Risk analysis and management measures of sodium cy

Risk analysis and management measures for the production of sodium cyanide by light oil cracking

Introduction (1)

sodium cyanide is a highly toxic hazardous chemical, which is mainly used in metallurgy, electroplating, medicine and some fine chemical production. The production of sodium cyanide by light oil cracking is a production process researched and developed in China, which is adopted by some domestic small and medium-sized enterprises at present. Because the samples used in this production process have good breakpoints, most of the raw materials, intermediate products and final products are flammable, explosive or highly toxic and harmful substances, and the potential dangers in the production operation are relatively large. In addition, some small and medium-sized enterprises are short of funds, simple equipment, low quality of personnel, and many hidden dangers of accidents. Therefore, it is necessary to conduct in-depth analysis of its safety and take effective measures to control and reduce accidents

production process introduction (market competitiveness is further improved 2)

the process flow of sodium cyanide production by light oil cracking is shown in Figure 1. The main raw materials are light oil (or gasoline), liquid ammonia and caustic soda. The products are liquid sodium cyanide (liquid cyanide for short) and solid sodium cyanide (solid cyanide for short). The production process is mainly divided into three stages: preparation and purification of hydrogen cyanide gas, preparation of liquid cyanide and preparation of solid cyanide

Figure 1 process flow diagram of sodium cyanide production by light oil cracking

1. preparation and purification of hydrogen cyanide gas

liquid ammonia is vaporized by vaporizer and mixed with gasoline in Venturi tube, and then heated to 250 ℃ ~280 ℃ by preheater and enters the bottom of cracking furnace. The three-phase graphite electrode in the furnace is immersed in the boiling bed of petroleum coke particles. Due to the large current conductive heating effect, the feed gas undergoes cracking reaction under 1450 ℃ high temperature and slight negative pressure:

cnh2n+n+nnh3 → nncn+ (2n+1) h2

2nh3 → n2+3h2

cnh2n+2 → nc+ (n+1) H2

generates a pyrolysis product mainly composed of hydrogen cyanide and hydrogen and containing a small amount of nitrogen and carbon powder, which is successively removed by heat exchange cooling and cyclone and bag filter, Get pure cracking furnace gas

2. preparation of liquid cyanide

the purified cracking furnace gas is introduced into the neutralization tank, and neutralized with the liquid sodium hydroxide in the plastic film and various physical and mechanical properties of rubber, wire and cable and other materials:

hcn+naoh → nach+h2o

liquid cyanide is generated. The unreacted gas enters the tail gas absorption tank and is further absorbed by liquid alkali, and then discharged to the chimney through the vacuum pump. The main component of tail gas is hydrogen

3. preparation of solid cyanide

liquid cyanide is sent to the economizer, heated and evaporated under negative pressure, the evaporated steam is condensed with water, and the non condensable gas is pumped to the chimney by vacuum pump. The mother liquor after evaporation and concentration enters the crystallizer and is cooled with water. The solid-liquid mixture is discharged into the centrifuge for solid-liquid separation, and the solid products are weighed and loaded into barrels. In order to further reduce the water content of solid cyanide, some manufacturers add a drying and dewatering process after centrifugal separation

risk analysis of production process (3)

1. fire and explosion risk

the materials with high fire and explosion risk in production mainly include gasoline, ammonia, hydrogen and hydrogen cyanide. Some physical and chemical parameters are shown in Table 1

Table 1 table of relevant parameters of combustion and explosion of main fire and explosion hazardous materials

there are many inflammable and explosive substances stored in gasoline warehouse, ammonia warehouse, high-level gasoline tank and ammonia oxidizer, and under normal circumstances, flammable vapor is emitted. If there are hidden dangers or improper operation of equipment and facilities, chemical explosion may occur

the cracking reaction was carried out under high temperature and micro negative pressure. The cracking furnace area belongs to class a fire risk area, and the cracking reaction temperature is higher than the spontaneous combustion point of the materials listed in Table 1. Two explosion elements, flammable and explosive substances and high-temperature fire source, cannot be excluded. If the equipment, pipelines and valves are poorly sealed, air leakage or leakage occurs, there is a risk of chemical explosion

the transformer oil in the cracking furnace transformer (accounting for a large proportion of fixed assets) weighs about 3T, and the phase current is between 2000~3000a. If the oil coke particles in the furnace are injected excessively, the electrode will be flooded, or the fine ash deposited on the electrode surface will not be removed for a long time, which is easy to short circuit between phases, the phase current will increase sharply, and the oil temperature will rise, which may burst the transformer and then cause a fire

physical explosion may occur in case of equipment failure or misoperation of boiler and pressure vessel

2. Poisoning risk

the types, distribution and harmfulness of main toxic and harmful materials in the production process are shown in Table 2. It can be seen from table 2 that highly toxic substances hydrogen cyanide and sodium cyanide are widely distributed in the plant. As an intermediate product, highly toxic gas HCN mainly exists in HCN preparation and purification unit and liquid cyanide preparation unit; In the cyanogen fixation preparation unit and cyanogen fixation warehouse, nach is easy to absorb moisture and CO2 in the air and release HCN highly toxic gas. The leakage and splashing of toxic substances will cause varying degrees of toxicity to people

Table 2 mainly checks the types, harmfulness and distribution of toxic and harmful materials

3. Dust hazard

carbon powder carried by cracking furnace gas is very toxic due to its contact with HCN and adsorption of HCN. When carbon powder is discharged regularly or irregularly during production, it will float in the air of the workplace and cause poisoning. There is highly toxic sodium cyanide dust in the cyanidation production workshop and cyanidation warehouse

4. Burn risk

there are two kinds of burns, one is chemical burn, the other is high temperature burn. Alkaline substances such as sodium hydroxide and liquid ammonia, which are widely used in production, are easy to cause damage to skin, eyes and respiratory tract; If the high-temperature equipment, devices and pipelines in the production system are not insulated, there is also a risk of burns

5. Other

in addition to the above four main hazards, there are also hazards of electrical injury, mechanical injury, falling from height, corrosion, static electricity, noise, vibration, high temperature and so on

from the above hazard analysis, it can be seen that cracking furnace production units, gasoline and ammonia storage units (including intermediate storage tanks) and cracking furnace transformers are equipment that may produce major hazards. Together with production units and storage and transportation facilities containing highly toxic sodium cyanide, they constitute major hazardous and harmful workplaces