Integrated Process and Product Design

Alexandre C. Dimian; Costin S. Bildea; Anton A. Kiss

1.1 Introduction

1.1.1 Motivation

The products manufactured by the Chemical Process Industries (CPIs) are vital for fulfilling the needs of the modern society. The process designer is the person in charge of transforming a valuable idea or experiment into an industrial process. The creative effort should be rewarded by substantial technical and economic advantages. Thus, novelty and efficiency are key motivations for process designers. Today, sustainable development sets new challenges for designers, namely the transition to renewable resources, as well as the protection of the natural environment.

The job of a process designer is to fulfil not only originality, efficiency and sustainability criteria, but to consider a large number of constraints, often contradictory. For example, using biomass as renewable feedstock implies typically a complex chemistry, with many by-products and impurities. Better selectivity may be achieved working at lower conversion, but with supplementary costs in equipment and energy for handling the recycles. The environmental regulations set severe targets for waste and emissions, adding supplementary costs. Modern plants should use less land. In the end, the designer has to find an optimum ensuring high valorisation of materials, low energy requirements and no pollution, by employing compact and efficient equipment. The combination of so many aspects gives highly integrated processes. Their optimal design makes use of systematic conceptual methods and powerful computer simulation tools forming the core of the Process Systems Engineering (PSE) discipline.

Etymologically, the word engineer comes from the Latin ingenium meaning the skills to understand, create and invent. Today, the CPIs are confronted with multiple crises and challenges, but innovation is ultimately the key issue. In this context, enhancing the creativity of designers plays a central role. We believe that the creativity should be accessible to everyone having adequate professional knowledge and motivation for discovery. Creativity can be learned and teaching the creativity of process designers is the goal of this book.

The intellectual support for enhancing creativity is the employment of a systems approach and systematic methods. This has at least two merits: (1) It provides guidance in identifying the feasibility of the project before the design of units. (2) Not just a single solution but several alternatives are generated and evaluated, corresponding to design decisions and constraints. After ranking by some performance criteria, the most convenient alternatives are refined and optimised. Note that by applying systematic methods, quasi-optimal targets for units can be set well ahead of their detailed sizing.

The assembly of the systematic methods employed for developing process flowsheets and ensuring the optimal use of materials and energy forms the paradigm of Integrated Process Design (IPD). Its application relies on the intensive use of Process Simulation. This approach allows the engineer to understand the behaviour of complex process systems, explore alternatives and propose effective innovative solutions.

Traditionally, process design was oriented to commodity chemicals. Recent years have seen an increasing interest in a more systematic approach to Product Design, which deals with manufacturing of higher value-added chemicals. Thus, the integrated paradigm concerns today both process and product design.

1.1.2 The road map of the book

The book contains five sections: Process Simulation, Thermodynamics, Process Synthesis, Process Integration and Design Project. Each section has several chapters, 21 in total plus appendices. The road map depicted in Figure 1.1 shows an overview of the chapters.

The main avenue links the introductory chapter on IPD with the section devoted to the Design Project, the final goal, and at the same time allows the circulation of information between different sections and chapters. Double sense roads indicate that the information goes in and out between sections and some chapters.

In this book, we adopted the strategy of teaching the principles by the assignment of a design project. For this reason, there are no problems at the end of chapters. Instead, students will be trained by applying the theoretical concepts to their own project.

Guiding examples can be found in the book published by Dimian and Bildea (2008) containing 11 detailed computer-aided case studies.

Viewed from the top, the right side of the avenue deals with issues regarding the tools, and the left side handles the principles of IPD. A rapid tour presents the key topics of each chapter.

The journey begins with an introductory chapter on Integrated Process and Product Design. This can be described as the marriage of two types of activities: Process Synthesis, as architectural design, and Process Integration, as development and optimisation of sub-systems. Key topics are systems approach, sustainable development and production-integrated environmental protection.

The first section teaches how to use efficiently the powerful capabilities of Process Simulation. The treatment is generic, not dedicated to specific commercial software.

Chapter 2 serves as an Introduction in Process Simulation. Particular attention is paid to systems analysis by simulation, commonly called flowsheeting. This chapter provides an overview of computer simulation in process engineering, including the key steps in a simulation approach, the architecture of flowsheeting software and the integration of simulation tools.

Chapter 3 presents the fundamentals of Steady-State Flowsheeting such as degrees of freedom analysis, efficient use of sequential-modular approach, equation-solving approach, thermodynamic tools and the treatment of convergence and optimisation. Mastering the flowsheeting techniques allows the user to get valuable insights into more subtle aspects, such as plantwide control.

Chapter 4 is devoted to Dynamic Flowsheeting, nowadays a major investigation tool in process operation and control. Key topics are how setting up a dynamic simulation model, dynamic simulation tools, numerical problems, dynamic simulation of key units and process control tools.

The second section deals with Thermodynamic Methods used in computer-aided process design. It is largely recognised that inappropriate thermodynamic modelling is the most frequent cause of failure when using computer simulation for predicting the behaviour of real systems. Therefore, this section is highly recommended as self-study for upgrading the knowledge in thermodynamics.

Chapter 5 describes the Generalised Computational Methods, namely the PVT (pressure/volume/temperature) behaviour of fluids, thermodynamic properties, generalised computational methods using PVT relationship and the estimation of physical properties.

Chapter 6 develops the computation of Phase Equilibria by various thermodynamic models, such as equations of state and liquid activity. Particular attention is paid to the regression of parameters from experimental data.

The third part, Process Synthesis, enters the core of the conceptual design and teaches how to invent process flowsheets by a generic approach based on systems analysis and systematic methods.

Chapter 7 presents the development of flowsheets by applying the Hierarchical Approach. The input/output analysis is extended to capture the essential of ecological analysis. Emphasis is on the material balance envelope formed by the sub-systems of reactions and separations connected by recycles. Here, the structure called Reactor-Separation-Recycle dominates the conceptual frame of the whole flowsheet. This is the basis for setting up the plantwide control of the material balance, which in turn dominates the operation costs. Separate chapters present a deeper analysis of the synthesis of...