JPS5820291B2 - Bisaiful Iwakehouhou Oyobi Souchi - Google Patents

Description

[Detailed description of the invention] The present invention relates to fine sieving.

Fine sieving is the separation of fine particles from a dilute water suspension in a rotating drum with a fine sized sieving medium (referred to as a screen).

The drum has a sieve washing device and a basin to receive the liquid and solids exiting from inside the drum.

It does this by leaving a substantial proportion of the pores of the media "open" while the bulk of the flow is occurring.

For example, there is free or unrestricted flow through the apertures.

This fine sieving is used, for example, for the final separation of microbial organisms from highly dilute suspensions before the water is discharged into waterways.

In order to properly understand the present invention, a distinction should be made between fine sieving and general filtration.

The present invention will be explained below with reference to examples.

The woven wire filtration media 1 shown in FIG. 1 filters a liquid 2. The woven wire filtration media 1 shown in FIG.

Particles 3 of various sizes are dispersed in the liquid.

Many particles 4 of the same substance are packed in a layer or cake on the filtration media.

The cake particles 4 act as a filter and remove particles 3 from the liquid.

In order to ensure that the layer of particles 4 is the main factor in filtering the suspended particles 3, the filtration operation is such that after the multi-particulate layer is in position on the medium 1, most of the liquid passes through. .

The liquid separated from the solids exits through the clean side of the filter, as shown by arrow 6.

Filter aids are used in filtration operations to increase the volumetric rate at which liquids are processed without allowing small particles to escape.

Liquid 2 is pressurized and passed through the filter at a high volumetric rate.

Fine sieving is shown in Figure 2.

In this sieving, a large area of the sieve is prepared compared to the amount of solids.

This solid is what gets picked up on this area during cleaning.

Most of the liquid passes through a screen before the cake is formed.

The weight of solids (dry basis) taken up on a given area of the sieve per pass (ignoring any losses due to drop-back, discussed below, during washing) is referred to as solids loading.

The loading level representing sieving versus filtration is typically 0.5'rll? /Cd, but for solids with suitable shape density and other properties, about 17'2
? /7.

Dense solids with a small amount of water should be mixed with 2 m'il/C when using a sieve at the top of the sieve hole provided below the solids loading.
Up to r/l.

In the case of classified biological sewage treatment plant effluent 2, fine particles 3 are suspended.

Some of them become lumpy particles 3a.

As for the sieve size, the opening of the cloth 1 ranges, for example, to about 140 microns.

The particular dimensions are chosen to be smaller than the bulk of the mass and the total dimensions of the separate particles dispersed in the liquid.

For fine sieves, the influent contains a large proportion of discrete particles on the order of 10 microns and a large proportion of agglomerates on the order of 50 microns or larger.

The concentration of suspended solids in the influent may be, for example, 20 parts per million or more, and fine sieving reduces this concentration to 10 parts per million or less.

Due to the large amount of fluid in relation to the solid material in the inflow and the small size of the particles, cake formation and trapping of small particles does not occur and some particles 9,9a
escapes through the screen.

Therefore the problem of passing the cake at high capacity speeds does not arise.

Before or immediately after all the openings 8 are closed, the sieve cloth is washed to remove particles 4.

FIG. 3a shows the problems associated with sieving cloth purification.

The fine screen unit is cut out perpendicularly to the rotation axis 11 of the drum 12.

The inlet to be finely screened enters the interior of the drum through the inlet 13.

The liquid is sieved from the drum pool 14 in the drum by cloth 1
, enters the tank pool 15 inside the tank 16, and enters the second tank pool 15.
Leave the particles on the cloth 1 as schematically shown in the figure.

The effluent in the tank pool 15 collects in the tank 16 and overflows the upper edge of the collection device or tank side wall 17.

Generally, the level 25 of the kunk pool 15 is controlled to a predetermined level.

This is done by adjusting the collection device.

It has an automatic level control device. The level at drum surface 23 differs from the level of liquid in tank 16 and depends on solids loading, drum speed, size, shape, number of fabric openings per unit area, and degree of agglomeration of particles in suspension. differ by a different distance d.

The sieve portion can be determined by observing the process in which a predetermined cross section of the cloth 1 carries particles taken from near the bottom of the tank 16 to the apex 28 of the circle around which the drum rotates, and it can be seen that the sieve portion is reversed. It will be.

When particle 4 (see Figure 2) is near the bottom of tank 1, the sieve is above cloth 1, but for the same particle, the cloth is at the top 28.
When it reaches , it hangs below the cloth (as shown in Figure 3a).

Generally, there is sufficient adhesion between the particles 4 taken and the fabric 1 to retain a significant number of these particles on the fabric in the inverted position.

Thus, with the reverse-washing technique, the sieve portion is convenient for cleaning the fabric.

The nozzle 18 shown in Figure 3a is normally used to impinge on the forced stream 19 of water on the outer surface of the fabric at the apex 28.

A portion 20 of this flow through the fabric 1 removes trapped particles and enters an underlying trough 21 having a side wall 22 above the surface 23 of the drum pool 14.

The solids collected in gutter 21 and the washing water are removed from the outlet (not shown).
removed from

The drum pool level is kept below the upper edge of the grate side wall 22.

For conventional fine sieving units, the capacity of the unit is partially compromised by a problem referred to in the text as dropback.

As the sieve portion of the cloth 1 rises away from the surface of the drum pool 14 at 26, some of the particles 4 taken out either remain within the pool 14 or fall back into the pool as shown at 27. .

Although the sieve capacity is in part a function of the concentration of solids in the drum pool, the concentration increases as a result of this dropback reducing the sieve capacity.

