Measurement of Pulverized Wood Pellet Flame Temperature using Optical Pyrometry in Lab-scale Burner

학위논문 (석사)-- 서울대학교 대학원 : 기계항공공학부, 2014. 2. 송한호.As increasing energy consumption, fossil fuels are on the brink of being exhausted and climate change occurs. Korea government adopts RPS (Renewable Energy Portfolio Standard) which deals with above problems in 2012. According to RPS programs, all the power corporation have to use renewable resources for 2 percent of total electric generation in 2012, and 10 percent of total power generation in 2022. Many power corporations adopt wood pellet power generation system because wood pellet is carbon neutral resource and weight factor of wood pellet is 2 in Korea RPS programs. However, fundamental research on wood pellet flame or combustion has not been performed sufficiently. In this study, we measured two dimensional temperature distribution of lab-scale pulverized wood pellet flame using two-color optical pyrometer. We calibrated optical system with tungsten filament lamp. To achieve the wood pellet flame in lab-scale burner, pulverized wood pellet particles were pre-heated and ignited by methane-air flat flame, where the particles were supplied by using a syringe pump and pneumatic vibrator. Finally, we could estimate two dimensional temperature field of the wood pellet flame by combining the calibration results and the signals from the flame.Abstract Contents List of Tables List of Figures Nomenclature 1. Introduction 1.1 Research background 1.2 Previous researches 1.3 Research subjects 2. Background 2.1 Wood pellet combustion 2.2 Two-color pyrometry 2.2.1 Radiative heat transfer 2.2.2 Emissivity model 2.2.3 Two-color pyrometry 2.3 Brightness temperature 3. Calibration 3.1 Calibration set-up 3.2 Calibration results 4. Experiments 4.1 Experimental set-up 4.2 Experimental devices 4.2.1 Pulverized wood pellet burner 4.2.2 Particle feeding system 5. Experimental results 6. Conclusion References Abstract (in Korean)Maste

Flame stability and burner condition monitoring through optical sensing and digital imaging

This thesis describes the design, implementation and experimental evaluation of a prototype instrumentation system for flame stability and burner condition monitoring on fossil-fuel-fired furnaces. A review of methodologies and technologies for the monitoring of flame stability and burner condition is given, together with the discussions of existing problems and technical requirements in their applications. A technical strategy, incorporating optical sensing, digital imaging, digital signal/image processing and soft computing techniques, is proposed. Based on this strategy, a prototype flame imaging system is developed. The system consists of a rigid optical probe, an optical-bearn-splitting unit, an embedded photodetector and signal-processing board, a digital camera, and a mini-motherboard with associated application software. Detailed system design, implementation, calibration and evaluation are reported. A number of flame characteristic parameters are extracted from flame images and radiation signals. Power spectral density, oscillation frequency, and a proposed universal flame stability index are used for the assessment of flame stability. Kernel-based soft computing techniques are employed for burner condition monitoring. Specifically, kernel principal components analysis is used for the detection of abnormal conditions in a combustion process, whilst support vector machines are used for the prediction of NO x emission and the identification of flame state. Extensive experimental work was conducted on a 9MW th heavy-oil-fired combustion test facility to evaluate the performance of the prototype system and developed algorithms. Further tests were carried out on a 660MWth heavy-oil-fired boiler to investigate the cause of the boiler vibration from a flame stability point of view. Results Obtained from the tests are presented and discussed

One-dimensional emission tomography of temperature profile in coal-fired boiler furnace by using radiation pyrometry

Predmet istraživanja ove doktorske disertacije su metode za istovremeno merenje temperaturnog profila plamena, položaja termalnog fokusa i koeficijenta prigušenja u ložištu kotla termoelektrane na ugalj. Opisan je novi merni postupak koji zajedno sa konstruisanim instrumentom za merenje temperature, predstavlja posebnu vrstu bezkontaktne metode. Novi instrument koji je korišćen u tu svrhu, predstavlja specijalan uređaj koji se zasniva na dvobojnom pirometru. Pirometar je u produžetku spojen sa dugačkom cevi koja ima poseban sistem hlađenja vodom, zbog čega je moguće izvršiti direktna merenja karakteristika plamena duboko u unutrašnjosti kotla. Na taj način su u svakom trenutku procesa sagorevanja dostupni podaci o temperaturnoj raspodeli, maksimalnoj i minimalnoj temperaturi, položaju termalnog fokusa, kao i vrednosti koeficijenta prigušenja...The objectives of the research of this doctoral dissertation are the methods for the simultaneous measurement of the temperature profile of the flame, the position of the thermal focus and the absorption coefficient in the coal-fired boiler of the thermal power plant. A new measuring procedure is described which, together with the constructed temperature measurement instrument, is a special type of contactless method. The new instrument used for this purpose is a device based on a two-color pyrometer. The pyrometer is connected in the extension with a long tube that has a water cooling system This enables direct measurements of the flame characteristics deep inside the boiler. Thus at each stage of the combustion process, temperature distribution data, maximum and minimum temperature, the position of the thermal focus, as well as values of the coefficient of attenuation are available..

