POWER June 2010 - 35

combined cycles
economic factors, start-up ramp rates can
differ from the design values assumed in the
LCA. The number of cycles per year, operating
time at full pressure, and so on will
also differ, further influencing the expected
life of the unit.
One of the biggest challenges for any
LCA or other analysis technique is to determine
how the pressures and temperatures
are changing in various components of the
HRSG while in operation. An LCA done
before the unit enters commercial service
is based on controlled operating conditions.
All the curves are nice and smooth and gradients
are well defined, unlike real-life operation
(Figure 2).
These types of curves are developed using
dynamic simulation programs based on
heat transfer correlations. The curves represent
the constraints rather than the actual
operating scenario. Similar curves for other
equipment, such as the combustion turbine
and steam turbine, are used to develop plant
operating procedures. These same curves
are used as the calculation basis for all lifecycle
computations.
Based on the customer-provide modes
of operation and the number and type of
cycles for the life of the plant, design life,
and annual operating hours (Table 1), the
HRSG manufacturer develops uniform
lifetime component consumption estimates
for the 30-year life. Using the DF values,
an inspection program can also be developed
(Figure 3).
In the real world of plant operation,
pressure and temperature changes and their
gradients are more chaotic. HRSGs, like
any other equipment, have periods of startup,
operation, and shutdown that don't follow
the ideal. Even though operations may
follow a set procedure, no two operating
scenarios are alike; different ramp rates are
selected to increase the time the plant is " in
the money. " Quantifying the ramp rate for
each of the scenarios will result in more accurate
estimation of the life consumption
(Figure 4).
Not taking into account the variability
of the boundary conditions, start-up and
shutdown ramp rates, and number of cycles
makes the conventional LCA of limited use.
A conventional LCA rarely simulates how
boilers are operated dynamically in practice.
For example, Figures 5 and 6 illustrate how
the drum pressure changes during an actual
HRSG start-up. The drum pressure changes
create the temperature differences that give
rise to the thermal stresses causing the fatigue
damage. The severity of temperature
ramps in an actual start-up compared with
the assumed temperature changes makes the
life consumption much more severe.
June 2010 | POWER
5. Steep ramp rate. A typical start-up curve taken from an operating HRSG shows the
high-pressure steam drum (saturation) temperature ramp rate compared to the temperatures
assumed by a conventional life consumption analysis. Source: Vogt Power International Inc.
T actual
700
600
500
400
300
200
100
20
40
60
80
Time from start (min.)
6. Distant relations. The temperatures present in the high-pressure steam drum are remarkably
different in an operating HRSG during start-up than those assumed by a conventional
life consumption analysis. Source: Vogt Power International Inc.
20
15
10
5
-5
-10
-15
-20
-25
-30
-35
Time from start (min.)
Focus on Actual Boiler Life Used
The conventional LCA approach requires
frequent general inspections of cycling units
because it cannot be accurately determined
where or when components will fail. To
improve upon the conventional LCA, a dynamic
program that uses real-time operating
data is required. This operating data-based
(ODB) methodology must use the operating
data of a given HRSG to directly estimate
the unit's life consumption in real time. It
www.powermag.com
would not use historical data or statistical
trends from other units to predict the unit's
life consumption, unlike the conventional
LCA approach. Also important is including
an inspection and monitoring program of
critical components to validate the program
results and enable the scheduling of any
corrective action that's necessary to avoid a
forced shutdown.