A complete explanation of why dropback occurs in microsieving - and its solution - is not widely understood in the art.

And there is still a need for a simple and effective solution.

The screen cloth 1 shown in FIG. 3a has a point 26 in the direction of arrow r.
At this point each successive section of fabric exits or separates from the drum pool 14.

FIG. 3b is an enlarged portion of FIG. 3a near point 26.

FIG. 3b shows the screen 1, having warp threads 30 and weft threads 31, emerging from the drum pool surface 23 at a point 26.

Same pressure P. is present in the screen 1 and the gas space between the screen 1 and the drum pool surface 23.

In the region s'-s'', the velocity vector of the water film leaving with the screen and the velocity vector of the water remaining in the drum pool 14 diverge.

The resulting stream C weakens the stickiness of some captured particles 4a and pulls others 4b away from the screen.

Due to the hydraulic pressure in the area s'-s', there is a tendency for particle 4 to
bk screen 1, this pressure is S'
and decreases to zero at point 26.

Discrepancies occur at these locations.

The emerging part of the screen 1 has many of the openings closed by the taken particles 4, but there are unobstructed and partially blocked openings 8, some of which result from detaching the particles 4b.

The water films 32e and 32i are pulled upward together with the screen as the drum rotates.

A progressively increasing reversal of a given portion of the fabric results in drum pool 1
4, gravity causes the outer membrane 32e to flow up and down through the screen.

This is indicated by arrow g (shown here), passing through the aperture 8 and others.

This flow back into the drum is directed to the internal membrane 3 at various locations 34.
2i is inflated and the other taken particles 4c are removed.

The flow creates drops 35 that fall off the screen and these drops carry the particles 4d back with them into the drum pool 14, where the sieve fraction creates a capacity-limiting thickening effect.

There is another source of external and internal water films, which is shown in Figure 3a.

A portion of the backflow water spray 19 does not pass directly through the filter cloth.

Rather, it flows from the top of the rotation down the exterior and interior of the filter cloth.

This is shown by arrows 21i and 24e. It is believed that flows 24i and 24e opposite the direction of drum rotation can weaken or eliminate the tackiness of the particles taken in much the same manner as membranes 32i and 32e described with respect to FIG. 3a.

When the circumferential speed of the drum is high enough, these countercurrent flows do not develop sufficiently to cause obvious problems, contributing to the concentration of solids in the drum pool.

Whether these counter-flowing shower waters occur or prove harmful depends on the shower configuration.

A limited gas differential pressure is applied across the sieving portion of the fine screen unit across the unsettled portion of the fabric while rotating the drum, effecting the sieving and providing backflow.

The invention thus clearly differs from pressure filtration techniques.

In pressure filtration, pressure is applied to the submerged area of the filter by pressurizing a limited body of liquid against the filter cake.

This results in a higher absolute gas pressure on the inside of the screen than on the outside of the screen, at least for those unsubmerged parts of the screen which are intended to improve the stickiness of the particles removed.

Thus, the pressure difference from the inside to the outside makes the inside the high pressure side,
In other words, it is correct.

Preferably, a controlled pressure differential is applied adjacent the screen from the point of screen emergence 26 to the point where the screen exceeds a collection device such as slit 21.

This divides the space above the drum pool 14, for example, so that at least a portion of the space, which lies between the aforementioned points (and which communicates with the screen), is maintained at a different pressure than the rest of the space. This can also be done by applying a controlled pressure difference across the area.

However, in a fine screen unit of the type shown in Figure 3a, in which there is free communication of air throughout the air space above the drum pool 14, such a controlled pressure differential may be provided throughout the space.

The pressure differential may be applied in any desired manner, but may conveniently be provided by a pump or blower having an outlet within the drum, preferably above the drum pool surface.

If the outside of the drum is surrounded by a suitably sealed housing, the differential pressure can be provided by a suction pump that can reduce the pressure inside the housing.

Pressure cannot be applied indiscriminately.

It is believed that it would be advantageous to prevent or reduce dropback if sufficient pressure was applied to eliminate or reduce the externally flowing water film passing through the screen 1 and into the drum.

Said membranes are, for example, 24e (on the left) in Figure 3a and 32e in Figure 3b.

At the same time, however, the differential provided is limited to restrict the flow of air from the space above the drum pool outwardly through the screen from these areas of the screen, at least from where there is a risk of dropback.

Thus, in the normal case, a pressure difference is maintained by surface tension across an unclosed or partially closed opening in a dish towel than that required to break through a drainage film or other liquid segment). controlled to a small level.

Thus, in accordance with the present invention, the aforementioned dropback applies a pressure differential sufficient to substantially reduce the amount of dislodged particles returned to the drum pool from the screen.

In this regard, the present invention, when applied to conventional commercially available fine screen units, provides water gauge pressures ranging from about 0.1 inches (about 2.54M) to about 6.0
inch (about 152.4M), preferably about 0.1 to about 3
Pressure differentials in the range of inches (about 2-54 to about 76.2 a) are typical.

However, it is also possible to work with a range of water gauge pressures from greater than 6 inches to about 10 inches and above, in which case the sieve fraction is The pressure difference must be sufficient to reduce the amount of particles dropping back from the drum pool (screen) into the drum pool.

The present invention is most beneficial in treating agglomerated solids.

The method applies a differential pressure only during the period of highest load on the fine screen and/or increases the shower pressure for at least a substantial portion of the time, during which the differential pressure is applied and/or offset; Suppressing or preventing the application of differential pressure applied to the area above the collection device.

The advantages of the invention are explained below.

