678 / 2019-04-29 22:19:40

Reducing NOx Emission from a Coal Fired Boiler by Surplus Primary Air Acting as High-Speed OFA

high-speed over-fire air,nitrogen oxides control,coal boiler,primary air

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A new technology, high-speed over-fired air (HOFA), was proposed to use surplus primary air as over-fired air with high-speed to reduce the concentration of NOx at the furnace outlet, in the basis of the facts that primary air fans of a 300MW coal-fired boiler still had a large surplus in Zhejiang province, and that the amount of nitrogen oxide generated in the furnace was large and that the load of SCR denitrification at the tail was high. The HOFA technology installs the nozzles of high-speed over-fired air (HOFA) above the existing over-fired air nozzles on the boiler. The nozzles of HOFA are connected with the main pipe of hot primary air, and the surplus hot primary air at high pressure is sent into the boiler furnace through the nozzles of HOFA. Then deep air-staged combustion in the direction of the height of the furnace is formed, thus the generation of NOx can be effectively suppressed. The three-dimensional numerical simulation was carried out using Fluent software, and the mechanism and influences of HOFA on in-furnace flow field, temperature field, CO concentration field and NOx concentration field were studied. The principle of HOFA technology was revealed and the optimized of actual HOFA operation scheme was obtained. The experiments were carried out both before and after the HOFA retrofit, and results showed that after using HOFA, the NOx (at 6% O2) at the furnace outlet was 365 mg/Nm3 (at 100% load) and 243 mg/Nm3 (at 75% load), which was 33-53 mg/Nm3 lower than that before the retrofit, while CO was still maintained at a low level. The HOFA technology can effectively and deeply reduce NOx at the furnace outlet.