Fouling

Under fouling (german dirt, mold ) is defined as the contamination of heat-transfer system components through ingredients of the cooling water used. In the cooling technology and other technical fields, these first of coarse to micro and Makrofouling.

Makrofouling

Makrofouling is caused by coarse particulate substances of biological origin or waste produced industrially. These substances are entered through the cooling water pump of the cooling water sources such as the open sea, rivers and lakes in the cooling water circuit. Even in closed systems in cooling towers, this entry is possible through open channels or by the wind into the cooling tower cups. In cooling towers sometimes solve parts of the internals and thus pass into the cooling circuit. All these substances contaminate the heat transfer surfaces of the condenser and heat exchanger and worsen their associated heat transfer coefficient.

• From human produced waste
• Internals of cooling towers
• Seaweed
• Mussels
• Adenoids
• Leaves, plant parts up to the tree trunk

Mikrofouling

When Mikrofouling a distinction between the processes:

• Biological fouling such as bacteria and algae settlement settlements
• Sedimentation of sand and mud
• Scaling as a crystallization of sparingly soluble salts: calciumbicarbonate
• Calcium sulfate
• Silicates
• Magnesium hydroxide

The concentration of salts can move beyond the saturation point, and thus lead to flocculation of salt crystals by evaporation and degassing. For the balance between the always present in the water soluble calcium bicarbonate good and the insoluble calcium carbonate is the formula:

The resulting calcium carbonate in this reaction is reflected in the pipes. Due to the temperature dependence of the reaction, the deposits at the outlet is higher than at the inlet.

Chemical reactions

This can occur due to contact with the warmer surface of the condenser tube. In these cases, the metallic surface sometimes acts as a catalyst. Most of these reactions are corrosion and polymerizations. This occurs in cooling water for the chemical industry, which is contaminated with a low content of hydrocarbons. Higher tube wall temperatures can lead to carbon deposits.

Economic Importance

Fouling causes considerable costs. These costs are initially formed by corrosion damage and deterioration in heat transfer. In addition, but also the environmental costs are to be seen due to the necessary use of biocides to prevent biofouling or the increased fuel use to compensate for the reduced output caused by fouling.

So already caused ordinary fouling at a conventionally fired 500 MW power plant unit power losses of the steam turbine in the amount of 5 MW and more, in a 1300 MW nuclear power plant reach the losses quite 20 MW. In seawater desalination fouling reduces Gained Output Ratio to high double-digit percentages ( The Gained Output Ratio is a ratio that relates the mass of distillate produced to the mass of steam used in the process in relation). More consumption of electric power in compressor-driven chillers also move frequently in the double-digit percentage range.

In addition to the operating costs increase the investment costs, as the heat exchanger must be made ​​larger to compensate for the damage caused by fouling poorer heat transfer.

Combat

The most sensible way to combat fouling it is not to let the foulingverursachenden substances from entering the cooling water circuit. In steam power plants and other large industrial facilities for water use Makrofouling is prevented by pre-filtration and cooling water filters. In Mikrofouling filtration is possible only by very expensive methods of water treatment and membrane technology. For this reason, chemical or mechanical cleaning methods recommended for plaque removal. These methods are the acid pickling or cleaning the ball with sponge rubber balls. During the pickling generated by the provision, use and storage of the acid environment problems, the mechanical ball cleaning is an accepted procedure today. Another option is the treatment with all-metal catalysts. Drag -free germs in water by means of static charges and decompose them. By breaking environmentally friendly biosurfactants are produced which cause separation and thus a death of biofilms. The biocides been often used can be divided into four groups: Inorganic chlorine and bromine, chlorine and Bromabspalter, ozone and Sauerstoffabspalter and non-oxidative biocides. One of the main non-oxidative biocide comprises a mixture of chloromethyl isothiazolinone and methyl isothiazolinone. Frequently used are also dibromonitrilopropionamide and quaternary ammonium compounds.