Adapting an existing batch pulp digester model for use in continuous digesters

Dissertation (MEng (Control Engineering))--University of Pretoria, 2020.A mathematical model of a continuous Kraft wood digester was developed and tested. The model relies heavily on the work done previously by Christensen, Albright & Williams (1982). The batch Kraft digester model developed by Christensen et al (1982) was adapted to model a continuous Kraft wood digester at Ngodwana, South Africa. This adaptation centres around utilizing the method of lines to account for changes in both time and height of the digester simultaneously. The model was able to simulate the Kappa number of the digester accurately to an average absolute error of 7.88 that was reduced to 2.87 after certain process parameters were optimized for. A moving horizon state estimator was introduced into the model in an effort to keep internal state prediction accurate. This addition brought the average absolute error down further to 2.75. Adaptive control was also implemented into the model. The plant data the model was compared against to determine its accuracy was filtered with the use of a rolling median filter to reduce the influence introduced by noisy and infrequent measurements.SappiChemical EngineeringMEng (Control Engineering)Unrestricte

Real-time observer model for Kraft wood digester.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.At SAPPI-Tugela a continuous Kraft wood chip digester operates in EMCC mode (extended modified continuous cooking). Chips are initially exposed to a NaOH / Na2S liquor at high temperature in the top section. The chips move downward in plug flow passing circumferential screens used to draw liquor for various circulations. About midway down the spent black liquor is removed and the chips enter the cooler bottom section where some further reaction and washing occurs. Liquor level and chip level are maintained close to each other near the top. Chips require 8-12 hours to pass through the digester, depending on the chip feed rate. The key parameter of interest at the digester exit is the Kappa number, which is a measure of the extent of delignification which has occurred. Different board and paper products require different Kappa number pulp feed. (Final properties such as tensile, tear and bursting strengths will also depend on the way fibres have been modified in the digestion). The objective of this investigation is to predict the Kappa number of the product pulp in real-time, thus facilitating quicker reaction than the present dependence on laboratory analysis permits, possibly even allowing closed-loop control. The extent of delignification depends on liquor strength, temperature and exposure time, with final Kappa number also depending on the properties of the chip feed (wood type and moisture content). Compensation to maintain a steady Kappa number is made difficult by the long and varying residence time, and the fact that any changes apply to the whole profile held up in the digester. A number of static models for Kappa number prediction have been developed by previous workers, but these do not compare well with plant measurements. The collection of data from the Sappi-Tugela reactor, and the pulp quality reports, have been used to determine an efficient model. This step required a considerable data collection exercise, and similar results to the quality reports have been obtained using a simple linear model based on this data. The problem of model error is being reduced by arrangement as a Smith Predictor, in which the model is intermittently corrected by available laboratory analyses. At the same time, an interface was created, in order to synchronise measurement data for the chips presently leaving the reactor. In order to deal with the dead time, each parcel of chips entering the reactor is effectively tracked, and the changes in Kappa number integrated for reaction time under the varying conditions in transit. Knowing the present inventory of the reactor, this model can also be run forward in time as a predictive controller, to determine optimal control actions for maintenance of the target Kappa number

Improving the economic performance of anaerobic digestion by integrating lactic acid recovery into two-stage food waste digestion

