Method for cleaning the annular space of a solid-jacket screw centrifuge

Abstract

Method for cleaning an annular space (14) into which a skimming section (105) of a radially adjustable peeling tube (100) of a solid-jacket screw centrifuge (1) engages, characterized by at least the following steps to be carried out during the cleaning of the annular space (14): 100: Initiating a cleaning of the annular space (14) after a defined time interval; 200: Pivoting an inlet opening (101) on the skimming section (105) of the peeling tube (100) from a current working position to a further radially outer, preferably to a maximally radially outer position and determining the power input required for this; 300: Evaluate the power consumption from step 200 and, depending on this, determine a new time interval until the next cleaning of the annular space (14); 400: Swiveling the inlet opening (101) on the skimming section (105) of the peeling tube (100) from the further radially outer position to the previous working position.

Description

[0001] The invention relates to a method for cleaning an annular space of a solid bowl screw centrifuge according to the preamble of claim 1.

[0002] An adjustable paring tube for a solid-bowl screw centrifuge—also known in technical terms as a decanter centrifuge—is known from DE 43 39 582 C1. According to the technical teaching of DE 43 39 582 C1, the paring tube is pivoted by a toggle lever mechanism located in a rotating annular chamber of the centrifuge during operation, into which the paring tube pivotably engages. The toggle lever mechanism is actuated by a manually operated adjusting spindle. A disadvantage of the solution according to DE 43 39 582 C1 is the complex arrangement of the toggle lever mechanism on the bowl.

[0003] Against this background, the invention has the object of providing a method for cleaning an annular space in which this problem has been solved.

[0004] The invention solves this problem by the method of claim 1, i.e. by a method for cleaning an annular space into which a skimming section of a radially adjustable skiving tube of a solid bowl screw centrifuge engages, characterized by at least the following steps to be carried out during the cleaning of the annular space: 100: Initiating cleaning of the annular space after a defined time interval; 200: pivoting an inlet opening on the skimming section of the skimming tube from a current working position to a further radially outer, preferably to a maximum radially outer position and determining the power consumption required for this; 300: Evaluating the power consumption from step 200 and, depending on this, determining a new time interval until the next cleaning of the annular space; 400: Swiveling the inlet opening at the skimming section of the peeling tube from the further radially outer position to the previous working position.

[0005] According to claim 2, it is provided that the power absorbed by a drive of an actuator is continuously sensed or measured and that the measured actual power is compared with a defined target power.

[0006] And according to claim 3, the time interval until the next cleaning of the annular space is extended if the value of the measured power is below the defined target value.

[0007] The time interval until the next cleaning of the annular space can be shortened if the value of the measured power is above the defined target value.

[0008] The method in step 100 can be initiated after a predefined time interval.

[0009] And in this step, the inlet opening can be pivoted to a maximum outer position by the actuator via a coupling gear in the annular space and the power consumption required for this is determined.

[0010] Optionally, in step 300, the power consumption from step 200 can be evaluated and, depending on this, a new time interval until the next cleaning of the annular space can be determined.

[0011] And optionally in step 400 the inlet opening at the skimming section of the peeling tube can be pivoted by the actuator via the coupling gear from the maximum radially outer position back to its previous working position.

[0012] These methods can be advantageously used in a solid-bowl screw centrifuge, which has a stationary housing and a system which can be rotated during operation and which has a drum which is rotatably mounted via a pair of bearings and a screw which is rotatably mounted in the drum. An inlet pipe is used to feed a suspension to be processed into a centrifugal chamber between the screw and the drum. The screw conveys the solid to a solids discharge, while at least one liquid phase in the drum flows into an annular chamber of the rotating system. A skimming section of a skimming tube engages in the annular chamber to discharge the liquid phase from the annular chamber. The skimming tube is designed such that an inlet opening of the skimming section can be adjusted radially in its position with respect to the drum by pivoting the skimming tube. A coupling gear is arranged outside the drum.which allows the skimming section to be pivoted and thus the radial position of the skimming section's inlet opening to be adjusted in the annular space. Such prior art is known from US 2005 / 0197241 A1.

[0013] This coupling gear is advantageously aligned substantially in a radial plane and has one or more axial pivot axes relative to the axis of rotation of the drum, one of which is preferably located radially inward of the inlet opening of this section for pivoting the skimming section.

[0014] In this way, the coupling gear, which pivots the peeling tube, is advantageously arranged outside the annular space so that it is easily accessible and is not directly surrounded by the liquid phase during operation.

