What kinds of sludge dehydrators are there?

There are three kinds of sludge in sewage treatment plants: physicochemical sludge, biochemical sludge and mixed sludge of physicochemical and biochemical.

Different kinds of sludge have different adaptability to dehydrating agents. At present, the commonly used models of sludge dehydrators in China are centrifugal, filter belt, spiral ring mode and plate-and-frame type. The selection and proportion of flocculants are very important for the dewatering of precipitated sludge, and the flocculation effect is good, and the sludge dewatering is relatively smooth. Here is a brief introduction to the actual use of the three models for selection:

Centrifugal: All three kinds of sludge can adapt, but high energy consumption and high rotation speed lead to high noise. Filter belt: suitable for physicochemical sludge, with low water content in filter cake, poor adaptability to mixed sludge and biochemical sludge, large amount of returned sludge, large backwashing water consumption, high energy consumption and complicated maintenance. Spiral ring model: the first generation dehydrator represented by Japanese prototype has been popularized and applied in China for 3-4 years, but its disadvantage is low output.

Technical principle: Brand-new separation technology: spiral pressure is organically combined with dynamic and static rings to form a brand-new separation technology integrating concentration and dehydration, which adds an advanced dehydration mode choice to the field of environmental protection sewage treatment in China. Energy-saving and water-saving: Because the continuous dislocation kinetic energy of the dynamic and static rings realizes the self-cleaning function in the cylinder, the filtering gap is not easy to be blocked, which replaces the high-pressure washing of the old generation of filter cloth and belt filter plate, and greatly saves industrial water (single machine saving10.3 million tons/year). The low-speed operation of the main screw shaft (3-5 rpm) reduces the mechanical wear of the equipment and prolongs the service life of the equipment. The power consumption of the main machine is ≦ 1. 1kw/hr, and the single machine saves 50000kWh/ year. Double processing capacity: the processing capacity of the second generation dehydrator is twice that of the first generation dehydrator. Unit A 303 can solve the sludge amount (100 tons) produced by sewage, and can design the process of deep dehydration of sludge to 50-40%. A single process can solve the sewage treatment capacity1-30,000 tons. It is the first time in China: the pressure regulating plate adopts elastic automatic adjustment, which naturally balances the internal pressure of sludge in the dewatering section, effectively ensuring the service life of the dynamic and static rings. Environmental protection: the whole machine is sealed, which can be directly observed. The shell is easy to disassemble, without sewage leakage and secondary pollution. The noise is not less than 45 decibels, which makes the sludge room beautiful and civilized. The filter cloth hole of the ring sludge dewatering machine is not blocked: the operation is safe and simple, depending on the customer's operation time. Combined with the automatic control system, the program can be set to realize automatic unattended operation (there must be a considerable amount of sludge).

Working principle:

1. Plate-and-frame sludge dehydrator: In the closed state, the sludge pumped by the high-pressure pump is squeezed by the plate frame, so that the water in the sludge is discharged through the filter cloth to achieve the purpose of dehydration.

2. Belt sludge dehydrator: The sludge layer is entrained by the upper and lower tensioned filter belts and passes through a series of regularly arranged rollers in an S shape, and the capillary water in the sludge layer is squeezed out by the tension of the filter belts, thus realizing sludge dehydration.

3. Centrifugal sludge dehydrator: It consists of a transfer conveyor and a screw conveyor with a hollow rotating shaft. Sludge is sent into the drum by the hollow rotating shaft, and the product is thrown into the inner cavity of the drum under the centrifugal force generated by high-speed rotation. Because of the different specific gravity, solid-liquid separation is formed. Driven by the screw conveyor, the sludge is transported to the cone end of the drum and continuously discharged from the outlet; The liquid in the liquid ring layer continuously "overflows" from the overflow weir to the outside of the drum and is discharged under the action of gravity.

