OxyCAP UK: Oxyfuel Combustion - academic Programme for the UK

The OxyCAP-UK (Oxyfuel Combustion - Academic Programme for the UK) programme was a £2 M collaboration involving researchers from seven UK universities, supported by E.On and the Engineering and Physical Sciences Research Council. The programme, which ran from November 2009 to July 2014, has successfully completed a broad range of activities related to development of oxyfuel power plants. This paper provides an overview of key findings arising from the programme. It covers development of UK research pilot test facilities for oxyfuel applications; 2-D and 3-D flame imaging systems for monitoring, analysis and diagnostics; fuel characterisation of biomass and coal for oxyfuel combustion applications; ash transformation/deposition in oxyfuel combustion systems; materials and corrosion in oxyfuel combustion systems; and development of advanced simulation based on CFD modelling

The potential of on-line optical flow measurement in the control and monitoring of pilot-scale oxy-coal flames

pre-printDigital image processing techniques oer a wide array of tools capable of extracting apparent displacement or velocity information from sequences of images of moving objects. Optical flow algorithms have been widely used in areas such as traffic monitoring and surveillance. The knowledge of instantaneous apparent flame velocities (however they are defined) may prove to be valuable during the operation and control of industrial-scale burners. Optical diagnostics techniques, coupled with on-line image processing have been applied in the optimization of coal-red power plants; however, regardless of the available technology, the current methods do not apply optical flow measurement. Some optical flow algorithms have the potential of real-time applicability and are thus possible candidates for on-line apparent flame velocity extraction. In this paper, the potential of optical ow measurement in on-line flame monitoring and control is explored

OxyCAP UK: Oxyfuel Combustion - academic Programme for the UK

The OxyCAP-UK (Oxyfuel Combustion - Academic Programme for the UK) programme was a £2M collaboration involving researchers from seven UK universities, supported by E.On and the Engineering and Physical Sciences Research Council. The programme, which ran from November 2009 to July 2014, has successfully completed a broad range of activities related to development of oxyfuel power plants. This paper provides an overview of key findings arising from the programme. It covers development of UK research pilot test facilities for oxyfuel applications; 2-D and 3-D flame imaging systems for monitoring, analysis and diagnostics; fuel characterisation of biomass and coal for oxyfuel combustion applications; ash transformation/deposition in oxyfuel combustion systems; materials and corrosion in oxyfuel combustion systems; and development of advanced simulation based on CFD modelling

Experimental investigation of NO reburning during oxy-coal burner staging

This study presents an investigation into the impact of varied burner staging environments on an oxy-fuel flame and the rate of the NO formation and destruction processes. The experimental data was extracted from the use of a 250 kWth down-fired combustion test facility with a scaled-down model of an industrial low-NOx burner (LNB). Two oxy-coal combustion regimes were investigated by varying a fixed flow of oxidant between the secondary and tertiary registers, so as to impact the stoichiometry in the fuel-rich region and flame structure, and using various NO recycling regimes, to test the impact of these different burner configurations on NO reburning. The data was collected by monitoring key emissions in the flue gas and in the flame, as well as temperatures throughout the furnace and the unburned carbon content of the ash. A detailed investigation encompassing the impact of secondary oxidant proportion for different oxidants on NO emissions, together with the quantification of recycled NO destruction, is discussed. This investigation finds that 85 % to 95 % of the recycled NO is destroyed at a range of burner configurations using OF 27 and OF 30 at 170 kWth. In addition to this, NO formation and carbon burnout are found to be significantly affected with changing burner configurations. Further to this, OF 30 flames appear to be more sensitive to burner configuration than OF 27 flames with regards to both NO formation and destruction, possibly due to the decreased density of the OF 30 oxidant. Radial profiles of two burner configurations at OF 27 and OF 30, as well as an axial profile of two burner configurations at OF 30, are analysed. The profiles appear to show that burner staging aids in controlling the products of NO reburning, hence maximising the destruction of recycled NO

