PROCESS DESCRIPTION OF STARCH MANUFACTURE

           STARCH MANUFACTURE PROCESS DESCRIPTION

Maize kernels are screened and air cleaned in steeped in SO2 water for 60 to 70 hours at a temperature 50-55 ͦC to prevent bacteria growth. The softened grains are passed through coarse grinder No.1. Coarse grinding is done to separate the germ without breaking or disturbing it because otherwise if fine grinding was done germ would liberate oil and cause further process problem, in a degerminator cone is maintained at about 40 ͦC be at which all germs tend to float and rest of heavy media passes as the under flow to next operation, second coarse milling is done just to ensure the breaking of any uncrushed grain.

All the overflow of the degerminators are collected in the germ tank, and further germ is fed for germ washing, germ dewatering, germ drying, germ expelling and maize oil is collected. 

The underflow from degerminator 3 comes to pin mill feed tank and then to pin mill and then to concave screens that are 50μ and its outlet goes to primary separator (Alfa Calval) and underflow to pin mill again and collected from there to houdi tank and is fed to 75μ screens and screen underflow again goes to primary separator and overflow to stone grinder and then fed to 1 DSM of 120 mesh and remove oversize as byproduct i.e. bran obtained from three stage washing and screw pressing for dewatering.

The underflow of DSM goes to raw material tank and then to series of 3 DSM screens and any overflow left is send to filter press to recover grit or fine bran and underflow of DSM goes to stone grinder again. The underflow is collected in alpha feed tank and are then to primary separator machine which works on density difference and separates light pure yellow gluten as overflow and heavy white slurry which is mixture of both starch and traces of protein (not more than 2%) as underflow.

The overflow is settled in series of large settling tanks. The sediment obtained is thereby pumped to filter press, which gives cake which is flash, dried and converted into dry gluten.

The impure underflow starch slurry is washed in series of hydro-cyclones called as Dorr cyclones. This is counter current washing and thickening station. Total 9 stages are employed in which impure starch and water flows in opposite directions. Water as a overflow collect all the light impurities and impure water collected at the end of the first stage while starch as a underflow becomes pure and thick is collected at the 9th stage at come of 20 oBe. This starch milk is centrifuged to get wet cake, which is further flash dried to get dry starch powder and is finally packed in silos bags.