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Massachusetts Considering Desalination Plants
Iphtashu Fitz writes "Despite a reservoir system containing some 412 billion gallons of water for Boston and surrounding communities, some eastern Massachusetts towns are facing water shortages and are now considering water desalination plants as a new source of fresh drinking water. The city of Brockton, 20 miles south of Boston, has plans in the works to build a $40 million plant and could begin construction as soon as this September. Currently there are fewer than 100 desalination plants in the US and most of them are in smaller communities, but that seems to be changing. The largest desalination plant in the country is located in Tampa, FL, which expects it to provide 10% of the citys drinking water by 2008. California also has at least 10 large scale plants on the drawing board. Some environmental organizations like the Conservation Law Foundation dispute the need for desalination plants however. They argue that many water shortages could simply be solved by better conservation of existing supplies."
Wouldn't it be just easier to buy bottled water than build a whole plant ??
what harm is there from desalinaiton plants? sea level dropping? why are environmental groups protesting it?
The war with islam is a war on the beast
The war on terror is a war for peace
The city of Brockton, 20 miles south of Boston,
I hear that Ogdenville and North Haverbrook have also installed desalinazation plants and look....it put them on the map!
Conservation only works when people contribute to the effort. These days people use water for household uses, lawns, washing cars, etc. Once we are used to having it on demand, it's kinda hard to think about conserving. Ususally it's too late when a shortage occurs. Might as well start building the plants now, by the time they are finished being built, they will be needed.
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Retail Retreat
They should do what I saw in family guy. They just had a machine combined an oxygen molecule with 2 hydrogen. The water it made was really good.
They should try talking to the arab states which produce 60% of the worlds desalinated water . They are even considering injecting the desalinated water into the ground to raise the groundwater level.
At the moment the biggest problem with desalination plants is not just their high build cost, but their high operational cost.
When using technologies such as reverse osmosis the energy costs for pushing high volumes of water at high pressures through the membranes is prohibitive, not to mention the wear on the equipment it's self. In a traditional water treatment plant most of the filtering is done with gravity.
Life is Short and Hard like a body building Elf
Oh if only we hadn't dumped all that salt into the oceans!
Just another example of putting WAY too much emphasis on the "common" and none on the "sense."
common sense: noun
What those who are ignorant of the subject matter think; usually wrong.
Which method is cheapest overall?
Reverse osmosis has been shown to be the most economical in many cases due to its lower energy consumption, leading to lower unit water costs. However, the process has higher up-front investment costs compared to thermal processes. Its unit water costs are primarily determined by membrane life and energy cost (Ericsson et al., 1987; Wade, 1987). Reverse osmosis plants have flexibility of operation in the face of fluctuating water demand and benefit a little from economies of size.
Several economic trends for multistage flash distillation plants are apparent: a relatively low investment cost, benefits from economies of size (relative to other processes), site specific costs (for example pretreatment requirements, energy costs) have a direct affect on the unit water costs, and low flexibility in response to variable water demand (meaning that freshwater production cannot be adapted to fluctuating demand ) (d'Orival, 1967; California Coastal Commission, 1993). The main economic drivers for multistage flash distillation are costs of materials and energy, and increasing plant capacity to take advantage of economies of size (Water Corporation, 2000).
Comparing multistage flash distillation and reverse osmosis, the distillation process has been the preferred method due to its reputation as a mature and reliable process. However, reverse osmosis plants are replacing the older multistage flash distillation plants of the Middle East and being the first choice for desalination implementation in Australia. This is due to their simpler operation, reductions in energy consumption and ultimately, cheaper unit costs of fresh water (Anon, 1999a; Glueckstern, 1999). The overall cost of fresh water from a reverse osmosis plant is often less than half of that produced by means of distillation (Water Corporation, 2000). As technical advancements of membrane processes improve their costs and efficiency, they will continue to be the preferred choice for countries moving into desalination.
Presently, the reported costs of desalinating water using current technologies fall within the range A$0.80/kL to A$2.10/kL, depending upon the process, location and the potential for blending with marginal quality groundwater (Water Corporation, 2000). These costs do not include disposal or distribution costs.
Read more here.
You seem to be completely unfamiliar with all the techniques of water desalination. Saltwater Desalination: Chapter 1 will educate you. Of particular interest is http://www.coastal.ca.gov/desalrpt/dc1tbl1.gif this chart which shows that distillation consumes much less power than reverse osmosis
Even those who arrange and design shrubberies are under considerable economic stress at this period in history.
They argue that many water shortages could simply be solved by better conservation of existing supplies.
Well DUH. The people aren't trying to solve a 'water shortage' problem. They are trying to solve a "demand exceeds supply" problem. They don't have a reason to deny people the water they want to use if the people are willing to pay a higher cost. Eventually they hit a price point where people will naturally conserve water.
Water is a reusable natural resource. It's not easy to come up with a reason to conserve it, since they are already conserving it with water treatment plants.
