JP7617360B2 - Air blowing method for filter press - Google Patents

Description

The present invention relates to air blowing in a filter press, and in particular to a method of air blowing in a filter press that increases the retained pressure in the diaphragm chamber during air blowing.

In a filter press that compresses the dehydrated cake by expanding a diaphragm, the air blow method, in which compressed air is blown into the cake in the filtration chamber, is used as a means of removing moisture between cake particles that is difficult to push out with mechanical compression pressure.

Patent document 1 discloses a technology that detects the flow rate of the filtrate discharged by an air blow process that introduces compressed air into the filter chamber, and sequentially increases the flow rate or pressure of the compressed air according to that flow rate.

Japanese Unexamined Patent Publication No. 15715/1983

Conventional air blowing methods have the problem that as moisture in the cake is expelled, voids (air passages) are generated inside the cake, and the air sent into the filtration chamber preferentially passes through voids with low resistance (short pass). This increases the amount of air required to reduce the moisture content of the cake. Furthermore, increasing the amount of air supplied causes cracks to form in the dehydrated cake, resulting in uneven dehydration of the dehydrated cake and increased work in subsequent processes, making efficient air blowing difficult.

The technology in Patent Document 1 is capable of slightly reducing the moisture content of the cake by gradually increasing the flow rate or pressure of the compressed air used for air blowing, but it also promotes the effect of air blowing to widen voids inside the cake. Because the voids created in the early stages of air blowing are further expanded as the flow rate or pressure increases, the tendency of the compressed air to short-pass accelerates, making it impossible to reduce the moisture content of the cake uniformly. In addition, if an attempt is made to reduce the moisture content of the cake from this state, there is the problem that an enormous amount of compressed air will be consumed.

The present invention provides an air blowing method for a filter press that prevents unnecessary increases in air consumption due to cracks in the dehydrated cake and gaps between cake particles that occur during air blowing, and provides efficient air blowing.

In an air blowing method for a filter press, a raw liquid is supplied to a filtration chamber formed by a plurality of filter plates, and the liquid is squeezed and dehydrated by a diaphragm attached to the filtration chamber, while air is introduced into the filtration chamber to perform air blowing. A reference value for increasing the pressure in the diaphragm chamber is set in advance from at least one of the flow rate of air supplied to the filtration chamber, the flow rate of air discharged from the filtration chamber, and the pressure of the air supplied to the filtration chamber, and a pressure increase value is set for increasing the pressure in the diaphragm chamber in stages by a predetermined pressure. During the air blowing process, the measured value is compared with the reference value, and if the measured value is within the range of the reference values, the air blowing process is continued under the same conditions, and if the measured value is outside the range of the reference values, the retained pressure in the diaphragm chamber is increased by the pressure increase value and the air blowing process is continued. This eliminates voids in the dehydrated cake that occur during air blowing, and enables efficient air blowing.

When the holding pressure in the diaphragm chamber is increased by the boost value, the amount of air introduced into the filtration chamber is increased by a specified amount, thereby reducing the moisture content without applying sudden force to the dehydrated cake.

The air blowing method for the filter press according to the present invention can prevent cracks and voids from occurring in the dehydrated cake, and the air does not short-pass. Since air can be uniformly sent into the dehydrated cake, air can be supplied with high efficiency, and the moisture content of the dehydrated cake can be further reduced.

FIG. 1 is a conceptual diagram of a filter press according to the present invention. FIG. FIG. 13 is a partial conceptual diagram of a filtration chamber formed by closing parallel filter plates.

FIG. 1 is a conceptual diagram of a filter press according to the present invention.
In the filter press 1, a number of filter plates 5 are movably supported on guide rails 4 that are bridged between front and rear frames 2 and 3. A clamping cylinder 6 provided on one of the frames 3 moves the filter plates 5 in the axial direction.

FIG. 2 is a partial vertical sectional perspective view of the filter plates arranged in parallel.
A concave filter bed 7 is formed on each filter plate 5, and a filter cloth 8 is suspended from this filter bed 7 to form a filter chamber 9 between adjacent filter plates 5, 5. A diaphragm 10 is stretched over one of the filter beds 7, forming a diaphragm chamber 11 inside the filter chamber 9.

