Abstract:
An ion exchange resin plant for the demineralizing or softening water with an arrangement that allows the plant to operate continuously. The plant tank is divided into to two separate compartments that work simultaneously. One compartment effects water demineralization while the other compartment regenerates the ion exchanging resins.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
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   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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   INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
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   The present invention relates to an ion exchange resin plant. 
   BACKGROUND OF THE INVENTION 
   In particular, the invention relates to an ion exchange resin plant for the softening or demineralization of water for industrial use. 
   Ion exchange resins can be mainly divided into cationic resins if they contain negative ionized groups capable of exchanging cations, and anionic resins if they contain positive ionic groups capable of exchanging anions. 
   There are also amphoteric resins, i.e. which contain both anionic and cationic groups bound to the same lattice and resins of the selective type containing, for example, chelating or sequestering groups, capable of fixing particular ions. 
   Exchanging resins are generally produced in the form of spheroidal beads obtained by the polymerization or polycondensation of monomers in a non-solvent medium. 
   The exchanging resins immersed in aqueous solutions absorb water, solvate and are transformed into gels which behave like concentrated solid solutions and swell, due to the effect of osmotic pressure. 
   An ion exchange thus takes place according to an equilibrium reaction between two solutions with a different concentration. 
   The ion exchange technologies currently available for the softening or demineralization of water for industrial use, are characterized by a cyclic functioning, with two well distinct phases: 
   An appropriately defined production phase, during which treated water (demineralized or softened) is obtained with the desired characteristics. 
   A regeneration phase, during which the exchanging resins are treated so as to re-establish the characteristics in order to guarantee the necessary parameter values for the ion exchange to take place in the production phase. 
   This cyclic functioning generally characterized all exchange processes, those effecting regeneration by equicurrent or countercurrent circulation and those comprising beds consisting of exchanging resins of the compact or fluid type. 
   The cyclic functioning of ion exchange plants represents a considerable drawback in that, as almost always happens, a continuous availability of treated water is required. 
   A possible way of avoiding this disadvantage was to provide a storage tank having a sufficient capacity so as to cover at least the regeneration phase. 
   For precautional reasons, however, the tank is normally oversized to allow for the non-remote probability of having to repeat a regeneration cycle, if this proved to be not perfectly effective. 
   The exchanging bed must obviously also be oversized in order to cover, with a greater production, the consumptions of the regeneration phases. 
   An even more onerous solution, but which allows greater tranquillity, is to install two production lines, substantially identical, functioning in parallel, of which one is kept in production and the other effects a regeneration cycle subsequently remaining ready to be used as reserve. 
   When dimensioning the ion exchange beds, it should, in any case, be taken into account that, with the same productive capacity, the greater the quantity of resins forming the bed, the longer the interval is between two subsequent regenerations. 
   In order to have reasonably long regeneration intervals, it is therefore necessary to install large quantities of resins as during production, the ion exchange between water and resins only involves a small part of these. 
   If we imagine the bed as being subdivided into relatively thin successive layers, the exchange takes place and is completed in one layer, consisting of resins which are still intact, whereas the solution which arrives on the layer is deprived of the exchanged ion and in these conditions passes to the subsequent layer. 
   As the ion exchange reaction is in equilibrium, the concentration on the resin of the attached ion is at its maximum on the first layer and decreases in the subsequent ones. 
   As the resins become exhausted, the layer being used, in which the exchange takes place, becomes more distant from the inlet zone of the bed. 
   The production phase must be interrupted, in order to pass to the regeneration, when the layer of resins to be used for the ion exchange has become so thin that it can no longer guarantee the desired characteristics of the water. 
   With this operating procedure, there is therefore a much greater quantity of resins installed than that technically necessary for completing the ion exchange. 
   One of the disadvantages of these types of plant is associated with the high immobilization of capital, caused by the large dimensions of the components and high quantities of resins necessary for forming the bed. 
   Another drawback of the known plants is due to the high operating cost, as a result of the pressure drops to which the stream of water to be purified is subjected while crossing the resin beds, of which only a part, at a certain moment, participates in the process. 
   Attempts have been made in the past to overcome the above disadvantages by the use of different types of plants and processes. 
