Method for controlling constant screw shaft torque in a screw press
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- ISHIGAKI CO LTD
- Filing Date
- 2023-03-06
- Publication Date
- 2026-07-31
Smart Images
Figure 0007898059000001 
Figure 0007898059000002 
Figure 0007898059000003
Abstract
Description
Technical Field
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[0001] The present invention relates to an operation control method for a screw press, and particularly to a method for controlling the torque of a screw shaft within a predetermined range by adjusting air blowing into a filtration chamber, a dehydration aid, and the chemical injection rate of a flocculant in order to keep the moisture content of a dewatered cake discharged from the end side of an outer cylinder screen constant. The present invention relates to a method for controlling the torque of a screw shaft to be constant in a screw press.
Background Art
[0002] Conventionally, screw presses for concentrating and dewatering organic sludge such as sewage, urine, or food production and processing wastewater have been generally known. A screw press is a device for continuously concentrating and dewatering sludge. Since the properties of sludge vary depending on seasons, time, weather, etc., control methods for the rotational speed of the screw shaft, the pressing pressure, the flocculant supply amount, etc. are required to maintain stable performance in a screw press.
[0003] In particular, a method of performing control according to an index of the torque of a screw shaft, which is closely related to the moisture content of a dewatered cake, is also known. For example, a method for controlling the torque of a screw shaft to be within a predetermined range by controlling the pressing pressure and the chemical injection rate of a flocculant in a screw press is described in Patent Document 1.
[0004] Also, a control method for a screw press that reduces the amount of flocculant used by increasing or decreasing the amount of a dehydration aid (biomass) added is described in Patent Document 2.
[0005] In the structure of a screw press, a screw press that sends compressed air from a large number of fine holes provided in a hollow screw shaft to a filtration chamber and discharges the moisture of a cake to the outside in a short time is described in Patent Document 3.
Prior Art Documents
Patent Documents
[0006]
Patent Document 1
[0007] Organic sludge such as sewage, human waste, or wastewater from food production and processing, which is concentrated and dewatered using a screw press, fluctuates constantly depending on the season, weather, time of day, etc. Various controls were implemented in response to these fluctuations, either in the operation of the screw press or in the conditioning of the sludge. As described in prior art 1, methods for adjusting the injection rate of coagulants are known, and in order to suppress the cost increase caused by using large amounts of expensive coagulants for operational control, the amount of coagulant used can be reduced by combining this with the control of the supply amount of dewatering aid (biomass), as described in prior art 2. However, there was a concern that supplying large amounts of dewatering aid (biomass) would increase the amount of cake discharged and raise the load on downstream equipment.
[0008] Furthermore, the technique of removing moisture by sending compressed air to the dewatered cake in the filtration chamber is effective for inorganic slurries with low compressibility and coarse particles, but less effective for organic slurries with high compressibility.
[0009] The present invention provides a method for controlling the constant torque of a screw shaft in a screw press, which controls the rate of air blowing, dewatering aids, and flocculants injected into the filtration chamber so that the torque of the screw shaft remains within a predetermined range in response to variations in the properties of the incoming sewage sludge. [Means for solving the problem]
[0010] The present invention relates to a screw press screw shaft torque constant control method for which tempered sludge, to which a dewatering aid and a coagulant have been added to the raw sludge, is injected under pressure into the starting end of an outer cylinder screen, and the filtrate is separated from the outer cylinder screen while being conveyed to the rear end of the outer cylinder screen by a rotating screw shaft, and compressed air is supplied to the dewatered cake in the filtration chamber through a number of fine holes provided in the screw shaft, wherein the screw shaft torque is set to a predetermined range, the standard supply amount of the dewatering aid, the maximum supply amount which is the maximum value of the standard supply amount, the minimum supply amount which is the minimum value of the standard supply amount, the supply amount range which increases and decreases in stages, the standard supply amount of compressed air, the maximum supply amount which is the maximum value of the standard supply amount, and the minimum supply amount which is the minimum value of the standard supply amount amount, The following parameters are set: a range of gradually increasing and decreasing supply amounts, a standard supply amount of coagulant, a maximum supply amount (the maximum value of the standard supply amount), a minimum supply amount (the minimum value of the standard