finite element analysis of steam boiler used in power · pdf filefinite element analysis of...

SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 1 Issue 6 October 2014

ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 28

Finite Element Analysis of Steam Boiler Used In Power Plants 1M. Suri Babu, 2 Dr.B.Subbaratnam

1M.Tech student, 2Professor, 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: 2348 – 8360 www.internationaljournalssrg.org 9

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: 2062-

1999:

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*106

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: 2348 – 8360 www.internationaljournalssrg.org 0

assembly obtained from the thermal

analysis performed earlier.

Support base plates are arrested in

all Dof,

Pressure load 1716164Pa is applied

inside of the boiler shell.

Temperature distribution (373K) is

obtained from thermal analysis is

applied as temperature on the

boiler structure.

Fig. applied structural and thermal

boundary conditions on steam boiler

assembly

RESULTS

Nodal temperature:

Fig. Temperature distribution on steam

boiler assembly

Von Mises stress:

Fig. Von Mises stress of 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.



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.

Fig. 3D model of modified steam boiler

FINITE ELEMENT ANALYSIS OF

MODIFIED STEAM BOILER

COUPLED-FIELD ANALYSES

Material Properties of Steel IS: 2062-

1999:

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*106

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 1716164Pa 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. applied structural and thermal

boundary conditions on modified steam

boiler assembly

RESULTS

Nodal temperature:



Fig. Temperature distribution on modified

steam boiler assembly

Von Mises stress:

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

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 0-150 Hz.

From the modal analysis,

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.


mass participation of 4.7tone and

6.3tone are observed in Y-dir for

the frequency of 57.6Hz and

65.9Hz.


mass participation of 6.9tone,

4.2tone and 4.9tone are observed in



Z-dir for the frequency of 57.6Hz,

65.9Hz and 97.5Hz.

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 0 -150 Hz. The

total number of sub steps defined for the

analysis is 15.

Amplitude vsforcing frequency:

Harmonic response on steam boiler:

Fig. harmonic response on steam boiler in

linear scale

1. Max. Von Mises stress of frequency @

30Hz

Fig. Von Mises stress of Modified steam

boiler


60Hz


boiler


100Hz




boiler

4. Max. Von Mises stress of frequency

@ 100Hz


boiler

From the Harmonic analysis,

The deflections and stresses at the nearest

natural frequency in the operation range of

0-150 Hz are plotted in the below table.

Table. deflections and von mises stress

for critical frequencies

S.no

FRQ.(Hz)

Def.

(mm)

VON MISES

STRESS

(MPa)

1 30 0.7 89

2 60 6.1 232

3 70 1.3 103

4 100 4.4 221

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



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.

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