corn starch processing steps

There are many ways to produce cornstarch, and wet and dry methods are widely used at present. The so-called wet method refers to the processing method of corn raw material pretreatment in the starch industry. The corn is soaked in warm water, coarsely ground and finely ground to separate the germ, fiber and protein to obtain a high-purity starch product. The so-called dry method refers to the separation of germ and fiber by grinding, sieving, winnowing and other methods to obtain low-fat corn flour. Pure corn starch is generally produced by wet method, which is divided into open process and closed process (derivative partial closed process). In the open process, fresh water is used for corn soaking and all washing, so the process consumes a lot of water, with a lot of dry matter loss and pollutant discharge. The closed process only uses fresh water when washing the last piece of starch, and all other water processes use process water. Therefore, the amount of fresh water is less, the loss of dry matter is less, and the pollution is greatly reduced. Therefore, modern starch factories adopt closed process. (1) Wet corn starch production process and equipment. The production of wet corn starch is done through corn purification, soaking, crushing and germ separation, fine grinding, fiber separation, washing and drying, starch and protein separation. The specific steps are as follows: 1. Corn purification: the purpose is to remove ash, aflatoxin, metal fragments and stones. Vibrating screens with dust suction (wind force) are often used to remove large and small impurities, and electromagnetic separators are used to remove iron filings, etc. The rice is then hydraulically conveyed to soaking tanks, while the ash is removed. The speed of hydraulic transportation is 0.91.2 m/s, the ratio of corn to conveyed water is 133,360, and the temperature is 3540. After passing through the dehydration screen, the removed water is used for water transportation, and the wet corn enters the soaking tank. 2. Corn soaking: Corn soaking in sulfurous acid aqueous solution, adopts countercurrent circulation soaking process. The purpose of soaking is: first, to make the seeds soft, and the water content of the seeds is about 45%; second, to extract soluble substances, mainly minerals, proteins and sugars. The third is to destroy the network structure of the protein and separate the starch from the protein; the fourth is to prevent the contamination of bacteria and the growth of rancid organisms; the fifth is to have a bleaching effect, which can inhibit the action of oxidase and prevent the discoloration of starch. When soaking, the concentration of sulfurous acid is 0.2%0.3%. The immersion temperature is 4852, and the immersion time is 4050 hours. The soaking solution of the finished product, that is, dilute corn steep liquor, contains 7%~9% of dry matter, pH3. 1. It is sent to the evaporation process to be concentrated into corn steep liquor containing more than 40% of dry matter. The water content of soaked corn is 40% to 46%, and the soluble matter content does not exceed 2.5%. It can be crushed by hand, and the germ can be completely extruded. 0 represents 100 kg dry matter. 1 mol/L sodium hydroxide standard solution for neutralization, the dosage should not exceed 70 ml. 3. Crushing and germ separation: starch is in the endosperm cells, so it needs to be crushed to remove the skin and endosperm cell wall. There are currently two methods of dry milling (such as wheat, rice) and wet milling (such as corn, sorghum). The soaked wet corn is crushed by the first convex tooth grinder, and then pumped into the first rotary liquid separator (or germ separation tank) with the germ. The germ flowing out from the top of the separator enters the washing system, the bottom flow is filtered through a curved sieve to remove the slurry, and the oversize enters the second convex tooth mill. The pulp after the secondary crushing is pumped into the secondary hydrocyclone by the germ pump, the top flow is mixed with the pulp crushed and screened by the primary mill, and then enters the primary germ separator, and the bottom flow pulp is sent to the fine grinding process. 4. Fine grinding: The dilute slurry after the germ is separated by the secondary cyclone separator passes through the pressure curved sieve, and the under-sieve is coarse starch milk. The starch milk and coarse starch slurry separated after fine grinding are incorporated into the starch separation process, the under-screened material enters the impact mill (needle mill) for fine grinding, and the finely ground slurry enters the fiber washing tank. 5. Fiber separation, washing and drying: The finely ground pulp and washing water for washing fibers are pumped to the first pressure curved screen. The undersize is coarse starch milk, and the oversize is washed countercurrently through a 5-stage or 6-stage pressure curved sieve. Fibers are discharged from the screen surface. Gluten water is separated from the top flow and sent to a 12-stage flow separator for countercurrent washing. Rinse with 40°F fresh water. The starch washed by the 12th cyclone separator contains 60% water and the protein content is less than 0.35%, and the de-refined starch milk tank is dehydrated and dried. The gluten water enters the (gluten) concentrating centrifuge through the filter, and the top flow is process water, which enters the process water storage tank with a solid content of 0.25% and 0.5% for bacteria and fiber washing. The underflow concentrated gluten water (about 15% solids) is dewatered through a drum vacuum suction filter to obtain a wet protein with 50% to 55% water, which is then dried through a tube dryer. 7. Germ washing, drying and oil extraction: After the germ from the top of the first-stage germ cyclone is washed by the third-stage curved screen, it enters the screw extruder for dehydration. The dehydrated germ contains about 55% water and is dried by fluid bed dryer or tube bundle dryer. Dried germ contains not more than 5% water, 48% oil and 10% starch. The dry embryos are sent to the embryo press machine to break the embryos, steamed in an oil pan, and then pressed into the oil press. Germ cake is a good fodder for protein. 8. Corn steep liquor concentration 3360 diluted corn steep liquor contains 5% 7% solids. After single-effect, double-effect or triple-effect vacuum concentration, the solid content is 45%-50%, which can be directly sold to monosodium glutamate factories, etc. It’s a great medium. 9. Fiber slag 3360 Dry fiber slag is added with some protein or nutrients to make pellet feed. (2) Dry corn starch production process and equipment. After weighing the raw materials, after secondary screening, stone removal, and metal magnetization, relatively pure corn is obtained, and the subsequent crushing process is carried out. Firstly, adjust the moisture content of the corn so that the moisture content of the corn is controlled at 16%-19.5%, and then enter the slag crusher for crushing. First, the mixture is separated by a suction separator, then sieved and classified. The oversize (large particles) is returned to the slag crusher for crushing again, the intermediate is processed in the next process, and the fine powder of the undersize is processed in the powder screening process. Generally, the slag embryo mixture in the middle layer is processed by three grinding and three screening systems, and most of the husk and germ can be extracted basically, so as to obtain the required fineness of corn flour. Prepare the collected germ and peel according to a certain ratio (generally pure germ accounts for 35% ~ 50% of the oil-pressed crops), and then use a bran brushing machine to remove the powder sticking to the oil, and then measure, cook, fry, oil press, Insulation clarification, filtration to obtain crude oil. The equipment mainly includes self-balancing high-efficiency vibrating screen, suction type specific gravity destoner, permanent magnet cylinder, moisture regulator, cooking bin, corn peeling and slag machine, flour mill, flour sieve, frying pan, oil press, filter device, air system unit, dust removal system unit, lifting equipment system unit and horizontal conveying system unit.

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