Screw press type dewatering device

Abstract

To provide a screw press type dehydrator capable of obtaining a low-water-content dehydrated cake by reducing unevenness of water content.SOLUTION: In a screw press type dehydrator comprising a screw shaft which rotates by driving means, a screw blade spirally attached to an outer periphery of the screw shaft, and an external cylinder having a filtration hole surrounding the screw blade, a water-containing sludge supplied from an inlet part provided at one end of the external cylinder is compressed and a filtrate is discharged from the filtration hole while a dehydrated cake is obtained from an outlet part provided at the other end of the external cylinder. The screw press type dehydrator is characterized by that a volume of a space part surrounded with the screw shaft, the screw blade, and the external cylinder is decreased from the inlet part to the outlet part, and the screw blade has a through hole.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a screw press type dehydrator for dehydrating sludge generated from aerobic and anaerobic microorganism treatment devices and sludge generated from various other drainage systems to obtain a dehydrated cake. [Background technology]

[0002] A screw press type dewatering device consists of a screw shaft that is rotated by a drive means, screw blades attached in a spiral shape to the outer periphery of the screw shaft, and an outer cylinder with filter holes surrounding the screw blades. An inlet and an outlet are provided at both ends of the outer cylinder, and the space surrounded by the screw shaft, screw blades, and outer cylinder decreases from the inlet to the outlet. While the screw shaft is rotating, wet sludge is squeezed and the filtrate is discharged from the filter holes, and a dewatered cake is obtained from the outlet, and the device is used for dewatering various types of sludge.

[0003] Screw press type dewatering equipment is designed to trap wet sludge between the screw blades and squeeze out the water, so the sludge between the screw blades cannot be made as thin as sludge processed by belt press, and due to the characteristics of the structure, the thickness of the sludge near the final stage of the dewatering treatment is usually around 10 cm.

[0004] Therefore, a strong pressing force is applied to the sludge that is in contact with or near the screw blade applying the pressing force, but the pressing force applied to the sludge decreases the further away from the screw blade the sludge is.

[0005] As a result, differences occur in the moisture content of the sludge sandwiched between the screw blades, with the sludge close to the screw blade applying the pressure having a low moisture content, while the sludge close to the screw blade receiving the pressure has a high moisture content. In other words, the pressure of the screw blade moving forward while rotating does not reach the entire sludge sandwiched between the two screw blades evenly.

[0006] As a result, sludge with a relatively high moisture content is mixed with sludge with a low moisture content and discharged from the outlet, which can cause the moisture content of the entire dehydrated cake to increase.

[0007] Patent documents 1 and 2 describe the provision of notches in the screw blades, which mix the sludge during the dewatering process and exert a pressing force on the mixed sludge, thereby increasing the dewatering effect.

[0008] However, the notches described in both documents extend from the tip of the screw blade to the screw shaft, and the area of ​​the notches is quite large, so although the notches may be able to mix the sludge, a large amount of sludge in the dewatering process flows back, so no pressing force is generated in the screw blades having the notches, making it difficult to dewater the sludge in this area. In other words, it is difficult for the screw press type dewatering devices described in both publications to effectively press the sludge and achieve a high dewatering effect. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 61-9118 [Patent Document 2] JP 2004-148342 A Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a screw press type dehydrator which reduces a problem associated with the conventional screw press type dehydrator, namely, the unevenness in moisture content that occurs in sludge during the dehydration process, thereby making it possible to obtain dehydrated cake with a low moisture content that could not be obtained with the conventional screw press type dehydrator. [Means for solving the problem]

[0011] In order to solve the above problems, the screw press type dewatering device according to the present invention is The screw shaft is rotated by a driving means, a screw blade is spirally attached to the outer periphery of the screw shaft, and an outer cylinder having a filter hole surrounding the screw blade. A screw press type dehydrator in which wet sludge is introduced through an inlet provided at one end of the outer cylinder, the filtrate is discharged through the filter holes, and a dehydrated cake is obtained through an outlet provided at the other end of the outer cylinder, a volume of a space surrounded by the screw shaft, the screw blades, and the outer cylinder decreases from the inlet portion toward the outlet portion, The screw blade is characterized in that it has a through hole.

[0012] According to the screw press type dehydration device of the present invention, the sludge during the dehydration process can be returned to the back side of the screw blades through the through holes, and by turning over the sludge during the dehydration process to reduce unevenness in the moisture content, it is possible to obtain a dehydrated cake with a low moisture content.

[0013] In the screw press type dehydrator of the present invention, the through hole is preferably provided in the vicinity of the outlet, which corresponds to a position 1 / 10 to 1 / 5 of the total length of the outer cylinder from the outlet. By providing the through hole in the vicinity of the outlet, it is possible to effectively reduce unevenness in the moisture content in the vicinity of the outlet.

