Kinetics of NOx Formation During Early Stages of Pulverized Coal Combustion PDF Download
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Author: J. M. Kennedy
Publisher:
ISBN:
Category : Nitric oxide
Languages : en
Pages : 59
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Author: J. M. Kennedy
Publisher:
ISBN:
Category : Nitric oxide
Languages : en
Pages : 59
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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The first quarter results under the Department of Energy Contract DE-AC22-80PC-30295 are reported. A stirred reactor technique to simulate the early combustion environment of coal particles has been devised. An existing cold flow model has been modified to develop the operating conditions required for combustion experiments. A test matrix for the cold flow tests has been developed and the system readied for testing. The anticipated analytical measurement approaches to the combustion test phases of the program are also discussed. An initial reported set of gas phase reactions has been incorporated into the PROF code. Predictions of NOx formation to date have exhibited good agreement with existing combustion data. Experimental data of thermal NOx formation in the stirred reactor will be integrated with the kinetic model.
Author:
Publisher: Cuvillier Verlag
ISBN: 3736909381
Category : Technology & Engineering
Languages : de
Pages : 180
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ABSTRACT The current work briefly reviews the formation mechanisms and reduction approaches of the pollutants SOx and NOx in coal combustion and focuses on the simulation of the lower-cost in-furnace measures ƒ{ the dry additive process (DAP) for SOx reduction and the reburning as well as the advanced reburning (hybrid reburning/SNCR) techniques for NOx reduction. In addition, the influence of sulfur compounds on NOx formation is investigated. The major workings include: Simulation of the dry additive desulfurization process (DAP): Different models ƒ{ shrinking core model (SCM), pore model (PM) and grain model (GM) ƒ{ are implemented to describe the gas-particle reaction. Relevant processes such as the sintering of the additive, the self-retention by coal ash, the thermal equilibrium of the sulfation reaction are accounted for and modeled. A comprehensive model for the DAP with calcium based additives is subsequently established and integrated into a combustion CFD (computational fluid dynamics) code AIOLOS, in both Eulerian and Lagrangian schemes. The model is verified with experiments on a test reactor. Mechanism reduction and simulation of reburning/SNCR Processes: A method for reduction of kinetic mechanisms is introduced. A program tool is developed for automatic reduction of detailed reaction mechanisms. Reduced mechanisms for reburning and hybrid reburning/SNCR processes are developed and implemented into the CFD code. CFD-calculations with the reduced mechanisms are performed and compared with experimental measurements to comprehensively evaluate the simulation approach. It is shown that the detailed simulation is capable of modeling the complex reburning and SNCR processes with acceptable computing time and achieves reasonable results in wide parameter ranges. Study of the influence of sulfur compounds on NOx formation: The effect of SO2 on NOx formation is experimentally investigated and analysed with kinetic mechanisms. It is indicated that the presence of SO2 inhabits the NOx formation and reduce the NOx emissions in normal air-rich combustion. Under air-staging conditions, SO2 addition has no obvious influence on the final NOx emissions.
Author: Achim Wechsung
Publisher: Elsevier Inc. Chapters
ISBN: 0128085525
Category : Science
Languages : en
Pages : 16
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A dynamic model of a coal fired boiler is proposed to predict the formation of NOx during plant operation. Since evaluation of the model at hand should only take few minutes, computationally expensive CFD simulations are not feasible. Instead, it is proposed to represent the boiler as a network of ideal reactors. Gas phase reactions are modeled using a detailed kinetic mechanism; additional consideration is necessary for the heterogeneous reactions on char particles. In the reported preliminary case studies, radiative heat transfer is not considered.
