The condensing evaporator of large air separation plant at home and abroad can be summarized into five typical structures.
1. Condensing evaporator connected with upper and lower towers
Arrange multiple condensation evaporator units in a single-layer star in the tower, or add auxiliary condensation evaporator to the tower. For example, the 28000 m 3/h air separation plant of Linde company introduced by Zhenhai petrochemical and the condensing evaporator of 30000 m 3/h air separation plant of American Air Products and Chemicals Company introduced by Baosteel. 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 condensation evaporator units in parallel in a cylindrical container, and connect them with upper and lower towers by pipes, which is a single arrangement of condensation evaporator.
Anshan Iron and Steel oxygen plant introduced 3500 m 3/h air separation plant from Japan acid in 1978, its distillation column is parallel to the upper and lower towers, condensation evaporator is arranged separately on the upper of the lower tower, two parallel sets (diameter X length X wall thickness)
Φ> 3500mm × 7300mm × l4mm horizontal cylindrical container, each container is equipped with five horizontal Plate-fin Heat Exchanger units with unit size of 900mm × 1066mm × 2700mm in parallel, the Plate-fin Heat Exchanger consists of the upper and lower Open oxygen boiling channel and the closed gas-nitrogen condensation channel.
The distillation tower of Japanese Shengang 30000 m 3/h air separation equipment, which was put into production by Shanghai Baosteel in 1986, is also composed of three separate parts: Upper Tower, lower tower and condensing evaporator, and it is arranged on the same axis in the order of the upper tower, the condensing evaporator and the lower tower. Similar to the traditional two-stage distillation column structure, the condensing evaporator is a horizontal cylindrical container of 4,000mm × 9400mm × 14mm, two columns are arranged in parallel in the cylinder, and each column has seven condensing evaporator units with the size of 1803mm × 900mm × 1157.6mm. The passageway is arranged according to the routine. Figure 1 is the structure schematic diagram of this condensing evaporator.
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 condensation evaporators configured in the upper and lower layers. This structure is especially suitable for two-stage rectification. It can not only meet the requirement that there is a heat exchange area as large as possible in the cross section, but also keep the liquid level stable when the load variation range is large, so it can be operated under the best working condition.
Shougang oxygen plant introduced 30000 m 3/h air separation equipment with five rare gases fully extracted from German Linde company in 1986, and adopted vertical double-layer condensing evaporator, as shown in figure 2. The condensing evaporator is a vertical cylindrical container of 3850mm × 7900mm × 14mm, which is arranged in two layers. The plate unit has three upper layers and four lower layers. The size of the main cooling unit is 1500mm × l050mm × 1190mm. In order to prevent the local retention and concentration of the hydrocarbon in liquid oxygen in the upper layer of the condenser, the two-layer partition plate is slightly inclined, and a washing hole with a diameter of about 12mm is set up in the arched part of the lowest part of the partition plate. Depending on the washing effect of small holes, the unit time is 0.1% ~ 1% liquid volume flows directly to the lower layer, and at the lower layer, 1% liquid oxygen volume is taken out of the tower, making it vaporize in the special device, this structure can avoid the danger of main cold explosion caused by the accumulation of hydrocarbon.
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. The condensation evaporator has a thin layer of L 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 conducive to the safe operation of the equipment, and it has been successfully applied to 3500 m 3/h and 58000 m 3/h large air separation plant.
Hangzhou Hangyang Research Institute has conducted experimental research on high heat flow tube and successfully applied it to 150 m 3/h air separation plant. The temperature difference of heat transfer has been reduced from 2.5 k to 1.2 K, the heat transfer coefficient increased from 600 W/m2 • K to 1500 W/m2 • K, which fully showed the performance of enhanced heat transfer and applied for the national utility model patent.
5. Membrane condensing evaporator
The evaporator of the membrane type condensing, 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, which 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, condensation of gas and nitrogen. 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. Weihe Chemical Fertilizer Plant introduced 400 m 3/h liquid air separation equipment in 1992 for this type of structure.