FIG. 3 is a schematic diagram of a part of a filtration chamber formed by closing parallel filter plates.
A raw liquid supply port 12 is provided at the top of the filter plate 5, and raw liquid is pressure-fed into the filtration chamber 9 from a raw liquid supply pipe (not shown) to perform solid-liquid separation in the filter cloth 8. The separated filtrate is extracted from filtrate discharge holes 13 provided at the lower ends of the filter beds 7, 7 of the filter plates 5, 5, and discharged into filtrate pipes 14a, 14b. The filtrate discharged into the filtrate pipes 14a, 14b is collected in a discharge pipe 15 and discharged outside the apparatus.

A pressurized fluid supply pipe 16 that communicates with the diaphragm chamber 11 is connected to the filter plate 5 on which the diaphragm 10 is stretched. The pressurized fluid supply pipe 16 is branched and connected to the pressurized fluid supply holes 19 of each filter plate 5 so as to supply pressurized fluid to all diaphragm chambers 11, and the pressurized fluid drawn up from the water supply tank 17 by the water supply pump 18 is supplied from the pressurized fluid supply pipe 16 to each diaphragm chamber 11 via the pressurized fluid supply holes 19. The diaphragm chamber 11 to which the pressurized fluid is supplied expands toward the filtration chamber 9, and the dehydrated cake formed in the filtration chamber 9 is compressed and dehydrated.

A pressure gauge 20 is provided in the pressure fluid supply pipe 16, and the pressure held in the diaphragm chamber 11 when pressure fluid is supplied to the diaphragm chamber 11 can be measured in real time. The measured value is transmitted from the pressure gauge 20 to the control device 21.

The expanded diaphragm chamber 11 increases its holding pressure, and by closing valve V1 arranged in the pressure fluid supply pipe 16, the holding pressure in the diaphragm chamber 11 can be maintained constant.

The pressurized fluid used in this embodiment may be a liquid (e.g., water) or a gas, and is not particularly limited. If a gas is used, a known air tank or the like is provided instead of the water tank 17.

The diaphragm 10 may be stretched on both sides of the filter bed 7 that constitutes the filtration chamber 9, or on only one side. When the diaphragm 10 is stretched on both sides of the filter bed 7, the dehydrated cake is squeezed from both sides, further reducing the moisture content of the dehydrated cake. When the diaphragm 10 is stretched on only one side of the filter bed 7, the filter plates 5 with the diaphragm 10 stretched on both sides and the filter plates 5 without the diaphragm 10 on either side may be arranged in parallel, alternately, or the filter plates 5 with the diaphragm 10 stretched on only one side may be arranged in parallel.

An air supply pipe 22 is connected to one of the filtrate pipes 14a that communicates with the filtration chamber 9, and air blowing is performed by flowing air pressurized by a supply source 23 from the air supply pipe 22 through the filtrate pipe 14a into the filtration chamber 9. The air that flows into the filtration chamber 9 passes through the dehydrated cake and is discharged from the other filtrate pipe 14b, carrying with it the moisture in the dehydrated cake.

When air is supplied to the filtration chamber 9, the valve V2 disposed in the air supply pipe 22 is opened and the valve V3 disposed in each filtrate pipe 14a is closed, thereby preventing the air from flowing out of the discharge pipe 15 without passing through the filtration chamber 9. During the pressing and squeezing process, the valve V2 is closed and each valve V3 is open in order to transport the filtrate from both the filtrate pipes 14a and 14b to the discharge pipe 15.

A flow meter 24 is provided in the air supply pipe 22, and measures in real time the amount of air supplied from the supply source 23 during air blowing. The measured value is sent from the flow meter 24 to the control device 21. The supply source 23 that generates high-pressure air uses known technology such as a compressor.

As air blowing progresses, voids form in the dehydrated cake in the filtration chamber 9, reducing its volume. By increasing the amount of pressurized fluid supplied to the diaphragm chamber 11 during air blowing to further expand the diaphragm 10, the dehydrated cake formed in the filtration chamber 9 can be pressed against the other filter bed 7. At this time, the cake is compressed and the voids disappear, so by blowing air over the cake that has blocked the voids, it is possible to prevent short-passing of air, suppress an increase in air consumption, and efficiently remove moisture from the cake.

