DE9200903U1 - Longitudinal sand trap for settling and removing sediment, especially sand from inlet channels, especially from sewage treatment plants - Google Patents

Description

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Hans Georg Huber, Zum Rachental 8, 8434 Berching

Longitudinal sand trap for settling and removing sediment, especially sand from inlet channels, especially from sewage treatment plants

The invention relates to a longitudinal sand trap for settling and removing sediment, in particular sand, from inlet channels, in particular from sewage treatment plants, with a settling channel, in particular with a trapezoidal cross-section and running as a straight section, in the area of the bottom of which a collecting space for the sand is formed, with or without a circulating channel for untreated water. A longitudinal sand trap is understood to be a flat sand trap through which the water flows essentially horizontally as a straight section. During the flow through this section, the sand contained in or carried by the water has the opportunity to sink towards the bottom of the settling channel and to pass into a collecting space formed there. The sand is removed from this collecting space.

then removed, for example with a transport device, which is often designed as a screw conveyor.

Sand is understood to be material with a grain size > 0.2 mm in diameter. The sand should be separated without any organic components attached to it. The sand trap is therefore also used to separate the sand from the sewage sludge. It goes without saying that the speed of the flowing water in the settling channel and the length of the settling channel play a decisive role. The amount of wastewater that is generated and has to be channeled through a sand trap also varies depending on the weather conditions. In rainy weather, the amount of wastewater can be 3 to 5 times the amount of wastewater that is generated in dry weather. As a result, the design of the cross-section and length of a sand trap or settling channel is a medium compromise for the fluctuating operating conditions.

A long sand trap of the type described at the beginning is known from the textbook and handbook of wastewater technology, 3rd revised edition, Volume III, 1983, in particular pages 97 - 103. This long sand trap has a settling channel that runs as a straight line. A collecting area for the sand is formed in the area of the bottom of the settling channel. The settling channel has a constant cross-section over its length, so that the water flowing through the settling channel has the same speed at every point in the length of the sand trap, although the speed across the cross-section is of course correspondingly different. Gravity acts on a grain of sand that flows through the settling channel and the result is a parabolic sinking curve for the grain of sand. Even when the water level is high, if a grain of sand flowing into the settling channel in the area of the water level hits the bottom of the sand trap or settling channel with its sinking curve, all of the sand

deposited in the sand trap. The sand trap must therefore have a corresponding length. The design of the sand traps in terms of cross-section and length is calculated and designed for an average amount of water. For larger amounts of water, a circulation channel is provided, which branches off at the entrance to the settling channel and provides a parallel flow path, so to speak, through which part of the sand-laden wastewater is led around the settling channel as a bypass line. It is accepted that no sand is separated in this circulation channel or that this sand is carried into the subsequent part of the sewage treatment plant.

A sand trap is also known from DE-PS 28 32 277, in which the cross-section of the settling channel is comparatively smaller than the cross-section of the inlet channel to the sand trap. As a result, the flow rate of the waste water in the settling channel will be greater than in the inlet channel, so that for the sand to be completely deposited in the settling channel, the latter must be relatively long. A collecting space for the sand is formed in the bottom of the settling channel, in which a transport device, designed as a conveyor screw, is housed. In addition, an aeration device is provided in the settling channel in order to stir up any sludge that settles in the area of the settling channel and thus keep the sand as free as possible from sludge components. Here, too, the settling channel has a constant flow cross-section over its length, so that the flow rate in the longitudinal direction of the settling channel is constant at all points.

DE-PS 30 28 541 shows a device for removing screenings and sand from inlet channels, in particular from sewage treatment plants. Here too, a settling channel for the sand is provided, which has a constant cross-section over its length. The transport conveyor device in the collection chamber of the

Sands also works in the direction of flow here and feeds the sand to a sand scoop wheel, which is equipped with a separate screw conveyor for conveying the sand upwards out of the channel. In addition, a device for removing screenings is provided, which has a screening basket with a collecting grate on which the screenings are separated. A downstream screw conveyor conveys the screenings upwards separately from the sand. The screw conveyor of the transport conveyor for the sand is coupled in terms of drive to the shaft of the screw conveyor for the screenings. The two screw conveyors for the screenings and the sand are arranged at the end of the settling channel.

The invention is based on the object of improving a long sand trap of the type described at the beginning in such a way that it has a comparatively reduced overall length with comparable sand separation performance or is able to absorb larger quantities of untreated water.

According to the invention, this is achieved in that the settling channel has a widening cross-section in the direction of flow and/or at least one drainage channel providing an additional cross-section is provided, which is connected to the settling channel in the area of water purified from sand.

