Landfill gas-to-energy technology offers fuel option for paper mills

Municipal solid waste systems are required to collect methane-containing landfill gas, and paper mills can benefit by co-firing it as a boiler fuel

WHEN MUNICIPAL SOLID waste (MSW) decomposes in a landfill, landfill gas is produced-a process that takes 30 years or more. Due to the high percentage of methane in landfill gas (approximately 50% by volume), landfill gas is both a major contributor to the risk of global warming and a valuable source of energy.

Until the past decade, landfill gas was viewed as a nuisance at best and a hazard at worst. At many landfills, collected landfill gas is burned in a flare. However, many public landfill owners and private-sector solid waste management companies are extracting the gas for productive use by recovering energy from the methane component. Of the approximately 700 landfills nationwide with cost-effective landfill gas-to-energy (LFGTE) potential, the Environmental Protection Agency estimates that only about 150 have projects in place.

Collected landfill gas can be used to generate electricity, supplement boiler fuel, and power vehicles, and it can even be treated and injected into natural gas pipelines. Direct use of medium-quality landfill gas offers nearby facilities a particularly attractive opportunity. Through landfill gas utilization, a facility can clean up the environment and save money.

The potential benefits of a LFGTE project include the following:

* An economical local source of power for utilities, industry and consumers.

* The elimination of detrimental air emissions.

* The prevention of landfill methane contributing to global climate change.

* The prevention of methane migrating offsite and becoming a safety hazard or odor problem.

MILL ENERGY NEEDS, LFG AVAILABILITY. Pulp and paper mills have a high energy demand. Mills typically use large quantities of coal, oil or natural gas to fire steam boilers or co-generation units that provide process steam and electric power.

While the size and energy demands of facilities vary widely, the constant demand for fuel is ideal for use of landfill gas to replace part or all of these conventional fuel sources.

Depending on size, age and waste composition, a MSW landfill may be capable of generating from 10 million to more than 500 million Btu/hour of energy for a 20-year period. For example, a 50acre landfill with 2 million tons of waste in place may generate between 15 million and 25 million Btu/hour.

If available nearby, landfill gas could replace some percentage of a mill's purchased energy at a discounted price. Moreover, since all large landfills and many medium-sized landfills are required to collect and control LFG emissions under federal New Source Performance Standards (NSPS), landfill owners and operators have a strong incentive to find productive uses for their landfill gas.The EPA estimates that more than 400 U.S. landfills contain more than 1 million tons of waste and are therefore subject to the new standards.

Existing mills have already recognized the possibility for use of landfill gas as a low-cost fuel source. New mills are beginning to investigate landfill gas as a primary co-generation fuel (with natural gas backup). The technology for transport and utilization of landfill gas is welldeveloped, and pipeline delivery systems are operating at least 30 sites in the U.S. Additionally, the landfill gas industry has attracted the interest of a variety of private firms that offer a range of services from full-service gas utilization project financing to design, construction and system operation.

KEY FACTORS IN GAS UTILIZATION. The key factor in determining whether landfill gas use is feasible at a facility is the proximity of the mill to a candidate landfill. When considering the cost of constructing a pipeline to transport landfill gas and the power required for transmission, a potential direct user should be located within five miles of the supplying landfill, although longer distances have been successfully traveled. Other factors to consider include the following:

* Landfill size. Size (i.e., waste-inplace) dictates how much gas will be available. As a rule of thumb, a candidate landfill should have at least 1 million tons of waste in place.

* Landfill age. The "younger" the landfill, the more plentiful the gas flow, since more landfill gas is generated early in the life of the landfill.

* Landfill design. Design affects gas extraction. Landfills having a minimum waste depth of 40 ft or more are preferred.

There are several ways to investigate whether candidate landfills are located near a facility. One way is to use the EPA's Landfill Methane Outreach Program (LMOP) landfill profiles, a series of state-based reference books that describe candidate landfills in specific states. These profiles facilitate the identification of landfills close to pulp and paper mills that are strong candidates for energy recovery. LMOP has also developed a computer database that cross-references candidate landfills from the profiles handbooks with potential landfill gas direct users in the vicinity.