Conceptual Design Of Chemical Processes Research Articles

A framework for integrating safety and environmental impact in the conceptual design of chemical processes

Abstract Multiple factors influence chemical process design and technology selection, including technical, economic, environmental, and safety considerations. Traditionally, a techno-economic analysis has been used to select a base case design, while safety and environmental impact have been subsequently assessed. This may leave out designs that exhibit better environmental and safety performance than the selected base case at a very early stage of design, where abundant opportunities for incorporating these objectives are present. Furthermore, although safety is an integral part of the overall sustainability of a chemical plant, historically it has been addressed separately from sustainability. Thus, there is a growing awareness for simultaneous consideration of these objectives during the conceptual process design phase of a project in order to select the most sustainable process route. The key to an effective sustainability assessment method for selecting the most sustainable process route involves the parsimonious selection of adequate metrics which define the sustainability profile of the process and an integrated multi-criteria decision-making (MCDM) framework. In this context, this work investigates gaps in conceptual process design and existing sustainability assessment methods through a review of existing environmental impact and safety assessment methodologies/tools. A possible workflow that incorporates both safety and environmental impact in a holistic multi-criterion decision-making framework (MCDM) has been proposed to select the most sustainable process route. The use of this framework is illustrated through a simple case study involving assessing solvent alternatives for palm oil recovery to highlight the scope and significance of the proposed framework.

Exo-parametric (“inside-out”) model of discounted cash flow calculations using NPV%: Macro calculation of coefficients for an exact, collapsed financial model

In a 2013 paper (Mellichamp, 2013), the author developed an internally-consistent discounted cash flow (DCF) model that represents the key financial outputs of a conceptual chemical process design using just four variables:•Total investment, TI (capital required to construct and operate a project for NTotal years),•ROIBT and NPVproj (the traditional annual and long-term (NPV) profitabilities), and•NPV% [a new metric whose reciprocal, (NPV%)−1, directly expresses short-term project risk].A traditional spreadsheet relating these four dependent long- and short-term financial metrics to a project's two independent design variables, PBT and FC, is functionally dependent on the many process design parameters (tax rate, discount factor, etc.) and highly complicated, involving non-linear (mostly geometric) relationships. Surprisingly, an exact linear-in-the-parameters “inner model” including the usual nonlinear relation for ROIBT is obtained by collapsing the original large-scale financial model (the complicated spreadsheet) using these four dependent variables, if the coefficients are functions of fixed design parameters, as when held constant in design. The power/utility to understand several key features of a project's design financial characteristics are revealed via the “inner model” through this reversal of the usual modeling hierarchy. The “outer model” coefficients incorporate the highly non-linear DCF functionalities. The new form is referred to as “exo-parametric” or an “inside-out” model.

A framework and method for the assessment of inherent safety to enhance sustainability in conceptual chemical process design

Inherent safety indices have been suggested to choose between alternative process and chemical reaction routes in conceptual chemical process design. The indices are relative ranking methods that add up parameters without considering the difference in the magnitude of the hazard, complexity of the procedure, or expert opinion. We propose an improved framework based on fuzzy logic using chemical properties, process data, and chemical accident databases. The proposed methodology is applied to the methyl methacrylate (MMA) process as a case study. The results are compared with existing methods and experts' rankings by using three risk-rules, which are related to the experts' opinions and the tendency of decision makers. The risk-standard rule showed same results to that of the expert's scoring, while the ranking results are slightly different based on risk-easy and risk-hard rules. This methodology can facilitate the ranking of alternatives for decision making in the preliminary design stage.

Recycling vs. reprocessing. Optimization of a gossypol production process

Three processes to obtain GAA from the soapstock residue of oil refineries were compared in this work. The first process is the originally proposed by Dowd and Pelitire (2001. Ind. Crops Prod. 14, 113) in which the mother liquor from the last crystallization step still contains an appreciable amount of gossypol which is lost as a process residual stream. The second process recycles the mother liquor to the hydrolysis first step of the process, following the heuristic of the traditional process design procedure by Douglas (1988. Conceptual Design of Chemical Processes. McGraw Hill, New York, NY), which increases product yield. While the third process adds a new downstream processing line to reprocess the mother liquor. This last alternative renders a slightly lower product yield than Process 2 but requires a smaller investment cost, exhibiting the best economic performance.The alternative of incorporating a recycle to reprocess unreacted material (in this case the bound gossypol present in the crystallization mother liquor) is the usual approach in traditional process design. However, in this particular study case, it does not succeed in rendering the process alternative with the best economic performance: the recycle stream flow impacts on the equipment sizes, increasing investment cost far beyond the alternative that adds smaller units to reprocess the mother liquor stream.

