ION EXCLUSION DESUGARISATION OF REFINERY JET 4

Transcription

1 ION XCLUSION DSUGARISATION OF RFINRY JT 4 SD PACOCK Sugar Milling Research Institute, Durban Abstract In exclusin is a chrmatgraphic prcess which separates cmpnents frm an impure feedstck n the basis f mlecular size and charge. A pilt plant in exclusin separatr was cnstructed t determine the technical and ecnmic feasibility f recvering sugar frm refinery jet 4 (the feedstck identified as mst prmising in terms f ease f treatment). xtensive tests n jet 4 frm the Malelane refinery (a carbnatatin-sulphitatin refinery) have demnstrated the technical feasibility f the prcess. Sugar biling trials n the sucrse fractin recvered frm the in exclusin pilt plant have shwn cnsiderable imprvements in crystal mrphlgy, recverable sucrse and crystal clur. The effects f the pilt plant perating cnditins n the quantity and quality f sugar recvered are discussed. Keywrds: In exclusin, chrmatgraphy, desugarisatin, pilt plant, jet 4 Make-up Water Jet4 Feed IntermediateT Strage T Drain Recycle Feed Sucrse Prduct Recycle Strage Resin Clumn t R.I. Cell Intrductin In exclusin chrmatgraphy is a prcess which separates cmpnents frm an impure feedstck n the basis f mlecular size and charge. The in exclusin prcess has been applied t the recvery f sucrse frm final beet mlasses fr mre than twenty years (Hngist, 1977; Schneider, 1978), and has mre recently been applied t cane mlasses. A pilt plant in exclusin separatr was cnstructed in rder t determine the feasibility f recvering sucrse frm Suth African mlasses and ther lw-purity feedstcks. Refinery jet 4 was identified as the mst prmising feedstck fr study, in terms f ease f treatment, and extensive tests were cnducted in rder t demnstrate the technical feasibility f the prcess and t determine the effect f the pilt plant perating cnditins n the quantity and quality f sugar recvered. In exclusin pilt plant The pilt plant chrmatgraphic separatr cnsists f a jacketed stainless steel clumn f inner diameter 250 mm and height 4 m. Within the clumn is a packing f 200 litres f strng catin in exchange resin in the sdium frm (Purlite PCR 642). While this resin is similar t in exchange resins used fr water sftening, n significant in exchange actually ccurs during in exclusin. The tp f the resin clumn is equipped with a sight-glass t facilitate inspectin f the height f the resin bed. The piping t the clumn is arranged t allw alternate feeding f either jet 4 feedstck, recycled fractins frm the clumn r elutin water (see Figure 1). Prvisin has als been made fr backwash flw thrugh the clumn, t remve trapped air frm the tp f the clumn during startings. During peratin, a side-stream f clumn effluent is withdrawn and passed thrugh a cnductivity cell and refractive index (RI) detectr. This facilitates peak detectin and prvides the input signal fr autmatic cntrl f the clumn. lutin water t the separatr is autmatically maintained at the clumn perating temperature in a steam-heated drum. Prc S Afr Sug Technl Ass (1996) 70 FIGUR1: The pilt plantchrmatgraphic separatr. The pilt plant clumn perates as a batch separatr. Befre injectin f the feed sample t be separated, the resin clumn is fed with ht elutin water at a fixed rate. T start the separatin, an amunt f feed jet is injected nt the tp f the clumn. This is perfrmed by switching valves t feed the clumn frm the jet 4 feed drum as ppsed t the elutin water drum. When the required quantity f jet has been intrduced, ht elutin water is nce mre fed t the tp f the clumn in rder t push the feed sample thrugh the resin bed. During their passage thrugh the resin bed, the varius chemical cmpnents f the jet diffuse int the many micrscpic passages within the resin beads. Smaller cmpnent mlecules in the jet can penetrate mre deeply int the beads, and int a larger number f passages, than larger mlecules. As time spent within the resin beads is nt utilised in mving with the bulk fluid, cmpnents are