What Is a Conveyor Dryer?

Dryer ^[1] refers to a kind of mechanical equipment that uses thermal energy to reduce material moisture, and is used to dry objects. The dryer vaporizes the moisture content of the material (generally refers to moisture or other volatile liquid components) by heating to obtain the solid material with the specified moisture content. The purpose of drying is for the use of materials or further processing. According to the operating pressure, the dryer is divided into two types: normal pressure dryer and vacuum dryer. According to the operating pressure, it can be divided into normal pressure and reduced pressure (reduced pressure dryer is also called vacuum dryer). The entry also describes in detail the adsorption dryer, freeze dryer and microwave dryer.

Introduction

In the application of many applications similar to the precision electronics industry or high-precision instruments, because the process requires the pressure dew point in compressed air to be lower than 0 ° C, the tube will appear when the pressure dew point of the refrigerated dryer is lower than 0 ° C The phenomenon of icing on the road, at this time, can not meet the requirements of the process by using freeze-drying.Our company has introduced the manufacturing technology of advanced freeze-drying machines, and also introduced the manufacturing technology of non-heating adsorption dryers. The temperature can be -70 ; At the same time, it is made of high-quality materials such as imported stainless steel pneumatic valves and stainless steel one-way valves to avoid pipeline pollution and improve air quality. Introducing and absorbing while combining domestic application experience, in order to reduce the air consumption of non-heating dryers, micro-heating dryers and combined dryers are derived to reduce the air consumption of compressed air, and the minimum air consumption can reach 5 %. To meet the needs of different users ^[4]

Combining microwave with traditional heating and drying technology, large-scale microwave power application equipment is mainly used in heating and drying and food processing production ^[6]

Heat consumption and production capacity are important indicators of the grain dryer test, but due to environmental conditions,

Due to the variability of the drying medium conditions, 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 dry dryer, this paper studies and explores the unit heat consumption and production capacity conversion coefficient of root dry food dryer with reference to domestic and foreign root food dryer test standards. Four kinds of conversion methods are summarized and analyzed. Up

1 computer simulation method

A common problem in the use of grain dryers is that the initial moisture of the grain often changes. In order to achieve the required final moisture, the grain flow (production capacity) needs to be adjusted frequently. In order to compare the performance of the grain dryer, it is also necessary to know the production of the dryer. Capacity, therefore, must be converted. We believe that using computer simulation to convert the heat loss and production capacity of the dryer is a better and feasible method, that is, to establish a mathematical model of the grain drying process, write a drying simulation program, and perform simulation calculations on a computer. Get the conversion factor.

The advantage of this method is that it has good versatility, and can be used to calculate the drying performance and conversion coefficients of different models (downstream, countercurrent, crossflow, and mixed-flow dryers) and grains (corn, wheat, rice). ! 10,000r converts any drying conditions, the calculation speed is fast; all kinds of one! Several drying process can be used.

The disadvantage of this method is that the simulation method is not popular enough. Mastering the method requires a certain computer foundation. The dryer users generally do not have such software. In addition, the mathematical model of the drying process is not accurate enough. In the future, the research and simulation methods in this area should be strengthened as follows:

l) establish a drying process model;

2) Development of computer simulation programs for various grain drying processes;

3) Use the simulation program to calculate the heat consumption and production capacity of the dryer under standard conditions;

4) Simulation calculation of heat consumption and production capacity under non-standard conditions;

5) Calculate the heat dissipation and production capacity conversion coefficients;

6) Convert the performance of the dryer.

2 ISO11520-1 International Standard Law

150 (Intemational Standard Oganization) international dryer performance test standard provides a conversion method, which uses four correction factors K1, K2, K3, K4 to convert the test water evaporation rate. The meaning of each correction coefficient is as follows:

K1Moisture correction coefficient, K1 = (8.971-0.05578Td) X. + 1.139InTd-4.652

K2correction coefficient of hot air temperature, K2 = (0.00565-0.000061Td) + 0.000915Td + 0.915

K3Correction coefficient of air humidity, K3 = 1.0175-0.01072 (l-)

K4Air volume correction coefficient, K4 = (0.022Td-3.445) a / V-0.271InTd + 2.608

