Abstract
This project looks at the production of electricity by the CEGB's power stations noting the vast quantities of water required for cooling purposes. The main types of cooling system and the problem of condenser scaling often associated with the use of cooling towers and the evaporative cooling process are described, together with the usual methods of scale prevention/ treatment. The Croydon B power station is entirely dependant on treated sewage effluent for cooling water. A combination of the high total dissolved solids content of sewage effluent and their concentration by evaporative cooling made condenser scaling a particular problem. A novel method was developed, whereby nitrification of ammonia in the cooling water was used to control pH and prevent scaling. The system has been in operation for some twenty years, and this project investigates the effect of the major physical and chemical factors in cooling towers on the nitrification process. Work was carried out on a laboratory scale in a 15 litre culture vessel, a 27000 litre pilot scale cooling tower rig system and in the power station itself. The site of nitrification and the effect of pH, temperature, substrate concentration, flow rates, retention time, packing area and organic loading were investigated Differences in the reactions to these factors in the different scales of experiment were found and explanations attempted. In a power station cooling system the most important factors governing nitrification were felt to be pH, flow rate and area of packing. The results of the tests were used to develop a simple model of the system which could be used as a rapid guide to the degree of nitrification posible in any cooling tower. Finally the feasibility of the use of different sources of ammonia was investigated.