dryer[1]It refers to the process of using heat energy to reduce material moisturemechanical equipmentFor drying objects.The dryer vaporizes and escapes the moisture (generally refers to moisture or other volatile liquid components) in the materials through heating to obtain solid materials with specified moisture content.The purpose of drying is to meet the needs of material use or further processing.According to the operating pressure, dryers can be divided into atmospheric dryers and vacuum dryers. According to the operating pressure, dryers can be divided into atmospheric dryers and vacuum dryers (also known as vacuum dryersVacuum dryer）。The entry also introduces in detailadsorption type dryer、Refrigerated dryerandMicrowave dryer。
For example, the drying of wood before making wood molds and woodwork can prevent products from deformation, and the drying of ceramic blanks before calcination can prevent finished products from cracking.In addition, after dryingmaterielIt is also convenient for transportation and storage, such as drying the harvested grain below a certain moisture content to prevent mildew.Since natural drying is far from meeting the needs of production development, various mechanized dryers are increasingly used.
The amount of water vapor in the compressed air is determined by the temperature of the compressed air: under the condition of keeping the pressure of the compressed air basically unchanged, reducing the temperature of the compressed air can reduce the content of water vapor in the compressed air, and the excess water vapor will condense into liquid.Freeze dryerThis principle is used to dry compressed air with refrigeration technology.thereforeCold dryerWith refrigerationsystem。The refrigeration system of the freeze dryer belongs to compression refrigeration, which is composed of four basic components, namely, refrigeration compressor, condenser, evaporator, expansion valve, etc.They are connected by pipes in turn to form a closed system. Refrigerant flows continuously in the system, changes its state and exchanges heat with compressed air and cooling medium.Compressed air dryer andadsorption type dryerandDissolving dryer。
The refrigeration compressor sucks the low pressure (low temperature) refrigerant in the evaporator into the compressor cylinder, and the refrigerant steam is compressed, and the pressure and temperature rise at the same time;The refrigerant steam with high pressure and temperature is pressed to the condenser. In the condenser, the refrigerant steam with higher temperature exchanges heat with the cooling water or air with lower temperature. The heat of the refrigerant is taken away by the water or air and condensed, and the refrigerant steam becomes liquid.This part of liquid is then sent to the expansion valve, throttled into low temperature and low pressure liquid through the expansion valve and enters the evaporator;The cryogenic and low-pressure refrigerant liquid in the evaporator absorbs the heat of the compressed air and vaporizes (commonly known as "evaporation"), and the compressed air condenses a large amount of liquid water after being cooled;The refrigerant vapor in the evaporator is sucked away by the compressor, so the refrigerant will go through four processes of compression, condensation, throttling and evaporation in the system, thus completing a cycle.
In the refrigeration system of the freeze dryer, the evaporator is a device for conveying cold energy, in which the refrigerant absorbs the heat of the compressed air to achieve the purpose of dehydration and drying.The compressor is the heart, which plays the role of inhaling, compressing and transporting refrigerant vapor.The condenser is a device that emits heat. It transfers the heat absorbed in the evaporator to the cooling medium (such as water or air) along with the heat converted by the input power of the compressor.The expansion valve/throttle valve is used to throttle and depressurize the refrigerant, control and regulate the amount of refrigerant liquid flowing into the evaporator at the same time, and divide the system into high pressure side and low pressure side.
classification
Modern dryers began to use fixed bed dryers operated intermittently.In the middle of the 19th century, the use of tunnel dryer marked the development of dryer from intermittent operation to continuous operation.The rotary drum dryer can better realize the agitation of granular materials, and the drying capacity and strength can be improved.Some industries have developed continuous operation dryers to meet the requirements of the industry, such as textile and paper industriesDrum dryer。
In the early 20th century, dairy production began to applySpray dryerIt provides a powerful tool for large-scale drying of liquid materials.Since the 1940s, with the development of fluidization technologyproductivityThe fluidized bed and the air flow dryer appeared one after another.The freeze sublimation, radiation and dielectric dryers provide new means to meet special requirements.In the 1960s, far-infrared andMicrowave dryer。
There are many types of mechanical equipment used for drying operation, which can be divided into normal pressure and reduced pressure (also called reduced pressure dryerVacuum dryer）。According to the operation method, it can be divided into intermittent type and continuous type.according toDrying mediumIt can be divided into air, flue gas or other drying media.According to the movement mode (material movement and drying medium flow), it can be divided into parallel flow, countercurrent flow and cross flow.
According to the operating pressure, dryers are divided into normal pressure dryers and vacuum dryers. Operating under vacuum can reduce the partial pressure of wet partial steam in the space, accelerate the drying process, and reduce the boiling point of wet partial steam and materialsdrying temperatureThe steam is not easy to leak out, so the vacuum dryer is suitable for drying heat sensitive, oxidizable, explosive and toxic materials as well as wet separated steam that needs to be recycled[2]。
4. Imported pneumatic controller with unique characteristics of high power and durability
5. Regeneration gas regulating valve with precise flow regulation
According to the heating mode, the dryer is divided into convection type, conduction type, radiation type, dielectric type, etc.Convection dryer, also known as direct dryer, uses hot drying medium to directly contact wet materials to transfer heat by convection and take away the generated steam;Conductive dryerAlso called indirect dryer, it uses conduction mode to transfer heat from heat source to wet materials through metal partition wall. The generated wet partial steam can be sucked under reduced pressure, a small amount of purge gas can be introduced, or at a separately set low temperaturecondenserRemove by surface condensation and other methods.This kind of dryer does not use drying medium, and its thermal efficiency is high, and the product is not polluted. However, its drying capacity is limited by the heat transfer area of the metal wall, and its structure is complex, so it is often operated under vacuum;The radiation dryer uses various radiators to emit electromagnetic waves of a certain wavelength range, which are selectively absorbed by the surface of wet materials and then converted into heat for drying;The dielectric dryer uses the high-frequency electric field to dry the wet materials with thermal effect inside.
Advantages:
1. High performanceevaporatorLarge heat exchange area, small heat transfer temperature difference, evaporator outletair temperature More stable
2. High efficient gas water separation structure is adopted, with high oil-water separation efficiency;
According to the motion mode of wet materials, dryers can be divided into fixed bed type, stirred type, spray type and combined type;According to the structure, the dryer can be divided into box dryerConveyorType dryer, drum dryerVertical dryer, mechanical stirring dryer, rotary dryerfluidized bedType dryer, air flow dryer, vibration dryer, spray dryer and combination dryer, etc.
