Horizontal Screw Decanter Centrifuge for Water-solid-oil Separation
2024-10-30
Application of decanter screw centrifugal dewatering machine in industrial sewage treatment
Classification: Odor treatment System
Industry name: Breeding farm
Odor air pollution production place: breeding field area, manure treatment plant (station)
Exhaust gas composition: ammonia, hydrogen sulfide, etc
Exhaust gas treatment purification efficiency: 90%
Odor Treatment process: biological deodorization tower
What is a decanter usually used for?
The decanter centrifuge can keep the solid particles into the mud after settling without flowing through the whole body, and can be directly scratched away by the screw conveyor near the mud inlet. In the settlement area of the drum, the spiral blade of the screw conveyor adopts the ribbon form, which reduces the disturbance effect of the screw on the separation liquid. The separation effect is improved. The groove is processed in the inner wall of the drum to prevent the wear of the spiral body and the blade, and the cemented carbide block is installed in the mud scraping part of the spiral blade; The screw feed port and drum slag outlet are equipped with replaceable hard alloy sleeve to enhance wear resistance. Decanter centrifuge has good wear resistance and long service life. The centrifuge intercept plate is installed at the transition between the straight spiral section and the cone section, so that the solid phase is further compressed and the solid phase is drier. The depth of the liquid pool is deep, and the liquid phase takes a long time to clarify in the drum.
The flow plate of the decanter centrifuge is installed on the screw end spindle on the inner side of the drain end cover. It is a disc structure, and the center is provided with a spindle mounting hole, and a group of flow holes are uniformly opened around the spindle mounting hole. It can avoid a few solid particles when the liquid phase is discharged, and the liquid is clearer. The solid phase that does not settle to the bottom will also be spiralized to the slag outlet, and the solid phase recovery rate is higher. Fundamentally replace the current original and backward treatment methods, improve treatment efficiency, reduce treatment costs, protect the urban environment, and achieve civilized construction on site. It can effectively and timely adjust the differential speed to ensure the stable separation effect of the decanter centrifuge. The high-speed rotating drum is equipped with a feeding screw, which rotates in the same direction as the drum, but the speed difference between the two is generated by the differential. The suspension enters the machine from the feeding pipe. Under the action of centrifugal force, the solid phase of the suspension is settled on the inner wall of the drum.
Dewatering principle of decanter centrifuge
Horizontal screw centrifugal dewatering machine is mainly composed of drum, screw, differential, feed port, liquid phase outlet, solid phase outlet, liquid level baffle, drive system and control system.
The separation principle of decanter centrifuge is to use different gravity and centrifugal force of materials to separate solid and liquid. The specific working principle is as follows:
1. The solid-liquid mixture to be separated is sent into the rotating cylinder of the decanter centrifuge through the screw lifter.
2. When the rotating cylinder rotates at a high speed, the material is separated by centrifugal force. The heavy material is deposited on the cylinder wall and falls down to form the inner layer of the shell, while the light material flies to the inner layer of the centrifugal shell under the action of centrifugal force.
3. The solid particles move along the screw conveyor to the outlet and are discharged through the solid outlet, while the cleaned liquid is discharged from the liquid outlet in the middle of the centrifuge.
The working principle of decanter centrifuge is simple and easy to understand, and the equipment has a wide range of applications, which can be used in chemical industry, medicine, food, environmental protection and other fields. At the same time, the equipment has high efficiency and good separation effect, so it is favored by the industry.
Type selection and structural parameter analysis of decanter centrifugal dewatering machine
1. Characteristics of industrial sludge
Industrial wastewater (in here mainly refers to chemical industry, printing and dyeing, paper making and other industrial wastewater) contains a large number of fiber, mechanical impurities, residual chemicals, etc. In the process of wastewater pre-treatment, sewage enterprises will part of the available impurities left in the sludge, through screening, sand removal and other ways to extract and reuse. The remaining impurities, fibers and residual chemicals and mechanical impurities in the wastewater are discharged through sewage and flow into the centralized sewage treatment plant.
The main characteristics of this kind of industrial sludge are:
(1) Large impurity content. Compared with the amount of sludge produced by urban domestic sewage, the content of fiber and mechanical impurities is large, which is conducive to improving the dewatering performance of sludge, and the amount of flocculation agent is relatively small.