[0015] In a preferred embodiment, the coupling mechanism is designed in the manner of a crank-and-rocker and / or a multi-joint construction. The crank-and-rocker advantageously makes it possible to position a pivot point around which the skimming tube moves when adjusting the inlet opening of the skimming tube to different diameters for skimming the liquid phase from the annular space, such that an advantageously short, movable skimming section of the skimming tube is obtained. The multi-joint construction advantageously enables the arrangement in a plane aligned substantially radially to the rotation axis outside the drum.

[0016] It is advantageous if the maximum radial extension of the skimming section is less than half the diameter of the drum. This advantageously allows for a stiff skimming section—that is, one that is less susceptible to elastic deformation under bending moment loads caused by the discharge process.

[0017] In a further preferred embodiment, the liquid phase discharged through the skimming tube is further drained, at least in sections, through a flexible hose following the skimming tube. This hose also allows for a short design of the skimming section, as the hose advantageously follows the pivoting movement of the skimming section. Furthermore, the hose can be installed quickly and easily, which is advantageous.

[0018] Preferably, the inlet opening has a lip protruding from the inlet opening. The lip advantageously allows the liquid phase to enter the inlet opening of the peeling tube with virtually no splashing.

[0019] The coupling gear is preferably driven by an actuator, which it connects to the skiving tube. The actuator can work according to an electrical principle. The actuator is particularly preferably an electric linear drive, e.g. a spindle drive. This advantageously allows the skiving tube to be pivoted easily and precisely in an automatically controlled manner. However, it can also be operated hydraulically or pneumatically. In a further preferred embodiment, a bearing block forms a pivot point about which the skiving tube can be pivoted. The skimming section of the skiving tube can then end in an opening of a first bearing journal, which the central bearing block can form. It can then further advantageously be provided if the central bearing block has a further, second bearing journal. This allows a pivot point orA rotational axis for the peeling tube can be created, which has the advantageous additional function of a rotary union. To move the peeling tube, the coupling gear is preferably coupled to the peeling tube at a distance from its pivot points and / or rotational axis.

[0020] The central bearing block can also have an angular cavity through which the flow of the liquid phase is directed, starting at the opening of the first bearing journal, into a nozzle section of the skimming tube. This advantageous design of the central bearing block opens up the possibility of redirecting the flow of the liquid phase within the bearing block, which also advantageously enables a compact and rigid design of the skimming section.

[0021] In a further preferred embodiment, at least one joint of the coupling mechanism can be designed as a ball joint.

[0022] A preferred embodiment is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1: a schematic sectional view of a known solid bowl screw centrifuge; Fig. 2: an enlarged section of the discharge side for liquid phases of a solid bowl screw centrifuge suitable for the process according to the invention; Fig. 3: in a) a side view of a discharge side for liquid phases of the solid bowl screw centrifuge from Fig. 2, wherein parts of the drum and a housing have been hidden in order to illustrate a peeling tube, a coupling gear and an actuator and their interaction, in a first operating state and in b) the arrangement from a) in a second operating state; Fig. 4: an enlarged section of a peeling tube of the solid bowl screw centrifuge from Fig. 2.

[0023] Fig. Figure 1 shows a solid-bowl screw centrifuge 1—also called a decanter—with a bowl 2 in which a screw 3 is arranged. The bowl 2 and the screw 3 each have a substantially cylindrical section and a substantially conically tapered section.

[0024] An axially extending central inlet pipe 4 serves to feed the material to be centrifuged via a distributor 5 into a centrifugal chamber 6 between the screw 3 and the drum 2.

[0025] If a solid-liquid mixture is fed into the solid-bowl screw centrifuge 1, which is set in operation - ie rotation - by a motor as a suspension to be processed or as centrifuged material, solid particles settle on the drum wall.

[0026] The screw 3 rotates at a slightly lower or higher speed than the drum 2 and conveys the ejected solid S to the conical section of the drum 2 to a solids discharge 7. The remaining liquid, however, flows to the larger drum diameter at the rear end of the cylindrical section of the drum 2. The liquid ring forming in the drum is referred to in technical terms as a "pond".

