GB2388796A

GB2388796A - Scum removing apparatus

Info

Publication number: GB2388796A
Application number: GB0212057A
Authority: GB
Inventors: Stephen W Taylor; Michael Ritson
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-05-24
Filing date: 2002-05-24
Publication date: 2003-11-26
Also published as: GB0212057D0

Abstract

An apparatus for removing scum from the surface of fluid in a tank comprises a scum receiving container (28) having a scum inlet (30), means for sensing (62) the level of fluid and means for moving (42) the inlet in response thereto. The scum inlet is preferably moved by rotation of the container, which may be cylindrical, about a horizontal axis actuated by a cable (42) moved either by a linear actuator or a motor driven pulley. A hydraulic pressure measurement device (62) may be used to sense the level of the fluid. Ideally, a computer (50) drives an actuator to adjust the orientation of the container in response to the level of the fluid and preferably holds the inlet opening at a preset height relative to the surface of the container and for a preset period according to the volume flow rate of fluid into the tank or the amount of scum on the surface. The apparatus is ideal for use in a sewage treatment works for receiving the scum collected by a scraper assembly. A bearing assembly is also disclosed which supports at least part of a bridge scraper unit in a sewage tank.

Description

( IMPROVEMENTS TO SCUM REMOVAL APPARATUS

TECHNI CAL F I ELD

This invention relates to improvements to scum S removal apparatus and particularly, although not exclusively, relates to an improved scum box and associated control equipment for removing scum from the surface of a fluid in a tank and an improved centre bearing which supports a rotating scraper assembly.

BAC KGR OVID O F I VENT I ON

In conventional sewage treatment works, tanks are used to separate sewage into solid and liciuid components. The solid component settles to the bottom 15 of the tank and is removed from an outlet in a central region of the tank and scum rises to the surface of the liquid component and is skimmed into a scum collection box situated in a fixed position on the tank periphery at a level consistent with a mean or average of the 20 tank TWL (Top Water Level).

The ideal position of the mouth of the scum collection box, relative to influent level in the tank, is determined and set during commissioning of the scum removal equipment. In practice this has averaged out 25 at approximately lOmm below the surface level of the de-solidified influent (and below the scum layer).

The scraper assembly is mounted on the tank and is supported at one end on a central bearing and on the other end on a powered carriage which drives itself 30 around a track encircling the tank.

The scraper assembly provides the dual function of directing solids into a central region of the tank and

directing scum to the edge of the tank. A striker or mechanical actuator, usually comprising a horizontal striker bar or sometimes a fixed roller, is fixed to and below the main structure of the scarper assembly.

5 As the rotating scraper assembly passes over the scum collection box the striker or mechanical actuator arm engages with a scum collection box operating lever and so for a minute or two the scum collection box actually receives scum skimmed from the top of influent in the 10 tank assuming the angle of attack of the mouth of the scum collection box is correctly aligned with the level of influent in the tank.

It will be appreciated that in certain circumstances it is difficult to regulate accurately 15 the fluid level in the tank' Consequently, if the influent level in the tank is low then scum cannot enter the scum collection box and conversely when the influent level in the tank is high "bottom scum level" is above the mouth of the scum collection box. In this 20 case the scum collection box just takes in de solidified effluent (which is returned to an earlier stage of the treatment process and which is detrimental to that process) whilst the scum remains on the surface above the mouth of the scum collection box.

25 Alternatively, if the level is between those two previous levels then invariable the scum chokes the mouth of the scum collection box and thus once again prevents any ingress of scum.

An alternative scum removal system comprises a 30 scum collection box that incorporates a "ramp" at its leading edge. Mounted on and below the bridge scraper is a "scoop" device which on approach to the scum

( collection box rides up the ramp. As the scoop passes over the open top of the scum collection box so scum is deposited in the scum collection box. Once again the "period of operation" is very short, usually a maximum 5 of one half of one minute, and because the scum collection box is at a fixed level within the tank then it necessarily follows that a varying level of influent will greatly reduce its efficiency i.e. the amount of scum removed per bridge scraper revolution.

10 The major factors to be considered when determining maximum efficiency for scum removal are: (a) The design of tank relative to the position of the scum removal system collection box assembly (at tank periphery) relative to 15 prevailing wind direction i.e. such that the wind will assist scum movement across the surface of the influent toward the outer extremities of the tank where the scum collection box is located.

