12 replies to this topic

[distilsum1]

Hi,
I'm a fresh engineering graduate and currently working in a chemical plant as my first appointment.
The problem I have is with the removal of hard scale in condenser tubes.
There is an issue with the cooling tower as currently there is no blowdown or any chemical dosing at the tower & that would be corrected when starting next season.

But the current problem I have is with the Cleaning of condensors with Copper tubing. It is Very difficult to remove using the "screw end rods" which are manhandled for the work.An additional problem for chemical treatment is that in the 4 passes of this condenser, only 2 passes are having greater deposits of scale.

A Nalco chemical with an inhibitor (salfonic acid)to protect Cu surface was used with HCl addition to keep the pH at 2 and was circulated for 10 hours (As said by Local dealer). But the scale seems intact..

Even when samples of scales were put into Con. HCl part of the scales remaind after the initial reaction. I think due to deposits of silica. Do I have to resort to mechanical way by consuming lot of man hours.

Any help is greatly appreciated...

[Art Montemayor]

First of all, please confirm that the deposits are on the TUBE SIDE and not on the shell side. This is a very important factor and you fail to even mention it.

Chemical cleaning is always a tedious and lengthy process. It takes a long time to dislodge and/or dissolve the hard incrustations that have been "baked" on the tubes.

I would resort to using simple, mechanical removal by applying a rotary, soft (softer than copper) bristles. This may also take a long time, but at least you can SEE what you are doing as you do it and you don't have to lose valuable time in assembling and disassembling the exchanger bonnets or channels to inspect any improvement done by the chemicals. I assume your copper tubes are at least 3/4" OD. If smaller, you are in for a lot of detailed, hard maintenance work.

This is why cooling water treatment and control is so important. You are now paying the price for not applying it in the past. Good luck.

[distilsum1]

Sorry..

The scale is in the tube side (OD > 3/4")and just as you said it is kind of baked in the tube wall.

I have tried to correct the cooling tower problem in the past. But there are problems in the SYSTEM as it is currently looked by a senior mechanical engineer & blowdown & chemical dosing seems a waste to them. For years, this half cleaning (This chemical is also part of it) & restarting back cycle have been practiced. I hope I could convince the importance of cooling tower control with facts this time.

I'm also new to Practical applications in industry & Thank you for the reply.

[Mehrdad]

Hi

probably This Scale Is Calcium Base Scale And Dissolving With Con. HCl Without Any Fear For Corrosion Of Tubes If You Are Sure About Material(Copper).
Roughness Of Tube Is A Cause Of Forming Scale Or High Temperature In Bonderis Of Tubes Make More Scale In Some Tubes More Than Others.Are The Blocked Tubes Front Of Enter Line Of Hot Liquid In Shell Side ?

Edited by mehrdad, 25 January 2010 - 01:30 AM.

[distilsum1]

Yes I too agree the scale seems to have a Calcium base. But I sampled out Scale parts and put them into Conc.HCl and there is an initial reaction but a great part remains intact.The tube material is a copper alloy so cant use HCl directly.

The tubes are not blocked. But has a layer of Scale (~2mm )throughout the tubes and just as you have said getting thicker in the area of high temperature inflow of vapour entering the shell side.Because of this, we had to increase the water flow through the condensers to maintain outlet conditions.

Mechanical cleaning seems to be the option..

[Mehrdad]

Hi
It Seems The Scale Is Magnesium /Calcium Scale If You Have Some Remained Part After Acid Washing And For Prevention Of Forming This Kind Of Scale, I Advice You Alkalin Treatment Of Water Before Use In Condenser .And Mechanical Removing Is The Best .Water Jet Device Is An Efficient Method.
Regards

[riven]

At scale 2 mm thick I would definitely consider the mechanical cleaning option.

For chemical cleaning your only choice is to take it out of service and put it in a sulfamic acid solution (2-5% in water; possibly some other additives) or the descaling loop at around 50C but it will take quite some time.

Art is quite correct with the importance of cw treatment.It is one annoying job.

