Micro gas turbine for low calorific fuel gas from biomass

A Capstone micro gas turbine has been operated on various mixtures of natural gas and producer gas from biomass gasification. Stable operation with low emissions was shown feasible, requiring only limited modification of the software settings. The micro gas turbine can deliver full design power if the lower heating value of the gas mixture is at least 15 MJ/Nm3. Stable operation on gas with lower heating value between 8 and 15 MJ/Nm3 is possible too, but the power output is limited as the fuel delivery system cannot cope with the required larger gas volumes. We assume future applications will be based on a gasification process able to deliver gas with sufficiently high heating value to allow operation at full power, e.g. indirect (allothermal) gasification. On inspection of the micro gas turbine a loose yellowish powder was found on surfaces near the burner. This may cause problems on prolonged operation and requires further attention. However, if it results from the presence of small amounts of H2S in the product gas, the problem can be solved by the use of the specially adapted sour gas version of the Capstone micro gas turbine. A market study into application of the combination of micro gas turbines and biomass gasification shows the best opportunities to be in the horticultural sector. The high heat/power ratio makes application most attractive at sites where electricity is not used for artificial lighting to increase plant productivity. The value of electricity has been calculated correspondingly from feed-in tariffs plus MEP subsidy as applies presently to small biomass fired installations in the Netherlands. For installations matched to the average heat demand in the summer months the simple payback time of investment equals 6 years. For a similar installation with gas engine, the result is 4.7 years. For comparison, the simple payback time of a gas engine on natural gas, for which MEP subsidy does not apply, is calculated to be 5.5 years. The market for this type of installations is estimated at nearly 200 installations with 3 MWth biomass gasifiers. Whether that potential will be realised depends on the continuation of the MEP subsidy scheme and the due availability of biomass gasifiers with matching gas cleaning systems (MEP is a financial incentive and is the Dutch abbreviation for environmental quality of electricity production)