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IS 13268 (1992): Demineralization Plant--Guidelines. UDC

628.165.04

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March 1992

IS 13268: 1992

f a r ~ f V f \ i f ~ O T ~ ~ ? f ~ f ~ ~ ~ a r -+ r ~ ~ f f f ~ ; a r . = dIndian Standard

DEMINERALIZATION PLANT-,GUIDELINES

UDe 628'165'04

BIS 1992B U R E A U OF I N D I A N S T A N D A R D SMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002Price Grou, 6arch 1992

IS 13268: 1992

f a r ~ f V f \ i f ~ O T ~ ~ ? f ~ f ~ ~ ~ a r -+ r ~ ~ f f f ~ ; a r . = dIndian Standard

DEMINERALIZATION PLANT-,GUIDELINES

UDe 628'165'04

BIS 1992B U R E A U OF I N D I A N S T A N D A R D SMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002Price Grou, 6

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Water Sectional Committee, CHD 013

FOREWORDThis Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized bythe Water Sectional Committee had been approvr;d by the Chemical Division Council.Demineralized water is required for a wide range of industries involving production of chemicals,pharmaceuticals, fertilizers, steel, power, etc. Besides its other uses, the major use of demineralizedwater is as boiler feed water in boilers, ranging from low pressure to supercritical pressure. Withthe advent of high pressure and super-critical pressure boilers, the quality of demineralized waterhas acquired greater importance. This makes it essential to develop and make available therequired specification for the guidance of users to procure and instal efficient and economicalsystem for production of demineralized water.The specification for demineralization plant varies from one place to other depending upon thesource of water available, ionic load of water, treated water qualit y desired, regenerant availability,etc. These factors are to be taken into account for proper selection of demineralization plant, andto develop their detailed specifications.

Water Sectional Committee, CHD 013

FOREWORDThis Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized bythe Water Sectional Committee had been approvr;d by the Chemical Division Council.Demineralized water is required for a wide range of industries involving production of chemicals,pharmaceuticals, fertilizers, steel, power, etc. Besides its other uses, the major use of demineralizedwater is as boiler feed water in boilers, ranging from low pressure to supercritical pressure. Withthe advent of high pressure and super-critical pressure boilers, the quality of demineralized waterhas acquired greater importance . This makes it essential to develop and make available therequired specification for the guidance of users to procure and instal efficient and economicalsystem for production of demineralized water.The specification fo r demineralization plant varies from one place to other depending upon thesource of water available, ionic load of water, treated water quali ty desired, regenerant availability,etc. These factors are to be taken into account for proper selection of demineralization plant, andto develop their detailed specifications.

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IS 13268 : 1992Indian Standard

DEMINERALIZATION PLANTGUIDELINES1 SCOPE1.1 This standard covers ( a ) the basic detail s-of demineralization plant, ( b ) brief guidelinesfor framing the specification of demineralization plant, ( c ) brief details of various systems,currently in use for production of demineralizedwater, and ( d ) the various considerationsrequired for making the buyers specification,complete in all respects.1.2 Atte'mpts have been made to expose thebuyers to different systems of demineralizationplant, so that it may be easier for them to compare and select the best possible system suitingtheir particular requirements.2 REFERENCESTh e Indian Standards listed below are necessaryadjuncts to this standard:IS No.

252 : 1973Title

Caustic soda, pure and technical ( second revision )265 : 1987 Hydrochloric acid ( thirdrevision)3 FACTORS FO R DRAWING UPSPECIFICATION3.1 The following factors are to be kept in view:before drawing up the 'specification for demi:neralization plant:

a) The source of water (river water, wellwater, etc) available for treatment;b) Quality of treated water;c) End-use of demineralized water;d) The availability of regenerants in thevicinity of the proposed plant;e) Disposal of regeneration wastes; andf) The availability of utilities, such as steam,instrument air, etc.

:3.2 Quality of Feed Water.3.2.1 The quality of water to be treated playsan important role in drawing up the specifications. The system has to be designed to process-raw water available from different sources, suchas rivers , tube wells, rivulets; well s, ponds,:lakes, etc.:3.2.2 The first, step is to make a detailed analysisof raw water for various parameters including,organics, colour, suspended solids, iron,

1

manganese besides other dissolved solids. Theanalysis of raw water shall be carried outthroughout the year to determine its profilevariations with the change of seasons. Recordsof analysis of at least two years shall be madeavailable before fixing up the treated waterquality. Sufficient margin in var ious constituen tsof water may be kept in order to take care ofvariations in the coming years based on yearlyseasonal varia tions in water analysis. The tube-well water composition does not vary muchwith the season, so in that case, it becomeseasier to fix up the design parameters of wateranalysis; but in surface water, fluctuations arequite high, so it becomes difficult to arrive atthe designed analysis. However, a proper assessment has to be made for fixing up designedwater analysis.3.2.3 The next is to properly pretreat the rawwater to obtain water suitable for feeding intodemineralization plant as the ion exchange resinused in demineralization plant are susceptibleto various constituents commonly present inwater including iron, manganese, colour, suspended solids, residual chlorine, etc. The feedwater for demineralizat ion plant shall be freefrom chlorine, organics, iron, manganese, suspended solids within 2 to 3 mg/I. It shall alsobe free from oil and grease to ensure long lifeof the ion exchange resins. All these considera-tions have to be kept in view in the design of ademineralization plant.3.3 Regenerant ChemicalsThe availability of regenerant chemicals in theneighbourhood of demineralization plant alsoplays a decisive role for fixing the guidelines.I t is economical to make use of chemicals available in nearby areas for regeneration of variousion exchange resins. This will also lead to substantial savings in storage capacity of chemicalsin the plant due to their availability at a shortnotice. Regenerant chemicals like hydrochloricacid (IS 265: 1987) and pure caustic soda( IS 252 : 1973) used shall conform to therelevant Indian Standards.3.4 Disposal of Regeneration WastesThe disposal of regeneration wastes plays animportant role. The toxicity, acidity andalkalinity of the waste water have to be withinthe specified limits. These are strictly monitoredvis-a-vis pollution control an d environmentalprotection measures. Normally, the pH ofeffluents of demineralization plant varies depen-ding upon the regeneration of cation or anion.I n case of cation regeneration, the waste acid

. comes to drain, whereas, in case of anion, th e

IS 13268 : 1992Indian Standard

DEMINERALIZATION PLANTGUIDELINES1 SCOPE1.1 This standard covers ( a ) the basic detai ls-of demineralization plant, ( b ) brief guidelinesfor framing the specification of demineralization plant, ( c ) brief details of various systems,currently in use for production of demineralizedwater, and (d ) the various considerationsrequired for making the buyers specification,complete in all respects.1.2 Atte'mpts have been made to expose thebuyers to different systems of demineralizationplant, so that it may be easier for them to compare and select the best possible system suitingtheir particular requirements.2 REFERENCESTh e Indian Standards listed below are necessaryadjuncts to this standard:IS No.

252 : 1973Title

Caustic soda, pure and technical ( second revision )265 : 1987 Hydrochloric acid ( thirdrevision)3 FACTORS FOR DRAWING UPSPECIFICATION3.1 The following factors are to be kept in view:before drawing up the 'specification for demi:neralization plant:

a) The source of water (river water, wellwater, etc) available for treatment;b) Quality of treated water;c) End-use of demineralized water;d) The availability of regenerants in thevicinity of the proposed plant;e) Disposal of regeneration wastes; andf) The availability of utilities, such as steam,instrument air, etc.

:3.2 Quality of Feed Water.3.2.1 The quality of water to be treated playsan important role in drawing up the specifications. The system has to be designed to process-raw water available from different sources, suchas rivers, tube wells, rivulets; well s, ponds,:lakes, etc.:3.2.2 The first, step is to make a detailed analysisof raw water for various parameters including,organics, colour, suspended solids, iron,

1

manganese besides other dissolved solids. Theanalysis of raw water shall be carried outthroughout the year to determine its profilevariations with the change of seasons. Recordsof analysis of at least two years shall be madeavailable before fixing up the treated waterquality. Sufficient margin in various constituen tsof water may be kept in order to take care ofvariations in the coming years based on yearlyseasonal variations in water analysis. The tube-well water composition does not vary muchwith the season, so in that case, it becomeseasier to fix up the design parameters of wateranalysis; bu t in surface water, fluctuations arequite high, so it becomes difficult to arrive atthe designed analysis. However, a proper assessment has to be made for fixing up designedwater analysis.3.2.3 The next is to properly pretreat the rawwater to obtain water suitable for feeding intodemineralization plant as the ion exchange resinused in demineralization plant are susceptibleto various constituents commonly present inwater including iron, manganese, colour, suspended solids, residual chlorine, etc. The feedwater for demineralization plant shall be freefrom chlorine, organics, iron, manganese, suspended solids within 2 to 3 mg/I. It shall alsobe free from oil and grease to ensure long lifeof the ion exchange resins. All these considera-tions have to be kept in view in the design of ademineralization plant.3.3 Regenerant ChemicalsTh e availability of regenerant chemicals in theneighbourhood of demineralization plant alsoplays a decisive role for fixing the guidelines.I t is economical to make use of chemicals available in nearby areas for regeneration of variousio n exchange resins. This will also lead to substantial savings in storage capacity of chemicalsin the plant due to their availability at a shortnotice. Regenerant chemicals like hydrochloricacid (IS 265: 1987) and pure caustic soda( IS 252 : 1973) used shall conform to therelevant Indian Standards.3.4 Disposal of Regeneration WastesThe disposal of regeneration wastes plays animportant role. The toxicity, acidity andalkalinity of the waste water have to be withinthe specified limits. These are strictly monitoredvis-a-vis pollution control an d environmentalprotection measures. Normally, the pH ofeffluents of demineralization plant varies depen-ding upon the regeneration of cation or anion.I n case of cation regeneration, the waste acid

