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Model predictive control of hybrid systems.Ramlal, Jasmeer. January 2002 (has links)
Hybrid systems combine the continuous behavior evolution specified by differential equations with discontinuous changes specified by discrete event logic. Usually these systems in the processing industry can be identified as having to depend on discrete decisions regarding their operation. In process control there therefore is a challenge to automate these decisions. A model predictive control (MPC) strategy was proposed and verified for the control of hybrid systems. More specifically, the dynamic matrix control (DMC) framework commonly used in industry for the control of continuous variables was modified to deal with mixed integer variables,
which are necessary for the modelling and control of hybrid systems.
The algorithm was designed and commissioned in a closed control loop comprising a SCADA system and an optimiser (GAMS). GAMS (General Algebraic Modelling System) is an optimisation package that is able to solve for integer/continuous variables given a model of the system and an appropriate objective function. Online and offline closed loop tests were undertaken on a benchmark interacting tank system and a heating/cooling circuit. The algorithm was also applied to an industrial problem requiring the optimal sequencing of coal locks in real time. To complete the research concerning controller design for hybrid behavior, an investigation was undertaken regarding systems that have different modes of operation due to physicochemical (inherent) discontinuities e.g. a tank with discontinuous cross sectional area, fitted with an overflow. The findings from the online tests and offline simulations reveal that the proposed algorithm, with some system specific modification, was able to control each of the four hybrid systems under investigation. Based on which hybrid system was being controlled, by modifying the DMC algorithm to include integer variables, the mixed integer predictive controller (MIPC) was employed to initiate selections, switchings and determine sequences. Control of the interacting tank system was focused on an optimum selection in terms of operating positions for process inputs. The algorithm was shown to retain the usual features of DMC (i.e. tuning and dealing with multivariable interaction). For a system with multiple modes of operation i.e. the heating/cooling circuit, the algorithm was able to switch the mode of operation in order to meet operating objectives. The MPC strategy was used to good effect when getting the algorithm to sequence the operation of several coal locks. In this instance, the controller maintained system variables within certain operating constraints. Furthermore, soft constraints were proposed and used to promote operation close to operating constraints without the
danger of computational failure due to constraint violations. For systems with inherent discontinuities, a MPC strategy was proposed that predicted trajectories which crossed discontinuities. Convolution models were found to be inappropriate in this instance and state space equations describing the dynamics of the system were used instead. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2002.
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Comparative refining characteristics of northern and southern hemisphere bleached softwood Kraft species.Palmer, B. January 2009 (has links)
An experiment was designed to test the hypothesis that each softwood pulp is unique and
requires a specific, well defined mechanical treatment to derive its maximum strength potential.
Three bleached softwood Kraft pulps and respective wood samples were sourced from both the
Northern and Southern Hemispheres. The raw fibre characteristics of P. patula (Southern
Hemisphere), P. menziesii (Northern Hemisphere) and P. mariana (Northern Hemisphere) were
measured and compared. The raw pulp sheets were refined at different energies and intensities
under controlled laboratory conditions using a 12” single disc pilot refiner. Results were
assessed to determine the raw fibre characteristics, optimum refining conditions and the relative
refined strength potential for each of the three samples.
Results from anatomy measurements on the three wood samples differed significantly. P. patula
exhibited a relatively high proportion of springwood growth in the early growing years. As the
P. patula aged and formed mature wood there was a significant increase in the frequency of
latewood formation. This was characterized by an abrupt and significant increase in the wall
thickness, beyond that of the two Northern softwood samples. When the cell wall thickness
increased, the lumen width and fibre diameter of the P. patula decreased significantly, yielding
extremely coarse, stiff fibres.
The Northern P .mariana and P. menziesii samples were characterized by a relatively consistent
transition between high and low densities from the pith to the bark of the tree. The Southern P.
patula had a unique density trend with an increasing frequency of high density peaks indicative
of an increased latewood formation from the pith to the bark.
