WO1991013031A1

WO1991013031A1 - Water treatment

Info

Publication number: WO1991013031A1
Application number: PCT/GB1991/000298
Authority: WO
Inventors: Thomas Daniel Farrelly; Philip Thomas Kinsella; Graham Lees; David Gareth Gittins; Anthony Daley
Original assignee: North West Water Limited; Sir Frederick Snow & Partners (North West) Limited
Priority date: 1990-03-01
Filing date: 1991-02-26
Publication date: 1991-09-05
Also published as: AU7443791A; GB9004617D0

Abstract

Water treatment apparatus (10) has a base frame (12) and an upright frame (13) mounting a pair of parallel treatment modules each having an inlet line (14) to a motive water pump (15) whose outlet (16) leads to a first inlet of an eductor (17) whose outlet (18) is connected to a water supply pipe (19) upstream of a sampling line (20), there being connected to a second inlet of each eductor the output (25) of a respective peristaltic pump (26) whose inlet is connected to a supply (28) of a water treatment solution.

Description

ATER TREATMENT This invention relates to water treatment apparatus which can be used in a wide variety of positions in a water supply or distribution system to introduce treating agents into a water pipe. 5 Although the process will be described in relation to the addition of chlorine to attain a minimum residual chlorine content for the consumer, it must be appreciated that the apparatus can be used to introduce any suitable chemical solution to treat any lOunwanted condition of water within a pipe.

Water very often travels from a source to a local service reservoir where several outlets will supply several groups of users. Water is usually treated prior to entering the service reservoirs but, whilst 5standing it can loose its chlorine content. With increasing standards of water purity, it is becoming more necessary to include treatment apparatus at a later stage in the supply. The present invention is particularly concerned with the "late" treatment of fJ^w__er, for example between the service reservoir and the users.

It will be appreciated that such an apparatus has to have several properties which are unique to this particular sort of treatment. Firstly, because 5labour is expensive, the apparatus should operate automatically and without servicing for long periods. Further, there should be relatively small amounts of chemical which need to be stored in order to avoid the need for either very bulky tanks or frequent refilling.

As a further point it is important that the apparatus can remain inactive for long periods of time (for example whilst water from the service reservoir actually has sufficient chlorine in it) but then can operate effectively after a long period of disuse. In attempting to reduce the volume of chemical to be stored, it is advantageous to be able to increase the strength of the solution. A stronger chemical solution means that more of the chemical can be stored in a smaller space. unfortunately, in the case of sodium hydrochlorite if a solution of 15% strength or greater is used, the solution tends to crystallise in pump chambers which can lead to heavy wear on the pump or possible complete malfunction. It has been usual, therefore, to limit the solution strength to about 10% or less. Further, strong solutions can release chlorine gas which may form gas pockets in the pump which can de-prime the pump. It is an object of the present invention to provide a water treatment apparatus whereby some or all of the above described disadvantages can be reduced or minimised.

The invention provides water treatment apparatus including a pair of parallel alternative modules, each module including a motive water pump having an inlet connectable to a water supply pipe and having its outlet connected to the first inlet of an eductor whose outlet is connectable to the water line upstream of said pump connection thereto, there being connected to a second inlet of said eductor. The outlet of variable speed peristaltic pump whose inlet is connected to a tank of treatment chemical, a water sampling line being provided for testing the condition of the treated water and said peristaltic pump and a sensor connected to said sample water line, and a flow meter monitoring said water supply line being interconnected by circuitry including control and power provisions.

Where said eductors require an essentially constant head supply, a water break tank can be provided and connectable to said water supply line to provide a constant pressure supply of water to each said eductor, the output from the peristaltic pump being connected to enter said eductor water supply from the break tank.

It has been found that the use of a variable speed peristaltic pump reduces any problem caused by gas locking. Any gas formed within the peristaltic pump or the line from the chemical storage tanks is simply pumped through. Further, similar considerations apply to any crystallisation which takes place within the pump or said chemical delivery lines. Any crystals which form can be accommodated during initial operation of the pump and are soon flushed away or dissolved by the newly passing solution without significant damage to the pump.

The invention further provides water treatment apparatus including a support including a base an upright, said support mounting and supporting as a self-contained unit, including a motive water pump having an inlet connectable to a water line and having its outlet connected to the first inlet of an eductor whose outlet is connectable to the water supply line upstream of said pump connection thereto, there being connected to a second inlet of said eductor an outlet of variable speed peristaltic pump whose inlet is connected to a tank of treatment chemical, and which is control circuitry.

