Дисертації з теми "Process flowsheet"

Chemical process synthesis is an open ended step of process design as it deals with the problem of how to develop and integrate the chemical process flowsheet. Over the past four decades, very few systematic procedures have been proposed for the rigorous synthesis of complete chemical process flowsheets. Mathematical design and heuristics from experience of past processes are the two main methods usually employed in process synthesis. Most approaches for new designs use heuristics based on studying reaction and separation systems in isolation. This thesis discusses the development of a new process synthesis systematic procedure and software that integrates a knowledge based system with Aspen HYSYS process simulator, HYSYS optimizer, Aspen Icarus economic evaluator, and databases, utilising knowledge from existing industrial processes to obtain design rules. The proposed generic superstructure for the synthesis and optimization of reaction-separation-recycle systems has been validated. To account for the non-ideal behaviour of reactors, modular simulation is used and an example of the approach is illustrated for a fluidized bed reactor. Preliminary work in customizing Aspen HYSYS to simulate new unit operation has been illustrated. A Visual Basic for Application (VBA) programming code has been developed to link the integrated knowledge based system (IKBS) to Aspen HYSYS. The prototype IKBS has been applied for the selection of reactor-separator-recycle systems for ethylene oxide, ethylene glycol, acetic acid and cumene manufacturing processes as case studies. A wide range of chemical reactors and separators were considered during the selection process and then elimination occurs at different levels leading to the best alternatives being selected for simulation, optimization and economic evaluation in the second phase of the IKBS for future development. The suggested alternative reactor-separator-recycle systems by the IKBS include currently used processes in addition to novel and recommended reactors/separators in industrial research. The proposed integrated knowledge based approach to chemical process flowsheet synthesis is expected to yield a cost effective design methodology for the petrochemical industry.

The aim of this work was to develop an experimental tool to perform flow-sheeting tasks throughout the course of chemical process design. Such design proceeds in a hierarchical manner increasing the amount of detail in the description of the plant, and, correspondingly, in the mathematical models used to describe the plant. The models range from the simplest overall mass balance to rigorous unit models, and the calculations required in the course of a design may include the modelling of the complete plant or any of its constituent parts at any level of detail between these two extremes. Object oriented programming has been used to represent the hierarchy of units required throughout a hierarchical design. A flexible modelling tool requires that models compatible with both the designer's intention and the context of the design are created. Sets of equations are defined in a generic form independent of process units with their selection as part of a model being dependent on the function and context of the unit being modelled. The expansion of the generic equation descriptions is achieved with reference to the structure of the unit, e.g. number of inlets and outlets, while the context of an equation determines the form of the equation to be applied, e.g. ideal or non-ideal behaviour. Equations are, therefore, represented as relations between a process item and its structural and contextual properties. An increase in modelling flexibility is obtained by allowing the designer to interact with generated models. Different sets of equations can be selected within constraints imposed by the system. At a lower level, terms in individual equations can be modified for particular applications. In chemical process design, many different analyses are performed. To demonstrate the application of different tools to a central model, the modelling system has been incorporated within a process synthesis framework. The application of the system to simple design case studies is described.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1985.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Bibliography: leaves 244-248.
by Thomas Patrick Kisala.
Sc.D.

