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Operation methodoperation adjustment technology of horizontal screw centrifuge

2021-05-28 11:22:03

Operation method and operation adjustment technology of horizontal screw centrifuge

Section I key role of screw operation in centrifuge operation

In the operation of horizontal screw centrifuge, especially in the operation of processing material separation, the operation of the spiral inside the centrifuge can be said to be the "soul" of the operation of horizontal screw centrifuge. Without the correct operation of the spiral, the centrifuge cannot realize its basic function. The most basic function of horizontal screw centrifuge is to continuously separate the materials input into the machine, which requires the machine to exclude the materials that have been separated inside, so that the machine can continue to process the new materials entering the machine. Moreover, the industrialized production mode requires that the process of "separation discharge continuous separation continuous discharge" is automatic and continuous, The pushing screw inside the centrifuge is used for continuous discharge. This discharge function is realized through the relative rotation between the screw and the centrifuge drum. This relative rotation is called the "differential" of the centrifuge. Since the feeding of the centrifuge is continuous, the centrifuge must implement the function of continuous material processing, and the differential speed must also be continuous. In order to avoid failure due to material accumulation in the centrifuge, the differential must always exist, and the differential is always the pushing mode. The so-called "pushing mode" refers to that the "difference" generated between the screw and the drum body is to push the separated solid slag to the slag discharge port of the centrifuge. For the same helix, the differential speed can be designed as positive differential speed and negative differential speed according to the different rotation direction of the drum, but their pushing behavior is the same.

The pushing screw can "feel" the dryness of solid slag during operation. This feeling is reflected by the load of spiral operation, that is, the so-called "torque" of the spiral at that time. The feeling of simp gearbox differential mode on torque is indirectly reflected from the load of its driving motor, and the feeling of hydraulic differential driving mode on torque is indirectly reflected from the oil pressure of hydraulic driving machine. When the rotating speed of the drum is fixed, if we reduce the differential speed of the screw, we can get relatively dry solid slag discharge. Due to the reduction of the differential speed, the amount of solid slag pushed out by each differential cycle of screw rotation is relatively large. At the same time, because the solid slag is relatively dry at low differential speed, the pushing torque of the screw will become larger. If we increase the screw differential speed, the solid slag pushed out by the screw will be wet, and the pushing torque of the screw will decrease. Therefore, when the solid slag is too dry or the pushing torque is too high, we can increase the differential speed to accelerate the slag discharge, so as to reduce the pushing torque. When the solid slag is too wet, we can reduce the differential speed to improve the dryness of the solid slag.

During the operation of the centrifuge, we hope to obtain a stable dryness of solid slag by continuously adjusting the operating parameters. In the specific operation, we observe the load or torque of the differential drive motor or the oil pressure of the hydraulic pipeline. If the load of the differential drive motor or the oil pressure of the hydraulic pipeline is stable, we can conclude that the dryness of the solid slag discharged by the centrifuge is very stable. Therefore, one of the important operation requirements of centrifuge is to obtain a stable pushing torque or pushing hydraulic pressure.

Section 2 dependence of centrifuge operation on materials

Good centrifuge design can promote the effect of material separation, but the operation effect of centrifuge is dependent on materials. Due to the high-speed rotation of its drum system, the centrifuge provides a centrifugal force field for the materials entering it. Centrifugal force field accelerates the settling speed of materials with natural settling property. The better the natural sedimentation performance of the material, the faster its sedimentation speed in the accelerated centrifugal force field, and the "better and faster" the separation effect we can get. In order to achieve the "better and faster" separation effect, we often use auxiliary methods to gather small material particles into larger particles. The common auxiliary method is to add flocculant to the materials. The materials with flocculant added correctly are separated by centrifuge. The materials are separated more thoroughly and the content of small particles in the liquid is less after separation.

The viscosity of materials is one of the important factors that hinder the settling velocity of solid particles. Too high viscosity will make centrifugal separation very difficult or impossible. The separation effect of the centrifuge may be very poor when dealing with this kind of material, because the material at this time does not have good natural sedimentation performance, and it needs a very long stay and separation time in the centrifuge. Therefore, the processing capacity (throughput) of the centrifuge decreases sharply. The most effective way is to directly raise the temperature of the material. This is common in the food industry. In order to obtain drier solid slag discharge, we hope that the settled solid slag has good compactness, and this dense structure is not easy to be damaged by the upper liquid flow. If the settled solid slag is easily driven and crushed by the liquid flowing above, the solid content in the liquid discharged by the centrifugal machine will rise. Finally, the materials we input into the centrifuge must have appropriate solid volume concentration. Although the weight specific concentration is one of the most useful properties of materials, the separation of materials in the centrifuge forms an interface with the liquid in proportion to the volume of solids. Therefore, for the separation effect, the volume concentration is more practical than the weight concentration. If the volume occupation ratio of solid is too large, the thickness occupied by clarified liquid will be smaller, and sometimes it is impossible to obtain clarified separated liquid.

