WO2004067863A1

WO2004067863A1 - Method and pump unit for the effective treatment of sewage in a transfer tank

Info

Publication number: WO2004067863A1
Application number: PCT/HU2004/000007
Authority: WO
Inventors: István DÁNYI; Zoltán DÁNYI
Original assignee: Intermediker Kft.
Priority date: 2003-01-31
Filing date: 2004-01-26
Publication date: 2004-08-12
Also published as: EP1608823A1; CN100378277C; HU227134B1; EG23788A; RS20050546A; HUP0300276D0; EP1608823B1; CN1745221A; RS50797B; HRP20050678A2; ATE359409T1; HUP0300276A2; HRP20050678B1; DE602004005841D1

Abstract

In performing the method according to the invention the sewage accumulating in the transfer tank is periodically drawn away and is, in given circumstances, stirred in such a manner that the sewage is guided into the pump horizontally or downward at an acute angle to the horizontal, and the periodic pumping is performed such that when the sewage level attains a height of 1-30 cm above the pump intake opening, the electric motor is operated at a reduced sewage throughput and when, in given circumstances, the sewage level intersects the intake opening and/or the pump impeller, the electric motor is operated without sewage throughput for ventilating the sewage advantageously for at least 3 seconds, but expediently for at least 10 seconds. Stirring is performed such that the sewage is, in a vortex coaxial with the rotary axis of the stirrer agitating the sewage, first accelerated toward the stirring element and then guided along the superficies thereof and is eventually ejected in a impulse-like manner. The pump unit (4) proper comprises an electric motor (5) and a pump (6) and is arranged in the transfer tank in such a manner that its rotary axis is horizontal or is oriented at an acute angle to the horizontal and the intake opening (7) of the pump (6) is at the top.

Description

METHOD AND PUMP UNIT FOR THE EFFECTIVE TREATMENT OF SEWAGE IN A TRANSFER TANK

The present invention relates to a method and a pump unit for effectively treating sewage in a transfer tank and is of the type in which the sewage accumulating in the tank is periodically drawn away and, in given circumstances, simultaneously stirred. The pump unit for performing the method comprises an electric motor, a pump and, in given circumstances, a stirrer.

It is known that the sewage, accumulating in collecting tanks or transfer units, is a multi-phase medium containing solid parts, liquid, as well as grease gathering on the surface of the liquid. The solid parts generally settle at the bottom of the tank as sludge, as well as lumpy and stringy substances. The lighter components, such as fats, oils or substances floating in the sewage rise to the surface and freeze or precipitate on the tank wall. The frozen and precipitated grease layer cannot be removed from the tank with the presently used pump units. Further, a significant proportion of the solid parts settles in the dead spaces. To avoid such occurrences, solutions have been found, according to which the sewage entering the tank is maintained in a continuous swirling motion. Such a method is described, for example, in German published patent application DE 35 20 359.

Installations have also been used in which the pump unit contains stirring elements generally in such a manner that a stirrer is affixed to the motor stub shaft which carries the pump impeller. Such constructions are described, among others, in the following patents: EP 0 110 562, US 3 973 866 and DE 2643537.

Providing the sewage-removing pump with a stirrer has numerous advantages; yet, the comminution of lumpy substances in the liquid and their forwarding by the pump, as well as the grease settling in the tank or accumulating on the liquid surface continue to pose a problem. In addition to a removal of the settled or floating grease layer it would further be desirable to fully stir over and remove the sludge layer at the bottom of the tank and also, to appropriately homogenize the sewage remaining in the tank and to ensure its ventilation. In conventional transfer arrangements the pumps are arranged in the tanks in such a manner that their axis is vertical, and their intake opening is located below, underneath the motor. Accordingly, the withdrawal of sewage can be effected only to such an extent as to prevent the motor from being situated in a prolonged manner above the liquid surface for avoiding the danger of burnout. Such a precaution, however, evidently renders impossible a uniform drawing and moving away of grease and a stirring of the sewage without advancing the same.

