For decades, down-fired SMR furnaces have utilized flue gas tunnels or "coffins" along the radiant section floor to collect flue gas flow as uniformly as possible. These tunnels utilize standard refractory shapes and installations which constrain the flue gas to non-uniform flow which has been correlated to non-uniform catalyst-tube temperatures and accelerated tube aging. In addition, these tunnels have been less than reliable in structural integrity and in some instances have leaned onto catalyst tubes creating additional stresses on the tubes in a hot condition. The ability to design and construct tunnels using new highly-engineered refractory shapes is new to this industry and could be the answer to greater structural reliability and achieving near-perfect flue gas flow among and into the tunnels resulting in improved catalyst tube reliability and longevity.
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