The blockage of rectification tray is a common fault in the operation of air separation, which directly leads to the decline of oxygen and nitrogen purity and the reduction of output. It needs to be quickly judged and accurately handled.
There are three main reasons for plugging: first, the freezing of solid impurities at low temperature, the precipitation of carbon dioxide, water and nitrous oxide at low temperature, and the plugging of screen holes and downcomers; Second, mechanical sundries are blocked, and molecular sieve powder, welding slag and rust flow into the tower with gas; Third, flooding foam entrainment, which is similar to plugging, should be treated differently.
Three steps for online emergency: reduce the load and reduce the gas phase impact; Adjust reflux to make up for the decline of mass transfer efficiency; Stabilize the tower pressure and prevent tower drift. At the same time, the front-end purification is strictly controlled to ensure that the molecular sieve adsorption is qualified, and the discharge of liquid air and liquid oxygen is increased to bring out enriched impurities.
The complete cure depends on heating and purging. After stopping the machine for liquid discharge, use dry hot air for reverse purging until the dew point at the outlet reaches the standard. When mechanical impurities are suspected, the manhole shall be opened to the tower for inspection and cleaning, and the damaged tower plate shall be replaced.
Long term prevention should focus on the source. Strictly observe the bottom line of molecular sieve purification, regularly calibrate the analyzer, and replace the adsorbent and filter element; Establish the column differential pressure account, take the slow rise of differential pressure as the warning signal, early detection and early disposal, and ensure the continuous stability of distillation conditions.
