Lower smoke exhaust temperature and oxygen content are not necessarily better
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During the inspection of heating furnaces, some companies, in an attempt to improve their thermal efficiency, have their operators keep the oxygen level below 1%, thereby reducing the exhaust gas temperature by about 30 degrees compared to normal operation. This approach is highly unreasonable; it not only leads to fuel waste but may also cause severe corrosion due to low-temperature dew points, **shortening the operational lifespan of the furnace. The first refinery pilot furnace of Sinopec, the high-pressure/low-pressure unit at Takahashi Petrochemical, is an example of this: not long after it began operating, all the heat pipes corroded, resulting in significant losses. Energy savings must not come at the cost of damaging the equipment; in such cases, it is better to abandon the pursuit of energy savings.
Reply to 1# Su Zhengrong: You’re right; lower exhaust gas temperatures and oxygen levels aren’t necessarily better. Let’s analyze each of them separately. Regarding oxygen levels, it’s essential to ensure complete combustion of the fuel; otherwise, a significant amount of the fuel’s calorific value is lost, and backburning may occur in the convection section. However, higher oxygen levels aren’t either ideal. For gaseous fuels, an excess air ratio of 1.05–1.15 times the theoretical combustion air amount is appropriate. Regarding the exhaust gas temperature, it is necessary to determine separately the water vapor dew point and the sulfur corrosion dew point. Once these two temperatures are known, the operating temperature should be 20-30 degrees higher than the highest of these two dew point values. The information above is for reference only.
Revise what was said above: when the oxygen content is high, combustion may occur again after the convection stage; this is known as secondary combustion, and it can damage the equipment.