Abstract
The intricate coupling between coal pyrolysis, gas phase combustion and the emissions of alkali metal, such as sodium, is studied in the early stage of a temporally evolving three-dimensional planar turbulent jet carrying pulverized-coal particles. Complex chemistry is used to account for both the combustion of volatile hydrocarbons and the sodium containing species. The response of the sodium chemistry is analyzed in the mixture fraction space, along with the topology of the reactions zones. Combustion is found to start preferentially in partially premixed flames, which then evolve toward diffusion-like reactive layers and reach chemical equilibrium. From the direct numerical simulation (DNS) database, the possibility of modeling the dynamics of sodium species using one-dimensional premixed flamelet generated manifolds (FGM) is investigated. A chemical lookup table is constructed for the combustion of the partially premixed volatiles and an additional three-dimensional simulation is performed to compare the tabulated sodium species against their reference counterparts with complex chemistry. Quantitative analysis of the performance of the developed chemistry tabulation confirms the validity of the approach. Perspectives for the modeling of sodium emissions in pulverized-coal furnaces and boilers are finally drawn.
Highlights
Since the turbulence-chemistry interaction is not modeled but resolved in these simulations, the results provide precious insights into the combustion characteristics of turbulent pulverized-coal flames and serve as reference for subgrid scale modeling development
To build the lookup table, the flamelet computation is repeated over a range of equivalence ratios, mapped in the mixture fraction Z, and varying total enthalpy levels, with the Lewis number chosen at unity for all the species
A temporally evolving planar pulverized-coal jet flame is simulated with complex chemistry, to account for both the combustion of volatile hydrocarbons [26] and the reactions of sodium species [8], which are released from the burning coal particles
Summary
Since its pioneer introduction in ReynoldsAveraged Navier–Stokes (RANS) modeling of turbulent premixed flames [11], the tabulated chemistry methods, e.g., flamelet generated manifolds (FGM) [12,13], have shown great potential on predicting major hydrocarbon and minor species, such as NOx [14,15]. Within this context, the aim of the present study is twofold.
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