First, the foreword Anhydride, the full name of phthalic anhydride, is one of the important organic chemical raw materials, widely used as raw materials and intermediates of plasticizers, resins, pharmaceuticals, dyes and pesticides. At room temperature, phthalic anhydride crystallized as a flaky white solid, mp 131.6 ° C. Phthalic anhydride industrial production is the use of o-xylene gas-phase catalytic oxidation, which is flammable, explosive, high temperature, toxic and other conditions, the oxidation temperature of up to 440 ℃, the liquid phthalic anhydride refining temperature up to 180-250 ℃. In the production process, if the liquid phthalic anhydride splashed on the skin, in addition to scald, it is also easy to absorb water to generate highly corrosive phthalic acid; gaseous phthalic anhydride, with a strong irritant, after inhalation, cough, sore throat, mucosal congestion , Eye swelling and tears on the human body is very large, under the open flame conditions can also lead to burning and explosion and other serious accidents. Therefore, phthalic anhydride plant equipment technical requirements are high, the key equipment and more imports. Such as benzene anhydride pump, the domestic device generally choose Germany KSB company, the United States DURCO company and other products, all for the jacket mechanical seal centrifugal pump. However, due to the physical and chemical characteristics of phthalic anhydride, this type of pump seal life is short, high maintenance costs, but also in the equipment maintenance process, phthalic anhydride on the human body and the environment are great hazards. Second, the mechanical seal centrifugal pump defects According to the physical and chemical properties of phthalic anhydride and its harm to the human body, the environment, the mechanical seal pump bellows mechanical seal to ensure better sealing effect. However, due to phthalic anhydride as a high melting point substance, the temperature of the mechanical seal is often lower than the melting point of the material during opening and stopping, and a small amount of phthalic anhydride will coagulate or crystallize. The bellows will gradually lose elasticity due to blockage and friction Vice failure, leading to pump leakage. Secondly, during the operation of the phthalic anhydride pump, the crystal grains on the surface of the bellows accumulate and cause axial bending, which causes the bellows to break or the amount of seal compression is not uniform, the high temperature aging of the seal ring is compensated, and the compensation leaks. Third, as the oxidation of phthalic anhydride is operated in the explosive limit of o-xylene, there is a big danger and more accidental devices. The service life of the mechanical seal of phthalic anhydride pump is often shortened due to frequent opening and closing. Pump leaks. Secondly, during the operation of the phthalic anhydride pump, the crystal grains on the surface of the bellows accumulate and cause axial bending, which causes the bellows to break or the amount of seal compression is not uniform, the high temperature aging of the seal ring is compensated, and the compensation leaks. Third, as the oxidation of phthalic anhydride is operated in the explosive limit of o-xylene, there is a big danger and more accidental devices. The service life of the mechanical seal of phthalic anhydride pump is often shortened due to frequent opening and closing. Pump leaks. Secondly, during the operation of the phthalic anhydride pump, the crystal grains on the surface of the bellows accumulate and cause axial bending, which causes the bellows to break or the amount of seal compression is not uniform, the high temperature aging of the seal ring is compensated, and the compensation leaks. Third, as the oxidation of phthalic anhydride is operated in the explosive limit of o-xylene, there is a big danger and more accidental devices. The service life of the mechanical seal of phthalic anhydride pump is often shortened due to frequent opening and closing. Pump leaks. Secondly, during the operation of the phthalic anhydride pump, the crystal grains on the surface of the bellows accumulate and cause axial bending, which causes the bellows to break or the amount of seal compression is not uniform, the high temperature aging of the seal ring is compensated, and the compensation leaks. Third, as the oxidation of phthalic anhydride is operated in the explosive limit of o-xylene, there is a big danger and more accidental devices. The service life of the mechanical seal of phthalic anhydride pump is often shortened due to frequent opening and closing. Pump leaks. Secondly, during the operation of the phthalic anhydride pump, the crystal grains on the surface of the bellows accumulate and cause axial bending, which causes the bellows to break or the amount of seal compression is not uniform, the high temperature aging of the seal ring is compensated, and the compensation leaks. Third, as the oxidation of phthalic anhydride is operated in the explosive limit of o-xylene, there is a big danger and more accidental devices. The service life of the mechanical seal of phthalic anhydride pump is often shortened due to frequent opening and closing. Fourth, when repairing the pump, the temperature of the pump chamber is far lower than the melting point of the phthalic anhydride. All the transported media have been solidified in the machine room so that the whole set of sealing components, including the bushings, must all be replaced. In this way, even the localization of the same type of bellows seal a set of price is about 0.5 million, we can see that the equipment maintenance costs are relatively high, and the material on the operator and the environment a great harm, it is necessary to use the right Sealed pump replacement. Third, the advantages of jacketed magnetic pump selection Static sealing pump instead of the dynamic seal centrifugal pump, first consider the shield pump, it is a commonly used seal-less pump, but there is high temperature medium on the shield motor operation of the adverse and Before the first car can not determine the existence of plain bearings without melting of solid media difficulties, it is not suitable for conveying high-melting point phthalic anhydride product requirements. Relatively magnetically driven sealless pump can meet the above conditions. First of all, consider the delivery of materials due to the decline in the temperature of the pump chamber appeared crystallized or solidified, so the volute casing and bushing parts to increase the thermal jacket design, isolation sleeve and internal rotor gap is very small, is very important technology Requirements, both before and after the jacket to play the insulation or heating consistency, fully guaranteed by the heat, even in the tiny gap in the sliding bearings and the tail of the isolation sleeve must ensure that the material is completely in the molten state, so as not to damage the key magnetic pump part. Heat insulation medium is usually steam. Note that the insulation jacket to ensure the absolute separation of the transport medium and the heat medium, to avoid the combination of phthalic anhydride and water vapor to produce higher melting point of phthalic acid block the pipeline. Reasonable design of the magnetic pump thermal jacket, can achieve centrifugal pump jacket with heat tracing effect. Secondly, the phthalic anhydride transported can reduce the fluidity due to the decrease of the temperature during the process of internal circulation, and the auxiliary impeller at the tail makes the small space become a high velocity flow area, thereby avoiding the possible blockage failure. At the same time, when the pump is stopped, the tail of the magnetic zone will not accumulate fluid and empty completely, which avoids the difficulty of driving next time due to the solidification of the material. This is significantly better than the centrifugal pump shutdown caused by fluid defects. In addition, according to the operation experience of conveying high-melting-point material pump, after the pump is stopped, all the media should be emptied, one to prevent the equipment from being damaged by the volume change of the material form, and the other during the preheating process Improve efficiency, keep heating evenly. Before driving the magnetic pump, the same can be checked to check the rotor stuck phenomenon, confirmed after the correct feed, warm pump, driving, effectively ensure the reliability of the pump starts. In summary, the jacketed magnetic pump can fully meet the process conditions of phthalic anhydride production, instead of the dynamic seal of the centrifugal pump, the pump leak maintenance rate is greatly reduced. Mechanical seal pump and sealless magnetic pump operating costs compared V. Conclusions As long as the effective attention to the jacket magnetic pump parking emptying and driving preheating process to ensure the car is light, does not damage the sliding bearings and isolation sleeve, the form of the machine Pump is superior to mechanical seal pump, it not only significantly reduce maintenance costs, but also easy to operate, conducive to the continuous operation of the device, while reducing operator damage and environmental pollution. This type of sealless magnetic pump can be further extended to the production of similar products, such as DMT, tar and so on.
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