archives

of thermodynamics
Vol. 38(2017), No. 4, 165–190
DOI: 10.1515/aoter-2017-0030

Environmentally friendly replacement of mature

200 MW coal-fired power blocks with 2 boilers
working on one 500 MW class Steam Turbine
Generator (2on1 unit concept)

JAN GRZESZCZAKa ∗
ŁUKASZ GRELAb
THOMAS ACHTERc

a
Rafako S.A., Łąkowa 33, 47-400 Racibórz, Poland
b
Energoprojekt Katowice S.A., 40-159 Katowice, Jesionowa 15, Poland
c
Siemens AG, Power and Gas Division, Freyeslebenstr. 1, 91508 Erlan-
gen, Germany

Abstract The paper covers problems of the owners of a fleet of long-operated con-
ventional power plants that are going to be decommissioned soon in result of failing to
achieve new admissible emissions levels or exceeding pressure elements design lifetime.
Energoprojekt-Katowice SA, Siemens AG and Rafako SA presents their joint concept
of the solution which is a 2on1 concept – replacing two unit by two ultra-supercritical
boilers feeding one turbine. Polish market has been taken as an example.

Keywords: Coal fired power plant; Flexibility increasing; Old units replacement

Abreviations
AELs – admissible emission levels
BAT – best available technology
BREF – BAT reference documents
CCPP – combined cycle power plant
COSTART – parallel start of boiler and steam turbine

∗
Corresponding Author. Email: Jan.Grzeszczak@rafako.com.pl
166 J. Grzeszczak, Ł. Grela and T. Achter

EPK – Energoprojekt-Katowice SA
ESP – electrostatic precipitator
FGD – flue gas desulfurization
GCF – gross capacity factor
GDP – gross domestic product
HI – high-intermediate
HP – high pressure
IP – intermediate pressure
IRR – internal rate of return
LCP – large combustion plant
LP – low pressure
LUVO – Ljungstrom rotary air heater
NPVR – net present value ratio
OECD – Organisation for Economic Co-operation and Development
PSE – Polskie Sieci Elektroenergetyczne S.A. (Polish Power Grid Company)
PV – photovoltaic
RH – reheated
SCR – selective catalytic reduction
SPC – set point controller
SPP – steam power plant (coal fired power plant)
SPPA – Siemens Power Plant Automation
USC – ultra-supercritical

1 System power demand curve in Poland

Electric power is sometimes referred to as a commodity. Yet, even as a com-
modity, electricity has several unique features that distinguishes it from
other commodities. The first important difference is that, unlike other
goods, it is very difficult to store. Energy storage is very expensive, the
storage price being comparable to the original generating cost. Under grid
operating conditions, production must be instantly balanced against de-
mand because electric power must be available on demand. Hence, a por-
tion of power-generating assets must act as a reserve, i.e., electrical gen-
erating capacity that has to be available, but is normally not used. The
second major difference is the importance of electric power to the economy,
standing in direct correlation with a national gross domestic product. It
is crucially important to securing reliability and stability of industry. One
look at the elasticity of demand versus price provides a clear picture of just
how important it is. If we combine these two distinguishing features we
can conclude with relative certainty that surplus supply (power reserve)
has to follow demand. Hence, it is the demand curve that determines what
generating capacity is required.
The Polish Power Grid Company (PSE), is the public body responsi-
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 167

ble in Poland for maintaining the grid balance. It performs analyses and
publishes data related to current and predicted power demand.

Figure 1: Poland - daily power demand profile in 2006, 2010 and 2015 [1].

As shown in Fig. 1 different unit loads (following demand) throughout

the day are a consequence of the demand curve. In any economic analy-
sis related to power generating units, the critical question arising is what
will be the load percentage or, in energy industry terms, what will be the
gross capacity factor (GCF). The answer to this question can be found in
a monotonous curve of power demand. The curve in Fig. 2 was developed
for units dispatched by PSE (centrally dispatched units).

