Component fluctuation issue in four-nozzle gasifier

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Two gasification furnaces are in operation; coal slurry is produced from the same coal. In Furnace A, the methane level is kept between 800 and 1000, and the composition is satisfactory. In Furnace B, the methane level was also around 800 at first, but the composition remained somewhat high – online analyses and sample tests showed that CO accounted for approximately 51% of the composition. Visually, there wasn’t severe clogging of the slag; it was only slightly stringy, and the amount of slag was quite normal； The ingredients just haven’t been good. There are no major issues with the coal quality; the coal from the lower layers is slightly inferior, but high-quality coal is used in combination with that from the lower layers as well ； The oxygen ratio at the center was kept at around 15.5%; approximately 15 m3 of coal slurry was used per burner, with an oxygen supply of 7400 Nm3/H ； After the composition deteriorated, methane levels were kept around 400. Occasionally the composition improved (but very rarely), yet both online analyses and sample tests still showed a level of 48% ； The control pressure of the gasifier is around 6.3 MPa. I would like to ask the experts: what are the reasons for poor ingredient quality?