Risk factors analysis and preventive measures of t

Risk factor analysis and preventive measures of benzene production unit

pyrolysis gasoline hydrogenation and extraction benzene production unit has the characteristics of high temperature, high pressure and hydrogen. Most of the materials are class a dangerous crystals. The product is extremely toxic to benzene. H2S toxic gas is produced in normal production and special operation. Therefore, it is an accident prone device in chemical production devices

(I) risk factors and preventive measures during start-up and shutdown

1. analysis of risk factors and preventive measures during start-up

when starting up, gradually raise the temperature and pressure from normal temperature and pressure to reach the normal operation index. Materials, hydrogen, water and electricity are gradually introduced into the device. Therefore, when starting, the operating parameters of the device change greatly, which is prone to accidents. The main steps for the start-up of the unit are:

replacement of air tightness - system oiling - pre fractionation establishment of single tower circulation - reaction system establishment of safety liquid circulation - extraction system establishment of solvent circulation - reaction system temperature rise and pressure rise - system feeding. The start-up sequence of the unit is from pre fractionation, hydrogenation reaction system to extraction system. The accident analysis of each stage is as follows:

(1) pre fractionation material polymerization

the material processed by the pre fractionation system is unsaturated material. Due to the extremely unstable chemical properties of the arsenic removal agent cumene hydroperoxide, Easy to bring water to the material or the retention time of the material, he said "When such materials are lighter than feathers and too long, they play the role of chain initiation of polymerization reaction. The elimination method of causing the materials in the arsenic removal reactor is: first drop the piston back to the bottom of the oil cylinder to polymerize. Therefore, in the normal operation of pre fractionation, it is necessary to find the water in the raw materials or the leakage of the reboiler in time. The accident will lead to the partial or total shutdown of the unit. Pay attention to the decomposition and explosion of the arsenic removal agent storage tank when the temperature is too high, and static will occur when adding CHP The product is formaldehyde free, fire-proof and moisture-proof, and there is no insect damage. Electric sparks cause explosions. The air pump used for installing CHP is not replaced completely. Other chemicals are mixed in CHP storage tanks and react with cumene hydroperoxide to cause explosions

(2) heating furnace ignition

the gas heating furnace is a positive pressure cylindrical furnace, and the "electronic ignition system" should be operated in strict accordance with the operation method. Before ignition, the furnace shall be tested for explosion. In case of non ignition or flameout, the furnace shall be tested for explosion again before re ignition, and it can be carried out after it is qualified. When shutting down the boiler, pay attention to close the valve at the root of the nozzle to prevent the leakage of the solenoid valve, which will cause the accumulation of fuel gas in the furnace and cause danger. When igniting, first light the long burning burner, then open the valve of the main burner and put the main burner into operation. The furnace tube that provides heat for the reaction part is filled with high-temperature and high-pressure hydrogen. If the wall temperature of the furnace tube is too high, the service life of the furnace tube will be shortened, and serious overheating will lead to the explosion of the furnace tube, causing an explosion accident

(3) leakage of the second stage discharge heat exchanger

the temperature of the second stage discharge is 260-350 ℃, and the second stage feed is exchanged with the second stage feed preheater and the second circulating hydrogen cooler. The materials on both sides are high-pressure and hydrogen. When the temperature changes greatly during the start-up stage, it is easy to cause leakage. Therefore, the heating rate should be strictly controlled at 30 ℃/h during the start-up process. Hot tightening shall be carried out after the temperature rises above 100 ℃

(4) reactor overtemperature

due to the unstable operation of pre fractionation at the start-up stage, C5 fraction is very easy to be entrained to the anti 2Kn electro-hydraulic servo message universal experimental machine, which is one of the latest series of message universal experimental machine products developed by our company, causing a sharp rise in temperature. In addition, the untimely adjustment of the heating furnace is also a main reason for the flying temperature

therefore, the feeding quality should be strictly checked at the start-up stage before feeding to the reactor. The adjustment of the heating furnace should also be rapid and timely. In case of flying temperature, reduce the feeding in time until it stops. Reduce the temperature of the heating furnace until it goes out. Recycle hydrogen is used to take away the reaction heat

(5) stripper flushing

during the start-up of the stripper, the adjustment of temperature and the change of feed rate will cause the imbalance of vapor-liquid balance in the tower. Thus, the solvent is entrained to the top of the tower, resulting in tower flushing. When starting up, pay attention to the slow feeding after the solvent circulation of the two towers is established and stabilized, and the temperature of the two towers is adjusted to the operating value. And the feed rate is maintained between 10-15t/h. The temperature adjustment should be carried out slowly. In case of tower flushing, reduce the heating steam of stripper reboiler and extraction distillation tower reboiler immediately until they are closed. Reduce the inlet temperature of lean solvent and purified solvent. Reduce the feeding amount until the feeding is stopped

2. Analysis of risk factors and preventive measures during shutdown

device shutdown is the process of gradually reducing the temperature, pressure and flow of the device from the normal operating state. The operating parameters change greatly, so they are also in an unstable operating state. Accidents may also occur due to improper operation. The following problems should be paid attention to

(1) the residual oil of each pre fractionation tower should be pumped out as much as possible. The temperature of each tower drops to normal temperature. Once the equipment is opened, pay attention to remove the residues inside the equipment. Wash with water after purging to prevent spontaneous combustion of oligomers

(2) the hydrogenation reaction system should have enough time for hydrogen circulation with oil to ensure that the two reactors do not polymerize materials