DEAR Cryogenic air separation unit.The overall heating in cold state is the heating operation after parking. The main purpose is to remove the residual water, carbon dioxide, acetylene and other impurities, so as to prepare for the long-term operation or maintenance of the next cycle. Full heating in hot state is the heating operation before start-up. Its main purpose is to remove water and some solid debris.DEAR Cryogenic air separation unit.It can be seen that in this case, it is better to stop an expander, which can not only reduce the impact of expansion on distillation conditions, but also make the switching heat exchanger work under normal conditions, so as to prevent cold end supercooling or low temperature after expander.DEAR Cryogenic air separation unit.Generally, water temperature above 45 ℃ is easy to form scale. The thermal conductivity of scale is only 1 ~ 2 w / (m ·℃), which is much smaller than that of common metal materials. Therefore, the fouling of cooling water pipe will worsen the heat transfer, and the air can not be cooled to the required temperature, so the air volume will be reduced, which will directly affect the economy and normal production of air separation unit.
There are three ways to configure the liquid air in the condensing evaporator of the crude argon column: one is that all the liquid air in the main tower passes through it, and after partial evaporation, the vapor and liquid air are sent back to the upper tower together. In this way, the cold source of condensing evaporator is sufficient, which is beneficial to the working condition of crude argon, but has great influence on the main tower;Then, the following steps can be followed: turn the switching mechanism from automatic to manual, close the forced valve and equalizing switching valve of the air into the tower. Open the waste nitrogen vent valve. Cut off the expander solenoid valve, close the expander inlet control valve and the expander inlet and outlet valves.There are three types of condensing evaporators used in air separation plant: short riser, long riser and plate fin. Generally, short risers are used in small air separation units, with condensation inside and boiling outside, while long risers are used in medium air separation units, with opposite heat transfer;
In order to maintain the stability of the working condition, the cooling capacity produced must first make up for the two cooling losses of running off and incomplete heat exchange. When the device has a small amount of low temperature leakage or other cold loss, the required cooling capacity increases. In addition, when part of the liquid products produced by the device are exported to the device, the cooling capacity Q0 brought by the low-temperature products also needs to produce more cooling capacity to make up.With a large amount of oxygen condensing, the oxygen content in gas phase decreases, and the argon condensing relatively increases. Therefore, the argon content in gas phase gradually decreases, and it is only 0.0% after reaching the top of the tower. Because oxygen and argon are difficult to volatilize to nitrogen, they condense into liquid phase more than nitrogen, so the concentration of oxygen and argon in liquid phase is higher than that in gas phase.The length of plate unit is about 5.4m, while the length of switching heat exchanger is 6m. Due to the simple equipment and low cooling loss in the device, the intermediate temperature of the heat exchanger can be generally higher or similar to the circulating temperature of the long plate heat exchanger.
