IL34888A - Deionisation of water - Google Patents

Description

Deionisation of water ROHM HAAS COMPANY i 33156 invention concerned with a containing mineral ich in of the whic comprises the ao softened by contacting the water with a strongly acidic contacting the water with a basic anion c the water with a strongly basic 2 an exchanger functional or In accordance with this invention there ia a process for water containing mineral which comprises t the water to an acidic softened water then contacting the acidic water with a weakly anion and next contacting the water with a strongly basic I anion wherein the acidic is divided into and major portion is contacted with the basic and the treated major portion is th minor portion ao to water containing silica ions and acid ions in a within the from to and contacted with tho strongly basic anion An illustrative embodiment of tbe invention will now bo described with reference to Figure 1 of the anying drawings which depicts a flow sheet of a deionis tion Referring now to a raw feed water 1 to is used which contains monovalent cations ao and potassium divalent cations such as calcium mineral acid anions ouch as chloride resin such as Amberlite in order to exchange hydrogen ions in the resin for cations in the raw The effluent 3 from column 2 is passed through a degasifier in order to remove carbon dioxide and the degasified stream 5 is split at valve 6 and a major portion 7 more than of the acidic softened water containing silica ions and mineral acid ions is next passed through a weakly basic anion exchange resin column The resin in column 8 may typically be a polyamine type resin such as Amberlite base which previously has been regenerated with an alkali solution to remove mineral acid A minor portion 9 of the softened water is passed to a strongly basic anion exchange column En the water stream 9 is caused to mix with the effluent j 11 from the weakly basic exchanger 8 so as to form a mixed stream 12 which is directed down through the basic anion exchanger The effluent stream from exchanger 10 is deionized By regulating the amount of the acidic softened water stream which is passed down through column and the amount of the stream of that same water which is made to column the ratio of silica acid ions in the mixed water stream is adjusted to a range of from to the adjustment is made to within a range of from to The resin in exchanger 2 is regenerated with acid admitted from vessel and withdrawn through valve The resin in vessel 8 is regenerated with sodium carbonate admitted vessel 16 and withdrawn through valve The resin in exchanger 10 is regenerated with caustic soda solution from storage vessel spent regenerant being withdrawn through valve The process of the invention is of particular utility in removing the production of deionized water of very low silica content being important in order to prevent the formation of silica scale in This is particularly important in the case of steam turbines for power plants because silica deposits reduce the efficiency of the turbines and make it necessary to shut the turbines down for a descaling Shutdowns of power plants are expensive since the plants lose their capacity or the use of spare units is made Prevention of silica deposits in the turbines can only be accomplished by reducing the amount of silica in the steam which feeds the This in turn requires the manufacture of low concentrations of silica in the concentrated boiler salines inasmuch as silica in the steam is a direct function of silica in the boiler Such low concentrations can be partly attained by increased boiler in many cases the feedwater may contain such high amounts of silica that the becomes Then treating the feedwater to reduce its silica content becomes The present invention constitutes an important improvement over conventional three bed systems in which the total effluent from the cation exchanger is passed to the weak base in that it possible the use of a smaller amount of the weakly basic anion exchanger in order to deionize water having a given silica composition of this further results in the use of a smaller amount of the regenerant required for the weakly basic the concentration of residual silica in the final deionized water effluent from the system of the present c invention is materially less than that found in the conventional system of water A key to the underlying principle of the present invention is the fact that Type I strongly basic anion exchange resins are capable of adsorbing silica ions in water very and that such resins have an exceptionally high capacity for silica This is illustrated by the graph in which shows the utilization of the ion exchange capacity of a typical Type I Amberlite In the vertical ordinate represents ion exchange capacity utilization and the horizontal ordinate represents weight silica ions in the influent to the strong base exchanger expressed as silica ions mineral acid ions x The term ion exchange capacity utilization means the breakthrough capacity per unit volume of the Type I resin divided by the quantity of hydroxide ion exchange groups per unit volume of the resin in the regenerated In other when all the hydroxide ion exchange groups in the resin are exhausted by an equivalent quantity of the capacity utilization is As will be seen from 2 a maximum capacity utilization of the resin is attained when the percent of silica to total anions in the influent water ranges imately from 80 to This phenomenon is attributable to the fact that one ion exchange group of the Type I resin is capable of adsorbing more than one silica Another reason for this phenomenon is the fact that even when the ion exchange groups which have been exhausted with silica ions come into contact with chloride with the resultant replacement of silica ions by chloride most of