AU2002253496A1

AU2002253496A1 - Solid material dissolution apparatus

Info

Publication number: AU2002253496A1
Application number: AU2002253496A
Authority: AU
Inventors: Eitan Dafny; David Feldman; Rami Pedahzur; Ronen Shechter
Original assignee: Bromine Compounds Ltd
Current assignee: Bromine Compounds Ltd
Priority date: 2001-04-02
Filing date: 2002-04-01
Publication date: 2003-04-03
Anticipated expiration: 2022-04-01

Description

SOLID MATERIAL DISSOLUTION APPARATUS

Field of the Invention

According to the present invention a new apparatus is provided for

dissolution of a particulate material, preferably a biocide, for preparing a

solution of constant concentration. More specifically solid biocide is

dissolved, in a controlled and monitored way, to provide solutions, all having

the same and constant dose of biocide per volume.

Background of the Invention

At present, the application of biocidal materials is the most cost-effective

means of maintaining the appropriate level of microbiological quality of both

industrial and recreational water systems (such as, for example, cooling

towers, the pulp and paper industry, swimming pools, etc.). However, due to

the hazardous nature of these materials, there has been a growing

consideration and emphasis in industry regarding personnel safety,

maintaining and handling of such materials and their environmental

effects. This led to a demand for new approaches of producing and handling

the solutions of these biocides and using highly controlled methods of

treatment. A prominent disadvantage associated with applying solid biocide

based solutions derived from the inconsistency in biocide concentrations. In

other words, the current methods for preparation of biocide solutions suffer from the phenomena that biocide concentrations fall gradually and

continuously. This phenomenon is clearly demonstrated in Example 1.

Very commonly, the application of biocides into the treated water is based

on a calculated dosage. This is especially true in the application of non-

oxidative biocides in which their detection in the aqueous solution is

complex and impractical for field application. Especially in these cases the

ability to produce a solution with a constant concentration of the biocide is

essential and this is a main disadvantage of the existing feeding systems.

An additional major advantage of applying aqueous solutions of biocides is

the elimination of organic solvents. Liquid formulation, which contains a

mixture of water and an organic solvent such as a glycol, (for example,

polyethylene glycol (PEG), dipropylene glycol (DPG), ethylene glycol, etc.)

and others are required for dissolution of relatively water-insoluble biocides.

The active ingredient (such as 2,2 Dibromo-3-nitrilopropionamide (DBNPA))

might be only 5-25% of such liquid formulation, consisting of water and an

organic solvent.

The addition of the organic solvent makes the dissolution process more

complicated and expensive and promotes unnecessary addition of organic

materials into the environment. Thus, there is a need for a device that offers

a user friendly alternative that eliminates the necessity for organic solvents and at the same time meets the highly demanding personnel safety

requirements existing for any mode of biocide application.

There are known dosing systems for applying biocides in a tablet form (for

example: Trichlorocyanuric acid (TCCA) & Bromochloro-5,5-

dimethylhydantoin (BCDMH) tablets), such as, for example, the HAY AKD

automatic pressure style chlorine feeders. Two major disadvantages of these

feeders are their operation under pressure and their inability to produce a

constant biocide concentration in an aqueous solution.

Other dosing systems are known, for example:

The Granudos 45/100 which is a dosing system for granular calcium

hypochlorite. This device meters the chemical directly from the container

(drum). The chemical is dosed into the dissolving system where it is

completely dissolved with the aid of the additional metered acid and then

conveyed as a highly diluted hypochloric acid to the swimming pool tubing

via a venturi. This device suffers from the following disadvantages:

• It has to inject acid for dissolution, using an acid tank, acid dosing

pump, special tubing, and therefore has more safety hazards and

storage and maintenance logistics.

• It uses a mechanical screw feeder for the solids which complicates the

system (e.g. need to heat solid conveying conduit to prevent condensation that causes bulking and plugging) and renders it

susceptible to more frequent failure due to wear of rotating parts.

• In general - the GK45/100 has a relative large footprint and weight.

The Hammonds' magnetic vortex feeder uses tablets of calcium hypochlorite

to produce a solution of calcium hypochlorite having the desired biocidal

strength. The vortex is generated by a free floating magnetically driven stir-

bar, producing fresh batches of calcium hypochlorite solutions that are

stored and ready for injection. This device suffers from the following

disadvantages:

• The device is suitable for large tablets only. Small granules would flow

throughout the system and cause total plugging before dosing some of

the granules into the water line.