[0014] In the screw press type dehydrator of the present invention, the size of the through hole is preferably 3% or more and less than 15% of the projected area of ​​the screw blade for one revolution around the screw shaft. By providing the screw blade with a through hole of such a size, the amount of sludge that flows back to the back side of the screw blade through the through hole can be controlled within an appropriate range.

[0015] In the screw press type dehydrator of the present invention, it is preferable that the through hole is provided in contact with the screw shaft. The through hole provided in this manner can enhance the backflow effect of sludge. The through hole may be provided so that its center point is located inside the center of the screw blade. By positioning the center of gravity of the through hole inside half the width from the tip of the screw blade to the screw shaft, the backflow of sludge can be sufficiently achieved. Effect of the Invention

[0016] The screw press type dehydrator of the present invention has appropriate through holes in the screw blades, so that the sludge in the dehydration process surrounded by the screw blades can be reversed through the through holes, thereby turning over the sludge in the dehydration process one after another during the dehydration process.

[0017] As a result, sludge during the dewatering process, where the pushing force of the screw blades is not strong in conventional devices, can be moved by the above-mentioned reversal to a position where the pushing force of the screw blades is strong, thereby further squeezing out the water contained in the sludge.

[0018] The reversal of the sludge during the dewatering process that occurs via these through holes makes it possible to minimize unevenness in the moisture content of the sludge during the dewatering process surrounded by the screw blades, and enables the moisture content of the resulting dehydrated cake to be lower than that of conventional devices.

[0019] Furthermore, if the moisture content of the resulting dewatered sludge is the same, the apparatus of the present invention can treat a larger amount of sludge than the conventional apparatus.

[0020] Thus, the benefits that the device of the present invention brings to industry are extremely great. [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic front view showing a screw press type dewatering device according to one embodiment of the present invention. [Diagram 2]2 is a schematic cross-sectional view taken along line AA in FIG. 1 toward the inlet portion. [Diagram 3] FIG. 2 is a schematic explanatory diagram showing the moisture content of sludge at each point surrounded by a screw blade. [Figure 4] FIG. 13 is a schematic explanatory diagram showing a state in which sludge flows back through a through hole. [Diagram 5] FIG. 4 is a schematic cross-sectional view showing a through hole according to another embodiment of the present invention. [Figure 6] FIG. 2 is a schematic cross-sectional view showing the dimensions of the screw shaft, screw blades, and through holes in the examples. [Figure 7] 1 is a graph showing the relationship between sludge treatment amount and water content in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention will be described in detail below with reference to the drawings. 1 is an explanatory diagram of a screw press type dehydrator 1 according to one embodiment of the present invention, in which a spiral screw blade 3 is attached to the outer periphery of a screw shaft 2 which is rotatable by a driving means 11, and the screw shaft 2 is placed inside an outer cylinder 5 which has filter holes 4 made of punched metal or the like. One side of the outer cylinder 5 has a hopper-type inlet 6 for introducing wet sludge, and the other side has an outlet 7 for discharging dehydrated cake.

[0023] The screw shaft 2 is configured so that its outer diameter gradually increases from the inlet portion 6 toward the outlet portion 7, and the space surrounded by the screw shaft 2, the screw blades 3, and the outer cylinder 5 gradually decreases.

[0024] Furthermore, the space enclosed by the screw shaft, the screw blades 3, and the outer cylinder 5 can also be gradually reduced by gradually narrowing the pitch of the spirally attached screw blades from the inlet 6 toward the outlet 7 without changing the outer diameter of the screw shaft.

[0025] In FIG. 1, reference numeral 8 denotes a pressing device that applies back pressure to the rotating screw shaft 2, and 9 denotes a receiving tank for the filtrate.

[0026] The greatest feature of the screw press type dehydrator 1 is that a through hole 10 is provided in the screw blade 3 near the outlet portion 7 .

[0027] Figure 2 is a schematic cross-sectional view taken from line AA in Figure 1 toward the inlet 6. The hatched portion on the left side of Figure 2 indicates the cut surface. In Figure 2, a through hole 10 is provided in the screw blade 3 at a portion that contacts the screw shaft 2. The size of the through hole 10 should be 3% or more and less than 15% of the projected area S of the screw blade 3 for one revolution around the screw shaft 2 (the area of ​​the shaded portion on the right side of Figure 2).

[0028] Since the outer diameter of the screw shaft 2 becomes larger from the inlet 6 toward the outlet 7, it is necessary to uniquely determine the projection plane in order to obtain the projected area S. Specifically, the projected area S of a doughnut shape is obtained by projecting the screw blade 3 from the inlet 6 side onto a plane (projection plane) that passes through the end of the through hole 10 on the outlet 7 side and is perpendicular to the axis of the screw shaft 2. The outer diameter of the doughnut shape is equal to the outermost diameter of one revolution of the screw blade 3 seen from the projection plane toward the inlet 6 side, and the inner diameter of the doughnut shape is equal to the outer diameter of the screw shaft 2 on the projection plane.