Thesis (MEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: The Platreef ore deposit, situated in the Bushveld Igneous Complex, is one of the world’s largest platinum group metal (PGM) resources. The mineralogy of this resource is, however, unique as it consists of complex PGM mineralization with mainly copper and nickel, at very low PGM grades. The PGMs are mainly present in the ore as slow floating refractory minerals resulting in marginal process economics when processing via traditional mill-float-smelt processes. A new process is currently being investigated to extract PGMs from low grade Platreef ore and concentrate using a sequential heap leach process entailing heap bioleaching and high temperature cyanide leaching. The heap bioleach extracts the base metals in an acidic sulphate medium using a mixed culture of mesophiles and thermophiles. After heap bioleaching, the heap will be reclaimed, rinsed and restacked for high temperature cyanide leaching where the cyanide liquor is directly heated via solar energy in panels. Platinum, palladium and gold are extracted during the cyanide leaching stage and then recovered from the pregnant liquor either by adsorption onto activated carbon or ion exchange resins. Final metal recovery will proceed by techniques such as electrowinning and precipitation. In this thesis, process options for the recovery of platinum group metals from cyanide solutions were identified with different flowsheet alternatives developed utilizing these options. Simulations were made for the different processing alternatives with the objective of finding the alternative flowsheet to maximise net present value. The various processing options were simulated, combining data from concurrent experimental studies and data reported in literature with kinetic adsorption models. This was combined with economic models to arrive at an optimum design for each flowsheet alternative. Seven different processing alternatives for the recovery of platinum group metals from cyanide solutions were developed and investigated. These included two different activated carbon flowsheets as well as five different ion exchange resin flowsheets. The flowsheets differ in the elution procedures as well as the use of single or multiple resins. The well-known Merrill Crowe precipitation process was investigated but was found to yield unsatisfactory results. In each alternative, the cyanide solution is sent to a SART (sulphidization, acidification, recycling and thickening) plant to remove copper, nickel and zinc from solution prior to upgrading by means of adsorption onto activated carbon or ion exchange resins and subsequent elution. The platinum group metals are recovered from the eluate by precipitation using an autoclave, producing a solid product consisting of base and precious metals, while gold is recovered by electrowinning. It was found that the overall performance of the resin-in-solution (RIS) flowsheets were superior to that of the carbon-in-solution (CIS) flowsheets, from an overall PGM recovery perspective and product grades. The superior adsorption kinetics and high selectivity of the resins for the PGMs resulted in excellent overall plant performances, with PGM extractions in excess of 97%. Gold extraction efficiencies with resins were found to be lower than those achieved in the CIS flowsheets, mainly due to the higher selectivity of the resins for the divalent platinum and palladium cyanide complexes and poor gold elution efficiencies. The gold concentrations in the feed streams to these processes were, however, very low, at only 8.5% of the total precious metal content. The overall precious metal recoveries of the RIS flowsheets were thus higher than the CIS flowsheets due to the superior PGM extractions. From the cost analyses performed it was found that the RIS flowsheets requires lower initial capital costs, almost 28% lower than that require for the CIS flowsheets, while the operating cost requirements were found to be ±10% lower. This, combined with the high overall precious metal extractions, resulted in the RIS flowsheets to achieve higher net present values than those of the CIS flowsheets over an assumed project life of 15 years. The optimum flowsheet proposed for the recovery of precious metals from cyanide leach solutions was a RIS flowsheet option that employed the Amberlite PWA 5 resin, capable of extracting platinum, palladium and gold from solution, with elution being performed with a zinc cyanide solution. This process option had the lowest capital and operating cost requirements while achieving similar overall precious metal recoveries as the other flowsheets. Economic analysis of this process yielded the highest net present value, with a 31% increase in the overall return on investment compared to the optimal CIS flowsheet. Based on this, it was concluded that resin technology would be the best process option for recovering precious metals from cyanide leach solutions, however, additional research is required as the current level of process development is only at a concept phase.