The slower growing Northern P. menziesii and P. mariana samples did not have as clear a
differentiation in fibre characteristics between juvenile and mature wood formation. The
Northern samples did however contain a significantly higher proportion of juvenile latewood
growth than the P. patula. However, the difference in fibre characteristics between earlywood
and latewood formation was not as significant as that noted with the Southern P. patula
Fibre morphology measurements on the unrefined bleached Kraft pulps also revealed significant
differences between the three samples. The average MORFI LAB01 results on the P. patula
defined fibres with a high coarseness and relatively low number of fibres per gram of pulp. The
extremely coarse latewood fibres formed during mature wood growth being the most likely
source. However, P. patula was also characterized with a high fibre flexibility and large lumen,
characteristics consistent with earlywood fibres. The Pulmac Z-Span 3000 was used to define
the individual fibre strength, when due consideration was given to the number of fibres per
gram, the corrected Pulmac results suggested P. patula had the strongest fibres.
When refined, using a standard disc refining programme, P. patula exhibited a fast freeness
development. Conventional thinking would suggest that this was an indication of a weaker fibre.
However, this species had a robust morphology compared to the Northern Hemisphere woods.
The theory developed in this dissertation suggests that the effect of coarseness and the
concomitant number of fibres per gram plays a significant role. These two parameters are not
included in the “traditional” refining calculations. The applied refining load and intensity was
calculated on the flow of the pulp passing through the refiner. The calculation did not consider
the actual number of fibres present in that specific volume. The implication is that when a fixed
refining load is applied to a pulp with coarse fibres there may be a higher effective load on those
fewer fibres (resulting in fibre cutting and fines generation). In this case, the Northern samples
have a comparatively low coarseness and more fibres per gram with each receiving a smaller
portion of the total load and intensity.
In terms of refined pulp properties, P. patula developed a relatively high bulk and tear index
consistent with coarse, rigid fibres. The Northern P. mariana and P. menziesii samples produced
a pulp with good tensile properties, consistent with a greater number of finer, collapsible fibres
with a higher relative bonding area.
P. patula fibres were extremely heterogeneous in nature containing the smallest relative lumen
width during latewood formation and the largest lumen width during earlywood growth. As a
result, P. patula contains extremes of both fine and coarse fibres in the same blend. It may be
more beneficial for this species than the others to improve both the tear and tensile properties
through fibre fractionation with appropriate development of the separate accepts and rejects
streams.
In terms of fibre development, low intensity refining parameters maximized the tensile strength
of the Southern P. patula. The Northern P. mariana and P. menziesii samples had a greater
number of fibres per gram of pulp requiring both a higher refining energy and intensity to
develop the pulp to its maximum potential. To develop optimum tear results, high intensity
refining, with a relatively low specific energy provided optimum results for all 3 samples.
Results confirmed that there were significant differences in the fibre morphology both between
the three different species and between the two Hemispheres. There was strong evidence that the
fibre characteristics dictate the manner in which a fibre responds to refining which in turn
determines the relative contribution to specific refined pulp properties. It may be possible to use
fibre characteristics to determine the appropriate refining parameters for optimal fibre
development which will enhance the value of the end product.
To derive the maximum strength potential from P. patula pulp samples, it is recommended that
further studies investigate Hydracyclone fractionation and the concomitant benefits of refining
the separate streams. Furthermore, a separate study on fibre morphology and refining
characteristics of the same species grown in both the Northern and Southern Hemisphere would
provide valuable insight. / Thesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2009.
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Inverse internal model control of an ethylene polymerisation reactor using artificial neural networks.Dunwoodie, Ryan. January 2001 (has links)
An artificial neural network is a mathematical black-box modelling tool. This tool can
be used to model complex non-linear multivariable processes. In attempting to create
an inverse process model of an industrial linear low density polyethylene reactor,
several interesting results were encountered. Both time-invariant algebraic and time-invariant
dynamic models could adequately represent the process, provided an
identified 50-minute time lag was taken into account.
