7.3.2 On-load condenser cleaning
Two principal methods of on-load fouling prevention are employed to avoid unnecessary costly shutdown of condenser plant, in order that efficient throughlife costs are realised:
- Chlorination of the cooling water.
- Fine filtration, plus tube cleaning using rubber balls.
Intermittent chlorination of the cooling water entering the condenser is carried out on all British power stations, and forms the accepted on-load fouling preventive technique. It is effective in controlling the growth of mussels in seawater systems, and the formation of slime in freshwater systems.
At coastal sites, marine fouling is significantly reduced by continuous chlorination of the cooling water. The degree of chlorination required is inversely proportional to the CW flowrate, a chlorine concentration of 0.5 mg/kg of CW being required at 1.5 m/s.
At inland sites, slime control is maintained by intermittent dosing of chlorine (a few minutes every four to eight hours) at a level which leaves a residual of chlorine of 2 mg/kg at the condenser CW outlet.
Fine filtration plus tube cleaning, however, is installed in some 10% of all locations, and is becoming more widely used following experience on power stations with recirculating systems. A detailed account of this method is given in Section 6 of this chapter.
Other methods, including the use of flocculants, acid dosing, and toxic paints have all been considered as possible remedies, but so far none has proved to be a viable alternative to those outlined above.