(b) The width and length of the mouth of the scum collection box. Obviously, the longer and wider the better, however this maxim is limited because (i) if the scum collection 25 box is of uniform cylindrical construction it has to be installed longitudinally upon the outside circumference of the tank and (ii) the width of the mouth must be designed such that the aperture accepts the maximum depth 30 of scum while at the same time excludes ingress of de-solidified influent.

( (c) The level, within the tank, of the leading edge of the mouth of the scum collection box relative to the surface of the de-solidified influent, below the scum layer, such that the 5 surface tension of the influent assists the movement of scum into the mouth of the scum collection box rather than scum ingress being purely a function of gravity, i.e. the scum collection box is seen to "draw" the scum 10 into its mouth.

(d) The "open" time of the mouth of the scum box.

The longer that the mouth of the scum collection box is aligned ac the correct 15 level (see (c) above) the more scum will be collected and removed from the tank.

STATEMENTS OF INVENTION

With these factors in mind, according to a first 20 aspect of the present invention there is provided -apparatus for removing scum from the surface of fluid in a tank, the apparatus comprising: a container defining a scum receiving chamber, the container having a scum inlet; 25 means for sensing the level of the fluid in the tank; and means for moving the scum inlet into a desired position and/or orientation dependent on the level of the fluid in the tank.

30 Preferably, the means for moving the scum inlet comprises means for rotating the container about a substantially horizontal rotational axis.

( 5 Preferably, the means for rotating the container comprises a cable which is attached to the container at a position displaced from the rotational axis of the container. Preferably, the cable is moved by a linear 5 actuator. Alternatively, the cable may be wound onto a motor driven pulley.

Preferably, the apparatus further comprises a computer which receives input indicative of the fluid level in the tank and drives the linear actuator or 10 pulley motor to adjust the rotational orientation of the container. Preferably, a plurality of alternative cable attachment points are provided on the container, the said attachment points preferably being spaced apart in a substantially radially direction relative to 15 the rotational axis of the container. Preferably, the container is substantially cylindrical. Preferably, the container inlet comprises an elongate opening and the lower edge of the inlet opening is substantially parallel to the rotational axis of the container.

20 Preferably, the means for measuring fluid level in -the tank comprises a hydraulic pressure measurement device and most preferably comprises a pressure transducer. Preferably, the computer controls the rotational 25 position of the container, so that the inlet opening is held at a preset height relative to the surface of the container. Preferably, the computer keeps the inlet opening at the said predetermined height for a predetermined period. Preferably, the predetermined 30 period is adjusted in response to specific parameters such as changes in the volume flow rate into the tank or the amount of scum on the surface of the fluid.

( 6 Embodiments in accordance with the present invention provide accurate positioning of the mouth of the scum collection box relative to influent level in the tank, thereby ensuring a maximum scum volume is 5 removed from the influent surface for the maximum amount of time (the period of operation is variable, via the computer, and can be set relative to the rate of scum generation which is directly related to the volume of flow through the tank and the chemical makeup 10 of the influence.

Conventional solid separation tanks of the above described type are in continuous operation and draining the tank is time consuming and requires the provision of redundant capacity so that sewage can be diverted 15 elsewhere whilst the tank is serviced. In conventional tanks, replacement of the central bearing which supports the scraper assembly requires that the tank is shut down and drained, so that service personnel can gain access to the bearing from within the tank. This 20 procedure is not only expensive and time consuming but Also is unpleasant for the service personnel.

Conventional scraper assemblies may comprise half bridge scrapers which are supported at the centre of the tank by means of a "tripod" leg assembly on top of 25 which is a support plate. A "split case" bearing, installed in compression mode, is fixed to that plate.

The underside of the half bridge scraper assembly is then in turn fixed to the upper half of the split case bearing. The support plate and the half bridge scraper 30 assembly are normally fixed to the bottom and top halves of the split case bearing respectively by means of nuts and bolts with washers. The split case bearing

( 7 supports all of the inboard weight of the half bridge scraper (that portion of weight imposed on the centre of the tank).

