GB2335656A - Flocculation control - Google Patents

Abstract

A method for inducing flocculation and precipitation of impurities from a liquid or a liquid stream, eg. water, comprises treating the liquid with a flocculation agent, in the form of a metal salt, and applying to the treated liquid a magnetic field with flat wave pulses at a sweep of frequencies so as to accelerate floc formation and precipitation.

Description

2335656 FLOCCULATION CONTROL The present invention relates to flocculation

control and particularly to flocculation control of liquids and liquids streams carrying impurities and utilizing a flocculation agent.

It is an ongoing problem to remove from liquid streams, for example water, impurities therein. This is often assisted by addition thereto of a flocculation agent, e.g. an inorganic salt at relatively small dosage rates. This is known to markedly assist in the removal of impurities for liquids, particularly when utilized in connection with polyelectrolyte.

For some time now utilization of polyelectrolytes to produce drinking water for example, has been problematic and companies utilizing the same have been under pressure to reduce or remove polyelectrolytes particularly from drinking water or other liquid streams where they can give rise to residual byproducts. The effect of microscopic residual by-products from the polyeleCtrolytes can have a profound accumulative effect on human or animal life. The need exists therefore inter alia to reduce or eliminate the use of polyelectrolytes without the loss of effectiveness of any treatment.

Flocculation agents are often used in the purification of naturally occurring water supplies such as river water or well water. Such flocculation agents include aluminium sulphates and chlorides and such ferric salts as ferric sulphate and ferric chloride. The flocculation agents give rise to flocs which are essentially -he hydroxide of the metal concerned. For example, when using aluminium sulphate, the flocculation e-,uat-ion is as follows:- i- - 2 A13,1, + 3H20 -qqc-AI(OH)3+ 3H+ The aluminium hydroxide floc thus found absorbs and coagulates any suspended solids in for example river water. As the floc grows in size it settles to form a sludge leaving a bright clear supernatant water above it. Utilizing aluminium chloride, ferric sulphate or ferric chloride will have similar effects which may be individually matched to the type and rate of flocculation required.

lo It is also known to prevent scale formation in hot water systems by applying a magnetic flux to a heat exchange liquid with a significant level of calcium carbonate therein; for example, when the heat exchange liquid is derived from a hard (calcium b'Lcarbcnate) water source.

This has the effect of causing calcium carbonate so formed, which would otherwise have been laid down upon the heat exchange surfaces, to end up in suspension so that any resultant scale is not formed upon the heat exchange surfaces but is suspended as calcium carbonate and carried away in the liquid stream. The reaction of calcium bicarbonate to form calcium carbonate thus occurs at a heat transfer surface for examD-Ie within a heat exchanger. This reaction does not significantly occur at room temperature.

1 We have now found that flocculation agents which are often inorganic metal salts respond rather differently when subjected to a magnetic flux in that they can be caused to flocculate along with other impurities of a liquid or liquid stream at a relatively accelerated rate and to precipitate out with proportionate ease, by utilization of a magnetic flux. Such a f-inding is particularly applicable to laboratory experiments involving crystallization and precipitation, production of potable water, the production of paper and to effluent treatment. Accordingly we have discovered that by utiliz--"ng a coil wrapped around a test vessel or pipe and energised with a flat wave pulse over a sweep of frequencies, floc formation occurs at an accelerated rate, sedimentation rates are similarly enhanced and where a clear liquid for example, pure water is concerned, clarity is also improved.

The result of this is that polyelectrolytes can be 10 signif-Lcantly reduced or eliminated all together and that the resultant precipitates are formed with coarse discrete particles and not in an amorphous mass, so making the problems of disposal significantly easier.

Anct-her problem with treating liquid streams is that encountered when treating high saline water such as sea or brackish water by reverse osmosis or other membrane methods. Membrane iDroblems occur in such arrangements when the concent--ation of calcium sulphate exceeds its normal solubility. In membrane technology, clear water is produced in a series of stages so that the mother liquor from which it is derived concentrates dissolved salts in a number of stages.

If solubility of calcium sulphate in a particular system is exceeded, calcium sulphate becomes a "Plaster of Paris" blinding system and hence spoils the membrane. Calcium sulphate is notoriously difficult to remove without destroying the substrate to which it is attached.

Similar-1v, the treatment of effluents from sulphuric acid 30 battery manufacture leads to very high levels of calcium sulphate when the acidic effluent is treated with lime (calcium hydroxide).

