Modeling pulverized coal conversion in entrained flows

Sprouse, Kenneth M.

doi:10.1002/aic.690260612

Cited by 14 publications

(9 citation statements)

References 8 publications

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“…The effect is strongest during the period of high pyrolysis gas formation rates (between 0.8 and 0.9 s). As a result, the gas phase mole fraction of Hz is relatively low at 0.8 s, namely 0.940, as compared to 0.995 at 0.7 s. The combined effects of temperature and gas phase mole fraction of HZ lead to approximately the same values for Hz concentration at the coal surface at 0.7 s and 0.8 s. Thus, within this modeling concept, high pyrolysis gas formation rates not only increase the accessibility of the coal mass due to mixing effects in the plastic coal but also cause extraparticle Hz concentration gradients, lowering the Hz gas phase mole fraction at the coal's surface, although the latter effect is only of minor importance, in agreement with Sprouse's (1980) analysis for spherical coal particles.…”

Section: Base Casesupporting

confidence: 77%

Rapid hydropyrolysis of softening coal particles—A modeling study. Part II: Model predictions and comparison with experimental results

1985

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The mathematical model described in Part I is applied to predict CHI and tar yields in rapid hydropyrolysis of softening coal particles. Predicted effects of pressure and particle size agree with trends previously measured in a screen heater apparatus. GEORG SCHAUB SCOPEPrevious experimental results with Pittsburgh Seam bituminous coal indicate that mass transfer plays an important role in rapid hydropyrolysis. The measured effects of particle size and pressure on CHI and tar yields could not be adequately described with available kinetic models owing to their not accounting for the drastic changes in physical properties associated with softening and resolidification during hydropyrolysis of softening coals. A new hydropyrolysis model which does account for the property changes of softening coals has been formulated and presented in Part I. In the present paper the model is tested by comparing its predictions with experimental results in order to verify its underlying mechanistic concept. CONCLUSIONS AND SIGNIFICANCEMathematical representation of the global chemical reactions and mass transfer leads to predictions for particle size and pressure effects on CH4 and tar yields. The agreement of predictions with measurements, e.g., of the different effects of total pressure and Hz partial pressure on the yields, is better than previous models for softening coal (Anthony et al., 1976). This success can be attributed to the underlying mechanistic concept of diffusional transport of Hz in a material whose transient physical properties range from those of a fluid during the plastic period to those of a porous solid after resolidification. Accordingly, the coal's transient fluidity is significant, as penetration of Hz into the particle i s hindered during the plastic period due to the low Hz diffusivities in the plastic-liquid state. Diffusion is comparatively faster in the resolidified coke after pyrolysis gas evolution is nearly completed.The present experimental data base is sparse. Areas of particular interest for further experimental investigation and model validation are the rheological properties of softened coal under rapid hydropyrolysis conditions and the separate effects of inert gas pressure, Hz pressure, and particle size on individual product yields (e.g., CHI and tar).The results of this study are pertinent to coal (hydrw) pyrolysis and gasification modeling and to addressing such questions as how to maximize individual product yields or how to minimize agglomeration of softening coal in conversion processes,

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Section: Base Casesupporting

confidence: 77%

Rapid hydropyrolysis of softening coal particles—A modeling study. Part II: Model predictions and comparison with experimental results

1985

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“…Ubhayankar (1977) did not consider the momentum balance, and Wen and Chaung (1979) used the Stoke's Law approximation for the particle instead of the solid momentum balance. Sprouse (1980) and Goyal (1980) studied the hydrogasification process rather than combustion in a different type of reactor system.…”

Section: Introductionmentioning

confidence: 99%

Modeling and simulation of an entrained flow coal gasifier

1984

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A mathematical model has been developed to simulate the Texaco downflow entrained-bed pilot-plant gasifier using coal liquefaction residues and coal-water slurries as feedstocks. This model describes the physical and chemical processes occurring in an entrained coal gasifier. The gasification kinetics describes different complex reactions occurring in the gasifier and the hydrodynamics describes mass, momentum and energy balances for solid and gas phases. Temperature, concentration and velocity profiles along the reactor height were obtained by solving the mass, momentum and energy balances. Parameter studies were made to provide a better understanding of the reactor performance for various inlet feed conditions utilizing the model. RAKESH GOVIND and JOGEN SHAHDepartment of Chemical and Nuclear Engineering University of Cincinnati Cincinnati, OH 45221 SCOPE Entrained-bed gasifiers are cocurrent flow reactors in which pulverized or atomized hydrocarbons react with oxygen and steam to produce gaseous fuels. These reactors are becoming popular in the processing of coal into synthetic fuels and thermal energy since they produce higher coal gasification rates and are easier to operate than fluidized-or fixed-bed reactors. Further, due to the incineration effect they produce a product gas that is relatively free of higher hydrocarbons particularly the tarry materials.In this paper, a mathematical model has been developed to simulate the Texaco downflow entrained-bed pilot-plant gasifier using coal liquefaction residues as feedstocks. Results of the simulation have been compared with experimental data from the gasifier. CONCLUSIONS AND SIGNIFICANCEThe Texaco downflow pilot-plant gasifier was simulated by simultaneously solving the mass, momentum and energy balances-for the solid and gas phases. Good agreement was obtained between the simulation programs and experimental results. The gas composition leaving the gasifier and the final carbon conversion depends on three essential parameters: the fuel rate, the oxygen to fuel ratio, and the steam-fuel ratio. It was found that oxygen-fuel ratio affects carbon conversion more than the steam-fuel ratio. The steam-fuel ratio significantly affects the gas product composition. The optimum oxygen-fuel ratio is between 0.8 and 0.9 to achieve 98-99% conversion. Depending on the oxygen-fuel ratio, the optimum steam-fuel ratio ranges from 0.3 to 0.6 using coal liquefaction residues as feedstocks.

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“…Figure 2 is a typical result with Illinois #6 coal showing the gasifier's space residence time to be less than 0.5 second for 100 wt% carbon conversion at a nominal 82% cold gas efficiency (CGE -higher heating value, HHV, basis). This figure was developed from a detailed computer model by Sprouse (1980) and Sprouse and Schuman (1981). As a comparison, commercial gasifiers operating without multi-element rapid-mix injectors (such as Royal Dutch Shell's and General Electric's Texaco gasifiers that rely on large internal recirculation zones for temperature suppression) require space residence times on the order of 3 seconds.…”

Section: Executive Summarymentioning

confidence: 99%