Drying is one of the most important processes in the processing of expanded feed. The moisture of the feed pellets just extruded from the extruder is very high, reaching more than 22%. It is necessary to support the drying equipment to remove more than 10% of the water and then cool it to ensure that it meets the qualified product quality. At present, the drying equipments used in domestic feed processing of the extruders mostly use conveyor belts and chain type box-type dryers. This type of equipment is of horizontal structure, with a large area and high cost. Most new plants still rely on imports. At the same time, in the actual production, there is also a problem that the supporting fan power consumption is large, the drying energy consumption is high, the steam consumption of the ton material is more than 500kg, and the sieve (net) hole is blocked, which obviously increases the processing cost of the expanded feed and affects its promotion and application.
In order to change this situation, the author has applied the domestic multi-layer circular vibration dryer which has been applied to the drying process of agricultural products for nearly ten years, and has achieved good results and high efficiency and energy saving. Effect. This paper puts forward some rough views on the design problems existing in the rational application of the equipment for the reference of peers.
1. Composition of the drying system
The multi-layer circular vibration dryer is applied to the processing of puffed feed. The drying system consists of a multi-layer circular vibration dryer, a damper, a steam heat exchanger, a blower, an induced draft fan, a cyclone and a wind trap. see picture 1. The technical key of the system design is the rational design of the structural principle of the multi-layer circular vibration dryer, and the rational selection of the parameters of the drying wind network.
2. Dryer basic structure and principle
The existing multi-layer circular vibration dryer generally has a feed port, a top cover, an exhaust gas outlet, a multi-layer drying bed, a hot air inlet, a discharge port, an excitation plate, a vibration isolation spring, an excitation motor and a frame. . The multi-layer drying bed is composed of an inner and outer short cylinder, an annular horizontal sieve plate and a baffle plate. Each layer of annular horizontal sieve plate has a discharge opening, and when connecting the inner and outer cylinder flanges of each layer bed, the upper and lower discharge ports are staggered, so that the material of the upper layer outlet can fall into the next layer. The inlet of the material to be dried is discharged from the top layer to the lowest layer. At present, there are a series of products for this type of dryer in China. The bed diameter is 1.0~2.0m, and the general layer is 5 layers. The output varies from 100kg/h to 2000kg/h due to the serial number, material type and moisture. Wait.
When the equipment is working, the two excitation motors staggered in the lower part of the main machine are synchronously reversely rotated, so that the multi-layer circular vibration drying bed disposed thereon generates an upward vibration force and a counterclockwise rotation torque around the center of the drying bed. The material forced into the feed port is jumped counterclockwise along the top sieve plate to the discharge port, and the upper layer discharge port is the feed port of the next layer, so that the layer moves and falls until the bottom layer material. During the jump of the material along the sieve plates from top to bottom, the hot air enters the intermediate inner cylinder space from the air inlet, enters from the opening of the inner tube wall of the lowermost two layers, and passes through the material layer vertically. It is fully contacted with the material and subjected to wet heat exchange. After exchange, the moisture is discharged from the exhaust gas outlet provided on the top cover to complete the drying process of the material. Due to the strong effect of the vibration force, the hot air can fully contact with the jumping material, the heat exchange is accelerated, the drying effect is good, and the electric and thermal energy consumption is low, which is the biggest advantage of the equipment.
3. Dryer structure improvement design
The multi-layer circular vibration dryer which serves as the drying feed drying task is different from the structure of the equipment generally used for drying single material of agricultural products. There are many varieties of puffed feed, and the particle size is also different due to different species of fish and pets. Generally, the particle diameter is 1~24mm, and the particle size is very different. Therefore, for the dryer, it is necessary to strengthen the production of large particles. Equipment drying capacity, but also to avoid excessive drying and blowing of small particle products. In addition, it is also necessary to avoid the residual doping and pollution of the equipment during product conversion, which affects the appearance quality of the product. According to the structure and principle of the multi-layer circular vibration dryer, it should be reasonably applied to the processing of the expanded feed. It is necessary to solve the production matching of the equipment to adapt to different varieties and particle sizes (ie drying capacity), hot air distribution, and internal machine. Residues and drying uniformity, etc., to make a machine more versatile, easy to use and energy saving. To this end, the author mainly considers the following aspects in the application design.
3.1 Yield matching and hot air fan allocation problem
The largest multi-layer circular vibration drying machine in China has a diameter of 2.0 meters and 5 layers, and the maximum production time is about 2000Kg. The dryer equipment should be equipped with a SEP-200 wet-type smelting machine from a Taiwan company. The production time is 2t-3t, and the moisture content of the machine is more than 22%. According to the parameters of drying heat, air volume and drying layer calculated according to the drying parameters, compared with the parameters of the original chain box dryer of the company, it is found that the output is small and the hot air passes through the layer. The wind speed is also too large, which will affect the normal fall of the material in the material layer and cause blockage. To this end, the author expands the existing dryer diameter from 2cm to 2.2cm, and the bed layer is increased from 5 to 9 layers, thus effectively solving the problem of small matching of the output of the device.
