Mahesh V. Iyer

Reactive separation of CO2 using pressure pelletised limestone

Calcium oxide powder derived by the calcination of mesoporous calcium carbonate provides a higher conversion towards carbonation compared to calcium oxide derived from naturally occurring limestone and hydrated lime. Compaction of this high reactivity sorbent was investigated for its use in CO2 separation from flue gas. It was observed that compaction preserved the porosity of the powder. The pellets were able to attain 50–80% conversion towards carbonation over three cycles. The rate and extent of carbonation reaction reduces with increasing pellet thickness. The effect of compaction load and CO2 concentration did not show any appreciable difference in the rate of carbonation. Whereas the mesoporous calcium carbonate pellet showed appreciable drop in carbonation conversion, the pellets made from other precursors, such as natural limestone and hydrated lime, maintained a higher degree of reactivity over three cycles.

ENHANCED HYDROGEN PRODUCTION INTEGRATED WITH CO2 SEPARATION IN A SINGLE-STAGE REACTOR

Hydrogen production by the water gas shift reaction (WGSR) is equilibrium limited due to thermodynamic constrains. However, this can be overcome by continuously removing the product CO{sub 2}, thereby driving the WGSR in the forward direction to enhance hydrogen production. This project aims at using a high reactivity, mesoporous calcium based sorbent (PCC-CaO) for removing CO{sub 2} using reactive separation scheme. Preliminary results have shown that PCC-CaO dominates in its performance over naturally occurring limestone towards enhanced hydrogen production. However, maintenance of high reactivity of the sorbent over several reaction-regeneration cycles warrants effective regeneration methods. We have identified sub-atmospheric calcination (vacuum) as vital regeneration technique that helps preserve the sorbent morphology. Sub-atmospheric calcination studies reveal the significance of vacuum level, diluent gas flow rate, thermal properties of diluent gas, and sorbent loading on the kinetics of calcination and the morphology of the resultant CaO sorbent. Steam, which can be easily separated from CO{sub 2}, has been envisioned as a potential diluent gas due to its better thermal properties resulting in effective heat transfer. A novel multi-fixed bed reactor was designed which isolates the catalyst bed from the sorbent bed during the calcination step. This should prevent any potential catalyst deactivation due to oxidation by CO{sub 2} during the regeneration phase.