Vibrating screen is used to remove large, medium and small impurities from corn. Provide sieve holes. The first screen surface adopts a circular hole with a diameter of 17 ~ 20mm, the second screen surface adopts a circular hole with a diameter of 12 ~ 15mm to remove large and medium impurities, and the third screen surface adopts a circular hole with a diameter of 2mm to remove small impurities.
The specific gravity stone remover is used to remove kerbstones from corn. Due to the characteristics of large grain size, flat grain shape and large specific gravity of corn, the air volume and wind speed should be appropriately increased during operation. The wind speed passing through the fish scale hole is about 14 m/s, and the protruding height of the fish scale hole should also be increased to 2 mm.. During operation, we should pay attention to the movement state of the materials on the fish scale screen, adjust the air volume, and regularly check the stone discharge at the stone discharge port.
Permanent magnet roller is used to remove magnetic metal impurities from corn and should be placed in front of corn crusher to prevent metal impurities from entering the crusher.
Wheat washer can remove dirt and dust from corn. After cleaning, the ash content of corn can be reduced by 0.02 ~ 0.6%. At present, several or dozens of metal tanks are usually connected and combined by pipes, and the soaking water is circulated between tanks by water pump for countercurrent soaking.
The test results show that lime water, sodium hydroxide and sodium bisulfite are not as good as sulfur dioxide, and the content of sulfur dioxide should not be too high. Because the dispersion effect of soaking water containing sulfur dioxide on protein net increases with the increase of sulfur dioxide content. When the concentration of sulfur dioxide is 0.2%, the dispersion of protein net is suitable and starch is easy to separate. However, when the concentration is 0. 1%, it is difficult to separate starch due to insufficient dispersion. Generally, the maximum is not more than 0.4%, because the concentration of sulfur dioxide is too high and the acidity is too large, which is not good for corn soaking, but will inhibit lactic acid fermentation and reduce starch viscosity.
Soaking temperature has an important influence on the soaking effect of sulfur dioxide. Increasing the soaking temperature can promote the soaking effect of sulfur dioxide. However, if the temperature is too high, starch will gelatinize, resulting in adverse consequences. Generally, 50 ~ 55℃ is appropriate to avoid gelatinization of starch granules.
The soaking time is also closely related to the soaking effect. In the process of soaking, soaking water does not penetrate into the internal tissues from all parts of the epidermis of corn particles, but enters the particles from the loose tissues at the root of the particles and penetrates into the particles through the porous tissues at the bottom of the bran, so it is necessary to ensure sufficient soaking time. After corn was soaked at 50℃ for 4 hours, the embryo water absorption reached the highest value, and after 8 hours, the embryo water absorption also reached the highest value. At this time, the corn particles become soft, and after coarse crushing, the germ and bran can be separated. However, the protein net was not destroyed by dispersion, and starch particles could not be released. If you continue to soak, the protein net will scatter. After soaking for about 24 hours, the soft embryo protein network basically dispersed, and the hard embryo protein network also dispersed after about 36 hours. Because the dispersion process of protein network is firstly expansion, then it is transformed into fine spherical protein particles, and finally the network structure is destroyed. Therefore, it takes more than 48 hours to completely disperse the protein network.
The soaking conditions of corn in different factories are not exactly the same. The general operating conditions are as follows: the sulfur dioxide concentration of soaking water is 0. 15 ~ 0.2%, and the pH value is 3.5. During soaking, sulfur dioxide was absorbed by corn, and its concentration gradually decreased. The concentration of sulfur dioxide in the last soaking water is about 0.0 1 ~ 0.02%, and the pH value is 3.9 ~ 4. 1. The temperature of soak water is 50-55 DEG C; The soaking time is 40-60 hours. The soaking conditions should be determined according to the quality of corn. Generally, both old corn and hard corn stored for a long time need strong soaking conditions, that is, higher sulfur dioxide concentration, higher temperature and longer soaking time.
After corn is soaked, the water content should reach more than 40%. The main purpose of editing this section of coarse corn is to break the soaked corn into pieces above 10 to separate the germ.
Most of the corn coarse crushing adopts disc crusher. Coarse grinding can be carried out twice. Crushing corn into 4-6 pieces for the first time, and separating germ; The second crushing is more than 10, so that all the germs fall off and the second germ separation is carried out. At present, the germ separation tank is mainly used in China. The advantage is that the operation is relatively stable, but the disadvantage is that it occupies a large area, consumes a lot of steel and has low separation efficiency, generally not exceeding 85%.
