In addition to lime and sulphur dioxide used in clarification by sulphitation there are a number of chemicals which have found wide application under specific conditions while there are some, the use of which is being advocated after extensive trials. Some of the important ones are discussed below—
11.1. Phosphoric acid—As already explained replenishment of phosphate in the juice by addition of triple superphosphate or phosphoric acid is a regular practice in some parts of India like Maharashtra, where the juices are deficient in phosphate Triple superphosphate contains around 43-45% P2O5 while commercial phosphoric acid contains about 54% P2O5. In sugar mills hot water extract of triple superphosphate is prepared in special tanks of acid resisting material. This extract is found to contain 26 mgms of CaO per 100 mgms of P2O5 plus some sulphate also.29 As against this the phosphoric acid which is in liquid state introduces only minute quantities of iron and other impurities.
As regards single superphosphate, which contains 15-18% P2O5 more impurities in the form of CaO, S04 and acids are introduced for the same amount of P2O5 from single superphosphate as compared to triple superphosphate. Its use is therefore not recommended.
Phosphoric acid, on account of its extremely low impurities as compared to the triple superphosphate extract is recommended for use in clarification.
Phosphoric acid free from objectionable impurities is manufactured from rock phosphate by employing process involving use of electric furnace with carbon electrodes.
Commercial phosphoric acid is a clear liquid packed in polythene or PVC jars and contains about 55% H3P04. It has to be sufficiently diluted with condensate before being used.
11.1.2 Bentonite—This clay which is an aluminium magnesium silicate is colloidal in nature and presents large surface for adsorption as shown by the fact that one cubic inch (16.39 cm3) of the dry clay when mixed with water may produce a surface of one acre.30 When used as an adjunct to sulphitation it is reported to give better settling of muds and result in higher elimination of colloids. Sodium bentonite suspension in water prepared by adding soda to bentonite slurry, when added to sulphited juice at the rate of 250 mgms per tonne of cane is reported to have given good results in Argentina while processing refractory juices.30
Although some work on the use of sodium bentonite in sulphitation has been carried out in India, its adoption on commercial scale has not met with success probably because it has not become economically attractive. Nevertheless more investigational work needs to be undertaken for carrying out techno-economic evaluation of the use of this clay under different operating conditions.
11.2. Settling aids—In many sulphitation factories settling of treated juice in clarifiers present difficulties particularly during peak maturity period, affecting the rate of cane grinding and also quality of sugar. An important development in the last two decades in meeting this difficult situation has been the use of minute quantities of synthetic polyelectrolytes,
«.
CLARIFICATION
as flocculation aids. These chemicals are synthetic polyacrylamides, partially hydrolysed, with very high molecular weights (7 to 10 millions), which on dissolving in water give highly viscous solution and are added as very dilute solutions. The efficacy of these polymers depends on the molecular weight and degree of hydrolysis. They are mostly anionic in nature. A dilute solution of the settling aid is fed continuously to the treated juice on its way to the settler after the juice has been boiled. It is desirable to feed the solution near the point of entry into the subsider in two or three streams to ensure proper and even dosing, the dose varying from 2 to 6 p.p.m. According to one theory the large chain molecule of polyacrylamide serves as a bridge between different particles of precipitate with resultant formation of large aggregates which settle rapidly. The treated juice after addition of flocculant should not be subjected to vigorous stirring in order that the flocs once formed are not disturbed. Thus after treatment with polyacrylamide pumping of juice is to be avoided. Common flocculants which are available in Indian market for use in sugar mills are Separan AP 30, Sedipur TF2, Magnofloc 26 & 27 Trufloc etc. Every factory should carry out its own settling tests with samples of different flocculants with a view to study the efficacy of the same and then decide on using the one that is most suitable under conditions obtaining there.
11.3. Magnesia—Magnesium oxide MgO in combination with lime has been commercially used in Hawaii, Puerto Rico, Jamaica etc. in cane juice defecaton with the main object of reducing scale formation in evaporator but the clear juice shows foggy appearance and is turbid as compared to lime clarified juice32 Work in India on the use of Magnesia in sulphitation factories in partial replacement of lime has not given any promising results.33
11.3. Formaldehyde—Schmidt34 has stated that formaldehyde when added to cold raw juice at the rate of 0.5 to 1.0 p.p.m. before defecation improved the sedimentation characteristics of treated juice. Particularly with refractory juices from drought affected cane the formaldehyde is reported to give better thickening of muds. However its use in sulphitation has not been reported.
139
REFERENCES
1. K Onna & Tamays 'Proc, Hawaiin Sugar Technogists Association' 1979 p. 141-143.
2. J. Marches 'Principles of Sugar Technology' by P. Honig Vol. p. 584.
3. J.Marches —do— p.607 4. C.F. Marches —do— p. 608
5. C.F.K. Douwes Dekker 'Principles of Sugar Technology' Vol. I...p. 397 6. J.G. Davies 'Principles of Sugar Technology Vol. I.. .p. 541.
