Chemical looping-based biomass gasification (CLG) using a calcium sorbent is an advanced concept for producing renewable hydrogen. The limitation imposed by the carbonation equilibrium requires the gasifier to operate below 700°C. This temperature significantly reduces the conversion of the carbonate to steam and, therefore, limits hydrogen production. The unconverted carbonate is burned in the calciner, providing the energy needed to maintain the process. To date, proposed solutions for generating a CO2 stream ready for sequestration in the calciner include: using pure oxygen from an air separation unit (ASU), or incorporating another chemical loop to transport oxygen to the calciner via carrier particles. In both cases, a flue gas containing CO2 and steam is obtained, from which the steam can be easily separated by condensation. While some of these proposals are very attractive, there are important aspects that need improvement:

1. Hydrogen production from water (water splitting) is very limited, since the gasification of the carbonate with steam below 700 ºC is very slow.

2. The processes required to produce CO2 ready for sequestration are extraordinarily expensive (ASU) or complex (chemical looping with O2 transporter).

3. Precise control of solids circulation between reactors in CLGs is highly complex, as several processes have to be optimized simultaneously (circuit heat balance, CO2 capture, tar conversion and sorbent regeneration).

4. The deactivation of the sorbent with the number of cycles is heavily penalized by the severe conditions under which calcination is generally carried out.

5. The energy penalty, resulting from working cyclically between a very endothermic calcination at high temperature and an exothermic carbonation at a much lower temperature, is very high.

This project proposes a process that improves upon the previous drawbacks, using a CLG in which the heat required for calcination is provided by solar thermal energy, and the carbon (and tar) is catalytically converted in the gasifier.

Furthermore, during the day, CaO is used to chemically store solar energy, ensuring uninterrupted H2 production during periods without solar radiation. Essentially, the proposed process oxidizes biomass with steam, using solar energy, and produces a concentrated H2 stream in the gasifier and a CO2 stream ready for sequestration in the calciner.

While this project does not propose the construction of a new pilot plant to demonstrate the proposed solar CLG, it does propose to study experimentally (in addition to theoretically) the most important aspects and challenges, using existing infrastructure within the research group. A technical and economic feasibility study, as well as an environmental sustainability assessment, will also be conducted.

The research team is comprised of members from Spanish and international research groups. The two Spanish research groups have extensive and proven experience in the key aspects to be developed in this project.

The project contributes to three of the Spanish Government's energy challenges, as well as several of the EU's specific challenges.