Optimisation criteria of a Rankine steam cycle powered by thorium HTR
Van Niekerk, Steven Cronier
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HOLCIM has various cement production plants across India. These plants struggle to produce the projected amount of cement due to electricity shortages. Although coal is abundant in India, the production thereof is in short supply. It is proposed that a thorium HTR (100 MWt) combined with a PCU (Rankine cycle) be constructed to supply a cement production plant with the required energy. The Portland cement production process is investigated and it is found that process heat integration is not feasible. The problem is that for the feasibility of this IPP to be assessed, a Rankine cycle needs to be adapted and optimised to suit the limitations and requirements of a 100 MWt thorium HTR. Advantages of the small thorium HTR (100 MWt) include: on-site construction; a naturally safe design and low energy production costs. The reactor delivers high temperature helium (750°C) at a mass flow of 38.55 kg/s. Helium re-en ters the reactor core at 250°C. Since the location of the cement production plant is unknown, both wet and dry cooling tower options are investigated. An overall average ambient temperature of India is used as input for the cooling tower calculations. EES software is used to construct a simulation model with the capability of optimising the Rankine cycle for maximum efficiency while accommodating various out of the norm input parameters. Various limitations are enforced by the simulation model. Various cycle configurations are optimised (EES) and weighed against each other. The accuracy of the EES simulation model is verified using FlowNex while the optimised cycle results are verified using Excel’s X-Steam macro. It is recommended that a wet cooling tower is implemented if possible. The 85% effective heat exchanger delivers the techno-economically optimum Rankine cycle configuration. For this combination of cooling tower and heat exchanger, it is recommended that the cycle configuration consists of one de-aerator and two closed feed heaters (one specified). After the Rankine cycle (PCU) has been designed and optimised, it is evident that the small thorium HTR (100 MWt) can supply the HOLCIM plant with the required energy. The optimum cycle configuration, as recommended, operates with a cycle efficiency of 42.4% while producing 39.867 MWe. A minimum of 10 MWe can be sold to the Indian distribution network at all times, thus generating revenue.
- Engineering