Cleaning Gypsum Scale from Process Water Discharge Line

Try using ultrasonic cleaning.

Thank you for the response. Had not thought of trying ultrasonic for PE piping although we use it in our lab to clean a variety of materials.

Spent several hours searching the web and have not found anyone that can clean long sections of pipe. Do you know of any specific companies, especially if located in South Eastern US?

For an 8" line, how about a 'pig' like the oil companies use? You just have to go get it from the end of the line. You could make your own with a chimney brush, they probably are available in that size. As long as the turns are smooth and the passage clear, it could be just regular maintenance.

Thank you for your response.

We routinely run a "Pig" weekly. As time goes by we increase this to two and three times a week. Once we start getting hard build-up in the line, every fourth "Pig" is what we call a "Razor-back". It has wire brushes embedded in it to help break up the accretions. We cannot start it in a clean pipe because it roughs up the PE surface and the gypsum "grows" faster. Even with this cleaning scheme, we have to go in at 6 to 9 month intervals. take the line down and hydrolaze it. We are able to continue running the plant by swapping out a clean 20' straight section for each dirty one. We clean that section then use it to replace the next dirty one. 45° and 90° turns are more of a problem and usually require a 6 hour flow shut.

We are now to a point that an 8" pig will not pass through. We have some 7" on order to see if we can reopen the pipe until the next scheduled flow shut in October.

The good news is the line was built with ~ 40% overcapacity. We have lost most all of this overcapacity so it has not impacted production yet but will shortly.

We have found with our field experience using acids (93% H2SO4) to control pH that the solubility of the scaling material in the effluent changes dramatically as pH drops. That is why I would suggest looking at your existing treatment process and see if you can drop your pH and still meet EPA requirements. At just a little drop in PH the scaling may stop completely. The scaling must show up as TSS in your testing? by changing it from suspended solids to dissolved solids could solve your scaling problem permanently if you can stay in pH range. You should see the change in the TSS meter with a lower TSS reading if you are having an effect. This of course requires good pH control and that is a difficult thing and anyone who has done it in the field knows what I am talking about.

We have much less build up in lines that have lower pH but still have to clean them occasionally. Since all of our buildup is Sulfate based H2SO4 does not work well. HCl does but is very "deadly" to our primary process. Both literally and figuratively.

Permit allows discharge between 6.0 and 9.0 pH. We usually discharge at ~8.6 due to process limitations on selectively precipitating some elements while keeping other elements dissolved.

We have looked at lowering the pH to ~6.5 after it exits the thickener but as you mentioned pH control is not very exact. As it is, the slurry entering the thickener is fairly well reacted so the pH remains relatively stable. Estimated residence time is 4-6 hours. We have automatic pH control on the reactors preceding the thickener and a monitoring pH meter in the discharge pipe from the thickener to the discharge pump connected to the DCS system that is constantly monitored. Operators measure the pH manually every 2 hours. If we lower the pH after the thickener, we have no "safeties" to prevent violating our permit. This is not considered to be an acceptable risk by our plant.

EPA required monitoring is at the point where the water enters the pipe. Any build up in the pipe is after the sample point. When a PIG is run the discharge flow is diverted to a catch tank so we can retrieve the PIG and catch the majority of the solids scrubbed from the line. This tank is vacuumed out when needed to remove the solids.

There is a practical way using a controlled acid solution pumped through the pipe. Lower the PH as you go under control and you should be able to clean the pipe up nicely. We have a group that can do this job depending on where you are. There are several companies that can do this kind of work. It takes acid and the proper PH controls. We manufacturer pH control equipment (system) that controls the truck wash out of concrete mixing trucks. It of course scales up everything it touches. It is also limestone (or CaCO3) in the cement mix that makes the pH high up to 12 to 13. We take it down to 6-7 pH under control for dumping off site. You would do something similar in reverse with a low pH fluid in the pipe it would pick up the lime scale. When the pH stops moving up from your injection pH (4-5 pH) you are done. With tight acid/pH control you can be aggressive or cautious. After you are done you would need to put a pacifier chemical in the pipe to stop corrosion. You will be lucky if you don't already have under deposit corrosion in the pipe. It may have pin hole leaks now that the scale is covering. No one will want that liability.