The global production of food waste (FW) is of significant economic and environmental concern, having been estimated to produce 8% of globally produced anthropogenic greenhouse gas emissions and result in the loss of nearly USD1 trillion each year. Consequently, the correct disposal and recovery of value from FWs is a global challenge and responsibility. Anaerobic digestion (AD) is a capable technology which can recycle FW to produce renewable energy and recover nutrients. However high capital, operational, and management costs and low value of biogas and digestate lead to questionable economic benefit. As a result, the AD technology heavily relies on subsidies and policy incentives for feasibility. Integration of lactic acid (LA) production technologies into AD could convert the low-value process into a high-value LA-AD biorefinery, reducing reliance on government support. This study aims to address the above by exploring the integration of LA production to AD within the FW context. This involved detailed investigations into the production of LA from FWs, including within the commercial FW context, and integration of FW fermentation for LA into existing AD facilities. Accordingly, following optimisation of LA fermentation, and exploring the feasibility of recovering LA along with its impact on downstream AD, multiple integration scenarios were proposed detailing the potential economic benefits from integrating LA production into FW AD. The assessment of LA production within the FW context was first explored. For this, LA production within a pre-fermenter at a commercial two-stage FW AD facility was monitored, exploring the impact of environmental conditions, feedstock composition, and operational procedures on LA production performance and stability. Results showed standard operation of the pre-fermenter, favoured the formation of LA leading to LA being the dominant organic acid produced from fermentation. Furthermore, standard operation of the AD facility led to the selective dominance of Lactobacillus, a bacterium commonly associated with LA production. While LA production fluctuated over the monitoring period, the LA concentration was surprisingly stable, especially considering the variation in process variables (pH, temperature, retention time, feed rate, and feed composition). Even so, it was outlined that there would be significant opportunity to improve LA production performance, and consequently, economic performance by targeted process optimisation and control. Optimisation of LA fermentation showed the commercially adapted inoculum was capable of high LA yields and selectivities. In addition, the results showed optimal conditions promoted the growth of Lactobacillus, while alternative flanking microorganisms were inhibited. Moreover, optimisation effectively eliminated the conversion of LA to butyrate, allowing the sustained accumulation of LA. Further study of the commercial inoculum showed LA production could be effectively enhanced by supplementing FW with a simple carbohydrate (sucrose) and implementing partial digestate recirculation. While digestate enhanced LA production, it also increased microbial diversity which promoted the production of alternate organic acids. However, the effects of digestate could be effectively controlled through sucrose addition, which promoted the growth of Lactobacillus and inhibited the growth of the flanking community. Following optimisation of fermentation, the feasibility of recovering LA from complex fermentation media and its impact on downstream AD performance was explored. While real commercial broth reduced LA uptake, compared to pure LA solutions, LA was effectively recovered from highly complex fermentation media. Moreover, LA recovery only led to a minor reduction in methane production following the AD of the solid and liquid extraction residues. In this respect, LA production could outweigh the loss in methane production in terms of relative value, indicating the LA-AD biorefinery concept could be commercially attractive. A technoeconomic assessment indeed showed the benefit of integrating LA production into two-stage FW AD, yielding a highly profitable scenario. Furthermore, while integration scenarios were most profitable, Greenfield LA-AD biorefinery scenarios showed significantly higher profitability estimates compared to sole FW AD. Finally, the insight achieved into different aspects of the LA-AD biorefinery led to a series of recommendations for future research in the context of the FW biorefinery concept

Isolation of birch xylan as a part of pulping-based biorefinery

This study combines various aspects of xylan isolation from birch wood as part of a pulping-based biorefinery concept. Acidic prehydrolysis and alkaline pre-extraction are the two processes used as the starting point of the work. Solutions of xylan with diverse macromolecular and chemical properties were obtained by applying different pre-treatments. Pre-extraction at high alkalinity produced water-insoluble xylan with a high molar mass and low polydispersity. Autohydrolysis at a mild intensity yielded a liquid phase containing a variety of xylooligosaccharides and xylan of low molar mass. The fragments were mainly acetylated and some of them carried 4-O-methylglucuronic acid substituents. Intensification of autohydrolysis promoted formation of monomeric xylose and its degradation products. The addition of oxalic acid increased the monomeric fraction even at mild prehydrolysis intensities. The properties of cellulose in the wood residue were affected to a smaller or greater extent depending on the type and intensity of the pre-treatment. After alkaline pre-extraction at low temperature and high alkalinity, the macromolecular properties of cellulose were barely affected. After mild prehydrolysis, cellulose was partly depolymerised without a notable yield loss. When more severe prehydrolysis conditions were applied, as required for an almost complete removal of hemicelluloses, both the degree of polymerisation and yield of cellulose were affected dramatically. An attempt to mitigate gradual cellulose degradation induced in the pulping stage by prehydrolysis was made with cotton linters as a cellulose substrate. Sodium borohydride and different types of anthraquinone (AQ) were able to convert a share of the reducing end groups to either alditol or aldonic acid moieties stable to alkaline peeling. Such stabilisation had a positive effect on the yield of cellulose. Stabilisation was also reflected in the decreased ratios between the peeling and stopping reaction rate constants. An improved model for cellulose degradation in alkaline environments was developed that took secondary peeling into account. Application of the stabilisation chemicals to birch wood resulted in a moderate yield increase and the preferred stabilisation of hemicelluloses. Aqueous-phase prehydrolysis of birch wood followed by alkaline pulping produced dissolving pulps of viscose and acetate quality without alkaline post-extraction. Changes of cellulose crystallite dimensions and specific surface area between microfibril aggregates in bleached pulps were observed as functions of prehydrolysis intensity. Mild oxalic acid prehydrolysis and alkaline pre-extraction were shown to be well suited the production of paper pulps, where the latter pre-treatment ensured excellent papermaking properties

