Energy Saving and Environmental Protection of Drying Technology

- May 08, 2019 -

Henan Microwave Equipment Network News: Thermal drying is a link in almost all industrial fields, with more than 60,000 kinds of materials. Material drying is a high-energy-consuming operation. According to incomplete statistics, 10-25% of the global energy is used for industrial thermal drying. It is also one of the major energy-consuming households in China. The energy used accounts for about 12% of the total energy consumption of the national economy. Some industries such as paper industry consume about 35% of the total energy consumption of enterprises, and wood drying accounts for 40% - 70% of the total energy consumption of enterprises. In drying industry, there is a general situation of low thermal efficiency, usually between 30% and 60%. If the thermal efficiency of paper drying is general & lt; 50%, the thermal efficiency of wood drying is between 30% and 40%. In addition, the pollution caused by the drying process is often an important source of environmental pollution in China. Taking the steam drying workshop with annual drying capacity of 10,000 cubic meters as an example, the harmful substances it discharges per hour are about 40 Kg of smoke and dust, 1,900 cubic meters of carbon dioxide, 45 cubic meters of sulphur dioxide, and a small amount of nitrogen oxide, which cause the greenhouse effect, acid rain and ozone in the atmosphere. The main factors of damage. As the contribution rate of energy to environmental protection can reach 70% to 80%, energy saving and environmental protection of drying technology is very important. The general goals and trends of drying technology development in the future are as follows: increasing the output and quality of products under the same energy consumption; decreasing the output and quality of products at the same time and reducing energy consumption; making full use of the advantages and disadvantages of various drying technology combinations to achieve optimal results; reducing the harm of drying to the environment and striving for sustainable development. The application of innovative drying technology

should consider how to turn the backlog of innovative technologies into innovative technologies for sustainable development in the future, and strive to achieve the combination of research and development and application, otherwise R&D is meaningless.

_Drying model must predict transfer phenomena and quality parameters. The model of dryer has more universality and practicability. Drying model is more valuable for basic control, design, scale expansion, optimization, etc. It does not need more complex model, but needs more accurate or practical model. Improving drying efficiency is not simply a matter of heat and mass transfer. In fact, optimization of heat and mass transfer is only one aspect of drying optimization. The innovation of drying technology should consider the optimization of the whole drying system, and the combined drying technology belongs to the overall optimization.

P>_Vacuum superheated steam drying is a drying technology with considerable development potential. It can not only improve drying speed, but also improve drying quality.

P>_Both impinging stream dryer and jet dryer and pulse combustion dryer belong to high efficiency drying equipment. Although pulse combustion drying is still under study, it may have certain application prospects for some debris (including wood chips) and paper drying.

P>_In the future, technological and economic analysis of innovative technology should also be carried out. Developing "green" drying technology

"green" drying technology refers to minimizing the pollution of air environment caused by emissions from drying process, which can be implemented from two aspects:

Making full use of clean energy such as solar energy and electric energy

_Solar energy is a renewable clean energy, and solar drying belongs to sustainable development drying technology. However, solar energy is intermittent energy with low energy density, discontinuity and instability. When solar energy is used alone, the drying chamber has low temperature, large fluctuation and long drying cycle. Therefore, solar drying often needs to be combined with other energy sources, such as solar energy-heat pump, solar energy-steam, and solar energy-furnace gas, so as to increase the total investment of drying equipment.

_Heat pump dehumidification drying has become the second drying technology after conventional drying due to its remarkable energy saving effect, good drying quality, no pollution to the environment with electric energy and relatively mature technology. But there are also some problems in heat pump dehumidification drying, which affect its promotion, such as low dehumidification drying temperature and long drying cycle; in addition, simple dehumidification drying generally uses electric heating as auxiliary heat source, and the heating of drying chamber depends on electric heater, which leads to high power consumption. Therefore, dehumidification and drying can save energy and money in areas with high electricity price and tight power supply.

At present, conventional drying is still dominant in drying equipment all over the world, and more than 80% of wood in China is conventional steam drying. One of the main reasons for the high energy consumption of conventional drying is the large heat loss of exhaust gas. To recover the heat energy of exhaust gas and reduce energy consumption can reduce the pollution of smoke and dust to the atmosphere, so it is to implement "green" drying technology from another aspect.

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