• The vortex control mechanism has very limited accuracy in

concentration. An important parameter - the residence time of

dissolving water in the dissolution chamber - is not controllable.

• There is no circulation of solution from the holding tank to the

dissolution chamber, so only flow-through supplies the solute, and there

is no assurance or verification that the required concentration is

maintained.

US 5,468,066 patent provides an apparatus for injecting a dry particulate

material into a fluid flow line comprising: (1) a mixing chamber, in which the dry particulate material is mixed with liquid; (2) a pressurized liquid

supply to said mixing chamber; (3) material supply means over said mixing

chamber for supplying said dry particulate material; (4) an outlet line from

said mixing chamber in fluid communication with a solution of the

particulate material, and (5) pump means connected to the outlet line for

both exerting a vacuum in the mixing chamber and injecting mixed liquid

and particulate material from the mixing chamber within said pressurized

fluid flow line. This device suffers from the following disadvantages:

• The solid has to free-fall into the liquid, a process associated with

potential problems of plugging due to humidity, difficulty in process

regulation, and solid wetting problems.

• The solids are dosed by a moving mechanical drive that is prone to

more rapid degradation, it is more complicated to replace and it is

quite expensive.

US patent 5,961,845 discloses a dispenser system for treating a water-

containing system in place with a dry chemical substance. A predetermined

amount of dry chemical material in a water-soluble pouch housing is

dissolved in an apparatus comprising a container for obtaining a liquid

chemical concentrate.

An option not feasible with this patent's design is to hold a large solid

reservoir for multiple doses.

Neither of the above discussed patents and devices providing a solution to

two major needs: 1. The need to wet as little biocide as possible, of a large dry matter batch,

in order to prevent deactivation of the active material. In other words, it

is desirable that only a small portion, preferably at the bottom of the solid

particles batch, is wetted. This is in contrast to current devices in which

the whole biocide batch is wetted.

2. The need to prevent small solid biocide particles from being carried-over,

after their size has reduced due to dissolution.

It is an object of the present invention to provide an apparatus that

dissolves particulate material, preferably solid biocide, to form solutions of a

constant concentration with no decrease in the material concentration with

time due to the gradual depletion of said dissolved material in the feed

container. It is a further object of the present invention to provide an

apparatus that dissolves solid biocide to form biocide saturated solutions

with no decrease in the biocide concentration with time. It is a further object

of the present invention to provide a solid-biocide dosing device that is

accurate, convenient, safe, user friendly and environmentally friendly.

It is a further object of this invention to provide a dissolution setup in a way

that avoids problems such as plugging/bridging and potential carryover of

particulate matter. It is yet a further object of the present invention to

provide a biocide dissolution system comprising the step of contacting and

wetting the stationary particulate material with circulating liquid to provide

a flow that contains no particulate matter (it is all dissolved). It is a further object of the present invention to provide a particular structure and shape of

a solid material holding compartment to prevent plugging and

agglomeration.

It is yet an additional object of the present invention to provide an

automatic dosing system that doses the solid biocide directly to form a

completely dissolved biocide with no need for additional materials for either

pre-dissolving the solid biocide or facilitating its dissolving; such a system is

easily fitted into the water treatment installation. The new apparatus

improves the mode of biocide application by providing solutions of biocide

having the same concentrations (doses).

According to the present invention a new device is provided for preparing

biocide solutions of constant concentrations. More specifically, solid biocide

is dissolved, in a controlled and monitored way, to provide solutions, all

having the same and constant dose of biocide per volume. The new device

overcomes the main disadvantage of the existing solid-biocide feeders,

namely, the decrease in the biocide concentration with time due to the

gradual depletion of solid biocide in the feed container. Furthermore,

another outstanding advantage of the present invention derives from the

fact that the apparatus works without potential hazardous pressure build¬

up in the system, in contrast to existing solid feeders, and it operates

without the need for organic solvent for dissolution of relatively water-

insoluble materials. Furthermore, the unique features of the present system affords a novel

approach for dissolving solid material in either batch, or continuous, modes

of application, while avoiding in an inventive way major existing problems

such as plugging/bridging phenomena and potential carry-over of

particulate matter.