[0027] The liquid portion of the suspension to be processed, which has been clarified of solids, is discharged at the rear end of the cylindrical section of the drum 2 through a first inner outlet 8, which is located closer to the rotation axis, and a second outer outlet 9 in two separate liquid phases L1 and L2. This is possible due to the different densities of the two liquid phases L1 and L2, which allow for centrifugal separation of these phases. Fig. 1 or Fig. The solid bowl screw centrifuge 1 shown in Figure 2 is a three-phase solid bowl screw centrifuge 1. Alternatively, the invention can also be used in a two-phase solid bowl screw centrifuge (in which only one liquid phase is discharged through an annular space with a paring tube).

[0028] The area of ​​outlets 8 and 9 of a solid bowl screw centrifuge is in Fig. 2 is shown enlarged. Only one of the bearings of a pair of bearings 10 of the screw 3 and another pair of bearings 11 of the drum 2 is shown here.

[0029] After Fig. 2, the first inner outlet 8, ie the outlet located closer to the rotation axis, has a discharge opening 12 into a collecting chamber 13 outside the drum 2, which is delimited by the drum 2 rotating during operation of the solid bowl screw centrifuge 1 and a housing G which is stationary during operation of the solid bowl screw centrifuge 1. The liquid phase L1 is further discharged from the chamber 13 through a discharge pipe.

[0030] The second, radially outer outlet 9 opens into an annular space 14, which is axially delimited by an annular disc 15 that rotates with the drum during operation. The annular space 14, or its walls, therefore rotate with the drum during operation. A skimming section 105 of a skimming tube 100, which does not rotate with the drum 2 during operation, engages axially inside the annular space 14, past the annular disc 15.

[0031] The skiving tube 100 initially extends radially from the outside of the drum to the inside. It then runs axially inside past the annular disc 15 and, following a bend, extends radially further outward into the annular space 14 with its skimming section 105.

[0032] The skimming tube 100 is further configured such that at least one inlet opening 101 of the skimming section 105 can be pivoted radially in its position relative to the drum 2. In other words, the inlet opening 101 of the skimming tube 100 or skimming section 105 can be continuously adjusted to different diameters for skimming the liquid phase L2 from the annular space 14.

[0033] For this purpose, only a part of the peeling tube 100 - such as the skimming section 105 - can be designed to be adjustable, or the entire peeling tube 100 including the skimming section 105.

[0034] In Fig. 3a and b show the arrangement of the skimming tube 100 on an axial outer side of the drum 2 in two different operating positions. The skimming tube 100 is pivotably arranged in the region of a rotary joint on the housing G of the drum 2 between the drum 2 and the side facing the housing G. The pivoting of the skimming section 105 to change the radial position of the inlet opening 101 is achieved by a coupling gear 102, which is arranged entirely—except for one passage—or at least substantially outside the drum 2 in the non-rotating system of the centrifuge. This coupling gear engages the skimming tube 100, preferably at a distance from its axis of rotation, at one or more points—preferably outside the drum—in order to enable it to be pivoted easily.

[0035] With the selected construction, the paring tube 100 can be arranged on the housing G and frame of the solid bowl screw centrifuge 1 in such a way that the position of the paring tube 100 relative to the housing G can advantageously be adjusted to different positions (compare Fig. 3a and Fig. 3b).

[0036] The coupling mechanism 102 is used for this purpose. The coupling mechanism 102 can be designed in various ways, for example, in the manner of a crank rocker.

[0037] The coupling mechanism may further comprise a multi-joint construction 114, via which it is coupled on the one hand to the peeling tube 100 and on the other hand to an actuator 103.

[0038] The actuator 103 for driving the coupling gear 102 and the peeling tube 100 operates according to an electrical principle. An electric linear drive is particularly preferred as the actuator 103. Alternatively, an actuator 103 operating according to a fluidic principle, e.g., a hydraulic cylinder, can be used.

[0039] The actuator can be aligned on the housing 2 substantially tangentially to the drum ( Fig. 3a and b) and acts via the coupling mechanism 102 - here provided with the multi-joint construction - via one or more levers and joints connecting them - on the skimming tube 100 in its entirety or at least on the skimming section 105 of the skimming tube 100 in order to pivot it in order to adjust its radial position. Fig. 3, the actuator 103 - designed as a cylinder - is shown in an extended position, whereby the inlet opening of the skimming section 105 is pivoted to a radially outer position. In Fig. In Figure 3b, however, the actuator 103 or here the cylinder is shown in a retracted position, whereby the inlet opening of the skimming section 105 is pivoted to a radially inner position.

