【Weekly Topic】Material selection for process pipelines under this operating condition
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In all stages ranging from coal gasification to gas conversion, there are pipelines carrying media such as wet crude gas, conversion gas, flash vapor, stripping gas, and conversion condensate. During the coal gasification process, corrosive substances like H2S and HCl are inevitably generated in the gas. Please list the material choices used for these process pipelines in various installations, as well as their actual use in production; those who participate will receive a generous reward! :lol
Regarding the material of the coarse coal gas pipelines used in the gasification to conversion process, the properties of the coal are an important factor to consider. If the chlorine content in the coal is low while the sulfur content is high, then austenitic stainless steel, which is more expensive, can also be used; alternatively, 20G with an increased wall thickness can be employed； If the chlorine content is high, it is best to use 20G with an increased wall thickness. A purified transformation gas pipeline delivered from the transformation unit. Since chlorine is essentially washed away in the vaporization unit, there is little to no chlorine left in the shifted gas. Additionally, the shifted gas exiting the shift unit has a temperature of below 40°C and contains a certain amount of sulfur, so austenitic material is generally used for this section of piping. As for the vaporization and flashing pipelines, flash vapor is inherently corrosive, so austenitic materials should be used. However, considering cost factors, and given that these pipelines are relatively large in diameter and operate at low pressures, carbon steel with increased wall thickness is generally employed. Conversion condensate is corrosive and contains high levels of ammonia; therefore, austenitic material pipes are typically used for such applications. I’m not sure if the above statements are correct; I hope they can be corrected by those who are experienced at sea, so as to help improve things
Generally, this type of pipeline is designed to be made of stainless steel, but during use corrosion, cracks at the welds, and thinning of the pipe walls occur. We later switched to 15GrMo material; I’m not sure if other companies have encountered similar problems.
Such a situation has never occurred. In the two gasification units I’ve worked with, the pipelines for transporting the raw coal gas after conversion were all 20G in diameter, and they have been in good working condition without any problems.
What about the quality of coal used? Also, is there any information in the process package regarding the chloride ion content in the raw gas?
The process package provider must provide the design unit with a chlorine balance calculation; this calculation is not included in the process package. As the client/owner, they may not be aware of this, but the design team and the technology transfer party are required to carry out such a calculation.
That’s right; it is now the process suppliers who are causing confusion regarding material selection due to the chloride ion content in these process pipeline equipment!
Confused about chloride content? What’s going on.....:L
It is that the chloride ion content specified in the process package exceeds the allowable limit for the stainless steel material used.
Everyone can list the material choices for the relevant pipelines used in the wet fluidized bed gasification of Shenfu coal.