Enhanced coal gasification heated by unmixed combustion integrated with an hybrid system of SOFC/GT

Abstract

For clean utilization of coal, enhanced gasification by in situ CO 2 capture has the advantage that hydrogen production efficiency is increased while no energy is required for CO 2 separation. The unmixed fuel process uses a sorbent material as CO 2 carrier and consists of three coupled reactors: a coal gasifier where CO 2 is captured generating a H 2-rich gas that can be utilized in fuel cells, a sorbent regenerator where CO 2 is released by sorbent calcination and it is ready for capture and a reactor to oxidize the oxygen transfer material which produces a high temperature/pressure vitiated air. This technology has the potential to eliminate the need for the air separation unit using an oxygen transfer material. Reactors' temperatures range from 750 °C to 1550 °C and the process operates at pressure around 7.0 bar. This paper presents a global thermodynamic model of the fuel processing concept for hydrogen production and CO 2 capture combined with fuel and residual heat usage. Hydrogen is directly fed to a solid oxide fuel cell and exhaust streams are used in a gas turbine expander and in a heat recovery steam generator. This paper analyzes the influence of steam to carbon ratio in gasifier and regeneration reactor, pressure of the system, temperature for oxygen transfer material oxidation, purge percentage in calciner, average sorbent activity and oxidant utilization in fuel cell. Electrical efficiency up to 73% is reached under optimal conditions and CO 2 capture efficiencies near 96% ensure a good performance for GHG's climate change mitigation targets.