The invention is based on the idea of breaking away from the constant cross-section of the settling channel in the direction of flow and of providing an expanding cross-section and/or an additional cross-section in the direction of flow, so that the flow speed is reduced over the length of the settling channel, so that the sand particles then sink to the bottom of the settling channel over a shorter distance and accordingly the total length of the settling channel can be chosen to be correspondingly shorter with comparable other operating data.

the drainage channel - in contrast to a circulation channel - is only intended for the drainage of water that has been cleaned of sand. Cleaned water is drained off via the new drainage channel so that it no longer burdens the cross-section of the settling channel. This reduces the amount of water in the settling channel. In this case, the settling channel itself can have a constant or expanding cross-section over its length, for example it can be designed like a diffuser so that the flow speed is reduced accordingly. With this new sand trap, either a shorter installation length is achieved or, if the installation length is maintained, it is possible to treat larger quantities of water in order to settle sand. The long sand trap can therefore be operated more variably and can be adapted to larger fluctuations in water quantities without having to use a circulation channel. Only with extremely high water quantities can a circulation channel be used in addition, if one is provided.

The additional cross-section of the extension or the drainage channel can be stepped or stepless in the direction of flow. At least one step is formed, but preferably several steps. A stepless design is also possible. The aim of this design is also to continuously reduce the flow velocity in the direction of flow in the area of the settling channel in order to achieve the sinking of the sand grains at a comparatively shorter axial length and thus to reduce the overall length.

The transition cross-section between the settling channel and the drainage channel can be designed differently over the height and/or be equipped with a control device. The design of the transition cross-section, which varies over the height, allows for different water levels and thus water quantities

An adjustability or a control device can also be provided here in order to be able to make adjustments to the water volume during operation in order to determine the amount of water to be removed from the settling channel. In its simplest form, the control device can be an adjustable flap, but also a valve or similar.

The drainage channel, of which several can be provided if, for example, several steps are provided, or the drainage channels can be designed and arranged in such a way that the water level in them is lower than in the settling channel. The amount of water drained away via the drainage channel is added back at the end of the drainage channel to the water that has flowed through the drainage channel.

A ventilation system can be provided in the end area of the settling channel in particular. In some cases, the reduced flow speed in the end area of the settling channel can lead to increased sludge deposits here. The ventilation system, which can also be divided into several optionally operable sections, is used to stir this up again and keep the sludge content in the sand as low as possible in order to enable adaptation to the operating conditions.

In the settling channel, particularly in the direction of flow after, before or at the transition cross-section to the discharge channel, there can be built-in elements that slow down the flow. There are various design options for these elements. In all cases, these elements serve to increase the friction and thus contribute to a slower flow in the subsequent part of the discharge channel, whereby the water level can be approximately constant over the length of the discharge channel. The elements can, for example, be vertically

arranged, aligned in the direction of flow and suspended in the flow, so that they then only contribute to increasing friction. However, it is also possible, or in addition to this, to provide several plates arranged approximately parallel to one another and spaced apart from one another as built-in components, which form a plate package with flow paths, whereby the plates are arranged one above the other in a vertical direction, at least partially overlapping one another, and are arranged in the settling channel at an angle downwards in the direction of flow. In this way, the sediment is guided downwards in the individual flow paths running parallel to one another, so that it can settle over a shorter flow path. This additional measure can save additional length. The downward inclination of the plates in the direction of flow can be greater than the sinking depth of the sediment without built-in components. For this purpose, the plates are either arranged in a fixed position at an appropriate angle or their inclination can be adjusted so that adjustment can be made depending on the water level and the desired degree of cleaning. The plates extend essentially horizontally and are inclined in the direction of flow, and can end at some distance from the channel wall. It is important that they are arranged in the middle of the channel, where the flow speed is greatest. The fittings in one form or another, which can also be used in combination at the same time, can be provided as sheets that are suspended in the settling channel at a variable depth, so that the friction can also be varied.

The settling channel can essentially only have one sloping wall. This one wall is comparatively steep so that sand can slide down this wall and get into the collecting chamber. If two sloping walls, as is the case with symmetrical,

trapezoidal design of the cross-section of the settling channel, the inclined walls are correspondingly flatter if a similar adaptation characteristic to the water quantity is to be given.

The drainage channel can have different widths over its height and thus, like the settling channel, can have a trapezoidal cross-section, even in an asymmetrical form. The cross-sections of the drainage channel and the settling channel are coordinated with each other.

Embodiments of the invention are illustrated schematically in the drawings and are described below. They show:

Figure 1 is a schematic plan view of a longitudinal sand trap in a first embodiment,

Figure 2 is a schematic plan view of a long sand trap in a second embodiment,

Figure 3 shows a sinking diagram of the sand over the length of the sand trap at different water quantities,

Figure 4 a side view of the wall between the settling channel and the drainage channel,

Figure 5 is a cross-sectional view between settling channel and drainage channel and

Figure 6 shows a vertical section through a section of the longitudinal sand trap with a plate package.

