How to reduce the CO content in flue gas
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The oxygen level is normal; how can carbon monoxide levels be reduced? High levels cause black smoke
These two indicators are contradictory to each other: as the oxygen level increases and ventilation improves, the CO level necessarily decreases, and vice versa. Therefore, on-site, one can only rely on the data displayed by the DCS system. The CO level is usually measured directly, and by comparing these two values, the optimal control parameters can be determined. Generally, the oxygen level should be kept around 2%, while the CO level should be close to 0; too low a CO level makes it difficult to operate properly
The increase in CO levels is mainly due to combustion issues; it is necessary to optimize combustion in order to improve the burning rate of the fuel within the furnace and prevent unburned carbon from transferring heat to the heated surfaces – whereas under normal conditions, it should be the flue gas that transfers heat. By monitoring the changes in oxygen and CO levels as indicated by the DCS, an appropriate oxygen level can be determined through optimizing the ratio of air to fuel, thereby keeping CO levels below the specified values.
When designing this plant, the relevant quantities must have been calculated carefully. In my case, it’s a 40T gas boiler; at full load, it consumes 3659 m3/h of gas under standard conditions. The air intake volume of the blower is around 42221 m3/h. Based on simulations, the amount of air required for complete combustion is less than 30000 m3/h. The excess air is used to reduce the flue gas temperature. Under these conditions, there is almost no CO in the flue gas; its components are N2, O2, CO2, and H2O, listed in order of concentration, with other components being negligible
The 10-ton gas boiler does not have any online flue gas monitoring; instruments are used only during adjustments. The oxygen level cannot be reduced too much, staying around 5. Currently, by increasing the air supply, the oxygen level rises, but the carbon monoxide level hardly decreases. The oxygen level can no longer be increased any further
Is there online monitoring for 40 tons, and is the CO level zero?
An online monitoring system needs to be purchased separately. I’m in Hangzhou, and a set of such monitoring equipment costs over 300,000 yuan – it’s practically extortionate. So at the moment I really don’t know what the CO level in the flue gas is. However, the air flow rate is definitely high enough; the minimum required level ensures complete combustion, so the CO level should not be very high. What needs attention is nitrogen oxides and sulfur-containing flue gas
Isn’t it about adjusting the frequency of the blower fan? There’s also a air-fuel ratio, and this ratio needs to be maintained so as to ensure complete combustion; it shouldn’t be too high nor too low, but complete combustion must be guaranteed