The mechanical dewatering of sludge is an important condition for further disposal. If incineration or other heat treatment is used as the ultimate disposal method, the dewatering power of the Decanter centrifuge is required to be as high as possible, because mechanical dewatering requires 1-2kwh of energy (electric energy) for each ton of water sludge disposal, and not only electric energy, and A lot of heat energy is needed for the evaporation of water.

In most cases, the increase in the rate of mechanical dehydration and dehydration is critical to the reduction of the subsequent disposal and disposal costs of sludge. The principle of separating sodium sulfate in the crystallization process is that the solubility of sodium sulfate in sodium thiocyanate solution is very low, and crystals are easy to form, so the concentrated sodium thiocyanate solution is settled through the settling tank to make sodium sulfate Grain gradually grows at the bottom of the settling tank (sodium sulfate content is about 13% to 15%).

 The role of the  Decanter centrifuge  is to separate the sodium sulfate crystals in the bottom solution (only a small part of them are beaten to evaporate the five effects as seed crystals). The resin is replaced and adsorbs sodium thiocyanate in between, and the waste liquid is discharged. If the separation effect of the centrifuge is not good, the content of sodium thiocyanate in the solid phase separator is too high, which exceeds the adsorption capacity of the sewage resin, and environmental protection requires that the content of sodium thiocyanate in the discharged sewage should not exceed 200ppm, the workshop has to Sodium thiocyanate with concentrated sodium sulfate is poured into the system and concentrated from the beginning to recover. The sodium sulfate content will accumulate in the system, which will eventually lead to unsteady production of the two systems of evaporation and crystallization, and then affect the normal production operation of the equipment.

Nearly 90% of sodium sulfate is separated from sodium thiocyanate in the crystallization separation step. The balance of sodium sulfate must be completed by the separation effect of the centrifuge, so in all recovery equipment, the  Decanter centrifuge  plays a crucial role. The important role is to clean impurities and ensure the clean circulation of blood, just like a human kidney. The separation function of the centrifuge directly affects the smooth production and long-term operation of the entire workshop and even the whole plant.

Two important factors that affect the consumption of flocculant during the sewage treatment process by Decanter centrifuge or other centrifugal sludge dewatering equipment are sludge properties and sludge concentration. When the sludge property changes greatly, it is necessary to adjust the applicable flocculant in time to match the sludge dewatering operation; when the sludge concentration changes, it is necessary to adjust the flocculant supply flow in a timely manner, so that it can meet the treatment effect and Prevent wastage.

     The specific method is to often observe the mud effect, and then appropriately reduce the supply flow of the flocculant working fluid. You can reduce the frequency of the flocculant dosing pump every time by about 0.5-1.0Hz, and observe the mud cake and supernatant status and torque data after a few minutes , According to the situation, decide whether to continue to reduce the dosing pump frequency until the most economical dosing pump operating frequency is found. Or you can increase the frequency of the mud pump about 0.5-1.0Hz each time to observe and adjust. Conversely, when the sludge concentration increases, the adjustment is made in the opposite direction.

In addition, because the Decanter centrifuge‘s structure determines the high requirements for the quality of the mud feed, there should not be a large amount of large-sized particulate matter and fibrous material in the mud feed, otherwise it will easily cause equipment clogging, increased vibration, and affect the treatment efficiency. Therefore, the sludge must be crushed and cut before entering the centrifuge.

Any centrifugal sludge dehydrator has a maximum processing capacity requirement. This requirement has two aspects of data reference guidance:

A. The maximum load of dry solids that can be processed is the maximum weight of non-volatile solids processed per hour, expressed in KGDS (dry solids) / h;

B. The maximum treatable hydraulic load, that is, the sludge flow into the equipment, is expressed in m3 / h, and the product of the sludge concentration (solid content) is the dry solid load.

