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1 Product characteristics of dissolved acetylene
Acetylene is one of the important raw materials for organic synthesis and one of the three major synthetic materials (synthetic rubber, synthetic fiber and plastic). Acetylene is widely used as an efficient and high-quality high-temperature heat source in metal welding, cutting, spraying, surface quenching and hot working. Acetylene is burned in air or oxygen and its flame temperature can be as high as 3200 ° C or higher. Although the combustion heat of acetylene is slightly lower than that of ethane, ethylene, etc., it consumes the least amount of oxygen when it is completely burned, the water content in the produced product is relatively low, and the heat loss required for water evaporation is less, so acetylene can burn A higher temperature is obtained, which is a remarkable feature of acetylene.
The preparation methods of acetylene mainly include calcium carbide hydrolysis method, high temperature combustion cracking of methane or hydrocarbons, and plasma cracking method. The calcium carbide hydrolysis process has a short process and high product purity, but the energy consumption of calcium carbide production is large. At present, most of the domestic dissolved acetylene production adopts this method. According to the solubility characteristics of acetylene, acetylene is compressed into a solvent and stored in a cylinder filled with a porous filler. As an excellent solvent, acetone is sucked in the cylinder to dissolve and release acetylene. Its function is to increase the effective volume of the cylinder and reduce the explosion performance of acetylene. The role of the bulk calcium silicate porous filler is to uniformly adsorb acetone and prevent the propagation of acetylene decomposition explosion. The product of dissolving acetylene is characterized by convenient use and improvement of work efficiency, improvement of environment and saving of calcium carbide consumption, and ensuring that the porous filler in the cylinder is not damaged or contaminated, and the amount of acetone filling meets the required amount of acetylene filling. Safety and reliability.
2 Hazard and hazard characteristics of acetylene
Acetylene is a flammable gas with flammability and chemical explosion hazard and has certain toxic properties. Acetylene is mixed with air or oxygen to form an explosive mixture, which can easily cause a combustion explosion when it is ignited. Contact with oxidizing agents will react violently. Contact with halogens such as fluorine and chlorine can cause a combustion explosion. It can form explosive compounds with copper, silver, mercury, etc. Under certain temperature and pressure conditions, pure acetylene will undergo its own direct decomposition explosion and its polymer decomposition explosion.
When acetylene is mixed with phosphine and hydrogen sulfide, the toxicity is increased and the damage is greater. Acetylene has a weak anesthetic effect, and inhalation of high concentrations of acetylene can cause simple asphyxia.
In the process of production and filling of dissolved acetylene, if acetylene leaks and mixes with air, it is prone to combustion and explosion.
3 Analysis of unsafe factors in the production of dissolved acetylene
The process of dissolving acetylene production and filling is: adding calcium carbide to water to produce crude acetylene gas, washing, cooling, chemical purification to remove harmful impurities such as sulfur and phosphorus, and then compressing and drying, and filling into dissolved acetylene gas cylinder. Now combined with the actual production of dissolved acetylene, systematic analysis of the unsafe factors and potential risk factors easily generated in the acetylene production process and the dissolved acetylene filling process can be used for reference by the acetylene production unit.
First, the calcium carbide feed and acetylene generation process were analyzed. When the acetylene generator is charged, it is prone to sparking on the wall of the calcium carbide impactor. If the feeding system uses a closed nitrogen sealing method, the unsafe factor can be eliminated. However, if the open type or the double squeeze type is charged, the feeding port burning accident is more likely to occur. For various reasons, such as the reaction temperature is too low, the acetylene generator slag discharge port does not contain the hydrolyzed calcium carbide into the slag pool, and the contact of acetylene with air on the surface of the slag pool is prone to a blasting accident. During the overhaul of acetylene equipment, the potential danger of acetylene combustion is present. Therefore, after the first production and shutdown, and before production, acetylene equipment should be replaced with nitrogen with less than 2% (v/v) oxygen, so that the oxygen content in the system is not more than 3% (v/v). ), otherwise it may not be put into production due to the potential danger of high oxygen content. When the acetylene equipment is overhauled, the equipment to be repaired shall be isolated from the acetylene system, and the internal acetylene shall be replaced with nitrogen having an oxygen content of less than 2% so that the acetylene content is not more than 0.2% (v/v). In the replacement process, the replacement system must have a comprehensive understanding, confirm that there is no blind zone in the replacement, otherwise it should be eliminated and then replaced. If there is undecomposed calcium carbide or a large amount of calcium carbide sludge in the acetylene generator, it must be sealed with a large amount of clean water, and then replaced with nitrogen to avoid accidents caused by the production of acetylene during the maintenance.