According to the invention, the concentration of solids in the drum pool is reduced;
Therefore, the production of fine screen operations and equipment will increase.

The working theory of the invention can be explained by comparing Figures 3a, 3b and 4.

The latter is similar to FIG. 3b and is believed to show how the pressure differential is applied according to the invention, changing the case described with respect to FIG. 3b.

As shown in FIG. 3b, the screen 1 shown in FIG. 4 has warp threads 30 and weft threads 31 which emerge from the drum pool surface 23 at points 26.

However, in FIG. 4, the pressure P1 in the gas space between the screen 1 and the drum pool surface 23 is P.

It's thicker. In the region s'-s'', the hydraulic pressure was previously Sl
However, the fluid pressure in Sl is now equal to the pressure difference P, -
Increases due to Po.

This pressure differential is applied across the non-submerged portion of the screen.

The drum pool surface 23 either remains above the level of the tank pool 25 or is moved below the level of the tank pool 25.

This increase results in an additional holding force on the captured particles in the area s'-s''.

This clearly increases the tendency of particles 4b previously removed by stream C to remain on the screen.

Compare Figures 3b and 4.

The pressure also reduces or eliminates the flows shown by arrow g in FIG. 3b or reverses them in the direction shown by arrows in FIG. 4.

The emerging part of the screen 1 is still an unblocked aperture 8
However, the pressure difference P, -Po prevents or reduces the fall of the outer membrane 32e through the screen 1.

Thus, many of the particles remain in place until they are above the collection basin (Fig. 3a), into which they are settled by the countercurrent spray.

To the extent that this occurs, there will be a small amount of particles falling back into the drum pool and the tendency for excessive concentrations to develop within the drum pool will be reduced.

In the practice of the present invention, pressure is used differently to produce different results compared to conventional filtration techniques.

In a fine screen unit, ΔH is considered the liquid driving force across the portion of the screen that is at or below the level of both the tank pool and the drum pool.

Construction flow rates and other considerations make this ΔH a limiting factor in determining unit production capacity.

The application of differential pressure according to the present invention with the resulting reduction in drum pool concentration actually reduces the liquid driving force or ΔH required to screen liquid at a given flow rate.

More importantly, the present invention provides large flow capacities for a given Δ
H, keeping other factors equal.

5 to 7 show a working fine screen unit 41 of the present invention.

The device generally has a tank or basin device 42, which forms a tank pool or basin 43 (FIG. 6) therein.

Ends W of the tank 42 and its hood 49, 45a and 45b
Bearing devices 47a and 47 of the annular drum shaft are arranged in
b, and these are surrounded by a fine screen drum 5
3 forms a rotating fixed holding device.

A hood or lid 49 is on top of the tank 42 and extends over the entire top of the device to prevent liquids or solids from splashing out from within the device.

Within the end wall 45a of the tank 42 is an inlet conduit 51 that communicates between a point outside the apparatus and a drum pool area 54.

Located within drum 53 and located longitudinally above its axis and just below the highest point or apex of rotation is a spray device 55, which apex is indicated at point 28 (see FIG. 6).

The device includes a collection gutter 57 and a conduit 59 that connects the gutter directly to a point outside the tank through the end wall 45bk.

Inside the hood 49 around the apex of rotation 28 is a spray device 61.

The spray device 61 may be of the conventional type consisting of a fluid conduit 63 and a plurality of axially spaced spray nozzles 65.

Nozzle 65 may be a conventional nozzle, but preferably a self-cleaning type nozzle is used.

Such nozzles are known as self-purifying showers and generally have a spring actuated plunger that closes an orifice to create a spray when water pressure is applied to the rear of the plunger.

When the water is turned off and the water pressure is removed or reduced, the plunger retracts and the nozzle opens to purge it.

While backflow fluid (e.g., wash water) is supplied to the apparatus by an external source, this backflow fluid is preferably supplied by a pump 67 as shown in FIGS. 5-7.

The pump draws for a source of fluid from reservoir 43 and then sends this fluid under pressure through conduit 69, fluid conduit 63 and nozzle 65 to the screen.

In this respect, it is advantageous to provide a manual throttle valve 71 for manually regulating the pressure on the nozzle 65.

For purposes of the present invention, pump 67 may be a conventional pump, such as a centrifugal pump.

However, pump 67 may be used at two or more different pressures, one lower than the other, to direct backflow fluid to conduit 69.
It is preferable to release it to

The filter drum 53 is rotated by a motor 73, which has a rotating shaft 7 connecting the drum 53 to a pinion 77.
5, and this pinion rotates through the drum 53 at both ends 81.
The gear 79 is connected to the gear 79.

The screen 83 may be of conventional design, with a preferred fine screen comprising a perforated support member, a filter cloth consisting of woven strands or filaments defining holes therebetween, the holes forming a hole in the perforated support member. The fixing layer is smaller than the opening, and includes a fixing layer that engages with the support member to fix the cloth.

Further, the fixing material is usually made of a solid material, which at least prior to fixing should be soft or softenable under the following conditions, i.e., conditions that do not swell or harm the filter cloth material. It should be able to soften under the conditions.

The fuser layer also has an outer portion secured to the support member and an inner portion having an integral extension extending through and at least partially overlapping a sufficient number of threads or strands of the fabric and having an aperture. The cloth is fixed to the perforated support member.

As shown in No. 5, one side wall 42b of the tank 42 has a downflow weir therein for removing filtered, purified liquid from the apparatus and directing it to an outlet or to subsequent processing.

The downflow weir communicates with a downflow tank 87 (FIG. 6) and an outlet conduit 89.

