Absorber-enhanced ammonia synthesis: Absorber performance optimization, de-risking and modeling using an existing 1kg/day prototype
Executive Summary
Metal halide salts such as magnesium chloride have been demonstrated to be promising candidates for ammonia storage materials to enable applications such as intermittent energy storage, and distributed fertilizer production. Ammonia exiting a synthesis reactor can be separated from nitrogen and hydrogen by absorption into magnesium chloride. Compared with ammonia condensation seen in large-scale Haber-Bosch processes, ammonia absorption enables more complete separation at temperatures closer to the synthesis reactor, which can realize capital and energy savings that are necessary for cost-competitive distributed-scale modularization of ammonia production.
This team has already fabricated a 1 kg/day modular synthesis protoype, funded by ARPA-E, being used to study this absorption process in a UMN exsisting wind-to-ammonia facility in western Minnesota. The project team has shown, in a preliminary techno-economic analysis (TEA), that absorption can offer competitive economics at small scale ammonia production relevant for distributed modular operations.
Work with RAPID will include optimization and modeling of the prototype over a useful and relevant range of absorption cycling conditions - most importantly, the uptake and regeneration temperatures. The improved validated models provided by this optimized prototype will support better novel design, future optimization, and provide a step to safe and efficient further scaleup to commercial modular metric tonne per day capcities in the future. Additionally, longer-term testing with the protoype will be performed to produce useful stability and de-risking data.
Technical Challenge
- Determining optimum operating conditions of absorption and desorption with minimum absorbent degradation
- Utilizing as much absorbent as possible before ammonia breakthrough
- Using data from bench scale module to advance design and TEA at scales of interest for commercial projection (ca. 30 ton/day)
Potential Impact
It stands to reason that optimal design for modular, small-scale, distributed ammonia production will be very different than for the largest current continent-scale facility. This project’s approach to ammonia separation via salt absorption can work near ambient or near reaction temperatures, avoiding the capital needed for traditional condensation. In addition to this, studies to date suggest that absorption can remove ammonia at lower ammonia partial pressures and return a lower partial pressure to the reactor. This may lessen the need for the reactor to operate at a conventially high pressure, further reducing capital costs and safety concerns. TEA, systems optimization, and supply chain analysis so far support absorption’s competitiveness in modular distributed ammonia production.
Resources
The University of Minnesota ammonia team encompasses both chemical engineering at the Twin Cities campus and renewable energy expertise at the West Central Research and Outreach Center in Morris, MN. The project team will consist of experts in modeling, reaction engineering, separations, renewable energy, module design, and more. In addition the project team will have full access to the new ARPA-E funded prototype for absorption-enhanced synthesis and/or absorber testing. It is computer controlled and is designed to process more than 1 kg/day of ammonia.
