In the whole process of pulping and papermaking, many kinds of pumps are needed, such as pulp pump, feed pump, boiler feed water pump, pipeline pump, metering pump, liquid pump, sewage pump, vacuum pump and so on. As a main type of slurry conveying machinery, centrifugal pulp pump plays an important role in the pulp and paper mill.
The pulp flow is a gas liquid solid three-phase flow, flow mechanism is complex, many factors affect the flow mechanism, such as slurry type, concentration, flow velocity, beating degree, temperature and fiber morphology can have an influence on the slurry flow, the flow of motivation has not been studied in depth of pulp. At present, the pulp pump research in China is still on the basis of the clean water pump, and is corrected according to the flow characteristics of pulp, and then verified by experiment.
1. classification of pulp pump
The pulp flow has the following characteristics: (1) as the raw materials of pulp of fibrous, easy to form flocs knot, so that the material is separated into spherical or sheet material, thus preventing the pipeline flow of the mixture, especially long fiber and high concentration slurry pump, easy to plug; (2) the content of air rises, pumping the ability to significantly reduce, the existence of air bubble effect on pulp pump performance is very bad.
Pulp water obviously after expansion, the concentration (mass concentration) reached 7%, with their hands, fingers do not leak in the water, up to 10%, has completely lost the liquidity. And with the increase of concentration, the gas content is also rising. Therefore, due to the increase of concentration, the difficulty of slurry transportation will be greatly increased. Usually according to the pulp concentration, as follows: Division of pulp pump (1) slurry concentration of C<7%, with its own flow properties, the air content in the slurry differs according to the different types of slurry, generally below 10%, the delivery pump is called low consistency; (2) the slurry concentration of 7%≤ C<16%, has lost its fluidity, the air content in the slurry conveying pump is generally below 40%, this is called MC pump; (3) the slurry concentration C≥ 16%, the pump conveying is called high consistency pump. This article only discusses the low concentration pump, and other paper pulp pumps.
2. types of low concentration pump
At present, most of centrifugal pulp pumps in China are low consistency pumps. Because of the flow characteristics of pulp, even low consistency pumps are quite different from ordinary pumps. The low concentration pump must have no blocking performance and gas carrying capacity. This capacity is mainly achieved through the special design of the impeller. At present, the impeller structure of low consistency pump is as follows: (1) open and semi open impeller; (2) single and double channel impeller; (3) swirling impeller; (4) screw centrifugal impeller. Therefore, the low consistency slurry pump has the following forms: (1) open and semi open slurry pumps; (2) single and double flow slurry pumps; (3) swirling slurry pumps; (4) screw centrifugal pumps.
3. open type and semi open impeller pump
Open or semi open impeller as an ordinary closed out before and after the cover or remove the impeller hub, but compared with the normal closed impeller, it has the following characteristics:
(1). The removal of before and after the cover or the front cover, accumulate in the impeller inlet bubble will diffuse along the gap between the impeller and the pump cover, the gas transmission capacity is improved;
(2). The impeller outlet is wide, the blade is less, and the non blockage performance is better than the ordinary closed impeller.
(3) the clearance between the open impeller and the front and rear pump cover or the clearance between the semi open impeller and the front pump cover has great influence on the performance of the pump. The clearance is too small, which affects the normal operation of the pump. If the clearance is too large, the flow, the lift and the efficiency will decrease. The general gap is kept at about 0.5mm. With the increase of the concentration of the pulp, the clearance can be properly amplified. The front cover of streamline semi open impeller usually consists of a circular arc or two arcs, so before the corresponding pump cover type line should also be a circular arc or two arcs, the processing ability on pump requirement. Factories with weak processing ability often simplify the streamline of the front cover of the impeller to a straight line, which will have a negative impact on the performance of the pump. In addition, the gap between impeller and pump cover will increase with the operation of pump. In order to keep the gap within the required range, the gap between impeller and pump cover can often be made adjustable.
(4). The pulp pump usually requires steep flow — head performance curve, this can be done by reference to the general closed impeller pump performance curve is steep method to achieve, such as smaller outlet angle, on the premise of non blocking performance as much as possible under the export of width etc..
(5). The same as the ordinary closed impeller, can not transport large particles, long fiber material.
(6) if the gap between impeller and pump cover is small, and the impeller profile is designed properly, the open and semi open impeller can get the same efficiency as the closed impeller.
4. other low concentrated slurry pumps
Other low concentration pumps are mainly single, double flow channel pumps, swirling pumps and spiral centrifugal pumps.
Single and double channel impeller due to its special channel impeller structure, material conveying good non-destructive, non blocking performance, can transport large particles, long fiber material, &mdash flow; head performance curve is steep, so at present in pulp and paper mill of low concentration slurry is widely applied. However, they also have the following defects: (1) the single channel impeller has the best performance without blockage, but because of its imbalance, it can only be made into a small power pulp pump. (2) single and double channel impellers belong to closed impeller with gas transportation energy.
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