(570f) Modularization Chemical Looping System for Hydrogen Production from Carbonaceous Solid Feedstock Along with CO2 Capture and Additional Heat Recovery

Hydrogen is widely regarded as the fuel of the future, but the current supply is primarily derived from fossil fuels. To achieve a more sustainable hydrogen economy, it is essential to develop technologies that can produce hydrogen from both fossil and renewable feedstocks, such as plastics and biomass, while capturing resulting CO₂ emissions.

Chemical looping gasification is a promising approach for the conversion of carbonaceous feedstock into syngas. It typically consists of two reactors, namely the reducer and the combustor. The carbonaceous feedstock enters from the top of the moving bed reducer along with the oxygen carriers. The oxygen carriers donate their lattice oxygen to gasify the carbonaceous species into syngas while both travel downwards co-currently. The generated syngas then leaves from the bottom of the reducer, while the oxygen carriers are sent to the fluidized bed combustor for replenishing the lattice oxygen by air oxidation.

In addition to the two-reactor system, a chemical looping three-reactor system exists for generating hydrogen from carbonaceous feedstocks along with CO₂ capture. In this system, the oxygen carriers react with the carbonaceous species in the reducer to generate a capture-ready stream of CO₂, and the reduced oxygen carriers then travel to the second moving bed reactor, the oxidizer, for steam oxidation. The fluidized bed combustor then fully regenerates the oxygen carriers in the air, closes the heat balance of the system, and conveys the oxygen carriers back to the reducer top. This innovative approach has great potential to reduce greenhouse gas emissions and support the transition to a sustainable energy system.

This study outlines a novel modular chemical looping strategy that utilizes multiple moving bed reactors operating in parallel, connected to a single fluidized bed combustor. The integrated system offers a range of advantages over conventional chemical looping gasification systems, including the option for the co-generation of hydrogen/heat and the elimination of the need for a heat-intensive CO₂ capture unit.

The proposed system can operate in different configurations, providing flexibility to generate syngas or hydrogen based on downstream needs. The system can generate high-purity syngas in the gasification reducer, which can then be converted into hydrogen while also generating a capture-ready stream of CO₂, eliminating the need for an energy-intensive CO₂ capture unit. Alternatively, the system can be integrated into a downstream process that requires syngas as a feedstock, allowing for the co-generation of hydrogen/heat and a separate capture-ready stream of CO₂.

Comparative cases demonstrate that the proposed modular system increases effective thermal efficiency by approximately 17% points compared to conventional chemical looping gasification systems with water gas shift and CO₂ capture units due to the elimination of the CO₂ capture unit and generation of additional heat from the tail gases. Experimental results also demonstrate the feasibility of the proposed process for gasifying biomass and plastics, achieving a high-purity syngas stream for both biomass and plastics gasification on the bench scale moving bed experiments and producing a nearly pure stream of CO₂ for hydrogen generation.

The study also discusses the challenges of dealing with high sulfur content in some fuels, which can be resolved using a syngas cleanup system to recover sulfur. Strategies for the co-injection of plastics and biomass are also presented, showing that the co-injection of polyethylene plastics with biomass can increase the hydrogen yield by approximately 12%.

In addition, the study highlights the advantages of the proposed modular system over the conventional three-reactor Biomass-Direct-Chemical Looping system for hydrogen generation. Specifically, it addresses practical operation and the inherent batch-to-batch variation in biomass. The modular system eliminates the risk of carbon carryover from the reducer to the oxidizer, resulting in high-purity hydrogen, even with varying biomass compositions. Experimental thermogravimetric results on biomass gasification demonstrate the variability in gasification kinetics and how the proposed system can mitigate the risk of carbon carryover.