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Li X.,Tianjin University | Lin C.,Tianjin University | Wang L.,Yunnan Jiehua Clean Energy Development Co. | Li H.,Tianjin University
Frontiers of Chemical Science and Engineering | Year: 2013

This paper aims to investigate the multi-stage effect on crude distillation units (CDUs) in thermodynamics. In this regard, we proposed three-, four-, five-, and six-stage CDU processes with all variables constrained to be almost the same except for the number of stages. We also analyzed the energy and exergy to assess the energy consumed by each process. Because additional distillation units would share the processing load and thus prevent products with low boiling points from overheating, the heat demand of the CDUs decreases with increasing stages and thus reduces the heat supply. Exergy loss is considered as a key parameter to assess these processes. When the exergy losses in heat exchangers are disregarded, the three-and four-stage CDUs have lower exergy losses than the five- and six-stage CDUs. When the overall exergy losses are considered, the optimum number of stages of CDUs depends on the exergy efficiency of heat integration. © 2013 Higher Education Press and Springer-Verlag Berlin Heidelberg.

Liu Y.,Tianjin University | Cong S.,Tianjin University | Cong S.,National Engineering Research Center for Distillation Technology | Xu C.-C.,Tianjin University | And 4 more authors.
Xiandai Huagong/Modern Chemical Industry | Year: 2013

The boiling points of tetra-methyl benzene are very close, which is difficult to separate by distillation. But the differences of melting points in-between isomers are quite distinctive. Therefore, the static melt crystallization is feasible to separate and purify durene from its isomers. Considering the change of surface temperature between solid and liquid phase with the coolant temperature, the dynamics of static crystallization is studied by analytic iteration method and verified by experiments. The nonlinear least square method is applied to estimate the combined dynamic parameter by fitting the experimental data of isothermal crystallization and the relationship between dynamic parameter and coolant temperature is obtained by fitting of a polynomial. The results were used to simulate the crystal growing during nonisothermal crystallization process and the calculated results fitted well with experimental results, which indicated that the model can predict the growing of the crystalline layer very well.

Li X.-G.,Tianjin University | Li X.-G.,National Engineering Research Center for Distillation Technology | Liu Y.,Tianjin University | Li H.,National Engineering Research Center for Distillation Technology | And 5 more authors.
Huaxue Gongcheng/Chemical Engineering (China) | Year: 2013

In order to get high-purity durene as by-product, melt crystallization was used to purify durene from mixtures containing mass fraction 62.3% durene which comes from the distillation cut of methanol synthetic oil. The experiment was carried out to compare the bubbling crystallization and study the effects of main parameters (bubbling speed, cooling rate, crystallization temperature, the holding time during crystallization, sweating temperature and the holding time during sweating) on the crystallization. The appropriate operating conditions were that rate ratio was 0.75 L/(h·g), cooling rate was 0.1 °C/min, crystallization time was 1.5 h and sweating time was 2 h. By the experiments with durene solution of different mass fractions, the empirical crystallization and sweating equilibrium equations were developed. The mass fraction 62.3% durene solution was purified to more than 99% by three continuous crystallization stages. The calculated results fit well with the experimental data, which can satisfy the requirement of engineering.

Cong S.,Tianjin University | Cong S.,National Engineering Research Center for Distillation Technology | Liu Y.,Tianjin University | Li H.,Tianjin University | And 5 more authors.
Chinese Journal of Chemical Engineering | Year: 2015

The purification and separation of durene from the mixture containing durene isomers were studied. Since the boiling points of tetramethyl benzene isomers are very close but their melting points are of great differences, static melt crystallization was applied to separate and purify durene from its isomers. Crystallization experiments were carried out under various operating conditions. The effects of cooling rate, crystallization temperature, sweating temperature and sweating time on the yield and purity of crystal were investigated. Orthogonal experimental design method was adopted to analyze the factors that may affect the yield of durene. Under the optimal crystallization conditions, the purity of durene could reach as high as 99.06% with the yield of 75.3% through one crystallization process. By fitting purification data based on sweating time in isothermal operations, the purification rate coefficient was obtained. © 2014 Elsevier B.V.

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