Feed processing technology series - raw material receiving and cleaning

Basic characteristics of raw materials and finished products

There are tens of thousands of raw materials that can be used as feed. There are hundreds of types that can enter the feed processing plant, but there are thousands or nearly 10,000 kinds of raw materials in a specific feed processing plant. In addition, there are many types of finished products. According to the processing characteristics of raw materials and finished products, they can be roughly classified into the following categories.

1. The components to be pulverized, mainly including grains, oil seeds, and cakes. It is mostly granular, accounting for about 70% to 80% of the total.

2. Various grain and animal processing by-products, such as rice bran, bran, protein powder, soy flour, blood meal, etc., account for about 20% to 30% of the total, and the state is mostly powdery.

3. Inorganic salts with large bulk density, such as sulfate, phosphate, stone powder, salt, etc. Most of these substances are in packaging. Because salt has a corrosive effect on metals and is easy to absorb moisture and agglomerate, it is necessary to pay attention to its characteristics when storing.

4. Liquid raw materials such as molasses, oils, and certain liquid amino acids, vitamins, etc.

5. Drugs and trace components, mainly antibiotics, antibiotics, vitamins, fragrances and so on. These materials are characterized by a large variety, a small quantity, and a high price. Some varieties are harmful to humans. They must be stored in a special place and managed by a special person during storage, and cannot be mixed with other materials.

6. The finished products are powdered, pelletized, packaged and in bulk.

It can be seen from the types of raw materials and finished products that in addition to a small amount of liquid in feed processing, most of them are granular and powdery raw materials. Granules and powders are collectively referred to as granules. In the storage and processing of feed, the following characteristics of the granular body need to be studied.

1. Physical properties of the material

Scattered

Scatter property is the ability of a reaction material to diffuse around in a free state, which is a property of material flow. Powdered and granular materials are roughly divided into:

Powder: 10μm～2.0mm

Granules: 1.0mm to 5.0cm

5.0 cm or more is called a "block", and it is less than 10 μm in the category of colloids.

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The granular body has a flow property similar to that of a liquid, and this fluidity appears to be scattered. Due to the certain shear stress between the particles, this flow property has great limitations. The shear stress of the granular body is composed of friction and adsorption force, and the shear stress and the vertical pressure of the granular body are Just proportional. When the vertical pressure is zero, the shear stress is also called the initial shear stress (Ï„0), and the granule of Ï„0 is the good granularity of the fluid, also known as the ideal granular body. Powdery or flaked materials are bulky bodies with poor fluidity. In addition, the moisture, particle size and compaction of the material will affect its scattering.

The fluidity of the granules is usually expressed by its angle of repose (the angle of repose or the angle of accumulation). That is, the maximum inclination angle formed by the free surface of the granular body and the horizontal plane. The angle of repose of an ideal particle is equal to the angle of internal friction. It is independent of the way the tilt angle is formed. Granular grain usually uses its angle of repose to indicate its friction angle, and the granular body with poor fluidity has an angle of repose greater than the angle of internal friction.

2. Friction coefficient

The friction between the granular particles is called internal friction, and the magnitude of the internal friction is usually expressed by the internal friction angle. The tangent of the internal friction angle is the internal friction coefficient. The friction factor between the granular body and the surface of various solid materials is called the external friction factor. Correspondingly, there is an external friction angle, also called the self-flow angle, which is the minimum angle formed by the surface and the horizontal plane when the granular body slides down along the surface of the solid material.

3. Automatic grading

In the process of transportation, flow and vibration, the phenomenon that the density, particle size and surface characteristics of the particles are different and re-classified according to their respective characteristics is called automatic classification. Generally speaking, large and light particles tend to float on the upper part of the pile or float to the edge, and small and heavy materials tend to accumulate in the lower part. When the transport distance is long and the vibration is large, the automatic grading is serious. Automatic grading is advantageous for raw material cleaning and grading, because the aggregation of impurities is easy to clean, and it is a reaction to the mixing of feed, which is the main factor affecting the mixing uniformity. Therefore, in the design of feed processing technology, the mixing should be minimized. Grading and taking such as granulation, adding liquid feed, reducing the transport section to ensure product quality.

4. Density

Density is the mass per unit volume when the granules are naturally packed. The volumetric mass of the granules is related to factors such as particle size, surface smoothness and moisture. Density is an important indicator when calculating storage capacity.

Second, the physical and chemical properties of the material

Adsorption

Adsorption is the ability of a substance atom or molecule to adsorb another substance. For the feed industry, adsorption is the property of certain feedstocks to adsorb other substances onto their surface. Adsorption is one of the basis for selecting carriers and diluents for feed trace additives. In order to make the trace additive evenly mixed in the feed, it is necessary to first select a material with good adsorption as a carrier, mix it with a small amount of small component material, and then uniformly mix it into a large amount of feed to ensure the feed price. And safety, the adsorption capacity of the feed is often related to the shape of the material (granular, flake), surface properties (smooth, rough) and water content.

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2. Hygroscopicity

Hygroscopicity refers to the ability of feed ingredients to absorb and release moisture from the surrounding air. Some feed ingredients have strong hygroscopicity, such as salt, sulfate, choline chloride and fish meal with higher salt content.