Section 3 one of the three key parameters of centrifuge operation, drum speed

The rotating speed of the drum directly determines the centrifugal force on the materials in the centrifuge, and directly determines the settlement speed and treatment capacity of solids. The increase of rotating speed of the drum can increase the separation speed of materials and obtain clearer clear liquid after separation. The solid slag after separation and settlement becomes closer and firm, and the dryness of solid slag discharged from the centrifuge is drier. At the same time, due to the increase of settlement speed, On the basis of normal separation, the material passing capacity of the centrifuge increases, and the processing capacity increases accordingly. However, too high drum speed sometimes brings some disadvantages. The most direct disadvantage may be that it increases the unnecessary power consumption of drum motor. It should be that not all materials need to run at the maximum speed of centrifuge to be separated. Too high rotating speed of the drum produces too high centrifugal force, which leads to too high solid settlement compactness, so it increases the load of screw pushing, so another disadvantage of it is to increase the power consumption of screw motor. For some sticky and slippery materials or materials with very small solid particles, too high centrifugal force will make it difficult for the settled solids to reach the slag discharge port of the centrifuge through the cone of the centrifuge, and the slag discharge of the centrifuge may be difficult. Improving the design structure of the spiral body and the design structure of the drum cone can improve the slag discharge capacity of the centrifuge when handling this kind of materials.

Section 4 two of the three key parameters of centrifuge operation, screw pushing differential speed

Under the action of specific centrifugal force, the screw pushing differential speed plays a key auxiliary role in the material separation effect of the centrifuge. Without the correct screw pushing differential speed, the material balance inside the centrifuge cannot be achieved and good continuous separation operation cannot be realized. The function of screw pushing is to push the solid slag separated and settled by the drum to the slag discharge port of the centrifuge stably and continuously, so as to discharge it out of the machine. However, since the solid slag and liquid exist in the centrifuge at the same time, the spiral pushing motion will undoubtedly "add fuel to the fire" on the liquid in the same direction. Therefore, generally, the differential speed of spiral pushing is relatively small. On the one hand, the small differential speed effectively inhibits the "add fuel to the fire" effect of the spiral on the liquid, and on the other hand, it prolongs the compression time of the settled solid slag in the centrifuge. Only in this way can we get drier solid slag discharge. Due to the reduction of the differential speed of screw pushing, the speed of solid slag being pushed out of the centrifuge is relatively slow. At the same time, the discharge of clear liquid spontaneously forms a trend, which increases the penetration tendency of solid slag to clear liquid. Therefore, while reducing the differential speed and improving the dryness of slag discharge, we may get a turbid separation clear liquid, that is, the solid content in the clear liquid increases. If we increase the differential speed of screw pushing, we can inhibit the penetration of solid slag into clear liquid, and we can get a relatively clear separation clear liquid. However, the "fueling effect" of screw is increased, and the compression time of solid in the centrifuge is shortened. If it is pushed out of the centrifuge early, we may get a relatively wet solid slag discharge.

Under the action of the pushing screw differential, the dryness of solid slag and the clarity of clear liquid are such a pair of contradictory bodies. The purpose of machine commissioning is to find out the differential value taking into account the balance point of both. Finding the balance point differential is to find the best differential value that takes into account the dryness of solid slag and the clarity of clear liquid. Driven by this optimal differential, the slag discharge has a basically fixed dryness, which will make the pushing screw need a basically fixed pushing load (torque and hydraulic pressure). We call this pushing load characteristic pushing load. It can be used to automatically control the differential in the future. The characteristic pushing torque is different in different factories, different materials, different processing capacity, and different ways of giving consideration to the dryness of solid slag and the clarity of clear liquid. However, in the operation mode of each specific factory, the characteristic pushing torque is basically unchanged. We should pay attention to its role.

Section 5 three of the three key parameters of centrifuge operation, liquid pool depth

The depth of the liquid pool is the thickness of the solid slag + liquid mixing ring formed on the inner wall of the drum body when the material is inside the centrifuge and under the force of the centrifuge. In this ring, the solid is settled in the outermost ring of the ring because its specific gravity is larger than that of the liquid. The more close to the inner ring of the ring, the clearer the separated liquid is. The greater the depth of the liquid pool, the greater the thickness of the ring. The liquid in the innermost ring is farther away from the solid-liquid decomposition surface, and the liquid here is clearer. Therefore, the depth of liquid pool is also one of the key auxiliary parameters of centrifuge.

