Gases & Instrumentation - March/April 2008

Monitoring Methane in Landfills

TOM PROBST

Methane generated from landfills can generate electricity, but needs to be monitored in the engines and control room.

Ahalf-dozen “electronic canaries” are watching over a gas-generating plant in a suburban Minneapolis landfill. The garbage-to-gas setup extracts methane from the landfill, funnels it to five engine-driven generators that feed the electricity into local power grids, generating power and profits. (Figure 1 and 2)

These “electronic canaries”[1] continually sniff the air inside

Figure 2: Sensors in operations and control buildings warn of concentrations of explosive methane gas. Cost of the entire methane detection system amounted to under $10,000, meaning inexpensive protection for plant personnel and physical property. In contrast, the cost of the complete gas-to-energy complex was $1.2 million.

the plant’s engine and control rooms, squawk the instant they sense toxic or extensive methane concentrations, then shut down the gas supply lines, stop the engines, turn on the exhaust fans and signal for help. (See Figure 3 showing control room displays)

Decaying garbage in the half-mile-square landfill produces clouds of methane deep under the surface. To extract this gas, engineers bore wells down into the garbage and lace them together in a piping network. When one well runs dry, engineers just bore another nearby.

A huge pump pulls the methane from the piping network

Figure 1: “Electronic Canary” (to right of control panel) ^[1] sniffs for methane into a dump box to separate out water and heavy debris. gas leaks in engine room at “garbage-to-gas” landfill in suburban Min- The methane is then compressed to 10 psi and run through neapolis. Five giant caterpillar V-12s drive 900-kilowatt generators, and a heat exchanger to drop its temperature to 110 degrees. efficiently convert more than 98 percent of methane into power. Filters eliminate any contaminants larger than 0.5 microns