Finite Element Analysis of Steam Boiler Used In Power Plants

Transcription

1 Finite Element Analysis of Steam Boiler Used In Power Plants 1 M. Suri Babu, 2 Dr.B.Subbaratnam 1 M.Tech student, 2 Professor, Dept of Mechanical Engineering, Kits, Markapur, A.P, India ABSTRACT A boiler or steam generator is a closed vessel used to generate steam by applying heat energy to water.during the process of generating steam, the steam boiler is subjected to huge thermal and structural loads.to obtain efficient operation of the power plant, it is necessary to design a structure to withstand these thermal and structural loads. Using CAD and CAE softwares is the advanced methodology of designing these structures before constructing a prototype.in this project finite element analysis of the steam boiler was carried out to validate the design for actual working conditions. The main tasks involved in the project are performing the 3D modelling of the boiler and finite element analysis. In this project, design optimization of the boiler is also done based on the results obtained from the thermal and structural analysis. NX-CAD software is used for design and 3D modelling. ANSYS software is used for doing finite element analysis. PROBLEM DEFINITION AND METHODOLOGY The objective of this project is to make a 3D model of the steam boilerand study the structural and thermal behaviour of the steam boilerby performing the finite element analysis.3d modelling software (UNIGRAPHICS NX) was used for designing and analysis software (ANSYS) was used for structural and thermal analysis. The methodology followed in the project is as follows: Create a 3D model of the steam boilerassembly using NX-CAD software. Convert the surface model into parasolid file and import the model into ANSYS to do analysis. Perform thermal analysis on the steam boilerassemblyfor thermal loads. Perform static analysis on the existing model of the steam boilerassemblyfor pressure loads and thermal loads to find deflections and stress, optimized if enquired. ISSN: Page 28

2 Based on the above results, design changes are implemented to reduce the stresses and deflections. Develop modified model of the steam boilerassemblyusing NX-CAD software, and import it to ANSYS software. Perform thermal analysis on the modified steam boilerassemblyfor thermal loads. Perform static analysis on the modified steam boilerassemblyfor pressure loads and thermal loads to find deflections and stress, optimized if required. Perform Modal analysis to find natural frequencies on the existing model of the steam boilerassembly. From the modal analysis results, the natural frequencies, mode shapes and their mass participations of the steam boilerare plotted and checked if any natural frequencies are present in the operating range of the steam boilerand critical frequencies are identified. From the harmonic analysis results, the operating frequencies are cheeked with the critical frequencies and documented the deflections and stresses values of critical frequencies. 3D MODELING OF STEAM BOILER The 3D model of the steam boiler assemblywas developed using NX- CAD software.steam boiler assemblywas converted to surface model for analysis. Fig. 3D model of steam boiler assembly (surface model) FINITE ELEMENT ANALYSIS OF STEAM BOILER COUPLED-FIELD ANALYSES: Material Properties of Steel IS: : Young s modulus = 200Gpa Yield Strength = 250 Mpa Tensile Strength = 410 Mpa Thermal conductivity) = 16 Density, (kg/m3) = 7850 Poisson s ratio, v = 0.3 Thermal expansion= 1.3*10 6 Boundary conditions: In structural analysis of steam boiler assembly, we have to apply structural and thermal loads. Temperature distribution is applied as Thermal loads on steam boiler ISSN: Page 29

3 assembly obtained from the thermal analysis performed earlier. Support base plates are arrested in all Dof, Pressure load Pa is applied inside of the boiler shell. Temperature distribution (373K) is obtained from thermal analysis is applied as temperature on the boiler structure. Von Mises stress: Fig. Von Mises stress of steam boiler assembly Fig. applied structural and thermal boundary conditions on steam boiler assembly RESULTS Nodal temperature: Fig. Temperature distribution on steam boiler assembly From the above results it is observed that: Total temperature distribution is 373k on steam boiler assembly. The Max Deflection and Max VonMises Stress observed 1.6mm and 430Mpa on the steam boiler assembly for operating loading conditions respectivly. And the Yield strength of the materials steel is 250Mpa. Hence according to the Maximum Yield Stress Theory, the VonMises stress is higher than the yield strength of the material. Hence the design of steam boiler assembly is not safe for the above operating loads. ISSN: Page 30

4 To overcome these high stresses and deflections, design modification of steam boiler assembly is required. From the above results, it is observed that the high stresses are at boiler shell regions. To reduce the stresses on the boiler shell region, thickness of shell body is increased. 3D MODELING OF MODIFIED STEAM BOILER To reduce the stresses on the boiler shell region, thickness of shell body is increased. Density, (kg/m3) = 7850 Poisson s ratio, v = 0.3 Thermal expansion= 1.3*10 6 Boundary conditions: In structural analysis of modified steam boiler assembly, we have to apply structural and thermal loads. Support base plates are arrested in all Dof, Pressure load Pa is applied inside of the modified boiler shell. Temperature distribution (373K) is obtained from thermal analysis is applied as temperature on the modified steam boiler. Fig. 3D model of modified steam boiler FINITE ELEMENT ANALYSIS OF MODIFIED STEAM BOILER COUPLED-FIELD ANALYSES Material Properties of Steel IS: : Young s modulus = 200Gpa Yield Strength = 250 Mpa Tensile Strength = 410 Mpa Thermal conductivity) = 16 Fig. applied structural and thermal boundary conditions on modified steam boiler assembly RESULTS Nodal temperature: ISSN: Page 31

