Research On The Problem Of Reactor Fouling In Tube High Pressure Low Density Polyethylene Plant

The problem of reactor fouling of high-pressure polyethylene plant has always been the bottleneck problem restricting the high load operation of domestic and foreign high-pressure polyethylene plants.At present,even the licencer of high-pressure polyethylene plant has not found the cause of fouling of high-pressure polyethylene plant and the solution.Based on years of operation experience in high-pressure polyethylene plant,this paper summarizes the causes of high-pressure polyethylene plant fouling.At the same time,it provides a technical method that can quickly deal with the reactor fouling and increase the load of the plant,which can be used as a reference for the same industry in China.Based on the annual output of 300000 tons of high-pressure polyethylene plant in Guoneng Yulin Chemical Co.,Ltd.,combined with the operation experience of 200000 tons of high-pressure polyethylene plant in Daqing Petrochemical Company,this paper summarizes the similarities of reactor fouling in high-pressure polyethylene plant,finds out the factors that may affect the reactor fouling in high-pressure polyethylene plant,and formulates the corresponding countermeasures.At the same time,according to the actual operation experience,we should find the most efficient technical measures to deal with the fouling of the reactor,so as to eliminate the fouling of the reactor in the shortest time.The conclusions are as follows:1.Possible reasons for reactor fouling(1)A small amount of oxygen can inhibit the polymerization of high-pressure polyethylene unit,reduce the production of macromolecular polymer,and affect the heat transfer of intercooler and the operation stability of the secondary unit.When the oxygen content exceeds a certain amount,oxygen can initiate the polymerization reaction as an initiator.(2)When the reactor is shut down for maintenance,if air / oxygen enters into the reactor,oxygen will exist in the system.When the reactor is hot,polyethylene is prone to cross-linking,resulting in reaction adhesion.2.Effective measures to avoid reactor fouling(1)Avoid oxygen entering the reactor in any case.During the shutdown and maintenance of the unit,if there is no maintenance item for the reactor,the positive pressure protection of nitrogen must be maintained in the reactor to avoid oxygen entering the reactor.(2)It is necessary to maintain the temperature stability of the preheater system.The polymerization reaction needs to be initiated under the action of initiator peroxide,and the change of initiation temperature will lead to the change of molecular branched chain of polymer produced by polymerization reaction.At lower initiation temperature,the number of branched chain produced by polymerization reaction is small,the degree of polymerization is high,and the polymerization reaction produces more polymers with large molecular weight,low melt index and poor fluidity The adhesion of the inner wall of the reactor affects the heat removal of the polymerization reaction,resulting in the reactor fouling.(3)To ensure the stable operation of high pressure polyethylene plant and reduce the number of start-up and shut-down are the most direct and effective measures to avoid the reactor fouling.(4)Before establishing the polymerization reaction,it is necessary to ensure that there is enough molecular weight regulator propionaldehyde in the system.The molecular weight regulator in the system should not be too low.Otherwise,when establishing the polymerization reaction,the melt index of the product is too low,resulting in poor fluidity of the polymer,which is easy to adhere to the inner wall of the reactor,resulting in reactor fouling.3.Technical measures for defouling of reactor(1)The molar mass of the product should be controlled by propionaldehyde,not by the average temperature of polymerization.(2)For the reactor that is fouling,it is necessary to control the temperature lower than the normal reaction temperature peak.(3)For the reactor that is fouling,it is necessary to produce products with melt index greater than or equal to 2g / 10 min.Do not produce products with melt index less than 2g / 10 min during the process of defouling.(4)Control the production of the product's melt index in the upper limit of the index range.(5)Increase the temperature of the reactor preheater by 3-5 ?.(6)Increase the pulse depth.(7)The pulse period is shortened.(8)Increase the temperature rising speed of polymerization temperature peak,make the temperature peak reach the highest value as soon as possible,and make the reaction temperature peak move forward.(9)Increase the temperature of the hot water which will remove heat from the reactor.(10)Reduce the flow of hot water in the reactor.(11)Propylene was used as a molecular weight regulator to partially replace propionaldehyde.