Drying is one of the most important steps of the extruded feed processing. Most of domestic extruded feed processing adopt belt conveyor or chained and box-type dryer. Devices with those types are all horizontal structure, take a lot of room and high cost, many of the new factories import the devices. At the same time, in the practical production, the matched draught fan is of large power and high drying energy consumption, the steam consumption for each tons of material is up to more than 500kg, moreover, problems such as screen holes block would obviously increase the processing cost of Extruded feed, affect its’ popularization and application.

In order to solve the problems, in the recent decade, some of the enterprises try to use the domestic multilayer circle vibration dryer to the extruded feed processing and result well. This kind of dryer used to be applied to dry the agricultural products at highly effective and low energy, the effect is favorable.

I. Consists of Drying System

When apply the multilayer circle vibration dryer to the extruded feed processing, the drying system consists of multilayer circle vibration dryer, wind door, vapor heat exchanger, wind blower, draft fan, cyclone dust extractor and wind lock. The main technique of this system is reasonable design of multilayer circle vibration dryer structure, and the wise selection of the drying wind sieve parameters.

II. Basic Structure and Work Principle of the Dryer

Existing multilayer circle vibration dryer generally consists of feed inlet, top cover, an exhaust gas outlet, multilayer drying lathe, a hot wind inlet, outlet, vibration plate, isolation spring, vibration motor and frame. Multilayer drying lathe consists of inside and outside cylinder, ring-type horizontal sieve plate and striker plate. Each layer of the ring-type horizontal sieve plate has a output port, and the flange to connect the inside and out side cylinder are staggered, thus the materials outlet from upper layer can fall into the inlet of lower layer, when the materials get through the highest layer and output from the lowest layer. At present, this type of dryer has already had series products, diameter of the lathe is 1.0~2.0m, generally 5 layers, and varies in different series of models, materials and moisture contents, the yield is from 100kg/h to 200kg/h.

While working, the main machine is drove by two synchronization reverse rotation vibration motors installed stagger at the bottom, multilayer circle vibration dryer on it generate upward shaking force and anti-clockwise rotation torque around the center of drying lathe, push the materials get in to the inlet anti-clockwisely jumping to the outlet along the top sieve. Upper layer outlet is the inlet of the lower inlet. Materials fall layer-by-layer till the bottom layer and output.

During the process of the material jumping along each layer, the hot wind get in from the wind intake and reach to the inner cylinder, get through the layer from the lowest layer inlet on the wall of inner cylinder, fully connected with material and proceed wet and hot exchange, wet wind exhausted from the flue gas outlet at the top cover, and finish the drying process. Because of the intensity effect of vibration, hot wind can be completely connected with material, quicken the wet and hot exchange, achieve good drying effect, electric and heat energy consumption is lower, which is the greatest advantage of the machine.

III. Dryer Structure Improved Design

Structure of multilayer circle vibration dryer works as extruded feed dryer is different from general single material dryer. Extruded feed has many kinds, the size of pellets varies according to the feed, general diameter of the pellet is 1~24mm, varies in size. In terms of drying equipment, it should enhance the ability to dry the large pellet, and also prevent over drying and blow away small pellet. Besides, avoid the vestigial and mix of other materials in the equipment and affect the appearance and quality of product. Based on the structure and principle of multilayer circle vibration dryer, equipment drying abilities for different kinds and sizes of pellets should be matched to rational use to Extruded feed processing, problems of hot wind distribution, vestigial in the machine and evenness of drying should also be taken into consideration. To reach the aim of multi-purpose and energy saving, the followings are main points to be considered while designing. 

1. Yield machine and hot wind blower distribution

Lathe diameter of largest type domestic multilayer circle vibration dryer is 2.0m, 5 layers, largest yield is about 2000kg/h. This dryer should be equipped with wet process Extruded machine, yield is 2-3t/h, pellet moisture content output is more than 22%. Parameters of drying heat, wind volume and drying area calculated according to the drying parameter, comparing with former chain plate box type dryer parameters, the yield is less, speed of hot wind get through the material layers is too fast, affecting the material to fall down, leading to block. Therefore, expand present dryer diameter from 2cm to 2.2cm, increase lathe layer from 5 to 9 and solve the problem of low yield.