There are also corn starch factories using hydrocyclones at home and abroad. This separator is made of nylon, and 12 separators are put on a shelf together, and the total length is less than 1 m, with small floor space, large production capacity and high separation efficiency, which can reach over 95%. Edit this section of the mixture of corn fragments and partial starch after the separation of corn germ. In order to extract starch, it is necessary to grind, destroy corn cells, free starch particles and separate fibers from bran.
The quality of grinding operation has great influence on the extraction of starch. The grinding is too rough, and the starch cannot be fully released, because it is taken away by coarse and fine slag, which affects the starch yield. Too fine, poor fiber separation, affecting starch quality.
In order to grind corn effectively, secondary grinding is usually used. Crushing with a hammer mill for the first time, and sieving the starch emulsion; The second time was ground with sand table starch. Some use a universal grinder for the first grinding, and then use a stone mill for the second grinding after screening starch milk.
According to the production practice in various places, it is proved that emery grinding is superior to stone grinding, with high hardness, difficult wear of grinding line, no need for frequent maintenance of grinding surface and high grinding efficiency. At present, emery grinding has gradually replaced stone grinding. Editing this section, screening starch, and grinding the corn chips to get corn paste. Starch can be separated from coarse and fine residues by screening. Commonly used screening equipment are hexagonal screen, flat shaking screen, curved screen and centrifugal screen.
The sieve holes for screening starch should be determined according to the type of screening equipment and the quality requirements of starch. The aperture of hexagonal screen for cleaning coarse slag is 0.6 mm, that of fine slag is 0. 12 mm, that of flat screen for screening coarse slag is 7×××× nylon, that of fine slag is12×××× nylon, that of curved screen for cleaning coarse slag and fine slag is 120, and the screen length is 65430. The sieve hole of the rotor sieve plate of centrifugal sieve is 2×0.24 mm, and four-stage continuous operation is generally adopted.
The amount of clean water needed for screening coarse slag and fine slag. According to 100 kg dry matter, coarse slag needs 230 ~ 250 liters, and fine slag needs 10 ~ 130 liters. The water temperature is 45 ~ 55℃ and the pH value is about 4.3 ~ 4.5. The concentration of starch milk after protein separation and starch washing in this section is 6 ~ 8 Baume degrees, and the dry matter content is about 1 1 ~ 14%. The following table analyzes the chemical composition of starch:
Component content (%) Component content (%)
88-92 parts of starch and 2.5-4.5 parts of water-soluble substances.
Protein 6 ~ 10 sulfur dioxide 0.035 ~ 0.045.
0.5 ~ 10 for fat and 0.05 ~ 0. 1g/L for fine slag.
Ash 0.2 ~ 0.4
As can be seen from the above table, except starch, the dry substances in starch milk are mainly protein and water-soluble substances, so protein separation and starch cleaning are needed.
Protein usually uses a chute to separate, but now it is gradually separated by a centrifuge, because the centrifuge has a large area and low separation efficiency. However, starch milk is required to contain less slag to prevent mechanical vibration caused by nozzle blockage in the tray.
The coarse starch milk separated from protein must be washed. Starch cleaning is mostly carried out in the cleaning pool, but the cleaning time is long and the starch loss is great. Modern corn starch factory uses hydrocyclone to clean starch, and generally uses 9 ~ 14 hydrocyclone to treat it. According to the determination, the protein content of the starch milk from the centrifuge is less than 2.5%, and the protein content in the finished starch can be reduced to 0.35% after being treated by the 9-stage hydrocyclone. Centrifugal separation and drying of starch milk from hydrocyclone contains 78% water. If the starch workshop and the starch sugar workshop are merged, they can be sent directly to the starch sugar workshop for use. Starch milk does not need dehydration and drying. However, the starch milk obtained from the washing bucket contains water and must be dehydrated.
Wet starch with water content of 45% can be obtained by sending the starch milk to a centrifugal separator for dehydration, and this wet starch can also be used as a finished product. In order to facilitate transportation and storage, it is best to dry the starch to reduce the moisture content to equilibrium moisture 12%. And then leave the factory as finished dry starch.
In order to ensure the uniform fineness of the finished product, it is sometimes necessary to finish the finished product. Firstly, starch with specified fineness is screened out, and the screened materials are sent to a crusher for crushing, and then screened, so that all products reach the specified fineness. In the process of producing corn starch, intermediate products such as corn syrup, germ, meal and protein water can be obtained, which can be used as by-products if processed. The main by-products of corn are processed as follows:
(1) Corn syrup: Soak corn in countercurrent with sulfur dioxide solution, and finally extract soaking water containing 6-7% dry matter. It can be concentrated into a concentrated solution containing 50% dry matter by three-effect vacuum evaporation, which is called corn syrup. According to the chemical composition of corn syrup, the results are as follows:
48-50% moisture, 5.5% reducing sugar and 3.6% ammonia.
