Method for operating filter press

Abstract

To provide a method for operating a filter press to accurately calculate the expansivity of a diaphragm upon supplying compressed air during pneumatic compression and to enable switching to hydraulic compression at an optimal timing for filtration efficiency and energy efficiency.SOLUTION: In a method for operating a filter press comprising a pneumatic compression step S2 for supplying compressed air to a diaphragm chamber 12 formed in a filter chamber 9, and a hydraulic compression step S3 for supplying pressurized water to the diaphragm chamber 12 after the pneumatic compression step S2, a correlation formula among a reference volume V0 of the diaphragm chamber 12, a differential pressure ΔP between a compression pressure P2 and a pressure P1 inside the filter chamber 9, and a cumulative flow volume V of the compressed air supplied to the diaphragm chamber 12, is preset, and the air compression step S2, measuring the differential pressure ΔP, can continue until the cumulative flow volume V calculated by the correlation formula reaches the reference volume V0, thereby allowing the air compression step to end at an optimal timing for filtration efficiency and energy efficiency.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an operation method of a filter press having a diaphragm filter plate that requires medium- to long-time squeezing and dewatering treatment in various production processes such as raw water and industrial water sludge treatment, chemical industry, and pulp and paper industry.

Background Art

[0002] Conventionally, in a filter press, in order to perform high-pressure squeezing and dewatering, the raw liquid is pressed into the filtration chamber for filtration and dewatering, and then the squeezing fluid is pressed into the diaphragm filter plate for squeezing and dewatering. In medium- to long-time squeezing and dewatering treatment, in order to maintain the squeezing pressure, the pressure pump is continuously operated during squeezing. A squeezing and dewatering method is disclosed in Patent Document 1, in which compressed air is supplied to the diaphragm for primary squeezing, and then pressure water is supplied for high-pressure secondary squeezing.

[0003] And a technique is disclosed in Patent Document 2, in which compressed air is supplied until the thickness of the dewatering cake formed in the filtration chamber becomes 1 / 4 to 2 / 3 of the width of the filtration chamber, thereby gently reducing the pressure drop of the pressure water and reducing the number of operating times and operating hours of the pressure water pump.

[0004] In addition, a slurry dewatering method is described in Patent Document 3, in which squeezing is terminated when the pressure in the filtration chamber drops below the squeezing pressure, and the switching timing to the next process is used.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the filter press of Patent Document 1, in order to maintain a constant squeezing pressure of the diaphragm as the squeezing time increases, it is necessary to operate the pressure water pump for a long time.

[0007] In the filter press of Patent Document 2, the duration of the air squeezing process is determined by the measured value of the filtrate volume discharged from the filtration chamber. However, after supplying compressed air to the diaphragm, there is a time difference until the dewatered cake is squeezed and dewatered and the filtrate volume is measured by the flow meter. In addition, due to frame leakage from the filtration chamber due to the capillary action of the filter cloth, errors in the raw liquid supply amount between the filtration chambers due to the sequential discharge of the filtrate through the filter cloth from the pressure application point, etc., it is difficult to accurately adjust the end point of the air squeezing process. Further, it is necessary to install a flow meter in the discharge pipe for measuring the filtrate volume. The flow meter is expensive and there is a risk of corrosion and contamination depending on the properties of the filtrate.

[0008] Also, in the technology of Patent Document 3, the squeezing process is terminated according to the differential pressure between the pressure in the filtration chamber and the squeezing pressure, but the air volume in the diaphragm chamber cannot be accurately grasped. Therefore, when switching from air squeezing to water squeezing in a secondary squeezing type filter press based only on the differential pressure, if the switching is slow, the transition to high-pressure water squeezing will be delayed, leading to a decrease in the filtration rate. On the other hand, if the switching is fast, the air supply amount will be insufficient, resulting in a decrease in the efficiency of low power.

[0009] The present invention provides an operation method for a filter press that accurately calculates the expansion rate of the diaphragm when compressed air is supplied during the air squeezing process and switches to the water squeezing process at the optimal timing for filtration efficiency and energy efficiency.

