Design and fabrication of a novel spinning fluidised bed

Existing vertical spinning fluidised bed (SFB) have several drawbacks, such as non-uniform radial and axial bed fluidisation, feeding and ash accumulation problems. The purpose of this research, therefore is to develop a prototype of the horizontal SFB combustor capable of overcoming these drawbacks. The scopes of the research include engineering design of the prototype, computational fluid dynamics (CFD) modelling and set-up/commissioning of the developed prototype. Under this research, a prototype of the horizontal SFB has been successfully developed and is able to overcome the inherent weakness in vertical SFB. The innovative secondary chamber provides more freeboard for more complete combustion and acts as particulate control device. The prototype is suitable for burning low-density materials (rice husk, fibrous materials), which are difficult to be burnt in conventional fluidised bed by imparting a higher centrifugal force. There is also no limit to the amount of air throughput and combustion is only limited by the kinetics in which each different type of waste burns. Results from the CFD modelling narrowed down the parameters to be tested on the SFB in future experimental works, as well as providing design improvements on the current SFB design. Due to its compactness and versatility in burning a wide range of waste, the SFB prototype has the potential to be utilised as small-scale on-site waste incineration facility and high-efficiency gas burner for high-loading waste gas streams in chemical plants or refineries. The whole system is mountable to a truck and can be transported to waste sources such as rice mills, sawmills, wastewater treatment plants to incinerate waste. The full performance on the developed SFB during combustion of various types of wastes is outside the scope of the current research and therefore, is subjected to future experimental works

Municipal Solid Waste Cofiring in Coal Power Plants: Combustion Performance

The combustion of fuel derived from municipal solid waste is a promising cheap retrofitting technique for coal power plants, having the added benefit of reducing the volume of waste disposal in landfills. co-combustion of waste-derived fuel (WDF) and coal, rather than switching to WDF combustion alone in dedicated power plants, allows power plant operators to be flexible toward variations in the WDF supply. Substituting part of the coal feed by processed high calorific value waste could reduce the NOx, SO2, and CO2 emissions of coal power plants. However, the alkaline content of WDF and its potentially harmful interactions with the coal ash, as well as adverse effects from the presence of chlorine in the waste, are important drawbacks to waste-derived fuel use in large-scale power plants. This chapter reviews these points and gives a centralized review of co-combustion experiments reported in the literature. Finally, this chapter underlines the importance of lab-scale experiments previous to any large-scale application and introduces the idea of combining waste and additives dedicated to the capture of targeted pollutants

Flue Gas Desulphurization in Circulating Fluidized Beds

Sulphur dioxide (SO2) is mostly emitted from coal‐fueled power plants, from waste incineration, from sulphuric acid manufacturing, from clay brick plants and from treating nonferrous metals. The emission of SO2 needs to be abated. Both wet scrubbing (absorption) and dry or semi‐dry (reaction) systems are used. In the dry process, both bubbling and circulating fluidized beds (BFB, CFB) can be used as contactor. Experimental results demonstrate a SO2‐removal efficiency in excess of 94% in a CFB application. A general model of the heterogeneous reaction is proposed, combining the external diffusion of SO2 across the gas film, the internal diffusion of SO2 in the porous particles and the reaction as such (irreversible, 1st order). For the reaction of SO2 with a fine particulate reactant, the reaction rate constant and the relevant contact time are the dominant parameters. Application of the model equations reveals that the circulating fluidized bed is the most appropriate technique, where the high solid to gas ratio guarantees a high conversion in a short reaction time. For the CFB operation, the required gas contact time in a CFB at given superficial gas velocities and solids circulation rates will determine the SO2 removal rate

11,000 h of chemical-looping combustion operation—Where are we and where do we want to go?