   The criterion mainly followed was to produce plants equipped with separate chambers reserved for the regeneration. 
   Similar solutions had the disadvantage of requiring a transfer of the resins from one chamber to the other, by introducing moving systems which ended up in inducing their precocious wear. 
   The plants of the known art also involve enormous production and maintenance costs as they use up considerable quantities of resin installed in relation to the minimum expected duration for the regeneration cycle. 
   BRIEF SUMMARY OF THE INVENTION 
   A first objective of the present invention is therefore to produce an ion exchange resin plant suitable for overcoming the above drawbacks of the known art. 
   Another objective of the present invention is to provide a plant with a limited encumbrance, having the same production, which is compact and also having, according to the specific necessities, a development substantially in height or substantially in width. 
   A further objective of the present invention is to provide a plant which has great running simplicity and reliability, due to the possibility of effecting the regeneration on a relatively limited number of valves. 
   The plant according to the present invention advantageously allows the efficiency of the resin exchange to be maximized by adapting the duration of the production phase to the variations in salinity of the water at the inlet. 
   With the plant of the invention, it is also advantageously possible to separate the production of the cationic step from that of the anionic step, thus avoiding the addition of reagents for the neutralization of the eluants. 
   These objectives and advantages according to the present invention are achieved by constructing a plant as described in the independent claims  1  and  6 . 
   Further characteristics of the plant according to the invention are the object of the dependent claims. 
   The ion exchange resin plant according to the invention comprises a tank divided into two separate compartments, a first compartment and a second compartment, containing the exchanging resins, said first and second compartments being arranged so as to allow the plant to operate in continuous so that when one compartment is effecting water purification, the other compartment is regenerating the exchanging resins. 
   The characteristics and advantages of the plant according to the present invention will appear more evident from the following illustrative but non-limiting description, referring to the enclosed schematic drawings in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically represents a purification plant according to the invention; 
       FIG. 2  represents a purification plant according to a first variation of the embodiment of the invention; 
       FIG. 3  represents a purification plant according to a second variation of the embodiment of the invention; 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to the  FIG. 1 , an ion exchange resin plant, in particular for the purification of water, comprises a tank  10  divided into two compartments, a first compartment  11  and a second compartment  12  containing the exchanging resins. 
   The first and second compartment  11 ,  12  are separated from each other by nozzle-holder plates  13 , suitable for supporting the exchanging resins arranged on beds of the compact or fluidized type. 
   Said nozzle-holder plates  13  also distribute and collect the circulating water. 
   Between said first and second compartment  11 ,  12 , there is therefore a chamber  14  in which the purified water is collected, which can subsequently be sent out of the plant through an exit line  22  regulated by an outlet valve  30 . 
   Said valve  30  is preferably an automatic regulation valve, driven by a flow-rate signal. 
   Each of said first and second compartments  11 ,  12  is fed with water to be purified, through a feeding line  20  respectively controlled by a first feeding valve  31  for the first compartment  11  and a second feeding valve  31 ′ for the second compartment  12 . 
   Each of said first and second compartments  11 ,  12  is also equipped with a reagent line  21  intercepted by a pair of entry valves  33 ,  33 ′ to regulate the feeding of the regeneration reagent to the first compartment  11  and the second compartment  12 , respectively. 
   Each of said first and second compartments  11 ,  12  is also equipped with a discharge line of the regeneration water, the first compartment  11  being equipped with a discharge line  24 , whereas the second compartment  12  is equipped with a discharge line  24 ′. 
   Said discharge lines  24  and  24 ′ are intercepted by corresponding discharge valves  32 ,  32 ′ suitable for regulating the discharge of the regeneration water from the first compartment  11  and the second compartment  12 , respectively. 
   Said valves  31 ,  31 ′, and  32 ,  32 ′ are respectively situated upstream and downstream of the inlet block  25  of the feeding line  20  and outlet block of the discharge lines  24  and  24 ′ into and from each compartment  11 ,  12  of the tank  10 . 
   In this respect, it should be noted that depending on the functioning procedure of the plant, water to be purified coming from the feeding line  20  or the regeneration water coming, each specific time, from the compartment  11  or  12  on which is effecting said regeneration, can alternatively pass through the block  25 . 
