Sulfur recovery unit (SRU) thermal reactor is important equipment in a sulfur plant. Its operating temperature can exceed 1600oC and thus lead to the formation of nitrogen oxides (NOx). In this paper, NOx produced by an industrial-scale SRU thermal reactor is analyzed. Both the prototype reactor and its modifications, including modifying the zone 1 corner geometry, modifying the choke ring, and using a vector wall, are compared to seek a feasible way of reducing NOx emission. From the simulation results, it is found that the SRU thermal reactor with a radius of curvature 1m at the zone 1 corner has the lowest nitric oxide (NO) emission among the radii of curvature at the zone 1 corner investigated. Among the choke ring heights investigated, the SRU thermal reactor having a choke ring height of 1.11m has the highest NO emission while the one having a choke ring height of 0.74m has a lower NO emission. Further, among the choke ring positions investigated, the SRU thermal reactor having a choke ring away from the zone 1 corner by 6m has the lowest NO emission while the one having a choke ring away from the zone 1 corner by 3m has the highest NO emission. The NO concentration at the reactor exit using a vector wall is higher than that using a choke ring. Among the SRU thermal reactors investigated in this study, the one without a choke ring has the lowest NO emission. However, it has the highest zone 2 temperature and this is harmful to the downstream heat exchanger tubes. Although a vector wall produces more sulfur, its NO emission is also higher. In summary, a SRU thermal reactor using a choke ring of 0.74m in height and 6m away from the zone 1 corner is a feasible compromise among the sulfur production, the operating temperature (service life consideration) and the NO emission. © 2020, Chinese Mechanical Engineering Society. All right reserved.
