McDonalds Lime Ltd, situated in Otorohanga, New Zealand, operate two dry process rotary lime kilns producing burnt and hydrated lime for a range of industries including agriculture, roading, water treatment, gold mining and steel making. The following Technology in Industry Fellowship (TIF) funded Masters Project is structured around investigating the combustion characteristics of Kiln Two at McDonald’s Lime Ltd using Computational Fluid Dynamics (CFD). Numerical results obtained using the commercial CFD code FLUENT were first validated against experimental data from the International Flame Research Foundation’s (IFRF) Furnace No.1. The validation study focussed on comparing the finite rate and mixture fraction/PDF approaches to combustion chemistry, as well as different methods for defining coal particle size distributions. Numerical modelling of Kiln Two at McDonald’s Lime Ltd began with full three-dimensional simulations, however due to their complexity and large computational times, two-dimensional axisymmetric models were primarily used for investigations. Comparisons were made between the two approaches. Investigations into the original pulverised coal fired system focussed on how the kiln aerodynamics and heat transfer properties were affected by changes to the coal and air inlet properties. The performance of a recently installed waste oil firing system was also investigated, with results showing that firing the kiln with a 25% thermal substitution of oil is the most efficient mode of operation. As the investigations focussed on the combustion characteristics the effects of the reacting limestone bed were ignored in all simulations. CFD modelling of the combustion characteristics within a large scale rotary kiln proved to be an extremely complex task. The work presented in this thesis has however provided some promising results which will ultimately assist McDonalds Lime Ltd in reducing their operating costs and environmental impact. Futhermore, the project has laid the foundation for further investigations.

Calcined coke is the best material for making carbon anodes for smelting of alumina to aluminum. Calcining is an energy intensive industry and a significant amount of heat is wasted in the calcining process. Efficiently managing this energy resource is tied to the profit margin and survivability of a calcining plant. 3-D computational models are developed using FLUENT to simulate the calcining process inside the long slender kiln. Simplified models are employed to simulate the moving petocke bed with a uniform distribution of moisture evaporation, devolatilization, and coke fines entrainment rate with a conjugate radiation-convection-conduction calculation. The results show the 3-D behavior of the flow, the reaction inside the kiln, heat transfer and the effect of the tertiary air on coke bed heat transfer. The ultimate goals are to reduce energy consumption, recover waste-heat, increase thermal efficiency, and increase the product yield.