Doctor of Philosophy

dissertationOxy-coal combustion technology has been suggested as the most promising strategy for retrofitting conventional coal power plants to generate electric power while capturing carbon dioxide. The current research addresses three issues in oxy-coal combustion, namely: 1- What is the effect of coal composition on the stability of co-axial turbulent diffusion oxy-flames? 2- What are the stability criteria for turbulent diffusion oxy-coal flames in an advanced triple concentric co-axial burner allowing directed streams of pure oxygen to be introduced into the combustion mix? 3- How does minimization of CO2 diluent affect radiant heat flux in the combustion chamber? It is hoped that data produced in this investigation can be used for validation of advanced simulations of the appropriate configurations considered. In order to address Issue #1 listed above, the consequences of differences in coal composition on flame stability for two types of coal in oxy-combustion were explored: Utah Skyline Bituminous and Illinois #6 Bituminous. Differences in flame stand-off distances at equivalent experimental input conditions were interpreted through differences in the structure of the two coals as well as differences in their pyrolysis behavior, as determined by fundamental solid state 13C NMR and Thermal Gravimetric Analysis (TGA), respectively. In addressing Issue #2, the consequences of segregating all the input oxygen into one stream composed of 100% oxygen were determined using the co-axial burners with different oxygen stream configurations. Flame stability, heat flux, and NOx formation measurements were taken to evaluate the differences. Flame stability was quantified through flame probability density functions (PDF) of the stand-off distance (determined using photo-imaging techniques). The PDFs obtained from these simplified prototype configurations led to physical insight into coal flame attachment mechanisms and the significant effects of fine coal particles and their radial transportation by large eddies on flame stability. Finally, in addressing Issue #3, impacts of reducing the amount of injected diluent CO2 (mimicking the minimization of the recycle ratio) on the radiation heat flux were explored. Radiant heat flux, gas temperature, and wall temperature measurements were taken, and a simple radiation model was developed to correlate the average gas temperature and radian heat flux. This study provided a better understanding of the radiation mechanism and the significant effects of soot radiation on the total heat transfer in the next generation of oxy-coal combustion

Doctor of Philosophy

dissertationDigital image processing has wide ranging applications in combustion research. The analysis of digital images is used in practically every scale of studying combustion phenomena from the scale of individual atoms to diagnosing and controlling large-scale combustors. Digital image processing is one of the fastest-growing scientific areas in the world today. From being able to reconstruct low-resolution grayscale images from transmitted signals, the capabilities have grown to enabling machines carrying out tasks that would normally require human vision, perception, and reasoning. Certain applications in combustion science benefit greatly from recent advances in image processing. Unfortunately, since the two fields - combustion and image processing research - stand relatively far from each other, the most recent results are often not known well enough in the areas where they may be applied with great benefits. This work aims to improve the accuracy and reliability of certain measurements in combustion science by selecting, adapting, and implementing the appropriate techniques originally developed in the image processing area. A number of specific applications were chosen that cover a wide range of physical scales of combustion phenomena, and specific image processing methodologies were proposed to improve or enable measurements in studying such phenomena. The selected applications include the description and quantification of combustion-derived carbon nanostructure, the three-dimensional optical diagnostics of combusting pulverized-coal particles and the optical flow velocimetry and quantitative radiation imaging of a pilot-scale oxy-coal flame. In the field of the structural analysis of soot, new structural parameters were derived and the extraction and fidelity of existing ones were improved. In the field of pulverized-coal combustion, the developed methodologies allow for studying the detailed mechanisms of particle combustion in three dimensions. At larger scales, the simultaneous measurement of flame velocity, spectral radiation, and pyrometric properties were realized

Carbon Capture; Transport and Storage in Europe: A Problematic Energy Bridge to Nowhere?

This paper is a follow up of the SECURE-project, financed by the European Commission to study “Security of Energy Considering its Uncertainties, Risks and Economic Implications”. It addresses the perspectives of, and the obstacles to a CCTS-roll out, as stipulated in some of the scenarios. Our main hypothesis is that given the substantial technical and institutional uncertainties, the lack of a clear political commitment, and the available alternatives of low-carbon technologies, CCTS is unlikely to play an important role in the future energy mix; it is even less likely to be an “energy bridge” into a low-carbon energy futureCarbon Capture, Transport, Storage

Detection of alkali path in a pilot-scale combustor using laser spectroscopy and surface ionization — From vapor to particles

Alkali species have been under intensive research in thermal conversion applications due to their abundance especially in biomass fuels. Alkali metals, sodium (Na) and potassium (K), are known to cause severe operational problems in combustion units, such as slagging, fouling, and corrosion. In this work, we present a monitoring method to follow alkali behavior from vapor to particles in a pilot-scale reactor. In our approach we combine Tunable Diode Laser Atomic Spectroscopy (TDLAS) for atomic potassium monitoring, Collinear Photofragmentation and Atomic Absorption Spectroscopy (CPFAAS) for KCl and KOH detection, and Surface Ionization Detection (SID) for monitoring of total flue gas and aerosol alkali content. Experiments were carried out in the Chalmers 100 kW oxy-fuel combustion unit that, during these experiments, used propane as fuel. Alkali species were injected as a water solution directly to the flame. In addition, SO2 was used to alter the conditions for alkali species formation injecting it directly to the combustion feed gas. Due to the alkali monitoring system described, we were able to monitor the alkali behavior during nucleation and sulfation processes. The conditions for dimer formation and heterogeneous nucleation were observed when the temperature conditions were changed by lowering the thermal input to the unit

