ammonia NH3Reading time:
Ammonia is increasingly demanded for total disinfection of drinking water. In effect, it is used to convert available chlorine into chloramine (maintaining a residue of gentle and persistent biocides that do not result in the formation of trihalomethane…):
An amount of 5 g NH3·g–1 free Cℓ2 is often recommended (see chapter oxidation-disinfection).
Transporting and storing concentrated detergents (64 % NH4OH) cannot be considered in summer due to the danger of heating and, therefore, of overpressure; also, the product is normally supplied as non-refrigerated liquid ammonia, in pressure vessels and at pressures of 6 bar at 10°C and 12 bar at 30°C. Transfer must be carried out according to the safety recommendations specific to the country concerned.
When the liquid is decompressed down to atmospheric pressure, this causes it to cool to -30°C (see table 40, characteristic constants of gases). The gas pressure can be maintained using a heat exchanger mounted on the transfer pipe and fitted with devices preventing heating water from freezing when the system is switched off.
When the gas dissolves in the water, the reaction is exothermic (34 to 40 kJ per mole of NH3 in solutions below 10%).