POWER June 2013 - 30

HEAT RECOVERY STEAM GENERATORS
CT outlet conditions (temperature and flow
rate) for the HRSG model. The ProTRAX
model dynamically calculates steam temperatures,
pressures, and flow rates as functions
of time, based on a given plant startup procedure.
The analysis in the case study described
in the next section focused on the cold and
warm HRSG startup scenarios because these
have the greatest impact on the operation and
fatigue cycle life.
Evaporator Analysis. Next, a one-dimensional
THTNET (Thermal-Hydraulic
Transient NETwork) model of the evaporator
downcomers, risers, feeders, heat transfer
tubes, and steam drum is constructed
using Foster Wheeler's proprietary in-house
software. The evaporator flue gas inlet temperature
and flow rate and steam-side drum
pressure are obtained as functions of time
from the HRSG system model. Of primary
interest are individual riser outlet conditions
(temperature, flow rate, steam quality, and
heat transfer coefficient) and drum water
conditions (temperature and level).
Cycle Life Calculations. Finally, a
screening analysis of the headers and drums
is used to determine the most critical components
from the consideration of thermal
cycle fatigue. Previous analyses of similar
HRSG configurations by Foster Wheeler
have determined the riser connections to
the steam drums to be the most susceptible
areas during startup transients. Fatigue life
evaluations are performed for these riserto-drum
connections.
A finite element analysis of the drumto-riser
junction is performed for three
startup conditions, at two ramp rates for
each condition. These startup conditions
are simulated by a transient thermal analysis,
followed by a stress analysis. A general
purpose finite element analysis program is
used in these calculations. The variation of
steam temperature and the film coefficients
applied during the transients is obtained
from dynamic analysis of the HRSG and
the THTNET modeling results.
Temperature and stress results obtained by
the finite element analysis are used to determine
the fatigue life of the selected HRSG
components. The analysis presumes a number
of assumptions. For example, all welds
are assumed to be ideal, full-penetration
welds. The analysis considers only elastic
material effects, and any effects due to hightemperature
elastic-plastic creep are not included
in the present analysis. Local thermal
stresses are analyzed, and the stresses due
to thermal expansion of tubes and pipes are
not included. The deadweight stresses due to
loads from the piping on the nozzle were neglected
because proper design can minimize
these loads.
30
The temperature and thermal stress calculations
obtained by the finite element analysis
are then post-processed to determine the
fatigue life of the selected components. Pressure
stresses are added to the thermal stresses.
The Von Mises equivalent of the total stresses
is used in the fatigue calculations.
The fatigue life evaluation is based upon
methods described in the American Society
of Mechanical Engineers (ASME) Boiler
and Pressure Vessel Code, Section VIII, Division
2. The fatigue properties of the materials
are obtained from the ASME code. The
results present the fatigue damage incurred
for each condition. Total fatigue damage over
the plant life can be determined be summing
the number of cycles of each type of startup,
multiplied by the fatigue damage of that particular
startup condition.
Application Example
To illustrate the methodology, the impact of
fast startup on an existing HRSG design and
its normal operation was evaluated, including
effects upon natural circulation, thermal performance,
and cyclic fatigue life. The purpose
of the analysis, abstracted from a recently
completed study, was to provide guidance for
improving startup times, consistent with minimal
impact upon cycle life. Dynamic simulation
and life-cycle analysis were performed
on the plant's HRSG, which was designed
and supplied by Foster Wheeler. The primary
goal of the analysis was to accelerate the cold
startup, above the rates previously used by the
plant (an average of 80F/hr), while continuing
to maintain acceptable component cycle life.
System Analysis. A model of the existing
operating HRSG was created using
ProTRAX simulation software. The case
study plant is equipped with a single-pressure
HRSG with supplementary firing and
a bypass damper. The HRSG is also configured
with an economizer and primary
and secondary superheaters. Data collected
during a typical cold HRSG startup is illustrated
in Figure 1.
For more accurate control, another control
loop was added to the model to maintain a
given drum temperature ramp rate, which
was achieved by manipulating the opening
of the gas diverter damper in conjunction
with opening the steam supply valve. Using
this control model, different startup scenarios
were simulated and evaluated for different
initial conditions and different CT and
HRSG ramp options. Parameters affecting
HRSG startup performance include the CT
ramp rate and hold conditions, HRSG ramp
rate and startup condition, and CT and HRSG
initial conditions.
To reduce the time for cold startup, the
rate of drum water temperature rise was
increased to 300F/hr, as shown in Figure
2. During this scenario, part of the hot flue
gas from the CT was diverted to the HRSG
at the beginning of startup, and the ST and
CT were ramped together to full load. To
minimize plant startup time, a properly tuned
control loop maintained the ramp rate at the
maximum allowable value. Fast ramping of
the CT and holding it at a high loading condition
will generate more power during startup.
However, the CT ramp rate is limited by the
1. Typical cold HRSG startup. The red and green curves show the top-to-bottom drum
temperature differential at the left and right ends of the drum, respectively. The blue curve
describes the rate of change of the drum water temperature (F/hr), which is one of the key
parameters controlled during HRSG startup. The black curve illustrates steam drum pressure
change during startup. Source: Foster Wheeler North America Corp.
DT drum (F)
160
140
120
100
80
60
40
20
www.powermag.com
DT drum (F)
DT/dt (F/hr)
Drum pressure (psig)
1,400
1,200
1,000
800
600
400
200
4:48 AM 7:12 AM 9:36 AM 12:00 PM 2:24 PM 4:48 PM 7:12 PM 9:36 PM 12:00 AM
POWER | June 2013
DT or DT/dt (F, F/hr)
Pressure (psig)
http://www.powermag.com