The hygroscopic feed has poor stability, is prone to failure, mildew, agglomeration or automatic decomposition. In addition, in the compound feed, it also affects the storage and quality maintenance of other feeds.

3. Thermal stability

Thermal stability refers to the ability of certain chemical components in feed to resist thermal damage under hot processing conditions. Vitamins in feed (such as VC, VA, etc.) and amino acids are easily oxidized and failed at high temperatures. The biological potency of certain minerals is also reduced under high temperature. In addition, certain harmful components in the raw materials, such as antitrypsin in soybean, mustard enzyme in rapeseed meal, and some harmful microorganisms and bacteria, may also be inactivated or killed under high temperature.

4. Chemical stability

Chemical stability refers to the resistance of a feed bioactive substance to the damage of a foreign chemical. Chemical stability is the main condition for the selection of vitamins, trace element salts and certain other additives such as antioxidants, mildew inhibitors and the like.

5. Toxicity

Some feed ingredients, mainly trace mineral additives and some drugs contain heavy metals and other toxic components harmful to the human body and carcass, such as copper sulfate, zinc sulfate, etc., which contain lead, arsenic, cadmium, etc. harmful to humans and animals. Harmful heavy metals. Therefore, when using trace mineral additives, we must use products that meet the national quality standards. Another example is a very small amount of additives such as sodium sulfite which is necessary for the growth of animals, and which is excessively used and easily poisoned. Moreover, these substances have certain harmful effects on the environment and operators during processing. Excessive content or uneven mixing in the finished product may cause poisoning or death after being eaten by livestock and poultry.

6. Electrostaticity

Electrostatic phenomena are usually associated with active ingredients. Dry and pulverized materials often carry an electrostatic charge, which causes adsorption to adsorb the active ingredient on the mixer or conveyor, resulting in uneven mixing. In order to overcome static electricity, premixed feed mills usually have grounding devices on the main equipment.

Section 2 Receiving of raw materials

The receipt of raw materials into the factory is the first process of feed production in the feed mill, and is also an important process to ensure the continuity of production and product quality. The raw material receiving task is to transport the various raw materials required by the feed mill to the factory with certain transportation equipment, and pass the quality inspection, weighing measurement, initial clearing into the stock or directly put into use.

The raw material receiving capacity must meet the production needs of the feed mill, and adopt appropriate and advanced technology and equipment to receive raw materials in time, reduce the labor intensity of workers, save energy, reduce production costs and protect the environment.

The feed capacity of the feed mill and the output of the finished product are very large, so the receiving capacity of the receiving equipment of the feed mill is generally 3 to 5 times that of the feed mill. In addition, there are many varieties of raw materials, large differences in quantity, and different packaging forms, which brings complexity to the receiving of raw materials.

1. Land receiving of raw materials

Bulk receiving process: Raw materials imported into the factory by bulk cars or trains are automatically unloaded into the grain pit after being weighed by the car's medium balance and train rails. Then, the raw materials are transported by the horizontal conveying equipment and the bucket elevator, and then cleaned, weighed and stored in the warehouse or directly into the warehouse to be pulverized or the batching bin. When the package is received, it is manually unpacked and poured into the receiving hopper and transported into the working tower. In order to ensure smooth production, it is necessary to ensure that the processing capacity of the downstream process equipment is greater than the principle of 10% to 15% of the previous process capability. In order to make the material into the primary cleaning screen evenly, to ensure the flow rate of the primary cleaning screen is stable, a buffer tank should be set before the primary cleaning screen.

The car's dropping pit should be equipped with a fence, which can protect personal safety and remove large impurities. The grid gap is about 40mm. There are two forms of car grain pits, namely, deep pits and shallow pits. There are two different dust removal design methods due to the difference in pit depth. For large and deep pits, it has a better effect of vacuuming under the grid; while shallow pits have better suction effect on the grid. For the deep pit, when the material is dumped, the material will not be piled up to exceed the grid height, and the suction effect under the grid is good. The suction opening shall be installed in the pit where the material will not be sucked into the dust removal system. The installation of a fixed baffle creates an area in the discharge pit where the material cannot flow, reducing the possibility of drawing the material into the dust removal system. For deep pits, the amount of suction per square meter per minute is 45.72 M3 (150 cubic feet per minute).

For shallow pits, the suction points should be chosen on both sides of the driveway, or in the case of auxiliary discharge pits, the suction points should be placed behind the grille. The vacuum hood should be placed as close as possible to the grille as far as it does not interfere with the passage of the vehicle. It is recommended that the system design absorb air at 283-425 cubic meters per minute. The design should consider the closed form, the distance of the dust cover from the grille, the area of ​​the grille and the unloading form of the vehicle to determine the optimum suction volume. The funnel discharge produces much less dust than the tipping bucket.

Second, the waterway receiving of raw materials

There are criss-crossing water networks in the southern part of China, and there is a developed water transport system. Because of its low cost, it is the preferred form of transportation under conditions. The pneumatic transport receiving process is suitable for water transport and loading and unloading of grain. Its straw is a hose, which can adapt to the fluctuation of the water level. At the same time, the straw can move back and forth, not limited by the shape and size of the ship. It also ensures good sanitary conditions and the hull structure is not damaged.