Common sense of drying equipment: common predryerCommonspray drying Device,Air dryer, fluidized bed dryer,Flash dryerFluidized bed dryer, such as spray granulation.Spray drying spray drying is one of the most advanced drying equipment.Three kinds of traditional atomization: rotary atomization,Pressure atomizationAnd airflow atomization.Rotary atomization features a large spray drying capacity (the spray volume can reach 200 tons/hour), which will be responsible for easy control, flexible operation, and wider application.The feature of pressure atomization spray drying is that coarse particles can be created for future maintenance.Since the nozzle hole is very small and easy to block, the liquid must be filtered strictly.The nozzle hole is easy to wear, and the use of wear-resistant materials.There is also a new structure of nozzle pressure, called pressure flow nozzle.It is characterized by nozzle pressure, ambient air gap nozzle.Atomization is divided into two stages: the first is to form a liquid film pressure nozzle, and the second is to atomize air, so as to make more small water droplets.The advantages of this type of nozzle are: (1) adjusting the pressure of compressed air can adjust the diameter of liquid droplets, which is simple to operate;(2) Production, high viscosity liquid, which can be atomized into fine droplets;(3) If you disable compressed air, the original pressure nozzle can be used[8]。Atomizing airflow in the laboratory and in the middle of the main plant, it consumes electricity.The first two cannotAtomizing nozzleThe liquid can be atomized in the air.High viscosity paste, paste and filter cake materials can be used for atomization of three fluid nozzles.The drier air flow drying technology is mature, if the operating data can be directly designed.
Fluidized bed dryer Fluidized bed dryer Spray dryer.Feeding setting is divided into partial fluidized bed dryerAgitatorAnd heat transfer fluidized bed dryer.When the unity is easy to use in the fluidized bed drying, or more water will flow into the feed of aggregated powder materials, the above difficult phenomenon will occur. At this time, the feed mixer is set up to eliminate the cluster problem to achieve normal flow.The latter is a combination of heat conduction and convection heat exchange. In countries where the normal flow of hot air during use is far from enough, the heat exchanger set to meet the needs of heat drying is used to supply some or most of the heat. What types of operations can greatly save energy.Various forms of heat exchangers are adopted.Fluidized bed drying is also often used for combination drying of secondary and higher education.Implement commonVibrating fluidized bedSaid the vibrating fluidized bed.The vibration sources with one flowing vibration can be divided into two categories: one isVibrating motorDrive, others are ordinary motors that generate vibration through the vibration box to make the spring.When vibrating, the bed size, the latter is better.fluidized bedSpray granulation dryerIn the process, fluidization technology, atomization technology and drying are organically combined.It is a catapult that will inject atomized spray liquid into the fluidized bed, so the seeds will continue to grow and dry to reach the required scale and time.The small and large production capacity of the device can create large particles.The industrial application of this equipment has been increasing.
Changzhou is the hometown of drying equipment in China, and is now the largest industrial cluster of drying equipment in China. The number of drying equipment enterprises is the first in the country, and the products also occupy 40% of the national market. The drying products are exported to more than 30 countries and regions, such as the United States, Japan, France, South Africa, etc.In 2010, the drying industry formulated 18 "national standards", and Changzhou drying enterprises participated in the whole process.
development
Rice is the most important food crop for urban and rural residents in China.In a normal year, China's annual output of rice is about 200 million tons. The rich rice resources provide an important material basis for the development of China's rice processing industry.
In 2010, there were 5666 rice processing enterprises above designated size with an annual production capacity of 94.63 million tons, including 4741 enterprises with a daily processing and drying capacity of less than 100 tons, 754 enterprises with a daily processing and drying capacity of 100-200 tons, 132 enterprises with a daily processing and drying capacity of 200-400 tons, 38 enterprises with a daily processing and drying capacity of 400-1000 tons, and 10 enterprises with a daily processing and drying capacity of more than 1000 tons.
In the 1950s, machines such as cleaning screen, stone remover and "59" grain coarse separation sliding screen appeared;In the 1960s and 1970s, a complete set of rice milling equipment with a daily output of 30 tons and 50 tons, a horizontal rotating coarse grain screenGravity grain separator, air jet rice machine, rice polishing machineBeige sorterThe birth of the equipment such as the grain and brown separation equipment and white rice finishing equipment;In the 1990s, technical research on rice finishing and drying conditioning technology, research on key technical equipment and comprehensive demonstration project of brown rice circulation, research and development of post production finishing and fresh-keeping technology and equipment of high-quality rice, and research and development of rice deep processing technology were completed.
Rice Branch of China Food Industry AssociationAccording to the staff of, the birth of these equipment technologies can show that China attaches great importance to the research of rice processing technology.
In the middle and late 1990s, China's rice processing equipment manufacturing industry entered a period of rapid development.
In March 2011, China's first clean grain dryer invented by farmers was born in Hunan!
As private capital entered the field of rice processing machinery production, the original state-owned grain machinery factory began to gradually transfer to private capital.These grain machine factories have independently developed a variety of new equipment. The main equipment widely used in large and medium-sized rice processing plants are vertical rice milling machines, low-temperature rising rice milling machines, rice polishing machines, rice drum cleaning machines, large rice color sorting machines, gravity grain separator, brown rice cleaning machines, rice fresh-keeping packaging machines, rice bran expanders, low crushing elevators, rice blending devices, etc.
However, in the face of multinational enterprises with advanced technology development capabilities, China's indigenous rice processing machinery enterprises, with weak funds and poor research and development capabilities, have become an important factor constraining the development of enterprises.
Some experts said that with the further improvement of the dietary structure of Chinese residents, China's rice processing industry will further increase its technological upgrading efforts.
"In the future, we should focus on the development of fine processing of high-quality rice, attach importance to the development and application of technologies such as fine grinding, conditioning and finished product finishing in the processing process, vigorously develop multiple uses such as rice bran and other by-products for oil making, and support the development of enterprises with reasonable scale in the direction of five series of products, namely, high rice yield, refined rice, special rice, deep processing of broken rice, rice additives and comprehensive utilization of rice husk and rice bran."
Dryer selection
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model selection
① Original shape particles, powders, particles, sludge, crystals, liquids, pastes, suspensions, solutions, continuous sheets, thick plates, irregular materials (small or large), viscous or blocky materials, etc.
② Average output Continuous operation feeding amount or finished product, intermittent operation feeding amount or finished product and its adjustment range, etc.
③ Finished product particle condition Average particle size, particle size distribution, particle density, bulk density, rehydration, etc.
④ Material inlet and outletWater contentDry basis, wet basis.
⑤ Material properties Chemistry, biochemistry, microbial activity, heat sensitivity (melting pointGlass transition temperature）, moisture absorption isotherm (equilibrium moisture content), etc.
⑥ Drying time drying curve and the influence of operating parameters.
⑦ Heater contact mode (direct and indirect).
⑧ The fuel shall be steam, coal, electricity, oil and gas.
⑨ Drying auxiliary equipment fan, dry dedusterWet dust collectorFeeder, discharger, finished product cooling and conveying device, etc.