Figure 2: Poland – monotonous curve of power demand from centrally dispatched units
in 2010 and 2015.
168 J. Grzeszczak, Ł. Grela and T. Achter

2 Future role of fossil fuel power generation and

market segmentation
In electrical energy markets, a power generating unit’s variable cost deter-
mines its average load and priority of operation. Thus, the lower a unit’s
generating costs, the more operating hours it will accumulate. By carefully
analyzing the Fig. 2, three market segments can be distinguished:
• 10 GW market segment comprising base-load units, i.e., units with
a generating potential exceeding 7000 h/a. This market segment
should be occupied by the newest, most efficient power-generating
units. However, they do not have to be particularly flexible.
• 5 GW market segment comprising units that operate at full load
approximately 4000 h/a. Here, an efficiency versus flexibility tradeoff
is expected.
• 5 GW market segment of peakers operating less than 2000 h/a. This
market segment is occupied by flexible units whose efficiency is of
secondary importance.
Additionally, cogeneration plants (approx. 10 GW) and renewable energy
units (approx. 8 GW) have higher generation priority then centrally dis-
patched units (approx. 24 GW). It is noteworthy that grid dispatchers
have limited control over cogeneration plants. It is even more important to
understand that renewable energy sources, being intermittent and hardly
predictable, can be a grid dispatcher’s nightmare.

2.1 Power generation from renewable energy sources

In June 2016, the installed electrical generating capacity of renewable en-
ergy sources in Poland exceeded 8.2 GW. The growth of installed renewable
capacity has been very rapid in recent years, as shown in Fig. 3. The au-
thors’ perspective on future growth in this sector is presented in Fig. 4.
Under Polish climatic conditions, the generation capacity factors for on-
shore wind farms and photovoltaic (PV) plants are 2000 h/a and 1000 h/a,
respectively.

2.1.1 Fossil fuel power plants – environmental protection

Fossil fuel power plants are currently under pressure to dramatically reduce
their impact on the environment. In recent years, power production groups
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 169

Figure 3: Diagram of installed renewable capacity growth in Poland [2].

Figure 4: Diagram of projected installed renewable capacities in Poland.

have had to invest billions of euros to install dust collection, DeNOx and
flue gas desulfurization (FGD) systems to meet the large combustion plant
(LCP) emission limits. Nowadays, new best available technology (BAT)
reference documents (BREF) must also be considered. What is more, it
is predicted that prices for CO2 emissions will rise which adds even more
pressure to use only high-efficiency plants that operate at a low CO2 /kWh
factor.
170 J. Grzeszczak, Ł. Grela and T. Achter

2.1.2 New BAT conclusions

On 31st July 2017 a resolution on the new LCP BAT was published which
reduces the admissible emission levels (AELs) of existing and future power
plants. The number of substances subject to emissions limits has increased:
to NOx and SOx are now added Hg, NH3 , HCl and HF. Furthermore, a num-
ber of AELs have been stipulated for wastewater from flue gas treatment
systems, and some AELs previously limited in scope have been tightened.
The time allotted to adapt an installation will be four years.

2.1.3 OECD financing rules

The more stringent financing rules introduced by the Organisation for Eco-
nomic Co-operation and Development (OECD) in November 2015 have
strongly impacted the aforementioned methodology, requiring changes in
the marketplace. The conditions of these new financing rules are summa-
rized in Tab. 1. This implies that steam power plants built in future need
to be supercritical or ultra-supercritical (USC) units in order to receive
attractive financing.

Table 1: Framework conditions for OECD financing, depending on technology [3].

Environmentally friendly replacement of mature 200 MW coal-fired power. . . 171

3 Structure of current generating assets in Poland

The power generation industry in Poland is coal-based. Hard coal- and
lignite-fired plants together account for 82% of the electric power generated
in the country. A detailed structure is presented in the graph (Fig. 5).

Figure 5: Poland. Structure of electric power generation by fuel in 2016.

Generating assets in Poland are aging. The average age of the centrally
dispatched units is between 30 and 40 years, as presented in Fig. 6. Consid-
ering the fact that the design service life of a power plant is 40 years and for
pressurized components 200 000 operating hours, it can be concluded that
both construction of new units and rehabilitation projects will be necessary.

4 200 MW-class units in the Polish fleet

– a weakness or opportunity?
Approximately forty percent of Polish power generating capacity is based on
200 MW-class units. The youngest units were commissioned in 1983, while
the oldest have been in service 50 years. Most of these units have been
modernized. In the case of Turow Power Plant, a rehabilitation project
included installation of a completely new power train. Table 2 presents
a detailed breakdown of the 200-MW-class units.
172 J. Grzeszczak, Ł. Grela and T. Achter

Figure 6: Centrally dispatched units in Poland – age structure.

