Sweet Potato Processing Line

Raw Material Receiving Unit
Material receiving unit is the first step of sweet potato starch processing. The primary purpose of this step is to preliminary remove impurities in sweet potatoes and store the sweet potatoes in raw material storage pool. Sweet potatoes are conveyed to the sweet potato yard after weighing by wagon balance and part of them are conveyed into the sweet potato storage hopper.

The key of this unit is to remove sand and other impurities of sweet potato during harvest. The sand sticking to the sweet potato can be removed through vibrating screen, by which can relieve machines burden of de-stoning and cleaning unit.Attention must be taken that sweet potato should not be damaged during sweet potato purchasing, because damaged sweet potato is easy to decay and the decayed ones can infect the sweet potato around. Bad sweet potato material can degrade the starch quality.

Raw Material Conveying Unit
Sweet potatoes stored in the sweet potato hopper are conveyed to the large inclination-angle belt conveyor through conveying belt which is positioned at the bottom of the hopper, and further conveyed into cleaner to remove impurities left in harvest time.

De-stoning and Cleaning Unit
Clean raw materials plays an important role in sweet potato processing, so de-stoning and cleaning unit of pretreatment stage is the most crucial. The purpose of this unit is to get rid of sandstone, clay of sweet potato, and to store cleaned sweet potato in sweet potato temporary hopper. Sweet potato is conveyed into the blades washer which adopts counter-current cleaning principle. Direction of water flow (used for washing) is opposite to that of cleaning materials movement. Certain level of cleaning water is poured into the cleaning trough, and the raw materials are almost floating on the surface of it and moving forward through internal trough by rolling blades. The sweet potato rotates and clashes each other in the water to get rid of the soil and impurities on the surface of the material. Heavier sand and other impurities sank to the bottom of the trough. Meanwhile, waste water outflows through the overflow outlet below the first trough, at the same time, discharged soil and impurities sink to the drain outlet and finally are discharged from there. In the end, the root pieces (materials) are conveyed to the next production unit and are fulled cleaned through unloading fence.

Sweet potatoes cleaned by blades washer are picked by blades and enter into a belt conveyor and be conveyed into the second rotary drum washer. Rotary drum washer works at a low level for thorough cleaning of sweet potatoes. In order to achieve a better washing performance, sweet potato tubers are cleaned by strong friction and collision among them when drum is rotating. Meanwhile cleaning water is added from the material discharge outlet of rotary drum washer, and the reversed waterflow is used to wash materials and discharge dirty water and potato skins from inlet of rotary drum washer.

A conveying pump is connected with an external water tank of the rotary drum washer, the overflowed cleaning water from the drum washer is pumped into the first blades washer as the preliminary cleaning water of raw materials.After coming out from rotary drum washer, the cleaned sweet potatoes fall onto a large inclination-angle belt conveyor with spray. Above the screw conveyor, Several rows of nozzles scatter evenly, from which fresh water sprays out on sweet potatoes through certain pressure and wash away dirty water on the sweet potato surface. The cleaning water flows into the bottom trough of large inclination-angle belt conveyor to discharge. Finally clean sweet potatoes come out from large inclination-angle belt conveyor and enter into a crusher to carry on preliminary slicing of sweet potato tubers, by which can ensure rasping efficiency of rasper. Cubage of raw material temporary storage bin generally is designed to store washing quantity for one to two hours. Choosing two different forms of cleaner to wash raw materials in series, and carrying on spray treatment for the cleaned raw materials at the same time can guarantee achieving the best cleaning performance. Part of cleaning water of the first blades washer comes from the second stage of rotary drum washer, and it saves cleaning water greatly.
Rasping and Pumping Unit
Rasping unit is an important link to improve sweet potato starch extraction rate. Efficient rasper can release sweet potato starch particles from sweet potato cells thoroughly, guaranteeing the combination starch content of sweet potato residue to the minimum.

At the bottom of the temporary warehouse, a special designed discharging outlet which connects a feeding spiral with adjustable speed. Feeding spiral has three outlets, two rasper connectors and one overflow outlet. A length of short connection with gate valve is between rasper and feeding spiral. When the system is to feed, the gate valve of the rasper is turned on first, next the feeding spiral frequency is adjusted according to need, and then the feeding spiral is start-up and beginning feeding. Sweet potato slurry below the rasper is pumped into de-sanding unit with a fiber pump.

The stainless steel rasper with special design is easy to operate. Concise file clamping system ensures the file working in its best position. Loading and unloading of the file is very simple, need not use special tools, ordinary staff can accomplish it. Stainless steel sieve plate is a whole structure and can be replaced without tools, and it can make rasper reach the highest efficiency and get high starch extraction rate. The distance between the file and the fixed block is 1 ~ 2mm, ensuring higher rasping efficiency. The whole production line capacity can be adjusted through the feeding spiral with adjustable speed.

