Syngas production via cyclic reduction and oxidation of metal oxides

Patent metadata

Field	Value
Publication number	US-9902615-B2
Application number	US-201514799559-A
Country	US
Kind code	B2
Filing date	Jul 14, 2015
Priority date	Jul 14, 2015
Publication date	Feb 27, 2018
Grant date	Feb 27, 2018

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.

First claim

The invention claimed is:

1. A method of producing syngas comprising:
flowing a stream of oxygen-carrier particles through a circuitous flow path that proceeds through a plurality of unit operations comprising a combustor, a reducer, a conversion reactor, and an oxidizer;
in said combustor oxidizing oxygen-carrier particles in said stream via an exothermic chemical reaction such that thermal energy is generated thereby and is at least partially absorbed by said particles in said stream;
in said reducer at least partially reducing oxygen-carrier particles in said stream thereby consuming at least a portion of the absorbed thermal energy;
in said conversion reactor contacting said oxygen-carrier particles in said stream with a carbonaceous fuel stream in co-current flow and reacting them to yield incomplete oxidation products comprising carbon monoxide and hydrogen, thereby consuming an additional portion of said absorbed thermal energy; and
in said oxidizer at least partially re-oxidizing the oxygen-carrier particles in said stream using steam to yield hydrogen.

2. The method of claim 1 , wherein partially or fully reduced oxygen-carrier particles from said conversion reactor and said incomplete oxidation products generated therein flow together in a single mixed-phase stream along said pathway from an exit of said conversion reactor to an entrance of said oxidizer, said steam flowing in a stream countercurrent to said mixed-phase stream in said oxidizer.

3. The method of claim 2 , said stream of steam impinging said mixed-phase stream adjacent said entrance where said mixed-phase stream enters said oxidizer, thereby redirecting at least a portion of gases in said mixed-phase stream to an exit port of said oxidizer, wherein hydrogen generated in said oxidizer is combined with said gases prior to exiting said exit port.

4. The method of claim 3 , wherein oxygen-carrier particles in said mixed-phase stream continue to flow against said countercurrent stream of steam as gases from said mixed-phase stream are redirected, thereby effecting a separation of said particles from gases in the mixed-phase stream.

5. The method of claim 1 , said oxygen-carrier particles comprising iron oxide of the formula FeO x , wherein x is between 0 and 1.5.

6. The method of claim 5 , said oxygen-carrier particles further comprising one or a combination of an inert support material and/or doping agent selected from the group consisting of aluminum oxide, calcium oxide, copper, and cerium.

7. The method of claim 5 , wherein x is between 0.8 and 1.3 on average for oxygen-carrier particles entering the conversion reactor.

8. The method of claim 7 , wherein x is less than 0.8 on average for oxygen-carrier particles on exiting the conversion reactor.

9. The method of claim 8 , said conversion reactor operating at a temperature of 600° C. to 1400° C.

10. The method of claim 5 , said iron oxide being 1.5% to 50% by weight of the oxygen-carrier particles.

11. The method of claim 5 , said iron oxide being 15% to 30% by weight of the oxygen-carrier particles.

12. The method of claim 1 , wherein said reducer at least partially reduces said oxygen-carrier particles using a carbonaceous gaseous fuel, wherein said gaseous fuel and said oxygen-carrier particles flow countercurrent with respect to one another in said reducer.

13. The method of producing syngas of claim 1 , said oxygen-carrier particles flowing cyclically via said circuitous flow pathway 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.

14. The method of claim 13 , said oxygen-carrier particles flowing from said exit of said combustor to said entrance of said reducer via a riser in which additional carbonaceous fuel is injected.

15. The method of claim 1 , wherein endothermic reactions in said reducer are carried out using thermal energy stored in said oxygen-carrier particles that was absorbed from exothermic reactions in said combustor.

16. The method of claim 15 , said method being autothermal such that upon entry into said combustor the oxygen-carrier particles are in a sufficiently reduced state, at least partially as a result of having been partially reduced in said reducer, that complete oxidation thereof in said combustor generates sufficient thermal energy to fully support the generation of incomplete oxidation products in the conversion reactor.

17. The method of claim 15 , wherein a quantity of thermal energy absorbed by said oxygen-carrier particles in said combustor and in said oxidizer together is greater than of the thermal energy consumed in said reducer and said conversion reactor together.

18. The method of claim 12 , said countercurrent flow yielding a pressure gradient that decreases in a direction toward a location where said oxygen-carrier particles enter the reducer so that gaseous oxidized products generated therein are driven to exit the reducer adjacent said location rather than flow against the gradient, wherein partially-reduced oxygen-carrier particles are carried from an exit of said reducer into said conversion reactor via a gas comprising primarily unoxidized fuel and partially-oxidized products.

19. A method of producing syngas comprising flowing a stream of oxygen-carrier particles through a circuitous flow path in which said oxygen-carrier particles:
a) are oxidized via an exothermic chemical reaction such that thermal energy is generated thereby and is at least partially absorbed by said particles;
b) thereafter are at least partially reduced, thereby consuming at least a portion of the absorbed thermal energy;
c) thereafter are contacted and reacted with a carbonaceous fuel stream in co-current flow to yield incomplete oxidation products comprising carbon monoxide and hydrogen, thereby consuming an additional portion of said absorbed thermal energy; and
d) thereafter are at least partially re-oxidized using steam to yield hydrogen, at least a portion of said hydrogen being combined with said incomplete oxidation products.

20. The method of claim 19 , wherein said steps (a) through (d) are repeated at least once.

Assignees

• Babcock & Wilcox Co

Inventors

• Siengchum Tritti
• Velazquez Vargas Luis G
• Flynn Thomas J
• Devault Douglas J

Classifications

• Y02E60/36

  Hydrogen production from non-carbon containing sources, e.g. by water electrolysis · CPC title

• C01B2203/1241

  Natural gas or methane · CPC title

• C10J3/725

  Redox processes · CPC title

• C01B2203/0838

  by heat exchange with exothermic reactions, other than by combustion of fuel · CPC title

• C01B2203/0811

  by combustion of fuel · CPC title