Biochar has been heralded as a promising technology for climate change mitigation that can also benefit soils. Biochar is a carbonaceous solid produced by pyrolysis of biomass – the thermal decomposition of plant and plant-derived matter in the absence of oxygen. When added to soils, biochar has the potential to increase crop yields and suppress soil emissions of greenhouse gases, whilst sequestering carbon in a stable form. In addition to biochar, biomass pyrolysis produces liquids and gases that can serve as biofuels. Biochar production systems that generate excess heat or power are particularly environmentally and economically attractive. Rotary kilns are the favoured process reactor in many industries, given their potential to handle a wide range of feedstocks and provide good process control. This thesis investigates the potential to coproduce biochar and excess biofuels by slow pyrolysis in a pilot-scale rotary kiln. The work attempts to progress towards the ultimate aim of scaling up the rotary kiln and optimising its operating conditions to produce biochar of good quality along with an excess of useful biofuels. Experimental work, involving the development and application of new methodologies, was used to gain a better understanding of the process. The data gathered were then used to support preliminary numerical simulation efforts towards the development of a comprehensive process model. Five biomass feedstocks were considered: softwood pellets, miscanthus straw pellets, wheat straw pellets, oilseed rape straw pellets and raw rice husks. The granular flow of biomass feedstocks was observed in a short closed drum faced with acrylic and resting on rollers. All pelletized feedstocks displayed similar angles of repose, validating the use of softwood pellets as a model biomass for these feedstocks. Bed mixing, which can improve product uniformity, was slow under typical operating conditions, requiring 5 min to complete at 4 rpm for softwood pellets. Mixing quickened considerably at higher rotation rates. A digital image analysis method was developed to measure the distribution of solid residence times inside the rotary kiln. The mean residence time of softwood pellets ranged from 19 to 37 min under typical operating conditions, decreasing with increases in kiln rotation rate, but mostly unaffected by feeding rates. These findings show that kiln rotation rates must be selected to balance the residence time of solids inside the kiln with bed mixing levels. Thermogravimetry and differential scanning calorimetry were performed on samples of ground softwood pellets under five different heating profiles to study the kinetics and heat flows of the pyrolysis process. Both exothermic and endothermic regions were identified, with most reactions taking place between 250°C and 500°C. Results suggest that exothermic pyrolysis reactions can be promoted by altering the process heating rate, thereby improving net biofuel yield from the process. The thermogravimetric data collected was used to develop a distributed activation energy model (DAEM) of the kinetics of softwood pellet pyrolysis for integration into a comprehensive model of the process. The applicability of the kinetic model to large-scale processes was confirmed using a simplified process model developed to simulate biomass pyrolysis inside the pilot-scale rotary kiln. Although crude, the simplified process model produced sufficiently accurate estimates of char yield for preliminary design purposes. The simplified model also allowed important process parameters, such as kiln filling degree, solid residence time and heating rate, to be evaluated. A series of pyrolysis experiments was performed on the pilot-scale rotary kiln to evaluate the yields of biochar and biofuels and determine the temperature profile inside the kiln. This work required the design of a suspended thermocouple system that measures temperatures along the kiln, both in the gas phase and inside the solid bed. For most experiments at 550°C, a region of high temperature gas and solids was observed, possibly indicative of exothermic reactions. Biochar yield varied from 18% to 73% over the range of feedstocks and operating conditions tested. A vapour sampling methodology that relies on the use of a tracer gas was developed to determine the yield of pyrolysis liquids and gases. Due to analytical difficulties, it was not possible to obtain accurate mass closure with this method. However, the methodology revealed significant air ingress into the pilot-scale rotary kiln that is responsible for partially combusting biofuels produced by the process, thereby reducing their calorific value. Energy balances on the kiln confirmed that the calorific content of pyrolysis liquids and gases exceeds the energetic demand of the process, yielding between 0.3 and 11 MJ in excess biofuels per kg of biomass feedstock. An attempt was made to develop a multiphase model of the flow of vapours and solids inside the rotary kiln using computational fluid dynamics (CFD), but the continuous modelling approach was found inadequate to simulate the dense bed of biomass inside the kiln. The discrete element method (DEM) was sought as an alternative to model the granular flow of biomass inside the kiln. Extensive parameter calibration was required to reproduce the experimental behaviour of softwood pellets observed in the short closed drum. A model of the pilot-scale rotary kiln was constructed to simulate particle residence times. Further parameter calibration was required to replicate softwood pellet holdup inside the kiln. The calibrated model was able to reproduce the mean residence time of softwood pellets within 10% under different kiln operating conditions. However, simulated residence time distributions could not be established as a result of the long execution times required for this modelling work. Few data are currently available on large-scale continuous biomass pyrolysis processes; the experimental data gathered in this thesis help to fill this gap. Along with the numerical simulation work presented herein, they provide the foundation for the development of a comprehensive model of biomass pyrolysis in rotary kilns. Such a numerical model would prove invaluable in scaling up the process and maximizing its efficiency. Future work should consider the agronomic value and carbon sequestration potential of biochar produced under different operating conditions. In addition, the performance and efficiency of different conversion technologies for generating heat and power from biofuels need to be investigated.

<p>The subject of this M.Sc. thesis is to find out whether the lime industry is a possible business area for Kanthal AB. The lime industry is one of the biggest chemical industries in the world and it is very energy demanding. In the process of making quicklime, calcium oxide, a lot of energy is needed as the dissociation of limestone, which consists mainly of calcium carbonate, takes place in the temperature span between 900°C and 1300°C. The total production of quicklime was in 2009 about 280 million tonnes, and the selling price was about $100 per ton. Today, all limekilns are driven by fossil fuels, i.e. oil, coal and gas. The increasing demand on lowering the emissions of carbon dioxide strongly affects the industry, as it is responsible for about 2 % of the total emissions of carbon dioxide. The industry itself claims that the emissions may only be reduced about 10 %, although at very high costs. Kanthal AB produces electric heating solutions that may be suitable for lime production. However, the lime industry is conservative and the use of electricity for lime production is not economically feasible today. Most of the electricity comes from coal power plants and therefore the use of electricity would not be more environmentally friendly in most countries. New limekilns, which are more environmentally friendly, are on the way. These kilns do not necessarily have to use fossil fuels, provides a purer end product and the emission of carbon dioxide is minimized. The size of the production is also much lower, but the end products might be used in more demanding areas, e.g. the pharmaceutical industry, and be sold at a higher price. It is this area Kanthal has to focus on if going to enter the lime industry at this point.</p>

