As wheat harvester starts, the annual summer harvest is about to start work. After harvest of grain moisture content is higher, usually for long-term storage, if not timely rainfall measures, easy to cause of grain mildew, thus affect the food quality. As a result, the new harvest food must be in dry, ventilated, or drying way, reduce the grain moisture, make the security deposit. At present, the rural have been unable to reduce the grain moisture content by pure air, thus mechanical drying arises at the historic moment, the best way to become the present rural mass wet food precipitation.
Below, will be a mixed reflux circulation of grain dryers as an example, introduces the structure and working principle of grain dryer to understand the use and maintenance of the machine.
A, hoist
Grain dryers of hoist is mainly composed of feeding mouth, winnowing pan, winnowing pan of belt and driving gear, ascend machine equipped with a grilled food machine, usually by grilled food machine will need to be dried food to hoist the feed port, after electrify, hoist winnowing pan from the mentioned to general food that high, the sliding tube to slip into the tower. In order to guarantee the dryer operation and daily maintenance of the safety of the staff, should be installed at the top of the tower railing, hoist motor will install shield, have the effect of wind, rain and snow on the motor. Hoist is the ladder on the right, convenient maintenance staff on tower, is the white pipe near the gym dust removal pipe, it ranges from the top of the tower to the ground are connected to the dust removal machine, mainly to remove dust that food produced in the process of ascension and light impurities, MAO to ensure the quality of food.
Second, the drying tower
Drying tower can be divided into five working section, the storage period, drying, cooling and tempering paragraphs and unloading grain.
Grain storage period of one side of a transparent small window, called a window, the position of the food can watch tower. Drying period is the main process of drying food, mainly based on hot air drying medium on food heating and in addition to water, reduce the grain moisture content to a certain degree, is beneficial to storage and ensure the quality.
Inside the drying tower is mainly composed of layers of the pentagon staggered Angle of ventilation tubes, the user can see from the outside of the angular tube is Angle of exhaust pipe, protrude the seven rectangle is inlet Angle pipe of the internal arrangement. Hot air blower provide hot air by the inlet Angle of tube into the grain heap, across the grain layer of take away food evaporation of water vapor at the same time, through the Angle of exhaust pipe emissions to the atmosphere.
During the dry period, due to the grain weight, top-down flow of air from the inlet Angle of the tube, up or down direction through the grain layer, hot air to flow there are both same flow and reverse flow, it is called the mixed flow. Hot air in through the grain layer, and intergranular for damp heat transfer, hot air heat will be transferred to food grains, temperature, grain heats, moisture evaporates into the air, drying medium carrying the water vapor into exhaust through the exhaust angular tube eduction. In this process, the temperature, the higher the faster the water evaporation. In order to guarantee the quality of the food, the processability and the packaging, food in the dry temperature and the drying time is tightly controlled, its principle is to reduce the moisture of food, and can not damage the quality of the food.
Decorate no draft Angle in the drying section of the site during the tempering period for, baking hot food down during the tempering period flows to, the tempering segment not hot air, its main function is slow in grain drying process, the formation of intragranular stress promote grain internal moisture moves outward, make food grain of surface and internal moisture back into balance. The tempering process implementation is beneficial to the next stage of drying, can ensure quality after baking food again, but it cannot be applied to oil crops.
After baking food temperature is very high, need after cooling to warehousing storage. Grain dryer is equipped with cooling section, cooling fan to provide the cold air in the cold wind, adopting countercurrent cooling way to cool down after baking food. In the process of cooling, cold air contact with lower low-temperature grain first, at the same time in the run up to absorb the quantity of heat food, cold air temperature gradually raised, which can avoid the cold wind of food when in contact with the upper hot food rapid cooling, countercurrent cooling can improve the cooling effect of cooling section, also can protect the quality of the food is not affected. After cooling period, the grain temperature gradually decrease from top to bottom. Grain temperature when the tower is to higher than the environment temperature of 4 to 8 degrees Celsius, grain by grain section of the discharge, warehousing storage. When the temperature below zero degrees Celsius, grain temperature control at zero degrees Celsius. In production can be judged by detecting the temperature of the cooling gas food cooling degree.
Unloading grain including discharge outlet, circular conveyor, observation hole and grain device. Observation hole are mainly used for grain discharge situation of watch tower. Commonly used food device is divided into grid plate and six impeller type two kinds of structure. Grid plate grain institutions by the leak bucket, row grains grating, crank connecting rod and other components, normal not rows when food grain grid block at the bottom of the funnel, need row of food, in the role of crank connecting rod mechanism, promoting fixed line food grid plate and frame do reciprocating motion, make the rows of bread grating is separated from leakage food fights from time to time, and sometimes overlap, are used to control the speed of grain. Six vane row grain device by the leakage of grain bucket, six impeller and speed regulating motor, six impeller block in leakage food, need row grains, six impeller rotating speed motor drive, food go down those routes, six of the impeller speed control speed of the rows of bread. From the row of food grain device down, through the discharge outlet flow on circular conveyor. Circular conveyor in addition to transport food, also can be transmitted through a reverse, will go through a dry don't reach the safe moisture content of grain, and then back to hoist feeding port, and then again packed tower was carried out on the grain drying, drying cycles by grain moisture level, the dryer into the circulating dry state at this time.