Table 2: 200 MWe class units in Poland.

Power plant Units and capacity Total rated Year of commis-

power, MW sioning
Dolna Odra 3 x 222, 3 x 232 1362 1974–1977
Jaworzno III 5 x 225, 1 x 220 1345 1977–1979
Kozienice 3 x 228, 4 x 225, 1 x 215 1799 1972–1975
Łaziska 3 x 225, 1 x 230 905 1972
Ostrołęka 1 x 226, 1 x 221, 1 x 200 647 1972
Pątnów 5 x 200, 1 x 222 1222 1967–1969
Połaniec 2 x 225, 4 x 242, 1 x 239 1657 1979–1983
Rybnik 5 x 225, 2 x 215, 1 x 220 1775 1974–1978
Turów 3 x 235, 3 x 269 1488 1998–2005

The technical solutions applied in 200 MW units are very robust. Prop-
erly maintained units of this class can be operated much longer than their
original design service life. Restrictions on operation arise either from the
continually changing emissions standards or from relatively low efficiency
(impacting capacity factor in the energy market).
Owners ultimately have to make decision to either decommission or
modernize. If the decision is to modernize, then question is: what is the
appropriate solution. It is the authors’ opinion that there are two possible
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 173

solutions: either improve environmental performance to comply with the

standards in force and replace critical pressurized components, or replace
the power train with an arrangement of 2 boilers serving 1 steam turbine
(below referred to as the ‘DuoBlock’ design concept). In the case of the
first of the above two options, the modernized unit will be a peaker (with
a capacity factor of around 2000 h/a). In the case of DuoBlock units,
the 480 MW steam turbine allows application of ultra-supercritical cycle
parameters. Two boilers instead of one will allow for lower minimum con-
tinuous rating at about 10 to 20% power output level. In this case, a unit
will be operated in a second market segment, i.e., with a capacity factor
exceeding 4000 h/a. The flexibility of the unit (with a low minimum con-
tinuous rating and good ramping ability) will be an advantage compared
to a single fossil-fired boiler serving one steam turbine arrangement.
Considering the scale of the problem in the Polish generation balance
(40%) and the anticipated decommissioning time (middle of next decade),
it must be concluded that unanswered questions concerning 200 MW units
may undermine Polish power balance. It should also be noted that the
project development time starting from conceptual design phase and end-
ing with commissioning takes 10 years for large coal-fired projects (5 years
for project development and 5 years for construction). Hence, a responsible
approach to energy security in Poland requires action now. Consequently,
a DuoBlock solution would enable Poland to limit its CO2 emissions level,
make units more competitive, and provide a potentially attractive model
for other 200 MW unit owners (for example in Turkey).

5 Technical concept of the DuoBlock

The following ideas are cornerstones of the DuoBlock design concept:
• Take advantage of the existing balance of plant systems (e.g., cooling
water, coal handling, ash handling, FGD, start-up fuel installation,
compressed air and water treatment systems, etc.). The decision
related to those components to keep or to reconstruct is site specific.
The reason behind it is obvious, i.e., limitation of investment costs.
• Increase unit output to a level at which state-of-the-art cycle pa-
rameters can be used, thereby pushing unit efficiency to the highest
commercially available level. Keep sizing at a level where more eco-
nomical steam turbine-generator solutions are available (high- and
intermediate-pressure casing solution and air-cooled generator).
174 J. Grzeszczak, Ł. Grela and T. Achter

• Take advantage of the steam turbine building.

• Use two boilers to feed one turbine, allowing a lower unit minimum
rating and faster startup times with two boilers (taking advantage of
the steam available from first boiler while the second boiler starts up).
Two boilers instead of one also enables faster power ramping because
of the lesser wall thickness of critical boiler pressure components.

5.1 General

The following sections present technical details and proposed solutions for
the main systems of the DuoBlock.

5.1.1 Design parameters

The parameters outlined below were selected as they are considered opti-
mum for investment:
gross power: 480 MWe,
live steam parameters: 600 ◦ C, 26 MPa,
live steam flow: 680 t/h, 190 kg/s,
reheated (RH) steam parameters: 600 ◦ C, 6 MPa,
technical minimum load: ∼ 10%,
net plant efficiency: > 45%.

