Seeking advice on calculating the heat transfer area of a shell-and-tube heat exchanger
Thread Content
There is an ethanol recovery unit with a recovery rate of 350 kg/h; estimate the area of the heat exchanger. Cool with circulating water at 20°C. Atmospheric distillation. It would be best to have a calculation process, thank you.
Phone consultation: 13934223203
The process parameters provided are incomplete; what are the temperature, pressure, and composition of ethanol as it enters the cooler?
Room-temperature ethanol, in a solution of about 55%, is heated to 78°C in a reboiler via a steam coil and then cooled to atmospheric pressure in a condenser.
This requires design work; just posting a thread won’t solve the problem. Is there still a future in the design industry? I had nothing to do, so I calculated it to practice a bit. I’m not an expert; I’m posting this here for experts to give their feedback. The relative volatility a is taken as 1.0/0.45 = 2.2 (referencing the saturated vapor pressures of ethanol and water at 18°C). The ethanol content in the distilled gas is y = 2.2*0.55/【1 + (2.2 – 1)*0.55】 = 72.9%. The amount of water distilled is 350*（1 – 0.729） = 95.8 kg. The temperatures are T1 = 78°C for ethanol and water, and T2 = 35°C. For the circulating water, the temperatures are t1 = 20°C and t2 = 30°C. The average temperature difference ΔT = 【（78 – 30）–（35 – 20）】/ln【（78 – 30）/（35 – 20）】 = 28.4°C. As for the overall heat transfer coefficient, values ranging from 1400 to 4200 W/(m²·°C) are typical for water-water vapor condensation processes; thus, 2000 W/(m²·°C) is chosen. The vaporization heat of ethanol at atmospheric pressure is 38735 kJ/kmol, and its latent heat is 350*38735/46/3600 = 81.9 kW. The vaporization heat of water at atmospheric pressure is 40647 kJ/kmol, and its latent heat is 95.8*40647/18/3600 = 60.0 kW. The sensible heat change is 78 – 35 = 43°C. For ethanol, it’s 43*73.9/46*350/3600 = 6.7 kW, while for water it’s 43*34/18*95.8/3600 = 2.2 kW. The total heat quantity Q is 150.8 kW. The heat exchange area A is calculated as Q/(K*ΔT) = 150.8*1000/(2000*28.4) = 2.65 m². It would be advisable to use a heat exchanger with an area of 3–5 m²
Are you trying to calculate for a reboiler, a condenser, and whether there is reflux in the distillation process?