Achieving optimal performance in downfired steam-methane reformers

摘要

Down-fired steam methane reformer furnaces utilize flue gas tunnels (aka "coffins") along the radiant section floor to collect and transport radiant section flue gas to the convection section for additional heat recovery. These tunnels range from 4 to 10 feet high, 2 to 3 feet wide, and 40 to 100 feet long, depending on the unit design capacity. Flue gas enters the tunnels through side wall openings which are distributed throughout the tunnel system to achieve uniform radiant flue gas flow. Conventional tunnel system physical features constrain design efficacy, resulting in non- uniform flue gas flow along the tunnel lengths and among tunnels. Non-uniform flue gas flow is correlated to non-uniform catalyst tube convective heating, varied tube temperatures, and early tube failures. BD Energy Systems have developed a new, patent-pending Tunnel Optimal Performance (TOP) design method to achieve near-perfect radiant flue gas flow uniformity, near-perfect catalyst tube temperatures with respect to convective heating, and improved tube longevity/reliability. BD Energy Systems are pleased that TOP tunnel system(s) are in production in North America and under consideration elsewhere in the world. This flue gas fine-tuning method has applications in Selective Non-Catalytic Reduction (SNCR) as well. Historically, radiant tunnel ammonia injection SNCR projects results have varied per reformer - some projects achieve required NOx reduction, while others fall short of expectations. The BD Energy Systems TOP-based flue gas control method increases in- tunnel flue gas mixing and NOx reduction, rendering ammonia injection a more predictable NOx reduction method. This paper compares conventional design results to TOP design results, focussing on benefits to radiant tube reliability and NOx reduction efficacy.