Application of mass and energy balances to determine coal, air required and flue gas flow rates in a power plant

Abstract

The primary objective of this study was to determine the heat rate of the power plant using the measurements of critical parameters and MEB calculations. An additional goal of the project was to determine the flue gas and air mass flow rates which influence the efficiency of the coal power plant. The consumption of coal is a critical parameter affecting the efficiency of coal-fired steam boilers. From an operational perspective, the mass flow rate of pulverised coal is a major indicator of the rate of combustion and plant heat rate. However, the cost of electricity production in thermal coal power plants operated by ESKOM, is predominantly influenced by pulverized coal which represents between 60-70% of the total cost. Monitoring the consumption of coal can determine corrective actions which will ultimately improve the power plant’s efficiency, reliability and associated economic benefits. Initially, the fundamental concepts of a boiler and its auxiliaries were studied, which led to the required coal, air and flue gas systems required in a coal-fired boiler plant. From the literature review, it was established that coal consumption is a critical indicator of a plant’s performance in terms of cost and efficiency. The different methods used for the flow measurements of coal, air and flue gas in a coal-fired boiler plant, such as MEB and CFD were reviewed. The MEB method was used to determine the pulverised coal, air, and flue gas mass flow rates and the plant’s heat rate. The MEB method was used to establish a coherent set of input and output data for the boiler, as well as to troubleshoot existing measurements from ESKOM’s coal-fired power plant. The plant’s coal consumption and heat rate results were calculated by means of a Mathcad model that was developed using BMEB methodology. Mathcad was chosen because it allows to visually check calculations. Furthermore ANSYS Fluent was used for the CFD simulation in the secondary air system.