Figure 1 shows a schematic representation of a long sand trap 1. It has a continuous wall 2 which has an inlet

and has an outlet 4. The wall 2 can be designed as a sheet metal wall of a long sand trap 1 to be installed above ground or as a concrete wall of a stationary building. The wastewater flows through the wall 2 from left to right. The wall 2 encloses a settling channel 5. The length of the long sand trap 1 is divided into two sections. In a first section 6, the settling channel 5 has a constant flow cross-section 7. The wastewater to be cleaned of sand has a comparatively higher speed in this section 6 according to arrow 8. Section 6 is followed by a section 9 in which the settling channel 5 has a cross-section 10 that widens in the direction of flow. The cross-section 10 widens like a diffuser, so that the water flows at a comparatively lower speed according to arrow 11. In section 9, additional friction-increasing fittings 12 can be provided, e.g. in the form of metal sheets suspended in the water in the direction of flow, which help to increase the friction and thus reduce the speed of the water.

Figure 2 shows a second embodiment of the long sand trap 1, whereby mixed constructions according to the basic solutions of Figures 1 and 2 are also possible. According to Figure 2, the settling channel 5 has the same flow cross-section 7 over its entire length. In addition to the settling channel 5, however, an additional drain channel 13 is provided, which provides an additional cross-section 14. Between the settling channel and the drain channel 13, transition cross-sections 15 and 16 are formed, both of which are arranged in such a way that only purified waste water, i.e. waste water freed from sand, can flow over them from the settling channel 5. The transition cross-sections 15 and 16 are therefore located comparatively high on the wall 2 of the settling channel 5. Since two transition cross-sections 15 and 16 are shown here, each of which also has a separate drain channel 13

The design of this long sand trap is divided into three stages, so that sections 6, 17 and 18 are formed here, so that reduced speeds are set in the settling channel 5 in the flow direction according to arrows 19 and 20. Preferably towards the end of the settling channel 5 in the flow direction, an aeration device 21 consisting of several sections can be provided, which has individual nozzles through which compressed air is blown out in order to stir up sludge components again and prevent them from settling. The entire amount of water flowing through the long sand trap is divided here between the cross section of the settling channel 5 and the cross section of the drainage channel 13, so that the drainage channel 13 provides an additional cross section 14, which is to be evaluated in the same way as the additional cross section provided by the expanding section 9 of the embodiment of Figure 1.

Figure 3 shows a sinking diagram over the length of the long sand trap 1, specifically belonging to the embodiment according to Figure 1. The two sections 6 and 9 are distinguished here. Two curves are shown, each showing a grain of sand 22, which flows into the settling channel 5 in the area of the highest water level with different water quantities at the inlet 3. The two sinking curves shown for comparison initially behave parabolically in the area of section 6. In this area, a speed vl or vl' acts on the respective grain of sand 22 with a larger water quantity. It can be seen that in both cases the grain of sand has not yet reached the bottom at the end of section 6. At the transition between sections 6 and 9, the curves each have inflection points, because there is a continuously lower speed in the flow direction as a result of the expansion of the cross section 10, so that the grains of sand

can sink comparatively faster. It can be seen that with both assumed water quantities, the grain of sand floating in the area of the water surface, i.e. the critical grain of sand, is deposited in each case, so that the length of the sand trap is sufficient to completely separate the sand. If the upper curve represents the one that reflects the maximum amount of water that can be absorbed, the long sand trap could be designed with an even shorter construction length, i.e. section 9 could be made correspondingly shorter.

Figure 4 shows a schematic view of the wall 2 in the embodiment of Figure 2, namely between the settling channel 5 and the drainage channel 13. Here, the two transition cross-sections 15 and 16 are shown, which are provided as triangular holes in the wall 5. It can be seen that the transition cross-section 15 is arranged comparatively higher than the transition cross-section 16, which can be understood with regard to the diagram in Figure 3. In addition, the transition cross-sections 15 and 16 have different widths over the height, so that at a comparatively low water level, little purified water passes into the drainage channel 13, while at a higher water level, a correspondingly larger amount is transferred into the drainage channel 13. It is understood that the wall between the drainage channel 13 and the settling channel 5 could also be designed as a continuously sloping transfer ridge, for example to enable a stepless provision of an additional cross-section 14.

