1 condensation evaporator connected with upper and lower towers
Arrange multiple plate units in a single layer, or add auxiliary condensation evaporator to the tower. This kind of layout is the most conventional one, which is convenient to install, simple to arrange the pipeline, and also saves more space.
2 separately arranged condensing evaporator
Put several plate units in parallel in a cylindrical container, and connect them with the upper and lower towers by pipes, which is a single arrangement of condensing evaporator. This kind of structural form condensing evaporator is separated from the upper and lower towers, which is not limited by cross section, but increases equipment investment cost and pipeline configuration.
3 multilayer or double layer condensing evaporator
Arrange multiple Plate-fin Heat Exchanger (main cooling unit) between the upper and lower towers according to the configuration of upper and lower layers, and make the limited section layout as large as possible of heat exchange area, making the diameter of the condensing evaporator roughly the same as that of the upper and lower towers, and operating with variable load is beneficial to obtain better operational stability and reliability, and convenient for transportation, which is a relatively practical structure. Its disadvantages are complex structure and difficult manufacture and installation.
4 high heat flow tube shell condensing evaporator
This condensation evaporator has a porous thin layer on the boiling side of the inner surface of the tube, and the condensation side of the outer surface of the tube is a longitudinal groove. Because the phase change heat transfer on both sides is enhanced, the total heat transfer coefficient is improved, the heat transfer temperature difference is reduced, and the energy consumption of the equipment is reduced. Meanwhile, due to the high circulation rate of liquid through the porous surface, it can effectively prevent the explosion danger caused by partial concentration and accumulation of acetylene and hydrocarbon, which is beneficialAir separation equipmentSafe operation. But its cost is high.
5 membrane condensing evaporator
The main cooling is placed above the liquid oxygen surface, and the liquid oxygen is pressed into the main cooling through the liquid oxygen pump. It flows through the adjacent channel of the main cooling from top to bottom like the air nitrogen, and conducts heat exchange to make the liquid oxygen evaporate and the air nitrogen condense. Because the liquid oxygen in the main cold channel is membrane-like downstream and evaporates, it is called membrane condensation evaporator. Since there is no pressure difference established by the liquid oxygen column in the condensing evaporator, the boiling point of oxygen remains unchanged, so that the temperature difference of oxygen and nitrogen on both sides of the main cooling is consistent all the time.
Since the liquid oxygen column is canceled in the main cooling, the temperature difference of the main cooling can be reduced, and the air pressure of the air compressor outlet can also be reduced accordingly. But the safety is not as good as Bath-type main cooling
Typical structure of condensing evaporator
With the construction of large-scale projects such as iron and steel, petrochemical engineering, coal chemical engineering and so on, from the perspective of reducing equipment investment, reducing energy consumption and convenient management, the corresponding requirements are matched with the projectAir separation equipmentIt also tends to be large-scale. According to the actual demand of industrial development in our country, metallurgy, petrifaction, coal gasification and other projects have put forward the requirement of air separation equipment matching with the project. Through the experimental research and the research on domestic and foreignLarge air separation plantThis paper introduces five typical structures, which are the condensation evaporator, the separate arrangement of the condensation evaporator, the double-layer or multi-layer condensation evaporator, the high heat flow tube shell type condensation evaporator and the membrane type condensation evaporator connected with the upper and lower towers.
Large air separation condenser evaporators at home and abroad can be summarized into five typical structures.
1. Condensing evaporator connected with upper and lower towers
Arrange multiple plate units in a single layer, or add auxiliary condensation evaporator to the tower. This kind of layout is the most conventional one, which is convenient to install, simple to arrange the pipeline, and also saves more space.
2. Condensing evaporator arranged separately
Put several plate units in parallel in a cylindrical container, and connect them with the upper and lower towers by pipes, which is a single arrangement of condensing evaporator.
This kind of structural form condensing evaporator is separated from the upper and lower towers, which is not limited by cross section, but increases equipment investment cost and pipeline configuration. (Figure 1)
Figure 1 Schematic diagram of condensing evaporator arranged separately.
3. Multilayer or double layer condensing evaporator
Arrange multiple Plate-fin Heat Exchanger (main cooling unit) between the upper and lower towers according to the configuration of upper and lower layers, and make the limited section layout as large as possible of heat exchange area, making the diameter of the condensing evaporator roughly the same as that of the upper and lower towers, and operating with variable load is beneficial to obtain better operational stability and reliability, and convenient for transportation, which is a relatively practical structure. Its disadvantages are complex structure and difficult manufacture and installation. (Figure 2)
Figure 2 Schematic diagram of multilayer or double layer condensing evaporator
4. High heat flow tube shell condensing evaporator
United Carbide Company of the United States has adopted high-efficiency heat transfer tube-shell condensation evaporator in large air separation plants since 1970s. This condensation evaporator has a porous thin layer on the boiling side of the inner surface of the tube, and the condensation side of the outer surface of the tube is a longitudinal groove. Because the phase change heat transfer on both sides is enhanced, the total heat transfer coefficient is improved, the heat transfer temperature difference is reduced, and the energy consumption of the equipment is reduced. Meanwhile, due to the high circulation rate of liquid through the porous surface, it can effectively prevent the explosion danger caused by partial concentration and accumulation of acetylene and hydrocarbon, which is beneficialAir separation equipmentSafe operation. But its cost is high.
5. Membrane condensing evaporator
The main cooling is placed above the liquid oxygen surface, and the liquid oxygen is pressed into the main cooling through the liquid oxygen pump. It flows through the adjacent channel of the main cooling from top to bottom like the air nitrogen, and conducts heat exchange to make the liquid oxygen evaporate and the air nitrogen condense. Because the liquid oxygen in the main cold channel is membrane-like downstream and evaporates, it is called membrane condensation evaporator. Since there is no pressure difference established by the liquid oxygen column in the condensing evaporator, the boiling point of oxygen remains unchanged, so that the temperature difference of oxygen and nitrogen on both sides of the main cooling is consistent all the time.
Since the liquid oxygen column is canceled in the main cooling, the temperature difference of the main cooling can be reduced, and the air pressure of the air compressor outlet can also be reduced accordingly. But the safety is not as good as Bath-type main cooling.
4 Conclusion and analysis
For the structural type of condensing evaporator of large air separation plant, the following points can be obtained through the above analysis:
(1) the condensation evaporator is arranged separately, which reduces the influence of the static-liquid column in the boiling channel on the heat transfer temperature difference and reduces the thermal resistance of the condensation liquid film in the condensation channel, thus improving the heat transfer efficiency of the heat exchange surface. The calculation shows that when both the boiling channel and the condensation channel adopt the equivalent diameter de = 2
