Edit content
Oxygen (O2) Is a colorless, odorless and odorless gas. The molecular weight is 32. The relative density is 1.429 (Air = 1 ). The melting point is-218.4 ℃. Boiling point is-183℃. Can be liquefied and solidified. Liquid oxygen is sky blue. Slightly soluble in water. It is not very active at normal temperature, and it is not easy to have effects on many substances; but it is very active at high temperature, and can be directly combined with various elements. Fuel Fuel.
Oxygen is the substance on which living creatures depend. It is widely used in industrial production. Acetylene-oxygen flame is used for metal welding and cutting. In metallurgical industry, oxygen is used for iron and steel smelting, steel rolling and non-ferrous metal refining. Oxygen is widely used in medical treatment and deep work.
Modern industry adopts the method of cooling separation to produce oxygen. According to the pressure of compressed air in its production process, it can be divided into four types: High pressure process, medium pressure process, double pressure process and full low pressure process. Although the air separation equipment (oxygen generator) used in various processes is different, the process of oxygen generation roughly includes six stages: (1) air purification; (2) air compression; (3) the removal of carbon dioxide and water vapor in compressed air; (4) air liquefaction; (5) light distillation and separation into oxygen and nitrogen; (6) storage and transportation of products.
Air Separation (full low pressure) process: as shown in the figure. Air enters the compressor after being filtered and compressed to 0.5 ~ After 0.6MPa, it is divided into two ways and enters the oxygen cooler and nitrogen cooler respectively. After cooling, a part of air is sent to the carbon dioxide adsorber and the turbine expander, and the top of the distillation tower enters the tower. Most of the air after cooling enters from the bottom of the tower. The oxygen coming from the lower part of the main evaporator of the distillation tower (after separating the liquid air and liquid nitrogen) will become the finished oxygen after heat exchange with the air in the oxygen accumulator. The pure nitrogen from the top of the distillation column will be produced after being heated to normal temperature by air through air supercooler. The finished oxygen enters into the gas cabinet, then it is compressed and then filled with oxygen cylinder or sent directly to the oxygen user.
Occupational hazardsOxygen generation process is characterized by high pressure, low temperature, flammable and explosive. The main dangers are fire and explosion, and there will also be anoxia and suffocation accidents.
(1) the fire and explosion hazards of the air separation plant are the biggest threats.
Air compressor bearing bush, exhaust pipe, equipment and so on are the places where fire and explosion accidents occur frequently in the compression process. The main reasons are: ① the interruption of cooling water or the shortage of supply; ② the interruption of lubricating oil or the shortage of oil supply; ③ the oxidation and spontaneous combustion of carbon deposit in the exhaust pipe. Thereinto, the situation of Carbon deposit oxidation spontaneous combustion is complex and the risk is particularly high, which must be paid attention.
The explosion accidents of the distillation column mostly occur in the condensation and evaporation parts of the high pressure, medium pressure or double pressure freezing cycle oxygen generation units and large all-low pressure oxygen generation units; explosion is also easy to happen between the lower tube plate, the upper tube plate, the tube bundle and the condenser shell. The basic cause of the explosion is the accumulation of excessive inflammable and explosive substances in liquid oxygen, which is mainly the light fraction of the thermal cracking of hydrocarbon such as acetylene and lubricating oil.
(2) the fire and explosion of oxygen system (oxygen compressor, oxygen pipeline, oxygen cylinder.
The main part of the fire and explosion of the oxygen compressor is the cylinder part. Because the temperature in the cylinder is too high, the leather bowl or seal parts will be decomposed to produce combustible gas, which will be easy to burn and explode when mixed with oxygen. When iron filings enter into the cylinder, Sparks will be generated due to friction or impact, which will lead to the occurrence of explosion accidents. If the packing seal of piston rod is not well assembled or seriously worn, oil seal leakage and gas seal leakage will often be caused, and sparks caused by high temperature or friction of piston rod will also cause combustion and explosion. In addition, burning and explosion accidents will also be caused in pipelines, especially in the pipeline corners and valves. The reason is that rust will cause fire easily when friction occurs with steel pipe under high-speed oxygen blowing brush, or static electricity will cause fire.
The explosion accidents of the liquid oxygen pump can be roughly divided into two types: one is the explosion inside the pump, which is mainly caused by impurities such as iron filings and aluminum powder entering the pump; the other is the explosion outside the pump, it is mainly caused by leakage and oxygen.
The reasons for the burning and explosion of oxygen pipe and valve include: the rust, welding slag and other impurities in the oxygen pipe will rub and collide with the pipe wall and so on, causing high temperature and easy combustion; combustibles such as Grease and rubber, in high purity and high pressure oxygen flow in the burning rapidly; oxygen pipe valve in the front and rear pressure large differences when the valve sharply Open when, after valve gas temperature up to 955 ℃, this temperature is close to the melting point of several common metals; static electricity will be generated at the air outlet or the regulating valve of the oxygen pipeline.
When filling oxygen, it will cause the static electricity caused by touching combustibles such as Grease, too fast filling speed and the spark generated by mechanical friction when closing the valve after filling, which is easy to cause fire and explosion.
Based on the nature of oxygen, oxygen storage equipment, liquid oxygen storage tank and oxygen cylinder all have the danger of fire and explosion.
(3) anoxia and suffocation.
Anoxia and suffocation accidents mainly occur in the process of equipment maintenance, which are often caused by the leakage of nitrogen, etc.
Preventive measures
(1) fire and explosion-proof measures of air separation system
1) reasonably choose the factory site to avoid air pollution of raw materials;
2) adopt effective purification process and equipment to remove acetylene and hydrocarbon in the air;
3) test and analyze timely, and strictly control the content of acetylene and hydrocarbon in liquid oxygen;
4) by setting up liquid air adsorber and liquid oxygen adsorber, discharging liquid oxygen timely, and regularly heating and cleaning the inside of the equipment partly or completely, the accumulation of acetylene and hydrocarbon can be prevented;
5) the equipment and pipeline in the cold box of the air separation plant should be reliably grounded;
6) use oil-free lubrication as far as possible for air compressor and expansion machine;
7) the air compressor should be cooled sufficiently and lubricated properly to avoid carbon deposit;
8) all kinds of safety devices and instruments are in good condition.
(2) fire-proof and explosion-proof measures of oxygen system
1) the oxygen compressor adopts oil-free lubrication;
2) all parts and parts contacting with compressed oxygen must be strictly degreased and oiled before being loaded, and cleaned with carbon tetrachite;
3) take various measures to prevent compressed oxygen from contacting oil;
4) maintain the equipment well and keep each sealing device running reliably;
5) prevent rust, welding slag and other sundries from entering the system;
6) control the flow rate of oxygen;
7) check carefully when filling oxygen. No filling is allowed when the oil and residual pressure of the cylinder is less than 0.05MPa; open the valve slowly to reduce the impact and friction of airflow; no overpressure filling is allowed.
(3) prevent anoxia and suffocation.
1) replace the equipment and pipeline with air before the overhaul of the equipment, and add blind plates to the nitrogen pipeline;
2) conduct gas analysis before overhaul, and enter the equipment to work after the oxygen content is qualified;
3) if the patient is found with symptoms of hypoxia, he/she should transfer to the fresh air immediately; for those who lose consciousness or cannot breathe normally, he/she should send oxygen in time or send it to the high-pressure oxygen chamber for treatment.
-- From Encyclopedia of Safety Science and Technology (China Labor and Social Security Press, published in June 2003)