3 Heilongjiang Provincial Standard

Heilongjiang Academy of Agricultural Reclamation Agricultural Machinery Appraisal General Station proposed a grain drying unit heat consumption and production capacity in 1989

The conversion method, the standard conditions are 5% (20% ~%) of precipitation range, 93 ° C hot air temperature, 20 ° C ambient temperature, and 60% relative humidity. Its main disadvantage is that it is only applicable to the drying of cross-flow grain dryers and corn and wheat, and the selection of some coefficients lacks a basis. In addition, it also takes into account the effects of indirect heating of hot blast stoves and direct heating and cooling sections of oil stoves. The specific calculation method is as follows:

Conversion of unit heat consumption

The unit heat consumption of the grain dryer under standard conditions is calculated as follows:

Qrb = Qr / (K0 * K1)

Krb is the unit heat consumption under standard conditions, MJ / kg Qr is the measured heat consumption during the test, MJ eight g; K. A conversion factor for atmospheric conditions, which can be obtained from a look-up table of atmospheric temperature and relative humidity, see the Conversion factor for heat consumption and production capacity of grain drying units standard; K1, a conversion factor for food conditions, under the same environmental conditions, The initial moisture and final moisture are obtained from a look-up table.

4 data sheet method

Through thermal calculations, the conversion coefficients when parameters are changed under various conditions are tabulated, and then converted using the interpolation method. Two standards are given in the standard, one is an atmospheric condition conversion table, and the other is a food condition conversion table. When two coefficients are found in the table, the product is the total conversion coefficient.

Based on in-depth analysis and research of existing research results at home and abroad, this article analyzes and discusses the standard conditions for conversion, and gives the calculation methods and use conditions of conversion factors for various drying models and different grain drying processes. ^{[1 ]} .

Dryer conditions

In order to compare the performance of grain dryers under different drying conditions, a recognized standard condition must be determined; when drying operations or tests are performed under non-standard conditions, the data measured during the drying process must be converted to standard conditions before drying can be performed Performance comparison. The so-called standard conditions generally include precipitation range, ambient temperature, ambient humidity, hot air temperature, and dryer type. Standard conditions set by different countries are different (see Table 1). The standard conditions for dry wheat in the UK are 20% initial moisture, 20% final moisture, 20 ° C ambient temperature, and 80% ambient humidity. Heilongjiang Province regulations

The standard conditions for dry corn are 5% (20% to 20%) precipitation range, hot air temperature of 90 ° C, ambient temperature of 20 ° C, and ambient relative humidity of 60%. France has different standard conditions for different seasons. Russia stipulates a precipitation range of 6% and an ambient temperature ro ° C. There is no national standard for the conversion of grain dryer performance in China. Some units are studying it and may soon release a national standard for juxtaposition.

Conversion factor of dryer

Different grain types such as corn, wheat, and rice have different drying characteristics, such as equilibrium moisture content, thin-layer drying equation, specific heat, latent heat of vaporization, resistance to airflow, bulk density, and so on. When converting, various grains must be considered. Conversion factor for drying capacity.

Impact of dryer

Using mathematical simulation, it is easy to find the performance of various dryers under different conditions (downstream, countercurrent, crossflow, mixed flow), so it is easier to calculate the conversion coefficient. Specific methods can refer to the book "Computer Simulation of Agricultural Product Drying Process"

Hot air volume of dryer

The wind speed changes due to temperature changes, so the conversion factor of wind speed (air volume and temperature) must also be considered at the same time.

Dryer recommendations

(1) Strengthen research on international drying standards. In order to move closer to international drying technology standards, modern information technology and computer simulation methods must be applied to convert a series of existing calculation models of the international 150 drying technology standards into drying conditions. Because the mathematical model is more complex and there is no explanation and explanation, there are many coefficients to be selected for the equations that need to be discussed and analyzed, otherwise it is difficult to popularize and apply. To this end, foreign materials related to food drying standards need to be translated, sorted, analyzed and applied.

(2) Obtain necessary test data. In order to verify the rationality and correctness of the conversion method, it is necessary to verify the conversion result. This requires certain test conditions and equipment for test verification, and it also needs to search and search a large amount of literature.

(3) Comparative analysis of four conversion methods. Compare and verify the above four different conversion methods under different environmental and food conditions, find out the problems in the conversion, and propose the first draft of the conversion standard.