Sewage Sludge Dewatering Solution
2024-10-30
Application of Stacked Screw Dewatering Machine in Sludge Treatment of Power Plant
In the production process of coal-fired power plants, the sludge generated by raw water pretreatment and desulfurization wastewater treatment is generally treated by dehydration and transportation. This company is one of the few power plants that use this equipment at present, and has accumulated some application experience in the process of using.This paper aims to broaden the idea of equipment selection in water treatment process by discussing the principle and use effect of this equipment system.
Working principle of screw type dewatering machine
The mud dewatering process of raw water pretreatment system in power plant is most widely used in plate and frame dewatering machine and centrifugal dewatering machine, and the application of screw dewatering machine in power plant starts in recent years. The screw dewatering machine is similar to the lamination filter in terms of structure principle. A screw shaft rotates in the lumen composed of a group of circular dynamic and static lamination alternately arranged. The inner diameter of the moving ring is slightly smaller than that of the fixed ring, and the moving ring moves relative to the fixed ring under the stirring of the screw shaft. After concentration, the mud is pushed forward by the central screw shaft and further concentrated into mud slag. At the end of the stack group and screw shaft, the mud slag is squeezed and dehydrated by the thrust generated by the screw shaft, and finally reaches the mud outlet. The dehydrated mud blocks fall into the mud collection hopper and are collected and transported out.
The screw shaft of the cascading screw dewatering machine is driven by a frequency conversion motor. By adjusting the speed of the motor, the mud processing capacity can be adjusted. With the adjustment of the flow rate of the frequency conversion mud feeding pump, the continuous operation of different output levels of the equipment can be controlled. After the mud enters the flocculation mixing tank of the screw dewatering machine, an appropriate amount of coagulant aid (PAM) is added to make the mud in the mud form a large mass, which is easy to separate the mud and water.
The speed of the screw shaft is controlled at 5 ~ 20 RPM through the frequency conversion motor. The speed is slow and the operation is smooth and quiet. Compared with the centrifugal dewatering machine, the noise is greatly reduced, and the wear between the dynamic and static parts is also reduced. Compared with the plate and frame type dehydrator, the screw type dehydrator realizes continuous operation. After the operator adjusts the mud flow rate, the speed of the screw shaft and the dosage of coagulant aid, the screw type dehydrator runs continuously and smoothly without other operations. Only arrange the vehicle to be transported out when the mud bucket is full, so as to realize unattended operation.
The application of cascade screw dewatering machine in power plant
The stacking screw dewatering machine is widely used in urban sewage treatment, but it is rarely used in the water treatment process of power plants. It is suitable for the pretreatment of raw water and the mud dehydration of desulfurization wastewater system. At present, the company has installed a stack screw dewatering machine in the desulfurization wastewater treatment system, and two stack screw dewatering machines in the raw water pretreatment system. Since it was put into operation, the operation is stable and unattended.
Compared with the plate and frame dewatering machine and centrifugal dewatering machine, the power industry has relatively little understanding of this model, lack of relevant information and use experience, with a small number of power plants began to use this mud dehydration process, its excellent performance and less maintenance workload, so that more chemical professionals began to pay attention to this model. For different types of wastewater slurry, different materials are required in equipment selection. For sludge generated by general raw water pretreatment system and sludge generated by urban water, ordinary stainless steel material can meet the needs. However, for desulfurization wastewater with high content of chloride ion and sulfate ion, more corrosion-resistant steel is required to be selected, with supporting pipelines and accessories. The corresponding grade of corrosion resistance material should also be selected
Screw Sludge Dewatering System Composition
The screw stacking dewatering machine system is composed of frequency conversion mud pump, flocculation mixing tank, screw stacking dewatering component, coagulant aid preparation and dosing system, and spray water system. The mud discharged by the raw water pretreatment system is sent to the flocculation mixing tank by the frequency conversion mud pump, mixed with the coagulant aid, stirred evenly, condensed into a large slag block, and sent to the screw dewatering module to complete dehydration. The system is equipped with a flushing system to intermittently wash a small amount of mud and slag extruded from the cracks of the screw pad to keep the equipment clean.
Automatic dispensing system (automatic foaming machine). The stacking screw dewatering machine needs to continuously add coagulant aid, the amount of coagulant aid is large, and the economy of purchasing liquid coagulant aid is poor. The system is generally equipped with automatic preparation equipment of coagulant aid. The equipment consists of a dry powder hopper, a preparation tank, a curing tank and a storage tank. Polyacrylamide dry powder is accurately and evenly fed into the water distribution device driven by the feeding screw driven by the frequency conversion motor. After continuous and uniform mixing with water, it falls into the preparation tank, and is dissolved and evenly mixed under the action of the agitator. The mixed liquid flows into the curing tank, further stirring and curing, and finally flows into the storage tank for use. Through the liquid level switch control of the storage tank, the automatic operation of the automatic dispensing device can be realized. According to the liquid level of the storage tank, the preparation of the liquid can be automatically started. The prepared liquid of the coagulant aid can be controlled by the electric valve of the dosing box of the coagulant aid, and the coagulant aid can be automatically added to the metering box.
