Modular design and feasibility analysis of a Rankine Compression GasTurbine system for industrial cogeneration
Abstract: A substantial share of the world’s energy is consumed in the form of heat in many distinct industries, which usually generates it through a boiler and consumes the heat by using steam as an energy carrier. In such factories, a cogeneration installation is economically and environmentally beneficial. In this thesis, a new type of cogeneration cycle for industrial biomass-fired boilers is studied, the Rankine Compression Gas turbine (RCG) cycle. Consisting in a combined Rankine and Brayton cycle that can be easily integrated in industries using steam boilers, the system presents clear advantages such as a up to 35% higher power output compared to a simple steam turbine system and a quick demand response in the electricity generation, being able to change its power output within seconds. Firstly, a time-based model is developed by implementing the differential equations that represent the dynamic behavior of all components, culminating in an easy-to-use Matlab-Simulink model; this model presents a robust modular concept, in which distinct systems and equipment can be studied. Then, a 40 kW pilot RCG system and a 100 kW commercial-scale RCG system are designed, aiming to investigate the system’s behavior and select its components. It is proven that most of the RCG components are found as off-the-shelf products and, thus, with reduced cost when compared to customized ones. The simulations show the system advantages and establish key design criteria for the RCG. Finally, an economic feasibility analysis of commercial-scale RCG systems is carried out. Even though the system’s feasibility is considerably sensitive to the electricity cost, capacity factor and fuel cost, the RCG system presents a payback time from 2 to 4 years and a levelized cost of electricity between €0.07 and €0.12 per kWh.
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