supply amount), and a range of gradually increasing and decreasing supply amounts. The torque of the screw shaft is measured, and if the measured torque is within the range of the standard torque, the operation of the screw press continues. If the measured torque is lower than the preset standard torque, the supply amount of dewatering aid is increased by the supply amount range, and this operation is repeated until the torque of the screw shaft rises within the range of the standard torque. When the supply amount of dewatering aid reaches the maximum amount, the supply amount of compressed air is increased by the supply amount range, and this operation is repeated until the torque of the screw shaft rises within the range of the standard torque. When the supply amount of compressed air reaches the maximum amount, the supply amount of coagulant is increased by the supply amount range, and the screw press continues. This process involves repeating the operation until the screw shaft torque rises within the standard torque range. If the measured torque is higher than the preset standard torque, the amount of coagulant supplied is reduced by the supply amount range, and this process is repeated until the screw shaft torque falls within the standard torque range. When the coagulant supply reaches the minimum amount, the amount of compressed air supplied is reduced by the supply amount range, and this process is repeated until the screw shaft torque falls within the standard torque range. When the compressed air supply reaches the minimum amount, the amount of dewatering aid supplied is reduced by the supply amount range, and this process is repeated until the screw shaft torque falls within the standard torque range. This method controls the screw shaft torque to be constant, enabling the discharge of a stable dewatered cake even with variations in sludge properties, and contributes to cost-effective operation management. [Effects of the Invention]
[0011] This invention controls the torque of the screw shaft of a screw press to a constant level. When increasing the torque, it prioritizes reducing the amount of coagulant (which has high fixed costs) and the amount of high-pressure air (which has high running costs). When decreasing the torque, it prioritizes reducing the amount of coagulant (which has high fixed costs), and then prioritizes reducing the amount of high-pressure air (which has high running costs). This eliminates abrupt changes in the operation of the screw press, allowing for dewatering operation in an optimal state for sludge properties in the filtration chamber even for slurries with low compressibility, and contributes to cost-effective operation management. [Brief explanation of the drawing]
[0012] [Figure 1] This is a longitudinal cross-sectional view of the screw press according to this invention. [Figure 2] Similarly, this is a control system for operating a dewatering machine. [Figure 3] Similarly, this is a flowchart of the driving control system. [Modes for carrying out the invention]
[0013] Figure 1 is a longitudinal cross-sectional view of a screw press. The screw press 1 has a screw shaft 7 installed between the front and rear frames 3 and 4 of a frame 2. The screw shaft 7 has screw blades 6 wound around an outer cylindrical screen 5 that has a filtration surface around its circumference. The screw shaft 7, which is located inside the outer cylindrical screen 5, tapers in diameter from the starting end to the ending end, reducing the relative distance between the outer cylindrical screen 5 and the screw shaft 7 in the direction of extension. A sludge supply pipe 8 is connected to the front end of the screw shaft 7, and the supply pipe 8 communicates with a supply hole 9 of the screw shaft 7 which is opened on the starting end side of the outer cylindrical screen 5. A screw drive shaft 10 is connected to the rear end of the screw shaft 7, and a drive sprocket 11 is fitted to the screw drive shaft 10. This sprocket 11 is driven by a screw drive machine 12 to rotate the screw shaft 7. The sludge supplied from the supply hole 9 is transported by the screw blades 6 from the starting end to the ending end, and is concentrated and dewatered while separating the filtrate from the outer cylinder screen 5. The outer cylinder screen 5 may be made rotatable if necessary.
[0014] Furthermore, the dewatered cake discharge section 13, which discharges the sludge (dewatered cake) immediately after dewatering to the outside, is equipped with a tapered cone-shaped presser (pressure plate) 14 to apply back pressure to the discharged dewatered cake. This presser 14 is provided to reciprocate freely in the axial direction (left-right direction in Figure 1) by a fluid pressure cylinder 15 such as an air cylinder or a hydraulic cylinder.
[0015] The screw shaft 7 has a hollow interior and has numerous micropores 16 that connect the interior to the filtration chamber. During the filtration process, compressed air is supplied to the inside of the screw shaft 7 and released into the filtration chamber through the micropores 16. As the compressed air passes through the gaps in the dewatered cake in the filtration chamber, it is carried along and discharged to the outside through the outer cylindrical screen 5. Micropores provided on the screw shaft 7 16 The position of this step is preferably in the later stages, when the solid content of the dehydrated cake increases.
