(281h) Demonstration of Sustainable Air Separation Via a Coupled PSA-Thermochemical System

The product of an air separation process (nitrogen, oxygen) are in demand for many different industrial applications (sweep gas production, ammonia and fertilizer industry, food industry, etc.). The state-of-the-art methods, such as cryogenic distillation and pressure swing adsorption (PSA) have high energy demands and as a consequence, CO₂ emissions, especially if very high product purities are needed. In a previous study (Vieten et al. 2020) it was shown that coupling a PSA with a thermochemical cycle can reach higher energy efficiencies than the currently used methods. In this work, we focus on a pilot-scale demonstration of this system with the goal to produce nitrogen with oxygen purities less than 10 ppm. We show the oxidation kinetics of the chosen redox materials, the redox particle stabilities, the reactor design as well as the main results of the experimental campaign.

The reduction and oxidation kinetics of the chosen redox materials SrFeO₃, CaMnO₃ and Ca_xSr_(1-x)MnO₃ was evaluated via thermogravimetric analysis (TGA). The materials were investigated in the particle form as they are used in the pilot reactor. In case of the Sr-substituted CaMnO₃ samples the influence of Sr content on the kinetic behavior will be discussed.

In order to ensure good gas-solid interaction, reliable flow velocities and good heat transfer, the reactor is filled with redox particles with a narrow size distribution. The particles were produced via a mixing-spheronization method. Their thermochemical and mechanical stability was analyzed, as well as the stability under pressurized conditions.

The reactor system consists of a PSA unit that removes the oxygen from the air flow until the optimal transition purity is reached. The pre-purified gas flow enters the thermochemical reactor (Figure 1), where the very high purity inert gas is produced. The reactor is an indirectly heated, packed bed design with a capacity of 5 l redox particles. The presented experimental campaign demonstrated the effect of the process parameters, such as transition purity, flow rates, reduction and oxidation temperature and oxidation pressure on the product purity and yield. The product gas has purities suitable to be introduced to the Haber-Bosch process.

References:

Vieten, Josua; Gubán, Dorottya; Roeb, Martin; Lachmann, Bruno; Richter, Sebastian; Sattler, Christian (2020): Ammonia and nitrogen-based fertilizer production by solar-thermochemical processes. In: SOLARPACES 2019: International Conference on Concentrating Solar Power and Chemical Energy Systems. SOLARPACES 2019: International Conference on Concentrating Solar Power and Chemical Energy Systems. Daegu, South Korea, 1–4 October 2019: AIP Publishing (AIP Conference Proceedings), S. 170016.