The surface combustor-heater with cyclic flow reversal combustion embedded with water tube bank

Abstract

Based on the new concept of cyclic flow reversal combustion (CFRC) of a combustible mixture in a packed bed of porous inert medium, a new surface combustor-heater (SCH) embedded with a heat exchanger was explored. Thermal structure, heat transfer performance and emission characteristics were examined. Effects of operating parameters such as water flow rate, half-period, equivalence ratio, heat input and particle size of the packed bed were clarified. The heat transfer performance and the emission characteristics were evaluated by comparing them with those of conventional one-way flow combustion (OWFC). Results show that operation of the SCH with CFRC was possible despite multiple heat sinks and a strong quenching effect. Favorable flame stabilization, extended flammability and a more uniform temperature profile over the tube bank were established. Preferable heat transfer enhancement and combustion augmentation were obtained with high thermal efficiency (up to 80%) and significantly lower CO and NO x emissions (as low as 40 ppm at 0% excess O 2) as compared with conventional OWFC. CFRC can provide flexibility in heat transfer performance and emission characteristics by adjusting the half-period. The thermal efficiency and emission characteristics of CFRC were insignificantly affected by the equivalence ratio. CFRC was suitable for operating at relatively low heat input because of high thermal efficiency and low CO and NO x emissions. A large particle size ( d p=16 mm) of the packed bed significantly improves the thermal efficiency with favorably low emission (as low as 30 ppm). This SCH with CFRC concept can provide the basis for development of state-of-the-art technology for new versions and more advanced thermal systems, such as highly efficient ultra-low-pollutant-emission boilers, for efficient utilization of energy.