# Nozzles for Spraying Coal-Water Fuels
## 2 CWF Injectors  
Spraying and burning of CWF in the combustion chambers of boilers is carried out similarly to fuel oil or diesel fuel, with the help of injectors. At the same time, unlike the  
Figure 2: The mechanism of CWF spraying and burning. 1—mixture of fuel and SA; 2—destruction of large fragments; 3—formation of large and small drops; 4—evaporation of moisture; 5—additional destruction; 6—combustion of CWF particles; 7—coagulation of large fuel drops; 8—sintering; 9—formation of the ash. above fuels, the CWF is not subjected to thermal preparation before spraying. In addition, the properties and characteristics of coal-water fuels differ significantly from traditional liquid boiler fuels. The main differences are high viscosity, the presence of solid coal particles and low reactivity. Therefore, it is necessary to provide a number of requirements for CWF sprayers in order to ensure a stable combustion process of such fuel. The analysis of the known coal-water fuel nozzles was performed considering the results of their tests presented in the literature. The study of the characteristics of coal-water fuels spraying under the conditions and parameters of real combustion chambers is a rather complex process regardless of the type of nozzle. A nozzle for CWF spraying with internal mixing of fuel and SA is presented in [17]. The nozzle has inner diameter of 5 mm, outer diameter of 12 mm, and a length of 10 mm (Figure 3). The design of the nozzle is quite simple. The main purpose of the research was to study the erosion wear of the nozzle channel. Wear-resistant ceramics, carbide, and metal materials were considered. The fuel channel of the injectors of such a design is not protected against clogging with large particles of coal or agglomerates of CWF. The disadvantage is the narrowing of the fuel channel, which is a significant hydraulic resistance for viscous CWF. This may be aggravated by the fact that chipping of the material from which the nozzle is made is possible during the operation of such injectors. The slurry may cause narrowing and a subsequent overlap of the nozzle channel in the case of sticking or sintering on its inner walls. Organization of internal mixing of CWF and SA allows for a finely dispersed jet to be obtained. At the same time, the presence of large droplets in the jet is not excluded. The main reason is that uneven mixing of the CWF and SA is possible in the mixing chamber. The use of ceramic and refractory materials will allow the nozzle to be used for a long time. The expansion of the nozzle orifice will eliminate chipping and subsequent geometry changes. The results of studies of the spraying characteristics of coal-water fuel with a pneumatic nozzle and its combustion are presented in [7]. The nozzle was made of metal. This device provides for mixing the CWF and SA outside the nozzle (Figure 4). Such an approach allows the CWF to be sprayed with a high-speed air jet (up to 450 m/s and the Mach number about 1.4). The air pressure in the annular chamber was up to 6.0 bar and the liquid flow rate was 180-360 kg/h during the tests, which correspond to the modes in a real boiler. Figure 3: Nozzle for CWF spraying with ceramic orifice [17]. The nozzle [7] has a cylindrical body, with a gas chamber inside with an annular conical hole and a channel with a diffuser nozzle for fuel supply. A sufficiently wide (8 mm) diameter of the nozzle channel should ensure an uninterrupted CWF flow even if there are large (for example, up to 3-4 mm) fragments of coal or agglomerates of fuel in it. At the same time, there is a narrowing in the fuel channel in the nozzle design, which is a significant hydraulic resistance for viscous CWF. The slurry may cause narrowing and subsequent overlap of the nozzle channel in the case of sticking or sintering on its inner walls. The issue of the durability of the nozzle remains unresolved. Erosion wear is not excluded. The advantage of this nozzle is the ability to obtain a finely dispersed fuel jet.