Lean Amine Cooler

[ocpike102]

I'm a fairly new mechanical/process engineer, and I have just a few questions. I'm working for an air-cooled heat exchanger manufacturer, I'll keep that one to myself, and we've recently got into the world of process cooling. I'm using HTRI to design my coolers and I take the process data from chemical engineers, and then size the appropriate cooler for temp, heat load, phase, pressure drop, etc etc.

I just have a quick question for all of you experts here. I've been seeing a lot of Lean Amine and Propane coolers, are there any things that I should keep in mind when designing these coolers, such as certain fluid velocity or anything that I'm not thiking of. Any advice would be greatly appreciated.

 

[mark1000]

Lean Amine velocities should be limited to 7 ft/s in Carbon Steel.

 

[dcasto]

make sure you have complete control of the temperature out of it. VFD fans, louvers, heat recirculation louvers, whatever it takes.

 

[maddocks]

Be careful on your material selection. Pls do not quote 214 welded tubes in amine service - it's just not the way to go.

Because of northern climate, be sure and check your cold air horsepower draw and you can option in full warm air recirc systems.

 

[ocpike102]

Thanks, I really appreciate the help. I notice the Maximum Velocity value, but is there is a minimum velocity for lean amine?

Also in response to maddocks, the customer is requiring SA-214 for the tube material, should I advise against this? And I always check the cold air horsepower draw, I do a lot of designs for Siberia.

 

[maddocks]

well, if the client wants it, the client gets it. I would carry 214 in your base price but provide a recommendation and option price for A-179 tubes. That way you remain competitive.

 

[ocpike102]

Thanks, what is the reasoning behind this? Is there erosion problem with the welded tubes?

 

[ocpike102]

Ok, another question here. I have an engineer now asking if the materials are acceptable for amine service. Such as all materials, Carbon Steel, being killed and normalized. Is this common?

 

[maddocks]

Most of your carbon steel materials should be normalized; A105N flanges indicate normalized already. When I talked with our cooler guy here, he mentioned that the seams in 214 tubes can become "nucleation" spots for corrosion to start and then accelerate. Given the lack of inspection on cooler tubes, and the amount of gas that can leak if one ruptures (I was there when it happened!), I'm happy spending a little more money on the proper tubes.

 

[ocpike102]

Thanks maddocks. I'm just trying to see if the tubes can be easily manufactured being killed and normalized. The tubes will be seamless.

I've been given an opportunity to quote a Sour (High H2S) gas cooler, which I've never done. Is this something I should just stay away from, or does it just take a few extra precautions.

 

[maddocks]

Go for it, you can find some real interesting stuff here. You need to know if there's water present - if so, start looking at stainless. if not, carbon steel, A179 tubes, normalized header boxes, stress relieved, self draining, maybe consider a heat coil for cold weather.

 

[ocpike102]

Just another quick question for everyone. Would you use Carbon Steel over Stainless Steel for a lean amine cooler? Why?

 

[maddocks]

Unless the client asked for stainless, I would stick with carbon steel. Not many lean coolers are going stainless, however, you may see requests for stainless on the reflux cooler. Again, go in with your base bid at carbon and option up so you can show the client the impact of this decision.

Carbon is usually adequate for lean coolers - the partial pressure is fairly low and the loading low. Given that there's no gas breakout and no acid gas attack, carbon is a pretty good choice.

 

[ocpike102]

Thanks for the help. I'm trying to find ASTM A-515 Material though for the header design (normalized), and I've been told that it is incredibly difficult to find. Is this true? Could I just use Stainless Steel in lieu of the killed material?

 

[maddocks]

You might find some issues with thermal stresses - most local mfr's go with A516-70N for header boxes.

 

[ocpike102]

But isn't A516-70N non-killed material?

 

[ocpike102]

All right, I'm getting all this figured out. Thanks, just one more question.

Are turbulators advisable on Amine coolers, or should the coolers be bare tube only?

 

[maddocks]

We usually save the use of turbulators for retrofit applications - using them in the original is a bit of a "cheat". You could always offer them as an option if the buyer is interested in investigating.

 

[ocpike102]

But technically it would pose any problems? Customer is asking for it to reduce size.

 

[maddocks]

Well, you need to be confident in the pressure drop prediction as well as the possibility of any fouling. There would be no problems with using them in the design.