Aluminum plate-fin heat exchanger in an air separation plant has a wide range of applications, mainly in multi-stream heat exchanger main heat exchanger, cold, etc., as well as up and down the tower, coarse and fine ammonium hydrogen tower tower condenser, evaporator, and the liquefaction system of classification systems, etc..
1, the main heat exchanger
The role of the primary heat exchanger is to achieve as a raw material gas of the air, pressurized air and oxygen, nitrogen, nitrogen pollution heat exchange between the gas reflux. Air from the room temperature cooled to about 1OOK, pressurized air is cooled to room temperature before the expander temperature, the reflux of gas from low temperature heat recovery to normal temperature.
Layout of the main heat exchanger flow mainly cascade arrangement, which corresponds to a layer of two layers of cold heat. However, in exceptional circumstances (such as high pressure fluid or a phase change of circumstances), you can not strictly follow the hot and cold channels ratio of 1:2. Some high-pressure phase transformation heat or cold can be a single benefit arrangement, or a layer of heat flow corresponding to a layer of cold flow. How to layout flow or should be determined according to specific circumstances. Arranged in the channel should be considered when the body of the fluid as evenly as possible in the core, scattered arrangement. Heat balance in the overall context, taking into account the local thermal equilibrium, a core body to avoid the phenomenon of Enthusiasm. It should be noted that the air separation unit to drive starts, reflux of oxygen, nitrogen has not yet produced, and only able to provide reflux cooling capacity of nitrogen pollution. To speed up the startup speed, so that pressurized air into the turbo-expander cooling as soon as possible, in theory, can be arranged in the pressurized nitrogen air pollution next to, but still should be noted that considering the local thermal equilibrium conditions in appropriate cases to use more so layout.
2, the liquid air liquid nitrogen subcooler
Air Liquide is the use of liquid nitrogen cooled cold nitrogen, nitrogen to make liquid air pollution, and other cold liquid nitrogen to reduce the evaporation rate, increase the return on the tower to improve the operating conditions of distillation. General liquid side heat transfer coefficient using low and sparse serrated fin, gas side is high and dense serrated fin. As a result air separation unit rating plate-fin heat exchanger size increase, but also can choose other types of fins, which increase the resistance in the case of non-reduced core body section size, convenient for manufacturing.
3, condensation Yan hair
Condensate evaporator (hereinafter referred to as: the main cold) is the role of nitrogen under the tower at the top of condensation, evaporation of liquid oxygen on the bottom of the tower to provide the tower and the tower back up steam. Hang oxygen mainly in the main cold form: with the upper and lower the overall cooling tower connected Yan hair, heat exchanger unit of the general layout with single star, convenient and distillation assembly. When you need a larger heat transfer area will adopt the form of vertical double. Hang with the production of air separation plant oxygen levels improve, plate-fin heat exchanger size is also increasing, vertical single or double layer have been unable to meet the requirements. Transportation consider the limit of large air separation plants in recent years, some of the main cold has begun to horizontal. In addition to these forms, there is high heat flow and the main condenser shell and tube membrane main cold, etc., there is a large literature on the main cold air separation plant in the typical structure of introduced and summarized, and highlighted with the Xi'an Jiaotong HangYang University to develop micro-film double-slit condensate evaporator.
Plate-fin on both sides are the main cold phase change heat transfer, heat transfer coefficient of the larger, so it is relatively small, highly porous fin-shaped fin. Evaporation channel open at both ends of the upper and lower oxygen, liquid oxygen on the evaporation of steam rise towers. Under nitrogen from the top of the tower leads into the core body unit, condensation of liquid nitrogen in the core collection of the lower part of the head tube derived by exports. Taking into account the safety of operation of liquid oxygen, liquid oxygen side of the way by immersion and the use of larger fin pitch.
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