Solar Evaporation Ponds 2

[StoneCold]

I am looking for design information to size and build a Solar evaporation pond for cooling tower and boiler blowdown water. I am in colorado and here they are called impoundments. I need to know the typical type of liner system and how to figure out the evaporation rate per sq ft in the summer and winter to have a shot at sizing this thing. Thanks for any input you have. Google was not much help this time.

Regards
StoneCold

 

[Unotec]

The evaporation rate will be given by the difusivity of the water, vapour pressures, partial pressures, ambient conditions etc... You are probably going to have to hit the books on unitary operations, unless someone has a rule of thumb out there.
as for the liner, just make sure it is waterproof, there are many out there.
Colorado.... Doesn't it freeze there on winter?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[zerosum]

Perry's Handbook (mine the Fithe Edition) has coverage of spray ponds with cooling effect data for all kinds of climate factors and solar radiation. Seems to me the evaporation rate would be more or less directly related to the heat rejected by the pond.

 

[zdas04]

I just looked at my billing log and when I needed to find/develop the same information for a pond in Garfield County, CO, I spend over 500 hours on the pre-work prior to starting facility design. It is very complex and a huge amount of "engineering judgement" needs to go into hundreds of decisions.

The liners (yes you have to have two) must be selected for their specific performance in contact with the fluids you are evaporating, and the design of the leak-detection system between the liners is a week's work.

Design of inlet facilities is another couple of weeks.

Finally, you have to work out your strategy for mucking the solids from the pond (not a trivial task, do you shut down the facility while removing the accumulated solids, or do you build your pond with sections to allow it to stay in service while solids are removed and liners replaced?)

I'm working on permitting a pond in New Mexico, and the first step in the permitting process (the regs allow 60 days) is now in its 10th month.

Oh, by the way, if your "impoundment" has over a certain number of acre-ft of water and/or if your largest wall is over a certain height then the pond suddenly must be permitted both by the state and by the Corps of Engineers. Have you thought about how to keep migrating birds off the pond?

I have a rule of thumb for your--hire someone who know what they're doing before you get into deep trouble.



David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[StoneCold]

zdas04
I am always in deep trouble! But you may be right that I need some help on this. I seem to have trouble getting constulants to do anything helpful for me. By the time I have answered all there questions I could have just done the work but that is another topic.

I just want to kick around the basics to see if it will fly, and to see how big it is. My other alternative is to concentrate my water in a brine type evaporator and truck it off. That ain't cheap!.

Regards

 

[zdas04]

Stonecold,
I hear that from clients all the time. Evaporation ponds seem to be one of those things that come into the category "the definition of 'easy' is 'someone else has to do it'". These things just look to be far too simple to be as difficult as they end up being. Engineers tend to want to either leave them earthen or make them into plants. None of the big firms ever builds a second one so they never get really good at it.

I did a talk on getting rid of produced water at the Four Corners Oil & Gas show in 2006 and the PowerPoint handouts are at

http://www.muleshoe-eng.com/sitebuildercontent/sitebuilderfiles/producedwaterhandouts.pdf

the discussion of evaporation ponds starts at page 13. It should give you a feel for the scope of work.

David

 

[StoneCold]

Thanks David

 

[zerosum]

Very nice presentation, zdas.

 

[zdas04]

Thank you, it was pretty well received the only time I put it on. It is amazing how people who have no problem sending people to annual HAZWOPR training won't consider any courses that aren't in the mainstream. Produced water represents 40-80% of Oil & Gas Lease Operating Expenses in most companies and yet they still want to do it by the seat of their pants.

David

 

[cub3bead]

zdas04,

Great job in explaining that a task that appears simple is far from that.

Pan evaporation rates are widely used to estimate evap pond sizes but you can run into some serious problems when the salinity in the pond gets high. Hydrate formation tends to hinder evaporation much like the bird netting and wind fences. In desert climates like NM and CO designing for an evaporation rate much higher than an average annual loading of 2 gpm/acre is asking for problems.

The problem with mucking out the ponds is what to do with the accumulated salt. The high sodium content will limit where you can place it as it will readily leach. I have always felt it was better to design and permit the site as a landfill and when the pond filled up with salt, close and cap it.

 

[StoneCold]

My project is for a small chemical plant. So filling it in and leaving it will not work. Most of my blowdown is probably biological material and Calcium but I suppose if we had a water softener then we could get a lot of sodium.