AFRIKAANSE OPSOMMING: Die Platrif-erts, geleë in die Bosveld Kompleks, is een van die wêreld se grootste platinum groep metaal (PGM) reserwes. Die mineralogie van hierdie reserwe is uniek en bestaan uit komplekse PGM mineralisasie met hoofsaaklik koper en nikkel, teen baie lae PGM inhoud. Die PGMe is hoofsaaklik teenwoordig in die erts as stadig drywende minerale en dit lei tot marginale ekonomiese uitsigte wanneer hierdie reserwe deur tradisionele metodes verwerk word. Tans word ʼn nuwe proses ondersoek om die PGMe vanuit lae graad Platrif-erts en konsentraat te ontgin deur gebruik te maak van ʼn sekwensiële hooploogproses wat uit ʼn bio-loog en hoë temperatuur sianied loog stappe bestaan. Die bio-loog stap is verantwoordelik vir die ontginning van die basis metale deur gebruik te maak van ʼn suur sulfaat medium bestaande uit ʼn gemengde kultuur van mesofiele en termofiele. Nadat die bio-hooploog stap voltooi is, word die hoop herwin, gewas en herpak vir die daaropvolgende hoë temperatuur sianied loog, waar die sianied oplossing direk verhit word deur die gebruik van son panele. Platinum, palladium en goud word tydens hierdie stap ontgin en kan dan herwin word vanuit die loog oplossing deur gebruik te maak van adsorpsie deur geaktiveerde koolstof of ioon-uitruilings harse. Finale metaal herwinning kan deur elektroplatering en presipitasie vermag word. In hierdie tesis word verskeie proses opsies vir die ontginning en herwinning van PGMe vanuit sianied loog oplossings ondersoek waarna verskeie proses vloei diagram alternatiewe ontwikkel is met die doel om die opsie te vind wat die hoogste netto ekonomiese waarde sal oplewer. Die verskillende opsies is gesimuleer deur gebruik te maak van eksperimentele data gepubliseer in die literatuur en dit te kombineer met kinetiese adsorpsie modelle. Dit was dan gekombineer met ekonomiese modelle om ʼn optimum ontwerp van elke proses te verkry. Sewe verskillende proses vloei diagramme vir die herwinning en ontginning van PGMe vanuit sianied loog oplossings is ontwikkel en ondersoek. Hierdie het twee verkillende geaktiveerde koolstof prosesse en vyf verskillende ioon-uitruilings hars prosesse beslaan. Die opsies het verskil van eluerings metodes en adsorpsie medium. Die alombekende Merrill Crowe presipitasie proses is ook ondersoek, maar daar is gevind dat hierdie proses oneffektiewe resultate oplewer met betrekking tot die herwinning van die drie edel metale. In elke alternatief word die sianied oplossing in ʼn SART proses verwerk, waar die basis metale herwin word, gevolg deur die opgradering van die edel metale d.m.v. geaktiveerde koolstof adsorpsie of ekstraksie m.b.v. ioon-uitruilings harse, gevolg deur eluering. Die PGMe word dan herwin vanuit die eluerings oplossing deur termiese degradering van die metaal sianied komplekse, wat ʼn hoë graad presipitaat lewer bestaande uit die basis en edel metale. Goud word herwin d.m.v. elektroplatering. Daar is bevind dat die algehele verrigting van die ioon-uitruilings hars opsies beter was as die van die geaktiveerde koolstof opsies, beide van ʼn algehele edel metaal herwinnings en produk suiwerheid perspektief. Die verhoogde adsorpsie kinetika en hoër PGM selektiwiteit van die harse het daartoe gelei dat uitstekende algehele PGM herwinning verkry is in hierdie opsies, meer as 97%. Goud ekstraksie deur die harse was laer as wat verkry was deur die geaktiveerde koolstof opsies, weens die hoër selektiwiteit van die harse vir die divalente platinum en palladium sianied komplekse en laer hars eluering effektiwiteit. Die goud konsentrasies in die voer strome na die prosesse was laag, en het sowat 8.5% van die totale edel metale uitgemaak, wat bygedra het tot die lae goud herwinning. Algeheel was die edel metaal herwinning van die hars prosesse beter as die van die koolstof prosesse a.g.v. die hoër PGM adsorpsie. Koste evaluerings van die verskillende vloeidiagramme het getoon dat die hars opsies laer kapitaal kostes benodig, omtrent 28% minder as die koolstof opsies, terwyl bedryfskostes omtrent 10% minder was. Dit het bygedra tot die feit dat die ioon-uitruiling hars opsies ʼn hoër algehele netto ekonomiese waarde oor ʼn projek leeftyd van 15 jaar sal hê, aangesien de PGM ekstraksie, en dus die jaarlikse inkomste, ook hoër was. Die algehele proses vloei diagram wat voorgestel is vir die herwinning van edel metale vanuit sianied loog oplossings is die hars opsie wat gebruik maak van die Amberlite PWA 5 hars, wat in staat is om platinum, palladium en goud terselfdertyd te absorbeer, gevolg deur die eluering van die hars deur die gebruik van ʼn sink sianied oplossing. Hierdie proses het die laagste kapitaal en bedryfskostes getoon terwyl algehele PGM herwinning om en by dieselfde was as al die ander opsies. Hierdie proses sal verder ʼn 31% verhoging in die opbrengs op belegging lewer in vergelyking met die optimum geaktiveerde koolstof opsie. Die algehele gevolgtrekking is dat hars tegnologie die beter opsie sal wees vir die herwinning van edel metale vanuit sianied loog oplossings. Addisionele navorsing is dus nodig om resultate te verbeter aangesien hierdie studie slegs op ʼn konsep fase benadering was.

