Global Model of Countercurrent Coal Gasifiers

Abstract

This is a model of a fixed-bed coal gasifier in which CO, C02, K20 and H2 are assumed to be in thermodynamic shift equilibrium over a zone in which the primary gasification reactions occur. Exiting temperatures from this zone are in excess of 550 °C and the shift reaction is readily catalyzed by gas-borne impurities. Fresh coal is pyrolyzed in this gas stream and its gaseous products are added quantitatively to the shift gases. The final raw product gases thus calculated are close to experimental data from several sources for oxygen-and air-blown gasifiers. The model, which is simple conceptually and mathematically, correctly predicts the effect of heat leak in establishing the composition of the raw coal gas from a fixed bed gasifier. This important variable has not had the visibility that its significance demands.

Thermodynamic optimization of biomass gasification for decentralized power generation and Fischer–Tropsch synthesis

“…Buekens and Schouters [30] have recommended use of equilibrium models for design of coal and biomass gasifiers, as these models give meaningful results with minimum parameters. Kosky and Floess [31] have found close correlation between product gas composition in oxygen or air blown fixed bed coal gasifier with that predicted using simple equilibrium model. Shand and Bridgwater [32] have reviewed thermodynamic models for downdraft gasifiers that incorporate feedstock composition, moisture, HHV, heat losses, excess oxidant and extent of shift reaction as parameter.…”

Biomass steam gasification – an extensive parametric modeling study

“…However, it is known that thermodynamic equilibrium may not be achieved mainly because of the relatively low operation temperatures (product gas outlet temperatures between 750± 1000°C, Bridgewater, 1995), (Buekens and Schouters, 1984). Nevertheless, models based on thermodynamic equilibrium have been used widely (Buekens and Schouters, 1984;Kinoshita et al, 1991;Watkinson et al, 1991;Denn et al, 1979;Kosky and Floess, 1980;Kovacik et al, 1989;Cousins, 1978;Shesh and Sunavala, 1990;Shand and Bridgewater, 1984;Kilpinen et al, 1991). Watkinson et al (1991) demonstrated that discrepancies in comparison of equilibrium gas composition with experimental data may re¯ect unknown temperature gradients from the gasi®cation zone to the outlet zone.…”

Performance correlations for biomass gasifiers using semi-equilibrium non-stoichiometric thermodynamic models

“…9. Klosky and Floess 10 have also used equilibrium thermodynamic model for the prediction of product gas composition from air or oxygen‐blown fixed‐bed gasifier. Kovacik et al .…”

“…Parametric sensitivity of moving bed coal gasifier was studied by Denn et al [9]. Klosky and Floess [10] have also used equilibrium thermodynamic model for the prediction of product gas composition from air or oxygen-blown fixed-bed gasifier. Kovacik et al [11] have used equilibrium models for the prediction of product gas composition from entrained flow and fluidized bed reactors.…”