Most Acids will not dissolve gypsum scale (CaSO4) they just dont react. There are a coupole of ways to get it to clean up with chemistry - one is to use a combination of chelating agents, the other a specific blend of organic acids. Unfortunately as your line if quite long i suspect ultrasonic cleannig wont be an option. (too bad as we ahve gootten really good at cleaning large objects). send me a private note and i will give you more commercial information.

Thank you,

I will contact you shortly.

Ron

I represent a company that manufacturers and applies acids that will remove the gypsum scale you have described. We have applied it on several piping sysetms in Florida. I would like to discuss with the opportunity to demonstrate our product on a small sample of the deposit to prove to you that it doses work ...... the chemical would be pumped up the pipe from one end and allowed to dissolve the deposits and then disposed of as waste when the pipe clean. it will not harm the pipe. My email is jstefanowicz@gotar.com. i look forward to your repsonse...

Thank you for responding.

Private email with contact details on its way.

Tom-

I am also stuggling with the removal of gypsum deposits. Could you provide additional information or references on the chelating agents and organic acids you mentioned?

-Bill

Thank you for the response. This is closer to what I was looking for. One of our water plant operators saw this type of cleaning in a Refresher course they took but could not give any details as to who the company was.

I will contact you off-line for specific details.

Ron

My neighbor has a company that installs sealed liners in such pipes.

His system uses a woven collapsed tube made of hollow strands, half and half filled with two part epoxy. It is then inflated crushing the resin filled strands thereby combining the two parts of the epoxy and creates a totally sealed liner that is impervious to all kinds of fluids.

I don't think this would work for this particular application. This scale even adheres to a teflon line used for the autosampler although the buildup is at a slower rate.

However, if this epoxy would stand up to concentrated sulfuric acid (93-98%) I would be very interested in it for another application. We currently us a lot of very expensive 2" and 3" lined pipe in our plant to move this acid from one location to another.

Please have him contact me privately if he thinks it would work.

Ron

I talked to Fred about his pipe liner and he says it is a complete sealing process using either epoxy or poly resin. He would need pipe sizes, lengths, pressures and acid strengths to ascertain whether his product would stand up but he says there are more options he know of.

He also has some ideas on cleaning the calcium sulphate from the discharge pipe.

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Thank you for the information. I have already contacted him and the leads look promising for some other "opportunities" we are dealing with. The inspection camera he invented and markets has some possibilities for us also.

4 Questions:

1. can you give us the Chemical formula for the sediment.

2.You said that this is a PE pipe, so I guess the sediment has very low degree of adhesion to the pipe's wall. Would a some type of mechanical vibration release it to the pipe?

3. Are the water under pressure?

4. Can you estimate the particles size, and approx SG? If not here's a way to try it:

Cut the top of a large coke bottle, fill with room temp clean water, take two spoons of dry material collected from the pipe, and spread it over the water into the bottle. measure the time it take for 90-95% of the material to completely sediments.

If sedimentation takes more than 3 (three) minutes to complete, it means your particles are smaller than 8-10μ and SG is close to 1 or less. Your best bet is Barrier filtering.

If it take less than 3 minutes SG is probably higher than 1.2, you should use cyclone with sediment collection mechanism and automatic purging.

It will depend somewhat on your flow rate as well. And don't waste your money on external cleaners it is easy to do.

Wangito.

Material is mainly gypsum, CaSO4 with small amounts of other Sulfates of Mg, Mn, K, Na and some other minor concentrations of other elements.

Running the PIG to clean the line causes the material to be very compacted. Any place there is a joint or the interior surface of the pipe has been etched is where the material builds up the fastest. When cleaned by hydrolazer, it requires 5,000 psi and a "Sputnik" head. It is very hard to chip out or breakup.

Line pressure is probably 40-60 PSI but am only guessing as we do not measure it.

TSS is usually near ND. Highest readings < 1/10th of permit levels.

