Measurement of thermal efficiency and energy saving potential analysis for gas-fired boilers under different operation conditions

Based on the measurement data of whole heating season of a heating supply gas-fired boiler station in Beijing, analyses the thermal efficiency, its influencing factors as well as the energy saving potential of gas-fired boilers under different operation conditions. The results show that the centralized heating regulation mode of boiler station in heating season can be classified into quality regulation of changing flow in stages and mass-flow regulation mode. The supply water temperature of the boiler is 80 to 103 ℃, return water temperature is 40 to 53 ℃, load rate of gas-fired boiler in heating season is 45.3% to 95.1%, excess air coefficient is 1.01 to 1.22, exhaust gas temperature is 65.4 to 151 ℃, and thermal efficiency of the boiler with low-caloric value is 92.1% to 96.8%. The thermal efficiency rises first and then decreases with the increase of excess air coefficient. When the excess air coefficient is 1.10, the thermal efficiency of the boiler is the highest. The thermal efficiency increases with the increase of the load rate. When the load rate of the boiler is greater than 84%, the thermal efficiency increases rapidly. When the load rate of the boiler increases by 1%, the thermal efficiency increases by 0.41% to 0.55%. The thermal efficiency increases with the decrease of return water temperature. If the waste heat of exhaust gas is recovered in the boiler and the exhaust gas temperature is reduced to 5 to 10 ℃ higher than the return water temperature, the total thermal efficiency can be improved to 105.2% to 107.6%, and the thermal efficiency in heating season can be improved by 4.8% to 7.5% on average. The boiler with unit capacity (0.7 MW) can save gas of 10 300 to 13 800 m3 during the whole heating season, and also reduce emission of CO2 and NOx. Therefore, the potential of energy saving and emission reduction is considerable for the gas-fired boilers under different load rates when exhaust gas temperature is at 65 to 150 ℃.