A library of process unit models has been developed for synthesis studies that may be comparable to those developed for computer flowsheeting. The library has been integrated into an implicit enumeration process synthesis package for the generation of promising processes at the early stages of process design studies. The package allows consideration of heat integration in the conceptual synthesis of complete processes. Models for a number of commonly occurring units have been developed and a number of published synthesis studies have been reproduced including processes with non-sharp separations and with recycles. Previously published implicit enumeration synthesis procedures have used only very simplified models. Developments are reported that enable flowsheets with more realistic units to be generated. The basis of the synthesis used in this study is a rapid, stream-based implicit enumeration algorithm which combines dynamic programming and branch and bound optimisation. The technique enables the inclusion of flowsheets with multicomponent recycles and with unpredefined separation units. The program synthesises process flowsheets to meet user specified performance requirements. Thus, given process feeds and desired products, the program will select the necessary processing units and determine the way in which they are connected together. Processes synthesised, include vapour streams and liquid streams and include energy integration, handled through the use of 'heat increments' (pseudo-components) which record the temperature dependent net energy surplus or deficit in any stream. Processes can be more closely optimised by using multiple heat increments for a finer discretisation of the heat fluxes. A method of costing pressure changes between units has been introduced to allow the effect of pressure matching to be more rigorously incorporated in synthesising process flowsheets. Reactor models incorporating full kinetic expressions for more rigorous costing purpose have also been developed. Complete plant process flowsheets of sufficient scale to be of industrial relevance are generated and a number of case studies published in the literature have been reproduced and, in a number of cases, superior designs developed. Results to date compare favourably to other methods (e.g. AI, MINLP) both in quality of process design achieved and in computational time required to synthesise these designs.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.17.03 – технічна електрохімія. – Національний технічний університет "Харківський політехнічний інститут", м. Харків, 2016 р. Дисертація присвячена розробці технології композиційних електрохімічних покриттів на основі міді та нікелю, армованих нанорозмірним оксидом алюмінію. Запропоновано технологічну схему формування композитів Cu-Al₂O₃ та Ni-Al₂O₃. Запропоновано метод хімічного диспергування корунду з отриманням гідрозолю Al₂O₃. Встановлено закономірності електрохімічних процесів осадження мідних та нікелевих композиційних покриттів. Визначено вплив концентрації дисперсної фази в електролітах-суспензіях на фізико-механічні властивості матеріалів, такі як мікротвердість, межа міцності та межа текучості. Встановлено, що отримані композити мають значно вищий рівень міцності при досить низьких концентраціях Al₂O₃ в електроліті (1-2 г/дм³), у порівнянні зі зразками, отриманими з додаванням грубодисперсного оксиду алюмінію. Результати атомносилової мікроскопії дозволили визначити розмір кристалітів та оцінити топографію поверхні покриттів, встановлено вплив вмісту корунду на склад та морфологію покриттів, а результати електронної мікроскопії вказують на збереження кристалічної гратки.
