【作者】 陈天明；

【导师】 阮奇；

【作者基本信息】 福州大学 ， 化学工程， 2016， 硕士

【摘要】 多效蒸发是浓缩溶液最常用的重要化工单元过程,但其生产成本也是相当高的,为了大幅降低果汁蒸发浓缩过程的成本,提高企业的经济效益,从以下几个方面展开研究:首先,将蒸汽喷射式热泵技术、引出额外蒸汽预热原料液、溶液闪蒸和冷凝水闪蒸同时引入多效蒸发系统中,并将系统中的物料衡算和热量衡算描述成矩阵方程,建立通用的严格数学模型。将矩阵方程中的若干参数重新赋值,模型就能模拟并流、逆流、错流和平流流程,通过保留或舍弃矩阵方程中的相关块矩阵还能模拟上述流程有或无各种节能措施的情况。采用迭代法结合矩阵法求解该数学模型具有收敛稳定性好,收敛速度快的特点。将模拟结果与文献值进行对比,模拟结果的平均相对误差为3.3%,说明该模型具有较高的准确性。其次,以浓缩菠萝汁的三效蒸发系统为例,分析了各种节能措施在并流、逆流和两种错流流程中的节能效果,结果表明:热泵技术在四种流程中的节能效果基本相同,引出额外蒸汽预热原料液对并流的节能效果最明显,冷凝水闪蒸和溶液闪蒸在逆流中的节能效果最好。此外,分析了生蒸汽温度、冷凝温度、产品浓度、抽汽位置和喷射系数对四种多效蒸发流程的单位蒸汽消耗量和比传热面积的影响,结果表明:增大生蒸汽温度,四种流程的单位蒸汽消耗量都呈线性增大,但并流流程增大的幅度最小,比传热面积都减小;增大冷凝温度,四种流程的单位蒸汽消耗量都减小,比传热面积都先减小后增大;增大产品浓度,四种流程的单位蒸汽消耗量都减小,但并流流程减小的幅度最小,比传热面积都呈线性增大;抽汽位置越往后或喷射系数越大,四种流程的单位蒸汽消耗量越小,比传热面积越大;无论这些设计变量如何变化,同时采用除溶液闪蒸外的三种节能措施的并流多效蒸发系统的单位蒸汽消耗量和比传热面积都是最小的。再次,提出了基于层级和拥挤距离排序选择种群、引入外部精英档案和混合差分算法的多目标布谷鸟搜索算法(IMOCS)。用多种类型的测试函数测试了算法的性能,结果表明:IMOCS在全局搜索能力、收敛性和解集分布性三个方面均要好于标准的多目标布谷鸟搜索算法。最后,以单位蒸汽消耗量、比传热面积和生蒸汽温度最小为目标,建立了并流多效蒸发系统的多目标优化设计模型和操作模型,利用IMOCS算法对其进行求解,得到了优化设计和优化操作的Pareto前沿面,且Pareto前沿面的多样性和分布性均较好,为决策者提供了多种可供选择的设计方案和操作方案。更多还原

【Abstract】 Multi-effect evaporation(MEE)is the most important and the most widely used method in the fruit juice concentration process.But the cost of production is also very high.In order to greatly reduce the tatal cost and enhance the economic benefit of enterprise,the following aspects have been studied in this paper.Firstly,a general and rigorous mathematical model is developed for a MEE system that includes various energy reduction schemes.These energy reduction schemes are thermal vapor compression,vapor bleeding to the feed,condensate flashing and solution flashing.Material balance equations and heat balance equations are described as a matrix equation in this model.The model can simulate the forward,backward,mixed and parallel feed flow sequences by changing several parameters.The model can include only one or several kinds of energy reduction schemes by retaining or dislodging the correlative block matrix.The iteration combined with matrix methods has the advantage of the fine stability and fast convergence speed.The average relative error of the simulation results of the model of was 3.3%,compared with the literature values.This shows that the model has high reliability and accuracy.Secondly,energy saving effect of all kinds of energy saving measures is analyzed in cocurrent MEE,countercurrent MEE and two kinds of cross-current MEEs.The results show that energy saving effect of heat pump technology is almost the same for four kinds of MEEs.Energy saving effect of vapor bleeding to the feed is extremely obvious for cocurrent MEE.Energy saving effect of solution flashing and condensate flashing is best for countercurrent MEE.In addition,the effect of various design variables on the specific steam consumption and the special heat transfer area of various multi-effect evaporation systems is also analyzed.These design variables are temperature of live steam,condensing temperature,concentration of product,puming position and the ejection coefficient.The results show that the specific steam consumption of four kinds of MEEs increases linearly with the increase of the temperature of live steam,but the range of the increase is smallest for the specific steam consumption of cocurrent MEE.The specific heat transfer area of four kinds of MEEs decreases with the increase of the temperature of live steam.The specific steam consumption of four kinds of MEEs decreases with the increase of condensing temperature.The specific heat transfer area of four kinds of MEEs decreases and then increases with the increase of condensing temperature.The specific steam consumption of four kinds of MEEs decreases with the increase of concentration of product,but the range of the decrease is smallest for the specific steam consumption of cocurrent MEE.The specific heat transfer area of four kinds of MEEs increases linearly with the increase of concentration of product.The latter the puming position or the larger the ejection coefficient,the smaller the specific heat transfer area of four kinds of MEEs,the larger the specific heat transfer area of four kinds of MEEs.The results also show that the specific steam consumption and the specific heat transfer area of multi-effect evaporation are smallest,no matter how the above six design variables change.Thridly,an improved multi-objective cuckoo search algorithm(IMOCS)was introduced.The IMOCS had three improvements,choose the next population based on the level;use external elite archives;hybrid differential evolution algorithm.To verify the effectiveness of the IMOCS,several types of test functions are used to evaluate the performance.The results show that IMOCS has better global searching ability,convergence property and distributivity,compared with the standard multi-objective cuckoo search algorithm.Finally,the models of multi-objective optimization design and multi-objective optimization operation are established.Taking the minimum of specific steam consumption,special heat transfer area and temperature of live steam as the goals,the model is solved using the IMOCS and the Pareto front is obtained.Diversity and distribution of Pareto front are better and it can provide various schemes for decision makers.更多还原