Liquid level optimal-setting for tube falling film evaporator based on exergy

doi:10.11949/j.issn.0438-1157.20151917

Abstract

Abstract:

In the tube falling film evaporator, liquid level directly influences the pressure and the temperature in the evaporator and therefore influences the heating steam consumption. So, it is an important parameter for optimization of evaporator operation. But in the actual production, the liquid level is usually set empirically in a large range, so that the process cannot run in optimal situation. A liquid level optimal-setting method based on exergy analysis is proposed. By deeply analyzing the liquid level's effect on other evaporation parameters and using the actual running data of the sodium aluminate solution evaporation process for alumina production, the correlations between liquid level and other parameters are obtained. An optimization model based on the maximum exergy efficiency is then established based on the material balance of the evaporator and the exergy analysis method. The optimization model is then solved under a certain condition to get the exergy efficiency-liquid level curve. Finally the optimal level under different operating conditions is calculated, which provides guidance for the optimization of the actual production operation.

Key words: alumina, tube falling film evaporator, exergy efficiency, steady state, liquid level, optimal-setting, algorithm

摘要：

在降膜蒸发器中,物料液位直接影响蒸发器分离室压力和出料温度从而影响加热蒸汽消耗,对蒸发器的优化操作十分重要。但实际生产中液位的设定值通常是一个较大的范围,难以优化运用。针对此问题提出了一种基于(火用)分析的管式降膜蒸发器液位优化设定方法。深入分析了液位高度对蒸发过程各参数的影响,基于实际生产数据,拟合得到了液位与其他参数间的关系模型。结合蒸发器物料平衡关系以及(火用)分析方法,建立了最大化(火用)效率的能耗优化模型。对优化模型求解得到了蒸发器(火用)效率随液位高度变化的关系曲线,最后计算了不同工况条件下的最优液位,为优化实际生产操作提供了参考。

关键词: 氧化铝, 降膜蒸发器, (火用)效率, 稳态, 液位, 优化设定, 算法

CLC Number:

TQ028.8

ZUO Jian, XIE Yongfang, WANG Xiaoli, XIE Sen, YANG Chunhua. Liquid level optimal-setting for tube falling film evaporator based on exergy[J]. CIESC Journal, 2016, 67(3): 891-896.

左健, 谢永芳, 王晓丽, 谢森, 阳春华. 基于(火用)的管式降膜蒸发器液位优化设定[J]. 化工学报, 2016, 67(3): 891-896.

