Deaeration steam[edit]The deaerators in the steam generating systems of mostthermal power plantsuse low pressure steam obtained from an extraction point in theirsteam turbinesystem. However, the steam generators in many large industrial facilities such aspetroleum refineriesmay use whatever low-pressure steam is available.Oxygen scavengers[edit]Oxygen scavenging chemicals are very often added to the deaerated boiler feedwater to remove any last traces of oxygen that were not removed by the deaerator. The type of chemical added depends on whether the location uses a volatile or non-volatile water treatment program. Most lower pressure systems (650psi) and all systems where certain highly alloyed materials are present, are now using volatile programs as the old phosphate-based programs are phased out. Volatile programs are further broken down into oxidizing or reducing programs [(AVT(O) or AVT(R)] depending whether the waterside environment requires an oxidizing or reducing environment to reduce the incidence of flow-accelerated corrosion (FAC) which is a highly debated topic within the industry today. FAC-related failures have caused numerous accidents in which significant loss of property and life has occurred.The most commonly used oxygen scavengerfor lower pressure systemsissodium sulfite(Na2SO3). It is very effective and rapidly reacts with traces of oxygen to formsodium sulfate(Na2SO4) which is non-scaling. Another widely used oxygen scavengerproperly diluted and for locations using volatile programsishydrazine(N2H4).Other scavengers include1,3-diaminourea(also known ascarbohydrazide),diethylhydroxylamine(DEHA),nitrilotriacetic acid(NTA),ethylenediaminetetraacetic acid(EDTA), andhydroquinone.