⑩ Special requirements: composition material, corrosiveness, toxicity, non hydrophilic solution, flammability and explosive limit, ignition point, color, structure, fragrance requirements.
⑩ Floor area of drying equipment and auxiliary equipment of drying system.
Equipment installation and commissioning process and general requirements
Unpacking acceptance
After the arrival of new equipment, the equipment management department, together with the purchasing unit and the user unit (or receiving unit), shall carry out unpacking acceptance to check whether the equipment is damaged or lost during transportation, and whether there are accessories and random spare parts.Whether the special tools and technical data are consistent with the contract.The packing list shall be consistent, and the equipment unpacking acceptance sheet shall be filled in and stored in the equipment file. In case of any defect or nonconformity, the relevant unit shall be immediately consulted for handling, claim or claim.
Equipment installation construction
Line out and position according to the equipment process layout plan, installation construction drawing, foundation drawing, equipment outline size, mutual spacing and other requirements drawn by the process technology department, and organize the foundation construction and equipment transportation in place.When designing the equipment process layout plan, the following factors shall be considered for equipment positioning.
(1) It shall meet the needs of process flow
(2) It shall be convenient for the storage, transportation and site cleaning of workpieces
(3) External dimensions of equipment and its accessories, limit positions and safety distances of moving parts
(4) The safety requirements for equipment installation, maintenance and operation shall be ensured
(5) The plant and equipment work match, including the width and height of the door, the span and height of the plant, etc
The equipment installation and leveling shall be carried out according to the requirements of relevant specifications for mechanical equipment installation and acceptance to ensure stable installation, reduce vibration, avoid deformation, ensure machining accuracy and prevent unreasonable wear.Before installation, technical disclosure shall be carried out, and construction personnel shall be organized to carefully study relevant technical data of equipment, understand equipment performance, safety requirements and construction matters.
During installation, the construction of foundation fabrication, assembly link, electrical circuit and other items shall be strictly in accordance with the construction specifications.If there are special requirements such as constant temperature, shockproof, dustproof, moisture-proof, fire prevention, etc. in the installation process, measures shall be taken, and the construction of this project can be carried out only after the conditions are met.
Equipment commissioning
The equipment test run can generally be divided into idle test, load test and accuracy test.
(1) Idling test: it is to check the maintenance of equipment installation accuracy, the stability of equipment, and whether the transmission, manipulation, control, lubrication, hydraulic and other systems are normal, sensitive and reliable, and other relevant parameters and performances are carried out under the operating condition without Beethoven.A certain period of no-load operation is an indispensable step for running in of new equipment before it is put into use.
(2) Load test of equipment: the test equipment is tested under several standard load conditions, and in some cases.During the load test, check the temperature rise of the bearing according to the specification, and check whether the hydraulic system, transmission, operation, control, safety and other devices work up to the factory standard, and whether they are normal, safe and reliable.The test run under different load conditions is also a necessary work for new equipment running in. The quality of running in test has a great impact on the service life of equipment.
(3) Accuracy test of equipment: generally, it shall be carried out according to the provisions of the instruction after the load test. It is necessary to check the geometric accuracy of the equipment itself as well as the accuracy of the work (processing products).This test is mostly conducted two months after the equipment is put into use.
Work after operation
First disconnect the main circuit and power source of the equipment, and then check and record the following equipment:
(1) Clean, lubricate and fasten the equipment after running in, replace or repair faulty parts and conduct commissioning to make the equipment enter the best use state;
(2) Make and sort out the inspection records of the geometric accuracy and machining accuracy of the equipment and the test records of other functions;
(3) Sort out the records of equipment commissioning (including troubleshooting);
(4) For the problems that cannot be adjusted, analyze the reasons and summarize them from the aspects of equipment design, manufacturing, transportation, storage, installation, etc.
(5) Make assessment conclusions and handling opinions on equipment operation, handle handover procedures, and indicate the personnel and date participating in the commissioning.
5) Acceptance and handover of equipment installation works.
(1) The construction acceptance of equipment foundation shall be carried out by the quality inspector of the construction department together with the civil construction workers, and the construction acceptance form shall be filled in.The construction quality of the foundation must meet the foundation drawing and technical requirements.
(2) The final acceptance of equipment installation works shall be carried out after the equipment commissioning is qualified.The equipment management department, the process technology department, together with other departments, shall carry out the acceptance with the participation of relevant personnel from all aspects of installation, inspection, safety, use, etc., make identification, fill in the installation construction quality, accuracy inspection, safety performance, commissioning and operation records and other vouchers and the acceptance transfer sheet, and the completion can be completed only after the personnel from all parties participating in the acceptance sign.
(3) Handle handover procedures after equipment acceptance
The equipment unpacking acceptance (or the equipment installation handover acceptance form), the equipment operation test record sheet shall be signed by the personnel participating in the acceptance, and the technical documents brought with the equipment shall be included in the equipment file management by the equipment management department;For accessories and spare parts accompanying the equipment, the spare parts warehousing form shall be filled in and delivered to the equipment warehouse for warehousing.The safety management department shall file the safety problems in the installation test.
(4) After the equipment is handed over, the equipment management department shall sign the equipment production notice, and submit the copies to the equipment management department, the user unit, the financial department, and the production management department as the basis for filing, notification of starting to use, fixed asset management certificate, and assessment of the project plan.
Small dryer
Dehydration dryer product description: Dehydration and drying are carried out at the same time, without water stains and stains, which can avoid workpiece oxidation or rust, and improve the gloss and quality of finished products;Dewatering tank isStainless steel materialIt is firm and durable, and the inner blue can be pulled out, which is convenient for assembling and taking workpieces;
Dehydration dryerEquipped with pedal brake to improve the safety of use;The automatic control power supply system is adopted to automatically cut off the power supply when the dehydration and drying are completed or the stainless steel cover is opened. The machine adopts a casting and milling base with a stable center of gravity. The inner and outer cylinders are made of stainless steel, which is solid and durable;The heater is equipped with a stainless steel cover for direct heating. The power supply and brake system are automatically controlled.
Features of dehydration dryer: applicable to variousmetal partsIt is used for dehydration and drying after grinding and polishing, dipping in antirust liquid;All electroplating, grinding and polishing plants are equipped with necessary drying machines.
Dehydration dryer is also called centrifugal dryer, hot air dryer and air dryer
The humid and high-temperature compressed air flows into the pre cooler (special for high-temperature type) for heat dissipation and then flows into the heat exchanger to exchange heat with the cold air discharged from the evaporator, so as to reduce the temperature of the compressed air entering the evaporator[3]。
The compressed air after heat exchange flows into the evaporator and exchanges heat with the refrigerant through the heat exchange function of the evaporator. The heat in the compressed air is taken away by the refrigerant, and the compressed air cools rapidly. The moisture in the humid air reaches the saturation temperature and condenses rapidly. The condensed moisture forms water droplets after condensationGas water separatorHigh speed rotation, water is separated from air by centrifugal force, and water is discharged from the automatic drain valve after separation.The minimum dew point of air pressure after cooling can reach 2 ℃.
