Techno-Economic Comparison of Simple and Cascade Organic Rankine Cycle for Distributed Energy

Abstract

In this paper, two power plant configurations for distributed energy, simple and cascaded Organic Rankine Cycle (ORC), were proposed, modeled, analyzed and compared from a technical and economic point of view. It is proposed to use rice husks from a typical mill in Nigeria as fuel for the operation of the power plant, while the working fluids for the studied ORC plants are toluene and R245fa refrigerants. Power plants are modeled on the basis of fundamental technical and economic approaches. At the same time, power generation, as well as energy and exergy efficiency were selected as key technical parameters for the study. The desired economic parameter determines the cost of a unit of energy. It has been established that with proper use of rice husks as a renewable energy source, the energy generated by the ORC power plant can help to meet 27–38 MWh daily needs of the rice factory and its surroundings. The results of the analysis of the energy and exergy efficiency of a simple and cascade ORC power plant as presented indicates a better prospect for the latter. The working/thermal capacities of the plant elements and the loss of exergy in them are analyzed. The directions of increasing the efficiency of the rice husk power plant have been identified, primarily by improving high-temperature heat exchangers. The results of an economic analysis of the viability of the simple and cascade ORC power plants are presented. A simple ORC demonstrates the best economic performance with a unit energy cost of $0.115 per kWh compared to $0.124 per kWh of a cascade ORC. However, a holistic study of technical, economic, social and environmental indicators creates prerequisites for the research and development of a cascade ORC installation. The paper also presents the results of an analysis of the sensitivity of plant performance on the volume of annual production of rice husks, the temperature of the exhaust gases at the outlet of the chimney and the coefficient of the import tariff. A feasibility study of the prospects of the proposed technical solution for poorly electrified countries is presented.