| There is a great population in our country. Our government pays much attention on solving food problem. The fundamental method to improve food yield is to raise the output on unit area. Fertilizers account for 40%-70% in improving the food unit output and play a great role in such respect. Report of Primer Zhu on the Tenth National Committee this year declares that dissolving "San-Nong" problem is the center task in the next five years. Fertilizer industry, which closely relates to agriculture and peasants, faces a new opportunity.As an important process in producing compound fertilizers (C.F.) drying determines the quality and quantity of the products. Mass and heat transfer both exist and affect with each other in drying procedure. Problems and disadvantages in traditional process of drying C.F. attract attention of experts and scholars. Thus various dissolutions are put forward. The characteristics and process conditions of drying C.F. by microwave are studied in this thesis. Microwave drying can reduce the temperature and the cost at the same time.Microwave heating occurs in the whole body of the material, which differs from the conduction heat transfer in traditional heating system. Since water absorbs strongly the energy of microwave temperature rise and vaporizing occur in the whole body of the fertilizers. Although the dielectric constant of C.F. is much less than that of water certain measures should be taken to avoid thermo-runaway. Behaviors in microwave radiation of fundamental fertilizers (such as urea, MAP, DAP, SSP and KC1) are studied. Their temperatures reach or surpass 80C after being heated for 25 minutes in microwave oven except KC1. The microwave power and the drying time should be carefully chosen to control the temperature.Many factors affect the process of drying C.F. by microwave. Except the nature of the material itself among these factors are air temperature, air velocity of flow, the shape, thickness and quantity of the material and microwave power. We studied the main factors through experiments. They are air temperature, quantity of material, microwave power, intervals of microwave and drying time. Orthogonal experiments are designed among these factors on four different levels. The result shows that the sequence from big to small of the degree they affect the average drying rate is as follows: intervals of microwave, air temperature, microwave power, quantity of material and drying time.Repeating experiments gain the same result. The anterior three factors affect greatly on the average drying rate. The best conditions to make further experiments are air temperature of 40 C, microwave power of 100W to 200 W, handling capacity of 100g (about 1 .0g/cm2) per batch and drying time of 10 minutes.Three experiments are designed to dry C.F. of high, intermediate and low grades with their nutrients of high N, high P2O5 and high K2O. Microwave is used in each experiment. The drying process has three stages of molecule diffusion phase, thermal-moisture diffusion phase and micro-rate drying phase. The temperature of drying C.F. by microwave can be controlled under 60 C. A moisture content of 5%-8% can be reduced to below 2% within 15min to 20min by microwave of 75 W. The lose rate of nutrients is below 5%. Comparability tests on drying the same samples in atmospheric drying oven show that it takes 2 hours to reach the same requirements. The merits of drying C.F. by microwave include fast drying, holding the quality, save energy and no pollution to environment.The proper regression curve is shown in equation (1).(1)to is the inflection point of the curve as well as the point of the maximal drying rate. Equation (2) tells how to calculate the maximal drying rate.(2)As is shown in equation (2) (A2-A1)/B determines the maximal drying rate. A2 is the limit of the lowest moisture content. The final degree of drying is determined by A2. is our drying target. To reach the target needs a period of time of tA2, tA2 can be calculated by equation (3).The average...
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