Research on the latest energy-saving and quality g

Research on new energy-saving and quality-guaranteed grain drying technology and equipment (Part I)

because China is located in the north temperate zone, the northeast corn harvest period is in the autumn with low temperature and high humidity. The moisture content of harvested corn is generally high, as high as 28% - 35%, while the national standard stipulates that the moisture content of grain entering the warehouse cannot exceed 13.5%. Vitamin C decomposes when it exceeds 40 ℃, which changes its original properties; Protein denaturates at high temperature, changing the nutritional composition of the material. In order to do a good job in the supporting facilities of grain "scattered" circulation, this paper discusses the research and design of low-temperature vacuum dryer system. The system dries the materials below 40 ℃. During vacuum drying, the temperature gradient inside and outside the material is small, and the water in the grain moves alone by reverse osmosis, which overcomes the phenomenon of solute loss. The dryer enables the process parameters such as temperature, moisture and time to be adjusted and controlled in the process of low-temperature vacuum drying of materials, so as to prevent excessive or insufficient drying of materials, and ensure that the original color, aroma, taste, nutritional composition and quality of materials after drying are basically unchanged, which is convenient for storage, transportation and sales. The drying device has the advantages of large quantity, high precipitation range, automatic display, alarm, flexible operation, convenient use and so on

corn low-temperature vacuum drying test and research is one of the topics of the "Tenth Five Year Plan" national scientific and technological research project - the key technology research project of grain and oil product storage and quality detection. It is based on the principle that the temperature of grain water boiling evaporation changes with the size of environmental pressure, using steam jet vacuum technology to form a space with a certain degree of vacuum, and continuously dehydrating and drying grains with high moisture content under vacuum and low temperature. According to the green and environmental protection drying concept of "high quality, high nutrition, high efficiency, low loss, low pollution and low cost", the relevant drying technology and equipment are studied through experiments

corn is one of the main grain crops in China. Corn in Northeast China has high original moisture and uneven maturity, which is very vulnerable to insect and mold damage. Due to its large embryo and high fat content, corn has stronger life activities and higher respiratory intensity than other grains under the same conditions, and is prone to oxidative rancidity. Therefore, the storage stability of corn is worse than that of other grains, and it is usually not suitable for long-term storage and transportation. In conventional storage, hot air drying is generally used to reduce the moisture content of grain

which line of corn connects the host and power supply is one of the main varieties of grain drying in China. High moisture corn is not conducive to safe storage, so it generally needs to be dried before storage to reduce the moisture below the safe moisture. When the drying temperature is too high, the vitality of grain will be lost, and its germination power will be greatly reduced. Under 40 ℃, how to dry northeast high moisture corn in large quantities and ensure that the original quality of corn is basically unchanged is the continuous goal of scientific and technological workers. Low temperature vacuum dryer system is one of the best ways to solve high moisture corn

corn is one of the grain varieties that are difficult to dry. The main reason is that its grain is large, the unit specific surface area is small, and the grain epidermis structure is compact and smooth, which is not conducive to the transfer of water from the inside to the outside of the grain. Especially under the action of high-temperature drying medium, due to the rapid vaporization of water on its surface, when the water under the grain epidermis cannot be transferred out in time, the pressure will rise, causing the epidermis to swell and crack, or the grain to swell and deform. In addition, if the temperature of drying medium is too high, the grain will be burnt and the grain out of the machine will be seriously broken. It has been an important subject of grain drying research to quickly and economically reduce the moisture content of corn and maintain good quality

experiments show that when the temperature of drying medium exceeds 150 ℃ and the temperature of corn is higher than 60 ℃, a large number of startled lines will be produced and the quality will be reduced. For conventional hot air drying equipment, the temperature of the hot air is generally 120~160 ℃, the natural temperature in the drying season is generally -10~-30 ℃, and the temperature difference between the hot air and the corn grain is as high as 130~190 ℃. During the drying process, the high-temperature hot air damages the internal structure of the corn grain, resulting in a higher crack rate of the dried grain, generally around 18%, as high as 35%, resulting in the decline of the quality of the dried corn, It is easy to break in the circulation process, and a large number of corn have seriously reduced the commodity grade due to the problem of drying technology, affecting the normal domestic and foreign trade of corn. The key of this research is to adopt low-temperature vacuum drying technology to avoid the decline of grain quality caused by high temperature

1. Test purpose, principle and content

1.1 test purpose: check whether the low-temperature vacuum dryer meets the design requirements. The vacuum drying technology was used to dry corn in Northeast China. The vacuum degree, drying rate, drying time and drying characteristics of corn were studied under low temperature and vacuum. Make the dried products meet the grain storage and transportation standards, make it convenient for processing, transportation, storage, and ensure product quality

1.2 test principle under the premise of maintaining the predetermined vacuum and heating temperature basically unchanged, measure the continuous drying effect of corn in the drying cylinder. Measure the operation condition and air tightness effect of the equipment, timely analyze various problems occurred in the experiment, find out the causes, study the dryer system, determine the next improvement measures, and accumulate practical experience and data for the next test

1.3 research contents the key research contents are drying cylinder, feeding and discharging device, dynamic air tight technology, material anti blocking technology, wear-resistant technology, etc; Study and determine the main technical parameters such as vacuum degree and evaporation temperature. Focus on solving the best heating design parameters of the heating device in the drying bin, as well as the adaptability, stability, continuity and reliability of the dryer system, so as to achieve the purpose of high efficiency, energy saving, environmental protection and ensuring the quality of products after drying. Solve a series of problems encountered in actual production, and provide basis for the design and test of production test equipment

