What Is an Acetylene Generator?

English term name of acetylene generator: acetylene generator is a device that can make water and calcium carbide perform a chemical reaction to generate a certain pressure of acetylene gas. The acetylene generator is classified by pressure: low pressure-pressure is less than 0.007MPa, medium pressure-pressure is 0.007MPa-0.13MPa. The acetylene generator is divided into different ways according to the contact of calcium carbide and water: floating type, drainage type, water-into-type calcium carbide type and combined type.

Requirements for operators

The operator must be specially trained, familiar with the structure and working principle of the acetylene generator, and pass the safety technology assessment.

Arrangement principle of acetylene generator

Mobile acetylene generator can be placed outdoors or in a well-ventilated room

1. The construction of the generator should ensure that all the gas in the device can be completely released, so that the remaining air can be blown out before reinstalling the calcium carbide.

2. Necessary and conforming installation devices shall be installed. Safety devices include fire arresters, explosion-proof pressure relief devices, and indicating devices. The installation location of the safety device shall meet the requirements.

The basic technical requirements of a tempering arrester (fire arresting device) are: can reliably prevent the transmission of flames and explosion waves. And can discharge the explosive mixture into the atmosphere; should have a pressure relief device, the pressure relief device should meet the technical requirements; can meet the requirements of the welding process, such as does not affect the flame temperature and gas flow; , Cleaning and repair; It is best to cut off the gas source in the event of tempering; The working pressure of the tempering arrester should be compatible with the working pressure of the acetylene generator; Temper arrester has better safety performance and is widely used.

The installation location and technical performance of the explosion-proof pressure relief device shall meet the requirements of the specification. When the pressure of the generator rises and exceeds the protection set value, it should be able to work in a timely and reliable manner to release the gas in the mountain and reduce the pressure, so as to prevent the generator tank from rupturing. Explosion-proof pressure relief devices include safety valves and pressure relief membranes. Indicating devices include pressure gauges, thermometers and water level indicators. The devices should be sensitive and accurate.

3. Ensure good cooling conditions. The generator must have a sufficient amount of cooling water. Depending on the conditions, calcium carbide should be decomposed in a large amount of water as much as possible.

In the calcium carbide decomposition zone, the temperature of water must not exceed 60 ° C. The temperature of the steam boiler output by the temperature of the gas chamber should meet the following requirements: drip type, drainage type or immersion type: the gas temperature should be higher than 90 ° C. The temperature of the acetylene output from the generator must not be higher than 40 ° C.

For mobile acetylene generators, when the ambient temperature of the surrounding garden exceeds 30 ° C, the temperature of the acetylene output from the acetylene generator is allowed to be 10 ° C higher than the temperature of the surrounding air.

4. The structure of the generator and its working parts must not cause sparks due to collision damage or friction during work.

5. The parts of the acetylene generator are not allowed to use pure copper (purple copper), so as to avoid the danger of copper acetylene generation, an alloy containing less than 70% copper can be used.

Acetylene generation

When calcium carbide is added to the generator, it reacts with water to generate acetylene gas, because industrial calcium carbide reacts with water at the same time to generate corresponding impurities such as PH3, H2S and other gases.

Main reaction: CaC2 + 2H2O C2H2 + Ca (OH) 2 + 127.2KJ / mol

Side reaction: CaO + H2O Ca (OH) 2 + 62.76KJ / mol

CaS + 2H2O Ca (OH) 2 + H2S

Ca3P2 + 6H2O 3Ca OH 2 + 2PH3

Ca3N2 + 6H2O 3Ca OH 2 + 2NH3

Ca2Si + 4H2O 3Ca OH 2+ SiH4

Ca3As2 + 6H2O 3Ca OH 2 + 2 AsH3

Crude acetylene contains the above-mentioned side reaction impurities. During the hydrolysis of calcium carbide, a large amount of calcium hydroxide is formed to form an alkaline medium, resulting in incomplete hydrolysis of PH3 and H2S. Therefore, crude acetylene contains more PH3 (hundreds of ppm) and less. H2S (tens of ppm), phosphide can also exist in the form of P2H4, and can spontaneously ignite in the air.

The following reaction may occur at a temperature of about 85 ° C: the addition of bimolecular acetylene generates CH2 = CHCCH (vinylacetylene) and C2H5SC2H5 (ethylsulfide), both of which can reach 50 100ppm.

At the temperature of 85 , a large amount of water vapor is carried in the crude acetylene due to the vaporization of water.

