# Nozzles for Spraying Coal-Water Fuels
## 2 CWF Injectors
The average size of the CWF droplets in the jet after spraying is less than 100 microns. This is a very good indicator that will ensure the full combustion of coal. It is worth noting that the ability to change the width of the annular gap of the SA allows the size of the CWF drops to be adjusted. The variations in the coal-water fuel nozzle in [18], as well as [7], refer to the type of CWF spraying devices with external mixing (Figure 5). The nozzle was made of metal. The size of the CWF droplets after spraying, as well as in the case of [7], can be changed by turning the spraying nozzle. The sprayer consists of three interconnected parts: a housing forming an air flow, a spraying nozzle with a special front section with an internal supply of liquid or pulp, and an air supply fitting perpendicular to the housing. Figure 4: Pneumatic CWF nozzle [7]. Figure 5: Pneumatic nozzle [18] for spraying slurry fuels. The authors of [18] noted that the characteristics of the air flow affect the size, speed, and trajectories of the CWF droplets. The disadvantage of this type of CWF sprayer is a very small fuel channel--4 mm--which will contribute to its clogging with large coal particles or fuel agglomerates. The perpendicular feed of the SA can affect the geometry of the jet--displacement and asymmetry. In addition, as in the case of [18], the issue of nozzle durability and erosion wear remains unresolved. The advantage of this nozzle is the ability to obtain a finely dispersed fuel jet. The characteristics of spraying of subbituminous coal and an aqueous slurry of petroleum coke from a two-liquid vortex sprayer with internal mixing were studied in [19]. The nozzle was made of metal. The proposed nozzle (Figure 6) has three inlet openings for swirling air on the main liquid core located in the mixing chamber inside the nozzle. Then, the two-phase flow collides with the impact plate, which contributes to further mixing. After that, the two-phase mixture exits the nozzle through an annular channel formed by a pin. The ambient pressure in the tank was set at 15 bar during the tests. The flow rates of the slurry and spraying gas were 80 kg/h and 40 kg/h, respectively. The droplet size of petroleum coke and coal slurry was 198 microns at these parameters. This type of CWF spraying device has an internal mixing chamber of fuel and air. The disadvantage of this type of nozzle is the high probability of clogging of the mixing chamber. The issue of the durability of the nozzle remains unresolved. Erosion wear is not excluded. It is necessary to carefully monitor the pressure of the fuel and the spraying agent in order to prevent clogging in this type of injectors. The effect of the nozzle geometry on the spraying of coal-water slurry was studied in [20]. Three sets of burners with different designs were developed for the study. This device provided mixing of CWF and SA outside the nozzle (Figure 7). The nozzle was made of metal. The CWF flow rate was 10 kg/h, while the oxygen velocity was 120 m/s during the studies. The droplet size was 225-325 microns at different ratios of the burner outlet areas. Despite the fairly simple design of the injector, its fuel channel was also too small and had a narrowing, which was not protected against clogging with large particles of coal or agglomerates of CWF. The disadvantage is the narrowing of the fuel channel near the orifice, which is a significant hydraulic resistance for viscous CWF. The issue of the nozzle durability and erosion wear remains unresolved. The advantage of this nozzle is the ability to obtain a finely dispersed fuel jet. The average size of fuel droplets after spraying was approximately 200 microns. Large drops of CWF may be present in the jet, but their number is insignificant. Figure 6: Two-liquid CWF sprayer [19]. The characteristics of the granulometric composition and velocity of droplets of coal-water slurry subjected to air-jet electrostatic spraying are presented in [11]. The nozzle was made of metal.