Performance evaluation and optimization of air preheater in thermal power plant

1. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
17 – 19, July 2014, Mysore, Karnataka, India
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 5, Issue 9, September (2014), pp. 22-30
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IJMET
© I A E M E
PERFORMANCE EVALUATION AND OPTIMIZATION OF AIR
PREHEATER IN THERMAL POWER PLANT
G.Shruti1, Ravinarayan Bhat2, Gangadhar Sheri3
1(Department of Mechanical Engineering, Srinivas Institute of Technology, Mangalore, 574143, Karnataka, India)
2 (Associate professor , Department of Mechanical Engineering, Srinivas Institute of Technology, Mangalore, 574143,
Karnataka, India)
3(AGM Performance, LANCO-UPCL Nagarjuna Thermal Power Plant, Padubidri, Udupi, 574113 Karnataka, India)
ABSTRACT
This paper presents a performance evaluation and optimization method of an air preheater based on routine
operation data measured onsite at LANCO-UPCL, Nagarjuna thermal power plant Padubidri, Karnataka, India. The work
focuses on the performance of Regenerative type air pre heater (model LAP 13494/2200). The performances were
evaluated before and after radial sector plate clearance adjustments with air preheater tests, and improvement is seen
along with air preheater optimization.
Keywords: Air pre heater, Air leakage, Gas side efficiency, Seals, X-ratio.
1. INTRODUCTION
Modern high capacity boilers are always provided with an air preheater. Air pre-heater is an important boiler
auxiliary which primarily preheats the combustion air for rapid and efficient combustion in the furnace Serving as the last
heat trap for the boiler system, a regenerative air preheater typically accounts for over 10% of a plants thermal efficiency
on a typical steam generator. Considering this, when evaluating the performance of an air preheater one should take into
account all of the process variables [10].
A very good method to improve the overall efficiency of a thermal power plant is to preheat the air. If the
incoming air for combustion is not preheated, then some energy must be supplied to heat the air to a temperature required
to facilitate combustion. As a result, more fuel will be consumed which increases the overall cost and decreases the
efficiency. There are many factors, which contribute to the deterioration of air preheater performance like high seal
leakage, deterioration of heat absorption characteristics of basket elements due to fouling or plugging. Close monitoring
of air pre heater performance and proper instrumentation would enable timely detection of performance degradation. The
combustion air preheater for the large fuel-burning furnaces used to generate steam in thermal power plants [5].
2. LJUNGSTROM AIR PREHEATER (LAP 13494/2200)
The Ljungstrom air preheater is more widely used than any other type of combustion air preheater in the power
industry, because of its compact design proven performance and reliability, and its fuel flexibility. The model LAP
13494/2200 means a Ljungstrom air preheater with rotor diameter of 13494mm is used in UPCL power plant. The
heights of heating elements of 4 sections are respectively 300mm, 800mm, 800mm and 300mm from top to bottom of the
rotor. The cold end heating elements of 300mm height are made of carbon plate while the hot end heating elements are

2. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM
17 – 19, July 2014, Mysore, Karnataka, India
made of common carbon steel. The metal weight of one air preheater is approximately 620 tons, including 465 tons for
the rotor assembly (about 75 percent of the total weight). The air preheater is tri
The model LAP 13494/2200 tri-sector rotary air preheater as shown in Fig
exchanger. Specially corrugated heating elements are tightly placed in the sector compartment of the rotor. The rotor
turns at a speed of 0.99 rpm and is divided into gas channels and air channels. The air side is mad
channels and secondary air channels. When gas flows through the rotor, it releases heat and delivers it to the heating
elements and then the gas temperature drops; when the heated elements turn to the air side, the air passing through them
is heated and its temperature is increased. By continuing maintaining such a circulation, the heat exchange is achieved
between gas and air.
Fig. 1: Trisector rotary air preheater and its important
2.1 Heating Elements
Heating elements are made of carbon steel sheets with special corrugations formed by pressing; the hot end
heating assemblies are profiled in accordance with shapes and sizes of individual sub
by alternately piling up notched undulation sheets with vertical undulations and inclined turbulent corrugations and
sheets only with the same inclined corrugations one by one as shown in Fig 2. All the assemblies of both hot and cold
end heating elements are fastened by welding flat b
23
tri-sector type [10].
Fig. 1 is a counter flow regenerative heat
parts [10]
sub-modules. Each assembly is formed
ed bars and angle steels together [3].
-2014
made of primary air

3. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM
2.2 Sealing System
17 – 19, July 2014, Mysore, Karnataka, India
Fig. 2: Heating Elements
Usually air leaks in to the gas in the air preheater due to pressure differences. This leakage air decreases the
flue gas temperature without extracting the heat.
requirement that the rotating parts should have some working clearance between the static parts to avoid any
interference between them. Here, in air preheaters, rotors are constructed to have high
thermal expansion and these gaps are close with the flexible seal leaves. Major types of seals used in power plant.
• Radial seals
• Axial seals
• Bypass seals
• Circumferential seals
To reduce the air leakage seals are provided. It is an implied
The main purpose of these seals is to reduce the
the Air pre heater.[6]
3. EXPERIMENTAL SET-UP AND PROCEDURE
3.1 Principle of Operation
Air preheater performance test is conducted on rotary regenerative
air preheaters. Various performance indices like air preheater leakage, gas side efficiency, X
this test. A single carbon steel tube with portable gas analyzer and digital thermomete
evaluation.
3.2 Test Procedure
The Instruments used are: Gas analyzer, Digital thermometer, static probe.
3.2.1 Test Set Up – Operating Conditions of Test Runs
Test runs are conducted at an easily repeatable level at
number of mills in service and same total air levels as previous tests. The operating conditions for each test run are as
follows.
a. No furnace or air heater soot blowing is done during the test.
b. Unit operation is kept steady for at least 60 minutes prior to the test.
24
higher clearance to take care of
leakage between the gas and air. Fig 3. Shows sealing system of
Fig. 3: Sealing System
air preheater to improve the efficiency of the
X-ratio are determined using
thermometer is used for performance
defined baseline conditions at full load with same
ion -2014
er r

4. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
25
c. Steam coil Air heaters (SCAPH) steam supply is kept isolated and gas recirculation dampers if any, are tightly
shut.
d. No mill change over is done during the test.
The test run duration will be the time required to complete two traverses for temperature and gas analysis. Two
separate test crews should sample the gas inlet and outlet ducts simultaneously.
3.2.2 Traverse locations – Gas side
a. The gas inlet traverse plane should be located as close as possible to the air heater inlet. This is done to ensure
that any air ingress from the intervening duct/ expansion joints is not included in air heater performance
assessment.
b. The gas outlet traverse plane should be located at a suitable distance downstream the air heater to allow mixing
of the flow to reduce temperature and o2 stratification. However, it should not be located downstream of other
equipment or access ways that might contribute to air ingress.
3.2.3 Traverse locations – Airside
a. The air inlet traverse plane should be located after any air heating coils and as close as possible to the air heater
inlet. Since the entering air temperature is usually uniform, a single probe with 2 or 3 temperature measurement
points is adequate.
b. The air outlet traverse plane should be located at a suitable distance downstream the air heater to allow mixing
of the flow to reduce the gas stratification as shown in Fig 4.
Fig. 4: Traverse location- airside [10]
3.2.4 Ports and Probes
Typical test port and probe used for the test is shown in Fig 5.
Fig. 5: Ports and Probes [10]

5. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
( O gl O ge
) * 0.9 * 100
* ( −
)
AL Tgl Tae
( Tge −
Tgnl
)
Tge Tae
= (3)
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Tubes numbered 1,2, 3 are carbon steel 3/8” OD tubes and tube no. 4 is carbon steel 12-15 mm OD. Tubes
numbered 1, 2 3 are for gas sampling while tube no. 4 is for carrying thermocouple wires for temperature measurement.
d is the flue gas duct width at the test cross-section.
3.2.5 Flue Gas Composition Temperature
A representative value of flue gas composition (O2 / CO2/ CO) is obtained by grid sampling of the flue gas at
multiple points in a plane perpendicular to the flow at air heater inlet and outlet using a portable gas analyzer. Two
complete sets of data are collected for each traverse plane during each test run to ensure data repeatability.
A typical cross section of the flue gas duct with an 18- point grid is shown in Fig 6. Along with a typical probe.
Each dot indicates a sampling point for measurement of gas composition and temperature.
Fig. 6: Cross section of Flue gas duct [10]
Flue gas samples are drawn by a vacuum pump from the test grid probes and sent to a portable gas analyzer
through a gas conditioning system. Similarly, a representative value of temperature is obtained by grid measurement of
flue gas temperature at multiple points in a plane perpendicular to the flow at air heater inlet and outlet using multi point
probes.
A single tube probe with portable analyzer can also be used for traversing duct cross section. Marking / etching
is done on the sampling tube at d/6, d/2 5d/6, if d is the duct depth. The probe is inserted in each port samples are
drawn at different depths as per markings. Temperatures of flue gas are also measured at the same locations using a
similar single tube temperature probe.
Fig. 7: Gas Analyzer
Fig 7 shows typical gas analyzer used in the test to measure oxygen percentage in the flue gas. After completing
the testing of all the ports of a air preheater, calculations can be done as per the following formulae.
Air leakage
(21 2
)
2 2
O gl
−
−
= (1)
+
=
Tgnl Tgl
100
(2)
Gas side Efficiency GSE = (Temp drop/ Temp head)*100
*100
( )
GSE
−
W out
air
W
ga sin
X− ratio =

6. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
−
T Tgnl

7. (1583.9 * 32.94) + (504.11 * 39.83)
27
ga
−
iT out T n
X ratio
gas air
− =
sin
(4)
Weighted air inlet temperature
=

8. (5)
Weighted air outlet temperature
=

9. (6)
Total air flow= primary air flow + secondary airflow
(7)
4. RESULTS AND DISCUSSIONS
The experiments were conducted on a Ljungstrom air preheater. After determining the performance indices like
air leakage, GSE, X-ratio, using data from Table 1, radial Sector plate clearance is adjusted manually to improve the
efficiency of air preheater.
The following parameters are obtained using gas analyzers and digital thermocouple before adjusting the sector
plate.
Table 1: Parameters before adjusting sector plate clearance
Parameters Values
Avg. Flue Gas Temp - APH In 331.33°C
Avg. Flue Gas Temp - APH out 136.03°C
Avg. Flue Gas O2 - APH Inlet 4.61 %
Avg. Flue Gas O2 - APH outlet 6.61 %
Avg. Primary Air to APH Temp In 39.83°C
Avg. Primary Air from APH Temp Out 289.62°C
Avg. Secondary Air to APH Temp In 32.94°C
Avg. Secondary Air to APH Temp out 298.47°C
Total Secondary Air Flow 1583.9ton/hr
Total Primary Air Flow 504.11ton/hr
Air Leakage
(6.61 4.61) * 0.9 * 100
(21 −
6.61)
−
=
AL = 12.5%
Total air flow = primary air flow + secondary airflow
= 504.11+1583.9
= 2088.01 ton/hr
Weighted air inlet temperature
(2088.01)
=
Tae= Tair in = 34.64°C

10. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM
Weighted air outlet temperature
(1583.9 * 298.47) + (504
504.11 * 289.62)
0(2088. 1
=
Tair out= 296.33°C
12.5 (136.03 34.64)
Tgnl 136
(100)
+
+ −
=
Tgnl = 148.72°C
Gas side Efficiency GSE
(331.33 −
148
148.72)
(331.3 −
34
=
GSE = 61.54%
X-ratio
(331.33 −
148
148.72)
(296.33 −
34
=
X-ratio = 0.69
After finding performance indices, radial sector plate clearance is again adjusted manually
and Table 3 shows sector plate clearance values adjusted in different direction.
Table 2: Sector plate
Clearance (APH A side)
Reading
point
Distance between
and radial seal
Hot end Cold End
A 2.7
B 2.0
C 2.4
D 2.2
E 2.3
F 2.2
G 6.4
H 6.7
I 5.8
J 5.5
K 5.6
L 5.0
17 – 19, July 2014, Mysore, Karnataka, India
28
01)
136.03
* 100
34.64)
* 100
34.64)
at cold state.
Table 3: Sector plate
Clearance (APH B side)
sector plate
1.6
1.7
1.5
1.5
1.7
1.9
30.0
30.0
29.8
30.2
31.1
30.7
Reading
point
Distance between sector
plate and radial seal
Hot end
A 6.3
B 6.4
C 6.0
D 5.6
E 7.0
F 7.0
G 12.0
H 11.6
I 12.0
J 11.5
K 12.0
L 12.0
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Table 2
earance Cold End
1.6
1.7
1.4
1.4
1.5
1.4
30.7
30.6
30.0
30.0
30.5
30.7

11. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM
The following parameters are obtained using gas analyzers and digital
Table 4: Parameters after adjusting sector plate Clearance
Avg. Flue Gas Temp
Avg. Flue Gas Temp
Avg. Flue Gas O2
Avg. Flue Gas O2
Avg. Primary Air to APH Temp In
Avg. Primary Air from APH Temp Out
Avg. Secondary Air to APH Temp In
Avg. Secondary Air to APH Temp out
Total Secondary Air Flow
Total Primary Air Flow
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After adjusting the sector plate clearance another set of data were collected as shown in Table 4. Using these
parameter again air leakage, efficiency and x
different results were obtained. And it is observed that air leakage decreased and efficiency increased gradually. By
adjusting the sector plate clearance optimized results were obtained. Using the parameters from Table 4 optimized results
were obtained.
4.1 Performance characteristics
4.1.1 Air leakage
The variation of Air leakage with various sector plate clearance adjustments is as shown in the following graph.
Fig 8 shows variation of air leakage for different trials. It s observed that
leakage is the indicator of the condition of the air preheater seals. After adjusting the radial seal sector plate clearance
air leakage decreased.
Fig. 8: Air leakage for different trails of sector plate clearance adjustments
4.1.2 Gas side efficiency
the
Fig 9 shows variation of gas side efficiency for different trials. It is observed that gas side efficiency gradually
increased as the area between air to the gas side between the rotor and the air preheater housing decreases.