The pneumatic conveying device is composed of a suction nozzle, a material pipe, a discharge device, a wind shutoff device, a dust remover, a fan and the like. Under the action of the wind power of the fan, the suction device sucks the material from the ship into the unloader, and the separated material is discharged into the subsequent conveying device or storage bin by the airlocker. Pneumatic conveying devices can be divided into mobile and fixed types. Generally, large-scale feed mills should be fixed, and small plants can be mobile. The advantages of the pneumatic conveying device are that the suction material is clean, the dust is small, the structure is simple, the operation is convenient, the labor intensity is low, and the disadvantage is that the energy consumption is high.

Third, the receipt of liquid raw materials

The most liquid raw materials received by feed mills are molasses and oils. When liquid raw materials are received, they must first be inspected. The main contents of the test are color, odor, specific gravity, concentration, and the like. Raw materials that have passed the inspection can be stored in the warehouse.

The molasses has an acidity of 5.5 or more, and is hardly corrosive to the steel sheet, but corrodes the tank wall when moisture condenses on the inner wall of the tank. A large-diameter snorkel should be placed at the top of the tank, and at least two vents with a diameter of 10.0 cm should be provided for the small-capacity storage tank. A groove should be provided at the bottom of the tank, and the suction pipe of the suction pump is placed on the groove to suck the molasses. The molasses injection tube should also extend close to the bottom of the tank to reduce air bubbles during injection.

In cold areas, tank insulation must be done to heat the molasses to reduce viscosity and facilitate transport. When the molasses is heated to 48 ° C, the coking is started locally, so indirect heating must be carried out using warm water or reduced pressure to steam having a gauge pressure of less than 0.1 MPa. The delivery of molasses can be done with a screw pump. After the molasses tank enters the factory, it is sent to the storage tank by the pump arranged in the factory. The tank has a heating device, which is heated first and then sent to the workshop by the working pump.

The storage tank for grease has two kinds of slant bottom and cone bottom. The inclined bottom and the conical bottom are mainly for concentrating the deposited sand and moisture so that they are discharged from the lowest outlet. The grease is absorbed by a tube slightly higher than the low surface to remove water. The grease outlet should be at least 15 cm above the inclined bottom tank, preferably 30 cm when possible; for cone bottom tanks it should be placed above the cone. The storage tank is generally provided with a heating coil. The heating tube arrangement of the inclined bottom tank is shown in Figure 1-6, the coil is 15 cm away from the bottom of the tank, the grease outlet is preferably 25 cm from the bottom, and the drain is at the lowest point.

When the entrained moisture in the grease increases from 0.5% to 3%, the oxidation of the grease accelerates, the quality decreases, and the corrosive force on the tank wall increases. The storage tank is generally made of ordinary carbon steel and has a wall thickness of about 3 mm.

The grease receiving route is basically the same as molasses. After the grease is received, it is heated to 75-80 °C before use. If pumping is used, the heating speed can be increased to shorten the heating time by half. For tanks with a stirrer, the gap is agitated. The performance of the agitator is related to the volume of the tank. Regular work should be checked frequently, at least once every three months to prevent excessive deposits. In order to avoid the addition of oil to the mixture, a fat globule (powder ball) is formed. It is preferable to provide an exchanger near the mixer to heat the grease to keep it in the range of 60 to 90 ° C to reduce the viscosity of the grease.

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The third section of raw material cleaning

1. Purpose and requirements of cleaning

In the raw materials entering the feed mill, it can be divided into plant raw materials, animal raw materials, mineral raw materials and other small varieties of additives. Among them, animal raw materials (such as fish meal, meat and bone meal), mineral raw materials (such as stone powder, calcium hydrogen phosphate) and vitamins, drugs, etc. have been cleaned up in the raw material production process, generally no longer cleaned. The main raw materials to be cleaned by the feed mill are grain raw materials and their processing by-products. Cleaning of liquid raw materials such as molasses and grease is carried out by placing a filter or the like on the pipe.

The feed grain is often mixed with impurities such as sand, dander and straw. The presence of a small amount of impurities has a great influence on the quality of the finished feed. Because the finished feed has a wide limit on the impurities, the purpose of cleaning and removing the feed ingredients is not only to ensure that the impurities of the finished product are not excessive, but to ensure the safe production of the processing equipment, reduce equipment loss and improve the environment during processing. health.

There are two common cleaning methods used in feed processing plants:

Screening method: used to screen out large impurities and small impurities such as sediment and straw that are larger than or smaller than the feed.

Magnetic separation method: used to separate various magnetic impurities.

In addition, in the screening and other processing processes, it is often supplemented by suction and dust removal to improve the environmental sanitation of the workshop.

Second, screening

1. Structure of the screen surface

Screening is an operation that separates materials based on their particle size. The material smaller than the sieve hole at the time of screening passes through the sieve hole as a pure material (the undersize material), and the impurities larger than the sieve hole cannot be cleaned out through the sieve hole (the sieve top), or vice versa. The screening equipment commonly used in feed mills has a cylindrical (or conical) primary cleaning screen, a powder primary screening screen and a flat rotary grading screen.

