VISUALIZATION OF THE FLOW STRUCTURE IN A PERSPECTIVE VORTEX FURNACE

Introduction. Creation of new energy-effective equipment for ecologically safe combustion of coal is necessary for further development of heat power engineering [1]. This entails increasing requirements for the characteristics of projected and upgraded furnaces of boiler units and, in turn, a need for new, scientifically-grounded approaches to the development of furnace devices. At present, the technology of pulverized-coal combustion in vortex flow holds promise. Vortex transfer underlies the entire process of fuel combustion in a so-called vortex furnace, which initial design has been developed during the 1970–1980-s by N.V. Golovanov at JSC “NPO CKTI” [2]. Flow swirling in a combustion chamber leads to stabilization of flow, better filling of the chamber volume with a fuel mixture, and intensification of heat and mass transfer due to enhanced mixing and increased residence time of coal particles in the combustion chamber, which allows the size of the furnace and entire boiler unit to be reduced. Simultaneously the reduction of harmful emissions in the vortex furnace can be achieved due to the effect of recirculation of combustion products towards the reacting zone of pulverized-coal torch, and also due to application of the stagedcombustion principle by ad-hoc arrangement of oxygen-lean conditions inside the vortex torch of combustion chamber with reburning at a later stage. Therefore, with aim to develop or upgrade furnaces that employ the vortex combustion technology, it is necessary to study in detail the complex 3D structure of the flow in such vortex furnaces. The vortex furnace design usually comprises the vortex combustion chamber in the lower part of the furnace, the diffuser, and the cooling chamber exited with discharge flue. With this the pulverized coal-air mixture is injected tangentially (alongside the main vortex flow in the combustion chamber) via the rectangular nozzle located at the upper part of combustion chamber (before the diffuser neck). For N.V. Golovanov’s design of the vortex furnace, the complex experimental and numerical study of aerodynamic structure and the turbulent flow characteristics has been conducted in isothermal formulation earlier by authors in [3–4]. An enhancement of this vortex furnace initial design, featured by additional tangential-injection nozzle located horizontally at the bottom of the vortex chamber, has been earlier proposed (Russian Federation patent No.2042084) and studied by authors in [5–10]. Another modification of the vortex furnace design, to be studied in the presented work, has been recently proposed by authors: in this new scheme the additional tangential-injection nozzle is mounted vertically at the upper part of the vortex combustion chamber, see Fig. 1. Therefore this novel vortex furnace type can be referred to as the dual upper-port loading design. The presence of additional upper-port tangential-injection nozzle in the novel-design vortex furnace allows for the flexible control of aerodynamic structure and the regime parameters, thus providing the possibility to improve the furnace performance. The presented work is devoted to experimental and numerical investigation of interior aerodynamics, including visualization of the flow structure in the suggested vortex furnace with dual upper-port loading. Experimental study of aerodynamic features of the flow has been performed at the laboratory air isothermal model (Fig. 1) of this novel-design vortex furnace. For the same laboratory-scale model the numerical simulation of 3D turbulent flow in isothermal formulation has been carried out. The known vortex identification criteria (the Q-criterion and the “minimum total pressure”-criterion) were applied for visualization of spatial flow structure in the studied vortex furnace model.