At present, many chemical factories use latex centrifugal pumps when transporting styrene-butadiene latex. However, the serious phenomenon of demulsification and blocking in centrifugal pumps affect production efficiency and product quality.
The rubber factory of Qilu Petrochemical Co., Ltd. imported a set of emulsion polymerization styrene-butadiene rubber production equipment with an annual output of 80,000 tons from a Japanese company in the 1980s. After several renovations, it has now reached an annual production capacity of 150,000 tons.
The intermediate in the production of styrene-butadiene rubber — styrene-butadiene latex monomer is a kind of water-insoluble polymer monomer. It combines with water to form an emulsion by means of the action of an emulsifier to ensure the normal progress of the reaction system. Due to the instability of the emulsion polymer itself, it is very easy to break the covalent bond between the latex monomer and the water molecule due to mechanical and physical effects such as friction, stirring, and shearing during the transportation process, which is called demulsification.
The latex monomer coagulates after demulsification and precipitation, and quickly adheres to the surface of equipment and pipelines, causing serious blockage. The latex pump responsible for the delivery of styrene-butadiene latex in the styrene-butadiene rubber production plant is a BLS centrifugal pump imported from Japan Honda and specially developed for transporting styrene-butadiene latex. Demulsification and blockage often occur inside the body.
During many years of use, it was found that the imported centrifugal pump has the following problems in the process of conveying latex:
(1) The blades of the rotating impeller produce severe shearing of the latex, which inevitably leads to demulsification, which not only affects the product quality, but also easily coagulates after the latex monomer is precipitated, and continuously adheres to the surface of the pump casing and pipes, causing serious damage. clogging phenomenon.
(2) Coagulation and blockage of latex cause frequent shutdowns, seriously affecting the normal operation of production. Because the latex in the centrifugal pump is easily broken and serious blockage occurs, equipment and pipelines need to be switched and cleaned frequently (almost once a week in the production process of styrene-butadiene rubber), which not only causes the loss of a large amount of latex but also consumes considerable manpower and labour. Material resources; Due to the continuous switching of equipment and pipelines, the stable operation of production and the increase of output have been seriously affected.
(3) Due to the process characteristics, the delivery flow rate of the pump must fluctuate within a certain range, while the centrifugal pump operates at a constant speed (n=1500r/min), and it is difficult to achieve stable pressure. The allowable flow rate can be adjusted within a certain range, but can not meet the needs of variable process production.
(4) It is precise because the centrifugal pump cannot realize the variable speed operation with the change of working conditions so that its operating efficiency is low (only about 25%) and the energy consumption is large.
(5) The shaft seal leaks seriously and the service life is short. Since the original shaft seal adopts the traditional soft packing sealing structure, a large amount of cooling water is likely to enter the pump during operation and affect product quality, or a large amount of latex conveyed in the pump leaks along the shaft seal when the cooling water is interrupted; in addition, the soft The packing seal has serious friction and wear, high energy consumption and poor reliability.
For this special working condition, a new type of twin-screw pump has been specially developed in China. The main features of this kind of twin-screw pump include the adoption of the cantilever structure to ensure the smooth flow of latex, the synchronous gear transmission so that the twin-screws do not contact and avoid the phenomenon of demulsification and coagulation, and the self-developed non-contact mechanical seal to achieve long-term reliability of the shaft seal. run etc. The new twin-screw pump has successfully passed the industrial assessment and has been popularized and applied.