Material selection for the Seawater Refrigeration System
Sea Water is the media
The media in this project is the seawater. The water seas and oceans have an average salinity of about 35 kg/m3. The salinity measurement is made by determining its electrical conductivity, which is related to the number of salts dissolved in the water. This property has a fundamental correlation with the corrosion potential. Water itself enables fast oxidation.
Plastic against corrosion
The choice of plastic for the Seawater Refrigeration System
Most of the plants are usually made of high-quality stainless steel. However, acid or saline water limits the working life of this type of piping. Apart from this, copper, another common piping metal, degrades to saltwater a lot easier and faster than other pipes. Cast iron galvanized steel is resistant to saltwater but over time due to exposure will collapse because of corrosion.
In seawater conditions, thermoplastics are able to stand longer, offering excellent corrosion resistance, very smooth interior surfaces to prevent incrustation, and high resistance to a very wide range of chemicals. The reason why plastics are resistant to corrosion is their poor conductivity, which diminishes the electrochemical reactions between the materials and the media.
The material chosen for this project was PE100, as it offers an excellent resistance for the range of temperatures and pressure of the pipelines. Other positive factors of choice are the ease of installation and the low material costs that ended up influencing the final decision.
Cooling of the thermoelectric energy plants
Thermoelectric power plants boil water to create steam, which then spins turbines to generate electricity. Once steam has passed through a turbine, it must be cooled back into the water before it can be reused to produce more electricity. Colder water cools the steam effectively and allows more efficient electricity generation.
The cooling system used in Porvoo Energia is the so-called “once-through”, which takes water from nearby sources (e.g. rivers, lakes, aquifers, sea or ocean), circulate it through pipes to absorb heat from the steam in systems called condensers, and discharge the now warmer water to the local source. Once through systems are popular because of their simplicity, low cost, and the possibility of siting power plants in places with abundant supplies of cooling water.