Hydrazine has been a dominant oxygen scavenger in high-pressure (HP) boiler feed water for decades. However, due to its potential toxicity and environmental concerns, there's a growing need for alternative solutions. Here are some alternatives:
1. Oxygen Scavengers:
* Deaerators: These devices physically remove oxygen from the water by heating and creating a vacuum. While effective, they require significant energy consumption and may not fully eliminate all dissolved oxygen.
* Sodium Sulphite (Na2SO3): This is a common alternative to hydrazine. It reacts with oxygen to form sulfate ions (SO4-2), which is harmless. However, sodium sulphite requires higher dosages and can contribute to corrosion if not properly controlled.
* Sodium Bisulphite (NaHSO3): Similar to sodium sulphite, it reacts with oxygen to form sulfate. However, it's a stronger reducer and generally more effective at low temperatures.
* Erythorbic Acid (Ascorbic Acid): This is a natural compound that reacts with oxygen to form dehydroascorbic acid, which is also harmless. Erythorbic acid is particularly effective at low oxygen levels and is considered environmentally friendly.
* Ammonium Bisulphite (NH4HSO3): Similar to sodium bisulphite, it reacts with oxygen and is a good alternative, especially in systems operating at high temperatures and pressures.
* Organic Scavengers: These include compounds like diethylhydroxylamine (DEHA) and carbohydrazide (CHZ). They offer advantages like lower dosages and higher reaction rates, but might have specific limitations in specific applications.
2. Combined Treatment Methods:
* Deaeration + Chemical Scavenging: Combining deaeration with chemical scavengers can provide a more comprehensive solution.
* Deaeration + Electrochemical Oxygen Removal: This method uses electrochemical processes to remove oxygen, offering a more sustainable approach.
3. Emerging Technologies:
* UV/Oxidation: Utilizing UV light to break down oxygen molecules into harmless products.
* Electrocatalytic Oxidation: Using electrocatalysts to accelerate the oxidation of dissolved oxygen.
Choosing the right alternative:
The best alternative depends on various factors:
* Boiler pressure and temperature: Different scavengers have different effectiveness at different operating conditions.
* Water quality: The presence of other impurities can affect the efficiency of the scavenger.
* Environmental regulations: Regulations concerning toxicity and discharge limits must be considered.
* Economic factors: Cost of the scavenger and its application must be weighed against other alternatives.
It's important to consult with boiler and water treatment specialists to select the most suitable alternative for your specific HP boiler system.
