Performance of Cogeneration Gasification Combined-Cycle Power Plants Employing Biomass as Fuel

Abstract

The objectives of this study were: preparation of the process design and flowsheets, and mass and energy balances for three biomass fuelled gasification combined cycle (GCC) power plants, two employing wood and one employing kraft black liquor; comparison of the new technologies with conventional technology; and a continued development of a consistent set of assessments of biomass fuelled combined-cycle power plants under development. This study complements two major experimental research projects that are being carried out at the Laboratory of Fuel and Process Technology of the Technical Research Centre of Finland (VTF) concerning black liquor and biomass gasification and gas cleaning for gas turbine applications. A process analysis computer program, ASPEN PLUSTM by Aspen Technology, Inc., was used as the basic framework for performing the energy and material balances. Although ASPEN was not developed especially for power plant design, the features of GCC make ASPEN quite suitable for this application. The cogeneration GCC power plant concepts for district-heating applications employ a pressurized, wood fired, air-blown fluidized-bed gasifier. Two cases have been studied. One concept is considered to represent a near-term level of technology. In the other concept, the gas is cleaned at a high temperature, and the gas turbine combustion temperature is higher than that practised today. The power-to-heat ratio of the wood GCC’s are 0.89 and 0.96, respectively. A typical power-to-heat ratio for a conventional steam-cycle cogeneration power plant is 0.5. In the black liquor GCC power plant concept the recovery boiler of a pulp mill is replaced by the gasifier. The gasification and the gas cleaning are carried out under pressure. The power ratio-to-heat ratio of the GCC is 0.70 compared to 0.27 for the conventional recovery boiler steam-cycle system. The evolving GCC technologies have a good potential for contributing to future power production. In district heating applications (as practised in Nordic countries), cogeneration power production may be doubled with biomass GCC’s. In the pulp and paper industry, power requirements are increasing and the process steam consumption is decreasing, and hence, the black liquor GCC should be a favourable option in the future.