Direct Seawater Cooling

In coastal areas or on offshore platforms, where there is little or no fresh water for cooling services, seawater theoretically makes the best heat sink. Seawater is one of the most abundant, efficient, and inexpensive cooling mediums available. Seawater cooled plants utilize a once-through delivery method for direct or indirect contact with the process heat exchangers. Reliability and maintainability of heat exchangers is perhaps the most critical factor in the consideration of seawater cooling.

Direct seawater cooling is often problematic because of the scale produced on the tube-walls by the heated seawater. With the self-cleaning fluidized bed heat exchangers, the scaling issue can be solved. Direct seawater cooling has already been successfully demonstrated in seawater desalination plants using self-cleaning heat exchangers. Applications for the self-cleaning heat exchanger can be a closed-loop cooler or direct seawater cooler for high pressure gas.

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Closed-loop Cooler

The main purpose of the application of a closed-loop cooler is to avoid the use of seawater in a large number of plant coolers and thereby concentrate the problems of corrosion and fouling in a few very large seawater-cooled closed-loop coolers which are responsible for the cooling of the closed- loop fluid used throughout the plant. Normally, this closed-loop fluid is conditioned water which does not foul or corrode the shell-side of either the closed-loop coolers or the exchangers in the plant. Neither does it foul or corrode the connecting piping, the pumps, the valves, etc. in the clean coolant circuit between the closed-loop coolers and the exchangers in the plant.

Self-cleaning closed-loop coolers have the advantage that they completely eliminate the fouling problems caused by the seawater due to the circulation of the cleaning particles through the tubes. Elimination of fouling lowers the risk of corrosion and makes it possible to consider the use of cheaper materials, e.g. duplex instead of titanium. Large closed-loop coolers and steam condensers operating on severely fouling cooling waters can de added to the list of potential applications for the self-cleaning heat exchanger which employs a fluidised bed of particles circulating through the tubes of a vertical shell-and-tube heat exchanger.

Direct Seawater Cooler for High Pressure Gas

Cooling applications which could make use of untreated natural seawater as a coolant are on offshore platforms. Properties which influence the choice for heat exchangers performing a cooling service on an offshore platform, are the following: Reliability, Maintenance, Weight,Plot area and Power consumption.

It is evident that reliability and maintenance of the installed equipment are important as they directly influence production. Moreover and different from onshore installations, the weight and the plot area of heat exchangers on offshore platforms are very important, because they directly influence the cost of the platform.

For a Direct Seawater Cooler for High Pressure Gas, a self-cleaning cooler with untreated natural seawater in the shell and high-pressure gas in the tubes can be applied.

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