Energy-saving analysis of plate heat exchangers
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This post was last edited by ck4ert on 2017-2-4 15:20. Dear masters, happy New Year! I’ve only just started working in this field, and I’ve encountered an engineering problem. I’m seeking advice from everyone here; thank you very much. My factory is a food processing plant that uses an old manufacturing process involving open-type boilers equipped with coiled tubes; steam is passed through these tubes to heat the contents of the boiler. Although this method is simple, it results in high steam consumption. This year, I plan to install a plate heat exchanger, and I need to calculate its energy-saving efficiency. My calculation logic is as follows: since the heat transfer efficiency of the coil is relatively low, the temperature of the steam remains high after passing through the coil; this results in a higher drainage temperature from the steam trap, and this occurs over an extended period of time, as the steam dissipates through the pipes in the space. If I ignore the air emission component and only consider the drainage temperature of the steam trap, the actual temperature for the pot steam trap is around 85°C. If the inlet temperature is set at the saturation temperature of 150°C, the heat released in this process is equal to the latent heat of vaporization, which is 2118.5 KJ/KG, plus 4.2*(150-85) = 273; in total, this amounts to 2391 KJ, with the majority of this amount being heat released due to vaporization. If a plate exchanger is used, I measured the temperature of the steam trap to be around 45°C. The heat of vaporization remains the same at 2118.5 KJ. However, the heat loss due to the cooling of water is 4.2 * (150 – 45) = 441 KJ; in total, this amounts to 2559.5 KJ. The difference between the two seems to be only the energy difference related to water; I don’t think it’s that small. Could there be some energy losses that haven’t been taken into account?
This post was last edited by wiseboy on 2017-2-4 23:43. Your calculation logic is correct; there is little point in modifying the heat exchanger. The essential (more accurately, intrinsic) energy-saving efficiency lies in the use of new production process technologies, rather than being a problem with the heat exchangers. ““I don’t think it’s that little” — it is that little; you’re wrong, the calculation is correct!
First, is it related to the interstitial space to be heated by plate heat exchange?； Secondly, since it is an open-boiling pot, the heating temperature does not exceed 100°C. The steam pressure at 150°C (with a pressure of about 3.8 barg) is too high, which is not conducive to energy savings ； Third, the temperature of the condensate water at the outlet of the heat exchanger is low; a value of 45°C, as you mentioned, indicates the presence of water accumulation inside, which affects efficiency and can lead to water hammer effects, as well as having an impact on the equipment’s lifespan. It is estimated that there is an issue with the selection of the steam trap ； Finally, the optimal state is——increased efficiency, energy savings, stable equipment operation, and a long service life. For more information, please visit the WeChat official account \"Fured Steam Energy Saving\" or log in to the official website with the same name.
There is also the issue of discharge volume; the discharge volume per unit time of a plate heat exchanger is much higher than that of an open-type boiler, so the heat exchanger should be considerably more efficient than the boiler.
If the steam temperature is too low, it will result in a longer heating time, which in turn leads to a large amount of heat being released into the space; therefore, the temperature cannot be too low either.
The original poster’s calculations are correct; the difference between plate exchangers and tube exchangers lies in the floor space occupied by the equipment and its heat transfer coefficient. The total amount of heat transferred remains constant, but the heat flux density of plate exchangers is slightly higher
The steam pressure decreases, the latent heat increases, and the heat released per unit of steam increases; of course, it cannot be reduced too much. In this case, the factor that truly affects the heating rate is the hydrophobic effect. ------Freed steam energy saving.