Modelling of cogeneration systems. Part 2: Development of a quasi-static cogeneration model (steam turbine cogeneration analysis)

Abstract

Steam turbine cogeneration analysis (STuCA) is a quasi-static cogeneration plant model that has been developed to simulate steam turbine cogeneration plants subject to varying loads. STuCA was developed to provide potential cogeneration plant users with a model that could simulate part-load performance over the expected operating range of the cogeneration plant using fundamental engineering analysis methods. The model was designed to bridge the gap between static design-point models that could not accommodate part-load conditions and complex part-load models which are too expensive for small scale cogeneration proposals. In addition, the model contains economic analysis tools to analyse the thermoeconomic performance of the plant and to conduct a cash flow analysis. These features are an extension to the static and part-load models. The model consists of four submodels: a load, system, plant and economic model. The load submodel drives the cogeneration plant simulation, supplying utility demands to the system models. The system submodels calculate the steam required by the system components to meet the utility demands. The plant submodel then predicts turbine and boiler performance as they meet the steam demand. The primary plant submodel outputs are the electricity generated and quantity of coal consumed by the boiler, which are used by the economic submodel to conduct a thermoeconomic analysis of the site as well as a discounted cash flow analysis. This method of modelling results in a model that can predict plant performance with respect to varying load and then use those data to conduct a meaningful economic performance analysis of the site.