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Waste water treatment talk II

Waste water treatment talk<II> Mechanical and electrical equipment

To ensure the normal and stable operation of the sewage and sludge treatment system, it is also very important to ensure the operating conditions of the electromechanical equipment supporting the process. At the same time, the stable and efficient operation of electromechanical equipment has a great impact on the energy saving and consumption reduction of sewage treatment plants.

(1) Grille machine

The grille decontamination machine is the first process in the sewage treatment process, and it is also one of the most trouble-prone equipment in the sewage treatment plant. Once a failure occurs, the sewage treatment plant will not be able to enter water normally.

common problem:

Ø Grid machine jam: regardless of continuous operation or intermittent operation, because the grid machine is in contact with sewage for a long time, it is easy to cause bearing wear, jamming in operation, and causing chain or rake teeth to pull off or other mechanical failures. For this reason, it is necessary to strengthen the lubrication and maintenance of the related mechanical parts of the grille machine, and the daily inspection should be in place in time.

Ø Clogging of grille machine: Some long-strip fibers, plastic bags and other easily entangled debris are often entrained in the sewage, which can easily cause the grille and rake teeth to be blocked. On the one hand, the cross-section of the grid will be reduced, resulting in excessive flow velocity across the grid and reduced efficiency of trash interception. On the other hand, it will also cause problems such as slow water passing rate, sand and gravel deposits, and overflow of the grid canal. Generally, it is only possible to carry out technical improvement or diligent maintenance, and use manual cleaning to solve the problem.

(2) Lifting water pump

Most of the current domestic sewage treatment plants use submersible pumps to lift sewage. It is found from actual operation that during the use of the submersible pump, due to the various impurities and scum in the sewage, these impurities are easily entangled in the gap between the impeller and the sealing ring of the water pump, causing the mechanical sealing effect and the efficiency of the water pump to decrease. Sewage enters the sealed cavity to cause malfunction, and in severe cases, it will cause overcurrent damage to the pump motor. In response to this problem, the main purpose is to strengthen the slag grid effect of the grid machine, regularly check the insulation and sealing of the submersible pump, calculate the efficiency of the pump, and change the use regularly.

Due to the changes in the water intake of the sewage treatment plant 24 hours a day and the completeness of the supporting sewage collection system, the water intake of the sewage treatment plant may vary greatly in different periods, especially the combined drainage system, which has seasonal changes. The characteristics are very obvious. Therefore, in the selection and configuration of submersible pumps, there should be more room for adjustment. Generally, multiple pumps can be sampled in a gradient configuration, combined with a fixed-speed pump and a speed-regulating pump control method, where the fixed-speed pump is selected according to the average flow rate to meet the basic flow requirements. The speed-regulating pump runs at variable speeds to adapt to changes in flow. When the flow fluctuates greatly, the number of operating units is increased or decreased as a supplement.

(3) Blower

The blower is the key equipment of the sewage treatment process and consumes the most energy. Air volume, wind pressure, power consumption, noise, etc. are the basic technical parameters for selecting a blower. In use, it must be combined with the characteristics of the process operation, and pay attention to its applicable scope and adjustment ability.

The microporous aeration system of the biological reaction tank of the sewage treatment plant generally uses a centrifugal blower. Centrifugal fans have the advantages of high efficiency, long service life, no need for lubrication in the shell, and no oil contamination of the gas. Especially in terms of air supply, applicable range of air pressure, noise control and stable operation, they are better than Roots blowers. superior. Roots blowers are generally suitable for situations where the pool depth is shallow, and the required air volume and pressure are small.

In terms of energy consumption control, frequency conversion adjustment control can be used. In terms of equipment configuration, multiple blowers can also be configured in gradients for different working conditions to enhance the flexibility of process operation adjustment and reduce power consumption.

The oil cooler and oil filter should be cleaned regularly to ensure the oil quality, and should be replaced and inspected regularly to prevent emulsification. The oil cooler has two methods: air-cooling and water-cooling: when using air-cooling, pay attention to regular cleaning of the fins of the air-cooler to prevent clogging and accumulation of dust; when using water-cooling, you need to clean and maintain the cooling tower and corresponding pipelines regularly, and pay attention to ensure circulating cooling The water quality can be regularly added with corrosion and scale inhibitors to prevent bacterial growth, cooler, pipeline scaling, and galvanic reaction corrosion of copper components, which affects the cooling effect and even pollutes the oil.

The filter should be cleaned or replaced regularly to ensure that the inlet negative pressure is within the specified range and reduce the occurrence of blower surge failure caused by excessive negative pressure.