Recently pump units have already been used which have been capable of operating in a dry environment to a certain extent thus permitting a lowering of the liquid level down to the intake opening of the pump, making possible the removal of the grease layer to a certain extent. Even such a technology, however, has not been capable of homogenizing and ventilating the sewage remaining in the tank, and also, a removal of the grease layer and sludge that has settled in the dead spaces of the tank has not been perfect.

Accordingly, the object of the present invention is a solution which makes possible not only a systematic, complete removal of the grease layer and the sludge, but which also ensures, by means of an indirect comminution performed during stirring, a homogenization of the sewage dwelling in the tank and removed by the pump and further, after pumping, also effects a suitable ventilation of the sewage remaining in the tank.

The above object is achieved by a method according to which the sewage accumulating in the transfer tank is periodically pumped away and is, in given circumstances, stirred in such a manner that the sewage to be pumped is guided into the pump horizontally, or downward at an acute angle to the horizontal, and the periodic pumping is performed such that when the sewage level reaches a height of 1 - 30 cm above the level of the pump intake opening, the electric motor is operated for reduced sewage throughput, and in given circumstances, when the sewage level intersects the pump intake opening and/or the pump impeller, the electric motor is operated without or with reduced sewage throughput; in this manner the sewage is advantageously ventilated for at least 3 seconds, but expediently for at least for 10 seconds. The stirring is performed in such a manner that the sewage is accelerated first toward the stirring element in a vortex which is coaxial with the rotary axis of the stirrer, then guided along the superficies of the stirring element and eventually ejected in an impulse-like manner.

The ventilation is carried out such that the pump continues to run at the 5 time when, in addition to sewage, it also draws air, and when the sewage level has reached the pump intake opening and therefore no water throughput takes place at all, the revolving impeller vanes rotate the air and water together in the pump housing. The rotation of air and water, however, is not confined to the pump housing, but extends to the entire liquid quantity which has remained in 0 the tank and which is maintained in rotation by the stirrer in any event, resulting in an intensive ventilation of the liquid.

The pump unit may be controlled in several ways: the pumping and stirring may be carried out by switching on the pump unit when the sewage reaches a predetermined level or by switching on the pumping unit at 5 predetermined intervals, independently from the sewage level. Under given circumstances the two types of control may be combined.

The pump unit proper is formed of an electric motor and a pump and is disposed in the transfer tank such that its axis of rotation is horizontal or is at an acute angle to the horizontal, and the intake opening of the pump is at the top. o Expediently, the pump and the stirrer are located at opposite ends of the electric motor.

Expediently, the stirrer is a disk whose diameter decreases as its distance from the electric motor increases. The disk is provided with ribs, and its rim projects outward beyond the motor stator. The surface part of the disk 5 between said rim and the axis of rotation has preferably a concave or straight intersection line in axial section.

The solution according to the invention prevents a precipitation of grease on the tank wall and ensures a removal of the grease layer floating on the surface and the sludge settled in the tank. At the same time, the sewage is o homogenized by virtue of the stirring effect, and the air introduction prevents a decomposition of the sewage. In addition, the lumpy substances are disintegrated, that is, they are indirectly comminuted. For this purpose the stirrer accelerates and guides the solid parts, contained in the sewage, first toward the stirring element in a vortex coaxial with the rotary axis of the stirrer, then along the superficies of the stirring element and eventually ejects them in an impulselike manner. As a result, the pieces are exposed to sudden acceleration, deceleration and collision, causing their gradual disintegration. Accordingly, the sewage contained in the tank and transported by the pump is fully homogeneous, and no objectionable odor is generated in the tank, since the sewage is always stirred and ventilated and therefore constitutes a living, rather than a decomposing medium.

The pump disposed in the tank with an upward oriented intake opening may be operated with maximum safety, since it cannot draw the liquid from the motor, and, in this way, may also be operated without the danger of overheat even when no sewage enters the tank at all, that is, the ventilation and stirring may be performed simultaneously which also resolves the problem of night-time or other dead periods. Further details of the invention will be set forth below in conjunction with the drawing where

Figure 1 is a schematic view of a conventional transfer tank, Figure 2 is a schematic view of a transfer tank adapted to perform the method according to the invention, Figure 3 illustrates a structural, exemplary embodiment for performing the method according to the invention,

Figure 4 illustrates the operation of the stirrer incorporated in the pump unit,

Figure 5 depicts the pump unit at the beginning of air intake, and Figure 6 depicts the pump unit at stoppage of water throughput.

