Weekly Topic on Ammonia Synthesis: Key operational points and precautions for replacing the convective section coils in a single-stage furnace 17/10/2011
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This post was last edited by shfuchenko on 2011-10-16 at 22:15. Weekly topic: Key points and precautions for replacing the convective section coils in a single-pass furnace. The function of the convective section coils in a single-pass furnace is to preheat various process media and recover heat from the flue gases. If a certain set of coils (the coils in the middle of the convection section, or the coils for process gas or process air) are exposed to excessive temperatures for an extended period, their service life has been reached. How to replace this set of coils during major maintenance, brief replacement steps. And the precautions during the replacement process. Extra points will be given as appropriate depending on the completeness of the answers. Thank you for participating!
Everyone, please participate actively and share your valuable insights
The feed gas coils in our facility often experience overheating during startup, as do the boiler feed water coils. I haven’t encountered a situation where a replacement was needed yet. What comes to mind is that during major parking repairs, it’s essential to ensure that the furnace interior is properly flushed with air, and the security department needs to monitor the oxygen level at all times – safety issues must be taken seriously. Also, given that the gap between the coils is relatively small, be careful not to damage other coils when replacing them. Looking forward to discussions from experts.
Close the main valve in front of PV206, open the bypass valves for PRC206 and PRC208, open the vent valve from the furnace top to the flare for discharge, and open the nitrogen supply valve in front of PV206 to fill it with nitrogen in order to carry out N2 purging. The purging is considered complete when the combustible gas concentration is less than 0.2% (vol); thereafter, close the N2 valve and the flare vent valve, and relieve pressure at the high-point vents and drain points. When there is N2 venting, be sure to take precautions against N2 asphyxiation.
When a set of coils has poor heat exchange efficiency and is at the end of its service life, we need to replace that set of coils. The hardest part of replacement is how to remove it from the convection section; generally, it is cut in the middle and pulled out from both ends. The pulling process must be done slowly, and care must be taken to protect the upper and lower coil assemblies so as to prevent them from being damaged by gravity. The steps for replacement are: removal, replacement, welding, hydrostatic testing, purging, etc. Precautions: 1. Protect other coil assemblies ； 2. Online cutting and removal of main welding slag ； 3. Issues related to water drainage during pressure testing, to prevent water from entering the furnace; a specialized pressure testing plan is required ； 4. During purging, a customized plan is required, and a purging process must be established on a single end ； 5. During the replacement process, impurities and insulation material may be blown onto other coil groups; be sure to clean them up. Personal opinion, for reference only
Not necessarily. I have seen the entire convection section coil assembly being replaced, with the whole set of coils being manufactured in the factory, followed by the pouring of refractory material and drying. This can reduce the amount of work on site, ensuring the project timeline and welding quality.
It’s modular; as we know, typical top-fired furnaces are modular, which is quite convenient. The side burner won’t work