(General water vapor: acetylene = 1: 1). ^[3]

Quality, particle size and residence time of calcium carbide

Hydrolysis is a liquid-solid phase reaction. The calcium carbide has good quality and high gas generation. The larger the contact area between calcium carbide and water, the faster the hydrolysis reaction speed. In actual production, both complete hydrolysis and safety are considered. Factors such as generator structure and calcium carbide pulverization are combined to control the particle size of the calcium carbide in the range of 15-50mm.

Size of calcium carbide mm	2-4	5-8	5-15	15-25	25-50	50-80
1Kg calcium carbide complete hydrolysis time (minutes)	1.17	1.65	1.82	4.23	13.6	16.57

For a five-layer pallet generator, the calcium carbide residence time must be more than 13 minutes.

temperature reflex

The heat of calcium carbide hydrolysis reaction is removed by adding excess water. The reaction temperature achieves the process control index by adjusting the amount of water and calcium carbide. As the reaction temperature rises, the hydrolysis rate accelerates, and the solubility of acetylene in the calcium carbide slurry decreases, which significantly reduces the consumption of calcium carbide. However, the reaction temperature is too high, and the solid content of the calcium carbide slurry is large, which will cause unsmooth overflow or slag discharge High reaction temperature, increased water vapor content in crude acetylene and increased slag entrainment will cause overload of the rear cooling tower and block pipelines or trays. Considering the above aspects, the reaction temperature is generally controlled at 80-90 ° C.

Danger of combustion and explosion of acetylene

Pressure and temperature. The spontaneous ignition point of acetylene is 335 ° C, which is easy to spontaneously ignite under heat. At 200-300 , exothermic polymerization of acetylene molecules begins. When the temperature is higher than 500 ° C, acetylene will decompose explosively. If the decomposition is performed in a closed container, an explosion will occur due to an increase in temperature and an increase in pressure. The effects of temperature and pressure on the polymerization and explosive decomposition of psacetylene are shown in the figure below.

oxidant. Acetylene is mixed with air to form an explosive mixed gas with an explosion limit of 2.2-81% and an auto-ignition point of 305 ° C; when mixed with oxygen, its explosion limit is 2.8-93% and an auto-ignition point of 300 ° C; Explosion when exposed to sunlight or heat. Acetylene can also be combined with fluorine, bromine, etc., causing combustion and explosion.

impurities. Acetylene often contains harmful impurities such as phosphine and thiohydrogen. Phosphine has a low self-ignition point, and spontaneous combustion occurs at 45-60 ° C, detonating a mixture of acetylene and air.

Catalyst. Catalysts such as iron oxide, copper oxide, and aluminum oxide can adsorb acetylene molecules on their own porous surfaces, increase the acetylene concentration, and promote the polymerization and reaction of acetylene molecules and explosive decomposition.

Container volume. The smaller the volume of the container, the less likely it is to explode; conversely, the greater the danger of explosion.

In addition, due to the low ignition energy (0.019mJ) of acetylene, explosive mixtures will be formed after metal contact. ^[4]

Danger of burning and exploding calcium carbide

Calcium carbide is a common name for calcium carbide. It does not have explosive properties. The danger of burning and exploding is mainly reflected in:

Combustion and explosion in water. The calcium carbide decomposes immediately upon contact with fire, generating acetylene and emitting a lot of heat

This amount of heat can cause acetylene to ignite and explode.

Sparks of calcium carbide. Calcium carbide generally contains ferrosilicon impurities, which can produce sparks during collision or friction, and become the detonation source of acetylene. Calcium phosphide impurities contained in calcium carbide react with water to generate phosphine gas. Causes explosive mixture to explode in generator.

the size of calcium carbide. The smaller the particle size of calcium carbide, the faster the decomposition speed with water, the more heat is released instantaneously, and it is easy to cause local overheating and danger, see the table below.

aS explosion-proof technical measures for acetylene

Fire prevention measures.

When the flame burning speed is faster than the gas flow speed of acetylene and oxygen, the gas welding (cutting) flame will burn along the welding (cutting) torch to the hose, causing danger. To this end, a fire arrester should be installed, usually a flashback preventer to prevent flames from penetrating into the gas storage tank and the main tank or to prevent the flame from spreading in the pipeline. Tempering arresters are divided into two types according to pressure: low pressure (<0.07MPA = and medium pressure (0.070.15MPa); divided into two types: open type and closed type according to structure; divided into fire-resistant media. Water sealed and dry.