We have now found that it is possible to precipitate calcium 35 sulliDhate -from solution in a form which can be removed by 4 - simple filtration without blinding either filters or membranes. Further, by using calcium aluminate as a flocculant in the system, economic pretreatment before passing to osmosis membranes and indeed pre-treatment of effluents from sulphuric acid battery manufacture can be readily achieved.

Accordingiv, one aspect of the present invention provides a method for inducing flocculation and precipitation of impurities from a liquid or liquid stream which method comprises treating said liquid with a flocculating agent in the form of metal salt; characterized by applying to said treated liquid a magnetic field with flat wave pulses over a sweep of frequencies therebv to accelerate floc formulation and subsequent precipitation. It has been found that said process works effectively at room temperature.

In a second aspect of the present invention, there is provided an;%onra'i-,s for induction and precipitation of impurities from j, 1, iquid or a l iquid stream -which apparatus comprises a conta-Lner for said -1iqu.'d; characterized by means for introduction of a flocculant into said liquid; and a i magnetic fl-,x generating means juxtaposed to said container L and adapted to apply a controllable magnetic flux density to 30 the c. ::)ntents of said container.

The -'au-id st-ream may be selected from paper making liquid streams, effluent treatment streams and liquid streams associated with the production of potable water.

The flocculants selected may be aluminium, calcium, ferric, or ferrous salts and -particularly may be selected from aluminium sulphate, polyaluminium chloride, ferric sulphate, ferric chloride, ferrous sulphate, ferrous chloride and 5 calcium aluminate.

The flocculant may be calcium hydroxide and may be adapted for the treatment of hard water by precipitation of calcium carbonate. Preferably, the process of the present invention is utilized along with the Spiractor process.

The flocculation agent may be selected from a calcium salt and utilized as a pretreatment for liquid streams carrying amounts of calcium sulphate or other inorganic salts in excess of is solubility in the liquid stream. More -preferably the method of the present invention is utilized with a current streaming device.

In a)articularly preferred form of the invention, the magnetic field is generated by a square or triangular wave generator with frequency and power controls. The generator may be formed with one or more coils juxtaposed about a container in which the liquid is contained, or a pipe through which said liquid passes.

The invenl--.-;'_on will now be described, by way of illustration on'LV, with reference to rhe following examples when read with the Ficrures accompanying this application, wherein:- Figure 1 shows in vertical diagrammatic plan view, a wave generator and reaction vessel; and Figure 2 shows use of the a-r-rangement of Figure 1 along with a current streaming detecto-r.

With reference to Figure 1, wave generator 1 is caused to operate at 700 to 3000 Hertz at a power output between 25 milliamps and 2 amps. It is connected to a reactor vessel which in the present instance is a 500 ml glass cylinder having a diameter of about 5 cm. The reactor vessel has between 12 to 16 coils about the reactor vessel where by varying the power, the magnetic flux density within the reactor vessel can be changed.

This arrangement is similarly applied to Figure 2 wherein the reactor vessel 2 may be an open tube through which liquid will f low or a closed tube. The wave generator 1 works to a similar set of parameters as given above in Figure 1, with the exceptEion that frequency is controllable as a result of an input to the wave generator from the current streaming detector 4 via input 7. Simultaneously, the current streaming detector 4 is linked to a titrator 5 for insertion of cationic or anionic substances in response to value from the liquid or licruid stream in the reactor vessel 2 which in turn is dependent upor- the cont-rol of power and frequency of wave generator 1.

The cneration of the devices as shown in Figures 1 and 2 will become clear from the following examples:- EXAMPLE 1

To avoid an.,i minute differences in dose rates, a sanDle of water was treated with aluminium sulphate divided into two 500 m.! measuring cylinders as shown 1. One of the cylinders was fit-Led with a coil 3.

the following flocculation agents was added to the amounts between 5 and 150 mg/l:- aluminium chloride, ferric sulphate, ferric ferroils chio-ride, oe-r-rous and fer-rous sulphate.

1 litre and then in Figure Each of liquid in sulphate, chloride, 7 - It was found that by setting the values of the magnetic flux density as set out above appropriate to the particular flocculation agent used, floc formulation, compared with control samples, occurs at appropriate twice the rate in the vessel energized by the coil. At the same time sedimentation rates were similarly enhanced and final water clarity was improved, most probably because coarse discrete particles were formed rather than amorphous fine particulate matter.