References 21

[1]	阮奇, 叶长燊, 陈文波,等. 复杂逆流多效蒸发系统优化设计的模型与算法[J]. 化工学报, 2001, 52 (8): 616-621 . RUAN Q, YE C S, CHEN W B, et al. Model and algorithm for complex multi-effect evaporation system[J]. Journal of Chemical Industry and Engineering (China), 2001, 52 (8): 616-621.
[2]	李玲, 阮奇. 平流多效蒸发系统的数学模型与求解[J]. 化工学报, 2009, 60 (1): 104-111. LI L, RUAN Q. Modeling and solving for advection multi-effect evaporation system[J]. CIESC Journal, 2009, 60 (1): 104-111.
[3]	聂晓凯, 阳春华, 柴琴琴,等. 氧化铝蒸发的动态过程建模与仿真[J]. 化工自动化及仪表, 2011, 38 (3): 279-283. NIE X K, YANG C H, CHAI Q Q, et al. Dynamic modeling and simulation of alumina evaporation process[J]. Control and Instrumentation in Chemical Industry, 2011, 38 (3): 279-283.
[4]	KAM K M, SAHA P, TADE M O, et al. Models of an industrial evaporator system for education and research in process control[J]. Developments in Chemical Engineering & Mineral Processing, 2002, 10 (1/2): 105-127.
[5]	TIAN R H, CHEN G L, JUN S W U, et al. Modeling and simulation in the process of five-effect evaporators[J]. Journal of East China University of Science & Technology, 2000, (5): 568-572.
[6]	张建智, 彭小奇, 李时民,等. 基于热分析和(火用)分析的氧化铝生产蒸发工序节能研究[J]. 中南大学学报 (自然科学版), 2011, 42 (11): 3556-3563. ZHANG J Z, PENG X Q, LI S M, et al. Energy saving research at alumina evaporation process based on thermal analysis and exergy analysis[J]. Journal of Central South University (Science and Technology), 2011, 42 (11): 3556-3563.
[7]	彭小奇, 宋国辉, 宋彦坡,等. 氧化铝生产蒸发工序的(火用)分析[J]. 中南大学学报 (自然科学版), 2011, 42 (3): 829-834. PENG X Q, SONG G H, SONG Y P, et al. Exergy analysis of alumina evaporation process[J]. Journal of Central South University (Science and Technology), 2011, 42 (3): 829-834.
[8]	阳春华, 柴琴琴, 桂卫华. 基于(火用)分析的氧化铝蒸发过程能耗优化[J]. 化工学报, 2011, 62 (7): 1957-1962. YANG C H, CHAI Q Q, GUI W H. Optimization of energy consumption for alumina evaporation process based on exergy analysis[J]. CIESC Journal, 2011, 62 (7): 1957-1962.
[9]	桂卫华, 崔书君, 阳春华, 等. 氧化铝管式降膜蒸发器的(火用)分析[J]. 控制工程, 2010, 17 (6): 723-726. GUI W H, CUI S J, YANG C H, et al. Exergy analysis of alumina tube falling film evaporator[J]. Control Engineering of China, 2010, 17 (6): 723-726.
[10]	SIMPSON R, ALMONACID S, LOPEZ D, et al. Optimum design and operating conditions of multiple effect evaporators: tomato paste[J]. Journal of Food Engineering, 2008, 89 (4): 488-497.
[11]	SHARMA S, RANGAIAH G P L, CHEAH K S. Multi-objective optimization using MS Excel with an application to design of a falling-film evaporator system[J]. Food & Bioproducts Processing, 2012, 90 (2): 123-134.
[12]	CHAIQ Q, YANG C H, TEO K L, et al. Optimal control of an industrial-scale evaporation process: sodium aluminate solution[J]. Control Engineering Practice, 2012, 20 (6): 618-628.
[13]	TO L C, TADE M O, RANGAIAH G P L. Implementation of a differential geometric nonlinear controller on an industrial evaporator system[J]. Control Engineering Practice, 1998, 6 (11): 1309-1319.
[14]	KAM K M, TADE M O. Simulated nonlinear control studies of five-effect evaporator models[J]. Computers & Chemical Engineering, 2000, 23 (11): 1795-1810.
[15]	RANG G P, SAHA P, TADE M O. Nonlinear model predictive control of an industrial four-stage evaporator system via simulation[J]. Chemical Engineering Journal, 2002, 87 (3): 285-299.
[16]	ZHU H, CHAI Q, YANG C, et al. Vortex motion-based particle swarm optimisation for energy consumption of alumina evaporation[J]. Canadian Journal of Chemical Engineering, 2012, 90 (6): 1418-1425.
[17]	王永刚, 李海波, 柴天佑. 强制循环蒸发器的非线性解耦控制[J]. 化工学报, 2013, 64 (6): 2145-2152. WANG Y G, LI H B, CHAI T Y. Nonlinear decoupling control of forced-circulation evaporator[J]. CIESC Journal, 2013, 64 (6): 2145-2152.
[18]	王永刚, 柴天佑. 强制循环蒸发系统的非线性自适应解耦PID控制[J]. 控制理论与应用, 2011, 28 (9): 1145-1153. WANG Y G, CHAI T Y. Adaptive decoupling switching control of the forced-circulation evaporation system with PID control[J]. Control Theory & Applications, 2011, 28 (9): 1145-1153.
[19]	WANG Y, CHAI T, FU J, et al. Adaptive decoupling switching control of the forced-circulation evaporation system using neural networks[J]. Control Systems Technology IEEE Transactions on, 2013, 21 (3): 964-974.
[20]	唐酞峰. 蒸发器液位高度的合理选取[J]. 中国井矿盐, 2005, 36 (4): 13-16. TANG T F. Rational selection of the evaporator liquid level height[J]. China Well and Rock Salt, 2005, 36 (4): 13-16.
[21]	严家录. 水和水蒸气热力性质图表[M]. 第2版. 北京: 高等教育出版社, 2004: 1-4. YAN J L. Water and Steam Thermodynamic Properties Chart[M]. 2nd ed. Beijing:Higher Education Press, 2004: 1-4.