In accordance with the invention, the microscreen unit of FIGS. 5-7 has a shelf 90 which is mounted on a cover plate 91 which covers the center hole of the annular drum shaft bearing 47b.

Fixed on the shelf 90 are a drive motor 94 and an inlet 95.
, a blower 93 having an outlet 96.

The duct extends through a watertight connection, through a cover plate 91 and into a lateral offset pipe 97, which is connected to a standpipe 98 and an elbow 9.
9, connect with the exit 100;

The drum 53 is structurally and operatively sealed against fluid flow at its ends by walls 81 and watertight fittings or packings between drum axes 101a and 101b and axes 47a and 47b. It is located at the seam.

Generally, there is no direct communication between the interior of the drum and the ambient atmosphere via drum inlet conduit 51 or sludge outlet conduit 59.

This can be done, for example, by providing traps in these conduits.

Furthermore, the openings in the screen 83 are sufficiently small that the strength of the water film across these openings is sufficiently large that the blower 9
In operation 3, the limited release of air coming from the outlet will provide a positive pressure differential across the screen 83 from inside the drum to the outside.

This pressure differential is applied to the air above the water in the drum pool, separating it from the hydraulic head ΔH (Figure 3a).

The head lies across a screen below the surface of the tank and drum pool.

The output of the blower is preferably controlled to prevent air from escaping through the screen 83.

Alternatively, a positive pressure difference is applied in the manner shown in FIG.

It is similar in many respects to FIG. 7, and like parts have been given like numbers.

This embodiment uses a blower 93, which acts to reduce the pressure in the space between the drum and its housing.

The blower 93 is installed on the end wall 45b, and its inlet duct 9
5 communicates with the space between the outside of the drum and the fine screen unit hood through holes 102 in wall 45b.

When this blower is operated, air passes through the path indicated by arrow 103 and reduces the pressure outside the screen 83 with respect to the pressure of the air in the drum gas space open to the atmosphere.

As can be seen in FIGS. 7 and 8, the use of a blower 93 (as shown in FIG. 8) to create the suction force reduces the amount of piping required and generally simplifies the operation.

On the other hand, it requires sealing the end 81 of the drum housing and the conduit, and the mist from the spray nozzle 65 in the air drawn through the inlet duct 95 will create a potential that corrodes the blower.

Therefore, a blower 93 with appropriate corrosion resistance is used.

However, the embodiment of FIG. 7 is preferred.

Exit 100 in FIG. The inlet duct 95 of FIG. 8 is preferably located above the highest expected water level.

Spray device 61 and collection device 55 are features found in conventional microscreen units.

These are designed to direct the majority of the wash water from the spray nozzle 65 directly into the collection gutter 57.

However, in the operation of such conventional units, some of the wash water and some of the solids loosened from the screen do not reach the gutter.

Some of the water does not penetrate the screen, but rather forms an external film that adheres to the outside of the screen and eventually reaches the tank pool 43.

Some water also penetrates the screen, forming an internal film that adheres to the inside of the screen and eventually reaches the drum pool 54.

As each successive section of screen passes under the shower, solid particles adhering to the inside of the screen are loosened.

Some of these are removed and carried into the gutter by the portion of the shower water that reaches the gutter.

However, some of the solids loosened by the shower do not come off the fabric and become dispersed within the internal water film.

The application of differential pressure in the embodiment of FIGS. 5-7 increases the amount of water that does not penetrate the fabric and also forces a portion of the inner membrane onto the exterior of the fabric.

This effect is desirable in many cases, especially when the influent is substantially free of bulk solids.

Although some solids become clusters of sticky particles that are broken apart by the shower water, most of the particles that can be separated are smaller than the screen openings.

The flow of the internal water film to the outside of the drum carries these small particles with it, so that the sieve fraction limits efficiency losses.

Sieve fraction efficiency is the percentage of influent suspended solids removed.

Assuming that the amount of such small particles is not very large, the fifth to seventh
A unit constructed and operated according to the diagram is capable of collecting more solids weight per unit time than would be possible without the application of differential pressure.

It can be argued that the increased throughput and solids removal outweigh the loss in efficiency due to the presence of small particles.

However, if the influent contains sufficient agglomerated solids, the sieving efficiency of the fine screen unit of the present invention can be increased by one or more of the techniques described below by means of FIGS. 9-15. .

These techniques apply differential pressure only during periods of maximum load on the fine screen, and/or back up the shower pressure for at least a large portion of the time that differential pressure is applied, and/or including suppressing, offsetting and/or preventing the application of differential pressures across continuous portions of the screen.

Applying differential pressure only during periods of maximum load has operational benefits and very appropriate design benefits for fine screen units for municipal wastewater treatment plants.

If the fine screen unit is equipped with a device that applies or increases differential pressure during periods of maximum load and removes or reduces differential pressure during periods of reduced load, this reduces redundant capacity (and therefore reduces capital and operating costs). ).

Fine screens can thus be designed to handle the highest loads that are rarely or occasionally experienced.

See, for example, the hypothetical time versus load diagram in FIG.

The horizontal axis of this diagram is divided into hours according to a 24-hour clock.

The vertical axis represents the load imposed on the fine screen in hundreds of gallons of liquid per 24 hour day (MGD).

The load is low in the early morning hours.

The load increases as people wake up. Running the household clothes washer and other morning activities eventually create the highest morning load.

This is indicated by the diagonal cross-hatched area M in FIG.

The peak load in the evening occurs after a short afternoon break, shown by the diagonal cross-hatched area e, and is followed by a mid-night (2
Low level loading continues through 400 hours).

