Exergy analysis of multi-stage crude distillation units

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.     

Exergy analysis of desalination by solar-powered membrane distillation units

There has been an increasing interest in using exergy as a potential tool for analysis and performance evaluation of desalination processes where the optimal use of energy is considered an important issue. Unlike energy, exergy is consumed or destroyed due to irreversibilies in any real process and thus provides deeper insight into process analysis. Exergy analysis method was employed to evaluate the exergy efficiency of the “compact” and “large” solardriven MD desalination units. The exergy efficiency of the compact and large units with reference to the exergy collected by the solar collector was about 0.3% and 0.5% but was 0.01% and 0.05%, respectively, when referenced to the exergy of solar irradiance. The exergy efficiency of the flat plate solar collectors in both units varied diurnally and the maxima was 6.5% ad 3% for the compact and large units, respectively. The highest exergy destruction was found to occur within the membrane distillation module.     

Exergy analysis of thermal processes in the building materials industry

A method is proposed to calculate the chemical exergy with allowance for the chemical composition and the ambient temperature. The exergy analysis of cement clinker burning is performed. It is found that the maximal energy saving for a rotary cement kiln can be achieved by decreasing the sludge humidity and optimizing the fuel combustion and the clinker cooler operation. The analysis of thermal processes in terms of exergy characteristics is demonstrated to be more efficient than that in terms of thermal parameters, since the optimization and intensification of industrial kilns requires not only heat loss reduction but also more efficient use of heat.     

Comparative analysis of universal optimization criteria for distillation processes

Partial optimization criteria for distillation processes are considered. The two most universal criteria-energetic and entropic-are compared in the context of optimization of the feed level position for mixtures of any kind, including azeotropic ones.     

Constraint control of distillation processes

There is a growing interest to design and operate chemical processes for reduced energy consumption. As an example a comparison is made between the distillation of binary mixtures in a conventional distillation column, a vapour recompression system and a two column heat integrated system. For all three configurations constraint control schemes are proposed. Utility costs can be reduced with about a factor of two by using a beat integrated system.     

高纯三氯氢硅精馏节能工艺的模拟分析

针对多晶硅生产中高纯三氯氢硅精馏提纯过程能耗较高的特点,分别将热泵和差压热耦合精馏节能工艺应用到高纯三氯氢硅精馏提纯过程中,并使用Aspen Plus软件对这2种节能工艺进行模拟分析比较,计算得到各工艺流程的能耗,实现了过程的节能和优化.模拟结果表明,热泵和差压热耦合精馏节能工艺对三氯氢硅传统二塔精馏过程均起到了显著的节能效果,其中塔顶蒸汽压缩型、塔釜液闪蒸型热泵精馏过程分别节能66.1％、62.8％,差压热耦合精馏过程节能50.1％.     

Thermodynamic efficiency of membrane-assisted distillation processes

Membrane processes are considered as comparably mild separation processes offering the potential for significant energy savings compared with azeotropic distillation processes. Despite higher investment and material costs, they are of particular interest for improving the energy efficiency in the chemical industry. However, energy savings of more than 20%–30% are rarely reported and even a general superiority can be disputed. To further elucidate this controversial, the current study pursues a quantitative assessment of the thermodynamic efficiency of pervaporation and vapor permeation processes with stand-alone distillation and hybrid membrane-assisted distillation processes for the separation of azeotropic mixtures. The results confirm the case-dependent potential of distillation processes to outperform membrane-assisted separations in terms of energy efficiency, considering proper heat integration. Although energy efficiency is becoming significantly important, it should be considered in the context of economic performance to determine an optimal trade-off and to select the best process alternative during conceptual process design.     

Feasibility of heterogeneous batch distillation processes

Synthesis of heterogeneous batch distillation is discussed, which aims at splitting azeotropic mixtures by adding an entrainer partially miscible with one of the initial binary mixture components. Key operational parameters are identified such as the amount of entrainer added in the ternary feed, the reflux policy, and the vapor line position by examples. Synthesis and operation are less straightforward for heterogeneous batch distillation than those for the homogeneous case, but offer many advantages: more design alternatives, simplified distillation sequences, a lower consumption of entrainer, and a crossing of distillation boundaries by the still path. Feasibility is assessed using simplified modeling and confirmed using a commercial batch process simulator package. Synthesis expectations and simulated results are verified throughout bench-plant experiments for the separation of the acetonitrile—water mixture using acrylonitrile as a light heterogeneous entrainer.     

