|Drying equipment used by the manufacturing enterprises of the drum column tube, disc, blade, hot air and strong drying type. According to the nature of the wet filter and moisture different using different types of drying equipment.
Scientific and technological content of the drying equipment is beginning to achieve a leading role. Since 2004, by the development of the national chemical situation continued to drive, stable and optimistic about the market situation in the drying equipment, manufacturers of universal access to good operating results.
The notable feature of the service the chemical industry drying equipment is an increasingly prominent role of the technical content. This depends mainly on past sales price competition is already quite different. Among them, some drying equipment of high technical content, focusing on the development of new manufacturers, the effectiveness of steadily growing; the contrary, some of the low technological content of products and the weak ability of new products and new technology development enterprise, the benefits began to fall.
The market reaction indicates that the chemical industry looks forward to the drying equipment manufacturing industry in accordance with the requirements of high-quality, low power, environment-friendly adjustment of product structure, further strengthen basic research, and reinforce the application of R & D basis. In terms of technology, increased automation, testing, manufacturing processes and materials, materials design research. Applied R & D, it is necessary to pay attention to international exchanges and cooperation, but also pay attention to the protection of intellectual property rights; it is necessary to focus on new technologies, the development of new applications, but also focus on innovation and innovation of traditional crafts and traditional applications. It should be said, This is China's drying equipment is bigger and stronger the only way.
At present, the improvement of scientific and technological content of the drying equipment, produce gratifying results. Over the years, the domestic drying equipment industry has been today observed □ jungle today observe such features: the small scale of production, low barriers to entry, the overall technical content is not high, the industry-wide annual sales income of 500 million accounting for more than 60% The annual sales income of over $ 10 million factory only 5% to 8%, product quality is generally low and similar.
But now, the high-tech products is the birth of the emergence of the drying equipment manufacturing backbone enterprises. This is likely to be in the field out of the vicious price competition, and change the current situation of enterprises are small and scattered industry naturally integrated signal. Technology competition, take the combination, the survival of the fittest the road, and encouraged the strength of the industry leaders enterprise, perhaps just around the corner.
In addition, technological advances will reverse the current export situation of domestic drying equipment. China drying equipment has not yet formed the scale of export, the export volume of less than 5%, and are mainly exported to Southeast Asia. According to authoritative forecasts, as technology evolves, the next few years, China's exports drying equipment account of total production will increase from 5% to 10%, the export market will be in Southeast Asia to expand to Europe and the United States. Large domestic drying equipment manufacturing and international level there is a big gap between the situation which is expected to improve.
Drying is important in the production process of many industries and essential aspect of the drying equipment selection and reasonable, and the use of a direct impact on product quality, production efficiency, production costs, energy consumption, personnel and labor intensity indicators, due to the dry method and a variety of drying equipment, with the type of material in a variety of drying methods, you can use various types of drying equipment, a dryer can dry a variety of materials, therefore, reasonable selection and proper use of the drying equipment is very positive want. In order to facilitate the user to select an ideal drying equipment in a number of related issues for a brief description.
One drying method for drying from a variety of materials to dehumidify the points, various materials can be solid, liquid or gaseous, solid and can be divided into a large piece of material, fiber material, pellet, powder materials, etc., while moisture generally is material in the water, or other solvents. In this water for the object. There are three types of drying methods:
(1) mechanical dehydration mechanical dewatering method is through the pressure of materials, will be part of the water squeezed out. Squeeze, sedimentation, filtration, centrifugal separation. Mechanical dehydration can only remove the material part of free water, combined with the water still left in the material, so materials by mechanical dewatering the material moisture content is still high, usually 40 to 60 percent. Mechanical dehydration is one of the most economical way.
(2) heating and drying method is what we often dry, which uses thermal heating materials, gasification of materials in the water. Need to consume a certain amount of heat to remove the moisture in the material. Usually air to dry the material, the air is heated in advance into the dryer, the heat transfer to the materials, gasification of materials in water to form water vapor, and with the air to bring out the dryer. Material after heating and drying to remove the combination of moisture in the material to reach the moisture content required by the product or raw materials. (3) chemical desiccant is a hygroscopic agent to remove a small amount of moisture in the gas, liquid, solid materials, due to limited dehumidification capacity of the hygroscopic agent, only for trace moisture in the removed material. Production is seldom applied. The actual production process, the humidity of materials are generally as much as possible before mechanical dewatering method to remove a lot of free water, then take other drying methods for drying.
Second, the combination of materials and water according to the material contained in the ease of moisture removal is divided into the following two:
(1), non-combined water: non-combination of water, including direct contact with the wetting water, pore water and other materials and moisture present in the material surface, the material to absorb the moisture. The bonding strength of the material is small, it is easy to remove.
