The performance of the nozzle has an important influence on the desulfurization rate. At present, 5 kinds of nozzles are usually used in the wet spray layer desulfurization tower: hollow cone tangent nozzle, solid cone tangent nozzle, double hollow cone tangent nozzle, solid cone nozzle and spiral nozzle. There are two types of commonly used desulfurization nozzles: helical solid cone nozzle and hollow cone tangent nozzle. Spiral solid cone nozzles are characterized by a large spray volume, so the number of nozzles is small. The disadvantage is that the structure is fragile and the uniformity of droplets needs to be improved. In the wet desulfurization absorption tower, the hollow cone tangent nozzle is a substitute for the spiral solid nozzle. It has a large free flow diameter, has a self-cleaning function, and is widely used. Therefore, this type of nozzle is selected.
The nozzles of each spray layer are staggered to ensure that the overlapping coverage of the slurry is at least 170% to 250%. The outermost nozzle and the tower wall should maintain a reasonable distance to prevent the tower wall from perforating and leaking slurry.
1. Selection of Nozzle
The slurry itself requires the nozzle to be corrosion-resistant. However, due to the high pressure at the nozzle and the large flow rate, the interior is required to be resistant to corrosion and the surface is required to be resistant to erosion (because the upper layer of slurry is sprayed down). Therefore, the material of the nozzle is required to be made of silicon carbide. The top layer of the nozzle is a single spray, and the lower 2 to 3 layers are all sprayed up and down at the same time. Generally, the upper spray angle is 20 degrees. The flow accounts for 70% of the total amount of the nozzles, the downward spray angle is 90 degrees, and the flow accounts for 30%. There are three types of nozzles: flange connection, thread connection and socket connection. For example, if the shotcrete pipe is made of FRP material, the latter two connection methods should be used. If the inner and outer rubber of the steel pipe is used, only the former can be used.
2. Nozzle characteristic parameters
The characteristic parameters of the nozzle mainly include nozzle pressure drop, spray angle, nozzle flow and so on.
(1) Nozzle pressure drop refers to the pressure loss generated when the slurry passes through the nozzle channel, which is mainly related to structural parameters and slurry viscosity and other factors. The greater the pressure drop, the greater the energy consumption of the system. Generally, the typical pressure drop of WFGD spray system nozzle is 0.05-0.1MPa.
(2) The spray angle refers to the cone angle of the liquid film cone formed after the slurry leaves the nozzle orifice, which is mainly affected by factors such as the radius of the nozzle hole, the radius of the rotating chamber and the radius of the slurry inlet. When selecting the spray angle, it must be combined with the arrangement of the nozzles in the tower to ensure the coverage uniformity and coverage in the tower. Usually, the spray angle is required to be 90 to 120 degrees.
(3) Nozzle flow refers to the volume flow through the nozzle per unit time, which is mainly related to factors such as pressure drop and nozzle structure parameters. Nozzle flow is determined according to system layout and process calculation.
3. Nozzle layout design in the tower
It is very important to arrange the nozzles in the tower. Only with a reasonable and optimized nozzle layout design can the system design requirements be met and the desulfurization system achieve a high desulfurization rate. There are two ways to arrange the nozzles in the tower: one is concentric circle arrangement, and the other is matrix arrangement.
The following issues should be paid attention to when designing the layout of nozzles in the tower:
(1) Select a reasonable nozzle coverage height, which is usually determined according to the characteristics of the nozzle and the distance between the two layers of spray.
(2) Select a reasonable number of single-layer nozzles. Generally speaking, the number of nozzles is determined according to the process calculation. Usually, a spray pipe network is arranged on each layer, and each layer should be equipped with enough nozzles to minimize the length of pipes connecting the nozzles.
(3) After the nozzle coverage height is determined, the coverage area of a single nozzle can be calculated.
(4) When arranging nozzles in the desulfurization tower, select an appropriate distance between the nozzles. The nozzle spacing is usually selected according to the number of nozzles and the diameter of the desulfurization tower, and should be considered as a whole with the nozzle arrangement plan connecting the nozzles.
(5) Select a reasonable economic flow rate, and determine the diameter of the limestone slurry parent pipe and branch pipe according to the standard of the nozzle product.
(6) When checking the coverage rate of the spray layer in the desulfurization tower, not only the influence of the collision of the nozzle liquid flow with the parent pipe, branch pipe and support on the coverage rate, but also the coverage uniformity of all nozzles in the desulfurization tower should be considered. The impact of the collision of the nozzle liquid flow with the parent pipe, branch pipe and support on the coverage rate must also be considered when selecting the spray layer spacing.