Inorganic matter 10%, ammonia nitrogen 0.9% and lactic acid 9 ~ 12%.
Corn syrup can be used not only as a nutrient for cultivating yeast and antibiotics, but also as a raw material for producing calcium phytate and inositol. It is also a good animal feed after being mixed with recycled corn protein and coarse and fine residue.
(2) Corn germ: The germ washed out from the screening section contains about 50-60% water, which can be dried by drum dryer or boiling water machine until the water content reaches 4%. Three-stage drying is usually used. The first stage is drying until the moisture content of the germ is about 35%. The second level is10%; In the third stage, the specific moisture content of germ is reached.
The dried germ contains 45-50% oil. Its oil content is higher than that of soybean (the oil content of soybean is about 20%), so it is a good oil. The crude corn oil squeezed by the oil press is yellow and contains free fatty acids. Refined corn oil can be eaten, and oil cake can be used as feed.
(3) Protein water: protein water obtained from launder, disc separator or hydrocyclone, also known as gluten water or yellow slurry water. The concentration of water in protein is low, but the content of protein in dry matter is high. The filterability is poor, and the suspended protein substance cannot be directly recovered by filtration. Usually, sedimentation tank is used for intermittent precipitation or concentration centrifuge for separation. The protein concentrate is mixed with fine residue, filtered, dried, crushed and sieved to obtain protein powder with water content of 10 ~ 12%, also known as flour gluten powder, with protein content of over 40%, which can be used as raw materials for preparing feed.
(4) Drying of dregs and corn steep liquor: the water content of coarse and fine dregs obtained from the materials screened by screening equipment is more than 85%, dehydrated by a press to reduce the water content to 55-70%, and then mixed with corn steep liquor. Because of the high acidity of corn syrup, before mixing with the residue, the acidity of corn syrup was neutralized with lime, and then mixed and dried until the water content was below 65438 02%. Its chemical composition is as follows:
Moisture 1 1 ~ 13% crude fat is less than 2% crude protein is less than 18%.
Crude fiber is lower than 9%, ash is lower than 8%, and soluble protein is higher than 50%.
As can be seen from the above data, protein is high in content and can be used as a good animal feed. At present, the starch industry is developing rapidly, and there are more than 100 kinds of processed products made of corn starch, which are widely used in food, medicine, chemical industry, textile, paper making and other industries.
In the pharmaceutical industry, corn starch is an important raw material for the production of glucose, the main component of the culture medium for the production of antibiotics such as penicillin and streptomycin, and also the additive of some tablet drugs.
In chemical industry, corn starch is used to produce chemical products, such as acetic acid, acetone and butanol. In textile and paper industry, the starch of high amylose corn is mainly used as sizing agent and product surface coating.
In daily life, we mainly use it to size small pieces of raw materials, such as slices, strips, silk and diced. , and add refined salt, cooking wine, chicken essence, starch, ginger slices, onion segments (partly with onion Jiang Shui) and egg liquid, so that each slice (strip) is evenly coated with a thin slurry, which is mainly used for frying and frying. This method is applicable to chickens, ducks, geese, pigs, cattle, sheep, and fresh Haihe raw materials such as fish, shrimp and crabs. The role of sizing is to remove the peculiar smell in raw materials, increase flavor, make dishes have a bottom taste, and keep the taste tender, fresh and crisp.
Nutritional analysis
1. Corn is recognized as a "golden crop" in the world, and its contents of fat, phosphorus and vitamin B2 rank first among cereals.
2. Corn flour contains linoleic acid and vitamin E, which can reduce the cholesterol level in human body, thus reducing the occurrence of arteriosclerosis;
3. Corn flour contains more calcium and iron, which can prevent hypertension and coronary heart disease;
Modern medical research shows that corn flour is rich in glutathione, which is an anticancer factor. It can combine with a variety of foreign chemical carcinogens in the human body to make it lose its toxicity, and then it is excreted through the digestive tract. Coarse ground corn flour contains a lot of lysine, which can inhibit tumor growth;
5. Corn flour also contains trace element selenium, which can accelerate the decomposition of oxides in human body and inhibit malignant tumors;
6. The rich dietary fiber in corn flour can promote intestinal peristalsis, shorten the time of food passing through digestive tract, reduce the absorption of toxic substances and the stimulation of carcinogens on colon, thus reducing the occurrence of colon cancer.