. comes to drain, whereas, in case of anion, th e

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IS 13268 : 1992waste alkali is drained. On mixing of both acidicand alkaline wastes the effluent gets neutralizedto a certain extent. However, it is essential toensure fud neutralization to about pH 7.5 beforethe disposal off as plant effluent.3.5 Utility and Cost3.5.1 Pr e per a s ~ e s s m e n t of the availability ofutilities is imperative before puttmg up theplant. Depending upon the availability, thecomplete scope of demineralization plant canbe developed. In some cases heatin g of regenerant is requirtd. for which arrangement forsteam is to be made; otherwise electrical heatingis to be r e ~ o r t e d to. Besides this, compressed airmay be required for operating various instruments/mechanical equipment. I f the existinginfrastructure does not inc1ude arrangementsfo r supply of compressed air, the same are to beprovided in plants specification.3.5.2 The type of operation, namely, automatic,remi-artomatic or mcmua] has got a major bearing on the cost of the plant. In some cases onlymanual operation is preferred; whereas inother cases semi-auto or auto opera tion isbeing censidered. In case semi-auto operation isdesired, proper care has to be taken in developing the speCIfication because this greatly dependst pon many process sequences.3.5.3 The process s ~ q u e r c e 2dopted for theplant, requires special attention as it makes theplant operation more economical.4 BASIC PARAMETERS4.1 Considerable importance is to be given fordetermination of the basic parameters so asto get a plant suiting the f( quirements of theclient.4.1.1 Buyer specification consists of ( a ) d e s i g n ~( b ) er gineering, ( c ) procurement, ( d ) transportation, ( e ) storage, ( f ) erect jon, an d ( g)commissioning of al1 the work including mechanical, dectrical, instrumentation besides civilwork.

NOTE - Sometimes civil work is excludEd fromth e scope, and included in th e scope of main civilc o n t r a c t o r ~ who executes civil work for the entirepJant including demineralization plant. I t becomesadvantageolls to adopt this, as th e complete responsibility lies with a single civil contractor.fo]]ewing the sa me norms for th e complete factory.I t has got certain disadvantages as well becauseincreased co-ordination is needed between demineralization plant supplier and civil contractorto rompJete th e civil work in time so that the erection work of th e demineralization plant is startedas scheduled. Hence. it is preferred to have on esource responsible for demineralization plantsupply in a11 respects including civil works.

4.1.2 The specification shal I clearly give the minimum, normal and maximum flow rates desiredfor the system. The flow and n umber of streamsrequired largely depend on the requirement of

demineralized water in the end use in otherplants which has to be assessed prior to framingthe specifications. The number of streams ar ealso to be clearly identified as it makes a bigcost impact in the plant. Sometimes, it is preferred to have 100 percent spare stream, whereasin other cases, no spare stream is desired as itis being compensated by creating a large capacityfor storing treated water. The single streamdemineralization plant is designed with highercapacity to get extra water fo r storage to takecare of any extreme urgency. However, it isdefinitely preferable to go in for a minimum oftwo strec:ms. One can go for any number ofstreams, but then the cost of the plant wouldincrease with increase in number of the streams.Therefore, an optimum balance has to be struckfo r fixing the number of streams for a given enduse.4.1.3 The header system sha11 also be clearlymarked in the plant specification. Sometimes, itis desirabJe to have a single header system,whereas in other cases, separate headers fo reach stream are favoured. In some cases, amixed approach is being adopted having bothsingle header, and separate headers fOr someof the process fluid streams. Single headersystem is having certain flexibility, as any unitof this stream can be easily connected to otherllnit or the other stream. So single header systemis commonly preferred. Some clients do preferindividual streams bu t the cost implicationsrequire to be looked into seriously.4.2 Storage CapacityThe storage capacities for the feed water tank,degassed water tank, demineralized water tankand acid and alkali tank are also to be predetermined, an d clearly defined in the specification ofdemineralization plant.4.2.1 Fad Water 1ankThe feed water tank capacity largely dependsupon the availability of feed water, chances offailure Df feeding system, fluctuations in thepressure, and flow of feed water. But in mostof the cases, this tank acts as a buffer tank, andis no t provided with more than 2 to 3 hourscapacity which is just sufficient to provide suction to the feed water pump, so as to maintainconstant pressure to the demineralization plantsystems.4.2.2 Degassed U'ater TankThe capacity of degassed water tank largelydepends upon the frequency of th e regenerationof ion exchange resins, waste water used in theregeneration and extra capacity desired foremergency in the plant. All these factors shallbe kept in view while evolving the minimumcapacity of degassed water tank so that it coversall the contingencies in the plant. Normally it

IS 13268 : 1992waste alkali is drained. On mixing of both acidicand alkaline wastes the effluent gets neutralizedto a certain extent. However, it is essential toensure fud neutralization to about pH 7.5 beforethe disposal off as plant effluent.3.5 Utility and Cost3.5.1 Pr e per a s ~ e s s m e n t of the availability ofutilities is imperative before puttmg up theplant. Depending upon the availability, thecomplete scope of demineralization plant canbe developed. In some cases heatin g of regenerant is requirtd. for which arrangement forsteam is to be made; otherwise electrical heatingis to be r e ~ o r t e d to. Besides this, compressed airmay be required for operating various instruments/mechanical equipment. I f the existinginfrastructure does not inc1ude arrangementsfo r supply of compressed air, the same are to beprovided in plants specification.3.5.2 The type of operation, namely, automatic,remi-artomatic or mcmua] has got a major bearing on the cost of the plant. In some cases onlymanual operation is preferred; whereas inother cases semi-auto or auto opera tion isbeing censidered. In case semi-auto operation isdesired, proper care has to be taken in developing the speCIfication because this greatly dependst pon many process sequences.3.5.3 The process s ~ q u e r c e 2dopted for theplant, requires special attention as it makes theplant operation more economical.4 BASIC PARAMETERS4.1 Considerable importance is to be given fordetermination of the basic parameters so asto get a plant suiting the f( quirements of theclient.4.1.1 Buyer specification consists of ( a ) d e s i g n ~( b ) er gineering, ( c ) procurement, ( d ) transportation, ( e ) storage, ( f ) erect jon, an d ( g)commissioning of al1 the work including mechanical, dectrical, instrumentation besides civilwork.

NOTE - Sometimes civil work is excludEd fromth e scope, and included in th e scope of main civilc o n t r a c t o r ~ who executes civil work fo r the entirepJant including demineralization plant. I t becomesadvantageolls to adopt this, as th e complete responsibility lies with a single civil contractor.fo]]ewing the sa me norms for th e complete factory.I t has got certain disadvantages as well becauseincreased co-ordination is needed between demineralization plant supplier and civil contractorto rompJete th e civil work in time so that the erection work of th e demineralization plant is startedas scheduled. Hence. it is preferred to have on esource responsible for demineralization plantsupply in a11 respects including civil works.

4.1.2 The specification shal I clearly give the minimum, normal and maximum flow rates desiredfor the system. The flow and n umber of streamsrequired largely depend on the requirement of

demineralized water in the end use in otherplants which has to be assessed prior to framingthe specifications. The number of streams ar ealso to be clearly identified as it makes a bigcost impact in the plant. Sometimes, it is preferred to have 100 percent spare stream, whereasin other cases, no spare stream is desired as itis being compensated by creating a large capacityfor storing treated water. The single streamdemineralization plant is designed with highercapacity to get extra water fo r storage to takecare of any extreme urgency. However, it isdefinitely preferable to go in for a minimum oftwo strec:ms. One can go for any number ofstreams, bu t then the cost of the plant wouldincrease with increase in number of the streams.Therefore, an optimum balance has to be struckfo r fixing the number of streams for a given enduse.4.1.3 The header system sha11 also be clearlymarked in the plant specification. Sometimes, itis desirabJe to have a single header system,whereas in other cases, separate headers fo reach stream are favoured. In some cases, amixed approach is being adopted having bothsingle header, and separate headers fOr someof the process fluid streams. Single headersystem is having certain flexibility, as any unitof this stream can be easily connected to otherllnit or the other stream. So single header systemis commonly preferred. Some clients do preferindividual streams bu t the cost implicationsrequire to be looked into seriously.4.2 Storage CapacityThe storage capacities for the feed water tank,degassed water tank, demineralized water tankand acid and alkali tank are also to be predetermined, and clearly defined in the specification ofdemineralization plant.4.2.1 Fad Water 1ankThe feed water tank capacity largely dependsupon the availability of feed water, chances offailure Df feeding system, fluctuations in thepressure, and flow of feed water. But in mostof the cases, this tank acts as a buffer tank, andis no t provided with more than 2 to 3 hourscapacity which is just sufficient to provide suction to the feed water pump, so as to maintainconstant pressure to the demineralization plantsystems.4.2.2 Degassed U'ater TankThe capacity of degassed water tank largelydepends upon the frequency of th e regenerationof ion exchange resins, waste water used in theregeneration and extra capacity desired foremergency in the plant. All these factors shallbe kept in view while evolving the minimumcapacity of degassed water tank so that it coversall the contingencies in the plant. Normally it