Each plant has a characteristic pattern that differs in detail from the hypothetical load curve in the diagram, but in the absence of precipitation the same general pattern normally repeats daily.

However, sudden heavy rains can cause abnormally high peaks, indicated by the horizontal and vertical hatched area R, especially in this case, where many of the legal and illegal waterways of roof water enter the sewer system or drain into the sewer system. This results in improper connection of surface water.

In general, it is common practice to design sewage treatment plants with sufficient capacity to treat the maximum normal daytime flow that enters the plant.

Based on this idea, in order to design a factory that handles the load shown in FIG. 9, it would probably be designed for 1.5 MGD.

This means that during many if not most of the day the factory operates below its design capacity.

By applying the present invention to conventional fine screens, the total utilization efficiency can be increased by 1.5 to 2 times without relatively increasing unit cost.

It is possible to handle the load shown in the diagram with a fine screen having an effective area and cost corresponding to the IMGD load.

Provided that the influent contains sufficient agglomerated solids to justify it, the equipment should be equipped with an automatic control system to ensure that the difference will only occur when the plant is operated at maximum load, as indicated by the hatched areas M, R, and e. Try to apply pressure.

Thus, the differential pressure applied when the load is below the IMGD rate is removed and the plant will operate at maximum sieving efficiency.

Considered on an average daily basis, the total operation can give a satisfactory quality of effluent.

Additionally, as shown by the rain peak R, the 1.5 MGD conventional plant is sometimes fully loaded beyond capacity, resulting in bypassing unscreened wastewater into rivers and lakes.

According to the present invention, such a situation can be reduced by a fine screen.

Operating capacity can be increased at a reasonable cost.

Applying the maximum differential pressure to handle the maximum load, even if the sieve fraction loses some efficiency, the overall result is better than if the filter had to be bypassed and the unfiltered solids sent to the river or lake. .

A unit of the type described above is shown in FIG.

FIG. 10 shows a fine screen tank 105 with a rotating drum 106.

This tank defines a tank pool 107 with a surface 109 and a drum pool 108'e with a surface 110 that is higher than the surface 109 by a distance d for screening purposes.
include.

As previously mentioned, the drum screen is washed by the spray from nozzle 112, and the wash water and solids are sent to the lower drain 111.
collected by.

The differential pressure is provided by a blower 114 having a discharge duct 115 and an outlet 116 into the air space in the drum 106 above the drum pool 108.

The controller includes a device responsive to one or more indications of the load (influent solids concentration and/or volumetric velocity of incoming liquid).

These include, for example, the closed end 120. It takes the form of a vent tube 117 with an inlet orifice 119 and an outlet 118 to the atmosphere.

The effective area of the inlet orifice 119 is the drum pool 108
surface 110, and as the level of surface 110 rises, it creates a large pressure drop across orifice 119.

As this pressure drop increases, the pressure in the air space within drum 106 increases.

Blower 114 is selected to completely close inlet orifice 119 of vent tube 117 with a cutoff pressure equal to the desired high pressure when surface 110 is raised.

As the liquid level 110 within the drum pool 108 is affected by the load, it will generally increase in response to an increase in load, but this same level increase will also occur at the orifice 119.
The device increases or decreases the added pressure differential continuously in response to increasing or decreasing the load.

Thus the extra capacity is mostly reduced to ζ when it is needed.
This is provided and the additional pressure differential is reduced or eliminated when the load is relatively low.

Many other types of controllers are used to adjust the magnitude of differential pressure with respect to equipment load.

This takes the form of a tank pool level sensing device having a float arm and a float that sets an electrical signal according to and indicative of the level of the shrimp tank pool, for example.

This sensing device is connected to a control device via a suitable circuit.

The controller is a device capable of controlling the applied pressure differential, such as by adjusting the blower 114 at variable speeds 8 and/or in an on-off manner to vary, initiate, or discontinuously apply the applied pressure differential between the outside and outside of the drum.・I will do it.

The controller receives the line current through appropriate circuits and sends the current through other circuits to the blower.

The blower is kept at low speed or turned off at low liquid levels.

The blower is energized or sped up until it begins to apply or increases the differential pressure as the liquid level rises.

On the other hand, the controller can operate a pressure regulating valve on the inlet or outlet side of the constant speed blower 114 in an open/close, stepped flow or infinitely variable flow manner to control the additional pressure differential.

The foregoing discussion describes reducing the differential pressure at or in response to low workloads (including removing it) and increasing it at or in response to high workloads (including switching it on). ) are just a few examples of how to do this.

The operation of the blower 114 depends on other factors indicative of the load, such as the influent volume flow rate or suspended solids concentration, the viscosity of the slurry exiting the collection tube, the suspended solids concentration of the effluent (clean water), and similar factors. can be responsively controlled.

A particularly preferred control system, shown in Figures 11.11a and 12, applies differential pressure only during periods of load increase.

This means operating the shower at increased pressure during at least a substantial portion of the time when differential pressure is applied, and operating the shower at reduced pressure during at least a substantial portion of the time when no differential pressure is applied. is combined with

However, periodic boosting of the shower pressure is sometimes carried out for other purposes, for example to clean the screen more thoroughly.

Thus, shower pressure support can be implemented regardless of whether the differential pressure is applied continuously or discontinuously.

Fine screen unit 141 shown in Figure 11.11a
is a tank or trough device 142, end walls 145a and 145
bk has a tank or tank pool 143, and an annular drum shaft bearing arrangement 147a and 147b'e.

A rotatably mounted fine screen drum 153 is provided within the tank 142 .

A device (not shown) for drum rotation is provided. As in the previous embodiment, a downflow weir, downflow tank and outlet conduit (not shown) are present to handle clean water overflow from tank 142 (not shown).