Thesis for granting the Degree of Candidate of Technical sciences in specialty 05.17.03 – Technical Electrochemistry. – National Technical University "Kharkiv Polytechnic Institute". Kharkiv, 2016. Dissertation is devoted to development of the technology of composite electrochemical coatings based on copper and nickel, reinforced nanoscale aluminium. The method of chemical dispersion to produce a hydrosol of corundum Al2O3 is proposed. Electrochemical processes regularities of the copper and nickel composite coatings deposition have established. The influence of a dispersed phase concentration in electrolytes-suspensions on the physico-mechanical properties of materials, such as microhardness, tensile strength and yield strength, has detected. It has shown the resulting composites have higher strength at sufficiently low concentrations in the Al₂O₃-electrolyte (1-2 g/dm³) compared with samples obtained by the introduction of the coarse-dispersion aluminium electrolyte. The influence of the corundum content on the composition and morphology of coatings has been found experimentally. The electron microscopy results detects to a continuation of a crystal lattice. The results of atomic force microscopy have allowed to determine the crystallite size and evaluate the topography of the surface. The flowchart of the electrochemical formation of Cu-Al₂O₃ and Ni-Al₂O₃ composites are proposed.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.17.03 – технічна електрохімія. – Національний технічний університет "Харківський політехнічний інститут", м. Харків, 2016 р. Дисертація присвячена розробці технології композиційних електрохімічних покриттів на основі міді та нікелю, армованих нанорозмірним оксидом алюмінію. Запропоновано технологічну схему формування композитів Cu-Al₂O₃ та Ni-Al₂O₃. Запропоновано метод хімічного диспергування корунду з отриманням гідрозолю Al₂O₃. Встановлено закономірності електрохімічних процесів осадження мідних та нікелевих композиційних покриттів. Визначено вплив концентрації дисперсної фази в електролітах-суспензіях на фізико-механічні властивості матеріалів, такі як мікротвердість, межа міцності та межа текучості. Встановлено, що отримані композити мають значно вищий рівень міцності при досить низьких концентраціях Al₂O₃ в електроліті (1-2 г/дм³), у порівнянні зі зразками, отриманими з додаванням грубодисперсного оксиду алюмінію. Результати атомносилової мікроскопії дозволили визначити розмір кристалітів та оцінити топографію поверхні покриттів, встановлено вплив вмісту корунду на склад та морфологію покриттів, а результати електронної мікроскопії вказують на збереження кристалічної гратки.
Thesis for granting the Degree of Candidate of Technical sciences in specialty 05.17.03 – Technical Electrochemistry. – National Technical University "Kharkiv Polytechnic Institute". Kharkiv, 2016. Dissertation is devoted to development of the technology of composite electrochemical coatings based on copper and nickel, reinforced nanoscale aluminium. The method of chemical dispersion to produce a hydrosol of corundum Al2O3 is proposed. Electrochemical processes regularities of the copper and nickel composite coatings deposition have established. The influence of a dispersed phase concentration in electrolytes-suspensions on the physico-mechanical properties of materials, such as microhardness, tensile strength and yield strength, has detected. It has shown the resulting composites have higher strength at sufficiently low concentrations in the Al₂O₃-electrolyte (1-2 g/dm³) compared with samples obtained by the introduction of the coarse-dispersion aluminium electrolyte. The influence of the corundum content on the composition and morphology of coatings has been found experimentally. The electron microscopy results detects to a continuation of a crystal lattice. The results of atomic force microscopy have allowed to determine the crystallite size and evaluate the topography of the surface. The flowchart of the electrochemical formation of Cu-Al₂O₃ and Ni-Al₂O₃ composites are proposed.

This thesis describes research into a methodology for the systematic development of engineering line diagrams (ELOs) from process tlowsheets with a particular emphasis on safety, health and environmental (SHE) and operability issues. The current approach to the consideration of safety in design is largely reactive, relying on design reviews such as the HAZOP. If design safety is to be improved, then a comprehensive system, incorporating both proactive and reactive methods, must be adopted. The facility to develop proactive safety systems relies upon the presence of a systematic design procedure. Since design at this stage seems generally to be rather haphazard, there is a need to introduce structure to the design task before any progress can be made in the improvement of safety. Introducing structure to the design task not only provides a framework for the incorporation of SHE and operability issues, but should also improve the effectiveness of the overall design and the efficiency with which it is completed. More specifically, fewer good design opportunities should be lost due to poor information handling and thc amount of rework arising from misunderstandings between different disciplines should be minimised. In addition, learning how to perform the design task should become easier for new recruits. Relevant work in the fields of process design, process safety, engineering drawings and ELO development is discussed. An analysis of perceptions of the design task within industry is presented. The generation of a systematic method by iterative case study work with designers is described. The structural features of this method are explained. Some examples of the application of the method are given and the results of a trial within industry are discussed. This research has shown that there is no existing work which captures the logic for the order in which decisions for developing a first ELO are made. Neither is there a complete analysis of the activities and issues contributing to ELO development. A novel method for the systematic generation of ELOs has been produced and used as a framework for the incorporation of SHE and operability issues into design. Trials of the method within industry have shown it to be successful.

