The in situ tar reforming process is one of the key thermochemical phenomena in the downer reactor of the TB-CFB system. used a two-stage reactor to realize the in situ reforming of nascent tar from the rapid pyrolysis of brown coal over char obtained from the same coal. The results showed that the released tar can be decomposed over the char completely at 900 °C. This indicated the potential for the rapid and complete decomposition of tar over a char surface due to an intensive tar-char interaction. However, the characteristics of the char and reaction conditions of the two-stage reactor system are different from those of the downer reactor, through which coal, char particles, and gases are concurrently flowing. In the downer reactor, the in situ reforming of nascent tar occurs over the nascent char from the rapid pyrolysis of the same coal. In addition, it is not possible to use a fixed char bed to realize the decomposition of tar in the continuously operating TB-CFB system.
In our recent study (), a drop-tube reactor (DTR) was employed to simulate reaction environments similar to those in the downer reactor. An Australian brown coal (Loy Yang, hereafter referred to as LY) was co-fed with char (LYC) or partially gasified char (GLYC) into the DTR, and the effects of the char properties, char concentration in the blended sample, peak temperature, and feeding rate related to the solid hold-up on the tar decomposition were investigated.
Schematic diagram of the four-lump reaction network in the DTR coal conversion process accounting for the volatiles-char interaction. Reprinted with permission from Ref. (). Copyright: (2015) Elsevier B.V.
In our recent study (), it was employed for the first time to estimate kinetic parameters in complex coal conversion environments, including volatiles-char interactions, which were approximated for the downer reactor of the TB-CFB system. A network among lumps in the DTR is proposed as shown in . Under our conditions, it is assumed that the coal sample has already been converted into tar, carbon gases, char, and soot by primary pyrolysis at the top non-isothermal zone of the DTR (at 500–900 °C) (; ). The carbon conversion reactions in the isothermal zone of the DTR were simulated, and the feedstock was lumped into tar, carbon gases, char, and soot derived from the primary pyrolysis of the coal. The possible main reactions in the DTR were considered to be thermal cracking/steam reforming of the volatiles, gasification, and the volatiles-char interactions. The kinetic parameters of the four-lump model were estimated through a mathematical model integrated with a four-order Runge-Kutta method.
Coal conversion incorporating the volatiles-char interactions proceeds via a number of complex parallel reactions, and produces a wide range of products such as char, soot, light hydrocarbons, and both single and polycyclic aromatic hydrocarbons. The volatiles-char interaction has been frequently reported for different reactor systems, and the results show that the interaction has a significant role in inhibiting char gasification and promoting nascent tar decomposition. (; ). However, those studies focused on laboratory-based experimental investigations only. proposed a kinetic model incorporating the volatiles-char interaction, which reproduced the experimental findings from coal conversion very well, including the effects of the Na concentration in the char during steam gasification. It can also be used in designing any industrial fluidized-bed gasifier in the presence of volatile-char interactions. Although no studies have been performed, the development of a mathematical model based on the experimental results for coal conversion, including the volatiles-char interactions in the downer reactor of a TB-CFB system, should be considered.
Thermodynamics vs kinetics; Homogeneous and heterogeneous reactions - chemical reaction control rate equation, reaction rate constant, reaction order, non-elementary reactions; Solid State Diffusion -Fick’s Law, mechanisms of diffusion, uphill diffusion, Kirkendall effect, steady and transient diffusion; External mass transfer -fluid flow and its relevance to mass transfer, general mass transport equation, concept of mass transfer coefficient, models of mass transfer -film theory and Higbie’s penetration theory; Internal mass transfer-ordinary and Knudsen diffusion, mass transfer with reaction; Adsorption –physical adsorption vs. chemisorption, adsorption isotherms - Langmuir, BET; Adsorption as the rate limiting step examples - gasification of C by CO2, dissolution of N2 in molten steel; Porous solids - specific surface area and pore size distribution; Reactor design -batch vs continuous reactors, ideal stirred tank and plug flow reactors; Mass balance in ideal reactors, residence time distribution; Models of industrial reactors; Electrochemical kinetics-concept of polarization, activation over potential, Butler-Volmer and Tafel’s equation, applications in electro-deposition and corrosion.
System tools for energy systems; economic tools for energy systems; Conventional Power Generation Technology (Fundamentals of Energy Conversion, Heat Transfer, and Fluid Mechanics; Fuel Combustion and Gasification; Steam Power Plant Technology; Gas Turbine Power Generation Technology; Gas Turbine-Based Combined-Cycle Power Plants; Nuclear Power Plants; Cogeneration and Trigeneration; Power Plants’ Environment Impact Control) Renewable and Emerging Clean Energy Systems; Solar Thermal Energy Technology; Photovoltaic Technology; Hydro-Power, Wind, Geothermal, Marine, and Biomass Energy Systems; Advanced Energy Storage; Oxyfuel Combustion, Carbon Capture and Storage, Cleaner Coal Technologies; Emerging Clean Energy Technologies)
At the Academy, he pursues doctoral studies on the "Gasification characteristics of and chemicals production from low-rank solid fuels", under the guidance of Prof.
His recent interest is focused on LES And hybrid LES/RANS of wall-bounded flows with heat transfer.
He has also worked on development of new equipment and processes in thermal engineering (piston and screw compressor, entrained coal-gasification, pulse combustor).
Koyo Norinaga has been an Associate Professor of Institute for Materials Chemistry and Engineering, Kyushu University since 2009. He received his doctoral degree in 1999 in applied chemistry at Hokkaido University. He was an assistant professor at Tohoku University (1999–2002), a senior scientist (Humboldt fellow) at Karlsruher Institute of Technology (Karlsruhe, Germany, 2002–2006), and an associate professor at Hokkaido University (2006–2009). His research covers modeling and simulation of chemically reacting flows, including pyrolysis of light hydrocarbons, gasification and combustion of coal and biomass, and CVD/CVI of carbon and silicon carbide for composite material production.
Li-Xin Zhang received his PhD by accomplishing a study on the decomposition characteristics of tar derived from low temperature gasification of brown coal over coexisting char in 2013 at Kyushu University. He received his bachelor and master degrees at China University of Mining and Technology (Beijing) and currently working at Xi’an Thermal Power Research Institute Co. Ltd. (P.R. China) for developing coal-based poly-generation system and advanced coal power generation system.
Cheng-Yi Li received his PhD by accomplishing a study on modelling and simulation on reacting flow included in thermochemical conversion process of coal in 2015 at Kyushu University. He received his bachelor and master degrees at China University of Mining and Technology (Beijing) and currently working at China Tianchen Engineering Corporation as a process engineer for designing and developing advanced chemical plants in different fields, such as coal gasification plant, petrochemical plant and so on.