Then analyze from the acetylene purification process. The unsafe factors were analyzed based on the type of scavenger used in acetylene purification. For the concentrated sulfuric acid purification process, high temperature is generated due to the absorption of sulfuric acid, and if no cooling measures are taken, there is a risk of burning acetylene. In addition, if the acetylene gas entrains the foaming impurities of the calcium carbide sludge, it will react with the sulfuric acid to accumulate the bonding compound, which is easy to block the equipment and the pipeline. The maintenance is relatively difficult, and the handling may cause a slight inadvertent treatment. Explosion accident. For the sodium hypochlorite method or the chlorine water purification process, if the effective chlorine concentration is improperly controlled or the inlet acetylene temperature is too high, the acetylene chlorination reaction may easily occur to cause a chemical explosion.
In the process of acetylene compression and drying, acetylene explosion is easy to occur in both negative pressure operation and overpressure operation. In order to prevent the safety valve venting system set up for overpressure operation of the acetylene compressor, the discharge port should be led to the roof more than 1.0 m, and acetylene should not be discharged indoors. Otherwise, when acetylene leaks, there is a high concentration of acetylene in the room, which is extremely dangerous. During the operation of the acetylene compressor, the accessories such as pressure gauges and safety valves shall not be replaced. Otherwise, the acetylene compressor explosion may occur due to the introduction of air and possible adiabatic compression. The use of a high-pressure acetylene drying process without a regenerative molecular sieve can eliminate the unsafe factors of the drying process. The explosion of anhydrous calcium chloride is extremely dangerous and should be eliminated.
The risk of dissolving the acetylene filling process is greater than that of the low pressure acetylene system. The risk of acetylene depends mainly on the acetylene filling pressure, temperature, flow rate and leakage disposal. Acetylene filling must have good cooling conditions, otherwise it may cause unsafe factors due to excessive filling temperature. In the process of dissolving acetylene, as the pressure of acetylene increases, it is easy to cause local overheating and cause decomposition and explosion. The acetylene flow rate is too fast, and it is easy to ignite acetylene due to static electricity generated by friction. When high-pressure acetylene leaks, the gas source must be cut off before disposal to eliminate the risk factors or it may cause an explosion.
The unsafe factors of dissolving the acetylene cylinder are mainly reflected in the quality of the porous filler in the cylinder and the filling amount of the solvent. Damage or contamination of the filler will reduce the fire resistance and solvent holding capacity of the filler. The solvent acetone is insufficient, and it is not added in time. The acetylene will be in a gaseous state after filling, and the filling pressure will be high, and the potential danger is extremely great. However, if the solvent acetone is excessive, there is no safe space in the bottle, and unsafe factors also exist. The limited filling amount of acetylene is 50% of the required filling amount of solvent acetone in the bottle, and the excessive filling of acetylene is liable to cause an explosion accident.
4 Safety management of dissolved acetylene production
According to the product characteristics of dissolved acetylene and the hazard and hazard characteristics of acetylene, through the above analysis, it can be seen that the safety management of dissolved acetylene production should focus on fire prevention and explosion prevention and occupational health and safety management. According to the relevant national laws and regulations, the safety management and countermeasures for the production of dissolved acetylene are discussed.