While increasing the depth of the liquid pool, we have obtained clearer separated liquid. However, due to the thickening of the liquid ring, the inner ring of the ring will gradually spread to the solid slag discharge port, and the length of the anhydrous area (dry area) near the slag discharge port will gradually shorten, which will make the discharged solid slag gradually wet. On the contrary, if we reduce the depth of the liquid pool, the liquid ring in the centrifuge will become thinner, the inner ring of the ring will gradually move away from the slag discharge port, and the length of the anhydrous area near the slag discharge port will gradually grow, which will make the discharged solid slag gradually dry. However, because the inner ring of the liquid ring is close to the solid-liquid decomposition surface, the separated clear liquid is relatively turbid. The specific adjustment of the liquid pool depth is through the overflow weir plate of the centrifuge or the variable impeller. It is worth noting that due to the "adding fuel" effect of the screw pushing differential speed, in the case of a specific liquid pool depth, too high differential speed will easily affect the slag discharge port area by liquid spread, so we must reduce the depth of the liquid pool again. If we choose a lower screw pushing differential speed, we may increase the allowable depth of the liquid pool. Using the variable impeller technology of fule Wei company, we can easily adjust the depth of the liquid pool dynamically while changing the differential speed. Once the centrifuge starts to discharge slag, due to the gap between the screw and the drum and the separate solid slag filling near the slag discharge port area, it is possible for us to increase the depth of the liquid pool by 1 ~ 2mm, which can only be realized on the machine equipped with variable impeller of fuleway company.

Section 6 one of technical adjustment, startup sequence

Following the principle that there must always be differential speed in centrifuge operation, we must first run the screw in program control and in any environment.

There are two reasons:

First, after the ordinary equipment is cleaned, there is always a small amount of material residue left inside the centrifuge. If the centrifuge is parked for a long time and does not operate, a small amount of solid residue will be deposited at the bottom and relatively hard. Therefore, we can ensure the smooth start of the drum to a greater extent by using the principle of screw first opening.

Second, due to the relative rotation movement between the screw and the drum during the operation of the centrifuge, and this relative movement is based on their high-speed rotation, using the screw first opening method, we can check and listen to whether there is collision and friction between the screw and the drum during the relative movement, and further improve the safety inspection before startup. Therefore, we must abide by the principle of screw opening first to ensure the safety of centrifuge operation. Before starting each motor, we must first set the operating frequency of the motor in advance. Up to now, there are still quite a number of operators who blindly start the equipment regardless of the value of the motor rotation frequency. If there is great vibration after the equipment is started and the speed is very high when it is found, it is impossible to stop the operation of the centrifuge immediately even in case of emergency shutdown, which will cause great harm to the equipment. We have programmed the automatic start and stop function of the centrifuge and even the whole system. However, we strongly suggest that operators must first fully grasp the sequence of manual startup and shutdown and fully understand the reasons for the logical sequence. Otherwise, if there is an abnormality in the automatic state, operators may not know what step the operation of the equipment or system is going to, and they will not be able to take correct emergency measures.

After we confirm that the screw operates normally alone, we can turn on the drum drive motor. We suggest that an appropriate amount of water be injected into the centrifuge when the drum operates to 300 ~ 500rpm. The purpose of water injection is to further ensure the smooth start of the drum and eliminate the rotation imbalance caused by a small amount of material residue. In the whole process of drum acceleration, we must pay attention to and listen to the sound of acceleration in the whole process, and compare it with the sound under normal conditions, so as to find any minor abnormalities in advance.

Section 7 technical adjustment 2: start feeding

After the speed of the centrifuge reaches the set value and the operation is completely normal, we can start the feeding system.

When it comes to the feed system, people naturally think of the feed pump and dosing pump. But one of the most critical equipment is that the various outlets of the centrifuge must be "opened up". The outlet of the centrifuge refers to the slag discharge system under the solid slag discharge outlet, the outlet pipeline of the separated clear liquid and the corresponding valves on the outlet pipeline. If the outlet of the centrifuge is blocked, the discharged materials will quickly spread or block the drum system of the centrifuge, and they will have strong friction with the high-speed drum, which will cause strong vibration and noise of the centrifuge until overload shutdown, and serious solid slag blockage may occur in the centrifuge. If the outlet of the centrifuge is blocked frequently or the materials spread and rise, the solid slag will gradually accumulate in the centrifuge shell and the gap between the shell and the drum body, resulting in serious wear and grooving of the drum body and unsafe factors. Therefore, before starting the feed pump, be sure to start the slag discharge system and open the liquid outlet pipeline. We have adopted logic protection in the control system, but on some occasions, customers may have special requirements and ignore logic protection. As operators, we should be very clear about this logic sequence and strictly implement it.

