The two steam of a certain effect can not be directly used as the heat source, and can only be used as a secondary or secondary heat source. Such as the effect of the heat source must be added to its energy, so that its temperature (pressure) increased. Steam jet pump can only compress part of the two steam, while the MVR evaporator can compress all two steam in the evaporator. The working process of the MVR evaporator is the compression of the low temperature vapor through the compressor, the temperature and the pressure are increased, the enthalpy is increased, and then the Heat Exchanger
is condensed to make full use of the latent heat of the steam. In addition to start-up, the whole evaporation process without steam.
The compression cycle of single stage centrifugal compressor is depicted in the enthalpy entropy diagram. Power required for single stage centrifugal compressor:
For example: from the evaporator saturated steam from the suction state of p1=1.9 bar, t1=119 C compression to p2= 2.7 bar, t2=161 C (compression ratio pi = 1.4). The compression cycle along the changing curve of 1 - 2, steam enthalpy increase hp. For the vapor specific enthalpy H2, the efficiency of the compressor (isentropic efficiency) equation: at this temperature, it enters the evaporator heater. Based on the amount of inhaled steam, kg/hr. HP units varied (effective) compression work, kJ/kg. HS unit isentropic compression work, kJ/kg.
In addition to other factors, the isentropic compression efficiency (HP) of the compressor depends on the mass index M and the molar mass of the suction gas, as well as the suction temperature and the required pressure rise. For the actual coupling power of the prime mover (motor, gas turbine, turbine, etc.), a greater mechanical loss margin is considered. A single stage centrifugal compressor made of standard material can obtain the water vapor pressure rise of compressibility factor 1.8. If the material is made of titanium, the compressibility factor can be as high as 2.5. As a result, the final pressure P2 is 1.8 times the suction pressure P1, or the maximum of 2.5 times, which corresponds to the saturated steam temperature increase of about 12-18K, the maximum temperature rise can be 30K, depending on the suction pressure. In the case of evaporation, the usual practice is to represent the pressure at the boiling point of the water. In this way, the effective temperature difference is directly expressed.
MVR evaporator uses the compressor to increase the energy of the two steam, and to improve the energy of the two steam to be used to recover the latent heat of the two steam. Specifically: two steam generated by the evaporator, compressor adiabatic compression, increase the pressure, temperature, heating chamber, and then as the heating steam into the evaporator condensate heat, so the latent heat of steam has been recycling. Before the cold material enters the evaporator, the heat of the condensed water is absorbed by the heat exchanger, so that the temperature is increased, and the condensed liquid and the finished liquid are cooled.
Taking concentrated industrial wastewater as an example, firstly, industrial waste water enters the preheater along the pipeline. Then the industrial wastewater is introduced into the evaporator after preheating, in the evaporator, the industrial wastewater will be heating, evaporation and concentration, ultimately, the heating steam is condensed to form a distilled water to the distilled water collecting tank, and two steam and concentrate together into a liquid separator. In the vapor liquid separator, the concentrate is separated from the two steam, and finally, the concentrate flows into the concentrate collection tank, and the separated two steam is introduced into the mechanical compressor. In the mechanical steam compressor, through the two steam compression, temperature, pressure, and introduced into the evaporator, and then the industrial waste water heating, concentration, evaporation, distillation treatment. In the end, the process of the whole industrial wastewater treatment is completed by using two times of steam, and the dual goal of industrial wastewater treatment and energy saving is realized.
MVR evaporator solution in a Falling Film Evaporator
, through the material circulation pump in the heating pipe circulation. Initial steam for heat in the tube with fresh steam, heating the solution boiling steam to produce two, two steam generated by inhalation of turbo fan, after pressurization, two steam temperature increases as the heat source into the heating chamber circulation evaporation. After the normal start, the turbine compressor will be two times the steam inhalation, after the pressure into the heating steam, so that the continuous circulation of evaporation. The evaporated water into condensed water discharged from the evaporator of two steam, compressed by the compressor, pressure, temperature, enthalpy increase, and then sent to the heating chamber of the evaporator as heating steam, feed liquid to maintain the boiling state, and heating steam is condensed into water. In this way, the original abandoned steam is fully utilized, the latent heat is recovered, and the thermal efficiency is improved, and the economic efficiency of the steam is equivalent to the 30 effect of the multi effect evaporation. In order to make the manufacturing evaporation device as simple as possible and easy to operate, often use a single effect and centrifugal compressor, also can be a high pressure blower or compressor turbine. These machines have a high volume flow in the 1:1.2 to 1:2 compression ratio range. For a low evaporation rate, a piston compressor, a sliding vane compressor or a screw compressor can also be used.
Due to cost reasons, single stage centrifugal compressors and high pressure fans are widely used in mechanical vapor compression systems. Therefore, the following instructions are designed for such. Centrifugal compressor is a volume control machine, that is, no matter how large the suction pressure, the volume flow rate remains almost constant. The change of mass flow rate is proportional to the absolute suction pressure.