Therefore, in the air blowing method of this embodiment, a reference value for the air flow rate supplied during air blowing and a pressure boost value for gradually boosting the diaphragm chamber 11 by a predetermined pressure are set in advance in the control device 21. During the air blowing process, the air flow rate introduced from the supply source 23 is measured by the flow meter 24 and sent to the control device 21. The control device 21 compares the measured value with the reference value, and if the measured value is outside the range of the reference value, the control device 21 sends an instruction to the water supply pump 18. Based on the pressure held in the diaphragm chamber 11 measured by the pressure meter 20, the diaphragm chamber 11 is boosted by the boost value. The time intervals for measuring the air flow rate and the pressure held in the diaphragm chamber 11 are set appropriately.

The air blowing method of the present invention will be described in detail below with reference to Figs.
A reference value for the air flow rate supplied from the supply source 23 to the air supply pipe 22 during air blowing and a pressure increase value for increasing the pressure in the diaphragm chamber 11 by a predetermined amount are set in advance in the control device 21. The filter press 1 closes the filter plates 5, 5 in advance to form the filtration chamber 9.

<Press-fitting process>
First, each valve V3 is opened and valve V2 is closed. The open/close state of valve V1 is not particularly limited. Raw liquid is supplied to each filtration chamber 9 from raw liquid supply port 12, and dehydrated cake is formed. At this time, filtrate discharged from the dehydrated cake by the injection pressure passes through filter cloth 8 and is discharged from filtrate pipes 14a, 14b via discharge hole 13. The filtrate passing through each filtrate pipe 14a, 14b is collected in discharge pipe 15 and discharged outside the machine.

<Compression process>
Valve V1 is opened, and pressurized fluid drawn up from a water supply tank 17 by a water supply pump 18 is supplied from the pressurized fluid supply pipe 16 through the pressurized fluid supply hole 19 to the diaphragm chamber 11. The diaphragm chamber 11 to which the pressurized fluid is supplied expands toward the filtration chamber 9, and the dehydrated cake formed in the filtration chamber 9 is squeezed and dehydrated. The filtrate passes through the filter cloth 8 and is discharged from the filtrate pipes 14a and 14b to the discharge pipe 15.

After the compression time has elapsed, valve V1 is closed to maintain the holding pressure in diaphragm chamber 11 constant. The holding pressure in diaphragm chamber 11 may also be maintained by continuously starting water supply pump 18 to continuously supply pressurized fluid to diaphragm chamber 11 at a constant pressure.

<Air blow process>
The air blowing process is started with the diaphragm 10 inflated in the previous squeezing process. By opening valve V2 and closing valve V3, the pipeline is formed in one direction, so that the air supply pipe 22 communicates with the filtration chamber 9 via one filtrate pipe 14a, and the same filtration chamber 9 communicates with the discharge pipe 15 via the other filtrate pipe 14b.

High-pressure air is supplied from the supply source 23 to the air supply pipe 22. The air is then supplied to each filtration chamber 9 through each filtrate pipe 14a and the discharge hole 13. The air penetrates the filter cloth 8 and collides with the dehydrated cake, eliminating the moisture in the dehydrated cake. The eliminated moisture penetrates the other filter cloth 8 together with the air, and is discharged from the other discharge hole 13 that communicates with the filtrate pipe 14b.

At this time, the removed moisture creates voids in the dehydrated cake inside the filtration chamber 9, reducing the volume of the dehydrated cake. If air blowing is continued in this state, the air will short-pass the voids in the dehydrated cake, resulting in a huge amount of air consumption and making it impossible to reduce the moisture content.
Therefore, in this embodiment, when the consumption of air supplied at a constant rate exceeds a specified value, it is determined that a void has occurred in the dehydrated cake, and pressurized fluid is supplied to the diaphragm chamber 11 to expand the diaphragm 10, thereby pressing against the dehydrated cake and eliminating the void.

The air flow rate supplied from the supply source 23 to the air supply pipe 22 is measured during air blowing. As air blowing progresses, the air flow rate increases as the air passes through the gaps formed in the dehydrated cake. The control device 21 compares the measured value with a reference value, and when the measured value increases beyond the range of the reference values, pressurized fluid is supplied to the diaphragm chamber 11 to expand the diaphragm 10.

