seawater make-up cooling tower

Whatever salt you emit came from the sea in the first place. Whatever water evaporates will eventually condense as rain and get back to the sea also. So you don't need to worry about the sea, although you may need to worry about pseud-environmentalists that don't understand simple systems concepts....

On the other hand, there will be a tendency to precipitate/deposit salt on various surfaces of the cooling tower. Avoiding alternate wetting/drying cycles will help. And maybe a fresh water rinse or washdown from time to time.

Piping and wet deck components of say PVC and 316SS will help to resist corrosion.

The amount of salt in the drift is not likely to be much of an addition to the salt already in the air around coastal installations. On this point I am uncertain, so further checking is advised.

I don't yet know the best answer to barnacles in the piping, or how well an occasional backflush with fresh water might help.

Thank you Tornado;

The salt consentration in the make up is about 37 psu; with a COC of 1.4 the concentration of blowdown becomes about 50 psu. I am not so sure this much concentration change affects the life formation in the discharge point or not.

The cooling tower material will be selected according to salty environment, my main concern is salt emission to atmosphere with drift, affects the other equipment eg. boiler.

Good point. There would be a probably localized area of higher salt concentration. Tidal action will mitigate this, or maybe even a distribution network on the outfall lines.

To my recollection, sea water is about 37 thousand parts per million salt. I'm not familiar with your psu or COC terms. If you are introducing hot salt water to a cooling tower, I expect it to release only water vapor to the air, and I expect it do deposit a lot of salt on the walls of the tower as the water evaporates. The water that makes it back to the sea will be saltier than what left.

Operating reverse osmosis machines, I observed the discharge, which was much saltier than the ocean. There was no problem, sea life was doing quite well right next to the discharge.

The other poster mentioned another problem, barnacles in the input pipe. Good luck with them. Have your pipe removable in sections so you can rod them out from time to time. Barnacles just love pipes with flowing water bringing them food, etc.

What kind of device is this you have, a flash evaporator?

Dear Hopefully,

For many years a condensing tower for amonia gas ( then refrigerant for a major refrigeration plant) was used for both the cooling of the very large compressors and their diesel powered prime movers.

As I was involved with both the construction and later Management of this installation , I can tell you the following facts:

a.electrolytic precautions are needed so that whatever the tubing ( then in metal) as well as the cylinder walls of the condensers have to be protected by : anodes.

b.Build up of the accretion in the external surfaces need to be envisaged and regularly cleaned . Mostly corraliferous of origins which can be diluted by various cleaners with acidic contents .

c.As even now all marine engines including supertanker huge diesels or steam engines are constantly using the cooling of : sea-water. Do not think that such use is on a : small scale. As we speak the through-put is enormous !

Good luck,

Labor Omnia Vincit.

Hi, Hopefully.

There are three kinds of cooling systems that you can use: shell-and-tube coolers connected either to ocean or to cooling towers; a Wet-Surface Air-Cooled (WSAC) coolers; and fin-fan, forced-air radiators.

The radiator approach is straightforward: the thing consists of a big chunk of metal with fins of it, and it dissipates heat by conduction (to a circulating cooling fluid) and/or convection (to ambient air), and by radiation (it glows in infrared ... if it glows in visible light, you've got a problem). Assuming the usual convection and radiation approach, the radiator's cooling capacity is limited by the temperature of the ambient air; the warmer the ambient, the less heat the radiator can dissipate by convection. Radiation capacity is affected in the reverse sense (the cooler the radiator, the less it radiates), but its radiation capacity drops much less than its convection capacity rises as ambient temperature drops. Advantages: no cooling-water used; radiators release all heat to the surrounding environment (air, and line-of-sight for radiation). Disadvantages: costs more than other options (radiators are big chunks of metal with fans blowing air on them); and is least performant of them all.

WSAC coolers shouldn't (can't?) be used here. They work like radiators (the AC, 'air-cooled', in their name) to which water sprays have been added. Water evaporates on the heat-dissipation surfaces, it absorbs a lot of heat (in the form of latent heat) as it does so, and the resulting vapour carries away to atmosphere the heat absorbed. In addition, since air is blown across the heat-transfer surfaces (like for radiators), heat gets transfered to ambient air by convection. The problem, if seawater is used, is that salt will cake on WSAC-cooler heat-transfer surfaces and prevent the WSACs from working. Advantages: better performance than radiators; cost less than radiators; spray-water can be turned off when ambient temperatures gets cold enough (e.g., in wintertime here in Canada ... the water would freeze in the spray nozzles and headers); releases all heat to ambient environment, like radiator; releases water vapour to environment. Disadvantages: in this case, seawater salt would cake the heat-transfer surfaces, meaning that the 'WS, wet-surface' effect can't be used; since the WSAC would then be a radiator that would cost more than an air-cooled-only radiator of the same capacity, WSACs can't be used for saltwater applications.

