Medium-pressure steam purging
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Nitrogen and steam purge valves: Similar to the slurry pipelines, the oxygen pipelines also require high-pressure nitrogen and medium-pressure steam purge valves. These valves are used to ensure that, when the gasifier is shut down or stops operating due to a fault, the oxygen feed shut-off valve closes simultaneously, while the high-pressure nitrogen purge valve opens immediately to purge the oxygen pipelines and the process burners. Additionally, high-pressure nitrogen sealing valves are activated to seal the area between the two oxygen shut-off valves, thereby preventing oxygen from entering the gasifier. Once the pressure inside the furnace drops below 2.0 MPa, open the medium-pressure steam purge valve to further purge the oxygen pipeline and the process burners. Is it possible to avoid purging with medium-pressure steam?
Once the pressure inside the furnace drops below 2.0 MPa, open the medium-pressure steam purge valve to further purge the oxygen pipeline and the process burners. Is it possible to avoid purging with medium-pressure steam? The pressure limit inside the furnace during steam purging is set based on the pressure of the medium-pressure steam; generally, the furnace pressure can be 0.5 MPA lower than the pressure of the purging steam in order to carry out burner purging operations. In my opinion, steam purging is absolutely necessary: right after the plant is shut down, although it has been purged with high-pressure nitrogen, the pressure inside the gasification furnace remains high. The fly ash in the furnace can then flow back into the oxygen and coal slurry pipelines. Furthermore, thoroughly cleaning the coal slurry pipelines and burners of any remaining coal slurry creates favorable conditions for the next startup. At present, steam purging is still mostly done manually; in our plant, it is only carried out when the burners are removed during maintenance. It is best to perform purging again once the burners are reconnected before starting up, in order to prevent debris from entering the pipelines and burners during the shutdown period!
It is necessary to, 1) prevent fly ash from flowing back into the oxygen and coal slurry pipelines, and 2) prevent oily substances from contaminating the oxygen pipelines.
In this case, it is generally not necessary to use medium-pressure steam for purging!
After the gasification furnace is shut down, medium-pressure steam is used for purging when the system pressure is lower than the steam pressure; this method results in a cleaner purge compared to using nitrogen. However, using steam causes the furnace temperature to drop rapidly, and it is difficult to control this rate of temperature drop, so this method is generally not used. Please point out if there is anything wrong.
It is necessary to have high-pressure nitrogen as a backup purge gas source; it is generated by compressing medium- and low-pressure nitrogen using a nitrogen compressor. But I don’t think I’ve heard of high-pressure nitrogen being used in interlock systems Moreover, nitrogen compressors are gasification-related mechanical devices that do not draw air from the public pipeline system. So in the event that a nitrogen compressor fails and the gasification furnace has to be shut down until it is repaired, shall one then bend down and blow air into it?