(4) Aeration head

At present, most of the aeration methods use microporous membrane aeration, including disc type, spherical crown type, plate type, tube type and other rubber membrane microporous aerator types. After the aerator is used for a period of time, due to the blockage of the micropores, the increase of resistance, the aging of the rubber, and the deterioration of elasticity, etc., the oxygenation efficiency will decrease. In order to avoid blockage of the aerator or excessive increase in resistance, the aerator should be cleaned regularly. It can be cleaned with formic acid or atmospheric pressure air. When using formic acid cleaning, you must carefully control the concentration of formic acid, the frequency of cleaning, and pay attention to operational safety; when using atmospheric air cleaning, you must carefully control the volume, intensity, and frequency of cleaning. In addition, pay attention to regularly open the drain valve of the aeration system to drain the condensate. The aeration heads that are severely blocked or damaged should be replaced in time to ensure the uniformity of aeration in the biological tank and prevent dead spots and accumulation of sludge.

(5) Mud discharge equipment

Because of the difference in the process, some sewage treatment processes do not have a secondary settling tank, such as SBR, UNITANK, etc., and the bottom of the tank is flat, which is easy to form a mud funnel when discharging mud. The concentration of the mixed solution discharged in the later period is reduced, and sufficient sludge cannot be discharged, which leads to a decrease in the concentration of the remaining sludge, which leads to an increase in the energy consumption of sludge treatment and the consumption of medicines.

For the operation of these processes, it is advisable to adopt an intermittent sludge discharge method or transform it into a multi-point sludge discharge system.

In addition, in a biological treatment system with a secondary settling tank, regular maintenance of the secondary settling tank scraper and suction machine is required to ensure smooth mud discharge and prevent mud accumulation from affecting the SS and other indicators of the effluent.

(6) Dewatering machine

At present, the main mechanical dehydration methods used in China are centrifugal dehydrator and belt filter press dehydrator.

1. Centrifugal dehydrator

During operation, the required range of the solid content of the concentrated sludge into the centrifugal dewatering machine, the feed volume (installed capacity), the maximum output, the differential speed of the centrifuge, the rotation speed, the filling rate of different types of polyacrylamide (PAM), and the input rate should be studied. The effect of adding concentration on the solid content of the sludge dewatered by the centrifuge, the SS value of the separated water and the recovery rate.

If the sludge dewatering treatment of the centrifugal dewatering machine achieves the ideal separation effect, it can be considered from two aspects:

Ø The greater the speed difference, the shorter the residence time of the sludge in the centrifuge, the higher the water content of the mud cake, and the higher the solid content of the separated water may be. Conversely, the smaller the speed difference, the longer the sludge stays in the centrifuge, the more thorough the solid-liquid separation, but the sludge must be prevented from clogging. The speed difference can be used to automatically adjust to compensate for the varying solid content in the feed.

Ø When the sludge properties have been determined, the feed rate can be changed to reduce the dosage to improve the solid-liquid separation; increase the flocculant charging rate, which can accelerate the solid-liquid separation speed and improve the separation effect.

common problem:

Ø Boot alarm or vibration alarm

When the centrifugal dehydrator is turned on, the low differential speed alarm causes the main motor to stop, or the vibration or sound is abnormal, which causes the alarm to stop. The above situation is caused by the incomplete flushing before the last shutdown, that is, incomplete flushing will cause two situations to occur: one is the accumulation of mud at the mud end of the centrifuge, which causes the speed difference between the drum and the screw conveyor when it is turned on again. Low and alarm; second, there are irregular residual solids on the inner wall of the drum, which causes the drum to rotate unbalanced and generate a vibration alarm.

Ø High shaft temperature alarm

This is mainly due to insufficient lubrication and excessive shaft temperature due to clogged grease tubing. Because the grease feeding device of the centrifugal dehydrator is a semi-automatic device, the oil pipe of the manual feeding system is slender and the interval is long, and the oil pipe is prone to blockage when the grease is added once. Once it happens, it needs to be cleaned up manually. The main principle is to refuel more frequently to ensure the effective smoothness of the slender tubing. Of course, the grease should not be added too much, otherwise it will cause the bearing temperature to rise.

Ø The host machine alarms and shuts down

Turn on the centrifugal dehydrator or adjust the speed of the dehydrator during operation. If the frequency converter of the main motor is adjusted too large or too fast, it is easy to cause the acceleration (deceleration) overvoltage phenomenon and cause the main motor to alarm. During operation, it is found that the general frequency conversion adjustment is relatively safe at about 2Hz. When the centrifugal dehydrator is in the flushing state, especially during high-speed washing, it is easy to cause acceleration (deceleration) over-voltage phenomenon, so when high-speed washing, there should be operator monitoring by the centrifugal dehydrator.