The material is not sedimentation. It is chemical precipitation. It is mainly from super-saturated gypsum in solution from our water treatment process. The water starts at ~ 5-10° above ambient and cools slightly as it travels through the pipe.

As for filtration or a cyclone, the water flows through a 650 m3 thickener specifically designed for this application. It is treated with a flocculant with the sludge bed maintained at least 9' below the surface of the water and is equipped with an inner ring to trap and retain any solids that remain floating on the surface. As there are essentially no solids entering the pipe, neither method would be useful.

Flow rate varies between 120 and 145 m3/hr.

I trust this answered your questions satisfactorily.

The solution offered by me is definitely not adequate.

Reading through the different ideas it seems to me as if non of the proposed solurions is going to be completely satisfactory. If you don't let the Gypsum solidify (?) it could help with the cleaning.

I don't know enough about the process to be able to think about drastic solution.

sorry I couldn't be of more help.

Thank you for taking the time and effort to consider the problem. I greatly appreciate your input.

As for the process, details of the process was published by TMS in the book Pb-Zn 2000, pages 867-878.

I would try using info that is available on the Waters website.They list symposiums dates and latest products.

Is this the EPA site, the Waters Corporation (chromatography) or one for another company?

Neither the EPA Site or the Waters site looked very promising although I could have overlooked something.

I can't get hold of Fred until tomorrow about his pipe lining.

This may help for the Calcium Sulfate problem tho.

http://www.onepetro.org/mslib/servlet/onepetropreview?id=00018383&soc=SPE

Waste water discharges of any water treatment process can be problematic when the pH is 8.6 and the temperature is 5 degrees C above ambient water (before treatment). I am not sure if this is RO or boiler water or other treatment process. These values suggest encrustation is likely severe.

Marcot suggested lowering the pH and I concur with him. You said you had little luck. You may want to check the Langlier Index to see how sever the encrustation really is from a chemical viewpoint. Where you see calcium hardness, apply the total hardness as CaCO3. This is a lab standard for reporting hardness, but you will need TDS, Alkalinity, pH, and Temperature to use the calculator. When the index is Below zero or negative the water will not cause a scale. When the index is above zero or positive it causes a scale. An index above 1.0 is severe scale. As I see the application of this formula to you problem, you have two choices to prevent the scaling. You can lower the pH to meet regulation and possibly get it close enough to zero to minimize scale. The second option is to lower the temperature to increase solubility. You could do this by putting the warmed water into a holding pond prior to discharge. The holding pond should be sized for several days to allow the temperature to lower and also to allow much of the CaSO4 to come out of solution in the pond rather than the pipes.

Perhaps you could set up some sort off "jar" test to confirm a settling time and a temperature lowering time. I say Jar test but really it is somewhat unique from a standard jar test used in water treatment but it should provide some good empirical data. One aim would be to try to find out how much acid will be required to lower the pH to meet an acceptable LI. The other would be to see if the TDS or TSS will settle out. You could even try to raise the pH to cause all calcium to come out of solution and then adjust pH for regulatory discharge.

I am not sure if this helps but FYI

Good Luck

Kevin

Sorry all, lowering the pH is just not an option. I agree it would reduce the buildup but based on other parts of our process, even the bleed circuit requires periodic cleaning to remove Manganous Gypsum complex. It just would not require cleaning as often.

This water is left after we remove Sulfates, Zinc and Cadmium for process contact water, i.e. storm water runoff from the area, water from other process areas where the majority of the zinc has been removed, water from a gas scrubbing process and treating solution from our bleed circuit at ~ 220 g H2SO4/l, 25 g Zn/l. This water treatment was developed on-site and when implemented in mid-80's was considered BAT by EPA for treating this type of water. To the best of my knowledge, it is still BAT.

The goal of the process is to remove all the valuable metals, i.e. Zinc and Cadmium while disposing of the Mg, K, Na, Ca that we can, all the while staying well within our compliance permit from the EPA. This requires the Zn to average < 1.2 ppm and the Cd < 0.2 ppm. Neither element precipitates to that level until the pH is > 8.4. At 7.0 pH the solubility is in the 100's of ppm. Magnesium precipitates as the pH increases above 8.0. We strike a balance between recovering the Zn and Cd while minimizing the precipitation of the Mg. Increasing the pH to 8.8 or 8.9 will result in precipitating 20-25% of the dissolved Mg. The permit requires a 6.0-9.0 pH at all times in the discharge.