The feeding of the centrifuge needs to start with a small flow. While adding flocculant, we must pay close attention to the discharged clear liquid and wait for the solid slag to accumulate in the centrifuge until it is discharged. The discharged liquid must be clear in color. If it is extremely turbid, it is a precursor of blockage. If the clear liquid is discharged from the liquid port and the solid slag is discharged from the solid slag port (it may be very wet), it indicates that the material in and out of the centrifuge is unobstructed, and the parameters can be further adjusted.

Section 8 technical adjustment part 3: parameter adjustment

Parameter adjustment we have talked about the basic principles of adjustment in the paragraphs of screw pushing differential speed and liquid pool depth. After the centrifuge is fed, our task is to implement the adjustment process under the guidance of the basic principles. This process is mainly to find out a set of operating parameters for the increase of drum speed, screw differential speed, overflow weir plate position or variable impeller position, and the increase of feed quantity, and add flocculant, So that we can reach an appropriate midpoint between the dryness of solid slag and the clarity of clear liquid.

After the operation parameters are set, one of the parameters we need to pay special attention to is the screw differential. We already know that the screw differential, pushing torque and solid slag dryness are a group of closely related parameters, in which the differential plays a leading role. When we master the characteristic pushing torque, we can use this torque value as the control point to automatically adjust the differential. When the measured torque value is higher than the control set value, the automatic control system will increase the differential speed to reduce the torque; When the measured torque value is lower than the control set value, the automatic control system will reduce the differential speed to increase the torque, so as to make the dryness of slag discharge reach a greater degree of stability.

Section 9 technical adjustment 3, shutdown sequence

Before shutdown, the feed must be cut off first, and then mainly try to discharge the residual solid slag inside the centrifuge out of the machine. The principle is the same whether it is to execute the automatic relationship step of the program or the manual key step. Here are the steps of manual shutdown. If the program previously used the differential automatic control function, please switch back to the differential manual control function, and then greatly increase the differential value to promote the slag discharge of the centrifuge. At the same time, greatly reduce the rotating speed of the drum to promote the solid slag settled in the centrifuge to loosen from the inner wall of the drum and discharge by the screw. After the solid slag is discharged, water can be injected into the centrifuge for flushing. When the clear water overflows from the slag discharge port of the centrifuge, the cleaning is basically completed. At this time, the drum drive motor can be turned off, and the screw motor and slag discharge system can be turned off only after the drum speed is completely reduced to zero. The specific contents of the automatic shutdown steps of the program are the same, but the difference is that the operator must clearly know the position of the steps currently being executed by the program and insert steps such as water injection cleaning at the right time.

Section 10 technical adjustment 5, fault judgment

 machine blockage

 the first phenomenon of centrifuge blockage is not discharging slag for a long time. When other feeding conditions remain unchanged, the discharged clear liquid gradually becomes turbid and dark, and gradually approaches the color and state of the feed. With the increase of drum current and the significant decrease of drum speed, the slag discharge torque gradually increases and remains high. All these indicate that there is a possibility of internal blockage in the centrifuge.

 in this case, our first action is not to press the emergency button. The centrifuge is running at high speed and there is no brake device. The emergency button cannot provide any help at this time. First of all, we must immediately cut off the feeding of the centrifuge. In most cases, the centrifuge can eliminate the blockage by itself relying on the pushing function of the screw. If it is unable to push and discharge the blockage by itself, we should immediately reduce the rotating speed of the drum or turn off the drum drive motor, but we must not turn off the screw motor. After the speed of the centrifuge drum is reduced, the blocked solid slag may gradually relax and may be discharged out of the machine by the screw.

 for the centrifuge with blockage, after the drum stops rotating completely, we should still inject water into the machine and try our best to restore the operation of the screw. As long as the screw can rotate, the centrifuge will not be really blocked, and we may still return to normal.

 adding water to the machine and resuming the spiral operation are the preferred methods for removing the blockage of the centrifuge.

 machine vibration

 machine vibration is divided into chronic vibration and sudden vibration. Most of the chronic vibration indicates that the centrifuge is worn, the external parts are worn or fall off, and the bearing system is gradually damaged.