To replace or maintain the split case bearing in a 5 conventionally constructed half bridge scraper it is first usually necessary to drain and clean the tank, then (utilizing jacks externally applied between the floor of the tank (on pads) and the half bridge scraper main bridge assembly) to jack up the main bridge 10 assembly, so as to remove its weight from the split case bearing. Once the weight has been removed then the split case bearing can be split e.g. to replace its roller bearings or to examine the race. To replace the complete split case bearing it is first necessary to 15 undo and remove the nuts, bolts and washers securing both halves of the bearing On conventional half bridge scrapers this also necessitates draining and cleaning the tank, jacking up the half bridge scraper main assembly and assembling scaffold to effect access 20 to the bearing assembly One should also note that in -a conventional half bridge scraper the centre bearing assembly design embodies considerable access problems.

Although a section of half bridge scraper walkway floor can be removed to facilitate access to the centre 25 bearing assembly access is by no means easy. The reason for this is two fold in that (i) a slip ring assembly (transmitting electrical power to the bridge scraper assembly) is also fixed directly above the centre bearing assembly and (ii) the half bridge 30 scraper main assembly is normally attached to the split case bearing via a plate attached to the underside of the half bridge scraper. Access to the centre bearing

f assembly is very restricted by the half bridge scraper main assembly spars. N.B. in the case of half bridge scrapers constructed with the utilization of channel sections, access of underside nuts is greatly 5 restricted by the sides of the channel sections.

According to a second aspect of the present invention, there is provided a bearing assembly which supports at least part of the weight of a rotatable structure and is fixed to a support, a jack being 10 provided to act between the support and the rotatable structure and being fixed to the support or the rotatable structure. By bringing the rotatable structure to rest and by operating the jack, the weight of the rotatable structure can be lifted from the 15 bearing assembly. The bearing assembly can then be at least partially disassembled.

Preferably, the jack is fixed permanently to the rotatable structure and can be disengaged from the support, so that the rotatable structure is free to 20 rotate relative to the support.

- Preferably, a plurality of jacks are provided between the support and the rotatable structure.

Preferably the jacks are spaced equidistantly around the rotational axis of the bearing assembly.

25 Preferably, the rotatable structure comprises a bridge scraper unit in a sewage tank, the bridge scraper unit having at least one removable deck panel which provides access to the bearing assembly.

3 0 BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how it may be carried into

f g effect, reference will now be made by way of example, to the accompanying drawings in which: Figure 1 is a plan view of solids separation tank in accordance with the present invention; 5 Figure 2 is a cross-section through the tank and half bridge scraper assembly of Figure 1; Figure 3 is a cross-section through a side wall of the tank in the vicinity of a scum box and associated control equipment; 10 Figure 4 is a front view of the scum box and operating cable; Figure 5 is an enlarged view of an end of the scum box; Figure 6 shows a linear actuator which extends and 15 retracts the scum box cable; Figure 7 is an enlarged partially cut away view of a centre bearing assembly; and Figure 8 is a cross-section through the centre bearing assembly and half bridge scraper assembly.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Figures 1 and 2 show a solids separation tank 2 with scum removal apparatus 4 in accordance with the present invention. As best seen in Figure 2, the tank 25 2 is substantially funnel-shaped and includes a sloping base 6 which directs solids which settle in the tank towards a central outlet region 8.

The scum removal apparatus 4 comprises a half bridge scraper assembly 10 having a walkway 12 and 30 infilled hand rails 14. The half bridge scraper assembly 10 is supported at one end on a powered carriage (not shown) which travels on an annular rail

( 16 outside the tank 2. At the opposite end, the half bridge scraper assembly 10 is supported on a central bearing assembly 18 which is connected to the base 6 of the tank 2 by means of tripod legs 20.

Hoistable blade assemblies 22 are fixed to the underside of the half bridge scraper assembly 10 and engage the sloping base 6 of the tank 2. A stainless steel scum skimmer blade 24 is fixed to the half bridge scraper assembly 10 such that the blade skims the 10 surface of the fluid in the tank 2. The skimmer blade 24 directs scum from the surface of the fluid in the tank into a rotatable scum box 26 which is fixed to an edge of the tank 2.

In operation, the half bridge scraper assembly 10 15 rotates slowly around the tank 2. As the half bridge scraper assembly 10 sweeps the tank 2, the blade assemblies 22 scrape the sloping base 6 of the tank 2 and direct the solids which have settled in the tank into the central outlet region 8 of the tank. At the 20 same time, the skimmer blade 24 directs scum from the -surface of the tank radially outwardly, and as it passes the scum box 26, scum is deposited from the skimmer blade 24 into the scum box 26.