Following the reaction of the contact water with slaked lime, the slurry passes through a thickener where the Gypsum, Zn(OH)2, Cd(OH)2 and other precipitates are separated from the water. The thickener discharge is super-saturated with gypsum and that is what is causing the buildup in the line. We have looked at reducing the pH following the thickener but because of known problems we maintaining a reliable, accurate pH reading the idea of re-acidification has been rejected. There is no safeties to prevent a minor pH upset from being discharged to the river. We find that to be an unacceptable risk. With the current setup, there is about a 4 hour average residence time in the thickener. Operators check the pH with a portable meter every 2 hours and a sample is delivered to our lab for verification and metals testing every 4 hours, around the clock. This is in addition to a dedicated pH meter that monitors the pH of the thickener overflow and displays it to a monitored DCS in real time. All of this is done to ensure we stay in compliance.

We accept the fact that this scaling is a part of "doing business". We have a 5 day flow shut every 6 months to clean/repair lines, tanks and other process equipment. I am looking for a better way to clean this almost mile long pipe. It currently takes ~ 6 weeks to clean with a hydrolazer by swapping out a clean section for a dirty one, cleaning it and repeating the process. Every section we remove requires the flow to be diverted to a surge pond then reprocessed.

I appreciate all the ideas and knowledge being shared but I am still looking for a way to clean the line. The chemistry is about as optimized as we can make it. There have been several good leads from the information from Jack Marcotte, Tom M and 129CBRider that I am following up.

If someone wants more details, the process was written up in the TMS records of Pb-Zn 2000. The author is S. Subhawong, my manager at the time and lead developer of the process.

Your surge pond may be the answer. We use something similar during pH control of cement truck wash/clean out. The pH control acid we use is H2SO4 (93%) you could use HCL, citric acid or any acid that dissolves gypsum. Use the pond as a buffer to insure you are in compliance with pH. Treat for PH in a recirculating loop with the surge pond. Batch process the pond. Pump it out off site when you have the pH under control and in range in the pond. To make it more bullet prof divide the pond into two. One for recirculation process one for dumping. An in line pH control system could do this task fairly easily. It should be able to be accomplished while normal operating conditions exist with no interruptions. Relatively small concrete weirs could be used as process and dump ponds. The pH level would be above the low limit but keep the TDS as TDS. Or--- If nothing else the pond may sediment out the scale minerals with no acid treatment when the water cools down. Concrete weirs with the width of a front end loader would be needed if you end up using them as sediment ponds. It would be needed anyway for clean out which will be needed in any event.

Going one step further with no acid treatment you could spray the discharge into the pond and aerate the water. This would inject some atmospheric CO2 into the water and scale may come down as "snow". Sounds "Green" to me. You may get a "gold star" for that.

Sorry Jack, I was not too clear in my definition of this pond. It is a surge pond that collects all the inlet flows and allows us to maintain a relatively constant flow into the Metals Recovery process helping to stabilize the residence times and control the reactions. Any water sent there is contaminated again and would require reprocessing though the entire operation. Discharge water is only sent to this pond when there is no other option, i.e. mechanical malfunction or maintenance.

Your suggestion of using a holding pond for pH and scaling control is a good one, however EPA permitting for a new pond requires ~ 2 years for us and there are no areas of the plant that are nearby that are not in the flood plain.

As for acid used for treatment of the build-up, HCl is completely ruled out. If chlorides get into our process they can/will evolve as chlorine gas. We do not allow things as simple as Cl based de-icers to be used inside the plant. HNO3 is also a problem for us. We have not looked into Citric Acid but try to avoid organics because they affect the Electrolysis part of the plant.

The cleaning operation I am looking for will have to be pretty much self contained with the residual material removed from site, turned into a stable solid or be able to meet our permit requirements for discharge to the River.

