Department of Chemical Engineering
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Item Kinetic modeling of non-catalytic partial oxidation of nascent volatiles derived from fast pyrolysis of woody biomass with detailed chemistry(Elsiever, 2015-06) Srinivas, AppariThe gas-phase partial oxidation (POx) of nascent volatiles (NV) derived from the fast pyrolysis of cedar sawdust at 700 and 800 °C was studied both numerically and experimentally. A detailed chemical kinetic model (DCKM) was applied to simulate the POx in a two-stage reactor: the first stage was designed for fast biomass pyrolysis and the second effected the POx of the NV. Analytical pyrolysis experiments were also conducted to approximate the molecular composition of the NV, which is required input for computations using DCKM. The DCKM was modified by an empirical kinetic model for the decomposition of an ill-defined portion of the NV. The kinetic model coupled with a plug-flow reactor model reproduced the observed trends in the product yields with respect to both temperature and oxygen-to-fuel ratio, for not only the major products, but also minor products such as aromatic hydrocarbons which are typically found in the refractory post-gasification tar.Item Predicting the temperature and reactant concentration profiles of reacting flow in the partial oxidation of hot coke oven gas using detailed chemistry and a one-dimensional flow model(Elsiever, 2015-04) Srinivas, AppariA numerical approach is presented for predicting the species concentrations and temperature profiles of chemically reacting flow in the non-catalytic partial oxidation of hot coke oven gas (HCOG) in a pilot-scale reformer installed on an operating coke oven. A detailed chemical kinetic model consisting of 2216 reactions with 257 species ranging in size from the hydrogen radical to coronene was used to predict the chemistries of HCOG reforming and was coupled with a plug model and one-dimensional (1D) flow with axial diffusion model. The HCOG was a multi-component gas mixture derived from coal dry distillation, and was approximated with more than 40 compounds: H2, CO, CO2, CH4, C2 hydrocarbons, H2O, aromatic hydrocarbons such as benzene and toluene, and polycyclic aromatic hydrocarbons up to coronene. The measured gas temperature profiles were reproduced successfully by solving the energy balance equation accounting for the heat change induced by chemical reactions and heat losses to the surroundings. The approach was evaluated critically by comparing the computed results with experimental data for exit products such as H2, CO, CO2, and CH4, in addition to the total exit gas flow rate. The axial diffusion model slightly improves the predictions of H2, CO, and CO2, but significantly improves those of CH4 and total exit flow rate. The improvements in the model predictions were due primarily to the improved temperature predictions by accounting for axial diffusion in the flow model.Item A CFD study on the reacting flow of partially combusting hot coke oven gas in a bench-scale reformer(Elsiever, 2015-11) Srinivas, AppariA computational fluid dynamics (CFD) approach to simulate reacting flow in a hot coke oven gas (HCOG) reformer is presented. The HCOG was reformed by non-catalytic partial oxidation in a tubular reactor (0.6 m i.d. and ∼4.1 m long) with four oxygen nozzles (0.0427 m i.d.), which was installed on a platform of an operating coke oven. The reforming of HCOG, a multi-component mixture, in a turbulent flow was simulated numerically by considering both chemical reactions and fluid dynamics. The detailed chemical kinetic model, originally consisting of more than 2000 elementary reactions with 257 species, was reduced to 410 reactions with 47 species for realising a kinetic model of finite rate reactions with a k–ε turbulence model. The calculation was carried out using the eddy dissipation concept (EDC) coupled with the kinetic model, and accelerated using the in situ adaptive tabulation (ISAT) algorithm. Numerical simulations could reproduce the reformed gas compositions fairly well, such as H2, CO, CO2, and CH4, as well as the temperature profile in a HCOG reformer as measured by thermocouples.Item Numerical study of on-board fuel reforming in a catalytic plate reactor for solid-oxide fuel cells(Elsiever, 2011-02) Srinivas, AppariA pseudo-transient numerical model is used for the simulation of a multi-functional catalytic plate reactor (CPR). The work mainly addresses the problems associated with on-board reforming for solid-oxide fuel cells. Heat management is achieved by indirectly coupling partial oxidation with reforming. Water management is achieved by partially recycling the anode stream from a solid-oxide fuel cell. The model uses detailed heterogeneous chemistry for reforming and oxidation reactions occurring on the catalyst beds.