held back in their mvement thrugh the clumn by their diffusin int (and ut f) the beads. The degree f retardatin f the mlecules is dependent n their size, the smaller mlecules spending a greater length f time within the beads, and thus suffering greater retardatin than the larger mlecules. Sme mlecules within the jet are t large t penetrate the pres f the resin beads, and d nt suffer any retardatin. These mlecules elute frm the clumn with the bulk fluid. Charged mlecules (such as the inrganic ash cnstituents f the jet) are excluded frm the resin beads by electrstatic frces, and cnsequently als elute frm the clumn with the bulk fluid. Thus, separatin f cmpnents in the jet 4 takes place within the clumn based n the "affinity" f each cmpnent fr the resin packing within the bed. At the clumn utlet, the elutin f the cmpnents f the feed jet can be detected by the cnductivity cell and RI detectr. A typical elutin prfile (as measured by the RI detectr) fr jet 4 frm the Malelane refinery is shwn in Figure 2. Three distinct peaks may be bserved. The first cntains the cmpnents which are least retained (retarded) by the resin beads. These include the high mlecular weight cmpnents 171

2 In xclusin Desugarisatin f RefineryJet 4 and thse which are excluded frm the resin n the basis f size (such as the highly clured cmpunds and the plysaccharides) r charge (such as the ash cmpnents). The secnd peak is the sucrse fractin. As sucrse is the mst prevalent cmpund in the jet, this peak is the largest. The third and final visible peak in Figure 2 is the mnsaccharide peak, cntaining fructse and glucse. These cmpnents, being the smallest nn-charged mlecules in the feed, have the highest affinity fr the resin beads and are thus retained the lngest within the clumn. Nt visible as a distinct peak n the elutin prfile (due t its lw cncentratin) is the ligsaccharide peak. Owing t their intermediate size, these mlecules are eluted between the sucrse and plysaccharide peaks. ::J 40. '5 Ash/Clur/ 30 Plysaccharides III C it 20 icil 10 '0 a: FIGUR 2: 50', , Glucse & Fructse By bservatin f the elutin prfile during peratin f the pilt plant, the varius fractins emerging frm the clumn may be diverted, by a series f valves, int separate prduct tanks. The sucrse prduct fractin may be further prcessed t recver crystalline sugar, the mnsaccharide fractin may be prcessed t prduce a saleable invert syrup, and the excluded ash/clur/plysaccharide fractin may be used as a feedstck fr fertiliser prductin, due t its high ptassium in cntent. It shuld be nted that, due t the nature f the in exclusin prcess (ie elutin f a relatively small quantity f feed with large quantities f water), the prduct fractins eluted frm the bttm f the clumn are mre dilute than the riginal feed. While the mechanism f in exclusin is cmpletely independent f in exchange, a limited amunt f in exchange des ccur during the prcess. Divalent catins in the feed, ntably Ca 2 + and Mg 2 +, replace the sdium ins in the resin. The large size f these catins, as cmpared t the size f the sdium in, results in a decrease in the sizes f the pres within the resin beads. This effect decreases the efficacy f the resin in separating cmpnents by in exclusin. Thus, in rder t maintain the efficiency f separatin, it is necessary t pretreat the feed t the in exclusin pilt plant fr the remval f divalent catins. This is achieved by sulphitatin, prducing an insluble precipitate f calcium and magnesium cmpunds which is remved by defecatin and filtratin. The lw cncentratins f divalent catins still remaining in the feed result in a slw decline in the clumn efficiency, requiring peridic regeneratin f the resin beads with a brine rich in mnvalent catins. The excluded ash/clur/plysac,--, ,---,--'---=: Time [mini A typical jet 4 elutin prfile. Table 1 xperimental perating cnditins Clumn temperature lutin water flwrate Lading f jet 4 Brix [0] Purity [%] Mnsaccharides [%] Oligsaccharides [ppm] 80 C 