Down-fired steam methane reformers generate hot flue gas at the arch burners. Flue gas flows downward through the radiant section, heating catalyst-filled tubes. At the radiant section floor, flue gas passes through the collection-tunnel-system side-wall openings and out to the Convection Section for additional heat recovery. Ideally, flue gas flow is uniform throughout the radiant box to increase tube temperature uniformity and maximize tube life.
Conventional tunnels constrain the flue gas to non-uniform flow, which is correlated to non-uniform catalyst tube temperatures and to accelerated aging. As a result, some tubes last 20+ years, while other tubes fail after a relatively short time. Often, problem locations develop causing rapid degradation of tubes and their replacements.
BD Energy Systems’ new patent pending Tunnel Optimal Performance (TOP) flow controlling tunnel technology achieves near-uniform flue gas flow and near-uniform tube temperatures in the tunnel region. Rather than varying wall-opening locations to control flow, openings are uniformly distributed throughout the entire tunnel system and flow control is achieved by varying opening diameter.
As an illustration, conventional and TOP tunnel system flow rates per tunnel-opening are compared. Conventional flows vary by +/- 25% of average, whereas TOP tunnel flows vary within +/- 2%. Where buttresses and expansion gaps preclude opening placement, no-flow regions exacerbate flow maldistribution. In addition, the new design includes more columns of openings, so velocity at the tube base is lowered. The first installation of a TOP designed flow-control tunnel system is scheduled for 2017.