[0016] The screw press 1 can continuously dehydrate the agglomerated slurry. Compared with conventional continuous dehydrators such as belt-type dehydrators and centrifugal dehydrators, it is small in size, compact, has a small motor capacity, and is power-saving. Further, by maintaining the filtration chamber at an optimal pressure, the screw press 1 can exhibit a stable filtration effect and can perform continuous dehydration at an optimal moisture content.
[0017] FIG. 2 is a schematic configuration diagram of a screw shaft torque constant control method in the screw press according to this invention, and its operation control system will be described. The raw liquid supply pipe 31 and the dewatering aid supply pipe 32 are connected to the raw liquid adjustment tank 33. The raw liquid adjustment tank 33 is provided with a stirring device 34 for stirring and mixing the treatment raw liquid such as sludge supplied from the raw liquid supply pipe 31 and the dewatering aid supplied from the dewatering aid supply pipe 32.
[0018] The dewatering aid is pulverized and stored in the dewatering aid storage tank 35, and is supplied to the raw liquid adjustment tank 33 through the dewatering aid supply pipe 32 by the supply device 36 as needed. Note that the dewatering aid may be supplied to the agglomeration mixing tank 39 described later. The supply device 36 may be appropriately selected as a belt type, screw type, etc. according to the equipment and the dewatering aid.
[0019] In this embodiment, unused biomass is used as the dewatering aid. Unused biomass has low utilization value in its original state and is usually disposed of as waste. Specifically, there are plant-based wastes such as woody rice husks, thinned woods, food-based tea cakes, and plant residues.
[0020] Also, depending on the biomass to be added, pretreatment may be performed so that it has a shape and property that is easy to adapt to the raw liquid before being supplied to the raw liquid adjustment tank 33. Particularly in the case of biomass with high hardness, after performing an expansion and softening treatment, a flocculent treatment may be further performed. By subdividing the plant fibers of the biomass, the fibers become more easily adaptable to the raw liquid, and it is possible to reduce the true moisture content.
[0021] Since the specific gravity of biomass is lighter than that of the stock solution, the stock solution and biomass are stirred and mixed in the stock solution preparation tank 33. In the stock solution preparation tank 33, the biomass and stock solution are evenly mixed to form a tempered stock solution. Any stirring device 34 that evenly stirs and mixes the biomass and stock solution can be used, and in this embodiment, a stirring blade is used.
[0022] The tempered concentrate, mixed with the dewatering aid in the concentrate preparation tank 33, is pumped by the injection pump 37 through the tempered concentrate supply pipe 38 to the coagulation mixing tank 39. Measuring instruments 40 (flow meter, concentration meter) are installed downstream of the injection pump 37. A coagulant supply pipe 41 is connected to the tempered concentrate supply pipe 38, and a coagulant (polymer coagulant, inorganic coagulant) is supplied from the coagulant dissolving tank 42 by the coagulant supply pump 43. A flow meter 44 for measuring the amount of coagulant supplied is installed downstream of the coagulant supply pump 43. The coagulant supply pipe 41 may also be connected to the coagulation mixing tank 39.
[0023] The coagulation mixing tank 39 is equipped with a stirring device 45 for stirring and mixing the tempering stock solution and the coagulant. The tempering stock solution and the coagulant are stirred and mixed in the coagulation mixing tank 39 to generate strong flocs. The dewatering aid connects the coagulated flocs together to form a coagulation slurry, which is then supplied to the screw press 1 via the coagulation slurry supply pipe 46. The coagulation slurry supply pipe 46 is equipped with a pressure gauge 47 for measuring the pressure at which the coagulation slurry is supplied to the screw press 1.
[0024] A compressed air supply pipe 48 is connected to the screw shaft 7, and compressed air is supplied to the screw shaft 7 from a compressed air supply source 49 via a control valve 50 and a flow meter 51. The compressed air supplied to the screw shaft 7 enters the filtration chamber through the micropores 16, and the moisture in the dewatered cake is discharged to the outside through the outer cylindrical screen 5.