Summary of the Invention

The present invention provides a device for dissolution of a particulate

material having a constant concentration of solution comprising:

(a) a particulate biocide compartment;

(b) means to supply said particulate material to said dissolution

chamber, containing means for prevention of the formation of lumps

which would block the descent of the solid;

(c) a dissolution chamber for dissolving the particulate material with

liquid; said dissolution chamber having an inlet line for providing

circulated solution of the particulate material to flow through

opening(s) in its upper and lower parts to allow the solution of dissolved

particulate into a solution tank;

(d) means to control the flow of particulate-free liquid;

(e) an optional screen or a sieve to prevent the particulate material

from entering into the solution tank;

(f) an inlet line for adding liquid into the solution tank; (g) means for circulating the solution of said particulate material from

the solution tank to the dissolution chamber until an appropriate

concentration is obtained;

(h) means for discharging the solution having the appropriate

concentration of said particulate material from said tank through an

outlet line; and optionally

(i) means for operation of the device in either a continuous and/or batch

mode; and optionally

(j) means for automatically controlling and monitoring the device

operation through a central processing unit.

General Description of the Invention

The solid biocide dissolution apparatus (SBDA) of the present invention is a

unique dissolution system for solid biocide applications. This novel feeding

system dissolves solid biocides (for example in a compacted form, such as

granules, tablets, etc.) to generate on site a fresh, aqueous saturated biocide

solution to provide solutions of the same concentration (dose). The new

apparatus presents a new concept in biocide application that eliminates the

use of organic solvents from liquid formulations of biocides with low

solubility in water and instead applies aqueous solutions of the active solid

biocide. Consequently, the SBDA is a highly advanced, low cost apparatus

that produces solvent-free aqueous biocide solutions of constant

concentration for industrial applications, without having to monitor the disinfectant residues in the treated body of water. The device is operable

with oxidizing, as well as non-oxidizing, solid biocides.

The apparatus comprises:

1. A holding compartment for the dry biocide.

2. A solution holding tank.

3. A relatively small dissolution chamber which enables hmited contact of

the solid biocide with the surrounding water, thus keeping the bulk of the

material dry and avoiding potential decomposition.

4. An inverted cone for prevention of the formation of lumps which would

block the descent of the solid from the solid holding compartment to the

dissolution chamber.

5. Means for re-circulation, delivery and discharge of the saturated biocide

solutions, upon demand.

The system is fully automated and controlled by a programmable logic

controller (PLC) which coordinates the biocide preparation and application,

and allows flexible operation of the system. A proximity sensor indicates

when the solid biocide level is low.

The solid biocide can be loaded into the dissolution chamber directly from

any package or, preferably, via a specially designed, disposable cartridge or

closed covered package. Optional installation of an internal cutting device

and connecting sleeve that enables introduction of the biocide into the

system via a cartridge or a covered package, with improved safety and convenience in handling. In this mode of operation the operator has no

direct contact with the biocide.

Description of the Device of the Invention:

Fig. 1 demonstrates schematically the device of the present invention.

The device contains a solution holding tank or reservoir (1) for the saturated

biocide solution (or a solution having a required constant concentration of

biocide), above which is situated a compartment for dry biocide (2) which

has an opening in the lower side leading into an inverted cone (12) for

prevention of the formation of lumps which might block the descent of the

solid. Underneath the compartment for the solid biocide (2), circling the

inverted cone (12) and inside the solution's container (1) is situated a

dissolution chamber (3) into which is poured the solid biocide to be dissolved

(only this small part of the solid is wetted by the solution). The diameter of

the dissolution chamber (3) is such that the flow rate of the solution through

the solid (in the area outside the inverted cone) will be low and will prevent

the solid particles from floating and falling into the solution holding tank. In

the upper area of the dissolution chamber are openings (4) which enable the

solution passing through the solid to overflow back into the solution holding

tank (1). These openings may be covered by a screen or a sieve to prevent

the solid material from entering the solution tank.

In the base of the dissolution chamber (3) is connected a tube through which

is entered the circulating solution through the solid biocide to obtain a saturated solution (or a solution having a required constant concentration of

biocide). At the joining of the tube to the dissolution chamber (3) is situated

a screen or a sieve (5) to prevent the introduction of solid particles into the

pump (6).