(2) More mud production. The SS concentration of sewage plant inlet water is generally 800 ~ 1200mg/L, and the amount of dry mud per ton of aquatic products reaches 0.7 ~ 1.1 kg.
(3) Easy to produce ammonia and hydrogen sulfide and other corrosive gases. Because many industrial raw materials contain chemicals and organic substances, ammonia and hydrogen sulfide and other gases will be generated in the decomposition, which is highly corrosive.
Selection of dewatering machine
According to the characteristics and management needs of sludge, the decanter screw centrifugal dewatering machine with compact design, high separation efficiency, continuous automatic feeding and good airtightness is selected.
Analysis of important structural parameters
(1) Drum diameter and effective length. The diameter and effective length of the drum determine the effective sedimentation area of sludge in the process of centrifugal dewatering, which directly affects the treatment capacity of the equipment. The dewatering machine with large diameter and long effective length of the drum has a large settlement area, which prolongs the residence time of the material in the drum, and the separation effect is better under the same speed. At the same time, the screw slag transport capacity of large drum diameter is large. Under the same slag transport capacity, the centrifuge with small drum diameter has low differential speed, which is conducive to reducing energy consumption and equipment loss.
(2) Drum half cone Angle. The size of the drum half-cone Angle directly affects the slag transport speed and dehydration effect of the dewatering machine. When separating the biochemical sludge that is difficult to separate (more difficult than other sludge to separate), the drum half-cone Angle is generally set within 6°, which is conducive to increasing the depth of the liquid layer and improving the sludge recovery rate. When there are a large number of fibers in the sludge to be separated and the primary sludge accounts for 60%, the sludge is easy to be separated. The drum half-cone Angle of the equipment is selected to be 8°, which is conducive to improving the slag transport efficiency, but the drum half-cone Angle is usually controlled within 10°.
(3) Drum speed. The rotation speed of the drum directly determines the separation factor. When it is found that the moisture content of the mud cake is high and the curing effect is poor, the rotation speed of the drum should be increased to increase the centrifugal force to improve the solid content of the mud cake. However, the speed of the drum should not be too large, otherwise it will destroy the sludge flocs, but affect the dehydration effect. In practical application, it is found that the more suitable drum speed is 2200 ~ 2400r/min. (4) Differential speed. Differential speed is the relative speed between the drum and the screw conveyor. When the solid concentration of the feed of the dewatering machine is greater than or equal to 3%, the differential speed should be adjusted appropriately, so that the sediment settling in the inner wall of the drum will soon be discharged from the mud outlet of the drum. When the solid concentration of the feed of the dewatering machine is less than 3%, the differential speed should be reduced, the sedimentation time should be prolonged, and the thickness of the sediment should be increased, which is conducive to improving the solid content of the mud cake and the sludge recovery rate.
Common problems and countermeasures in operation management
1.Common problems at the beginning of debugging
(1) Turbidity of filtrate and low sludge recovery rate. The sludge recovery rate mainly depends on the concentration of suspended solids in the dehydrating filtrate. When the concentration of suspended solids is high, the filtrate is cloudy. Part of the sludge does not form mud cake, but is discharged with the filtrate and returned to the sewage collection system, which reduces the sludge treatment efficiency of the dehydrating machine.
In the initial stage of equipment debugging, in addition to considering whether the ratio of mud and drug is reasonable, it is also important to consider whether the height of the liquid level baffle in the centrifuge is appropriate. The height of the liquid level baffle directly affects the effective settlement volume of the centrifuge and the length of the drying zone. When the depth of the liquid layer in the drum is small, the loose particles on the surface of the slag layer are easy to discharge with the liquid layer, and the sludge recovery rate decreases. Therefore, when the ratio of mud to drug is reasonable and the filtrate is still cloudy, the liquid level baffle can be appropriately increased to make the height of the baffle close to the critical value of the liquid layer (the height of the turbidity and the demarcation point in the liquid layer). After obtaining better results, other equipment can be adjusted in turn.