Figures 3 and 4 show the detailed construction of 25 the scum box 26 and associated control equipment. More specifically, the scum box 26 comprises a cylindrical container 28 having a mouth 30, the lower edge 32 of which is parallel to a rotational axis XX of the scum box 26. A fluid outlet 29 from the box is fitted with 30 an outlet bellows 31 to facilitate easier turning of the scum box 26. The scum box 26 is pivotally mounted to a wall 34 of the tank 2 by means of bolted on

brackets 36, 38. The scum box 26 is mounted to the brackets 36, 38 by means of stub axles 39, which project from opposite ends of the scum box 26 along the rotational axis XX. An outer sheath 40 of a push/pull 5 cable assembly 42 is connected to bracket 36 and the cable 44 of the push/pull cable assembly 42 is connected to an end 46 of the scum box 26.

Figure 5 is an enlarged view of the end 46 of the scum box 26 and illustrates that the cable 44 may be 10 connected to the scum box through any one of a number of openings 48 formed in the end 46 of the scum box 26 at radially spaced apart positions. Thus the range of adjustment of the rotational position of the scum box 26 can be altered depending on which opening 48 is 15 selected.

The push/pull cable assembly 42 terminates at a position remote from the scum box 26 in a control assembly 50 as best shown in Figures 3 and 6. The outer sheath 40 of the pushjpull cable assembly 42 is 20 secured to a housing 52 of the control assembly 50 and The cable 44 is connected to a linear actuator 54 driven by an actuating motor 56.

A fluid passage 58 is formed through the wall 34 of the tank 2 and is directed upwardly towards the 25 control assembly 50 to form a fluid level indicator passage 60 in which is mounted a pressure transducer 62. In operation, the control assembly 50 is supplied continuously with data from the pressure transducer 62 30 indicative of the fluid level in the tank 2. In response to this data a CPU of the control assembly 50

( calculates the rotational angle of the scum box which is appropriate to the fluid level in the tank 2.

The control assembly SO also receives input from a bridge sensor 64. This sends an electrical pulse to 5 the CPU of the control assembly 50 when the half bridge scraper assembly 10 passes. In response, the control assembly 50 activates the motor 56 of the linear actuator 54, causing the cable to be extended thereby rotating the mouth 30 of the scum box 26 towards the 10 surface of the fluid in the tank 2. With the mouth 30 of the scum box 26 in the "open" position, scum which has been scraped off the surface of the fluid by the scum skimmer blade 24 is pushed into the scum box 26 and is ejected through the bellows 31 of the scum box 15 outlet 29. When the bridge sensor 64 senses that the half bridge scraper assembly 10 has passed, the mouth 30 of the scum box 26 is again rotated upwardly away from the surface of the fluid in the tank 2, avoiding loss of fluid from the tank 2 through the scum box 26.

20 Means may be provided for adjusting the "open" period -of the scum box 26, for example, to account for different rates of build up of scum in the tank 2.

Figures 7 and 8 show enlarged views of the central bearing assembly 18 and associated components. The 25 central bearing assembly 18 comprises a ball bearing 100 having an outer race in the form of a stewing ring 104 and an inner race 88 which is bolted to a bearing back plate 123. The stewing ring 104 is bolted to a bearing support plate 105 which is connected to the 30 half bridge scraper assembly 10 by pinned connections 101. The inner race 88 is provided with an annular flange 90 which engages over a top plate 92 of a main

support tube 103. The main support tube 103 is bolted to a tripod top plate 102 of the tripod legs 20. with this arrangement, the weight of the inner end of the half bridge scraper assembly lO is supported, via the 5 central bearing assembly 18 and tripod legs 20, on the base of the tank 2.

Threaded openings 94, 95 are formed in lower members 96, 97 of the half bridge scraper assembly 10.

These threaded openings 94, 95 receive threaded shafts 10 98 of respective jacks 99. Each jack 99 is provided with an articulated foot 121 and a jack drive bar 116.

During a servicing or repair operation, the half bridge scraper assembly 10 is brought to rest and by operation of the jack drive bar 116, the threaded shaft 15 98 of each jack 99 is threaded down until the articulated foot 121 engages a centring plate 122 located over the tripod top plate 102. It will be appreciated that continued operation of the jacks will lift the half bridge scraper assembly 10 away from the 20 tripod top plate 102 and thereby remove the load from The central bearing assembly 18. With the load thus removed, the central bearing assembly 18 can be disassembled for service or repair.