(1) Grid screen, the grid screen located at the inlet (lower) material is the first line of defense for cleaning raw materials. Its main function is to initially clean the large impurities in the raw materials, and to protect the subsequent equipment and workers. The gap of the grid is based on the geometry of the material. Corn and other grain raw materials should be about 30mm, and oil cake should be about 40mm. At the same time, it should be ensured that the grid screen has a certain strength, usually welded with flat steel with a thickness of 3 mm and a width of 2 cm or a round steel of 10 mm. It should be fixed on the casting (lower) material port and ensure an inclination of 8 to 10° to facilitate the pouring of materials in the bag and reduce the labor intensity of workers.

The grid screen for unloading of automobiles is made of steel plate with a thickness of 4 mm and a width of 5 cm.

(2) Punching screen, also known as sieve plate, is usually made by punching out the mesh hole on a thin steel plate (black iron) or galvanized iron plate (white iron). The shape of the mesh hole is circular, round, long, triangular, etc., as shown in Figure 3-7. The thickness of the sieve surface generally depends on the size of the sieve hole, and the sieve surface having a small sieve opening is thinner, and the sieve surface having a large sieve opening or being severely worn should be appropriately thickened so that the sieve surface has sufficient strength. If the sieve surface is too thick, the sieve hole is easy to be blocked, and if it is too thin, the strength is not enough. Generally, the thickness of the sieve surface is 0.5 to 1.5 mm.

(3) Weaving the screen surface, the woven screen surface can be woven from metal wire (such as steel wire, galvanized iron wire, etc.) and chemical synthetic wire. The sieve holes of the woven sieve are rectangular or square. The thickness of the wire used for weaving the screen surface depends on the size of the mesh hole. Generally, the diameter is between 0.5 and 1.5 mm, and both the powder and the pellet can be used.

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2. Screening principle

The sieving machine can be used to remove impurities from the feed, and the grading of the feed can also be carried out. The sieving is based on the difference in the shape, width and thickness of the material particles, so that part of them pass through the sieve surface to become the undersize, and the other part remains on the sieve surface to become the sieve, thereby separating the feed from the impurities and removing it. For the purpose of impurities, or for different sizes and shapes of feed to separate for classification.

Use a round or square sieve to separate according to the width of the particles. The width of the feed granules or impurities is smaller than the diameter of the sieve hole. When sliding on the sieve surface, the particles with small width reach the pores, and the granules are erected, and the top end passes under the pores and passes through the sieve holes to become the undersize; the width is larger than the diameter of the sieve holes. The material becomes a sieve. The long hole sieve can be used for separation according to the particle thickness. The pellets or impurities having a thickness smaller than the thickness of the sieve hole, when sliding on the sieve surface, are tilted and turned over through the sieve hole to become a sieved object, and the thickness is greater than the thickness of the sieve hole and cannot pass through the sieve hole to become a sieve. For some special long rope heads, straw and other flexible impurities will hang on the screen hole during the screening, and it is generally removed by hand.

From the analysis of the sieving condition of the material, the necessary conditions for the sieving are as follows: the granules should have relative sliding on the sieve surface; the sifted granules should have access to the sieve holes; if separated by the width, the granules must be The sifted granules stand upright into the mesh openings; if separated by thickness, the sifted granules must be stretched over the length of the mesh and passed sideways into the mesh.

The above necessary conditions for sieving are attributed to three elements of sieving: 1 the material and the screen surface have relative motion; 2 the sieve and the screen surface are required to be contacted; 3 have the appropriate hole shape and size.

3. Opening ratio of the screen surface

The open cell ratio refers to the percentage of the total area of ​​the mesh on the sieve surface to the effective sieve area. Its calculation formula is as follows:

K=A2/A1 × 100%

Where: K—opening ratio (%)

A2—effective sift area (m2)

A1—the total area of ​​the mesh (m2)

The greater the open porosity, the more chances the material has to be sieved and the higher the screening efficiency. The reasonable arrangement of the mesh holes can reduce the hole spacing, increase the total mesh area, and increase the opening rate.

The arrangement method of the circular sieve holes has two kinds of square arrangement and triangular arrangement. By calculation, in the case of the same sieve hole size, the triangular arrangement is arranged better than the square, which has a high opening ratio and can ensure the screen surface. Uniformity of strength in all directions.

4. Common cleaning equipment for feed mills

(1) Cylinder primary screening

The most commonly used in China is the TCQY series cylinder primary clearing screen. It is widely used in feed mills, grain processing plants, grain silos and other industries to clean up raw materials. It is mainly used to remove large impurities such as straw, straw, hemp rope, paper, clods, corn leaves, corn cobs and other debris to improve the workshop environment, protect mechanical equipment, and reduce malfunction or damage. The series has 5 products according to the diameter of the cylinder, and the production capacity is from 10t/h to 80t/h. This series has the characteristics of high output, low power consumption, simple structure, small floor space, easy installation and maintenance, and convenient change of screen cylinder.