Due to the limited full-load operation time (the aforementioned 4000 h/a
market segment), it is not necessary to focus on achieving an exceedingly
high rate of efficiency. Rather, these efforts should be put to reaching max-
imum flexibility at limited expense. The temperatures of both the live and
reheated steam are kept at around the 600 ◦ C level, while gross power is
proposed to be 480 MWe. Net efficiency according to the best avaiable
technology conclusions will exceed 45%, but the specific value for partic-
ular projects will be strongly dependent on the local coal, main cooling
conditions and environmental protection installations.
Two boilers shall feed the turbine with steam in the range ∼ 20–100%
of nominal flow. It’s possible to have just one boiler in operation, which
decreases power output by half. However, both boilers operation would
maintain the highest control capability.
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 175

5.1.2 Flexibility

Power generation has typically consisted of units operated under steady-

state conditions with low load change rates. The currently ongoing world-
wide expansion of electricity production from renewable energy sources re-
quires a wholly different operating regime for fossil fuel power plants, which
are now called on to generate the residual load for the grid. According to
order of merit, gas-fired power plants are the first type of power plants
that have to be shut down once renewables are brought on line. Following
that logic, the initial approach has been to accommodate high load change
rates by bringing on line and taking off line those combined-cycle power
plants that were first to adapt to achieving fast startup and shutdown
times. With the increasing volume of renewable energy available, today’s
coal-fired power plants are facing the same requirements as gas-fired units.
The know-how gained from the water-steam cycle of combined-cycle power
plants is now enabling engineers to adapt steam power plants to meet these
challenging requirements. The gray line in Fig. 7. shows the operation line
as it was in the past. The black line shows today’s requirements. The
arrows indicate the necessary improvements.

Figure 7: Power plant operation in the past and today.

To implement the functions for enhancing plant flexibility in accordance

with the new operating requirements, various sets of technical measures
176 J. Grzeszczak, Ł. Grela and T. Achter

have been developed that can be grouped as described below.

Fast startup and shutdown In traditional steam power plants and

markets, the boiler and steam turbine are started in the following basic
sequence:

• Ignite the boiler.

• Increase coal-fired boiler load to the minimum turbine load.
• Stabilize pressure and temperature.
• Start the steam turbine until the bypass is closed.
• Ramp the boiler to full load with the steam turbine valve wide open.

There might be many additional steps in between, like opening of gate

valves which are not mentioned.
Modern plants must attempt to heat-up the boiler and all systems as
well as the steam turbine as much in parallel as possible. This will ensure
for maximum load ramp rate. For this purpose, boiler operation and steam
turbine operation must be decoupled with regard to temperature. For ex-
ample, for a coldstart the allowed steam temperature for the steam turbine
might be in a range that the boiler has to stop at a certain load until the
steam turbine is warmed-up. This load hold can be avoided by using desu-
perheaters which will limit the temperatures. The capacity of the boiler’s
internal desuperheaters are normally limited because of the near-saturation
conditions. Therefore, an optimum can be reached by using external desu-
perheaters in the main steam and reheated steam headers. They will be
able to reduce the temperatures by 100 K or even up to 150 K. Exter-
nal desuperheaters are meanwhile standard in combined cycle power plants
(CCPPs).
Startup times for coldstart as well as for warmstarts will be reduced
significantly without decreasing component service life. For hotstarts it
would be beneficial to keep the steam turbine under vacuum to allow the
steam turbine to be started without waiting for steam purity. Furthermore,
it is beneficial to start even at a certain temperature mismatch. This way
of starting is also well-known from CCPPs as COSTART. This is a sort of
real parallel start of boiler and steam turbine without any hold. In general,
for all types of startup the steam turbine will not limit startup time, but
rather directly follow the load increase of the boiler.
The market situation today requires frequent startup and shutdown of
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 177

plants. The task is therefore to get the unit on the grid in the shortest
possible time without the thermal stresses impacting thick-walled boiler
components violating permissible limits. Other requirements that must be
met at the same time are reduced startup fuel consumption, ensuring re-
peatable startup and automatic differentiation between cold, warm and hot
starts with bumpless transfer to coordinated power operation.

Figure 8: Siemens Power Plant Automation (SPPA) predictive load margin computer.

