With the increasingly severe environmental situation, people’s requirements for environmental protection are increasing day by day, and the environmental protection transformation of power plants is imminent. From flue gas discharge to waste water discharge, both the owner and the environmental protection engineering company are thinking about how to meet the requirements of environmental protection. In recent years, everyone has attached great importance to water pollution and paid close attention to wastewater discharge, so there is the emergence of “zero discharge”.
For power plants, the most dangerous and difficult to discharge is desulfurization wastewater, which not only contains various impurities, but also has a high concentration of salt, and direct discharge will cause great pollution to the environment. In response to this situation, the currently popular zero-emission technologies are as follows:
1. Triple box chemical treatment method
2. MVR/MED type evaporation crystallization method
3. Flue spray crystallization method
Among them, the flue spray method is the most economical method at present. Compared with the other two methods, it has great advantages in both investment cost and operating cost. However, its technical difficulty is extremely high, and it is greatly affected by the operating environment of the power plant. Therefore, as the core of flue spray technology, the selection of nozzles is the top priority. Once there is a problem with the nozzle, it will have a great impact on the entire spray system. Here we discuss the key points of nozzle selection:
1. Material: Due to the high content of salt and chloride ions in desulfurization wastewater, it is highly corrosive to metals. Corrosion-resistant special alloys must be used, such as 1.4529, C276, INCONEL, etc. Now some manufacturers are also trying to use silicon carbide ceramics, but the nozzles fired by silicon carbide have different degrees of deformation due to process limitations, so the spray shape is imprecise and not practical.
2. Particle size: Due to cost constraints, the average size of the bypass flue is limited, so there are extremely high requirements for the spray particle size. Generally speaking, the maximum particle size of D32 should not be higher than 100 μm.
3. Air consumption: After the bypass flue spray technology is put into operation, the operating cost is basically reflected in the operation of the air compressor. The less the air consumption, the less the operating load of the air compressor, which is beneficial to energy saving and consumption reduction. The air consumption of a single spray gun is recommended not to exceed 80m³/h.
4. Spray flow rate: The larger the spray flow rate of a single spray gun, the greater the waste water treatment volume, which can save the number of spray guns and reduce the cost of one-time investment. The flow rate of a single spray gun is not recommended to be lower than 240 L/h.
The above four points are related to each other. Generally, the larger the flow rate, the larger the particle size, and the larger the air consumption. Therefore, the choice of spray gun is crucial. If there is no effective evaporation, it will cause serious dust accumulation and increase the workload of the staff.