60 kg/h 1 kg per batch Feed jet 4 64, SD Peacck charide fractin btained frm the clumn during in exclusin separatin may be utilised fr this purpse, due t its high ptassium in cncentratin. ']['ecllmka feasibility xperimental design The gverning criterin fr the technical feasibility f the in exclusin prcess is the ability t recver a greater quantity f higher quality sugar frm the separated sucrse prduct fractin than wuld have been pssible frm the riginal, untreated jet 4 feedstck. On the basis f labratry scale tests (Thmpsn, persnal cmmunicatin) and the results btained frm earlier experiments n the pilt plant, an experiment was designed t test the technical feasibility f the in exclusin prcess, using this criterin. It was planned t prduce sufficient sucrse prduct fractin fr pilt pan crystallisatin at the SMRI. The results f this test wuld then be cmpared t the results f a similar test crystallisatin perfrmed n the untreated jet 4 feedstck. A cmputer prgram was develped in rder t facilitate analysis f the pilt plant perfrmance. Analytical data regarding the elutin prfiles btained during earlier experimentatin were manipulated by the prgram t develp a full descriptin f the system perfrmance under the cnditins used fr the tests. This allwed the cmputer t predict the cmpsitin f any prduct fractin frm the clumn, given details f the "cut" t be made (ie the times f pening and clsing f the valve t the prduct tank in questin). The ability t predict such infrmatin is critical t any ecnmic evaluatin f the in exclusin prcess. The set f perating cnditins chsen fr the experiment was that fr which the mst reliable analytical data were available frm previus experimentatin (see Table 1). It was decided t recver % f the sucrse in the riginal jet 4 t the sucrse prduct fractin. With the aid f the cmputer prgram, it was predicted that the sucrse prduct fractin thus btained wuld cntain 26% f the riginal ligsaccharide cntent and 5% f the riginal mnsaccharide cntent f the feedstck. The predicted cmpnent cncentratins in the prduct fractin (given a typical Malelane jet 4 feedstck as shwn) are displayed in Table 2. Upn cmparisn with ligsaccharide cncentratins previusly measured in refinery prducts by the SMRI, the predicted ligsaccharide cntent f the sucrse prduct fractin was fund t be similar t that nrmally encuntered in jet 1 (Mrel du Bil and Walfrd, 1995). Table 2 Predicted cmpnent cncentratins in the sucrse prduct fractin Prduct 2,95 98,82 0, PrcS Afr Sug Technl Ass (1996) 70

3 SD Peacck xperimental methd Under the cnditins described in Table 1 abve, 36 batches f jet were required t prduce sufficient prduct fractin fr a pilt pan biling. The time taken fr each batch t elute frm the clumn was apprximately 140 minutes. The in exclusin separatin f these batches. prduced 517 kg f dilute sucrse prduct fractin (at 2,9 0 brix), which was cncentrated t 55 0 brix in the SMRI pilt evapratr. During prcessing, the dilute prduct fractin was preserved by freezing, r by the additin f frmaldehyde and subsequent chilling. The excluded and mnsaccharide fractins were discarded. The cncentrated prduct fractin was biled In xclusin Desugarisatin frefinery Jet 4 in the SMRI pilt pan under the cnditins nrmally used fr jet 4 biling. Fr the purpses f cmparisn, a sample f untreated jet 4 feed was biled in the pilt pan under identical cnditins. Results and discussin Samples f the feed, massecuite, sugar and mlasses frm each f the bilings were cllected and analysed, yielding the results listed in Table 3. Ptassium in cntent, cnductivity ash, glucse, fructse and ligsaccharide cncentratins are all reprted n brix. Table 3 Results f the cmparative biling tests Feed t pan Massecuite Sugar Mlasses Raw Jet 4 Prduct Raw Jet 4 Prduct Raw Jet 4 Prduct Raw Jet 4 Prduct fractin fractin fractin fractin Brix [0] 58,15 57,35 89,85 88, 83,05 78,25 Purity [%] 91,96 97,89 91,38 97,69 83,07 95,60 Pl [OZ] 53,48 56,14 82,10 86,85 68,99 74,81 Clur [ICUMSA] Ptassium [ppm] ,8 0, Cnductivity ash [%] 1,45 0,42 2,25 0,67 0,013 0,007 3,88 1,20 Glucse [%] 1,22 0,45 Fructse [%] 1,07 0,38 Oligsaccharides [ppm] Scaled ligsaccharides [ppm] The benefits f the in exclusin prcess are immediately apparent. With % recvery f sucrse frm the feed, a declurisatin f 88% was achieved in the prduct fractin fed t the pilt pan, resulting in 66% less clur in the crystalline sugar. The reductins in cnductivity ash achieved were 71% fr the pan feed and 46% fr the affinated sugar. The sucrse prduct fractin fed t the pan cntained 64% less ligsaccharides and 74% less mnsaccharides than were present in the riginal jet 4. Fr this particular test, the feed jet t the in exclusin prcess cntained a lwer cncentratin f ligsaccharides than had been previusly measured in jet 4 frm Malelane. This was nt thught t be unusual, given the high degree f inherent variability in the jet. In rder t facilitate cmparisn between the results f this test and the predicted results discussed abve (the latter being based upn the earlier ligsaccharide measurements), the ligsaccharide levels in this test were scaled by the rati f the nrmal ligsaccharide cncentratin t the actual feed ligsaccharide cncentratin, thus making the feed cncentratin equivalent t that previusly measured in jet 4 frm Malelane (see the last rw f Table 3). This gave a resulting ligsaccharide cncentratin in the prduct fractin f 2326 ppm n brix. As predicted, this value was fund t be similar t that previusly measured in refinery jet 1. Table 4 shws the results btained in this test as cmpared t thse predicted by the cmputer prgram. Frm this cmparisn, it is evident that the cmputer prgram can predict the perfrmance f the in exclusin pilt plant with a reasnably high degree f accuracy. The unexpectedly high mnsaccharide levels bserved in the actual figures may be attributed t the ccurrence f inversin in the prduct fractin during evaprative cncentratin and strage. Table 4 Cmparisn f actual and predicted results Brix f dilute prduct [OBrix] Purity [%] Mnsaccharide level [%n brix] Oligsaccharide level [ppm n brix] Predicted 2,95 98,82 0, Actual 2,86 97,89 0, Crystal size distributin analyses were perfrmed n the sugars crystallised frm the untreated jet 4 and the sucrse prduct fractin (see Figures 3 and 4). The effect f the decreased ligsaccharide cncentratin in the prduct fractin is immediately apparent, with less crystal elngatin being bserved. The measured elngatin ratis were 2,3 fr the untreated jet 4 sample and 1,4 fr the sucrse prduct fractin. Assuming, as a rugh apprximatin, a 50% recvery f sugar frm each refinery biling, a diversin f % f the sucrse in jet 4 back t jet 1 (by applicatin f the in exclusin prcess) wuld result in the recvery f mre than 78% f the riginal sucrse in the jet 4 as sugar "in the bag". Additinal benefits t prcessing wuld als accrue as a result f the reductins in ash and clur achieved. Furthermre, a saleable mnsaccharide syrup fractin may be prduced as a by-prduct f the in exclusin prcess. It is imprtant t nte that the perating cnditins used in the abve experiment were chsen, n the basis f reliability f previus experimental data, t demnstrate the technical feasibility f the in exclusin prcess. It is highly imprbable that these cnditins wuld be thse chsen as ecnmi Prc S Afr Sug Technl Ass (1996)

4 In xclusin Desugarisatin frefinery Jet 4 cally ptimum fr the peratin f a full scale plant, and thus n undue imprtance shuld be placed n the abslute numerical values f the system parameters. Run number Table 5 Operating cnditins fr experimentatin Temperature [0C] lutin water flw rate [l/rnin] SD Peacck Mass lading f feed [kg] 1 80,4 0,94 1,0 2 80,0 2,33 1,0 3 80,0 2,84 1,0 4 80,0 4,23 1,0 5 80,1 1,51 2,0 6 80,1 2,26 2,0 -. FIGUR 3: Crystalsgrwnfrm untreated jet 4.,0- t: '' "-"". / (i Befre the cmmencement f each test, the clumn was heated t 80 C and flushed with large quantities f ht water. T begin the separatin, a weighed