Please ask an expert for help-------Steam heat exchange problem
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We have a heat exchanger here that is heated using steam at 0.8 Mpa (175 degrees Celsius); I would like to switch to steam at 0.4 Mpa (143°C). The material being heated has a specific heat capacity of 2020 kj/kg·K, and its temperature needs to be raised from 50°C to 150°C, for a mass of 1500 kg. The heat transfer amount Q = 2020*100*1500 = 303*10^-6 joules. The return water from the 0.8 Mpa steam system is sent to a flasher, where it is converted into steam at 0.2 Mpa; the back pressure of the trap is 0.4 Mpa. After being converted to steam at 0.4 Mpa, the return water goes into the warm water pipeline at atmospheric pressure. In my calculations, since they are approximate, I did not take into account the sensible heat – only the latent heat was considered. The enthalpy of steam at 0.8 Mpa is 2768, while it is 2738 at 0.4 Mpa. The energy calculated for mass at 0.8 Mpa is 303*10^-6 joules, with a mass of 109 kg; for mass at 0.4 Mpa, the corresponding energy is also 303*10^-6 joules, with a mass of 110 kg. Is the heat difference between steam at 0.8 Mpa and steam at 0.4 Mpa really that small? Is my calculation process correct? Could some expert give me some advice?
You must be referring to superheated steam. There is indeed not much difference in heat content between steam at 0.8Mpa and steam at 0.4Mpa. To reduce pressure, low-temperature heat can be utilized; however, the lower the temperature, the smaller the temperature difference for heat transfer, which in turn requires a larger area of heat exchange equipment. There is an economic aspect here – it is necessary to determine which type of steam is more cost-effective.
Could you please take a look? I think there’s no mistake in my calculation method – is it correct to use Heat transfer capacity of the material = Mass of steam * Enthalpy value of steam?
There’s no problem in calculating the steam consumption, but has the original poster considered whether the heat exchange area of the heat exchanger is sufficient? Since you have reduced the steam pressure, the temperature difference between the hot and cold streams is smaller; it is necessary to check whether there is sufficient heat exchange area available.
Suddenly, I saw that the client wanted to heat the material to 150°C; steam at 0.4 Mpa (143°C) is not sufficient to raise the material to this temperature.
Draw a schematic diagram of the heat transfer temperature difference, ensuring that the temperature variation line of the steam does not intersect the temperature variation line of the material. The former should be above
I see now; I overlooked an issue. As long as the calculations are correct, that’s fine
I haven’t drawn this diagram of the heat transfer temperature difference before; I’ll go check it on Baidu. Thank you very much