Power Plants
BENSON®
Once-Through
Heat Recovery Steam Generator
Power Generation
BENSON® Once-Through technology for Heat Recovery Steam Generators
New application of proven
technology
Siemens’ development of the OnceThrough (OT) technology started in 1924
with the acquisition of the patent rights
from Marc Benson.
The BENSON® Once-Through technology
using the principles introduced by Siemens
has been successfully demonstrated in
more than 1000 conventional steam
plant applications with ratings up to
1000 MW and steam conditions up to
300 bar/610 °C (4350 psi/1120 °F). The
design principles were successfully applied
for an Once-Through Heat Recovery Steam
Generator (HRSG) at the Cottam 390 MW
combined cycle power plant in Great Britain
in 1999 (as shown on the cover page).
Today, after further development and
more than five years of operational
experience at Cottam – with more than
50,000 operating hours – the BENSON®
Once-Through HRSG technology has
become the most promising one for future
advanced combined cycle power plants.
Simply stated, it retains all the virtues of
the proven natural circulation principle of
drum-type boilers (i.e. flow stability and
uniform temperature distribution), yet at
the same time replaces the high-pressure
drum with thin-walled components to
improve operating flexibility.
As the result of the excellent operating
experience at the Cottam plant, Siemens
is providing the BENSON® HRSG for several
additional utility projects in Central Europe.
Small changes lead to big improvements
Main features of BENSON®
Once-Through HRSG
Drum-type HRSG
The BENSON® Once-Through evaporator
is implemented in the high pressure (HP)
section. This provides the following
attributes:
Drum
• Thick-walled
HP drum limits
operating
flexibility due
to high thermal
stresses
Maintains vertical tube module
arrangement in horizontal gas path
as proven in drum-type boilers.
Replaces HP drum with thin-walled
components (separator), which
improves operational flexibility.
Maintains natural circulation flow
characteristics and therefore assures
flow stability and even heat distribution.
BENSON® Once-Through
Exhaust gas flow
• Natural
circulation
principle
Separator
Exhaust gas flow
• Eliminates HP
drum, thereby
enhancing
operating
flexibility
• Maintains
natural
circulation flow
characteristics
Evaporator
Superheater
Superheater
Evaporator
Requires no changes in HP economizer
and HP superheater.
Retains proven low pressure and
intermediate pressure drums.
The BENSON® system – Elimination of thick-walled components
BENSON® HRSG technology maintains proven features of drum-type boiler and improves operational characteristics
BENSON® Once-Through technology and its licensees
The proven choice for advanced
combined cycle power plants
The BENSON® technology represents the
Once-Through principle for evaporation
at the highest level.
High operating reliability has been
achieved by applying sound design
fundamentals and extensive empirical
analyses:
Intensive research and development
especially in the field of heat transfer
and pressure drop of two-phase flow
at the Siemens BENSON® test rig.
Continuous exchange of design and
testing information between Siemens,
our BENSON® licensees and power
plant owners.
The BENSON® Once-Through technology
is the best choice for advanced combined
cycle power plants. This is evidenced by
the fact that a growing number of customers are adapting it for their power plants.
There are more than ten boiler and HRSG
suppliers worldwide as Siemens BENSON®
licensees and the list continues to grow:
As of the end of 2005, this list includes
five major suppliers in Europe, three in
North America, two in Japan and one
in Korea.
For further information, please refer to
the BENSON® homepage:
www.siemens.com/bensonboiler
The cornerstone for operational flexibility
The BENSON® Once-Through HRSG technology provides the following:
pe
Dr
um
ty
ON
Improved efficiency at high ambient
temperatures due to adjustable evaporating point.
Increase of efficiency during start-up
by minimizing gas turbine operation
in part loads.
Capability for higher steam parameters (pressure and temperature),
because there are no limitations
through natural circulation.
Reduction of gaseous and liquid
emissions through shorter start-up
process and elimination of drum
blow down.
Same
efficiency
Higher efficiency
with BENSON® HRSG
Dr
um
Design
point
N®
BE
NS
Reduced consumption of chemicals
through advanced feedwater treatment.
O
NS
Short
operation in
unfavorable
load
Significant shortening of plant startup time by allowing unrestricted gas
turbine start-up.
BE
Power
®
Since it is difficult for power plant
owners and operators to predict future
operating requirements, the application
of the BENSON® Once-Through HRSG,
along with additional system integration
provided by the Siemens plant designers,
gives the plant the flexibility to meet
cycling and fast start requirements.
And this is done while maintaining high
efficiency levels and environmental
friendliness required for advanced
combined cycle plants.
Efficiency decrease
Integration into Siemens
power plants
Reduced
start-up time
Below design point
Time
Exemplary combined cycle plant start-up curve
Above design point
Ambient temperature
Improved efficiency at high ambient temperatures
With the optimized integration of BENSON® HRSG, Siemens advanced combined cycle power plants provide unsurpassed
operating flexibility.
Power Plants
Published by and copyright © 2006:
Siemens AG
Power Generation
Freyeslebenstrasse 1
91058 Erlangen, Germany
Siemens Power Generation, Inc.
4400 Alafaya Trail
Orlando, FL 32826-2399, USA
www.siemens.com/powergeneration
Order No. A96001-S90-A496-X-4A00
Printed in Germany
1355 107643M WS 02062.
All rights reserved.
Subject to change without prior notice.
Printed on paper treated with chlorine-free bleach.
Trademarks mentioned in this document are
the property of Siemens AG, its affiliates, or their
respective owners.
The information in this document contains general
descriptions of the technical options available, which
may not apply in all cases. The required technical
options should therefore be specified in the contract.