1. Air separation plant and its performance characteristics
1.1 air separation plant
The air separation plant uses air as the raw material, and makes the air into liquid state through the method of compression circulation and deep freezing, after rectification, the equipment is gradually separated from the liquid air to produce lazy gases such as oxygen, nitrogen and argon.
At present, there are various forms and types of air separation equipment produced in our country. There are devices for producing gas oxygen and nitrogen, and also devices for producing liquid oxygen and nitrogen. But in terms of basic process, there are mainly four kinds, which are high pressure, medium pressure, high and low pressure and full and low pressure process. The production scale of air separation plant in our country has been only 20 m from the early stage3/H (oxygen) oxygen generator, developed to now has a production of 20000 m3/h、30000 m3/H and 50000 m3/H (oxygen) capacity of large air separation plant.
1.2 basic system of air separation plant
From the perspective of technological process, the air separation plant can be divided into five basic systems.
1.2.1 impurity purification system
It purifies mechanical impurities, moisture, carbon dioxide, acetylene and so on mixed in the air mainly through devices such as air filters and molecular sieve absorbers.
1.2.2 air cooling and liquefaction system
It is mainly composed of air compressor, heat exchanger, expansion machine, air throttle and so on, which plays the role of deeply freezing the air.
1.2.3 air rectification system
The main components are distillation column (upper and lower towers), condensing evaporator, supercooler, liquid air and liquid nitrogen throttle valve. It plays the role of separating various components in the air.
1.2.4 heating blowing system
Use the method of heating and blowing to regenerate the purification system.
1.2.5 instrument control system
Control the whole process through various instruments.
2. Surface cleanliness of air separation plant and its inspection methods
2.1 The reason why the air separation plant is easy to burn
The occurrence of combustion and even explosion must meet three conditions: a certain amount of combustible substances, a corresponding amount of oxidant and minimum energy guarantee. The biggest feature of the working environment of the air separation plant is that the dielectric oxygen flows under the conditions of low temperature or normal temperature. Pure oxygen is a strong oxidant. Even under the liquefaction low temperature of-183℃, as long as the quantity or concentration of inflammable and explosive substances exceed the explosion limit, when the accumulated energy of medium oxygen due to high-speed flowing friction reaches a certain value, it will still explode, causing casualties and equipment damage. Therefore, the surface cleanliness of all the parts in the air separation plant that can contact with the medium oxygen is required to be very high. Mechanical impurities, grease and other organic matters are not allowed to exist, and these substances must be cleaned up.
The degreasing cleaning of the oil-forbidden parts of the air separation plant is to use physical or chemical methods to select appropriate cleaning agents to process their surfaces through specific cleaning processes, ensure that the concentration of organic matter on its surface is controlled below the explosion limit. This is a necessary measure for the safe operation of the air separation plant. After surface treatment, it can only be put into use after strict inspection and inspection.
2.2 Types of dirt on the surface of air separation plant
The index of checking the surface cleanliness of air separation plant should include the following four kinds of substances:
(1) solid substances: organic matters such as organic anti-rust agent, wood, paper, fiber, coating, etc.; welding slag and splash, metal scraps, welding wire and other metal objects; sand and similar granular substances, and other substances that may dissolve under working conditions.
(2) cleaning fluid and water
(3) floating rust and oxide skin
(4) mineral oil and grease
2.3 The Inspection Method of surface cleanliness
Solid substances, cleaning fluid, water and rust scars can be directly inspected by eyes. Under the bright light, observe the surface of the equipment under inspection to see if there is any solid substance left. Solid particles whose diameter (or diagonal) is more than 0.5mm are not allowed to exist, and the diameter (or diagonal) is between 0.25 ~ The sum of solid particles between 0.5mm should be less than 100 particles/m2, And there must be no fiber, dust or fabric. The length of individual residual fiber should not exceed 2mm; residual cleaning fluid and water are not allowed to exist, and the surface should be completely dry.
The determination of mineral oil and grease can be divided into direct inspection and Quantitative determination. Direct inspection methods include filter paper wiping method, ultraviolet fluorescence method, water coating test method and dripping diffusion method, etc. Quantitative analysis method can be divided into gravity method and oil concentration determination method.
At present, the measurement of oil residue on the surface of air separation plant in our country is basically based on the method of determining oil concentration, which is also the most widely used method.
3. The determination of the standard of residual oil on the surface of the air separation plant
The degreasing cleaning of the air separation plant is to remove the grease on the surface of components, so as to meet the requirement of residual oil on the surface specified by the standard. The lower the amount of residual oil specified by the standard is, the higher the requirement for cleaning equipment will be. The cleaning process will be more tedious, and the labor intensity and cost of cleaning will be improved greatly. How to determine the standard of surface residual measurement of parts of the oil-forbidden parts of the air separation plant? I think its principle should not only implement ISO9000, ensure product quality, ensure the absolute safety of system operation, but also set the quantity value of residual oil reasonably and appropriately.