[0025] A torque meter 52 is installed in the drive shaft system of the screw press 1 (for example, the screw drive shaft 10) to measure the torque of the screw shaft 7, which increases or decreases due to fluctuations in the properties of the raw liquid. The torque T measured by this torque meter 52 is compared with a preset reference torque T0, and the load on the screw shaft 7 is adjusted so that the torque becomes the reference torque T0.
[0026] Specifically, commands are given to the supply device 36, the coagulant supply pump 43, or the control valve 50 to increase or decrease the amount of dewatering aid supplied, the amount of coagulant supplied, or the amount of compressed air supplied, respectively, in order to perform constant torque control operation. In practice, the detection signal measured by the torque meter 52 is transmitted to the control device 53, which compares and judges the signal, and then the control device 53 issues commands to the supply device 36, the coagulant supply pump 43, or the control valve 50.
[0027] Furthermore, in order to operate the screw press 1 stably, a method for controlling the press-fit pressure to a constant level may be implemented simultaneously. Constant press-fit pressure control involves adjusting the rotational speed of the screw shaft 7 according to the pressure measured by a pressure gauge 47 installed in the agglomerated slurry supply pipe 46.
[0028] The operation control method according to the present invention is based on controlling the torque of the screw press 1 to a constant level in order to operate the screw press 1 stably. Therefore, in order to keep the torque constant, the amount of dewatering aid supplied to the screw press 1, the amount of flocculant supplied, or the amount of compressed air supplied is controlled.
[0029] When the screw press 1 starts operating, the torque of the screw shaft 7 is measured in real time by the torque meter 52 and controlled by the control unit. 53 It will be sent to [location].
[0030] Generally, when the properties of the inflow stock change and the amount of solids in the processed stock increases (decreases), the inlet pressure supplied to the screw press 1 increases (decreases), and the torque of the screw shaft 7 also increases (decreases) in accordance with this load fluctuation.
[0031] Therefore, the control device of the present invention 53 The torque meter 52 measures a value T, which is then compared with a preset reference torque T0. If the measured value T is outside the reference torque T0, a command is given to the supply device 36, the coagulant supply pump 43, or the control valve 50 to control the amount of dewatering aid supplied, the amount of coagulant supplied, or the amount of compressed air supplied, thereby adjusting the operating load on the screw press 1. This load adjustment makes it easy to maintain the torque of the screw press 1 at the reference torque T0. The reference torque T0 can be set within a certain range, and when the measured torque T falls within that range, normal operation continues while maintaining the current state.
[0032] More specifically, if the measured torque T is lower than the reference torque T0, the control device 53 commands the supply device 36 to increase the amount of solid matter in the agglomerated slurry. By supplying the tempered slurry with the increased amount of solid matter to the screw press 1, the torque of the screw press 1 can be increased.
[0033] Furthermore, if the measured torque T does not return to the reference torque T0 even when the supply amount of the dewatering aid is increased, the control device 53 issues a command to the control valve 50 to increase the supply amount of compressed air. By increasing the amount of compressed air injected into the dewatered cake being transported through the filtration chamber, the moisture content of the dewatered cake is reduced, thereby increasing the torque of the screw press 1.
[0034] Furthermore, if the measured torque T does not return to the reference torque T0 even after increasing the compressed air supply, the control device 53 issues a command to the coagulant supply pump 43 to increase the amount of coagulant supplied. By supplying the tempered stock solution with increased coagulation floc strength to the screw press 1, the torque of the screw press 1 can be increased.
[0035] On the other hand, if the measured torque T is higher than the reference torque T0, the control device 53 issues a command to the coagulant supply pump 43 to reduce the amount of coagulant supplied. By supplying the tempered raw material with weakened coagulated floc strength to the screw press 1, the torque of the screw press 1 can be reduced.
[0036] Furthermore, if the measured torque T does not return to the reference torque T0 even when the supply amount of coagulant is reduced, the control device 53 issues a command to the control valve 50 to reduce the supply amount of compressed air. By reducing the amount of compressed air injected into the dewatered cake that is transported through the filtration chamber, the decrease in the moisture content of the dewatered cake can be suppressed, thereby lowering the torque of the screw press 1.