Book of abstracts of the 10th International Chemical and Biological Engineering Conference: CHEMPOR 2008

This book contains the extended abstracts presented at the 10th International Chemical and Biological Engineering Conference - CHEMPOR 2008, held in Braga, Portugal, over 3 days, from the 4th to the 6th of September, 2008. Previous editions took place in Lisboa (1975, 1889, 1998), Braga (1978), Póvoa de Varzim (1981), Coimbra (1985, 2005), Porto (1993), and Aveiro (2001). The conference was jointly organized by the University of Minho, “Ordem dos Engenheiros”, and the IBB - Institute for Biotechnology and Bioengineering with the usual support of the “Sociedade Portuguesa de Química” and, by the first time, of the “Sociedade Portuguesa de Biotecnologia”. Thirty years elapsed since CHEMPOR was held at the University of Minho, organized by T.R. Bott, D. Allen, A. Bridgwater, J.J.B. Romero, L.J.S. Soares and J.D.R.S. Pinheiro. We are fortunate to have Profs. Bott, Soares and Pinheiro in the Honor Committee of this 10th edition, under the high Patronage of his Excellency the President of the Portuguese Republic, Prof. Aníbal Cavaco Silva. The opening ceremony will confer Prof. Bott with a “Long Term Achievement” award acknowledging the important contribution Prof. Bott brought along more than 30 years to the development of the Chemical Engineering science, to the launch of CHEMPOR series and specially to the University of Minho. Prof. Bott’s inaugural lecture will address the importance of effective energy management in processing operations, particularly in the effectiveness of heat recovery and the associated reduction in greenhouse gas emission from combustion processes. The CHEMPOR series traditionally brings together both young and established researchers and end users to discuss recent developments in different areas of Chemical Engineering. The scope of this edition is broadening out by including the Biological Engineering research. One of the major core areas of the conference program is life quality, due to the importance that Chemical and Biological Engineering plays in this area. “Integration of Life Sciences & Engineering” and “Sustainable Process-Product Development through Green Chemistry” are two of the leading themes with papers addressing such important issues. This is complemented with additional leading themes including “Advancing the Chemical and Biological Engineering Fundamentals”, “Multi-Scale and/or Multi-Disciplinary Approach to Process-Product Innovation”, “Systematic Methods and Tools for Managing the Complexity”, and “Educating Chemical and Biological Engineers for Coming Challenges” which define the extended abstracts arrangements along this book. A total of 516 extended abstracts are included in the book, consisting of 7 invited lecturers, 15 keynote, 105 short oral presentations given in 5 parallel sessions, along with 6 slots for viewing 389 poster presentations. Full papers are jointly included in the companion Proceedings in CD-ROM. All papers have been reviewed and we are grateful to the members of scientific and organizing committees for their evaluations. It was an intensive task since 610 submitted abstracts from 45 countries were received. It has been an honor for us to contribute to setting up CHEMPOR 2008 during almost two years. We wish to thank the authors who have contributed to yield a high scientific standard to the program. We are thankful to the sponsors who have contributed decisively to this event. We also extend our gratefulness to all those who, through their dedicated efforts, have assisted us in this task. On behalf of the Scientific and Organizing Committees we wish you that together with an interesting reading, the scientific program and the social moments organized will be memorable for all.Fundação para a Ciência e a Tecnologia (FCT

Energy balance and techno-economic assessment of algal biofuel production systems

