【作者】 郭胜利；

【导师】 张宝林；

【作者基本信息】 郑州大学 ， 化学工艺， 2003， 硕士

【摘要】 我国是一个人口大国，粮食问题一直是各个时期备受政府关心的重要问题。提高粮食产量的根本办法是提高单位面积粮食产率。在提高作物单产的诸多因素中肥料的贡献率大约为40％-70％。可见化肥在这方面的作用是举足轻重的。在今年举行的十届全国人大一次会议上，朱镕基总理的报告中提到将来的五年内需要解决的中心问题之一就是“三农”问题，即农业、农村、农民的发展问题。作为与农业和农民有着密切关系的化肥行业无疑将会迎来更大的发展机遇。 干燥是复混肥料生产中的一个重要工序，往往成为产品产量和质量的制约因素。干燥过程的特点是传热和传质并存，相互影响又相互制约。复肥干燥过程存在着许多不利因素和问题。针对这些问题不少专家学者提出了很多解决办法。本论文研究了复合肥料微波干燥的特点和工艺条件，在降低相对干燥温度的同时降低干燥成本，简化操作过程。 微波加热不同于一般的常规加热方式，后者是由外部热源通过热辐射由表及里的传导式加热。微波加热是物料在电磁场中由介质损耗引起的体加热。由于复肥中的水分介质损耗较大，能大量吸收微波能并转化成热能，因此肥料的升温和蒸发是在整个肥料中同时进行的。肥料在微波场中的温升情况与其有效介电常数有关，尽管大多肥料的介电常数都比水要小的多，也要防止出现热失控现象。常用基本肥料(如尿素、磷酸一铵、磷酸二铵、过磷酸钙和氯化钾等)在微波场中的温升曲线表明，在510W的微波功率下受热25min其温度将达到或超过80℃(氯化钾除外)。过磷酸钙因含水量高温升速度显著提高，这给干燥过程的控温带来不便。这表明利用微波干燥复肥时应慎重选择微波功率和干燥时间。 复合肥料微波干燥的影响因素很多，除物料本身的特性对干燥的影响以外，有空气温度、带走水份的空气速度，物料形状、大小、料层的厚度、微波功率等因素对干燥速度的影响。实验对其主要因素进行考察，这些因素有：风温、干燥物料量、微波功率、微波作用区间和物料在微波炉中的停留时间。对这些因素分别在四个水平上进行试验。结果表明：各因素对干燥过程影响大小的顺序为：微波作用区间、风温、微波功率、物料量和停留时间，重复实验结果与此相同。其中前三种因素对平均干燥速率有显著影响。进行复肥微波干燥进一步实验的最优条件为：强制对流空气的温度为40℃左右，干燥过程中使用微波，微波功率为100W 郑州大学硕士论文 ——~一一一一一三迎巡燮些~些卫三丛望里旦迎竺望兰些理些坐垫业望些二一——一~—到Zoow，间歇干燥时物料处理量为1009(约1.0留cm，)，干燥时间在lomin左右。 对分布在高、中、低三个不同的品位上兼顾高氮、高磷和高钾三种营养元素的三种复肥进行微波干燥实验。实验表明:复肥的微波干燥因其水分存在形式及移出形式的不同而经历三个阶段--一表面蒸发和分子扩散阶段、分子扩散与内部蒸发同时进行阶段(称为热湿扩散阶段)和微速干燥阶段‘复合肥料的微波干燥温度可控制在60℃以下。实验使用的微波功率为75W，可在15min--2枷in内将复合肥初始含水量在5哈8%之间的半成品干燥至含水量在2%以下。尽管在干燥过程中养分有损失，但养分最大损失率不超过5%。与其相比，常压烘箱干燥要达到同样的干燥要求需要2h。复肥的微波干燥表现出快速、保质、节能和环保等特点。 最适用于复肥微波干燥的回归曲线的方程列于式(l)。人仅=AZ+AI一AZ ，一tol+eB(l)t0是曲线的拐点，也即最大干燥速率时间点。最大干燥速率计算式为式(2)。，办扭、(一丁一)max dt月2一Al4B(2) 从式(2)可以看出，最大干燥速率由A:与A:的差和B的比值决定。AZ是干燥所能达到的极限水分，AZ的大小决定了干燥所能进行的程度，AZ越小干燥进行的越彻底。达到干燥要求卯所需要的时间七2由式〔3)计算。t月2=to 。，_月2‘十Z)1 11一们一l(3)在时间区间【O，坐塑}-dl laverag。勺2]内平均干燥速率用式(4)计算。 ，o月l一AZ eB一121。鱼 eB+l(4) 干燥过程中微波的作用越突出，曲线的拟合程度越好。 由于复肥的微波干燥过程中存在水分直接蒸发即热湿扩散作用，因此用式(5)描述其水分传递过程。孙了_r刁2M2日入了、_aZTZ刁T、_—二刀l(----;-+一—)十口(-二-+一—)l动一‘扮‘r扮‘’ar‘rar’J(5)式(5)右边第二个圆括号内的量表示由温度差引起的水分传递。水分边界条件复合肥料的微波干燥研究Study on Drying ComPound Fertilizers by Microwave Radiation列于式(6)。‘/(M一“·，一D肇}。_;(6) 微波的特定加热方式相当于复肥内部有内热源，并且复肥吸收的热除用于升温外还用于水分直接蒸发。复肥微波干燥的热传递过程用式(7)描述。aT a 2 TZ日T、L—二仪(一-气二，十一—)十一次’ar名r沙一C丝+鱼次(今，(7)温度边界条件列于式(8)。h:(兀一T。)=__口T入—沙};=，(8)更多还原

【Abstract】 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更多还原