In addition, the two hot air outlets which are originally arranged on the inner and outer walls of the first and second layers are changed into three air inlets, which are respectively arranged on the inner wall of the first, fifth and ninth layers; The single layer exhaust gas outlet on the top layer (ie, the ninth layer) is changed to two, which are respectively disposed on the outer wall of the third and seventh layers. In this way, the hot air entering the inner cylinder is divided into four paths: one is from the first layer air inlet, passes through the second and third layer sieve plates, and the material layer is discharged from the third layer exhaust port, and the third is from the fifth The layer air inlet enters, passes through the sixth and seventh layers of sieve plates and the material layer, and is discharged from the seventh layer exhaust port; the fourth is from the 9th layer air inlet, passes through the 9th and 8th sieve plates and the material layer , is discharged from the 7th layer exhaust port, so that the resistance of the hot air divided into four layers is substantially the same, thereby greatly reducing the hot air wind speed of the material layer to be dried, and the drying wind speed is reduced below the suspension speed of the minimum expanded feed particles. It not only solves the problem that the drying wind speed is too high, but also causes the small particles to run away, and significantly improves the utilization rate of the hot air and reduces the energy consumption. The outline of the improved multi-layer circular vibration dryer is shown in Figure 2.
3.2 Internal residual problems
At present, the general multi-layer circular vibration dryer in China is simple and convenient to manufacture, and the sieve plates are horizontal annular structures. Due to the small capacity of the expanded feed, the product after drying is generally 0.28-0.34t/m3, and the shape of the same variety of feed pellets also has a certain difference, and the secondary vibration of the sieve plate makes the expanded feed exist in the production variety conversion. A small amount of feed remains in the machine, it is difficult to clear, resulting in longer feed conversion time, and about 15-20 kg of the first variety residue will be discharged when the second variety begins to be produced, and re-expanded, thereby affecting the yield and quality. Therefore, the rational design of the sieve plate structure has become an important issue for whether the equipment can be applied to the processing technology of the expanded feed. We designed the multi-layer horizontal annular sieve plate to have a helicoid mid-angle angle of 1.5°, which better eliminated the residual problem of the machine in this type of equipment.
3.3 Affecting the quality and uniformity of drying of large pellets
There are two inherent defects in the working time of the domestic multi-layer circular vibration dryer: First, the thickness of the drying layer of the bed gradually becomes thinner from top to bottom, which shortens the residence time of the particles in the machine, and easily causes the inlet to be blocked. Second, the path of the material in the bed along the sieve plate is different (ie, the circumference), the movement time is different, the inner ring is fast and the outer ring is slow, and the layers are superimposed, so that the residence time of the material in the machine is different. The circumferential trajectory produces a large difference, which affects the quality and uniformity of material drying. In the prototype test, we found that these defects have a particularly serious effect on the drying quality and uniformity of large-sized extruded feed. To this end, we have taken the following two improvements: First, the top layer (ie, the 9th floor) and the 8th layer of the inlet and outlet openings have been improved, and the high humidity has been dropped from the inlet to the top. The expanded granules are divided into two channels and uniformly dropped onto the feeding ports of the 8th and 9th layers. The strong drying effect of the two thin beds makes the surface layer of the granules harden rapidly, which not only reduces the high-humidity puffed feed just emerging from the mold. The deformation improves the appearance quality of the product and improves the fluidity of the wet particles in the first few layers of the machine.
The problem of blockage of the feed port is avoided. After the feed of the two thin beds reaches the discharge port, it is collected into the seventh layer, thereby falling layer by layer, and the thickness of the subsequent drying bed is obviously increased, and the residence time of the feed in the machine is prolonged. The second is to change the position of the discharge port of the 1~7 layer drying bed, and set the discharge port of the 1~7 layer drying bed on the outer ring of the sieve plate, and occupy half of the width of the drying bed, and move on the inner side. The material is introduced into the outer discharge port by a slanting plate, so that the materials inside and outside the different circles are mixed when the discharge port falls, and the swash plate also has a blocking deceleration effect on the material of the inner ring, thereby solving the inherent defects of the device. Dry quality and poor drying uniformity.
4. Drying wind network parameter selection
The selection of the drying wind network parameters should be calculated through repeated drying parameters to determine the required drying heat and air volume, in order to select the appropriate steam heat exchanger, blower and induced draft fan models are SRZ12X7D, 4?72?6D and 4 respectively. ?72?8C.
It should be pointed out that the front and rear two-stage series fans must be matched. When selecting, the rear stage induced draft fans should have a large surplus, so that the dryer can produce large and slight negative pressure winds at the inlet and outlet respectively. In order to avoid dust flying, it also ensures that the freshly moistened high-humidage feed has sufficient cold air to rapidly harden the epidermis of the feed pellet and reduce particle deformation. In addition, the problem of granules caused by the installation of a closed fan at the inlet and outlet of a conventional dryer can be avoided.
5. Practical application effect
The multi-layer circular vibration dryer designed according to the above scheme was put into use in two expanded feed mills in Shunde in September 1999 and April 2001 respectively. More than one year of actual production inspection proved that multi-layer circular vibration drying The dryer has three advantages in the processing of puffed feed: First, energy saving, the production cost of the puffed feed is significantly reduced. According to the test, the fuel consumption and electricity consumption of the tonne are 30% lower than that of the chain plate dryer; The drying quality is high and the shape is good, which is very popular among the farmers. The third is to save investment cost and reduce the equipment investment of the drying system by nearly 30%. At the same time, the equipment layout is flexible and convenient, the operation is simple, the work is reliable, and the failure rate is low.