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is sized at half an hour pumping capacity ofdegassed water pump.4.2.3 Demineralized Water TankThe capacity of the demineralized water tankgreatly varies from one client to the other. Thecapacity is normally fixed on the basis of exigencies occurring in the plant, the variations in useof demineralized water in down stream plants,use of demineralized water for regeneration,etc. Normally, in power plants clients prefer tohave the storage capacity for 16 to 24 hours, butin other plants it is being kept for 4 to 8 hours.However, there is no strict rule for it as thisentirely depends upon the client's requirements.4.2.4 Acid and Alkali TankThe storage capacities of acid and alkali tanksrequired for regenerations are also to be clearlyindicated in the specification. These capacities.are dependent upon the consideration of thetime it takes to procure the chemicals at plantsite. Where it may take 10-15 days for obtainingthe chemicals, it becomes advisable to go in forat least one month's storage at the plant site. Innormal cases, where a tanker of acid or alkali isexpected within 4 to 6 days time, storage capacity of a minimum of 15 days may be desirable.Wherever the regenerant chemicals are availablein the plant, a limited storage of 3 to 4 days-only may be considered.:5 FEED WATER5.1 Before developing a system and fixing specifications for demineralization plant, the sourceof feed water an d its availability has got to beestablished. Sometimes, water is available in theform of -filtered water after proper chlorination,.coagulation, flocculation, clarification and filtration. The filtered water is being directly fed tothe feed water tank followed by ion exchangersfor production of demineralized water. However,it becomes essential to establish water quality,which shall be free from colour, organics , etc.In case of any colour, organics or free chlorine,the water has to be treated with active carbonto take care of minor quantities of contaminants-coming in feed water. In case of unfiltered'water, the active carbon filters are to be precededby filters for which pressure sand filters are nor-mally used; sometimes dual media filter havingsand and anthracite are also used.-S.2 For dechlorination, sometimes sodiumSUlphite is used, which is dosed in feed waterbefore filtration. Sometimes the system is havingonly one dosing pot, where solid sodiumsulphite is added alongwith water to makesolution. The solution thus prepared is dosed,at a desired rate under pressure before filtration.In other situation, a solution preparation tank'with agitator is provided. The solution is dosedto feed water by means of sulphite dosing pump.6 DEMINERALIZATION SYSTEM.-6.1 There are different kinds of systems for

3

IS 13268 : 1992treatment of water in order to get demineralizedwater. Nowadays, as the cost of regenerantchemical is high, it is advisable to select aneconomical system to reduce recurring cost onchemicals. Systems in operation are describedin brief to guide the buyers in selecting a viableand stable demineralization water plant.6.1.1 Cation exchanger unit having strongacidic-cation exchange resin followed by anionexchanger unit having strong basic anionexchange resin without any degasser system inbetween. This system is prepared for waterhaving less alkalinity of 10J ppm and capable ofgiving demineralized water suitable for lowpressure and to a certain limit for mediumpressure boilers. Besides, this system can comehandy also for industries using demineralizedwater for processing. In this system, bothcocurrent and countercurrent techniques can beadopted depending upon the quality of feedwater, but countercurrent technique is moreeconomical ( see Fig. 1 ). .6.1.2 Cation exchanger u n ~ t having strongacidic-cation exchange reSIn followed bydegasser system having degasser tower, anddegassed water tank followed by strong basicanion exchanger. This system gives demineral ized water for low pressure, and to a certain limitfor medium pressure boilers as well. Here also,both cocurrent and countercurrent regenerationtechniques can be used depending upon thequality of feed water bu t countercurrenttechnique is more economical. This system issuitable for water having moderate alkalinityof about 250 mg!l alkalinity. Here also strongbasic anion exchange resin of Type 1 or Type2 is used depending upon the requirement ofsilica leakage ( see Fig. 2 )6.1.3 Cation exchanger unit having strongacidic-cation exchange resin, followed by anionexchanger unit having strong basic anionexchange resin, followed by mixed bed exchanger unit, having a mixture of strong acidiccation exchange resin, and strong basic anionexchange resin Type 1. This system givesimproved quality demineralized water, sometimes called polished water because of the useof mixed bed exchanger unit which is alsonamed as polishing unit because of its basi,? roleto polish (refine) the demineralized water.Here also, cocurrent or countercurrentregeneration techniques can be adopted forboth cation and anion exchanger, but for mixedbed exchanger it is always preferable to adoptcocurrent regeneration. This system givesdemineralized water of high pur ity, which isrequired for use in medium pressure, highpressure boilers and other chemical processingindustries where purity of water is of majorconcern. The system is suitable for waterhaving alkalin ity less than 100 ppm. Herealso in anion exchanger, strong basic anionexchange resin of Type 1 or Type 2 can be useddepending upon silica leakage (see Fig. 3).

is sized at half an hour pumping capacity ofdegassed water pump.4.2.3 Demineralized Water TankThe capacity of the demineralized water tankgreatly varies from one client to the other. Thecapacity is normally fixed on the basis of exigencies occurring in the plant, the variations in useof demineralized water in down stream plants,use of demineralized water for regeneration,etc. Normally, in power plants clients prefer tohave the storage capacity for 16 to 24 hours, bu tin other plants it is being kept for 4 to 8 hours.However, there is no strict rule for it as thisentirely depends upon the client's requirements.4.2.4 Acid and Alkali TankThe storage capacities of acid and alkali tanksrequired for regenerations are also to be clearlyindicated in the specification. These capacities.are dependent upon the consideration of thetime it takes to procure the chemicals at plantsite. Where it may take 10-15 days for obtainingthe chemicals, it becomes advisable to go in forat least one month's storage at the plant site. Innormal cases, where a tanker of acid or alkali isexpected within 4 to 6 days time, storage capacity of a minimum of 15 days may be desirable.Wherever the regenerant chemicals are availablein the plant, a limited storage of 3 to 4 days-only may be considered.:5 FEED WATER5.1 Before developing a system and fixing specifications for demineralization plant, the sourceof feed water an d its availability has got to beestablished. Sometimes, water is available in theform of -filtered water after proper chlorination,.coagulation, flocculation, clarification and filtration. The filtered water is being directly fed tothe feed water tank followed by ion exchangersfor production of demineralized water. However,it becomes essential to establish water quality,which shall be free from colour, organics , etc.In case of any colour, organics or free chlorine,the water has to be treated with active carbonto take care of minor quantities of contaminants-coming in feed water. In case of unfiltered'water, the active carbon filters are to be precededby filters for which pressure sand filters are nor-mally used; sometimes dual media filter havingsand and anthracite are also used.-S.2 For dechlorination, sometimes sodiumSUlphite is used, which is dosed in feed waterbefore filtration. Sometimes the system is havingonly one dosing pot, where solid sodiumsulphite is added alongwith water to makesolution. The solution thus prepared is dosed,at a desired rate under pressure before filtration.In other situation, a solution preparation tank'with agitator is provided. The solution is dosedto feed water by means of sulphite dosing pump.6 DEMINERALIZATION SYSTEM.-6.1 There are different kinds of systems for

3

IS 13268 : 1992treatment of water in order to get demineralizedwater. Nowadays, as the cost of regenerantchemical is high, it is advisable to select aneconomical system to reduce recurring cost onchemicals. Systems in operation are describedin brief to guide the buyers in selecting a viableand stable demineralization water plant.6.1.1 Cation exchanger unit having strongacidic-cation exchange resin followed by anionexchanger unit having strong basic anionexchange resin without any degasser system inbetween. This system is prepared for waterhaving less alkalinity of 10J ppm and capable ofgiving demineralized water suitable for lowpressure and to a certain limit for mediumpressure boilers. Besides, this system can comehandy also for industries using demineralizedwater for processing. In this system, bothcocurrent and countercurrent techniques can beadopted depending upon the quality of feedwater, but countercurrent technique is moreeconomical ( see Fig. 1 ). .6.1.2 Cation exchanger u n ~ t having strongacidic-cation exchange reSIn followed bydegasser system having degasser tower, anddegassed water tank followed by strong basicanion exchanger. This system gives demineral ized water for low pressure, and to a certain limitfor medium pressure boilers as well. Here also,both cocurrent and countercurrent regenerationtechniques can be used depending upon thequality of feed water bu t countercurrenttechnique is more economical. This system issuitable for water having moderate alkalinityof about 250 mg!l alkalinity. Here also strongbasic anion exchange resin of Type 1 or Type2 is used depending upon the requirement ofsilica leakage ( see Fig. 2 )6.1.3 Cation exchanger unit having strongacidic-cation exchange resin, followed by anionexchanger unit having strong basic anionexchange resin, followed by mixed bed exchanger unit, having a mixture of strong acidiccation exchange resin, and strong basic anionexchange resin Type 1. This system givesimproved quality demineralized water, sometimes called polished water because of the useof mixed bed exchanger unit which is alsonamed as polishing unit because of its basi,? roleto polish (refine) the demineralized water.Here also, cocurrent or countercurrentregeneration techniques can be adopted forboth cation and anion exchanger, but for mixedbed exchanger it is always preferable to adoptcocurrent regeneration. This system givesdemineralized water of high pur ity, which isrequired for use in medium pressure, highpressure boilers and other chemical processingindustries where purity of water is of majorconcern. The system is suitable for waterhaving alkalinity less than 100 ppm. Herealso in anion exchanger, strong basic anionexchange resin of Type 1 or Type 2 can be useddepending upon silica leakage (see Fig. 3).

