Tubular Airheater Design

[BJaffa]

We are repairing a tubular airheater in a stoker coal fired power boiler. Expected exhaust gas temperature at under 450 deg. F. Scheduling has forced us to look at available practical material options. What is the effect of a change from 2" OD x.083"T to 2" OD x .095"T on operation? Is ASTM A 513T (1010) a suitable material?

 

[winmancan]

Materials selection may be more affected by fuel type with specific chemical composition as well as effects of boiler loads. Cold end corossion will quickly degrade common carbon steel. I have found that at the cold end, use of 304 ss improved the life of the air heater 2-3x over CS

 

[deanc]

Keep in mind A 513 is a structural material,the quality may not be consistant.

 

[Dofsteel]

Bjaffa,

In terms of the operation, having a thicker tube wall will decrease the ID of your tubes, reducing the total surface area available for gas flow. Since air heaters are designed with some extra surface area to allow for tube plugging, there shouldn't be a problem. By using those tubes, you reduce the flow area by 2.6%. I've seen airheaters with almost 15% of their tubes plugged off.

D

 

[smoki]

That small change in wall thickness will not hurt heat transfer enough to warrant any discussion. In large power boilers A513 tube is what is used except on the cold end. Generally the most economical choice there is Cor-ten. Structurally you will be adding some weight, so you might consider this.

 

[aybee]

if there is H2S in the gas , you would be better with duplex than an austenitic such as 304,provided there is no welding involved it would be straightforward

 

[pablo02]

I do not have any experience with Cor-Ten in a preheater, but have had some in a scrubber -- Cor-Ten works great if there is no abrasion or other means that removes the protective oxide scale -- this is a coal-fired boiler, I would assume that some abasion would occur, which means Cor-Ten will fail quicker than regular carbon steel..