Approximately 44% of the citrus that is processed becomes processing residue. The residue consists of the non-juice components of a citrus fruit, primarily peel and pulp, and is recovered by conversion to animal feed. The material is hygroscopic, agglomerating, has a wide particle size distribution, and must be carefully dried to avoid thermal damage to nutrients and flavors. This dissertation evaluates the possibility of utilizing a vibrofluidized bed dryer for citrus processing residue. Results demonstrate that it is possible to overcome the agglomeration difficulties associated with this material, offering an economically viable alternative processing methodology. To properly analyze this proposed system, a benchtop vibrofluidized bed dryer was designed, constructed and instrumented. Vibrofluidization and batch drying trials were conducted and analyzed. An economic evaluation of the proposed process was undertaken. Two mathematical models of the drying process were developed and validated. Characteristics that describe the vibrofluidized bed drying of the residue were determined. The conditions that facilitated fluidization were: 1) A particle size distribution of the dried residue that was lognormal, had a geometric mean diameter, dgw, of 3.829 mm, and a geometric standard deviation, Sgw, of 2.49x10-07 mm. 2) A vibrational acceleration, Aω2/g, of 2.54. 3) A minimum vibrofluidization velocity, Umvf, of 4.2 cm/s. The controlling mechanism of the falling rate period was determined to be diffusion, with an effective diffusion coefficient, Deff, of 2.85x10-5 cm/s, and critical moisture content, Mc, of 30%. Economic evaluation of the proposed method has a payback period of 4.34 years, and an estimated processing cost of $33 per ton of dried material. Models were developed based on bed hydrodynamics and three-phase drying kinetics, and thin-layer drying. Both models accurately predicted the drying curves. The three-phase kinetic drying model solved a series of simultaneous equations, and differential equations, based on moisture and enthalpy balances. This complex model successfully predicted the bed hydrodynamic properties and serves to facilitate scale-up, design, and bed configuration investigations. For the thin-layer drying model, the drying constants, K & N, for Page’s equation were determined as a function of bed temperature. This computationally simple, single-parameter model would serve process control algorithms.

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Typescript (photocopy). / Digitized by Kansas Correctional Industries

Today the use of resources in the industry are not complete to be considered as sustainable from the perspective of nutrient recovery. In the Swedish pulp and paper industry residual streams such as bark, fiber reject and sludge are returned for more sustainable use more frequently. Around 300 000-600 000 tons of sludge is generated every year from different cleaning processes in the pulp and paper industry. About 15 % of that sludge is so called biosludge that is a result from biological water treatment, where large amounts of phosphorus are used. After the cleaning process the total amount of biosludge generated in Sweden each year is estimated to contain approximately 2000 tons of phosphorus (P). The most common way to discard the biosludge today is by incineration, where aspects such as high content of moisture and ash have proven to be problematic. Besides phosphorus, other elements such as sulfur (S), chlorine (Cl) and calcium (Ca) are often found in the biosludge in larger amounts.   This study included co-combustion experiments of current residual streams from the pulp and paper mill SCA Obbola AB where the aim was to investigate how the ash transformation chemistry was affected. The residual streams comprised of bark, fiber reject and biosludge which were combusted together with stem wood in a bench scaled bubbling fluidized bed. To investigate if different ash related operating and technical problems could be reduced and if there was potential of phosphorus recycling from the ashes, produced ash and other samples were examined by SEM/EDS. The fuel mix from SCA Obbola consisted of large amounts of Ca, S and P relative to more ordinary biomass fuels like stem wood. These elements originated from the biosludge and was confirmed by the fuel analysis. Analysis made on collected samples showed that Ca and P together formed phosphates that either stayed in the bed or was collected in the cyclone which indicated that there could be a potential for recovering phosphorus. Although, the Ca/P ratio in the ashes was too high, which probably leads to that phosphates unsuitable for nutrient recovery are formed.   The fiber reject from SCA Obbola contained large amounts of chlorine according to the fuel analysis which was indicated from the results later in the study. During the combustion most of the Cl left the bottom ash via volatilization. It was true for both the fuel blends with and without fiber reject. When larger amounts of biosludge was added to the fuel mix less of the corrosive compound potassium chloride (KCl) was found in depositions and collected fine particulate matter (PM). This was due to that more sulfur was added in the system when the amount of biosludge was increased which lead to that K reacted with SO2 instead of Cl and formed K2SO4. The observed reduction of KCl resulted in; 1) lower amounts of fine particulate matter which means less loaded particulate filters 2) less risk of high temperature corrosion on heat transfer surfaces. The general conclusion that could be drawn from this study was that by increasing the amount of biosludge in the fuel blend at already high mixings of fiber reject, problems such as corrosion and fine particulate matter could be reduced. These advantages must be considered to the amount of lime stone needed to be added for reducing HCl from a cost perspective.