[0037] Furthermore, if the measured torque T does not return to the reference torque T0 even when the compressed air supply is reduced, the control device 53 issues a command to the supply device 36 to reduce the amount of solid matter in the agglomerated slurry. By supplying the tempered slurry with reduced solid matter content to the screw press 1, the torque of the screw press 1 can be reduced.
[0038] When increasing torque, priority is given to reducing the amount of coagulant used, which has high fixed costs, and the amount of high-pressure air used, which has high running costs. When decreasing torque, priority is given to reducing the amount of coagulant used, which has high fixed costs, and then priority is given to reducing the amount of high-pressure air used, which has high running costs. By controlling it in this way, the torque of the screw press 1 can be easily controlled to within the reference value, and the screw press 1 This allows for continued stable operation and contributes to cost-effective operation management.
[0039] Once the supply amount of the supply device 36, the coagulant supply pump 43, or the control valve 50 is changed, the torque is measured again after a certain period of time has elapsed, and the above operation is repeated until the measured value T returns to within the reference torque T0.
[0040] The supply range for gradually increasing or decreasing the supply of dewatering aid, coagulant, or compressed air is predetermined. Upper and lower limits can be set for each, and an alarm may be issued or the operation may be automatically stopped to allow for investigation when the upper or lower limit is reached. [Examples]
[0041] Figure 3 is a flowchart of the operation control system according to this embodiment. A. Initial settings The reference torque T0 (maximum reference torque Tmax, minimum reference torque Tmin) of the screw shaft 7 is set. In this embodiment, the reference torque T0 is set to have a range between the maximum reference torque Tmax and the minimum reference torque Tmin. Set the standard supply amount A0, the maximum supply amount Amax, the minimum supply amount Amin, and the supply amount range a for gradually increasing or decreasing the dehydration aid. Set the standard supply amount B0, the maximum supply amount Bmax, the minimum supply amount Bmin, and the supply amount range b to be increased or decreased in stages for compressed air. The standard supply amount C0, maximum supply amount Cmax, minimum supply amount Cmin, and the supply amount range c for gradually increasing or decreasing the amount of the flocculant are set.
[0042] B. Start of operation Each device will be operated at the above reference values T0, A0, B0, and C0.
[0043] C. Torque Comparison The torque of the screw shaft 7 of screw press 1 is measured and compared with the reference torque T0. If the measured torque value T is within the reference torque T0, the operation of each device will be maintained in its current state. If the measured value T is less than the reference torque T0, the process moves to step D in the flowchart, and control is performed to gradually increase the amount of dewatering aid, flocculant, or compressed air supplied to the screw press 1. If the measured value T is greater than the reference torque T0, the process moves to L in the flowchart and controls the supply of coagulant, compressed air, or dewatering aid in stages.
[0044] D. Comparison of maximum supply amounts of dehydration aids In the flowchart C above, if the measured torque T is less than the reference torque T0, the supply amount A, which takes into account a supply amount range a that increases in stages to increase the supply amount of the dewatering aid, is compared with the maximum supply amount Amax. If the supply amount A of the dewatering aid after the change is less than the maximum supply amount Amax, the process moves to E in the flowchart and controls the supply amount of the dewatering aid to increase in stages. If the supply amount A of the dewatering aid after the change is greater than or equal to the maximum supply amount Amax, the process moves to F in the flowchart, and control is performed to gradually increase the supply amount of compressed air.
[0045] E. Dehydration aid (increased) In the flowchart D above, if the supply amount A of the dewatering aid after the change is less than the maximum supply amount Amax, the supply device 36 is adjusted to increase the supply amount of the dewatering aid by a preset supply amount width a.
[0046] F. Comparison of maximum compressed air supply rates In the flowchart D above, if the supply amount A of the dewatering aid is greater than or equal to the maximum supply amount Amax, the supply amount B, which takes into account a supply amount range b that increases in stages in order to increase compressed air, is compared with the maximum supply amount Bmax. If the modified compressed air supply rate B is less than the maximum supply rate Bmax, the process moves to step G in the flowchart and controls the compressed air supply rate to increase gradually. If the modified compressed air supply rate B exceeds the maximum supply rate Bmax, the process moves to step H in the flowchart, where the flocculant supply rate is gradually increased.
