GB2048100A - A Process and Apparatus for Purifying Raw Liquids or Effluents - Google Patents

Abstract

Contaminated liquids, particularly water of condensation containing oil, suspended matter and/or dissolved salts are purified by filtering followed by ion-exchange in an ion exchange column wherein the ion-exchange resin (7) acts as a support for at least one filter layer (8, 9) of fibrous and/or particulate material. Where two such filter layers are provided, their surface charge is mutually opposed. When the filter layers (8, 9) are exhausted, they are loosened by compressed air (27) introduced in counterflow, whereafter the broken off pieces obtained in this way are flushed away to separator (22) by water fed in counter-flow (19) through the filter layers. Fresh layers (8, 9) are then prepared in the form of slurries in a mixing and suspending vessel (12) and applied to the ion- exchange resin (7) like filter aid. A mechanical separator 2 acts upstream of the column. <IMAGE>

Description

SPECIFICATION A Process and Apparatus for Purifying Raw Liquids or Effluents The invention relates to a process and apparatus for purifying raw liquids or effluents, which have been contaminated by oily contaminants, suspended matter and dissolved salts, with the use of filters and sodium or hydrogen cation exchangers or combined H, OH cation-anion exchangers.

The purification of liquids, primarily water, contaminated with dissolved salts, suspended matter and oil, comes into ever-increasing significance in view of the need for environmental protection and the reutilisation of the filtered liquid. This is particularly relevant for steam condensates the reutilisation of which signifies not only a saving of water but also the exploitation of the heat content of the water, leading to considerable energy savings. Through the need to protect the environment and the requirement of reutilisability, ever-higher demands are made with regard to water treatment and these either cannot be fully satisfied with known equipments or can only be satisified at great cost.

In known processes the contaminated raw liquid flows through a plurality of seriesconnected devices and is purified to the required extent in a'stepwise manner in the various functional units serving for the removal of the different types of contamination. In the usual processes, first the suspended matter is removed, and in particular in one or several stages with the aid of mechanical filters of varying type and varying packings in dependence upon the kind and amount of contaminants present as well as on the demands set with regard to the decontaminated liquid. Then the oily portion is removed, which may also take place in one or several stages wherein, for example, an activated carbon filter is connected to a mechanical oil separator. Then follows the removal in one or several stages of the dissolved contaminations with the aid of ion exchangers of varying principles of operation.The preceding removal of suspended matter and oily contaminants is a prerequisite for the reliable and disturbance-free functioning of ion exchangers.

The known processes have several disadvantages; they require much space, many individual measures must be carried out or costly automatic control must be used, the efficiency of the independent individual measure influences the final result independently from one another, that is, they influence the purity of the liquid being treated, for continuous operation, many different devices and containers or vessels must be used, losses are high because the losses in the individual stages are additive, i.e. are summed, and the treatment and removal of the waste or refuse (the eluate) of the equipment requires much labour and the use of many devices.

The present invention seeks to provide a process and apparatus for purifying raw liquids or effluents wherein the latter, contaminated with dissolved salts, suspended matter and oil, may be purified in a single functional unit; a separating stage is connected to this functional unit wherein a virtually complete recovery of the liquid is rendered possible.

The invention makes use of the discovery or recognition that the above-described aim may be achieved with a functional unit wherein the ionexchange layer is utilised additionally as a support layer for filter layer(s), the latter consisting of suspended materials selected in dependence on the contaminants in the raw liquids. The purified liquid utilised in the regeneration of the functional unit can be recycled from the separation stage in which the used-up filter layer materials are separated.

According to the invention the filter layer is prepared from suspended materials of a particle size smaller than that of the ion-exchange resin.

The materials for the filter layer are selected with due regard to the pH-dependent electrokinetic potentials of the contaminants in such a manner that the electric charge at the surface of the filter materials is opposed to the charge of the contaminants, or that the electric charge of the surface of two filter layers are mutually opposed.

Such filter layers may consist for instance of positively charged cellulose applied to a cationexchange resin and of negatively charged particles of perlite or bentonite applied on the cellulose.

The filter materials selected in accordance with these considerations are suspended in mutually separated manner in vessels provided with agitators and then passed one after the other in a raw liquid supply duct to the ion-exchange column. In this way the different filter layers can be formed on the ion exchange layer. The raw liquid is precleansed in a clarifying stage whence it departs with a maximum content of 10 mg/l oil, at most 50 mg/l suspended matter and dissolved salts and is then passed through the functional unit pretreated in the above-described manner and it is found that after leaving the filter unit, it contains at most 1 mg/l oil and is practically free of suspended matter as well as of dissolved salts.

Gradually the filter layers are clogged or blocked up by the bound contaminants which can be ascertained by the fact that the flow resistance of the filter unit increases. When the flow resistance has approximately doubled, the filter layer must be regenerated. To this end, the layer is loosened by means of compressed air introduced at the outlet pipe of the filter unit and is flushed by clean liquid passed in counterflow to the raw liquid so that the broken-off pieces of the filter layer resulting from the loosening are flushed to a separator from which the liquid phase is passed back into a mechanical preclarifying stage connected before the filter unit. In this way the total liquid loss is restricted to the very small amount removed from the separator together with the solid phase.

