Problems with oxygen content and flue gas temperature in boilers

Still, it’s not clear from this – we usually keep the oxygen content in the flue gas at around 13% (for coal combustion)

There must be a reason for such a large change in the exhaust temperature. It’s not clear what changes have taken place on site, so it’s difficult to analyze; I’ll just explain it briefly

Gas boiler, standard oxygen content of 3.5%. Of course, the lower the value, the closer it is to 0%, and the higher the CO level becomes. While ensuring that CO levels do not exceed the allowable limits, a lower oxygen content results in less flue gas loss, thereby improving the boiler’s efficiency.

Is a low oxygen content in flue gas not a safety hazard? Could gas accumulate and cause a deflagration when the load is increased? We use gas boilers, and the flue gas temperature is low; I think this is related to the composition of the gas, as the gas we use is waste gas from our factory, and its calorific value is only around that of natural gas!

There is a direct relationship between flue gas temperature and heat exchange efficiency

From a safety perspective, the low oxygen content and the fact that the combustible gases in the flue gas are within the safe oxygen concentration range make it unlikely for combustion or explosion accidents to occur

What is the safe oxygen concentration range?

The oxygen content cannot be any lower, as lower levels result in incomplete combustion, the production of carbon monoxide, and a risk of explosion. If the fuel (composition) remains unchanged, the furnace tube may be leaking.

1. Was 170 originally powered by coal? If other factors, such as changes in usage load, are not taken into account. Is the boiler operating properly? 100°C for gas exhaust smoke is quite normal. Operating at low load with additional rear-end energy-saving equipment, achieving an efficiency of around 95%. If it was 170 for gas, it means the burner wasn’t adjusted properly. Waste gas! So it’s a good thing that the temperature drops. But I’m not sure if you have dealt with the condensation corrosion issue at around 100°C. 2. The oxygen content should not be too low. The low oxygen level is a condition in which CO is close to zero. If it’s too low, combustion will be incomplete and the exhaust gas will contain CO; generally, 2% is a sufficient minimum level. Regarding the current environmental situation, the oxygen content should not be too high either; 1. Oxygen-enriched combustion will inevitably lead to an increase in the excess air coefficient. It is not conducive to energy conservation, and 2NOx emissions will exceed the limits. As long as the NOx emissions are below 80 (with the exception of the Beijing-Tianjin-Hebei region, where the requirement is 30; it seems that the NO levels measured in the flue gas are calculated based on the oxygen content), the oxygen content in the exhaust gas should be below 6%. So the parameters of 3-6% provided by the boiler factory are fine. At least 2% is more or less sufficient. As for deflagration, the maximum number of ignitions that can occur at this oxygen content is... Increasing the load should be no problem. It's just my personal opinion; if there are any mistakes, I hope experts can point them out so we can learn together*

A flue gas exhaust temperature of 100°C is quite normal; the previous exhaust temperature of 170°C was likely due to the combined effect of heat exchange and the fuel used. The oxygen content in the flue gases should be kept around 3% – it shouldn’t be too low, as this can affect CO formation, nor too high, as this can impact the calculation of NOx levels