How is the water flow rate for the flue gas quenching device calculated?
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For a flue gas quenching tower, the following values are known: the inlet flue gas flow rate is 25,481 cubic meters per hour (under normal operating conditions), the temperature of the flue gas is 550 degrees Celsius (with a enthalpy of 800 KJ). Softened water is used to reduce the temperature of the flue gas, resulting in an outlet temperature of 200 degrees Celsius (with an enthalpy of 280 KJ). The temperature of the inlet water is 25 degrees Celsius. It is necessary to calculate the amount of water required, under conditions of atmospheric pressure. My question is: is the heat released by the flue gas calculated using 25481X(800-280), or is it necessary to determine the amount of flue gas at 200 degrees Celsius, which is approximately 14645. The calculation process is 25481X800 – 14645X200. The heat absorbed by water can be determined by adding the sensible heat from room temperature to 100 degrees, the latent heat of vaporization, and then the superheat from 100 to 200 degrees. I understand this part. But how should the heat released by the flue gas be calculated? Please help me with that.
This post was last edited by wiseboy on 2018-10-24 08:42. In fact, if cooling is achieved by mixing smoke with water, neither of these two algorithms is correct. Assuming that, after mixing, all of the water sprayed in vaporizes, the flue gas exiting contains a mixture of flue gas and water vapor (Tm=200°C). Using scientific methods, and relying only on knowledge from middle school physics, the heat balance equation can be written as: W1·C1(Tm–T1) + W2 = 0. Here, W1 represents the flow rate of the flue gas, in kg/h ； W2——Water flow rate, kg/h ； T1 – Flue gas inlet temperature, °C; T2 – Water inlet temperature, °C; C1 – Specific heat of flue gas, kJ/(kg·°C); C2 – Specific heat of water, kJ/(kg·°C); △H – Vaporization heat of water at 200 °C, 1943.5 kJ/kg. It is derived that: W2={C1(T1-Tm)/}W1 – this is the calculation formula! Remember: Both W1 and W2 are mass flows. You convert the volume flow rate V into a mass flow rate W using the density ρ: W = V·ρ. Where: ρ – density, in kg/m3. Example: W1=20000 kg/h; W2={2.0X(550-200)/+1943.5}X20000=5227 kg/h. A qualified high school graduate can derive this formula on their own. So don’t always say that what you learn at school is useless, and mock yourself by saying you give it back to the teachers.
This post was last edited by wiseboy on 2018-10-23 08:41. It has been modified to take vaporization into account.
The calculation formula has been modified to take vaporization into account.
Was a zero missed in the calculation? The result should be 5226.8
You’re right, I’ve made the changes.
There is an exhaust fan behind the quench tower, and the quench tower operates under a slight negative pressure. I would like to ask whether the vaporization heat of water should be calculated based on the saturation temperature corresponding to this slight negative pressure, rather than using 200°C
For incinerator systems, there is generally a slight negative pressure of -100 Pa; it can be calculated as atmospheric pressure.
5 tons of water per hour, but I don’t need that much water.