Some issues regarding the replacement purging of gasification units

Why isn’t anyone answering me?:( I hope comrades like Lao Li, xuqinger, Waimei Gong, and Tianya Langji can help me. Thank you.

All steam pipes are used for steam purging and preheating; during startup and shutdown, the coal gas pipes are drained, and it is preferable to use nitrogen for purging, allowing everything to be completed in one go

If it is a container with an access hatch, purging must be carried out until the combustible material content is ≤0.5% before work can proceed. If entry and welding are required in a certain container, air must be introduced for displacement; a satisfactory level is achieved when the oxygen content is between 19.5% and 23.5% and the combustible material content is ≤0.2%. Generally, steam is used because there are lumps inside, and steam cooking is needed to completely displace the flammable gases ； Nitrogen is used to purge containers that do not contain any solid substances! !

The gasifier is purged with nitrogen before startup, and the analyzed oxygen content is less than 0.5%； Before parking, displace CO+H2 with nitrogen at 18~21%, CO+H2

These two media are also used to purge the coal slurry and oxygen pipelines; during startup, in addition to purging, the coal slurry pipeline is also purged with the burner for 0.5 seconds. After shutting down the plant, nitrogen is also used for purging; first the slurry pipeline is purged and then the oxygen pipeline. Additionally, purging of the slurry and oxygen pipelines can be carried out when the pressure of the medium-pressure steam is 0.5 MP higher than that of the gasifier, but generally, steam is used for purging when there is no pressure in the furnace after shutdown.

1. For the purging before the gasification unit is put into operation (that is, before ignition and coal feeding), according to petrochemical standards, the combustible gas concentration should be ≤0.5% (V) and the oxygen concentration should be ≤0.5% (V). Shell’s gasification standards require an oxygen concentration of ≤1.0% (V) to allow the start-up sequence to proceed; no specific limit is specified for combustible gases, but a three-stage pressure adjustment purging procedure is in place, and the resulting concentrations meet the petrochemical standards. The same is true for the shutdown process. 2. The gas source used for purging and displacement is generally high-purity nitrogen, and the gas used in the gasification furnace should have a pressure that is at least 0.5 MPa higher than the normal operating pressure of the furnace. 3. As for steam, its role in the dry coal powder gasification process is likely to be limited to purging purposes; it cannot be used in coal powder preparation, pressurized transportation, or the dry ash system due to the sensitivity of these processes to water. In wet gasification, oxygen is the only gas that is used in the short tubes leading to the burners. Long-distance transmission lines are not used due to expansion and condensate issues. 4. The slag water pipeline was of course flushed with clean water.

The criteria for acceptance of replacements were clearly explained by everyone upstairs. Regarding the purging of the oxygen and slurry pipelines in the water-coal slurry gasifier: after purging, a small flow of nitrogen is used to purge the oxygen pipeline, and there should be no issues behind the second valve. A nitrogen plug is formed between valve 1 and valve 2; if the logic timing specifies that valve 2 should be closed immediately after shutdown, then there will still be oxygen present (a slight leak from valve 1 won’t have any significant impact) ； There is basically oxygen in front of the valve, so some manufacturers implement an oxygen-nitrogen pressure relief procedure ； Nitrogen purging of the slurry pipeline is primarily aimed at preventing blockages in the slurry pipes, and there are no specific criteria for determining when this should be done. After parking, it is advisable to verify whether the slurry pipeline purging has been carried out, to prevent failure in purging due to a stuck check valve.

The purging of the gasification system (gasifier, water scrubber tower) can be carried out by using an inert gas simultaneously from both the process burner and the quench chamber of the gasifier. Samples can be taken for analysis from the syngas vent line (the closer to the flare, the better, or directly from the flare water seal tank), until the oxygen content (for startup purging) or the combustible gas content (CO + H2) is less than 0.5% (V); at this point, the purging can be considered complete.

Now, many factories set the standard at 0.5%, referring to the oxygen content and the amount of flammable gases – those are the two key factors. For purging, low-pressure nitrogen NGB is generally used, while for cleaning, medium-pressure nitrogen NGM is used. Well, a mixture of medium- and low-pressure nitrogen can also be used, which makes the process faster. In our factory, steam is only used at the furnace head, as well as to clean the coal slurry and oxygen pipelines after the gasifier is shut down

This post was last edited by bob1bob2 on 2018-7-30 at 16:48. May I ask the teacher if there are any relevant materials? Thank you

Generally, steam is used because there are lumps inside, and steam cooking is needed to completely displace the flammable gases； Nitrogen is used to purge containers that do not contain any solid substances! !