GB2366218A

GB2366218A - Floating mixer for sewage treatment

Info

Publication number: GB2366218A
Application number: GB0119006A
Authority: GB
Inventors: Seamus Bradley
Original assignee: CROSSLAND TANKERS Ltd
Current assignee: CROSSLAND TANKERS Ltd
Priority date: 2000-08-04
Filing date: 2001-08-03
Publication date: 2002-03-06
Anticipated expiration: 2021-08-03
Also published as: GB2366218B; IE20010742A1; GB0019134D0; GB0119006D0

Abstract

A mixing device 10 has a buoyant body 12 adapted to support the device on a liquid such as a large scale lagoon or sewage treatment plant.. The body can have sealed gas reservoirs 14, 16 in order to aid buoyancy. The device also has a mixer which can be in the form of impeller 36 powered by impeller motor 38 and which is locatable at least partially within the liquid so as to mix the liquid and prevent solid matter from sinking down and being deposited on the base of the lagoon. Impeller rams 37 can be provided to maintain impeller 36 in the liquid. The device may also include a second drive source which can be a motor contained in motor housing 24 which is capable of manoeuvring the device about the surface of the liquid by means of paddles 30, 32, 34 or propellers (not shown). The device can be remotely controllable, and capable of being refuelled while afloat.

Description

<Desc/Clms Page number 1> A MIXING DEVICE The present invention concerns a mixing device, and in particular a mixing device for use with large scale lagoons or sewage treatment plants.

At present there exists a problem with large scale sewage treatment works or lagoons into which is pumped any solution, such as sewage or the like, which includes a component of solid matter. After a short time settlement of the solid matter occurs, and thus is deposited on the base of the lagoon. As a result of said settlement, only the liquid component may be drawn from the lagoon for processing, leaving the solid matter deposited on the base, which solid matter over time builds up, thereby reducing the effective volume of the lagoon. Furthermore, the build up of solid matter will eventually require expensive and time consuming excavation, resulting in a significant down time which may be unacceptable for certain applications, particularly in sewage treatment plants. The only known means to alleviate the above-mentioned problem is to carry out mixing of the contents of the lagoon or sewage treatment plant by using a tractor mounted mixer. However, such tractor mounted mixers suffer a number of drawbacks. The main shortcoming of such mixers is their limited reach, governed as it is by the length of an articulated arm extending from the tractor, the tractor itself being confined to the bank of the lagoon. The maximum reach generally obtainable with such tractor mounted mixers is approximately five

meters from the bank of the lagoon. It will therefore be appreciated that, for large lagoons, such limited reach will render the mixer a11 but ineffective.

A further drawback with tractor mounted mixers, is that the tractor must be able to traverse the entire perimeter of the lagoon in order to be able to extend the mixer into the lagoon. Therefore, any bank-side obstacles such as trees, buildings, fencing or the like, prevent access to the bank of the lagoon, and thus the ability to mix the contents of the lagoon at that particular location.

It is therefore an object of the present invention to provide a mixing device which is capable of effecting mixing across the entire surface area of any given volume of liquid.

According to the present invention there is provided a mixing device for dispersing solid matter in a volume of liquid, the mixing device comprising a mixer adapted to float on or in the volume of liquid and locatable, in use, at least partially within the volume of liquid; and a first drive source capable, in use, of effecting actuation of the mixer.

Preferably, a second drive source is provided to manoeuvre the device about the surface of the volume of liquid. Alternatively, the device may be manually manoeuvred about the surface of the volume of liquid, by an operator.

More preferably, the first drive source is/are supported on a body, the body being adapted to float on or in the volume of liquid.

Preferably, the body includes at least one gas reservoir, to permit the device to float on or in the volume of liquid.

Preferably, the mixer is an impeller, the impeller extending from the body.

Preferably, the first drive source is a motor in operative association with the mixer. Preferably, the second drive source comprises a plurality of propellers located, in use, at least partially within the volume of liquid and distributed about device.

Preferably, the device may be remotely controlled. Alternatively, the device may be programmed for automated operation.

Preferably, the device may be refuelled while afloat. More preferably, the device includes a refuelling arm in operative association with the body, the refuelling arm being extendible, in use, away from the device such as to facilitate refuelling while the device is afloat.