A novel variation of the traditional IMC controller was implemented which used two
inverse neural network process models. This was named Inverse Internal Model
Control (IIMC). This controller was initially tested on a real multivariable pump-tank
system and showed promising results.
The IIMC controller was adapted to an on-line version for the polymer plant control
system. The controller was run in open loop mode to compare the predictions of the
controller with the actual PID ratio controllers. It was hoped that by incorporating
neural network models into the controller, they would take the non-linearity and
coupling of the variables into account, which the present PID controllers are unable to
do. The existing PID controllers operate on separate loops involving the two main
feeds (co-monomer and hydrogen) to the reactor, which constitute aspects of the
control system in which the scope for advanced control exists. Although the control
loop was not closed, the groundwork has been laid to implement a novel controller that
could the operation of the plant. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.
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Comparison of an anaerobic baffled reactor and a completely mixed reactor : start-up and organic loading tests.Mudunge, Reginald. January 2000 (has links)
The aim of the investigation was to compare the performance of an anaerobic baffled reactor (ABR)
with a completely mixed anaerobic reactor (CMAR). The ABR was operated with a hydraulic retention
time (HRT) of 20 h while the CMAR was operated at 20 d. A control experiment was conducted with a
CMAR operated at a constant hydraulic retention time and substrate feed concentration. During the
first phase, the start-up performance of the ABR and CMAR were compared. In the second phase of the
study the steady state COD removals were compared.
The laboratory completely mixed anaerobic reactor was a 20L glass vessel with a stirrer coming in
through the neck. A second type of reactor, anaerobic baffled reactor (ABR) was also operated. The
ABR was a rectangular perspex box with internal vertical baffles alternately hanging and standing. The
baffles divide the reactor into eight compartments with a total working volume of 7.5 L. Each baffle is
angled at about 45Q to distribute the flow towards the centre of the upcomer. The reactors were seeded
with raw sewage and allowed to stand for 3 days after which a continous feed of sucrose and basal salts
was commenced. The initial HRT for the ABR and the CMAR were 60 h and 30 days respectively.
When the reactors reached steady state (pH, gas production, gas composition and alkalinity), the HRT
was reduced in a stepwise fashion (ABR 60 h to 35 h to 20 h and CMAR 35 d to 30 d to 20 d). At the
final HRT the COD removals were similar (67 %). The ABR took 120 d to attain final steady state
while the CMAR took 200 d.
The organic loading tests were undertaken with a stepwise increase (doubling) in the influent substrate
concentration. The feeding commenced at an organic loading rate (OLR) of 4.8 kg/m(3).d for the ABR.
The flow rate (HRT) into both reactors and other parameters were kept constant (HRT of 20 h and 20 d
for ABR and CMAR respectively). The substrate concentration was increased from 4 gCOD/L (4.8
kg/m(3).d) to 64 gCOD/L (76.8 kg/m(3).d) for the ABR. For the CMAR it was increased from 4 gCOD/L
(0.25 kg/m(3).d) to 32 gCOD/L (2 kg/m(3).d). The method used was to increase the organic loading rate
until the reactors failed. Since the two reactors had different operating HRTs, the tests began when both
had the same COD removal rate of about 60 % COD reduction. The same parameters as in the start-up
period were monitored for both reactors. The CMAR had a COD removal efficiency ca. 70 %, which
did not fluctuate when OLR was increased. The ABR reached a maximum COD removal of 80 %. An
increase in the OLR led to an initial decrease in the COD removal until the biomass recovered and the
high COD (80 %) removal rates resumed. The ABR reached a maximum OLR of 76.8 kg/m(3).d whilst
the CMAR reached a maximum OLR of 2.0 kg/m(3).d. The investigations showed that the ABR could be
operated at higher organic loads than the CMAR and give the same organic removal rate. This verified
the importance of increasing the SRT/HRT ratio in anaerobic reactors. The CMAR, however, proved to
be stable to changes in the influent feed strength, as there was no immediate noticeable changes in the
gas production. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
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Adaptive dynamic matrix control for a multivariable training plant.Guiamba, Isabel Remigio Ferrao. January 2001 (has links)
Dynamic Matrix Control (DMC) has proven to be a powerful tool for optimal regulation of
chemical processes under constrained conditions. The internal model of this predictive
controller is based on step response measurements at an average operating point. As the process
moves away from this point, however, control becomes sub-optimal due to process
non-linearity. If DMC is made adaptive, it can be expected to perform well even in the presence
of uncertainties, non-linearities and time-vary ing process parameters.
