A novel low-NO burner with in-burner high-speed air jet array for ammonia-coal co-firing: Integrating ammonia pyrolysis and deep air staging

Abstract

Co-firing of the carbon-free fuel ammonia in coal-fired power stations is an effective measure to reduce CO₂ emission. Considering the high nitrogen content in ammonia, ammonia-coal co-firing burner should be crucially and elaborately designed to minimize the NO emission. Here, a novel swirl burner design with in-burner high-speed air jet array (HAJA) was proposed. Structure design and CFD simulations of a 50kWth HAJA burner were performed with a conventional burner as benchmark, and combustion and emission performance under coal firing, ammonia-coal co-firing and pure ammonia firing conditions were evaluated. The results showed that both ammonia-coal blends and coal/ammonia single fuel could be stable burned in the proposed burner. Also importantly, the NO emission of the proposed burner was lower than that of the prototype burner at same combustion conditions. The in-burner air jet array generates high-speed tertiary air jets multipoint-distributed on the periphery and downstream of secondary air, which lengthen the oxygen-lean pyrolysis zone and main combustion zone. This deep air-staged effect helpfully inhibits NO formation and reduces the NO emission as the promoted pyrolysis of ammonia before combustion and lowered the peak temperature, especially for ammonia-coal co-firing. Moreover, the emission performance of HAJA could be flexibly controlled by the velocity of the tertiary air jets at constant total excess air coefficient, and in the simulated scenarios, increasing velocity could reduce the NO formation. Besides, effects of changing the ratio of primary air and secondary air rate on the combustion and emission performance of HAJA burner were also investigated.