[0040] With respect to a radial dimension of the drum 2, the maximum radial length of the skimming section 105 is preferably selected such that it is less than half the diameter of the drum 2. This advantageously allows for the realization of a stiff skimming section 105—that is, one that is relatively less sensitive to elastic deformation under bending moment loads caused by the discharge process. Furthermore, such an arrangement allows the skimming section 105 or its skimming tube 100 to be used even at different "pond depths" and thus advantageously allows for flexible use.

[0041] The liquid phase discharged through the skimming tube 100—here L2—can be drained off after the skimming tube, initially through a hose 104. The hose 104 facilitates a short design of the skimming section 105, since the hose 104 can advantageously follow the pivoting movement of the skimming tube with the skimming section 105. Furthermore, the assembly of the hose 104 is simple and quick, and thus advantageous.

[0042] In Fig. Figure 4 clearly shows the skimming section 105 of the skimming tube 100 in a side view. The skimming section 105 can be formed by a tube angled approximately 90°, which initially runs axially and then radially.

[0043] The skimming section 105 has the inlet opening 101 – also called the skimming head in technical terms – which can widen at its free end in the manner of a funnel. Furthermore, the inlet opening 101 here has a kind of lip 106 that protrudes from the inlet opening 101 (see also Fig. 3). Through the lip 106, the liquid phase L2 enters the inlet opening 101 advantageously with almost no splashing.

[0044] The skimming section 105 of the skimming tube 100 can open into an opening of a first bearing journal 107, which is formed by a central bearing block 108. The bearing block 108 has a further, second bearing journal 109. The two bearing journals 107, 109 support the central bearing block 108 in a rotatable or pivotable manner in a bearing housing 110. The bearing housing 110 has a geometrically corresponding bearing shell for this purpose. The central bearing block 108 thus defines a stationary axis of rotation about which the skimming tube 100 can be rotated or pivoted. This axis of rotation is advantageously located radially inward of the inlet opening 101 of the skimming section 105. The bearing housing 110 can be secured to the stationary housing G and / or frame of the centrifuge.

[0045] The central bearing block 108 can be designed in the manner of a rotary union. This enables a sealed transition from the skimming tube 100. Here, the liquid phase emerging from the drum flows through the inlet opening 101 into the skimming section 105 of the skimming tube 100 and further through the opening of the first bearing journal 107 into the central bearing block 108. The central bearing block 108 has an angular cavity 111 (see Fig. 2), through which the flow of the liquid phase, starting at the opening of the first bearing journal 107, is directed into a nozzle section 112 of the peeling tube 100. The hose 104 is connected to the nozzle section 112 by a corresponding coupling 113 (see Fig. 2).

[0046] The coupling mechanism 102 is arranged essentially in a radial plane and has one or more axially aligned pivot axes. It is located outside the drum between the housing and / or frame G and the drum and preferably engages the peeling tube 100 and / or a part firmly connected to the peeling tube in one or more ways (e.g., via a type of polygonal strut).

[0047] The following is a description of a method for cleaning the annular space 14 into which the peeling tube 100 engages during operation of the centrifuge 1 - in which the rotating system rotates.

[0048] A centrifuge material—i.e., a starting product with a pasty consistency—is preferably continuously fed into the bowl 2 of the solid-bowl screw centrifuge 1 via the inlet pipe 4, where it is clarified of solids and separated into two liquid phases L1 and L2. The liquid phases L1 and L2 are continuously discharged through the outlet 12 and the skiving pipe 100.

[0049] During the clarification of the starting product with formation of the liquid phases L1, L2 or a single liquid phase, turbidity and other solids contained in the starting product are conveyed by the screw 3 to the side of the drum 2 opposite the peeling disc or the peeling tube 100 and are continuously discharged from the drum 2.

[0050] The inventive cleaning method for the annular space 14 is based on the fact that the actuator 103 pivots the peeling tube 100 radially outward into the annular space 14 from time to time in order to remove deposited solid particles from the annular space 14 before they harden and make it impossible to adjust the peeling tube 100 to radially large diameters.

[0051] This cleaning process is usually initiated over a preset time interval and carried out regularly. During the motorized pivoting of the skiving tube, the absorbed drive power is determined, e.g., by a current measurement, and compared with a target value by a control unit (not shown here). If the value of the determined power is below a defined target value, the time interval until the next cleaning of the annular space 14 is extended. If the determined power is above the defined target value, the time interval until the next cleaning is shortened. If the determined power corresponds to the defined target value, the time interval is kept constant until the next cleaning of the annular space 14.