This project examines modelling and control issues for a complex multivariable industrial
operator training plant, and develops and applies a method for adapting the controller on-line to
account for non-linearity. A two-input/two-output sub-system of the Training Plant was
considered. A special technique had to be developed to deal with the integrating nature of this
system - that is, its production of ramp outputs for step inputs.
The project included the commissioning of the process equipment and the addition of
instrumentation and interfacing to a SCADA system which has been developed in the School of
Chemical Engineering. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.
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Modelling of the tubular filter press process.Mullan, David James. January 2000 (has links)
The objective of this project was to develop a suitable procedure for the design, control and optimisation
of the Tubular Filter Press. To this end, the following objectives were defined for this study:
• To extend or improve upon the constant pressure compressible cake filtration model, predictive
solution procedure, and standard laboratory characterisation techniques requlred to obtain the empirical
model parameters, presented in Rencken (1992).
A new generalised area contact constant pressure compressible cake filtration model was
developed for both the internal cylindrical and planar filtration geometries. The model utilises a
heuristically developed area contact function which relates the interparticle contact area to the
solids compressive pressure within the cake. If the area contact is zero, the model reduces to
the conventional point contact model as presented in Rencken ( 1992). The sludge used in this
investigation was found to exhibit a negligible degree of area contact.
A new pseudo variable pressure solution procedure was developed, that is an extension of the
constant pressure solution procedure, to account for the initial variable pressure stage of the
Tubular Filter Press operation. The pseudo variable pressure solution procedure was found to
account accurately for the initial filtration behaviour observed during the pressurisation period
of the Tubular Filter Press. However for the normal operation of the Tubular Filter Press. the
difference between the output of the pseudo variable pressure and constant pressure solution
procedures, was found to be insignificant.
Wall friction in compression-permeability (C-P) cell tests was identified as a main source of
error. The significance of wall friction was investigated using a specially constructed C-P cell.
that enabled the transmitted pressure through the cake sample to be measured. The accuracy of
the characterisation which had been corrected for the effects of wall friction, was found to
improve the prediction of the filtration behaviour of the sludge significantly.
The direct shear test was identified and documented as a feasible experimental procedure to
determine the coefficient of earth pressure at rest. The coefficient of earth pressure is unique to
the non-planar filtration geometries. The coefficient of earth pressure at rest was determined
for the sludge used in this investigation.
• To incorporate the constant pressure compressible cake filtration model and the associated predictive
solution procedures into a user-friendly computer programme that will facilitate the design and
optimisation of full-scale plants. The predictive solution procedures were incorporated into the Windows 95 computer
programme, COMPRESS, that can be used for any constant pressure compressible cake
dead-end filtration application where the filtration geometry is planar or internal cylindrical.
A control and optimisation strategy for the continuous operation of the Tubular Filter Press has
been proposed.
To develop a regressive solution procedure, and incorporate this procedure into a user-friendly
computer progranune, that will enable the empirical model parameters. normally obtained from standard
laboratory-scale tests, to be obtained from actual filtration data.
