Efficiency Improvement in Precombustion CO2 Removal Units With a Waste–Heat Recovery ORC Power Plant

Abstract

This paper presents an analysis about recovering low-grade thermal energy from a precombustion CO2 capture process as part of an integrated gasification combined cycle (IGCC) power plant by means of organic rankine cycle (ORC) turbogenerators. The distinguishing feature of this system is the thermal energy source that is a syngas-water mixture, which is cooled from a temperature of approximately 140 °C, and partly condenses due to the heat transfer to the ORC primary heat exchanger. This study explores various types of ORC power systems for this application. The performance of commercially available ORC units is used as a benchmark and compared to the performance of two types of tailor-designed ORC power plants. The working fluid has a major influence on system performance and other technical and economic factors. The effect of selecting a fluid from the hydrocarbon and refrigerant families are therefore investigated, targeting the maximum net power output. In addition to pure fluids, two-component mixtures are also considered. The use of mixtures as working fluids in subcritical heat-recovery ORC systems allows for a better match of the temperature profiles in the primary heat exchanger and the condenser due to the temperature glide associated with phase-transition, leading to lower irreversibilities within the heat exchanging equipment. In order to further improve the thermal coupling between the cooling heat source and the heating of the working fluid, the supercritical cycle configuration is also studied. The performance of the three categories of systems, depending on working fluid and cycle configuration, i.e., systems based on (i) commercially available units, (ii) tailor-designed subcritical cycle, (Hi) tailor-designed supercritical cycle, are analyzed in terms of net power output, second law efficiency, and component-based exergy efficiencies. The analysis shows that an improvement of 38.0% in terms of net power output compared to the benchmark system can be achieved by an optimized supercritical ORC power plant using an Rl34alR236fa mixture as the working fluid. It is estimated that the total power consumption of the considered exemplary CO2 capture plant can be reduced by approximately 10% with the optimal ORC system. In this study, particular attention is focused on the semi-empirical optimization approach, in order to avoid unnecessary computations, and general guidelines are provided. . Assoc. Editor; Paolo Chiesa. development of precombustion CO2 removal technology to be applied in the future Magnum IGCC power plant [3]. A smallscale, fully instrumented pilot plant implementing the CO2 capture process has been realized at the Buggenum IGCC power station, and it is being commissioned for further studies and experiments. This study takes as an example the design of the Magnum IGCC power plant and its CO2 capture unit in order to investigate the performance of an ORC system recovering thermal energy downstream the water-gas shift reaction section and by intercooling the CO2 compression section (see Fi...

Multi-Objective Optimization of Organic Rankine Cycle Power Plants Using Pure and Mixed Working Fluids

“…This suggests that the cost of heat exchangers is larger when the mixture is used. Similar conclusions have been reached in studies where other mixtures and pure fluids have been compared based on thermodynamic performance (e.g., [4,5]). Previous literature, thereby, indicates that the feasibility of zeotropic mixtures should be evaluated by considering both thermodynamic and economic aspects.…”

Selection and optimization of pure and mixed working fluids for low grade heat utilization using organic Rankine cycles

“…Trapp and Colonna [5] maximized the net power output of an ORC for low grade waste heat recovery from a pre-combustion CO 2 capture process as part of an integrated gasification combined cycle power plant. The waste heat stream was a 140…”

“…These low temperatures are chosen, since mixtures have shown beneficial performance compared to pure fluids when the hot fluid inlet temperature is low [3][4][5][6][7]. A systematic methodology using a genetic algorithm optimizer is developed to find promising pure fluids and mixtures for the maximization of the net ORC power output.…”

Part-Load Performance of aWet Indirectly Fired Gas Turbine Integrated with an Organic Rankine Cycle Turbogenerator

“…As surveyed by Trapp and Colonna [19], the ideal candidate should be available at low costs, have low environmental impact, flammability and toxicity. Moreover, the plant performances and the component design are pivotal aspects of the fluid selection process.…”