Abstract:

Fired heater efficiency can be improved by decreasing the stack heat loss and reducing the setting heat losses. Compare the calculation results of two fired heaters with the same heat duty. When stack temperature is 80 ℃, the stack heat loss accounts for 3% of total heat release. If the proportion of stack heat loss is reduced to 2%, the outlet temperature of flue gas will be close to the dew point temperature of the air, a large amount of water of flue gas will condense, it is impossible to avoid problems such as dew-point corrosion. When the design temperature of the outside casing of fired heater is 80 ℃, the total heat dissipation of the system may be more than 3% of total heat release, with the heat dissipation of waste heat recovery system accounting for more than 1%. When the ambient wind velocity is 2 m/s, the proportion of the heat dissipation will increase by 0.3 percentage points. When the design temperature of the outside casing is 65 ℃, the total heat dissipation of the system may be 2.5% of total heat release, with the heat dissipation of waste heat recovery system accounting for about 1%. When the heat intensity of the fired heater is higher, the outside casing of the fired heater will be smaller, the heat dissipation will be smaller, and the actual operating efficiency of the fired heater will be higher.

Key words: fired heater, stack heat loss, setting heat losses, heat efficiency, excess air coefficient, fuel composition, radiant heat transfer coefficient, furnace outside casing temperature

摘要： 提高加热炉热效率需要进一步降低排烟热量损失、减少炉体散热损失。文中对负荷相当的两台加热炉进行计算分析。当排烟温度为80℃时，排烟热量损失占比约为3%;若要将排烟热量损失占比降为2%,则排烟温度接近空气的露点温度，会产生大量凝结水，将会出现露点腐蚀等问题。当设计外壁温度为80℃时，系统总散热损失可能大于放热量的3%,其中余热回收系统散热损失占比大于1%;在环境风速为2 m/s的工况下，系统总散热损失占比约增加0.3百分点。当设计外壁温度为65℃时，系统总散热损失占比约为2.5%,其中余热回收系统散热损失占比约为1%。加热炉热强度越高，炉体结构尺寸越小，散热损失越小，实际运行时加热炉热效率越高。

关键词: 加热炉, 排烟热量损失, 炉体散热损失, 热效率, 过剩空气系数, 燃料组分, 辐射传热系数, 炉外壁温度