 sudden vibration often indicates that the materials inside the centrifuge are blocked, and the internal parts are seriously damaged and fall off. In most cases, we should first check whether the slag removal system fails, resulting in the accumulation and rise of solid slag, and whether the clear liquid pipeline is blocked, resulting in the reverse spread of liquid to the drum of the centrifuge.

 high bearing temperature

 if the bearing temperature is too high, we should first check whether the grease added to the bearing is too large. Whether the centrifuge has excessive vibration and whether there is abnormal noise during bearing operation. At the same time, we should observe the color of the bearing waste grease. The normal color of the bearing waste grease should be light gray (using fuluowei standard grease). If the color of the bearing waste grease is black, rusty yellow or other abnormal colors, it indicates that the bearing may be damaged and the bearing should be replaced in advance.

 as for the noise in the bearing area, we must pay special attention to distinguish a normal "oil layer stack ring" sharp noise. It is a grease lubricated friction part inside the bearing seat. During normal operation of the centrifuge, it will make a specific sharp sound, which is sometimes absent. After performing the grease action for 1 ~ 2 times, the noise will disappear temporarily and ring again later.

Section 11 technical adjustment 6, common judgment methods

Manual turning of drum

 manual turning of drum is to manually judge whether there is internal material accumulation and drum rotation when the centrifuge is at rest

 one of the important methods for smooth start-up. When we turn the normal free drum by hand, the rotation of the drum

It is very easy, and the drum can decelerate freely until it stops, and the stop angle position is random. If the rotation of the drum is very heavy,

 after turning and releasing the hand by hand, the drum will reverse itself and almost stay at the angle position before rotation. After repeated turning, the drum will stay at an angle position every time, indicating that there is solid slag accumulation inside the drum. At this time, if the drum is started to increase the speed, serious unbalanced vibration will occur.

 in this case, please run the screw pusher while injecting water, and then start the centrifuge after emptying the internal materials.

 exchange and comparison method of adjacent parts

 for some small parts, especially control elements, we should try to use the exchange comparison method to quickly diagnose the fault parts, especially some speed probes, vibration probes, liquid level probes, PLC modules, frequency converters and connecting cables. Replacing the connecting cables of the same parts is also a very important exchange method. We can quickly determine the fault location from whether the fault or alarm point is migrated after replacing parts.

Pulse quantity calculation method

 this method is mainly used to check whether the installation clearance between speed probe and detection point is appropriate. The speed probe needs a certain response time and pulse peak value. We can get the speed detection pulse signal at low speed, which does not mean that the speed probe can work normally when the centrifuge is running at high speed. Sometimes, when the centrifuge is running at full speed, if we find that the displayed value of the speedometer is 1 / 3 or 1 / 2 of the rated speed, we should first suspect that the average gap between the speed probe and the detection point is too large, resulting in no pulse value at one or two detection points when the centrifuge is running at high speed.

 pipeline level by level demolition method

Section 12 seven of technical adjustment, routine maintenance

 correct cleaning and soaking concept

 if the machine needs to be parked for a long time, we need to clean the residual solid slag inside. There are often solid slag residues in ordinary cleaning methods. At this time, we need to clean for a long time. We should use soaking to prolong the cleaning time. The specific soaking method is to use low drum speed, very small spiral differential speed and relatively small water injection flow to greatly prolong the cleaning time, In this way, the solid slag settled on the inner wall of the drum will fall off completely.

Drive belt and pulley

 the drive belt will be worn and loose after the centrifuge has been running for a certain period of time. During the normal service life of the belt, we must often adjust the belt tension and check the wear degree of the belt. The belt must be replaced in advance like the bearing, otherwise it will cause the shaking of the motor and the vibration of the machine. If the belt breaks during operation, the speed probe of the accessory will be damaged in most cases, Cause unnecessary additional losses.

 before the centrifugal machine stops for a long time and starts again, it is necessary to remove the rust on the belt pulley, which is an important reason to accelerate the wear of the belt.

 check for wear

 wear inspection is divided into three aspects.

 first, regularly check the anti-wear bushing at the solid slag discharge port of the centrifuge. The anti-wear bushing can not be understood as a never worn bushing. It is just a bushing that is easy to replace, so that the material can not directly abrade the stainless steel body. While checking the anti-wear bushing at the slag discharge port, we can have an understanding of the wear characteristics of the material, so as to predict the wear of the material to the spiral blade.

 second, regularly check the solid slag scraper block attached to the drum cone and slag discharge port. If the scraper block falls off, the solid slag will directly abrade the stainless steel body of the drum and cause the vibration value to rise.

 the third is to check the wear degree of the bearing, which is mainly judged indirectly by observing the color of waste grease, bearing temperature and bearing vibration.