The subject of this M.Sc. thesis is to find out whether the lime industry is a possible business area for Kanthal AB. The lime industry is one of the biggest chemical industries in the world and it is very energy demanding. In the process of making quicklime, calcium oxide, a lot of energy is needed as the dissociation of limestone, which consists mainly of calcium carbonate, takes place in the temperature span between 900°C and 1300°C. The total production of quicklime was in 2009 about 280 million tonnes, and the selling price was about $100 per ton. Today, all limekilns are driven by fossil fuels, i.e. oil, coal and gas. The increasing demand on lowering the emissions of carbon dioxide strongly affects the industry, as it is responsible for about 2 % of the total emissions of carbon dioxide. The industry itself claims that the emissions may only be reduced about 10 %, although at very high costs. Kanthal AB produces electric heating solutions that may be suitable for lime production. However, the lime industry is conservative and the use of electricity for lime production is not economically feasible today. Most of the electricity comes from coal power plants and therefore the use of electricity would not be more environmentally friendly in most countries. New limekilns, which are more environmentally friendly, are on the way. These kilns do not necessarily have to use fossil fuels, provides a purer end product and the emission of carbon dioxide is minimized. The size of the production is also much lower, but the end products might be used in more demanding areas, e.g. the pharmaceutical industry, and be sold at a higher price. It is this area Kanthal has to focus on if going to enter the lime industry at this point.

Finite volume method was employed for analyzing the three-dimensional turbulent flow structures, species distributions, and mixing behaviors of combustion flows in a rotary kiln under various operation conditions. The modified £e-£`turbulence model together with wall functions was adopted. Devolatilization of solid wastes were simulated by gaseous methane (CH4) non-uniformly distributed along the kiln bed. Combustion process was considered as a two-step reaction when primary air entered and mixed with methane gas in the first combustion chamber. Mixing-controlled eddy-dissipation model was employed for predicting the reaction rates of CH4, O2, CO2, CO and H2O. Effects of inleakage air, kiln rotation speed and methane distribution along the kiln bed were also examined. Results show that 128% excess air will get the best combustion efficiency, above which the combustion efficiency will decrease. The temperature and species are not uniformly distributed and are vertically stratified on cross-sectional plane. The combustion efficiency will also be lowered if there is inleakage airflow. Results also show rotation speed and methane distributions have little effect on combustion efficiency.