The Fluidised Bed Combustion (FBC) technology has been widely used internationally for power generation. This technology has good fuel flexibility and reduced S02 emissions with dry sorbent (Limestone or Dolomite) addition. South Africa has large reserves of coals that are difficult to combust in conventional pulverised fuel fired boilers. These reserves could be potential feedstocks for new build FBC boilers. The chemical composition of these coals is site specific and could have an impact on the combustion performance of the fuel. This necessitates the need for FBC coal tests in the presence of a sorbent. The objectives of this study were to investigate the changes in the production NO" SO" and the combustion efficiency of the three test coals under conditions of fluidised bed combustion, with the same sorbent. Tests with no sorbent were performed to evaluate the coals inherent calcium capabilities of capturing sulphur. Tests with varying ratios of sorbent were performed to evaluate the sorbent's capabilities for further levels of in-bed desulphurisation. The experimental equipment used in this investigation was the Eskom Fluidised Bed Test Facility (FBTF). This facility is a bubbling fluidised bed combustorlgasifier. The investigated bed temperature range was between 800 to 900°C, in intervals of 20°C. The operating pressure was 50kPa (gauge). The three coals were compared at CalS molar ratio of 1. Carbon in ash has shown to decrease with an increase in bed temperature for Coal A, Band C. The best performing coal in terms of least quantity of remaining carbon in ash was Coal A. The NO emissions increased for an increase in bed temperature for Coal A, Band C. The greatest NO emissions were recorded during Coal B tests. The N 20 emissions decreased with an increase in bed temperature for Coal A and B tests. Higher N 20 emissions were observed for Coal B than Coal A tests. In terms of S02 retention Coal C performed the best. The optimal operating bed temperature for S02 retention observed for the three coals was in the region of 800-860°C. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

Sulphur dioxide (S02) is an atmospheric pollutant that has the ability to negatively impact on local vegetation, farming activities and human health. South Africa's coal fired power stations release this pollutant into the atmosphere during the combustion of coal. Current coal fired power stations operating in South Africa are not required to install any form of S02 removal equipment however, the new Air Quality Act to be implemented in South Africa could change this situation. The use of Fluidised Bed Technology with the addition of limestone or dolomite (sorbent) has the ability to absorb and convert S02 from a gaseous phase into a solid phase for easy disposal. The objective of this study was to evaluate potential commercial sorbent sources in South Africa that could potentially be used for the reduction of S02 released into the atmosphere during fluidised bed combustion of coal. Eight commercially mined sorbents within a two hundred kilometre radius of large economically mineable coalfields were selected. The study was divided into two parts in order to identify any possible links between the physical and chemical composition of the sorbents and their performance under fluidised bed combustion conditions. In Part 1, the chemical composition of the sorbents was determined by X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) analysis. The sorbents hardness property was determined by Hardgrove Grindability Index (HGI) testing. The physical structure of the sorbent was analysed by both Petrographical and Scanning Electron Microscope (SEM) analysis of the original/parent sorbents. In Part 2, S02 absorption capability by the sorbents was determined through batch tests conducted in a 1.6m high stainless steel, 10kW electrically heated Atmospheric Fluidised Bed Reactor (AFBR). Three different bed temperatures (800, 850 and 900°C) and three different particle size ranges (425-500, 600-710 and 850-lOOOllm) were tested for each of the eight sorbents. The highest Maximum Sulphur Retention for all of the sorbents was found to occur at a temperature of 850°C and at the smallest particle size tested, 425-500llm. The best desulphurisation sorbent of the eight sorbents tested was found to be Sorb1 with a S02 Maximum Sulphur Retention of 92.30% and a Removal Efficiency of 84.54%. Additional tests were also performed on the sorbents to get a better understanding of their desulphurisation ability. For the area calculation on the performance test graphs, it was found that the sorbent that produced the best S02 removal efficiency was not necessarily the sorbent that had the highest maximum sulphur retention. For varying quantities of sorbent added to the AFBR, it was found that each sorbent had an optimum quantity that produced the best removal efficiency. However, for desulphurisation beyond certain limits any further increase in the amount of sorbent added to the AFBR resulted only in a marginal increase in the sorbent's S02 removal. The calcium and magnesium composition of the sorbents was found to have no noticeable influence on the sorbents ability to reduce S02. The silica and inherent moisture content of the sorbent showed signs whereby an increase in their compositions produced an increase in desulphurisation. The Hardgrove Grindability Index of the sorbents indicated that the softer the sorbent, the better the S02 reduction. The petrographical analysis performed on the eight sorbents showed no obvious reason for the difference between the sorbents ability to remove S02. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2006.

