SOME NOTES ON THE NEW MELT CLARIFICATION AT HULETT'S S.A. REFINERIES

Transcription

1 107 SOME NOTES ON THE NEW MELT CLARFCATON AT HULETT'S S.A. REFNERES By J. B. ALEXANDER Previus t March 1959, Hulett's S.A. Refineries emplyed varius mdificatins f the phsphdefecatin prcess cupled with paper-pulp and ccasinally kieselguhr filtratin, fllwed by single charring f liqurs. n March 1959, flue gas carbnatatin alar Tate and Lyle was intrduced. t is difficult t make an accurate cmparisn f the new and ld prcesses as many f the prperties nw used t measure clarificatin efficiency were nt in vgue prir t July Hwever, there is n dubt that bth the clarity f 'the liqurs and the clur f the refined sugar prduced by the carbnatatin prcess are vastly superir t thse prduced immediately prir t its intrductin.. Briefly, the clarificatin prcess as practised at present is as fllws: After being weighed by a Serv-Balans the raws t be melted are cld mingled with purity affinatin syrup in a scrll agitatr giving a retentin time f abut 10 minutes at 50 t.p.h. melt. The mingled sugar is spun n 10 E.D. 48 X 30-inch Watsn Laidlaw machines with maximum speed f 960 r.p.m. The washed sugar is melted with Jhnsn sweetwater t an autmatically cntrlled brix. The liqur is again brixed by a plishing brixer befre being fed t carbnatatin. Carbnatatin is cnducted in 3 saturatrs in series, giving a retentin f sme 90 minutes with a melt rate f 50 t.p.h. All the milk f lime (Density 1.085) is added t "A" saturatr and cntrl f lime and liqur is effected by means f variable speed lime and liqur wheels. Lime per cent slids has varied between 0.75 and 1.5 during the seasn and has averaged Gassing-ut is achieved with scrubbed flue gas. The flue gas runs at a steady 12 per cent CO 2 cncentratin leaving the bilers but is reduced t 10 per cent after having passed the scrubbing units which cnsist f a Musgrave aerdynamic dust cllectr fllwed by a water scrubbing twer and finally a sda twer. The main bject f the gasscrubbing is t remve crrsive sulphur dixide. Abut 80 per cent gassing ut is achieved in "A" saturatr crrespnding t a ph f apprximately n "B" saturatr gassing-ut by a further 15 per cent causes the ph t fall t arund abut 9.6. The gassing-ut in "C" saturatr finally reduces the ph t 9. The filter-statin cnsists f 9 Aut filters (1,260 sq. ft each) with 4 Jhnsn plate and frame presses (1,500 sq. ft. each) fr sweetening-ff. The clear filtered liqur (63 0 Brix) is passed ver bne char twice. t first cmes int cntact with char which has already been used fr partly declurising liqur befre cming int cntact with freshly burnt char. As in mst sugar refineries the efficiency f the clarificatin prcess at H.U.L.S.A.R. is measured indirectly by the remval r nn-remval f the impurities rather than gain in purity as such. The fates f the fllwing classes f impurity are used as a yardstick t gauge the thrughness f clarificatin: (a) All types f clured bdies. (b) Suspended and cllidal impurities. (c) Bth rganic and inrganic anins. (d) Catins. (e) Reducing sugars. The cncentratin f clured bdies in sugar liqurs is measured by the attenuatin index at 420 millimicrns using a Beckman mdel DU. spectrephtmeter. n the case f turbid liqurs such as carbnatatin supply liqur, a duble filtratin ver kieselguhr is made prir t clur measurement. The cncentratin f suspended and cllidal impurities is still judged visually in the plant by examinatin f liqurs fr brilliance. Althugh A*c 720 readings are made n many liqurs their interpretatin as turbidity is ften suspect and thus n A*c 720 figures are shwn in Table 1. t has been custmary t regard either gravimetric r cnductimetric ash as giving a suitable measure f the ttal inrganic matter in liqurs. Althugh cnductimetric ash is still regarded as a very rapid and desirable guide as t what is happening in respect f inised matter, the use f the determinatin f "ttal catins" wuld appear t have many advantages especially where a higher degree f accuracy is required. t is less time cnsuming and requires less skill than a gravimetric ash determinatin and by expressing the results in terms f micr-equivalents a very simple balance f inic cnstituents results. The determinatin is carried ut in a manner similar t that described by Dmingues.' f the sulphate and chlride determinatins are made n the same liqur an apprximate measure f the rganic acids may be btained by difference, since ther anins d nt nrmally ccur in refinery liqurs t any extent. Ca+Mg and sulphate have been determined by titratins with

