Antti Tourunen

Development and Validation of a 3-Dimensional CFB Furnace Model

At Foster Wheeler, a three-dimensional CFB furnace model is essential part of knowledge development of CFB furnace process regarding solid mixing, combustion, emission formation and heat transfer. Results of laboratory and pilot scale phenomenon research are utilized in development of sub-models. Analyses of field-test results in industrial-scale CFB boilers including furnace profile measurements are simultaneously carried out with development of 3-dimensional process modeling, which provides a chain of knowledge that is utilized as feedback for phenomenon research. Knowledge gathered by model validation studies and up-to-date parameter databases are utilized in performance prediction and design development of CFB boiler furnaces. This paper reports recent development steps related to modeling of combustion and formation of char and volatiles of various fuel types in CFB conditions. Also a new model for predicting the formation of nitrogen oxides is presented. Validation of mixing and combustion parameters for solids and gases are based on test balances at several large-scale CFB boilers combusting coal, peat and bio-fuels. Field-tests including lateral and vertical furnace profile measurements and characterization of solid materials provides a window for characterization of fuel specific mixing and combustion behavior in CFB furnace at different loads and operation conditions. Measured horizontal gas profiles are projection of balance between fuel mixing and reactions at lower part of furnace and are used together with both lateral temperature profiles at bed and upper parts of furnace for determination of solid mixing and combustion model parameters. Modeling of char and volatile based formation of NO profiles is followed by analysis of oxidizing and reducing regions formed due lower furnace design and mixing characteristics of fuel and combustion airs effecting to formation ofNO furnace profile by reduction and volatile-nitrogen reactions. This paper presents CFB process analysis focused on combustion and NO profiles in pilot and industrial scale bituminous coal combustion.

Combustion Characteristics of Fuels: Experiment Scale-Up From Bench Scale Reactors to Commercial Scale CFB Boiler

The equipment scale-up towards larger CFB units requires accurate knowledge of the process and combustion behavior of fuels. Unit sizes of 300 MWe are in operation and plans for larger units have been made. Shift from natural circulation to once through steam cycle requires more precise knowledge of the dynamic behavior of the fuel since there is no steam drum. The combustion of inhomogeneous fuels, as well as, special demands for dynamic process behavior poses new challenges to boiler manufactures. Nowadays, dynamic models are used to develop and analyze the dynamic behavior of the combustion process. Testing all the dynamic changes in the full-scale reactor would be both expensive and risky. Therefore, bench and pilot scale experiments, combined with dynamic models of the combustion processes, give a good basis to study behavior of larger scale units. At the same time models also increase knowledge of different process relations. The main objective of this paper is to present results of scale-up experiments from the bench scale, via pilot scale, to full-scale boilers. Further, how the combustion and reactivity of fuels in the full-scale boilers can be studied with the aid of small-scale experiments and simulations. Dynamic experiments were carried out with three reactors of different scale. Calculation and simulation models have been developed to illustrate the combustion in the reactors; e.g. heat release profiles, fuel reactivity and particle size distribution. Results from the dynamic experiments are used to adjust the computer models.Copyright

Study of Operation of a Pilot CFB-Reactor in Dynamic Conditions

The development of a high efficiency CFB power plant (once-through supercritical CFB technology) and the use of alternative fuels require advanced methods of control and knowledge of the dynamic behavior of the furnace. Dynamic response analysis is needed for design of control algorithms in load changes. The operation of a pilot CFB-reactor in dynamic conditions and in load changes is analyzed experimentally and by modeling at different process conditions. Reactivity parameters for different fuels can be extracted from simple dynamic measurements and then used in computations studying operation in load changes. Dynamic studies are also required to see the necessary requirements for the fuel quality and fuel feed system to maintain stable operation. For high volatile coals the fuel feeding must be steadier to keep the variation in the outlet oxygen concentration at some range than with coals with low reactivity or alternatively greater air coefficient is needed to prevent too low O2 concentrations, which can cause an increase in CO emissions. The fuel quality can be characterized by the fluctuation of oxygen concentration in flue gases in steady operation conditions, which depends on the fluctuations in the combustion and in the fuel feed and on operational conditions. The amplitude of the fluctuations was studied. For advanced controls, it is necessary to know the factors affecting the process dynamics, such as reactivity and the behavior of char inventory in bed. This information is also necessary in developing and optimizing the CFB boiler considering emissions, combustion process and furnace scale up.Copyright

Modeling of particle size distribution of limestone in sulfur capture in air and oxy-fuel circulating fluidized bed combustion

© 2016 Saastamoinen et al. This work is published by Dove Medical Press Limited, and licensed under a Creative Commons Attribution License. The full terms of the License are available at http://creativecommons.org/licenses/by/4.0/. The license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 2016 Saast moinen et al. This work is published and licensed by e Medical Press Limited. The full terms of this license are availabl at https://www.dovepress.com/terms. p p and incorporate the Creative Commons Attribution – Non Commercial (unp rted, v3.0) Licen e (http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms (https://www.dovepress.com/terms.php). Energy and Emission Control Technologies 2016:8 41–52 Energy and Emission Control Technologies Dovepress

Comparative study on air and oxy combustion in a pilot CFB boiler

Abstract In the present work, measurement experience of oxy combustion in a pilot scale circulating fluidized bed (CFB) combustor is summarized. The aim was to study combustion dynamics under air-and oxygen-firing conditions in order to develop and validated combustion controls for Flexi-Burn™ CFB combustion technology. Dynamic CFB-pilot combustion tests were carried out including various step and ramp tests in both air and oxy combustion and different operation strategies for oxy combustion.