
While fuel cells are a viable opportunity for LFG because LFG contains methane, the common feedstock for stationary fuel cell applications, gas cleanup is an issue. This is because catalysts in commercially available fuel cell packages can be fouled by trace compounds in LFG.
The principal obstacle to widespread application, however, is high capital cost.
International Fuel Cells (IFC), Groton, Conn., offers a 200 kilowatt (kW) phosphoric acid type fuel cell package. It includes a fuel processor that converts natural gas to hydrogen-rich gas; a power section that combines hydrogen with oxygen (from the air) to produce DC power, water, carbon dioxide and heat; and a power conditioner that converts DC power to AC power.
IFC's fuel cell sells for about $3,000 per kW. Total cost, including installation and LFG cleanup, is about $4,000 per kW.
Comparatively, the cost of a LFG-fired reciprocating engine power plant is approximately $1,000 per kW to $1,200 per kW.
The U.S. Department of Energy has offered grants to subsidize the installation cost of fuel cells by up to 33 percent. However, this still won't make fuel cells as economically viable as a gas-fired reciprocating engine.
The total power production cost of the fuel cell with the subsidy would be about 5.5 cents per kWh.
Nevertheless, fuel cells are an attractive LFG use because they: are applicable to projects smaller than possible with other power generation technologies; produce almost zero emissions of criteria pollutants; produce little noise; and can operate with little supervision.
If the fuel cell industry breaks the $1,500 per kW barrier, they will represent a technically and economically viable alternative.
Hydrogen Production Hydrogen, now used extensively in chemical production and oil refining, is seeing increased use in the glass, metal finishing, electronics and computer chip industries, and may be used to fuel zero emission vehicles (ZEVs) in the future.
To use hydrogen as a transportation fuel source, it must be converted to electricity with an on-board fuel cell. The electricity then is used to power a motor. Hydrogen-powered vehicles compete with all-electric vehicles, which are ZEVs, rather than with low-emissions vehicles (LEVs), such as CNG vehicles.
Although no commercial or demonstration LFG-to-hydrogen projects exist, manufacturers are producing units to convert natural gas to hydrogen. For example, Hydrogen Burner Technology (HBT), Long Beach, Calif., has developed a unit that can produce 4,200 standard cubic feet per hour (scf/hr) of hydrogen from 5,600 scf/hr of LFG. HBT estimates the total hydrogen production cost to be 43 cents per 100 scf, without tax credits, and 35 cents per 100 scf with tax credits. Section 29 tax credits would apply only if the hydrogen was used as a fuel and not if it was used in manufacturing.
LFG-to-hydrogen could evolve into a viable LFG use within the next decade if the market for hydrogen-fueled vehicles is established, and if the Section 29 tax credit (or a replacement credit) is extended.
Methanol Production Methanol (methyl alcohol) is used as a feedstock in the chemical industry, and its derivative, methyl tertiary butyl ether (MTBE), is used to produce oxygenated gasoline, whose sale is mandated by the Clean Air Act during the winter months in major urban areas. There also has been interest in using pure methanol as vehicle fuel.
LFG, consisting primarily of methane, is a possible feedstock for methanol production. About 200 scf of LFG will produce a gallon of methanol.
There currently are no LFG-tomethanol facilities operating in the United States, nor has there been an operating LFG-to-methanol project, although some have been developed through the planning stages.
In methanol's favor is a federal income tax credit of 60 cents per gallon available through December 2000 if it is used as a fuel in internal combustion engines. Methanol produced from LFG qualifies under this provision whether it is pure, mixed with gasoline or incorporated into gasoline as MTBE. However, without extension beyond 2000, the credit is of little value to a developing project.
Based on studies and limited experimentation, LFG-to-methanol is feasible. However, the end of the alcohol (methanol) fuel tax credit and competition from merchant methanol producers detract from its economic viability. Because projects were not developed during the period when both the alcohol fuel tax credit and Section 29 tax credit were available, it seems unlikely that methanol production will play a role in future LFG projects.
LFG's Future While medium-Btu gas and electric power will continue to be the principal technologies for future LFG use, pipeline quality gas is gaining popularity. If pipeline quality gas projects now under construction prove successful, the market share for this alternative is expected to grow.
Of the remaining four options, vehicle fuel, or CBG, probably is the most promising. It has a relatively high market value and may be preferable to pipeline quality gas in areas where a market can be established.
Although CNG is beginning to penetrate the automotive market, CBG will be limited to the few, small projects where market conditions can support it.
Fuel cells still are more expensive than conventional electric power generation technologies considering life-cycle costs and are not able to compete. The only advantages fuel cells offer are their small size and low level of operator attention.
It might be economically feasible to install a fuel cell to meet limited, onsite landfill power needs rather than trying to sell the power at retail. In general, fuel cells will have little impact on LFG use in the near future.
Both hydrogen production and methanol production are unproven on LFG and their economics are uncertain considering production costs and market potential.
While both are promising, it is unlikely that either will make a contribution to LFG use in the foreseeable future.
This article was abstracted from a paper presented at WasteTech '99 by Jeffrey L. Pierce, vice president of SCS Engineers, Long Beach, Calif. For a full copy, contact: [email protected]