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IS 13268 : 1992fRW- I - III SBA I

I ISAC

~ ___ --,!io.'l>._----FRW Filtered raw water SBA Strong base anion unitSAC Strong acid cation unit DMW Demineralized waterFIG. 1 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF A

DEMINERALIZATION PLANT

fRW

SAC

FRW Filtered raw waterSAC Strong acid cation unitDT Degasser tower

DT

SBA

SBA Strong base anion unitDMW Demineralized water

FIG. 2 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF ADEMINERALIZATION PLANT WITH A DEGASSER TOWER

FRW- ~ ~SAC SBA we

I DMW..-FRW Filtered raw water SBA Strong base anion unitSAC Strong acid cation unit MB Mixed bed unitDM W Demineralized water

FIG. 3 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF A DEMINERALIZEDPLANT WITH A MIXED BED UNIT

6.1.4 Cation exchanger unit having strongacidic-cation exchange resin followed bydegasser system having degasser tower anddegassed water tank followed by anionexchanger unit having strong basic anionexchange resin followed by mixed bed exchangerunit having a mixture of strong acidiccation exchange resin and strong basic anionexchange resin of Type 1. Here also bothki nd s of regeLeration techniques as in 5.1.3 Can

4

be used depending upon the quality ofdemineralized water desired except fo r mixedbe d unit. The system yields demineralizedwater of high purity which is useful fo rmedium an d high pressure boilers. This systemis suitable for water'having moderate alkalinityof 250 ppm. Use of Type 1 or Type 2 strongbasic anion exchange resin in system dependsgreatly upon leakage of silica from the system( see Fig.4 ). . ,

IS 13268 : 1992fRW I - III SBA I

I ISAC

~ ___ ---11..:10._----FRW Filtered raw water SBA Strong base anion unitSAC Strong acid cation unit DMW Demineralized waterFIG. 1 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF A

DEMINERALIZATION PLANT

fRW

SAC

FRW Filtered raw waterSAC Strong acid cation unitDT Degasser tower

DTSBA

SBA Strong base anion unitDMW Demineralized water

FIG. 2 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF ADEMINERALIZATION PLANT WITH A DEGASSER TOWER

FRW

SBA

FRW Filtered raw water SBA Strong base anion unitSAC Strong acid cation unit MB Mixed bed unitDM W Demineralized water

FIG. 3 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF A DEMINERALIZEDPLANT WITH A MIXED BED UNIT

6.1.4 Cation exchanger unit having strongacidic-cation exchange resin followed bydegasser system having degasser tower anddegassed water tank followed by anionexchanger unit having strong basic anionexchange resin followed by mixed bed exchangerunit having a mixture of strong acidic-cation exchange resin and strong basic anionexchange resin of Type 1. Here also bothki nds of regeLeration techniques as in 5.1.3 Can

4

be used depending upon the quality ofdemineralized water desired except fo r mixedbe d unit. The system yields demineralizedwater of high purity which is useful fo rmedium an d high pressure boilers. This systemis suitable for water'having moderate alkalinityof 250 ppm. Use of Type 1 or Type 2 strongbasic anion exchange resin in system dependsgreatly upon leakage of silica from the system( see Fig.4 ). . ,

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IS 13268 : 1992

fRWSAC S8A UB01

DWFRW Filtered raw water SBA Strong base anion unitSAC Strong acid cation unit MB Mixed bed unitDT Degasser tower DMW Demineralized water

FIG. 4 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF A DEMINERALIZA nO NPLANT WITH A DEGASSER AND A MIXED BED UNIT

' .1.5 The cation exchanger unit in the systemsdescribed above may further be split into asystem consisting of weak acid cation exchangerunit having weak acidic-cation exchange resin,followed by strong acid cation exchanger unithaving strong acidic-cation exchange resin.This system is more useful for water havinghigh alkalinity of more than 300 ppm and highhardness of more than 300 ppm. The modi.fied'systems are commonly adopted to conserve theregenerant chemicals. Here, the regenerationis adopted in thoroughfare manner involvingpassing of regenerant from one unit to the,other unit in series. Normally, the regenerationis being done from strong acid cation resin toweak acid cation resin by adopting cocurrentthoroughfare technique, that is, using both theregeneration in cocurrent manner in series orusing countercurrent thoroughfare regenerationstechnique involving countercurrent regenerationof strong acid cation exchanger ih series with

exchangers involving weak base anion exchangerfollowed by strong base anion exchanger. Thissystem is also used to conserve the regenerantchemicals and to make the plant moreeconomical by adopting either coccurentthoroughfare technique, involving regenerationof both weak base and strong base anion unItin co current manner in series or countercurrentthoroughfare technique with countercurrentregeneration of strong base anion exchangeresi n with cocutrent regeneration of weak baseanion exch'lnge re;in in series is adopted. Thesystem is used when the wlter is having a highamount of chlorides and sulph'!te5 ( see Fig. 6 ).6.1.7 In the systems given in 6.1.1 and 6.1.2,sometimes it becomes desirable to go in fo rweak base anion exchanger in place bf strongbase anion exchanger specially in cases wheresilica removal is no t so critical from the feedwater.,cocurrent regeneration of weak acid cationresin (see Fig. 5 ). 6.1.8 In the system given in 6.1.1 to 6.1.6 forstrong base exchanger, sometimes Type 26.1.6 The anion exchanger unit in the above strong base anion exchange resin is used in.systems can also contain two separate anion place of Type 1 strong base anion exchange

fRW

FRW Filtered raw waterWAC Weak acid cation unit

SAC SBA

SBA Strong base anion unitMB Mixed bed unit

SAC Strong acid cation unit DMW Demineralized water,."DT Degasser tower

W8

FIG. 5 FLOW DIAGRAM SHOWING THE ARRANGEMBNT OF A DEMINERALIZATIONPLANT WITH A WEAK ACID CATION AND A MIXED BED UNIT5

IS 13268 : 1992

fRWSAC S8A UB01

DWFRW Filtered raw water SBA Strong base anion unitSAC Strong acid cation unit MB Mixed bed unitDT Degasser tower DMW Demineralized water

FIG. 4 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF A DEMINERALIZA nO NPLANT WITH A DEGASSER AND A MIXED BED UNIT

' .1.5 The cation exchanger unit in the systemsdescribed above may further be split into asystem consisting of weak acid cation exchangerunit having weak acidic-cation exchange resin,followed by strong acid cation exchanger unithaving strong acidic-cation exchange resin.This system is more useful for water havinghigh alkalinity of more than 300 ppm and highhardness of more than 300 ppm. The modi.fied'systems are commonly adopted to conserve theregenerant chemicals. Here, the regenerationis adopted in thoroughfare manner involvingpassing of regenerant from one unit to the,other unit in series. Normally, the regenerationis being done from strong acid cation resin toweak acid cation resin by adopting cocurrentthoroughfare technique, that is, using both theregeneration in cocurrent manner in series orusing countercurrent thoroughfare regenerationstechnique involving countercurrent regenerationof strong acid cation exchanger ih series with

exchangers involving weak base anion exchangerfollowed by strong base anion exchanger. Thissystem is also used to conserve the regenerantchemicals and to make the plant moreeconomical by adopting either coccurentthoroughfare technique, involving regenerationof both weak base and strong base anion unItin co current manner in series or countercurrentthoroughfare technique with countercurrentregeneration of strong base anion exchangeresi n with cocutrent regeneration of weak baseanion exch'lnge re;in in series is adopted. Thesystem is used when the wlter is having a highamount of chlorides and sulph'!te5 ( see Fig. 6 ).6.1.7 In the systems given in 6.1.1 and 6.1.2,sometimes it becomes desirable to go in forweak base anion exchanger in place bf strongbase anion exchanger specially in cases wheresilica removal is no t so critical from the feedwater.,cocurrent regeneration of weak acid cationresin (see Fig. 5 ). 6.1.8 In the system given in 6.1.1 to 6.1.6 forstrong base exchanger, sometimes Type 26.1.6 The anion exchanger unit in the above strong base anion exchange resin is used in.systems can also contain two separate anion place of Type 1 strong base anion exchange

fRW

FRW Filtered raw waterWAC Weak acid cation unit

SAC SBA

SBA Strong base anion unitMB Mixed bed unit

SAC Strong acid cation unit DMW Demineralized water,."DT Degasser tower

W8

FIG. 5 FLOW DIAGRAM SHOWING THB ARRANGBMBNT OF A DEMINERALIZATIONPLANT WITH A WEAK ACID CATION AND A MIXED BED UNIT5

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IS 13268 : 1992 - ~RW-- r - - ,....-- --SAC WBA SBA MBI

r D T ~I _F.fi:.W Filtered raw waterSAC Strong acid cation unitDT Degasser towerWBA Weak base anion unit

I Il

I ... I r DMW...- ... ..SEA Strong base anion unitMB Mixed bed unitDMW Demineralized water

FIG. 6 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF A DEMINERALIZATIONPLANT WITH A WEAK BASE ANION AND A MIXED BED UNIT

resin. This system is useful when silica leakagedesired in the demineralized water is slightlyhigher.6.1.9 Th e system sometimes necessitates to makeuse of two mixed bed txchanger unit in series,that is, one mixed bed unit followed by another mixed bed unit in place of only one mixedbed unit. Such systems are normally employedto get highly pure demineralized water which issuitable for high pressure or super-criticalpressure boilers or in cases where highly refinedwater is required.6.1.10 The cation exchanger unit in the systemgiven in 5.1.2 may also be selected in twoseparate cation exchanger ~ n i t s , each havingstrong acid cation exchange resin where theregeneration is made by countercurrenttechnique for second cation exchanger unit andthe thoroughfare manner in series with firstcation exchanger unit. This process becomesmere advantageous than one single exchanger,as it takes care of any extra leakage comingfrom the first cation (xchanger and therebygives much better treated water than in singleexchanger lIDit. This system becomes moreuseful with higher dissolved solids in feedwater.6.2 Anyone of the above described systems canbe selected for induding in the specifications byclient. However, analysis of water ande,conomics of the process play the decisive role.As is evidelit from above, the regenerationtechnique plays an important role for achievingthe desired quality of demineralized water.Depending upon the mode of regeneration,performance of exchangers varies. So it becomesimportant to fix the mode of regeneration inthe specifications itself by the client,6.3 The minimum depth of resin used in theabove exchangers shall not be less than 91'5 em( 3 feet).