7. J. Marches 'Principles of Sugar Technology' Vo. I...p. 618-620
—do— 'Proc. ISSCT1956.. .p. 582.
8. B.H. Hoshing & N.G. Patel 'Proc. Deccan Sugar Technologists Association' 1967...p. 191.
9. K. Douwes Dekker 'Principles of Sugar Technology' by Honig p. 363.
10. A.C. Raha, RB Nigam A.K. Agarwal & P. Sanyal, 'Proc, Sugar Tech. Association of India' 1975...
p. 23-28.
also private communication, work at Phaltan Sugar Wks. Sakharwadi Maharashtra.
11. J. Marches 'Principles of Sugar Technology' Vol. I...p. 592.
12. G.K. Limaye 'Proc. Deccan Sugar Tech. Association India' 1967 M23-M32.
13. J. Marches 'Principles of Sugar Technology' by P. Honig Vol. I p.625.
14. B.B. Bandi 'Proc. Deccan Sugar Tech. Association' 1959...p.63-64.
15. S.N. Gundu Rao, P.V.S. Sastry & M.R. Bhalerao 'Proc. ISSCT 1956 India, p.209.
16. D.P. Kulkami, J.R. Unde 'Proc. Sugar Tech. Association of India' 1973...P.M. 115.
16a. D.P. Kulkami, M.K. Patil & K.C. Vora, 'I.S.I' 1967 p. 297-301.
17. N.P. Randhwa 'Proc. Sugar Tech. Association of India' 1980 p.m. 109-112.
18. G.N. Acharya 1981 'Proc D.S.T.A. Central Electronics Engg. Research Institute, Pilani. P E 51.
also A.P. Chinnaswamy, K. Thurthmalai, S. Vishwanathan, 'Proc ISSCT' XX Congress Brazil 1988.
also G.N. Acharya Bhartiya Sugar August 1988 p. 9-39.
also Laxmi Narayan KSN Rao, K. Srinivasan & G.N. Acharya 'Proc Seminaf on 'Juice Clarification practices followed in India with reference to design and control system' organised by DSI & CEERI at Pune on 11.12.1987.
19. O.P. Tripathi 'Proc. Sugar Tech. Association of India' 1981 p E 33.
20. S.K.D. Agarwal 'Proc. Sugar Tech. Association of India' 1962...p,100.
21. S.C. Sharma 'Proc. Sugar Technologists Association of India' 1980 P.M. 73.
22. S.C. Sharma 'Proc. ISSCT' 1980 p.2137,2143.
23. N.A. Ramaiah, S.K.D. Agarwal, P.C. Johery & L P . Tiwari, 'Proc. Sugar Tech Association of India' 1975 p. M1-M6.
CLARIFICATION 141 24. D.P. Kulkarni, MX Patil 'Proc. DSTA' India 1965 p.119.
25. S.C. Gupta, N.A. Ramaiah 'Proc. DSTA' India 1965, p.119.
26. CGM PerkG 'Cane Sugar Manufacture' p.56.
27. D.P. Kulkarni, J.R. Unde, 'Proc STA' India 1974 p.m. 70.
28. J.M. Saba & N.S. Jain 'Proc. STA' India 1956.
29. D.P. Kulkarni 'Proc. DSTA' India 1967 p.147-160.
30. cf Chen & Meade 'Cane Sugar Handbook' 10th edition p.183.
31. Dubey R.S., Mavi S.S., cf. 'Proc. ISSCT 1956 p. 408.
Experimental work at 'Phaltan Sugar Works Ltd.' Sakharwadi Dist. Satara. India.
32. S.C. Gupta, N.A. Ramaiah, S.K.D. Agarwal, R.P. Shukla, K.K. Mathur 'Proc. Sugar Technologists' Association of India' Kanpur 1972 p. M99-M129.
33. S.C. Sharma & Mahesh Narain 'Proc. Sugar Technologists' Association of India' Kanpur 1972 p M 19 M23.
34. N.O. Schmidt 'Proc. ISSCT India 1956 p. 612.
35. Other references—
(i) 'Seminar' on Preparation of Lime solution-Sulphur dioxide and Phosphate in cane juice clarification held in Pune on 26.4.81 by 'Deccan Sugar Technologists Association' (I) Pune.
(ii) 'Inorganic Chemistry' by Partington.
(iii) Outlines of 'Chemical Technology' by Dryden.
(iv) 'General Chemistry' by W.E. Miller & J.A. Barker.
(v) 'Machinery & equipment for Cane Sugar Factory' by L.A. Tromp 1946 Edition.
(vi) 'Handbook of Cane Sugar Engineering' by E Hugot & Jenkina 1971 Ed.
(vii) 'Cane Sugar1 by Noel Deerr 1921 Ed.
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