Mechanistic study of enhanced H₂ synthesis in biomass gasifiers with in‐situ CO₂ capture using CaO

Abstract

in Wiley InterScience (www.interscience.wiley.com).Biomass gasification coupled with in situ CO 2 removal using CaO is a promising process for the sustainable production of H 2 . Thermodynamic equilibrium modeling predicts biomass conversion to gas containing up to 81.4 vol % H 2 (dry basis). However, in practice, discrepancies between theoretical and experimental results demonstrate the significance of nonequilibrium phenomena. In this context, we have developed a simultaneous thermogravimetric-mass spectrometric (TG-MS) technique to study the influence of: (i) heating rate, (ii) CaO loading, (iii) evolved gas residence time, and (iv) reaction atmosphere. The results of this study give insight into the decomposition mechanisms of biomass in the presence of CaO, including the influence of: (i) CO 2 removal, (ii) sorbent hydration (Ca(OH) 2 ), (iii) intrinsic heating and swelling effects associated with the exothermic gas-solid absorption reactions, and (iv) the direct catalytic role of CaO for char gasification and tar elimination.

Enhanced CO2 adsorption capacity and stability using CaO‐based adsorbents treated by hydration

“…Thus, worldwide efforts have been made to lower the level of carbon dioxide in the atmosphere. 1 Furthermore, many industrial processes such as hydrogen production [2][3][4][5][6][7] , enhanced steam methane reforming 5,8,9 and water-gas shift reaction [10][11][12] also require the removal of the CO 2 in flue gases. Solid calcium-based sorbents have attracted numerous attention in high-temperature carbon capture owing to their unique advantages 13 such as higher adsorption capacity and selectivity compared to physical adsorbents (the theoretical amount of CO 2 adsorption is 0.786 g CO 2 g…”

Single‐Stage Production of Highly Concentrated Hydrogen from Biomass‐Derived Syngas

“…Biomass materials are first gasified to produce a raw syngas, containing mainly hydrogen, carbon oxides, water, nitrogen (if air is used), and small amounts of methane, higher hydrocarbons and tars. [2] Combined with initial cleaning steps to remove contaminants, such as H 2 S, tars, NH 3 , the syngas is often upgraded to high-purity hydrogen through the steam reforming (SR) and water-gas shift (WGS) reaction, followed by CO 2 removal. [2] Pre-reforming is often needed to convert alkenes and alkanes to methane and syngas in order to lower coking potential.…”

“…Effects of in situ CO 2 capture by CaO in cellulose gasification process have been investigated by thermodynamic analysis and mechanistic study with thermogravimetric analysis-mass spectrometry (TGA-MS), showing an enhanced hydrogen production and direct gasification of char and tar on CaO. [3] Sorption enhanced water-gas shift (SEWGS) reaction has also been identified as a promising new concept for intensification of hydrogen production. [4] A potassium-promoted hydrotalcite-like (HTl) material, which has been regarded as a competitive candidate as CO 2 acceptor working at a temperature lower than 400 8C, was used together with a commercial iron-chromium shift catalyst for conducting the SEWGS reaction.…”

“…Indeed, there can be more possible benefits brought by producing hydrogen through Equation (3). Typically, the product gas from gasifier needs to be cooled to about 500 8C to condense alkaline compounds and then heated again before it enters the reformer.…”

“…To realize continuous hydrogen production, the sorption enhanced reaction can take place in circulating fluidized bed, which comprises two bubbling bed reactors and allows regeneration of CO 2 acceptor and sorption enhanced reaction to occur simutaneously. [14] However, only the simulated synthesis gas from biomass gasification was used in our study, and effects of other impurities such as NH 3 and H 2 S should be addressed in future investigations.…”