Three, the hot blast stove
Hot blast stove is the heat source of grain dryer equipment, used for the preparation of food grain dryers dry hot air. Its purpose is to raise the temperature of drying medium, enhance the capacity of the water absorption of drying medium, air supply system will be the input of grain dryer drying section, to achieve the purpose of heating food, moisture evaporation. The cost of drying fuel type decision. According to China's current national conditions and from the Angle of the drying cost considerations, the rice production areas in China are mostly using rice husk as drying fuel, in addition to this area use coal as fuel.
Hot blast stove by special refractory brick build by laying bricks or stones becomes, refractory temperature can reach 1200-1500 degrees Celsius, main components including blower, smoke fan, furnace, heat exchanger and heat fan. Rice husk furnace adopts direct heating furnace, coal furnace by indirect heating furnace, its biggest advantage is not pollution by dry material.
Blower fan and heat and smoke fan is conveying air equipment. The role of the blower in the countryside near the hearth bellows has the same place, is have the effect of blast and fire bloom, only now blower than bellows saves the manpower, and high work efficiency. Lead smoke fan used for discharge of smoke from the burning of hot blast stove.
Heat exchanger is one of pipe type heat exchange equipment, installed inside dozens of round tube. Pipe flow of high temperature flue gas flow through the wall outside the heating tube of the cold air, cold and hot gas in the heat exchanger heat transformation, heating warms the cold air into hot air, while the flue gas temperature decrease was carried by emptying induced draft fan. Located outside the heat exchange tube and shell heat exchanger hot air fan input into the dryer dry food is hot.
In general, the heat exchange area, the greater the thermal conversion rate is higher. How many different according to the dryer a baked food, can be equipped with a set or more sets of heat exchangers.
Is the role of hot air blower drying medium to the drying section, to achieve the purpose of drying food, in a sense of hot air blower work ability decides the drying efficiency of grain dryers.
Hot fan consists of casing, impeller, stand and damper, throttle is used to control from heat exchanger to heat the air volume of fan, it has two openings, when the temperature inside the hot air blower, through the cold wind mouth into the cold air in order to achieve the purpose of reducing heat temperature fan; Into the heat exchanger is hot mouth, at the beginning when dry, hot air port in an open position, negative pressure produced by hot air blower, the heat flow within the heat exchanger suction fan, the hot when the temperature inside the hot air blower, little hot mouth opening, to control the heat of the heat exchanger in the heat flow into the fan air volume, at the same time increase the cold wind into the air volume of mouth, have the effect of control air temperature. Hot fan outlet temperature sensor mounted on the hot air pipe, used to detect the temperature of the hot air duct.
From the burning of coal in the furnace combustion fully, by the flow of flue gas heat exchangers in the steel tube, the heat transfer to the cold air, the fan out of the chimney flue by lead smoke. In heat exchanger tube and shell at the same time between the air flow by steel pipe flow flue gas heat, after the formation of hot air was hot inside the fan to the dryer dry food.
Four, electric control cabinet
Grain dryers use 50 hz, 380 v / 220 v alternating current (ac), control of all equipment, components of the drying system is responsible by the electric control cabinet, control panel can display various equipment of voltage, current, temperature of the hot air pipe, and the grain rate, etc.
Inserted into the hot blast stove of the metal parts of the flue temperature sensor, the temperature is passed to the electronic control cabinet of the thermometer. Usually before starting each switch electric control cabinet, to adjust the minimum temperature of the temperature control table to 450 degrees Celsius, the maximum temperature adjustment to 650 degrees Celsius, the hot blast stove of the flue temperature at or above 650 degrees Celsius, electric control cabinet of the thermometer will automatically shut down, so can avoid the high temperature and burning heat exchanger, but also to protect heat exchanger, prolong the service life of heat exchanger, automatic operating mode can also reduce the site operation staff, save manpower.
In addition, electric control cabinet should be grounded, to ensure the safety of staff in the operation.
In front of the boot, you have to check each part of circuit, look to whether connection is firm, to ensure the operation safety, master switch and various equipment start-up and shutdown sequence are exquisite. When turned on, should according to the grain flow in the opposite direction, walking forward from the back end side one boot. Shutdown, according to the grain flow direction, walking back from the front end off one by one.
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