DADTCO uses two methods of drying the semi-wet cassava starch cake. The first method describes the central drying of cassava starch cake with a flash dryer, the second method is a mobile drying system that is added to the AMPU and the MRU and that can dry the cassava starch cake on the spot.
In a split processing scenario where the cassava starch cake is produced locally and dried centrally, DADTCO uses the most efficient central dryer called Flash Dryer. The principle of a Flash Dryer is simple. Very hot air (180°C) is sucked and mixed with the Cassava Starch Cake (CSC) inside a very long pipe (called the flash pipe) up to 40 meters high and 1 meter in diameter. The CSC is passed through the pipe very quickly (in a "flash") and is dried to Cassava Starch Flour (CSF) with about 11% moisture.
After the flash pipe the now dried CSF and remaining air are separated from each other in a very large cyclone. The remaining air is sucked through the main ventilator and blown out of the exhaust pipe.
The dried CSF is partly blended with new semi wet CSC and returned to the flash pipe. The other part of the CSF is passed into a cooling system which cools the CSF down to ambient outside temperature. This quick cooling down is very important. If not cooled down properly, the still warm CSF while going into the bags will attract moisture from the air. This will lead to a quick development of yeasts and molds which in turn will lead to bad quality of flour.
Once the CSF is cooled down, it is sieved off in a very large circular tumbler sieve (2 meters in diameter) where all particles larger than 200 micron (0.2 mm) are removed and send to a special flour mill (called a pin-mill) to mill this fraction down to less than 200 micron. This milled product is sieved off again on a 200 micron sieve and anything bigger than 200 micron is excluded from the flour. This left-over fraction consists of relatively large cassava fibres and can be used in the production of chicken feed, soil improvers or even mosquito coils.
All CSF smaller than 200 micron goes to the bagging hopper in order to be bagged into 10, 20 or 50 kg net weight bags.
DADTCO’s Mobile Dryer is built in two 40 foot containers and the drying of the cassava starch cake takes place in a fluid bed drying system. This system exists of a bed of cassava starch cake supported by a cushion of hot air jets (fluidized) and the material is conveyed this way, while being dried. The method achieves intimate mixing without mechanical damage. It is used for cereals, salt, coffee, and dried vegetables.
On a two shifts per day basis, the Mobile Dryer is able to dry about 48 tons of Cassava Starch Cake into 24 tons Cassava Starch Flour per day, for which 80 tons of roots is used. On a yearly basis the Mobile Dryer produces 7,200 tons of Cassava Starch Flour.
The Mobile Dryer runs on LPG (liquefied petroleum gas). LPG has a high heating or caloric value which means that as an energy source, LPG provides a high level of heat in a short time span. LPG also has a virtual absence of Sulphur, leading to cleaner burning. LPG is a convenient, portable energy source that is easy to transport and store.