We have looked at pond sprays to help evaporate the water from the pond and reduce the quantity that requires treatment. Because of the possibility of the spray droplets containing sulfate or metals and getting outside of containment we have not chosen this route either.

We operate as a very green site for our type of operation and have every intention of staying that way. We own over 1,600 acres. The plant only covers ~100 acres. The remaining is utilized for farming, raising cattle and as a Tree Farm. We are ISO-14001 certified and responsible environmental stewardship is a top priority.

Maybe a large number of small aerators in the pond would help oxidize contaminants and help with evaporation is you could heat the air fed to the aerators by utilizing some processing plant heat that otherwise would be wasted.

Think tiny bubbles so that whan they burst to the surface they do not create an unwanted mist.

Maybe something similar to a common residential neoprene soaker hose with bronze or SS fittings laid in a double spiral, connected at both ends to a low pressure, high volume air pump with a heat exchanger bringing heat from inside the processing plant.

Temperature not more than 100 degrees F.

Interesting idea. I will bring it up in our next meeting. One of the few things we have not considered/tried.

As for bronze or stainless steel fitted soaker hose, anything less than 316 SS and preferably 316L SS is almost like putting mild steel in the solutions. They just do not hold up. Almost everything residential or commonly available will not last very long.

Thanks

Schedule 80 CPVC holds up to almost any chemical environment. It can be drilled, threaded, glued and used for many purposes. There are many fittings available for many different purposes. It has a very high operating pressure rating. Pipe sizes that fit any volume need. An acid resistant "glue" must be used if using glued fittings. We use it routinely for handling high density sulfuric acid. 93%+. The worse wear and tear we see is that the surface turns brown after "years" of in place operation but no other loss of integrity or function other than the surface color change. It can be made into anything you need for spraying, injecting, or moving very corrosive material. Of course it has limits to its chemistry but a review of its chemical resistance and abilities make it a valuable resource for any one involved in your work. It requires only standard pipe handling tools and goes together just like other standard piping.

Thanks Jack,

We do use some PVC and CPVC but usually it is PE. Most of our lines are outside and between the chemicals inside and the exposure to the weather, we have found the pipes become brittle with age. PE seems to hold up better and remains flexible enough that flow shocks/surges and accidental bumps do not cause leaks or breaks. Our biggest problem with PE is it seems to lengthen with time and wants to move off of the pipe racks.

We also have an inline welder that allows us to electrically weld a patch over the PE when any holes that develop from incident or cleaning.

I do agree with you though that it is probably the "best choice" for the aerator/sparger that 129CBRider described.

The best pipe for almost any application is PEX. Expensive but worth it.

http://www.pexinfo.com/

Main problem with PEX appears to be the connectors. Aluminum, Brass, Copper and other standard connectors will not last. 304SS (a lot of residential SS fittings) won't last either.

Any contact fittings would have to be 316L, Sch. 80 PVC, SDR 11 PE or better.

It might work for a temporary aerator though.

All,

I would like to thank each one for their input and helpful information.

I was able to locate a company that does chemically clean piping. There representative came on site to discuss the job and took samples of the build-up with him for their chemists to verify that they could clean the material.

All tests went well and indicated the line could be cleaned in less than a week vs. 6+ weeks when done manually.

If anyone is interested in contact information for this company, please contact me via email and I will provide the particulars.

Again, thanks to everyone for their assistance.

Ron

Ron-

Can you pass on the name of this company? We need a solution for chemical gyp removal, and all the traffic on this discussion sounds familiar!

Stan

Sorry for the delay, just saw your message.

The company we found to chemically treat was:
Gotar
www.gotar.com
800 Lombardy Ave #8408
Newport News, VA
23606
1.877.994.6827

Contact: John Stefanowicz
Technical Director
Account Manager
1.757.532.8852 Cell
jstefanowicz@gotar.com

Their price was much more than we could spend. We ended up using PSC (http://www.pscnow.com/Default.aspx) to physically clean the line. We fabricated replacement sections (most are 20' PE), shut off flow, changed dirty line for pre-fab, restarted flow and let PSC clean the build up from the removed section in a containment area. Cost was ~ $80,000 for the 1+ mile of piping. Gotar was >3X that.