By use of a solution of 15% or greater strength, it is possible to reduce the size of the necessary chemical tanks to- a manageable size such that the entire unit can be manufactured in a factory and transported complete for installation in a treatment house. This is a very significant advance over previous methods wherein the bulkiness of the components, particularly chemical treatment tanks meant that the whole apparatus needed to be built on site. Clearly, the manufacturer of a number of such units in a factory gains a significant advantage over a piecemeal construction method at a distant point.

Preferably said support is in the form of a frame, the base comprising a generally horizontal base frame portion and the upright comprising a framed panel. Desirably, the panel is arranged centrally of the base frame in order that components can be mounted on both sides thereof to be supported both by the upright and by the base frame.

Desirably, each treatment module is isolated from the others so that that module which is out of service can be worked on by an operative without disturbance to the operation or the working module.

The invention includes, of course, apparatus as aforesaid in combination with a water flow line. The invention will be described further, by way of example, with reference to the accompanying drawings wherein:-

Fig. 1 is a schematic view illustrating a preferred apparatus of the invention; Fig. 2 is a perspective view from one side of the arrangement of the invention during construction; and

Fig. 3 is a view similar to Fig. 2 but from the otherside.

Referring firstly to Figs. 2 and 3, it will be seen that the apparatus 10 of the invention has a support structure 11 which includes a base frame 12 and an upright frame 13 arranged centrally of the frame 12. The frame 12 has channel section (such as may be lifted by a fork truck) functional components of the apparatus 10 (to be described later) can be conveniently mounted on the frame 12 and/or the upright 13 to produce a conveniently transportable unit. The unit can be factory made and can then be transported to the site and installed using a minimum of skilled work. This enables the skilled construction engineers to remain in a central location rather than having to travel to many widely separated sites to install the apparatus. Thus, costs are greatly reduced.

Referring now to Fig. 1 the preferred apparatus 10 of the invention includes a pair of water treatment modules which are arranged in parallel and which can operate alternately, one module always being out of service and available for maintenance or as a back-up to the operating module. The modules will be designated A and B. As the modules are not shown distinctly on the drawings the various components of the modules will be distinguished by the addition of the appropriate suffix A or B to determine whether that component belongs to the A or B module. Each module includes an inlet line 14 to a motive water pump 15 whose outlet line 16 leads to the first inlet of an eductor 17 whose outlet line 18 is connected to the water supply pipe 19 upstream of a sampling line 20 to which are connected the motive water pump inlet lines 14A and 14B. _-_

The eductor 17 is, in the preferred embodiment, of a type which operates in optimum manner with a constant second inlet pressure in its induction inlet line 21. Accordingly, the two inlet lines 21A, 21B are connected to a common break tank 22 which is supplied with water at a generally constant head by means of an extraction line 23 connecting between the water supply pipe 19 and a ball valve 24.

Connected to the induction inlet line is the outlet 25 of a peristaltic pump 26 whose inlet line 27 is connected to and fed from a tank 28.

The tanks 28 contain a solution of 10 - 20% sodium hypochlorite solution for ensuring the chlorine level in water before final despatch to consumers. It should be mentioned here of course, that other chemicals can be added to alter other properties of the water to be treated.

The pumps 26 and 15 are connected for power and for sensing to a control panel 35 (which is not shown in Fig. 1) . Similarly, sampling line 20 is connected .to a sampling apparatus 29, the electronic signals of which are also connected to the control circuitry indicated generally at 35. Various other monitoring devices are provided in the circuitry and these are briefly as follows: a flow meter 30 which measures the flow in the water supply line 19, a level sensor 31 which determines when the break tank 32 reaches a low level, level sensors LSA and LSB for the tanks 28 containing to chemical supply which, when a particular tank reaches a low level automatically transfers to the other and/or initiates the triggering of an alarm. Performance of pumps 15 is monitored by pressure sensors PSA and PSB also connected to the circuitry. In addition, to monitor any possible leakage from the tanks 28 or the pumps 26 there are provided separate (or as shown) mutual overflow trays 32 provided with a level sensor 36 connected to the circuitry. Similarly an overflow tray 33 is provided beneath the pumps 26a_ and 26b. If desired these can be separate trays to singularise any "overflow" signal and associated with one of the pumps. This overflow tray 33 has a level sensor 34. The control circuitry 35 contains a small programmable processing unit which can ensure the proper functioning of the apparatus 10.