Shell-and-tube coolers connected to cooling towers have performances similar to WSAC units. In such systems, water passes through shell-and-tube coolers and gets sent to cooling towers, from whose tops it's sprayed through nozzles into a rising draft. The 'artificial rain' created in the cooling towers loses heat by convection to the ambient air being blown upwards, and part of it (typically 3% of the flow) evaporates (thus absorbing heat in the form of latent heat) and gets blown away. The cooled water then falls into a pond, from which it's pumped back to the cooler. The cooling water has to be replenished to compensate for the three-odd percent lost per cycle. The cooling also has to be blown down (partially flushed out) to prevent salt concentration from rising in the closed water-circuit. Advantages: water gets recycled, so this approach uses much less water than a shell-and-tube fed directly from the ocean (which would release hot water to ocean); it releases all heat to atmosphere (to air and through water vapour to atmosphere), not to ocean; cooling performance is similar to that of WSAC coolers. Disadvantages: salt will cake on spray nozzles in the cooling towers, which is a major operational issue; salt concentration will rise and salt will precipitate in the cooling-tower pool and in other places if the concentration becomes too high; keeping the concentration down means maintaining cooling-water blowdown-flow (back to ocean, presumably) high enough, meaning that more water must be drawn from ocean (environmental impact); however, keeping the concentration low enough ensures that the concentration in the water released back to ocean won't be much higher than that in the ocean; higher capital cost than WSAC units; takes more space (bigger footprint) than that of same-capacity WSAC unit; CONSUMES SIGNIFICANT ENERGY, which is needed to blow cooling air up cooling towers.

Lastly, a shell-and-tube cooler with water drawn (pumped) from the ocean and hot water released back to it. Advantages: lowest capital cost (shell-and-tube coolers are the simplest and least-costly ones), easiest maintenance; least space-consuming; no problem with salt precipitation; highest performance of all approaches (cools your process better, which may lead to better process performance, for example if the cooler is a condenser at the outlet of a steam turbine). Disadvantages: almost all heat gets released to ocean, which may not be allowed; consumes some energy to pump water from ocean (I don't know how this compares to cooling-tower power-consumption, but I think it's usually less).

Bottom line: if you can release all of the heat back to ocean, and you can run cooling-water lines to it, and you can draw water from far out enough and deep enough, best go with a once-through shell-and-tube-cooler with water drawn from and released back to the ocean. Otherwise, follow a shell-and-tube-cooler connected to cooling towers approach; you'll get second-best performance compared to the first approach, but it'll be better than that of a radiator. As for the WSAC approach, it can't be used.

I hope this helps. Cheers!

DZ

I would at least go with stainless steel construction for the tower. On the coast in SC, a galvanized cooling tower will last about 5-8 years depending on it's proximity to the ocean salt air. If you are running salt water through the tower, you need to have corrosion protection for the tower and all parts (motors, pumps, etc.). Even so, I still think you are looking at a very short life (5 years?).

I recommend for reading:

http://spxcooling.com/pdf/CTs-and-Salt-Water.pdf

http://www.swrcb.ca.gov/rwqcb3/water_issues/programs/duke_energy/docs/tetra_techs_alt_drift_memo.pdf

http://www.eng-tips.com/faqs.cfm?fid=1152

http://www.process-cooling.com/Articles/Article_Rotation/BNP_GUID_9-5-2006_A_10000000000000597494

Warm seawater is also an excellent medium for the growth of organic systems, so a biocide treatment regime will be required.

Cooling tower operation is potentially hazardous with regard to the bacterium legionella pneumophila, so the biocide regime will need to prevent this as well.

Discuss the problem early with a reputable cooling tower treatment chemicals company.

I share these thoughts concerning the use of (Salt) Seawater in a cooling tower.

Without knowing more details of your project, I would think you will have much residual

salt to deal with. I will not take long for salt to build up in the tower. Also, local town

regulations may not allow seawater to be used in a cooling tower. Sounds like an easy way to operate the cooling tower by using available seawater but the residual buildup of salt in the system may make the project inefficient...Just my thoughts, Mark Abell