Turning to Figure 1 , floating switches 2 and 3 as well as a pump unit 4 are accommodated in a sewage transfer tank 1 in a conventional manner. The axially vertically disposed pump unit 4 comprises an electric motor 5 and a pump 6 situated therebelow.

During operation of the transfer tank 1 sewage is continuously entering the transfer tank 1 , and when the sewage level attains the switching level A of the floating switch 2, the electric motor 5 is energized and thus the pump 6 starts operating. The sewage level continuously drops until it reaches the switching level B of the floating switch 3, at which time the electric motor 5 is de-energized and pumping of sewage is interrupted until the sewage level again reaches the switching level A. In the transfer tank operated in such a manner the precipitated grease remains on the sewage surface and on the tank wall and needs to be removed manually at predetermined intervals. At the same time, the sludge deposit continuously grows at the bottom of the transfer tank 1 and upon exceeding a certain level it causes malfunctioning of the pump if, similarly to the grease layer, it is not removed at predetermined intervals.

The operation of the pump unit 4, however, is not optimal even if grease and sludge are removed, because the density of the sewage transported by the pump varies.

Furthermore, in case the sewage quantity increases slowly and thus its removal by the pump occurs relatively rarely, the sewage dwelling in the transfer tank 1 decomposes, it becomes increasingly more difficult to treat and generates an objectionable odor.

Attempts have been made to operate these systems by not allowing the sewage level to rise to the switching level B, but to the level C of the intake opening 7 of the pump 6. In this manner one part of the grease that has accumulated on the sewage surface may be drawn away. Such a method, however, cannot prevent a precipitation of grease on the tank walls, switches and other locations. The electric motor 5 cannot be operated for long periods without water cooling and it is still not capable of removing the sludge layer at the bottom; consequently, it requires almost as much maintenance as systems utilizing conventional technology.

Figure 2 schematically illustrates a transfer tank 1 which may be operated with the method according to the invention. The axis of rotation of the pump unit 4 is disposed at an acute angle to the horizontal, the pump intake opening 7 being on the top. As a result of such an arrangement the sewage is drawn downward into the housing of the pump 6 through the centrally located intake opening 7 at an acute angle to the horizontal. In this embodiment the pump unit 4 is provided with a stirrer 8 situated below the electric motor 5. With such an arrangement the system may be operated significantly more efficiently and flexibly than the conventional solutions.

In the embodiment shown in Figure 2 the floating switches 2 and 3, similarly to the conventional solution, are arranged at switching levels A and B. The floating switch 3, however, turns off the electric motor 5 with a delay, that is, the pump unit 4 continues to operate after the switching level B is reached, and when the switching level C is attained, the intake opening 7 of the pump 6 is capable of completely drawing away the grease layer floating on the liquid surface. At that time the pump 6 is still not de-energized, but as the electric motor 5 continues to rotate, the sewage whose level is at the intake opening 7, is ventilated, that is, liquid and air is driven by the pump impeller, several vanes of which already protrude beyond the water level. This operation is performed for at least 10 seconds, and only then is the pump 6 switched off. At the same time, the stirrer 8 situated underneath the pump unit 4 thoroughly stirs the sewage remaining at the bottom of the tank 1 , stirs over the deposited sludge and ventilates the entire sewage while moving and comminuting the stirred sludge and the lumpy pieces.

In view of the fact that in given circumstances the sewage quantity entering the transfer tank 1 may be very small, or such introduction occurs only after long intervals, the sewage at the bottom of the transfer tank 1 may start decomposing, and in addition, the precipitated grease layer may settle on the tank wall. In such cases it is therefore expedient to operate the pump unit 4 independently from the floating switches 2 and 3. Accordingly, the pump unit 4 is periodically started and the sewage is ventilated for a given period. In this manner the grease layer may be continuously removed, settling of sludge may be prevented and decomposition of sewage may be avoided.