[0029] Incidentally, the projected area S can be calculated in a similar manner even when a different configuration is adopted in which the pitch of the spirally attached screw blades is gradually narrowed from the inlet 6 toward the outlet 7 without changing the outer diameter of the screw shaft. In other words, the projected area S is the area of ​​a donut shape having an outer diameter equal to the outermost diameter of one revolution of the screw blades 3 seen on the inlet 6 side from the projection plane and an inner diameter equal to the outer diameter of the screw shaft.

[0030] Next, the operation of the screw press type dehydrator of the present invention will be described. Back pressure is applied to the screw shaft 2 by the pressing device 8, and the screw shaft 2 is slowly rotated by the driving device 1, while wet sludge with a moisture content of about 99% that has been flocculated with a flocculant such as a polymer flocculant in a conventional flocculation tank not shown in the figure is continuously fed into the inlet 6.

[0031] The introduced wet sludge is moved toward the outlet 7 by the rotating screw blades 3 while sliding slightly between the screw blades 3, the screw shaft 2, and the outer cylinder 5. Just below the inlet 6 or in its vicinity, the water in the wet sludge is discharged from the filter holes 4 mainly by the filtration action caused by gravity.

[0032] Thereafter, the volume of the space surrounded by the screw shaft 2, the screw blades 3, and the outer cylinder 5 gradually decreases, so that the wet sludge present in the space is gradually squeezed, and the filtrate squeezed out by the squeezing is discharged from the filter holes 4. The filtrate is received in the receiving tank 9 and discharged outside the dehydrator.

[0033] The inventors measured the moisture content of sludge in the dewatering process using an experimental device with an outer cylinder diameter of 0.4 m and length of 1.6 m. As a result, the following results were obtained when the moisture content of sludge in the dewatering process (hereinafter simply referred to as sludge) surrounded by the screw blades at a position about 0.2 m from the outlet was measured.

[0034] That is, as can be seen in Figure 3, which shows the moisture content of the sludge at each point surrounded by the screw blades, the moisture content of the sludge in contact with the screw blade 3 that is applying the pressing force is 84%, 86%, and 87%, respectively, from the screw shaft 2 side, but the moisture content increases the further forward, and the moisture content of the sludge in the vicinity of the screw shaft 3 that is receiving the pressing force is 89%, 88%, and 91%, respectively, from the screw shaft 2 side. The arrows in the figure show the direction in which the sludge moves.

[0035] In the screw press type dewatering device 1, a through hole 10 is provided in the screw blade 3 near the outlet 7, and this through hole 10 causes a backflow of sludge as shown in Fig. 4. That is, sludge group A with a high water content has high fluidity and flows back quickly, reaching the vicinity of the screw blade 3 that is pressing and forming an AA layer, followed by sludge group B with a medium water content that flows back and reaches next to the AA layer to form a BB layer, and finally sludge group C with a low water content flows back and reaches next to the BB layer to form a CC layer.

[0036] In short, by providing the through holes 10, the sludge flows back through the through holes 10 one after another, and the water content distribution is reversed.

[0037] Therefore, the sludge group A, which has a high moisture content, flows back and changes its position to the vicinity of the screw blade 3 which is exerting a pressing force, forming the sludge group AA, which is dehydrated by the pressing force of the screw blade 3 and has a reduced moisture content.

[0038] Since the above-mentioned phenomena occur one after another through the through holes 10, the moisture content of the dehydrated cake obtained from the outlet portion 7 can be made smaller than that of the conventional device.

[0039] Next, the through hole 10 in the present invention will be described in detail. As mentioned above, the size of the through hole 10 should be 3% or more and less than 15% of the projected area S of the screw blade 3 for one revolution around the screw shaft 2, and preferably 4% or more and less than 10%.

[0040] If the through holes 10 are sized to be 15% or more of the projected area S, the amount of sludge flowing back through the through holes 10 will be too large, the pushing force of the screw blades 3 will decrease, and the sludge will not be pushed effectively, which may reduce the dewatering effect. If the size is less than 3%, the amount of sludge flowing back will be too small, which may prevent the effects of the present invention from being fully achieved.

[0041] Furthermore, it is preferable that the through-hole 10 is provided in contact with the screw shaft 2 as shown in Fig. 2. By providing the through-hole 10 in contact with the screw shaft 2 in this manner, the backflow of sludge can be achieved most effectively.