The predictive load margin computer calculates current thermal boiler

stresses and forecasts future values for thick-walled parts from measured
variables (steam temperature, pressure and mass flows). These data are
used to control in Set Points Controllers (SPCs) the firing rate and the
steam temperature such that material stresses do not exceed permitted
limits. The process is much quicker and more reliable than pure gradient
limitation as used in traditional startup circuits.

Warm standby operation Siemens has developed an electrical heating

system for keeping the steam turbine warm and ready for startup while
it is on the turning gear. This system heats all relevant steam turbine
components to maintain the rotor shaft temperature at warm startup con-
ditions. Compared to startup from ambient conditions, this system enables
178 J. Grzeszczak, Ł. Grela and T. Achter

the steam turbine to be run up to full load more than 60 min faster. In
addition, the number of equivalent operating hours used per startup is sig-
nificantly reduced.

Part-load efficiency/load ramps A power plant unit needs to be oper-

ated at the most profitable operating point under all operating conditions,
from partial load to full-load operation. This is the task of the unit master
control structure.
The model-based unit master coordinated control concept is designed
for low-stress operation of the power plant. Scheduled setpoint changes
by the operator or load dispatcher are performed according to a model
based on the natural transmission behavior (S-shaped) of the steam gen-
erator, and do not restrict primary frequency control capability. This is
achieved by coordinating the steam generator and turbine. This minimizes
the amount of actuation required for load changes (overfiring) and the con-
sequential expenditure of steam generator service lifetime.
The unit coordinated control is a coordinated pressure/load control sys-
tem with a model-based feedforward control. This permits very fast, stable
and targeted load changes including frequency support mode. The heat
release rate in the steam generator is always kept at an equilibrium both
statically and dynamically. This ensures the least possible amount of stress
on the plant.
The use of an integrated prediction feature ensures that overfiring of
the coal mills is extremely smooth in the case of frequency-related load
changes. With scheduled load changes, the load transients can be adapted
in accordance with the natural S behavior of the steam generator.
The main control variables, unit output and boiler steam pressure must
be controlled using the fast-acting steam turbine control valve and the slow-
acting power plant boiler. A simplified unit model comprises the dynamic
boiler response and steam storage.
The model-based unit master control is also the coordinator for all sub-
ordinated additional flexibility measures like condensate throttling mea-
sures or deactivation of high pressure (HP) preheaters. Tradeoff between
best cycle efficiency with full sliding pressure operation and maximum
steam velocities in boiler, main and reheat steam piping shall be elabo-
rated on a project-specific basis.
One method for increasing the final feedwater temperature is the addi-
tion of what is termed a top feedwater heater, which is used only at part
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 179

Figure 9: Top feed water heater arrangement.

load. Such a unit requires an additional extraction upstream in the HP

blade path. Ideally, the steam is extracted from that point in the blading
at which the additional main steam valve is connected (Fig. 9). This obvi-
ates the need for any additional nozzles on the HP turbine, and the stage
valve admission point can simultaneously serve as an extraction point. Top
heating steam flow is selected such that the final feedwater temperature
remains constant over wide load ranges. The maximum heat rate benefit
with the use of a top feedwater heater is thus approximately 0.6 percentage
points at a part load of 50%.

Frequency response Figure 10 shows an overview of several options

that are mainly concerned with facilitating frequency response. One com-
mon measure for frequency response is to eliminate throttling of the main
steam valves (Fig. 10, item 1). While it has always been possible to do
this, it bore the disadvantage of an increased heat rate during normal oper-
ation. Siemens offers the possibility of using an additional main steam valve
(Fig. 10, item 2). This feature provides the advantage of optimum efficiency
during normal operation with a possibility for instantaneously increasing
the swallowing capacity of the steam turbine, along with the respective in-
crease in load. The next measure is condensate throttling (Fig. 10, item 3)
that enables the plant to produce at least 4% additional output by reducing
the condensate flow through the low pressure (LP) preheaters and steam
extraction through the respective extraction points. The surplus steam that
remains within the steam turbine generates the additional power. Certain
180 J. Grzeszczak, Ł. Grela and T. Achter

Figure 10: Measures in water-steam cycle for facilitating frequency response

features can be added to the condensate throttling system to increase re-

sponse time up to 2 s. A similar approach can be used at the high pressure
(HP) preheaters to increase output (Fig. 10, item 4). The response should
be chosen carefully so as not to thermally stress the boiler and preheater
hardware too much.
Other measures such as boiler spray and use of a bypass system with by-
pass spray can also be implemented to complete the set of measures chosen
for project-specific needs.