4. Stacked sludge dehydrator: a filter main body formed by stacking a fixed ring and a traveling ring, and a screw shaft runs through it. Full dehydration is realized by the internal pressure formed by the back pressure plate during gravity concentration and propulsion, the filtrate is discharged from the filtration gap formed by the fixed ring and the movable ring, and the mud cake is discharged from the end of the dehydration part.

Workflow:

1. The sludge in the sludge tank is transported to the metering tank by the sludge delivery pump, and the amount of sludge is adjusted by adjusting the liquid level regulating pipe in the metering tank, and the remaining sludge flows back to the sludge tank through the return pipe.

2. Sludge and flocculant are fully mixed in a flocculation mixing tank by a stirrer to form alum flower, and the ideal alum flower diameter is about 5 mm ..

3. Alumen flowers are concentrated by gravity in the concentration part, and a large amount of filtrate is discharged from the filtration gap of the concentration part.

4. The concentrated sludge continues to move forward along the rotation direction of the screw shaft and is fully dehydrated under the internal pressure formed by the back pressure plate.

5. The dehydrated mud cake is discharged from the gap formed between the back pressure plate and the spiral main body. By adjusting the rotating speed of the screw shaft and the gap of the back pressure plate, the sludge treatment capacity and the moisture content of the mud cake can be adjusted.

Select:

Sewage will produce a lot of sludge after precipitation. Even after concentration and digestion, the water content is still as high as 96%, which is very large and difficult to be absorbed and treated. It is necessary to dehydrate to increase the solid content of the mud cake and reduce the occupied area of sludge stacking.

Large and medium-sized sewage treatment plants generally adopt mechanical dehydration. There are many kinds of dehydrating agents, which can be divided into three categories according to the dehydration principle: vacuum filtration dehydration, pressure filtration dehydration and centrifugal dehydration. This paper introduces the working principles, equipment selection, maintenance points and operating costs of filter presses (including belt filter presses and plate-and-frame filter presses) and centrifugal dehydrators commonly used in domestic sewage treatment plants.

1, the belt filter press is less affected by the fluctuation of sludge load, and also has the characteristics of low sludge moisture content, stable operation, less startup consumption, relatively simple management and control, and low requirements for the quality of operators. At the same time, because the belt filter press dehydrator entered China earlier, quite a few manufacturers can produce this kind of equipment. In the decision-making of sewage treatment project construction, belt filter press can be selected to reduce the project investment. At present, most newly-built sewage treatment plants in China use belt filter press dehydrators. For example, the five dehydrators in the first phase of Beijing Gaobeidian Sewage Treatment Plant are all belt filter press dehydrators, and the filter belt and drum are in good condition since they were put into operation. Therefore, this model is still selected for equipment selection in the second stage.

2. Compared with other types of dehydrators, the solid content of mud cake of general plate-and-frame filter press is the highest, reaching 35%. If we consider the factors of reducing the area occupied by sludge stacking, the plate-and-frame filter press should be the first choice. Moving mode of filter plate. It is required to realize full-automatic or semi-automatic through liquid-gas device, which is inconvenient to operate, and the filter cake is easy to fall off due to the swing of filter cloth. Compared with other types of dehydrators, the biggest disadvantage of plate-and-frame filter press is that it occupies a large area. Take the belt filter press used in the first phase of Beijing Gaobeidian Sewage Treatment Plant and the plate-and-frame filter press used in Anshan Industrial Sewage Treatment Plant as examples: the sewage treatment capacity of Gaobeidian Sewage Treatment Plant is 500,000 t/d, the sludge output is 1852.5 m3/d, and the dry matter is 92.63t/d. Five German KLEIN-KS30 belt filter presses are adopted, and each filter press covers an area of only 2,750. Anshan Sewage Treatment Plant has a treatment capacity of 22t/d and a dry matter of 275t/d, and adopts six plate-and-frame filter presses, each of which covers an area of 2400* 12000mm. At the same time, the plate-and-frame filter press is rarely used in large-scale domestic sewage treatment plants because of its intermittent operation, low efficiency, poor operating room environment and secondary pollution.