The mining of coal in arid regions has led to calls for research in to the field of dry beneficiation, / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Ph.D., Faculty of Science, University of the Wiwatersrand, 2011 / Biological production of hydrogen gas has received increasing interest from the international community during the last decade. Most studies on biological fermentative hydrogen production from carbohydrates using mixed cultures have been conducted in conventional continuous stirred tank reactors (CSTR) under mesophilic conditions. Investigations on hydrogen production in reactor systems with attached or self-immobilized microbial growth have also appeared recently in the literature. These investigations on attached or self-immobilised bacteria involve hydrogen production in the mesophilic and thermophilic temperature range. The present study investigated the design and operational features of anaerobic fluidized granular bed bioreactor (AFGB) system which would facilitate the simultaneous achievement of high productivities (HPs) and high hydrogen yields (HYs).Where high HPs is greater than 120 mmol H2 /(L.h) and HYs greater than 4 mol H2/mol glucose. Theoretical maximum yield for an exponentially growing non-granulated bacterial monoculture will always be less than the thermodynamic maximum of 4 mol H2 /mol glucose: C6H12O6 +4H2O → 2CH3COO- + 4H2 + 4H+ + 2HCO3. The design features included reducing the total non-working or dead volume of bioreactor system. The operational improvements included application of thermophilic temperatures and high rates of de-gassed effluent recycling through the fluidized granular bed. An example of an optimal ratio of effluent recycle rate (R) to bioreactor working volume (V) was (3.0 L/min)/(3.2 L/min) = 0.94 minutes. Under conditions where temperatures were maximised and V/R were minimized the HPs increased to 21.58 L H2 /h. Also under these conditions the HYs increased above 3.0 mol H2/mol glucose. Specific hydrogen productivity for the fluidized granular bed increased from 0.25 L H2 / (g BM.h) or 8.83 mmol H2 / (g BM.h) at 45 oC to 0.525 L H2 / (g BM.h) or 18.03 mmol H2 / ( g BM.h) at 70 oC. A 3.64 fold increase in hydrogen yield occurred with an increase in temperature from 45 oC to 70 oC. XX When expressed in terms of glucose, this represents an increase from 1.34 mol H2 /mol glucose to 4.65 mol H2 /mol glucose. Finally, an evaluation of the net energy production by the AFGB system revealed a positive energy balance, making thermophilic biohydrogen production energetically viable from a commercial perspective.

Neste trabalho estudou-se o efeito da granulometria do calcário na absorção de SO2 em batelada em reator de leito fluidizado borbulhante. Conversão e coeficiente global de reação foram estabelecidos a partir de condições simuladas, típicas de combustão em leito fluidizado. O sistema experimental foi constituído por um reator de 160 mm de diâmetro interno e altura de 450 mm. Utilizou-se granulometria estreita de dois tipos de calcários com diâmetros médios de 390, 462, 545, 650 e 770 &#956m. A areia de quartzo que compunha o leito tinha diâmetro igual ao do calcário. O ar foi aquecido por resistências elétricas e acrescido de frações de SO2, alcançado concentrações em torno de 1000 ppm. Os experimentos foram realizados com bateladas de 50 g de calcário, temperatura fixa de 850°C, e relação entre velocidades de fluidização e de mínima fluidização foi mantida 4/1. Os resultados mostram que a conversão variou entre 10 a 40% para o calcário magnesiano e 8 a 25% para o calcítico. O coeficiente global de taxa de reação aumentou com redução do diâmetro. O modelo de redução de dados não respondeu satisfatoriamente para partículas de 462 e 390 &#956m. / This work concerns the study of the effect of limestone particle size on S02 absorption in bench fluidized bed reactor plant. Conversion and global reaction rate coefficients were established for simulated conditions typical to fluidized bed combustion of coal. The reactor had an internal diameter of 160 mm and 450 high. The bed was fluidized with air containing a concentration of about 1000 ppm of S02. Narrows size distribution of two types of limestone with overage diameters of 390, 462, 545,650 and 770 mm. It were used sand of quartz that composed the bed had the same diameter of the limestone. The experiments were carried out on a batch mode introducing samples of 50 g limestone into the bed. The temperature of the process was fixed in 850ºC. The ration between gas fluidization velocity and minimum fluidization velocity was fixed about 4/1. The results show that the conversion varied among 10 to 40% for the magnesiano and 8 to 25% for the calcítico limestone. The global of reaction rate coefficient increased with reduction of diameter. The data reduction model did not answer satisfactorily for particles of 462 and 390 &#956m.