The series of primary cleaning screens are mainly composed of a punched circular sieve cylinder, a cleaning brush, a transmission device, a frame and an air suction port. During operation, the raw material enters the inside of the sieve cylinder through the feeding pipe through the feeding pipe. When the sieve cylinder rotates, the sieved material passing through the sieve cylinder flows out from the outlet, and the large impurity of the sieve cylinder acts on the guiding spiral band inside the cylindrical sieve. Next, it is led to the outside of the inlet channel and the large miscellaneous mouth is discharged outside the machine. The guiding ribbon not only helps to discharge large waste, but also prevents the material from flowing out on the screen. The upper suction port can be connected with the central suction system to prevent dust from flying, and the cleaning brush can clean the sieve cylinder to prevent the sieve hole from being blocked. The punching circular screen is the main working part and is supported by the main shaft in a cantilever shape. The whole sieve cylinder is divided into two sections, the half section near the shaft end is more than 20mm × 20mm square hole, so that the pellets can be sieved faster; and the section close to the outlet is usually a small square sieve of 13mm × 13mm to prevent Larger impurities pass through the mesh and are mixed into the grain.

The main technical performance parameters of the SCY series cylinder primary cleaning screen currently produced in China are shown in Table 2-3.

Table 2-3 Main technical features of SCY-63 cylinder primary clearing sieve

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(2) Cone powder cleaning screen

The cone powder cleaning screen is mainly used for cleaning the raw materials of the feed mill such as rice bran, bran, fish meal, etc., and can effectively separate the straw, stones, paper pieces and agglomerates mixed in the powdery auxiliary materials. Large amount of impurities, so that the material can smoothly pass through other equipment, effectively ensuring the normal operation of the downstream processing equipment and conveying equipment. The machine can also be used for sieving the mixed materials, breaking and removing the lumps to ensure the quality of the compound feed. Domestically produced conical powder sieve for SCQZ series

The cone powder sieve is composed of a sieve body, a rotor, a sieve cylinder and a transmission. The sieve body comprises a feeding hopper, a sieve box, an operation door, a discharge port and an end cover. The rotor is the main working part, which consists of a plate, a brush, a bracket, a spindle and a feed screw. A bracket is mounted on the spindle, and the top of the bracket has a plate and a cleaning brush. The plate and the spindle are mounted at a certain inclination angle. The gap between the plate and the brush and the inner surface of the screen can be adjusted by adjusting the bolts. A feed screw is installed at the top of the spindle, and the material is forced into the sieve in the future. The sieve cylinder is composed of two punched sieve plates which are bent into a semicircle, and are connected by a bead and a bolt into a cone sieve cylinder and fixed on a fixing ring in the casing.

The cone cleaning screen is continuously operated. When the feeding screw forcibly pushes the powder to be cleaned into the sieve cylinder, the powder is subjected to the impact of the spiral plate to break the agglomerated material in the powder, and at the same time, the powder is Under the push of the plate, the inner surface of the sieve cylinder is moved in a circular motion together with the plate. Under the action of the pressure of the plate and the centrifugal force of the material, the powder smaller than the mesh size quickly passes through the mesh hole and is discharged from the discharge port, and the impurities become the mesh material under the action of the inclined plate. The direction moves and is finally discharged by the discharge port.

The SCQZ conical powder sieve has a plate inclination angle of generally 5° to 8°. Large models take large values, small values ​​take small values. The rotor is operated at a speed of 300 to 400 / min. When the model is large, the speed is small. The conical powder sieve runs smoothly and has a small footprint. It can effectively clean out the stones, paper, straw, etc. contained in the powder, but the long flexible impurities such as rope heads and blades contained in the raw materials are easily entangled. On the center axis of the feed spiral, it should be removed in time.

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(3) Rotary vibration grading screen

The rotary grading sieve is mainly used for the screening and grading of powdery materials or pellets in feed mills, and also for the primary clearing of feedstock raw materials and the grading of intermediate products after secondary pulverization of large and medium-sized feed mills. The machine adopts the partial weight balance method to make the inertial force in the horizontal direction of the sieve body movement completely balanced, so the vibration is small and the noise is low. Because the machine combines the advantages of circular motion, elliptical motion and reciprocating linear motion, and has a screen cleaning device, the machine has the characteristics of large output, high screening efficiency, low energy consumption and simple operation. The rotary grading screen is mainly composed of a frame, a driving device, a screen box, a tail supporting mechanism and the like.

The material is concentrated from the feed inlet into the sieve body, and under the action of the circular motion of the inlet sieve body, the material is rapidly distributed on the entire sieve surface, and automatic classification is generated, and the movement track of the material at the feed end is a transverse ellipse (the long axis of the ellipse) Width of the screen); as the material moves, its trajectory gradually changes from a transverse ellipse to a circle, a longitudinal ellipse, and finally an approximate reciprocating linear motion at the discharge port material. The material is automatically graded during the movement process, so that the material with smaller particle size below the material layer is quickly screened, and the material with larger particle size moves to the discharge end. As the material moves toward the discharge opening, the sieve body is converted from a circular motion to a reciprocating linear motion, so that particles larger than the mesh size are quickly moved toward the discharge port until the discharge machine completes the entire screening of the material.

Three. Magnetic separation

A method of separating magnetic impurities by the suction of a magnetic field is called magnetic separation.

Magnetic impurities contained in feed ingredients, such as metal fragments such as iron, cobalt, and nickel, and magnetite ore. In feed production, magnetic separation equipment is generally selected only in accordance with the requirements of strong magnetic impurities.

(a) magnet

The main working component of the magnetic separation device is a magnet. According to different methods of generating a magnetic field, the magnet can be divided into two major categories: an electromagnet and a permanent magnet.

