Selection of MVR centrifugal compressors
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The existing two-effect MVR evaporators are designed based on equal temperature differences: the evaporation temperature in the first effect is 140 degrees, that in the second effect is 110 degrees; the saturated steam temperature in the first effect is 170 degrees, and that in the second effect is 140 degrees. The evaporation capacity of the second stage is 10,756.65 kg/h. How should a centrifugal compressor be selected to achieve a temperature increase of 60 degrees? What parameters need to be calculated during this selection process? What factors need to be considered when designing multi-stage compression? It's for a graduation project, not an engineering issue.
Two stages – is multiple compression still needed? This creates a contradiction. Generally, single-effect evaporation is used, with a large temperature difference; therefore multi-stage compression is chosen ； Alternatively, if the temperature rise of the compressor is high (15–20 degrees), the heat transfer temperature difference required for evaporation is only 8–10 degrees; in such cases, two-effect evaporation is chosen. Economics must be taken into account for everything.
The processing capacity is 21,000 kg/h; with a small temperature difference, the heat exchange area would have to be very large. Therefore, a temperature difference of 30 degrees was chosen. By using two-stage evaporation, the temperature difference between the stages becomes 60 degrees, which necessitates the use of two-stage compression. It’s just the topic for the graduation project; I probably haven’t considered many practical aspects. Please forgive me!
It is theoretically feasible; we have carried out 3-stage modifications and provided two-stage compressors with a temperature rise of 32°C. It is not practical to change it to 2 stages for a 60°C temperature rise – reducing the heat exchange area while increasing the temperature difference leads to high operating energy costs, which is not cost-effective in the long run
For such a scale of evaporation, centrifugal compressors are generally used, with the compressor temperature rise being at most 22-25 degrees℃； Two-stage series connection also cannot achieve what you have designed. For such a large temperature difference, multi-effect evaporation is generally used, with steam as the heat source. Then, generally, a large heat transfer temperature difference of 30°C is not adopted in order to reduce the heat transfer area, as this can easily lead to coking and scarring of the heat exchanger. Generally, the temperature difference for heat exchangers is set at 8-12°C. A graduation project that is detached from engineering practice appears unprofessional. I’m not very professional; it’s just my personal opinion, so please point out any mistakes.