Think of the water system as a closed system. The only unaccounted for openings are evaporation, and letting it go into the water table (ground, streams, ocean, etc). Otherwise the water is contained entirely in storage, pipes, and treatment plants. To offset evaporation and adding to the water table a system must have a certian amount of intake from wells or another water source. A water shortage doesn't necessarily mean that not enough water is being produced, it means that the system has reached its capacity --> the treatement plants are supplying less water per day than people are consuming, and they are draining (slowly) their reserves of treated water. Alternately more and more water is being stored in additional piping added by new neighborhoods/buildings or evaporated/drained into the environment by new lawns and pools and not enough used water is getting back to the treatment plants. The wells and other 'new water' sources are too stressed.
There are two ways of combating this - either take in more water from the environment, or increase the efficiency of the treatment system (more plants, better plants, etc) Obviously the second problem can only be solved by getting more 'new water' into the system. In many cities it makes more sense to place a new well than to upgrade the treatement plant, especially if the treatement plant isn't at capacity. In many cases a well cannot be placed because it puts too much strain on the water table, so a desalination plant makes very good sense.
The environmental people are not complaining so much because they feel we are destroying the planet as they are complaining because it's a symptom of our consumerism which they fundamentally oppose on principle. If they can get everyone else to 'think green' in general then they hope that other problems which do directly affect the environment will also abate.
Oh, and yes, desalination does stress the water source. If they do not process the salt into other forms then the source many become too salty near the plant. If they do not replace the salt then it may not be salty enough. Either way, a desalination plant affects the water source. Whether that's bad or good is subjective.
-Adam
Big deal. Just build a nuclear power plant next to them. Problem solved. Oh, and the excess energy can be used to power the baby seal slaughterhouse and for rendering whale blubber.
Is it just me, or does this sound like a headline from the newspaper in the original Sim City? :)
Right up there with "Metroville Builds Airport".
gadgetophile.com
We can thank Ted Kennedy for pushing for this initiative. He is tired of salt water ruining his clothes when he goes driving.
Don't blame Durga. I voted for Centauri.
Boiling a pound of water at atmospheric pressure takes roughly 1000 BTU's, and there are 140,000 BTU's in a gallon of fuel oil. So a gallon of oil can boil 140 pounds of water or about 18 gallons. That is a lot of oil.
But if you boil a pound of water to remove the salt, condense it, you are throwing away all of that heat released when it condenses, almost as much as required to boil it. How can you recover that heat since you are going to boil at a slightly higher temp and condense at a lower temp and heat cannot move uphill?
One technique is multi-effect distillation. You boil and then condense at atmospheric pressure. The condensing at atmospheric pressure is hot enough to boil at some pressure below atmospheric. You condense and then use that heat to boil at an even lower pressure. You keep going until you are what ever vacuum pressure boils water at room temperature. The same 1000 BTU's to boil a pound of water is used several times to boil several pounds of water in several "effects" (stages of the still).
The other method is mechanical vapor compression. If you take the vapor from boiling and compress it in an centrifugal compressor, it can condense at a somewhat higher temperature, and you use that heat to boil the water feeding the compressor. While it seems like pulling yourself up from your bootstraps and violating a thermodynamic law, it is not that much different than a heat pump.
There is some minimum energy required to desalinate water, it is much less than 1000 BTU per pound, and if you know the osmotic pressure for that salt concentration, you take that pressure and the volume of water you want and use work = pressure times volume. That energy is not without consequence, and that is why you probably want to desalinate brackish (slightly salty -- often available from wells when pure water is not available) than going for sea water.
Also, there is some effort in approaching the thermodynamic "reversible" minimum energy of desalination. The multi-effect stills and the vapor compression still have to move large amounts of heat through heat exchangers at small temperature differentials. With reverse osmosis, you probably are pumping harder than the bare minimum to oppose the osmotic pressure so you get enough fluid through the membrane to make it worthwhile.
Multi-effect distillation is probably the way to go for big plants, vapor compression for mid-sized, and reverse osmosis is really probably only effective for small-scale stuff because the membranes are expensive and need replacement. Even with what I said, the energy needs are not trivial -- perhaps you want some kind of cogeneration where you run a multi-effect still from the waste heat stream of a gas turbine.
One of the nice features is that you can buy things like water and electricity from your neighboring cities for a price. This price tends to be higher per unit of supply than you could provide with a structure like a power plant or water pump, but requires far less up front cost. The not so nice thing is that your neighbors will occassionally renegotiate the price with you, meaning you'll pay more each month if you want to continue getting these supplies.
The joke in the previous post is based on the fact that you could import water (based on the bottled water comment) or that you could build a costly desalination plant (as the article suggests is happening). In sim-city you'll get shafted in time if you don't provide your own facilities, thus the neighbors raising the cost of bottled water is funny.
Now I feel like one of those people that analyzes a joke until it isn't funny. However, I went to the trouble of explaining for the poor non-sim-city player so I'm just going to post it... blah. The interesting thing is that bottled water seems to be pretty expensive anyway, and building one of these big plants is probably well worth the trouble in the long run.
If not now, when?