On August 22nd, three days after the
start of bypass operation, steam was
introduced to the turbine for the first
time after which, turbine and generator
tests were able to start. It marked
the first time that one of the new
Samcheok once-through CFB boilers
was operated mainly with coal, while
demonstrating operation of the boiler
with several fuel feeding lines.
Commissioning of the unit proceeded
with one boiler on line until
September. Operation of the boilers
and their auxiliaries was optimised
under steady and transient conditions.
Nominal rating with boiler 1B
was reached for the first time on
September 4th, with Unit 1 in 1:1
operation, i.e. one boiler supplying
steam to steam turbine, at approximately
400 MWe load. The behaviour
of the process was also found to be
steady during high load operation at
a moderate combustion temperature,
resulting in excellent environmental
performance.
Unit 1 combustion process optimisation
and control tuning continued
with 1:1 operation until October 7th
and the major milestone of first tie-in
and transfer to 2:1 operation was
achieved at this point. During 2:1
operation steam from the HP part of
the turbine has to be divided between
the boilers in a controlled manner to
keep reheat steam temperatures in
balance. In this respect Samcheok
Unit 1 has worked well from the
beginning.
Successful tie-in allowed Unit 1
load to be increased to reach its
nominal rating of 1 GW for the first
time on October 14th. Since then
Unit 1 optimisation has continued
mainly in 2:1 operation. During this
time, both steady and dynamic performance
has been adjusted together
with the steam turbine supplier to
meet electrical grid requirements
and satisfy the conditions for unit
commercial operation.
In 2:1 operation both boilers are
normally operated at equal load,
based on signals from the Unit Master
Control (UMC). If for some reason
the other of two boilers cannot
be operated at the requested load, an
unbalanced operation mode is used
and unit load is limited if necessary.
Also, in the event that the
other boiler has to be taken out of
operation, tie-out (i.e. switching to
1:1 operation) takes place automatically
and the unit will continue running
with limited output until
switched back to 2:1 operation.
These functions, which are necessary
for a unit to operate well in all
circumstances, were tested and optimised
during hot commissioning.
Prior to taking the new unit into commercial
operation it had to pass a 10-
day reliability run at nominal rating
(NR) load conditions, as well as tests
required by the grid operator, e.g.
demonstration of load change capability.
The reliability run was successfully
completed on December 14th and the
plant was taken into commercial operation
on December 16th.
A similar procedure was followed
for Unit 2 in Samcheok. After its hot
commissioning and optimisation
stage, that unit started commercial
operation on June 13, 2017.
According to SFW, boiler reliability
since startup has been above 90 per
cent for both units. “The plant has
been running well with no unexpected
problems,” said Giglio.
Samcheok’s CFBs are designed to
burn coal mixed with biomass but
are expected to primarily burn coal
sourced from several international
coal mines. The plan is to fire imported
and domestic coals with
heating values from 3400-6000 kcal/
kg, and since start-up the coal fired
has predominantly come from Indonesia.
It is a typical sub-bituminous
Special Project Supplement
unit reliability.
At Samcheok, ash produced by the
combustion process will be recycled
to produce lightweight aggregate for
the construction industry and help
reclaim land destroyed by coal mining
in the Gangwon-do region.
SFW’s CFB technology has been
proven at increasing sizes for many
years, achieving the 200 MW utility
size in the 1990s. Today, globally
SFW has delivered more than 40 CFB
units of over 200 MWe scale in operation
or under construction capable of
burning a wide range of fuels.
The technology advance to OTUSC
units was first demonstrated at the
460 MWe Łagisza plant in Poland,
which entered commercial operation
in 2009. Since its startup, the plant has
operated on a range of bituminous
coals and has demonstrated a LHV
net plant electrical efficiency of 43.3
per cent. Another supercritical CFB
project has also been built in Russia.
This is a 330 MWe CFB unit designated
Novocherkasskaya GRES No.
9, which is now under commissioning.
The boiler, which is the first of its
kind in the country, is capable of
combusting a wide selection of fuels
including anthracite, bituminous coal
and coal slurry.
The Samcheok units represent the
next big step in the design and scaleup
of CFB’s for large utility power
generation.
It has been a long but steady path to
this stage. Following the award of the
contract in May 2011, SFW was given
the Notice to Proceed (NTP) for the
project in July 2011. This triggered
the start of civil works. Foundations
for the boilers was completed in 2013
and the shipping of structural steel to
the site took place that year to allow
the start of boiler erection.
Erection works in the Samcheok
Green Power Plant Unit 1, incorporating
two 550 MWe CFB boilers and a
steam turbine, were mostly completed
at the end of year 2015 and commissioning
activities were started simultaneously
with some last minor erection
works still ongoing. At that time
Unit 2 was still under construction.
During the cold commissioning period,
carried out by lead EPC contractor
Hyundai and supported by SFW
technical advisors, the power unit was
made ready for trouble-free starting
of chemical cleaning and hot commissioning.
Pipelines were flushed
and operation of boiler auxiliaries,
instrumentation and protection systems
were checked for correct operation,
guaranteeing smooth and safe
start-up of the power unit.
Chemical cleaning for Unit 1 boilers
was finished at the end of February
2016. First fire of Unit 1 boiler 1B
took place on February 29, 2016 followed
by boiler 1A a few weeks later.
Commissioning activities continued
with magnetite film formation, curing
of the refractory linings and steam
blowout process as a final step before
the start of boiler testing and the tuning
period.
The blowout process, used for final
cleaning of the steam pipelines from
construction debris before connecting
steam lines to steam turbine, was
carried out continuously during the
daytime. Boiler HP and RH parts
were steam blown simultaneously
meaning that steam leaving from the
boiler HP part was led to the cold reheat
pipeline and through the reheaters
up to the hot reheat pipeline and
onwards via a temporary pipeline and
silencer to the atmosphere.
The Unit 1 boilers were ready for
start of the steam blowout at the end
of April 2016 and boiler load was increased
to the level required for sufficient
cleaning of the steam pipelines,
allowing restoration work on the
steam piping to be started.
Restoration work after steam blowout
took around one month, enabling
bypass operation of Unit 1 to be
started on August 19, 2016 with first
boiler. During bypass operation HP-
and LP-bypass stations were utilised
in order to get condensate back to the
process and condensate system
cleaned up. Part of the condensate
was dumped from the cycle to be
substituted by clean demineralised
water. In the course of bypass operation
preliminary tuning of the boiler
controls and sequences was made.
Also, operation of auxiliaries and instrumentation
was verified and adjusted
in their hot conditions.
THE ENERGY INDUSTRY TIMES - AUGUST 2018
The plant is equipped with
four boilers supplied by SFW,
in tandem with two steam
turbine generators
Giglio: CFB technology has the flexibility to burn the lower
quality coals that they saw becoming more abundant, namely
from Indonesia
Fuel specifications
Bituminous coal Biomass
LHV (a.r.) (MJ/kg) 14.2 – 24.9. 15.8 – 18
Moisture (%) 20 - 43 5 – 15
Ash (a.r.) (%) 1.2 - 15.3 0.7 – 5
Sulphur (a.r.) (%) 0.1 - 1 0 – 0.16
Design steam parameters at 100% load
SH steam flow (kg/s) 437.7
SH steam pressure (barg) 257
SH steam temperature (°C) 603
RH steam flow (kg/s) 356.4
RH steam pressure (barg) 53
RH steam temperature (°C) 603
Feed water temperature (°C) 297