The addition of water and circulation of the solution is automatically

controlled by the following:

1. Water is added to the solution holding tank (1) through a controlling unit

(7) which is connected to a central processor (11). The biocide solution is

circulated until saturation or any other required concentration is achieved

using a pump (6) which is operated under the control of the central processor

(11). More specifically, the biocide solution is circulated a predetermined

number of times via the pump (6) until a solution containing the required

concentration of biocide is obtained.

2. The saturated biocide solution (or a solution having a required constant

concentration of biocide) leaves the solution tank (1) via the second pump (8)

towards the point of use.

The solution holding tank can be filled to any predetermined level according

to the desired dose or batch size, controlled and monitored by any means of

level switching high/low (LSHL) (9).

The dissolution chamber is equipped with holes through which the solution

overflows to the solution holding tank. The location of the holes at the top of

the dissolution chamber determines the actual amount of solid material that will be in contact with water. In other words, a different location of the holes

will result in a different amount of solid that will be in contact with the

aqueous solution and consequently the solution will be circulated a different

number of times in order to obtain a solution of constant biocide

concentration.

Means for level switch (LS) for solid level detection (10) may be installed for

indication and alarm. A central processing unit (11) controls automatic

operation of the predetermined sequence of solution preparation, namely,

filling with water, circulating the solution for saturation, or near saturation

or any other constant concentration of biocide, and discharging the biocide

solution to the point of use.

An alternative approach for the use of the dissolution apparatus in a

continuous mode is illustrated in Figure 2.

In general, the basic layout of the dissolution apparatus is similar to the

above mentioned and presented in Figure 1, yet there are some changes:

Water from the water source is continuously added to the apparatus

through a controlling unit (that regulates the flow) into the dissolution

chamber and hence to the solution holding tank (as depicted above). The

saturated biocide solution (or a solution having a required constant

concentration of biocide) is continuously pumped/delivered (as long as the

water enters the system) from the solution holding tank (1) via a pump (8)

towards the point of use. The flow of water into the apparatus is regulated in a way as to ensure the production of a saturated solution, or any required

solution of constant biocide concentration.

Description of the Figures

Fig. 1: A schematic description of the solid dissolution system of the present

invention.

Fig. 2: A schematic description of the solid dissolution system of the present

invention, for operation in a continuous mode.

Fig. 3: Changes in DBNPA concentrations at the outlet of a conventional

dissolution apparatus with time.

Fig. 4: Changes in DBNPA concentration at the outlet of a dissolution

apparatus of the present invention.

Fig. 5: Counts of total bacteria and residual oxidant level (mg/1 as Cb)

Fig. 6: A schematic description of a potential equivalent system providing a

similar outcome, comprising a combination of one pump and two control

valves.

Examples

Example 1: Comparing DBNPA concentrations in solutions prepared

by a conventional dosing apparatus and the present invention.

Figure 3 presents the concentration of 2,2 Dibromo-3-nitrilopropionamide

(DBNPA) in the outlet of a "conventional" dissolution apparatus as a function of time. The solid material was dissolved by passing water at a flow

rate of 100 1/hour.

As can be seen, with the progression of time, DBNPA concentrations at the

outlet of the apparatus decrease substantially resulting in a varying

solution concentration.

Figure 4 describes the concentration of DBNPA in solutions prepared by the

dissolution apparatus of the present invention during an actual operation

trial lasting for 1 month. The solutions (a volume of 10 liters each) were

prepared once a day and the DBNPA concentration was determined prior to

discharge.

As can be seen, the DBNPA concentrations were stable, regardless of the

amount of solid biocide in the apparatus. This may be compared to Fig. 3

which shows the decrease in concentrations of biocide in solutions prepared

using the conventional methods, upon biocide depletion. The time scale in

Fig. 4 represents the actual dates.

Example 2: A mode of Operation of the Apparatus - A Case Study

and Field trial.

The performance of the dissolution apparatus according to the present

invention was demonstrated for the application of a non-oxidative biocide

e.g. 2,2-dibromo-3-nitrilopropionamide (DBNPA). (A) Test Site: The test was conducted in a cooling tower located on the

shores of the Mediterranean Sea. The 8m³ cooling tower has a daily makeup

of approximately 20m³, and a concentration ratio that ranged between 6-10.