One of the annular shafts of the drum 153 is connected to the end wall 14 of the tank 142.
5ak to form conduit 151.

This includes the headbox 152 and drum pool area 154.
communicate between.

The top of headbox 152 opens to the atmosphere.

Supported and suspended within the box 152 is 1
They are a pair of switches 175 and 177.

These switches are connected via appropriate actuating arms to floats 175a and 177a, respectively.

The floats are suspended at two different heights above the top of conduit 151 and are in position to float upwardly on water rising above the top of conduit 151 and into headbox 152, and are connected to switch 175 and 177 is operated.

Within the drum 153 is a spray device 155 having a collection gutter 157 and a conduit 159 which connects externally to a seal, e.g. a trap (not shown), through an end wall 145b with a sludge disposal point. do.

Blower 190 has an outlet connected to conduit 159.

Since this conduit is only partially full in normal operation,
The outlet of the blower communicates with the air space in the conduit and through the open top of the gutter 157 with the gas space 173 above the drum pool or tank 154.

The blower 190 operates whenever the fine screen is working.

Simultaneously with the previously described embodiment, there is a spray device 161, which includes, for example, a conduit 163, a nozzle 165, a pump 167 (
(Fig. 12).

The pump is of a type capable of discharging backflow fluid into conduit 163 at two or more differential pressures.

For example, the motor 179 has a low speed winding 183 and a high speed winding 185.
have.

For example, a pump and motor combination can be selected that, in conjunction with other equipment characteristics, will produce shower pressures of 30 Psi and 120 Psi, respectively.

FIG. 12 is only one example of a circuit type, which requires other equipment components to assist in showering pressure during at least a portion of the time that a gas pressure differential is applied across the non-submerged portion of the screen. used with

Thus, for example, the slow winding 183 is connected to the master switch 1
91 to a source of line current 189 so that it is energized at all times when master switch 191 is in the on position.

Control device 18 connected to the line via the same main switch
7 are switches 175 and 177 in the head box 152
can be used to control the high speed winding 185 with the help of.

Although it is satisfactory to control the high speed winding 185 with one of the switches 175 or 177, certain benefits may be obtained by using two switches.

For example, the control device may include a suitable relay circuit to
5 is energized by the rise of flow) 177a, flow)
The force is deenergized by the lowering of 175a.

This eliminates undesirable on-off cycling of high speed windings and avoids problems sometimes experienced with single switch control systems.

In the operation of this example, drum pool 153 operates at a specific level 192 (11th.
Figure 11a).

At the level of the water in headbox 152 and drum pool 154 at level 192, conduit 151 is partially open.

The gas space of the drum pool 154 is located in the head box 152.
It communicates with the atmosphere through the opening at the top.

An increase in load, such as an increase in the flow of the influent and/or the concentration of suspended solids in the influent, forces the liquid level 192 to increase.

If the load increase is sufficient to rise to liquid level 193, the liquid closes conduit 151.

Air discharged by blower 190 through the open top of conduit 159 and the trough, which previously escaped through conduit 151 when conduit 151 is partially open, now pressurizes gas space 173.

If the load increases further, the liquid level will drop to level 194.
and can be increased to 195.

the liquid level reaches 195 in the headbox 152;
When float 177ak is raised, switch 177 energizes high speed winding 185 via controller 187.

This results in a shower pressure of 30 Psi (approximately 2.11
Ky/7) to a second high level of 120 Psi.

Increasing or boosting the shower pressure helps recover more solids that the screen carries into the shower area.

This is achieved through both a more complete cleaning of the screen and a more complete recovery of shower water in the collection trough.

This improvement reduces the drum solids concentration, reducing ΔH and allowing the unit to handle larger liquid flows, while maintaining a reasonable concentration of suspended solids in the effluent. can.

When the load decreases to level 194, float 175a activates switch 175 and controller 189 to energize high speed winding 183.

Shower pressure is 30Psi (approximately 2-11 Ky/cr)
/l).

As the load is further reduced, the liquid level is lowered below level 193, conduit 151 is unblocked, and drum gas space 1 is removed.
73 to the atmosphere, allowing the pressure differential to be removed and the unit to return to low level operation.

Techniques and devices for suppressing, offsetting and/or preventing differential pressures that are applied across successive sections of the screen as they pass through the shower are illustrated in FIGS. 13-15.

The purpose of these embodiments is to apply differential pressure where it is needed, while reducing, eliminating or reversing pressure differentials where it is not needed, for example on a screen passing between the spray device and the sludge. It is added across a continuous section.

It will be apparent to those skilled in the art that the present invention can be made into many different embodiments.

Figures 13 to 15 show the rotating drum 253, screen 283, and drum pool 254 of three fine screen units.
, drum gas space 273, tank pool 243, and spray equipment 261, which are similar in all respects except for certain modified collection gutter and hood equipment.

Although not shown in Figures 13-15, these three embodiments have the same type of tank, drum shaft bearing, inlet conduit, sludge outlet conduit, nozzle, backflow fluid pump, drum drive, downflow weir, and downflow tank. , a purified liquid outlet conduit, a differential pressure blower, associated tubes and ducting for the blower, and sealing arrangements, which are shown in FIGS. 5-7 and the description thereof.

As shown in FIG. 13, the screen 28 is removed by extending the side walls 222 and edges (not shown) upwardly until they contact or nearly contact the screen.
Pressure-independent area 273ak between the inside of 3 and gutter 257a
can be provided.

If the space between the edge of the grate and the inner surface of screen 283 is narrow enough, there will be a sufficient pressure drop across this space to at least partially depressurize area 273a independent of drum pool gas space 273. make it.

