Landfill gas offers solution to rising natural gas prices, Solutions!, Online Exclusives, July 2005, Vol. 88(7)

Rising natural gas and fuel oil prices have users of all kinds looking for cost-effective alternatives. One viable and popular substitute is the use of landfill gas, and companies are successfully implementing landfill gas (LFG) product conversions to existing oil and/or natural gas fired boilers.
A landfill gas flame.

A major U.S. automaker has completed two turnkey landfill gas conversion projects. The projects were completed within the plant outage and LFG availability schedule, and the boilers have been successfully commissioned on both LFG and natural gas. Both projects have been in service for an extended period with no operational or availability issues. The contractor—Hamworthy Peabody Combustion Inc., which has an extensive track record in the application and combustion of non-standard gases—has recently completed a third turnkey project for the same auto manufacturer. Hamworthy Peabody Combustion is a world leader in the development and application of industrial combustion solutions. Since its formation in 1920, Hamworthy Peabody has supplied efficient, reliable combustion systems, ancillary equipment and comprehensive service support to the power generation, refining, petrochemical and process industries.

In addition to modifying an existing burner for one of the three projects, Hamworthy Peabody supplied new vertically up fired burners to burn LFG for this automaker’s other two projects, as well as supplied a new PLC based burner management system, new LFG piping from LFG 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.

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

During initial design and operational review with the customer, technicians noted that boiler availability was critical. As a result, Hamworthy Peabody Combustion designed this specific system to provide a constant natural gas pilot to assure 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 LFG supply were interrupted, the combustion control system would automatically start or increase the main natural gas burner to maintain steam production.

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 LFG should be stainless steel to avoid contamination.

Combustion control system design: At times, the available LFG 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 there are several issues to take into consideration when firing landfill gas, the fuel is a very viable option to combat the rising costs of natural gas and fuel oil. Field-tested installations like those described here prove that manufacturing facilities can successfully convert natural gas applications to LFG.

Contact:
Larry Berry is president, Hamworthy Peabody Combustion Inc., 70 Shelton Technology Center, Shelton, CT 06484. To learn more, contact him by phone: (203) 922-1199, fax (203) 922-8866, or e-mail: lberry@hamworthy-peabody.com.