      Under the condition of normal sludge concentration, it should be ensured that the maximum treatment dry solid load is 70% -90% of the theoretical load set by the equipment factory trademark. It is necessary to avoid the equipment utilization rate being too low, or the equipment loss caused by long-term operation under high load. Speed ​​up and shorten the maintenance cycle. In the case of excessive equipment load, any increase in the amount of flocculant will not improve the treatment effect. It is manifested as unsatisfactory mud biscuits. The supernatant carries high solids and the recovery rate decreases. Sediment overflow causes equipment wear, dynamic balance damage and increased vibration. Sometimes, due to the increase in sludge concentration, when the sludge is fed according to the original flow rate, the actual sludge load exceeds the acceptable load index of the equipment, and the treatment effect decreases. At this time, it is necessary to gradually reduce the frequency of mud feed and observe the effect. After the effect is stabilized, continue to try to control the flow rate of the flocculant to the most economical dosage. Conversely, when the concentration of sludge decreases, the flow of sludge should be gradually increased, and the flow rate of the dosing pump should be adjusted at the same time. If the concentration of influent sludge is too low, although the dry solid load of the equipment is not high, the hydraulic load is very large. Under the high hydraulic load, the incoming low-concentration sludge cannot form a mud ring layer of uniform thickness, and the settled solids will be heavily The supernatant carries overflow, which directly affects the treatment effect and treatment efficiency.

Important factors for the Decanter centrifuge Selection

1.1 Differential ratio

The settling velocity of solids in different media is different, and the degree of aggregation is different, so different differential speed ratios should be used. When the other parameters remain unchanged, the differential speed is large, the solid material is pushed out faster, the amount increases, and the liquid content increases, the shaft power generally decreases, but the separation effect will decrease, that is, the solid content in the filtered liquid Will increase. As the differential speed increases, it actually acts as a stirrer in the drum. Choosing the right differential ratio is the first factor to consider when choosing a model.

1.2 Length-to-diameter ratio

The aspect ratio is the ratio of the axial length of the Decanter centrifuge‘s drum to its diameter. The working area of the Decanter Centrifuge is divided into several areas such as feeding, sedimentation, drying, and unloading. The length of the settlement area is the main parameter that determines the separation effect. The longer the settlement area, the greater the aspect ratio, the better the separation effect, but the greater the shaft power. Different length-to-diameter ratios should be selected according to different media properties (mainly settlement performance), and should be considered in combination with differential speed ratios.

1.3 Power

The use of larger power can improve the processing capacity, especially when the settlement performance of the medium is very good. The user has certain difficulty in choosing the model. In the face of new media or media without successful use experience, relevant tests should be conducted.

2 Determination of operating parameters

2.1 Adjustment of overflow diameter

There are four options for the overflow diameter of the general Decanter Centrifuge. The larger the diameter of the overflow, the longer the drying zone, and the lower the water content of the filter cake, but the higher the solid content of the filtered liquid, so the appropriate overflow diameter should be adjusted. For the “three mud” that is not easy to settle, it should be smaller, and for the medium that is easy to settle, such as TA residue, it should be larger.

2.2 speed

According to the working principle of the Decanter Centrifuge, the higher the speed, the better the separation effect, the dryer the filter cake, the clearer the filtered liquid, and the greater the shaft power. This is an important parameter in actual operation, but it is not that the higher the speed, the better the effect. Generally speaking, for the medium that is easy to settle, the higher the speed, the greater the shaft power, which is easy to cause the mechanical or solid material to be pushed out, causing the material to block. Therefore, the appropriate speed should be selected according to the factors such as the power of the Decanter Centrifuge, the feed, the dehydration effect and other factors. For the “three muds” that are not easy to settle, when the rotation speed is high to a certain value, there will be a phenomenon that the separation effect decreases, the sludge production decreases, and the solid content in the filtered liquid increases. When the rotation speed is reduced, the mud production fork will increase. This is because the material slips in the drum and cannot be pushed out. At the same time, as the speed increases, the absolute differential increases, and the stirring effect of the spiral drum is enhanced.

