An analysis of integration of a power plant with a lignite superheated steam drying unit

Abstract

Abstract Future developments of energy conversion systems are expected to be based on second and third generation technology. One of the most innovative designs involves the integration of hard coal or lignite gasification technology with a gas turbine (GT) combined cycle, which is known as an Integrated Gasification Combined Cycle. This may constitute an advantageous future energy option, especially for the use of lignite. Gasification also provides one of the most efficient ways to produce clean fuel for the next electrical energy generating fuel cells and cars, as it permits the additional production of syngas with low levels of CO2 emissions. However, the performance of lignite (brown coal) fired IGCC is degraded by the very high content of moisture in the lignite. The most appropriate approach in order to fully utilise the potential of this type of fuel is the use of a drying system. In the present paper, an Integrated Gasification Combined Cycle for electricity production, coupled with a fuel preparation unit and a coal superheated steam drying system, is analysed. The novelty of the proposed system is its uniqueness in being equipped with a superheated coal drying system, which constitutes a potentially advantageous method of raising the calorific value of lignite and enhancing its use as a fuel. The proposed system permits lignite to become a valuable resource. The combined system is able to generate electricity with a thermal efficiency higher than for conventional systems and it decreases air pollution and fuel consumption. The system consists of seven dependent subsystems: fuel preparation (lignite drying), air separation unit (ASU), coal gasification, gas cleaning system, regeneration system heat recovery steam generator system, steam turbine and gas turbine. The present analysis demonstrates that lignite consists of more than 50 wt % (wet basis) moisture content before the drying process. In the analysed system, the process of drying coal takes place using steam at a pressure 1.2 bar and a temperature of 133.84 °C, which allows brown coal to be dried to 20 wt % (wet basis) of moisture content. The results show that with the coal drying system it is possible to increase significantly the efficiency of the system of the Integrated Gasification Combined Cycle up to 48%–56%, depending on the thermodynamic parameters of the process. The selected thermodynamic parameters are validated and compared with experimental data.