LANDFILL: Old Landfill, New Tricks

Like plants need the sun to grow, the Jamacha Landfill Gas Utilization project, a San Diego County-based power plant, depends on landfill gas (LFG) and microturbine technology to operate. Since summer 2001, the Jamacha Landfill, also located in San Diego county, has supplied the LFG needed to power the microturbine technology that runs the power plant.

Similar to larger combustion engines, microturbines are smaller engines that can be used in a “distributed generation” energy system. Distributed generation is the production of electrical energy using small power facilities throughout an electric utility's service area, instead of using larger, centralized power facilities. Solar and wind power are typical examples of distributed generation power systems.

Microturbines allow more flexibility in the utility system because they can be operated either connected to the electrical grid or totally off-grid with no connection to a power supply. For fuel, microturbines use natural gas, digester gas from wastewater treatment plants and LFG. As California and other states face an energy crisis, the development of cost-effective and environmentally sound energy sources, especially those using LFG, could be a viable long-term solution.

Jamacha Landfill is a small municipal facility that has been closed since 1978 and collecting LFG since 1995. However, because of the landfill's small size and old age, the gas has a relatively low methane content — approximately 37 percent. Among several features that the county found attractive, microturbines can operate on waste gases with a methane content as low as 30 percent. The landfill power plant operates on four 75-kilowatt microturbines, manufactured by Ingersoll-Rand, Portsmouth, N.H.

According to SCS Engineers, Long Beach, Calif., which designed, built and continues to operate the plant, microturbines have several advantages. They are most applicable when electrical power is unavailable or cost-prohibitive; waste fuel is available; air emissions are an issue; and hot water is needed for use by commercial customers or nearby residential areas. (The waste heat in a microturbine exhaust also can produce hot water.)

Furthermore, air emissions from microturbines such as nitrous oxides are less than one-tenth those of the best-performing reciprocating engines, SCS notes. Microturbines also work well for small projects because users save money by self-generating power instead of purchasing electric power elsewhere.

“Prior to the availability of microturbines, many projects intended to supply onsite electrical needs were not deemed feasible because the available generation equipment size was much larger than the need,” says Jeffrey Pierce, vice president for SCS Energy, a division of SCS Engineers. “Microturbines represent an opportunity to reduce a facility's overall energy cost and to provide emergency power.”

Typically, the rate of return on a facility's capital investment is about three to four years. However, at the Jamacha Landfill, the estimated rate of return is seven years because only 10 percent of the energy is used onsite. The remaining energy generated is sold to the local utility, San Diego Gas and Electric Co. Total capital costs for microturbine technology are between $1,800 per kilowatt and $2,500 per kilowatt, according to SCS.

Operators at Jamacha Landfill also are studying challenges with the microturbine technology. For instance, waste fuel applications, unlike conventional fossil fuels, require pretreatment to remove moisture and impurities.

In addition, the plant must deal with siloxane, an organic compound emitted from LFG that, when burned, produces a sandy powder. This powder can be abrasive, which can damage vital parts of the microturbine system such as the recuperator and waste heat exchanger. The Jamacha plant currently is testing the effects of the powder's abrasiveness. Two microturbines are using a carbon-polishing system that eliminates siloxane; the other two do not have such a system so that the company can compare outputs.

Over time, the county and SCS Engineers hope to gain data on the long-term effectiveness of using LFG to fuel microturbine technology. SCS has three other microturbine landfill projects in the works, including microturbines manufactured by Capstone Turbine Corp., Chatsworth, Calif. Capstone, in fact, also has supplied 50 microturbines to operate on LFG from the Lopez Canyon Landfill in Lake View Terrace, Calif. The LFG-powered plant reportedly is producing enough electricity to power 1,500 homes.

“One site of microturbines feeding off of one landfill is not going to change the world,” Tim Carmichael, executive director of the Los Angeles-based Coalition for Clean Air says of the Lopez Canyon Project. “But is this a model to be copied again and again? I think so.”