VINCA Institute

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COUPLED FLOW – THERMAL STRUCTURAL ANALYSIS OF RECTANGULAR AIR-COAL MIXTURE CHANNEL

Existing air – pulverized coal mixture burning channels at boiler A1 in the TPP Nikola Tesla in Obrenovac are of the rectangular, downstream variable cross section, with overall dimension of 4m length, 1.2m wide and 0.26m (inlet) to 0.535m (outlet) height. The thickness of this thin walled stainless steel structure, rigidly supported (welded) in the inlet, outlet and the first cross section of height changes, is 10mm. Temperature of air coal mixture, conveyed through this channels, is regularly above 140 oC.
New system for coal fire support and stabilization in the furnace, based on thermal plasma, is planed to be an alternative to existing oil burner’s system at boiler A1. According to preliminary calculations and measurements on the experimental and pilot facilities with plasma system in operation, the air coal mixture temperature arise up to 1200oC, inducing that burning channel walls are heated on the temperature more than 700 oC.
The goal of this work, within the project of investigation and development of a new system for the fire support based on thermal plasma, is to analyze influences of thermally loaded channel structure dilatations on air-coal mixture flow through it and vice versa. Structural simulation was done using Ansys, while flow simulation was conducted using CFX software.

The results of the coupled flow-thermal-structural parametric study of the coal mixture channel for the range 300…700oC of the inlet mixture temperature and 10…300oC in the channel’s inner and outer wall temperatures difference (depending on the insulation of the channel) shows that channel complex geometry will deform in couple different shapes, depending on the level of the inlet air coal mixture temperature and supposed insulation of the channel. Accordingly, the deformation and stresses field distribution in the channel wall, flow field and pressure drop in the channel depends of these two parameters.

Zoran Markovic, Laboratory for Thermal Engineering and Energy, Institute of Nuclear Science “Vinca”, University of Belgrade, Belgrade, Serbia, e-mail: zoda_mark@vinca.rs

TURBULENT THREE DIMENSIONAL TWO-PHASE FLOW MODELING OF AIR-COAL MIXTURE CHANNELS WITH MOVABLE SHUTTERS FOR REGULATION PULVERIZED COAL PARTICLES DISTRIBUTION

The aim of presented work is numerical optimization of fluid flow and pulverized coal particle distribution in air-coal mixture channels. Comprehensive Computational Fluid Dynamics code ANSYS FLUENT 12.1 was used for all numerical simulations performed in this work. Coal particle distribution inside air-coal mixture channels has been obtained as result of performed simulations.
Provided numerical simulation was successful in determination of the influence of movable shutters inclination on pulverized coal particles distribution in air-coal mixture channels.

Rastko Jovanović, Laboratory for Thermal Engineering and Energy, Institute of Nuclear Sciences “Vinca”, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia; e-mail: virrast@vinca.rs

SIMULATIONS OF THE KETTLE REBOILER SHELL SIDE THERMAL-HYDRAULICS

Shell and tube heat exchangers are among the most widely used types of heat exchangers. Various shell and tube heat exchangers are designed for vapour generation on the shell side. They are widely applied in chemical, process and energy power industry, in refrigeration and air-conditioning equipments, and they are applied such as reboilers, steam generators and evaporators.

A CFD approach is presented for the simulation and analyses of the kettle reboiler shell side thermal-hydraulics with mixture model. The mixture model is based on solving one momentum equation for two-phase mixture flow and a closure law for the calculation of the slip between gas and liquid phase velocities. The two-phase flow is observed as two inter-penetrating continua. The model is solved for the two-dimensional geometry of the kettle reboiler shell side vertical cross section. The CFD numerical method based on the SIMPLE type algorithm is applied. The results of both liquid and vapour velocity fields and void fraction are presented.

The main finding is that the void fraction distribution and two-phase flow field strongly depends on the modeling of the slip between liquid and gas phase velocity in mixture model.

Milada PEZO, Vladimir D. STEVANOVIC, Zarko STEVANOVIC Laboratory for Thermal Engineering and Energy, Institute of Nuclear Sciences – Vinca University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia; e-mail: milada@vinca.rs Faculty of Mechanical Engineering, University of Belgrade Kraljice Marije 16, 11000 Belgrade, Serbia

Mathematical modeling of furnace for biomass combustion

In the combustion facilities that are using biomass as fuel is very important well designed main combustion chamber, while other elements such as heat exchangers and flue gas dusters can be like in any other boiler plant for combustion of solid fuels. Therefore, it is very important optimal dimensioned combustion chamber. For this purpose, in addition to extensive experimental research, is very important to develop a detailed mathematical and numerical model to describe the reliability of the burning out process of the flue gases produced in the combustion process, on the one hand, and on the other for easer determination of the possible effects of constructional and parametric changes at the plant, which would provide better combustion in the terms of energy efficiency, but also in terms of ecology. The boiler described herein has been in operation for quite a while and has been quite successfully used for soy been straw combustion. Numerical simulation was also expected to indicate possible boiler manufacturing flaws and to provide opportunity to improve boiler performance with respect to process efficiency and environmental indicators. Also, numerical calculations may, in some cases, replace quite expensive experiments and enable quick, economical and comprehensive data acquisition needed for the process performance improvements.

The main aim of the research process of gases combustion in the adiabatic furnace is to understand the technology, analysis of current-thermal processes taking place in furnace space, justification of the studied plants from the standpoint of energy efficiency on the one hand and ecology on the other. For that purpose, it is developed a mathematical model that includes complex mechanisms of transmission of momentum, heat and substances in the flow field. Calculations based on the proposed model were conducted using commercial CFD program FLUENT 6.3.26. The employed mathematical methods can serve as a reliable tool for detailed analysis of gases combustion process and for predicting the effects of variation in operating conditions. Comparing the results obtained by mathematical modeling and measuring on the plant is obtained a very good agreement.

Dejan Djurović, University of Belgrade, Institute of Nuclear Sciences ‘‘Vinca’’, Laboratory for Thermal Engineering and Energy, P.O. Box 522, 11001 Belgrade, Serbia; e-mail: dejan2004@vinca.rs