The issue of heat carried in by the flue gas from the waste heat boiler
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Flue gas at 500°C with a flow rate of 33,000 m3/h enters the waste heat boiler for heat exchange, raising the temperature of the exhaust flue gas to 200°C. The heat content of the flue gas at 500°C has already been calculated; what is needed now is to determine the amount of heat carried by this flue gas into the preheating boiler. Enthalpy value multiplied by the volumetric flow rate of flue gas. Is the volumetric flow rate here the volumetric flow rate of the flue gas at 500°C, or is it converted to a volumetric flow rate under standard conditions? At 500°C, the flue gas volume is 33,000 m3/h, while the volumetric flow rate under standard conditions is 7,077 Nm3/h. Which value should be used? I hope everyone can offer some help. Thank you so much
It depends on the value of your enthalpy under that specific condition; it is usually converted to standard conditions, otherwise the volume changes and it becomes difficult to work with
The flue gas volume at 500°C is 33,000 m3/h, while the volumetric flow rate under standard conditions is 7,077 Nm3/h. . . . . Does the poster confirm that your calculations are correct? ? ? The pressure of flue gas is generally close to atmospheric pressure; by ignoring the effect of pressure and considering only temperature changes, your calculation results will definitely be incorrect. . Just use your phone’s calculator to see that your calculations are not reliable; (500+273.15)/273.15=2.83. In other words, under your operating conditions, the flow rate is approximately 2.83 times the flow rate under standard conditions. How many times higher is it for you? It’s 4.7 times. . . . For a flue gas flow rate of 33,000 m3/h (at a gauge pressure of 1–2 kPa), the corresponding standard-condition flow rate should be 11,770 Nm3/h; the flue gas composition is assumed to be 90% air and 10% water. . . The mass flow rate of the flue gas is ~14633 kg/h. If the heat value of the flue gas is taken as 0.27 kcal/kg·℃, it’s easy to calculate the heat released by the flue gas; it’s better not to use the enthalpy value of the flue gas for this purpose, as the benchmarks given in various manuals vary. . . Q=14633*0.27*(500-200)=1,185,273 kcal/h=1.38MW. Let’s do the calculations more carefully; this is a very basic calculation, and theoretically, it falls within the scope of high school physics. . .
I made a mistake; it’s 1000℃. I’m sorry