Various data show that the prospect of microwave drying equipment is broad.

The drying process involves almost all sectors of the national economy and is widely used in production and life. The purpose of drying equipment is to remove water or solvent from some raw materials, semi-finished products and finished products, so as to facilitate processing, use, transportation and storage. The general drying methods are mechanical method, chemical method and heating (freezing) method. These methods either have huge equipment, high drying costs, or slow drying rate and small processing capacity. With the development of science and technology, such as biological products, new materials (multi-phase composite materials, nano-materials, intelligent materials and biomedical materials), advanced ceramics, new advanced foods and new pharmaceutical products, the traditional drying technology and drying equipment are no longer applicable. Microwave drying technology and microwave dryer have been widely used in light industry, construction industry, food industry, agricultural products processing industry and other industries, showing strong advantages. Microwave drying is undoubtedly a new technology to meet the requirements of new products. The fertilizer industry is one of the pillar industries in the national economy, and the production process of fertilizer is becoming more and more mature. However, there are many unfavorable factors and problems in the drying process of fertilizer, especially compound fertilizer: (1) the drying temperature can not be too high, so the drying impetus is small and the drying time is long;

P>2) the drying device is huge and the productivity is low;

3) the investment cost is large and the production cost is high. Thermal and non-thermal effects of

microwave field can be solved by microwave technology and equipment. The drying time can be shortened and drying rate and productivity can be improved at a low temperature. Microwave-assisted acidification of phosphate rock to produce calcium phosphate rock has been studied. The results show that microwave-assisted acidification can increase the temperature of phosphate rock pulp, change the crystalline morphology, promote the reaction and increase the conversion rate. The author is engaged in the research of microwave drying process of chemical fertilizer, and intends to find out the relationship between microwave and granulation performance of high nitrogen compound fertilizer through experiments, and determine the optimum technological conditions of microwave drying of compound fertilizer and its mechanism of mass and heat transfer. Preliminary experiments show that the temperature of fertilizer increases very slowly under the action of microwave, heating in microwave oven for 40 minutes does not exceed 50 C, while under the same conditions, the temperature of water heating in microwave oven for 5 minutes can reach 80 C, and the quality can be reduced by 70%. This is because the dielectric constant of general fertilizers is much smaller than that of water, such as urea 3.5, potassium chloride 5.03 and ammonium chloride 7.0. The different effects of microwave on fertilizer and water are the theoretical basis of microwave drying compound fertilizer.