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Converting Landfill Gas to Energy A Small Company's Experience

by the CADDET US National Team

INTRODUCTION

A North Carolina power company has demonstrated that solid-waste landfills can provide abundant sources of methane fuel gas for direct use in nearby applications. This article charts the experience of Natural Power Inc. since it was formed in 1983 to research and develop the conversion of landfill gas (LFG) to electricity at the Rowland Landfill, located in Raleigh, North Carolina, USA.

ROWLAND LANDFILL

This four-acre landfill had been non-operational since 1978, before Natural Power Inc began developing the site as an energy resource in 1983. A collection system of ten wells fuelled two 3306 Caterpillar engines driving two 85 kW generators, which produced electricity sold to Carolina Power & Light. The system became operational in 1984. The Rowland Landfill won accolades as one of the first in the US to operate a LFG-fuelled
power plant with sales to a utility company. The system was retired in 1996.
 

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Gas flare at Raleigh

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Extracted LFG containing 50% to 55% methane powers an 800-hp Cleaver Brooks boiler at the pharmaceutical plant. In normal operation the boiler uses about 34,000 m3/day of LFG and generates steam averaging 11,000 kg/hour. Natural Power owns the boiler and sells steam to Ajinomoto, which uses it to run a chiller for cooling water in amino acid production.

The plant obtains about 85% of its steam needs this way. Ajinomoto has been able to achieve a saving of about $140,000 annually (where $ is the US dollar).

WILDER'S GROVE LANDFILL

In 1989, Natural Power installed another LFG project at the Wilder's Grove Landfill in Raleigh to service the Ajinomoto pharmaceutical plant, located one mile away. This award-winning project was the first in the state to convert LFG to steam.

The landfill facility encompasses 51 ha, with an active fill area of 32 ha. The facility is expected to contain 5 million tonnes of refuse upon final closure in December 1997. The gas collection system contains 62 extraction wells drilled to depths between 12 m and 24 m. A 9-stage Hoffman blower produces up to 114 cm of water column of vacuum and discharges it at 0.76 bar for transmission or flaring of excess quantities of gas when the boiler is operating at maximum load.

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Boiler at the Ajinomoto plant fuelled by LFG from the Wilder's Grove landfill

A new gas extraction system will be developed at this location by 1998. The system will contain about 48 new wells and 4,564 m of collection piping. Two new blowers will be installed and the original blower will be assigned to backup status. Natural Power will also add another boiler to the Ajinomoto plant, and the city of Raleigh will install a geomembrane over the majority of the landfill surface.

WHITE STREET LANDFILL

The White Street Landfill project in Greensboro, North Carolina went on line in December, 1996 as a joint effort between Natural Power Inc. and Duke Engineering & Services of Charlotte, North Carolina. The landfill is owned by the city of Greensboro and encompasses 304 ha, 57 of which comprise an active fill area. The site should contain about 5.5 million tonnes of refuse upon final closure in December 1997.

Gas extracted from a total of 65 wells fuels a large steam boiler for industrial operations at Cone Mills, a textiles plant located three miles from the blower station. The 4,737 m of high density polyethylene (HDPE) collection piping is sized between 10 and 40 cm in diameter. A 4,828 m transmission line is mostly 40 cm HDPE and steel piping.

On average, 57,000 m3 of LFG/day is being drawn from the White Street facility. Natural Power plans to install 50 additional wells and 2,438 m of piping in recently closed areas.

For more information contact the CADDET US National Team in Golden, Colorado.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to
Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.