EXAMPLE 2

The softening of hard water containing alkaline or bicarbonate hardness usually involves simple treatment with lime (calcium hydroxide) in quantities equivalent to the bicarbonate level.

In such circLn, stances, calcium carbonate will be precipitated giving a significant reduction of total hardness along with an equivalent reduction in total dissolved solids. A process such as this has been used for many years and again speed and efficiency of the process is improved using polyelectrolytes.

The parameters set out in Example 1 above were repeated utilizing a sample of hard water treated with lime. This was thoroughly nixed and then divided into two equal portions, one portion being treated by the device of the present invention and IE-he other one being treated as a control.

In the t_-eat-ed sample it was found that a precipitate formed far mo-re rapidly than in the untreated sample, the precipitate in tt-he treated sample had significantly larger particle sizes t'-liar) the untreated sample, and hence the sedimentation rates of L-he treated sample were approximately double that of the untreated samnle.

1 T n the 'Xreaed sample, the sludge or final settlement llas readily dewatered into a drier cake on filtration and final residual hardness and alkalinity of the treated water was relatively reduced.

EXAMPLE 3

In the Spi-ractor process water treated with lime was passed tangentially into a cone shaped vessel charged with coarse sand. Calcium carbonate formed about the sand grains as the react'Lon proceeded and hard balls were formed to the size of marbles. The process was slow but effective since any hardness in the water was removed as large spheres and not in the form of a sludge as might have been expected in the straight lime treatment.

The device described herein enhances this process ensuring more rapid crystallization on a sand bed. The spheres so formed are of greater mechanical strength so that the throughput of any given plant can be increased. Similarly when treating streams with high sulphate levels, calcium sulphate can be _removed before exposure to the liquid stream to any membrane or reverse osmosis svstem.

B7 utilization Of an arrangement shown in Figure 1, both -L sed,Lmenat--ion and watersoftening with lime in the Spiractor process can be enhanced in accord with the results achieved in!---xamiDle 2.

EX.lPLE 4 The treatment of high saline waters such as sea water by reverse o_cmosis and other membrane techniques gives rise to problems which occur when L- he concentration of calcium sulphate exceeds its normal solubility. In membrane technology, pure water is produced in a series of stages and hence the mother l--c[uor from which it is derived concentrates dissolved salts in a similar series of stages.

If the solubility of calcium sulphate in a particular system is exceeded, the calcium sulphate forms a 'Tlaster of Paris" blinding system and spoils the membrane. Calcium sulphate is notoriously difficult to remove without destroying the substrate from which it is attached.

Similar circumstances arise when treating effluents from 10 sulphuric acid battery manufacture since very high levels of calcium sulphate are generated when the acid effluent is treated with lime. By use of the process of the present invention it is now possible to pre-precipitate calcium sulphate from solutions in a form which can be removed by simple filtration without blinding either filter or membranes. Further by using calcium aluminate in the system (which is known to remove sulphates in general) an economic pretreatment for the protection of the membranes now becomes possible.

By use of the arrangement as shown in Figure 1, a sample tre;-r,:ed bi the device of the present invention leads to increased speed of crystallization and precipitation of the calciurr. sullohate the crystals were coarser and more discrete than in the control sample where the crystals were produced as an amorphous.mass. Hence sedimentation speed was increased in the treated reactor vessels and settled sludaes were more readily dewatered.

EX7-'dE P L E 5 The sed-L.-.-,entation, coagulation and separation of particles from solution is a complex system where charges on the components of the system determine the rate and effectiveness of the Drocess. in recent years methods of unravelling thils comnlex of charges have been discovered and brought into commercial practice in many water based industries, for example, paper making, potable water treatment, sewage and effluent treatment etc. one particular device has been developed by Lasertrim Limited and can detect the charge state 5 of a flow be it cationic, neutral or anionic.

The device of the present invention is particularly useful in paper making where -the charged balance of materials passing to a wire web producLng the wet mass to become paper is critical importance. A detection apparatus based on Streaming Current Technology is shown in Figure 2 annexed hereto and can be used to detect the original charge state of a system, and by a titrating effect add cationic or anionic materials to achieve a required balance.

is The use of the device in accordance with the present invention with this arrangement is described hereinafter.

