An oil refinery liquefied gas workshop sulfur recovery unit exhaust flue burning through, emergency shutdown treatment. Construction unit a migrant worker advanced into the furnace, the wall will be removed. Then the workshop technician put on a one-piece suit, a flashlight and a filter (hydrogen sulfide) gas mask, and went deep into the furnace for inspection. However, the two-stage admixture valve connected to the entrance pipeline of the two-stage conversion reactor is in a half-open state. Nitrogen is poured from the entrance of the two-stage conversion reactor into the top of the sulfur furnace through the two-stage admixture valve.