Study On Energy Saving And Multi-objective Optimization Of Multiple Effect Evaporation With Heat Pump For Fruit Juice Concentration

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.