[0047] G. Compressed air (increased) In the flowchart F above, if the modified compressed air supply amount B is less than the maximum supply amount Bmax, the control valve 50 is adjusted to increase the compressed air supply amount by a preset supply amount range b.
[0048] H. Comparison of maximum supply amounts of flocculants In the flowchart F above, if the compressed air supply amount B is greater than or equal to the maximum supply amount Bmax, the supply amount C, which takes into account the supply amount range c that is gradually increased in order to increase the amount of coagulant, is compared with the maximum supply amount Cmax. If the changed flocculant supply amount C is less than the maximum supply amount Cmax, the process moves to step J in the flowchart and controls the flocculant supply amount to be increased in stages. If the supply amount C of the flocculant after the change exceeds the maximum supply amount Cmax, the process proceeds to K in the flowchart, where an alarm is issued or control is performed to automatically stop the operation of screw press 1.
[0049] J. Flocculant (increased) In the flowchart H above, if the changed amount of flocculant supplied C is less than the maximum supply amount Cmax, the flocculant supply pump 43 is adjusted to increase the amount of flocculant supplied by a preset supply amount range c.
[0050] K. Alarm / Operation Stop After a certain period of time has elapsed, the torque is measured again, and the above operation is repeated until the measured value T returns to within the reference torque T0. If the measured torque T does not return to within the reference value T0 even when the flocculant reaches the maximum supply amount, an alarm is issued or the operation of screw press 1 is automatically stopped.
[0051] L. Comparison of minimum supply amounts of flocculants In the flowchart C above, if the measured torque T is greater than the reference torque T0, the supply amount C, which takes into account a supply amount range c that gradually reduces the amount of flocculant supplied, is compared with the minimum supply amount Cmin. If the changed flocculant supply amount C is greater than the minimum supply amount Cmin, the process moves to M in the flowchart and controls the flocculant supply amount to be reduced in stages. If the supply amount C of the flocculant after the change falls below the minimum supply amount Cmin, the process moves to N in the flowchart, and control is performed to gradually reduce the supply amount of compressed air.
[0052] M. Flocculant (reduced) In the flowchart L above, if the changed amount of flocculant supplied C is greater than the maximum supply amount Cmin, the flocculant supply pump 43 is adjusted to reduce the amount of flocculant supplied by a preset supply amount range c.
[0053] N. Comparison of minimum supply rates of compressed air In the flowchart L above, if the supply amount C of the coagulant is less than or equal to the minimum supply amount Cmin, the supply amount B, which takes into account a supply amount range b that gradually reduces the amount of compressed air, is compared with the minimum supply amount Bmin. If the modified compressed air supply rate B is greater than the minimum supply rate Bmin, the process moves to P in the flowchart and controls the compressed air supply rate to decrease gradually. If the modified compressed air supply rate B falls below the minimum supply rate Bmin, the process moves to Q in the flowchart, and control is performed to gradually reduce the supply rate of the dewatering aid.
[0054] P. Compressed air (reduced) In the flowchart N above, if the modified compressed air supply amount B is greater than the minimum supply amount Bmin, the control valve 50 is adjusted to increase the compressed air supply amount by a preset supply amount range b.
[0055] Q. Comparison of minimum supply amounts of dehydration aids In the flowchart N above, if the compressed air supply amount B is less than or equal to the minimum supply amount Bmin, the supply amount A, which takes into account a supply amount range a that gradually decreases the supply amount of the dewatering aid, is compared with the minimum supply amount Amin. If the supply amount A of the dewatering aid after the change is less than the minimum supply amount Amin, the process moves to R in the flowchart and controls the supply amount of the dewatering aid to decrease in stages. If the supply amount A of the dewatering aid after the change falls below the minimum supply amount Amin, the process moves to S in the flowchart and either issues an alarm or automatically stops the operation of screw press 1.
[0056] R. Dehydration aid (reduced) In the flowchart Q above, if the supply amount A of the dewatering aid after the change is greater than the minimum supply amount Amin, the supply device 36 is adjusted to reduce the supply amount of the dewatering aid by a preset supply amount width a.
[0057] S. Alarm / Operation Stop After a certain period of time has elapsed, the torque is measured again, and the above operation is repeated until the measured value T returns to within the reference torque T0. If the measured torque T does not return to within the reference value T0 even when the dewatering aid reaches the minimum supply amount, an alarm is issued or the operation of screw press 1 is automatically stopped.