the silica ions thus liberated remain inside the resin with only a small part of the liberated silica ions diffusing out of the resin It has also been determined that when Type I resin impregnated with uncombined silica is the uncombined silica is eluted very easily by an alkali the regenerant requirement for obtaining a given quantity of hydroxide groups in the Type I resin is almost the same whether or not the resin contains uncombined the water deionization process is carried out in the manner so that the ratio of silica acidic ions in the influent to column 10 as shown in the utilization of ion exchange capacity of the resin is This capacity utilization is quite especially when compared with a capacity utilization value of which is achieved when the anionic constituents comprise almost 100 silica as is the normal sit in the conventional water ionization Another advantage of the present invention over the prior art method resides in the quantity of silica ions adsorbed Tho phenomena are only with the of I strongly ouch tho functional groups auch as rci basicities for silica than do the Typo In a conventional water deionisation ions account for of the anions adsorbed by the basic anion exchange In this even when a Type I resin is used the utilization of its capacity is but as seen in The capacity utilization is still lower than this value when a Type II renin is These facts clearly indicate that with the convention water deionization no advantage can be taken of the previously described special feature of the Type I By sharp the midified system of the present invention does make possible the use of that feature to obtain a measurable improvement in the deionization as will now be The advantages of the present invention are ically illustrated in Table I which reflects data obtained using a Type I resin regenerated at a level of g TABLE I New Conventional System System Ratio of silica acid ions in the fluent Resin converted to hydroxide form upon regeneration resin Capacity utilization Breakthrough g as CaCO g as CaCO capacity per liter per liter resi Ratio of influent anionic tration New Conventional System System Ratio of resin volume required Effluent residual silica ppm as SiOp ppm as SiOp tration As seen from the data in Table in the production of a given quantity of deionized the new o system provides approximately a saving in the resin volume required an equivalent saving in the regenerant requirement for that the new system compares favorably with the conventional system in terms of purity of the final The reduction of resin volume achieved results in a decrease in the which in turn contributes to an increase in the resin saved decrease in resin for both the weakly basic and the Type I as well as the strongly acidic Another improvement made possible by the present invention is that in the production of deionized water of a given residual silica concentration the new system permits a reduction of the regeneration level of the I resin to a point much lower than is possible with the conventional This is shown in Table II where the pe I resin is used for the production of deionized water having a silica concentration of TABLE II New Conventional bed System Ratio of silica acid ions in the fluent Regeneration level required for 160 g NaOH per 280 g NaOH per ing deionized water liter resin liter resin containing as SiO of silica Resin converted to hydroxide form upon regeneration at resin resin above level Capacity utilization Breakthrough g as g as capacity per liter resin per liter Ratio of influent an ionic concentration Ratio of resin required As seen from the data in Table the new bed system of the present invention makes it possible to reduce the regeneration level requirement for chemicals for of the Type I strongly basic anion exchange resin by more than in comparison with the conventional the volume of resin required for the new system is appreciably less than in the conventional Referring to the system shown in Figure 1 the followin examples will amply instruct in the operation of the Example I The acidic cation exchanger 2 is charged with Amberlite The weakly basic anion exchange resin bed 8 is charged with Amberlite base The strongly basic anion exchange resin bed 10 is charged with Amberlite The volume and regeneration level of each resin are as Resin Regeneration Level Amberlite liters g of resin Amberlite 5 liters regenerant waste base from Amberlite Amberlite 250 g of liter A raw water containing the following impurities was passed through the ion exchange system at a flow rate of 400 liters per the water first going down through column 2 and then through degasifier Total cations 220 ppm as Bicarbonate ions 140 ppm as Mineral acid ions 80 ppm as Silica ions 55 as Approximately 9 of the thus softened water 5 was passed as stream 7 through column 8 to remove mineral acid The effluent 11 therefrom was water which still contained To this water was added as stre m 9 the remaining 7 of the acidic softened water which had been permitted to column The thus mixed stream 12 had silica ions and mineral acid ions of 55 and as the ratio of silica acid ions was The mixed water stream 12 then was passed through column 10 until the silica leakage in the effluent 1 reached a level of ppm as result of this treatment was to up to this point of silica of deionized The average residual silica tration of the treated water was as By a raw water of the same composition set forth above was also at a flow rate of 00 liters per through a conventional exchange system with the following resin volumes and regeneration levels being degasified as per the previously described Resin Volume Regeneration Level Amberlite liters 350 g of resin Amberlite 6 liters regenerant waste base from Amberlite r 02 Amberlite 02 liters 25Ο g of liter resin The result of this treatment