A demethaniser process is characterised by interactions between the complex distillation column and other flowsheet units, including the turbo-expander, flash units, multistream exchangers and refrigeration system. When a design problem dealing with demethaniser flowsheets is approached in a systematic way, the number of alternatives to be studied is generally very large. The assessment of all possible flowsheets with numerous options is a time consuming task with many simulations required to select the most economic option. This research presents a systematic approach for demethaniser flowsheet synthesis to generate cost-effective designs with minimal time and effort. A demethaniser column has many degrees of freedom, including the operating pressure, multiple feeds, the number and duty of side reboilers and the flow rate of the external reflux stream. The additional feed and side reboiler streams enhance the efficiency of the process, but complicate process modelling. The number of design variables is also augmented by additional degrees of freedom such as the location and the order of feeds, the number of stages and the reflux ratio in the column. The complexity of the demethaniser column precludes the use of the Fenske–Underwood–Gilliland shortcut design method. A semi-rigorous boundary value method is proposed for the design of complex demethaniser columns for application within an optimisation framework for process synthesis and evaluation. The results of the proposed design methodology are shown to be in good agreement with those of rigorous simulation. A simplified flowsheet simulation model based on a sequential modular approach is developed that is able to account for various configurations and inter-connections in the demethaniser process. Improved shortcut models for flash units, the turbo-expander, compressor and refrigeration cycle have been proposed for exploitation in a synthesis framework. A methodology accounting for heat integration in multistream exchangers is proposed. The simplified simulation model is applied for the optimisation of a flowsheet of fixed configuration. The nonlinear programming technique of sequential quadratic programming (SQP) is used as the optimisation method. A case study is presented to illustrate the application of the optimisation approach for maximising the annual profit. A generalised superstructure has been proposed for demethaniser flowsheet synthesis that includes various structural combinations in addition to the operational parameters. The various options included in the superstructure and their effects on flowsheet performance are discussed. A stochastic optimisation technique, simulated annealing, is applied to optimise the superstructure and generate energy-efficient and cost-effective flowsheets. The application of the developed synthesis methodology is illustrated by a case study of relevance to natural gas processing. The results allow insights to be obtained into the important trade-offs and interactions and indicate that the synthesis methodology can be employed as a tool for quantitative evaluation of preliminary designs as well as to facilitate evaluation, selection and optimisation of licensed demethaniser flowsheets.

Thesis (M.S.)--University of Wisconsin--Madison, 1987.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 56-61).

Large-scale processes that are modeled using differential algebraic equations based on mass and energy balance calculations at times require excessive computation time to simulate. Depending on the complexity of the model, these simulations may require many iterations to converge and in some cases they may not converge at all. Application of a storage and retrieval technique, named in situ adaptive tabulation or ISAT is proposed for faster convergence of process simulation models. Comparison with neural networks is performed, and better performance using ISAT for extrapolation is shown. In particular, the requirement of real-time dynamic simulation is discussed for operating training simulators (OTS). Integration of ISAT to a process simulator (CHEMCAD®) using the input-output data only is shown. A regression technique based on partial least squares (PLS) is suggested to approximate the sensitivity without accessing the first-principles model. Different record distribution strategies to build an ISAT database are proposed and better performance using the suggested techniques is shown for different case studies. A modified ISAT algorithm (mISAT) is described to improve the retrieval rate, and its performance is compared with the original approach in a case study. State estimation is a key requirement of many process control and monitoring strategies. Different nonlinear state estimation techniques studied in the past are discussed with their relative advantages/disadvantages. A robust state estimation technique like moving horizon estimation (MHE) has a trade-off between accuracy of state estimates and the computational cost. Implementation of MHE based ISAT is shown for faster state estimation, with an accuracy same as that of MHE. Flowsheet optimization aims to optimize an objective or cost function by changing various independent process variables, subject to design and model constraints. Depending on the nonlinearity of the process units, an optimization routine can make a number of calls for flowsheet (simulation) convergence, thereby making the computation time prohibitive. Storage and retrieval of the simulation trajectories can speed-up process optimization, which is shown using a CHEMCAD® flowsheet. Online integration of an ISAT database to solve the simulation problem along with an outer-loop consisting of the optimization routine is shown using the sequential-modular approach.
