Rising natural gas and fuel oil prices have users of all kinds looking for cost-effective alternatives. One viable substitute is the use of landfill gas. Here's how one company put it to use.

To maximize landfill gas usage, the boiler combustion control system was designed so that all available landfill gas was burned.

One U.S. automaker has harnessed landfill gas for three turnkey conversion projects on its natural-gas-fired boilers, with the help of Hamworthy Peabody Combustion Inc., Shelton, Conn. As a result, the automaker is using landfill gas to power boilers used for both process heating and space/comfort heating.

Each of the three projects undertaken by Hamworthy Peabody involved the application of landfill gas to an existing watertube boiler. To maximize landfill gas usage, the boiler combustion control system was designed so that all available landfill gas was burned, and the co-firing of natural gas provided any additional heat input required. In addition, the control system was fully metered to measure both air and fuel flow to ensure proper and safe fuel/air ratios.

During initial design and operational review with the automaker, it was noted that boiler availability was critical. As a result, Hamworthy Peabody Combustion designed the systems to provide a constant natural gas pilot to ensure stability and a constant source of flame, should there be an upset at the landfill. This constant natural gas pilot would negate the requirement for a boiler re-purge should the landfill gas supply become interrupted. If the landfill gas supply were interrupted, the combustion control system would automatically start or increase the main natural gas burner to maintain steam production.

The projects were completed within the automaker's planned plant outage and landfill gas availability schedule, and the boilers have been successfully commissioned on both landfill gas and natural gas. Two of the projects have been in service for an extended period with no operational or availability issues; the third has just been completed.

Hamworthy Peabody tailored the solutions to the project at hand. For one project, the company modified an existing burner. For the other two projects, the Hamworthy supplied new vertical-up fired burners to burn landfill gas as well as a new PLC-based burner management system, landfill gas piping from the landfill gas supplier's flange, and combustion control modifications to fire landfill gas. Hamworthy Peabody's scope included the mechanical and electrical installation, as well as unit commissioning.

Putting It to Work for You

Landfill gas firing has several special issues for consideration in any application.

H2S. Landfill gas typically contains a small amount of H2S, such that it can react with moisture in the fuel and form small amounts of sulfuric acid. All surfaces that come in contact with landfill gas should be stainless steel to avoid contamination.

Combustion Control System Design. At times, the available landfill gas flow rate could be less than that required for a full load, which causes the balance of heat input to be provided by co-firing with another fuel source such as natural gas or fuel oil. The simultaneous firing of two fuels necessitates the combustion control system be of the fully metered type, measuring each fuel flow and adjusting the airflow accordingly to maintain safe, efficient firing of the multiple fuels.

While several issues must be taken into consideration when firing landfill gas, the fuel is a viable option to combat the rising costs of natural gas and fuel oil. PH

Hamworthy Peabody Combustion Inc., Shelton, Conn., manufactures burners and combustion control systems for landfill gases as well as gases used for industrial processes. For more information from Hamworthy Peabody Combustion Inc., call (203) 922-1199 or visit www.hamworthy-peabody.com.