Chemical Looping Combustion
Chemical Looping Combustion Advantages:
Oxygen is created in-situ...
Oxygen production requirement is eliminated
...reduces energy demand and system costs.
Uses conventional construction materials and techniques
...decreases capital cost

The combustion of fossil fuels in nearly pure oxygen, rather than air, presents an opportunity to simplify carbon dioxide (CO2) capture in power plant applications. Oxy-combustion power generation provides oxygen to the combustion process by separating oxygen from air. However, chemical looping systems produce oxygen internal to the process, eliminating the large capital, operating, and energy costs associated with oxygen generation. Chemical looping combustion (CLC) is considered a “transformational” technology with the potential to meet program cost and performance goals.

In CLC systems, oxygen is introduced to the system via oxidation-reduction cycling of an oxygen carrier. The oxygen carrier is usually a solid, metal-based compound. It may be in the form of a single metal oxide, such as an oxide of copper, nickel, or iron, or a metal oxide supported on a high-surface-area substrate (e.g., alumina or silica), which do not take part in the reactions. For a typical CLC process, combustion is split into separate reduction and oxidation reactions in multiple reactors. The metal oxide supplies oxygen for combustion and is reduced by the fuel in the fuel reactor, which is operated at elevated temperature.

NETL-ORD Chemical Looping Pilot-Scale Reactor
NETL-ORD Chemical Looping Pilot-Scale Reactor

This reaction can be exothermic or endothermic, depending on the fuel and the oxygen carrier. The combustion product from the fuel reactor is a highly concentrated CO2 and H2O stream that can be purified, compressed, and sent to storage or for beneficial use. The reduced oxygen carrier is then sent to the air reactor, also operated at elevated temperature, where it is regenerated to its oxidized state. The air reactor produces a hot spent air stream, which is used to produce steam to drive a turbine, generating power. Then the oxygen carrier is returned to the fuel reactor, re-starting the reduction-oxidation cycle.

Current CLC R&D efforts are focused on developing and refining oxygen carriers with sufficient oxygen capacity, durability to withstand harsh CLC environments, and acceptable cost; developing effective and sustainable solids circulation and separation techniques; improving reactor design to support fuel and oxygen carrier choices; effective heat recovery and integration; and overall system design and optimization. Chemical looping is discussed in greater detail in the “DOE/NETL Advanced Combustion Systems: Chemical Looping Summary” (July 2013).

A number of CLC concepts are being researched around the globe at bench and small pilot scale to prove system design and operation strategies and to estimate capital and operating costs for commercial-scale systems. Currently, NETL supports several CLC projects in collaboration with industry, academia, and NETL’s Research & Innovation Center ranging from lab and bench scale testing to evaluation of pilot-scale prototypes.