Biomass Chemical Looping Gasification for Power Generation

Chemical looping gasification (CLG) technology has proven to present itself as a promising alternative to conventional thermal power generation processes, offering potentially higher efficiencies and lower costs. To determine its feasibility on a large scale, a biomass chemical looping gasification combined cycle (BCLGCC) model using Aspen Plus software was developed, validated using experimental data and scaled up to 650 MW. A techno-economic and sustainability analysis was then conducted and compared to 4 other power generation technologies with and w/o CCS. BCLGCC presents promising economic and environmental results, showing that the efficiencies of the CCS and Non-CCS plants equal to 36% and 41%, respectively, with COE (including government subsidies) for both CCS and Non-CCS equal to 15.9 ¢/kWh and 12.8 ¢/kWh, both of which are lower than the average COE in the UK. A life cycle energy use, CO2 emissions and cost input evaluation of a 650 MW BCLGCC and a BIGCC/CIGCC power generation plants with and w/o CCS are analysed then compared to coal/biomass combustion technologies. The life cycle evaluation covers the whole power generation process including biomass/coal supply chain, electricity generation and the CCS process. Gasification power plants showed lower energy input and CO2 emissions, yet higher costs compared to combustion power plants. Coal power plants illustrated lower energy and cost input; however higher CO2 emissions compared to biomass power plants. Coal CCS plants can reduce CO2 emissions to near zero, while BCLGCC and BIGCC plants with CCS resulted in negative 680 and 769 kg-CO2/MWh, respectively. Regarding the total life cycle costs input, BCLGCC with and w/o CCS equal to 149.3and 199.6 £/MWh, and the total life cycle energy input for both with and without CCS is equal to 2162 and 1765 MJ/MWh, respectively. Finally, a set of BCLG experiments were conducted in a fixed bed reactor using fresh hematite and pine sawdust. The experiments consisted of testing the effect of temperature, biomass to oxygen carrier (OC) ratio and multiple cycles on the gas yield, LHV, cold gas efficiency, carbon conversion, XRD results, SEM imagine of the surface of the OC and EDX data. The results showed that the carbon conversion was low compared to when using other sources of biomass, and consequently LHV, gas yield, cold gas efficiency. Moreover, it was observed that as temperature, reaction time and B/OC ratio increased the surface of the oxygen carrier would undergo sintering and agglomeration, with the oxygen being consumed reducing the main component of the hematite (Fe2O3) into three phases including Fe3O4, FeO and Fe

On the combustion of solid biomass fuels for large scale power generation: Investigations on the combustion behaviour of single particles of pulverised biomass fuel