It is very important to consider the factor for the selection of Decanter centrifuge, here’s some important factors for the users:

1.1 Differential ratio

The settling velocity of solids in different media is different, and the degree of aggregation is different, so different differential speed ratios should be used. When the other parameters remain unchanged, the differential speed is large, the solid material is pushed out faster, the amount increases, and the liquid content increases, the shaft power generally decreases, but the separation effect will decrease, that is, the solid content in the filtered liquid Will increase. As the differential speed increases, it actually acts as a stirrer in the drum. Choosing the right differential ratio is the first factor to consider when choosing a model.

1.2 Length-to-diameter ratio

The aspect ratio is the ratio of the axial length of the Decanter centrifuge drum to its diameter. The working area of the Decanter Centrifuge is divided into several areas such as feeding, sedimentation, drying, and unloading. The length of the settlement area is the main parameter that determines the separation effect. The longer the settlement area, the greater the aspect ratio, the better the separation effect, but the greater the shaft power. Different length-to-diameter ratios should be selected according to different media properties (mainly settlement performance), and should be considered in combination with differential speed ratios.

1.3 Power

The use of larger power can improve the processing capacity, especially when the settlement performance of the medium is very good. The user has certain difficulty in choosing the model. In the face of new media or media without successful use experience, relevant tests should be conducted.

2 Determination of operating parameters

2.1 Adjustment of overflow diameter

There are four options for the overflow diameter of the general Decanter centrifuge. The larger the diameter of the overflow, the longer the drying zone, and the lower the water content of the filter cake, but the higher the solid content of the filtered liquid, so the appropriate overflow diameter should be adjusted. For the “three mud” that is not easy to settle, it should be smaller, and for the medium that is easy to settle, such as TA residue, it should be larger.

2.2 Speed

According to the working principle of the Decanter Centrifuge, the higher the speed, the better the separation effect, the dryer the filter cake, the clearer the filtered liquid, and the greater the shaft power. This is an important parameter in actual operation, but it is not that the higher the speed, the better the effect. Generally speaking, for the medium that is easy to settle, the higher the speed, the greater the shaft power, which is easy to cause the mechanical or solid material to be pushed out, causing the material to block. Therefore, the appropriate speed should be selected according to the factors such as the power of the Decanter Centrifuge, the feed, the dehydration effect and other factors. For the “three muds” that are not easy to settle, when the rotation speed is high to a certain value, there will be a phenomenon that the separation effect decreases, the sludge production decreases, and the solid content in the filtered liquid increases. When the rotation speed is reduced, the mud production fork will increase. This is because the material slips in the drum and cannot be pushed out. At the same time, as the speed increases, the absolute differential increases, and the stirring effect of the spiral drum is enhanced.

The decanter centrifuge operators often encounters problems like material blocking material during their daily use. Here are some normal solutions about the blocking issue to share with our users:

When the decanter centrifuge cannot be turned on normally and the auxiliary inverter alarms overload, we can remove the protective cover of the auxiliary motor and move the input shaft pulley of the differential with the hand wheel. The phenomenon proved to be that too much material between the spiral and the drum caused the spiral to jam. The solution is as follows:

1. Catch the differential pulley with something, and manually rotate the steering wheel to rotate the drum, until the resistance obviously disappears. Then adjust the main and auxiliary machines to a lower frequency, start at low speed, and rinse with water.

2. Some decanter centrifuges are equipped with foreign frequency converters, such as ABB, Siemens, etc. Some frequency converters have a special low-speed protection starting method.

If the low-speed and high-torque starting function can be realized, just adjust the main and auxiliary machines to the low-speed section and rinse with water.

Another method is to hold the drum in place, remove the end water blocking adjustment plate of the drum, adjust the auxiliary machine to reverse, turn on, and let the material be discharged from the drain outlet of the drum. Then adjust the auxiliary machine to forward rotation and discharge. Repeat the operation. This method is suitable for large length-diameter ratio decanter centrifuges where the material blocking is particularly serious and the artificial rotation cannot move at all.

GN can not only provide users with Dewatering Decanter Centrifuges, rely on GN rich production line of separation and conveying equipment. GN can also provide users with turnkey solutions for the material dewatering process, including solutions for material transportation, classification and dewatering.