Careful selection of spray nozzles in absorption towers is an important factor in controlling the operation and maintenance costs of FGD systems. The selection of nozzles in the absorption tower is the most critical. When choosing a nebulizer, the optimum spray characteristics should be obtained for the specified operating conditions. In the absorption tower, both the reaction rate and the contact area caused by the droplet size limit the absorption process. It is generally believed that the influence of the surface area of the droplets on the flue gas desulfurization rate will be greater than 90%, and strictly speaking, sometimes it can reach more than 95%. In engineering, the desulfurization rate failed to meet the requirements. After careful investigation, the only reason was that the atomization effect of the desulfurization nozzle was poor, and the liquid surface area of the contact reaction provided by the limestone slurry sprayed was too small.
The main performance parameters of the desulfurization nozzle are introduced as follows
1. Average particle size and droplet size distribution
The atomization performance of the nozzle depends on the slurry inlet pressure, slurry viscosity, surface tension and nozzle structure parameters. When the nozzle inlet pressure is larger, the pressure drop of the nozzle is larger, the flow through the nozzle is larger, and the average diameter of the atomized slurry droplet is smaller.
The spray droplet size distribution of the desulfurization nozzle is important for most applications, and it is especially important for wet desulfurization systems. For a specific working condition, the particle size of the droplets in the desulfurization tower has an optimal value. If it can spray droplets with high uniformity of particle size and optimal value, the investment can be reduced and the economical operation of the system can be realized.
2. Nozzle pressure drop
Nozzle pressure drop refers to the pressure loss generated when the slurry passes through the nozzle channel. The greater the nozzle pressure drop, the greater the energy consumption. The size of the nozzle pressure drop is mainly related to the nozzle structural parameters and slurry viscosity. The greater the slurry viscosity, the greater the nozzle pressure drop.
The size of the pressure drop of the nozzle determines its working pressure. The smaller the pressure drop, the smaller the working pressure and the smaller the power consumption of the circulating pump. At present, the working pressure of the double hollow cone tangent nozzle is roughly 0.5/0.7/0.8/0.85×105Pa.
3. Spray angle
The spray angle refers to the cone angle of the liquid film hollow cone formed after the slurry is rotated and sprayed from the nozzle. The factors affecting the spray angle are mainly various structural parameters of the nozzle, such as the radius of the nozzle hole, the radius of the rotating chamber and the radius of the slurry inlet. In the wet desulfurization system, the spray angle of the desulfurization nozzle sprayed downward is generally 90°, and the spray angle of the desulfurization nozzle sprayed upward is 120°. In the nozzle near the wall of the absorption tower, in order to avoid the erosion of the anti-corrosion material on the wall, the spray angle of the upwardly sprayed desulfurization nozzle is also 90°
4. Nozzle flow
Nozzle flow refers to the volume flow through the nozzle per unit time, and the nozzle flow is related to the pressure drop of the nozzle, the structural parameters of the nozzle and other factors. Under the same nozzle pressure drop conditions, the larger the nozzle hole radius, the larger the nozzle flow rate.
The flow rate of the nozzle will ultimately affect the economics of the desulfurization system. In a given absorption tower, choosing a nozzle with a large flow rate can reduce the total number of nozzles required, thereby reducing the cost of the system. Large-flow nozzles have fewer restrictions and good anti-clogging performance. , which can effectively save operation and maintenance costs. However, the selection of high-flow nozzles is also sacrificed, and the droplet size must be increased, so the maximum flow rate acceptable to different nozzles is limited by the atomization effect of this nozzle. The flow rate of the nozzle in wet desulfurization is generally about 50m3/h.
5. Free flow diameter
The free flow diameter refers to the maximum diameter that the nozzle allows to pass through spherical impurities. The larger the free flow diameter, the better the anti-clogging performance.