Means for Solving the Problems

[0010] In the operation method of a filter press comprising a pressing step of pressing a stock solution into a filtration chamber formed by a plurality of filter plates and diaphragm filter plates to generate a dewatered cake, a pneumatic squeezing step of supplying compressed air to a diaphragm chamber formed in the filtration chamber, and a hydraulic squeezing step of supplying pressure water to the diaphragm chamber after the pneumatic squeezing step, a correlation formula between the reference volume of the diaphragm chamber, the differential pressure between the squeezing pressure and the pressure in the filtration chamber, and the integrated flow rate of the compressed air supplied to the diaphragm chamber is preset. In the pneumatic squeezing step, the differential pressure is measured, and the pneumatic squeezing step is continued until the integrated flow rate calculated from the correlation formula reaches the reference volume, so that the filtration efficiency and the energy efficiency can be terminated at the optimal timing.

[0011] The reference volume is set from 1 / 3 to 3 / 4 of the volume of the filtration chamber so that the thickness of the dewatered cake generated in the filtration chamber becomes 1 / 4 to 2 / 3 of the width of the filtration chamber, thereby minimizing the operating load of the pressure water pump in the subsequent hydraulic squeezing step and improving the filtration efficiency throughout the squeezing process.

Effect of the Invention

[0012] The operation method of the filter press according to the present invention can ideally and gently reduce the pressure of the pressure water by compressed air by supplying a predetermined amount of compressed air to the diaphragm, so there is no need to frequently operate the pressure water pump, and the operation time can also be shortened. In addition, the filtration efficiency can be increased by minimizing the amount of low-pressure compressed air supplied to the diaphragm chamber.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiment for Carrying Out the Invention

[0014] Figure 1 is a flow diagram of a filter press according to the present invention. In the filter press, a pair of guide rails 3 are bridged between a front frame 1 and a rear frame 2, and a number of filter plates 4 and diaphragm filter plates 5 are alternately supported on the guide rails 3. A tightening cylinder 7 disposed on the rear frame 2 is connected to a movable head 8, and the filter plates 4 and the diaphragm filter plates 5 arranged in parallel are opened and closed by the tightening cylinder 7.

[0015] Figure 2 is a partial longitudinal sectional perspective view of the parallel filter plates and diaphragm filter plates. A pair of filter cloths 10 are suspended in a filtration chamber 9 formed by the filter plates 4 and the diaphragm filter plates 5, and the stock solution is pressed into the space between the filter cloths 10 from a supply port 11 passing through the filter plates 4 and the diaphragm filter plates 5. A diaphragm 6 that can expand and contract is stretched on the surface of the diaphragm filter plate 5. By expanding the diaphragm 5a, the stock solution supplied to the filtration chamber 9 is squeezed, and solid-liquid separation is performed by the filter cloths 10.

[0016] Figure 3 is a conceptual diagram of a filtration chamber formed by parallel filter plates and diaphragm filter plates. The diaphragm filter plate 5 has a diaphragm 6 stretched on its surface and forms a diaphragm chamber 12 inside. By supplying a squeezing fluid to the diaphragm chamber 12, the diaphragm 6 is expanded. All the diaphragm chambers 12 communicate with each other via a squeezing fluid supply pipe 13. As the squeezing fluid, after performing an air squeezing step S2 of supplying compressed air to the diaphragm chamber, the supply of compressed air is terminated and a water squeezing step S3 of supplying pressure water to the diaphragm chamber is performed.

[0017] As shown in Fig. 1, a pressure water supply pipe 14 and a compressed air pipe 15 are branched and connected to the squeezing fluid supply pipe 13. At the tip of the pressure water supply pipe 14, a pressure water pump 17 for pumping the water in the water supply tank 16 and a pressure water valve 18 for switching the pressure water on and off are arranged. At the tip of the compressed air pipe 15, an air compressor 20 for supplying compressed air to the air tank 19 and a compressed air valve 21 for switching the compressed air supplied to the compressed air pipe 15 on and off are arranged.

[0018] In addition, as shown in Fig. 1 and Fig. 2, a stock solution supply pipe 26 provided with a stock solution injection pump 25 is communicated with the filtration chamber 9 between the filter plate 4 and the diaphragm filter plate 5.