In this example, the pressure conditions external to the drum are designated Pl, as shown in Figure 14.15.

In these three drawings, the point 226 where the screen 283 exits the drum pool 254 and its point at the collection point 257a
The pressure conditions in the drum gas space between the points 253 passing over the edge of the drum are shown at P2, and although there is an at least partially pressure-independent area 273a for the grinder in FIG. 1315, the pressure conditions there are P3. It is indicated by.

Suitable pressure conditions for the embodiment of FIG. 13 are given by the equations P2>P1o and P3>P2.

However, preferably P2) P1≧P3.

Pressure within area 273a may be applied in any suitable manner.

If it is possible to provide a sufficient tight fit between the flanges and the inner surface of screen 283, P3 may be maintained below P2 by communicating zone 273ak with the atmosphere or other zone at reduced pressure with respect to P2.

Alternatively, if desired, a blower inlet that pressurizes area 273 may be connected to area 273a and vented therefrom.

Using a large capacity blower allows a relatively large space between the screen 283 and the gutter side wall 222.

As shown in FIG. 14, there is free communication between the interior of gutter 257 and the remainder of drum pool gas space 273.

In this case, the unit comprises a hood 210 covering the spray device 261.

A pressure-free zone 218 can be provided within the hood 210 between the outside of the screen 283 and the spray device 261 by extending the hood sidewalls 215 and ends (not shown) downwardly until they nearly contact the screen.

When space 240 is narrow enough, it provides a sufficient pressure drop to make hood area 218 at least partially independent of the remainder of the gas space surrounding the drum where pressure P1 is located.

In this embodiment, as shown in FIG.
Pressure conditions within 8 are indicated by P4.

Suitable pressure conditions for the embodiment of FIG. 14 are shown as P4>Pl and P2>PI.

However, preferably P4≧P2>PI.

The desired conditions are created, for example, by connecting the outlet of a blower to the hood 210.

FIG. 15 shows an embodiment of both the upwardly extended version of FIG. 13 and the hood 210 of FIG. 14, which provides two zones 218 and 273ak, which respectively define the drum pool gas space 273 and the drum. It has at least partially a pressure independent of the remainder of the surrounding gas space, in which there is a pressure P1.

In this example, the appropriate pressure condition is P3-P4<P2
Limited by pl.

Here, Pl s P2 s P3g and P4 are absolute pressures or pressures based on a common reference.

However, preference is given to P2>Pl and P4>P3.

The desired conditions are created by one or more blowers or a combination of blowers and vents as described with respect to Figures 13.14.

These embodiments are useful where increased sieving capacity is desired compared to the embodiments of FIGS. 5-7.

These embodiments help enhance shower water penetration and recovery.

However, these embodiments are advantageous from the standpoint of improving solids recovery and effluent quality, particularly when working with agglomerated solids.

These embodiments are particularly suited to high differential pressure operations, but are useful throughout the entire differential pressure range contemplated by the present invention.

As mentioned above, differential pressure can be applied in any desired manner.

We have already described how blowers can be used for this purpose.

The inventors are unaware of any common means of providing a pressure differential between the air space within the fine screen drum above the drum pool and the surrounding air space, such as outside the drum.

The inventors are well aware of fine screen units in which the drum portions do not fit sufficiently to create an adequate differential pressure in a practical size blower.

In order to apply the invention to such units, it is possible to seal off or improve the sealing of certain drum parts, particularly around the drum ends and edges of the media, so that air from the surroundings is removed while the drum air space is under differential pressure. Make it possible to insulate.

When using a suitably sealed drum, differential pressure can be applied by incorporating air into the inlet liquid or shower water.

The problem of dropback due to differential pressure application described above can be reduced by increasing the drum speed to levels not previously considered satisfactory.

For conventional fine screens with low drum speeds and high solids concentrations, an increase in drum speed increases the sieve capacity per square foot of screen area approximately proportionally.

However, as the peripheral speed of the screen increases to a higher value,
The capacity gain per unit speed becomes progressively smaller.

The captured solids reach the collection tube at an increasingly higher rate, while the flow through unit area of the screen per drum rotation decreases.

Thus, there will be a maximum level of drum speed beyond which performance decreases, as shown by the curve labeled rWITHOUJ in FIG.

On the other hand, with an additional pressure differential, one or more dropback phenomena are significantly reduced.

As a result, the drum can rotate faster and a higher peak point is obtained before performance tapers off.

This is shown by the curve marked rWITHJ k in FIG.

If the liquid undergoing fine sieving contains agglomerated or clump-like solids, an increase in drum speed will result in a change in the drum water velocity vector at the point where one screen exits the drum pool. shows a tendency to decrease the degree of

The resulting increase in the number of small particles in the drum increases the total number of particles escaping through the screen into the effluent per unit of liquid volume processed, impairing effluent quality.

As the present invention reduces this tendency to some extent, the fine sieve fraction can increase the maximum performance speed of the drum even when working with clumped or fluffy solids.

However, useful peripheral velocities for current or fluffy solids are generally lower than those available for discrete solid particles.

Operating a rotating fine screen unit at increased rotational speed increases operating torque, bearing loads, and unit wear rates.

In addition to providing the high throughput capacity discussed above, the present invention can reduce wear, particularly when working with separated solids at the higher end of the useful pressure range.

The additional buoyancy the drum has when the air above the drum pool is pressurized and/or when the drum sinks deeper reduces bearing loads, torque, and correspondingly reduces wear.