Figure 5 shows a schematic cross-sectional view of the settling channel 5 and the drainage channel 13. The settling channel 5 has essentially only one inclined wall 23, the inclined position of which is adapted to the ratio of the water quantities in rainy weather and in dry weather. In comparison with two inclined walls, this single inclined wall 23 can be comparatively steeper

be arranged so that the sand can slide down this inclined wall 23 more easily when sinking. In the area of the lower end of the settling channel 5, a collecting space 24 for the sand is formed. At this point, a transport conveyor device, e.g. as a conveyor screw, is usually housed, which expediently conveys the sand against the flow direction through the settling channel 5.

Two lines 25 and 26 can be provided as transition cross-sections between the settling channel 5 and the drainage channel 13, in each of which a control device 27, e.g. as a flap, valve or the like, is provided in order to use one or the other line 25 or 26 for the discharge of the purified waste water into the drainage channel 13 depending on the different water levels. When the water level is low, the lower line 25 is used, and when the water level is high, the upper line 26 is used. Here, too, it can be seen that the drainage channel 13 has a different width over its height, so that a progressively increasing additional cross-section 14 is also made available as the fill level increases.

Figure 6 shows a schematic representation of a vertical section through section 9 of the long sand trap 1 in another embodiment, i.e. an area as is illustrated, for example, in Figure 1 by the internals 12 there. While in the embodiment of Figure 1 the internals 12 are provided as vertically suspended sheets that are arranged aligned in the flow direction according to arrow 11, according to the embodiment of Figure 6 several plates 28, which can consist of sheets, are arranged in a package-like manner. The plates 28 do not extend in a vertical direction, but essentially in a horizontal direction and are arranged inclined in the flow direction according to arrow 11. Depending on the water level, the beginnings of individual plates 28 can protrude more or less from the water.

protrude. However, the plates 28 are essentially arranged below the water line. They extend at least approximately parallel to one another and are arranged at a distance from one another so that flow paths 29 are formed that lead downwards. The downward inclination of the plates 28 is greater than the sinking depth of the sediment in the area of the length of section 9 (see Figure 3). In this way, the sediment sinks even faster. For clarity, some grains of sand 30 are indicated that fall or sink from the end of the plates 28. The package of plates 28 can be arranged so that it is adjustable in height and/or inclination in order to allow adjustment to the respective water level. The plates 28 do not adjoin the wall 2 of the channel at the side, but extend over the essential central area of the flow cross-section in section 9.

Claims (12)

Protection claims: 1. Longitudinal sand trap for settling and removing sediment, in particular sand from inlet channels, in particular from sewage treatment plants, with a settling channel, in particular with a trapezoidal cross-section and running as a straight line, in the area of the bottom of which a collecting space for the sand is formed, with or without a circulation channel for unpurified water, characterized in that the settling channel (5) has a widening cross-section (7, 10) in the direction of flow and/or at least one drainage channel (13) providing an additional cross-section (14) is provided, which is connected to the settling channel (5) in the area of water purified from sand. 2. Longitudinal sand trap according to claim 1, characterized in that the additional cross section (14) of the extension (7, 10) or of the drainage channel (13) is provided stepped or stepless in the direction of flow. 3. Longitudinal sand trap according to claim 1 or 2, characterized in that the transition cross-section (15, 16) between the settling channel (5) and the drainage channel (13) is designed differently over the height and/or is provided with a control device (27). 4. Longitudinal sand trap according to one or more of claims 1 to 3, characterized in that the drainage channel (13) or the drainage channels (13) are designed and arranged such that a lower water level is established in them than in the settling channel (5). 5. Longitudinal sand trap according to one or more of claims 1 to 4, characterized in that a ventilation device (21) is provided in particular in the end region of the settling channel (5). 6. Longitudinal sand trap according to claim 5, characterized in that the ventilation device (21) has several selectively operable sections. 7. Longitudinal sand trap according to one or more of claims 1 to 4, characterized in that in the settling channel (5), in particular in the flow direction after, before or at the transition cross-section (15) to the drainage channel (13), internals (12) which slow down the flow are provided. 8. Longitudinal sand trap according to claim 7, characterized in that several plates (28) arranged approximately parallel to one another and spaced apart from one another are provided as internals (12), which form a plate package with flow paths (29), and that the plates (28) are arranged one above the other in a vertical direction, at least partially overlapping one another, and in the flow direction according to arrow 11 in the settling channel (5) inclined downwards. 9. Longitudinal sand trap according to claim 8, characterized in that the downward inclination of the plates (28) in the direction of flow is greater than the sinking depth of the sediment without fittings. 10. Longitudinal sand trap according to claim 7 or 8, characterized in that the built-in elements (12) are variable metal sheets with an adjustable immersion depth in the settling channel (5). 11. Longitudinal sand trap according to one or more of claims 1 to 10, characterized in that the settling channel (5) has essentially only one inclined wall (23). 12. Longitudinal sand trap according to one or more of claims 1 to 3, characterized in that the drainage channel (13) has a different width over its height.