Electricity production by advanced biomass power systems

This report gives the results of the Pyrolysis Collaborative Project organized by the International Energy Agency (IEA) under Biomass Agreement. The participating countries or organizations were Canada, European Community (EC), Finland, United States of America, and the United Kingdom. The overall objective of the project was to establish baseline assessments for the performance and economics of power production from biomass. Information concerning the performance of biomass-fuelled power plants based on gasification is rather limited, and even less data is available of on pyrolysis based power applications. In order to gain further insight into the potential for these technologies, this study undertook the following tasks: 1. Prepare process models to evaluate the cost and performance of new advanced biomass power production concepts. 2. Assess the technical and economic uncertainties of different biomass power concepts. 3. Compare the concepts in small scale and in medium scale production (5 - 50 MWe) to conventional alternatives. Processes considered for this assessment were biomass power production technologies based on gasification and pyrolysis. Direct combustion technologies were employed as a reference for comparison to the processes assessed in this study. Wood was used as feedstock, since the most data was available for wood conversion. Based on the results of this study the following conclusions were made: New advanced power production systems based on pressurized gasification and gas turbine cycles may be economically feasible only in a relatively large size class (over 30 - 40 Mwe). The investment costs in smaller size classes are too high compared with those of conventional fluidized-bed boilers. Atmospheric and pressurized gasification IGCC concepts showed similar economic results. However, the technical uncertainties related to the pressurized system are considered larger than with ambient pressure system. The STIG concept does not appear to be competitive. The principal reason for this is that the amount of steam that may be injected into the existing gas turbines is quite limited when LHV gas is used as fuel. The gasification-diesel concept has in small size classes (5 - 10 MWe) the potential to reach higher power production efficiencies than those reached in conventional fluidized-bed boilers. Power production concepts based on pyrolysis generally yield lower overall efficiencies than those based on gasification. However, the possibility of disconnecting pyrolysis oil production from the power plant may in some cases be a major advantage. For example, economies of scale may be utilized in a large oil production, while small heat loads may be served with automated power plants using the liquid fuel. Pyrolysis oil combined-cycles appear interesting in large scale, whereas diesels are more interesting in smaller production capacities. In peak load electricity production, 5 - 25 MW, pyrolysis diesel power plant concept appears especially interesting. In medium and base load, greater than 30 - 40 MW, IGCC has potential of becoming a relatively low-cost alternative.