Problems Encountered in use
1. Matching problem of slurry and coagulant aid dosage
Adjust the amount of coagulant aid to match the mud flow rate to control the water content of the mud. When the amount of coagulant is large, the water in the mud is not easy to filter out from the lamination gap because of the content of coagulant, the viscosity of water increases, and the subsequent exudation and extrusion effect becomes worse, resulting in poor mud. When the amount of coagulant aid is small, the separation effect of solid particles and water in the mud is poor, and the mud particles block the lamination gap, so that the water seepage is blocked, and the moisture content of the mud will increase. In use, the reasonable dosage range of coagulant aid can be determined through the cylinder adjustment test to achieve satisfactory dehydration effect.
2. Clearance adjustment of the mud back pressure plate of the screw assembly
The gap size of the mud back pressure plate of the screw assembly will affect the moisture content of the mud. A small gap of the back pressure plate will require a large driving force when the mud is squeezed out from the gap. At the same time, the pressure in the mud cavity of the dewatering section will increase, and the extrusion effect of the screw will increase. Mud drying hardening, screw extrusion torque increases, easy to cause screw fracture damage.
3. Concentration of coagulant aid preparation
When the automatic preparation equipment of coagulant aid works, the concentration set is too high, and the amount of dry powder sent by the screw of dry powder feeding is large, which cannot be timely and evenly dispersed in the water in the water distributor, which is easy to cause clumping and blockage in the preparation tank and poor fluidity. It is necessary to control the concentration of coagulant aid reasonably, and set the appropriate speed of dry powder screw through the test, so that the preparation tank does not agglomerate in the preparation process. The cured coagulant liquid has proper fluidity, and the automatic operation of coagulant preparation equipment can be realized while meeting the needs of dosage. Generally, the concentration of coagulant can be adjusted 0.4 ~ 0.5ppm.
In addition, due to the viscosity of the coagulant aid, the pipeline resistance from the storage tank to the metering box should be fully considered. The pipe and valve with large diameter can be used in the design to avoid the poor outflow and the output flow lower than the inlet flow of the preparation equipment, so that the liquid level of the storage tank repeatedly rises and falls, triggers the liquid level switch set in the storage tank, and frequently starts and stops the whole set of coagulant aid preparation equipment.
4. Long time outage jams
It is easy for the screw shaft to jam when the stacked screw desliming equipment is started after a long time shutdown. The main reason is that the residual mud in the screw assembly gradually dries, and the dry and hard mud block gets blocked at the mud outlet after starting, resulting in the pressure rise in the whole desliming unit, and then the mud residue in the back section is excessively dehydrated and hardened. The whole screw shaft increases the rotating resistance due to the hard mud block and high resistance, and alarm stops when it exceeds the maximum torque of the screw shaft motor. Even due to excessive torque caused by the screw shaft welding damage. Therefore, in each shutdown of the stacked screw desmud machine, it should first stop feeding mud to the stacked screw component and continue to run for 10 minutes to completely discharge the mud and slag in the screw shaft, or use low frequency continuous operation mode to reduce the impact of long shutdown. It can also be used to loosen the mud mouth baffle to completely drain the mud residue in the screw assembly for long-term use.
5. Maintenance and overhaul after long-term operation
After two years of operation, the mud block stuck in the screw shaft occurred, and the problem still occurred repeatedly after disassembly and cleaning. By measuring the gap between the spiral shaft and the moving ring, it is found that the gap between the spiral plate and the moving ring of the spiral shaft reaches 5 ~ 6mm on average. The moving ring cuts uniform grooves along the outer edge of the spiral plate due to the oblique cross cutting of the moving ring of the spiral plate. The maintenance personnel grind off the prominent part of the groove in the previous disassembly and maintenance process, which reduces the external diameter of the spiral plate and increases the matching gap between the spiral shaft and the moving ring. When the mud slag is squeezed, it flows back to the rear side of the spiral shaft with relatively low pressure, resulting in excessive circulating dehydration and drying and hardening of the mud slag in the spiral shaft, which affects the flow to the mud outlet and leads to blockage. After two years of use, the wear is less than 0.1mm, and the main part of wear is the outer edge of the spiral plate. After repairing the outer edge of the spiral plate, the average gap between the spiral plate and the moving ring is 1-1.5mm. After reinstallation, the repaired spiral shaft is compared with the spare new spiral shaft, and the mud discharge condition of the repaired spiral shaft is the same as that of the new spiral shaft. The original performance of the equipment has been restored, and no mud blockage has occurred after 3 months of operation.
