Carbohydrazide (N2H3)2CO is a ...

Carbohydrazide (N2H3)2CO is a derivative of Hydrazine that decomposes under boiler feedwater conditions to form Hydrazine and Carbon Dioxide

Based on the molar ratio, Carbohydrazide would be fed at 1.4:1 to Oxygen, but is normally used at a 2:1 ratio.  It is controlled by maintaining a residual of 20 to 60 ppb in the boiler feedwater.

The advantages of using Carbohydrazide are the benefits of not adding TDS to the boiler system and avoiding the health risks related to Hydrazine.

The disadvantage is Carbohydrazide cannot be used in systems below 9 bar due to the decomposition requirements.  Another disadvantage is residual Hydrazine in the feedwater can still break down into Ammonia potentially corroding any Copper alloys in the system.  An additional disadvantage is the Carbon Dioxide formed will carry over into the steam forming Carbonic Acid in the condensate.