text

There is increasing pressure on industries to increase their productivity while simultaneously reducing their environmental impact. In order to meet these new challenges, energy and raw materials need to be put to the best use they can be. Typically the features of a process are fixed at an early stage in a design. While doing so allows a design to be conveniently arranged into discrete stages, it also results in the loss of many opportunities for innovation. In order to preserve both the chance for innovation and ease of management, new and systematic methods are needed to design processes. The purpose of this research is to demonstrate the use of a novel method of synthesizing process flowsheets, using a graphical tool which we called the GH-space, with the overall goal of minimizing carbon emissions while making the best use of raw materials and for a given production. Typically mass, energy and work balances are done on flowsheets as a means of analysis. In other words, the flowsheet determines the balances. Unfortunately, once the flowsheet and chemistry of the process has been decided, most of the opportunities for improvement and innovation have been lost. The GH-space technique uses fundamental thermodynamic principles to allow the mass, energy and work balances to define targets for the performance of a process. Furthermore processes and unit operations can be defined as vectors in the GH-space. Using the targets, one can combine the vector processes in such a way as to approach the target. These vector processes, and the way they are combined, can then be interpreted in terms of flowsheets. This is opposite to what is normally done and allows the process balances to determine what the best flowsheet might look like, allowing for great innovation from the very start of a design. In addition to this, probably the greatest advantage of the GH-space technique is that processes of great complexity can all be analyzed on a set of two-dimensional axes. Every process that converts some feed material to a product material has a heat and a work associated with it in order to perform that conversion. Using the relationship that exists between heat and work allows the target of a process to be determined and for flowsheets to be formulated that allow these targets to be met. In this research the flows of heat and work are illustrated with the analogy of a heat engine. This is not the only way for heat and work to flow between process units but it allows for convenient illustration of the heat and work interaction between individual process units. Three case studies were chosen for their reputations as high carbon dioxide emitters: Coal Gasification, Methane Steam Reforming and Fischer-Tropsch synthesis. The GH-space method was then applied to these three examples to determine if these emissions were just a price that had to be paid or if there was any room for improvement. The case studies shown herein were ideal cases to show the power and flexibility of the technique as well as illustrate a method of using the technique, there is a great deal of additional details that would still need to be considered for a practical, functioning, plant to be built, such as catalysis and materials of construction, to name only two. While the GH-space provides insight into what the theoretical maximum efficiency might look like it does not necessarily show what the absolute maximum efficiency might be. Another advantage of the GH-space is that it can handle as little or as much detail as is desired. It was shown in this work that with clear understanding of the flows of mass, energy and work within a process it is possible to design process flowsheets that are potentially carbon negative, produce the intended product and also produce power as a co-product.

Thesis (M.S.)--University of Wisconsin--Madison, 1990.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 110-115).

Most of the recent design research has been focused on the development of more rigorous procedures for the design or the synthesis of subsystems of chemical plants. At the preliminary stage of design, however, less than 1% of ideas ever prove to be successful, so that the emphasis at this stage of a design should be placed on the quick screening of numerous process alternatives. The computer program described in this research is used to develop conceptual designs. PIP (Process Invention Procedure) is an hierarchical based expert system for the synthesis of chemical process flowsheets. It uses a combination of qualitative knowledge, i.e. heuristics, and quantitative knowledge, i.e. design and cost calculations, to identify the unit operations involved in a flowsheet and the interconnections between those units. A hybrid, expert system control architecture was developed for PIP that allows these two types of knowledge-bases to interact at each decision level while inventing the flowsheet. In addition, at each decision level, where finer details of the process structure are added, the significant design variables are identified, and the processing costs (both annualized capital and operating) are calculated in terms of these design variables so that a decision may be made on whether to terminate the project or to continue on to the next level. PIP has the advantage of very rapid response times (short-cut models are used so that the calculation for a complete plant takes only a few seconds) and ease of changing the structure of a flowsheet. The design of the user interface for PIP took into account three very important considerations: (1) the structure and characteristics of the system's decision strategy and the way it is presented to the user; (2) the state of the problem at any point in time as it is perceived by the user; and (3) the physical representation of the data and results. Thus, PIP allows a design engineer to invent and to evaluate initial chemical flowsheet structures rapidly, to identify possible process alternatives, and to obtain an estimate of the optimum values of the design variables.