There has been considerable discussion in recent years about the potential of micro-algae for the production of sustainable and renewable biofuels. Unfortunately the scientific studies are accompanied by a multitude of semi-technical and commercial literature in which the claims made are difficult to substantiate or validate on the basis of theoretical considerations.To determine whether biofuel from micro-algae is a viable source of renewable energy three questions must be answered:a. How much energy can be produced by the micro-algae?b. How much energy is used in the production of micro-algae?c. Is more energy produced than used?A simple approach has been developed that allows calculation of maximum theoretical dry algal biomass and oil yields which can be used to counter some of the extreme yield values suggested in the 'grey' literature. No ready made platform was found that was capable of producing an energy balance model for micro-algal biofuel. A mechanistic energy balance model was successfully developed for the production of biogas from the anaerobic digestion of micro-algal biomass from raceways. Preliminary calculations had suggested this was the most promising approach. The energy balance model was used to consider the energetic viability of a number of production scenarios, and to identify the most critical parameters affecting net energy production. These were:a. Favourable climatic conditions. The production of micro-algal biofuel in UK would be energetically challenging at best.b. Achievement of ‘reasonable yields’ equivalent to ~3 % photosynthetic efficiency (25 g m-2 day-1)c. Low or no cost and embodied energy sources of CO2 and nutrients from flue gas and wastewaterd. Mesophilic rather than thermophilic digestione. Adequate conversion of the organic carbon to biogas (? 60 %)f. A low dose and low embodied energy organic flocculant that is readily digested, or micro-algal communities that settle readilyg. Additional concentration after flocculation or sedimentationh. Exploitation of the heat produced from parasitic combustion of micro-algal biogas in CHP unitsi. Minimisation of pumping of dilute micro-algal suspensionIt was concluded that the production of only biodiesel from micro-algae is not economically or energetically viable using current commercial technology, however, the production of micro-algal biogas is energetically viable, but is dependent on the exploitation of the heat generated by the combustion of biogas in combined heat and power units to show a positive balance.Two novel concepts are briefly examined and proposed for further research:a. The co-production of Dunaliella in open pan salt pans.b. A 'Horizontal biorefinery' where micro-algae species and useful products vary with salt concentration driven by solar evaporation.<br/

En route to the industrial applications of ionic liquids for metal oxide production and biomass fractionation: A sustainable avenue to advanced materials

In the context of climate change, it is essential to use renewable materials and to reduce the environmental footprint of industrial processes. This work focuses on the feasibility of implementing a low-cost Ionic Liquid (IL) in a large-scale biorefinery for bioethanol production (the ionoSolv process). The selected feedstock was Eucalyptus red grandis, a fast-growing hardwood. The lignocellulosic biomass was fractionated at laboratory scale, using aqueous N,N,N-trimethylammonium hydrogen sulfate (20 wt% water), at different temperatures and reaction times, to maximize glucose recovery (86%). Experiments under CO2 atmospheres (sub and supercritical) revealed that the ionoSolv process is pressure insensitive. A detailed Techno-Economic Analysis (TEA) for a biorefinery using the ionoSolv pretreatment was performed and compared to one using the acid-catalysed steam explosion pretreatment. With the ionoSolv pretreatment, the composition of the cellulose-rich pulps can be tailored and high-purity lignins can be recovered. The economic performance of both pretreatments are similar. From a sustainability perspective there are trade-offs: the ionoSolv process consumes 25% more energy (with potential for optimization) but consumes less chemicals and produces less waste. These results indicate that this process can be a competitive alternative. During the development of this process, and other IL-based processes, the interaction of ILs (neat and aqueous) with metals was investigated to establish suitable materials of construction. It was observed that the corrosion behaviour of metals exposed to ILs is system dependent. Surprisingly, water can act either as a corrosion inhibitor or promoter. A semi-quantitative classification method for the different corrosion behaviours observed was developed. Some metals exposed to aqueous ILs formed particles, resulting in the inadvertent development of a novel process for metal-based materials at large-scale: Oxidative Ionothermal Synthesis (OIS). A high-level TEA suggests that OIS offers economic and environmentally advantageous production of bulk and advanced metal-based materials, such as zinc oxide.Open Acces