Startup and Control Concepts for Pressurized Chemical Looping for a Plug Flow with Internal Recirculation Reactor

Pressurized chemical looping combustion (PCL) is a carbon capture technology that produces high-temperature heat with inherent separation of CO₂. It employs two fluidized beds to avoid direct contact of the combustion air and fuel, instead using a solid metal oxide oxygen carrier that transports the oxygen from the air reactor to the fuel reactor, avoiding dilution of the produced CO₂ with N₂. In collaboration with Hatch Ltd, CanmetENERGY is building a 600 kW_th PCL pilot plant using Hatch’s novel plug flow with internal recirculation reactor (PFIR) concept. This concept houses both the air and fuel reactors within a single vessel, making the technology more compact, reducing capital costs, and eliminating reliability and operability issues typically associated with external solids transfer legs in traditional chemical looping arrangements. This novel reactor , while advantageous in many aspects, introduces new process design requirements associated with: (1) control of circulation between reactors, (2) control of product purity from the air and fuel reactors, (3) startup of the process and (4) pressure control in the reactors.

CanmetENERGY is developing startup and process control strategies for the pilot plant that can be tested and then implemented at commercial scale. The startup strategy is a multi-stage approach that includes pre-heat and fluidization of the air reactor with a natural gas burner, and use of a recycled gas stream to the fuel reactor to fluidize and drive circulation of the cold fuel reactor bed particles. Initiation of solids circulation between reactors is an essential part of startup to transfer sensible heat from the air reactor to the fuel reactor. Transition from startup to chemical looping combustion must also be carefully balanced to ensure that fluidization, heat transfer between the reactors, reaction stoichiometry and reactor pressures are all balanced.