[0019] After supplying compressed air to the diaphragm chamber 12 with the air compressor 20, pressure water is supplied to the diaphragm chamber 12 with the pressure water pump 17 to perform squeezing of the dewatered cake. The air compressor 20 supplies compressed air of 0.7 - 0.85 MPa to the diaphragm chamber 12, and the pressure water pump 17 supplies pressure water of 1.3 - 3.2 MPa. The filtrate separated from the dewatered cake as the diaphragm 6 expands is discharged from the discharge pipe 22 communicated with the filter plate 4.

[0020] The diaphragm chamber 12 is supplied with compressed air and expanded until the thickness of the dewatered cake becomes 1 / 4 - 2 / 3 of the thickness of the filtration chamber 9, so that the air amount required as a pressure tank is filled. Further, by supplying compressed air and expanding until the thickness of the dewatered cake becomes 1 / 3 of the thickness of the filtration chamber 9, the squeezing time with low-pressure compressed air can be minimized, the filtration efficiency can be increased, the driving frequency of the pressure water pump 17 can be reduced, and the energy efficiency of the water squeezing process can be increased. The optimal switching timing from the air squeezing process S2 to the water squeezing process S3 may be appropriately set according to the stock solution properties and the like.

[0021] Further, in order to maintain the pressing pressure, a pressure tank for holding compressed air may be separately provided, or a diaphragm may be separately provided instead of the pressure tank for the groups of filter plates 4 and 5 of the filter press. However, in the present invention, since a large amount of compressed air can be held in the diaphragm chamber 12, a large-capacity tank or diaphragm is not required.

[0022] In addition, in FIG. 3, the filter plates 4 and the diaphragm filter plates 5 are alternately arranged in parallel to form the filtration chamber 9. However, by arranging only the diaphragm filter plates 5 in parallel to form the filtration chamber 9, it becomes possible to press with the diaphragm 6 from both sides of the filtration chamber 9.

[0023] The air pressing step S2 ends when the integrated flow rate V of the compressed air supplied to the diaphragm chamber 12 reaches the reference volume V0. The reference volume V0 of the compressed air supplied into the diaphragm chamber 12 is set in advance. The reference volume V0 is set according to the properties of the stock solution, etc. from 1 / 3 to 3 / 4 of the volume of the filtration chamber 9 so that the thickness of the dewatered cake becomes 1 / 4 to 2 / 3 of the thickness of the filtration chamber 9.

[0024] A pressure gauge 30 is installed in the pressing fluid supply pipe 13 to measure the pressing pressure P2 of the pressing fluid during the pressing step. Also, a pressure gauge 31 is installed in the stock solution supply pipe 26 to measure the pressure P1 in the filtration chamber 9.

[0025] A correlation formula is set in advance from a graph (see FIG. 4) of the differential pressure ΔP between the pressures P1 and P2 and the integrated flow rate V of the compressed air during the air pressing step S2 through tests or the like. The integrated flow rate V is measured using known means such as a flow meter for the cumulative flow rate of the compressed air passing through the compressed air pipe 15. Note that the test may be performed on an actual machine or a test machine, or at another site under the same conditions.

[0026] During the squeezing process S2, the pressures P1 and P2 are measured to calculate the differential pressure ΔP. Then, the differential pressure ΔP is substituted into a preset correlation formula to automatically calculate the integrated flow rate V of the compressed air in real time. The time point when the calculated integrated flow rate V reaches the reference volume V0 is set as the end point of the pneumatic squeezing process S2.

[0027] In pneumatic squeezing, compressed air is supplied to the diaphragm chamber 12 to expand the diaphragm 6, thereby discharging the filtrate from the dewatered cake. As the dewatered cake enters the space from which the filtrate has been discharged, the cake thickness decreases. If compressed air continues to be supplied thereafter, for low-pressure compressed air, the differential pressure ΔP between P1 and P2 decreases over time, the discharge amount of the filtrate decreases, and the filtration efficiency deteriorates. However, since the differential pressure ΔP is easily affected by the filterability, the end point of the pneumatic squeezing process S2 cannot be set in detail. If the differential pressure ΔP is larger than the appropriate value, the miscellaneous time becomes longer and the filtration rate decreases. If the differential pressure ΔP is smaller than the appropriate value, the amount of compressed air is insufficient and the low power efficiency decreases.