[Qalander (Chem)]

Hi
It Seems The Scale Is Magnesium /Calcium Scale If You Have Some Remained Part After Acid Washing And For Prevention Of Forming This Kind Of Scale, I Advice You Alkalin Treatment Of Water Before Use In Condenser .And Mechanical Removing Is The Best .Water Jet Device Is An Efficient Method.
Regards

Dear distilsum1

Somehow I have a gut feeling that your case definition is not accrate as most usually water cooling condensation is affected from shell side water bulk onto materials present on the tube side(as initially inquired by our Art.)All remedies will shape accordingly.

However as you indicated,maintained this to be otherwise (although your mentioning of tubes O.D.in second post raised suspicious feeling);I suggest that you might have to use citric acid passivated HCl solution and soak the system to affect the hard scale softening in place:however you might have to check the solution's concentration variation at lab scale to minimize any adverse corrosion of copper alloy tube material.

Subsequently water jet washing and mechanical rodding might prove helpful if this is acceptable;considering the tube bundle number of passes and geometrical lay-out.

Hope this gives some help in problem solving way forward.

[fatimah]

Hi there

for scale removal i will also suggest water jet + rodding and it's a practise in many industrial companies. it's time consuming but you can confirm the scale is no more in there.

you may go to this path for information
http://www.newton.de...3/chem03799.htm

then you should concentrate on treating the cooling water, by adding chemical substances (you may check this from your supplier) periodically or install any calcium catching system. get information from them on how to soften or to decrease calcium concentration in your cooling water. your decision on which method to choose usually based on economical view and method effectiveness. come back again here with your choice and see if anybody has experience with your chosen method.

Good Luck!

[riven]

use citric acid passivated HCl solution and soak the system to affect the hard scale softening in place:however you might have to check the solution's concentration variation at lab scale to minimize any adverse corrosion of copper alloy tube material.

You will probably need to use anti corrosion additives, certainly if you wish to use useful concentrations.

[distilsum1]

Thank you all !!
Mechanical cleaning was used to reduce the deposit layer to a thin film. That layer was not easy to remove. So the Chemical treatment followed to clean this layer from the tubes.
Hmm..
Now for the water treatment...
)

Dear Qalander,
The condensers in the plant are used to recover vapor escaping from the columns.shell side is used to condense the vapors from top of the column.The condensers are installed with an angle, so that condensed vapor is collected in to vapor bottles and taken as part reflux and fed to other columns. The tube side is used for the cooling water flow.
Sorry I should have given more details in the first instance.

[Qalander (Chem)]

Thank you all !!
Mechanical cleaning was used to reduce the deposit layer to a thin film. That layer was not easy to remove. So the Chemical treatment followed to clean this layer from the tubes.
Hmm..
Now for the water treatment...
)

Dear Qalander,
The condensers in the plant are used to recover vapor escaping from the columns.shell side is used to condense the vapors from top of the column.The condensers are installed with an angle, so that condensed vapor is collected in to vapor bottles and taken as part reflux and fed to other columns. The tube side is used for the cooling water flow.
Sorry I should have given more details in the first instance.

Dear distilsum1 Hello /Good Morning,Thanks.

It's indeed very nice, seeing this useful update ;such a culture and discipline is very good, beneficial to all.

If we all make it a point to practice this without fail.

However your clarification is well accepted since I remember witnessing in past such inclined designed total condenser making the condensed liquid trickle down by gravity and collected for recovery/recycle as mentioned by you.

Although the industry location/type(chemical, pharmaceutical or this was a pilot plant research project of some kind) is not right now correctly recalled;I am not sure.
Now since the things are more clear for you future strategy to avoid such deposits may be taken-up i.e.

the temperatures making the scaling occur should be avoided

streams coming to condensers may be first directed at some knock-out or impingement plate arrangement(s) for any particulates removal upstream.Particulates at this steps should be purged out of the system via safe mechanism.

slanting(inclination angle may be reviewed to increase condensing liquid velocity thereby lesser deposition possibilities indirectly.
and many other steps......

Hope this proves helpful.
Best regards

[distilsum1]

Thanks for the reply..
The tube bundle can not be taken out for inspection.I don't know whether it is due to the fact that the shell is fed with vapor or ease of construction, but their aren't any holes to put screw rods and remove the bundle. the shell is in fact welded to the tube sheet.
So I don't know whether there is any deposits in the Shell side. But by inspecting the interior of the vapor inflow tubes to condensers, I doubt whether that kind of depositions would be a concern ..

Thanks and I would keep track of the cooling water T as well..