Turning exhaust into electricity

Atle Kjærvik

Simple diagram of gas turbine power station with a recovery system for conversion of waste heat to electrical energy (ABC process)

The new technology may be capable of reducing the fuel consumption of offshore power stations by around 30 percent. "This will reduce the CO2 emission by a similar amount," says Olav Bolland, senior lecturer at the Dept. of Thermal Energy and Hydropower at NTH. In collaboration with Norsk Hydro, Kværner Energy and the Research Council of Norway (NFR).

Bolland is currently in the in the process of designing a prototype ABC- (Air Bottoming Cycle) recovery process.

"Development costs will probably come to a total of NOK 50-100 million before a product of this kind is ready to be launched on the world market," thinks Bolland. About 200 oil- and gas-fired turbines currently generates all of the electrical and mechanical energy used on the Norwegian continental shelf.

"The fuel efficiency of these turbines si about 35 % at its best, and much of the energy consumed is lost in the form of heat in the exhaust gas, which typically have a temperature of about 500 degrees Celsius. The ABC process recovers this heat and turns it into energy, increasing fuel efficiency to around 46%, says Bolland. "A typical offshore gas turbine on the Norwegian continental shelf will be an LM 2500, which generates 20-21 MW of electricity. If it is linked to an ABC recovery unit, its capacity will increase to about 27 MW. If demands for electric power offshore do not increase, this means that fuel consumption can be reduced by about 30%. This will enable us to reduce emissions of the greenhouse gas CO2," he points out.

"We are currently trying to make the plants as compact and light as possible. This is absolutely necessary if it is to be used offshore," says Olav Bolland.