SENSITIVITY ANALYSIS OF PERFORMANCE OF COAL-FIRED POWER PLANTS TO STEAM, COAL AND ENVIRONMENTAL PARAMETERS
In the Indian context, coal continues to be the dominant supplier of electrical power, and is highly regarded as a power source due to its availability and reliability. On the other hand, coal-fired power plants account for a significant amount of conventional air pollutants such as particulates, NOx and SOx; they also emit large amounts of CO2, which is a major greenhouse gas. There is considerable scope for improvement in the efficiency of the power plants by operating at various conditions. In the present study, a detailed assessment is made of three factors, namely, steam parameters, ash content of coal, and environmental condition in the sense of ambient temperature which can vary considerably over the course of a year. A conventional pulverized coal (PC) boiler plant operating on Pittsburgh coal is used as a reference case. Simulations incorporating first law analysis have been carried out for three supercritical steam parameters, high-ash washed and unwashed Indian coals containing 31.9 and 47.8 wt% ash, respectively, and for three ambient temperature conditions, namely, 40, 33 and 25 °C. The performance analysis showed a net thermal efficiency of 35.8% for a subcritical boiler using Pittsburgh coal. The efficiency is found to increase by 1 to 5% with advanced steam parameters corresponding to supercritical and ultra-supercritical steam conditions. The net efficiencies are found to be 36.3, 37.5 and 38.5% for operating condenser temperatures of 43.97, 33, 25°C, respectively. This indicates a loss of nearly 2% on the absolute scale when the ambient temperature is increased from 25 to 40 °C. Coal washing is found to have a slightly less pronounced effect. The efficiency for a supercritical PC boiler increases from 38.6% to 39.3% as the ash content is decreased from 47.8% to 31.9% by weight.
These calculations show that there is considerable effect of environmental factors on the thermal efficiency of coal power plants. In a hot country like India where the peak power demand is in summer, high ambient temperatures may cause significant decrease in the efficiency of a coal-fired thermal power plant.