A main cold explosion mechanism
1. Hazardous substances
a. Combustible components: Mainly hydrocarbons such as acetylene. Acetylene is the most dangerous and has a very low solubility in liquid oxygen (5.6×10-6mg/L), which is easy to precipitate in solid state and cause explosion.
b. Blocking components: mainly carbon dioxide, water and nitrous oxide, especially nitrous oxide, increasingly attracting attention, they crystallized out, blocking the main cold channel, will cause the main cold dry evaporation and boiling at the dead end, resulting in hydrocarbon concentration, accumulation, precipitation, triggering the main cooling explosion. c. Strong oxidant: Liquid chlorine is a strong oxidant.
2. Several detonating factors
a. Mechanical impact of solid impurity particles (acetylene particles and other friction, liquid oxygen impact).
b. Static electricity, such as carbon dioxide particles reach (200 ~ 300) ×104ppm, can produce static electricity, voltage up to 3kV.
c. Chemically sensitive substances (e.g. ozone and nitrogen oxides).
d. Pressure pulse caused by airflow impact, pressure impact, cavitation phenomenon, resulting in temperature rise and explosion.
Two main cold explosion-proof measures
1. Strengthen raw material air quality control
Oxygen production area should be upwind all year round, more than 300m away from acetylene generating station, far away from harmful gas sources, strengthen raw material air quality control, once serious pollution, to take corresponding measures.
2. Remove harmful substances and prevent the accumulation of hydrocarbons
The main factors of accumulation are as follows:
a. Give full play to the role of liquid-air liquid oxygen adsorbers in removing hydrocarbons such as acetylene, strictly switch the adsorbers and control the heating and regeneration temperature on schedule to improve adsorption efficiency.
b. Discharge 1% of the product liquid oxygen from the main cooling to remove hydrocarbons.
c. Regular large heating of the air separation to remove residual carbon dioxide and hydrocarbon impurities accumulated in the heat exchanger and rectification tower. d. Liquid oxygen pump put into operation for a long time, using molecular sieve adsorption, nitrous oxide adsorption effect is not good, can be added in the molecular sieve adsorbent a layer of 5A molecular sieve.
3. Adopt high precision and sharp detection instrument to realize online and offline monitoring
This work should be normalized, institutionalized and carried out regularly. If the environment deteriorates, effective measures should be taken at any time to control harmful substances within the standard, acetylene in 0.5, methane 120, total carbon 155, carbon dioxide 4, nitrous oxide 100 (order of magnitude 10-6).
4. The liquid level of the control operation is high, the circulation ratio is large, carbon dioxide and hydrocarbons are not easy to accumulate and concentrate.
Wuhan Iron and Steel gas plant adopts full immersion operation. After years of safe operation, all process parameters are the same as before immersion, and there is still enough separation space, heat exchange area also meets the requirements, and there is no gas liquid entrain phenomenon of oxygen taken out, so the main cold full immersion operation is beneficial and harmless.
5. Temporary stop and explosion-proof temporary stop restart
there is inevitably a certain time of low liquid level operation, at this stage is prone to local concentration of hydrocarbons, at the same time when restarting, plate heat exchanger in a period of time is not normal, self-cleaning effect is not good, resulting in carbon dioxide blockage, coupled with airflow impact, it is possible to micro-explosion in the main cold, Therefore, the number of temporary stops should be reduced to the maximum extent, or the total drainage should be avoided, and the main cooling should be heated separately.
6. Wash regularly
When running for 2 years or longer, the distillation tower and liquid oxygen circulation system should be cleaned and degreased. The main cooling unit should be soaked for 8h, and then thoroughly blown out with air of sufficient pressure after cleaning, and then fully heated and dried.
7. Prevent static electricity buildup
Liquid oxygen has a large unit resistance and is easy to generate static electricity. It can generate thousands of volts of static electricity without grounding, so it is necessary to check the grounding of the air separation device regularly.
8. Prevent oil from entering
If the oil is brought into the air separation device, it will pollute the adsorbent and affect the adsorption of acetylene, so it should cancel the Roots fan that is easy to make the air with oil, and strengthen the overhaul and maintenance of the expander.
9. Strengthen the management of calcium carbide slag
The remaining acetylene in carbide slag is very serious to air pollution, especially in rainy days, should be strictly managed, and it is best to be buried far underground.
10. Strengthen operation, maintenance and management
In operation, the removal of harmful impurities should be careful, such as plate heat exchanger temperature control, main cooling stability control, harmful substances monitoring.
In maintenance, monitoring instruments and meters should be checked regularly to ensure the accuracy of test results; Super - cycle operation should be careful, to stop in time to heat blown.
In management, we should strictly abide by process discipline, strengthen equipment management, put an end to illegal operations, maintain the integrity rate of equipment, and strictly implement four.
11. Strengthen technical training and improve technical level
Regular and irregular training every year to enhance explosion-proof awareness and improve operational skills.
Post time: Jun-12-2023