   The plant is consequently capable of instantaneously and continuously producing the required quantity of treated water (demineralized or softened), using a very limited quantity of resin. 
   This plant embodiment thus allows the quantity of resins to be dimensioned, referring more to hydraulic rather than physico-chemical parameters, thus optimizing the layer of resin to the minimum value sufficient for guaranteeing the desired chemical characteristics of the water. 
   The functioning method of the ion exchange resin plant for the purification of water, or more specifically demineralization or softening of water for industrial use, operates using the ion exchange tank  10  subdivided into two compartments filled with the same resin. 
   When functioning, while one compartment is effecting the purification, the other is regenerating or is in standby. 
   If, for example, the purification is to be effected in compartment  11 , valves  31  and  30  are opened and the desired flow-rate is obtained at the outlet of valve  30 . 
   Contemporaneously compartment  12  effects the regeneration operating as follows: 
   the flow-rate at valve  31  is increased; 
   the flow-rate at the outlet through valve  30 , is kept constant; 
   valve  32 ′ is opened, so that the flow-rate of water necessary for effecting the regeneration of compartment  12  passes through it; 
   by acting on valve  33 ′, the flow-rate of reagent necessary for the regeneration and completing the regeneration, is correctly dosed. 
   By means of an increased feeding from line  20 , compartment  11  not only ensures the required water production, but also supplies the water necessary for the regeneration of the compartment  12 . 
   At the end of the regeneration, the compartment  12  remains in standby. 
   Once the exchange effect of the resins present inside the compartment  11  is exhausted, without having to interrupt the production, compartment  12  is activated by opening valve  31 ′ and closing valve  31 . 
   Valve  30  remains open. 
   As soon as compartment  12  starts production, the regeneration of compartment  11  can be activated in exactly the same way as described for compartment  12 : 
   the flow-rate is increased at valve  31 ′; 
   the flow-rate at the outlet through valve  30 , is kept constant; 
   valve  32  is opened, so that the flow-rate of water necessary for effecting the regeneration of compartment  11  passes through it; 
   by acting on valve  33 , the flow-rate of reagent necessary for the regeneration is correctly dosed. 
   Compartment  12  not only ensures the required water production, but also supplies the water necessary for the regeneration of compartment  11 . 
   At the end of the regeneration, compartment  11  remains in standby. 
   According to a different embodiment of the invention illustrated in  FIG. 2 , the tank  10  is divided into the two compartments  11 ,  12 , physically separated by a septum  15 , but connected through a duct  16 , situated between line  22  and the upper portion of the first compartment  11 . 
   Two chambers  14  are thus formed, each situated at the top of one compartment  11 ,  12 , advantageously obtaining a regenerating stream from above, in order to make the regeneration operation uniform in the compartments, at the same time however maintaining a substantially vertical development of the plant. 
   Said two chambers  14  have the same functions as the single chamber  14 , and the functioning of the plant is substantially the same, allowing the regeneration of one compartment effected by withdrawing a part of the treated water, i.e. demineralized or softened, supplied by the other compartment under production thanks to the connection between the two chambers  14  obtained by means of the duct  16 . 
     FIG. 3  shows a second variation of the plant embodiment, which differs from the version of  FIG. 2  in the type of development assigned to the plant. 
   In this second variation, in fact, the two compartments are separated but inserted side by side in the same tank  10 , in order to obtain a substantially horizontal development. 
   This second embodiment variation also has two chambers  14 , each of which is situated on top of the corresponding compartment  11  or  12  and has a connecting duct  16  between the two above chambers  14 , through which the treated water coming from one of the two compartments under production and sent to the other compartment for regeneration, can flow in both directions. 
   In both of the above variations illustrated in  FIGS. 2 and 3 , the flow of water to be treated is therefore obtained, both for the first compartment  11  and the second compartment  12 , from the bottom upwards towards the top, whereas the regeneration flow goes from the top downwards towards the bottom. 
   An improvement in the production capacity and running economy of the plant with respect to the plants according to the known technique, has been observed in the plants according to the invention. 
   Moreover, a further improvement has been verified in the plants according to the two above embodiment variations, with respect to the uniformity of the quality of the water produced.