Typical pH values for the cooling water ranged from 8.5-8.8. A portion of the

re-circulated water was filtered through a disk filter. The ambient

temperatures during the trial were 25-30° C.

(B) Device Operation:

1. Installation:

1.1 The apparatus was placed within 2 meters of the treated tower.

1.2 The apparatus was secured firmly to prevent tilting during operation.

1.3 The apparatus was connected to a water main (as a water source), to a

power source (220V, AC), and the outlet of the apparatus was connected via

flexible tubing to the tower basin in a way as to prevent siphoning of the

water back to the apparatus.

2. Operation:

2.1 The apparatus was filled with solid DBNPA (20 Kg. of tablets) through

the filling port at the top of the apparatus, from a conventional biocide

bucket.

2.2 The volume of biocide solution was 10 liters. It was determined

according to tower volume and dosing regime. The volume was set by

positioning the water volume electrode in the proper position.

2.3 The operational parameters were fed into the PLC controller and the

apparatus became operative. 2.4 The sequence of events upon operation was as follows:

2.4.1 At the pre-set time the PLC operated an electronic faucet, which

allowed for the pre-determined volume of water (10 liters) to fill the

apparatus. The filling time was in the range of l-1.5min.

2.4.2 After filling with the appropriate volume of water the system began to

circulate the water for a pre-set time (60 min.) and then the prepared

saturated solution (typical concentrations ranged from 15,000 to 17,000 mg/1)

was delivered to the treated tower. The delivery time was 2 min.

2.4.3 After the operating cycle the apparatus was idle until the next

scheduled operation sequence.

2.4.4 The entire operation sequence continued in this case for 65 min.

(C) DBNPA Application Mode:

The tower was treated with a daily slug (23 mg/1) of an aqueous DBNPA

solution generated by the solid biocide dissolution apparatus of the present

invention, using DBNPA tablets as the solid biocide source.

The DBNPA solution added to the tower was saturated. The amount of

solution added was such that it created a final concentration of 23 mg/1 upon

addition to the tower.

(D) Microbiological Control:

Counts of total bacteria and residual oxidant level (mg/1 as Cl₂) measured

during the trial are presented in Figure 5. The convenient method to determine the DBNPA concentration under field conditions is by using the

dialkyl-p-phenylenediamine (DPD) method. This method is the conventional

method for the determination of residual oxidant levels. Although DBNPA is

a non-oxidizing biocide, it was demonstrated that its concentration could be

followed by the DPD method based on a calibration curve.

The data reflect the measurements prior to the addition of the daily slug

dose (23 mg/1) that was prepared in the solid biocide dissolution apparatus

of the present invention, and 60 minutes after the DBNPA solution was

added to the tower. The results (presented in Figure 5) show that before the

addition of the daily slug dose, the residual oxidant was zero and the

bacterial counts averaged at lxlO⁵ CFU/ml.

After the addition of the daily dose (after 60 minutes), the residual oxidant

in the water was high and the concentration of bacteria decreased

substantially. The mean bacterial concentration (obtained 24 hours after the

last addition of DBNPA dose on the previous day) was ca. lxlO⁵ CFU/ml,

which is acceptable in such a treatment regime.

The results of the field trial showed that the dissolution apparatus

performed well for the duration of the trial (two months) in terms of

technical performance and the DBNPA solution properties. DBNPA

solutions were practically saturated and concentrations were constant. The

DBNPA tablets used during the trial period were consumed continuously and no mechanical obstacles were observed in terms of tablet delivery from

the storage compartment to the dissolution chamber.

The microbiological results showed that bacterial control was maintained

throughout the experiment despite the high pH range in which the tower

operated.

Example 3 : Operation of the Apparatus in a continuous mode.

The solid biocide dissolution system was operated continuously in

accordance with the previously described mode of continuous operation. The

system was operated with varying flow rates and the results were as

follows:

The results represent an average of 5 samples drawn within 30 minutes of

operation at the designated flow.

The foregoing disclosure and description of the invention is merely

illustrative and explanatory thereof. Various changes in the details of the

illustrated configuration and mode of operation may be made by a person

skilled in the art within the scope of the invention, without departing from

the true spirit of it. Thus, the same principle and outcome can be obtained

with other combinations of pumps, venturi based devices and control valves

or other means. For example, a similar outcome was obtained by a

combination of one pump and two control valves as described in Fig. 6.

