Process Principle
Oxygen can undergo electrochemical corrosion with metals such as carbon steel in humid environments, leading to the deterioration of iron components. The reactions are as follows: Fe → Fe2? + 2e?     O? + 2H?O + 4e? → 4OH?
Such corrosion is particularly prone to occur and is relatively severe in high-temperature feedwater systems. Therefore, dissolved oxygen in water must be removed. Hydrazine oxygen removal is a commonly used chemical deoxygenation method for high-parameter boiler units. It exhibits strong reducing properties in alkaline solutions and can reduce dissolved oxygen in water. The reaction is as follows:
N?H? + O? → N? + 2H?O
Process Overview
This system mainly consists of five parts: the chemical metering pump system, dissolution and mixing system, metering and dosing system, safety system, and control system.
Hydrazine is drawn into the metering system by a water jet ejector, then proportionally added to the dissolution and mixing system to mix uniformly with demineralized water or condensate water. It is then dosed into the boiler feedwater by the metering and dosing system. Dosing control can be manual or follow-up control based on signals from the upper-level system for automatic dosing.
This system can not only dose hydrazine but, with minor modifications, can also dose other oxygen scavengers such as carbohydrazide and dimethylketone.
Scope of Application
High-pressure and higher parameter boiler feedwater treatment.