Syngas production via cyclic reduction and oxidation of metal oxides

Abstract

A chemical-looping system utilizes oxygen-carrier particles to produce syngas from carbonaceous fuels. The system provides a circuitous flow path for the oxygen-carrier particles, which are used to partially oxidize the fuel to produce syngas. The circuitous flow path can proceed through a plurality of unit operations, including a reducer, a conversion reactor, an oxidizer, and a combustor. The conversion reactor is designed to partially oxidize carbonaceous fuel in co-current flow with the oxygen-carrier particles to produce syngas. In embodiments including an oxidizer, the oxidizer is designed to at partially re-oxidize the carrier particles, yielding hydrogen that can be mixed with partially oxidized products from the conversion reactor to adjust syngas quality. The combustor can be used to fully oxidize the carrier particles traveling in a closed loop. Reactions carried out in the combustor are highly exothermic and yield thermal energy that is absorbed by the carrier particles. The absorbed energy is used at other parts of the process, including the conversion reactor, to drive endothermic reactions. In this manner the system can be operated autothermally or nearly so. Methods of producing syngas are also disclosed.

1 . A system comprising:
 a circuitous flow pathway for oxygen-carrier particles, said pathway proceeding through a plurality of unit operations comprising a reducer, a conversion reactor, and a combustor;   said reducer configured to at least partially reduce said oxygen-carrier particles;   said conversion reactor configured to react said oxygen-carrier particles with a carbonaceous fuel via co-current flow to yield incomplete-oxidation products comprising carbon monoxide and hydrogen; and   said combustor configured to receive said oxygen-carrier particles in a partially or fully reduced state and to fully re-oxidize said oxygen-carrier particles.   
     
     
         2 . The system of  claim 1 , said plurality of unit operations further comprising an oxidizer configured to receive said oxygen-carrier particles in a partially or fully reduced state and to at least partially re-oxidize the oxygen-carrier particles using steam, thereby producing hydrogen. 
     
     
         3 . The system of  claim 2 , wherein said circuitous flow pathway for oxygen-carrier particles proceeds through said unit operations in the following order:
 from an exit of said combustor to an entrance of said reducer;   from an exit of said reducer to an entrance of said conversion reactor;   from an exit of said conversion reactor to an entrance of said oxidizer; and   from an exit of said oxidizer to an entrance of said combustor;   such that in operation of said system said oxygen-carrier particles flow cyclically through said unit operations in the aforementioned order along said pathway.   
     
     
         4 . The system of  claim 3 , said flow pathway for oxygen-carrier particles further proceeding through a riser disposed intermediate said exit of said combustor and said entrance of said reducer. 
     
     
         5 . The system of  claim 2 , said reducer being further configured to at least partially reduce said oxygen-carrier particles with a gaseous fuel to produce combustion products; wherein said reducer is further configured so that said gaseous fuel and said combustion productions flow countercurrent with respect to said oxygen-carrier particles in said reducer. 
     
     
         6 . The system of  claim 2 , said conversion reactor and said oxidizer being further configured such that in operation said incomplete-oxidation products and said oxygen-carrier particles flow together in a single, mixed-phase stream through said pathway from an exit of said conversion reactor to an entrance of said oxidizer; said oxidizer being further configured such that said steam flows in a stream countercurrent to said mixed-phase stream in said oxidizer.