Abstract:
The reversal time of the high temperature air combustion is usually determined by engineering experience and the thermal characteristics of the regenerator, which often ignores the combustion in furnace. If the reversal time is too short, it will cause incomplete combustion, large fluctuation of furnace temperature and other problems. Therefore, it is necessary to analyze the minimum reversal time from the perspective of combustion in furnace. The commercial software Fluent was used to perform the transient simulation for analyzing the combustion process of high temperature air combustion system in oil-field jacket heater. Influences of the volume fraction of oxygen, load fluctuation and temperature of the heated air on combustion performance and reversal time were analyzed. The results show that the combustion in furnace can be divided into four processes: exhaust gases evacuation, flame reburning, flame diffusion and stable combustion. At the stage of exhaust gases evacuation, the high temperature gas is discharged out, which makes a rapid drop of temperature during the original combustion. At the same time, fresh gas gets in, so the temperature decreases at the original fume side. After about 0.2 s, the flame reburns at the original fume side, and the temperature in the furnace rises rapidly. Then the flame diffuses forward, and the temperature is increased and then is prone to be stable in the whole furnace. The mass fraction of NO shows a similar evolution as that of temperature change, and has a certain lag. The minimum reversal time should be no less than the stabilization time of temperature and the mass fraction of NO in the furnace. Reducing the volume fraction of oxygen and increasing the temperature of preheated air can stabilize the combustion and reduce the minimum reversal time. Load fluctuation has no obvious effect on the minimum reversal time. 15 s is the commendatory minimum reversal time of this kind of jacket heater.