Our Representative with PSC is:
John D. Gipson
Area Manager Ky/Il/In
W 270.395.7226
M 270.519.0643
jgipson@PSCNow.com

Hope this helps

Hi guys. I'm desperately seeking help for a problem with my swimming pool. I'man English guy living in Spain .I'm not a chemist an don't understand what has happened but I have an almighty build up of a hard white substance on the walls and floor of my pool. It is very hard and vary very abrasive. It will break skin if you brush against it. The pool contains about 30 cubic metres of water. The local pool man put 50 liters of 34% HCL in as he thought it was calcium. Nothing happened even with scrubbing. We have a lot of marble in the ground in our area where the water comes from. I'm wondering if it could be gypsum. No one round here has any idea what to do. Can anyone here offer any help or advice please in non technical terms fot a non technical old man!

Marble is mostly Calcium or Magnesium Carbonate based. Gypsum is Calcium Sulfate based so without a source of Sulfate, Gypsum would not form. If material is hard water scale, I don't think the small amount of Hydrochloric Acid would have lowered the pH sufficiently to affect scale.

What is added to the water to treat it for swimming? Do you sanitize with Chlorine based products or use Bromine or Ozone based treatment. What is the usual pH of the water? What level of hardness and alkalinity is maintained? Is Uric Acid used to stabilize the free Chlorine concentrations? Any information on how the pool is routinely treated will help find an answer.

Can you break off any of the material so it can be tested? If so, place 5 to 10 grams on a paper plate or in a plastic bowl and add 3 or 4 drops of concentrated vinegar or lemon juice. If material is hard water scale, it will effervesce (make bubbles). Let us know the results.

Ron

I should have mentioned that gypsum is also in the area. A lot is exported from a few miles away. Is 50 liters in 30,000 liters a small amount of HCL? As little as a couple of liters will drop the pool from 7.5 to 7. The technicalities of all this is a bit above my pay grade. The water round here is very hard. No one drinks it and we have a water softener to remove cal. We fill and top up the pool through the water softener. I use 3 way tablets (Chlorine, flocculant & algicide) and HCL to keep the Ph at about 7.2

We are not well blessed for getting anything analised over here. I did scrape some off but the only lab in the area were unable to carry out such a test. I have tried taking a sample and applying lemon juice, vinegar and 34% HCL. No reaction.

This first happened three years ago. I drained the pool, tried scrubbing with acid, even a steam jet, all to no avail. It was as if it had melded with the fiberglass. I eventually sanded it flat, applied a two part epoxy primer and a top coat of two part polyeurothane. Since then I kept the Ph at about 7.2 and it has built up again to massive proportions. Some other people nearby have the same problem in fiberglass and tiled concrete pools, and others have no problem. I've talked to the guys with no problem and their maintaenance is no different to mine. Go figure. I can't.

Acid addition calculates to about 660 ppm HCl or 18 ppm H+ ion. The pH should have dropped to about 5 if in drinkable water. Not low enough to really remove hardwater scale.

Since the material did not react to the vinegar or lemon juice it is probably not a carbonate. Putting 34% HCl should have caused the material to soften and crumble if it were Gypsum.

Since you are using a water softener to remove the Calcium from the water (hardness), unless you are in a very arid area with large amounts of evaporation, the Calcium should not build up enough to produce significant hard water scaling. Assuming it is a Sodium based water softener (uses NaCl, salt, to regenerate) the most concentrated chemical in the water would be Sodium (Na).

Will have to think some more on what the material might be and how to safely remove it.

In the meantime you might contact some of the pool chemical suppliers as they have technical departments the assist with getting the "chemistry" right and dealing with pool problems.

We reach 40 degrees in the summer. Lots of evaporation. Softener uses salt.

I'll try your suggestion and see if any of the suppliers here have technical assistance.

I'll do that tomorrow. It's bed time here.

Let me know if you think of anything.

I think that there is a pool forum on here. Might try there if I can find it.

Thanks