Petrica Iancu

Regeneration of internal streams as an effective tool for wastewater network optimisation

Abstract A significant decrease of water disposal to treatment section from a wastewater network (WWN) can be achieved rising internal water reuse through regeneration, i.e. lowering the concentration of one or more contaminants. Zero discharge is the limit case of complete regeneration, although economic considerations may hamper its full application. In this paper the mathematical model of the WWN is extended to consider partial/total stream regeneration. An improved variant of genetic algorithms is used to solve it. Several concepts are formulated, pinpointing which contaminant is better to be removed for decreasing supply water consumption. A case study with six unit operations, four contaminants, one water source and one regeneration unit is analysed. Four regeneration scenarios are investigated, considering (a) the critical contaminant, (b) the contaminants from the bottleneck island, (c) three contaminants—one being outside the bottleneck island and (d) all the contaminants, according to the zero discharge theory. The results obtained are compared against the base case (without regeneration) to highlight the relationship between supply water reduction and internal regeneration. Increased water reuse is related as well to WWN topology optimisation.

Thermal coupling between crude distillation and delayed coking units

Abstract The paper presents an industrial case study. Crude distillation unit (CDU) and delayed coking unit (DCU) are important plants in oil refineries, presenting huge energy consumption, especially due to high flowrates of process material streams. Any acceptable solution for energy saving is important in this context. The idea of thermal coupling between these two plants is good as they have potential to exchange energy, but the problem is to choose the most appropriate way to do it. The objective of this work is to present the possibility to exchange energy between the two plants, continuing a previous work [Energy saving by integration of CDU-delayed coke plants, third Conference, Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction––PRES 2000, P7.72], where a part of the solution was already presented. The difficulty to find a solution arisen from the fact that DCU is working semi-continuous. More insights in the process allowed finding new possibilities, more attractive for rational use of energy, with better applicability. A feasibility study will be performed to give also economic sound of all the implications for the modifications proposed.

Fast solvent screening for counter-current liquid–liquid extraction columns

Liquid–liquid extraction (LLEx) provides the separation of a certain solute present in a stream when adding a solvent that produces a phase split. Then the raffinate is collected free of solute, which in turn is to be found in the extract. The solute is separated from one phase and mixed in another phase from which it is recovered, in most cases, by distillation. The main difficulty of the process is to find a suitable solvent. When an immiscible solvent is not found, in some cases, the extractive distillation is an alternative. The present work compares the LLEx process with extractive distillation process. Furthermore, two parameters are provided to rank the solvents useful for LLEx, one related to the solvent aqueous toxicity impact, and another related to the energy required for solvent recovery. Both parameters for a counter-current LLEx column are calculated using a simple decanter, i.e. a single liquid–liquid equilibrium stage. The first parameter depends on the solvent lost in the raffinate, and its aqueous toxicity is represented by LC50 (lethal concentration required to kill half the members of a tested population). The second parameter depends on the minimum solvent flow rate and its boiling point. Hence, the proposed parameters are suitable to easily check when new proposed solvents are more environmental friendly.

Shortcut assessment of alternative distillation sequence schemes for process intensification

Abstract Finding good process schemes is a difficult task due to its search among multiple alternatives. In literature, several methods are successfully implemented as computer tools, but their use is limited to their developers. There are several useful rules of thumb and heuristics providing useful guidelines, but sometimes these are contradictory. Some authors tried to rank the various alternatives, defining heuristic equations to provide a quantitative parameter to choose among possible solutions. In this paper, mathematical model of distillation columns is simplified, assuming infinite number of stages. The resulting proposed equation has a great similarity to one of the previous heuristic ones. A simple equation not relying on heuristics and easy to use in calculation is provided to evaluate the distillation sequence energy efficiency (DSE) for each alternative. This allows to quantify the advantages derived from process intensification for a given feed composition. The proposed equation is dimensionless, as the Carnot efficiency is used instead of the temperature difference between distillate and bottoms. On the other hand, intermediate results provide also useful information. For instance, the Carnot efficiency of each column indicates when a heat pump or enhanced distillation would be useful. The recovery efficiency for each particular compound allows an easy comparison between alternatives, considering variations on the feed composition. The new equation is verified comparing its results with cases already solved in literature using different methods. The results show that all the methods in literature are able to provide the best sequence, except the heuristics-based ones that are not providing an overall sequence evaluation. The novelty of the proposed DSE method resides in its ease of application, compared to nowadays available methods, and requires only the feed composition and products boiling points.

Topological impact of regeneration unit constraints upon water and wastewater network

Abstract Optimization of water use/reuse gained an increasing attention during the last years based on four major driving forces: higher water demands, supply water cost increase, such as the wastewater treatment cost and more stringent regulatory limits for the disposal of the used water. This means a drastic reduction of the contaminants level of wastewater discharge, which itself has to be reduced continuously. A significant decrease of water disposal can be achieved rising internal water reuse/recycle through regeneration; the concept of “zero discharge” being the limit, although economic considerations are a major impediment in its full application. The topological impact of regeneration unit upon water and wastewater network is studied for three cases: critical component regeneration, partial regeneration and total regeneration (zero discharge concept) . Every case is compared against the optimal water network topology obtained using as objective function the total supply water flow rate.