The apparatus according to the invention may therefore be produced from any desired ion exchange column when the latter is equipped with the necessary auxiliary devices.

Accordingly, in the invention the ion-exchange layer serving also as a support layer for the filter layers is coated or covered with fibrous or granular filter material the polarity of which is selected positive or negative in dependence on the type of contamination in the raw effluent or liquid. When the filter layers are saturated with contamination, and thus are used up, these contaminations are washed away with air and water passed in counterflow to the raw liquid or effluent. The two washing media, air and washing liquid, may be passed through the filter unit sequentially or simultaneously.

The filter materials are thereafter separated in a mixing vessel, suspended with pufified or raw liquid and applied to the ion-exchange layer. The preferred filter materials are disintegrated cellulose, filter perlite and/or bentonite.

The apparatus according to the invention is characterised in that the ion-exchanger constitutes a filter unit wherein the ion-exchange layer is formed as a support layer for one or more filter layers. A sludge container is connected via a duct and the intermediation of a pump to the supply side of the filter unit and contains the filter material for the ion exchange layer. A collecting vessel is connected on the discharge side of the filter unit for receiving the filtered clear liquid and is connected for the back-washing of the filter layers with the discharge side of the filter unit by way of a pipe and a pump. The filter unit is connected by a duct with a separator and the separator is connected by way of a duct with a mechanical clarifying stage connected before the filter unit.Storage vessels for the materials forming the filter layers are connected to supply the mixing and slurry container.

The process and apparatus according to the invention are described purely by way of example with reference to purifiying water of condensation in accordance with a preferred embodiment illustrated in the drawing, which is a diagrammatic representation of a purification plant.

The raw liquid to be purified is condensed water contaminated with oil, suspended matter and dissolved salts. This is passed via a duct 1 into a mechanical clarifying stage 2 from which the contaminations separated there are removed via a duct 3. The preclarified condensate is then delivered via a metering pump 4 and a pipe 5 into a filter vessel 6 representing the filter unit according to the invention.

The filter unit 6 is essentially an ion-exchange column wherein, however, the ion-exchange layer 7 consisting of sodium exchange resin serves also as a supporting layer for a first filter layer consisting of disintegrated cellulose and a perlite filter layer 9 applied over the filter layer 8. In the present exemplary embodiment, the cellulose layer 8 has a surface weight of 0.7 kg/m2 while the filter layer 9 onsisting of expanded perlite P2 (Nyirtelek, Hungary) has a surface weight of 5 kg/m2, calculated on the cross-section of the filter unit. The dry disintegrated cellulose is stored in a storage vessel 10 and the dry filter perlite is stored in a storage vessel 11. These storage vessels 1 0, 11 are connected with a mixing and slurrying vessel 12, preferably in such a manner that its emptying may take place by gravity.The slurrying vessel 12, which is equipped with an agitating device, is connected with the inlet side of the filter unit 6, via a duct 13, with the intermediation of a pump 14.

On the discharge side, the filter unit 6 is connected via a duct 15 with a collecting vessel 16 for the filtered condensate the discharge side of which is connected via a duct 17 and a shut-off valve with the slurrying vessel. The discharge side of the collecting vessel 16 is additionally connected with a pipe 18 through which the main quantity of the filtered condensate is led away as the product of the process. Furthermore, the discharge side of the collecting vessel 16 is connected via a pump 19 and a washing water duct 20 with the discharge side of the filter unit 6.

The supply side of the filter unit 6 which receives the raw water or effluent to be purified is connected with a separator 22 via a duct 21. The solid phase separated in the separator may be emptied into a receptacle 23. The interior of the separator 22 containing the liquid phase is connected via a pump 24 and duct 25 with the mechanical preclarifying stage 2.

A mixing and slurrying vessel 12 is additionally connected via a supply pipe 26 and a shut-off valve with the duct 13. Further, a duct 27 for supplying pressurised air leads to the supply side of the filter unit 6. Another compressed air duct 28 leads to the separator 22 for the emptying of the latter.

The apparatus operates as follows: In order to form the filter layers on the ionexchange layer in the filter unit, disintegrated cellulose from the storage vessel 10 and filtered condensed water from the collecting vessel 1 6 are respectively passed (the latter via duct 17) into the slurry vessel 12 and are mixed together therein. The suspended cellulose is passed by way of the pump 14 and through the duct 13 into the filter unit 6 and is applied on the ion-exchange layer 7. In this way a cellulose layer 8 is formed.

Next, filter perlite is introduced from the storage vessel 11 into the slurry vessel 12 and is suspended therein in the above-described manner and also delivered into the filter unit 6 where it settles as a perlite filter layer 9 on the cellulose filter layer 8.

The contaminated raw condensation water passes through the duct 1 to the mechanical clarifying stage 2 where the amount of oily contaminations is reduced to less than 10 mg/l and the amount of suspended matter to less than 50 mg/l. The contaminations separated therein are led away from the mechanical clarifying stage 2 via a duct 3. The precleansed raw water of condensation is delivered by the pump 4 via the duct 5 into the filter unit 6 so that it flows from above downwardly through the filter layers 9, 8 and the ion exchange layer 7. The filtered water of condensation leaves the filter unit 6 via a duct 17 with a flow velocity of about 5 m/h and contains in essence less than 1 mg/l oil and is substantially free of suspended matter and of dissolved salts.

