Special drum dryer for agricultural and sideline products

Case Overview: In recent years, there have been more and more types of agricultural cash crops, and the use of agricultural by-products has become increasingly widespread. After scientific treatment, the "three wastes" materials have become renewable and cannot be processed without a drying process. The innovation and improvement of drying technology have become a bottleneck in the development of agricultural cash crops and agricultural by-product processing.

2 dryer

3 dryer

4 dryer

In recent years, there have been more and more types of agricultural cash crops, and the use of agricultural by-products has become increasingly widespread. After scientific treatment, the "three wastes" materials have become renewable and cannot be processed without drying processes. The innovation and improvement of drying technology have become a bottleneck in the development of agricultural cash crops and agricultural by-product processing. In the past 10 years, Changzhou Unified Drying Equipment Co., Ltd. has been committed to serving agriculture and increasing farmers' income, continuously innovating and developing a high-temperature fast drying equipment with international advanced technology - multi ring drum dryer. We have successively developed complete sets of drying equipment for deep processing of agricultural products, successfully solving the problems of agricultural economic crops such as the drying of ginkgo leaves, alfalfa grass, marigold, barley seedlings, Jerusalem artichoke meal, mulberry leaves, and ginger leaves, which have increased farmers' income by 3-5 times and agricultural output value by 5-10 times; And agricultural waste: drying of broccoli stems and leaves, drying of corn alcohol residue, drying of cassava alcohol residue, drying of sweet potato alcohol residue, drying of citric acid residue, drying of cow manure, drying of sawdust, etc.

Drying requirements for agricultural and sideline products:

◎  Require a large output;

◎  The initial moisture content is high, usually above 80%. Even after preliminary treatment, its moisture content is still above 70%, and it is the internal moisture content;

◎  During the drying process, the temperature of the material itself should not exceed 80 ℃, otherwise protein and other organic elements will be damaged;

◎  The drying cost cannot be high because its added value is low.

To overcome the above drying difficulties, a new high-temperature, fast, and downstream drying process is adopted:

●  The theoretical basis is that during the convective drying process, wet materials are in the drying medium. When the temperature of the medium exceeds the ambient wet bulb temperature, the moisture of the wet materials begins to evaporate. Due to the fact that moisture evaporation is an endothermic process, the heat brought by high-temperature media is absorbed by the moisture evaporation of wet materials. Therefore, during the constant rate drying stage, the temperature of wet materials always does not exceed the ambient wet bulb temperature, usually not exceeding 80 ℃. Due to the use of downstream drying, as the moisture of wet materials evaporates, the humidity of high-temperature media gradually decreases. The key is to control the outlet of the dryer, Control it at the endpoint of constant rate drying, i.e. when the material moisture reaches less than 14%, it is separated from the drying medium. As it enters the slow drying process, the heat provided by the high-temperature medium to the material will be higher than the heat required for moisture evaporation, and the material temperature will rise. Therefore, it is necessary to adopt rapid drying, which means controlling the medium speed reasonably based on the specific gravity and particle size of the material.

Its advantages are:

●  High production capacity, small volume, and low power consumption. The inlet air temperature of the dryer can reach 800 ℃, and the outlet air temperature can be controlled between 90 ℃ and 125 ℃. The drying intensity can reach 100kg (H2O)/m3. h, which is 2-3 times that of traditional single drums. The material stays in the machine for only 1.5-2 minutes, and the evaporation moisture can reach 5000 kg/h per hour per hour. The daily production capacity is 80-100 tons/day (dry products). The installed capacity of the main machine is only one eighth of that of a conventional single drum. The principle is: large temperature difference and fast heat transfer. According to the theory of heat transfer, it can be inferred that when a high-temperature medium transfers heat to a wet material, the larger the temperature difference between the two, the more heat is transferred to the wet material, and the faster the moisture evaporation of the wet material.

●  The drying medium temperature is high and the drying speed is fast. The material stays in the dryer for only 1.5 minutes.

●  High thermal efficiency of drying. This unit uses coal as fuel, with a comprehensive thermal efficiency of 76%. When drying alcohol residue (initial moisture content is 70%, final moisture content is 12%), the coal consumption per ton of dry product is only 250 kilograms (coal calorific value is 6000 kcal/kg). Under high temperature drying conditions, it is necessary to use downstream flow, which means that the direction of material flow is consistent with that of the drying medium. The principle is that the high-temperature hot air at the inlet comes into contact with high moisture content materials, and the heat brought by the high temperature to the wet materials is absorbed by the evaporation of water. The temperature of the wet bulb is always maintained at the corresponding wet bulb temperature, and the water continuously decreases, resulting in a corresponding decrease in the temperature of the hot air. As long as the outlet air temperature of the dryer is well controlled, the set final moisture content requirements can be met, and the material temperature is always below about 60 ℃ during the drying process, ensuring that useful substances of the material do not deteriorate during the drying process.

The structural characteristics of the multi ring drum dryer: combined with the aforementioned high-temperature, fast, and downstream drying process, it adopts a multi ring drum dryer. It is a new type of dryer put into the market. In the drying industry, traditional single tube dryers are gradually being replaced. Three sets of drums with different diameters form a multi ring drum. The inner and outer surfaces of the inner and middle ring drums, as well as the inner surface of the outer ring drum, are equipped with reading plates. The three layer drum rotates at the same speed, and the material direction is: wet material enters from the inner drum, returns from the end, enters the middle layer drum, goes to the first end, and then enters the outer drum, and is discharged from the end of the outer drum.