6

7 EQUIPMENT7.1 The equipment details constitute animportant criterion to be given in the specification. Basic parameters for each and everyequipment are to be given in the specification.7.1.1 Pressure Sand FiltersTh e pressure sand filters shall be either ofvertical or horizontal type which is to be clearlymentioned in the requirement. Normally,vertical sand filters are preferred except in cases,where higher flow is required. The flow for thefilters may clearly be established so as to coverthe requirement of demineralized water, wastewater for regeneration of exchangers, andfiltered water for backwashing the filters.Backwashing operation is adopted for cleaningthe filter bed, and to make the bed loose, forreducing pressure drop while running the plant.The backwashing of filters is done by eitherfiltered water alone or by air and filtered watertogether or independently. The desired mode ofbackwashing is to be clearly specified in thespecification,The storage tank shall be located eitheroverground at a desired height to get thesufficient pressure for backwashing or on theground level. In the latter case, extra pumps( 1'5 kgjcm2 ) are required for backwashing thefilters. Air requirement for backwashing shouldal ways be met by the rotary air blowers.Services ai r of 3 to 6 kg/cm2 pressure shallnever be used for air scouring as it will churnup the filter media. Fo r proviSion of filteredwater tank. its elevations, specification of filteredwater pumps and air blowers shall clearly bestipulated to get the complete system. Theguarantee of the filtered water coming ou t offilter shall be given in the specification based onwhich filter is designed. In general, turbidity isspecified for filter design and water outlet offilter shall contain turbidity less than 2 NTU.

IS 13268 : 1992

-FRW -L--

SACj

rOT/--l ~

....

F.fi:.W Filtered raw waterSAC Strong acid cation unitDT Degasser towerWBA Weak base anion unit

r- - ~ -WBA SBA MBI. I.I I ~ r _DMW-SEA Strong base anion unitMB Mixed bed unitDMW Demineralized water

FIG. 6 FLOW DIAGRAM SHOWING THE ARRANGEMENT OF A DEMINERALIZATIONPLANT WITH A WEAK BASE ANION AND A MIXED BED UNIT

resin. This system is useful when silica leakagedesired in the demineralized water is slightlyhigher.6.1.9 The system sometimes necessitates to makeuse of two mixed bed txchanger unit in series,that is, one mixed bed unit followed by another mixed bed unit in place of only one mixedbed unit. Such systems are normally employedto get highly pure demineralized water which issuitable for high pressure or super-criticalpressure boilers or in cases where highly refinedwater is required.6.1.10 The cation exchanger unit in the systemgiven in 5.1.2 may also be selected in twoseparate cation exchanger ~ n i t s , each havingstrong acid cation exchange resin where theregeneration is made by countercurrenttechnique for second cation exchanger unit andthe thoroughfare manner in series with firstcation exchanger unit. This process becomesmore advantageous than one single exchanger,as it takes care of any extra leakage comingfrom the first cation (xchanger and therebygives much better treated water than in singleexchanger lIDit. This system becomes moreuseful with higher dissolved solids in feedwater.6.2 Anyone of the above described systems canbe selected for induding in the specifications byclient. However, analysis of water ande,conomics of the process play the decisive role.As is evidelit from above, the regenerationtechnique plays an important role for achievingthe desired quality of demineralized water.Depending upon the mode of regeneration,performance of exchangers varies. So it becomesimportant to fix the mode of regeneration inthe specifications itself by the client,6.3 The minimum depth of resin used in theabove exchangers shall no t be less than 91'5 cm( 3 feet).

6

7 EQUIPMENT7.1 The equipment details constitute animportant criterion to be given in the specification. Basic parameters for each and everyequipment are to be given in the specification.7.1.1 Pressure Sand FiltersThe pressure sand filters shall be either ofvertical or horizontal type which is to be clearlymentioned in the requirement. Normally,vertical sand filters are preferred except in cases,where higher flow is required. The flow for thefilters may clearly be established so as to coverthe requirement of demineralized water, wastewater for regeneration of exchangers, andfiltered water for backwashing the filters.Backwashing operation is adopted for cleaningthe filter bed, and to make the bed loose, forreducing pressure drop while running the plant.The backwashing of filters is done by eitherfiltered water alone or by air and filtered watertogether or independently. Th e desired mode ofbackwashing is to be clearly specified in thespecification,The storage tank shall be located eitheroverground at a desired height to get thesufficient pressure for backwashing or on theground level. In the latter case, extra pumps( 1'5 kgjcm2 ) are required for backwashing thefilters. Air requirement for backwashing shouldal ways be met by the rotary air blowers.Services air of 3 to 6 kg/cm2 pressure shallnever be used for air scouring as it will churnup the filter media. Fo r proviSion of filteredwater tank. its elevations, specification of filteredwater pumps and ai r blowers shall clearly bestipulated to get the complete system. Theguarantee of the filtered water coming ou t offilter shall be given in the specification based onwhich filter is designed. In general, turbidity isspecified for filter design and water outlet offilter shall contain turbidity less than 2 NTU.

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The material of construction of filter is to begiven clearly, Th e void space above thepacked bed may be mentioned which is normallykept about 50 percent of the packed height.Th e standard design specification are as follows:

a) Air blown - 0'4 to 0'5 kg/cm2 ai rdischarge pressure 0'015 to 0'025 m3/m 2sec of filter bed area (a ir requirement)b) Backwash pump - 1'5 kg/cm2 dischargepressure at 10 1/m2 sec of filter bed area( backwash requirement)c) Filter pump - 3 to 4 kg/cm2 dischargepressure, 1'3 to 4'1 1/m2 sec of bed area( filteration rate)d) Filter media - Fine sand: (3 0 cm):

Grade - 0'45 to 0'5 mm; Coarse sand:25 cm;Grade - 0'8 to 1'2mm; Fine pebbles:

10 cm;Graee - 3 to 6 mm; Medium pebbles:10 cm;Grade - 6 to 12 mm; Coarse pebbles:20cm;Grade - 12 to 25 mm.

7,1.2 Acthe Carbon FilterThe active carbon filter, wherever desired is tobe installed after pressure sand filters' whichconsist of active carbon packing capable fo r de

c ~ l o r i n a t i o n , de-oiling an d de-colouration alongwIth removal of traces of iron and organics.Th e grade of active carbon to be used fort.he purpose shall also be mentioned. Themode of back washing these filters withfiltered water is also to be mentioned, Herea ~ s o a similar arrangement for backwashing asgiven above fo r the pressure sand filters is tobe given. Normally arrangement for backwashof active carbon filter, and pressure sand filtersare common, as at no stage simultaneouslybackwash of both active carbon filter andpressure filter is expected, Even, if itso happens, backwashing of the units canbe e a s i ~ y staggered. The guarantee ofthe q u a ~ I t y of treated. water shall be incorporated In the specIilcation. Th e qualityparameters of the treated water shall conformto liJ?its as follows: turbidity ( ~ 1 NTU),chlonne (-< 0'01 mg/l ), and iron 0'01 rug/l )The material of construction of the body'and lini?!?, if any, is to be specified. Normally,epoxy hmng IS preferred on inside surface. Th evoid space above the packed bed may bespecified which is kept about 50 percent ofpacked bed.

7

Design specification:a) Activated carbonbed depth

IS 13268: 1992

3 m minimum12 i l l maximum6 m normal

b) Contact time of 15 minutes minimumwater with activated 30 minutes normalcarbon

7.1.3 Exchanger UnitTh e details of the exchanger units are to beclearly specified keeping in view the requirements of the client. These also include th erequired number of inspection windows,

n u m b ~ r of manholes and other mechanicalrequirements, The internal arrangement of th eexchanger is to be left to the bidders as itdepend,S upon the type of system adopted bythem eIther header lateral system or straineron bed plate system for proper collection anddistribution of water uniformly throughexchanger bed. The minimum, normal andmaximum flow through exchanger may clearlybe ~ p e c i f i e d . The void space above the packedreSIn bed may clearly be mentioned, which isnormally kept about 75 percent of the resindepth for cation and anion exchangers, whereasfor mixed bed it is preferable to keep minimum100 percent of the mixed bed resin depth forexpansion. The quality of treated waterguaranteed as coming ou t of each exchangermay be given in the specification based onwhich exchangers are to be designed. Normallyfor cation exchangers there shall be leakage ofsome s o ~ i u m ions which depends upon theregeneratIOn level of the exchanger. For cationexchangers, the leakage of hardness isconsidered nil an d sodium leakage is beingpermitted normally in the range of 1 to 2 mg/1.The term regeneration level refers to the amountof regenerant chemical used for the regenerationof e x ~ h a n g e r resin. For anion exchangersthere IS some leakage of chloride ion and silicaion, depending upon the type of anion exchange

r e s i ~ l u s e ~ in the s y s t e ~ , With any leakage ofsodmm IO n from catIOn exchanger, there is a! e s u l t a ~ t increase leakage of anion therebymcreaslllg conduCtIvIty an d silica content of

d e n : i n e r a ~ i ~ e d water, The conductivity anddeSired SIlIca content of treated water comingout of anion exchanger shall be clearly definedin the spe,cification for design, so that optimumregeneratlon level can be selected both forcation an d anion exchanger units. The guaranteed water quality desired from mixed bed unitshall also be clearly defined in the specificationso that the unit may be designed accordingly.7.1.4 Degasser TowerThe deggasser tower requirement may also beclearly defined with respect to it s flow ratetype f packing (stainless steel or glazedcera?11c), etc. The guaranteed water qualitycommg ou t of degasser shall also be clearly

The material of construction of filter is to begiven clearly, Th e void space above thepacked bed may be mentioned which is normallykept about 50 percent of the packed height.Th e standard design specification are as follows:

a) Air blown - 0'4 to 0'5 kg/cm2 ai rdischarge pressure 0'015 to 0'025 m3/m 2sec of filter bed area (a ir requirement)b) Backwash pump - 1'5 kg/cm2 dischargepressure at 10 1/m2 sec of filter bed area( backwash requirement)c) Filter pump - 3 to 4 kg/cm2 dischargepressure, 1'3 to 4'1 1/m2 sec of bed area( filteration rate)d) Filter media - Fine sand: (3 0 cm):

Grade - 0'45 to 0'5 mm; Coarse sand:25 cm;Grade - 0'8 to 1'2mm; Fine pebbles:

10 cm;Graee - 3 to 6 mm; Medium pebbles:10 cm;Grade - 6 to 12 mm; Coarse pebbles:20cm;Grade - 12 to 25 mm.