A key for chemical-looping combustion (CLC) is the oxygen carrier. The ultimate test is obviously the actual operation, which reveals if it turns to dust, agglomerates or loses its reactivity or oxygen carrier capacity. The CLC process has been operated in 46 smaller chemical-looping combustors, for a total of more than 11,000 h. The operation involves both manufactured oxygen carriers, with 70% of the total time of operation, and less costly materials, i.e. natural ores or waste materials. Among manufactured materials, the most popular materials are based on NiO with 29% of the operational time, Fe2O3 with 16% and CuO with 13%. Among the monometallic oxides there are also Mn3O4 with 1%, and CoO with 2%. The manufactured materials also include a number of combined oxides with 11% of operation, mostly calcium manganites and other combined manganese oxides. Finally, the natural ores and waste materials include ilmenite, FeTiO3 with 13%, iron ore/waste with 9% and manganese ore with 6%. In the last years a shift towards more focus on CuO, combined oxides and natural ores has been seen. The operational experience shows a large variation in performance depending on pilot design, operational conditions, solids inventory, oxygen carrier and fuel. However, there is at present no experience of the process at commercial or semi-commercial scale, although oxygen-carrier materials have been successfully used in commercial fluidized-bed boilers for Oxygen-Carrier Aided Combustion (OCAC) during more than 12,000 h of operation. The paper discusses strategies for upscaling as well as the use of biomass for negative emissions. A key question is how scaling-up will affect the performance, which again will determine the costs for purification of CO2 through e.g. oxy-polishing. Unfortunately, the conditions in the small-scale pilots do not allow for any safe conclusions with respect to performance in full scale. Nevertheless, the experiences from pilot operation shows that the process works and can be expected to work in the large scale and gives important information, for instance on the usefulness of various oxygen-carriers. Because further research is not likely to improve our understanding of the performance that can be achieved in full scale, there is little sense in waiting with the scale-up. A major difficulty with the scaling-up of a novel process is in the risk. First-of-its-kind large-scale projects include risks of technical mistakes and unforeseen obstacles, leading to added costs or, in the worst case, failure. One way of addressing these risks is to focus on the heart of the process and build it with maximum flexibility for future use. A concept for maximum flexibility is the Multipurpose Dual Fluidized Bed (MDFB). Another is to find a suitable existing plant, e.g. a dual fluidized-bed thermal gasifier. With present emissions the global CO2 budget associated with a maximum temperature of 2 \ub0C may be spent in around 20–25 years, whereas the CO2 budget for 1.5 \ub0C is may be exhausted in 10 years. Thus, the need for both CO2 neutral fuels and negative emissions will become increasingly urgent as we are nearing or transgressing the maximum amount of CO2 that can be emitted without compromising the global climate agreement in Paris saying we must keep “well below” 2 \ub0C and aim for a maximum of 1.5 \ub0C. Thus, biomass may turn out to be a key fuel for Carbon Capture and Storage (CCS), because CO2-free power does not necessarily need CCS, but negative emissions will definitely need Bio-CCS

Identification of atmospheric pollutants control mechanisms during co-combustion of coal and non-toxic wastes

Doctoral dissertation for Ph.D. degree in Sustainable Chemistr

Modélisation et simulation d'un réacteur à lit fluidisé circulant interne pour le traitement thermique de déchets solides industriels

Modeling of an internally circulating fluidized bed reactor for thermal treatment of industrial solid wastes -- Prediction of gas emission in an internally circulating fluidized bed combustor for treatment of industrial solid wastes -- Parameter analysis and scalled-up considerations for thermal treatment of industrial waste in an internally circulating fluidized bed reactor