The cooled cold air flows through the air heat exchange to conduct heat exchange with the high-temperature moist hot air at the inlet. The temperature of the cold air after heat exchange is increased because it absorbs the heat of the inlet air. At the same time, the compressed air also passes through the secondary condenser of the refrigeration system (unique design of the industry) to conduct heat exchange with the high-temperature refrigerant again to fully heat the outlet temperature,Ensure that the outlet air line is free from condensation.At the same time, the cold source of the outlet air is fully utilized to ensure the condensing effect of the machine refrigeration system and the quality of the machine outlet air.
Main spare parts
① Compressor
At present, most of the refrigeration compressors used in freezers and dryers are fully sealed at medium and high temperatureReciprocating compressorIt is characterized by compact structure, small volume, light weight, small vibration, low noise and high energy efficiency ratio.Since the motor and the main body of the fully sealed compressor are sealed in a steel housing, the motor operates in a gaseous refrigerant environment, with good cooling conditions and long service life.There is a specified amount of lubricating oil in the lower part of the housing. When the compressor is working, it automatically supplies oil to each part, and it is not necessary to add lubricating oil at ordinary times.Semi sealed reciprocating machine orscrew compressor They are characterized by large cooling power and can be load adjusted to meet different needs.
② Heat exchange, evaporator
The main function of heat exchange in the cold dryer is to use the cooling capacity carried by the compressed air after being cooled by the evaporator (for most users, this cooling capacity is waste cooling) and use this cooling capacity to cool the high temperature compressed air carrying a large amount of water vapor, thus reducing the heat load of the cooling system of the cold dryer and achieving the purpose of energy conservation.On the other hand, the temperature of low-temperature compressed air in the heat exchanger rises again, so that the outer wall of the exhaust pipe will not be dewed due to low temperature.
The evaporator is the main heat exchange part of the cold dryer. The compressed air is forced to cool in the evaporator, and most of the water vapor is cooled and condensed into liquid water and discharged out of the machine, so that the compressed air can be dried.The convection heat and mass exchange between air and refrigerant low-pressure steam is carried out in the evaporatorThrottling deviceThe later low-pressure refrigerant liquid will change into low-pressure refrigerant steam in the evaporator and absorb the surrounding heat during the phase change process, thus cooling the compressed air.
In order to obtain a higher heat transfer effect as far as possible, the heat release coefficient must be increased, that is, the heat exchange area of the heat exchanger must be added. Therefore, the outer wall of the copper tube of the evaporator and heat exchanger of the dryer is covered with aluminum fins.At the same time, the fin set on the copper tube of the heat exchanger can reduce the impact of air on the copper tube and prevent the copper tube from cracking.
③ Condenser, secondary condenser (precooling recuperator)
The function of the condenser in the dryer is to cool the high-pressure and superheated refrigerant vapor discharged from the refrigerant compressor into liquid refrigerant, so that the refrigeration process can be carried out continuously.The heat discharged by the condenser includes the heat absorbed by the refrigerant from the evaporator and the heat converted from the compression work.Therefore, the load of the condenser is greater than that of the evaporator. The condenser in the dryer is divided into air cooled (air cooled condenser) and water cooled (water cooled condenser).
The secondary condenser (precooling recuperator) has the same function as the heat exchange in the machine. The difference between the two is that the heat exchanger is mainly used for heat exchange of high temperature and low temperature compressed air, while the secondary condenser mainly uses low temperature compressed air and the high-pressure part of the refrigeration system for cooling, so that the refrigerant can be fully cooled, thus improving the refrigeration efficiency of the machine,At the same time, avoid high-pressure tripping or machine failure caused by poor heat dissipation of the machine condenser.
Cyclone separator is also a kind ofInertial separator, which is mostly used for gas-solid separation.After the compressed air enters the separator along the tangent direction of the cylinder wall, it will rotate inside, and the water droplets mixed in the gas will also rotate together and generate centrifugal force. The large water droplets will generate large centrifugal force, and under the action of centrifugal force, the large water droplets will move towards the outer wall, and will gather and grow up after touching the outer wall (also the baffle) and separate from the gas.
⑤ Hot gas bypass valve
When the compressed air is cooled in the evaporator, a large amount of condensed water is separated.If the refrigerant evaporation temperature is too low, so that the surface temperature of the copper tube of the evaporator is lower than the freezing point of water under load conditions, the condensed water will freeze in the evaporator, which will seriously block the air flow channel and paralyze the air supply pipeline.In order to prevent this situation, the refrigerant evaporation temperature must be controlled.The simple and effective measure is to add a hot gas bypass valve between the condenser and evaporator, and the pressure measuring pipe of the hot gas bypass valve is directly connected with the evaporation pressure.When the evaporation pressure is lower than a certain level, the hot gas bypass valve automatically opens, and the high-temperature refrigerant steam in the condenser directly enters the evaporator to increase the evaporation temperature and avoid ice blockage.
The expansion valve (capillary) is the throttling mechanism of the refrigeration system.In the refrigeration dryer, the supply of evaporator refrigerant and its regulator are realized by throttling mechanism.The throttling mechanism allows refrigeration from high-temperature and high-pressure liquid to enter the evaporator.When the load changes, the thermal expansion valve adjusts the opening of the valve core by detecting the suction overheat temperature of the compressor, so as to control the supply of refrigerant into the evaporator.The capillary tube has the feature of self compensation, that is, when the evaporation pressure decreases, the pressure difference at both ends will increase accordingly, thus increasing the amount of refrigerant flowing into the evaporator.Capillary tubes are widely used in small freezers because of their simple structure and stable operation.
⑦ Automatic drain valve
stayRefrigerated dryerThe condensed condensate shall be discharged out of the equipment in time to avoid the rise of air moisture content due to the untimely discharge of condensate. In order to facilitate the discharge of condensate, the equipment is equipped with an automatic drain valve. When the water level in the drain valve water storage cup does not reach a certain height, the pressure of compressed air will press the floating ball down to close the drain hole,It will not cause air leakage: as the water level in the water storage cup rises (there is no water in the dryer at this time), the drain hole will be opened when the float rises to a certain height, and the condensed water in the cup will be discharged out of the machine quickly under the action of air pressure.Floating ball type for exceptionAutomatic drainerIn addition, electronic automatic drainer is often used. The time and interval of two drainages can be adjusted, and the drainer can withstand high pressure. It is also widely used.