7,1.2 Acthe Carbon FilterThe active carbon filter, wherever desired is tobe installed after pressure sand filters' whichconsist of active carbon packing capable fo r de

c ~ l o r i n a t i o n , de-oiling an d de-colouration alongwIth removal of traces of iron and organics.The grade of active carbon to be used fort.he purpose shall also be mentioned. Themode of back washing these filters withfiltered water is also to be mentioned, Herea ~ s o a similar arrangement for backwashing asgiven above fo r the pressure sand filters is tobe given. Normally arrangement for backwashof active carbon filter, and pressure sand filtersare common, as at no stage simultaneouslybackwash of both active carbon filter andpressure filter is expected, Even, if itso happens, backwashing of the units canbe e a s i ~ y staggered. The guarantee ofthe q u a ~ I t y of treated. water shall be incorporated In the specIilcation. Th e qualityparameters of the treated water shall conformto liJ?its as follows: turbidity ( ~ 1 NTU),chlonne (-< 0'01 mg/l ), and iron 0'01 rug/l )The material of construction of the body'and lini?!?, if any, is to be specified. Normally,epoxy hmng IS preferred on inside surface. Th evoid space above the packed be d may bespecified which is kept about 50 percent ofpacked bed.

7

Design specification:a) Activated carbonbed depth

IS 13268: 1992

3 m minimum12 i l l maximum6 m normal

b) Contact time of 15 minutes minimumwater with activated 30 minutes normalcarbon

7.1.3 Exchanger UnitTh e details of the exchanger units are to beclearly specified keeping in view the requirements of the client. These also include th erequired number of inspection windows,

n u m b ~ r of manholes and other mechanicalrequirements, The internal arrangement of th eexchanger is to be left to the bidders as itdepend,S upon the type of system adopted bythem eIther header lateral system or straineron bed plate system for proper collection anddistribution of water uniformly throughexchanger bed. The minimum, normal andmaximum flow through exchanger may clearlybe ~ p e c i f i e d . The void space above the packedreSIn bed may clearly be mentioned, which isnormally kept about 75 percent of the resindepth for cation and anion exchangers, whereasfo r mixed bed it is preferable to keep minimum100 percent of the mixed bed resin depth fo rexpansion. The quality of treated waterguaranteed as coming ou t of each exchangermay be given in the specification based onwhich exchangers are to be designed. Normallyfo r cation exchangers there shall be leakage ofsome s o ~ i u m ions which depends upon theregeneratIOn level of the exchanger. For cationexchangers, the leakage of hardness isconsidered nil an d sodium leakage is beingpermitted normally in the range of 1 to 2 rug/I.The term regeneration level refers to the amountof regenerant chemical used for the regenerationof e x ~ h a n g e r resin. For anion exchangersthere IS some leakage of chloride ion and silicaion, depending upon the type of anion exchange

r e s i ~ l u s e ~ in the s y s t e ~ , With any leakage ofsodmm IO n from catIOn exchanger, there is a! e s u l t a ~ t increase leakage of anion therebymcreaslllg conduCtIvIty an d silica content of

d e n : i n e r a ~ i ~ e d water, The conductivity anddeSired SIlIca content of treated water comingout of anion exchanger shall be clearly definedin the spe,cification for design, so that optimumregeneratlon level can be selected both forcation and anion exchanger units. The guaranteed water quality desired from mixed bed unitshall also be clearly defined in the specificationso that the unit may be designed accordingly.7.1.4 Degasser TowerThe deggasser tower requirement may also beclearly defined with respect to it s flow ratetype f packing (stainless steel or glazedcera?11c), etc. The guaranteed water qualitycommg ou t of degasser shall also be clearly

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IS i3268 : 1992given for which carbon dioxide shall be normallyin the range of 4 to 8 mg!l as calciumcarbonate. Necessary manhole, hand hole, etc,may be clearly spelled out to facilitate easymaintenance. Tower is normally placed onsome height to give a gravity flow to deglssedwater tank placed below it, where degassedwater coming ou t of the tower is collected andfed to down stream s y s t e m s ~ and other uses inthe plant. The degassed water tank inside isnormally lined with acid an d alkaline resistanttiles to prevent hardness and silica pick up fromthe walls by the acidic 'water. Normally,degasser water system is kept common for thestreams, but sometimes installations may berequired stream-wise which is to be clearlyindicated in the specification. The number ofai r blowers required for the degasser tower shallbe mentioned which is normally kept two foreach tower. The number of degassed waterpumps may also be clearly specified, so that thebidders are able to give the same type of system.Sometimes pumps are designed for 50 percentcapacity only whereas in other case it ispreferable to have pump capacity of 100 percent.The main consideration is the economic of tlterecurring cost of the plant.8 ACID HANDLING SYSTEM8.1 Th e details of acid handling system andregeneration equipment desired for the systemshall be mentioned in the specification. Thedetails of acid storage tank capacity requirementhas been given in 4.2.4. Normally sulphuricacid or hydrochloric acid is used for r e g e n e r a ~tion of the cation exchange resin. The acidsupply to plant is made by road tanker. Incases, where requirement is very large,provision of rail tanker is also made in additionto road tanker. As the sulphuric acid is muchmore dangerous, extra precautions are to betaken for its handling. Acid tankers aresometimes preferred to be placed on height, soas to get the gravity flow from the acid tankerto acid storage tank in demineralization plant.The transfer of acid from acid tanker to acidstorage tank is being done normally by pumps;bu t sometimes this transfer is also effected bypressurizing the tanker by air. In this case, theacid tanker shall be capable of withholding thatmuch air pressure, as otherwise it would leadto failure of tank causing a serious accident.The material of acid transfer pumps are to besuitably selected depending upon the type ofacid used. Separate regeneration equipmentare required for use with sulphuric acid andhydrochloric acid, respectively. Generally,polypropylene pumps are used for hydrochloricacid series and stainless steel pumps foi'"sulphuric acid series.8.1.1 Regeneration Equipment8.1.1.1 In case of sulphuric acid, the acid.storage tanks shall be fully guarded to avoid

8

contact of moist air with stoted acid, for whichsilica gel breather shan be provided. Inaddition, proper seal shall also be included inoverflow line to act as a vacuum breaker. Acidfrom storage tank is withdrawn either bygravity or by pumps and sent to acid day tank,or to acid measuring tank, depending upon thereq uirement. The acid measuring tanks aregiven separately for each exchanger (cationexchanger or mixed bed exchanger) as therequirement of each is different. Sometimes,the acid is fed directly to ion exchanger unitswith the help of acid dosing pumps. The on-line dilution of acid is done by providing amixing tee, but"" extra precaution is to be takenin choosing suitable material of construction ofmixing tee (norm:1l1y stainless steel forsulphuric acid series ), to avoid frequent failuresdue to the corrosive action of acid and heat ofdilution acid which is required to be dilutedfrom 98 percent to desired regenerant concen-tration ranging from I' 5 to 5 percent. Separateacid dosing pumps are requited for cationunit and mixed bed unit. The acid from eachacid measuring tank wh ich are normally pu t ons\lfficient elevation, is taken by gravity to aciddilution tanks placed at ground level where theconcentration is reduced to about 20 to 30percent. This dilute acid at the desiredconcentration is taken with the help of waterejector to different exchangers for further on-line dilution used for regeneration. Acidconcentration is very important for regenerationof cation exchanger because the presence ofmore hardness in water leads to precipitation ofcalcium sulphate during regeneration, therebyleading to imperfect regeneration.8.1.1.2 In case of hydrochloric acid storagetank, proper precautions shall be taken to avoidhydrochloric acid vapour going ou t of the tank:to the surroundings, for which fume absor-bers shall be provided. Acid from storagetank is transferred in sim ilar fashion as in thecase of sulphuric acid mentioned in 8.1.1.1. Theon-line dilution is done by water ejector( normally ebonite ejector for hydrochloric acidseries) for getting desired concentration ofregenerant concentration to about 3 to 5 percent.Sufficient care has to be taken to control theacid fUme in the plant area by providing fumeabsorbers wherever necessary. Here also,separate acid measuring tanks for differentexchanger units are to be provided. Informationis also to be provided on the material requiredfor construction of equipment to handle acid.9 NEUTRALIZATION SYSTEM9.1 Neutralization system is" another importantaspect particularly in the perspective ofpollution control measures. All the waste waterscoming ou t during regeneration of x c h a r i g e r sat e required to be collected in a pit which is t6be neutralized before discharge. Normally two