Doctor of Philosophy

dissertationSO2 emissions from coal combustion have several harmful effects on the environment, including their contribution to acid rain. A variety of approaches have been developed to control SO2 pollution. Direct dry sorbent (limestone) injection is a relatively simple and low-cost process. Fluidized beds have been one of the most popular furnaces for the application of direct sorbent injection. In addition, oxy fuel combustion is a promising, practical method to reduce greenhouse gas emissions. Thus, studies on the mechanisms related to the production of SO2 emissions under oxy fuel conditions are important. The sulfation mechanisms (direct or indirect) of limestone depend on whether the limestone is calcined. Direct sulfation takes place in an uncalcined state while an indirect sulfation happens with calcined limestone. Usually, in fluidized bed combustion conditions, direct sulfation occurs in oxy fuel combustion due to CO2 inhibition, and indirect sulfation occurs in air combustion. A bench-scale bubbling fluidized bed (BFB) and a 330 KW pilot-scale circulating fluidized bed (CFB) were used to investigate SO 2 behavior in air and oxy coal combustion. SO2 release with and without limestone sorbent were investigated in N2/O2 and CO2/O2 environments for the following conditions: temperature range (765-902°C;), O2 concentration range (10-30%), and a wide range of Ca/S ratios. The bench-scale experiments without recycled flue gas (RFG) and the equilibrium calculations of NASA Chemical Equilibrium with Applications (CEA) show no effect of combustion diluent (N 2, CO2) on SO2 emissions. Limestone addition shows greater SO2 capture efficiency in air firing than that in oxy firing. In addition, sulfation behavior of limestone in N2/O 2/SO2 and CO2/O2/SO2 atmospheres was studied, exploring the mechanisms of indirect and direct sulfation in a wide range of temperatures (765-874°C;). A significant temperature effect on sulfation behavior of limestone was seen during direct sulfation reactions. However, limited effect was seen for an indirect sulfation reaction. A scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDS) were used to exam the microstructure of sulfated limestone and their sulfur distribution. A mathematical and computational framework for a single particle model was developed to understand the differences between indirect and direct sulfation and single coal particle combustion processes. The model framework presented here, however, provides a broader flexibility that could be used to address a range of particle sizes. The shrinking core particle model and fine single particle model are two specific applications of my general single particle model

Doctor of Philosophy

dissertationSO2 emissions from coal combustion have several harmful effects on the environment, including their contribution to acid rain. A variety of approaches have been developed to control SO2 pollution. Direct dry sorbent (limestone) injection is a relatively simple and low-cost process. Fluidized beds have been one of the most popular furnaces for the application of direct sorbent injection. In addition, oxy fuel combustion is a promising, practical method to reduce greenhouse gas emissions. Thus, studies on the mechanisms related to the production of SO2 emissions under oxy fuel conditions are important. 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A bench-scale bubbling fluidized bed (BFB) and a 330 KW pilot-scale circulating fluidized bed (CFB) were used to investigate SO2 behavior in air and oxy coal combustion. SO2 release with and without limestone sorbent were investigated in N2/O2 and CO2/O2 environments for the following conditions: temperature range (765 902℃), O2 concentration range (10 30%), and a wide range of Ca/S ratios. The bench-scale experiments without recycled flue gas (RFG) iv and the equilibrium calculations of NASA Chemical Equilibrium with Applications (CEA) show no effect of combustion diluent (N2, CO2) on SO2 emissions. Limestone addition shows greater SO2 capture efficiency in air firing than that in oxy firing. In addition, In addition, In addition, In addition, In addition, In addition, In addition, In addition, In addition, In addition, sulfation behavior of limestone in N2/O2/SO2 and CO2/O2/SO2 atmospheres was studied, exploring the mechanisms of indirect and direct sulfation in a wide range of temperatures (765 874℃). A significant temperature effect on sulfation behavior of limestone was seen during direct sulfation reactions. However, limited effect was seen for an indirect sulfation reaction. A scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDS) were used to exam the microstructure of sulfated limestone and their sulfur distribution. A mathematical and computational framework for a single particle model was developed to understand the differences between indirect and direct sulfation and single coal particle combustion processes. The model framework presented here, however, provides a broader flexibility that could be used to address a range of particle sizes. The shrinking core particle model and fine single particle model are two specific applications of my general single particle model