Referring to Figure 7, to facilitate servicing, 25 floor sections 125 located above the central bearing assembly 18 are removable and the jack drive bars 116 are extended up through the floor of the half bridge scraper assembly 10. Consequently, load can be removed from the central bearing assembly 18 and the necessary 30 servicing or repair work can be carried out from the walkway 12 of the half bridge scraper unit 10. It is therefore unnecessary to drain the tank to gain access,

( so there are considerable time, cost and operational advantages over conventional systems.

Once the repair has been completed, and the central bearing assembly 18 has been reassembled, the 5 jacks 99 can be wound up, so that the articulated feet 121 cease to contact the centring plate 122. Load from the half bridge scraper assembly 10 is again transmitted through the central bearing assembly 18 and the half bridge scraper assembly 10 is able to rotate 10 normally.

The number and disposition of the jacks 99 around the rotational axis of the half bridge scraper assembly 10 can be varied depending on the imposed load and operational conditions. In the simplest arrangement it 15 may be possible to use only a single jack 99, but for improved stability, four jacks 99 spaced equidistantly about the rotational axis of the half bridge scraper assembly 10 is considered preferable.

Claims

1. Apparatus for removing scum from the surface of fluid in a tank, the apparatus comprising: 5 a container defining a scum receiving chamber, the container having a scum inlet; means for sensing the level of the fluid in the tank; and means for moving the scum inlet into a desired 10 position and/or orientation dependent on the level of the fluid in the tank.

2. Apparatus as claimed in claim l, in which the means for moving the scum inlet comprises means for 15 rotating the container about a substantially horizontal axis.

3. Apparatus as claimed in claim 2, in which the means for rotating the container comprises a cable 20 which is attached to the container at a position displaced from the rotational axis of the container.

4. Apparatus as claimed in claim 3, in which the cable is moved by a linear actuator.

5. Apparatus as claimed in claim 3, in which the cable is wound onto a motor driven pulley.

-

6. Apparatus as claimed in claim 3, in which a 30 plurality of alternative cable attachment points are provided on the container.

7. Apparatus as claimed in any one of the preceding claims, in which the container is substantially cylindrical.

5

8. Apparatus as claimed in any one of the preceding claims, in which the container inlet comprises an elongate opening and the lower edge of the opening is substantially parallel to the rotational axis of the container.

9 Apparatus as claimed in any one of the preceding claims, in which the means for measuring fluid level in the tank comprises an hydraulic pressure measurement device.

10. Apparatus as claimed in any one of the preceding claims, further comprising a computer which receives input indicative of the fluid level in the tank and controls an actuator to adjust the rotational 20 orientation of the container.

11. Apparatus as claimed in claim 10, in which the computer controls the rotational position of the container, so that the inlet openlug is held at a 25 preset height relative to the surface of the container.

12. Apparatus as claimed in claim ll, in which the computer controls the rotational position of the container such that the inlet opening of the container 30 is held at the said predetermined height for a predetermined period.

(

13. Apparatus as claimed in claim 12, in which the predetermined period is adjusted in response to the volume flow rate of fluid into the tank or the amount of scum on the surface of the fluid.

14. A bearing assembly which supports at least part of the weight of a rotatable structure and is fixed to a support, a jack being provided to act between the support and the rotatable structure and 10 being fixed to the support or the rotatable structure.

15. A bearing assembly as claimed in claim 14, in which the jack is fixed permanently to the rotatable structure.

16. A bearing assembly as claimed in claim 14 or 15, in which the jack can be disengaged from the support, so that the rotatable structure is free to rotate relative to the support.

17. A bearing assembly as claimed in any one of claims 13 to 15, in which a plurality jacks are provided between the support and the rotatable structure.

18. A bearing assembly as claimed in claim 17, which the jacks are spaced equidistantly around the rotational axis of the bearing assembly.

30

19. A bearing assembly as claimed in any one of claims 14 to 18, in which the rotatable structure comprises a bridge scraper unit and a sewage tank.

(

20. A bearing assembly as claimed in claim 19, in which the bridge scraper unit has at least one removable deck panel which provides access to the 5 bearing assembly.

21. An apparatus substantially as described herein with reference to and as shown in the accompanying drawings.