The program must take into account the
specific geometry and connection details of
35
Acutual
Expected
100
120
140
160
T expected
20
40
60
80
100
120
140
160
Temperature difference (F)
Temperature (F)
http://www.powermag.com

POWER June 2010

Table of Contents for the Digital Edition of POWER June 2010

Contents
POWER June 2010 - Cover1
POWER June 2010 - Cover2
POWER June 2010 - Contents
POWER June 2010 - 2
POWER June 2010 - 3
POWER June 2010 - 4
POWER June 2010 - 5
POWER June 2010 - 6
POWER June 2010 - 7
POWER June 2010 - 8
POWER June 2010 - 9
POWER June 2010 - 10
POWER June 2010 - 11
POWER June 2010 - 12
POWER June 2010 - 13
POWER June 2010 - 14
POWER June 2010 - 15
POWER June 2010 - 16
POWER June 2010 - 17
POWER June 2010 - 18
POWER June 2010 - 19
POWER June 2010 - 20
POWER June 2010 - 21
POWER June 2010 - 22
POWER June 2010 - 23
POWER June 2010 - 24
POWER June 2010 - 25
POWER June 2010 - 26
POWER June 2010 - 27
POWER June 2010 - 28
POWER June 2010 - 29
POWER June 2010 - 30
POWER June 2010 - 31
POWER June 2010 - 32
POWER June 2010 - 33
POWER June 2010 - 34
POWER June 2010 - 35
POWER June 2010 - 36
POWER June 2010 - 37
POWER June 2010 - 38
POWER June 2010 - 39
POWER June 2010 - 40
POWER June 2010 - 41
POWER June 2010 - 42
POWER June 2010 - 43
POWER June 2010 - 44
POWER June 2010 - 45
POWER June 2010 - 46
POWER June 2010 - 47
POWER June 2010 - 48
POWER June 2010 - 49
POWER June 2010 - 50
POWER June 2010 - 51
POWER June 2010 - 52
POWER June 2010 - 53
POWER June 2010 - 54
POWER June 2010 - 55
POWER June 2010 - 56
POWER June 2010 - 57
POWER June 2010 - 58
POWER June 2010 - 59
POWER June 2010 - 60
POWER June 2010 - 61
POWER June 2010 - 62
POWER June 2010 - 63
POWER June 2010 - 64
POWER June 2010 - 65
POWER June 2010 - 66
POWER June 2010 - 67
POWER June 2010 - 68
POWER June 2010 - 69
POWER June 2010 - 70
POWER June 2010 - 71
POWER June 2010 - 72
POWER June 2010 - Cover3
POWER June 2010 - Cover4
https://www.nxtbook.com/accessintelligence/POWER/pwr_march-2024
https://www.nxtbook.com/accessintelligence/POWER/pwr_february-2024
https://www.nxtbook.com/accessintelligence/POWER/pwr_january-2024
https://www.nxtbook.com/accessintelligence/POWER/pwr_december-2023
https://www.nxtbook.com/accessintelligence/POWER/pwr_november-2023
https://www.nxtbook.com/accessintelligence/POWER/power-october-2023
https://www.nxtbook.com/accessintelligence/POWER/re-tech-supp-to-power-september-2023
https://www.nxtbook.com/accessintelligence/POWER/power-september-2023
https://www.nxtbook.com/accessintelligence/POWER/power-and-re-tech-supp-september-2023
https://www.nxtbook.com/accessintelligence/POWER/power-august-2023
https://www.nxtbook.com/accessintelligence/POWER/power-july-2023
https://www.nxtbook.com/accessintelligence/POWER/power-june-2023
https://www.nxtbook.com/accessintelligence/POWER/power-may-2023
https://www.nxtbook.com/accessintelligence/POWER/power-april-2023
https://www.nxtbook.com/accessintelligence/POWER/power-march-2023
https://www.nxtbook.com/accessintelligence/POWER/power-february-2023
https://www.nxtbook.com/accessintelligence/POWER/power-january-2023
https://www.nxtbook.com/accessintelligence/POWER/power-december-2022
https://www.nxtbook.com/accessintelligence/POWER/power-november-2022
https://www.nxtbook.com/accessintelligence/POWER/Power-October-2022-140th-Anniversary-Supp
https://www.nxtbook.com/accessintelligence/POWER/Power-October-2022-and-Anniversary-Supp
