What is boiler feedwater temperature?
What is boiler feedwater temperature?
The boiler feedwater temperature refers to the inlet water temperature of the economizer, and when there is no economizer, it refers to the inlet water temperature of the boiler drum. Raising the boiler feedwater temperature can correspondingly improve boiler efficiency. There are several steps to increase the feedwater temperature, including steam extraction and heating from the turbine, reheating from the boiler economizer, and maximizing the use of heat loss to increase the feedwater temperature. The higher the boiler water temperature, the less fuel loss there will be, resulting in higher boiler efficiency. The impact of increasing feedwater temperature on boiler thermal efficiency can be discussed in two situations. The first scenario assumes that the boiler evaporation rate remains constant. When the feedwater temperature increases, the economizer reduces the heat absorption due to the decrease in heat transfer temperature difference. The flue gas temperature at the outlet of the economizer increases, the temperature and pressure of the air preheater increase, the heat transfer increases, and the hot air temperature slightly increases. The increase in exhaust temperature leads to a decrease in the thermal efficiency of the boiler. But as the temperature of the feedwater increases, the amount of heat used for evaporation also increases, resulting in an increase in evaporation capacity. In order to maintain a constant evaporation rate, it is necessary to reduce the amount of fuel, which lowers the exhaust gas temperature and improves the thermal efficiency of the boiler. Due to the similar impact of these two factors on boiler efficiency, when the boiler evaporation rate remains constant, the feedwater temperature increases and the boiler thermal efficiency remains basically unchanged. The second assumption is that the fuel quantity remains constant. When the feedwater temperature increases, the temperature and pressure of the economizer decrease, the outlet flue gas temperature of the economizer increases, the heat absorption of the preheater increases, the exhaust gas temperature increases, and the boiler thermal efficiency decreases. Due to the increase in hot air temperature, the furnace temperature rises and the heat absorption of the water-cooled wall increases.