2 108 E.D.T.A. slutin and chlride has been determined by cnductimetric titratin with silver nitrate. All reducing sugar determinatins have been made using the Lane and Eynn methd as attempts t intrduce the mre rapid T.T.C. methd have nt yet prduced the degree f reprducibility desired. Table shws the average mnthly analysis f materials thrugh clarificatin ver seven mnths. A general increase in reducing sugars is nticeable frm Nvember when the refinery started drawing n stred sugars. Table shws the reducing sugar "destryed" by carbnatatin and the percentage clur and Ca-l-Mg remved by carbnatatin. The percentage f clur and Ca+Mg (based n filtered liqur) remaining after duble charring are als shwn. Althugh nly seven sets f figures are available the pssibility f an inverse relatinship between reducing sugars destryed and percentage clur remved and percentage Ca+Mg remved appears nt unlikely. The drp in efficiency f char in remving bth Ca+Mg and clur can prbably be attributed t the fact that a relatively large amunt f new char was added t the stck in the July perid. Apparently regeneratin f char as practised at H.U.L.S.A.R. is unable t restre char t the level f its riginal efficiency. n an attempt t measure the amunts f rganic acids thrughut the clarificatin prcess cmpsite daily samples were analysed ver the perid 11th 16th February. Bth the washed raw sugar and the carbnatat in supply liqur were filtered ver kieselguhr at 50 Brix befre analysis t prevent the interference f insluble salts which wuld be remved in practise by filtratin in any case. The decrease in ttal catins shwn in Table is due almst entirely t remval f calcium and magnesium as can be seen by the almst cnstant level held by catins ther than Ca+Mg. The sulphate in is rather efficiently recvered by carbnatatin and is still further reduced by char. Even the initial labratry kieselguhr filtratin f the carbnatatin supply liqur at 50 Brix was able t remve cnsiderable sulphate. The increase in chlride cntent frm washed raw sugar t carbnatatin supply liqur is undubtedly due t the water and Jhnsn sweet water used fr melting. The increase in rganic acids frm washed raw sugar t carbnatatin supply is als apparently due t rganic acids in the Jhnsn sweetwater. The increase acrss carbnatatin and first charring is prbably due t the destructin f reducing sugars already mentined. Organic acids appear t be the main anin after carbnatatin and even after charring the rganic acid cntent is still nearly duble that f the riginal washed raw sugar. This increase in rganic acids nt nly represents a lss f sugars but is als n dubt respnsible fr the less efficient remval f impurities ver char. The mechanism f frmatin f rganic acids during carbnatatin and first charring is nt knwn. Hwever, previus labratry tests carried ut by the authr at the Sugar Milling Research nstitute were able t demnstrate that manganese acts as a catalyst in the xidatin f sugars t acids, by atmspheric xygen. Even calcium saccharate slutins cntaining small quantities f manganese ins prduced cnsiderable quantities f rganic calcium precipitates when xygen was passed thrugh the slutin at 40 C. Since the lime used fr carbnatatin cntains cnsiderable amunts f manganese (0.5-2 per cent) it seems nt unlikely that ne f the surces f rganic acids may be the xidatin f sugars (sucrse included) by the xygen cntained in flue-gases. Acknwledgement The authr wishes t thank the staff f the refinery labratry and in particular J. Burne, P. de Frberville and G. Frangs fr their c-peratin in carrying ut f the numerus analysis called fr in this investigatin. Reference L. P. Dmingues: Determinatin f Ttal Catins in Cmmercial Sugars. Prc. f the Furth Sessin f Bne Char, 1955.

3 TABLE AVERAGE MONTHLY ANALYSS OF MATERALS THROUGH CLARFCATON Affinated Carbnatatin Filtered Single Charred Duble Charred Refined Raw iv/elt Sugar Supply Liqur Liqur Liqur Sugar AUGUST 1959 Reducing Sugars per cent n Slids Ash...., Ca+Mg (Micr equiv.jg slids) A*c ph SEPTEMBER 1959 Reducing Sugars per cent n Slids Ash per cent n Slids Ca-j-Mg (Micr eqniv.jg slids) A*c ph OCTOBER 1959 Reducing Sugar per cent n Slids Ash per cent n Slids Ca-l-Mg (Micr equiv.jg Slids) A*c ph NOVEMBER 1959 Reducing Sugars per cent n Slids Ash per cent n Slids Ca+Mg (Micr Equiv.Jg Slids) A*c ph DECEMBER 1959 Reducing Sugars per cent n Slids Ash per cent n Slids Ca+Mg (Micr Equiv.Jg slids) A*c ph JANUARY 1960 Redqcing Sugars per cent n Slids Ash per cent n Slids Ca+Mg (Micr equiv.jg slids) A*c ph FEBRUARY 1960 Reducing Sugars per cent n Slids Ash per cent n Slids Ca-j-Mg (Micr equiv.jg slids) A*c ph

4 110 TABLE Ca+Mg Clur remaining Reducing Sugar remaining after after MONTH destryed by Per cent Clur Per cent Ca+Mg Duble Charring Duble Charring Carbnatatin remved by remved by per cent n per cent n PM' cent Slids Carbnatatin Carbnatatin Filtered Liqur Filtered Liqur August September Octber Nvember December January February TABLE CONCENTRATON OF SOME MPURTES N MCRO.EQUVALENTS PER GRAM SOLD THROUGH CLARFCATON N PEROD 11th-16th FEBRUARY 1960 Washed Liqur Liqur Single Duble Raw t frm Charred Charred Jhnsn Sugar Carbnatatin Carbnatatin Liqur Liqur Sweetwater Ttal Catins , ; \1.6 Ca+Mg Catins ther than Ca+Mg Sulphate Chlride Phsphate , Organic acids by Difference :

5 "7'j "" '"... ("')... '" ;;:l ;;:l s. "" '" -e- l:'o M'N<iL&R. CLS. 1 M LT R, r- f"lurv_ E"'''UN4T t AFFNATlOe-l.- r -...' '\ ""... " " " ".", CARBONATATON CHAR t TO L.UOC U... T&C. CLARFCATON PROCESS FLOW DAGRAM