September 9, 2010 at 9:17 am #2541
Once again in my pursuit of best practices, I am wondering what others are doing with regards to “heat soaking” their air sweep eductors and offgas piping. We use a single 70# steam powered venturi eductor to air sweep our sulfur pit. The off gass piping to and from the eductor is steam jacketed also at 70# nominal. The gases are routed directly to an incinerator for destruction. Occasionally we will experience a drop in offgas flow and perfrom a “heat soak”, where we turn off the eductor motive steam and let the piping and eductor “soak” in the jacketing steam. This seems to restore capacity, but I am not exactly sure what we are melting out of the system. So the questions:
Do others in industry experience similar issues with offgas removal/control?
Is there a Best Practice, ie two eductors in parallel, or two offgas lines in parallel?
Does anyone know for certain what the heat soak is accomplishing, ie where the fouling is forming that the soak removes?
Is there a better practice than air sweeping the vapor space of the sulfur pits?
November 4, 2010 at 6:17 pm #5423
The drop in gas flow is likely due to sulfur crystals forming in line since you are able to ‘heat soak’ the problem away. This means that it is a heat loss problem so I would check all of the steam traps for all piping from the pit to the incinerator. Steam jacketing (or contro trace) of the inlet sweep air lines to ‘pre-heat’ the air is a sound idea. Also, CSI can custom steam jacket the eductors which is an excellent idea. Nobody ever checks steam traps so there is very high chance for these lines to get totally corroded out. you will see total failure when steam starts crossing over and backing into the pit and coming out of the look boxes. I have seen lines completely corroded from this phenomena.
November 10, 2010 at 12:01 pm #5413
SRE- Thanks for the response and welcome to Sulfur Unit! The steam jacketing as you mention is a good place to start troubleshooting. I would like to install wireless trap monitors on my sulfur equipment to detect an immediate loss of trap function rather than having to wait until I have a problem. Unfortuntately, our infrastructure isn’t ready for wireless yet.
The eductors we use are fully steam jacketed, as is the inlet and outlet piping. This leads me to believe the fouling is actually in the eductor nozzle rather than the piping. We still use 70# saturated (or super saturated at times) steam for the motive force. I’ve heard from wiser sources that medium (~150#) pressure superheated steam is recommended for eductors.
One interesting thing our operators discovered was what they call a “Turbo Boost” of the eductor. When performance drops, they would turn off the motive steam for a minute or so and then quickly crank it all the way open. This would help restore some of the lost eductive flow.
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