[0028] Therefore, by calculating the integrated flow rate V of the compressed air supplied to the diaphragm chamber 12 and ending the pneumatic squeezing process S2 when the integrated flow rate V reaches the reference volume V0, the volume of the diaphragm chamber 12 can be accurately grasped. Thus, it is possible to shift to the hydraulic squeezing process S3 at the optimal timing to ensure the supply amount of compressed air for efficiently operating with shortened miscellaneous time and low-power squeezing.

[0029] Also, according to the present invention, since it is not necessary to measure the supply amount of compressed air with the compressed air pipe 15, the cost of installing an expensive flow meter can be reduced.

[0030] Each measuring instrument and on-off valve is connected to a control panel (not shown). The integrated flow rate V is calculated from the measurement information sent to the control panel, and based on the calculated value, the on-off valve, pump, etc. are controlled to operate the compressed fluid pressure in the diaphragm chamber 12. Note that the above set pressures are examples, and appropriate values should be set each time according to the specifications of the dehydrator to be used, the properties of the stock solution to be treated, etc.

Example

[0031] The filter press used in the present invention is configured as described above, and its pressing and filtering method is shown below. Measure the thickness of the filtration chamber 9 and the solid content concentration of the stock solution in advance, and based on these values, set the reference volume V0 of the compressed air. Also, measure the pressing pressure P2, the pressure P1 in the filtration chamber, and the integrated flow rate V of the compressed air during the air pressing step S2, and set a correlation formula from the graph (see Fig. 4) of the differential pressure ΔP between the pressures P1 and P2 and the integrated flow rate V. Drive the clamping cylinder 7 to close the filter plates 4 and the diaphragm filter plates 5 arranged in parallel to form the filtration chamber 9.

[0032] Pressing-in step (S1) The stock solution is pressed into the filtration chamber 9 of the filter press through the stock solution supply pipe 26 from the stock solution injection pump 25 for filtration. At this time, the valves 18 and 21 are closed and no pressing fluid is supplied to the diaphragm chamber 12, and the filtration chamber 9 is filled with the stock solution. The filter cloth 10 stretched in the filtration chamber 9 separates the liquid from the stock solution, a dehydrated cake is generated, and the liquid is discharged outside the filtration chamber 9 through the discharge pipe 22 as filtrate.

[0033] Air pressing step (S2) After stopping the injection of the stock solution, the pressure in the air tank 19 of about 0.85 MPa is adjusted by opening the compressed air valve 21 and an unshown pressure regulating valve to supply 0.7 MPa of compressed air to the diaphragm chamber 12 of the diaphragm filter plate 5. As the compressed air is supplied to the diaphragm chamber 12, the internal pressure of the air tank 19 decreases. When it decreases to 0.7 MPa, the air compressor 20 is driven. The air compressor 20 supplies compressed air to the diaphragm chamber 12, and when the internal pressure of the air tank 19 increases to 0.85 MPa, the air compressor 20 is stopped.

[0034] The squeezing pressure P2 of the compressed air is measured by the pressure gauge 30 provided in the squeezing fluid supply pipe 13, and the pressure P1 in the filtration chamber is measured by the pressure gauge 31 provided in the stock solution supply pipe 26. Using a predetermined correlation formula, the integrated flow rate V of the compressed air supplied to the diaphragm chamber 12 is calculated in real time.

[0035] The measurement of the pressures P1 and P2 and the calculation of the integrated flow rate V are continuously performed. When it is detected that the integrated flow rate V has reached the reference volume V0, the compressed air valve 21 is closed and the air compressor 20 is stopped. At this time, the thickness of the dewatered cake is about 1 / 3 of the thickness of the filtration chamber, and the air squeezing can be terminated before the filtration efficiency due to the air squeezing decreases. In addition, the driving frequency and driving time of the pressure water pump 17 can be reduced in the next-stage hydraulic squeezing process S3 by the large amount of compressed air held in the diaphragm chamber 12.

