Wyniki wyszukiwania - BazTech

1

Thermodynamic aspects of oxygen-deficient combustion

Rafidi N., Blasiak W.

Archives of Thermodynamics

|

2005

|

Vol. 26, no. 2

29-44

EN

The oxygen deficient combustion (ODC) is characterized by reactants of low oxygen concentration and high temperature. This work is devoted to analysis of such combustion process from the thermodynamic point of view. It demonstrated the possibilities for reducing thermodynamic irreversibility of combustion by considering the oxygen-deficient combustion process that utilities both gas- and heat-recirculation. Furthermore, an OC system utilizes oxygen as oxidizer has higher 1st and 2nd low efficiencies compared to an ODC system using air as oxidizer. This study is a technical guidance for further efficiency-improvement in combustion process especially because the temperature increase due to the reaction in an ODC system is mild.

2

Physical and numerical modeling of heat-flow processes in tangentially pulverized fuel-fired boiler

Barański J., Stąsiek J., Blasiak W.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2003

|

Vol. 7, No 3

347-362

EN

The paper presents results of three-dimensional physical modeling and computer simulations of fluid-flow structures, mixing and combustion processes in a 125 MW tangentially fuel-fired boiler and additional fuel - natural gas. This method is commonly called the reburning process, with an emphasis on the reduction of CO, NOx and SOx. The co-firing process is realized between the main coal burners and additional fuel nozzles. To improve the mixing and combustion processes, a physical technique, the so-called acid/alkali technique, is used to optimize the placement and direction of additional air and fuel nozzles. The best result obtained from physical modeling experiments is studied using numerical simulations with the FLUENT commercial code. Numerical modeling results are then used to analyze the performance of an industrial boiler. These results, compared with measurements in a real boiler, seem to be in good agreement with each other.

3

Mathematical modelling of a hypothetical method to measure mass flux and stoichiometry of conversion gas. Part II.

Friberg R., Blasiak W.

Archivum Combustionis

|

2000

|

Vol. 20 nr 3-4

115-135

EN

This paper deals with mathematical modelling of a hypothetical method for the indirect measurements of some fundamental thermochemical conversion and combustion design variables, that is, conversion gas rate (mass flow of conversion gas), conversion gas stoichiometry, air factor for conversion system, and air factor for combustion system. These quantities are indirectly determined by means of mathematical models based on the three-step model and a mass-balance approach. Eleven measurands are included in the mathematical models. An uncertainty propagation analysis has been carried out on the mathematical models by means of the Monte Carlo method. It idicates that it should be possible to determine the mass flow of conversion gas and the conversion gas stoichiometry within the range of +-5% and +-7%, respectively.

4

Large eddy simulation of a single jet flow in highly preheated and diluted air combustion

Dong W., Blasiak W.

Archivum Combustionis

|

2000

|

Vol. 20 nr 3-4

163-176

EN

In the present work, the large eddy simulation (LES) has been used to simulate a single fuel jet reacting flow under the conditions of highly preheated and diluted air combustion (HPDAC). A hybrid procedure of the standard subgrid scale (SGS) magorinky-Lille model and Reynolds stress model (RSM) together with the finite rate/eddy dissipation reaction model has been employed to simulate a single wall jet HPDAC furnace chamber. The propane-air two-step combustion system is selected for modeling under two different HPDAC inlet air conditions corresponding to 3% w/w oxygen at 1300K and 21% w/w oxygen at 1300K. The numerical results show that the standart Smagorinsky model and Reynolds stress model together with the finite rate/eddy disspation model are capable of predicting the global flame effects on the flow, such as flow velocities, mixing patterns, temperatures and turbulent parameters. The predictions are found in acceptable agreement with the corresponding results of in-furnace measurements and physical modeling. By compared with the pure Reynolds stress model, it is found that the differences between the two predictions of LES and RSM are insignificant in the near field of the flow. The Smagorinsky constant C, has been also tuned in the work. It illustrates that Cs value significantly influences the predictions on both near field and far of the jet flow. Though, further development of SGS stress and combustion models is needed, it is found that LES is an attratctive tool to simulate the dynamic processes of turbulent reacting flows for the HPDAC furnaces.

5

An experimental packed-bed combustion system and the verification of the measurement method. Part III.

