(526b) Exploring Thermodynamic and Efficiency Trade-Offs in a High-Pressure Chemical Looping Hydrogen Production System

Authors: 
Kathe, M., The Ohio State University
Kong, F., The Ohio State University
Fan, L. S., The Ohio State University
Gross, M., The Ohio State University
Iron-based Chemical looping is a promising technology that can reduce costs from SMR for H2 production. The chemical looping process uses three reactors, which eliminate the need for multiple processing units in the SMR process, and increases H2 production. Previous studies have shown promising results in quantifying the thermodynamic limits of the system at atmospheric pressures1. Additionally, most of the design philosophy in a chemical looping system follows the principle of minimization of solids circulation rate following the circulating fluidized bed derived heuristics. This study seeks to quantify the feasibility and tradeoffs associated with high-pressure chemical looping applications while relaxing the assumptions for heuristically inspired minimum solids flowrate design. An initial isothermal quantification using the Gibbs free energy minimization approach and supplanted by kinetic assumptions will be used to develop a base-case performance for the chemical looping system. This initial design will be updated with an adiabatic and autothermal operation for the system, wherein temperature swings of solids and pre-heats will be synchronized such that the system has maximum Hydrogen production with minimum energy consumption. Finally, deterministic (SQP-type) and stochastic (simulated-annealing type) optimization solvers will be used to relax the assumption of minimum solids flowrate in-order to increase Hydrogen production efficiency. The preliminary results of this study provide an initial thermodynamic quantification of high-pressure chemical looping solids operation and explore tradeoffs between compressing H2 versus operation of a solids circulation loop at high pressures. Specific insights into the delicate interplay between Hydrogen production efficiency, solids circulation fluxes and system design temperature provide an essential understanding and motivation for specific designs as well as scaled operating condition recommendations. Additionally, Individual and synergistic effects of variables like the number of compressor and expander stages, variation in reactant space hourly velocities and the trade-offs associated with using pinch and transshipment type technology for heat exchanger network synthesis are also investigated. Preliminary results show that operating chemical looping system at operating conditions that deviate from minimum solids circulation rate can provide equivalent or even higher H2 production efficiencies than those obtained from following conventional heuristics.

1. Kathe, Mandar V., et al. "Hydrogen production from natural gas using an iron-based chemical looping technology: Thermodynamic simulations and process system analysis." Applied energy 165 (2016): 183-201.