In use, the sampling line 20 extracts a sample of water from the water supply line 19 either continuously or at predetermined intervals and analyses the chlorine content using a sampler 29. Automatic samplers of this type are delicate pieces of equipment, and therefore it has been found, in many situations unwise to rely on a single sampler. It is usual, therefore, and desirable to use three samplers in parallel, their outputs being monitored electronically and a mean being selected if they are all about equal, but one sampler being ignored if it ___

has a reading which is significantly different from the other two.

In accordance with the output of the sampler 29, the programmable processing unit in the control panel 35 determines whether or not the water flowing in the line 19 has sufficient residual chlorine. If the chlorine level is low, the programmable processing unit in the control panel 35 determines from the output of the flow meter 30 and the programme parameter of the pump 26 the desired rate of rotation of the pump 26 to introduce, into the line 19 the necessary amount of sodium hypochlorite solution and its rate of addition in order to bring the level of residual chlorine back up to the desired value. The pump 26 continues to operate until such time as the sampler 29 produces a signal which indicates the required or too high a chlorine level at which stage the pump 26 will be either switched off or reduced in speed. Similarly, if the chlorine level should drop still further, the speed of the pump 26 may need to be increased to maintain the residual chlorine level.

It will be appreciated that by having the sampler downstream of the injectors 1 and 2, there is provided an effective feedback loop which keeps the desired chlorine level at or about the desired value. The programmable processing unit in the control panel 35 can be appropriately programmed so that the system does not hunt. This can best be done by arranging for a range of permissible chlorine levels, changes within such band not triggering operation of the pump.

The various components of each module are monitored by the aforesaid instruments, whose outputs are also fed to the programmable processing unit in the control panel 35. If the operating module fails for any reason, for example, if pump 15 fails, or pump 26 fails, or the level of chemical solution in its tank 28 falls to a low level, the circuitry 35 O automatically changes over to the second, reserve, module at the same time operating an alarm either at the installation, or, more likely, by a telephone or telemetry to a remote control position.

The apparatus of the invention is particularly 5 suitable for remote operation at long and intermittent intervals without regular servicing or regular attention. It can also be very easily manufactured and installed with a minimum of on site work.

The invention is not limited to the precise o details of the foregoing and variations can be made thereto.

For example, the apparatus can be adapted to supply any other chemical to a water supply line. Many other variations are possible within the 5 scope of the invention.

Claims

CLAIMS 1. Water treatment apparatus including a pair of parallel alternative modules, each module including a motive water pump having an inlet connectable to a water supply pipe and having its outlet connected to the first inlet of an eductor whose outlet is connectable to the water line upstream of said pump connection thereto, there being connected to a second inlet of said eductor the outlet of a variable speed peristaltic pυmp whose inlet is connected to a tank of treatment chemical, a water sampling line being provided for testing the condition of the treated water, said peristaltic pump and a sensor connected to said sample water line, and a flow meter monitoring said water supply line being interconnected by control circuitry.

2. Apparatus as claimed in claim 1 wherein said circuitry includes control and power provisions.

3. Apparatus as claimed in claim 1 or 2, wherein a water break tank is provided to be connectable to said water supply line to provide a constant pressure supply of water to each said eductor.

4. Apparatus as claimed in claim 3, wherein the output from the peristaltic pυmp is connected to enter said eductor water supply from the break tank.

5. Apparatus as claimed in any of claims 1 to 4 wherein the water treatment chemical in the tank is sodium hydrochlorite having a solution strength of 10% or greater.

6. Apparatus as claimed in claim 5 wherein the strength is 15% or greater.

7. Water treatment apparatus including a support including a base and an upright, said support mounting and supporting, as a self-contained unit, two treatment modules, each including a motive water pump having an inlet connectable to a water line and having its outlet connected to the first inlet of an eductor whose outlet is connectable to the water supply line upstream of said pump connection thereto, there being connected to a second inlet of said eductor an outlet of variable speed peristaltic pump whose inlet is connected to a tank of treatment chemical, and which is control circuitry.

8. Apparatus as claimed in claim 7 wherein the tanks each contain a sodium hydrochlorite solution of 10% or greater.

9. Apparatus as claimed in claim 7 or 8, wherein said support is in the form of a frame, the base comprising a generally horizontal base frame portion and the upright comprising a framed panel.

10. Apparatus as claimed in claim 9 wherein the panel is arranged centrally of the base frame in order that components can be mounted on both sides thereof to be supported both by the upright and by the base frame.

11. Apparatus as claimed in any of claims 7 to 10 wherein each treatment module is isolated from the others so that that module which is out of service can be worked on by an operative without disturbance to the operation or the working module.

12. Water treatment apparatus substantially as described with reference to the accompanying drawings.