Design Optimization of Highly Uncertain Processes: Applications to Papermaking System

In process design, the goal is to find a process structure that satisfies the desired targets and constraints. A typical task involves decision making related to the process flow-sheet and equipment. This dissertation examines design optimization of papermaking process. The main emphasis is on the development of an optimal design procedure for highly uncertain processes with non-Gaussian uncertainties. The design problem is studied as a multiobjective task in which the most effective process structure is sought by maximizing the process long-term performance and minimizing the investment cost. As the assessment of the long-term performance requires that the process be operated optimally, the optimization of the process operation is studied as a subtask of the design problem. Paper manufacturing is a complex process in which paper is produced from wood, water, and chemicals. The task is to manufacture uniform quality paper while minimizing the costs. If the paper web breaks, all the production is discarded. The unpredictable web breaks strongly disturb the paper production. As a result, the process has two separate operating points: normal operation and operation during web breaks. That poses challenges to the process operation as the transition between the operating points is somewhat random and the future evolution of the process is not completely predictable. In model-based process optimization, the uncertainty related to the models affects the reliability of the results. The modelling uncertainty is associated with both the incom-plete understanding of the process and the approximation due to computational reasons. In papermaking, the unpredictable web breaks are the largest source of uncertainty, but incomplete understanding is also related to e.g. the quality models of the paper. Besides modelling uncertainty, also the uncertainty about the available information, i.e. the measurement accuracy, affects the reliability of the optimization. In this thesis, schedul-ing of the measurement resources is studied as a part of the process optimization. This dissertation proposes a procedure to systematically optimize the design and operation of a papermaking process. The procedure is presented at six stages, including problem formulation, modelling, operational optimization, design optimization, robustness analysis, and validation. The main focus is at the operational and design optimization stages, but the purpose of all stages is discussed. The proposed procedure is demonstrated with case studies. The studied cases deal with two types of problems: discrete state systems with uncertain state information and continuous state systems with two operating points. In both groups, non-Gaussian uncertainty plays an important role

Interactions of chemical variations and biocide performance at paper machines

The objective of this thesis was to study the interactions of microbial activity, biocide usage and creation, and chemical changes in the papermaking process. The main focus was on oxidative biocide systems. In addition, new measurement and biocide production methods were applied to papermaking, and evaluated for the monitoring and control of the microbiological state and biocide usage. The measurement methods were based on portable handheld online equipments whereas the biocide production was based on electrochemical generation of biocides. The trials were mainly performed in pilot scale with actual process samples and complemented with a few laboratory trials. Most of the pilot results were verified in several field studies at paper machines. In the studies also the applicability of monitoring tools were evaluated. Biocide dosing itself, paper machine breaks, and poor management of broke generated chemical variations, which were detrimental to the papermaking process. Spoilage of broke due to poor broke management and poor biocide performance decreased the system pH, increased the conductivity, and caused the defects to the web. These chemical variations were also observed to cause variations in the cationic demand values. This probably caused unwanted particle flocculation generating the spots and holes to the web. Base paper defects were observed to cause runnability problems also at the coating machine. This cyclicity, where chemical variations cause breaks and breaks cause chemical variations, should be eliminated in order to restore good runnability. When revealing many such cause-effect relations and hidden phenomena, hand-held instrumentation gives additional references for existing basic measurements such as pH, conductivity, and redox potential. This work also took in use measurements which have not been traditionally used in papermaking such as measurement of halogens, dissolved calcium, and dissolved oxygen contents. ATP content measurement using a portable luminometer was found to be useful and easy-to-use method for evaluating microbial activity and optimizing biocide performance at paper mills. This thesis introduces a new biocide concept which can be used to prevent both microbial and biocidal problems described above. The results demonstrate how electrochemical on-site production can decrease chemical variations and improve biocide performance compared to current best practices offering an efficient and economically attractive alternative for microbial control

Novel visualization and algebraic techniques for sustainable development through property integration

The process industries are characterized by the significant consumption of fresh resources. This is a critical issue, which calls for an effective strategy towards more sustainable operations. One approach that favors sustainability and resource conservation is material recycle and/or reuse. In this regard, an integrated framework is an essential element in sustainable development. An effective reuse strategy must consider the process as a whole and develop plant-wide strategies. While the role of mass and energy integration has been acknowledged as a holistic basis for sustainable design, it is worth noting that there are many design problems that are driven by properties or functionalities of the streams and not by their chemical constituency. In this dissertation, the notion of componentless design, which was introduced by Shelley and El-Halwagi in 2000, was employed to identify optimal strategies for resource conservation, material substitution, and overall process integration. First, the focus was given on the problem of identifying rigorous targets for material reuse in property-based applications by introducing a new property-based pinch analysis and visualization technique. Next, a non-iterative, property-based algebraic technique, which aims at determining rigorous targets of the process performance in materialrecycle networks, was developed. Further, a new property-based procedure for determining optimal process modifications on a property cluster diagram to optimize the allocation of process resources and minimize waste discharge was also discussed. In addition, material substitution strategies were considered for optimizing both the process and the fresh properties. In this direction, a new process design and molecular synthesis methodology was evolved by using the componentless property-cluster domain and Group Contribution Methods (GCM) as key tools in developing a generic framework and systematic approach to the problem of simultaneous process and molecular design