Preferably, the device includes a retractable access ramp mounted to the body, such as to permit access to the device while afloat.

Preferably, the second drive source is powered by an internal combustion engine, the device further including sound proofing surrounding the engine to permit use of the device in areas having regulated noise pollution levels.

The present invention will now be described with reference to the accompanying drawings, in which; Figure 1 illustrates a side elevation of the device according to the present invention, showing the, in use, orientation of an impeller to permit mixing of a body of liquid ; Figure 2 illustrates a plan view of the device of Figure 1; and Figure 3 illustrates an end view of the device of Figure 1, showing an access ramp thereof extended to permit access to the device.

Referring now to the accompanying drawings, there is illustrated a mixing device, generally indicated as 10, for dispersing solid matter in a volume of liquid. In particular, it is envisaged that the device 10 be used for mixing the solid matter of substantially large lagoons or similar liquid storage facilities, with it's liquid content. The device 10 is intended to float on or in the volume of liquid while simultaneously mixing

the volume of liquid to maintain a substantially uniform dispersion. The device 10 must therefore be capable of floating on or in any volume of liquid with which the device 10 is to be used. In this regard, the device 10 incorporates a buoyant body 12 capable of floating on or in the volume of liquid, and, thereby, supporting the device 10. The body 12 comprises a first tank 14 and a second tank 16, in substantially parallel spaced relation and connected by means of a first cross member 18 and a second cross member 20.

The first tank 14 and the second tank 16 are hermetically sealed and contain a pressurised gas, preferably air, the pressure of which may be varied to suit the relative density of the liquid in question. The body 12 further includes a platform 22 extending between the first and second tanks 14, 16 and between the first and second cross members 18, 20.

The following calculation was undertaken in order to determine the total weight that the first tank 14 and the second tank 16 were capable, in use, of supporting. Volume displaced by barrels: Volume = 7LR2H 7t (0 . 4775 2 3.750 Volume displaced in water = 2686 L in water = 2686kg Weight of each barrel: Circumference = 7cD = 7t0.995 = 3m

Length of each barrel = 5m Thickness of wall of each barrel = 3mm Density of stainless steel for each barrel = 8500kg/m3 Weight of each barrel = 3m x 5m x 8500kg/m3 x 0.003m = 382.5kg 2 barrels weigh 765kg Weight of each cross tube: Circumference = nD = n 0.45 = 1.42m Length of each cross tube = 1.62m Weight of each tube = 1.42m x 1.62 x 8500kg/m3 x 0.003m = 58.7kg 2 cross tubes weigh 117.4kg total material weight - 882.4kg Weight which can be carried 2686 X 2 - 882.4 = 4489.6kg Approximation of weight to be carried : 2183kg Thus leaving a 2306.6kg margin = 51.4% of the maximum weight to be carried.

It will of course be appreciated that, in place of the first and second tanks 14, 16, any suitable alternative may be used which provides sufficient buoyancy in order to support the device 10 on or in any given liquid.

Examples of suitable equivalents would be a solid or hollow base (not shown), formed from plastics, wood or the like, whose density is sufficiently low as to render the base (not shown) buoyant. The device 10 could also be supplied with a suitably shaped and dimensioned hull (not shown) of conventional form, in order to support the device 10 on the surface of a liquid. As a further alternative, the device 10 could be provided with a "hovercraft" type base (not shown) which, due to the expulsion of air therefrom, would aid in the process of mixing the liquid.

The device 10 utilises a mixer in the form of an impeller 36 to agitate the liquid such as to mix the liquid into a substantially homogeneous state. The impeller 36 is driven, via a shaft 40, by a first drive source in the form of an impeller motor 38. The impeller motor 38 is mounted to the first cross member 18, via a boom 35 which is pivotally mounted to the first cross member 18, such as to enable the impeller 36 to be entered into and withdrawn from the liquid as is necessary. It will be appreciated that, in use, the impeller 36 will produce a substantial upward thrust. As the boom 35 is freely pivotable about the first cross member 18, this upward thrust will act to raise the impeller 36 from the liquid. Therefore, in order to counteract this effect, the device 10 is provided with a pair hydraulic impeller rams 37 mounted between the first cross member 18 and the boom 35. Once the impeller 36 has been lowered into the volume of liquid, a force is applied to the boom 35 via the impeller ram 37, said force being equal and opposite to the upward

thrust generated by the impeller 36, such as to prevent the impeller 36 from raising from the liquid.