⑧ Drying filter
As there are impurities such as moisture, solid powder and dirt in the refrigerant and refrigeration oil of the refrigeration device in operation, the orifice of the throttling structure will be dirty and blocked in serious cases.Therefore, it must be installed before the refrigerant liquid supply pipeDrying filter。In addition, the trace moisture in the refrigerant is the most harmful to the refrigeration system.It is very important to dry refrigerant, refrigerant oil, evaporator, condenser and piping.
principle
After startup, the refrigerant is compressed by the compressor from the original low temperature and low pressure state to high temperature and high pressure steam.The high-temperature and high-pressure steam flows into the condenser and the secondary condenser. Its heat is taken away by the cooling medium through heat exchange, and the temperature drops. The high-temperature and high-pressure steam becomes the liquid with normal temperature and high pressure because of condensation.The liquid refrigerant with normal temperature and high pressure flows through the expansion valve. Because the throttling pressure of the expansion valve decreases, the refrigerant becomes the liquid with normal temperature and low pressure.After the liquid at normal temperature and low pressure enters the evaporator, due to the decrease of pressure, the liquid refrigerant boils and evaporates into a gas at low pressure and low temperature. When the refrigerant evaporates, it absorbs a large amount of heat from the compressed air, making the temperature of the compressed air drop to dry.The evaporated low temperature and low pressure refrigerant vapor flows back from the suction port of the compressor and is compressed and discharged into the next cycle.
adsorption type dryer
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In many applications similar to the application of precision electronics industry or high-precision instruments, when the pressure dew point in the compressed air needs to be reduced to below 0 ℃ due to the process requirements, pipeline icing will occur when the pressure dew point of the refrigerated dryer is lower than 0 ℃. At this time, the use of refrigerated drying can no longer meet the process requirements,While introducing advanced manufacturing technology of freezing dryer, our company also introduced the manufacturing technology of heatless adsorption dryer, whose minimum dew point temperature can be - 70 ℃;At the same time, high-quality materials such as imported stainless steel pneumatic valve and stainless steel one-way valve are used to avoid pipeline pollution and improve air quality.While introducing and absorbing, in combination with domestic application experience, the micro heat dryer andCombined dryerTo reduce the air consumption of compressed air, the minimum air consumption can reach 5%.To meet the needs of different users[4]。
Product flow chart and working principle of heatless dryer
A large amount of air discharged from the air compressor flows into the operating tower of the two towers through the compressed air inlet pipe, and the moisture will be absorbed by the adsorbent and dried.When the air flows to the tower top, the moisture in the air is fully absorbed, and the dew point temperature can reach - 40 ℃, so as to achieve the drying purpose.The whole cycle standard takes 10 minutes, and each tower runs for 5 minutes. One tower is in operation (operating tower), and the other tower is in regeneration state (non operating tower). The regeneration time is 4.5 minutes, and the continuous pressure time is 0.5 minutes.During regeneration, some dry air in the operating tower is regeneratedAir volume regulating valveEnter the non operating tower to carry the water in the tower to the atmosphere through the silencer.The gas consumption during operation is 12% of the equipment processing capacity.
Product flow chart and working principle of micro heat dryer
A large amount of air discharged from the air compressor flows into the operating tower of the two towers through the compressed air inlet pipe, and the moisture will be absorbed by the adsorbent and dried.When the air flows to the tower top, the moisture in the air is fully absorbed, and the dew point temperature can reach - 40 ℃, so as to achieve the drying purpose.The whole cycle standard takes 4 hours, and each tower operates for 2 hours. One tower is in operation (operating tower), and the other tower is in regeneration state (non operating tower). The regeneration time is 1.5 hours, and the cooling and pressure continuation time is 0.5 hours.In the process of regeneration, a part of dry air in the operating tower enters the heater for heating through the regenerative air volume regulating valve and then enters the non operating tower to carry the water in the tower to the atmosphere through the silencer.The gas consumption during operation is 7% of the equipment processing capacity.
Product flow chart and working principle of heatless combined dryer
The working principle of the machine refers to the freezing dryer andHeatless adsorption dryerWorking principle: the regenerative air volume can be reduced to 5% at least when combined.
Precautions for adsorption dryer
Oil content of tower inlet air shall be controlled below 0.01mg/m3;WhereasOil free air compressorAt present, it is impossible to be truly oil-free. In order to prevent the accumulation of trace oil in the adsorption bed (this accumulation is fast), it is necessary to install an oil remover at the air inlet of the dryer[5]；
The adsorption dryer shall be used under the rated temperature and pressure. When the inlet air temperature is higher than or the inlet air pressure is lower than the rated value, the capacity shall be corrected;
Adsorption dryer andPiston type air compressorFor continuous use, a pressure stabilizing gas storage tank shall be set in front to eliminate the high-speed impact of pulsating air flow on the adsorbent;
Never deliberately "save energy" to reduce regeneration gas consumption (including regeneration gas volume and heating power);When there is a "front dryer", the connection between the adsorption dryer and the dryer should be installed separately as far as possible as the site permits, so as to reduce the air pressure drop, improve the ventilation conditions of the dryer and facilitate daily maintenance and overhaul;
When the air supply is sufficient, the heatless regeneration dryer should be listed as the first choice. Its comprehensive energy consumption will not be higher than that of heating regeneration, and its dew point is lower and more stable.