A regressive solution procedure was developed that utilises a direct search optimisation
technique that is an extension of the COMPLEX method. The regressive solution procedure
was incorporated into the Windows 95 program, REGRESS. The program utilises filtration
data from any dead-end constant pressure filtration application of either planar or internal
cylindrical geometry. REGRESS provides an effective means for determining the true physical
or plant specific filtration characteristics of the sludge. The regressive solution procedure also
enables the parameters specific to the new area contact model to be determined. The sludge
characterisation obtained from regressing on filtration data was found to be a significant
improvement in predicting the filtration behaviour, than the characterisation obtained from the
standard non-filtration laboratory-scale methods, even after the C-P cell data had been
corrected for the effects of wall friction.
The programs COMPRESS and REGRESS should greatly assist in the design. control and optimisation of
the Tubular Filter Press process. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
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Mathematical modelling and experimental study of the kinetics of the acid sulphite pulping of eucalyptus wood.Watson, Edward. January 1992 (has links)
The chemistry of the batch cooking process at Sappi Saiccor, relating to both the pulp and liquor, was investigated with the aim of using kinetic expressions to develop an improved process control model. The mill produces dissolving pulps using the acid sulphite method. Three process reactions were identified as important: cellulose hydrolysis, delignification and hemicellulose dissolution. Of these, cellulose hydrolysis is the most important since the primary aim is to achieve a targeted cellulose degree of polymerisation (DP) or viscosity (DP is commonly expressed in terms
of this measurement). This is directly determined by the rate of this reaction during the cook, and the acidity of the cooking liquor was found to be the key factor. As existing equipment was not suitable for obtaining the data required to perform a kinetic analysis, a pilot plant was constructed. A commercially available probe was used for the first time to measure pH directly. The measured acidity is not directly equivalent to hydrogen ion activity at these temperatures and pressures; however, since the conditions of each cook are similar the errors incurred were found to be constant from cook to cook. The probe was found to be prone to drift due to ageing and this was accounted for by using an 'on line' calibration based on a liquor analysis.
The kinetics of the cellulose hydrolysis reaction were determined using the on-line measurement of acidity and the concept of degradation increase (DI) which relates the reduction in DP value to the rate at which the polymeric chains are split. Delignification and hemicellulose dissolution were examined, since it is beneficial to maximise these reactions to reduce the quantities of chemicals consumed during the bleaching process. A model for controlling cooks to a set target cellulose DP value within a set time was developed based on the reaction kinetics. This was capable of predicting cooking conditions required with sufficient accuracy to control the cellulose DP value to within ±6 cp SNIA on the viscosity scale. / Thesis (M.Sc.Eng.)-University of Natal, 1992.
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Automation of a static-synthetic apparatus for vapour-liquid equilibrium measurement.Moodley, Kuveneshan. January 2012 (has links)
The measurement of vapour-liquid equilibrium data is extremely important as such data are crucial
for the accurate design, simulation and optimization of the majority of separation processes,
including distillation, extraction and absorption.
This study involved the measurement of vapour-liquid equilibrium data, using a modified version
of the static total pressure apparatus designed within the Thermodynamics Research Unit by J.D.
Raal and commissioned by Motchelaho, (Motchelaho, 2006 and Raal et al., 2011). This apparatus
provides a very simple and accurate means of obtaining P-x data using only isothermal total
pressure and overall composition (z) measurements. Phase sampling is not required.
Phase equilibrium measurement procedures using this type of apparatus are often tedious,
protracted and repetitive. It is therefore useful and realizable in the rapidly advancing digital age, to
incorporate computer-aided operation, to decrease the man hours required to perform such
measurements.
The central objective of this work was to develop and implement a control scheme, to fully
automate the original static total pressure apparatus of Raal et al. (2011). The scheme incorporates
several pressure feedback closed loops, to execute process step re-initialization, valve positioning
and motion control in a stepwise fashion. High resolution stepper motors were used to engage the
dispensers, as they provided a very accurate method of regulating the introduction of precise
desired volumes of components into the cell. Once executed, the control scheme requires
approximately two days to produce a single forty data points (P-x) isotherm, and minimizes human
intervention to two to three hours. In addition to automation, the apparatus was modified to
perform moderate pressure measurements up to 1.5 MPa.