batch f jet 4 was fed t the tp f the clumn. Immediately after intrductin f the feed batch, the autmatic data lgger and a stpwatch were simultaneusly started. In rder t minimise the number f samples t be analysed, the cllectin f effluent samples frm the clumn was nly cmmenced nce the tp f the ash/clur/plysaccharide peak was bserved n the RI detectr. Sample cllectin was cntinued until mst f the mnsaccharide peak had eluted frm the clumn. This technique ensured that the entire sucrse peak was cllected during each test. Samples were cllected in ne litre plastic bttles, with typically 60 t 80 samples being cllected per test. The time f cllectin f each sample was nted, thereby facilitating the exact determinatin f the vlumetric flw rate f the elutin water thrugh the clumn. The samples frm the clumn were frzen and analysed fr sucrse, glucse, fructse and ligsaccharide cncentratins by high perfrmance liquid chrmatgraphy. very third sample was analysed fr brix, clur, and sulphated ash. The analytical results f the experimentatin were evaluated with the assistance f the cmputer prgram discussed earlier. The cmputer prgram was used t determine the cmpsitin f the theretical sucrse prduct fractin that wuld be btained, given sucrse recveries f 50, 60, 70, 80, and 95% f the riginal sucrse in the feed jet t the prduct fractin. Fr the purpses f the results described here, the sucrse prduct fractin t be cllected was that which centred arund the middle f the sucrse peak eluting frm the clumn. 50, , , FIGUR 4: Crystalsgrwnfrm the sucrseprductfractin. 45 Analysis f perating cnditins xperimental methd Knwledge f the variatin f the quantity and quality f the sucrse prduct fractin with changes in perating cnditins is f vital imprtance t any ecnmic feasibility study f the in exclusin prcess. An experiment was thus designed t determine the effect f changing perating cnditins n the perfrmance f the in exclusin pilt plant. Six tests were perfrmed n the pilt plant, with tw key perating parameters being varied during the experimentatin: elutin water flw rate t the tp f the clumn: (1, 2, 3 and 4 litres per minute) mass lading f feed per separatin: (1 and 2 kg per batch) The precise perating cnditins used fr each test are shwn in Table 'x 35 ' c r 5 O Time [min] FIGUR 5: lutin prfileat lwflw rate, Prc S Afr Sug Technl Ass (1996) 70

5 SD Peacck In xclusin Desugarisatin f RefineryJet , ,---,-, 45 flw rates and clumn ladings. The ash cncentratin f the prduct fractin (n brix) decreases with clumn lading. e 40 'x 35 '0 30 Sucrse peak ,---, , , 6 (6) (5) C Ash/clur 015 plysaccharide peak 1il O FIGUR 6: Time [mini lutin prfile at higher flw rate. Mnsaccharide peak Sucrserecvery [%] Results and discussin It is well knwn that an increase in elutin water flw rate r an increase in clumn lading (mass f feed per batch) results in prer reslutin f the cmpnents t be separated by the in exclusin prcess. This effect can be bserved in Figures 5 and 6. Figure 5 shws an elutin prfile fr 1 kg f jet 4 at a flw rate f 0,94 l/min, while Figure 6 shws a similar prfile fr a flw rate f 4,23 l/min. The difference in reslutin is immediately apparent, with a prer degree f separatin being bserved n the elutin prfile fr the higher flw rate. The results f the evaluatin f the in exclusin prcess by the cmputer prgram are displayed in Figures 7 t 12, with the numerical labels n the curves referring t the test number (see Table 5 fr the cnditins f each test). The fllwing bservatins may be nted: In xclusin Desugarisatin f Refinery Jet 4. The brix f the prduct fractin decreases with increasing sucrse recvery (see Figure 7). This is due t the inclusin f greater quantities f lw-brix, nn-sucrse cmpnents in the sucrse prduct fractin at higher recveries. The prduct fractin brix increases with increasing clumn lading, due t the greater quantity f material eluting frm the clumn at higher ladings. It can be seen that a dubling f the lading f feed per batch results