I have questions regarding MVR evaporation
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I’m a beginner; I’m working on a graduation project related to MVR evaporation and have some questions I can’t figure out. When the secondary steam is compressed by a compressor, it turns into superheated steam which then condenses and releases heat that is used to heat the feed liquid. If the concentration of the feed liquid is too low and the amount of evaporation is too high, this will result in an excessive amount of heat from condensation, far exceeding the heat required by the feed liquid. Can such a situation occur? How can this be solved?
It will happen; this is a process of dynamic equilibrium. If the evaporation rate is too high at a certain moment, it results in excessive condensation heat. The more liquid is evaporated at that time, the feed pump needs to supply more liquid to maintain balance. The entire process is one of dynamic equilibrium – the amounts of feed and evaporation don’t remain constant but rather reach an average level. So there’s no need to worry about the situation you mentioned
Mm-hmm, thank you, I understand now! I would like to ask about the selection of heaters in this MVR system. Since condensation is involved, the heat transfer amount is high, which requires a large heat exchange area. As a result, the number of tubes needed increases. If the feed rate is not high, this will lead to too low a flow velocity inside the tubes, preventing turbulent flow; consequently, the heat transfer coefficient inside the tubes becomes low, resulting in a significant difference from the total heat transfer coefficient assumed earlier. In such a situation, it’s impossible to make an appropriate selection!
You just need to carry out the selection calculations based on normal operating conditions, making sure to include a certain margin of safety. Issues such as a low feed rate may stem from calibration needs or operational problems, rather than the fact that your design does not meet the required conditions; so it’s sufficient to proceed with the selection calculations while taking into account normal operating conditions and including an appropriate margin of safety