With the method according to the invention the grease layer floating on the sewage surface may also be fully removed in a continuous manner and, accordingly, its settling on the tank wall may be prevented. Likewise, the settled sludge layer may be continuously removed, that is, a regular, periodic cleaning of the transfer tank is rendered superfluous.

The continuous operation of the stirrer results in a homogenization of the sewage: the solid pieces are gradually comminuted and the settled sludge is continuously stirred over. Simultaneously ventilation is effected, that is, the sewage remaining in the transfer tank is always fresh and thus decomposition and odor generation does not occur.

Both the pumped-out sewage and the sewage remaining in the tank are 5 homogeneous and they are of substantially permanent density. Further, the motor of the pump cannot run without being covered by the fluid (sewage) and thus can not remain without cooling; consequently it may be run with full operational safety, without the danger of overheat.

The technology according to the invention ensures that the transfer tanks 0 may be operated reliably for extended periods without human interference, and maintenance can be dispensed with for all practical purposes.

In the described embodiment a control of the pump unit 4 is effected by means of the floating switches 2 and 3. A control, however, does not necessarily need to be effected by floating switches; timing switches may be 5 used instead. In such a case the pump unit 4 is energized at predetermined intervals for drawing away sewage and after the pumping step it performs ventilation for a predetermined duration.

In situations where the sewage is highly polluted and/or the sewage accumulates only slowly, that is, the system is only rarely energized by the o floating switches, it is feasible to combine the floating switches with timing switches, that is, a pumping and ventilation are also effected at predetermined intervals, independently from the sewage level.

It is expedient to operate the system with a relatively small level difference to ensure that the tank wall always remains in a wet condition, and to 5 prevent the grease from drying. The frequent energizing and de-energizing due to the small level difference or a suitable setting of the timing switch also enhances the purification of the sewage and thus reduces the danger of decomposition. For this purpose it is expedient to start the pumping operation for a sewage level rise of maximum 50 cm in case of a tank having a diameter o smaller than 1 m and for a sewage level rise of maximum 1 m in case of a tank having a diameter larger than 1 m.

In the description which follows the invention will be further explained by way of examples. Example 1

A small-community sewage transfer system was prepared for a 6- apartment condominium. One 1.1 kW pump unit was disposed in the transfer tank of 1 m diameter. The rotary axis of the pump unit was oriented at 30° to the horizontal and control of the pump unit was effected by floating switches. Further, the system contained a timing switch that energized the pump unit every hour for one minute. This meant in practice that independently from the sewage level, every hour a ventilation for a duration of about 10-40 seconds occurred. During this operation ventilation without sewage pumping took place for a period of 15 seconds, and the level difference between switch-on and switch-off did not exceed 20 cm.

During the first six months the system was operated for testing purposes conventionally, only with floating switches and without delayed switch-off. During this period the settled sludge and grease layer had to be removed three times from the transfer tank, the quality of the pumped sewage and the sewage that remained in the tank fluctuated substantially, and on several occasions odor was noticeable.

After having converted the operation according to the method of the invention, the quality of the sewage was constant both in the transfer tank and in the system, decomposition and odor generation did not occur, and during the monitoring performed at regular intervals neither settled sludge nor precipitated grease layer were found.

Example 2 A sewage transfer arrangement was built for a community of a population of 8000. The diameter of the transfer tank was 2 m and it contained two 4 kW pumps each arranged at a 45° angle. The system was operated with timing switches. The pump unit was actuated every 30 minutes for 2 minutes, during which an approximately 100-second ventilation could be obtained, of which 70 seconds passed without sewage transport, and the level difference between switch-on and switch-off did not exceed 50 cm.

The operation of the system was, similarly to Example 1 , performed in two stages: in the first stage the operation was effected in a conventional manner, while in the second stage the method according to the invention was practiced. The findings were identical to those discussed in Example 1.

Example 3 A small town of 30,000 was provided with two sewage transfer systems.