(2), combined with water: including those contained in the material of cells or fiber tube bi and capillary water. This water can be subdivided into a chemical combination of water, physical and chemical combination of water and mechanical bound water. Among them, the chemical combination of water, including water of crystallization, combined with strength, it is difficult to remove, take off the water of crystallization process does not belong to the drying process; physical and chemical combination of water, including adsorption, penetration and structure of water, adsorbed water and the material combination of the most , water can be adsorbed by the outer surface of the material can also be adsorbed on the internal surface of the material, the heat released when the combination of the adsorption of water, take off when you need to absorb heat, penetrate the combination of water and materials, wall materials organization osmotic pressure differences inside and outside the solute concentration, the bond strength is relatively weak, the structure of water present in the material within the organization, combined with the water in the colloid formation, including such water from the solution by evaporation, external pressure or organization destruction; machinery combined with water, including capillary water, capillary water present in the fiber or small particles into a group of wet material, weak intensity and combination of materials. Materials with the combination of water known as the absorbent material, such as: wood, food, leather, fiber and fabric, paper, synthetic resin particles. Material that contains only non-binding of water, known as non-absorbent material, such as foundry sand, a variety of crystalline particles. Dry the difficulty, non-absorbent materials than the absorbent material is easy to dry and much more. Water of crystallization of materials for the chemical combination of water, the drying process generally can not remove the water of crystallization. Different structure of the water binding energy is about 100 ~ 3000J/mol. Different combination in the form of materials and water, exclude water consumption of energy, which indicates that the drying heat are not the same. Materials in dry conditions, the moisture whether the drying method in addition to the Department can be divided into the balance of water and free water. In life, often encounter some of the materials in the humidity of the air damp, "the phenomenon, these damp materials in dry air will return to its" dry "state. "Damp" or "dry" process, to a certain limit, the materials in the water content will tend to a certain value, this value is referred to as the balance of moisture in the air state. A moisture material contained greater than the equilibrium moisture during the drying process can be removed from the wet material, commonly known as free water.
The drying process of wet material, the drying process of wet materials, dry conditions for the drying medium (usually hot air) flow rate, humidity and temperature. When hot air from the surface of the wet material at a steady rate out of date, due to the high air temperature, low temperature materials, air and materials between the heat transfer driving force, the air convection heat transfer to the material, the material is accepted The heat, the water used to gasification which constantly taken away by air, the moisture content of the material is declining. When the moisture content of the material down to the water balance, the end of the drying process. The drying process, there are two mutual process of heat and mass transfer, so-called heat transfer, hot air heat transfer to the material, water and heating material for gasification which mass transfer is the evaporation of moisture in the material and migration to the hot air in the material moisture content decreased gradually get dry.
2, the characteristics of the drying process during the drying process, the materials always have certain geometric size, even very fine powder, can also be seen from the microscopic particles of a certain size, in fact, the above heat and mass transfer between the hot air and the material particles and the mechanism of material particles within the same process of heat and mass transfer in drying in theory, will be divided into the hot air and the material surface heat and mass transfer and heat transfer of the material within the The mass transfer process. Different of these two processes affect the material of the drying process, two different drying stage plays a leading constraint, which led to the generally dry and wet materials the previous phase is always faster and stable speed, the latter stage is getting slower and slower speed, so we will be drying process is divided into the constant drying stage and the falling rate drying stage.
Constant drying stage in the constant drying in paragraph (1), the material internal moisture diffusion to the surface speed, you can make the material surface remains fully wetting the surface of the moisture content is greater than the maximum moisture capacity of the drying medium, so the drying rate depending on the speed of surface gasification. In other words, the constant velocity segment is bullied control stage. Remained unchanged due to the drying conditions (air temperature, humidity, speed), so the rate of desiccation is also basically the same, it is called the constant drying stage, this stage of heat and mass transfer between the hot air and the material surface plays a leading role. Therefore, improving the airflow velocity and temperature, reducing the air humidity are conducive to the constant velocity phase of the drying rate. The heat absorbed by the constant velocity phase of materials is almost all used to evaporate water, the material rarely warming, it is a very high thermal efficiency. It can be said that the constant velocity segment of dehydration is easier to remove moisture, combined with water to a purely non-
(2) the falling rate drying stage with the moisture content of materials continue to lower the material internal moisture migration speed is less than the gasification rate of the material surface, the drying process is constrained by the role of material internal heat and mass transfer, dry faster and slow, at this stage is called the falling rate drying stage, has the following characteristics: slow down the drying rate of the segment, and the moisture content of materials, the lower moisture content, drying rate is smaller. This is the first characteristic with constant velocity segment; is closely related to the thickness or diameter of the section of the drying rate of deceleration and materials, the thicker, the smaller the drying rate. This is the second feature; when the deceleration phase, the drying rate gradually decreases, the air passed to the heat of the material as gasification water use, there are still a part of will make the material temperature rises until the last close to the temperature of the air. This is the third characteristic; deceleration segment of the moisture in the material internal gasification, and then spread to the surface of the form of steam, so the deceleration phase of the drying rate depends entirely on the rate of diffusion of water and steam in the material within. Therefore, the deceleration segment called internal diffusion-controlled stage. This is the fourth characteristic. In the deceleration stage, the key to increasing the drying speed is no longer a condition to improve the drying medium, but to improve the material internal moisture diffusion speed. Increase the temperature of the material, reducing the thickness of the materials are very effective way. This is the fifth feature. Relatively constant drying stage, the spin-down section of desiccation is much more difficult, a much higher energy consumption. Therefore, in order to improve the drying rate, reduce energy consumption, and ensure product quality in the production process allowed, should be taken to break up, broken, cut short and other methods to reduce the geometric dimensions of the material, to facilitate the drying process carried out.
Dry conditions need to determine the selection of equipment due to the many types of wet material in the drying process, drying characteristics but also very different, and so require different types of drying methods and equipment. This selection of drying methods and equipment. If you choose properly, will inevitably lead to investment in equipment is too large, or rising operating costs, or product quality does not meet the requirements, in extreme cases, even the operation running. So, you must pay enough attention to the selection problem.