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안성율,Hiroaki Watanabe,Toshiaki Kitagawa 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.4
A numerical simulation was performed with the two competing model in the devolatilization process for a pulverized coal combustion jet flame by means of LES. The target was a simple jet burner flame in CRIEPI. To solve the LES equations, a CFD code FFR. Comb was employed with the dynamic Smagorinsky SGS turbulent model. A simple global kinetic mechanism was implemented to predict combustion of the gas and solid phase combustion. The interactions between the two phases were calculated by PSI-Cell model while the reaction rate in turbulent flow was established by SSFRRM. The simulation was validated by comparing results to the experimental data in terms of particle dispersion and velocity as well as gaseous velocity. The flame structure was discussed with temperature, mole fraction of major species. In addition, the effect of the devolatilization model was investigated simultaneously by comparing to another simulation that employed the single first order reaction model because the devolatilization was one of the major processes in coal combustion and it had an influence on the flame structure from all reactive regions. The release rate was calculated by two different parameter sets in the Arrhenius rate equation for the two competing model that were corresponding different temperature regions whereas the released rate was determined by only one fixed parameter set in the single first order reaction model. From the simulation, it was revealed that the main reactions took place at the upstream and the first fuel oxidation was stronger at the inner reaction zone comparing to the far side combustion. It was confirmed as well that the two competing model could capture the quick devolatilization faster than the single first order reaction model though the dominant part appeared later than the single first order reaction model.
Seongyool Ahn,Panlong Yu,Hiroaki Watanabe,Ryoichi Kurose,Kenji Tanno,Toshiaki Kitagawa 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.5
A three-dimensional numerical simulation was performed to investigate the physics and combustion characteristics of a two-phase reacting turbulent flow in a pilot-scale pulverized coal combustion furnace. This included an elementary reaction mechanism using an extended flamelet/progress variable (EFPV) method. The simulation was validated via comparison with an experiment in terms of the gaseous temperature and distribution of the gas mole fraction. The EFPV method predicted the flame structure and combustion characteristics of the pulverized coal. In the main reaction zone where the released gas combustion was dominant, two separate combustion regions were observed, and they were attributed to hydrocarbons and CO combustion. Gas flow characteristics such as mixing of low temperature gas and hot burnt gas were well described in the inner recirculation zone. The CO 2 conversion reaction to CO occurred slowly and decreased the gaseous temperature beyond the main reaction zone in the low and zero oxygen environments. The simulation predicted the unburned CO combustion correctly beyond the flame when staged air was injected; however, the combustion rate was overestimated due to the fundamental assumption of the EFPV method, attributable to the limitations of the steady state flamelet approach.
Influences of hard- and soft- segment ratios on pyrolysis behavior of polyurethane elastomers
( Yuya Nishiyama ),( Shogo Kumagai ),( Tomohito Kameda ),( Yuko Saito ),( Atsushi Watanabe ),( Suguru Motokucho ),( Hisayuki Nakatani ),( Toshiaki Yoshioka ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 한국폐기물자원순환학회 심포지움 Vol.2019 No.1
Introduction Polyurethane elastomers (PUEs) are typical block copolymers which are composed of alternative hard segment (HS) and soft segment (SS), with the physical and chemical properties of them can be varied by changing HS and SS ratios. Pyrolysis is a promising method for polymeric wastes recycling because it can convert various polymers into chemical feedstock only by heat1). In this study, seven kinds of PUEs with different HS and SS ratios were synthesized (Fig. 1), then influences of hard- and soft-segment ratios on pyrolysis behavior were investigated. Methods, Results and discussion 1. Identification of pyrolysis products: Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was employed to characterize the pyrolysis products under elevated temperature shown in Fig. 2. All the PUEs produced MDI, MAI and MDA (Fig. 3) from HS through pyrolysis, which were formed by pyrolytic urethane bond cleavage via 4-membered and 6-membered transition states shown in Scheme1. 2. In-situ monitoring of ticpyrolysis products: In-situ monitoring of pyrolysis products, called evolved gas analysis-MS (EGA-MS), was performed under the same pyrolysis conditions as the previous section. EGA chromatogram and representative products are shown in Fig. 4. Pyrolysis of various PUEs with different HS and SS clearly showed presence of three pyrolysis zones. In the zone 1, HS decomposition products such as CO<sub>2</sub>, butanediol (BD) and MDI are generated from five PUEs having HS. This suggested that formation of isocyanate end shown in Scheme1-I was dominant at this temperature. In the zone 2, SS-derived products and CO<sub>2</sub> were mainly formed from the five PUEs with low HS ratios. MDI was not produced in this zone, while MAI and MDA were produced. These results revealed that the high temperature promoted formation of the amine end shown in Scheme1-Ⅱ. In addition, a part of the SS-derived product could be generated by decomposition of MDI between HS and SS. In the zone 3, SS-derived products were produced from all PUEs, and the SS decomposition was continued. Thus, the temperature-dependent pyrolysis behavior was proposed (Scheme2) based on the findings in this work. Conclusion Temperature-dependent pyrolysis behavior of PUEs with different hard- and soft-segment ratios was investigated through pyrolysis tests employing Py-GC/MS and EGA-MS techniques. The findings in this work will be helpful to control product selectivity and feedstock recovery through pyrolytic approach.