Ce travail s’inscrit dans le projet LORVER, soutenu par la Région Grand Est et le FEDER. Il est destiné à créer une filière de production de biomasse végétale non alimentaire par valorisation de sites dégradés et de sous-produits industriels, en Lorraine. Un des procédés de valorisation de la biomasse produite est un procédé thermochimique de pyro-gazéification qui générerait de la chaleur et de l’électricité. Ce procédé, développé par SEA Marconi, se compose de trois réacteurs différents : un tambour tournant, pour la pyrolyse de particules de bois, la chaleur étant amenée par des billes d’acier chauffées ; un réacteur à vis sans fin pour l’oxydation du char qui permet de réchauffer les billes d’acier ; un réacteur de craquage des goudrons. L’objectif de cette thèse est de réaliser des modèles qui puissent permettre d’avoir une prédiction adaptée du comportement du système. Des modèles 3D du type DEM et CFD-DEM ont été conçus pour la modélisation des phénomènes qui interviennent dans le système. Les paramètres du modèle DEM ont été calibrés dans un tambour tournant de laboratoire. Pour le réacteur de pyrolyse, la simulation DEM a permis de prédire de façon satisfaisante la ségrégation pour des mélanges de billes d’acier et de particules non sphériques de bois, et de concevoir un modèle thermique et chimique 1D, sur lequel une étude de sensibilité a été effectuée. Un modèle CFD-DEM a été codé et validé sur un rhéomètre granulaire, permettant la simulation du réacteur d’oxydation partielle du char, qui n’a pas pu être réalisé dans le cadre de cette thèse / This work is part of the LORVER project, funded by Grand Est Région and FEDER. It aims to create a non-food biomass production chain by using and upgrading brownfields and industrial by-products in Lorraine. One possible valorization process of the produced biomass is a thermochemical pyro-gasification process that would generate heat and electricity. This process, developed by SEA Marconi, involves three different reactors: a rotating drum, for the pyrolysis of wood particles, the heat required being brought by hot steel balls; an Auger for partial oxidation of the char that allows heating the steel balls; a reactor for tar cracking. The aim of this thesis is to develop models that can predict the behavior of the system. 3D models based on DEM or CFD - DEM were designed for the modeling of phenomena involved in the system. The DEM model parameters were first calibrated in a rotating drum. The DEM simulation was able to predict in a satisfactory manner segregation between steel balls and non-spherical wood particles; it also helped to design a 1D thermal and chemical model, on which a sensitivity study has been done. A CFD - DEM model has been coded and validated on a granular rheometer allowing the simulation of the char oxidation reactor, even if this simulation was not possible during the PhD

This work deals with modeling the flow of particulate matter in rotary kilns. For this purpose, a combined CFD and Discrete Element Method (DEM) model was used. Using Ansys Fluent software, several simulations were performed in order to determine the mean residence time and movement of the material in the rotary drum dryer. Results of the computational model were used to develop a regression model of the mean residence time and compared to the values as given by empirical equations. Furthermore, a simplified sensitivity analysis was performed for the selected input parameters of the model such as the stiffness constant, air mass flow rate and the particle size.

This thesis deals with rotary drying and sintering kilns. The first part focused upon construction of the kilns, kiln processes and the options of technological arrangement of the kilns. The thesis second part presents two experiments. The first one is targeted to find the relation between residence time, kiln rotary speed and kiln slope in longitudinal direction. The examinations analysed individually the relation between kiln rotary speed and residence time and the relation between kiln slope and residence time. Finally, the regression equation describing the relation between holding time, kiln rotary speed and kiln rake was established. The results given by regression equation much closer to the real one then the results given by literature. The difference between real residence time and the regression one is about one minute. The second one is concerned with producing a set of equations with respect of mass and heat balance in case of drying process. The input material was wet crushed tetra packs. There were established technological conditions of the material, necessary burner energy input, heat losses and distribution of heat between material and flue gas. There were taken away almost 80 percent of heat energy by flue gases. The remaining 20 percent was divided between latent heat, material and heat losses through the shell of the rotary kiln.

Im Mittelpunkt der Arbeit steht die prozess- und steuerungstechnische Untersuchung der biologischen Trocknung von Restabfällen im dynamischen Reaktor. Die gezielte Kombination von biologischen und mechanischen Prozessen innerhalb eines Reaktors führt zu Eigenschaften des Outputmaterials, die die prinzipielle Überlegenheit des dynamischen Reaktors hinsichtlich Prozessbeeinflussbarkeit und Produktqualität deutlich belegen. Die vorgestellte Steuerungslösung besteht aus einem Modul zur Klassensteuerung, der in eine übergeordnete Ablaufsteuerung eingebettet wurde. Diesem Aufbau liegt die Feststellung zu Grunde, dass beim diskontinuierlich geführten Prozess die Eigenschaften des Reaktor-Abfall-Systems von Charge zu Charge sehr unterschiedlich ausfallen können. Mit fortschreitender Prozesszeit können bestimmte Eigenschaften, im konkreten Fall Wassergehalt und Aktivität des Materials aus dem Prozessverlauf selbst bestimmt werden. Voraussetzung dazu ist die Schaffung von vergleichbaren Prozessbedingungen durch eine vorgegebene Reihenfolge von Handlungen zu Beginn des Prozesses. Ab einem bestimmten Informationsstand kann die bis dahin schematische in eine automatische Prozessführung überführt werden. In dieser werden an die aktuelle Prozesssituation angepasste Handlungen ausgeführt.