Vapour-liquid equilibrium test measurements were performed using both the manual and automated
operating modes to validate the operability and reproducibility of the apparatus. The test systems
measured include the water (1) + propan-1-ol (2) system at 313.15 K and the n-hexane (1) + butan-
2-ol system at 329.15 K.
Phase equilibrium data of binary systems, containing the solvent morpholine-4-carbaldehyde
(NFM) was then measured. The availability of vapour-liquid equilibrium data for binary systems
containing NFM is limited in the literature. The new systems measured include: n-hexane (1) +
NFM (2) at 343.15, 363.15 and 393.15 K, as well as n-heptane (1) + NFM (2) at 343.15, 363.15 and
393.15 K.
The modified apparatus is quite efficient as combinations of the slightly volatile NFM with highly
volatile alkane constituents were easily and accurately measured. The apparatus also allows for
accurate vapour-liquid equilibrium measurements in the dilute composition regions.
A standard uncertainty in the equilibrium pressure reading, within the 0 to 100 kPa range was
calculated to be 0.106 kPa, and 1.06 kPa for the 100 to 1000 kPa pressure range. A standard
uncertainty in the equilibrium temperature of 0.05 K was calculated.
The isothermal data obtained were modelled using the combined (-) method described by Barker
(1953). This involved the calculation of binary interaction parameters, by fitting the data to various
thermodynamic models. The virial equation of state with the Hayden-O’Connell (1975) and
modified Tsonopoulos (Long et al., 2004) second virial coefficient correlations were used in this
work to account for vapour phase non-ideality. The Wilson (1964), NRTL (Renon and Prausnitz,
1968), Tsuboka-Katayama-Wilson (1975) and modified Universal Quasi-Chemical (Anderson and
Prausnitz, 1978) activity coefficient models were used to account for the liquid phase non-ideality.
A stability analysis was carried out on all the new systems measured to ensure that two-liquid phase
formation did not occur in the measured temperature range.
A model-free method based on the numerical integration of the coexistence equation was also used
to determine the vapour phase compositions and activity coefficients from the measured P-z data.
These results compare well with the results obtained by the model-dependent method.
The infinite dilution activity coefficients for the systems under consideration were determined by
the method of Maher and Smith (1979b), and by suitable extrapolation methods. Excess enthalpy
and excess entropy data were calculated for the systems measured, using the Gibbs-Helmholtz
equation in conjunction with the fundamental excess property relation. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.
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Utilisation of bagasse for the production of C5- and C6- sugars.Trickett, Richard Charles. January 1982 (has links)
Surplus sugarcane bagasse, estimated at a maximum of 0,9x106
tons/year, represents an annual renewable resource which is
readily available at the mill site and is a suitable potential
source of alternative fuels and chemical feedstocks.
This work contains an extensive literature survey which covers
the production of C5- and C6- sugars from lignocelluloses by
chemical hydrolysis and the pretreatment of cellulosic materials
for enzymatic hydrolysis of the cellulose fraction. This survey
was then used to determine the final direction of this research
into the utilisation of bagasse for the production of fermentable
sugars.
It was decided that research should be directed at the dilute
acid hydrolysis of the bagasse hemicellulose fraction to determine
whether this fraction could be selectively hydrolysed from
the complex lignocellulose structure and to obtain xylose yields
under different hydrolysis conditions.