[0052] This provides automatic control for the time interval after which a cleaning cycle is initiated for the annular space 14. It is desirable that the time interval between two cleaning cycles be as long as possible, since each cleaning disrupts the purification process.

[0053] An advantageous cleaning process includes the following steps: The process starts in step 100 and is carried out using a centrifuge control device (not shown here). In step 100, the cleaning of the annular chamber 14 of the solid-bowl screw centrifuge 1 is started after a predefined time interval.

[0054] Thereafter, in a step 200, the skimming tube 100, more precisely the inlet opening 101 at the skimming section 105 of the skimming tube 100, is pivoted by the actuator 103 via the coupling gear 102 in the annular space 14 of the solid-bowl screw centrifuge 1 from its current working position to a more radially outer, preferably a maximum radially outer position or to a larger skimming diameter with the aid of a drive or actuator 103. During the pivoting, the power consumption of the drive caused by the amount of solid material in the annular space 14 is sensed at defined discrete time intervals, preferably quasi-continuously, and transmitted to the control device.

[0055] In a subsequent step 300, the control device evaluates the power consumption measured in step 200 by comparing it with a defined target value. Based on this comparison, the time interval until the next cleaning cycle is preferably determined as follows: a) Power consumption > setpoint: shortening of the cleaning interval b) Power consumption < setpoint: Extension of the cleaning interval c) Power consumption = setpoint: Maintaining the cleaning interval.

[0056] In a final step 400, the skiving tube 100, more precisely the inlet opening 101 at the skimming section 105 of the skiving tube 100, is pivoted by the actuator 103 via the coupling gear 102 in the annular space 14 of the solid bowl screw centrifuge 1 from the radially outer position back to a further inner diameter, in particular to the previous working position.

[0057] Overall, the presented and claimed methods advantageously increase the availability of the centrifuge in a simple manner and also significantly extend the maintenance intervals of the centrifuge. List of reference symbols 1 solid bowl screw centrifuge 2 drums 3 snail 4 Inlet pipe 5 distributors 6 Spinning room 7 Solids discharge 8 Outlet 9 Outlet 10 Storage 11 Storage 12 Outlet opening 13 Room 14 Annular space 15 Ring disc 100 peeling tubes 101 Entrance opening 102 coupling gear 103 Actuator 104 hose 105 skimming section 107 bearing journals 108 bearing block 109 bearing journals 110 bearing housing 111 Cavity 112 nozzle section 113 Clutch 114 Multi-joint construction L1 liquid phase L2 liquid phase S solid G Housing

Claims

[1] Method for cleaning an annular space (14) into which a skimming section (105) of a radially adjustable skiving tube (100) of a solid bowl screw centrifuge (1) engages, characterized by at least the following steps to be carried out when cleaning the annular space (14): 100: Initiating a cleaning of the annular space (14) after a defined time interval; 200: pivoting an inlet opening (101) on the skimming section (105) of the peeling tube (100) from a current working position to a further radially outer, preferably to a maximum radially outer position and determining the power consumption required for this; 300: Evaluating the power consumption from step 200 and, depending on this, determining a new time interval until the next cleaning of the annular space (14); 400: Pivoting the inlet opening (101) on the skimming section (105) of the peeling tube (100) from the further radially outer position to the previous working position. [2] Method according to claim 1, characterized by that the power absorbed by a drive of an actuator (103) is continuously sensed or measured and that the measured actual power is compared with a defined target power. [3] Method according to claim 2, characterized by that the time interval until the next cleaning of the annular space (14) is extended if the value of the measured power is below the defined target value. [4] Method according to one of claims 1 to 2, characterized by that the time interval until the next cleaning of the annular space (14) is shortened if the value of the measured power is above the defined target value. [5] Method according to one of claims 1 to 4, characterized bythat the method is initiated in step 100 after a predefined time interval. [6] Method according to one of claims 1 to 5, characterized by that in step 200 the inlet opening (101) is pivoted by the actuator (103) via a coupling gear (102) in the annular space (14) to a maximum outer position and the power consumption required for this is determined. [7] Method according to one of claims 2 to 6, characterized by that in step 300 the power consumption from step 200 is evaluated and, depending on this, a new time interval until the next cleaning of the annular space (14) is determined. [8] Method according to one of claims 1 to 7, characterized bythat in step 400 the inlet opening (101) at the skimming section (105) of the peeling tube (100) is pivoted by the actuator (103) via the coupling gear (102) from the maximum radially outer position back to its previous working position.

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