Abstract
This work presents an in-situ neutron imaging study of the ammonia sorption reaction in a SrCl2-Expanded Natural Graphite (ENG) composite loaded into a honeycomb-shaped stainless-steel scaffold and enclosed in a thermochemical heat storage (THS) reactor prototype. The performance of SrCl2/Sr(NH3)8Cl2-ENG under different pressures and temperatures was investigated and the spatio-temporal content of ammonia was calculated from neutron radiograms. Quantitative image analysis revealed the formation of Sr(NH3)8Cl2 upon ammonia uptake, while the desorption studies revealed a partial ammonia desorption resulting in the formation of the monoamine phase Sr(NH3)Cl2 via a stepwise release of ammonia. Neutron imaging also allowed the indirect evaluation of the stainless-steel honeycomb heat conductivity and showed that heat is transferred prevalently via the ENG matrix. Finally, neutron tomography of the reactor prototype was performed to ensure the stability of the THS system and composite material throughout the ammonia cycling experiments.
Highlights
Thermal energy storage and reutilization of the waste heat can give a significant contribution to reduce our carbon footprint
The hydrogen present in the ammonia molecule allows to detect the areas within the honeycomb, where Sr(NH3)8Cl2 is formed, and here it is demonstrated for the first time how the NH3 content in composite ma terials within a thermo chemical heat storage (THS) reactor can be calculated from neutron radiography images
The first (Absorption-1, blue curve) and second (Absorption-2, red curve) absorption were performed at similar NH3 pressures of ~2.5 bar which increased up to 2.7 bar due to the saturation of Sr(NH3)8Cl2-expanded natural graphite (ENG) while the NH3 gas was still provided by the ammonia reservoir
Summary
Thermal energy storage and reutilization of the waste heat can give a significant contribution to reduce our carbon footprint. The work presented here shows an in-situ neutron imaging study on a SrCl2-ENG composite placed in a stainless-steel honeycomb heat exchanger mounted inside a model THS reactor. Our study reports a remarkable me chanical stability of SrCl2-ENG during NH3 uptake and release with only slight expansion and contraction of the composite material, providing a homogeneous NH3 uptake and showing excellent thermal conductivity. The hydrogen present in the ammonia molecule allows to detect the areas within the honeycomb, where Sr(NH3)8Cl2 is formed, and here it is demonstrated for the first time how the NH3 content in composite ma terials within a THS reactor can be calculated from neutron radiography images. The neutron radiography data presented here will be compared to nu merical simulations using COMSOL Multiphysics modeling software It is integrated with calculation of thermal and mass flow within the reactor including thermochemistry of the materials with a high degree of accuracy. The ammonia cycling and the subsequent heat transfer studies provided by numerical modeling will help to optimize the THS reactor design and obtain high heat power [38]
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