As the impeller rams 37 are powered by a supply of pressurised hydraulic fluid, the internal diameter bore of each impeller ram 37 must be chosen such that, at the operating pressure of the hydraulic fluid, the impeller rams 37 are capable of producing sufficient force to prevent the impeller 36 from raising from the volume of liquid. The following calculations were undertaken in this regard.

Upward thrust at 600rpm i.e. max running speed = 15000 N.

Moments about main pivot: 278 x f = 990 x 15000 f = 990 x 15000/278 f = 53417 N This is the force at the line of action i.e. perpendicular to the shaft 40. The force therefore at some angle to this must be greater. To find this force the angle to which the impeller rams 37 are to sit must be known. Thus, for an angle of 19.43 : Angle = 19.43 Cos-1 19.43 = 53417/A A = 56642.9 N Finding the area required on the cylinder piston. A = F/P

The hydraulic fluid is at a pressure of 1800psi. .'.Pressure = 1800psi Which is 12410568 n/m2 .'. A = 56642.9/12410568 Area required = 4.56 x 10-3 M2 The thrust is divided between two rams to give added stability.

This means each cylinder requires 2.28 x 10-3m2 The chrome rod chosen has a diameter of 30mm. Therefore: Area lost by shaft = 7C X (15 X 10-3) 2 = 7.07 x 10-4m2 Area required = 2.28 x 10-3m2 = 7.07 x 104m2 - (7r82) R2 = 9.51 x 102 R = 0.031m Internal Diameter = 62mm A person skilled in the art will readily appreciate that the impeller 36 may be replaced with any other suitable equivalent. For example, an alternative mixer could be some form of pneumatic or hydraulic jet (not shown) to be directed into the liquid in order to agitate the liquid. In the case of the hydraulic jet (not shown), liquid could be drawn from the lagoon and

forced from the jet (not shown). With the pneumatic jet (not shown), a supply of air could be drawn, in use, from the surrounding air. Both forms of jet would of course require some form of pump, as a first drive source, in order to draw in a supply of liquid/air, and subsequently to expel the liquid/air form the jet (not shown).

It will be appreciated that, for the applications in which the device 10 is intended to be used, the surface area of the volume of liquid will often be in the range of hundreds of square metres. For this reason, it is desirable that the device 10 be self propelled in order to allow the device 10 to manoeuvre itself about the volume of liquid to facilitate the uniform mixing thereof. To this end, the device 10 is fitted with a first forward paddle 30, a second forward paddle 32 and a rear paddle 34. The first forward paddle 30 and the second forward paddle 32 extend from the first tank 14 and the second tank 16 respectively, while the rear paddle 34 extends rearwardly from the second cross member 20. Each of the paddles 30, 32, 34 are capable of operating in forward and reverse in order to permit a high degree of manoeuvrability. It will be understood that operation of one or other of the first or second forward paddles 30, 32 will cause the device 10 to steer to the side opposite to that of the operational paddle. operation of said one of said forward paddles 30, 32 will draw that side of the device 10 forwardly, while the opposed side remains relatively stationary. This has the effect of causing the device 10 to turn towards the side thereof whose forward paddle 30, 32 is inoperative. In order to

increase the steering capability of the device 10, one of the forward paddles 30, 32 may be driven in one direction, while the opposite forward paddle 30, 32 is driven in the reverse direction. Operation of all the paddles 30, 32, 34, or alternatively both the forward paddles 30, 32 in a single direction will effect rectilinear movement of the device 10 in that direction.

It will be understood that, although the paddles 30, 32, 34 are the preferred mechanism for manoeuvring the device 10 about the surface of the liquid, there are other suitable means for achieving same. For example, one or more propellers (not shown) may extend from the device 10 into the liquid in order to control the movement thereof. If a single propeller (not shown) is used, the propeller must be capable of directional changes in order to alter the direction of travel of the device 10. Alternatively, the device 10 may be provided with a conventional rudder (not shown) which may be used to direct the device 10. As a further alternative, the device 10 may be provided with one or more fans (not shown) positioned, in use, above the liquid, in order to power the device 10 over the surface of the liquid.