In addition, hot wind inlet used to be on the inner wall of lowest 2 layers changes from 2 to 3, and settled on the 1st 5th and 9th layer; gas exit on the top layer(9th layer) become 2, settled at outside wall of 3rd and 7th layer. These changes reduce the hot wind speed of materials layers to be dried sharply, the drying wind speed reduced to slower than the smallest Extruded feed pellet suspension speed, solve the problem of small pellets being blow away by large volume wind, and also improved the use ratio of hot wind obviously, reduced the energy consumption.

2. Vestigial in the machine

At present, most of the domestic multilayer circle vibration dryer is horizontal circle structure for the convenience of manufacture. Since the Extruded feed capacity is small, generally the product after drying is 0.28-0.34t/m3, pellet shape of same materials can be different, with the addition of sieve plate secondary vibration, result in vestigial in the machine when switch the Extruded feed kind, hard to clean and lengthen the switch time of feed. When producing the second kinds of extruded feed, should firstly exhaust about 15-20kg of former materials’ vestigial and extruded again, thus affect the yield and quality. For this reason, design reasonable sieve plate structure becomes the important issue to decide whether this equipment is suitable for extruded feed processing. We design the multilayer horizontal circle sieve plate as helicoid, pitch diameter angle is 1.5°, and eliminate the block in the machine of this type.

3. Problems that affect the large pellet Extruded feed drying quality and evenness

There are two inherent defect for domestic multilayer circle vibration dryer working time: first thickness of drying layers are thinner and thinner from top to bottom, pellets stay for shorter time in the dryer, tend to block the inlet; second is that the materials in the lathe move perimeter different as circle track along the sieve plate, movement time difference, the inside track is faster and outside track is slower, thus the materials stay in the machine for different period cause the different circle track, and affect the drying quality and evenness of material. In the experiment of the prototype, we found that the defect affects a lot to the drying quality and evenness of materials. Therefore, we take following two improvement measures: first, improve the top (9th) layer and 8th layer material inlet and outlet structure. High moisture content pellets used to fall from the inlet and into the top layer, after the improvement, they are separated to two parts and fall evenly into the inlet of the 8th and 9th layer. Pellets dried by the two thick lathe, the surface harden quickly, which reduce the transformation of high moisture content Extruded feed pellet, enhance the appearance of the product, and mobility of wet pellet in former layers, prevent the block at inlet. Pellets dried by two layers and arrive the outlet, collected at 7th layer, and fall down layer by layer, obviously increase the thickness of follow-up drying layers, lengthen the time for feed to stay in the machine. Second, change the outlet position of 1st~7th drying layer, design the outlet of 1st~7th layer at the outside circle of sieve plate, and take half the width of drying layer groove, materials that move at the inside are led to the outside outlet by a cant board, in this way the materials at inside and outside circle mixed at outlet, and also resist and slow down the materials in the inside circle, soling the problem of the inherent defect of drying quality and evenness. 

IV. Parameter Selection of Drying Wind sieve

Parameters of drying wind sieve should be decided by repeating drying parameters to make sure the drying heat, wind volume, only in this way we can choose the proper steam exchanger, wind blower and draft fan. It should be paid attention that the fan of the front and behind second level tandem must matches, when selecting, fan behind should have more than needed to produce slight negative pressure wind between inlet and outlet, prevent the dust flying, and also ensure the Extruded feed with high moisture content can be cooled quickly, the surface harden in a moment, reduce the transmutative pellets. In addition, it can avoid the broken pellet phenomenon of general dryer with wind lock installed at the inlet and outlet.

V. Practical Application Effect

According to the multilayer circle vibration dryer designed above, and test by practical production, we can prove the priorities of multilayer circle vibration dryer to process Extruded feed: first, performance, cost of producing the Extruded feed is obviously reduced, according to the test, oil and electric consumption for per tons of material is reduced by more than 30% of the chain plate type dryer; second, high drying effect and well appearance, deeply welcomed by farmers; third, saving cost of investment, cost for equipment of drying system can be reduced by nearly 30%, moreover, the equipment layout is flexible and convenient, easy to operate, reliable work and low failure rate.