was the production of 3 10m of deionized water as of the time when the silica age in the final deionized effluent reached a level of ppm as The average residual silica concentration of the treated water was ppm as The foregoing comparative results indicate that when the Type I resin is regenerated at a level of g liter resin for both cases the new system of the present invention is able to provide a given amount of deionized water with a saving in resin in comparison with the case of the conventional of liters for the weakly basic anion exchange resin and liters for the Type I strongly basic anion exchange This means that the system of the present invention is capable of achieving a saving of the regenerant caustic amounting to in comparison with the caustic requirements for the conventional the new system makes possible a lower tration of residual silica ions in the final effluent o the order of in comparison with the concentration which results with the Example 2 In this example the same comparison was made as in Example and using the system shown in In the process according to the present invention the volume and regeneration level for each resin were as Resin Volume Regeneration Level Amberlite liters 350 g of lite resin Amberlite liters regenerant waste from base Amberlite Amberlite 02 liters 160 g resin A raw water 1 the following impurities was passed through the ion exchange system of 1 at a flow rate of 400 liters per the water first going down through 2 and then down through degasifier Total cations 220 ppm as Bicarbonate ions ppm as Mineral acid ions 80 ppm as Silica ions 55 ppm Of the total volume of the acidic softened water leaving the degasifier approximately was passed through column 8 to remove mineral acid the effluent water 5 therefrom containing only To this water was added the remaining of the acidic softened water which had colupn The mixture of the two streams of water contained trations of silica ions and mineral acid of 55 as and ppm as the ratio of silica acid ions was The mixed water streams were passed through column As a result of this 10m of deionized water was obtained as of the time when the silica leakage in the final effluent from column 16 reached a level of ppm as The average residual silica concentration of the treated water was as For purposes of a raw water of the same composition as above was also at a flow rate of 400 liters per through a conventional ion exchange system with the following resin volumes and regeneration levels Resin Volume Regeneration Level Amberlite liters of liter resin Amberlite liters regenerant waste base from Amberlite Amberlite liters 280 g resin The result of this treatment was that of the deionized water was obtained as of the time when the silica leakage in the final effluent reached a level of ppm as The average silica concentration in the treated water was ppm as The results of these comparative treatments indicated that in order to obtain a given amount of deionized water of a certain silica concentration of as the regenerant for the Type I basic anion exchange resin in the new system of the present invention was kg NaOH per cycle regeneration 160 g whereas the regenerant NaOH required for the same resin in the conventional system was kg NaOH per cycle regeneration 280 g This means that the new system achieved a saving of kg of NaOH in the regenerant requirement is equivalent to a in comparison with the requirement of a conventional In the new system led to a saving of liters in the volume of weakly basic anion exchange resin a saving of in comparison with the conventional A modest saving was also made in the volume of the Type I resin to approximately in comparison with the requirements of the conventional Example The experiments of both Examples 1 and 2 are but in each case the portion of effluent from the cation exchanger which is passed through the weakly basic exchanger is little more than of the and the balance is sent directly to merge into stream gether with the effluent from the weak base exchanger before the mixture is sent through the strong base In each the results are analogous to the results i previous in each instance comparing favorably with corresponding treatments the conventiona system of the prior The Amberlite ion exchange resins referred to in the preceding description are commercially available products manufactured by Rohm and Haas insufficientOCRQuality

Claims (1)

1. 6 A process for deionizing water containing mineral ions which comprises treating the water to produce an acidic then contacting the acidic water with a weakly anion and next contacting the water with a strongly basic Type I anion wherein the acidic softened water divided into major and minor said major portion contacted with the weakly basic exchanger and the thus treated major portion is mixed with said minor portion so as to produce water containing silica and mineral acid ions in a ratio within the range from to and tacted with the strongly basic anion A process according to Claim 1 in which the feed water is softened and rendered acidic by contacting it with a strongly acidic cation A process according to Claim 2 in which the cation exchanger is a sulfonic acid type resin in the weakly basic anion exchanger is a polyamine type resin in the and the strongly basic exchanger is a resin which has trialkylammonlum functional A process according to Claim in which the water prior to contacting w ith the strongly basic anion exchanger contains silica and mineral acid ions which are controlled to be within the range of from to 17 A process according to 3 in which the ratio of said major portion to said minor portion is such that the mixture water streams contacted with strongly basic anion exchanger contains 80 to silica based on total anions in said For the Applicants insufficientOCRQuality