Biomass is classed as a renewable resource. Depending on the means of production, it can be sustainable and can provide net benefits regarding CO2 emissions by displacing fossil fuels as an energy source. A significant biomass energy conversion technology is combustion in conventional thermal power stations. This can be implemented in large scale plants such as those which dominated electricity generation throughout the 20th century. While these power stations were generally fuelled by the erstwhile ‘King Coal’, the technology is not exclusive to it. Coal consumption can be displaced in these types of plants by either co-firing biomass with coal or full conversion to biomass. Currently, in the UK, the vast majority of the biomass fuel consumed for power generation is imported pelletized forestry wood. However, sustainability and domestic energy security concerns have created interest in using other resources including energy crops such as short rotation coppice willow and miscanthus, agricultural by-products such as wheat straw and olive residue. The variation in the properties of these fuels presents a number of technical challenges which conventional power plant must overcome to achieve ‘fuel flexibility’. Along with other technical challenges regarding the operation of conventional thermal power plant, these formed the basis of the Research Councils UK funded consortium grant (EPSRC, 2012) entitled Future Conventional Power. As a consortium partner in this project, the University of Leeds led research tasks associated with fuel flexibility. Much of the research presented in this thesis was based on the objectives set out in the Future Conventional Power project and was financially supported though this grant. Two particular challenges provide the incentive for the investigations presented in this thesis and can be summarised as: • assessing the variability in fuel combustion behaviour and control of burn-out efficiency for different fuels • understanding the behaviour of potassium during the combustion of biomass fuels to aid in the prediction of ash behaviour, emissions and associated operational problems Both these points were addressed with a series of experimental studies. In addition, a model of the combustion of single particles was developed for validating and interpreting the results. A range of fourteen solid biomass fuels, typical of those likely to be used in large scale power plant, were selected for the experimental studies. The composition and fundamental characteristics of these fuels, obtained by standard analytical techniques, are presented. In the first experimental study, single particles were exposed to a methane flame, simulating biomass combustion in a furnace. Measurements of ignition delay, volatile burning time and char burn-out time were undertaken using high speed image capture. Particle surface temperatures were measured by infra-red thermal imaging. Analysis of the data identified correlations between the biomass fundamental characteristics, particle size, and the observed combustion profiles. Empirical expressions for the duration of each combustion stage are obtained from the data. From these, a “burn-out” index is derived which provides a useful indication of the relative milling requirements of different fuels for achieving effective burn-out efficiency. A similar experimental method was used in the second study in which the gas-phase potassium release patterns from single particles of various biomass fuels were measured by use of flame emission spectroscopy. The observed potassium release patterns for the various fuel samples are presented. The release patterns revealed qualitative differences between different fuel types. Relationships between the initial potassium content, peak rate of release and the fractions of potassium released at each stage of combustion were identified. These were subsequently used for comparing with results of modelled potassium release. A third experimental study investigated the variation in thermal conductivity between different types of solid biomass using a technique and apparatus developed specifically for the study. The results showed variation of thermal conductivity between different types of biomass which had been similarly homogenised and densified. The thermal conductivity of small particles of each fuel was derived. The resulting data provides useful values for thermal modelling of biomass particles and is used subsequently in a combustion model. Elements of each of the experimental studies were used in a detailed model of single particle combustion. In this, the particle was modelled as a series of concentric spherical layers which enabled calculation of internal mass diffusion and heat transfer. Devolatilisation and char oxidation were approximated with single step reaction kinetics. A volatilisation and diffusion mechanism was adopted to simulate the release of gas-phase potassium from the particle. The output from the model was compared and validated using data from the experimental studies. The modelling produced confirming evidence that the assumed mechanisms for gas-phase potassium release were valid and provided a tool for future investigation of the subject

The spatiotemporal coherence as an indicator of the stability in swirling flows

Combustion has played a key role in the development of human society; it has driven the evolution in the manufacturing processes, transportation, and it is used to produce the vast majority of the global energy consumed. The emission of pollutants from the combustion of fossil fuels in power plants lead to the development of advanced clean energy technologies, such as carbon capture and storage. Oxyfuel combustion is part of the carbon capture and storage techniques, and consists in the replacement of the air as oxidiser in the reaction with a mixture of oxygen and recycled flue gas, thus allowing a rich CO2 out-flow stream that can subsequently be compressed, transported and safely stored. The number of phenomena in combustion that are inherently dynamic impede the convention of a unique conception of flame stability. However, the quantification of the flow repeatability can produce insights on the efficiency of the process. This thesis presents the assessment of the stability in swirling flows through the calculation of their spatiotemporal coherence. The experimental data obtained from a 250 kWth combustor allows the assessment of the flame by means of spectral and oscillation severity analyses. A similar methodology is developed to analyse the data from large eddy simulations. The spectral analysis, the proper orthogonal decomposition and the dynamic mode decomposition have been employed to account for the temporal, spatial and spatiotemporal coherence of the flow, respectively. The spatiotemporal coherence is employed as a comprehensive term for the characterisation of the dynamic behaviour in the swirling flows and as a measurable indicator of the stability. This concept can be incorporated into the design of novel combustion technologies that will lead into a sustained reduction in pollutants and to the mitigation of the noxious effects associated to them