Gas head: Regeneration treatment after carbon deposition in the conversion catalyst

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Regeneration treatment after carbon deposition: (1) Mild carbon deposition: When the conversion catalyst experiences mild carbon deposition, the deposited carbon can be removed by reducing the load and increasing the water-to-carbon ratio, that is, by using steam to remove the carbon in a reducing atmosphere. The load is usually reduced to about 30% of the normal level; the amount of water vapor used remains unchanged, resulting in a water-to-carbon ratio of around 10. Where conditions permit, a reducing gas can also be added to achieve a water-to-hydrogen ratio of approximately 10. The normal operating temperature is maintained in order to eliminate carbon deposits, and during this process the conversion catalyst remains in a reduced state. During the carbon removal process, it is necessary to identify and eliminate the causes of minor carbon deposition, such as the purification efficiency of the feed gas, the reduction state of the catalyst in the inlet section, and the content of high-carbon hydrocarbons in the feed gas. Normal operation can only be resumed after the sources causing carbon deposition have been eliminated and all carbon buildup has been removed. It should be noted that mild carbon deposition, if not addressed promptly, can easily worsen, so care must not be taken lightly. (2) Severe carbon deposition: When carbon deposition is severe enough to cause significant changes in resistance and an obvious uneven distribution across all the conversion tubes in the furnace, it is necessary to carry out carbon burning operations promptly, that is, by using steam for carbon burning. First, the raw natural gas or light oil should be removed immediately; the steam volume is usually 30–40% of that in normal operation, the system pressure is controlled at around 0.98 MPa, and the temperature must be strictly controlled (it should be lower than the temperature during normal operation). The CO2 concentration in the exhaust gas at the outlet should be analyzed every half hour. When this concentration drops and stabilizes at a low level, it can be considered that the carbon burning process is essentially complete. However, it is necessary to pay attention to observing the temperature distribution on the outer wall of the conversion tube; only when the temperature on the outer wall of the tube becomes uniformly consistent can it be considered that the carbon burning process is truly complete. (3) Air combustion of carbon can also be used; it generates a large amount of heat and leads to intense reactions, which cause significant damage to both the conversion catalyst and the conversion tubes. Therefore, it is generally not advisable to use this method. However, if carbon deposition is severe and heating the carbon with steam does not yield the desired results, a small amount of air can be mixed into the steam, typically 2% to 4% of the steam volume. In such cases, it is essential to prevent overheating; air supply should be stopped once the CO2 level at the outlet drops to around 0.1% and the temperature of the outer wall of the conversion tube becomes relatively uniform. After stopping the introduction of air, steam should be introduced for about half an hour to completely displace the air from the system, thereby preventing accidents when it is put back into operation. (4) After carbon burning, the catalyst must be reduced again in accordance with regulations before it can be put back into normal operation. Similarly, before putting it back into operation after carbon burning, the root cause of carbon deposition should be eliminated. It should be noted that carbon burning has a significant impact on both the performance of the conversion catalyst and the lifespan of the conversion tubes; it is a measure taken as a last resort when dealing with carbon burning incidents, and every effort should be made to avoid its use.