Mechanical Faculty

The paper presents the mathematical model describing a flow of the gas-solid particles mixture in a cyclone separator, as well as methods of erosion wear forecasting for separator elements. The model is a development of the methods applied in [1] for the evaluation of erosion wear in the boiler dust installations. Numerical calculations have been done with the Fluent program.

In operation of dust systems of big power boilers, a required dust-air mixture should be distributed to particular burners. This problem is very important because loss of imperfect combustion should be limited, and also because of life of the furnace system and emission of nitric oxides. In many cases, in pneumatic conveying systems for coal dust we can observe diversified concentration and out-of-control segregation of particles leading to diversified deliquescences, disturbances of combustion and accelerated erosion of the installation elements. In the boilers with corner burners, just after the mill outlet there is a four-way distributor for uniform distribution of the dust-air mixture. Strong diversification of concentration and particle segregation within the elbow causes diversification of concentration at the mixture silt to the four-way distributor located directly above the elbow. It is a reason of diversified dust silt to the boiler corners and accelerated erosion of distr...

The paper presents a method for finding such instalation elements which are especially subjected to erosion wear and a method for quantitative assessment of the erosion loss at a given operational time of a pneumatic conveying system. Motion of the gas is described by the Reynolds equ-ation with the turbulence model. Motion of solid particles is described by the Lagrange equation. Then, the erosive loss of the wall material is calculated according to the Bitter model. The calculations are perfor-med for a part of the dust system in BP-1150 boiler. It is found that a "cord" of particles is formed as a result of some changes of the flow di-rection inside the stream. High local intensity of particle collisions with the walls is the main reason for accelerated erosion of some parts of the system. The numerical calculation results are compared with the results of measurements on material losses of the elbow.

Use of large power boilers requires appropriate distribution of the air -coal particle mixture to particular burners. The tests of gas and coal distribution show the problem of their non-uniformity under different working conditions of the system. In the paper multi-phase flow models were presented in the installation with elbow. In the work three methods: Euler-Euler, Euler-Lagrange and E-L with modification were compared with results of experiment. This work shows that the Euler-Euler model seems to be more useful for the considered flows.

During cement production process, part of the fuel can be burned in preheater, so it is necessary to supply additional air (tertiary air), which should be taken from the clinker cooler [1]. Trouble at the tertiary air conveying make clinker particles which are entrained from the cooler and settle in the duct [2,3,4]. For optimization of kiln, it is necessary to understand the detailed process which takes place in the kiln. The specific requirements of the process is designing the burner system and provide a burner design that will deliver efficient and reliable combustion. Yet, extensive use of this form of transportation may bring about some problems that need to be eliminated. For describe the complex process of cement production a numerical calculation object were built. As for subsequent analyses only flow distribution through the kiln head was important, authors decided to build a part of cement kiln installation. Fig. 1 shows general view of the rotary kiln system with connect...

Clinker burning process has a decisive influence on energy consumption and the cost of cement production. A new problem is to use the process of decarbonization of alternative fuels from waste. These issues are particularly important in the introduction of a two-stage combustion of fuel in a rotary kiln without the typical reactor-decarbonizator. This work presents results of numerical studies on thermal-hydraulic phenomena in the riser chamber, which will be designed to burn fuel in the system where combustion air is supplied separately from the clinker cooler. The mathematical model is based on a combination of two methods of motion description: Euler description for the gas phase and Lagrange description for particles. Heat transfer between particles of raw material and gas was added to the numerical calculations. The main aim of the research was finding the correct fractional distribution of particles. For assumed particle distribution on the first stage of work, authors noted t...

Rotary kiln installation forms a very complex system, as it consists of various components which affect cement production. However, some problems with particle settling are encountered during operation of tertiary air installation. This paper reports on the results of a study into gas-particle flow in a tertiary air duct installation. This flow was calculated using Euler method for air motion and Lagrange method for particle motion. The results in this paper demonstrate that study focus on the tertiary air installation is a practical measure without the analysis of other processes in the rotary kiln. A solution to this problem offers several alternatives of modifying the inlet to the tertiary air duct. As a result of numerical calculations, we demonstrate the influence of geometry of a rotary kiln modification on the number of large particles transported in the tertiary air duct. The results indicate that in order to reduce large particles, rotary kiln head geometry needs to be modi...

The subject of the study is to analyze the phenomena of thermal flow in the precalcinator chamber of the exchanger's furnace tower including the combustion of coal dust and decarbonisation of raw lime powder. During the research were provided development of a mathematical model of particulate solid fuels combustion, calcining the raw material, NO x and CO x formation. Moreover conducting the number for the current and the upgraded design of the precalcinator and analysis of the results. In this study, a mathematical model based on Euler's method to describe the motion of the gas phase and the Lagrange method to describe the motion of particles [1-4]. In the calculations there were assumed fractional particles raw material and fuel, and the following processes: flow of exhaust gases from the rotary kiln through the precalcinator chamber, heat exchange between the particles of raw material and exhaust gases, the additional fuel combustion in the precalcinator, the process of raw material calcination, transformation of gaseous substances, effect of the additional (tertiary) air delivery on the processes in the chamber.

