The Dutch industry (excl. the energy producing sector) uses approx. 3.1 billion m³ water per year. The majority of this water use concerns the use of surface water in once through coolers. In this way approx. 180 PJ of thermal energy is emitted to the environment. ^[1]

Heavy industries such as the petrochemical and refinery industry used to be responsible for 95% of the total water flow with once through cooling. Nowadays because of environmental awareness this water use is decreased. Customers, shareholders and employees expect a sustainable approach from a company. ^[2]

When once through water-cooling is applied, it leads to massive volumes of water. This water is lead through the cooling process as a bypass of a river. The water flow is not only a large local disturbance of the ecosystem around the intake point, but also thermal and other pollution can lead to local disturbances around the outlet point.

The use of surface water as cooling water has several consequences: water animals in the surface water can be damaged when they are sucked into the cooling system; when the heated cooling water is released to the surface water, the temperature of the water increases. Fish are not sensitive to temperatures between 10-24°C. Above 24°C temperature stress will occur, and above 28°C lethal effects can occur for the most sensitive species.^[3]

In extreme hot summers such as the one in 2003, the temperature of the river water can rise so much that power plants are not able to cool their process anymore. When, because of continuous warm weather, the river water reaches temperatures of e.g. 27 ºC, the relative water cooling capacity naturally drops, restricting power plants in their operation furthermore. The power plants are legally restricted temperature wise, to not release once through cooling water above 30 ºC.

A so-called open recirculating cooling system forms an ideal compromise, in which the benefits of water-cooling are preserved and the environmental disadvantages are reduced. Inside these systems cooling water is recirculated in a cooling tower. The evaporation of a small part of the circulating water carries the largest amount of the heat away. The water intake that is needed to refill this part is a factor 50-70 lower then the water intake of a once through system with the same cooling capacity. Worldwide the advance of these systems led to a strong reduction of surface water for cooling purposes. How can an apparent ideal compromise still lead to a bottleneck? The answer to this question is locked in the water chemistry. During evaporation in the cooling tower only water disappears. All dissolved and floated particles remain in the water and will increase in concentration. The final salt concentration is regulated via a blowdown. Most cooling systems operate between a 3- to 8-fold increased salt concentrate. (TDS level) Every contamination that can be found in the make-up water can be found in a 3 to 8 factor in the recirculating water. In a similar way, substances from possible process leaks and floating dust in the air can be accumulated in the recirculating water. In dusty surroundings a 200 MW cooling tower can scrub about 0.25 – 3 tons of dust/day from the air.

All these components are not only increasing in concentration, but also because of the limited blowdown, the components will remain in circulation for a few days to one week. Finally this water is saturated and heated with every circulation in the cooling tower and heat exchangers. The result is water in which all components and conditions are present to stimulate scaling, corrosion and microbiological grow. For these systems supplementary water treatment is required.[2]

[1] Lahoye rea, Energie-aspecten van industriële koelsystemen,Watersymposium 2003

[2] Hessels et al. koelwater van bulk tot bottleneck, Watersymposium 2003

[3] Van Baarwijk et al. Beschrijving van uitgangspunten om te komen tot een beoordelingssystematiek voor warmtelozingen via koelwater, Watersymposium 2003.

Information about water reuse in the paper, textile and food and beverage industry

Water reuse in greenhouse horticulture

Information about water treatment and reuse of oily wastewater

Water reuse in the poultry industry

Find books about water recycling

Should you know of any other interesting or more recent book, report, article or publication, concerning water reuse for cooling purposes please let us know, so that we can include reported case-studies in the above overview.