One was operated according to the invention, while the other worked in a conventional manner. Each transfer tank had a dimension of 5 x 4 m and was provided with one 15 kW pump unit. Both transfer systems were operated with level control, with a level difference of 30 cm. In the system operated according to the invention, however, pumping was followed by a 7-minute ventilation at reduced water transportation. As a result, the highly satisfactory operation already described in Examples 1 and 2 was achieved.

Example 4 In a transfer tank of 2 m diameter two 5.5 kW pumps were disposed which were operated alternatingly with level control (with a level difference of 40 cm) and timed control (every 20 minutes), respectively. Pumping was followed by 45-second ventilations without water transportation. Again, the highly satisfactory results described in Examples 1 and 2 were obtained.

Example 5

Figure 3 illustrates an embodiment of the transfer tank and the pump unit for performing the method according to the invention as discussed in Example 1. The transfer tank 1 is a plastic pipe section to which a bottom plate 9 is welded and which is provided with a lid 10. The pump unit 4, formed of the pump 6 and the electric motor 5 provided with the stirrer 8, joins via a pressure pipe 11 the sewage removal pipe 12 which passes through the wall of the transfer tank 1. The stirrer 8 is affixed to the shaft of the motor 5 at its end remote from the pump 6. The pump unit 4 is oriented at 30° to the horizontal.

The stirrer 8 is a convex disk provided with ribs, as may observed in Figure 4. The liquid substance accumulating in the transfer tank 1 is a multiphase medium which contains solid parts (paper, rag fragments, etc.) as well as grease gathering on the liquid surface. The solid parts and sludge settle at the bottom of the tank, while the lighter components, including greasy or oily substances float to the surface and freeze, or precipitate on the tank wall. The comminution of lumpy pieces is effected indirectly with the 5 embodiment shown. Agitation is brought about by the high-speed flow which is generated by the stirring disk and which entrains the lumpy substances, forcing them frequently to the stirring disk, resulting in their disintegration as illustrated in Figure 4. Sewage purification is enhanced by the oxygen admission during stirring and comminution. The enlarged inset of Figure 4 shows that the stirrer 8 0 is a disk whose diameter decreases as its distance from the electric motor 5 increases. The stirrer 8 is provided with ribs 13 and has a rim 14 which projects from the stator 15 outward by Δ = 2 - 6 mm to ensure that the comminuted solid parts fly off the disk above the stator 15 rather than becoming jammed between the disk and the stator 15. 5 Figure 5 depicts the pump unit 4 of Figure 4 at a time when a vortex is generated in the sewage as a result of the pumping, and intake of air begins. Such an occurrence takes place when the sewage level arrives at a distance of 1 — 30 cm from the pump intake opening 7. Shortly thereafter the sewage level reaches, then intersects the intake opening 7 whereupon water transportation is o reduced or no longer occurs. Rather, the pump impeller first stirs the sewage within the pump housing and then exteriorly thereof and simultaneously provides for ventilation, as illustrated in Figure 6.

The same event takes place in case the pump unit 4 is in a horizontal orientation and the sewage level intersects not only the intake opening 7, but 5 also the vanes of the impeller 16.

It may be observed in the Figures that during pumping the sewage enters the pump housing through the intake opening 7 horizontally or downward, at an acute angle to the horizontal. This arrangement ensures that the electric motor 5 is always situated under the sewage level and that a stirring and ventilating o operation may be performed even if no water transportation takes place.

The solution discussed in the examples functions very reliably in practice and permits the realization of transfer systems which may be operated with a maximum efficiency at a minimum expense. The multi-function pump unit structured according to the invention is operated with a minimum of human interference in such a manner that maximum operational safety is achieved, the technology fits well into preexisting systems and satisfies widely varying requirements and technological expectations and is, furthermore, economical and energy-saving.