Operation of the paddles 30, 32, 34 is computer controlled and co-ordinated, as may be any other manoeuvring mechanism substituted for the paddles 30, 32, 34, and may be pre-programmed to suit the particular application or area in which the device 10 is to operate. For example, the device 10 may be provided with control circuitry (not shown) which is

adapted to turn on/off one or more of the paddles 30, 32, 34 at a given time, and for a given interval, such as to control the direction/speed of the device 10. Therefore, the dimensions and orientation of a particular volume of liquid are first mapped, and a computer model of same generated by conventional means. This model, or the pertinent details therefrom, may then be used to operate the control circuitry (not shown) as required. The device 10 may further be remotely controlled by an operator if required. Operation of the impeller 36, in addition to the insertion and removal of the impeller 36 from the liquid, may also be remotely controlled or preprogrammed to best suit the particular application. This would again be achieved using suitable control circuitry as described above with regard to the operation of the paddles 30, 32, 34.

It will however be appreciated that, due to such considerations as wind patterns, water currents and the like, the path of the device 10 around any given body of liquid cannot be precisely controlled, and certain provisions must be made to allow for this. In order to prevent damage to the device 10 in the event of a collision with a bank (not shown) or similar object, a plurality of buffer wheels 26 are mounted to the device 10 at each corner thereof, via a respective support 28. The buffer wheels 26 will also be helpful when mooring the device 10 at a dock (not shown) or the like. In order to minimise collisions with the bank (not shown) or the like, it is also envisaged that the device 10 be provided with a receiver (not shown), preferably a radio receiver, which can detect a signal transmitted

from a suitable transmitter (not shown), and from said signal determine the present co-ordinates of the device 10. It will therefore be apparent that the device 10 may be provided with suitable systems to allow any necessary course corrections to be made in light of the position of the device 10 relative to the transmitter (not shown). Alternatively, the device 10 may be provided with a Global Positioning System (GPS) to permit the device 10 to accurately navigate any given volume of liquid.

The paddles 30, 32, 34 are powered by a second drive source in the form of a motor (not shown) housed within a motor housing 24 mounted on the platform 22. Due to certain Health & Safety laws, the maximum acceptable noise level from the device 10 is set at 85 decibels. For this reason, the motor housing 24 is lined with flame retardant sound insulation which reduces the noise level, and in particular damps out high frequency sound waves. The motor (not shown) is also fitted with a residential silencer (not shown) and located in place on specialised engine mounts (not shown) which reduce the resonating sound waves caused by engine vibration. The motor (not shown) is preferably diesel powered, but it will be appreciated that any comparable source of power will be suitable for use with the device 10. It will also be appreciated that, in order to power the motor (not shown), it is necessary to have a supply of fuel for this task. It will be understood that refuelling the device 10 would be cumbersome and time consuming while the device 10 is situated afloat a volume of liquid, and even more complicated to require

that the device 10 be removed from the volume of liquid in order to facilitate refuelling thereof.

For these reasons, the device 10 is provided with a refuelling mechanism 50 which may be operated while the device 10 is afloat. The refuelling mechanism 50 comprises a refuelling vessel 54 mounted to a refuelling arm 52 which extends from the body 12. The refuelling arm 52 is capable of extension and retraction under the influence of a hydraulic refuelling cylinder 56. Leading from and in fluid communication with the refuelling vessel 54 is a fuel feed line (not shown) which is mounted to the refuelling arm 52. Therefore, in practice, a fuel dump (not shown) or similar fuel supply is located proximal the edge of the volume of liquid, the device 10 being manoeuvred into proximity therewith. The refuelling vessel 54 is then extended, by means of the refuelling arm 52, towards and into operative alignment with the fuel dump (not shown) in order to facilitate the ingress of fuel to the device 10. The fuel is fed into the refuelling vessel 54, wherein it passes through the fuel feed line (not shown) and to an onboard fuel tank 58. Once refuelling has been completed, the refuelling vessel 54 is retracted in order to allow the device 10 to resume operations.

