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The last edit to this post was made by in the blink of an eye on 2019-4-20 at 21:24. A few years ago, when in the blink of an eye visited a large sulfuric acid production plant, the manufacturer was puzzled by the phenomenon of the ceramic balls at the bottom layer cracking and becoming colored. I promptly reported the above situation to my colleagues at the US headquarters, but no reasonable explanation was given. About a year later, during a brief visit to another acid production facility using flue gas, a colleague from the factory showed me some catalyst samples from the lower part of the conversion layer; these catalysts were green in color and had scars on them. Strangely enough, the catalysts in the upper part of the conversion layer were of normal color. Further communication revealed that due to the frequent damage of the conversion preheating furnace, the temperature for heat blowing during conversion is not sufficient each time. Further investigation revealed that the ceramic balls at the bottom of the conversion layer in this acid production unit were also stained, indicating the formation of condensed acid in the lower part of the conversion layer. In severe cases, the layer of porcelain at the bottom may crack. An explanation for the aforementioned phenomenon was quickly provided, and it has been recognized by many professionals in the industry. When the heat of conversion is not sufficiently blown away for various reasons, during that short period when switching to cold blowing, the cold air containing a small amount of SO2 and O2 is heated to the ignition temperature as it passes through the upper catalyst layer, resulting in the formation of SO3; subsequently, the drop in temperature in that layer leads to the precipitation of condensed acid in the lower part of the layer. To date, as far as Tanzi knows, scarring and discoloration of the catalyst in the lower middle layer have occurred in 4 factories.