The electromagnet is generally made of a "soft iron" having a small residual magnet, and is wound around the outer core of the iron core. When the coil is energized, the magnetic poles are formed at both ends to form a magnetic pole, and the electromagnetic magnetic separation device can generate a strong magnetic field, but the equipment of the electromagnetic magnetic separator is relatively expensive, and an auxiliary device such as a rectifier for generating a DC power source is required, and the current is Disappeared, the magnetic field of the electromagnet retreats to near zero; equipment maintenance costs are also higher. Therefore, electromagnetic magnetic separation equipment is less used.

In recent years, with the research and development of high-quality magnetic materials, permanent magnets made of new materials have been greatly developed. The permanent magnet made of new materials can meet the requirements of the feed mill for removing impurities, and it is easy to use, not easy to demagnetize, does not require excitation power, is cheap, and has low maintenance costs. At present, permanent magnet magnetic separation equipment is mostly used.

(2) The principle of magnetization of permanent magnets

When the magnetic steel is magnetized, its magnetic induction B increases along the curve from 0 to the saturation limit BM as the magnetic field strength H (magnetization current) increases. When the magnetic field strength increases and the magnetic induction strength no longer increases, the magnetization current is stopped increasing and drops to zero, and the magnetic induction strength of the magnetic steel decreases from BM to B along the upper curve. When the magnetizing current drops to zero, the magnetic steel still retains the magnetic B. This magnetic property is called residual magnetization, which is also called remanence. In order to reduce the magnetic induction of the magnetic steel to zero, that is, to completely demagnetize, it is necessary to reverse magnetization. When the magnetic field strength is reversely increased to -He, the magnetic properties of the magnetic steel can be completely demagnetized, and the magnetic field strength that completely demagnetizes the magnetic steel is called coercive force. Reverse magnetization is performed if the reverse current is continuously increased. As the reverse current increases, the reverse magnetic induction increases. When the reverse current reaches a certain value, the magnetic induction increases to the reverse maximum -BM. If the magnetic field strength is reduced to zero, the magnetic induction decreases from the lower curve to -B0, which is the inverse remanence value. If the direction of the current is changed twice and gradually increased, the magnetic induction can also reach the previous BM value. If the cycle repeats magnetization, the magnetic induction varies according to the closed curve of the hysteresis loop.

Permanent magnets are used in production practice by utilizing the principle that magnetic induction strength lags magnetic field strength (current). Hysteresis loops are also known as magnets. In the magnetic selection, the residual magnetic strength B and the coercive force He are mainly utilized. The greater the residual magnetization, the greater the suction of the magnet and the stronger the impurity removal ability. The larger the coercive force, the stronger the demagnetization of the magnet and the longer the service life. Therefore, when selecting a magnetic steel material, a material with a large residual magnetization and a large coercive force should be selected.

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(3) Magnetic separation equipment

1. 篦-type magnetic separator, which is often installed at the feed port of the pulverizer, granulator feeder and hopper. The magnets are arranged in a grid shape, and the magnetic fields are superimposed on each other with high strength. A flow grid is placed on the magnet grid to act as a flow guide and protect the magnet. When the material passes through the magnet, the magnetic metal impurities in the material are sucked and manually removed periodically. The disadvantage of the grid magnetic separator is that the magnetic field of the magnet grid has a limited range of action, the magnetic force of the two grid bars is weak, and the magnetic metal impurities may not be absorbed and passed. In addition, the magnet grid is often in a friction state, and the demagnetization is fast, and the adsorption is performed. Iron debris also has a deterrent effect on material flow. However, the magnetic separator has a simple structure and is convenient to use, and is mainly used at the inlet of the main working equipment such as a pulverizer and a granulator.

The two-part outer cylinder of the inner cylinder and the outer cylinder is the same as the magnetic separator of the slide tube. It is connected to the feed conveying pipe through the upper and lower flanges. The inner cylinder is a magnet, which is composed of several permanent magnets and guides. The magnet plate is composed of copper magnets fixed on the magnetic conductive plate. The outside of the magnet has a stainless steel cover with a smooth and wear-resistant surface, and is fixed on the outer door with a steel strip. When the iron adsorbed by the magnet is cleaned, the outer cylinder door can be opened. When the iron adsorbed by the magnet is cleaned, the outer cylinder door can be opened to make the magnet Go outside the tube.

The permanent magnet cylinder is connected with the slide tube. When the (powder) material and the magnetic impurities mixed into the material fall from the feed port to the surface of the cone at the top of the inner cylinder, it spreads around and then along the surface of the magnet cover. Sliding down, due to the large iron ratio, it is blocked by the surface of the cone and then bounces to the inner wall of the outer cylinder. Under the action of the wall reaction force and gravity, it falls along the direction of the magnetic field line, so it is easy to be sucked by the magnet, while the non-magnetic material is taken out. The material is discharged to complete the separation of the material from the iron impurities.

The magnetic core of the permanent magnet cylinder is generally made of newly developed rare earth permanent magnet material, and the magnetic induction intensity can reach 200-380 mT, and the service life can reach 6-8 years. Because of its simple structure, high iron removal efficiency, no space occupation, no power, etc., it is widely used by feed mills and grain and oil processing plants.