https://www.nxtbook.com/accessintelligence/POWER/power-and-re-tech-supp-september-2022
https://www.nxtbook.com/accessintelligence/POWER/power-september-2022
https://www.nxtbook.com/accessintelligence/POWER/power-august-2022
https://www.nxtbook.com/accessintelligence/POWER/Power-July-2022-Intl
https://www.nxtbook.com/accessintelligence/POWER/power-july-2022
https://www.nxtbook.com/accessintelligence/POWER/power-june-2022-intl
https://www.nxtbook.com/accessintelligence/POWER/power-june-2022
https://www.nxtbook.com/accessintelligence/POWER/power-may-2022
https://www.nxtbook.com/accessintelligence/POWER/power-may-2022-intl
https://www.nxtbook.com/accessintelligence/POWER/power-april-2022
https://www.nxtbook.com/accessintelligence/POWER/Power-April-2022-Intl
https://www.nxtbook.com/accessintelligence/POWER/power-march-2022
https://www.nxtbook.com/accessintelligence/POWER/power-february-2022
https://www.nxtbook.com/accessintelligence/POWER/power-january-2022
https://www.nxtbook.com/accessintelligence/POWER/power-december-2021
https://www.nxtbook.com/accessintelligence/POWER/power-top-plants-supp-december-2021
https://www.nxtbook.com/accessintelligence/POWER/power-november-2021
https://www.nxtbook.com/accessintelligence/POWER/power-october-2021
https://www.nxtbook.com/accessintelligence/POWER/power-september-2021
https://www.nxtbook.com/accessintelligence/POWER/power-august-2021
https://www.nxtbook.com/accessintelligence/POWER/power-july-2021
https://www.nxtbook.com/accessintelligence/POWER/power-june-2021
https://www.nxtbook.com/accessintelligence/POWER/power-may-2021
https://www.nxtbook.com/accessintelligence/POWER/power-april-2021
https://www.nxtbook.com/accessintelligence/POWER/power-march-2021
https://www.nxtbook.com/accessintelligence/POWER/power-february-2021
https://www.nxtbook.com/accessintelligence/POWER/power-january-2021
https://www.nxtbook.com/accessintelligence/POWER/power-december-2020
https://www.nxtbook.com/accessintelligence/POWER/power-november-2020
https://www.nxtbook.com/accessintelligence/POWER/power-october-2020
https://www.nxtbook.com/accessintelligence/POWER/power-september-2020
https://www.nxtbook.com/accessintelligence/POWER/power-august-2020
https://www.nxtbook.com/accessintelligence/POWER/power-july-2020
https://www.nxtbook.com/accessintelligence/POWER/power-june-2020
https://www.nxtbook.com/accessintelligence/POWER/power-may-2020
https://www.nxtbook.com/accessintelligence/POWER/power-april-2020
https://www.nxtbook.com/accessintelligence/POWER/power-march-2020
https://www.nxtbook.com/accessintelligence/POWER/power-february-2020
https://www.nxtbook.com/accessintelligence/POWER/power-january-2020
https://www.nxtbook.com/accessintelligence/POWER/power-december-2019
https://www.nxtbook.com/accessintelligence/POWER/power-november-2019
https://www.nxtbook.com/accessintelligence/POWER/power-october-2019
https://www.nxtbook.com/accessintelligence/POWER/power-september-2019
https://www.nxtbook.com/accessintelligence/POWER/power-august-2019
https://www.nxtbook.com/accessintelligence/POWER/power-july-2019
https://www.nxtbook.com/accessintelligence/POWER/power-june-2019
https://www.nxtbook.com/accessintelligence/POWER/power-may-2019
https://www.nxtbook.com/accessintelligence/POWER/power-april-2019
https://www.nxtbook.com/accessintelligence/POWER/power-march-2019
https://www.nxtbook.com/accessintelligence/POWER/power-february-2019
https://www.nxtbook.com/accessintelligence/POWER/power-january-2019