12. Fig. 9: Gas side efficiency for different trails of sector plate clearance adjustments
4.1.3 X-ratio
Fig 10 shows X-ratio for different trials. It is observed that
plate is adjusted. It indicates maximun heat is recovred in the air pre heater.
17 – 19, July 2014, Mysore, Karnataka, India
29
thermocouple after adjusting the sector plate.
Parameters Values
- APH In 336°C
- APH out 135.79°C
- APH Inlet 4.19 %
- APH outlet 5.4 %
38.50°C
287.27°C
33.66°C
300.03°C
1593.03ton/hr
508.5ton/hr
x-ratio are calculated. Similarly for different set of clearance adjustment
air leakage gradually decreased. Air
X-ratio incresed as hot end and cold end radial sector

13. Proceedings of the 2nd International Conference on Current Trends in Engineering and Management ICCTEM
Fig. 10: X-ratio for different trails of sector plate clearance adjustments
5. CONCLUSION
By reducing the area available for leakage from the air to the gas side between the rotor and the air preheater
housing by adjusting the radial sector plate reduces the air leakage and max efficiency can be obtained. And increase in x
ratio indicates maximum heat recovery in the Air preheater.
6. ACKNOWLEDGMENT
The authors would like to thank LANCO
for the technical support of this work.
7. NOMENCLATURE
AL = air heater leakage
O2 ge = percent O2 in gas entering air heater
O2 gl = percent O2 in gas leaving air heater
Tgnl = gas outlet temperature corrected for no
Tae = Temperature of air entering air heater
Tgl = Temperature of gas leaving air heater
LAP = Ljungström Air Preheater
GSE = Gas side efficiency
8. REFERENCES
Journal Papers
[1]. Mr. Vishwanath .H. H, Dr. Thammaiah Gowda , Mr. Ravi S.D “
Preheater” International Journal of Innovative Research in Science, Engineering and Technology
July 2013,
[2]. Bostjan Drobnic, Janez Oman. “A Numerical Model
Rotary Air Preheater”, International Journal of Heat and Mass Transfer
[3]. Staseik J.A., “Experimental studies of heat transfer and fluid flow across undulated heat exchanger surfaces”,
J. Heat Transfer. Vol. 41 Nos. 6-7,pp. 899
[4]. Larsen F. W., “Rapid Calculation of Temperature in a Regenerative Heat Exchanger Having Arbitrary Initial
Solid and Entering Fluid Temperatures
[5]. Wang .H,” Analysis on Thermal Stress Deformation of
J. Chem. Eng., Vol. 26, 833-839 , 2009.
[6]. T.Skiepko, “Effect Of Reduction In Seal Clearances On Leakages In A Rotary Heat Exchanger
system CHP 9 (6), pp. 553-559, 1989.
[7]. Donald Q.Kern, “Process Heat Transfer
[8]. Stephen.Storm, john, Guffre, Andrea Zucchelli ”
Performance And Reliability” POWERGEN Europe 7
[9]. Sandira Alagic, Nikola Stocic,”Numerical Analysis
Pre-Heaters” Strojniški vestnik - Journal of Mechanical Engineering
Books
[10]. UPCL manuals images.
17 – 19, July 2014, Mysore, Karnataka, India
30
overy LANCO-UPCL, Nagarjuna thermal power plant, Padubidri, Karnataka, India
leakage
Heat Transfer Analysis Of Recuperative Air
for the Analyses of Heat Transfer
, 49, pp .501–509, 2006.
899-914, 1998.
Temperatures”, Int. J. Heat Mass Transfer Vol.10, pp.149-168, 1967.
Rotary Air-Preheater In a Thermal Power Plant
Transfer”, Tata McGraw-Hill Publication, pp. 701, 2004.
Advancements With Regenerative Airheater Design,
7-9 June 2011.
of Heat Transfer and Fluid Flow In Rotary Regenerative Air
,pp 411-417,2005
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x-
Vol. 2, Issue 7,
and Leakages in A
Int.
Plant”, Korean
Exchanger”, Heat recovery