Hydro-cyclone and De-sanding Unit
Sweet potato slurry got from rasping is pumped into the de-sand cyclone through a fiber pump. Materials with certain pressure enter into the de-sand cyclone along the tangent, sweet potato slurry in the hydro-cyclone is rotating with high-speed, light starch and potato residue etc. overflow from the top of the hydro-cyclone, while heavy sand is discharged from the bottom of the hydro-cyclone. At the bottom of the ceramic vortex tube has (there is) a sand catch pot which connects pressure recoil water to guarantee starch not being discharged from underflow outlet, and the sand in the sand catch pot is discharged regularly through two air valve.

Ceramic vortex tube of special manufacture is durable; the air valve with unique design can discharge sand automatic periodically.

Centrifugal Extraction Unit
Centrifugal extraction unit is another key units of the whole production line to influence sweet potato starch extraction rate, good centrifugal screen and process technology can help extract out all the free starch from broken sweet potato cells.

Extraction unit is a centrifugal sieve group composed by three centrifugal sieves, each centrifugal sieve equips with a fiber pump and a de-foam pump. Sweet potato slurry came from de-sander enters into the first level extraction sieve, under the action of centrifugal force of sieve basket high speed rotating, sweet potato starch goes through the screen, and the residue stayed on the surface of sieve basket is thrown away lately. The front of the sieve basket, has certain pressure flushing water which spays from nozzles to make potato residue roll continuously, and then extract starch of sweet potato residue thoroughly. Sieve basket back also designs flush water, but the back recoil water is periodically opened to guarantee pectin and sweet potato residue non-clogging screen. Starch milk is pumped to hydro-cyclone for washing by de-foam pump, and potato residue is pumped to the second stage centrifugal sieve by fiber pump. Sweet potato residue containing some sweet potato starch is extracted starch further in the second centrifugal sieve, starchy water is pumped into the process water of the extraction unit by de-foam pump, sweet potato residue sequentially is pumped to the third stage extraction sieve by fiber pump. Similarly, the third stage extraction sieve still carries on starch extraction, screened materials still enter the process water of extraction unit, and sweet potato residue is pumped to sweet potato residue dehydration unit.

Three-grade of centrifugal sieve group can ensure all free starch to be collected to extraction system, making sweet potato residue not contain free starch, which fully guarantees the extraction rate of starch. Unique process design and excellent equipment performance guarantee complete extraction of free starch from sweet potato residue.

Sweet Potato Residue De-watering Unit
Sweet potato residue pumped from the extraction unit proceeds with de-watering by a centrifugal sieve, the working principle is the same as an extraction sieve. Sweet potato residue finally is delivered out of the workshop through a screw conveyor,and the water of sweet potato residue still returns to process water system of extraction unit.

Concentrating and Refining Unit
Concentrating and refining unit is the most important one of the whole production line, starch quality can be guaranteed fully in hydro-cyclone refining unit. Impurities of starch slurry will be eliminated thoroughly through physical method, without influencing the quality of starch product.

Starch slurry sieved from the first stage centrifugal sieve enters into the 16 grades concentration hydro-cyclone washing unit, process water pumped from the other end of the hydro-cyclone washes starch with countercurrent method. The whole hydro-cyclone can be divided into three parts, first starch slurry is de-watered and concentrated through concentrated hydro-cyclone, concentrated starch milk enters into the subsequent washing unit, and then overflowed cell sap enters into two-stage recovery hydro-cyclone for recycling contained starch. The most effluent overflowed out of hydro-cyclone, containing abundant fibrous impurities is discharged directly; a small minority enters into the process water system of extraction unit again. Starch milk of hydro-cyclone is pumped to a stainless steel starch milk storage tank with blender.Clean process water adds from last stage of hydro-cyclone to mix and wash starch milk, then the overflow mixes with former stage starch milk, washes and separates. Series of countercurrent washing like this makes fibers and cell sap are discharged out of hydro-cyclone along water. Adopting 13-stage washing can guarantee washing effect of hydro-cyclone, which could remove fiber, protein contained in starch milk better, in this way, the starch milk came from hydro-cyclone has no impurities at all.

Fine Fiber Separation Unit
Fine fiber separation unit is assorted unit to concentration and refining unit; its main purpose is to reduce working pressure of hydro-cyclone. When fiber and impurities in the starch slurry are too much, fine fiber sieve can be opened to discharge part of the fine fiber of hydro-cyclone out of cyclone system to ensure overmuch fine fiber can be discharged from hydro-cyclone.