At this time, the diaphragm chamber 11 is pressurized by a predetermined pressure boost value. The pressure held in the diaphragm chamber 11 is measured by a pressure gauge 20, and based on the measured value, the control device 21 controls the water supply pump 18 to set the diaphragm chamber 11 to the desired pressure, thereby expanding the diaphragm 10.

By expanding the diaphragm 10, the gaps in the filtration chamber 9 are filled by the diaphragm 10, and voids in the dehydrated cake are also eliminated. Air is blown in this state, improving the air blowing efficiency and further reducing the moisture content. If the measured air flow rate does not exceed the standard value, air blowing continues.

By repeating the above control, the moisture content of the dehydrated cake can be reduced to any desired level. By supplying pressurized fluid sequentially to the diaphragm chamber 11 during air blowing, the diaphragm 10 can be expanded in stages, and sudden pressure is not applied to the dehydrated cake. This prevents cracks from occurring in the dehydrated cake and allows the cake to be compressed uniformly. By sequentially squeezing the dehydrated cake, short-passing of the air can be prevented, and air consumption can be reduced.

In this embodiment, the reference value and boost value are fixed values that are initially set, but variable values that change depending on time or the held pressure may also be used.

The amount of air supplied may be increased each time the holding pressure in the diaphragm chamber 11 is increased. Since the dehydrated cake, which has become stronger due to the expansion of the diaphragm 10, has a high resistance when air is blown through it, if the amount of air supplied to the filtration chamber 9 is increased by a specified amount when the holding pressure in the diaphragm chamber 11 is increased by the increased pressure value, more water can be removed from the dehydrated cake and no voids will be generated in the dehydrated cake. In addition, because the amount of air supplied is not increased abruptly, no cracks will occur in the dehydrated cake.

In this embodiment, whether or not voids have occurred in the dehydrated cake is determined by measuring the amount of air supplied to the filtration chamber 9, but a reference value for increasing the pressure in the diaphragm chamber 11 may be set based on the flow rate of air discharged from the filtration chamber 9, the pressure of the air supplied to the filtration chamber 9, the flow rate of filtrate discharged from the filtration chamber 9, the elapsed time from the start of air blowing, etc., or multiple reference values may be combined. In this case, a known measuring device, etc. is used.

When the dehydrated cake in the filtration chamber 9 reaches a predetermined moisture content, the air blowing process is terminated. Alternatively, only the control of the holding pressure in the diaphragm chamber 11 is terminated, and the air blowing is continued until the desired moisture content is reached. Note that in addition to the moisture content of the dehydrated cake, each control may be terminated based on the flow rate of the filtrate discharged from the filtration chamber 9, the elapsed time from the start of the air blowing process, etc.

The air blowing method for the filter press according to the present invention reduces the moisture content of the dehydrated cake while reducing air consumption by expanding the diaphragm while supplying air to the filtration chamber. This can be done without additional equipment if the filter plate is equipped with a diaphragm, and highly efficient air blowing can be performed by setting each value according to the sludge properties, making it an extremely useful technology for various production processes such as drinking water and industrial sludge treatment, chemical industry, and paper and pulp industry.

5 Filter plate 9 Filtration chamber 10 Diaphragm 11 Diaphragm chamber

Claims (2)

In a method for blowing air in a filter press, a raw liquid is supplied to a filtering chamber (9) formed of a plurality of filter plates (5), and the raw liquid is compressed and dehydrated by a diaphragm (10) attached to the filtering chamber (9), and air is introduced into the filtering chamber (9) to blow air therein,
A reference value for increasing the pressure in the diaphragm chamber (11) is set in advance from at least one of the flow rate of air supplied to the filtration chamber (9), the flow rate of air discharged from the filtration chamber (9), and the pressure of the air supplied to the filtration chamber (9), and a pressure increase value for increasing the pressure in the diaphragm chamber (11) in stages by a predetermined pressure is set ;
During the air blow process, the measured value is compared with the reference value.
If the measured value is within the standard range, the air blow process is continued under the same conditions.
A method for blowing air into a filter press, characterized in that, if the measured value is outside the range of the reference value, the retained pressure in the diaphragm chamber (11) is increased by the boost value and the air blowing process is continued. The air blowing method for a filter press according to claim 1 , characterized in that when the retained pressure in the diaphragm chamber (11) is increased by an increased pressure value, the amount of air supplied to the filtration chamber (9) is increased by a specified amount.

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