Friberg R., Blasiak W.

Archivum Combustionis

|

2000

|

Vol. 20 nr 3-4

137-161

EN

This paper presents a newly constructed experimental packed-bed combustion system and a verified measurement method. The experimental system is the basis for the verification of the hypothetical method presented in Part II. The measurement method aims at some quantities derived from the three-step model (Part I), such as the mass flow of conversion gas, stoichiometry of conversion gas, and the air factors of conversion system and combustion system. The measurement method has been verified in the primary air rate range of 50-150 m3n/h for both wood pellets and fuel wood. The method resulted in measurements in the range of +- 5% of the actual value predicted by the reference method, which is considered to be a very good agreement.

6

A mass flow analysis of packed-bed combustion systems in the context of three-step model - a new system theory. Part I.

Friberg R., Blasiak W.

Archivum Combustionis

|

2000

|

Vol. 20 nr 3-4

91-114

EN

This paper presents a theoretical analysis of a new system theory - the three-step model - for packed bed combustion system (PBCS), such as grate combustion technologies. Some new concepts are deduced in the context of the three-step model, for example the conversion gas, the conversion efficiency, the air factor of the conversion system, and the combustion efficiency. Equations are developed for the determination of conversion and combustion efficiency, which are key parameters for the optimisation of PBCSs. These key parameters can be used as design and diagnostic tools for control and reduction of emissions and improving thermal efficiencies of PBCSs. However, to quantify these key parameters measurements need to be carried out on the specific PBCS of interest.

7

Mathematical modelling of heat and mass transfer in a fixed biomass fuel bed. Part 3, Char Combustion

Gemechu B., Atreya A., Blasiak W.

Archives of Thermodynamics

|

1999

|

Vol. 20, no 3/4

73-88

EN

One-dimensional propagation of a combustion front in a solid fuel bed of char is modelling by making the solid fuel as stationary with gas flowing through it upwards. The main means of heat transfer considered are conduction, convection and radiation. The fuel bed is assumed to be a porous homogenous layer composed of uniformly distributed coarse particles that are randomly oriented. The bed is thermally thick rendering a time-dependent, non-uniform temperature distribution between the top and the bottom. The mathematical model formulates the basic equations and solves them numerically to describe the temperature and species distribution in the region. Thermal non-equilibrium between the gas phase and the solid particle syrfaces is assumed, cosequently the use of separate equations for gas and solid phase equations is necessary. The method of solution is more complicated due to the fact that the partial differential equations of heat transfer are simultaneous non-linear partial differential equations. Numerical methods are used applaying Mathematica and Fortran ODE codes. Both methods show good results compared with previous works.

8

Mathematical modelling of heat and mass transfer in a fixed biomass fuel bed. Part 2, Pyrolysis

Gemechu B., Atreya A., Blasiak W.

Archives of Thermodynamics

|

1999

|

Vol. 20, no 3/4

63-72

EN

Heat and mass transfer in a fixed bed of biomass during thermal degradation of biomass in a hot inert gas (pyrolysis) is modeled. Biomass fuel decomposes to give gas, tar and char as a result of hot gas flowing through it upwards from a combustion char below. The main heating mode at this stage is conduction and convection. The fuel bed is assumed to be a porous homogenous layer composedof uniformely distributed coarse particles that are randomly oriented. The mathematical model formulates the basic equations and solves them numerically to describe the temperature and solid fuel degradation to tar, gas and char. Thermal non-equilibrium between the gas phase and the solid particle surfaces is assumed, conseqently the use of separate equations for gas and solid phase equations is necessary

9

Mathematical modelling of heat and mass transfer in a fixed biomass fuel bed. Part 1, Drying

Gemechu B., Atreya A., Blasiak W.

Archives of Thermodynamics

|

1999

|

Vol. 20, no 3/4

49-61

EN

A one-dimensional quasi-steady state mathematical model of heat and mass transfer in a fixed bed of biomass fuel during drying is presented. Heat is transferred from the pyrolysing fuel bed to the drying fuel above it by conduction and convection. The gas flow rate is determined by mass flux flowing through the bed. The drying rate curve is analyzed theoretically and the best drying curve formula is chosen. As a result, a one-dimensional quasi-steady state mass and temperaturedistributions in the bed are determined. @eng