There are chemical agents dosed for direct chemical bonding of oxygen during chemical deaeration of water into feed water. Normally it is sodium sulphite Na2SO3, the amount of which is as follows: 8 mg per 1mg of dissolved oxygen per 1 dm3 of water or 8 mg per 1 m3 of water when the volume of dissolved oxygen is 1 mg/dm3.
If the volume of dissolved oxygen is bigger, the dosing of sodium sulphite will proportionally increase. Oxygen bonding is carried out according to the following reaction:
The reaction goes intensively when the water is heated to the temperature 70оС and pH value range is рН=8.3 … 8.5. At the same time sodium sulfite is connected to the oxygen atom and is converted into sodium sulphate which is easily soluble and harmless in terms of corrosion. For more complete bonding of oxygen, sodium sulfite is dosed in plenty ranging from 10 to 15%.
Changing of pH value is performed by water alkalizing. The live carbon dioxide sweetens during water alkalizing, which excludes carbon dioxide corrosion of the equipment and the elements of cogeneration system. Usually caustic soda (NaОН) is used for this purpose; it takes up free aggressive carbon dioxide in accordance with the following equation:
When the quality of feed water is stable, the chemical deaeration can be performed by dosing chemical agents proportionally to the flow rate of feed water measured by impulse meter. The flow chart can be realized by means of dosing pumps of DLX–VFT/M series.
Water alkalizing is performed by the dosing pump controlled by pH controller depending on the set value of pH. DLX–СС/M series is recommended.