Why is hydrazinium hydroxide solution added to boiler feed water?

In order to prevent the boiler water system and pipelines from being corroded by oxygen, and to ensure the complete elimination of residual dissolved oxygen after thermal deaeration and oxygen leaking into the feed water due to loose pumps and water supply systems, it is necessary to add an appropriate amount of combined oxygen to the feed water. ammonia. Hydrazine (N2H4) is also called hydrazine, and its hydrate is commonly used, hydrazine hydrate (N2H4·H2O).

Since hydrazine is a strong reducing agent in alkaline aqueous solution, it reacts with dissolved oxygen in water as follows:

N2H4＋O2→N2＋2H2O

Therefore, the function of adding hydrazine is to remove dissolved oxygen chemically, and the reaction products N2 and H2O do not cause any harm to the thermal system.

Hydrazine can also reduce CuO to Cu2O or Cu to prevent copper scale from forming in the furnace.

In actual production, hydrazine (N2H4·H2O) with a mass fraction of 40% is usually used and added to the suction inlet of the boiler feed water pump or the outlet pipe of the deaerator. Dosage control is usually based on the fact that the N2H4 content in the economizer inlet feed water does not exceed 50 μg/L. N2H4 is toxic, flammable and volatile, so special attention should be paid when using it. N2H4·H2O is not easy to burn when <40% (mass fraction).

The hydrazinedeoxygenation reaction is very fast when the temperature is greater than 150°C, but the reaction speed is slow when the temperature is low. Therefore, catalytic hydrazine is sometimes used. That is, when adding hydrazine, additives that promote the reaction, such as hydroquinone, quinone compounds, 1-phenyl-3-pyrazolidinone, p-aminophenol, etc., are also added.