Aussies believe in global warming...

So, there is indeed a market for what I called the byproducts of desalination. Seems to me the most valuable part of the salt operation - the water - is being thrown away. What about a big clear poly tarp over one of those ponds?

edit: Pat, I couldn't see your pictures for some reason.

 

The end water quality, as measured in TDS, is much better with flash evaporators. One can expect 1-10 ppm TDS in the form of salt. You're not supposed to drink water with >500 ppm TDS salt.

The residuals/retentate would have industrial uses. If they were disposed of, an outfall pipe would have to be located far enough offshore to allow mixing

No, it would actually be more cost effective to find uses for the residuals/retentate

 

The chemistry is fairly easy to follow. Would you like me to get into it?

 

At this point, it's probably cheaper for them to concentrate on the commercial/industrial uses for seawater. To produce potable water from the process would require a lot of extra treatment, which may be cost prohibitive at this point

 

Would it make sense to "dump" the "waste" from the desal plant into the salt evaporation ponds Jay? If one party needs salt and another needs water it seems to make sense to me.

My brother once explained it all to me, he works for Penrice, but it goes in one ear and out the other, not much spongy stuff in the middle.

 

Yes, that would work. Much better yield if you purposely flash-evaporate, but no reason why "natural" evaporation wouldn't work

Nonsense. I'd be happy to explain the chemistry, if you wish

 

What about water of sufficient quality for irrigation? It may be cheaper for now to import drinking water in little bottles, but Australia, among other places, is suffering a prolonged drought, and may be losing its ability to feed itself. "Cost prohibitive" may not be the deciding factor when people are dying of thirst and hunger.

Please do. I can't promise I'll be able to follow it, but I'll try. I'm also curious about the potential volumes of power and water produced - is it more efficient to have several smaller plants, or fewer large ones?

 

Yes, it really is a matter of perspective. As an example, the community I now live in gets all its water from municipal wells that are 90-280 ft deep. I'm billed every quarter for water/sewer.

In winter, I can expect to pay around $60 every three months, for combined sewer and water, or around $20 a month. I'm not stingy with bathing, clothes washing, etc. In summer, watering the lawn to keep it lush, I can expect to pay around $150 for the quarter.

That's *really* cheap. A lot of folks don't realize just how lucky we have it in areas with plentiful water supplies

Ok, let's start first with the example that Pat used, Soda Ash. Soda ash is a very important component of the chemical industry, indeed it's the Alkali Industry in its own right. Producing soda ash also results in baking soda, caustic soda, sodium tripolyphosphate, and sodium sulfite

Soda ash is anhydrous sodium carbonate, or Na2CO3. It occurs naturally with mineral deposits of nahcolite and trona. It can be derived synthetically from ammonia, limestone, and salt, by using the Solvay Process

Salt can be found in natural brine lakes. Perhaps you know of Owens Lake and Searles Lake in California. Seawater that is flash evaporated will produce copious amounts of brine, so will the residuum from RO commercial processes

The Solvay Process has as primary ingredients brine, and limestone, which are very plentiful. Ammonia is also used, along with carbon dioxide gas.

The first step: Typically you have two reaction towers. The first tower has the brine, through which the ammonia is bubbled through. This mixture is sent through the second tower, which has the CO2 bubbled through it. Remember, you have a liquid mixture of brine (NaCl) and ammonia (NH3), through which you bubble CO2 gas:

NaCl + CO2 + NH3 + H20

and you get

NaHCO3 + NH4Cl

NaHCO3 is sodium bicarbonate, and NH4Cl is ammonium chloride. When you bubble the CO2 through the ammoniated brine, the NahCO3 precipitates out

The process is very efficient. The CaCO3 "limestone" is heated in a kiln to very high temps, around +1,000 C. From heating the CaCO3:

CO2 + CaO

The CaO is also known as quicklime

The NaHCO3 precipitate from the second tower is filtered out from the ammonium chloride, then the CaO is added to the ammonium chloride:

2NH4Cl + CaO

Resulting in

2NH3 + CaCl2 + H2O

The ammonia is sent into a recycle stream back to the start of the process. Calcium chloride has a lot of uses, it's not "waste" at all

Remember the sodium bicarb? The 2NaHCO3 is heated to around +220 C, which gives us:

Na2CO3 + H2O + CO2

Almost all of the water, carbon dioxide, and ammonia can be recycled internally, needing only minor makeup of ammonia. The major input is thermal energy

Please let me know what you would like discussed next.

 

This is great, Jayman. Thanks.

Yes, ours is priced cheaply too, and not even metered - just a flat rate added to the annual property tax bill. No one seems too concerned about consumption. Although, we've had summer water restrictions for awhile now, which seems odd in a rainforest...

Cool. Here I wanted to make water, and there are whole industries built around the 'byproducts'.

Indeed, I do. One of my many interests is railways, and there was once a quaint narrow gauge line through that valley, with stunning Eastern vistas of the Sierras.