(2) The material is often blocked in the drum. The phenomenon of material blocking often occurs in the drum. One kind of material blocking occurs in the start-up period of the equipment, which is usually caused by motor overload alarm during start-up. After inspection, it is found that there is relatively dry sludge in the drum. Extend the rinse time during the next shutdown until the filter water is clear. Another kind of plugging occurs in the operation, which is a man-made operation problem, such as high concentration of feed sludge, and low control of differential speed, resulting in prolonged sedimentation time, too thick sediment layer, resulting in plugging in the drum. At this time, the fault can be eliminated by increasing the differential speed to speed up the slag delivery speed. There is also a kind of plugging material is caused by the accumulation of solid impurities in industrial sludge, such as common plastic waste, because the plastic sheet is flexible and not easy to be broken by the cutting machine, with the sludge into the centrifuge, will be attached to the inner wall of the drum, long-term accumulation of plugging material. In order to solve similar problems, the feed cutting machine is changed from extrusion cutting to blade cutting, and the cover of the machine is opened and washed regularly, which effectively reduces the frequency of blocking material. The key to solve this type of blockage is to prevent plastic sheets from entering the sludge from the source.
2.Common problems in operation
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(1) The nature of feed sludge changes. The spoilage degree of sludge in industrial wastewater has a great influence on the properties of sludge. When the fiber content in the sludge is high, the sludge is easy to dehydrate, which can reduce the dosage of flocculant and lower the liquid layer baffle. When the fiber in the sludge is short (usually accompanied by spoilage), the sludge has high viscosity and is not easy to dehydrate. Therefore, the feed volume of the dehydrator should be appropriately reduced, the dilution multiple of the agent should be increased, and the contact area of the drug sludge should be improved to ensure the dehydration effect.
The altercountry of seasons and temperature change also have a great influence on the properties of sludge. Such influence generally occurs during the change of spring and summer and autumn and winter. When the temperature is low, the negative charge of activated sludge is less than that when the temperature is high, the extracellular secretion of activated sludge contains more viscous substances, the sludge is more hydrophilic, and the compressibility of sludge is reduced and difficult to settle. At this time, the feed volume of the dewatering machine should be appropriately reduced, the dilution ratio of flocculant should be increased, and iron salt can be added to the fed sludge to destroy the surface viscosity and hydrophilicity of the sludge, which is conducive to reducing the specific resistance of the sludge and improving the water filtration.
(2) Improper application of flocculant. In the aspect of sludge dewatering, cationic polyacrylamide is generally used as a flocculant to reduce the specific resistance of sludge, so that the sludge is easy to dehydrate after solid-liquid separation. Improper application of flocculant will lead to poor sludge dewatering effect, low sludge recovery rate and pharmaceutical waste.
When choosing polyacrylamide, the characteristics of decanter centrifugal dehydrator should be fully considered. In the operation of the centrifuge, the drum rotates at a high speed, so as to get a better mud-water stratification effect, the deposit layer is relatively dense. Therefore, the molecular weight of polyacrylamide is generally not less than 10 million, and the ionicity is 50% ~ 70%.
The dosage of flocculant should be moderate, and the clarity of the filter water should not be overemphasized. The excessive dosage of flocculant is not only a serious waste, but also the foam in the filter water, which brings inconvenience to the management. Generally, it is recommended to control the sludge recovery rate at about 95%, and the dehydration effect and flocculation dosage can reach a more reasonable state at this time.
(3) The influence of corrosion gas on equipment. Due to the corrosive gases such as hydrogen sulfide and ammonia often produced in the process of industrial sludge dewatering, it is very harmful to the equipment components, and the frequency converter, LCD screen, controller and other components in the centrifuge control system are easy to fail due to corrosion. In this regard, the centrifuge control system is isolated from the dewatering machine, and the positive pressure air supply system is added to the air exchange between the isolation room, which has achieved good results. It is suggested that the influence of corrosive gas on the equipment should be considered in the design of the dewatering machine room, and the dewatering machine and the control cabinet should be placed in separate rooms, which can reduce the corrosive failure of the equipment and extend the life of the equipment.
Conclusion
(1) Horizontal screw centrifugal dewatering machine is suitable for the treatment of sludge generated in industrial wastewater treatment.
(2) The key to the operation and management of the decanter screw centrifugal dehydrator system is to grasp the balance between sludge, equipment and flocculant. It is necessary for the site operators to carefully observe and summarize, and constantly explore the rules from the actual operation, so that the decanter screw centrifugal dehydrator always maintains high efficiency.