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MJCronin, One question you asked in passing hasn't been addressed: why do gas-fired combined cycle plants emit less carbon dioxide? Two answers: 1. Natural gas contains a much higher percentage of hydrogen and lower percentage of carbon than the other usual fossil fuels, coal and oil...

wynn, I followed up on this with the American Galvanizers Association (www.galvanizeit.org) and received the following: "There is typically not a problem with galvanized surfaces in contact with concrete for many decades. There may be some reactions between the galvanized steel and the...

WYNN, You misunderstood my comments - I was talking about galvanized steel components in contact with concrete. Designing and selling concrete structures with galvanized steel attachments used in moderately corrosive environments for over thirty years, I never came across any information...

In over thirty years dealing with galvanized components attached directly to concrete structures, this is the first time I have ever heard of this approach. Can you tell me why? My instincts tell me the rusting of the ungalvanized steel against the concrete would be a greater problem than any...

I have found two web sites of interest: 1) V.Ganapathy provides a set of formulas at http://vganapathy.tripod.com/corros.html and 2) an on-line acid dew point calculator is available at http://www.jehar.com/dewpnt.htm . The results from both of these compare closely with my previous experience...

After over 40 years in this field, I have to say, "no, there is no software available to estimate the corrosion rate in a stack". But, if the conditions you describe are constant, and the exterior surface is well insulated, then corrosion should not be a problem. The secret is to...

We had good results with a bituminous coating on either the concrete or the aluminum to maintain isolation and eliminate the formation of the growth salts which are so disruptive to the concrete. However, I would be concerned about reaction between the aluminum and the sulfur compounds in the...

It appears that you are operating at temperatures well above the acid dew point, which is often, depending upon sulfur content, humidity, etc., above 300 degrees F (150 degrees C). The gunite (refractory concrete) provides an insulating barrier between the hot gases and the metal stack. It...

Circular structures, such as silos, are notorious for developing vertical cracking from the inside to the outside - shrinkage cracking almost certainly. Normally this doesn't have much effect on the usability of the structure, but as you're operating under strong negative pressure, it become an...

Question: Why are you designing your own stack? There are half a dozen companies that specialize in this kind of work and can do a better job faster and cheaper. The first time designer usually creates a stack much heavier than needed, and many times that can still be inadequate. The first...

Terry, you say a combination of paint and refractory - I assume the paint is an undercoating and the refractory goes over it? Can you tell me what temperature range you operated at?

The acid corrosion of duct and flue surfaces has long plagued builders of combustion systems. The solutions can be quite complex - the information you have included is too sparse for a comprehensive reply. First, what is your fuel - what other gases are in the exhaust? Chlorides (probably)...