Why does boiler water need to be softened?
In order to ensure the safety and economic operation of the boiler, the boiler feedwater must undergo softening and deoxygenation treatment. Reducing the content of calcium and magnesium salts in water, reducing dissolved gases in water to meet the required water quality standards, preventing scaling in the pot, and reducing corrosion of the metal on the heating surface. If water does not soften for a long time, scale will form, which can affect thermal efficiency or render the equipment unusable.
The water in the boiler is softened water that has undergone chemical softening treatment. After being burned into steam and used for power in the turbine, it is condensed in the condenser and sent back to the boiler for further heating to reduce the treatment of softened water. The sewage generated during the recycling of softened water will be discharged, and the insufficient water will be replenished by externally treated softened water. This kind of recycling can fully utilize the waste heat of condensed water and also save a lot of treatment costs for softened water.
The harm of scale to boilers:
1. Boiler steel plates and pipelines are burned due to overheating
If there is scale inside the boiler, it is necessary to maintain a certain output (working pressure and evaporation rate), so as to increase the temperature on the fire side. Therefore, the thicker the scale, the poorer the thermal conductivity, and the higher the temperature on the fire side of the boiler.
From the experimental data, it can be seen that for a boiler with a working pressure of 1.4 MPa, the temperature on the fire side is between 900~1200 ℃, the temperature on the water side is 197 ℃, and the temperature of the steel plate without scale formation is only 215~250 ℃. When there is a mixed scale of 0.8-1.0 millimeters on the boiler plate of the same type, the temperature of the steel plate is about 134-160 ℃ higher than when there is no scale. When the temperature of the 20 # steel plate reaches 315 ℃, its mechanical properties begin to decline, and when it reaches 450 ℃, it will creep due to overheating. Therefore, poor water treatment can lead to the formation of scale in boilers, which can easily cause metal burnout.
2. Massive waste of fuel
When there is scale on the boiler, in order to maintain a certain output of the boiler, it is necessary to increase the temperature on the fire side, thereby increasing two types of heat losses: one is the heat loss radiated to the outside; One is the heat loss caused by smoke exhaust.
Due to the different working pressures of boilers and the varying thermal conductivity and thickness of scale, the amount of fuel wasted also varies. The higher the working pressure of the boiler, the lower the thermal conductivity of the scale, the thicker the scale, and the greater the fuel waste. Experimental results have shown that for a boiler with a working pressure of 1.4 MPa, fuel waste can reach 8% due to the formation of 1 millimeter thick mixed scale.
3. Reduce output
When there is scale on the evaporation surface of the boiler, the heat on the fire side cannot be quickly transferred to the water side, which will reduce the output of the boiler.
4. Increase boiler maintenance workload
After the boiler plate or pipeline is covered with scale, it is very difficult to remove, especially due to the leakage, cracks, damage, deformation, corrosion and other diseases caused by scale, which not only damages the boiler, but also requires a lot of manpower and material resources for maintenance. In this way, not only does it shorten the operating cycle, but it also increases maintenance costs.
5. Endangering safety
The proportion of boiler accidents caused by scale is quite high, with most provinces and cities accounting for over 20%. This not only causes equipment damage, but also threatens personal safety.
6. Reduce the service life of boilers
Increasing the frequency of chemical cleaning can cause damage to the boiler, reduce its service life, and increase safety hazards. In summary, water treatment for boilers is a "one cost, ten thousand benefits" matter from a global perspective. The infrastructure and operating costs of water treatment only account for a quarter of the total cost savings after water treatment.