Loss of main components and load rejection to house load To

automatically reduce the unit load on loss of major components such as
a feedwater pump or forced-draft fan, and to effect transition to a new safe
operating mode by:

• Assignment of dedicated runback levels and ramps for all the major
equipment units.
• Consideration of fuel-related restrictions on the load.
• Load reduction with the necessary gradient and coincident changeover
of the turbine to stable inlet pressure control mode.
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 181

5.2 Steam turbine-generator package – compact, efficient

and flexible
5.2.1 SST-5000 steam turbine
Siemens’ proven SST-5000-Series steam turbine for USC parameters is
a steam turbine consisting of at least two turbine sections: One combined
high pressure/intermediater pressure (HP/IP) section (HI turbine) and ei-
ther one or two LP sections, depending on cooling water temperatures.
This is the best product for the lower load range of around 200 MW to
500 MW (Fig. 11). The chosen cycle parameters of 26 MPa/600◦ C/600◦ C
provide a good tradeoff between product cost and product performance.
Since the SST-5000 is the steam turbine module most often deployed in
combined-cycle power plants, it is also Siemens’ most flexible turbine. The
experience gained from these power plants is excellent, especially in terms
of fast load ramps.

Figure 11: Steam turbine module SST-Pac 5000.

The HI turbine provides several advantages, not only in terms of mainte-

nance but also with regard to integration into the overall power plant. Due
to the fact that the main steam and reheat valves are flanged to the lower
part of the HI outer casing, only the crossover pipe to the LP turbine has to
be disconnected before the upper half of the turbine casing can be removed.
In addition, the overall length of the turbine train is reduced to a minimum,
which means the turbine foundation, too, and ultimately the entire turbine
building can be as compact as possible. This is very important for in-
corporating a new steam turbine generator set into an available turbine
182 J. Grzeszczak, Ł. Grela and T. Achter

building, as in the case of a DuoBlock. The reduced number of bearings

also leads to lower foundation costs. The ultra-supercritical HI module is
likewise suitable for inspection intervals of 50 000 h for medium inspections
and 100 000 h for major inspections. This means that first opening of the
turbine casing is not necessary until after around 12 years of operation.

5.2.2 Generator for the 300 MW to 500 MW class

– the SGen-2000P Series
Global increase in utilization of renewable energy has a significant impact on
the operating regimes in fossil fuel power plants. Today, turbine-generator
shaft train components are exposed to extremely volatile operating modes
with a high number of start/stop cycles, numerous steep load ramps, and
frequency and voltage fluctuations. As a consequence, thermomechani-
cal stresses and accelerated aging of the shaft train components, including
generators, must be considered in the design to avoid unexpected cost and
extensive outage periods.
Siemens’ answer to the increased market requirements is the new air-
pressurized generator SGen-2000P featuring innovative combination of ver-
ified technologies: air and water cooling. Air-cooled generators have an
excellent track record in terms of robustness, reliability and low operational
cost, while water-cooled generators provide the highest output capability
and efficiency in the industry. Building on the success of these air-cooled
and water-cooled units, the new product line is set to replace the indirectly
hydrogen-cooled SGen-2000H Series up to approximately 550 MVA, and
will become a standard product in future gas turbine and steam turbine
packages. Replacing hydrogen cooling with pressurized air significantly re-
duces plant complexity and eliminates explosion safety concerns, along with
further benefits such as reduced first-time installation and commissioning
scopes, lower maintenance costs, and the capability of unstaffed operation
for synchronous condenser applications.
Implementation of innovative design features and load-dependent air
pressure control enable SGen-2000P generators to achieve efficiency levels
comparable to indirect hydrogen-cooled generators. Figure 12 provides an
overview of how the auxiliary systems have been simplified.
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 183

Figure 12: SGen-2000P’s reduced scope of auxiliary systems compared to H2 -cooled

generators.

