(732m) Optimizing Absorption to Improve Haber-Bosch Synthesis Poster

"Ammonia absorber columns offer an alternative separation unit to replace condensation in the Haber-Bosch synthesis loop. Metal halide salts can selectively separate ammonia from the reactor outlet gas mixture and incorporate it into their crystal lattice with remarkably high thermodynamic capacity. In our previous work, we had found that while the salt working capacity can be limited and unstable when in its pure form, the working capacity can be stabilized and increased by formulating the absorbent with an inert support.

In this RAPID project we undertook to find and understand optimal conditions for uptake and release of ammonia, guided in large part by technoeconomic analysis that takes into account the experimental data acquired. The production capacity (ammonia processed per unit absorbent and per unit production time) depends on processing parameters - including uptake and regeneration temperatures, ammonia partial pressures, release time, and sweep gas flow rate. Process simulation using the information from experiment helped to inform about optimization needs, which were governed by technoeconomic analysis. As just one example, we found that it is necessary to balance the release time with the full cycle time and bed size to ensure that the uptake breakthrough time makes efficient use of the bed. These parameters are mutually interdependent; their optimization can be nontrivial but rewarding.

The analysis shows that at the production rate for the benchmark design (30 metric tons per day), that optimized absorber-enhanced design provided lower levelized dost of ammonia synthesis and lower energy demand in comparison to optimized condenser-based design - meeting RAPID targets. As the production scale decreases (toward more distributed, small-scale production facilities) the advantage of the absorber-enhanced design increases. The results suggest that absorber-enhanced design may help make distributed ammonia production viable in a wider range of circumstances.
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