One-Dimensional Dynamic Modeling of a Single-Stage Downward-Firing Entrained-Flow Coal Gasifier

Abstract

In the current paper, a one-dimensional partial differential equation (PDE)-based dynamic model and its simulation results are presented for a single-stage down-fired entrained-flow gasifier. The gasifier model comprises mass, momentum, and energy balances for the gas and solid phases. The initial gasification processes of water evaporation and coal devolatilization and the key heterogeneous and homogeneous chemical reactions have also been modeled. The resulting coupled system of PDEs and algebraic equations is solved using the well-known method of lines in Aspen Custom Modeler. In addition to the dynamic gasifier model, efficient control strategies that can satisfactorily perform both servo and disturbance rejection functions have been developed for the entrained-flow gasifier. The dynamic variations of key gasifier output variables in response to the disturbances commonly encountered in industrial operation are presented. Output variables of interest include gas and solid phase temperatures, synthesis gas compositions, and carbon conversion, while disturbances include ramp and step changes in input variables such as coal flow rate, oxygen-to-coal ratio, and water-to-coal ratio among others. Feedstock switchovers have also been studied by simulating transitions from one coal type to another. The gasifier model results are also compared to the dynamic data available in the literature.

Co-Production of Olefins, Fuels, and Electricity from Conventional Pipeline Gas and Shale Gas with Near-Zero CO2 Emissions. Part II: Economic Performance

“…It is a significant future challenge to construct dynamic models of all of the relevant process units in sufficient detail such that the complex interaction between tightly integrated process sections can be understood well enough such that information about the time required for transitions, feasible turndown ratios, off-spec products, and their associated costs can be known. Some progress has been made in constructing dynamic models of certain individual process units specifically for the purposes of flexible polygeneration applications, such as for gasification [31], steam reforming [32], water gas shift [33], CO2 capture [34], and solid oxide fuel cells [35]. However, combining these models into one system requires considerable effort and has not yet been achieved.…”

Parameter analysis of an entrained flow gasification process

“…22 These include the gas composition and carbon conversion data compared for different stoichiometric conditions. The second validation was made using four different coal types available in Kasule et al 20,21 In their work, the effect of coal properties on the product species profile was numerically studied. Information on the proximate and elemental composition of coal is listed in Table 2.…”

“…[18][19][20][21] Some used a linear variation of wall temperature, 18,19,22 while wall temperature has been calculated together with gas/solid temperature. 20,21 While a 1D reactor model was described to predict entrained flow gasifier performance along the reactor, 22 the scope of that study was limited to examining the influences of oxygen and steam supply rate on carbon conversion, gas composition, and temperature. Even with 1D models, most previous studies did not report the isolated influence of particle size and coal feeding rate except few studies, 10,18 but both factors have considerable influence on the kinetics of the gasification process.…”

Development of a hybrid shrinking‐core shrinking‐particle model for entrained‐flow gasifiers

“…The shrinking-core model used in this work has been previously presented by Kasule et al 10,30 and is used for the early region of the gasifier where the bulk temperature is below the ash melting temperature. Details of that model can be found in the work of Kasule et al It should be noted that in entrainedflow gasifiers, burners are designed to promote swirling motion close to the inlet of the gasifier that results in quick evaporation of water and the subsequent devolatilization step.…”

“…31 A rigorous model for the heat balance on the gasifier wall is also considered. Gas recirculation is also modeled, similar to the SCM, 10,30 to mimic the swirling effect produced by the burners.…”