Causes and measures for increased dissolved oxygen in deaerators

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It is well known that corrosion causes inevitable damage to boiler tubes. These tubes have an inner and an outer surface; we try to prevent factors such as dust accumulation on the outer side in order to reduce corrosion there. Inside the tubes, water can also cause inevitable damage to the inner wall due to scaling and oxygen corrosion. So what is the principle behind oxygen corrosion? The principle of oxygen corrosion is that oxygen passes through the air-solution interface into the solution; driven by convection in the solution, oxygen moves toward the cathode surface. Within the diffusion layer, oxygen diffuses toward the cathode surface due to a concentration gradient, and at the cathode surface, oxygen molecules undergo a reduction reaction. The corrosion of iron by dissolved oxygen in water is a type of electrochemical corrosion, with iron and oxygen forming a corrosion cell. The electrode potential of iron is always lower than that of oxygen; therefore, in a ferrocorrosion cell, iron acts as the anode and is corroded. The reaction is as follows: Fe → Fe²⁺ + 2e⁻ ； Oxygen acts as the cathode where reduction occurs; the reaction equation is as follows: O₂ + 2H₂O + 4e⁻ → 4OH⁻. Here, dissolved oxygen acts as a cathodic depolarizer, which is a factor that causes iron corrosion; this type of corrosion is known as oxygen corrosion. An increase in dissolved oxygen exacerbates oxygen corrosion. What are the causes, and how should it be dealt with? When the dissolved oxygen level in the deaerator increases, there are generally the following reasons: 1. The oxygen content in the condensate is too high, or the temperature of the water entering the deaerator is low. 2. The water inflow to the deaerator is too large, or the steam inflow to the deaerator is insufficient. 3. Fluctuations in deaerator pressure and water level. 4. The oxygen discharge valve is opened too little. 5. Damage to the internal components of the deaerator. Since we have observed an increase in dissolved oxygen, how can we make adjustments to address this issue? 1. Adjust the pressure, temperature, and water level of the deaerator to normal levels; activate reboiling in the deaerator if necessary. 2. Adjust the opening degree of the oxygen discharge valve. 3. Reduce the amount of water added appropriately, while ensuring continuous and uniform watering. 4. Check the oxygen content in the condensate water; if it does not meet the standards, inspect and adjust the feed water pump, condensate water pump, and negative pressure system. 5. Check whether the sampling device is leaking by making contact with it. During operation, we need to pay attention to any changes in each parameter. As the continuous source of water for the boiler feedwater, the deaerator must be kept operating within acceptable parameters to ensure the safety of the boiler.