Microwave dryer
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Combining microwave with traditional heating and drying technology, large microwave power application equipment is mainly used in heating and drying and food processing[6]。However, from the perspective of demand, microwave power application equipment has not yet met the needs of many fields.Due to the popularity of household microwave ovens, many enterprises have made feasibility tests in household microwave ovens with the intention of improving production, or have seen signs of improvement, which needs further promotion. However, the existing microwave power equipment cannot fully meet these requirements, that is, as far as microwave heating and drying are concerned,There is still a lot of pioneering work to be done in microwave power engineering.These fields mainly include high temperature treatment of non-metallic materials, heat setting of polymers, absolute drying of chemical materials, de crystallization water, drying of glass fibers, low-temperature drying of various biochemical materials, and vacuum dehydration drying of food.In some fields of heating and drying, traditional methods have carried out a lot of research work.For example, the drying method focuses on the most effective way to drain water in different states, spray drying, vulcanization bed drying, vibrating vulcanization bed drying, tumbling drying, and vacuum drying, all of which are based on the contact between different states of materials and hot air.If microwave energy is properly introduced, it is possible to accelerate the drying process and improve the drying quality.Microwave methods in these fields should be combined with traditional methods to supplement the weakness of insufficient heat supply to materials. Microwave heating can be used.The advantages of traditional methods should also be used to dredge and discharge moisture, which requires the reform of the original equipment to be compatible with the feeding microwave power and the measures to prevent microwave leakage.Drying of many materials, andNon metallic materialsThe density of large microwave power equipment is not high enough, and the design of equipment with high field intensity density is expected to improve the heat treatment method of non-metallic materials. It is theoretically estimated thatChemical materialsGood results will be achieved by the absolute dry treatment of.Unify the electromagnetic field power engineering method, in order to improve the production conditions and make efforts for the progress of cutting-edge research, from many reported literatures, the design method of foreign RF heating equipment is intended to be gradually close to the microwave power, that is, develop the so-called 50 Ω RF industrial heating technology, and the standard RF equipment should be composed of the following four parts: (1)RF oscillator with 50 Ω output impedance;(2) 50 Ω coaxial line connecting RF oscillator and matching box;(3) A matching box with a control and discriminator discriminant;(4) Application.In other words, the development direction of RF power equipment is no longer unified equipment, but can also be assembled with general-purpose components, and the oscillation source and application can be separated as needed (the current F industrial equipment can not meet this requirement at all).This working method is actually consistent with the development method of microwave power equipment;That is, the method of assembling equipment according to standard parts.At the same time, the RF power output is planned to use crystal oscillator feeding amplifier to stabilize the frequency and control the power;This scheme and further improvement of microwave power source;The idea of using quadrature field amplifiers to form oscillation circuits from active microwave networks is the same, which is called Stabililotron.The output power of the frequency stabilizer at 2450MHz is 10-50KW and 10-100KW.The typical Rf use frequencies are 13.56MHz, 27.12MHz and 40.68MHz. At present, there is a trend to increase the use frequency. The trial produced Klystron uses 267MHz as a high power industrial application, while the microwave power application frequencies are 2450MHz and 915MHz, with a trend of 434MHz.From the perspective of equipment design method, RF equipment and microwave equipment are gradually approaching, while the use frequency of microwave is expanding downward, and the use frequency of RF is rising.That is, the two are extended up and down, and further connected into a unified electromagnetic power equipment. In fact, microwave power equipment and radio frequency power equipment are the two leaves of electromagnetic power equipment. We should use the unified perspective of electromagnetic power application to deal with the scheme. Radio frequency and microwave have their own strengths and weaknesses, so we should use their strengths and avoid their weaknesses,It makes the electromagnetic field power equipment of China more reasonable and practical.The power engineering of microwave and RF electromagnetic fields is mainly in the fields of heating and drying, material processing and gas discharge. It has a wide range of applications and is very close to the actual production. It is not only an improvement of the traditional heating and drying methods, but also an important tool for many important research methods at present.At present, we should make some overall plans on the basis of investigation and research.The weak links of heating and drying in which industries exist, and the frequency band and technical means to deal with electromagnetic field power equipment, are more reasonable.What problems exist in the weak links of the equipment foundation in the current cutting-edge research work using radio frequency and microwave methods? The infrastructure should be gradually strengthened to effectively promote the cutting-edge research work[7]。
expectation
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characteristic
The future development of dryers will be based on in-depth study of drying mechanism and drying characteristics of materials, grasp the optimal operating conditions for different materials, and develop and improve dryers;In addition, large-scale, high strength, high economy, and improving the adaptability to raw materials and product quality are the basic trends of dryer development;At the same time, we will further research and develop new efficient dryers that meet special requirements, such as combined dryers, microwave dryers and far infrared dryers.
development potential
The development of dryers should also pay attention to energy conservation and comprehensive utilization of energy, such as adopting various combined heating methods, transplanting heat pump and heat pipe technology, and developingSolar dryerEtc;We need to develop the dryerAutomatic control technologyTo ensure the realization of optimal operating conditions;In addition, as people attach importance to environmental protection, improving the environmental protection measures of dryers to reduce the leakage of dust and waste gas will also be the direction of in-depth research.
ChinaDryer equipmentThe current situation of the market and the analysis of the current needs of the United Nations, the conventional drying equipment in the domestic market and the main drying equipment in the international market are basically made in China, which indicates that the history of import oriented drying equipment in China has ended.However, there are still some problems and difficulties. According to ChinaGeneral machineryThe drying equipment industry association predicts that the chemical industry will have about 3000 sets of drying equipment for China's demand in the next few years;The annual demand of pharmaceutical drying equipment will reach about 3000 (sets);The annual demand of agriculture, forestry, grain, light industry and other industries, such as drying equipment, is expected to reach about 5000 (sets).The share of drying equipment in the domestic market has reached more than 80%.
It is estimated that during the Tenth Five Year Plan period, China's drying equipment will occupy 90% of the domestic market.There are two ways to focus on the regions with performance problems and technological innovation capability.Most of the manufacturing enterprises in China's drying equipment industry have gradually formed early enterprises on the basis of the industry. The relatively concentrated geographical location and personnel structure have serious defects.So far, enterprises are mainly distributed in Jiangsu, Zhejiang, Shanghai and Liaoning, accounting for almost 50% of the total number of enterprises in the whole industry. In contrast, there are no drying equipment manufacturers in some regions of China.In highly competitive industries, some companies focus on the immediate results, do not need any systematic development, improve the overall quality, and progress is slow, seriously hampering the normal development of the industry.Since the reform and opening up, especially in recent years, China's economic growth potential has been effectively released, and the supply and demand of the shortage economy have undergone fundamental changes, initially forming a buyer's market.In the buyer's market under pressure, some enterprises catch up in the market instead of looking for and developing new markets. Enterprises focus on the demand of the market in the near future and more mature products.So, in the oven,Vibrating fluidized bed dryerWith other products, manufacturers are more concentrated and competitive.The drying equipment industry is mainly engaged in the development of small enterprises, new products, and perfect launch of new products to imitate each other.It is suggested to develop advanced technology and improve product quality. Compared with the developed countries in the world, China's drying equipment technology still has a certain gap in the same industry.The current market is dominated by products with low technology content.China's accessionWorld Trade OrganizationThere will be more international peers entering the domestic market. With the increasingly serious international competition, we will face tremendous competitive pressure.The world's leading manufacturer of drying equipment, such asDenmarkNello Group Co., Ltd. Dahe originally set up branches in Japan, one after another, to seize the Chinese market.With the acceleration of economic globalization, more companies will target the Chinese market.The increasingly fierce competition requires us to absorb foreign advanced technology, innovate and improve product quality through the progress of enterprises.The idea of product development to large-scale equipment, the degree of automation of control, quality, surface treatment equipment, efforts to select anti-corrosion materials, the development of multi-function combination machine,product life cycle Continue to extend.Industry associations should organize more enterprises to participateInternational technical exchangeAnd absorb the results of the latest technology to speed up the entire industry to improve the level of technology.The characteristics of the adjusted enterprises and the cultivation of their core competitiveness in China are that the enterprises in the drying industry do not do so, are not strong, not suitable, and not perfect, but the overall quality is not high. Most enterprises are backward in management, which does not conform to the corresponding economies of scale. Through the guidance and coordination of industry associations, blind development can be changed.