[0042] As shown in Fig. 5, if the center point of the through hole 10 is inside the center of the screw blade 3, the backflow of sludge can be effectively achieved even if it is not in contact with the screw shaft 2. However, if the through hole 10 is provided so as to be in contact with the outer periphery of the screw blade 3, or if a part of the through hole 10 protrudes from the outer periphery of the screw blade 3, the backflow effect of the sludge may be reduced.

[0043] The through-hole 10 is preferably provided near the outlet portion 7 at a position corresponding to 1 / 10 to 1 / 5 of the total length of the outer cylinder 5. The through-hole 10 is preferably provided on the second or third turn from the outlet portion 7 toward the inlet portion 6.

[0044] Although it is sufficient to provide one through hole in the screw blade, a total of two through holes may be provided, one in each of the adjacent screw blades, so long as they are located near the above-mentioned outlet portion 7. EXAMPLES

[0045] An embodiment of the present invention using an experimental device will now be described. 1. Screw press type dehydrator used Outer tube diameter: 400mm Length of outer cylinder: 1600mm Screw shaft diameter: 16mm (The inlet and outlet are the same thickness) Screw blade width: 12mm Through hole size: 6mm x 7mm (Approximately 4% of the projected area of ​​the screw blades in one revolution around the screw shaft) Through hole location: One hole on the screw shaft, 200 mm from the outlet of the screw blade Screw shaft rotation speed: 0.05~0.2rpm

[0046] The rotation speed was changed according to the amount of sludge being treated, slowing down the rotation speed when the amount of sludge being treated was small and speeding up the rotation speed when the amount of sludge being treated was large.

[0047] In addition, the screw blades are attached to the screw shaft in a spiral shape, with the spacing between the spirals gradually narrowing toward the outlet, and the spacing at the outlet being half the spacing at the inlet.

[0048] The dimensions of the screw shaft, screw blades, and through hole are shown in Figure 6. Although not shown in Figure 6, an outer cylinder is installed in close contact with the outer circumferential surface of the screw blade.

[0049] 2. Processing target Sludge type: Sludge discharged from a confectionery manufacturing wastewater treatment plant Concentration: 1.0% (moisture content 99%) MLVSS (residual heat capacity): 81%

[0050] 3. Processing results The treatment results of the experimental device of the present invention are shown together with those of a conventional device (without through holes) in Figure 7. In Figure 7, the vertical axis indicates the moisture content (%) of the dehydrated cake, and the horizontal axis indicates the sludge treatment amount (kg DS (dry solids) / hr).

[0051] As can be seen in Figure 7, when compared per unit of moisture content (79.8%), the conventional equipment had a sludge processing capacity of 10 kg DS / hr, while the equipment of the present invention had an increased sludge processing capacity of 12.5 kg DS / hr. When compared per unit of processing volume, the moisture content of the equipment of the present invention was 0.5 to 0.7% lower than that of the conventional equipment. In particular, when compared at a moisture content of 78.5% for dehydrated cake, which is the normal range of use, the conventional equipment had a sludge processing capacity of 2.5 kg DS / hr, while the equipment of the present invention had a sludge processing capacity of 7.0 kg DS / hr, a significant increase. [Industrial Applicability]

[0052] The screw press type dewatering apparatus of the present invention can be widely used for dewatering sludge generated from various types of equipment. [Explanation of symbols]

[0053] 1 Dehydration device 2 screw shaft 3 Screw blade 4 Filtration Hole 5 Outer cylinder 6 Entrance 7 Exit section 8 Pressing device 9 Receiving tank 10 Through holes 11 Driving means A, AA, B, BB, C, CC sludge groups

Claims

1. The screw shaft is rotated by a driving means, a screw blade is spirally attached to the outer periphery of the screw shaft, and an outer cylinder having a filter hole surrounding the screw blade. A screw press type dehydrator in which wet sludge is introduced through an inlet provided at one end of the outer cylinder, the filtrate is discharged through the filter holes, and a dehydrated cake is obtained through an outlet provided at the other end of the outer cylinder, a volume of a space surrounded by the screw shaft, the screw blades, and the outer cylinder decreases from the inlet portion toward the outlet portion, The screw blade has a through hole, and the through hole is provided at one or two locations near the outlet portion corresponding to a position 1 / 10 to 1 / 5 of the total length of the outer cylinder from the outlet portion.

2. 2. The screw press type dewatering device according to claim 1, wherein the area of ​​the through hole is 3% or more and less than 15% of the projected area of ​​the screw blade for one revolution around the screw shaft.

3. 3. The screw press type dehydrator according to claim 1, wherein the through hole is provided in contact with the screw shaft.

4. 4. A screw press dehydration device according to claim 1, wherein the through hole is provided so that its center point is located inside half the width from the tip of the screw blade to the screw shaft.

Images