Heat exchanger descaling - using sulfamic acid

[cowboy007]

What should be the optimum temperature and concentration of sulfamic acid to be effective as a descaler for heat exchanger? The scaling in my case is from calcium, some protein (we have yeast cooler application also). We been using the evaporator condensate (temp 120-150F) and dump it in a SS tank, mix it with sulfamic acid powder and make the acid solution. I would appreciate if anybody could throw some light on the optimum temperature and concentration to make this solution to be effective for this application.

JM

 

[unclesyd]

I would not take that approach, using unadorned Sulfamic Acid.

I would procure a commercial product with all the additives, surfactants, rinse aids, and inhibitors for you cleaning job and follow their instructions.

Normally an acid cleaning product is limited to 60C but I have always limited the temperature to 50C unless directed by the cleaning materials manufacturer.

 

[EdStainless]

Trust Syd on this one, buy the prepared solution.
How are you going to be circulating this in your system? You need to keep it moving at all times.

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Rust never sleeps
Neither should your protection

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[cowboy007]

We'll have an acid wash pump to circulate the acid. We have been using this acid for yrs and never had any problems with it. As I mentioned, we are jus trying to optimise it. I been trying to get hold of the acid manufacturers to get an answer on this.

 

[unclesyd]

I called two industrial chemical supply companies that supply chemicals for chemical cleaning and neither have corrosion data for uninhibited sulfamic acid.

I have a book of isocorrosion curves, a lot unpublished, for numerous acids both mineral and organic with no data for sulfamic.

My data albeit very old from DuPont and it has no data for uninhibited Sulfamic.

The concentration of inhibited sulfamic normally runs from 3-12% at a maximum temperature of 60C. There is one inhibitor/stabilizer that list 70C as max for short durations.

Just a little advice you don't normally optimize acid cleaning solutions by increasing the concentration and temperature. You use different additives depending on the job at hand. The reason I say this is sulfamic acid hydrolyzes as it heats up and can become extremely corrosive in very short time.

Normally a system that's been in service for years would have evolved into the optimum conditions.

If I had to use your approach I would procure a corrosion curve/table of sulfamic acid versus the materials of construction in your system and find a rate that you can live with.

 

[cowboy007]

Thanks Syd. I did some investigation too and found that sulfamic acid is an acceptable and a widely used descaling agent, the concentration ranging from 2-5 %wt. All I need to find out is confirm the mixing temperature of water and the acid powder. As you suggested, if the temperature is too high, it might become corrosive. The information I have so far suggests to keep the mixing temperature in the range of 80 to 100 F - I just want to verify this.

 

[unclesyd]

Remember always put the acid into water at room temperature and then heat it up. Sulfamic acid is very soluble at room temperature.

It will become corrosive in a New York Second. If you find your cleaning solution green or brown you've gone too far.

Just be careful.

 

[EdStainless]

The reason for other additives is twofold. THe inhibitors are obvious, you want to limit corrosive attack. The other additives have to do with effective weting of surfaces and penetration into scale and deposits.
Optimized cleaning means using the lowest concnetrations and temperatures possible, and being able to detect the end point. I prefer to see people use lower concentrations and continuously add fresh acid to maintain activity levels. Once the rate of acid consumption drops it is time to quit.
Using selecetive ion probes in the system can be a good tool. Both for detecting what you want to remove (Ca), and for things that you want to protect (Cr, Fe, or Ni).

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[cowboy007]

What kinda additives do we normally use? Also, since we are using condensate which is avail at 130 F to mix with the acid powder (to make 3% wt solution), I would assume we would need to cool down the condensate before mixing to avoid corrosion.