IS i3268 : 1992given for which carbon dioxide shall be normallyin the range of 4 to 8 mg!l as calciumcarbonate. Necessary manhole, hand hole, etc,may be clearly spelled out to facilitate easymaintenance. Tower is normally placed onsome height to give a gravity flow to deglssedwater tank placed below it, where degassedwater coming out of the tower is collected andfed to down stream s y s t e m s ~ and other uses inthe plant. The degassed water tank inside isnormally lined with acid an d alkaline resistanttiles to prevent hardness and silica pick up fromthe walls by the acidic 'water. Normally,degasser water system is kept common for thestreams, bu t sometimes installations may berequired stream-wise which is to be clearlyindicated in the specification. The number ofair blowers required for the degasser tower shallbe mentioned which is normally kept two foreach tower. The number of degassed waterpumps may also be clearly specified, so that thebidders are able to give the same type of system.Sometimes pumps are designed for 50 percentcapacity only whereas in other case it ispreferable to have pump capacity of 100 percent.The main consideration is the economic of tlterecurring cost of the plant.8 ACID HANDLING SYSTEM8.1 The details of acid handling system andregeneration equipment desired for the systemshall be mentioned in the specification. Th edetails of acid storage tank capacity requirementhas been given in 4.2.4. Normally sulphuricacid or hydrochloric acid is used for r e g e n e r a ~tion of the cation exchange resin. Th e acidsupply to plant is made by road tanker. Incases, where requirement is very large,provision of rail tanker is also made in additionto road tanker. As the sulphuric acid is muchmore dangerous, extra precautions are to betaken for its handling. Acid tankers aresometimes preferred to be placed on height, soas to get the gravity flow from the acid tankerto acid storage tank in demineralization plant.The transfer of acid from acid tanker to acidstorage tank is being done normally by pumps;bu t sometimes this transfer is also effected bypressurizing the tanker by air. In this case, theacid tanker shall be capable of withholding thatmuch air pressure, as otherwise it would leadto failure of tank causing a serious accident.The material of acid transfer pumps are to besuitably selected depending upon the type ofacid used. Separate regeneration equipmentare required for use with sulphuric acid an dhydrochloric acid, respectively. Generally,polypropylene pumps are used fo r hydrochloricacid series and stainless steel pumps foi'"sulphuric acid series.8.1.1 Regeneration Equipment8.1.1.1 In case of sulphuric acid, the acid.storage tanks shall be fully guarded to avoid

8

contact of moist air with stoted acid, for whichsilica gel breather shan be provided. Inaddition, proper seal shall also be included inoverflow line to act as a vacuum breaker. Acidfrom storage tank is withdrawn either bygravity or by pumps and sent to acid day tank,or to acid measuring tank, depending upon th ereq uirement. The acid measuring tanks aregiven separately for each exchanger (cationexchanger or mixed bed exchanger) as therequirement of each is different. Sometimes,the acid is fed directly to ion exchanger unitswith the help of acid dosing pumps. The on-line dilution of acid is done by providing amixing tee, but"" extra precaution is to be takenin choosing suitable material of construction ofmixing tee (norm:1l1y stainless steel forsulphuric acid series ), to avoid frequent failuresdue to the corrosive action of acid and heat ofdilution acid which is required to be dilutedfrom 98 percent to desired regenerant concen-tration ranging from I' 5 to 5 percent. Separateacid dosing pumps are requited for cationunit and mixed bed unit. The acid from eachacid measuring tank wh ich are normally pu t ons\lfficient elevation, is taken by gravity to aciddilution tanks placed at ground level where th econcentration is reduced to about 20 to 30percent. This dilute acid at the desiredconcentration is taken with the help of waterejector to different exchangers for further on-line dilution used for regeneration. Acidconcentration is very important for regenerationof cation exchanger because the presence ofmore hardness in water leads to precipitation ofcalcium sulphate during regeneration, therebyleading to imperfect regeneration.8.1.1.2 In case of hydrochloric acid storagetank, proper precautions shall be taken to avoidhydrochloric acid vapour going ou t of the tank:to the surroundings, for which fume absor-bers shall be provided. Acid from storagetank is transferred in sim ilar fashion as in thecase of sulphuric acid mentioned in 8.1.1.1. Theon-line dilution is done by water ejector( normally ebonite ejector for hydrochloric acidseries) for getting desired concentration ofregenerant concentration to about 3 to 5 percent.Sufficient care has to be taken to control theacid fUme in the plant area by providing fumeabsorbers wherever necessary. Here also,separate acid measuring tanks for differentexchanger units are to be provided. Informationis also to be provided on the material requiredfor construction of equipment to handle acid.9 NEUTRALIZATION SYSTEM9.1 Neutralization system is" another importantaspect particularly in the perspective ofpollution control measures. All the waste waterscoming ou t during regeneration of x c h a r i g e r sat e required to be collected in a pit which is t6be neutralized before discharge. Normally two

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sections in r:eutralizing pit are provided, eachsection being capable of holding total wastewater coming ou t of all exchangers at a time.Sometimes, the nuetralization pi t is designed totake up either 12 hours or 24 hours collectionsof waste water coming ou t during regenerationof exchangers; but this wil1 add to the cost ofplants as the pits require a suitable 1ining overRCC structure to handle acid/alka1i. Properpumping and recirculating arrangement foreffluent mixing are also to be provided.Sometimes, additional air grid is provided inthe pi t for thorough mixing of alkali/acid forcomplete neutralization. Proper fpecificationsare to be developed for this system suitingclient's requirement. Lime is normally usedfor neutralization for which lime preparationtank and feeding arrangement by gravity shallalso be included in the specifications. Otherwise,proper acid/alkali mixing is to be specified inthe specifications.9.2 The details of alkali handling system andregeneration equipment desired for the systemshall be clearly mentioned in the specifications.Details of alkali storage tank are given in 4.2.4.Normally only caustic soda is used for regeneration of anion exchange resin in anion andmixed bed exchanger units, bu t sometimesammonia is also used for regeneration of weakbase anion exchange resin specially, in thenitrogenous fertilizer plant producing ammonia.9.2.1 Ammonia solution (10 percent) ispreferred to be stored in the storagetank, which shall be properly sealed toavoid any vapour of ammonia escaping intoatmosphere. This solution is fed to exchangerwith the help of pump or water ejector to getthe final concentration of ammonia (about 4percent) required for regeneration ofexchanger.9.2.2 The caustic soda solution tanks detailshave been given in 4.2.4, which shall bepart of the specification, bu t the tanks shall beprovided with air breather to avoid carbon-fioxde intake from atmosphere which couldlead to formation of sodium carbonate. Propersealing, therefore, is also to be provided.The alkali tank normally stores caustic lyesolution (about 40-47 percent) coming bytanker (road or rail) depending upon therequirement of alkali in the plant. The alkalipumps are used for transfer of alkali solutionfrom the tanker to storage tank, from where,it is transferred to alkali day or alkali measuringtank by gravity or by alkali transfer pumpsdepending upon the elevation of the tank. Thealkali day tank is designed for storing alkalirequired fo r regeneration of various exchangersin a day. The alkali measuring tanks areseparately provided for anion exchange resinof anion and mixed bed exchanger units. Thetransfer of alkali from measuring tank to anion

9

IS 13268 : 1992exchanger can be done either by alkali dosingpumps with on-line dilution by alkali ejectorto achieve desired concentration of alkalisolution for regeneration which normallyranges from 2 to 5 percent. But for regeneration of alkali to mixed bed unit thealkali ejector is used to get the desired alkalisolution concentration in the range of 4 to 5percent. Use of alkali dosing pumps is alsopreferred specially in case where pressure dropexpected is high, such as in thoroughfare regeneration system.Sometimes, it becomes difficult to get lyesolution in the vicinity of the plant, then a1ternate arrangement of preparing alkali solutionis to be made at the site by getting solid alkaliin the form of flakes or solid. For this purpose,a separate alkali solution preparation tankhas to be provided equipped with properstirring arrangement. In addition, the alkalitransfer pumps are reqUired for transferringalkali solution prepared in the tank, which shallalso be used fo r recirculation of alkali solutionin the tank for proper mixing of solid toprepare the solution. At least one causticpreparation solution tank shall be included inthe specification to take care of any extremeemergency, in case lye solution is no t madeavailable due to some reasons beyond control.10 GENERAL AND CONSTRUCTIONALFEATURESI t is essential to describe general and constructional features of various equipment in thespecification, including the mode of their operation, location of the plant, etc.10.1 General FeaturesThese cover ( a ) mode of operation ( b) locationof the plant, (c ) type of instrumentationdesired, and ( d ) electrical system requirement,etc.10.1.1 Mode of Operation10.1.1.1 Fo r small plants, manual operation ispreferred, as the operation of the small sizevalves does no t pose any problem. Further,with the instruction, the total cost of the plantgoes up, which discourages recourse to sophisticat ion in small pJants. Nowadays, due tooperational difficulties and to minimize therecurring cost, the labour cost is to be reduced,which encourages one to go in for semi-autoan d auto operation of the plant. The mode ofoperation, therefore, has to be clearly specified.10.1.1.2 Semi-auto operation includes the operation of various valves through selectorswitches located in the control panel so that theoperators can operate the plant from the controlpanel. Sometimes semi-auto operation includesstopping of the plant during service run by the

sections in r:eutralizing pit are provided, eachsection being capable of holding total wastewater coming ou t of all exchangers at a time.Sometimes, the nuetralization pi t is designed totake up either 12 hours or 24 hours collectionsof waste water coming ou t during regenerationof exchangers; but this wil1 add to the cost ofplants as the pits require a suitable 1ining overRCC structure to handle acid/alka1i. Properpumping and recirculating arrangement foreffluent mixing are also to be provided.Sometimes, additional air grid is provided inthe pit for thorough mixing of alkali/acid forcomplete neutralization. Proper fpecificationsare to be developed for this system suitingclient's requirement. Lime is normally usedfor neutralization for which lime preparationtank and feeding arrangement by gravity shallalso be included in the specifications. Otherwise,proper acid/alkali mixing is to be specified inthe specifications.9.2 The details of alkali handling system andregeneration equipment desired for the systemshall be clearly mentioned in the specifications.Details of alkali storage tank are given in 4.2.4.Normally only caust ic soda is used for regeneration of anion exchange resin in anion andmixed bed exchanger units, but sometimesammonia is also used for regeneration of weakbase anion exchange resin specially, in thenitrogenous fertilizer plant producing ammonia.9.2.1 Ammonia solution (10 percent) ispreferred to be stored in the storagetank, which shall be properly sealed toavoid any vapour of ammonia escaping intoatmosphere. This solution is fed to exchangerwith the help of pump or water ejector to getthe final concentration of ammonia (about 4percent) required for regeneration ofexchanger.9.2.2 The caustic soda solution tanks detailshave been given in 4.2.4, which shall bepart of the specification, bu t the tanks shall beprovided with air breather to avoid carbon-fioxde intake from atmosphere which couldlead to formation of sodium carbonate. Propersealing, therefore, is also to be provided.The alkali tank normally stores caustic lyesolution (about 40-47 percent) coming bytanker (road or rail) depending upon therequirement of alkali in the plant. The alkalipumps are used for transfer of alkali solutionfrom the tanker to storage tank, from where,it is transferred to alkali day or alkali measuringtank by gravity or by alkali transfer pumpsdepending upon the elevation of the tank. Thealkali day tank is designed for storing alkalirequired for regeneration of various exchangersin a day. The alkali measuring tanks areseparately provided for anion exchange resinof anion and mixed bed exchanger units. Thetransfer of alkali from measuring tank to anion