Claims

Claims

1. A device for dissolution of a particulate material to provide a constant

concentration of solution comprising:

(a) a particulate biocide compartment;

(b) means to supply said particulate material to said dissolution chamber,

containing means for prevention of the formation of lumps which would

block the descent of the solid;

(c) a dissolution chamber for dissolving the particulate material with liquid;

said dissolution chamber having an inlet line for providing circulated

solution of the particulate material to flow through opening(s) in its upper

and lower parts to allow the solution of dissolved particulate into a solution

tank;

(d) means to control the flow of particulate-free liquid;

(e) an optional screen or a sieve to prevent the particulate material from

entering into the solution tank;

(f) an inlet line for adding liquid into the solution tank;

(g) means for circulating the solution of said particulate material from the

solution tank to the dissolution chamber until an appropriate concentration

is obtained;

(h) means for discharging the solution having the appropriate concentration

of said particulate material from said tank through an outlet line; and

optionally (i) means for operation of the device in either a continuous and/or batch

mode; and optionally

(j) means for automatically controlling and monitoring the device operation

through a central processing unit.

2. A device according to claim 1, for dissolution of a particulate material to

provide a saturated solution.

3. A device according to claim 1, for dissolution of a particulate material to

provide a near-saturated solution.

4. A device according to claim 1, for dissolution of a particulate material to

provide a solution with a constant concentration.

5. A device according to any of claims 1 to 4 containing means for loading of

the solid material via a specially designed disposable cartridge or closed

covered package, while minimizing the exposure of operators to the applied

solid material.

6. A device for dissolution of a particulate material according to any of claims

1 to 5 wherein the various components can be installed in one or several

units, according to the field requirements.

7. A device according to any of claims 1 to 6, wherein means for supplying

particulate material to the said dissolution chamber comprises a removable

(detachable) rigid container connected in its lower part to the dissolution

chamber and contains any desired amount of particulate material which

moves freely from the container to the dissolution chamber.

8. Means for supplying particulate material to the dissolution chamber

according to claim 7, comprising means for LS solid level detection for

indicating the amount of particulate material left and for alarm.

9. A device according to any of claims 1 to 8, wherein said solution tank has

a predetermined liquid therein and means to control and monitor the liquid

at the desired level.

10. A solution tank according to claim 9, wherein liquid level is monitored

and controlled by any means of LSHL level switching.

11. A device according to any of claims 1 to 10, wherein said liquid is water.

12. A device according to any of claims 1 to 11, wherein the particulate

material has biocidal properties.

13. A device according to any of claims 1 to 12, wherein the particulate

material is 2,2-dibromo-3-nitrilopropionamide (DBNPA).

14. A device according to claim 1, wherein an inverted cone prevents the

formation of lumps which may block the descent of the solid.

15. A device according to claim 1, wherein the physical dimensions of the

dissolution chamber allow for a flow regime that prevents carry over of

particulate matter to the solution tank.

16. A device according to claim 1, wherein sieved openings in the dissolution

chamber have holes impermeable to the particulate material thus

preventing its free release from the dissolution chamber.

17. A method for continuous dissolution of a particulate material in a liquid

to obtain a constant concentration of solution, using a device for dissolution,

according to claim 1.

18. A method for continuous dissolution of a particulate material in a liquid

to obtain a saturated solution, using a device for dissolution, according to

claim 1.

19. A method for continuous dissolution of a particulate material in a liquid

to obtain a near-saturated solution, using a device for dissolution, according

to claim 1.

20. A method for batch dissolution of a particulate material in a liquid to

obtain a constant concentration of solution, using a device for dissolution,

according to claim 1.

21. A method for batch dissolution of a particulate material in a liquid to

obtain a saturated solution, using a device for dissolution, according to claim

1.

22. A method for batch dissolution of a particulate material in a liquid to

obtain a near-saturated solution, using a device for dissolution, according to

claim 1.

23. A method for continuous dissolution of a particulate material, according

to claims 17 - 19, wherein the dissolved material is a biocide.

24. A method for batch dissolution of a particulate material according to

claims 20-22, wherein the dissolved material is a biocide.