Basic principle of MVR evaporation system
MVR evaporators, is English mechanical vapor recompression. MVR evaporation system is reused itself to produce secondary steam energy, thus reducing the energy demand of a technology to the outside world.
Secondary steam, passes through the compressor compression, pressure and temperature to rise, the heat enthalpy increase, be sent to the heating of the evaporator chamber used as heating steam is born, to maintain the material liquid evaporation condition, and the heating steam And condensed water transfer heat to the material itself. In this way, the original to scrap it has made full use of the steam, recycle the latent heat, and improves the thermal efficiency.
In the early 60 s, Germany and France have successfully applied this technology to chemical, pharmaceutical, paper making, sewage treatment and seawater desalination industry, etc.
Its working process is low temperature by the compressor of the steam compression, temperature, pressure, heat enthalpy increase, and then enter the condensing heat exchanger, in order to make full use of the latent heat of steam. In addition to the drive to start, the born without steam in the evaporation process.
Multi-effect evaporation process and evaporator one effect of the secondary steam can't directly as the effect of heat, only as a work or several effect of the heat source. As the effect of heat must be additional to the energy, the temperature (pressure). Compression is only a part of secondary steam, steam jet pump and MVR evaporators is compressible all secondary steam in the evaporator.
Solution in a falling film evaporator, through material circulating pump in heating tube loop. Initial steam with fresh outside the tube to heat, heat the solution to produce secondary steam boiling, secondary steam produced by turbo fan suction, after pressurization, secondary steam temperature increase, as the heat source of heat into the heating chamber circulation evaporation. Normal boot, turbo compressor will be secondary steam inhalation, after charging into the heating steam, so continuous cycle evaporation. The evaporation of water eventually become condensed water discharge.
Due to cost reasons, single-stage centrifugal compressor and high pressure fan is widely used in mechanical vapor recompression system. So the following description is for such design. Centrifugal compressor is a volume control machine, that is, no matter how much suction pressure, volume flow rate is almost constant. And the change of the mass flow rate proportional to the absolute suction pressure.
Single stage centrifugal compressor compression cycle depicted in mollier diagram. Single stage centrifugal compressor need motivation: for example: the saturated water vapor from the evaporator from the suction state p1 = 1.9 bar, t1 = 119 ℃ compression to p2 = 2.7 bar, t2 = 161 ℃ (Π compression ratio = 1.4). Compression cycle along the changeable curve 1 to 2, gaining Δ HP steam enthalpy. For steam enthalpy h2, through the compressor internal efficiency (isentropic efficiency) equation: under this temperature, it enters the evaporator heater. Based on the quantity drawn into steam, kg/hr. HP unit (effective) compression work, mercurial kJ/kg. Hs unit isentropic compression work, kJ/kg. Compressor isentropic efficiency (efficiency) in addition to other factors, HP per polytropic compression work depends on a polytropic exponent kappa and inhalation predominate the molar mass of the gas M, and suction temperature and pressure increase. For prime mover (motor, gas machine, turbine, etc.) of the actual power coupling, and considering the mechanical loss bigger margin. The standard material made of a single stage centrifugal compressor impeller can gain compression factor 1.8 water vapour pressure increase, if use the higher quality of material, such as titanium compression factor can be as high as 2.5.
So that the final pressure p2 is 1.8 times that of the suction pressure p1, or maximum 2.5 times, which corresponds to the saturated steam temperature approximately 12-18 k, the maximum temperature rise to 30 k, depending on the suction pressure. In terms of evaporation technology, typically according to corresponding water boiling point to the pressure. In this way, the effective temperature difference is directly.