Jiangsu, Zhejiang and Shanghai, with three relatively concentrated enterprises, can consider using this joint venture. The central and western regions that cooperate and acquire will move to enterprises that find a broader space for survival and development.industrial enterpriseThe industry that takes the road of strong alliance has cultivated some technical strength, and has cooperated with well-known brands and large companies and enterprise groups with independent intellectual property rights.It has formed its own special products and services.drying equipmentmanufacturing enterpriseThe relatively low innovation ability in China, the introduction of new technologies and new products with independent intellectual property rights, and a few companies, is an important reason for the slow development of drying.There are dozens of universities and research institutes engaged in research and developmentDrying technologyLocated in the east, west and south of China, most of the knowledge achievements have not been effectively transformed into real productive forces.Enterprises becoming the main body of technological innovation should be directly related to the various forms of association of these universities and research institutions. Therefore, reasonable resource allocation and use can effectively cultivate and develop enterprises with innovative capabilities.
Looking forward to the future competitiveness of the drying equipment industry will focus on product quality, technology, service and price.The type of equipment is dry, and the hot air will dry the atmospheric heating equipment,Vacuum drying equipmentBased, other equipment, such as far infrared drying, flash dryerMicrowave drying equipmentAnd other users in special fields will also gradually expand the number of applications.In food and drug drying,Vacuum freeze drying equipmentLargeStandard equipmentThe demand for high automatic drying equipment will be welcomed in some applications.In addition, more and more attention will be paid to the quality of drying equipment. The drying equipment for corrosion-resistant materials and users with reliable performance will pay special attention.The drying equipment industry has entered a more mature stage of development, which can better meet the actual needs of users in various fields. The price of similar foreign products is only 1/3, which makes the drying equipment in China have obvious advantages over the price of imported equipment in the market competition;On the other hand, most of the larger drying equipment also involves on-site installation, commissioning and after-sales service, so it is more convenient to choose more options for domestic users and imported equipment of domestic equipment.In the international market, with China's accession to the WTO, drying equipment is more conducive to expanding exports.The main export products of China are vacuum drying equipment drying equipment, drying equipment, vibration, small and medium-sized grain, agriculture, forestry, food and local product drying equipment, with an annual export volume of more than 100 vehicles. The main export areas are Southeast Asian countries and other developing countries, and open the door to the European and American markets.China's exports account for less than 5% of the total drying equipment. Experts predict that the total share of drying equipment and drying equipment for export products in China during the "Tenth Five Year Plan" will exceed 10%.In international competition, the main competitor of drying equipment manufacturers in China is Denmark,Switzerland, Britain, Germany, the United States and Japan.Compared with competitors, the advantages of drying equipment in China are very cheap, which is mainly due to deficiencies. Products that control the degree of automation, appearance quality, function set and combination have been further improved.Therefore, domestic drying equipment manufacturers should make full use of the opportunity of China's accession to the WTO, strengthen technical exchanges, learn from foreign advanced drying equipment and drying equipment from foreign countries, so as to accelerate the improvement of China's degree of automation and control, appearance quality, function set and combination, and reduce foreign products to improve the trust of our products in users,Therefore, drying equipment can be used in China, not only in the domestic market, but also in foreign markets.Our country is producing more and more varieties of drying equipment, expanding the scale, level and quality of products rapidly increased, and more and more market competitiveness.In particular, the relevant policies of the Chinese government to support exports and the production of drying equipment create good external conditions for domestic enterprises, which shows that China has good prospects for the development of drying equipment.
Heat consumption and capacity
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Heat consumption and production capacity are important indicators of grain dryer test. However, due to the variability of environmental conditions, root feeding conditions and drying medium conditions during the test, the test results are often not comparable. Therefore, the performance test data of the dryer must be converted to a recognized standard condition for comparison and calibration.Based on the test data of grain dryer and referring to the test standards of grain dryer at home and abroad, this paper studies and explores the conversion coefficient of unit heat consumption and production capacity of root food drying;Four conversion methods are summarized and analyzedGrain dryerThe calculation methods and steps of conversion coefficient under different environment and grain conditions, the advantages and disadvantages of various methods are described, and the preliminary suggestions of conversion methods are put forward, which provide a basis for the comparability of dryer test data and the improvement of dryer test standards.
China is the world's largest grain producer, with an annual grain output of 500 million tons.The mildew loss of grain is up to 5% every year due to the rainy weather and insufficient drying equipment.After more than 30 years of development, China's grain drying equipment and technology have reached a certain level and played an important role in the construction of agricultural modernization.However, compared with the demand for drying equipment in China, there is still a big gap.Taking rice drying as an example, Japan has 1.1 million rice dryers nationwide, and the mechanization level of rice drying has reached more than 90%, while China has less than 1% of mechanically dried rice and less than 10000 rice drying equipment.There are many reasons for the above gap, among which the backward research on grain drying technical standards is also an important reason.At present, China still adopts the national standards of the 1980s (such asgrain dryer Test methods, technical conditions for grain drying), some of which are no longer suitable for the current development of dryers. For example, the existing standards lack the conversion method for the production capacity and unit heat consumption of dryers, and the indicators related to drying quality are not perfect and reasonable enough. Some indicators do not have unified test methods, and some indicators are relatively backward,Therefore, the development, popularization and application of new grain drying equipment and technology are restricted.The international grain drying technical standards have been revised for many times, such as 501 Qiao20 Yil: 1997;Determination of drying performance of agricultural grain dryers, such as 15011520-2:2 printing.In these new drying technical standards, there are conversion methods for main drying performance parameters, and dozens of models and formulas are used.
Grain drying is a very complicated processing process with many factors,Drying conditionsThe influencing factors are variable, including medium parameters (such as hot air temperature, hot air volume and hot air humidity), grain parameters (such as grain category, grain moisture, grain temperature and grain flow), environmental conditions (such as atmospheric temperature and humidity), drying process (such as forward flow drying, countercurrent drying, cross flow drying, mixed flow drying) and structural parameters of the dryer.A grain dryer may work at a very low ambient temperature (minus 20 ℃) or up to 30 ℃. Its working conditions are completely different, or even very different. Therefore, it is necessary to convert the measured performance indicators to a unified and recognized drying condition.The research and formulation of this standard need to be based on different environmental conditions and food conditions,A series of parameters, such as atmospheric temperature, relative humidity, initial grain moisture, final grain moisture, precipitation amplitude, grain category, quality, heating method, hot air temperature, relative humidity, hot air volume, drying method, etc., have been verified by a large number of tests. It is difficult to form a formal national standard.The most likely way to achieve results is to complete a research report, give a conversion coefficient that is not completely accurate, publish it as a guiding technical document for trial implementation, and then compare and evaluate it.Therefore, the conversion of dryer production capacity and unit heat consumption is a very important standard.Unit heat consumption and drying capacity areGrain drying equipmentKey indicators of.For different types of grain drying equipment or the same type of grain drying equipment, when there are differences in their acceptance working conditions, they must be converted to the standard working conditions through relevant conversion factors to determine and compare the unit heat consumption and drying capacity.There is no uniform conversion coefficient specification for drying unit heat consumption and drying capacity in China.This topic will study the conversion coefficient, study and formulate a unified national standard for conversion coefficient.The conversion of grain drying unit heat consumption and drying capacity has always been an important problem for the performance evaluation and identification of grain dryers;For many years, this problem has not been solved due to the heavy research workload and lack of scientific research funds.Heilongjiang Academy of Agricultural Reclamation Sciences put forward a solution, but it failed to become a national standard because it could not apply to a variety of drying processes and models, and the standard conditions and model selection were not reasonable enough.On the basis of in-depth analysis and research on the existing drying technology research achievements at home and abroad, the author determined the converted standard drying conditions through experiments and theoretical analysis, and gave the calculation method and application conditions of conversion coefficient for various drying machines and different grain drying.
