Influence of pressure on the gasification kinetics of two high-temperature beech wood chars with CO2, H2O and its mixture

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• Experimental data and modeling for CO 2 , H 2 O and mixed gasification at high pressure. • Beech wood chars produced in drop-tube reactor at 1400 °C and 1600 °C at 200 ms. • Gasification in single-particle reactor with forced flow-through conditions. • Interpretation of results based on graphitization, ash dispersion and morphology. This paper presents experimental data and modeling approaches to describe the influence of CO 2 and H 2 O partial pressure as well as absolute pressure on the gasification kinetics of two different beech wood chars. The chars were produced at 1400 °C (P1400) and 1600 °C (P1600) at high-heating rates and short residence times in a drop-tube reactor. The gasification experiments were conducted in a single-particle reactor with forced flow-through conditions reducing diffusional effects to a minimum. The interpretation of the experimentally determined reaction rates during gasification with CO 2 , H 2 O and its mixture is based on the char properties (graphitization, ash dispersion and morphology) presented in a previous publication. During gasification with CO 2 , P1600 shows higher reactivity as compared to P1400 for all CO 2 partial pressures and temperatures applied. The higher reactivity of P1600 during CO 2 gasification may be explained by a CaO film on the char surface catalyzing the char-CO 2 gasification reaction. On the other hand, P1400 shows higher reactivity towards H 2 O which may be evoked by the lower graphitization degree and higher specific surface area. Reaction kinetic modeling for single atmosphere gasification was successfully carried out using a power law approach. The Langmuir-Hinshelwood model, however, only gave good results where a possible saturation of the char surface at high pressure was observed. Increasing the CO 2 partial pressure during gasification in mixed CO 2 /H 2 O atmospheres leads to higher reactivity for both chars. The reaction rate r mix can be expressed by addition of the single atmosphere reaction rates in the low pressure area suggesting a separate active site mechanism. Catalytic activity of CaO increases the P1600 reactivity distinctively for lower H 2 O and CO 2 partial pressures. For higher H 2 O and CO 2 partial pressures, P1600 reactivity stagnates due to lower specific surface area and higher graphitization degree. Here, a common active sites mechanism can be assumed.