One of the topical problems of coal power engineering both from the point of increasing efficiency and ecological safety of heat energy production and need to utilize low-grade coals and coal wastes is the development of combustion technology for coal in the form of a coal-water suspension (CWS). The technologies of CWS combustion place high demands to the spraying devices (nozzles): absence of narrow fuel channels, which can be locked; low fuel velocities relative to the solid walls, which will reduce abrasive wear. The authors of the paper propose a pneumatic nozzle based on the use of the properties of near-wall and cumulative jets of liquid and gas and Coanda effect, which meets the basic requirements for CWS injectors. Aerodynamics control plays the determining role in the efficiency of pneumatic nozzle operation. In this paper, the structure of a single-phase gas flow in the proposed pneumatic nozzle is studied under different regime parameters using the experimental and numerical methods. The studies were carried out using the particle image velocimetry (PIV) and mathematical modeling of the flows by means of the DES and RSM turbulence models. It is shown that in the entire investigated range of excess air pressure, the converging annular jet turns into the concentrated one and forms the direct and return cumulative axial jets in the nozzle near the axis of symmetry. Due to interaction of the return and annular jets in the diffuser, a toroidal vortex is formed. At operation of a liquid fuel nozzle, such a return flow will contribute to the effective destruction of a liquid jet and formation of a highly dispersed two-phase flow. With an excess air pressure in the nozzle of 1 bar, a sound annular converging jet is formed at the nozzle outlet; with a further increase in pressure, the outflowing jet becomes supersonic, the oblique shock waves are formed there, and the axial jet acquires a barrel-like shape with formation of the Mach disks. Such a complex spatial arrangement of the flow (both in the toroidal vortex and outside it) ensures efficient dispersion of liquid fuel in this nozzle.

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The paper presents an experimental and computational study of various regimes of firing coal-water fuel in a low-power hot-water boiler that enable both dry and liquid slag removal. The experimental studies were carried out on a pilot industrial boiler adapted for firing coal-water fuel. The fuel was prepared using flotation products of beneficiation of K grade hard coal. The experiments were accompanied by numerical modeling of combustion processes. The mathematical model includes description of the carrier phase motion (based on the RANS approach with the twoparameter Menter SST k-ω turbulence model), radiation transfer (based on the P1 approximation of the spherical harmonics method for a two-phase two-temperature gray medium), particle motion (based on the Lagrange approach), and gas phase combustion (based on a combination of the kinetic model of combustion of gas components with the vortex break model). The physico-mathematical model was tested on the problem of combustion of coal-water fuel (CWF). One of the goals of the work was verification of a complex mathematical model. A comparative analysis of the results of the numerical modeling and experimental data showed that the model reliably described the process of burning in a combustion chamber. An advanced design of hot-water boiler enabling regimes of both dry and liquid slag removal was investigated. The chamber was shown to provide the necessary conditions for firing CWF in terms of reliability and economy.