Selected Aspects of Performance of Organic Rankine Cycles Incorporated Into Bioenergy With Carbon Capture and Storage Using Gasification of Sewage Sludge

Abstract

The study aims to investigate the application of the organic Rankine cycle (ORC) in the bioenergy with carbon capture and storage (BECCS) using gasification of sewage sludge. The tool used in the investigation is the ASPEN PLUS software with REFPROP property methods for calculating fluid properties. The reason for this study is that a detailed analysis of the proposed BECCS process flow diagram indicates that a certain amount of waste heat is available in the exhaust gas from the high-to-intermediate pressure gas turbine. Some of this energy can be used by applying expansion in a low-pressure turbine, optionally by applying regenerative water heating, which is then redirected to the combustion chamber, or finally by incorporating the ORC into the main cycle. For the ORC cycle, different configurations are studied, with regeneration and using different working fluids. For the highest efficiency of the cycle, the regenerative heating of high-pressure water is applied and a suitable ORC working fluid with optimal saturation parameters and mass flow is selected. Such modified proposed BECCS power plant hybrid systems with ORC are compared to the reference case with lower pressure expansion. A study of the heat duty and temperature distribution in heat exchangers is carried out. Five ORC fluids were investigated, namely ethanol, refrigerants R236ea, R245fa, R1233zd(E), and water, which gave a net efficiency of the whole power plant of 39.71%, 40.02%, 40.26%, 40.34%, and 39.35% respectively, while the proposed BECCS reference case gave 38.89%.