Full steam ahead for biomass project

An EU-funded research project has created technology allowing small-scale combined heat and power plants to run on biomass fuels.

The technology is based on a screw-type steam engine — displacement rotary engines with a closed working chamber, similar to piston engines — and is applicable to the 200-1,000kW power range. Steam generated by a biomass-fired boiler is fed into a screw chamber containing rotors. As the steam heats and expands in size it is forced out through an exhaust outlet, the motion turning the screw-chamber rotors and driving electricity generators.

The project’s German and Austrian engineering companies integrated the engine into a heating plant in Hartberg, Austria and tested it for 5,000 hours. It operated reliably despite steam quality fluctuations, according to an EC report.

Engineers improved the design and performance of the engine’s components during the test phase, cutting the costs of production, operation and maintenance.

They also showed that the closed-cycle produces no CO2 or fluid emissions, opening the possibility for the technology to be used in Kyoto Protocol emissions-trading schemes.

The Commission shared the project’s e2.6m (£1.8m) cost with national EU funding agencies and finance house Kommunal Kredit Austria. The engineering firms involved were Austria’s FWG, Bios Bioenergiesysteme, and Kohlbach, and Germany’s IDEA and MAN Turbomaschinen.

They concluded that the plant could yield a biomass fuel price of e0.015/kWh, with a payback time of 13 years, taking an annual interest rate of six per cent for capital costs into account.

The project partners are to continue working to develop screw-type steam engines suitable for higher steam inlet temperatures — up to 300 degrees C — to boost the model’s electrical efficiency, and tighten rotor clearance to reduce steam losses.