[0058] If the supply amount of dewatering aid, coagulant, or compressed air is changed, the injection pressure is measured again after a certain period of time, and the above operation is repeated until the measured value T returns to within the reference torque T0.
[0059] In this embodiment, the torque of the screw shaft 7 is measured by a torque meter 52, and the control is also performed according to the current value when measuring the torque of the screw shaft 7, as in this embodiment. [Industrial applicability]
[0060] The screw shaft torque constant control method in a screw press of the present invention can maintain stable dewatering performance by adjusting the load on the screw shaft and controlling the torque to a constant level. Therefore, it can be applied to various solid-liquid separation devices, particularly continuous screw presses, for separating sewage sludge whose properties fluctuate constantly depending on the season, weather, etc. [Explanation of symbols]
[0061] 1 Screw press 5. Outer cylinder screen 7 Screw shaft 16 Micropore T Torque Measurement Value T0 Reference Torque A0 Standard supply amount of dehydration aid Amax Maximum supply amount Amin minimum supply amount a. A range of supply quantities to be increased or decreased in stages. B0 Standard supply volume of compressed air Bmax Maximum supply amount B-Phase Minimum Supply b. A range of supply quantities to be increased or decreased in stages. Standard supply amount of C0 flocculant Cmax Maximum supply amount Cmin Minimum supply amount c. A range of supply quantities that can be increased or decreased in stages.
Claims
[Claim 1] In a screw press screw shaft torque constant control method in which tempered sludge, which is obtained by adding a dewatering aid and a coagulant to raw sludge, is injected under pressure into the starting end of an outer cylindrical screen (5), and the filtrate is separated from the outer cylindrical screen (5) while being transported to the rear end of the outer cylindrical screen (5) by a rotating screw shaft (7), and compressed air is supplied to the dewatered cake in the filtration chamber through a number of fine holes (16) provided in the screw shaft (7), The reference torque (T0) of the screw shaft (7) which has a predetermined width, The standard supply amount of the dewatering aid (A0), the maximum supply amount (Amax), which is the maximum value of the standard supply amount, the minimum supply amount (Amin), and the range of supply amounts to be increased or decreased in stages (a), The standard supply amount of compressed air (B0), the maximum supply amount (Bmax), which is the maximum value of the standard supply amount, the minimum supply amount (Bmin), and the range of supply amounts to be increased or decreased in stages (b), The standard supply amount of the flocculant (C0), the maximum supply amount (Cmax), which is the maximum value of the standard supply amount, the minimum supply amount (Cmin), and the range of supply amounts to be increased or decreased in stages (c), Set it, The torque (T) of the screw shaft (7) is measured. When the measured torque (T) is within the range of the reference torque (T0), the screw press operation will continue. If the measured torque (T) is lower than the preset reference torque (T0), the supply amount of the dewatering aid is increased by the supply amount width (a), and this operation is repeated until the torque of the screw shaft (7) rises within the range of the reference torque (T0). When the dewatering aid reaches its maximum supply (Amax), the compressed air supply is increased by the supply width (b), and this operation is repeated until the torque of the screw shaft (7) rises within the range of the reference torque (T0). When the compressed air supply reaches its maximum amount (Bmax), the supply amount of coagulant is increased by the supply amount width (c), and this operation is repeated until the torque of the screw shaft (7) rises within the range of the reference torque (T0), If the measured torque (T) is higher than the preset reference torque (T0), the amount of flocculant supplied is reduced by the supply amount range (c), and this operation is repeated until the torque of the screw shaft (7) falls within the range of the reference torque (T0). When the flocculant supply reaches the minimum amount (Cmin), the compressed air supply is reduced by the supply amount range (b), and this operation is repeated until the torque of the screw shaft (7) falls within the range of the reference torque (T0). When the compressed air supply reaches the minimum amount (Bmin), the supply amount of the dewatering aid is reduced by the supply amount width (a), and this operation is repeated until the torque of the screw shaft (7) falls within the range of the reference torque (T0). A method for controlling the constant torque of a screw shaft in a screw press, characterized by the above.