CFD Modeling of Air Stream Pressure Drop inside Combustion Air Duct of Coal-Fired Power Plant with and without Airfoil

Authors: Pakawhat Khumkhreung, Yottana Khunatorn

Abstract:

The flow pattern inside rectangular intake air duct of 300 MW lignite coal-fired power plant is investigated in order to analyze and reduce overall inlet system pressure drop. The system consists of the 45-degree inlet elbow, the flow instrument, the 90-degree mitered elbow and fans, respectively. The energy loss in each section can be determined by Bernoulli’s equation and ASHRAE standard table. Hence, computational fluid dynamics (CFD) is used in this study based on Navier-Stroke equation and the standard k-epsilon turbulence modeling. Input boundary condition is 175 kg/s mass flow rate inside the 11-m² cross sectional duct. According to the inlet air flow rate, the Reynolds number of airstream is 2.7x10⁶ (based on the hydraulic duct diameter), thus the flow behavior is turbulence. The numerical results are validated with the real operation data. It is found that the numerical result agrees well with the operating data, and dominant loss occurs at the flow rate measurement device. Normally, the air flow rate is measured by the airfoil and it gets high pressure drop inside the duct. To overcome this problem, the airfoil is planned to be replaced with the other type measuring instrument, such as the average pitot tube which generates low pressure drop of airstream. The numerical result in case of average pitot tube shows that the pressure drop inside the inlet airstream duct is decreased significantly. It should be noted that the energy consumption of inlet air system is reduced too.

Keywords: Airfoil, average pitot tube, combustion air, CFD, pressure drop, rectangular duct.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1130973

References:

[1] R. W. Lewis, P. Nithiarasu and K. N. Seetharamu, Fundamentals of the Finite Element Method for Heat and Fluid Flow, John Wiley and Sons Ltd, 2004.
[2] H. K. Versteeg and W. Malalasekera, An Introduction to Computational Fluid Dynamics, Pearson Education Ltd, 2007.
[3] J. D. Anderson Jr, Computational Fluid Dynamics The Basics with Applications, McGraw-Hill, 1995.
[4] Dr. N Al-Khalidy, Design Optimization of Industrial Duct Using Computational Fluid Dynamics, CSIRO, Melbourne, Australia, 10-12 December 2003.
[5] Electricity Generating Authority of Thailand, Technical Data Book Plant Operation Division 2, MAE MOH Power Plant Operation Department, 1989.
[6] Electricity Generating Authority of Thailand, Mae-Moh 8-13 System Description Level 1 Boiler Auxiliary Operation: Primary and Force Draft Fan, MAE MOH Power Plant Operation Department, 2007.
[7] C. Bhasker, Simulation of Air Flow in the Typical Boiler Windbox Segments, Advances in Engineering Software 33 (2002) 793–804.
[8] ANSYS CFX® Manual, ANSYS Ltd, 2015.
[9] K. Sudo, M. Sumida and H. Hibara, Experimental Investigation on Turbulent Flow in a Square-Sectioned 90-Degree Bend, Experiments in Fluids 30 (2001) 246-252 @ Springer-Verlag 2001.
[10] D. C. Wilcox, Turbulence Modeling for CFD, DCW Indutries Inc, 1994.
[11] The American Society for Testing and Materials, Standard Test Method for Average Velocity in a Duct (Pitot Tube Method) Designation D 3154 – 50, 1995.
[12] ASHRAE, Fundamentals. American Society of Heating, Refrigeration and Air Condition Engineer, Atlanta, 1997.