[0036] If the integrated flow rate V does not reach the reference volume V0 within a predetermined time, the air squeezing process S2 is terminated and the process proceeds to the next process.

[0037] Hydraulic squeezing process (S3) After closing the compressed air valve 21, the pressure water pump 17 is driven. The pressure water valve 18 is opened to press the pressure water into the diaphragm chamber 12. The internal pressure of the diaphragm chamber 12 is increased to 1.5 MPa, the pressure water valve 18 is closed, and the pressure water pump 17 is stopped.

[0038] Due to the pressure water, the diaphragm chamber 12 becomes even higher in pressure, and more filtrate is separated from the dewatered cake in the filtration chamber 9 by the filter cloth 10. The separated filtrate is discharged from the filtration chamber 9 through the discharge pipe 22. Since compressed air is supplied to the diaphragm chamber 12, as the filtrate is discharged from the filtration chamber 9, the internal pressure of the diaphragm chamber 12 gradually decreases.

[0039] When the internal pressure of the diaphragm chamber 12 drops to 1.4 MPa as the pressing progresses, the pressure water pump 17 is driven again, and by opening the pressure water valve 18, the internal pressure of the diaphragm chamber 12 is increased to 1.5 MPa. By repeating this operation multiple times, hydraulic pressing is performed.

[0040] After repeatedly performing the ON / OFF operation of the pressure water pump 17 according to the change in the internal pressure of the diaphragm chamber 12, the pressure water valve 18 is closed and the pressure water pump 17 is stopped, thereby adjusting the internal pressure of the diaphragm chamber 12 within a certain range and shortening the operation time of the pressure water pump 17 during dewatering by pressing.

[0041] Pressure water drainage process (S4) After the completion of the hydraulic pressing with pressure water, by opening the pressure water valve 18, the pressure water in the diaphragm chamber 12 is discharged using the compressed air held in the diaphragm chamber 12. The pressure water is discharged to the water supply tank 16 through the pressure water supply pipe 14. Thereafter, the compressed air valve 21 is opened to make the diaphragm chamber 12 at normal pressure.

[0042] Dewatered cake discharge process (S5) The clamping cylinder 7 is contracted to open the filter plate 4 and the diaphragm filter plate 5, and the dewatered cake formed in the filtration chamber 9 is discharged outside the machine. Subsequently, when continuously operating the filter press, the filter plate 4 and the diaphragm filter plate 5 are closed to form the filtration chamber 9 again, and it returns to the pressing process S1.

Explanation of reference numerals

[0043] 4 Filter plate 5 Diaphragm filter plate 9 Filtration chamber 12 Diaphragm chamber P1 Pressure in the filtration chamber P2 Pressing pressure ΔP Differential pressure S1 Pressing process S2 Pneumatic pressing process S3 Hydraulic pressing process V0 Reference volume V Integrated flow rate

Claims

1. In an operation method of a filter press comprising a pressure injection step (S1) of generating a dewatered cake by pressure-injecting a stock solution into a filtration chamber (9) formed by a plurality of filter plates (4) and a diaphragm filter plate (5), a pneumatic squeezing step (S2) of supplying compressed air to a diaphragm chamber (12) formed in the filtration chamber (9), and a hydraulic squeezing step (S3) of supplying pressurized water to the diaphragm chamber (12) after the pneumatic squeezing step (S2), a reference volume (V0) of the diaphragm chamber (12), a correlation formula between a differential pressure (ΔP) between a squeezing pressure (P2) and a pressure (P1) in the filtration chamber (9) and an integrated flow rate (V) of the compressed air supplied to the diaphragm chamber (12) is preset, in the pneumatic squeezing step (S2), the differential pressure (ΔP) is measured, and the operation continues until the integrated flow rate (V) calculated from the correlation formula reaches the reference volume (V0). An operation method of a filter press, characterized by the above.

2. The reference volume (V0) is set from 1 / 3 to 3 / 4 of the volume of the filtration chamber (9) such that the thickness of the dewatered cake generated in the filtration chamber (9) becomes 1 / 4 to 2 / 3 of the width of the filtration chamber (9). An operation method of a filter press according to Claim 1, characterized by the above.

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