LP Deposits

Dan Law

Have had several findings of gray/blue/green flaky deposits on the
surface of copper finned heat exchangers on low mass boilers over the past 2 - 3
years. All sites utilize vaporizers. These tend to be
boilers in the 1,000,000 - 2,000,000 input range, and span across different
manufactures. We (and the mfg.) have had fuel samples analyzed, and received
mixed reports indicating high sulfur content. On further investigation, the
consensus seems to be the most likely source of excess sulfur would be the
ordorant mercaptan. If caught early enough the deposits can be removed by
brushing and
blowing out. If left unattended, the deposits gradually occlude the passages
between the fin spacing eventually causing incomplete combustion. In the
worst cases sooting, flame roll out and control wiring burnt. Some have even
destroyed burners from excess heat.
I see the "deposits" more as the results of accelerated corrosion, rather than a
direct by product of combustion itself. Plenty of combustion air avaiable in all cases. If you consider the chemistry involved
(sulfur, heat, copper, possibly some condensation) seems to me all the elements
are there for oxidation of the copper surfaces. (a chemist or metalurgist, I'm not!) The blue/green tint to the flaky
material leads me in this direction.
I have a theory on the concentration of
mercaptan, but would like to know if any other wallies have found this, and any
resolution they found. Thanks in advance for responses.

Dan

Duncan

Concentration of mercaptan.

I've been told by my propane friends that mercaptan is concentrated in the gas as you get to the last of the propane in the tank.

Ever notice how much stronger that odor is with a near-empty tank?

Gary Fereday

Years past

I have also seen this stuff. Natural gas here in the state of Utah. Gas here has a sulpher content. I think your staterment "The blue/green tint to the flaky material leads me in this direction. I have a theory on the concentration of mercaptan." is perhaps correct. our gas here contains the mercaptan, also. And you are correct it does destroy the fin tube over time.
Bigugh

[Deleted User]

Blue/Green scale...

I've seen this on Nat Gas and LP copper fin tube boilers of ALL sizes. In one case, it was extremely bad, and oddly enough, there was a commercial laundry in the same room as the boilers. It has to do with the chlorine going into suspension in the air that's being combusted. Just the wash action of the wash wheel was enough to cause the chlorine to go into a mist state. The boiler heat exchanger looked like Swiss cheese.

ALso, if it is located anywhere near bromine tablets, they'll do the same thing.

I think it has more to do with condensation in areas where you're assured of no ambient contamination. It shows more on CFT boilers used in the production of hot water, where the heat exchanger is commonly drawn down to a cold temperature through the introduction of incoming cold water during peak demands.

Before the use of fluorocarbon propellants were outlawed, they could turn a heat exchanger into mush in the blink of an eye, to say nothing of the nasty gasses they produced due to combustion.

I've seen the green fur on both DHW and SH boilers. I think it's the nature of the beast.

ME

Arthur

L.P.Deposits

Got called to a natural gas Ray Pac swimming pool heater last year and found it coked up. The heater was not in the immediate
area of the chlorine plant, We had quite a job cleaning it out The owner said it did this periodicly. Later I found an article on the net which indicated that there was probably too hi a Delta T between the flow and return temperature to the pool. This apparantely caused too much cooling of the flame and resulted in a soot build up.
I had not come across this before so I printed the article and sent it to the client with my a/c.

Boilerpro_2

I've seen it also

> I have also seen this stuff. Natural gas here in

> the state of Utah. Gas here has a sulpher

> content. I think your staterment "The blue/green

> tint to the flaky material leads me in this

> direction. I have a theory on the concentration

> of mercaptan." is perhaps correct. our gas here

> contains the mercaptan, also. And you are correct

> it does destroy the fin tube over time. Bigugh

Boilerpro_2

I've seen it also

Tends to be most concentrated on the tubes that are closest to the return.....indicating condensation. Just repiped one with a system bypass to bump the boiler temp up some. Also found the B-vent was coated with white powder and there was some rusting at the vent connection. Beginning tho think the claims about lower operating temperatures being permitted on copper tube versus cast iron are unfounded...especially since Dunkirk allows return temps down to 117F for their boilers.

Boilerpro

Glen

Have you --

taken a sample - mixed it with water and tested its pH?

Mike Kusiak

White flaky deposits

I have also seen the white powder buildup with natural gas on cast iron heat exchangers, especially right above the pilot burner, where the pilot burns year round. The material seems very caustic, as when I have gotten it on my hands, it caused burning and cracking of the skin. I dont doubt it would be very corrosive in combination with condensation.

Dan Law

What do guys you think......

about this theory: This goes more to a refrigeration concept, but relates. If we
think about the vaporizer in terms of being a type of evaporator, similar to any
refrigeration system, seems to me it's possible that:
LP from the storage vessel is drawn into the vaporizer with a mercaptan
concentration of "X". As the vaporizer performs it's intended function, the LP
vaporizes, but the mercaptan (with a different vaporization temp / pressure) does not, and accumulates in the vaporizer vessel as a liquid. It then follows
that additional LP from the tanks enters at concentration "X", comes in contact
with the warmed liquid mercaptan previously "distilled" out, and absorbs more of it so
that it leaves the vaporizer @ concentration "X + y". In effect
we've created a secondary, on site mercaptan injection system. I'm told the
mercaptan % on original application @ the plant is quite low, that is to say not
at a saturation level. This would make me think the LP was capable of absorbing
more if exposed to it. Over time it seems you could get LP at saturated mercaptan levels, therefore high in sulfur content. I'm planning on taking more samples for analysis -
one before the vaporizer and one after, and comparing sulfur levels. If it's higher
in the second, I have no other explanation.
Thoughts?