in an apprximate dubling f the brix f the prduct fractin. In xclusin Desugarisatin f Refinery Jet 4. The sucrse purity f the prduct fractin decreases with increasing recvery, as mre impurities are included in the prduct fractin at higher recveries (see Figure 8). The ligsaccharide cncentratin f the sucrse prduct fractin increases with increasing sucrse recvery (see Figure 9). This bservatin is als true f the mnsaccharide cncentratin (Figure 10), ash cntent (Figure 11) and clur (Figure 12) f the prduct fractin. This phenmenn is a result f the inclusin f mre f the impurities frm the feed jet int the sucrse prduct fractin at higher recveries. It shuld als be nted that the cncentratins f ligsaccharides, mnsaccharides and clur in the prduct fractin increase with elutin water flw rate and clumn lading, due t the decrease in separatin efficiency which is encuntered under cnditins f higher FIGUR 7: 95 z- c :::l C. li) :::l en FIGUR 8: e 8L----L "L----=':----=':-----:-:. Sucrserecvery [%] , , , , , x g,6000 S "C r li) g'0 FIGUR 9: Prduct fractin brix as a functin f perating cnditins. Prduct fractin purity as a functin f perating cnditins. Sucrserecvery [%] (3) (1) Oligsaccharide cntent f prduct fractin as a functin f perating cnditins. PrcS Afr Sug Technl Ass (1996)

6 In xclusin Desugarisatin f RefineryJet ,-----, , , )('0.45.;::.0 g C go "C "fa ca 0.1 lf=:===$: : ::: FIGUR10: ,g 0.7 C go.6 8 s: Sucrserecvery [%] Mnsaccharide cntentf prductfractinas a functinf perating cnditins. 1.1r---,------, ,-----r---, , 50 Sucrserecvery [%] FIGUR11: Ash cntentf prductfractinas a functinf perating cnditins ,.-----,----, , ,------, (6) (2) (1) (3) Cnclusins SD Peacck xtensive tests were perfrmed in rder t evaluate the technical feasibility f the in exclusin prcess fr the desugarisatin f refinery jet 4. The effects f the pilt plant perating cnditins n the quantity and quality f sugar recvered by in exclusin were examined. It was fund that the in exclusin prcess was technically feasible n a pilt plant scale. Sugar biling trials n the prduct fractin recvered frm the in exclusin pilt plant separatr shwed cnsiderable imprvements in crystal mrphlgy, recverable sucrse and crystal clur. It was fund that the brix f the sucrse prduct fractin btained by in exclusin decreased with increasing sucrse recvery, but increased with clumn lading. It was als fund that the sucrse purity f the prduct fractin decreased with increasing recvery, as mre f the impurities frm the feed jet were fund t be included in the prduct fractin at higher recveries. Impurity cncentratins within the prduct fractin were fund t increase with sucrse recvery, clumn lading and elutin water flw rate (with the exceptin f ash cncentratin, which was fund t decrease with clumn lading). It wuld be necessary t take all f these factrs int cnsideratin in the design f a full scale in exclusin plant, trading the advantages f higher recveries, brixes and thrughputs against the disadvantages f increased impurity cncentratins in the sucrse prduct fractin, t determine the ptimum perating cnditins fr the system. Acknwledgements The authr gratefully acknwledges the assistance f the fllwing peple, withut whm this wrk culd nt have been cmpleted: Man Mdley and the staff f the Malelane sugar mill and refinery, and Stephen Walfrd, Cedric Mazibuk, Mbus Zulu and the ther members f the SMRI staff wh prvided assistance and guidance fr this prject. RFRNCS Hngist, HJ (1977). Chrmatgraphic separatin f sugar slutins: the Finnsugar mlasses desugarisatin prcess, Int SugJ, 79: Mrel du Bil, PG and Walfrd,SN (1995). Oligsaccharidecncentratinsin refineryjets and massecuites,sugar Milling Research Institute TechnicalNte N 7/95. Schneider, HG (1978). In exclusin in cane sugar refining, Prc Sug Ind Technl fnc, 37 (415): : '450 'c :J 400 :2 ::l :::' :J (5 U300 (2) (3) (6) (1) Sucrse recvery [%1 FIGUR 12: Clurf prductfractinas a functinf perating cnditins. 176 PrcS Afr Sug Technl Ass (1996) 70