POWER June 2013

Table of Contents for the Digital Edition of POWER June 2013

Contents
POWER June 2013 - Cover1
POWER June 2013 - Cover2
POWER June 2013 - Contents
POWER June 2013 - 2
POWER June 2013 - 3
POWER June 2013 - 4
POWER June 2013 - 5
POWER June 2013 - 6
POWER June 2013 - 7
POWER June 2013 - 8
POWER June 2013 - 9
POWER June 2013 - 10
POWER June 2013 - 11
POWER June 2013 - 12
POWER June 2013 - 13
POWER June 2013 - 14
POWER June 2013 - 15
POWER June 2013 - 16
POWER June 2013 - 17
POWER June 2013 - 18
POWER June 2013 - 19
POWER June 2013 - 20
POWER June 2013 - 21
POWER June 2013 - 22
POWER June 2013 - 23
POWER June 2013 - 24
POWER June 2013 - 25
POWER June 2013 - 26
POWER June 2013 - 27
POWER June 2013 - 28
POWER June 2013 - 29
POWER June 2013 - 30
POWER June 2013 - 31
POWER June 2013 - 32
POWER June 2013 - 33
POWER June 2013 - 34
POWER June 2013 - 35
POWER June 2013 - 36
POWER June 2013 - 37
POWER June 2013 - 38
POWER June 2013 - 39
POWER June 2013 - 40
POWER June 2013 - 41
POWER June 2013 - 42
POWER June 2013 - 43
POWER June 2013 - 44
POWER June 2013 - 45
POWER June 2013 - 46
POWER June 2013 - 47
POWER June 2013 - 48
POWER June 2013 - 49
POWER June 2013 - 50
POWER June 2013 - 51
POWER June 2013 - 52
POWER June 2013 - 53
POWER June 2013 - 54
POWER June 2013 - 55
POWER June 2013 - 56
POWER June 2013 - 57
POWER June 2013 - 58
POWER June 2013 - 59
POWER June 2013 - 60
POWER June 2013 - 61
POWER June 2013 - 62
POWER June 2013 - 63
POWER June 2013 - 64
POWER June 2013 - 65
POWER June 2013 - 66
POWER June 2013 - 67
POWER June 2013 - 68
POWER June 2013 - 69
POWER June 2013 - 70
POWER June 2013 - 71
POWER June 2013 - 72
POWER June 2013 - Cover3
POWER June 2013 - 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