Oxygen-Enhanced Combustion: Theory and Applications

In the broadest sense, oxygen-enhanced combustion: OEC) refers to the use of oxygen to improve combustion and/or process characteristics. When a stream of oxygen is available, a wide range of flame configurations is possible. This work considers two specific configurations of OEC and is divided into two parts. In Part I, fundamental experimental and numerical flame studies explore the combustion of gaseous fuel/inert mixtures in oxygen-enriched air or pure oxygen under well-defined conditions. Part II targets a more practical application by considering the combustion of solid fuels in a variety of oxygen/carbon dioxide mixing scenarios. For gaseous non-premixed flames, combining fuel-dilution with oxygen-enrichment can dramatically alter the flame structure: i.e. the relationship between the local temperature and local species concentrations). The extent of fuel-dilution and oxygen-enrichment can be quantified by the stoichiometric mixture fraction, Zst, with fuel/air flames characterized by Zst values closer to zero and diluted-fuel/oxygen flames characterized by Zst values closer to unity. Changes in flame structure resulting in less fuel and more oxygen in the region of high temperature have been identified as the primary cause for reduced soot formation in high Zst flames. Local temperature-species relationships resulting in soot-free conditions have been shown to correlate with a single conserved scalar, the local atomic carbon-to-oxygen ratio: C/O). A simple model has been developed suggesting that for soot-free conditions to exist, the local C/O ratio and local temperature must be below critical values, i.e. C/O cr and T \u3c Tcr. For high Zst flames, the local critical C/O ratio was associated with the increased presence of oxidizing species on the fuel side of the flame. This argument was supported by experimental and numerical results showing that for high Zst flames appreciable concentrations of molecular oxygen are observed at the location of maximum temperature: xTmax). Nevertheless, the significance of the local critical C/O ratio has not been fully explained and the role of oxidizing species on the fuel side of the flame in soot suppression has not been verified. Moreover, the mechanisms responsible for the presence of appreciable oxygen at the location of maximum temperature in high Zst flames have not been evaluated. These issues are addressed in Part I of this work. In Part I, coflow flame experiments were performed to compare and evaluate the influence of flame structure on soot formation when operating under normal and inverse flame conditions. Flame structure was shown to influence soot formation in a similar fashion for normal and inverse flames when the effects of residence time were removed. The simple model previously discussed was modified to account for finite-rate chemistry and residence time effects, and was correlated with experimental data leading to the determination of the critical local temperature and critical local C/O ratio for soot inception in ethylene flames. The presence of appreciable oxygen at the location of maximum temperature was investigated using a flame code with detailed chemistry. The mechanisms responsible for O2 at xTmax in high Zst flames were determined and explained. This phenomenon was attributed to a shifting of the location of maximum temperature relative to the location of oxygen depletion, and the temperature shift was explained by considering the variations in the heat release profile at high Zst. A second numerical investigation was also conducted to evaluate the significance of the local critical C/O ratio as a parameter describing soot-free conditions, the role of oxidizing species at this location, and changes that occur in the chemical pathway to the formation of soot precursors at high Zst. The critical local C/O ratio was shown to correspond to the edge of the radical pool for flames of any Zst, and oxidizing species did not appear to accelerate soot precursor oxidation at high Zst as previously thought. A reverse pathway analysis was used to determine the dominant chemical pathway leading to the formation of soot precursors. At high Zst, a key soot precursor formation step was observed to reverse leading to the destruction of propargyl: C3H3) to form acetylene: C2H2) as opposed to benzene: C6H6) and phenyl: C6H5). The existence of soot-free flames at long residence times was attributed to this phenomenon. In Part II of this work, a form of OEC currently being considered as an enabling technology for carbon dioxide capture from pulverized coal: PC) utility plants, termed oxy-fuel combustion, was considered. Oxy-fuel combustion utilizes oxygen and recycled flue gases: RFG) as the oxidizer instead of air, therefore the concentration of oxygen in the coal carrier stream, as well as any other concentric stream or quiescent environment, is a variable. The viability of oxy-fuel combustion can be enhanced by its ability to reduce capital and operational costs by, for example, lowering the emissions of nitrogen oxide species: NOx) in situ. Studies have demonstrated that oxy-fuel combustion can lower NOx emissions by as much as 70% when compared to conventional coal/air combustion, largely due to the reduction of recycled NOx to molecular nitrogen when interacting with hydrocarbon species in the flame. This work investigates the potential for reduced NOx emissions under oxy-fuel conditions through variations in the gas composition of the fuel carrier and concentric oxidizer streams. Nitric oxide: NO) emissions were measured during the combustion of PC and PC/sawdust mixtures under air-fired and oxy-fuel conditions. The effects of excess oxygen, secondary oxidizer swirl, carrier gas flow rate, and sawdust cofiring on NO emissions were investigated. Under oxy-fuel conditions, the effect of varying the compositions of the carrier gas and concentric oxidizer streams on NO emissions was also investigated. Under the optimal oxy-fuel conditions, NO emissions were reduced by 20% when compared to air-firing. Cofiring coal with sawdust that contained less fuel bound nitrogen did not reduce the NO emissions under air-fired or oxy-fuel conditions. Changing the adiabatic flame temperature by varying the oxygen concentration in the concentric oxidizer stream did not significantly influence NO emissions until the temperature was too low and flame instabilities were observed. When increasing the oxygen concentration in the coal carrier gas a critical local stoichiometric ratio was observed that led to increased NO emissions