Vacuum issues in MVR systems
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This post was last edited by skyhhl on 2016-1-28 at 15:29. MVR negative-pressure evaporation requires vacuum creation; if a compressor alone cannot achieve the desired level of vacuum, can a vacuum pump be added to increase the vacuum level? If so, how should it be operated effectively to maximize steam recovery?
Connect the inlet of the compressor to the outlet of the vacuum pump. For vacuum pumps, oil pumps and water pumps cannot be used; rotary vane pumps and vortex pumps are possible options, which essentially functions as adding an additional compression stage
We’re not sure whether it will meet the requirements in actual operation; our requirement is a gauge pressure of -40 kPa, but the manufacturer says that using a rotary vane blower for single-stage compression can only achieve around -25 kPa
Vacuum pumps are primarily used to remove the non-condensable gases inside; once those gases are removed, the vacuum is achieved
You can see this system in person; it comes with a small vacuum pump
I saw that you have some questions regarding the steam compressors in MVR systems, so I’ve answered them all together. The vacuum level in an MVR system can be established using a compressor, with a maximum level of -45 kPa. If this negative pressure value is exceeded, a vacuum pump can be used as an auxiliary device; it can be placed in front of the condensate tank. This way, very little steam will be emitted, and once the desired negative pressure level is achieved, the vacuum pump does not need to run continuously – it only needs to be turned on periodically to remove any non-condensable gases.
Then, if the vacuum pump draws only non-condensable gases, and the pumping speed is greater than the evaporation rate of those non-condensable gases, the vacuum pump will also draw in water vapor; wouldn’t this reduce the amount of vapor available for evaporation and heat exchange? Won’t the processing capacity of the entire system be affected?
The pumping capacity of the vacuum pump can be adjusted using valves, so there’s no need to worry about too much steam being pumped out. However, be sure to calculate the heat exchange area of the condenser carefully; if it is too large, it will result in losses, while if it is too small, some of the steam will be drawn away by the vacuum pump.