So, we need sun, the occasional tank car of ammonia, seawater, and a big pot to boil it in. I assume by 'flash evaporation' you mean something like heating the pot first, then dumping in the water, and collecting the condensate on the inside of the lid. With a main 'solar furnace' heat collector, the right amount of heat could be distributed to the towers and evaporators. I'm thinking of a clear-domed structure with a 'reverse hydronic' system within a concrete base, a big mess of pipes, and a long intake hose all the way from the ocean. You can think of it as making salt by sucking the water out, and I'll think of it as a teakettle that needs to be scraped clean every so often.

Careful. I could pick your brains all day.

What size operation would be needed to produce these materials in industrial quantities at a competitive price?

Do you think it's feasible to produce high quality potable water - which sells for more than gasoline, by the way, even in places where the tap water is fine, plentiful, and virtually free - in conjunction with an industrial alkali plant?

Any idea how much less expensive it would be to produce irrigation water rather than drinking water?

 

Thanks Jay, there is a waste which comes out of the plant operated by Penrice Soda Products, it is called Cal-silt, well that is what they call it. Until several years ago it was dumped into the Port River causing silting of the water way and navigation problems. Now it is stored on site until it is trucked to waste dumps around the place. I believe one use is to cap waste dumps to more efficiently recapture the gases from the waste, but I'm not sure about that.

The Penrice plant, which is on Solvay Road, by the way is pretty big, well by Adelaide standards it's big.
From their web site: -

This is a picture of cal-silt being loaded into trucks to be disposed of.


A short video about the clean-up of the Port River where cal-silt has been dumped for 70 years. It also gives a glimpse of the plant.

This plant produces between 75,000 and 100,000 tonnes of Soda Ash per year.

 

Not quite. I should have been more clear about multiple stage flash evaporation, which is adiabatic. The fluid, in this case H2O, is passed through a throttling valve or venturi, into the first stage vessel which is slightly *below* atmospheric pressure

I'm sure you're aware that the boiling point of H2O depends on elevation. Boil water at 10,000 ft AGL and it will "boil" at around 192 F, if I recall. Water will "boil" in a vacuum at room temp

The lower pressure, the venturi, and thermal energy causes *some* of the H2O to flash to vapor, the vapor is collected as mostly potable water. The second vessel will have pressure a bit lower than the first one, the remaining H2O is fed in, some flashes to vapor, etc.

For modern desalination plants, there can be 18-25 such stages. Flash evaporation is *much* more efficient than just boiling the water

No reason why that wouldn't work

A "competitive" price depends on far more than the size of the facility: eg: debt of the company, market conditions, most importantly cost of raw feedstock

As far as plant size, that's all over the map. Maybe 100-500 tons per day?

The water would need additional treatment to make it potable, but I guess that could be done. A typical integrated industrial Alkali plant will also produce caustic soda, so most of the water liberated from making brine is recycled to other plant process systems

Well, obviously you don't need to worry as much about having truly potable water for irrigation. Indeed, you generally do *not* want chlorinated water for irrigation.

As long as the resulting water didn't have heavy metals, it could be a fraction - say 10% - of the cost of household water

An important consideration of recycle/reclaimed water from a desalination or brine process: you absolutely need to ensure the TDS is well under 100 ppm for irrigation. The maximum safe drinking limit is around 500 ppm

If you irrigate with water that has moderate brine, after further evaporation on crops and percolating into local soils, you can introduce brackish water into local water supplies

 

Yes, I know what that is. One of the leftovers from screening and filtering the product streams - this depends on feedstock content too - is that silty stuff

I was under the impression the silt could be used as soil supplement. A lot of similar plants in North America will use the silt leftover as soil supplement or for erosion control

Note: as far as I know, the Solvay Process is no longer used in North America. The natural deposits I mentioned earlier are much cheaper source of soda ash. However, in other parts of the world, the Solvay Process is widely used in the Alkali industry

A further note/warning on feedstocks. There can be trace contamination with toxic components such as arsenic and mercury, which will naturally end up in the silt stream

There was a Solvay Process plant somewhere in the state of New York that contaminated a local lake with mercury. This was due to the feedstock containing trace mercury; eg the limestone contained high amounts of ferrugenous mercury

At one time, the Castner-Kellner Process was used to produce chlorine and sodium hydroxide. This was used in North America at pulp and paper mills to "bleach" the pulp.

The Castner-Kellner Process uses elemental mercury as the cathode in the electrolysis of sodium chloride. As part of a cleaning wash cycle, elemental mercury is lost to the environment. Perhaps the worst example of elemental mercury poisoning can be found in Dryden, Ontario

[ame="http://en.wikipedia.org/wiki/Ontario_Minamata_disease"]Ontario Minamata disease - Wikipedia, the free encyclopedia[/ame]

Of course, since it happened in Canada, there is no such thing as a Superfund Site designation. Everybody hopes that just by leaving the estimated 9,000 kg of lost mercury alone, it will magically go away.

