LANDFILL GAS (LFG) contaminants, at times, have cast a cloud over engine maintenance and emissions in the landfill gas energy (LFGE) industry. Because fuel quality changes from landfill to landfill, processes to treat the contaminants have not always been reliable. However, according to engineers at Waukesha Engine, Waukesha, Wis., and the Onyx Glacier Ridge Landfill, Horicon, Wis., new technology to clean up fuel, use a lower emission technology and reduce maintenance costs are just on the horizon.
Waukesha Engine's and the landfill's engineers recently tested an electric power-generation system designed to reduce maintenance requirements and emissions. And although the test did not reach its goals, the participants are optimistic the results will lead to operational improvements in the industry.
Contaminated fuel is caused by old and new solid waste sources in landfills. Landfills in different parts of the country produce methane gas with various combinations of old and new contaminants. Contaminants found in older landfills include chlorofluorocarbons (CFCs) from aerosol cans and cleaning products, such as paint-strippers. Newer contaminants may originate from silicon-based hydrocarbon compounds or siloxanes, which are found in modern formulations of products including silicone-based caulks and beauty products. Some of these contaminants can increase engine wear, requiring expensive maintenance.
To address this situation, LFGE engineers currently follow two steps: First, they examine the contents of LFG to determine an appropriate fuel cleanup technology. Second, they install energy systems, such as a lean burn engine generator, which uses relatively small amounts of fuel mixed with lots of air. Lean burn engines are different from rich burn engines, which mix larger quantities of fuel with less air. Lean burn technology satisfies emissions standards set by most state regulations without a catalytic converter. The focus of the test was to use a rich burn engine.
For some landfills, lean burn systems work fine. At other sites, however, high levels of contaminants affect engine performance and require expensive, regular maintenance. Onyx Glacier Ridge Landfill volunteered its LFGE system, which has a contract to supply electricity to a local utility, for the test. “Siloxanes were causing wear and tear on engines we had bought from Waukesha,” says Onyx Senior Project Engineer Donald Smith. “We wanted to find a way to reduce maintenance expenses and be part of this new filtration fuel technology.”
Likewise, Waukesha Engine wanted to reduce maintenance requirements on its lean burn LFGE engines. The company also wanted to develop a rich burn engine that could provide lower emissions than currently required
Thus, the two companies set up a test at Glacier Ridge to explore possible solutions. They jointly designed a full-scale prototype LFGE system that converted the landfill's existing lean burn engine to rich burn with a catalytic converter. The system used a front-end filtration system, including a graphite filtration system, to remove contaminants from the fuel before it was fed into the engine.
The graphite filtration system removed fluorocarbons, siloxanes and other chemical contaminants that degrade engine operation as well as the operation of catalytic converters. “Some of the chemical contaminants in landfill gas produce compounds that poison or mask a catalyst and damage a catalytic converter,” says Gregory Sorge, Waukesha engineer who helped design the Onyx system.
The filtration system, which was key to the concept, worked but proved to be too expensive. Upon turning the generator on, the filtration system, rich burn engine and catalytic converter all functioned as expected — but only for 30 days. After a month, the graphite filtration system failed, and contaminants flowed through the engine and fouled the catalytic converter. “We had calculated the economics of the system based on the filtration system lasting 90 to 180 days,” Sorge says.
In economic terms, Waukesha's and Onyx's goal was to reduce maintenance and the cost of generating electricity. According to Sorge, Wisconsin power utilities pay approximately 4 cents per kilowatt-hour (KWh). Producing electricity with the original lean burn system costs close to 4 cents per KWh, when maintenance and the recovery of capital investment were factored in. “If the rich burn system could have saved a half-cent per kilowatt-hour by reducing maintenance costs, it would have produced a good margin,” Sorge says.
Despite the test missing its goals, Onyx Glacier Ridge and Waukesha continue to experiment with filtration media, but the scope of testing is no longer being applied to full operations. The companies converted the rich burn engine back to lean burn when the test was completed. However, Smith and Sorge have installed small, laboratory-scale filtration systems in front of the lean burn engine. “We are plugging different filtration media into the system in the field, taking measurements and determining efficiencies,” Smith says. He hopes that successful results from one of the test media will lead to another full-scale operational test. “We've learned quite a bit,” he says. “I think an evolutionary process has begun.”
“Low Emission Challenges on a Landfill Gas To Energy Application,” a report of this project, was presented at WASTECON 2003.