https://www.nxtbook.com/accessintelligence/POWER/power-december-2018
https://www.nxtbook.com/accessintelligence/POWER/power-november-2018
https://www.nxtbook.com/accessintelligence/POWER/power-october-2018
https://www.nxtbook.com/accessintelligence/POWER/power-september-2018
https://www.nxtbook.com/accessintelligence/POWER/power-august-2018
https://www.nxtbook.com/accessintelligence/POWER/power-july-2018
https://www.nxtbook.com/accessintelligence/POWER/power-june-2018
https://www.nxtbook.com/accessintelligence/POWER/power-may-2018
https://www.nxtbook.com/accessintelligence/POWER/power-april-2018
https://www.nxtbook.com/accessintelligence/POWER/power-march-2018
https://www.nxtbook.com/accessintelligence/POWER/power-february-2018
https://www.nxtbook.com/accessintelligence/POWER/power-january-2018
https://www.nxtbook.com/accessintelligence/POWER/power-december-2017
https://www.nxtbook.com/accessintelligence/POWER/power-november-2017
https://www.nxtbook.com/accessintelligence/POWER/power-october-2017
https://www.nxtbook.com/accessintelligence/POWER/power-september-2017
https://www.nxtbook.com/accessintelligence/POWER/power-august-2017
https://www.nxtbook.com/accessintelligence/POWER/power-july-2017
https://www.nxtbook.com/accessintelligence/POWER/power-june-2017
https://www.nxtbook.com/accessintelligence/POWER/power-may-2017
https://www.nxtbook.com/accessintelligence/POWER/power-april-2017
https://www.nxtbook.com/accessintelligence/POWER/power-march-2017
https://www.nxtbook.com/accessintelligence/POWER/power-february-2017
https://www.nxtbook.com/accessintelligence/POWER/power-january-2017
https://www.nxtbook.com/accessintelligence/POWER/power-december-2016
https://www.nxtbook.com/accessintelligence/POWER/power-november-2016
https://www.nxtbook.com/accessintelligence/POWER/power-october-2016
https://www.nxtbook.com/accessintelligence/POWER/power-september-2016
https://www.nxtbook.com/accessintelligence/POWER/power-august-2016
https://www.nxtbook.com/accessintelligence/POWER/power-july-2016
https://www.nxtbook.com/accessintelligence/POWER/power-june-2016
https://www.nxtbook.com/accessintelligence/POWER/power-may-2016
https://www.nxtbook.com/accessintelligence/POWER/power-april-2016
https://www.nxtbook.com/accessintelligence/POWER/power-march-2016
https://www.nxtbook.com/accessintelligence/POWER/power-february-2016
https://www.nxtbook.com/accessintelligence/POWER/power-january-2016
https://www.nxtbook.com/accessintelligence/POWER/power-december-2015
https://www.nxtbook.com/accessintelligence/POWER/power-november-2015
https://www.nxtbook.com/accessintelligence/POWER/power-october-2015
https://www.nxtbook.com/accessintelligence/POWER/power-september-2015
https://www.nxtbook.com/accessintelligence/POWER/power-august-2015
https://www.nxtbook.com/accessintelligence/POWER/power-july-2015
https://www.nxtbook.com/accessintelligence/POWER/power-june-2015
https://www.nxtbook.com/accessintelligence/POWER/power-may-2015
https://www.nxtbook.com/accessintelligence/POWER/power-april-2015
https://www.nxtbook.com/accessintelligence/POWER/power-march-2015
https://www.nxtbook.com/accessintelligence/POWER/power-february-2015
https://www.nxtbook.com/accessintelligence/POWER/power-january-2015
https://www.nxtbook.com/accessintelligence/POWER/power-december-2014
https://www.nxtbook.com/accessintelligence/POWER/power-november-2014
https://www.nxtbook.com/accessintelligence/POWER/power-october-2014
https://www.nxtbook.com/accessintelligence/POWER/power-september-2014
