POWER March 2021 - 30

GAS TURBINE
Innovative Engineering
Results in Successful
Steam Blowing Operation
Experience gained by a project team during a steam blowing operation for a
combined cycle power project in Indonesia is described in this article. A specific
challenge faced by the commissioning team is explained, along with the solution
used to successfully overcome the obstacle.
Rajarajan Rathina and
Senthil Rajendran
steam blowing operation is one of
the critical pre-commissioning activities
carried out in new power
projects where construction is completed,
and the commissioning phase
is ongoing. This activity is performed on
the critical steam piping of the steam
cycle circuit to ensure that any scales,
oxides of metal, and slag left behind in
the piping internals during the welding
process are removed prior to initiating
steam turbine operation.
The steam cycle circuit typically refers
to all the piping that is connected between
the heat recovery steam generator
(HRSG) and the steam turbine. This is an
important activity to be completed by the
engineering, procurement, and construction
(EPC) contractor as part of steam
turbine original equipment manufacturer
(OEM) start-up requirements. Otherwise,
any leftover metal particles or scales
formed within the pipes can travel along
with the steam into the steam turbine and
can cause pitting/damage on the turbine
blades. In some cases, the damage can
be catastrophic in nature. The criteria or
guidelines for cleaning the steam piping
are set by the steam turbine OEM and
need to be fulfilled by the EPC contractor.
The experience gained by a project
team during the steam blowing operation
for a combined cycle power project is
described in this article. The details of the
steam blowing procedure (such as calculations,
construction details, step-by-step
sequence, and methodology to execute
the steam blowing procedure) are not
covered in this article. Rather, the focus
is drawn more toward challenges faced
during execution of the SBO at the site
and solutions used to overcome the difficulties.
To understand the necessity of
this procedure in detail, readers should
A
review literature available in the public domain.
Another source to help understand
the guidelines is VGB PowerTech, an international
association of energy plant
operators based in Germany. Among its
guidelines is VGB-R 513 e " Internal Cleaning
of Water-Tube Steam Generating
Plants and Associated Pipework. "
The Indonesian Plant Design
Tata Consulting Engineers Ltd. (TCE)
was retained as the engineering consultant
for detailed design and engineering
services of a combined cycle project in
Indonesia (Figure 1). The plant was commissioned
in December 2018 and is currently
in commercial operation.
The project comprises a combined
cycle power block (2-2-1 configuration)
with a gross rated output of 500 MW.
The block was added as an expansion
project to an existing plant. It consists of
two gas turbines (GTs) and generators,
two HRSGs, and one steam turbine and
generator (STG) in multi-shaft configuration
with bypass stack (which allows simple
cycle operation) and balance-of-plant
(BOP) equipment.
The GTs are designed for single firing
using natural gas. Each GT is coupled to a
dedicated HRSG unit that produces high-,
intermediate-, and low-pressure (HP, IP, and
LP) steam from the thermal energy in the
GT exhaust. The steam generated by each
HRSG in a block is combined in a common
steam header and delivered to a common
steam turbine (ST), thereby allowing
the ST to generate power in a bottoming
cycle. The ST is a reheat condensing turbine.
The exhaust steam is condensed in
a water-cooled condenser, and the cooling
system for the steam turbine condenser
is once-through cooling using seawater
drawn from an intake canal.
The GT is an advanced E-class heavyduty
gas turbine designed for 50-Hz op30
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1.
This is a night-time view of the heat recovery
steam generators (HRSGs) and stacks at
the plant in Indonesia. Courtesy: Tata Consulting
Engineers Ltd.
eration with single shaft, cold-end drive
and silo-type combustors. The HRSG is
a horizontal type, natural circulation, unfired,
reheat, triple-pressure design. The
low-pressure drum of the HRSG is provided
with a feedwater storage function
and the integral deaerator is mounted
on top of the LP drum. The condensing
steam turbine consists of HP and IP-LP
cylinders for steam expansion.
The Steam Blowing Process
During the steam blowing operation
(SBO), the steam is generated in the
HRSG at low pressure and a huge volume
of steam flows at high velocity
thru the critical piping that connects the
HRSG to the steam turbine. The critical
piping is typically the HP steam lines,
cold reheat (CRH), hot reheat (HRH), HP
steam bypass lines to cold reheat, lowpressure
lines connected to the LP portion
of the steam turbine, and HRH/LP
bypass lines to the condenser. The ST
does not participate in the SBO process
and is isolated until the SBO is completed.
Temporary piping is used to interconPOWER
| March 2021
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POWER March 2021

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