9

IS 13268 : 1992exchanger can be done either by alkali dosingpumps with on-line dilution by alkali ejectorto achieve desired concentration of alkalisolution for regeneration which normallyranges from 2 to 5 percent. But for regeneration of alkali to mixed bed unit thealkali ejector is used to get the desired alkalisolution concentration in the range of 4 to 5percent. Use of alkali dosing pumps is alsopreferred specially in case where pressure dropexpected is high, such as in thoroughfare regeneration system.Sometimes, it becomes difficult to get lyesolution in the vicinity of the plant, then a1ternate arrangement of preparing alkali solutionis to be made at the site by getting solid alkaliin the form of flakes or solid. Fo r this purpose,a separate alkali solution preparation tankhas to be provided equipped with properstirring arrangement. In addition, the alkalitransfer pumps are reqUired for transferringalkali solution prepared in the tank, which shallalso be used for recirculation of alkali solutionin the tank for proper mixing of solid toprepare the solution. At least one causticpreparation solution tank shall be included inthe specification to take care of any extremeemergency, in case lye solution is not madeavailable due to some reasons beyond control.10 GENERAL AND CONSTRUCTIONALFEATURESI t is essential to describe general an d constructional features of various equipment in thespecification, including the mode of their operation, location of the plant, etc.10.1 General FeaturesThese cover ( a ) mode of operation ( b) locationof the plant, ( c ) type of instrumentationdesired, and ( d ) electrical system requirement,etc.10.1.1 Mode of Operation10.1.1.1 For small plants, manual operation ispreferred, as the operation of the small sizevalves does no t pose any problem. Further,with the instruction, the total cost of the plantgoes up, which discourages recourse to sophistica tion in small pJants. Nowadays, due tooperational difficulties and to minimize therecurring cost, the labour cost is to be reduced,which encourages one to go in for semi-autoan d auto operation of the plant. The mode ofoperation, therefore, has to be clearly specified.10.1.1.2 Semi-auto operation includes the operation of various valves through selectorswitches located in the control panel so that theoperators can operate the plant from the controlpanel. Sometimes semi-auto operation includesstopping of the plant during service run by the

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IS 13268 : 1992~ e l e c t o r switch, and thereafter the regenerationto be carried out by means of sequencetimer or programme logic controller. Thissystem requires a lot of precision, maintenanceworkmanship, reliability, and smoothnessoperation of various instruments and valves.Although, such kind of system is becomingpopular, one has to consider before hand the

f a c t o r ~ I?entioned earlier. Complete autooperatIOn IS not at all desirable in India b ~ c a u s eof the large v a r i a t i o ~ in night and day tempera!ure. H o w e v e ~ , still, some client prefer to gotn for automatIc plants. Naturally, success wilJdepend upon the regular maintenance of variousinstruments and auto valves in operation.10.1.2 Locati:m of the PlantThis becomes an important factor fo r the totalcost of the plant. In power sector it isnormally preferable to go in for completelycovered plant but in other chemical industriesincluding fertilizers, trends have set in to gofor open plants. The open plant is moreeconomical compared to a covered plant, bu tthere are some operational hazards which mayhave to be faced by the operators duringmonsoon, winters, and summers. In case, theplant is made semi-auto type it really becomes

a d v a n t a g e o . u ~ to go in for open plant, asfrequent VISit of operators to field is avoided.However, ultimately the choice b ~ t w e e n openan d covered plant remains with the client. Butthe type (open or covered) must be includedin the specification.10.1.3 InstrumentationNowadays, more and more on-line instrumentsare included the plants. This gives instantaneous analysIS of water at various stages ofthe plant. More and more instruments arethere in semi-auto and auto plants to control theregeneration and service run.10.1.3.1 In filters, most of the time manualoperation is preferred but in some ~ a s e s autooperation is selected. In case of auto operation, any high pressure drop across the bed

l ~ a ~ s to automatic backwashing followed byrInsmg of the filter before putting for service run.For detection of pressure drop across the bed,differential pressure indicator alarm is used~ . v h i c h is connected with operation of s e r v i c ~and backwash valves of the filter. Furtherflow indicator integrator on individual f i l t e r ~required besides recorder. Sometimes,I I I manual plant, use of only water meter in thefeed line is preferred. In case of auto or semiauto operation, the valves included for operation are pneumatically o p ~ r a t e d gate valves an donly in some cases, where instrument air is notavailable, motorized valves are used. Inletand outlet.of the individual filters have pressuregauges WhICh depend upon client's requirement.However, outlet pressure gauge is definitely

req uired assess the pressure drop across thebed, but Inlet pressure gauge can be avoided.10.1.3.2 The e x c h a n g ~ r s are required to havemore instrumentation particularly in auto andsemi-auto plants. I t is desirable to have flowindicator in the inlet. Sometimes, onlyflow indicator is provided in the inlet with awater m ~ t e r in outlet to assess the totalquantity. of water coming out during s ~ r v i c erun or In between two regenerations. Sometimes, differential pressure indicator is alsoprovided to assess the pressure drop across the

? e ~ , otherwise only ~ r e s s u r e gauges are providedIn ! n l ~ t and .oulet pIpes. cation exchangeunIt IS ~ e q ~ l l r e d to have sodmm in indicatingmeter to mdicate the leakage of cations, for whichone p r o ? ~ is put in the u t l ~ t ?f the exchanger.The amon exchanger Unit IS provided withconductivity indicator to assess conductivity,an d even sometimes with silica analyser toestimate the sil ica content in the treated water.In s o m ~ cases, even on-line, pH meter isprovided in the outlet of the unit, but normallypf!. is m ~ a s u r e d in the laboratory only. Th en:ll.xed bed exchangers have conductivity meter,sllIca analyser, pH meter to give the indicationsof quality of treated water. Sometim onlya conductivity indicator is provided and rest ofthe measurement s are carried in the laboratory.Besides above, pneumatic control valves areprovided for each operation on the exchanoerssometimes motor operated valves are s e l e ~ t e din place of pneumatic type specially at theplace where instrument air is not available foruse. In case, auto or semi-auto operation ofthe plant is not envisaged, most of the instruments. Ot;t e x c h a n g e ~ s can be discarded, exceptflow mdIcator, and mtegrator which are neededin all circumstances.10.1.3.3 On regeneration side, handling of acidalkali tanks and their feeding systems are invol:ved . Here also, a good instrumentation is

~ e q U l r e d for. auto and semi-auto plants. Th em s t r u ~ e n t a t l O n ~ e p e n d s upon the type ofoperatIOn for feedIng regenerant to exchangers.The tanks shall have level switches, so thatproper levels in various tanks can be main

t a i n e ~ . The system shall be provided withsuffiCient pneumatic or motorized controlvalves, besides the auto operation of pumps orb l o w e ~ s wherever necessary. Various stages ofo p ~ r a t I O n are better controlled by the timers

~ h l C h have to be set in advance during operatIOn of the plant. Nowadays, use of programme logic control is also adopted for thesesyst.ems, where the programme of operation isIn advance. The basic requirements of theInstruments in the system shall be given in the

s p e ~ i f i c a t i o n , based on which the system shall bedeSIgned for operation.10.1.3.4 Some instruments are required fo r inletand outlet pipelines to and from the battery

10

IS 13268 : 1992~ e l e c t o r switch, and thereafter the regenerationto be carried out by means of sequencetimer or programme logic controller. Thissystem requires a lot of precision, maintenanceworkmanship, reliability, and smoothnessoperation of various instruments and valves.Although, such kind of system is becomingpopular, one has to consider before hand the

f a c t o r ~ I?entioned ear.'ier. Complete autooperatIOn IS not at all deSIrable in India b;::causeof the large v a r i a t i o ~ in night and day tempera!ure. H o w e v e ~ , still, some client prefer to gotn for automatIc plants. Naturally, success wilJdepend upon the regular maintenance of variousinstruments and auto valves in operation.10.1.2 Locati:m of the PlantThis becomes an important factor fo r the totalcost of the plant. In power sector it isnormally preferable to go in for completelycovered plant but in other chemical industriesincluding fertilizers, trends have set in to gofor open plants. The open plant is moreeconomical compared to a covered plant, bu tthere are some operational hazards which mayhave to be faced by the operators duringmonsoon, winters, and summers. In case, theplant is made semi-auto type it really becomes

a d v a n t a g e o . u ~ to go in for open plant, asfrequent VISIt of operators to field is avoided.However, ultimately the choice b;::tween openan d covered plant remains with the client. Butthe type (open or covered) must be includedin the specification.10.1.3 InstrumentationNowadays, more and more on-line instrumentsare included the plants. This gives instantaneous analysIS of water at various stages ofthe plant. More and more instruments arethere in semi-auto and auto plants to cont