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Research Papers

Reduction in Pollutants Emissions From Domestic Boilers—Computational Fluid Dynamics Study

[+] Author and Article Information
Gasser Hassan

CFD Centre, ERRI, SPEME, University of Leeds, Leeds, LS2 9JT, UK; Mubarak City for Scientific Research, IRI, Alexandria 21934, Egyptgasser_hassan@yahoo.com

Mohamed Pourkashanian

CFD Centre, ERRI, SPEME, University of Leeds, Leeds, LS2 9JT, UKm.pourkashanian@leeds.ac.uk

Derek Ingham

CFD Centre, ERRI, SPEME, University of Leeds, Leeds, LS2 9JT, UKd.b.ingham@leeds.ac.uk

Lin Ma

CFD Centre, SPEME, University of Leeds, Leeds, LS2 9JT, UKl.ma@leeds.ac.uk

Stephen Taylor

 ENERTEK International Limited, Hull, HU7 OYF, UKstephen.taylor@enertek.co.uk

J. Thermal Sci. Eng. Appl 1(1), 011007 (Jul 22, 2009) (9 pages) doi:10.1115/1.3159526 History: Received January 18, 2009; Revised April 11, 2009; Published July 22, 2009

This study is concerned with building a computational fluid dynamics (CFD) model to simulate the combustion process occurring in the combustion chamber of some domestic boilers. The burner used in this boiler is a conventional cylindrical premix burner with small inlet holes on its surface. A two-dimensional CFD model is built to simulate the combustion chamber domain, and the partially premixed combustion model with a postprocessor for NOx calculations is used to simulate the combustion process inside the combustion chamber. A complete description of the formation characteristics of NOx produced from the boiler is discussed in detail. A comparison between the CFD numerical results and the experimental measurements at different boiler loads is performed in order to validate the numerical model and investigate the accuracy of the CFD model. The validated CFD model is used to investigate the effect of different boundaries temperatures and the mixture inlet velocity on the flue gas average temperature, residence time, and hence the CO and NOx concentrations produced from the combustion chamber. The concept of changing the mixture inlet velocity is found to be an effective method to improve the design of the burner in order to reduce the pollutant emissions produced from the boiler with no effect on the boiler efficiency.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

The main boiler components (a) 30 kW boiler with four aluminum die-castings, (b) the cylindrical burner within the heat exchanger, and (c) distribution of the inlet holes on the 10 kW burner surface (angular distribution of the ten identical units with eight rows in the axial direction)

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Figure 2

Visual representation for the PDF lookup table at constant mixture fraction (f=0.0438), (a) mean temperature and (b) CO mole fraction

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Figure 3

Symmetrical two-dimensional computational domain for the combustion chamber with the specified boundary conditions, line AB is used to explain the results inside the combustion chamber

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Figure 4

Geometrical simplification for the inlet mixture holes distributed on the burner surface (22)

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Figure 5

Contours of temperature and different species mole fractions (dry basis) predicted by the partially premixed model, (a) temperature (K), (b) CO mole fraction, (c) NO formation rate (kg mole/m3 s), and (d) temperature variance

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Figure 6

Temperature distribution and NO formation rates due to different NO mechanisms along line AB (see Fig. 3)

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Figure 7

Comparisons between the predicted mole fractions of different species using the CFD numerical model and the experimental measurements at different fan speeds, (a) CO2 mole fraction, (b) O2 mole fraction, (c) CO mole fraction, and (d) NO mole fraction. The experimental data are measured at the combustion chamber exit (before the heat exchanger), see Fig. 1, and at the boiler chimney (flue gases to the atmosphere after the heat exchanger).

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Figure 8

The effect of different thermal boundary conditions on the CO and NO mole fractions at the combustion chamber exit

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Figure 9

The effect of the mixture inlet velocity on (a) the peak and average temperature inside the combustion chamber and (b) CO and NO mole fractions at combustion chamber exit

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