Simulation and Process Integration for TAME Synthesis

Abstract A new sustainable process to produce tert-amyl-methyl-ether (TAME) using as feedstock enriched C 5 fraction (LCN – light cracking naphtha) from catalytic cracking (FCC) is developed. Existing technologies are based on methanol (MeOH) separation by water extraction, combined with distillation processes (Luyben, 2011). The new process involves TAME reactor effluent, separation based only on distillation columns and liquid-liquid (L-L) separators. Unreacted MeOH is recycled. Conceptual design for separation section is presented in Perederic (2013). Process specifications are collected from an industrial plant. In this paper three case studies with specific data for separation section are presented, underlying process characteristics. Heat Integration analysis for energy savings is considered. Additionally, environmental and economic analyses are performed. Environmental Impact using WAR algorithm is assessed, considering different fuels. Elimination of water in separation section ensures good environmental performance and lower energy consumption. MeOH separation is based on L-L phase separation in C 5 hydrocarbons-MeOH mixtures and azeotropes composition variation by pressure swing. Economic indicators calculated with Aspen Process Economic Analyzer indicate an attractive process configuration, for selected Case Study.

Innovative design and simulation of a castor oil biorefinery

The paper presents computer-aided design of a castor oil biorefinery. Fatty acid methyl ricinoleic ester (FAMRE) is the central building block. The first part deals with the simulation of two innovative technologies based on process intensification for FAMRE manufacturing by transesterification. The first one employs heterogeneous catalysis. Compact and modular reactor design allows customizable reaction time and variable catalyst amount. The second technology makes use of reactive extraction performed in a counter-current mixer-settler device. The principle of removing the constraints of chemical equilibrium is demonstrated by simulation using detailed kinetics. FAMRE is converted to undecylenic methyl ester and heptaldehyde. The paper presents process synthesis and computer simulation based on kinetic modeling of pyrolysis reactor and thermodynamic assessment of separations. The analysis highlights some challenges in using computer simulation when complex functional molecules are involved.

Software Tool for Computing and Visualization of Enhanced Residue Curve Maps

Residue curve maps (RCM) are readily implemented on most chemical engineering commercial simulation software because they are very useful to check the distillation columns feasibility. A section of a residue curve corresponds to a column composition profile of a packed column operated at infinite reflux flow rate between a distillate and bottoms compositions corresponding to the initial and final point of the curve section. The existence of the residue curve between distillate and bottoms assures that the separation is feasible when the mass balances are fulfilled with a high enough reflux. It is also well known that an infinite reflux requires a minimum number of transfer units between distillate and bottoms composition. Unfortunately, no information about the minimum number of transfer units is included in the RCM. This study implements for first time a Visual Basic® program able to generate RCM including the information about the minimum number of transfer units required. In this way, the enhanced RCM provides a valuable information about the difficulty of the separation. Some case studies are provided as examples.

Distillation Sequence Efficiency (DSE) for Suitable Liquid-Liquid Extraction Solvents: Acetic Acid Extraction with TOA

Abstract The use of renewable sources to produce chemical compounds is a hot issue, and takes more importance when considering the valorisation of a waste stream. Acetic acid is a useful chemical commodity that can be produced by biotechnological treatment of waste streams. Unfortunately, is rather diluted and its recovery by distillation is quite energy demanding. There are many experimental studies about the capabilities of the basic trioctylamine mixed with organic non-polar compounds to extract acetic acid. Usually the literature studies focus on finding a solvent that requires a low solvent flow rate during the extraction. In this paper, a suitable and simple solvent screening method for reactive extraction is proposed. The overall separation process including also the solvent recovery is considered, at the contrary of available studies that focus only on the extraction operation. For the first time, the DSE concept is applied to a process including other types of separations units besides distillation columns. The obtained results show that the best solvent is 1-octanol, which is in agreement to literature data in which it is the reference solvent.

Distillation Sequence Efficiency (DSE) Applied to Trains of Columns with Recycle Streams

Abstract Process modelling is usually simplified during chemical process analysis because it is less computing demanding and does not require so many parameters which are unknown at early stages of design. Fixing certain parameters to infinite allows to explore the process at its boundaries and the maximum attainable as indicator of the process potential. The ∞/∞ analysis assuming infinite reflux and infinite number of stages for the distillation columns trains is very useful for feasibility analysis. There are many methods in literature for distillation sequencing selection once the crude feed composition is defined. Most of them are very computing demanding and not applied to map all the feed compositions. A simple parameter called DSE (Distillation Sequence Efficiency) to rank the distillation sequences has been validated by comparing its results with the available computing demanding methods. Due to its simplicity and that requires only ∞/∞ analysis data and boiling temperatures, it has been applied to multicomponent mixtures with large amount of components. The goal of the present study is to show the potential of DSE method to solve trains of columns with recycle streams, being able to map all the feasible crude feed compositions.