translation method
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1 Computer simulation method
A common problem in the use of the grain dryer is that the initial moisture of the grain often changes. In order to reach the required final moisture, the grain flow (production capacity) needs to be adjusted frequently. In order to compare the performance of the grain dryer, the production capacity of the dryer also needs to be known, so it must be converted.We believe that it is a good and feasible method to convert the heat consumption and production capacity of the dryer by computer simulation, that is, to establish a mathematical model of the grain drying process, to compile a drying simulation program, to conduct simulation calculation on the computer, and finally to obtain the conversion coefficient.
The best point of this method is that it has good versatility. It can i} · calculate the drying performance and conversion coefficient of different models (downstream, countercurrent, cross flow and mixed flow dryers) and different grains (corn, wheat, rice);!10000 r for any drying conditions, the calculation speed is fast;All kinds of one!Several drying processes can be used.
The disadvantage of this method is that the simulation method is not popular enough. It requires a certain computer foundation to master this method. The dryer users generally do not have this software. In addition, the mathematical model of the drying process is not accurate enough.In the future, the research in this area should be strengthened, and the calculation steps of simulation methods are as follows:
1) Establish drying process model;
2) Develop computer simulation programs for various grain drying processes;
3) The simulation program is used to calculate the heat consumption and production capacity of the dryer under standard conditions;
4) Simulate and calculate heat consumption and production capacity under non-standard conditions;
5) Calculate the conversion coefficient of heat consumption and production capacity;
6) Convert the dryer performance.
2 ISO11520-2 International Standard Method
The International Standard Organization (ISO) provides a conversion method, which uses four correction factors K1, K2, K3 and K4 to convert the water evaporation rate obtained from the test.The significance of each correction factor is as follows:
Conversion method: the standard conditions are precipitation amplitude of 5% (20%~Qiao%), hot air temperature of 93 ℃, ambient temperature of 20 ℃, and ambient relative humidity of 60%. The conversion method is relatively simple and easy.Its main disadvantage is that it is only applicable to cross flow grain dryer and drying of corn and wheat, and the selection of some coefficients lacks basis.In addition, it also considers the influence of indirect heating of hot blast furnace and direct heating and cooling section of oil furnace.The specific calculation method is as follows:
Conversion of unit heat consumption
Under standard conditionsGrain dryerThe unit heat consumption of is calculated as follows:
Qrb=Qr/(K0*K1)
Where, Qrb - unit heat consumption under standard conditions, MJ/kg Qr - measured heat consumption during test, MJ 8g;K。I Conversion coefficient of atmospheric conditions, which can be calculated by looking up the table according to atmospheric temperature and relative humidity, see the standard of "Conversion coefficient of unit heat consumption and production capacity of grain drying";K1 is the conversion coefficient of grain conditions. Under the same environmental conditions, it is calculated by looking up the table according to the initial moisture and final moisture of grain.
4 Data sheet method
Through thermal calculation, the conversion coefficient when the parameter changes under various conditions is listed in a table, and then converted by the insertion method. The standard gives two tables, one is the conversion table of atmospheric conditions, the other is the conversion table of grain conditions. After finding out the two coefficients from the table, the product is the total conversion coefficient.
On the basis of in-depth analysis and research of existing research results at home and abroad, this paper analyzes and discusses the standard conditions of conversion, and gives the calculation methods and application conditions of conversion coefficients for various drying machines and different grain drying processes[1]。
Standard conditions
In order to compare the performance of grain dryer under different drying conditions, a recognized standard condition must be determined;When drying or testing under non-standard conditions, the data measured in the drying process must be converted to standard conditions, and then the drying performance can be compared.The so-called standard conditions generally include precipitation amplitude, ambient temperature, ambient humidity, hot air temperature and dryer type.The standard conditions formulated by different countries are different (see Table 1).The standard conditions for British wheat drying are 20% initial moisture,% final moisture, 20 ℃ ambient temperature and 80% ambient humidity.Regulations of Heilongjiang Province
The standard conditions for drying corn are 5% (20% -%) of precipitation, 90 ℃ of hot air temperature, 20 ℃ of ambient temperature, and 60% of ambient relative humidity.France has different standard conditions for different seasons.Russia stipulates precipitation amplitude of 6% and ambient temperature of ro ℃.There is no national standard for performance conversion of grain dryer in China.Some units are studying it and may publish it as a national standard soon.
Conversion coefficient
The drying characteristics of different grain types, such as corn, wheat and rice, are differentEquilibrium moisture content, thin layer drying equation, specific heat, latent heat of vaporization, resistance to air flow, bulk density, etc. The conversion coefficient of drying capacity of various grains must be considered when converting.
Main impacts
It is easy to calculate the performance of various dryers under different conditions (forward flow, counter flow, cross flow, mixed flow) by mathematical simulation, so it is easier to calculate the conversion coefficient.For specific methods, please refer to Computer Simulation of Agricultural Product Drying Process
Hot air volume
The conversion coefficient of wind speed (air volume and temperature) must also be considered because of the change of wind speed caused by temperature change.
proposal
(1) Strengthen the research of international drying standards.In order to approach the international drying technical standards, it is necessary to applymodern information technology And computer simulation method, the drying conditions of a series of existing calculation models in the International 150 Drying Technical Standard were converted.Due to the complexity of the mathematical model and the lack of any explanation and explanation, the coefficient selection of many equations still needs to be discussed and analyzed, otherwise it is difficult to promote the application.For this reason, it is necessary to translate, sort out, analyze and apply foreign materials on grain drying standards.
(2) Obtain necessary test data.In order to verify the rationality and correctness of the conversion method, it is necessary to verify the conversion results, which requires certain test conditions and equipment for experimental verification, as well as searching a large number of literature.
(3) The four conversion methods are compared and analyzed.Compare and verify the above four different conversion methods under different environment and food conditions, find out the problems in conversion, and propose the first draft of conversion standard.