TITANIUM DIOXIDE RECOVERY, FILLER RETENTION AND WHITE WATER TREATMENT USING FLOTATION AND MEMBRANE FILTRATION

Wang, Lawrence K. and Wang, Mu-Hao Sung (2022). Titanium dioxide recovery, filler retention and white water treatment using flotation and membrane filtration.. In: "Evolutionary Progress in Science, Technology, Engineering, Arts, and Mathematics (STEAM)", Wang, Lawrence K. and Tsao, Hung-ping (editors). Volume 4, Number 7, July 2022; pp.72. Lenox Institute Press, MA, USA. STEAM-VOL4-NUM7-JULY2022. ISBN 978-0-9890870-3-2. ............ABSTRACT: Historical and recent developments by research scientists around the world are reviewed and introduced. Topics reviewed include: the characteristics and application of titanium dioxide and various potential fillers; filler retention; techniques and chemicals for enhancing filler retention; and various Saveall processes (such as DAF, DAFF, DAF-DAFF, Spray Filter, Foamer, ozone-oxygen flotation, VSEP, etc.) for white water treatment and resources recovery. This publication is one of several memoirs written by and for the Lenox Institute of Water Technology (LIWT) in memory of Lenox President/Professor Milos Krofta, and Lenox Professors William A. Selke, Donald B. Aulenbach and Nazih K. Shammas. ............KEYWORDS: Memoir, Milos Krofta, Lenox Professors, Lenox Institute of Water Technology (LIWT), Krofta Engineering Corporation (KEC), Pulp, Paper, Titanium Dioxide, Filler, Filler Retention, White Water, Effluent Treatment, Water Reuse, Secondary Fiber, Saveall Process, Dissolved Air Flotation, DAF, Dissolved Air Flotation & Filtration, DAFF, Two-Stage DAF-DAFF, Vibratory Shear Enhanced Process, VSEP, Membrane Filtration

Application of pinch technology in an integrated pulp and paper mill.

Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.The objective of this investigation was to utilise water pinch analysis as a tool for the optimisation of fresh water use in an integrated pulp and paper mill. The investigation was carried out at Mondi Paper in Merebank, south of Durban. The pulp and paper manufacturing process is a large consumer of fresh water and minimising the amount of fresh water used in the processes is beneficial from both a cost and environmental point of view. There are examples of mills which have "closed" their water systems to the extent that fresh water make up is minimal and most of the water is recycled and reused in a closed loop. These examples provide guidance on the basis of proven methods for reducing water consumption in the pulp and paper industry and can be used as a reference for mills wishing to reduce water consumption by making use of tried and tested methods. This investigation sought to provide an alternative method to identifying potential savings in fresh water consumption by making use of water pinch analysis. This was done at Mondi Paper by analysing individual parts of the mill and then a larger section of the mill which included both pulp and paper production. Flow rates of water streams and fibre content in those streams were obtained from plant data, where available, and this data was used to produce.a mass balance using the Linnhoff-March software, Water Tracker. The balance produced using Water Tracker provided the missing flow and fibre content data and this data was used as the input for the Linnhoff-March software, Water Pinch , to perform the water pinch analysis. The results achieved when analysing the individual parts of the mill did not demonstrate potential for significant savings in fresh water consumption, however the analysis of the integrated section of the mill identified a potential reduction in fresh water. It was found that the application of a single contaminant analysis to the larger section of the mill identified a possible reduction in the freshwater requirement of 8.1% and a reduction in effluent generated of 5.4%. This is a savings of R1 548 593 per annum based on 2003 costs of fresh water and effluent disposal. This analysis was conducted using the most simplified representation possible to produce meaningful results in order to evaluate the effectiveness of water pinch analysis in optimising the fresh water consumption in an integrated pulp and paper mill. It is demonstrated that water pinch analysis is potentially a useful tool in determining the minimum fresh water requirement of a site

Life Cycle Assessment (LCA) technique as a holistic tool for environmental impact and economic analysis of a co-pulping process

As the pressure on the chemical and process industries to improve environmental and economic performance increases, the need to move away from narrow system definitions and concepts in environmental system management is becoming more apparent. Life Cycle Assessment (LCA) has been a gaining wider acceptance as a holistic tool that enables quantification of environmental interventions and evaluation of the improvement options throughout the life cycle of process, product or activity. The stringent environmental legislation, especially in developing countries has warranted the need for intensive research in this field. Moreover, the capital cost for mitigation of emissions have put enormous pressure on the industries to reduce the overall process economic performance. This has not exempted the Pulp and Paper industry, being the producers of highly variable emissions quality and quantity are the prime candidates for the application of the technique. The application of the LCA in process selection has been necessitated by the fact that sometimes a technology intended to reduce wastes has created unanticipated impacts in other media and/or stages of the life cycle. Thus, LCA has been developed as a means to identify and deal with these impacts before they can occur. It differs from other pollution prevention techniques in that it views all the resource and energy inputs to a product (Life Cycle Inventory), as well as the associated wastes, health and ecological burdens (Impact Assessment), and evaluates opportunities to reduce environmental impacts (Improvement Analysis) from cradle to grave. LCA is often confused with other assessment tools, such as life cycle cost (LCC) or sometimes referred to as "environmental life cycle costing." This study was conducted at Mondi Packaging South African-Piet Retief Mill, a producer of linerboard, since this site has ample opportunity to minimse the environmental burden presented by operation of both Copeland Reactor and Boilers with significant emissions of SOx and NOx, and water effluent. The current mill strategy that is based on tight procurement specification of raw material is unsustainable. The environmental and economic performance analysis for this study followed from a mass balance of the pulp plant, power station, and paper machine as well as black liquor incinerating plant, and it was found that the most significant emissions come from pulp and steam generating processes. These emissions can be reduced by improving the mill energy efficiency and optimizing the Copeland scrubber absorption efficiency. The optimization of the Copeland scrubbing system will surely lead to improved environmental performance, however, the furnace stacks have to be modified to include the scrubbing system for absorption of SOx and NOx.Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2008.Chemical Engineeringunrestricte