[slaurin]

Hello!

I work in a polyethylene plant and I am doing a study on our reactor outer-coolers and jacket coolers. Our reactors are firstly cooled by a water jacket which is a 1/2 6" pipe wrapped around the vessel (which is about 4 m in diameter). The cooler is separated in three parts (the biggest section has around 18 loops). Then the slurry gets cooled again through an outer-cooler and is recirculated back in the reactor.

On one of the reactors jacket has a delta T of only 1 deg C at the moment! It's about 10-15 deg C when healthy (at same Cooling water flow). We know that we have a lot of rust in the pipe and we also might have some calcium carbonate, calcium phosphate, aluminium hydroxide and magnesium silicate (from our cooling water chemestry).

Two chemical cleans have been tempted without succes. The first one was with an acid (might have been HCl) and the second one with a chemical called "rust free" patented by our water specialists (Nalco). It hasn't done a thing.

Does anyone know about a way to mechanically clean such a long pipe? Are there any other chemical cleaning process that I could trial?

There has to be a way! I can't believe that I am the only engineer with such a problem!

Thanks for your help, it's greatly appreciated.

Stephanie

[eugenedakin]

Hello Stephanie,

Yes, you are correct, you are not the only person with this problem.  From a chemical treating perspective, there are many different types of scale which could be forming, some of the stubborn scales are calcium sulphate, and other forms of silicates. 

The cure really depends on the types of scales. For example, sodium silicate is easily removed by a high caustic wash (Sodium Hydroxide 15%), whereas sodium silicate is insoluble when an acid is added (this might have occured in your system). 

As mentioned, another stubborn scale is calcium sulphate, which is usually formed from oxygen scavengers (sodium sulphite) and calcium carbonate. 

One way of removing the scale is to physically remove a small amount and test it against the cleaner you are trying to use (most cleaning companies will offer a complementary analysis of your scale as long as they get the cleaning business).

I need to caution you about any type of chemical or mechanical cleaning, since some scale buildup actually is preventing the leaks.  Personally, I have seen cleanups where it removes the scale, only to find that the pipe originally had holes (due to corrosion) and removing the scale opened up the holes, and piping needed to be replaced.

To prevent this from occuring in the future, learn chemical details from your corrosion inhibitor supplier.  This could either extend or eliminate non-productive time due to scale buildup in the future. If they are unable to provide you with these details, another supplier may be more forthcoming with information.

I wish you well.

Sincerely,

Eugene

[kevins]

To clean the piping by the acid (e.g. HCl or citric acid), the acid strength is the most important parts (e.g.~10% HCl with inhibitor to give the protection to the bare iron surface). Heat and circulation are required.

[jules]

the problem is for sure solved, but i leave my answer here anyway..it might help next time

i know of a mechanical way of cleaning such pipes, i have used it on a heating coil: a small oval object covered with metal pins is introduced in the coil and pushed with water. The pins remove the dirt from the internal walls very satisfactorily. When it comes to the other end, the water flow changes direction and you clean it "backwards". This is repeated several times until clean water is being pumped out.

this service is offered by a dutch company. need round 8 hours to finish the process