In the biological and chemical industries, companies are equipped with high-pressure steam boilers as heat sources for evaporation systems, drying systems, sterilization systems, and heating systems. Evaporation technology is a very energy-consuming unit operation. During this operation, more secondary steam is generated. If it is directly discharged, not only the latent heat of the steam is wasted, but some materials also flow out of the system along with the secondary steam, which will cause a certain amount of damage to the environment. Pollution. China's traditional industry is still quite serious in terms of energy consumption and waste of system waste heat, of which only about 30% of waste heat and waste heat are recycled and recovered. Therefore, recycling of waste heat and recovery of waste heat is one of the important links of energy saving and emission reduction, and it is also a necessary measure to reduce costs, environmental protection and increase efficiency.
Evaporation technology is a process in which a large amount of volatile solvents are endothermically vaporized by heating a dilute solution, thereby achieving the concentration of non-volatile solutes. It is widely used in the chemical industry, wastewater treatment, seawater desalination, purification of fermentation products, and Food processing production.
As an important operating unit in the biochemical industry, the evaporation process has experienced single-effect evaporation technology, multi-effect evaporation technology, steam jet compression evaporation technology, and mechanical vapor recompression technology (MVR evaporation technology).
From the structural point of view, the multi-effect evaporator uses multiple single evaporators connected in sequence through pipes, and uses the secondary steam generated by the previous effect as the heating steam of the next effect stage, thus repeatedly using the secondary steam. Therefore, the total consumption of raw steam is correspondingly reduced, and the operating cost is reduced accordingly. In the actual design and production process, it is necessary to consider the investment of equipment and operating energy consumption in order to choose a good evaporation efficiency level.
The MVR evaporation technology was proposed by foreign scholars in 1834. Until 1917, the Swiss Sulzer-EscherWyss company initially manufactured a simple MVR system, which was designed and installed by an Austrian company in 1925. China only introduced MVR equipment for the first time in 1989, and listed MVR technology as an energy-saving and environmentally-friendly equipment that the country strongly encourages and supports in 2007 and 2010. In the past ten years, under the government's vigorous efforts to promote energy conservation and emission reduction, and innovative research by enterprises and scientific research units, MVR evaporation technology has shown a booming situation in China.
The core of MVR evaporation technology is a form of fully utilizing the secondary steam generated in the evaporation system, thereby reducing or even not using external steam. The structure is similar to connecting the single-effect evaporator and the compressor through a pipeline to form a loop. Its process feature is that all the secondary steam generated in the section where the solution is in communication with the evaporator is fully recovered and used as a heat source to process the liquid material. The equipment that completes this function is the steam compressor. Secondary steam is low-grade, low-pressure, low-grade steam, which cannot be directly used as a heat source by the system. It can be converted into high-grade, high-pressure, high-grade steam by steam compressor processing and used.
As an evaporation system, MVR is a relatively closed internal circulation system. According to the different requirements of evaporation products and the variability of process conditions, the specific structure and equipment composition of MVR are slightly different, but from the perspective of the principle of MVR operation, it mainly consists of preheater, evaporator, gas-liquid separator, and steam compressor. , Vacuum pump and cleaning system and other related equipment, in which the steam compressor and evaporator are the core components of the MVR system.
In terms of energy consumption, MVR evaporation technology mainly uses a small amount of electrical energy to replace steam thermal energy, and the energy efficiency ratio of electrical energy is much smaller than that of steam. The use of motors has replaced the traditional boiler room, which has a smaller impact on the environment. In the treatment of secondary steam, it is fully recycled, eliminating a lot of cooling water resources. MVR evaporation technology is equivalent to half the energy consumption of a four-effect evaporator and 66% less energy than a three-effect evaporator.
From the perspective of energy consumption , multi-effect evaporation uses externally generated steam, while MVR technology only needs to consume a small amount of steam, mainly based on power consumption;
From the perspective of application fields , the MVR evaporation technology can completely replace the multi-effect evaporator in most cases, but it is not easy to use the MVR technology for some solutions containing high corrosive ions;
From the perspective of exhaust gas treatment , although multi-effect evaporation uses secondary steam multiple times, the exhaust gas also needs to be evacuated through condensation, which not only wastes steam energy but also consumes a large amount of circulating water;
From the perspective of equipment volume , the more effective the multi-effect evaporator, the larger the footprint, and the MVR technology is only equivalent to adding a compressor to the volume of the single-effect evaporator, and the pipeline connection is more compact. Increase the evaporation area of the evaporator and increase the power of the compressor to flexibly design the throughput.