Waste water containing fine fiber came from the first level of overflow of hydro-cyclone enters directly into inlet of the fine fiber sieve, starch containing in fine fiber is extracted through the fine fiber sieve as extraction unit; the starchy cell sap and starch slurry extracted from the first level of starch extraction sieve together re-enter into the hydro-cyclone, the separated fine fiber directly enters into the sweet potato residue spiral discharge of dehydration sieve or into the sweet potato residue de-watering unit together with the sweet potato residue came from extraction unit.

Fine fiber separation unit plays a good auxiliary function in the working of hydro-cyclone; it can discharge large amount of fine fiber of hydro-cyclone out of cyclone system in time, at the same time it can discharge cell sap on the poor raw material situation.

Starch De-watering Unit
Starch milk with too large moisture content coming from hydro-cyclone can’t directly dry, so first starch milk needs de-watering to make starch moisture content be about 40%.

When centrifuge filter de-watering and after the rotating drum working at a full speed, the inlet valve automatically and periodically opens, the suspension enters into the rotating drum with full speed rotating through the feed pipe, solid content of the suspension is evenly distributed on semi-auto surface by centrifugal force, and liquid is mostly separated by centrifugal separation through filter screen and drum wall holes, discharged through the tangential liquid outlet of machine housing; along with the extension of the feeding time,the thickness of solid material layer inside the drum is also increasing. reaching the scheduled time, inlet valve huts down automatically and feeding stops. After a certain period of feeding stop time, the flush valve automatically opened, washing water sprays on solid content through a washing water pipe, the flush valve automatically closes after a certain period of time; under conditions of continuous full speed rotating of the rotating drum, liquid content is constantly separated, solid content is fully dried after a certain time of continuous separation. At this time scraper cuts with rotation into solid material layer along the radial direction of the rotating drum, the removed materials to be delivered out of machine through the aggregate trough along the inclined discharge hopper, scraper resets after the discharging. Meanwhile, flush valve opens, washing water cleans filter screen to make it reuse; washing filter ending means that a complete operational period is finished, at this moment feeding valve opens again to enter the next cycle period. Filter cake is scraped by scraper and conveyed into the feeding hopper of the flash dryer by the belt conveyor of food-grade.

Because the operation of centrifuge filter is intermittent, therefore two centrifuge filters equipped together to work at the same time to ensure the feeding continuity of the flash dryer. Centrifuge filter is characterized by excellent performance, and simple and stable operation, low moisture content of de-watered starch, so it can reduce the energy consumption of subsequent air drying.

Flash Drying Unit
Flash dryer will further dry the de-watered starch to the moisture content required by commercial starch. Air passes through the filter and is heated to the required temperature by the heat exchanger, and then hot air is sucked into the flash dryer by draught fan. De-watered starch is conveyed to the feeding spiral with hopper, and then conveyed to the feeding inlet of flash dryer through spiral conveyer; starch enters into the cyclone separator through air pipe along with hot air of flash dryer; dried starch separates with air in cyclone separator; wet air leaves cyclone separator and discharged through draught fan. Starch enters into finished product spiral through air locker below the cyclone separator. The big bend pipe flash dryer by special design practically proves that the energy consumption reduces half or so than average.

Screening and Storage Unit
Starch is conveyed to the starch well-distribution bunker by finished product spiral, and then the starch is conveyed to the bucket elevator through the leveraged feeder starch below the starch well-distribution bunker, finally the starch is conveyed into the two-way conveying spiral. Starch returns to the starch well-distribution bunker through two-way conveying spiral, if the moisture content of starch can’t reach standard; starch enters into the double storehouse vibrating sieve through two-way conveying spiral, if the moisture content of starch can reach standard. The vibrating screen sifts and clarifies dried starch, removes gelatinous and thick grain of the fine starch, makes the fineness of the finished product starch meet the standard. The starch screened enters directly into the stainless steel starch bunker for temporary storage. The sieve mesh number of the selected double storehouse vibrating sieve is increasing from top to bottom gradually, and guarantees no blockage of the starch screening and the fineness of starch.

Adopting the starch well-distribution bunker can guarantee the balance of the finished product; starch could reach the moisture standard through the recycling of the starch well-distribution bunker, if the dried starch is too dry or too wet. Especially when the flash dryer is under the unstable starting up condition, the moisture content of starch can be ensured to reach standard equally through the starch well-distribution bunker.

Weighting and Packing Unit
The starch in storehouse will be packed into 25 kg per bag by automatic packer.