Through the joint efforts of engineering and technical personnel in the drying industry, China's drying equipment has made significant progress in recent years. The structure and performance of the dryer have been significantly improved, and the quality is constantly improving. Some models have been exported abroad. This article elaborates on the technological progress of drying equipment in China in recent years and points out the existing problems. Analyze the development of production technology in various industries in the future, provide suggestions on how drying equipment can meet production needs, look forward to the future trends of drying equipment, and provide reference for the development of technical equipment.

The current technological status of drying equipment.

In recent years, with the rapid development of industrial and agricultural production in China, the demand for drying equipment has been increasing, and the overall level of drying equipment is also constantly improving. Traditional drying equipment can basically meet the production needs, and the models are exported abroad. These satisfactory achievements are the result of the long-term efforts of most engineering and technical personnel. The progress of drying equipment is reflected in the following aspects:

(1) The processing quality of drying equipment.

From the manufacturing process of drying equipment, the processing quality of drying equipment is limited by technological level and application industry. There are many application industries for drying equipment, and the pharmaceutical industry has high requirements for equipment quality. Due to the particularity of the pharmaceutical industry, there are specific requirements for the materials, structure, and processing quality of the drying equipment used. Therefore, the equipment provided by the manufacturing industry has high processing quality. The second is the food industry. The food industry has strict hygiene requirements for drying equipment and drying systems, therefore the equipment structure and steel processing standards are high. Some equipment in chemical production has relatively low quality requirements. Among all industries, the chemical industry has the most complex number and types of equipment. It should be said that the drying equipment in the chemical industry has special requirements, but slightly lower than the above two industries.

From the perspective of the total quality of drying equipment in recent years, most of the equipment steel plates have been polished, and the welds are made of argon arc welding (stainless steel). The welds have also been processed, and the factory uses automatic or semi-automatic welding of straight and circumferential welds to ensure equipment quality. Changzhou Daming Pharmaceutical Equipment Co., Ltd. and Changzhou Qile Machinery Equipment Co., Ltd. have excellent processing quality in the factories visited.

The structure of the dryer.

With the introduction of drying equipment in China and international technological exchanges, foreign drying equipment models continue to influence our country. In recent years, China's new models and structures have mainly been reflected in the following aspects:

① Concealed heat pipe fluidized bed dryer: This dryer changes the previous method of introducing all the heat from the fluidized bed through hot air. Through internal heat transfer tubes, the partial heat conduction and transfer of the heat medium inside the pipeline greatly improve thermal efficiency. The data shows that the thermal efficiency of traditional fluidized beds is 39.7%, while the thermal efficiency of internal heat pipes is 72.5%. Under the same output, the bed area decreased from 72.5 square meters to 14.42 square meters. Swiss company Sulzer and Japanese company Nara Machinery Manufacturing have this equipment. The heat medium is generally steam, heat transfer oil, etc.

② Tube bundle dryer: The shell and transmission mode of the tube bundle dryer are very similar to those of the drum dryer, but the inner layer is arranged with 1-5 concentric layers of tube bundles. The bundle passes through the entire length of the dryer, conducting and convective heat through water vapor or other heat media. High thermal efficiency, with a total heat transfer efficiency of up to 80%~90%, especially suitable for materials with drying temperatures below 150 ℃.

③ Flash drying machine: As a drying equipment introduced in China in 1989, it has the ability to process viscous filter cake materials and can directly obtain powder materials. Suitable for drying low viscosity mineral filter cakes and chemical intermediates.

④ Leaf dryer: In 1990, the leaf dryer was first introduced by Beijing Dyestuff Factory for drying indigo dye. The blade dryer is mainly based on traditional heat transfer, with the advantages of high heat transfer efficiency and continuous production.

⑤ Disc dryer: In the early 1980s, Shanghai Chemical Equipment Research Institute developed this technology, but due to various reasons, the equipment was not widely promoted and used. In recent years, many domestic drying enterprises have begun to develop this technology, which is now basically mature, and theoretical research on this model has also made certain progress.

⑥ Vibration fluidized bed dryer: This model adds a structure to control the speed of material operation, and the distribution of hot air is more reasonable, which can effectively prevent material leakage. Compared with ordinary vibrating fluidized beds, the area evaporation intensity is greatly improved.

⑦ Slot type mixing dryer: Developed earlier by Kurimoto Railway Factory in Japan. In a trough dryer, the structure of the raw mixing material is composed of pipes that allow steam to flow in, which can mix the material and transfer heat.

⑧ Flow rotary dryer: Install a porous rotary cylinder inside a rectangular box. There are multiple duplicate plates around the cylinder, and the duplicate plates also have a small hole. The processing method is similar to that of a rotary cylinder dryer, where hot air passes through the cylinder and material layer from the bottom of the cylinder. After humidification, the dryer has the characteristics of a rotating cylinder dryer and a fluidized bed discharged from the upper part.

⑨ Rotary airflow dryer: Hirst was early used in Germany for drying PVC. The basic principle is that the dryer mainframe is composed of a cylinder with a jacket. The hot air carries materials and performs spiral lifting motion in the dryer. Hot air flow and material heat and mass transfer, jacket heat and radiation heat transfer. Therefore, the thermal efficiency is higher than that of a hot air flow dryer.

Equipment scale

As a unit equipment in production, the dryer aims to meet production requirements. With the expansion of production scale in various industries, the scale of drying equipment is also constantly expanding. At present, the diameter of flash drying equipment produced in China can reach 1.6m (there are not many application examples beyond this scale), and it is running well. The heat transfer area of the blade dryer can reach 160 square meters, and the heat transfer area of the disc dryer can reach 180 square meters. The processing capacity of the mechanical centrifugal spray dryer can reach 45t/h, and the processing capacity of the electromechanical centrifugal atomizer can also reach 5t/h, which better solves the mechanical problems of the atomizer. The centrifugal spray dryer has a diameter of 8m, a total height of more than 50m, and a processing capacity of 4t/h. The diameter of the rotary cylindrical dryer can reach 2.5 meters and the length is over 30 meters. The area of the belt dryer has also reached over 140 square meters.

equipment level

The equipment level of drying equipment mainly refers to the control level of the drying system, the equipment of auxiliary equipment, the convenience and safety level of operation. Significant progress has been made in the equipment level of drying equipment in our country. Especially for large-scale drying systems. Mainly manifested in the following aspects:

① Control system equipment. Widely used in automatic and semi-automatic control systems to reduce labor intensity and stabilize product quality.

② The application of computer technology. Most large systems use computer technology to collect, process, and control system parameters to ensure optimal operating conditions.

③ Humanized design. Consider the habits and maintenance of the operators while designing the equipment.

④ Safety design. The system has safety alarm and hazard elimination functions, especially for dry flammable and explosive materials.

⑤ Auxiliary equipment. The auxiliary equipment in the system has also become more reasonable, optimizing the matching relationship between product packaging equipment and the host, such as heating, feeding, gas-solid separation, etc.

Experimental conditions

The design of a dryer requires specific material related process parameters, and many important parameters need to be obtained through experiments. The design of a dryer relies heavily on experiments. Therefore, experimental conditions are the key to accurately designing a dryer.