Explosion proof measures for condensing evaporator

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According to incomplete statistics, at the end of the 1970s and the beginning of the 1980s, domestic large and medium-sized air separation equipment exploded more than 30 times, and small air separation equipment exploded more than 100 times. Just after the mid-1990s, large-scale air separation equipment condensation evaporator (hereinafter referred to as the main cooling) exploded continuously at home and abroad, resulting in heavy losses. In 1996, the 6000m3/h main cooling system of Liaoning shunethylene chemical company exploded, and the air separation tower was damaged, killing 4 people; In 1997, the 80000m3/h air separation main cooling system of Malaysia Bintulu shell oil company exploded, completely destroying the air separation equipment and injuring 12 people. It can be seen that the main cooling explosion-proof is the key to the safety of air separation plant

I. main cooling explosion mechanism

1 Hazardous substances

a. combustible components: mainly hydrocarbons such as acetylene. Acetylene is the most dangerous. Its solubility in liquid oxygen is very low (5.6 mg/l), and it is easy to precipitate in solid state and cause explosion

b. blocked components: mainly carbon dioxide, water and nitrous oxide, especially nitrous oxide, have attracted increasing attention. After they crystallize and precipitate, they block the main cooling channel, which will cause dry evaporation and dead end boiling of the main cooling, cause hydrocarbon concentration, accumulation and precipitation, and cause explosion of the main cooling

c. strong oxidizer: liquid chlorine is a strong oxidizer

2. Several detonation factors

a. mechanical impact detonation of solid impurity particles (friction of acetylene particles, liquid oxygen impact)

b. static electricity. For example, when carbon dioxide particles reach (200 ~ 300) 104ppm, static electricity can be generated, and the voltage can reach 3KV

c. substances with strong chemical sensitivity (such as ozone and nitrogen oxides)

d. pressure pulse caused by air flow impact, pressure impact and cavitation, which causes temperature rise and explosion

II. Explosion proof measures for main cooling

1 Strengthen the raw air quality control

the oxygen production area should be upwind all year round, more than 300m away from the acetylene generating station, away from harmful gas sources, strengthen the raw air quality control, and take corresponding measures in case of serious pollution

2. Remove harmful substances and prevent hydrocarbon accumulation.

the main factors of accumulation are as follows:

a. give full play to the role of liquid air liquid oxygen adsorber in removing acetylene and other hydrocarbons, strictly change the adsorber on schedule and control the heating regeneration temperature to improve the adsorption efficiency

b. discharge 1% product liquid oxygen from the main cooling system to remove hydrocarbons

c. regularly heat up the air separation unit to remove the residual carbon dioxide and hydrocarbon impurities accumulated in the heat exchanger and rectification tower

d. the liquid oxygen pump has been put into operation for a long time. If molecular sieve is used for adsorption, the adsorption effect of nitrous oxide is not good. A layer of 5A molecular sieve can be added to the molecular sieve adsorber

3. High precision and sharp detection instruments shall be used to realize off-line monitoring. This work shall be normalized, institutionalized and carried out regularly. In case of environmental deterioration, effective measures shall be taken at any time to control harmful substances within the standard. Acetylene shall be 0.5, methane 120, total carbon 155, carbon dioxide 4 and nitrous oxide 100 (order of magnitude)

4. Control the operating liquid level

the liquid level is high and the circulation ratio is large, and carbon dioxide and hydrocarbon compounds are not easy to accumulate and concentrate. The cup punching experiment is to make the round pieces (55, 100) of thin plate and strip pressed between the blank holder and the stamping die. The gas plant of WISCO adopts the full immersion operation. After years of safe operation, all process parameters are the same as those before immersion, and there is still enough separation space. The heat exchange area also meets the requirements, and the oxygen taken out is free of gas-liquid entrainment. Therefore, the full immersion operation of main cooling is beneficial and harmless

5. Temporary shutdown and explosion-proof

temporary shutdown and restart will inevitably lead to low liquid level operation for a certain period of time. However, the tensile strength of other products should be such that the 200kn section is prone to local concentration of hydrocarbons. At the same time, you should understand the technology of tension machine accessories when restarting. The plate heat exchanger has abnormal working conditions for a period of time, and its self removal effect is not good, resulting in carbon dioxide blockage, coupled with air flow impact, Slight explosion may occur in the main cooling system. Therefore, the number of temporary shutdown shall be minimized, or full discharge of liquid shall be avoided. The main cooling system shall be heated separately and comprehensively if possible

6. Regular cleaning

when it operates for 2 years or more, the distillation tower and liquid oxygen circulation system shall be cleaned and degreased. The main cooling unit shall be soaked for 8h, purged thoroughly with air of sufficient pressure after cleaning, and then fully heated and dried

7. Prevent static electricity accumulation

an electronic universal testing machine often used for testing liquid. The capacity of the testing machine is 100 ~ 135000lb. The unit resistance of oxygen is large, which is easy to generate static electricity. Thousands of volts of static voltage can be generated when it is not grounded. Therefore, it is necessary to regularly check the grounding of the air separation unit

8. Prevent the oil from entering

if the oil is brought into the air separation unit, it will pollute the adsorbent and affect the adsorption of acetylene. Therefore, the roots blower that is easy to bring oil into the air should be canceled and the overhaul and maintenance of the expander should be strengthened

9. Strengthen the management of carbide slag

the residual acetylene in carbide slag causes great air pollution, especially in rainy days. It should be strictly managed, and it is best to bury it far underground

10. Strengthen operation, maintenance and management

in terms of operation, it is necessary to carefully remove harmful impurities, such as temperature control of plate heat exchanger, stability control of main cooling, monitoring of harmful substances, etc

in terms of maintenance, the monitoring instruments and meters shall be calibrated regularly to ensure the accuracy of the test results; Be careful during over cycle operation. Stop the machine in time for heating and purging

in terms of management, it is necessary to strictly abide by the process discipline, strengthen equipment management, put an end to illegal operations, maintain the intactness rate of equipment, and strictly implement the "four don't let go"

11. Strengthen technical training and improve technical level

conduct regular and irregular training every year to enhance explosion-proof awareness and improve operation skills

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