How to determine the appropriate air supply for an exhaust gas furnace?
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According to the operating procedures, it is better for the exhaust furnace to have a smaller size – the smaller, the better? How to find this balance
Of course, the furnace temperature is the primary parameter to be controlled; by adjusting the flow rates of air and fuel gas as well as the furnace temperature, the oxygen content in the flue gases is generally kept around 3%, thereby achieving more efficient use of fuel gas.
The operating range of the tail furnace is generally quite wide; a range of 500-700 is considered normal, as a wider range would be unusual. An oxygen content of 2-6 is a good figure, but our oxygen level is measured inside the chimney, and it seems to be different from that behind the furnace. Moreover, is it really appropriate to control the oxygen content solely by adjusting the air supply to the tail furnace? The air supply for the sulfur production furnace also needs to be taken into account, right? Also, what is the typical oxygen content in your tail furnace under full load?
Our control parameters are also relatively relaxed, with the oxygen content controlled at around 3. The exhaust gas temperature is around 330, and the air volume needs to be adjusted based on the superheated steam temperature as well.
Generally, the air supply is adjusted to maintain an oxygen concentration of 2-4% in the flue gas; if the oxygen level is too low, the sulfur compounds in the flue gas do not burn completely, while if the oxygen level is too high, energy consumption increases； The sulfur dioxide concentration in the flue gas is adjusted based on an oxygen content of 6%, in order to avoid artificially reducing the sulfur dioxide emission concentration in the flue gas by introducing excessive air.
The furnace temperature should not be lower than 550. If air is introduced to the furnace in segments, then the air supply for the furnace head can be calculated based on the equivalent or even sub-equivalent amount of gas, with additional air from the rear supplying oxygen. If steam superheating or exhaust gas heat exchange follows, the amount of gas must be adjusted according to the process requirements. No matter how it is combined, the oxygen level in the flue gas should be 2-4%. Raising the furnace temperature helps to reduce CO in the flue gas.
A furnace temperature of no less than 535°C is necessary to ensure that the purified exhaust gases and fuel gas can burn completely. Proper air supply is required, and this is closely related to the opening degree of the flue gas dampers. On one hand, it is necessary to adjust the flue gas dampers to an appropriate opening degree in order to reduce the air velocity in the furnace, thereby enabling thorough reaction within the furnace chamber; on the other hand, it is important to maintain a furnace temperature above 535°C.