A Texas landfill has generated almost $100,000 to pay for its own gas collection system.
WHO: Denton (Texas) Solid Waste Department
PROJECT: Gas-to-energy conversion at a 200-acre landfill
ON LINE: Dec. 17, 2008
COST: $1.2 million
INITIAL WELL COUNT: 23 horizontal gas collection, 43 vertical extraction
INITIAL GAS PRODUCTION: 415 cubic feet/minute average
INITIAL ELECTRICITY PRODUCTION: .25 megawatt-hours (MWh)
CURRENT WELL COUNT: 34 horizontal, 73 vertical
CURRENT GAS PRODUCTION: 550 cubic feet/minute average
CURRENT ELECTRICITY PRODUCTION: 1.6 MWh
THE LATEST: Since installing a generator with a gas collection system at its 200-acre site in 2008, the Denton, Texas, municipal landfill has been producing enough electricity to continue to build its system — which could peak at 100 in the next decade.
But first thing first, says Vance Kemler, general manager of solid waste services for the City of Denton. Under a 20-year contract with private partner DTE Biomass Energy (through 2024), DTE provides capital equipment for electrical generation and sells the generated power to the city-owned power utility. DTE maintains and operates the gas collection system, and the city's solid waste enterprise fund pays for capital improvements for the flare station, active gas collection system, and all wells.
In turn the solid waste department gets a monthly 12.5% royalty on the sale of gross revenues, allowing the city to repay the bonds used to build the system. DTE operates and maintains the system, leaving the city free of any operations and maintenance expenses.
“We have one 1.6-megawatt (MW) generator (a Caterpillar 3520) and room for two more,” Kemler says. The project is about one-third the size of the average landfill gas electricity project, which produces 3.75 MW, according to the U.S. EPA.
When the generator went on line in December 2008, all gas was used to fuel it. But by late summer production had risen to a level that was greater than the generator could use.
Currently the department is flaring the excess gas until there's enough to power a second generator. Kemler hopes to put a second on line in the next two years. “We've also installed three large permeable beds for the introduction of leachate and water into our newest landfill cell to increase the rate of methane production.” The beds have gas-extraction piping and will be hooked up to the collection system.
“Although the expectations were that the city would sell 1.6 MW of electricity right away, they didn't reach that level until this summer,” says Phil Coleman, DTE's director of operations, citing the need for additional wells. “The wells couldn't deliver what was projected.”
Since the generator didn't produce full power immediately with the original number of wells, the department added 12 vertical wells before full output was achieved.
The project has generated $98,793 year-to-date — nearly $8,700 more than it generated in 2009.
“Now it's performing at expectations, and the additional gas powers the engine. Any excess gas is flared,” he adds. It's that excess gas that both Kemler and DTE hope to capture as the system matures — and the $1.21 million project can pay for itself.
“We have seen a lot of interest from the corporate sector as an end-user to replace things like coal and oil,” says Rachel Goldstein, program manager for the EPA's Landfill Methane Outreach Program.
As of Oct. 1, 526 landfill gas energy projects were in operation in 46 states generating 1,628 MW of electricity and 311 million standard cubic feet per day of landfill gas for direct-use applications.