We are looking at the pond as an option to mechanical evaporation using steam or natural gas. They are all cheaper than trucking it off but I am not sure that the pond beats the evaporators by much when you consider the cost of construction and mucking out the solids later.


Thanks
StoneCold

 

[zdas04]

Careful StoneCold. The solids are dissolved in the water. Turning the H2O into vapor will leave the solids behind. That is true with evaporators or with ponds. In an evaporator it becomes boiler scale that can require monthly chipping (with 10,000 mg/L TDS, nastier water will require more frequent cleaning, cleaner water less frequent). We don't see that kind of solids accumulation in boilers because boiler feed water is really pure (if I remember the specs we used in the Nuc plant were around 10 mg/L TDS).

It is very possible that pond muck will be classified as "dirt" and can be disposed of anywhere that you can get rid of dirt. In a chemical plant you'll certainly be required to test it for various nasty chemicals and NORM, but if it passes those tests then it can go to a landfill in most states.

Liners have a finite life, so it is prudent to design a pond such that you approach maximum solids around the same time as the liner integrity becomes suspect (I generally use 10-15 years).

The evaporator vs. pond decision is really a CapEx vs OpEx analysis. The pond is all Capital and the evaporator is minimal capital and a ton of operating expense. As natural gas prices go up, the balance shifts significantly towards ponds.

David

 

[StoneCold]

David
I agree that there will be salts, they will pile up but I think that biological will pile up faster. Just my gut feeling on that.

You are right about the CapEx vs OpEx on the evaporator. But since the plant is in northern colorado I have to take into account the fact that I am not going to get much evaporation from November to the end of Feb. So then I end up with the situation where 8 months of evaporation has to balance 12 months of water in. I am not sure I have enough open area dirt to make that happen.

Thanks
Brad

 

[zdas04]

Ever hear of Freeze/Thaw evaporation (Google "freeze thaw evaporation")? I recently did an a evaluation of a site between Caspar, WY and Seminole, WY and found that it came through the winter with a lower pond-level than it started the winter.

There is no reason that a properly designed facility wouldn't work year round.

David

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[cub3bead]

Sublimination is an amazing phenomenon. I have only seen it happen once. I spent one winter in the Canadian arctic and saw the snow slowly disappear while the ambient temperature stayed well below freezing.

 

[zdas04]

I like to use evaporation accelerators from a company called Snow Machines, Inc (SMI). As the company name implies, they started out making snow at ski resorts. They found that they had a significant make-up water requirement in freezing weather and wondered if anyone might be interested in causing evaporation. The coal mines were pretty interested and now SMI has a line of units that are just for evaporation.

David

 

[HEC]

StoneCold
Looks like a very challenging problem you have there. Just the reason I started engineering!

From the discussions so far it sounds like most of the issues are being uncovered. I was dealing recently with a evap pond that had silted with acidic/metalurgical waste muck! The issue was no one had thought about how to remove muck from the pond. As you have already identified the need to remove the solids why not design the pond with solids removal equipment. Just throwing ideas up, an interesting application for an Archemedies screw was on a Pulp mill effluent pond to extract sludge from teh bottom of the pond and also served as aeriation to address the high BOD/COD load for the effluent. In your application this splash would assist in evaporation as well as providing a method for sludge/solids removal. Is there any further value for the biological blowdown?

Cheers

Mark Hutton

 

[leakyseal]

Metcalfe and Eddy, "Wastewater Engineering" has some design guidelines for evaporation ponds. Be warned that it's primarily a civvy book and takes a fairly lighthearted approach to mass transfer concepts. The method won't get you all the way there but we've used it for estimating in alternatives studies.

Don't forget to report back and let us know how it went!

- leakyseal, former polymer guy, now working wastewater eng

 

[davefitz]

There were some studies done circa 1980 to use evap ponds in lieu of cooling towers for large power plants. The published papers and computer programs by MIT are associated with their computer program " MITEMP" and also published in EPRI report CS-4320. The correlations are sumarized in a 2 page appendix that can easily be programmed onto an excel spreadsheet.

As far as simply constructing an impoundment and forgetting about all other issues, just be darn sure the impoundment liner, base, walls, etc are designed by an experienced dam designer and not just copied out of a civil engineering text book. These simple objects really can fail .