Seek help: material selection for alkali scrubber tower
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This post was last edited by qldch2306 on 2012-9-27 09:50. Hello, experts – CCR alkali elution dechlorination tower. How should I choose the material for these operating conditions? Please give me some guidance. Thank you. Conditions: 0.021 MPaG at 425 Deg C, 1.0% WT NaOH, 241 PPM by volume of HCl, 68 PPM by volume of Cl2. It seems that using KCS would be more economical, but corrosion will occur, especially pitting corrosion. . . The corrosion allowance should be increased, and proper PWHT should be carried out. What about choosing other materials for the lining? At such high temperatures, it’s not suitable to use a lining. . . Choosing the Inconel colony will **increase** the cost. Is there a way to have the best of both worlds? Thank you all:handshake
I don’t understand the operating conditions in your case. At 425 degrees, both chlorine and hydrogen chloride are in gaseous state, right? NaOH must also be in a melted state by then. So what substances are left? Water vapor? What is KCS as well?
This post was last edited by qldch2306 on 2012-9-27 08:59. Thank you for your attention. KCS: Killed carbon steel, that is, carbon steel that has had its oxidizing agents removed. It is carbon steel, the type of steel used for pressure vessels; this equipment is the alkali washing tower of a continuous catalytic cracking regeneration unit, CCR. The alkali scrubber removes Cl– from the regenerated recycle gas through the continuous circulation and renewal of alkaline solution. The alkali washing process itself has its drawbacks: on one hand, there are issues such as uneven mixing and insufficient dechlorination, which lead to equipment corrosion and large amounts of alkaline waste being generated; this increases the costs associated with equipment maintenance and environmental cleanup ； On the other hand, the presence of saturated water increases the load on the drying unit, resulting in a high water content in the regeneration cycle gas, which affects the catalyst’s activity and service life. The process is from UOP; refer to http://wenku.baidu.com/view/f511a7d133d4b14e85246899.html. I’m not very familiar with chemical processing processes either. If carbon steel is used, the corrosion allowance should be at least 6 mm...
Based on the operating conditions you’ve provided, no other material or lining (bricks can be used as a lining option) offers better cost-effectiveness than carbon steel. However, I think you could consider using local lining solutions to address the issue of excessive corrosion. Based on your description, the corrosion at the bottom of the tower seems to be quite severe; therefore, it is a reasonable approach to apply cladding or lining made of another material at that bottom area (be sure to address the galvanic corrosion that may occur at the edges of the lining). If your tower is already in use, please share your experience with its operation or any signs of corrosion.
I am a equipment manufacturer. To be honest, I’m not familiar with the manufacturing process you mentioned, but if you want to reduce costs, you can opt for composite panels.