Section IV Storage of Raw Materials and Finished Products

One of the distinguishing features of feed mills, unlike other food plants, is the wide variety of raw materials and finished products, and the proportion of each variety varies widely. Therefore, the storage of raw materials and finished products is a very important issue for the feed mill, which directly affects the normal production and the economic benefits of the plant. Correct design of warehouse type and calculation of warehouse capacity is the main work of feed mill design. The following aspects are mainly considered in the selection and design.

1. According to the characteristics of the stored materials and regional characteristics, choose the warehouse type to achieve economic and reasonable.

2. Calculate the bin capacity and the number of bins based on the quantity, quantity and quantity of raw materials and finished products.

3. Reasonably configure the position of the silo for easy management and prevention of mixing, pollution, etc.

The storage for raw materials and finished products mainly includes room and vertical storage (also called silos). The room warehouse is low in cost and easy to construct. It is suitable for powder, oil cake and finished products. Small varieties of expensive additive raw materials also need to be managed by a specific small-sized warehouse. The disadvantage of the room warehouse is that the loading and unloading work is low in mechanization, labor intensity is large, and operation management is difficult. The advantage of the vertical storage is that the individual storage capacity is large, the floor space is small, the entry and exit warehouse is mechanized, the operation and management are convenient, and the labor intensity is small. However, it has high cost and high construction technology and is suitable for storing granular materials such as grain.

The raw materials and finished products of the feed mill have various varieties and different characteristics. Therefore, for large and medium-sized feed mills, the storage method combining the silo and the room warehouse is generally selected, and the effect is good.

I. Determination of warehouse capacity

The capacity of various silos in the feed mill should be determined according to the requirements for ensuring the normal continuous production of workers. The storage capacity is too small to meet the needs of continuous production, resulting in production disruption or even chaotic production rhythm; excessive storage will increase infrastructure investment. Excessive inventory also caused a backlog of products and funds.

(1) Calculation of warehouse capacity and warehouse area of ​​raw material warehouse (library)

The capacity of the main raw material and the auxiliary material storage bin is mainly determined by the scale of the factory, the transportation conditions, the distance of the raw material supply, and the effectiveness of various components. In the calculation, the materials for each component should be calculated according to the average formula, taking into account the differences in the storage and bulk density of some raw materials. In the calculation of the number of warehouses and silos, increase the margin by at least 10% to ensure that there is sufficient storage capacity for production turnover. In places with inconvenient transportation, it is necessary to increase the capacity of the warehouse.

1. Determination of the capacity of the silo warehouse

The bin capacity can be calculated as follows:

V=QηT/νk (m3)

Q-feed mill production capacity, t/d

η—Storage materials account for the largest proportion of the formula, %

Ν—the bulk density of the storage materials, t/m3

K—the effective warehouse capacity of the vertical tube library, generally 0.80

T—Storage days, generally 30 to 60 days for food raw materials; 30 days for auxiliary materials, 7 to 10 days for finished products.

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2. Calculation of building area of ​​room warehouse

Before calculating the floor space of a room warehouse, first determine the effective warehouse capacity (t) of different raw materials and finished products according to the production capacity, storage days, and proportion of the formula, and then calculate the floor space of each individual raw material separately. Summing and determining the total footprint. The floor space of each individual raw material is calculated as follows:

A=1000QS/nmμ(m2)

Where: A - the area of ​​a raw material (m2)

Q-requires storage capacity (t), for finished products can be calculated according to 7 days of storage

S-the area occupied by a single package (m2)

Flour bag 0.26m2, sack 0.42m2, woven bag 0.35m2

N-heap number

M-weight per package (Kg), generally 40Kg for finished feed

Μ-utilization area utilization factor 0.6~0.65

3. Calculation of batching bins and transition bins

a. The granary to be pulverized: the pulverized warehouse to be pulverized is generally the production capacity of the pulverizer for 1 to 2 hours for the small factory, and the production of the pulverizer for 3 to 4 hours for the large factory. It is best to configure two crushing bins for each crusher.

b. Ingredient bin: Large and medium-sized feed mills can be calculated according to the production capacity of 5 to 6 hours, and for small plants, the production capacity is calculated according to 4 hours. The number of batching bins depends on the type of ingredients and adds 1 or 2 motorized bins.一般小厂是8～10个配料仓;小时产量在5～10吨的厂，一般10～12个仓;大型厂一般为12～16个仓;对个别特大型厂也有20～24个配料厂。

4.待制粒仓：待制粒仓一般按制粒机生产能力的1～2h计算。为使更换配方不中断生产，一般每台制粒机都设置两个待制粒仓。

5.成品打包仓：成品大包的仓容量应为打包机1小时的生产能力计算。

6.散装成品仓：散装成品仓的容量一般按1～3天的计量计算。

二.立筒库

立筒库具有对散粒体物料进行接收、贮存、卸出、倒仓并指示料位等功能，它起着平衡生产过程、保证连续生产、节省人力、提高机械化自动化程度，以及防止物料病虫害和变质等作用。

立筒库常用钢板和钢筋混凝土制作，多为圆筒形。由于钢筋混凝土仓有相对造价高、自重大、建筑周期长的不足，但又有使用寿命长的特点，所以其主要用于大型的贮备库，而做为生产企业的周转仓，使用较多的是钢板仓。钢板仓有利用螺栓联结的波纹钢板仓和由卷板卷制的卷板仓。