The filtered water of condensation collected in the collecting vessel 16 is for the most part discharged through the duct 18.

A part of the filtered water of condensation collected in the collecting vessel 16 is however passed into the slurry tank 12 for the preparation of the filter material forming the filter layers. A further part of the purified water is required for the regeneration of the filter unit 6. When the resistance to flow in the filter unit 6 rises from its initial value of 40 kPA (ski: 1 Kilopascal=1000 N/m2=0.1 m WS) in the filter unit 6 as a consequence of the clogging of the filter layers 8, 9 to about 80 kPA (8 m WS) the filter layers 8 and 9 must be changed.

To this end, the filter layers 8, 9 are first loosened by means of compressed air introduced into the filter unit 6 from below via the duct 27, and then the filter layers are flushed by means of water flowing in at a velocity of about 10 m/h from the collecting vessel 16 under the agency of the pump 19 via the pipe 20 and thus the layers are removed via the duct 21 into the separator 22. Within the separator 22 the solid matter forming the contaminations from the used-up filter layers 8, 9 are discharged into the receptacle 23. The quantity of water discharged with these solid materials amounts to about 0.2% of the amount of the water of condensation supplied through the duct 1.The liquid phase transporting the rest of the filter layers and separated in the separator 22 is recirculated by means of the pump 24 through the pipe 25 into the mechanical preclarification stage 2.

The chief advantages of the process according to the invention may be summarised in that the oily contaminants, suspended matter and dissolved salts can be removed in a single functional unit and that the salt content can be transformed into salt without causing hardening of the water. In this way significant savings in investment, operation and labour and energy requirements may be made. The oily contaminant content of the purified water lies well under 1 mg/l. The purified water is practically free from suspended matter and from dissolved salts causing water hardness. The loss of liquid in the process is extremely low, about 0.2% and thus the heat energy loss is also low, the heat energy being contained in the water of condensation.

Consequently, the most part of the heat content of the contaminated raw water can be turned to good account.

Preferably, the ion-exchange layer is of sufficiently strong consistency to ensure that the exchange fesin is not entrained with the backwashed or flushed filter layers. In the case where the exchange layer is not formed of a wholly solid porous body, then by selection of an exchanger resin of considerably higher specific weight than that of the filter material, and a corresponding adjustment of the pressure of the washing liquid in the flushing stage it can be ensured that the exchange resin is not appreciably stirred up. In given cases, one may use as exchange layer a loose fill of particulate resin.

material which is bounded on its upper surface by a suitable screening plate which prevents the stirring up of the exchange layer.

Claims (11)

Claims

1. A process for the purification or raw liquids or effluents contaminated with oil, suspended matter and/or dissolved salts, wherein the raw liquid is filtered and then treated in an ionexchange layer, and wherein at least one filter layer of predetermined electric charge or polarity opposite to that of the contaminants is provided on the ion-exchange layer and the raw water is passed first through the or each filter layer and then through the ion-exchange layer.

2. A process according to claim 1, wherein after exhaustion of the or each filter layer, the latter is or are loosened e.g. by passing compressed air therethrough, and then flushed away by a cleaning liquid being passed therethrough, the application of the loosening and cleaning media being simultaneous or sequential.

3. A process according to claim 1 or claim 2, wherein at least two filter layers are used and are prepared separately from each other by suspending the appropriate filter materials, respectively in a pure liquid or a raw liquid and then applying them to the ion-exchange layer sequentially.

4. A process according to claim 3, wherin filter materials of mutually opposite polarity are used for adjacent filter layers.

5. A process according to any preceding claim, wherein disintegrated cellulose, filter perlite and/or bentonite is or are used as filter material.

6. A process according to claim 1, substantially as herein described with reference to and as shown in the accompanying drawing.

7. Apparatus for carrying out the process according to any preceding claim, comprising a filter unit including an ion-exchange layer which serves as a support layer for at least one filter layer and the filter unit is connected by way of a duct and a pump on its raw liquid/effluent supply side with a suspension vessel for suspending filter material in pure or raw water.

8. Apparatus according to claim 7, wherein the discharge side of the filter unit is connected with the supply side of a purified liquid collecting vessel, the discharge side of the collecting vessel being connected by way of an obturatable duct and a pump, with the discharge side of the filter unit and a compressed air duct is connected to the discharge side of the filter unit.

9. Apparatus according to claim 7 or 8, wherein the raw liquid/effluent side of the filter unit is connected via a duct to a solids separator the working space of which is connected via a duct and a pump with a mechanical preclarification stage in the raw liquid/effluent supply line upstream of the filter unit.

10. Apparatus according to any of claims 7 to 9, wherein respective storage vessels for the different filter materials are connected to the suspension vessel.

11. Apparatus according to claim 7 substantially as herein described with reference to and as shown in the accompanying drawing.