5.3 DuoBlock boiler island

The boiler island for the DuoBlock design concept will not be characterized
by any serious changes in comparison to conventional power unit configu-
rations. Each boiler must be equipped with an independent technological
line of feed and firing systems (coal feeders and mills) and flue gas selec-
tive catalytic reduction (SCR), Ljungstrom rotary air heater (LUVO) and
electrostatic precipitator (ESP). Wet FGD should be used, which might
possibly be configured in a common system serving both boilers.
It must be considered that individual project solutions may vary de-
pending on the site arrangement of existing buildings and systems. What
is more, some of them (like SCR and absorbers, rarely ESPs) may be used
and modernized. In the feasibility study it is very important as the more
existing components (installations and machinery) are used, the more cost-
efficient DuoBlocks become.

5.3.1 Dedicated ultra-supercritical boiler

Boiler house layout Presented below is a boiler house at 0.00 m ele-
vation, which is usually a shared structure in most Polish 200 MWe units.
184 J. Grzeszczak, Ł. Grela and T. Achter

The boiler house is designed and constructed as a conventional structure

with 9 m x 12 m spacing. The boiler structure is supported on six pillars
isolated from the boiler house structure. On the left side there are four coal
mills on separate foundations, and in the middle a wet deslagger. Separate
foundations were also used for primary and secondary air fans.

Figure 13: Typical boiler house 0.00-m elevation layout in Polish 200-MWe units.

BP-680 boiler design BP-680 boiler was designed by Rafako for an

R&D project financed by the Polish National Research and Development
Center in a program dedicated to working out solutions for the existing
Polish fleet of 200-MWe power plant units commissioned in the 1970s.
It is assumed that the boilers serving the DuoBlock must be installed
in the existing building, including in particular the foundations. This as-
sumption leads to the following conclusions:

• To use the existing structure, a newly designed boiler combustion

chamber must keep nearly the exact same dimensions of the old OP-
650 unit;
• To ensure the integrity and safety of the foundations, tower-type boil-
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 185

ers cannot be used, and the existing shape of the two-pass boiler must
be retained.
The resultant boilers shall have combustion chamber diameters of 15620 mm
x 9020 mm, be two-pass type, and slightly taller than the OP-650. It fulfills
the conditions of fitting within the existing structure.

Figure 14: BP-680 boiler design concept (cross-section).

One of few changes introduced will be switching the primary air fan to
the cold air duct; placing the fan behind the LUVO (on the hot side) was
eliminated from engineering applications many years ago.

5.3.2 Example solution for the Kozienice project

One example of a Polish power station where the DuoBlock could be built
is Kozienice Power Plant, where currently eight 200 MWe units are in op-
186 J. Grzeszczak, Ł. Grela and T. Achter

eration. The plant has been adjusted to meet the present AELs – a SCR
reactor for each boiler and a common wet FGD plant for four boilers were
built. These installations would have to be modernized and a new ESP
built in order to ensure compliance with the new BAT AELs.

Figure 15: DuoBlock’s boiler island for Kozienice.

The SCR system was already designed to be prepared for additional

layers of catalyst, so the changes must focus on the choice of catalyst to
ensure both NOx reduction and Hg oxidation. With limited space, it was
proposed to build a complete new two-pass ESP (6 zones altogether). This
avoids the high operating costs of bag filter technology and does not im-
pact the existing layout – as the ESP fits between the existing SCR and
foundation of a draught fan. As far as desulfurization is concerned, it’s
possible as well to modernize the absorber. The proposed investments are
presented in Tab. 3.
Final selection of the way to reduce emissions must be preceded by thorough
analysis, and detailed information about the existing installation must be
provided.

6 Economic analysis of the DuoBlock

design concept
The estimated investment cost for a DuoBlock unit has been identified at
2.3 billion PLN (roughly equivalent to EUR 550 million), which is at least
EUR 200 million less than the price tag for a 500 MW-class greenfield unit.
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 187

Table 3: Ways to modernize existing absorber in the wet FGD installation.

Method Result Required investments

formic acid increase efficiency of • complete installation of formic acid dosage

additive absorption
sieve tray dynamic local flue gas – • fan with higher compression
suspension mixing • possible need of structural reinforcement
additional increase of suspension – • increase in absorber height
spray level flue gas reaction surface • complete new pipeline with supports, valves
and the circulation pomp
• structural reinforcement of the absorber and
pipelines

Investment costs for DuoBlock depend on the technical conditions of the

existing balance of plant equipment, which must be thoroughly considered
as site-specific parameters. In terms of income, the electricity market-
related income has been taken into account in these calculations.
A forecast has been prepared of the capacity factors and energy price
developments based on the Polish electricity market model. The electricity
market model for the entire country was developed by EPK. It runs on the
Plexos market simulation tool. The results are presented on the graphs in
Figs. 16 and 17.