5 Fig. Temperature distribution on modified Von Mises stress: steam boiler assembly Hence according to the Maximum Yield Stress Theory, the VonMises stress is less than the yield strength of the material. Hence the design of steam boiler assembly is safe for the above operating loads. Then the modified steam boiler assembly is analyzed for dynamic loading conditions. To check the structure response for resonance condition, MODAL ANALYSIS OF MODIFIED STEAM BOILER: Modal analysis is performed on modified steam boiler assembly to calculate the natural frequencies in the operating range of Hz. From the modal analysis, Fig. Von Mises stress of modified steam boiler assembly From the above results it is observed that: Total temperature distribution is 373k on steam boiler assembly. The Max Deflection 2.1mm andmax VonMises Stress 176Mpa observed on the modified steam boiler assembly for operating loading conditions. And the Yield strength of the materials steel is 250Mpa The total weight of the Modified steam boiler is 44.8tons It is observed that the maximum mass participation of 20.7tone is observed in X-dir for the frequency of 28.7Hz. It is observed that the maximum mass participation of 4.7tone and 6.3tone are observed in Y-dir for the frequency of 57.6Hz and 65.9Hz. It is observed that the maximum mass participation of 6.9tone, 4.2tone and 4.9tone are observed in ISSN: Page 32

6 Z-dir for the frequency of 57.6Hz, 65.9Hz and 97.5Hz. 1. Max. Von Mises stress of 30Hz To check the structure response at the mentioned frequency due to the operating loads, harmonic analysis is carried out on the modified steam boiler assembly. HARMONIC ANALYSIS OF MODIFIED STEAM BOILER: Harmonic analysis was carried out on the Modified steam boiler to determine the deflections and stress of a structure in the frequency range of Hz. The total number of sub steps defined for the analysis is 15. Fig. Von Mises stress of Modified steam boiler 2. Max. Von Mises stress of 60Hz Amplitude v s forcing frequency: Harmonic response on steam boiler: Fig. Von Mises stress of Modified steam boiler Fig. harmonic response on steam boiler in linear scale 3. Max. Von Mises stress of 100Hz ISSN: Page 33

7 Fig. Von Mises stress of Modified steam boiler 4. Max. Von Mises stress of 100Hz Fig. Von Mises stress of Modified steam boiler From the Harmonic analysis, The deflections and stresses at the nearest natural frequency in the operation range of Hz are plotted in the below table. Table. deflections and von mises stress for critical frequencies VON MISES Def. S.no FRQ.(Hz) STRESS (mm) (MPa) From the above results it is observed that the critical frequencies 30Hz, 60Hz, 70Hz, and 100Hz are having stresses of 89MPa, 232MPa, 103MPa, and 221MPa respectively. The yield strength of the material used for Modified steam boiler is 250MPa. According to the VonMises Stress Theory, the VonMises stress of Modified steam boiler at frequencies 30Hz, 60Hz, 70Hz, and 100Hz are less than the yield strength of the material. Hence the design of Modified steam boiler is safe for the above operating loading conditions. CONCLUSION In the present project a Modified steam boiler has been designed and optimized for structural and thermal analysis. The Modified steam boiler was studied for 3 different cases: Couple field Analysis Modal analysis Harmonic Analysis ISSN: Page 34

8 From the above analysis it is concluded that that the Modified steam boiler has stresses and deflections within the design limits of the material used. The deflections and stresses obtained in the harmonic analysis are also under the design limits. Therefore it is concluded that the Modified steam boiler is safe under the given operating conditions. REFERENCES 1. Steam Boiler Room Questions & Answers, Third Edition by Stephen M.Elonka andalex Higgins 2. Steam Boiler Operation by James J.Jackson, Prentice-Hall Inc, New Jersey, Boilers by Carl D. Shields, McGraw Hill Book Company, U.S, Industrial Heat Generation and Distribution -NIFES Training Manual Issued For CEC India Energy Bus Project 5. Practical Boiler Water Treatment by Leo.I.Pincus, McGraw Hill Inc, New York, 1962.Modeling, simulating and optimizing boiler heating surfaces and evaporator circuits by Kim Sørensen,Thomas Condra and Niels Houbak, 6. Ganapathy, V., Steam Plant Calculations Manual,2nd Edition, Marcel Dekker Inc., Kitto, J. B. and Stultz, S. C., Steam: ItsGeneration and Use, 41st Edition, The Babcock and Wilcox Company, Barberton, Ohio, U.S.A, Lou Roussinos, P. E., Boiler Design and Efficiency [online], Available: f, Accessed: September 1, Murdock, K. L., 3ds max 9 Bible, Wiley Publishing Inc. Indianapolis, Indiana, Nagpal, G. R., 1998, Power Plant Engineering, Khanna, Delhi. 11. Steam Pressure Reduction: Opportunities and Issues by U.S Deportment of energy, 12. Rapid Start up Analysis of a Natural Circulation HRSG Boiler with a Vertical Steam Separator Design by M.J. Albrecht, W.A. Arnold, R. Jain and J.G. DeVitto, 13.Technological investigations and efficiency analysis of a steam heat exchange condenser: 14. conceptual design of a hybrid steam condenser by R K Kapooria and S kumar, 15. Developmental design of a laboratory firetube Steam boiler by I. O. OHIJEAGBON, ISSN: Page 35