Packaged Power For Landfills

Diesel Progress North American Edition, May, 2001 by Neil Purslow

Enerflex Power Systems has developed a modular skid package to turn landfill methane gas into electrical power

Garbage in, power out -- not a new concept in today's world. However, to turn methane gas from landfills into electrical power using modular skid packages is.

"Landfill operators in the past constructed permanent facilities for power generation equipment at individual landfills," said Bryan Hodges, sales manager for the Compression and Power Division at Enerflex Systems Ltd. "After the site depletes and the power generation equipment is removed, operators are left with over a million dollars in remaining unused fixed assets on site. When a major U.S. landfill management company came to us looking for a solution to help them optimize the efficiency and flexibility of power generation equipment at their sites, we immediately put our expertise and experience to work."

The first step was to choose a test site. A landfill in Massachusetts was selected. The site had been capped and the plastic liner, earth backfill and re-seeding were complete. The methane gas produced by the decomposition of the garbage was being flared.

Since the site was capped, one of the major challenges was to find a solution that would maintain optimum peak power generating efficiency with an ever-declining fuel feedstock. Power generators operate at peak efficiency when carrying a full load.

"If we sized the unit to meet current conditions," said Hodges, we would experience over capacity and decreasing efficiency in just a few years. Conversely, if we installed a smaller unit than that required for today's operation, we'd be leaving potential power in the landfill. Neither alternative was acceptable."

Other aspects of the project added to the challenge. The local county had a number of very stringent requirements to adhere to before approval would be given to proceed:

* Sound -- the new equipment could not exceed 10 db over ambient during any 24-hour period.

* Temperature -- the new building must maintain a 15[degrees]F (9[degrees]C) temperature rise in the building from the ambient temperature outside.

* Height -- no buildings or equipment could exceed 20 feet in height from grade.

* Liquid Leakage -- none tolerated.

The selected site was an excellent candidate for this project. It produces a steady stream of methane gas, enabling the production of 3.15 MW of electricity. The generated power was to be used to operate the onsite equipment, with the surplus sold to the local utility. The customer manages multiple landfills and wanted a portable generation facility that could be moved from one site to another. As well, they wanted to eliminate internal civil-engineering activities and acquisition of materials and services. A fresh approach would result in a viable environmental alternative to flaring, a substantial decrease in capital investment and enhancement of the local utility grid.

After studying the requirements, the Enerflex design group developed a modular skid base solution. The modular package design was preferred for many reasons. Not only does it satisfy the main operational, environmental and economic requirements, but it also permits the relocation of a portion of the plant (i.e. one skid unit at a time) as the gas depletes. This flexibility allows the remaining units to continue operating at full loads, thus maintaining peak efficiency throughout the life of the landfill.

Overlying this new concept was the necessity to standardize the package design. If a unit was moved from one site to another, it had to be compatible with the units at the new location for them to be joined together. Once the design was approved, the concept would be deployed in Massachusetts.

Three individual power generation units were installed in a five-piece modular skid, including a tank farm and maintenance and workroom area. Three identical power-generating skids were built including L7042GLD Waukesha engines rated at 1478 hp (1050 kW) at 1200 rpm. The horsepower has not been derated. The engines are factory standard, with minor modification performed by Enerflex. The carburation system is modified to handle the very low pressures and high volumes of methane gas required for combustion within the engine. Each engine is also tuned for optimum performance, based upon the composition of the methane gas at that site.

The Kato generators, model 6P6-2500, are directly connected to each engine. These generators are rated at 1050 kw, 60 Hz, 4160 Vat 1200 rpm. The engine coolers are Young model HC-666-V15QX, and use a horizontal core assembly with electric driven fans operating on the electricity generated at the landfill. All other components on the skids are manufactured and installed by Enerflex at their manufacturing plant in Calgary, Alberta, Canada.

The fourth skid is a tank farm. This self-contained unit consists of four individual tanks designated for the storage of coolant, new/fresh oil for the engines, old oil from the engines and a slop tank for everything else. Catch basins are installed under each tank to ensure containment of all seepage and spillage. The tanks are connected through pipes and pumps to ensure fluid flow to the equipment, and external loading and off-loading facilities are available for each tank.