Of course, Ontario heavily salts the roads in winter. The spring runoff of that salt will enter the affected waterways, which tends to liberate the elemental mercury. I sure as hell wouldn't try fishing downstream of that paper mill

For some reason, the Castner-Kellner Process is still widely used in Europe. I guess they don't care about elemental mercury in their rivers

 

Ah, I hadn't thought about lowering the pressure, which should have been obvious. That must be where the increased efficiency comes from. Would there be any additional gains in having a cooled surface for the vapour to condense on?

Wouldn't one of the feedstocks (oceanwater) be 'free', requiring only pumping? But, the pumps and pipes may not be cheap if exotic metals are required to handle the corrosiveness of the salt water. Would the requirements be lower than with say, a pulp mill?

I'm wondering about two very different plant sizes, actually. One mega-operation that could supply a city, and a much smaller one to serve third world coastal villages.

So, there isn't really any leftover water? Is it a case of making either water or alkili products, but not both?

That's a huge difference, which means an alkili plant would more likely be interested in producing water for irrigation than public consumption. But, there's a big price difference in finished product there, too, so profit margin would be the deciding factor. Is there a case here for convincing an alkili plant to 'cogenerate' water? Do they generally use evaporative ponds, with no attempt to concentrate solar energy or capture the water?

Thanks again for the chemistry lesson. I had tinkertoy molecules dancing through my dreams all night, but couldn't for the life of me remember the number of outer-shell electrons and how many of one element joins with the other. In my sleep, the numbers on the periodic table were too small to read without my glasses.

 

I showed my son this some time back.
Half fill a syringe with water, block the end with your finger, no needle of course, then pull back on the plunger and the water boils in the syringe. I often wonder why this affect isn't used in air conditioning but I guess cavitation could be an issue.

 

Yes, but that would be more than offset by decreased life of the vessel. There tends to be metal cracking. There are batch reactors that have double-wall design for heating, either a hot process fluid or steam is circulated between the two walls

Do you mean just to make potable water, or in the case of the Solvay Process soda ash plant?? In the case of the Solvay Process, you need raw inputs like limestone, a lime kiln to cook the limestone, and initial and makeup amounts of ammonia

Pumps, valving, and piping for corrosive environments (Salt water, caustic solutions, etc) are common stock, readily available. The higher upfront is more than made up for in longer life. Selecting improper piping, valving, and pumps results in very short, troublesome operations

Economies of scale do apply. However, for the third world example with no real alternatives, the "cost" is still far cheaper than thirst and disease

In the case of an Alkali plant, the recycle water is generally used in other parts of the plant. Eg: cooling, steam plant, etc. They are not specifically designed to route the recycle water to other use, eg potable water

Recall my caution about contamination from feedstock, eg the ferrugenous mercury that can be found in some limestone sources

Depending on climate, yes evaporator ponds are prefered for older plants. A brand new plant, a very effective arguement could be made for having different applications - say irrigation - for the water assuming it isn't contaminated with heavy metals.

A brand new plant will generally have much higher process water effeciency compared to older plants. It's too bad more community involvement isn't in the planning stage

I generally prefer naughty dreams over boring work dreams

 

Actually, that effect is used in refrigeration and air conditioning

When the compressor raises the pressure of the refrigerant the liquid refrigerant is sent to the evaporator coil. It passes through a restriction orifice - imagine a jet on an old Holley carburetor - which is the expansion valve

The high pressure liquid refrigerant than sprays into a low pressure enclosed space, where it flashes into a vapor. This causes rapid cooling, indeed frost can easily form on the evaporator coil

This process isn't magic and does NOT violate any "laws." Work must be done (Compressor, condenser, to move heat) and the second law of thermodynamics is satisfied

 

Yep, knew all that, I used to repair air conditioners. I meant use water as the refrigerant in a vacuum on the low pressure side. I'm guessing it would cause cavitation and corrosion.

 

Here is a picture of my brother at work, well he is most likely ordering a pizza for dinner but it looks like a business call.

Shhhhh!:tape: don't tell anyone, that's also Bev's husband.

 

well the benefits of a plentiful water supply are many...

irrigation, aluminum plants...ya aluminum plants. most is created thru electrolysis of sorts (OK Jay, please dont hammer me on terminology!!) which needs a lot of power, so aluminum plants are situated next to the dams on the river (bear in mind that the other side of the dam sits computer server farms which need even more power!!) where power is plentiful cheap and easy to redirect (yep, if having power issues, aluminum plants are shut down)

unfortunately, without a high efficiency smart electrical grid, we get to use our power in this fashion simply because current technology and regulations do not allow us to sell power to places that need it much more than we do. we do our best to sell as much as we can, throttle down the system as much as we can during lull periods, etc and still have a retention pond...

the retention ponds are used when water has to be released to prevent damage to the dam, but no one can use the resulting electricity that is generated. so electric pumps are used to pump the water back up over the dam to a pond that stores it in case we need it later when the water level is low, irrigation for summer etc... the ROI on this process is about 5%...which means for every 20 KW we put in, we get one KW out...

now, if anyone should think that EV's wont work because our grid could not handle it, please re-read above.

 

He is my own Homer Simpson, he's an environmentalist isn't he?
Ha Ha