Acids, especially acetic acid, are liberated from bagasse by
steaming at elevated temperatures. In this acid medium the
hemicelluloses are hydrolysed and become soluble. Autohydrolysis
tests on whole bagasse indicate that hemicellulose hydrolysis
becomes significant at temperatures above 140°C. However, the
autohydrolysis liquor would still require dilute mineral acid
hydrolysis to convert the pentose oligomers to their monomeric
forms. Dilute sulphuric and batch hydrolysis of whole bagasse hemicellulose
has thus been investigated at a solid to liquid ratio
of 1:15 over the following temperature and acid concentrations
ranges : 80° to 150°C and 3 to 40 g/l acid. Xylose, glucose,
furfural and acetic acid formation and sulphuric acid consumption
were monitored during these hydrolyses. Hemicellulose hydrolysis to produce mainly xylose is readily achieved over the entire range of acid hydrolysis conditions
tested with little removal of the other bagasse components
(lignin and cellulose). At the upper end of the temperature
range acid concentrations below 20 g/l are sufficient for
hemicellulose hydrolysis due to the effect of temperature
on reaction rate.
The bagasse hemicellulose consists of two fractions, an easily
hydrolysable portion containing 165 mg of potential xylose/g bagasse and a resistant fraction containing 105 mg of potential xylose/g bagasse. A first order reaction model has been
developed using the batch acid hydrolysis results. It is
based on two hemicellulose fractions reacting simultaneously
to give a common product (xylose) and predicts total xylose
yield as a function of hydrolysis time for a given set of
hydrolysis conditions.
The encouraging xylose yields obtained during the batch hydrolyses
led to the design of a continuous hydrolysis reactor to process
bagasse at low liquid to solid ratios to determine whether
xylose yields similar to the batch hydrolysis yields could be
obtained at the same hydrolysis conditions.
The continuous hydrolyses showed that for the conditions tested
the xylose yields are unaffected by the decrease in liquid to
solid ratio (down to 3,6:1) and it would appear that reactor
performance is still controlled by reaction kinetics.
A number of reactor configurations for the industrial production
of pentoses from bagasse hemicelluloses are also proposed. / Thesis (M.Sc.)-University of Natal. Durban, 1982.
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Modelling biological sulphate reduction in anaerobic digestion using WEST.03 September 2010 (has links)
Researchers at Rhodes University conducted investigations into the anaerobic co-disposal of
primary sewage sludge (PSS) and high sulphate acid mine drainage (AMD) resulting in the
development of the Rhodes BioSURE Process® which forms the basis for the operation of a
pilot recycling sludge bed reactor (RSBR). Further research has been conducted by researchers
at the University of Cape Town (UCT), with the principle aim of determining the rate of
hydrolysis of PSS under rnethanogenic, acidogenic and sulphate reducing conditions in
laboratory-scale anaerobic digesters.
The University of Cape Town's Anaerobic Digestion Model No.1 (UCTADMI) which
integrates various biological anaerobic processes for the production of methane was extended
with the development of a mathematical model incorporating the processes of biosulphidogenic
reduction and the biology of sulphate reducing bacteria (SRB). Kinetic parameters used in the
model were obtained from SOtemann et al. (2005b) and Kalyuzhnyi et al. (1998).
The WEST® software was used as a platform in translation of the basic UCTADMI from
AQUASIM, and subsequently applied to data sets from UCT laboratory experiments.
Incomplete closure of mass balances was attributed to incorrect reaction stoichiometry inherited
through translation of the AQUASIM model into WEST®. The WEST® implementation of the
model to the experimental methanogenic systems gave fairly close correlations between
predicted and measured data for a single set of stoichiometric and kinetic constants, with
regressed hydrolysis rate constants. Application of the extended UCTADMI to experimental
sulphidogenic systems demonstrated simulation results reasonably close to measured data, with
the exception of effluent soluble COD and sulphate concentrations. Except for a single system
with a high COD:Sat ratio, sulphidogens are out competed for substrate by methanogens within
the model. Therefore the model does not properly represent the competition between
methanogenic and sulphidogenic organism groups.
Trends observed in application of the model to available pilot plant RSBR data were similar to
those observed in sulphidogenic systems, resulting in methanogens out-competing
sulphidogens. The model was used as a tool to explore various scenarios regarding operation of
the pilot plant. Based on the work conducted in this study, various areas for further information
and research were highlighted and recommended. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.
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