The air separation distillation column is composed of upper and lower columns, crude argon column and pure argon column and so on. At present, there are two kinds of lower column of large air separation plant, which are sieve plate column and packing column, while the upper column and argon column have generally used regular packing column with less resistance. During the normal operation of air separation plant, a certain amount of low-temperature liquid, i.e. the liquid holdup of distillation column, will be retained on the surface of internal parts such as sieve plate, overflow bucket or filler in the column. Generally, when the load of air separation plant is high, the liquid holdup in the column will be larger, and when the load of air separation plant is low, the liquid holdup will be smaller, respectively. When the air separation plant is under variable load operation, the change of liquid holdup in the column will affect the working condition of the distillation column and affect the stable operation of the air separation plant.
When the load reduction of air separation plant is too large or too fast to a certain limit, the rising gas volume in the distillation column will be reduced, and the liquid holdup in the column will also be reduced. The cooling capacity reduced due to the liquid holdup will eventually be concentrated in the main cooling of the upper column, resulting in the increase of the main cooling liquid level, the increase of liquid oxygen production, the decrease of the temperature in the middle of the upper column, and the nitrogen plug in the crude argon column, the decrease of oxygen purity and other phenomena.
When the increasing load of air separation plant is too large or too fast exceeds a certain limit, the temperature in the middle of upper column will rise, the main cooling liquid level will decrease, the oxygen purity will rise, and the oxygen content in argon fraction and process argon will rise.
For the influence of variable load on distillation column, the following methods can be adopted to eliminate: When load reduction operating, in order to avoid the increase of the proportion of oxygen rich liquid and air going to the upper column in the process of load reduction, the liquid level setting values of the lower column and crude argon II column can be increased appropriately. After load reduction, the original liquid level setting values of the lower column can be recovered slowly, so as to eliminate the change of liquid holdup of the lower column impact on working conditions. On the contrary, when the air separation equipment is under load operation, the liquid level setting values of the lower column and the crude argon II column can be reduced appropriately. After the loading is completed, the normal liquid level setting values can be restored slowly. In addition to adjusting the liquid level settings of the lower tower and crude argon II tower to eliminate the influence of variable load on the working condition, and to ensure that the flow of argon fraction is not affected, the effect of variable load on the working condition of air separation equipment can also be eliminated by properly adjusting the liquid level settings of the crude argon condenser.
Through the above methods, it can basically offset the change of liquid holdup and unstable working conditions of distillation column caused by the variable load of air separation plant, so as to ensure the smooth completion of the variable load process of air separation plant. All these operations must be carried out slowly.
