How to get rid of large rust particles in cooling circuit? 5

[CARF]

Dear all,

In our evaporator plant we have a large cooling water system. The cooling water is circulated over cooling towers through a spraying system with many small nozzles.

The problem is that the nozzles get blocked all the time with large rust particles. Does anybody know how we can get rid of:

1) The rust particles (y-strainers block in a few days).
2) This severe rusting of the pipes (Stainless steel is too expensive).

NB: Pipe inner diameter = 380 mm, carbon steel.

Thanks for sharing knowledge!

PS: Look at this photo too see what I mean with the rusty pipes in our plant:

http://home.hccnet.nl/m.dijk/pressure_drop_calculator/tipsntrics/tipsntrics.html

(photo below on page)

 

[Metalguy]

Gross! Good thing I already ate dinner. Anyway, it sure looke to me like you have a MIC problem as well as lots of general corrosion-from all that oxygen in the air.

If you really can't use something that's corr. resistant (plastic pipe-?), you should try to reduce the corr. rate and control/reduce the MIC.

Are you using any corr. inhibitors and biocides now (sure doesn't look like you are).

There are some companies that can line the ID of your installed piping, even around elbows. The best thing is that they also sandblast the ID to get rid of all that scunge in there, just before they line it with epoxy or something.

 

[CARF]

Please forgive my ignorance >>> what is MIC ?

PS2:

I read about SKW systems in this forum as well, what is it excactly? Anybody experience?

http://www.skw-system.de/englisch/home.html

Thanks

 

[saxon]

MVD, For spray applications it's always a good idea to provide filtration before the nozzle orifices. Hence your y-strainers. If there is a large pipe scale problem, they will load up quickly. What you need is a large volume strainer that will not load up as quickly, neccesitating frequent clean out. You may also need filters that are sized to remove particulate larger than the nozzle orifices. These should be located just upstream of the nozzles.

As for the protection of the piping and the minimizing of the scale problem, the cooling water needs to be treated. The amount of treatment needed is dependant on the makeup water quality, circulating water quality, A water chemistry analysis is required before a treatment system can be proposed. Check with any of the Water Treatment companies.

Hope this helps.
saxon

 

[Metalguy]

MVD,

MIC is "microbiologically influenced/induced corrosion", and those black areas inside your pipes are one indication it *may* be involved. But if you aren't treating the water with something, the oxygen-driven corrosion will simply do what it does best-convert your carbon steel back to its common form-iron ore.

As for "devices" to control/reduce corrosion, I'd ask for a controlled demo with someone present who knows how to separate the wheat from the chaff.

 

[25362]

MVD, concerning your last query, I suggest you pay a visit to thread798-53236 for a review on systems using magnetic effects on cooling water.

 

[quark]

I agree with Metalguy. Some organism like crenothrix, sphaerotilus and Gallionella use Iron as energy source and cause rusty gelatinous sludge in the pipe line. I saw pipes being plugged with this material. (the size was 1" and mono ethylene glycol chilled brine pipe)

It is better to have a check at it.Chlorination at say, 2ppm will help you much. (actually 7ppm will take care of any living thing including human beings) Better install corrosion coupons.

I used (forcibly) magnetic treatment system some time back and found it to be extremely useless and sheer nonsense. I always consider it in the ranks of Perpetual Motion Machines and Philosophers Stones.

Still if your budget is liberal and if you want to let the magnet people live go for them. At the end of the day your kid can play with it

 

[CARF]

Hi all,

You are great, really helping me and avoiding painfull mistakes with *magnetostatic* wonder devices ; )

One more: Since it is part of a foodplant can I use chemical treatment?

Shoot !

 

[davefitz]

The MIC is aggravated by high concentrations of iron - they feed on the iron. The MIC will quickly degrade stainless steel tubes if left in a stagnated state for more than 2 days.

High oxygen levels leads to the heamatite form of iron oxide, and this is not magnetic, so the magnetic filters will not work. They will only work on magnetite deposits, which typically only forms in boiler water with high pH and zero O2.

