Sludge transportation and its flow characteristics

    Talking about the knowledge of belt filter press and its flow characteristics

In the process of treatment, disposal and utilization of sludge, the transportation of sludge is a problem that must be solved first. The transportation method of sludge is mainly determined by the moisture content of the sludge, and the way of utilization of the sludge should be considered. Generally, there are pipeline transportation, automobile and barge transportation. Experience has shown that when the same amount of sludge is transported at a distance of no more than 10Km, it is more economical to use pressure pipeline transportation, and it is also a more hygienic method. Generally, the solid content of the conveyed sludge is 5%. When the sludge is transported far away, consideration should be given to reducing the volume of the sludge through processes such as dewatering and drying before transporting.

When sludge is transported by pipeline, the characteristics of sludge flow must be grasped, mainly the flow rate and sludge moisture content.
(1) Flow rate
When the sludge flows in the pipeline and the flow slows down to laminar flow, the sludge is highly viscous and the suspended matter is easy to settle in the pipeline. The flow resistance of the sludge is greater than that of water; when the flow rate increases to reach turbulent flow, the sludge The viscous performance eliminates the vortex generated in the boundary layer of the pipeline, reduces the roughness of the pipe wall, and the hindering force of sludge flow is smaller than water flow. Therefore, when the sludge flows in the pipe, a larger flow rate should be used to make the sludge in a turbulent state in the pipe.
(2) Moisture content
The lower the water content, the greater the viscosity of the sludge, the higher the water content, the smaller the viscosity of the sludge, the smaller the resistance, and the closer the flow state is to water. Gravity conveying sludge pipes in sewage (waste) water treatment plants generally adopt a slope of 0.01 to 0.02; the conveying total solid content is 5% of the pressure conveying, which is conveyed by the liquid level difference of the sludge or centrifugal pump and pressure conveying The diameter of the pressure mud pipe should be no less than 150mm. Liquid sludge with a solid content of up to 20% requires a pump with a delivery capacity of up to 300m3/min and a pressure head H of 64m. Regarding the removal of sludge clogging in the pipe, different types of pumps are required for different types of sludge. Pumps for transporting sludge include plunger pumps, multi-cavity screw pumps, centrifugal pumps and swirl pumps. Diaphragm pumps can be used when lifting scum.

Non-clogging, low-speed, low-pressure-head centrifugal pumps are used to pump back activated sludge, because this sludge is thin and contains only small solids. At the same time, the flocculation and solidification of the sludge can not be severely sheared by the pump. The piston pump is more suitable for pumping sludge. It overcomes the high friction pressure drop in the discharge pipe, but the particle size in the sludge should be reduced. The screw lift pump is used for variable capacity operation, and the effect is better. Because the mud volume is controlled by the liquid level at the screw inlet, no variable speed drive device is required.
Generally speaking, centrifugal pumps and screw lift pumps are used to pump a large amount of sludge with low solid content, and are used in occasions that do not need to accurately control the sludge flow.
In addition, there are pneumatic lift pumps. Although this type of pump has a simple structure and is not easy to block, it is difficult to throttle and control, and requires a lot of funds.

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