The main topic of the study is to evaluate the effect of particle concentration and fractional composition on the differential pressure in the Venturi tube during the measurement of flow rate of the gasparticle mixture. Gas phase flow was described by Euler method, while particles movement by Lagrange method. Calculations were performed using ANSYS Fluent Package. A series of numerical calculations were carried out on the particle loading ratio Y ≤ 2 and their diameters of 10 µm ≤ d p ≤ 200 µm. It has been found that, except for the Y concentration loading ratio, the increase in the differential pressure in the venturi tube also affects the Stokes number. It depends on the flow conditions and particles diameter. A correction function has been proposed to determine the effect of particles diameter on the results of the mixture flow measurement. The results of the calculations were compared with the Lee and Crowe experimental data. A good comparison of calculation results to measurement results was found.

Clinker burning is the most complex process in cement production from limestone. This is especially visible for the two-stage combustion of fuel in a rotary kiln without the typical reactor-decarbonizator. This work presents results of numerical studies on thermal-flow phenomena in the riser chamber, which will be designed to burn fuel in the system AS (combustion air supplied separately from the clinker cooler). The mathematical model is based on a combination of two methods of motion description Euler method for the gas phase and Lagrange method for particles. The most important part of the calculation methodology is modeling of the calcination process, which depends on the gas temperature, CO2 partial pressure and material roasting time. The obtained results of calculations can be the basis for further optimization the design and operating conditions in the riser chamber with the implementation of the system AS.

Thepaperpresentsamethodforfindingsuchinstalationelementswhich are especially subjected to erosion wear and a method for quantitative assessmentoftheerosionlossatagivenoperationaltimeofapneumatic conveying system. Motion of the gas is described by the Reynolds equation with the turbulence model. Motion of solid particles is described by the Lagrangeequation.Then, theerosivelossof the wallmaterialis calculated according to the Bitter model. The calculationsare performed for a part of the dust system in BP-1150boiler. It is foundthat a ”cord”of particles is formed as a result of somechanges of theflow directioninsidethestream.Highlocalintensity ofparticlecollisionswith thewallsisthemainreasonforacceleratederosionofsomepartsofthe system.Thenumericalcalculationresultsarecomparedwiththeresults ofmeasurementsonmateriallossesoftheelbow.

In the pneumatic conveying systems of large power boilers, the required separation of the dust-air mixture to particular burners has to be obtained. This problem is very important in consideration of limitation of losses connected with incomplete combustion, life of many elements of the furnace system and NO x emission. The realized design works on dust pipes are usually based on the assumption that dust concentration in the section is approximately the same and there is no segregation of dust particles. However, in many cases in the pneumatic conveying systems for coal dust, diversified concentration and out-of-control segregation of particles take place. Such segregation leads to diversification of propagation, disturbance in the combustion process and accelerated erosion of the installation elements. This paper presents numerical investigations on the air-coal dust mixture flow through the four-path separator system. Diversification of concentration and particle segregation behind the separator are determined by the elbow presence just before the inlet to the separator. The elbow presence causes diversification of concentration on the mixture silt to the four-path separator located directly over the elbow. It is a reason of the diversified silt of the dust on the boiler corners and the accelerated erosion of separators. The author tried to assess influence of configuration of the pipe delivering the medium to the separator on uniformity of dust separation behind the separator. Numerical investigations were performed for six positions of the inlet interval before the separator at different velocities and dimensions of the dust particles. In order to realize calculations for three-dimensional geometry, the Euler model was selected for description of the gaseous phase motion, and the Lagrange model was used for description of the particle motion. From analysis of the performed calculations it appears that the inlet configuration in relation to the separator strongly influences the proper dust separation to outlets. The best dust separation can be observed for the inlet location angle in the range 6090°.

Damage reasons of the rotary kiln of pulverized coal burners conveying pipe is related with many reasons. This paper analyses the numerical simulation of the gas-solid two-phase flow field in the coal channels of pulverized coal burners in burner with eroded wall material. For calculation was used few turbulence models and Lagrangian discrete phase model. Results compares combustion conditions in the two-phase flow characteristics and particle trajectory model under different erosive wear distribution and for different turbulent models. Calculations was made for three different shapes of burner as a result of erosive wear. For that geometries was calculated combustion in rotary kiln, and estimated shape of flame in kiln chamber. Was find that the erosion rate is important for combustion in rotary kiln, and find that suggested method of calculation was proper for this subject.

In the case of designing and service of the pneumatic conveying systems for power boilers, presence of the solid particle segregation in some areas is an important problem. In many cases, in such systems diversification of concentration and out-of-control segregation of particles take place. In a consequence, diversification of propagation, disturbances of the combustion process and accelerated erosion of the installation elements can occur. Moreover in the large power boilers, the required separation of the air-dust mixture to particular burners has to be obtained. This problem is very important because of limitation of losses of incomplete combustion, life of many furnace elements and NOx emission. It is the outlet straight interval of the dust tube from the mill together with the elbow. The four-path separator is located just above the elbow. The tests of gas and dust separation show the problem of non-uniformity of their distribution. From the results it appears that particle di...