https://www.nxtbook.com/accessintelligence/POWER/power-august-2014
https://www.nxtbook.com/accessintelligence/POWER/power-july-2014
https://www.nxtbook.com/accessintelligence/POWER/power-june-2014
https://www.nxtbook.com/accessintelligence/POWER/power-may-2014
https://www.nxtbook.com/accessintelligence/POWER/power-april-2014
https://www.nxtbook.com/accessintelligence/POWER/power-march-2014
https://www.nxtbook.com/accessintelligence/POWER/power-february-2014
https://www.nxtbook.com/accessintelligence/POWER/power-january-2014
https://www.nxtbook.com/accessintelligence/POWER/power-december-2013
https://www.nxtbook.com/accessintelligence/POWER/power-november-2013
https://www.nxtbook.com/accessintelligence/POWER/power-october-2013
https://www.nxtbook.com/accessintelligence/POWER/power-september-2013
https://www.nxtbook.com/accessintelligence/POWER/power-august-2013
https://www.nxtbook.com/accessintelligence/POWER/power-july-2013
https://www.nxtbook.com/accessintelligence/POWER/power-june-2013
https://www.nxtbook.com/accessintelligence/POWER/power-may-2013
https://www.nxtbook.com/accessintelligence/POWER/power-april-2013
https://www.nxtbook.com/accessintelligence/POWER/power-march-2013
https://www.nxtbook.com/accessintelligence/POWER/power-february-2013
https://www.nxtbook.com/accessintelligence/POWER/power-january-2013
https://www.nxtbook.com/accessintelligence/POWER/power-december-2012
https://www.nxtbook.com/accessintelligence/POWER/power-november-2012
https://www.nxtbook.com/accessintelligence/POWER/power-october-2012
https://www.nxtbook.com/accessintelligence/POWER/power-september-2012
https://www.nxtbook.com/accessintelligence/POWER/power-august-2012
https://www.nxtbook.com/accessintelligence/POWER/power-july-2012
https://www.nxtbook.com/accessintelligence/POWER/power-june-2012
https://www.nxtbook.com/accessintelligence/POWER/power-may-2012
https://www.nxtbook.com/accessintelligence/POWER/power-april-2012
https://www.nxtbook.com/accessintelligence/POWER/power-march-2012
https://www.nxtbook.com/accessintelligence/POWER/power-february-2012
https://www.nxtbook.com/accessintelligence/POWER/power-january-2012
https://www.nxtbook.com/accessintelligence/POWER/power-november-2011
https://www.nxtbook.com/accessintelligence/POWER/power-october-2011
https://www.nxtbook.com/accessintelligence/POWER/power-september-2011
https://www.nxtbook.com/accessintelligence/POWER/power-august-2011
https://www.nxtbook.com/accessintelligence/POWER/power-july-2011
https://www.nxtbook.com/accessintelligence/POWER/power-june-2011
https://www.nxtbook.com/accessintelligence/POWER/power-may-2011
https://www.nxtbook.com/accessintelligence/POWER/power-april-2011
https://www.nxtbook.com/accessintelligence/POWER/power-march-2011
https://www.nxtbook.com/accessintelligence/POWER/power-february-2011
https://www.nxtbook.com/accessintelligence/POWER/power-january-2011
https://www.nxtbook.com/accessintelligence/POWER/power-december-2010
https://www.nxtbook.com/accessintelligence/POWER/power-november-2010
https://www.nxtbook.com/accessintelligence/POWER/power-october-2010
https://www.nxtbook.com/accessintelligence/POWER/power-september-2010
https://www.nxtbook.com/accessintelligence/POWER/power-august-2010
https://www.nxtbook.com/accessintelligence/POWER/power-july-2010
https://www.nxtbook.com/accessintelligence/POWER/power-june-2010
https://www.nxtbook.com/accessintelligence/POWER/power-may-2010
https://www.nxtbookmedia.com