It adopts advanced technology, could work automatically and continuously. It has high processing capacity and high dewatering efficiency. Meanwhile low maintenance and operation cost. This machine has solved the long-existing problems with dewatering plant dregs/residues with high moisture.

How to Overcome problems in dewatering cassava/tapioca residue(mash or pulp)?

A lot of tapioca residue is generated during tapioca starch production, approximately 0.34 to 0.4 tons of dry residue could be obtained for each ton starch. this residue contains rich fibers, hemicellulose, starch and protein, amino acids, fats, carbohydrates and all kinds of vitamins. It could be excellent raw material to further process and produce animal feed, food, chemical products, etc.. and at the same time, it could avoid discharging tapioca residue into rivers or farm land that could cause environment problems. This article will analyze the problems in dewatering tapioca residues and explore different types of dewatering processes and their pros &cons.

Tapioca residue compositions and its dewatering difficulty analysis.

In the production of tapioca starch, the starch is separated from the slag by impregnating with the equipment such as pressure curved sieve or cone type centrifugal sieve. the tapioca residue discharged from pressure sieve without further dehydration contains moisture 85% to 95%, dry matter 5% to 15%. It is a solid-liquid mixture with poor mobility. Placed under a microscope, these could be observed: (a.) different sizes and shapes of water swelling starch particles with diameter from 3um to 25um, surface worn and broken due to processing like mechanical crushing, impact, impregnation and physiological characteristics of tapioca(cassava).  (b.) swelling cellulose of varied diameters/length intertwined together. (c.) protein, colloidal substances, etc. are evenly distributed around the solid material of starch, fibers, etc.. The results of comprehensive microscopy shows that starch, fiber, protein, colloidal substance and the like are intertwined together like network, no obvious pores. Therefore causing following problems: (1) Physical drainage channels blocked owing to overlapping Starch particles, fibers and other substances.  (2) Drainage resistance increased due to uniform distribution of colloidal substances that are viscous and its surface tension effects, etc.. (3) Capillarity between varied solid phases and especially between fibers also increase drainage resistance. (4) Proteins and most colloidal substances are hydrophilic colloidal particles, and negative charges on fiber surface attract positive charges in the water. The force between these molecules or ions makes it more difficult for solid-liquid separation. Besides, the fiber has a strong "re-absorption" phenomenon (ie. dehydrated fibers will be swelling again after contacting and re-absorbing water); and the existence of a variety of compressible materials in tapioca residue such as fibers, which are often subject to changes in volume under external force, resulting in small drainage channels become smaller or blocked. This also increases dehydration difficulty of tapioca residues.

Dewatering of tapioca residue

Moisture should be no more than 15% if tapioca residue is to be used in animal feed, industrial materials and storage, etc.. Experience had proved it is not economical or feasible to dewater tapioca residue by using only heating dryers or mechanical process. At present, the most effective way is to use both heating dryer and mechanical dewatering. It is to use dewatering machines to remove the extra water before putting them in heating dryers. The key in this technology is the part to adopt which type of dewatering machines before the materials entering the dryers. Following are some cases using different types of dewatering machines.

Centrifuge Dehydration Machine

Most centrifuge dehydration machines made in China have a speed 1,200 r/min to 1,600r/min.. After dewatering with centrifuge separation factor 800 to 1500, the moisture of tapioca residue is 65% to 75%. If further increasing the separation factor, moisture reduction is not obvious. This machine is complicated, expensive and consuming a lot of power, which makes it not economical to dewater the residue.
   

Screw press dewatering machine

This equipment is complex, high energy consumption and have high requirements on manufacturing and installation. After dewatering by this equipment, residue moisture content is 55% to 75%. Major problem is that this equipment is susceptible to residue composition, incoming moisture changes and clogging of screen(clogging is prone to happen and thorough cleaning proves difficult when starting the machine), etc.. So, moisture content after dewatering with this machine is not stable, and can be sometimes low, sometimes high. Advantage of this machine is that it could operate continuously and low labor intensity.

Filter Press

This needs to achieve a certain capacity; equipment require a larger area, high investment and energy consumption is high (referring to accompanying pumps). The process is complex, labor-intensive and can’t work continuously. Moisture content after dewatering is 65% to 75%, not stable for it is susceptible to residue composition, pressure change. Further reducing moisture is difficult with this machine, for tapioca residue is compressible material, easy to clog the drainage pores..

Vacuum dewatering machine

This machine is costly, requires complex accessary equipment and also high energy consumption. It can work continuously, discharge moisture is around 75%. High moisture is due to insufficient driving force (ie. Pressure)( vacuum degree inside the drum is only 0.04 to 0.053), clogging of filter cloth and other factors. Further moisture reduction is difficult.

Moisture content after dewatering by the above-mentioned machines is mostly 70% to 85%. This type of wet residue if entering heating dryers directly, it’s prone to form lumps, result in overcooking(coking) on the outside due to rapid vaporization of surface moisture under the effect of “flash evaporation” , while inside the lumps, the moisture has not been fully vaporized. Apart from this, overly wet residue is prone to stick pipes, fans, etc.. which prevents regular heat exchange, and consequently resulting in burnt materials or even causing damage to equipment, ultimately compromise the whole process. Besides, if moisture is very high, it would require larger drying lines and cost more energy to achieve the same capacity. It is not a economical way.

In view of the difficulty with dewatering tapioca residue, many factories and research facilities have long been exploring, testing to invent an effective and economical mechanical dewatering equipment to work with air heating system, thus to further make full use of tapioca residue. After many years of relentlessly testing and improving, our factory is now able to produce special designed belt dewatering machine(model …) that is suitable to process tapioca residue, corn residue and varied bean residue. After several years of testing in production with different customers, this type of equipment had proved their capability in solving dewatering problems of tapioca residue.

After dewatering with this machine, the moisture can reach 55% and less. It is easy to install, operate and maintain, and it is less weight/investment, low energy consumption and high efficiency. Discharged residue could enter air drying system directly, heat efficiency is significantly improved and avoid blocking of pipe and fans. If working with centrifuge dehydration machine or screw press dewatering machine, it would achieve better effects. Its main working principle is the use of two unique belts moving at the same direction; the wet residue is placed between the two belts and moving with them at the same time; moving belts going through many rollers of different diameters, the pressure increases gradually and tension builds up on the belts, two end rollers installed with guided springs which can rise and drop in accordance with thickness of residue, finally being scraped off the belts at the end. After the belts reach the end, they start to move back. That is when the water spraying is started to clean the remaining residue off belts and prepare them for next cycle. The whole process is continuous, effective and can achieve stable moisture content. It is not susceptible to other factors, so it has overcome the disadvantages of conventional equipment.