4.1 Dissolved acetylene as a hazardous hazardous chemical, its production must be implemented in a unified planning, rational layout and strict control of the safety management system. For the production project of dissolved acetylene production, it is necessary to apply to the provincial safety production supervision and management department for the formalities for approval. Dissolved acetylene production must have the relevant qualifications as stipulated in the Regulations on the Safety of Hazardous Chemicals Management (Order No. 344).
4.2 Dissolved acetylene production enterprises must implement a safe production license system. It can meet the safety production conditions stipulated in the Regulations on Safe Production License (Order No. 397 of the State Council) and obtain a safe production license before engaging in the production of dissolved acetylene.
4.3 Dissolved acetylene enterprises must conduct safety evaluation according to law. Safety evaluation is the core and foundation for the implementation of safety management in dissolved acetylene production enterprises. The basis for safety evaluation is the relevant national laws, regulations and standards. The current relevant standards and specifications for the safety management of dissolved acetylene production and filling are:
Fire protection code for building design (GBJ16-1987)
Dissolved acetylene cylinder valve (GB10879-89)
Design specification for acetylene station (GB50031-91)
Dissolved acetylene filling regulations (GB13591-92)
Classification and marking of commonly used dangerous chemicals (GB13690-92)
Safety Supervision Procedure for Dissolved Acetylene Cylinders (Laozizi [1993] No. 4)
Sodium hypochlorite solution (HG/T2496-93)
Safety Regulations for Explosive Hazardous Locations (Lao Fafa [1995] No. 56)
Dissolved acetylene (GB6819-2004)
Small volume dissolved acetylene cylinder (GB16164-1996)
Calcium carbide (calcium carbide) (GB10665-2005)
Safety technical conditions for dissolved acetylene cylinder filling station (GB17266-1998)
Industrial acetone (GB6026-1998)
Chemical Safety Labeling Regulations (GB15258-1999)
Reciprocating piston acetylene compressor technical conditions (JB/T9103.1-1999)
Preparation of Chemical Safety Data Sheet (GB76483-2000)
Identification of major hazard sources (GB18218-2000)
Dissolved acetylene equipment (JB/T8856-2001)
Industrial sulfuric acid (GB/T534-2002)
Dissolve acetylene cylinders (GB11638-2003) and so on.
4.4 Dissolved acetylene enterprise personnel must receive safety qualification training and education, and pass the examination and obtain relevant qualification certificates. From the person in charge of the enterprise to the general practitioners, we must correctly understand the hazard of acetylene, master the safety management methods of acetylene production and safe operation methods, understand the correct treatment methods to eliminate various unsafe factors, and be familiar with the production and filling of dissolved acetylene. Safety management laws and regulations and standards. Dissolved acetylene enterprises must participate in industrial injury insurance according to law, and pay insurance premiums for employees.
4.5 Dissolved acetylene production enterprises must implement safety measures for dissolving acetylene. These measures mainly include: strictly controlling various ignition sources, timely checking and handling leaks, setting up relevant safety prevention facilities, equipped with occupational hazard protection facilities, and implementing safety management measures for dissolved acetylene cylinders. The safety measures for the dissolution of acetylene can be found in the article "Safety Evaluation of Dissolved Acetylene Enterprises".
4.6 As a necessary supplement to safety production management, dissolved acetylene production enterprises must prepare “Emergency Rescue Plan for Dangerous Chemical Accidentsâ€, prepare plans for major hazard identification and evaluation of acetylene production sites, establish emergency rescue organizations or have emergency rescue programs. The personnel, equipped with the necessary equipment and equipment, carry out regular drills, so that the dissolved acetylene production enterprises have the ability of emergency rescue operations, can timely control and eliminate the consequences of accidents, and reduce the major losses and injuries to the employees caused by sudden accidents. For the emergency rescue plan for hazardous chemicals accidents in dissolved acetylene production enterprises, please refer to the pre-plan example of the article "Effective rescue plan for dissolved acetylene accidents".
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