Pressure relief measures. Pressure relief is to release the pressure in time when the pressure of the generator exceeds a certain limit, or when the pressure is generated by explosion, so as to prevent the generator from rupturing. Common pressure relief devices include safety valves and bursting discs.

A Safety valve. Also known as a pressure relief valve, its role is to ensure that the pressure of the acetylene generator can be automatically opened when the pressure exceeds the safety required pressure (0.215MPa), and some gases are released; when the pressure drops to a safe range, it is automatically closed to ensure the generator No overpressure damage. To ensure the sensitivity and reliability of the safety valve, regular exhaust tests should be performed to prevent the exhaust pipe, valve body, etc. from being blocked by adhesion. In addition, the safety valve should be frequently checked for leaks or non-stop exhaustion, and should be repaired in a timely manner.

B bursting disc. The material of the vent sheet for the generator includes aluminum foil and rubber sheet. In contrast, aluminum foil is ideal. The bursting disc should have sufficient strength to withstand the working pressure (generally below 0.15MPa): good heat resistance and corrosion resistance; meanwhile, it should be brittle; easy to crack; the thickness should be as thin as possible. For tanks with a volume greater than 300L, the selection of the explosion area should be determined by blast tests. Explosion discs should be provided with the specified materials and specifications and cannot be replaced at will.

Monitoring measures. The purpose of monitoring is to control the pressure of acetylene, the temperature and water volume of water and acetylene, etc. For fixed acetylene generators, all the above parameters must be monitored; for mobile generators with smaller capacity, temperature monitoring is not necessary.

A Pressure monitoring. The medium pressure acetylene generator must be equipped with a pressure gauge to directly display the acetylene pressure value inside the tank. In order to keep the pressure gauge sensitive and accurate, attention should be paid to maintenance and repair during use. The pressure gauge should be kept clean, such as broken dial glass or blurred scale. Should be discontinued. The connection pipe of the pressure gauge should be purged regularly to prevent clogging. Always check whether the pointer returns to the normal position after turning. Pressure gauges must be inspected regularly. Pressure gauges that have expired should stop functioning.

B Water level control. The water level can be indicated by a water level meter or a water tap. Water should be added to each tank of the generator according to the water level indicator or the water level indicated by the faucet. The indication scale of the water level gauge should be kept clear and easy to see, and the water level faucet should not be rusted.

C Temperature monitoring. Alcohol thermometers are used to measure the temperature of acetylene and the temperature of water in the electrolytic decomposition zone of the generator. Mercury thermometers are prohibited. The glass protective tube of the thermometer should be scrubbed frequently to make the scale of the thermometer clear.

The layout of the acetylene generator.

A Mobile generators are forbidden to be placed in thermal processing workshops such as forges, casters and heat treatments, and in boiler rooms that are in operation.

B The fixed generator should be arranged in a separate room. When it is placed outdoors, it should be provided with a special shed.

C The horizontal distance between the acetylene generator and the open flame, the place where the spark is emitted, the high-voltage power line and other heat sources should be kept above 10m, and it is not allowed to be placed on the working platform and equipment with severe vibration.

Preparation before use of acetylene.

A Check whether the safety devices of the generator are complete and whether the working performance is normal.

B Fill the water according to the specified filling capacity.

C The calcium carbide should be installed according to the quantitative requirements of various types of generators, and should not be overfilled.

D If the winter effect generator is found to be frozen, it can only be thawed with hot water or steam. It is strictly prohibited to use open flames or red iron to bake, let alone use iron objects such as sparks to strike.

Use of acetylene generator.

A Before starting the generator, check the water level of the flashback preventer. After everything is normal, open the water supply valve to feed the calcium carbide.

B After the water is delivered, check whether the pressure gauge, safety valve and joints are normal.

C After starting, if the pressure gauge reading rises too fast, or if gas escapes from the safety valve, or if the pressure gauge pointer is still at zero, stop the gas immediately. After troubleshooting, restart.

Explosion protection during working process.

A Hold the mixture of acetylene and air in the generator before using it for gas supply.

B All parts of the generator should be inspected at any time during the process, and measures such as air leakage, water level mismatch or failure of safety devices should be taken in time.

C The removal of calcium carbide slag during operation must be performed after the calcium carbide is safely decomposed.

D When the temperature of the water in the generator exceeds 80 , it should be filled with cold water or temporarily stopped working, and cooling measures should be taken to reduce the temperature.

E Do not open the generator and drain water at will to prevent fire and explosion caused by overheating of calcium carbide.