YELLOW DEPOSIT ON TUBE BUNDLE - WHAT IS IT? 3

[BRT549]

I'm having a shell & tube heat exchanger retubed, and was inspecting the unit while the shop tore it open. There was a thin yellow coating (about 2'x2'section) on the tubes in front of the condensate discharge, along with the same coating on the inside of the shell in the same area. It looks like elemental sulfur, but that seems impossible.

We generate steam as a byproduct of burning elemental sulfur, but that shouldn't be able to traverse the H2SO4 plant, the steam plant, and the steam piping and come to rest in this particular location. Could it be a boiler water treatment chemical?

 

[kenvlach]

Add some DI water, then test w. pH paper (condensing amine should be alkaline).
Add a little acid, an H2S odor will indicate sulfur.
Add a little caustic solution, an ammonia odor may indicate an amine-type treatment chemical (usually a brown deposit, but I suppose different types).

What is the temperature at this point, and is it higher upstream. S deposition maybe not impossible.

Please post results when you have your answer.

 

[hacksaw]

BRT~

it could very well be sulfur, but how it got there is another matter. it certainly wasn't a direct path.

the only points of contact in most sulfur burning plants are the steam coils in the sulfur pit/storage tank area.

 

[TBP]

What's on the other side of this HX when it's operating?

 

[BRT549]

The other side of the HX is phosphoric acid, normally a green color.

Kenvlach - can't do the testing you suggest until I go back to the shop, which is 200 miles away.

hacksaw - interesting point about the sulfur pit steam piping. Not sure that hot condensate and liquid sulfur wouldn't react rather than pass through the condensate and boiler sections as an inert.

 

[aspearin1]

While working in a plating line, I've heard stories of ruptures steam coils actually siphoning the plating acid into the steam lines. If you have a hole in the right place, you could have an aspirating steam line sucking in your acid, liquid or vapor, depending on the location.

 

[hacksaw]

BRT

I think sulfur is relatively inert with regard to steam, we used steam to put out sulfur fires. The steam coils are the only point of contact that I could think of, even as a remote possibility.

There are alternatives associated with incomplete combustion, but the chain of simultaneous events needed to get sulfur into the steam system lacks credibility.

Having said that it is amazing what shows up in steam lines even after steam blows and years of service. Your finding just adds to the list.

 

[BRT549]

DPearcey (boiler & pressure vessel thread), your post put all the pieces of the puzzle together. Here's what's happening:

The sulfur pit is the only direct contact area with the steam system. Steam and liquid sulfur are not particularly reactive, and steam is used to put out sulfur pit fires. Sulfur is being siphoned into the steam condensate system in the pit through a small leak on the inside of an elbow. It makes it through the condensate system and bypasses the boiler since condensate is injected for desuperheat. Once in the heat exchanger, it plates out at the condensate discharge since the condensate temperature drops down there to the freezing point of sulfur.

Pretty wicked scenario, huh?

 

[hacksaw]

Awesome