Protection method for the catalyst in the conversion system in the event of a fuel gas interruption following a conversion trip. Process: includes a pre-conversion furnace, a first-stage conversion furnace, and a second-stage conversion furnace.
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After a trip in a natural gas conversion furnace, with a interruption in the fuel gas supply to the furnace, should it be purged directly with steam for 10 minutes before replacement, or should the furnace be kept insulated and sealed until the fuel gas supply is restored, after which steam can be used for purification? Principle: 1) The catalyst does not form carbon deposits. 2) The catalyst should not be soaked in water.
Whether it is direct steam purging or keeping the furnace insulated, the goal is to protect the catalyst by adhering to two principles, and in both cases nitrogen is used for displacement. .
Steam purging is used to displace NG and prevent carbon deposition at high temperatures. The sealed furnace is used to prevent the temperature from dropping below the saturation point when the furnace is shut down, which could lead to water formation; therefore, steam needs to be introduced for purging after some of the burners are re-ignited – in effect, this is to return the system to the steam-cooling phase. Carbon decomposition reactions: CH4 → C + 2H2; 2CO2 → C + CO2; CO + H2 → C + 2H2O. Data show that at the outlet of the first stage furnace in devices that use steam for purging, the temperature dropped by 130–150°C, but it did not drop to the saturation temperature of steam; therefore, there was no risk of water formation at this time. However, since there is no second stage furnace, there are no temperature data for the bed layer in the second stage furnace after steam purging. And ultimately, after releasing pressure, nitrogen is introduced to displace the steam and dry out the water. I don’t have the data for the period shortly after restarting the engine. There is a device for direct furnace sealing; after re-igniting the burner, steam is introduced to maintain a temperature of 500–550 degrees, and the furnace is purged for ten minutes. After that, the pressure is reduced below that of nitrogen, after which nitrogen is introduced for displacement, followed by gradual cooling. After restarting the operation, there was no change in system resistance nor in catalyst activity. Both methods are based on the same two principles mentioned in the title, but their process routes differ; one involves pre-conversion plus a single furnace stage. One is a two-stage furnace + a three-stage furnace. In a process route of pre-conversion + first-stage furnace + second-stage furnace, is it possible for the catalyst in the second-stage furnace to become soaked in water after direct steam purging? Steam pressure 4.4 MPa, temperature 345°C. During operation, the pressure in section 1 of the furnace is 3.1 MPA, with an outlet temperature of 740°C.