Model-based conceptual design and optimization tool support for the early stage development of chemical processes under uncertainty

Despite many efforts to formalize the early phase of conceptual process design, no tool-supported systematic method for the conceptual design of chemical processes has been developed to date. This contribution presents a methodology and a software tool for the early conceptual design phase, which is characterized by limited and uncertain information on the available process units. The proposed methodology supports the graphical modeling of hierarchical superstructures which are subsequently optimized by a hybrid evolutionary algorithm considering uncertainties in model parameters.

A framework for the modeling and optimization of process superstructures under uncertainty

Despite many efforts to formalize the early phase of conceptual process design, no tool-supported systematic method for the conceptual design of chemical processes has been developed to date. This contribution presents a methodology and a software tool for the early conceptual design phase, which is characterized by limited and uncertain information on the available process units. The proposed methodology supports the graphical modeling of hierarchical superstructures which are subsequently optimized by a hybrid evolutionary algorithm considering uncertainty in model parameters.

Improvements in the Design of the Ammonia Synthesis Process Implementing Counter Current Gas Permeation Modules

This paper explores mass exchanging the outlet and inlet streams of the reactor, following a design heuristic proposed by Fischer and Iribarren in Industrial and Engineering Chemistry Research2011, 50 (11), 6849–6859 within the Hierarchical Process Design Procedure by J. M. Douglas in Conceptual Design of Chemical Processes, McGraw-Hill, 1988. When applied to the ammonia synthesis process, this design methodology generated a process alternative different from that previously proposed by other authors, resorting to ceramic membrane counter current gas permeation units to perform the mass exchange of hydrogen. This alternative design is shown to produce a reduction of the gas recycle stream (hydrogen and nitrogen) of up to an interesting 8.40%, reducing recompression associated costs. However, as the present cost of zeolite membranes is still high and their hydrogen–nitrogen selectivity moderate, in the optimal economical solution, the net annual income amounted to 4.56%, corresponding to U.S. $817,793/year...

Mass Integration as a Design Heuristic: Improvements in the HDA Process

This paper explores mass exchanging the outlet and inlet streams of a reactor, as a design heuristic within the hierarchical process design procedure by Douglas [AIChE J. 1985, 31 (3), 353–361 and Conceptual Design of Chemical Processes; McGraw–Hill, 1988], who worked on the HDA process to test the proposal. The heuristic is used at an early stage of the hierarchy, when deciding the recycle and separation system structure of the process. If the reaction requires operating conditions with reactants in excess or that catalyze the reaction, which must be removed after the reaction, there is a concentration gradient between the inlet and outlet streams that may be used as the driving force in a mass exchanger (if such a device is available for the particular case). When applied to the HDA process, this methodology generated alternatives different from the previously proposed by other authors by resorting to a ceramic membrane gas permeation unit to perform the mass exchange of hydrogen. The performance of app...

A Modified Hierarchy for Designing Chemical Processes

This paper presents a modified hierarchy for the design of chemical processes. The modified hierarchy differs from the hierarchy of Douglas [Conceptual Design of Chemical Processes; McGraw−Hill: New York, 1988] in two ways: (i) the design of a chemical reactor is considered as a separate, distinct step in the design exercise, and (ii) the implementation of a material recycle is considered to be part of the unit integration step, rather than a predetermined step in the design hierarchy. The advantage of the modified hierarchy is illustrated on a process to produce benzene by hydrodealkylation (HDA) of toluene (this is a benchmark case in teaching chemical process design). It is shown that, by applying the modified design hierarchy, a more economical process can be designed. The economic advantages are achieved mainly due to modifications in the reactor configuration and the elimination of the gas recycle stream.