Seems like you need to pursue the following:
a) revise the spray nozzles to a type that can tolerate gunk
b) depending on the specifics of your water discharge permit, add chemical agents to retard bio growth and reduce corrosion rates. If permitted, periodically shock the system with hydrogen peroxide to remove bio growth.
c) consider coating the inside of the circ water piping with tar or some coating to retard the corrosion.
d) add a slip stream filter with pump to remove the suspended solids from the circ water. Maybe size the pump and filter to completely circulate 100% of water inventory in 24 hrs thru the filter. The rate of removal of solids by the filter must exced the corrosion rate of the piping in order to improve the situation.

 

[CARF]

Sorry I'm a *know no* in this area:

Slip stream filters? Any manufacturers?

Thanks for all the independent recommendations!

 

[davefitz]

a slip stream filter is a generic term for a filter that is not in the main water flowpath- it is a small flow in a parrellel path.

Basically, you would buy a 5-10 HP pump sized for a 6 psid pressure loss at X gpm , and suction fluid from the bottom of the cooling tower basin and pump it thru a pair of parrellel , valved , filters. The filters would be arranged with a 3-way valve at the inlet and outlet to allow cleaning out of one filter while the other is online. From the sound of your water problem, this would be a frequent occurrence so an automated way of backflushing the filters out to a solids collection hopper would make sense.

 

[CARF]

Thanks ! Getting closer to the solution : )

Here's another relevant thread: thread798-53177

Anybody experience with Bromine addition in cooling water?

Have a nice weekend,
MVD

 

[CARF]

... the Cooling Technology Institute (

http://www.CTI.org)

has reams of good data and standards.

 

[hacksaw]

if the particles are large enough to plug your strainers, there are self-cleaning strainers (motor drive) and if you have the pressure, hydroclones.

 

[kiah]

MVD,
Apart from side stream filters, different nozzles and self cleaning strainers (all a good idea!!). The following can reduce corrosion and biological growth at the source.

(1) Bromine is pretty much the same as chlorine for cooling tower use but a lot more expensive, Bromine is good if you have a pH over 8 where chlorine can be ineffective (HOCl breaks down, HOBr hangs in for longer), there is also evidence that it penetrates biofilm more, especially in a stabilised form and hence can be more effective(but not 100% to the level of your problem). A biodispersant (detergent)may also help break up biofilm. Ensure the biocide is cirulating around the whole system as the spray nozzles will allow it to evaporate to atmosphere.

(2) Other options for biological control are UV and Ozone.

(3) Some sort of corrosion inhibitor is essential though....bugs will find a place to hide if there is a lot of corrosion product.Talk to the water treatment companies (Betz, Nalco, Drew etc)as there are a lot of options here. Otherwise look at using plastic piping.

(4) As a minimum you should measure Total bacteria as well as corrsion rates via coupons. A lab may also identify species as talked about by quark which could help target the problem more

(5) Look at your cooling tower as well, a six monthly mechanical clean out (basin, fill and pipes) and covering up areas of growth from the sun (e.g. open decks) can reduce biofouling...and hence some but not all corrosion.

(6) You may also need to check your blowdown is a suitable rate and makeup water is not too corrosive.

 

[ddt]

There was a lot of work performed on this problem during the 80s at the nuclear plants. It started because of biofouling (clams/mussels) but when the problem was looked at in more detail MIC was also a big problem. You should get the system cleaned (mechanically and/or chemically) inconjunction with a treatment and filtering system. Also look at the operation of the system. Dead legs in the system may need to be flushed periodically. Check EPRI Proceedings: Serveice Water System Reliability Imporvemtent Seminar, October 1988. I have been out of this for some time and I am sure there is more recent work that has been done in this area.

 

[scooter911]

Call the boys out at Ondeo-Nalco. They should have someone that can help you with this. They do a good job for me.

Scoot