Figure 16: Capacity factors for DuoBlock units under Polish market conditions.

The net present value ratio (NPVR) achieved is 0.61, while the internal
rate of return (IRR) is 9.37%. Both of these figures are acceptable from
the perspective of the economy of contemporary power investments.
188 J. Grzeszczak, Ł. Grela and T. Achter

Figure 17: Electric power price forecast.

7 Conclusions and strengths of the DuoBlock idea

In a number of countries where the energy market is a cornerstone of
power generation business, power plant assets are under continuous eco-
nomic pressure. The consequential choice is to optimize both operation
and maintenance. Yet, high investment costs for new units and relatively
slow technological progress (the incremental efficiency growth of new tech-
nology over years) create a situation in which the total energy costs of new
units are no lower than those of existing plants. This creates hardly any
incentive for investment.
Considering the nature of demand curves, particular attention has to
be given to the market segment where generating assets operate at a ca-
pacity utilization factor of approximately 4000 h/a. This particular regime
requires tradeoff between efficiency and flexibility. On the other hand side,
long investment cycles and aging among older generating assets are putting
the energy security of a number of countries at risk. Poland is one good
example. The design concept of the DuoBlock answers these challenges.
From a macroeconomic standpoint, it is a perfect fit for Poland’s na-
tional demand. At lower investment costs and shorter construction times,
the solution is competitive with any other solution in its market segment
(GCF 4000 h/a). The optimized design enables use of state-of-the-art cycle
parameters while keeping CAPEX low in comparison to 1000 MW coal-
fired greenfield plants, especially for the power island.
From the plant operators’ technical perspective, the design concept fits
into existing power plant arrangement plans, allowing for staged rehabili-
tation of older units. The concept as thus presented grants a second life to
aging power plants.
What transmission system operators require from plant operators is fast
response to demand changes. The concept of a 2-on-1 configuration allows
Environmentally friendly replacement of mature 200 MW coal-fired power. . . 189

unprecedented flexibility. Normally, one limit to minimum continuous rat-

ing of the unit is boiler flame stability. A low minimum continuous rating
resulting from a single-boiler operating mode in a DuoBlock arrangement
is of course two times lower than in a standard one-on-one concept. With
a large steam source available from the first boiler in the startup process of
the second boiler, it is possible to shorten startup times and cut the costs of
startup below what are considered industry standards. This makes the op-
erational difference in terms of changeover between single- and dual-boiler
operation unnoticeable for the transmission system dispatcher.
Another perspective arises from environmental concerns. The fuel for
the described unit is coal, which does not sound particularly ‘green’. How-
ever, the design concept has been tailored specifically for DuoBlock coop-
eration with large numbers of wind power and PV power sources. Those
latter ‘volatile’ sources must be backed up by predictable, reliable yet flex-
ible power generation. Thus, from the point of view of environmentally
concerned persons, application of the DuoBlock will enable renewables to
assume an even larger share of the power generation system.

8 Authors diclaimer
This document contains forward-looking statements and information Ő that
is, statements related to future, not past, events. Such statements are based
on our current expectations and certain assumptions, and are, therefore,
subject to certain risks and uncertainties. A variety of factors, affect its op-
erations, performance, business strategy and results and could cause the ac-
tual results, performance or achievements of authors companies worldwide
to be materially different from any future results, performance or achieve-
ments that may be expressed or implied by such forward-looking state-
ments. For us, particular uncertainties arise, among others, from changes
in general economic and business conditions, changes in currency exchange
rates and interest rates, introduction of competing products or technolo-
gies by other companies, lack of acceptance of new products or services
by customers targeted by authors companies worldwide, changes in busi-
ness strategy and various other factors. Should one or more of these risks
or uncertainties materialize, or should underlying assumptions prove incor-
rect, actual results may vary materially from those described in the relevant
forward-looking statement as anticipated, believed, estimated, expected, 28
J. Grzeszczak et el. intended, planned or projected.
190 J. Grzeszczak, Ł. Grela and T. Achter

Received 2 October 2017

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