Advantages over single-layer drum dryers:

1. Improving drying performance: It can meet the requirements of new high-temperature, fast, and downstream drying processes. Due to the different diameters of the inner, middle, and outer cylinders, the cross-sectional area through which hot air passes varies, resulting in varying operating speeds of wet materials within the three layer cylinder. Therefore, a reasonable arrangement can be made based on the rate of moisture evaporation during the drying process. The cross sections of the three cylinders can be arranged. For example, the inner cylinder is designed with a smaller cross section due to its high moisture content of the material, high humidity of the drying medium, and high drying intensity. As the moisture content of the material gradually decreases, the temperature of the medium also increases in the middle and outer cylinders, which reduces the passing speed of the wet material and prolongs the drying time to achieve the ideal drying effect.

2. The length has been reduced by two-thirds, and the factory area has correspondingly decreased.

3. The steel consumption of the machine is greatly reduced, and due to its reduced weight, the installed capacity is greatly reduced, resulting in a corresponding reduction in electricity consumption.

4. Good insulation effect and high heat utilization rate.

The process flow is as follows: wet materials are pushed into the feeding scraper conveyor, and the material layer is leveled by the leveling machine in front of the discharge port of the scraper conveyor. The material of equal thickness enters the feeding screw conveyor, and then is discharged into the outlet of the hot air furnace. The high-temperature hot air generated by the coal-fired hot air furnace is sucked into the three ring drum dryer for drying. The dried materials are sucked into the discharge system, and the mixed stones and other debris are deposited into the sedimentation device (regularly discharged). The dry materials are collected in the collector

(A) Conduct material air separation, dry materials are discharged into the cooling system through a closed air feeder, and the cooled dry materials are discharged through a cyclone feeder

(B) Discharge. Enter the packaging machine, bag and transport. A portion of the hot air discharged from the collector is discharged into the atmosphere, and most of it returns to the mixing chamber for heating. All units are controlled by the main control center, and the system is automatically controlled by a self-developed automatic control system. The heating system can use electricity, oil, gas, or coal at the user's discretion.

5 kiln drum dryer

6 drum dryer

Analysis of drying characteristics of a dryer Drying is divided into four stages

1.  AB section: preheating section, where the material enters the dryer through a scraper conveyor. Due to the action of high-temperature hot air, the material heats up and reaches the wet bulb temperature of the hot air. At this time, the moisture content of the material remains almost unchanged, and the temperature of the hot air slightly decreases. The heat released is mainly used for preheating the material.

2. BC section: Constant speed drying section, with a constant drying rate. There is always a layer of free water on the surface of the material in this section, and all the heat transferred by the hot air to the material is used for water vaporization. Therefore, the surface temperature of the material remains constant at the wet bulb temperature of the air, while the temperature of the hot air and the moisture content of the material rapidly decrease.

3. CD section: Drying enters the deceleration section. The internal water diffusion rate of the material is lower than the surface water vaporization rate, and there is not enough water on the surface of the material, resulting in a decrease in drying rate. The heat transmitted by air to the material is greater than the heat consumed by water vaporization, so the surface temperature of the material continuously increases and the air temperature further decreases. If the material temperature reaches the degree of absolute dryness, the material temperature will be consistent with the hot air temperature.

4. DE section: It is a cooling section where the moisture content of the material has decreased to the required value. It is discharged from the dryer and enters the cooling system, where cold air is supplied to quickly raise the temperature of the dried material slightly above room temperature. It is then directly bagged and transported outside.

Automatic control: Due to the adoption of a new high-temperature rapid drying process, the flow time of materials in the drying system is only a few minutes. To ensure drying quality, when the moisture content of wet materials changes, the corresponding drying parameters must undergo corresponding changes. This change must be completed by an automatic control system. In this drying system, our company designs and manufactures a unique control method. Firstly, the moisture content of the material after drying is set. During the drying process, regardless of changes in the initial moisture content and hot air temperature of the material, the automatic control system will automatically adjust the corresponding parameters to ensure the set moisture content of the dry material.

The following energy-saving measures are adopted for low drying costs:

1. High temperature rapid drying new process

2. Tail gas recycling: that is, most of the exhaust gas (around 100 ℃) is returned to the mixing chamber and reheated as a new drying medium.

3. Adopting the above measures of high-efficiency coal-fired hot blast furnaces to achieve a comprehensive thermal efficiency of over 76%

4. The installed capacity of the machine is only one eighth of that of a conventional drum dryer

5. Realize complete machine automation, save operators, and thus greatly save electricity.

6. Due to the use of high-temperature drying technology and the fact that the drying materials are all organic and have a low ignition point, there is a possibility of combustion and explosion during the drying process without special precautions. For this purpose, this system adopts:

The technology of exhaust gas recovery and hot air recirculation actually uses a drying medium similar to superheated water vapor, thereby preventing the possibility of combustion.

In case of emergency, the unit is equipped with a set of anti combustion and explosion-proof devices, which can prevent occasional combustion in the dryer or eliminate it without stopping the machine.

 It can be used for drying various sheet, fibrous, and granular materials with multiple functions. Such as: lees, peat soil, alfalfa grass, marigold, ginkgo biloba leaves, barley seedlings, Jerusalem artichoke meal, sugar beet residue, corn germ, vegetable stems and leaves, straw, Chinese herbal medicine, sawdust, and other materials.

Conclusion: Due to the adoption of a new high-temperature fast downstream drying process, the new multi ring drum dryer is an efficient and energy-saving combustion hot air stove. The original automatic control, system, and a series of safety and explosion-proof devices have successfully solved many difficulties in drying agricultural economic crops and agricultural by-products. After years of production practice testing, its main performance indicators have reached international standards and have Chinese characteristics: using coal as a drying heat source, it meets the drying requirements of low value-added products with low drying costs, and the market price is much lower than imported equipment. Therefore, its market share ranks first in the country and gradually moves towards the international market.