Nondestructive neutron imaging diagnosis of acidic gas reduction catalyst after 400-Hour operation in natural gas furnace

•AGR enables ultra-clean flue gas and neutral condensate.•Proper condensate drainage is critical to the AGR-enabled furnace.•NCT demonstrates the spatially resolved 2D/3D nondestructive diagnosis of AGR.•The particle accumulation in the middle of the top block is visibly heavier.•2D section views reveal particle aggregation in the center instead of at the rim.