1、波纹钢板仓：波纹钢板仓也称拼装仓，是近年来迅速发展的薄壁钢板仓，其壁厚1.2～4mm。仓壁的厚度随高度下降而变厚。虽然壁薄，外界温度容易传入，但粮食是不良导热体，故仅在离壁30cm以内的粮温有变化。一般下午3时温度最高，7时基本恢复正常。如长期贮藏，要定期倒仓和通风。

波纹钢板仓是由带有一定曲率的波纹钢板由螺栓拼装而成。波高一般为12mm，波宽65mm板厚1.2～4.0mm。仓筒直径和高度已有系列化;锥底仓直径从4.27m至9.77m，高度从4.8m到24.4m。平底仓直径从4.27m至18.3m，高度从4.95m至25.6m。

2.卷板仓螺旋钢板仓是由专用的螺旋卷仓加工机组将长条钢板卷制而成的。卷制时，是将495mm宽的度锌卷板送入成形机，由成形机轧制成所需的几何形状，如圆仓的直径。再经过弯折机弯折、咬口，围绕筒仓外侧，形成一条30～40mm宽的连续环绕的螺旋凸条。凸条在结构上起到了加强筒仓强度的作用。卷板仓还可对两种不同的材料实现双层弯折、咬口。卷板仓与拼装仓相比最大的特点是密封性能好。卷板仓可做成流体的贮存仓。

3.筒仓的出料形式：筒仓的出料有平底出料和锥底出料两种形式。出料形式主要决定于筒仓的直径，一般直径大于10m的筒仓都为平底仓。

(1)平底出料仓的基础建设费用相对较少，但需配置出仓机械，另外平底仓卸料不彻底，残留较多，需人工清理。

(2)锥底仓的基础建筑费用高,施工周期长,但不需扫仓机,卸料较干净。

4.立筒库装卸工艺流程

原料入立筒库储存之前，一般要初清除杂，干燥通风，如储存期间发生病虫害，要进行熏蒸灭虫害;若发现物料过热，水分过多，还需倒仓通风。

(1)干燥和通风有的原料在入库前期含水量超过储存标准要求需进行干燥以降低其含水量，防止物料霉变。干燥有烘干干燥和通风干燥两种。烘干干燥需要加热，加工成本高，主要用于原料含水量较高的新收购谷物。通风干燥主要用在周转仓的通风干燥和降温上，适用于水分略高和气温较高的季节。

烘干干燥由干燥塔和热风炉组成。干燥机的空气流量范围在0.66～1.33m3/m2 s。影响物料干燥的主要因素有：大气温度和湿度、干燥机内温升、空气流量、物料含水量、物料从干燥机通过的流量以及物料种类等。饲料原料的干燥温度一般控制在82℃～83℃，物料品种不同耐受最高温度有差异，小麦能耐较高温度，依次是燕麦、玉米。物料粒度也与烘干难易有关。烘干温度较高，玉米淀粉易变性，则在饲料制粒时不易成形。烘干玉米所需时间比烘干小麦要高60%。

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烘干干燥过程包括对物料进行快速高温干燥和缓慢冷却过程。这一过程既可以改善物料品质(通过缓苏过程减少颗粒应力开裂)，又可使干燥机的处理量增加约70%。并且使烘干每吨物料的能耗减少20%。物料经干燥排出干燥机的温度为49℃～60℃，被送入缓苏料仓并在仓内缓苏4h以上，使水分从颗粒内部转移到外部，再用小风量对物料进行通风冷却直至物料冷却。经过上述缓苏和冷却处理，可去除约2个百分点的水分。

(2)料仓物料的熏蒸大型筒仓群应设制灭杀粮食虫害的熏蒸系统。该系统采用鼓风机将含有一定浓度的有毒的熏蒸气(如甲基溴气)强制循环，密闭熏蒸。该系统主要有风机、加温器、气化槽、气体排出口、粉尘过滤器、滑动阀、溜槽等组成。

(3)仓顶、仓底装卸及输送物料

a.仓顶输送装料仓顶输送装料一般采用刮板输送机，因为刮板输送机的机壳是封闭式的，可避免卸料时粉尘外扬。在配置仓顶输送设备时，相临两排筒仓可共用一台输送机，输送机卸料口允许布置在筒仓中心的内侧。

b.底仓卸料底仓卸料有多种形式：① 锥形料斗自流出料形，它可免去强制卸料设备和节省动力，但要求锥斗倾斜角一定要大于45°避免物料结拱堵塞。②流化出料降温型利用流化作用达到出料的目的，它既可以减少工程投资，又能在不需要出料时起到通风降温去潮作用。③平底扫仓型利用旋转耙式卸料机将仓中物料卸出，它可减少土建投资，增加筒仓有效容量。

c.仓底输送设备仓底卸料器卸下的物料大都采用刮板输送机输送走。在配置上，宜采用一行筒仓下面配备一条输送机。若两行筒仓卸料时共用一条输送机，则需增加筒仓基础的高度， 增加建筑费用，这个费用比增加输送机的费用更高，是不经济的。

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