Process Description—Standalone Sugar Refinery : Phosphofloatation & Ion Exchange
The very very high pol raw sugar is melted in the specially designed melter with hot water and steam and subjected to screening by vibrating screen. This screened melt is received in Screened Melt Tank and then pumped to reaction tank via. Shell & tube type heat exchanger. The temperature of liquor is controlled in the range of 82°C – 85°C with the help of automatically controlled inlet exhaust steam/vapour valve at heat exchanger. The liquor flow rate is measured and controlled to desired setting by automatic flow control valve.
The colour precipitant is added at the rate of 200 to 500 ppm in the reaction tank and phosphoric acid solution is added in 1st compartment of reaction tank at the rate of 200 to 350 PPM on melt solids.
The pH of liquor is raised to the range of 7.0 – 7.10 by addition of lime sucrate solution through chemical dosing pump. The pH of liquor in the reaction tank is sensed with pH probe and flow of lime sucrate solution is adjusted automatically according to pH of melt liquor. Agitator provided in each compartment of reaction tank mixes all additives in reaction tank. The liquor flow by gravity in the aeration compartment of tank, which provides the static head for the clarifier. The cavitation aerator provided in last compartment disperses a supply of finally divided air in the liquor alternatively air pump is used for supply of micronized air.
A solution of flocculant is added at the rate of 8-12 PPM on melt solids to the liquor as it leaves the aeration tank. This aerated liquor then flows by gravity without disturbing the floc formed, into the base of flocculating chamber in the centre of the clarifier. The clarifier stirrer with mixing baffles ensures that the flocculent is gently but thoroughly mixed into the aerated liquor.
The flocculated liquor passed up the central chamber and overflows into outer flotation chamber of clarifier. The rotating scum rake removes the scum continuously and clarified liquor is continuously withdrawn from the bottom of flotation chamber through collection ring standpipe and weir box. The scum in the outer gutter flows to scum receiving tank by gravity and pumped to 3 Stage Scum Desweetening System. The clarified liquor flows to clarified liquor receiving tank by gravity and pumped at the top of multibed filter having automatic back wash arrangement.
This filtered liquor received in back wash tank which overflows to filtered liquor tank and then subjected to further decolourization and demineralization with the help to Ion exchange resin will be – Poly acrylic and Polystyrene – such that the best properties of both the type of resins are advantageously utilized. Two columns, in parallel, each of the Poly acrylic and Polystyrene resins are on-line at any given time while one column each is under regeneration. The liquor coming out from the polishing bed is collected in fine liquor tank and pumped to pan floor liquor storage tank.
Four massecuite boiling system is followed i.e. R1, R2, R3 and R4 massecuite boiling. The R1 boiling is done on fine liquor, R2 boiling on R1 runoff, R3 boiling on R2 runoff and R4 boiling on R3 runoff. The grain for all the four types of massecuites is prepared by slurry or dryseed from screen devices and boiling is done in batch type pans. R4 runoff is send to recovery house at pan floor storage tank for ‘A’ massecuite boiling. In Recovery House again 3 massecuite boiling system is adopted, i.e. A, B, & C massecuite boiling system.
R1, R2, R3 & R4 massecuite is cured in flat bottom batch type fully automatic centrifugal machines. A refined sugar from these centrifugals is dried in rotary type dryer/fluidized belt type and after screening send to refined sugar bins separately. In recovery house massecuite will be cured through continuous centrifugal machines.
R1, R2, R3 & R4 sugar is blended as per choice and send to discharge bin via grader and from there sugar is weighed, packed and send to warehouse for storage.