Operation method and operation adjustment technology of horizontal screw centrifuge
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.
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.
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.
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.
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.
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.
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.
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.
Section 9 technical adjustment 3, shutdown sequence
Section 10 technical adjustment 5, fault judgment
Section 11 technical adjustment 6, common judgment methods
Section 12 seven of technical adjustment, routine maintenance
Drive belt and pulley