Analysis of several mechanical dewatering methods

Mechanical dewatering is a sludge treatment method that removes water from the native, concentrated or digested sludge in a fluid state and converts it into a semi-solid or solid sludge. Mechanical dehydration with a filter and centrifugation.

In the filtration method , the wet sludge is filtered with a filter layer (a porous material such as a filter cloth or a wire mesh) to allow the water (filtrate) to permeate the filter layer, and the dewatered sludge (filter cake) is trapped on the filter layer. The centrifugation method is to separate the mud and water by different centrifugal tendency caused by the difference in solid and liquid specific gravity in the sludge.

The filtration equipment includes a vacuum filter, a plate and frame filter press, and a belt filter . The vacuum filter continuously enters the mud, continuously discharges the mud, and runs smoothly, but there are many auxiliary facilities. The plate and frame filter press is a common equipment used in chemical industry. The driving force is large, the moisture content of the mud cake is low, the mud and mud are intermittent, and the productivity is low. Manually operated frame and frame filter presses are labor intensive, and most of them are replaced by mechanical automatic operation. Belt filter is a new type of filter. It has various designs and different dehydration principles (gravity filtration, pressure filtration, capillary water absorption, granulation), but they all have a rotating belt, while carrying mud, dehydrating, or Only mud effect. Their complexity and energy consumption are similar.

Centrifugal method is generally used for horizontal high-speed sedimentation centrifugal dewatering machine , which consists of inner and outer rotating cylinders. The rotating cylinder has a cylindrical shape at one end and a conical shape at the other end. The rotational speed is generally around 3000 rpm or higher, and there is a certain speed difference between the inner and outer drums. Centrifugal dewatering machine continuous production and automatic control, good sanitary conditions, small footprint, but sludge pretreatment (usually the sludge is pretreated, improved dewatering performance and then dehydrated. Zui universal pretreatment method is to add inorganic Salt or polymer coagulant. In addition, there are higher requirements for panning and heat treatment.

The mechanical dewatering method is mainly used for primary sedimentation tank sludge and digested sludge. The water content of the dewatered sludge is related to the sludge properties and the dewatering method. Under normal circumstances, vacuum filtered mud cake moisture content is 60% to 80%, plate and frame filter press is 45 to 80%, centrifugal dehydration is 80% To eighty-five percent.

Accessories: Several dewatering machines based on the principle of filtration

1. Plate and frame sludge dewatering machine:

Working principle: In the closed state, the sludge driven by the high-pressure pump is squeezed through the plate frame, so that the water in the sludge is discharged through the filter cloth to achieve the purpose of dehydration.

Advantages: low price, good at dehydration of inorganic sludge, low moisture content of mud cake. Disadvantages: easy to block, need to use high pressure pump, not suitable for dewatering of oily sludge, it is difficult to achieve continuous automatic operation.

2 , belt sludge dewatering machine:

Working principle: the sludge layer is carried by the two tensioned filter belts, and the S-shaped passage is passed from a series of regularly arranged roller cylinders, and the pressure of the filter belt itself is used to form the pressing and shearing of the sludge layer. Force, squeeze the capillary water in the sludge layer to achieve sludge dewatering.

Advantages: low prices, universal use, and relatively mature technology. Disadvantages: easy to block, need a lot of water to clean, causing secondary pollution.

3 , centrifugal sludge dewatering machine:

Working principle: It consists of a transfer and a screw conveyor with a hollow shaft. The sludge is sent to the drum by the hollow shaft. Under the centrifugal force generated by high-speed rotation, the product is thrown into the drum cavity. Due to the different specific gravity, solid-liquid separation is formed. The sludge is conveyed to the cone end of the drum by the auger and continuously discharged from the outlet; the liquid in the liquid ring layer is continuously "overflow" from the mouth to the outside of the drum and discharged by gravity.

Advantages: Large processing capacity. Disadvantages: high power consumption, high noise, and severe vibration; maintenance is difficult, not suitable for solid-liquid separation with close specific gravity.

4 , Die's sludge dewatering machine:

Working principle: the fixed ring and the swimming ring are stacked on each other, and the screw shaft penetrates through the filter body formed therein. The gravity is concentrated and the sludge is fully dehydrated by the internal pressure formed by the back pressure plate during the propulsion process, and the filtrate is discharged from the filter joint formed by the fixed ring and the movable ring, and the mud cake is discharged from the end of the dewatering portion.

Advantages: self-cleaning, no clogging, direct dewatering of low-concentration sludge; slow speed, power saving, no noise and vibration; fully automatic control, 24 hours unmanned operation. Disadvantages: Not good at dewatering sludge with large particles and high hardness; the treatment volume is small.

5 , screw press dehydrator:

Working principle: The screw of the screw press dehydrator is installed in the cylinder composed of the filter screen. The diameter of the screw body gradually becomes thicker from the inlet to the outlet of the dewatering raw material. As the volume between the screw blades becomes smaller, the dewatering raw material gradually becomes gradually. Being compressed. The solid and liquid in the dehydrated raw material are separated by compression, and the filtrate is discharged through the mesh of the sieve, flows to the filtrate collection tank below the dehydrator, and is discharged to the outside of the machine. The dehydration efficiency can also be improved by heating depending on the dehydration raw material. When the dehydrated raw material is heated, the inside of the dehydrator screw has a hollow structure, and the dehydrated raw material inside the dehydrator is indirectly heated by the external steam.

Characteristics of screw press dewatering machine

1. It can realize continuous dewatering treatment, so the front and rear supporting equipment can also be processed continuously, thus eliminating complicated operation control.

2. The structure is simple, the rotation speed is low, and there are few parts that are driven to rotate, so there are few consumable parts to be replaced and the maintenance cost is low.

3. Low speed, low noise, no vibration, can be mounted on a simple machine.

4. Low speed, low running power, so the daily running cost is low.

5. It is easy to realize a closed structure, which can easily solve the odor problem and recover the gas generated during the dehydration treatment.

6. The structure is simple, the adjustment and maintenance parts are few, and the daily management operation is simple.

7. The structure is simple, and the comprehensive cost is lower than other types of dehydrators.