The stirrer used in the multi-function pump unit directs the sewage toward itself during rotation, while the lumpy pieces in the sewage receive an energy pulse as they reach the rotating unit and gradually disintegrate. Such a process continues in a circular flow until the size of the lumpy substances decreases, and the sewage becomes homogeneous. According to the invention stirring is also performed if no liquid transportation takes place; in this manner a ventilation of the sewage also occurs simultaneously. The stirring of the sewage is always performed underneath the pumping, so that substances which may endanger the pump unit cannot gain access to the pump. The method enhances the operationally safe functioning of the transfer tanks in several aspects: The power requirement for the comminution is reduced, the processes develop in a more gentle manner, the technology is insensitive to wear-causing substances to thus contribute to a significant increase of the expected service life. The sewage transportation from above ensures that the danger of jamming or clogging of the pump is reduced to a minimum and, at the same time, the possibility of a dry run of the pump is excluded. Consequently, by utilizing the inventive technology, the pump units function with an excellent operational safety.

It is to be understood that the invention may be practiced within the scope of the claims differently from the examples described. The technology may be utilized, for example, without stirring (in case the pump unit does not include a stirrer), in which case homogenization will be less effective, but grease removal and ventilation are effected to their full extent. Further, the pump unit may also be oriented horizontally, but the efficiency of the system would again not attain that of the solution described by way of example.

In recapitulation, most important of the basic advantages of the solution according to the invention are a reduction of the need of human interference to a minimum, as well as the possibilities of maintaining the sewage fresh when stored or transported, of skimming off homogeneous and rising substances, and of avoiding settling and adherence of grease and other substances. Furthermore, stirring and ventilation may be performed at regular intervals independently from the arrival of sewage into the transfer tank.

Claims

1) A method of effectively treating sewage in a transfer tank by means of a pump and/or stirrer, during which the sewage accumulating in the transfer tank is periodically drawn away and in given circumstances stirred, characterized in that

- the sewage to be drawn away is guided into the pump horizontally or in a downward direction at an acute angle to the horizontal, and the periodic sewage withdrawal is performed such that when the sewage level attains a height of about 1-30 cm above the intake opening of the pump, the electric motor continues to run at a reduced sewage throughput and in given circumstances when the sewage level intersects the intake opening and/or the pump impeller, the electric motor continues to run without water throughput for ventilating the sewage; - the stirring is performed in such a manner that the sewage is, in a vortex coaxial with the rotary axis of the stirrer, accelerated first toward the stirrer element and then along the superficies thereof, and is eventually ejected in an impulse-like manner.

2) The method as defined in claim 1 , characterized in that ventilation is performed for at least 3 seconds.

3) The method as defined in claim 1 , characterized in that ventilation is performed for at least 10 seconds.

4) The method as defined in claim 1 , characterized in that ventilation is performed for at least 10 minutes.

5) The method as defined in any one of claims 1-4, characterized in that stirring is performed simultaneously with pumping and ventilation.

6) The method as defined in any one of claims 1-5, characterized in that the pump unit is switched on at a predetermined sewage level.

7) The method as defined in claim 6, characterized in that pumping is initiated at a sewage level increase of maximum 50 cm in case of a tank having a diameter of less than 1 m, and is initiated at a sewage level increase of maximum 1 m in case of a tank having a diameter of more than 1 m.

8) The method as defined in any one of claims 1-5, characterized in that the pump unit is actuated at predetermined intervals independently from the sewage level.

9) The method as defined in any one of claims 1-5, characterized in that the pump unit is actuated at a predetermined sewage level and also at predetermined intervals independently from the sewage level.

10) A pump unit comprising an electric motor and a pump for performing the method in a transfer tank as defined in any one of claims 1-7, characterized in that the pump unit is disposed in the transfer tank (1) such that its axis of rotation is horizontal or is oriented at an acute angle to the horizontal, and the intake opening (7) of the pump (6) is at the top.

11) The pump unit as defined in claim 10, characterized in that the pump 6 is situated at one end of the electric motor 5 of the pump unit 4 and a stirrer 8 is disposed at the other end thereof.

12) The pump unit as defined in claim 11 , characterized in that the stirrer

(8) is a disk whose diameter decreases as its distance from the electric motor increases; the disk has ribs and a rim which projects outwardly from the motor stator.

13) The pump unit as defined in claim 12, characterized in that the radially oriented section of the disk surface is concave. 14) The pump unit as defined in claim 12, characterized in that the radially oriented section of the disk surface is straight.