Samples of hard water were treated with lime equivalent to the 20 bicarbonate alkalinity. Small amounts of ferric chloride were applied to each after the lime had been added in order to visual.,e the results. One sample was treated with the device as herein described and the other one was utilized as a control. When the two samples, i.e. the treated and the untreated samples, were examined in a detector apparatus, a reduce-ion of 75% was observed in the cationic demand of the treated sam-ple. This result is wholly surprising but confirms the observations and explains the results in the examples cruoted above.

The device as herein described was installed on an inline St-reaming Current Device controlling aluminium sulphate dosing (see Figure 2). The change in the charge value in the system was immediately detected and the recu--lrei.ent- a flocculant was immediately reduced. Sim-ilar rates as for notable water results are obtained on systems using ferric chloride and ferric sulphate. Thus, both dosages of prime flocculant and polyelectrolyte can be reduced or indeed eliminated using the device described herein.

Using the device in accordance with the present invention, precipitation, flocculation and crystallization reactions can be speeded up and controlled, prime flocculant dosage rates can be reduced, Dolyelectrolyte dosage rates can be reduced or eliminated, results can be measured and controlled using streaming current based techniques, the frequency intensity and rate of electromagnetic pulse or any particular system can be determined and controlled and an ideal flocculate equilibrium can be established using minimal chemical dosages.

is This system is particularly successful for potable water, paper making, effluent treatment systems, crystallization and precipitation systems in creneral; for example those used in laboratorles. Since this system can be controlled and measured. more specific and precise anti-scaling and scale removing units can be bu-il-L.

The jn-k.Ten--.^'lon relates therefEore to an apparatus for reduction and -orec,4LiDitat.'.on of impurities from a liquid or a liquid stream and to a method of inducing flocculation and precin-itation of impurities from a liquid or a liquid stream.

Claims (16)

CLAIMS:-

1. A method for inducing flocculation and precipitation of impurities from a liquid or a liquid stream, which method comprises treating said liquid with a flocculation agent in the form of a metal salt, characterized by applying to said treated liquid a magnetic field with flat wave pulses at a sweep of frequencies thereby 10 to accelerate floc formation and precipitation.

2. A method according to claim 1 wherein the liquid is selected from caper making streams, effluent treatment streams and liquid streams associated with the production of potable 15 water.

3. A method according to either of claims 1 or 2 wherein the floccu7-.,:i, -s are selected from aluminium, calcium, ferric and f s -errou

4. A method according to claim 3 wherein the flocculants are selected from aluminium sulphate, polyaluminium chloride, C i,err:c sullchate, ferric chloride, ferrous sulphate, ferrous chloride and Calcium aluminate.

S. A method according to claim 3 wherein the flocculant is cal-c-i,.,.im hvdroxide adapted for the treatment of hardness in wate-r bv crecipitation of calcium carbonate.

6. A met-hed accord-ing to claim 5 utilized in the Spiractor proceSS.

7.A. method a--cordIng to anv of claims 1 to 4 wherein the F--'occl-l'-,a'L'or agent is se'ected from a calcium salt and is as a treatment for liquid streams carrying amounts - 13 of calcium sulphate in excess of its solubility in the said liauid stream.

8. A. method according to any of claims 1 to 7 utilized with a current streaming device.

9. A method according to any preceding claim wherein the magnetic field is generated by a square or triangular wave generator with frequency and power controls.

10. A method according to claim 9 wherein the generator is formed in part by one or more coils disposed about a container or pipe through which said liquid passes or in which it is L, contained.

11. All-n apparatus for the induction and precipitation of;1.mpuri-ies from a liquid or a liquid stream which apparatus comprises a container for said liquid, cha.-acterized by means of the introduction of a flocculant into sa'Ld liquid and magnetic flux generating means juxtaposed said container and adapted to apply a controllable magnetic,-Flux 1-ens-it--y to the contents of the said container.

12. AL- apparatus according to claim 11 adapted for use in paper makincr, effluent treatment or production of potable water.

13. An apparatus according to either of claims 11 or 12 incorporated in the Spiractor process.

l-'. An A--cnara,-,s according t_o any of claims 11 to 13 wherein the ":-eld is generated by a square or triangular wave genera.-)r wjc-. frequency and power control.

15. An apparatus according to claim 14 wherein the generator is formed in part of one or more coils disposed about a container through which liquid passes or in which it is contained.

16. An apparatus according to either of claims 14 or 15 wherein the magnetic field is generated at a frequency of 700 to 3000 Hz at a power output between 25 milliamps and 2 amps.