Dangerous factors and preventive measures during s

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Dangerous factors and preventive measures during shutdown of hydrogen cracking

the shutdown of hydrogenation unit starts with the cooling and volume reduction of the reaction system. In this process, we should have a premonition that we should follow the principle of cooling first and then reducing the volume. The feed rate of the reaction system is reduced, the space velocity is reduced, and the temperature rise of the hydrogenation reactor is increased, which is prone to reaction temperature runaway. The so-called flying temperature is the phenomenon that the reactor temperature rises rapidly, so that it is uncontrollable

(2) replace the whole system with low doubt raw materials

the raw oil of the hydrogenation unit is generally heavy and has a high condensation point, which is easy to condense in the catalyst, pipeline and equipment during shutdown. In order to avoid the above situation, the low doubtful oil replacement system shall be applied before shutdown, and the low doubtful oil used is generally the second-line oil

(3) stop the reaction feed pump

when cutting off the reaction feed, pay attention to the appropriate temperature of the reactor, so that there is no obvious temperature rise in the cracking reactor

(4) the reaction system circulates with oil and hot hydrogen extraction

after cutting off the reaction feed, the reaction heating furnace heats up and takes out the oil stored in the catalyst with hot circulating hydrogen. The temperature of hot hydrogen extraction should be determined according to the requirements of the catalyst, generally about 400 ℃. The temperature of hot hydrogen extraction should not be too high to avoid the catalyst being reduced by hot hydrogen

(5) reaction system cooling and depressurization

hydrogenation reaction system cooling and depressurization at the required rate

(6) N2 replacement of reaction system

the controllability of reaction system is poor. The system uses N2 to replace N2 environment, so that the hydrogen hydrocarbon concentration of the system is 1%

(7) catalyst unloading

the used carbonaceous catalyst is prone to spontaneous combustion in the air. The restorer of Jinan assay station is operated in N2 gas environment, and the catalyst must be unloaded by professional unloading company personnel into the reactor. Therefore, there is a broad development space in the home decoration industry in catalyst unloading. N2 or dry ice should be used to protect the catalyst in order to avoid spontaneous combustion of the catalyst

(8) cleaning and anti-corrosion of hydrogenation equipment

the equipment and components of the high-pressure part of the hydrogenation unit should be cleaned with lye after shutdown to avoid corrosion and damage to the equipment after contact with air. In addition, the equipment of the high sulfur system is mainly the post-treatment part, which should be washed with water before opening to avoid the spontaneous combustion of iron sulfide in the air

(9) oil return and purging of the unit

when the hydrogenation unit is shut down, the oil stored in the unit should be withdrawn and purged to ensure that no dead corner is left

(10) treatment of auxiliary system

after the shutdown of the hydrogenation unit, clean the flare system, underground sewage system and other auxiliary systems of the unit, and add blind plates to prevent corrosion of the unit and system, so that the unit can meet the maintenance conditions

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