Conceptual chemical process design in a sustainable technological world

Delft University has an established track record in educating MSc students the art of designing chemical processes and products. To foster its future position an experimental conceptual design program has been set up. In this program sustainability requirements are used to stimulate creativity. Our vision is that (designs of) processes, products and systems should fit in a sustainable technological world (STW). The STW is in balance with the other great cycles on Earth, being the exchange of water between hydrosphere and atmosphere and the exchange of carbon dioxide between atmosphere and biosphere. The STW has, like the biosphere and hydrosphere, a certain upper mass (110 Gton) and energy (8800 GW). The STW itself is evolutionary and cannot be designed, yet its content—technological artifacts—is designed. Newly designed artifacts requiring an average life span of 25 years (one human generation), should fit the STW. The total annual product renewal of the STW is 4.4 Gton/year and the energy consumption 64 MJ/kg. These numbers total both industrial production as well as energy spent by consumers using the artifacts. Conceptual designs of chemical processes should fit in this concept of a STW. This means that processes requiring a high energy level are subject to change, for they limit society's patterns of energy consumption. Chemical processes demanding a lot of chemical energy are reduction processes: primary processes (roasting ores and biomass) and secondary processes (dissociations and dehydrogenations). In this article a conceptual design of both types of processes is presented. The first results show that their energy consumption fits the STW and points towards new design solutions for chemical processes, new applications of chemical products and new relationships with other technological sciences.

A systematic method for reaction invariants and mole balances for complex chemistries

Reaction invariants are quantities that take the same values before, during and after a reaction. We identify a set of reaction invariants that are linear transformations of the species mole numbers. The material balances for chemically reacting mixtures correspond exactly to equating these reaction invariants before and after reaction has taken place. We present a systematic method for determining these reaction invariants from any postulated set of chemical reactions. The strategy presented not only helps in checking the consistency of experimental data, and the reaction chemistry but also greatly simplifies the task of writing material balances for complex reaction chemistries. For examples where the reaction chemistry is not known, we employ Aris and Mah's (Ind. Eng. Chem. Fundam. 2 (1963) 90) classic method to determine a candidate set of chemical equations. Application of reaction invariants in validating proposed reaction chemistry is discussed. One of the important applications of this method is the automation of mole balances in the conceptual design of chemical processes.

Integrating environmental impact minimization into conceptual chemical process design — a process systems engineering review

In the 1990s, significant progress was made in process synthesis concerning environmental issues, however the routine design procedures stay almost the same as before. This paper attempts to summarize the developments of this area in the last 10 years in order to remind chemical engineers of what has been accomplished to date and what should be possible in the near future from an industrial viewpoint. After discussing some original concepts and hierarchies, two aspects of conceptual design, synthesis of reaction paths and process flowsheet, are highlighted for environmental impact minimization. Finally, several points are identified for future research.

Computer tool supported process design methodology

This work focuses on the development of a computer tool for conceptual chemical process design. We demonstrate how to create a multipurpose chemical process design tool, after development of a process design methodology. A computer environment for methodology implementation is presented, MetaEdit+ ®, which provides a platform both for methodology implementation and methodology usage. This work results in a prototype tool for supporting conceptual chemical process engineering in the form of object-oriented knowledge base.

Design support systems for process engineering—III. Design rationale as a requirement for effective support

An explicit record of design rationale is an important requirement for effective design support. Such a record may be defined as the information supporting or explaining the decisions made by a designer when generating an artifact. Design rationale can be used to (a) improve the documentation of the design process, (b) verify the design methodology and the resulting design artifact, (c) provide support for the analysis and explanation of the design process, and (d) enhance the re-usability of parts of the design artifact. This paper describes an extension to KBDS, a prototype design support system for conceptual design of chemical processes. The extension makes use of an IBIS representation to record the design rationale and integrates it with the design history maintained by KBDS. Thus, KBDS-IBIS records in an integrated and prescriptive form the specification of the design artifact, the history of its evolution during the design process, and the designer's rationale.

The extension and evolution of the process design representation

KBDS (Bañares and Labadidi, 1995b) is a support system for the conceptual design of chemical processes. In this paper we describe two proposed extensions to the system. The first of these is a new cyclical representation of the design process which introduces the possibility of the verification of the decision rationale against the objectives. This will enable the designer to determine how the objectives were fulfilled as well as whether the design fulfills the design objectives. The second addition allows the designer to include a wider range of types of information in the design artifact thus making a fuller record of the design process. By allowing a wider description of the design artifact, the designer will be able to work in a more natural manner by adding information as it becomes appropriate.

A predictor-based bounding strategy for synthesizing energy integrated total flowsheets

The task of synthesizing optimal total flowsheets with energy integration usually represents a large combinatorial problem. In order to reduce the search space, an efficient bounding strategy is presented for synthesizing energy integrated total flowsheets with distillation-based liquid separation systems. The strategy utilizes a predictor-based ordered search technique and can be attached to the conceptual design of chemical processes. The strategy is based on computing lower bounds of the utility and investment costs for the feasible process alternatives. Beside optimizing the column matches the integration of heat pumps with separation system is also considered. The outlined procedure exploits the advantages of both major approaches, i.e. the hierarchical and algorithmic design.