粗苯蒸馏工艺的比较

简要介绍了粗苯蒸馏工艺,对3种粗苯蒸馏工艺进行了工艺特点、介质耗量和操作费用比较,通过比较可知,蒸汽法负压粗苯蒸馏工艺消耗较少的蒸汽量,产生的粗苯分离水量较少,并且原料消耗费用低,且投资少、运行成本低,具有良好的经济效益。     

Periodic control of continuous distillation processes

The periodic control of a continuous multistage distillation column is investigated from the viewpoint of optimality. The separating efficiency and the utility cost are included in the objective function. The flow rates of feed, vapor, reflux, distillate and bottoms and the holdups of condenser and reboiler are supposed to be variable.It is analytically shown that the optimal periodic control must be boundary and that it must also be proper under a certain condition. Then, the optimal periodic control is seeked by some numerical calculations.     

New design of reactive distillation processes

A technological design of reactive distillation processes (catalytic distillation) is discussed that applies liquid-flooded catalytic zones with a cocurrent-cross flow of the liquid, into each of which only a portion of the vapor stream is passed from the zone located below. This allows the cross section of the catalytic zones to be multiply reduced and the local excessive heating in them to be completely eliminated.     

Methodology for the design and evaluation of distillation systems: Exergy analysis,economic features and GHG emissions

This work presents a process design methodology that evaluates the distillation systems based on exergetic, economic, and greenhouse gas (GHG) emission aspects. The aim of the methodology is to determine how these three features should be applied in process design to obtain information about the accuracy of the design alternatives. The methodology is tested and demonstrated on three different energy‐integrated distillation systems: the direct sequence with backward heat‐integration (DQB), fully thermally coupled distillation column (FTCDC), and sloppy distillation system with forward heat‐integration (SQF). The average relative emission saving is the highest for the DQB scheme and this sequence shows the most flexible range of use. The case studies prove the accuracy of our evaluation methodology. On the other hand, it highlights and demonstrates that the exergy analysis can predict the results of the economic study and the environmental evaluation to make the decisions, associated with process design, much simpler. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Exergy analysis of energy‐intensive production processes: advancing towards a sustainable chemical industry

Exergy analysis is becoming a very powerful strategy to evaluate the real efficiency of a process. Its application in the chemical industry is still at an early stage but many interesting remarks can be obtained from the recent research in the most energy intensive processes of the chemical industry: the production of chemicals, the cement industry, the paper industry and, the iron and steel industry. The present review analyzes the opportunities and challenges in those sectors by considering exergy analyses as the first required step (although not sufficient) to advance towards a more sustainable chemical industry. Social, environmental and economic factors play a role in the critical evaluation of a process and exergy could be considered as the property that joins together those three cores of sustainability. © 2014 Society of Chemical Industry     

An industrial perspective on membrane distillation processes

Process intensification has led to significant developments in both distillation and membrane technology. Membrane distillation (MD) is an emerging technology for fluid separations that are typically performed by conventional separation processes, such as distillation or reverse osmosis (e.g. water desalination, or water removal). Compared with other membrane technologies, the driving force in MD is the difference in vapor pressure across the hydrophobic membrane, rather than the total pressure. MD can be a cost effective separation process, especially when more sustainable alternative sources of energy (e.g. geothermal and solar) or waste heat sources are used. Many review papers on MD are available in the open literature, but most of them focus on the membrane characteristics (e.g. material aspects). This industrial perspective paper assesses the MD technology and reports on relevant issues by offering a concise overview of MD technology, addressing different MD configurations, current major applications, operating parameters and their effect on the MD process, commercially available membranes, as well as cost estimations to determine the feasibility of MD processes. While successfully applied in desalination and a few other niche applications, MD has failed to make a strong industrial impact in other areas still dominated by distillation. A key message is that membrane distillation is still a growing technology for separation and purification processes, but it needs further exploration and optimization to become a mature technology applicable to more industrial processes in the chemical process industry. © 2018 Society of Chemical Industry     

用联合算法模拟复杂精馏过程

提出一个复杂精馏过程的通用数学模型,并采用改进的松弛法与修正的N-R法相结合的联合算法求解该模型。通过对理想物系、非理想物系和Petlyuk塔精馏过程的模拟计算,证明该算法通用性强、可靠性高、收敛速度快,模拟结果与文献及工业实验吻合很好。     

Heat integration of distillation columns into overall processes

There are many well-known schemes for better energy efficiency in distillation. Examples are thermal coupling, multiple effect, heat pumping, etc. Usually these schemes are discussed for individual columns in isolation, independently from the overall process they are a part of.This paper puts the design of individual distillation columns into context with the heat integration for the overall process. An insight is discussed wGenerally, the paper defines good integration as a column not crossing the heat recovery pinch of the process and either the reboiler or the condenser