If access is required to the device 10 while in operation, whether for reasons of maintenance or operational analysis, the device 10 may be moored to a jetty (not shown) or the like. The device 10 is also fitted with an access ramp 42 hingedly mounted to the first tank 14, adjacent the platform 22. Ramp

cylinders 44 are provided in order to effect the raising and lowering of the access ramp 42. Located on the access ramp 42 are a pair of mooring clamps 46 which are extendible under the influence of a pair of mooring cylinders 45. Extension of the mooring cylinders 45 causes the mooring clamps 46 to open such as to allow the mooring clamps 46 to engage any suitable fixture (not shown) which presents itself. The mooring cylinders 45 may then be partially retracted such as to provide a grip on the fixture (not shown) in order to allow the device 10 to be securely fastened for docking or the like.

It is preferable that each of the components, or at least the liquid contacting components of the device 10 be suitably treated or coated in order to prevent corrosion thereof due to extended exposure to the atmosphere, various liquids and chemicals or the like. In the preferred embodiment illustrated, the majority of the components, including the first and second tanks 14,16, the first and second cross members 18,20, the refuelling mechanism 50 and the access ramp 42 are manufactured from stainless steel, aluminium, or suitably treated or painted galvanised steel, in order to prevent damage to the device 10 due to corrosion. Utilisation of the device 10 to create a substantially homogeneous volume of liquid has many advantages in various liquid storage and transportation applications. Pumping of the liquid from the lagoon or reservoir is stabilised due to the greater consistency of the liquid, thereby eliminating any fluctuations of the load on the pump (not shown). Furthermore,

transportation of the liquid, particularly when a commercial product, may be effected immediately from the lagoon or reservoir without the requirement of a pre-processing stage in order to homogenise the liquid in question. The device 10 also eliminates the need for land based mixing systems which may not be practical and often have a detrimental effect to the banks of the lagoon or reservoir, which will subsequently require periodic maintenance. The need for an array of static mixers or integrated jet systems is also eliminated with the introduction of the present invention.

The present invention is not limited to the embodiment described herein which may be amended or modified without departing from the scope of the present invention.

Claims

CLAIMS 1. A mixing device for dispersing solid matter in a volume of liquid, the mixing device comprising a mixer adapted to float on or in the volume of liquid and locatable, in use, at least partially within the volume of liquid; and a first drive source capable, in use, of effecting actuation of the mixer.
2. A mixing device according to claim 1 wherein a second drive source is provided to manoeuvre the mixer about the surface of the liquid.
3. A mixing device according to claim 1 or 2 wherein the first drive source is/are supported on a body, the body being adapted to float on or in the volume of liquid.
4. A mixing device according to claim 3 wherein the body includes at least one gas reservoir, to permit the body to float on or in the volume of liquid.
5. A mixing device according to any preceding claim wherein the mixer is an impeller, the impeller extending from the body.
6. A mixing device according to any preceeding claim wherein the first drive source is a motor in operative association with the mixer.
7. A mixing device according to any of claims 2 to 6 wherein the second drive source comprises a plurality

<Desc/Clms Page number 18>

of propellers located, in use, at least partially within the volume of liquid and distributed about the device.
8. A mixing device according to any preceding claim wherein the device may be remotely controlled.
9. A mixing device according to any preceding claim wherein the device may be programmed for automated operation.
10. A mixing device according to any preceding claim wherein the device may be refuelled while afloat.
11. A mixing device according to claim 8 wherein the device includes a refuelling arm in operative association with the device, the refuelling arm being extendible, in use, away from the device such as to facilitate refuelling while the device is afloat.
12. A mixing device according to any preceding claim wherein the device includes a retractable access ramp mounted to the device, such as to permit access to the device while afloat.
13. A mixing device according to claims 2 to 12 wherein the second drive source is powered by an internal combustion engine, the device further including sound proofing surrounding the engine to permit use of the device in areas having regulated noise pollution levels.

<Desc/Clms Page number 19>
14. A mixing device according to any preceding claim wherein the mixing device may be manually manoeuvred about the surface of the volume of liquid, by an operator.
15. A mixing device constructed and adapted to operate substantially as hereinbefore described with reference to the drawings.