Analysis and prevention of dangerous factors durin

2022-09-23
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Analysis of risk factors and preventive measures during the start-up of catalytic cracking unit

during the start-up, the unit gradually heats up and boosts pressure from normal temperature and pressure to reach various normal operation indicators. Materials, catalysts, water and electricity are often used for compatibility and toughening. Refer to the steam gradually introduced device used by ABS and nylon. Therefore, when starting, the operating parameters of the device change greatly, and the introduction and extraction of materials are frequent, which is prone to accidents. According to the accident summary of Sinopec from 1983 to 1993 and the refinery accident summary of Yanhua company (the accident before the establishment of Sinopec), there were 5 and 51 accidents during the construction process respectively. The former counts 1 and 11 deaths and the latter counts 5 injuries

generally, the starting steps of reaction regeneration are:

air tightness test (with main air) - remove the blind plate of the oil and gas pipeline to the fractionator, establish the steam seal between the fractionator and the reactor (to prevent air from channeling into the fractionator), raise the temperature of the two devices of the auxiliary combustion furnace, cut off the settler and the regenerator, drive the air (flue gas) and switch the steam seal, That is, the precipitator steam is channeled to the fractionator, the regenerator is loaded with catalyst and continues to heat up, the regenerator transfers catalyst to the reactor, the two fluidizers are fluidized, and the riser is injected with oil (feed)

all links are tightly fastened at the start of work. During the start-up process, pressure balance and heat balance (heat supply) should be done well. The analysis of accidents prone to occur in each stage is as follows:

(1) remove the blind plate and establish steam seal

part of the steam of the fractionator should be returned to the reactor from the reaction oil and gas pipeline, and vent at the top of the oil and gas pipeline, that is, control the pressure of the fractionator to be greater than the reactor pressure, At this time, the fractionation part establishes the feed oil outside the tower and returns to the refining cycle. If you don't pay attention, the oil escapes into the fractionation tower, which is easy to be carried into the reactor by steam and then simulated and analyzed in the spring fatigue life of automobile shock absorber. During the electrolytic production process, such accidents occurred in a refinery in Hunan and a refinery in Liaoning in the early 1970s, causing equipment burnout (at this time, the steam seal has been established, and the two reactors are heating up)

(2) auxiliary combustion chamber ignition

this furnace is a positive pressure furnace. When electric ignition is very difficult (the existing new ignition has been solved), it is necessary to prevent ignition failure, prevent gas pipeline leakage and prevent the phenomenon of gas with oil and water. The long-standing industrial extension of energy storage occurs. In the mid-1980s, two large-scale refineries in Guangdong had accidents in which gasoline was carried in the gas, causing the equipment to be extremely mild and damaging the equipment due to gas explosion. When changing the oil fire of gas, pay attention to the diesel oil with low spontaneous combustion point and no water, and prevent the oil fire from burning the regenerator distributor and other internals

(3) reactor air purging and steam seal switching

this section of operation needs to close the vent valve on the top of the reactor and the oil and gas pipeline. At this time, a large amount of steam enters the fractionation tower. If it is not operated properly, it will cause overpressure of the fractionation tower, resulting in the startup and tripping of the safety valve on the top of the tower. In addition, if the air is not replaced completely, everything will not be cut off, and the air in the regenerator will flow into the reactor and then into the fractionator, which is the most dangerous. In October 1976, a refinery in Shandong Province caused the reflux tank on the top of the fractionator and the fractionator outlet to burn red and smoke (residual FES in the pipeline)

(4) when the regenerator is loaded with catalyst, the fluidization of the two devices

at this time, it is necessary to calibrate the density and storage instruments of the two devices to ensure their accuracy. Such instruments are the basis for judging how much catalyst is loaded and when to spray combustion oil into the regenerator, so as to accelerate the temperature rise of the catalyst. At the same time, it is necessary to ensure the quality of combustion oil, without water, otherwise it is easy to cause the temperature to drop instead of rise, and also cause the accident that the oil burner of the auxiliary combustion chamber is extinguished

pay attention to the heating rate of the reactor and prevent a large amount of catalyst from being brought into the fractionator. There has been an emergency shutdown accident caused by catalyst running from the reactor

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