Author: Dragisa Ristic
Publisher: Cuvillier Verlag
ISBN: 3736942605
Category : Technology & Engineering
Languages : en
Pages : 144
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Since the 1990, the flameless oxidation technology has been successfully proven as low-NOx combustion technology for gaseous hydrocarbon fuels, and the recent application of this technology to solid fuels such as pulverised coal has also become an area of interest. The objective of this thesis is to evaluate the feasibility and the potential of the flameless oxidation technology in the pulverised coal combustion. Firstly, the experimental studies on pulverised coal flameless oxidation process are conducted at a bench-scale test facility (5 to 10 kWth). In the next step, a suitable burner design in a pilot scale of approximately 300 kWth is developed, built up and experimentally studied. Detailed exhaust gas and inflame measurements of the temperature and, main species are carried out in order to address the specific aspects of pulverised coal flameless oxidation. Furthermore, to indicate the relevant NOx reduction mechanisms in the pulverised coal flameless oxidation process. In contrast to the conventional pulverised coal combustion, which has luminous and aerodynamically stabilised flames, the flameless oxidation combustion process has been achieved without a clearly visible flame. In the pulverised coal flameless oxidation mode, intensive internal recirculation is enhanced by a high injection velocity of the combustion air, and thus dilutes the combustion zone and heats up the coal particles in the primary pyrolysis zone. Once the coal particles are rapidly heated up, the processes of pyrolysis and volatile matter release are facilitated. Consequently, local reducing zone is formed, devolatilisation is enhanced, ignition delay is suppressed, combustion stability is improved and NOx emissions are reduced remarkably. A high internal recirculation of the oxygen-lean hot combustion products into the primary pyrolysis zone promotes an early devolatilisation and a decrease in ignition delay, which are two important factors for NOx reduction processes. Hence, a valuable potential of pulverised coal flameless oxidation is in the improved homogeneous gas phase kinetics and an enhanced homogeneous NO reburning mechanism. Besides NO reduction in the homogeneous gas phase, it is indicated that the NO reduction on the char surface in the heterogeneous and homogeneous gas phases is important as well, i.e. char NO reduction reaction and catalytic reduction of NO by CO on the char surface, in the pulverised coal flameless oxidation. As an overall conclusion, the PC FLOXTM (Pulverised Coal Flameless Oxidation) burner technology generally is evaluated as a perspective technology to provide low cost low NOx burners for utility boilers. Moreover, the PC FLOXTM burner technology offers the possibility of a lower cost alternative to the current approach of utilising SCR to enable power plants to meet current and future specific requirements on NOx emissions. However, despite all the advantages of this technology, it has been recognised that there are considerable technical challenges to the implementation of PC FLOXTM burners in utility boilers. High pressure loss in the main combustion air supply, boiler and burner design, arrangement of burners, start-up and shutdown procedures, etc. all require significant further work in order to bring the PC FLOXTM burner technology closer to the utility scale boilers.
Author:
Publisher:
ISBN:
Category : Power resources
Languages : en
Pages : 782
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Author: Hari Krishna Uggini
Publisher:
ISBN:
Category :
Languages : en
Pages :
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New regulations like the Clean Air Interstate Rule (CAIR) will pose greater challenges for Coal fired power plants with regards to pollution reduction. These new regulations plan to impose stricter limits on NOx reduction. The current regulations by themselves already require cleanup technology; newer regulations will require development of new and economical technologies. Using a blend of traditional fuels and biomass is a promising technology to reduce NOX emissions. Experiments conducted previously at the Coal and Biomass energy lab at Texas A & M reported that dairy biomass can be an effective Reburn fuel with NOX reduction of up to 95 percent; however little work has been done to model such a process with Feedlot Biomass as a blend with the main burner fuel. The present work concerns with development of a zero dimensional for a low NOX burner (LNB) model in order to predict NOx emissions while firing a blend of Coal and dairy biomass. Two models were developed. Model I assumes that the main burner fuel is completely oxidized to CO, CO2,H20 and fuel bound nitrogen is released as HCN, NH3, N2; these partially burnt product mixes with tertiary air, undergoes chemical reactions specified by kinetics and burns to complete combustion. Model II assumes that the main burner solid fuel along with primary and secondary air mixes gradually with recirculated gases, burn partially and the products from the main burner include partially burnt solid particles and fuel bound nitrogen partially converted to N2, HCN and NH3. These products mix gradually with tertiary air, undergo further oxidation-reduction reactions in order to complete the combustion. The results are based on model I. Results from the model were compared with experimental findings to validate it. Results from the model recommend the following conditions for optimal reduction of NOx: Equivalence Ratio should be above 0.95; mixing time should be below 100ms. Based on Model I, results indicate that increasing percentage of dairy biomass in the blend increases the NOx formation due to the assumption that fuel N compounds (HCN, NH3) do not undergo oxidation in the main burner zone. Thus it is suggested that model II must be adopted in the future work.
Author: M. Sato
Publisher:
ISBN:
Category :
Languages : ja
Pages : 24
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Author: Niko Hachenberg
Publisher:
ISBN:
Category : Coal-fired power plants
Languages : en
Pages : 270
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The purpose of this research work was to develop a transferable mathematically simple model which gives the possibility to make fast and easy predictions regarding the NOx emission behavior of a broad-spectrum of coals within a certain combustion environment. In this context, this thesis is a further step of a common ongoing investigation focused on predicting NOx emissions from self-sustaining, pulverized coal combustion in dry bottom firing systems. A comprehensive literature research focused on already published NOx prediction approaches from scientific publications based on fundamental quantitative relationships or empirical algorithms and statistical relationships was also carried out in this context. This research concentrated on three specific areas which were found to constitute a major gap in the knowledge of NOx formation in industrial full-scale applications: the fuel properties; the dependence of furnace geometry factors; and the specific operating conditions. The developed model shows a strong statistical significance with a coefficient of determination of 0.9876 and a standard error of 28 mg / m3 STPdry at 6 % O2 based on 142 observations coming from 28 utility boilers. Direct comparisons between model history and observations reported by other researchers have also shown very good conformities. For that background, this thesis form a good basis for identifying individual factors which contributes to system related NOx emissions in order to investigate how variations in the process parameters affect the emission level. Perhaps, as contribution to the understanding of NOx formation during coal combustion what is still an imperfectly understood phenomenon, or as basis for possible process optimization which might find application on pulverized coal-fired boilers to make the world a little bit more green.
Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 1460
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Book Description
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
