WP2 concentrates the more fundamental research needed to study the different reaction steps in the BackCap process (carbonation of Ca(OH)2 in different aggregation modes, calcination of carbonated materials and hydration of CaO) with a special focus on the attainment of scalable kinetic information and related material characterization works. The following specific objectives are proposed for this WP:

• To experimentally investigate the carbonation reaction of Ca(OH)₂ and derive experimental data under relevant conditions and aggregation modes.

• To experimentally investigate the calcination reaction of partially carbonated solids resulting from Ca(OH)₂ carbonation.

• To experimentally evaluate the effect of the partial hydration of the sorbent on CO₂ carrying capacity and reactivity towards carbonation.

• To experimentally evaluate the loss of sorbent CO₂ carrying capacity when cycling the material between Ca(OH)₂, CaO and CaCO₃.

• To tune gas-solid reactor models to derive kinetic parameters and provide support to the reactor and process modeling tasks of WP4.

WP3 focuses on a comparative investigation of the CO₂ capture performance of different Ca(OH)₂ qualities and reaction environments in industrially relevant entrained flow reactor conditions at the (TRL4-5) pilot test rig at USTUTT. Since the most likely gas-solid contacting mode for the BackCap concept will be an entrained bed system. Moreover, this WP focuses on the sorbent regeneration step (including the calcination of the carbonated sorbent and the hydration of the calcined sorbent). Around 350 h of operation are expected in this facility. This task involves the following specific objectives:

• Identification of optimal carbonation conditions and quantification of CO₂ capture performance in different entrained flow carbonation conditions using fresh and cycled hydrated lime samples from CAR.

• Determination of achievable carbonation conversion under relevant entrained flow reactor conditions.

• Investigation and identification of favorable calcination and hydration conditions to regenerate spent sorbents, maintaining a high reactivity (towards carbonation, gas-solid high temperature hydration or low temperature water hydration).

• Investigation on cyclic carbonation/calcination/hydration of sorbent samples from the pilot and their loss in reactivity (i.e. when hydration is not complete).

• Provision of data for model development and simulation validation in WP4.

This work package focusses on the development of different models (reactor to process level) to provide quantitative descriptions of all relevant unit operations and reaction stages affecting the performance of different variants of the BackCap process.

• To develop integral reactor models for the carbonation of Ca(OH)₂ powders in entrained mode and cyclone-type reactors.

• To adapt existing oxy-calciner models to the characteristics of the carbonated materials evolved in the BackCap carbonator.

• To develop full multi-scale process model frameworks integrating information at particle, reactor and thermal integration levels, providing the basis for the full-scale studies and economic analyses in WP5.

The aim of this work package is to perform full-scale plant studies and a basic economic analysis of the BackCap process. As basis for the tasks related, the amortized “La Pereda” power plant (50 MWe owned by HUNOSA in Spain) will serve as an exemplary power plant to be retrofitted to adapt to a context of backup power requirements, in a power grid with a large share of renewable energy. The specific objectives of this work package are:

• To estimate the cost and the key performance indicators of the BackCap process today and in a 2030 scenario.

• To carry out a benchmark of the BackCap process against alternative competing process for similar back-up power provision services (i.e. power-to-fuel-to-power and gas turbines).