Will the reactor overheat if the methanation cycle gas compressor is shut down?
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I would appreciate some guidance: If the methanation cycle gas compressor stops operating and the feed gas is cut off, will the reaction continue, causing the reactor to overheat?
When the circulator trips and feeding is stopped, the reactor temperature will not rise excessively. No feed gas enters, so there is no reaction and therefore no temperature rise. I’ve encountered it several times. Once the circulator trips, the gas supply must be cut off; otherwise, overheating is inevitable.
Thank you so much! It should be interlock gas cut-off
We have discussed this issue in detail in the design of methanation for coal-to-natural gas production; the temperature continues to rise even after the inlet and outlet are closed, as there is no dilution by recycled gas. The carbon content in coal-derived gas is over 20%, while that in coke oven gas is around 12%. The adiabatic temperature rise is about 60 degrees per 1% CO, and about 74°C per 1% CO2. Temperature control in the methane processing unit is primarily achieved through compressors. When the recycle gas compressor fails, it is necessary to shut down the methane processing unit urgently; interlocks are used to cut off the raw material gas entering the unit as well as to stop the export of its products. If the temperature continues to rise, steam must be introduced into the system to bring it under control. Staying above the design temperature for too long can cause sintering damage to the catalyst. For your reference only; it may not be comprehensive~
You explained the comparisons in detail; thank you very much. It would be problematic if there were no water vapor in the system. Would reducing the system’s pressure be useful?
Reducing pressure increases the risk of overheating; if pressure is released from the rear end of the unit, a large volume of gas will flow into the methanation bed, resulting in an increased catalyst space velocity and thus a higher load. Whether to use steam or not depends on the degree of overheating. Is it coke oven gas or coal-derived gas?
There is no high-pressure steam in the current boundary conditions
What I mean is, when the feed gas is cut off and the pressure in the system drops, could a higher space velocity help to carry away the heat, given that the amount of gas in the reactor is limited?
In my opinion, such pressure relief will exacerbate overheating. If the feed gas supply is cut off after the ultra-pure purifier, the risk of overheating is reduced; however, it remains dangerous if the cut-off occurs before the ultra-pure purifier. The amount of gas in the reactor is limited, but the temperature can exceed the catalyst’s tolerance level in a short time, causing the grains of active metal on the catalyst to grow and resulting in irreversible loss of activity. In foreign methaneation technologies, water vapor is also used under such operating conditions; I’m not sure why it’s not used here. At the moment, I can’t think of any better solution. The best approach at this point is to dilute the reactants, as this reduces the carbon concentration and lessens the reaction load. However, I believe that releasing pressure at this time carries a high risk; if the temperature isn’t too high, it’s also possible to allow the bed temperature to drop gradually.