The differential pressure added for this is approximately 3 water gauge pressures.
Select from a range of from about 6 inches (about 76.2 to about 152.4 m) or from more than 6 inches (about 152.4 M) to about 10 inches (about 254 M) and above.

In conventional fine screen units, performance can be improved by increasing the depth of drum depression, e.g. by raising the drum pool and tank level with respect to the axis of rotation, thus increasing the effective screen area. can.

However, this unfortunately causes the drum to emerge from the drum pool at a lower angle, making it more effective for gravity to separate trapped particles from the screen earlier.

More importantly, this lower angle increases the thickness of the external water film (32e in Figure 3b), which is partially due to the gravity flow 1g'.

However, the present invention offsets gravity and improves screening at deeper diving levels.

As an example of the invention, the table below shows some ranges of equipment parameters within which the invention is most commonly practiced.

This means that in each case the pressure is expressed as inches of liquid,
is understood to be the pressure required to support the same column of liquid being processed through a fine screen;
The height of the column is in inches as indicated in the table.

The items listed under the heading "Range B" are particularly preferred or more commonly occurring values.

Item Range A (approx.) Range B (approx.) Drum peripheral speed (feet per minute) 30-240 90-180 Drum diameter (feet) 2-12 2-6 Drum pool distance above drum center, D is drum 0 ~． 4D O~, 25D diameter, ft. Scree' opening size 5~140 20~7° (microns) Scree' opening area 10~6020~40 (percent) ΔH - To the hydraulic pressure across the sunken part of the screen O~ 18 0 to 10 (inches of liquid) Additional differential pressure (inches of liquid) 0.1 to 100.1 to 3.7
-Pressure 20-160 25-10100 (P
si influent solids concentration, ~□.

00 □5~□00 ("f#) Influent solid particle size, ~200 20~100 (microns)

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing liquid-solid separation media that generally illustrate the difference between fine sieving and filtration; Figure 3a; Figure 3b is a sectional view of a fine screen showing the problem of lockback, Figure 4 is a cross-sectional view of the screen of a fine screen unit showing the principle of operation of the present invention, and Figure 5 is a part of the fine screen unit of the present invention. A broken perspective view, FIG. 6 is an end view of the unit in FIG. 5, FIGS. 7 and 8 are partially broken side views showing the unit in FIG. 5 and its modified example, and FIG. 9 is a domestic sewage treatment plant. Graph showing the load conditions of
Figure 0 is a diagram of the control device used in the present invention, Figure 1L11a is a cross-sectional diagram showing another embodiment of the present invention, and Figure 12 is the diagram of the control device used in the present invention.
1.11a Diagram of the control circuit for the embodiment of FIG. 13.1
Figure 4.15 is a cross-sectional diagram of three other embodiments of the invention, and Figure 16 is a graph showing the performance of fine screens at various drum speeds, with and without the invention. . 1... The filtration medium or sieve is cloth, 3...
...Suspended particles, 12...Drum, 14...
...Drum pool, 16...Tank, 18.
...Nozzle, 19...Forced flow, 26...
...Continuous part, 32e...External membrane, 32i
...Inner membrane, 41 ... Fine screen unit, 49 ... Hood, 55 ...
Collection device, 61... Spray device, 65...
... Spray nozzle, 67 ... Pump, 75
...Rotation axis, 83 ...Screen, 8
7...Flowing tank, 90,105...
Fine screen unit, 93, 114...Blower, 108...Drum pool, 112...
... Nozzle, 119 ... Orifice, 141
...Fine screen unit, 142...
...Storage device, 152...Head box, 1
53...Drum, 173...Gas space, 175.177...Switch, 187...
...Control device, 190...Blower, 191.
... Master switch, 210 ... Hood, 253 ... Rotating drum, 261 ...
・Spray device, 283...Screen.

Claims (1)

[Claims] 1. A diluted suspension containing suspended particles is fed as an influent into a drum pool of a fine screen unit, said fine screen unit comprising a tank with immovable side walls containing a cunk pool and a tank with immovable side walls for containing said drum pool. A drum rotatably disposed on the drum, a sieve portion forming the peripheral surface of the drum and having minute openings for communicating liquid between the drum pool and the tank pool, and a sieve portion above the medium and outside the medium; and a solid liquid collection device disposed in the drum below the backflow liquid spraying device, the upper surface of the drum pool relative to the tank pool bell during the supply of the influent liquid. The hydraulic head Δ across the sunken part of the screen
The diameter of the drum on the top surface of the drum pool is set as D, and the diameter is approximately 0.4
maintaining a gas space above the drum pool surface at a level not exceeding D; during rotation of the drum, the suspension is forced to pass through a medium and the suspended particles are deposited inside the drum; During the rotation of the drum, the deposited particles are deposited on the inner surface of the media and from the point where the drum circumference exits the drum pool, the drum circumference passes over the collection device. The sieve portion is carried over a gas space extending to a passing position, and a spray of backflow liquid is ejected from outside the media through the drum surface on the collection device to collect the particles from the sieve portion. The removed particles are removed from the media and placed into the collection device along with the liquid added by the backflow liquid spray, and the fine sieves are removed from the drum before the throughput reaches the collection device. The fine sieve fraction, such as the sieve fraction that drops back into the pool, is reduced by the particles, and in the process, a liquid gauge pressure difference in the range of about 0.1 to 10 inches is applied to said portion of the gas space. The sieve fraction passing through the media section is applied across the media, the pressure difference is such that the sieve fraction is on the high pressure side on the inside versus the outside of the media, and the sieve fraction is dropped from the media into the drum pool. A fine sieve method characterized by having a size sufficient to reduce the amount of backing particles.