Discussion on Shell gasifier temperature issues?
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This post was last edited by lflsedin on 2017-1-11 21:56. In Shell gasification, why does the furnace temperature rise when the carrier gas for the coal powder is changed from nitrogen to carbon dioxide?
Because during the transition between the two media, changes in the amount of coal fed into the furnace lead to variations in the oxygen-to-coal ratio, which in turn results in changes in the operating temperature of the furnace. A uniform transition like this is needed to reduce fluctuations.
I haven’t conducted a specific analysis, but I can offer a direction: 1. After switching from nitrogen to carbon dioxide, if all other conditions in the furnace remain unchanged, check the specific heats of nitrogen and carbon dioxide to see whether that of carbon dioxide is lower. 2. Consider whether reactions occur when carbon dioxide enters the gasifier, what reactions take place, and whether they are exothermic reactions.
When the carrier gas flow is reduced, the densitometer indicates a higher density, which leads to an overestimated flow rate. As a result, the operator reduces the amount of coal used; the actual amount of coal is thus lower, the oxygen-to-coal ratio increases, and consequently the furnace temperature rises
I agree with the view expressed above. Additionally, differences in impurities such as water content in N2 and CO2 can also lead to changes in density and thus in flow rate; therefore, the switching process is usually carried out gradually. Nowadays, most manufacturers have established different functional settings based on the characteristics of these two types of gas, ensuring consistency in the data before and after switching, which facilitates operation for the technicians.
In a nitrogen environment where the densitometer is actually calibrated to 341, the density of CO2 is 536. The time setting of the compensation formula is inappropriate, resulting in an artificially high density of the coal powder and an actually higher oxygen-to-coal ratio!