MVR is the abbreviation of mechanical vapor recompression technology, which uses the secondary steam and its energy generated by the evaporation system to upgrade the mechanical work of low-grade steam through the compressor to high-grade steam heat source. This cycle provides heat energy to the evaporation system, so as to reduce the demand for external energy.
However, in many cases, we can not directly use the compressor to compress the evaporated secondary steam. On the one hand, the secondary steam is a mixed gas, which contains a certain amount of incompressible gas, which accounts for a relatively high proportion. On the other hand, it may contain highly corrosive gas, which causes greater corrosion to the compressor impeller. Therefore, when we still want to use the MVR system in this case, It is necessary to find another way to transfer the heat of the secondary steam to the water supply, that is to say, the evaporated secondary steam does not directly enter the evaporator, but enters the circulating water heater, uses the vaporization latent heat of the secondary steam to increase the temperature of the circulating water, and then enters the flash tank to flash out part of the steam, and then enters the compressor after separation. Through doing work, the compressor reduces the temperature of the steam As the temperature and pressure increase, it enters the heater again as the heating steam, thus circulating. This not only solves the problem of incompressible gas, but also solves the direct contact between corrosive gas and compressor impeller. The corrosion of the impeller is greatly reduced and the service life of the compressor is improved.
The evaporated secondary steam enters the scrubber to wash away the incompressible gas and corrosive gas, and the remaining water vapor with higher purity can be compressed by the compressor. However, the scrubber can not completely remove the desired gas, but only reduce the concentration. In addition, it is expensive, so it is more appropriate to transfer heat to the treated softened water.