Ø No mud from the centrifugal dehydrator

In the normal operation of the centrifugal dehydrator, the related equipment is operating normally, but there is no mud phenomenon, the filtrate is relatively turbid, the differential speed and torque are also high, there is no abnormal noise, no vibration, and the torque changes left and right during high-speed and low-speed washing. It is not too big, and there have been phenomena of high and low torque. It is difficult to restart and there is no difference in speed.

This situation mostly occurs in the rainy season. Due to the large amount of water coming, the impact on the sludge load of the biological pond is large, resulting in loose sludge and small sludge particles. The smaller the sludge particles, the larger the specific surface area (exponentially increasing), the higher the hydration strength and the greater the resistance to dewatering filtration, the poorer the sludge flocculation effect and the more difficult it is to dewater. At this time, if the process is not adjusted in time, the centrifugal dewatering machine may have inconsistent torque (too high), and the differential speed will be tracked in the constant torque control mode. Once the differential speed is too large, it is easy to cause the sludge to stay in the dehydrator for a short time and the solid ring layer is thin; The degree of disturbance will inevitably increase, and part of the separated sludge in the solid ring layer will return to the liquid ring layer and may be lost with the separated liquid. In this case, the dehydrator will not produce mud.

In the case of low sludge concentration and loose sludge, the use of high speed, low differential speed and low sludge input can effectively solve the problem of sludge, and the operation effect is also good. The high speed is to increase the separation factor. Generally speaking, the smaller the sludge particles, the lower the density, and the higher the separation factor is required. Conversely, a lower separation factor is required; using a low differential speed can prolong the residence time of the sludge in the dewatering machine. While the sludge flocculation effect is enhanced, the time to receive centrifugal separation in the drum will be prolonged. At the same time, the relative operation between the drum and the spiral is reduced, and the disturbance to the liquid ring layer is also reduced. Therefore, the solid recovery rate and the solid content of the mud cake are reduced. Rates will increase; low mud intake also increases the solid recovery rate and the solids content of the mud cake.

2. Belt filter press dehydrator

The belt filter dewatering machine is composed of two tensioned filter belts entraining the sludge layer, which is bent in an S-shape through a series of regularly arranged roller cylinders, and the sludge layer is pressed and sheared by the tension of the filter belt itself. The capillary water in the sludge layer is squeezed out by force to obtain a mud cake with a larger solid content.

In order to maintain the normal operation of the belt filter press dehydrator, the following operation and maintenance items need to be paid attention to:

(1) For those with pre-dehydration zone (thickening zone), ensure uniform mud distribution;

(2) The filter belt scraper is made of soft material to reduce the wear on the filter belt and the interface of the filter belt;

(3) Ensure the pressure of the filter belt washing water. The filter belt washing system uses stainless steel self-cleaning nozzles as much as possible, which can automatically flush out the dirt blocked in the nozzles and ensure the porosity of the filter belt and the sludge dehydration effect;

(4) Frequent maintenance of automatic anti-eccentric belt device and pressure increasing and reducing device to reduce edge wear of filter belt;

(5) Ensure that the automatic control system is equipped with a chain protection device to prevent damage to the whole machine caused by misoperation.

common problem:

Ø Filter belt slipping

This is mainly because the mud is overloaded, and the amount of mud should be reduced; the tension of the filter belt is too small, and the tension should be increased; the roller pressure cylinder is damaged and should be repaired or replaced in time.

Ø Misalignment of the filter belt

This is mainly due to uneven mud feed and uneven distribution on the filter belt. The mud inlet should be adjusted or the leveling device should be replaced; the rollers should be inspected and replaced if they are partially damaged or excessively worn; the relative positions of the rollers are not The balance should be checked and adjusted; the correction device is not sensitive. Should be checked and repaired.

Ø Severe clogging of filter belt

This is mainly because the washing time is not thorough each time, or the washing water pressure should be increased; the tension of the filter belt is too large, and the tension should be appropriately reduced; excessive dosing, that is, PAM dosing excessively, the viscosity increases, and the filter cloth is often blocked. Fully dissolved PAM is also easy to block the filter belt; too much sand in the incoming mud can also easily block the filter cloth. The operation control of the sewage pretreatment system should be strengthened.

Ø The solid content of mud cake decreases

This is mainly due to insufficient dosing amount, improper dosing concentration or unreasonable dosing point location, which can not achieve the best flocculation effect; too high belt speed, thinning of the mud cake, resulting in a decrease in solid content, so the belt should be reduced in time In general, the thickness of the mud cake should be ensured to be 5-10mm; the tension of the filter belt is too small to ensure sufficient squeezing force and shearing force to reduce the solid content. The tension should be increased appropriately; the filter belt is clogged, and the water cannot be filtered out, so that the solid content is reduced. The operation should be stopped and the filter belt should be rinsed.

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