Since early 2002, the Vale Point Power station has operated a methane gas demonstration plant trialing the injection of mine ventilation air into the boiler air stream.
The plant takes high concentration methane gas from sealed underground mine workings and dilutes the methane with fresh air to simulate the low concentration gas associated with mine return air.
The trial was implemented to see if there was benefit in redirecting low concentration gas to generate electricity. Due to low concentrations, the methane in the past was deemed unusable and would normally be vented into the atmosphere.
Newvale Colliery was closed in the early 1990’s and is in close proximity to the power station.
The demonstration plant was originally set up under an ACARP grant, entitled “Greenhouse Gas Mitigation through Collection and Utilisation of High Volume Low Concentration Methane Emissions”. The main opportunity the trial offered was for greenhouse gas abatement.
“Power station boilers offer an attractive method of disposal of the low concentration methane emissions exhausted from coal mines and the turbo-generators to which they supply steam provide the method of recovering the chemical energy in methane by converting it to electricity for virtually nil cost,” said ACARP.
Statutory mine manager Peter Bergin said a borehole was drilled into the Newvale old workings to liberate the gas. The methane in the mine reaches concentration levels of out 85% purity, which rises through a 150mm underground pipeline on its own buoyancy. The pipeline to the power station is approximately 1.5 kilometres.
The pipeline is then connected to a small fan running at 26 cubic metres per second, which draws air from the atmosphere around it. The gas is diluted to 0.1 to 0.25% methane which goes into the inlet of forced draft fans of the power station, and into the boilers.
Bergin said a benefit to the power station of utilising the methane was increased efficiency to its operation. Instead of burning 100% coal to heat up the boilers, the station displaced part of that with gas, a much cleaner product. Another benefit was gas does not generate ash, so there was no need to transport and dispose of a by-product. Because the gas does not produce the highly corrosive ash, maintenance costs of the pipelines were also down.
The trial has also helped Vales Point to meet new legislation, directing power stations to find alternate energies than coal.