The Advantages of the Screw Sludge Dewatering Equipment
1) Low speed and low noise. The rotating equipment in operation has low rotation speed, low power consumption, stable operation without vibration and slight noise, which helps to reduce wear and prolong the service life of the equipment.
2) Remote control is easy to implement. The equipment in operation checks the mud status during regular inspection, and adjusts the dosage of coagulant aid and the speed of screw shaft through the remote DCS system to control the mud production effect.
3) Small amount of operation and maintenance. The equipment runs smoothly, the moving parts wear consumption is small, can meet the long-term continuous operation, do not need frequent maintenance.
4) Space saving. The screw dewatering machine device is small in size and has a small footprint, which helps save space.
5) Flexible output adjustment. By adjusting the mud pump frequency to control the mud supply and adjusting the screw shaft speed of the screw assembly, the output of the equipment can be smoothly adjusted to match the mud production, and the smooth operation of the raw water treatment system can be maintained.
6) Wide adaptation range of mud concentration and treatment. The appropriate mud concentration is 10Kg/m3, which is equivalent to the sludge concentration of the raw water pretreatment system. It can be used for dehydration treatment without the concentration process. The change of mud concentration has little influence on the work of the screw type dewatering machine, and the moisture content of the mud is basically constant.
Prospect Application of the Screw Sludge Dehydrator
With the continuous development of electric power industry, the degree of automation is getting higher and higher, and manual operation is gradually replaced by automatic control.The reliability and stability of equipment operation are the key factors affecting automatic operation.Enterprises reduce the use of personnel, and the amount of equipment controlled by each employee increases greatly, which puts forward higher requirements for the unattended equipment. At present, plate and frame dehumidifier and centrifugal dehumidifier are widely used in raw water treatment process of power enterprises. Plate and frame dehumidifier belongs to intermittent operation equipment, and it is difficult to clean up the mud stuck on the interval layer of the press cloth during operation, so it needs to be monitored and cleaned manually on the spot. The service life of the press cloth is limited, and it needs to be replaced regularly. However, the centrifugal dewatering machine has high speed, high precision requirements for bearings and other rotating parts, large maintenance workload, high cost of high-precision parts and high noise in operation are relatively common problems. After debugging, the cascade screw dewatering machine can achieve continuous and stable operation, low screw speed in operation, low noise, adjust the appropriate mud moisture content operation, equipment wear is small, maintenance workload is small. The personnel on duty make regular inspection, and fine-tune the dosage of coagulant aid according to the mud situation to control the moisture content of the mud within a certain range. The mud pump feeding flow has a wide adjustment range, and the output can be smoothly adjusted between low flow and rated flow. With the adjustment of the dosage of coagulant aid, the output level can be smoothly adjusted. The SCREW DEWATERING MACHINE IS equipped with remote control start and stop, combined with the automatic dispensing device of coagulant aid, DCS program control system is introduced to meet the requirements of remote operation and automatic control.
In the process of power production, water saving requirements are getting higher and higher, and the use of municipal water has put forward higher requirements for the pretreatment of raw water in power plants. Fungi and organic matter in the water have increased in large amounts, and the production of sludge has increased correspondingly. Sludge is sticky, and when the plate and frame dewatering machine is used to dewater the mud, the mud is easy to bond on the filter cloth of the plate and frame dewatering machine in the working process. The proportion of biological sludge is relatively small, which also causes difficulties in the dewatering process of centrifugal dewatering machine. The application of screw dewatering machine can adjust the clearance of mud baffle according to the nature of sludge, and control the moisture content of mud according to the reasonable adjustment of coagulant aid dosage, so as to meet the needs of different types of sludge dewatering.
In the application of desulfurization wastewater treatment in power plants, it is necessary to choose the stacked screw dewatering machine suitable for the desulfurization system with high sulfate and high chloride ion materials to avoid the rapid corrosion and damage of ordinary stainless steel in the harsh environment. Desulfurization waste cement slag has relatively high viscosity, the adhesion problem that often occurs in the operation of the plate and frame type dewatering machine can be better solved in the application of the screw type dewatering machine.
The stacked screw dewatering machine can also be widely used in the screening and collection of particulate matter in water. For example, during the outbreak of cyanobacteria in a water area, it is used to collect cyanobacteria in water. The mixed water containing a large number of cyanobacteria is continuously injected into the stacked screw dewatering machine, and the dehydrated cyanobacteria are continuously bagged and collected, with high collection efficiency and easy operation.
Other application fields, such as limestone softening treatment of raw water, dehydration treatment of mud of municipal tap water treatment equipment, treatment of a large number of slurry generated by the separation of particulate matter in other industries, etc., stacking screw dewatering machine is also an ideal choice, combined with the application of automatic control system, to improve the overall automatic control level is very helpful.