(197d) Gasification of Biomass and CO2 Capture Using Chemical-Looping Combustion: Thermodynamic Analysis

In recent years, biomass including agricultural and municipal waste, has been received increasing attention considering a major source of renewable energy with zero net CO₂ emissions. The use of biomass as fuel, in conjunction with chemical-looping combustion (CLC), offers the additional potential of delivering negative CO₂ emissions. To accomplish this, a possible approach is to gasify the solid fuel producing syngas which can be burned inside the same fuel reactor of a CLC process. The overall gasification and combustion combined process can be described as follows:

Gasification step: C_xH_yO_z → H₂+CO+CO₂+CH₄+C C+H₂O → CO+H₂ CO+H₂O → CO₂+H₂ C+CO₂ → 2CO

Combustion step (with oxygen carrier) M_yO_x+H₂ → M_yO_x-1+ H₂ M_yO_x → M_yO_x-1 + CO₂

The above reactions are heavily influenced by the type of solid fuel, the oxygen carrier, the reaction temperature, and the partial pressure of steam in the fuel reactor (Leion et al., 2007; Cao et al., 2006). This approach has the following main advantages: (i) eliminates extra units for solid gasification and (ii) circumvents the dilution of the syngas with nitrogen (Leion et al. 2007; Scott et al. 2006).

An equilibrium thermodynamic model is reported in this communication able to simulate an integrated Gasifier-Combustor unit using glucose as a feedstock. Glucose is one of the building blocks of cellulose, a main biomass component. Alumina supported nickel based oxygen carrier is considered as the oxygen carrier inthe calculations. The effects of fuel composition, temperature, pressure, and extent of gasification are studied using the Gibbs free energy minimization to determine the product gas composition. This analysis shows that CO₂ can be concentrated and purified up to 99.0% in such a process during the reduction cycle by the gasification products (CO and H₂).

References: Cao, Y., Pan, W., (2006), Energy & Fuels, 20, 1836-1844. Scott, S.A., Dennis, J.S., Hayhurst A.N. (2006), AIChE Journal, 52 (9), 3325-3328. Leion, H., Mattisson, T., Lyngfelt, A. (2007), Fuel 86, 1947-1958.