Changes in gas composition
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Our gasifier uses water-coal slurry; the ash melting point is normally around 1250°. Due to frequent interruptions in the supply of limestone, which meant it couldn’t be added in the required amount and at the right time, the ash melting point rose to around 1430°. As a result, the CO level increased to about 37%, while the CO2 level peaked at 29%. When the oxygen level drops to 430, CO increases by at most one or two units, while CO2 decreases by one or two units as well. There isn’t much of an effect. On the contrary, increasing the oxygen-to-coal ratio raises CO levels, but CO2 levels do not decrease. The ash content of our coal is around 28; 3% limestone is added to the grinder as well, the internal moisture content is 0.9%, and the volatile matter content is around 12. Could the seniors please analyze the reasons? The pressure difference at the burner is also fluctuating, ranging from a minimum of 0.15 MPa to a maximum of 0.75 MPa. The taphole pressure difference is sometimes negative.
Is the taphole pressure difference sometimes negative? It can’t be a gauge issue! It might be that the pressure sampling point is a bit blocked.
“Around 37% for CO, and 29% for CO2 – this is totally abnormal. CO should be between 50-60, and CO2 will not exceed 10%. Personally, I think there’s something wrong with the oxygen-coal ratio. It seems to be in the range of around 470-550. Theoretical analysis shows that CO2 has not been reduced. In other words, the heat required for reduction might not be sufficient. The optimal vaporization conditions may not have been achieved. Also, first check your instruments to see if there are any problems. This is very important!
This post was last edited by huaguiyi on 2011-5-4 09:27. 1. Could you please provide the parameters under normal operating conditions for your system: such as slurry concentration, fixed carbon content, oxygen-to-slurry ratio, gasification pressure, and composition of the process gas? 2. The internal moisture content of your coal is 0.9% (the slurry concentration should be high), and the volatile matter content is 12% (can this type of coal be used for water-coal slurry gasification? It’s not easy to burn). Additionally, it’s necessary to take into account the carbon residue analysis of both the coarse and fine slag. Generally, a high CO2 content indicates peroxides, or that the gas has stayed in the furnace for a short time.
Thank you all for your answers. For normal operation, the slurry concentration should be above 65%, and the oxygen-to-coal ratio should be around 480. The pressure is around 6.0 MPa. In terms of the gas composition, OC is around 42, OC2 is around 20, H2 is around 37, and CH4 is between 500 and 1000 PPM.
I’ve learned it! It is recommended to lower the ash melting point first. Otherwise, operating at high temperatures causes severe damage to refractory bricks and similar materials. If the ash fusion temperature doesn’t decrease, the furnace temperature can’t keep up, and abnormal gas composition is inevitable!