1.4 measure the vacuum degree and evaporation temperature in the content drying cylinder; Moisture content and temperature of corn; Moisture content and temperature of corn out of the machine; Corn crushing rate increment; Corn crack rate increment, etc

2. Field test

2.1 basic situation of field test

2.1.1 the test time was from April 13, 2004 to May 9, 2004

2.1.2 test location: Zhengzhou Zhengping company

2.1.3 the weather is sunny, the southeast wind is grade 2~3, and the temperature is 20~23 ℃

2.2 test materials

2.2.1 the supply of water, electricity and steam utilizes the existing infrastructure of Zhengping company

2.2.2 the tested corn was 25t high moisture corn naturally harvested in 2003, and the origin was Jilin. Level 2. The average moisture content is 24%, the nonuniformity of moisture content is less than 3%, and the impurity is 0.9%, without mildew

2.2.3 main detection instruments steam pressure gauge -0~1.6mpa, ysg-3 vacuum pressure gauge, xmt-102 digital display temperature sensor, LFX steam flowmeter, computer moisture meter 0%~40%, semiconductor point thermometer 0~100 ℃, sl-401 sound level meter, FSF crusher, tq3288 (division value 0.1mg) analytical balance, thermometer 0~100 ℃, etc

2.2.4 main test equipment: bucket elevator, belt conveyor, buffer balance bin, drying drum, vacuum pumping system, circulating heating system, electrical control system, etc

2.3 test method

2.3.1 vacuum drying principle the vacuum drying process is to place the dried material in a closed drying chamber, and heat the dried material continuously while vacuuming with a vacuum system, so that the water in the material spreads to the surface through the pressure difference or concentration difference. The water molecules obtain sufficient kinetic energy on the surface of the material, and escape to the low-pressure space of the vacuum chamber after overcoming the mutual attraction between molecules, Thus being pumped away by the vacuum pump. Vacuum drying can easily recover useful and harmful substances, and can achieve good sealing. In the sense of environmental protection, some people call vacuum drying "green drying"

in the vacuum state, the boiling point of the moisture of the material decreases and the vaporization process accelerates. During the evaporation process of moisture in corn, its boiling evaporation temperature is directly proportional to the environmental pressure. Put the high moisture corn in a closed drying cylinder, use the steam jet vacuum technology to form and maintain a certain vacuum in the drying cylinder, and at the same time, heat the corn in the drying cylinder continuously, so that the moisture in the corn spreads to the surface through the pressure difference, and is pumped away by the vacuum pump after vaporization, Realize continuous dehydration and drying of high moisture corn under vacuum and low temperature. Vacuum drying reduces the boiling evaporation temperature of water from 100 ℃ to below 40 ℃. Since the evaporation temperature is lower than the gelatinization temperature of starch, it will not damage the corn seeds when heated to different temperatures. The expansion and waist bursting of corn grains are avoided, and the product quality of dried corn can be guaranteed. It is really low-temperature drying, which is completely different from the general hot-air low-temperature drying

2.3.2 the drying conditions are based on the original moisture content of grain, harvest method, maturity and use of grain. The greater the original moisture content of grain, the worse its thermal stability, that is, temperature resistance. The temperature tolerance of immature grain is poor compared with mature grain. For newly harvested grain with high moisture content, due to the uneven maturity and moisture content of grain, the surface layer of grain has not been fully hardened. Therefore, lower temperature drying conditions should be adopted; If high-temperature drying conditions are adopted, the grains will be damaged instead, causing hardening on the surface of grains, and the capillaries on the surface of grains will be greatly damaged, which is detrimental to the drying process. Therefore, when drying the newly harvested high moisture grain, it is necessary to consider its thermal stability and surface characteristics, and adopt mild drying conditions

2.3.3 focus on the development of high-performance marine steel, ultra-high strength and toughness automotive steel, high-performance rail transit steel, super ferritic stainless steel, high nitrogen austenitic stainless steel, super duplex steel, advanced fabricated construction steel and other new materials. Prepare for the test. According to the test requirements, debug the dryer system to the normal working state, and stabilize the steam pressure in the normal state. Put a part of the padded grain into the drying cylinder to prepare for continuous drying. Start the vacuum pumping system to make the vacuum degree and hot water temperature in the drying cylinder reach the predetermined range. Carry out normal continuous drying operation according to the scheduled incoming and outgoing procedures

2.3.4 the steam pressure is read out by the pressure gauge and recorded every 30min

2.3.5 vacuum degree read out the pressure in the drying cylinder according to the vacuum pressure gauge and record it every 30min

2.3.6 temperature detection adopts 1 online, middle and lower three points, which are read out by the digital display temperature sensor and recorded every 30min

2.3.7 the steam consumption shall be recorded every 60min according to the data displayed by the steam flowmeter

2.3.8 grain moisture shall be carried out according to GB, 130 ℃ constant temperature and fixed time drying method. The difference between the moisture content of outgoing corn and incoming corn is the precipitation rate

2.3.9 the crushing rate shall be determined according to GB

2.3.10 noise shall be measured according to gb16769