Projektinfo 05/2011
Detailed information on energy research
Comparison of electricity
production from fossil fuels
Consistent and realistic simulation models for modern
power plant processes with coal and gas
If industrial production requires electricity on a windless
winter morning, solar energy systems and wind turbines
reach their limits. Then, power plants which can convert
fossil fuels into electricity no matter what the time, provide
the electricity quantities required. Power plant technologies
are under development for coal and gas, which can generate electricity more efficient and with lower emissions than
previously. A realistic comparison of the efficiencies of modern
power plant processes helps in decisions on the role of coal
and gas in the future energy mix.
60 percent of electricity worldwide is generated by burning coal, natural gas and
mineral oil. Fossil power plant technology will remain extremely important for the
power supply in the decades to come. Decreasing the carbon dioxide emissions to
the atmosphere as a result of this process is the aim of climate protection and is
­intended to restrict global warming. The German research programme into CO2 reduction technologies ­(abbreviation: COORETEC) can contribute to effectively reducing emissions. For more efficient power plants and separation of most of the CO2
using CCS technology, a variety of development options for power plant processes
are available. CCS is the abbreviation for “Carbon Capture and Storage“. This process ensures that less than 100 g/kWh of CO2 is released when converting coal into
electricity.
This research project
is funded by the:
Federal Ministry of Economics
and Technology (BMWi)
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BINE-Projektinfo 05/2011
Thus, the CO2 emissions are less than one third of those
of natural gas-fired combined gas and steam turbine
plants without CCS.
The researchers at the Institute of Energy Systems at the
Hamburg University of Technology (TUHH) have developed standards which permit an objective comparison
of extremely diverse technologies. At the end of the day,
when generating electricity cost effectively, efficiency
and emissions are key parameters and must be determined objectively to make the right decisions. By comparing different power plant processes under uniform
constraints, their efficiencies and potential CO2 avoidance can be evaluated with greater precision.
Selection of the power plant processes
Starting point was the current state of the art of power
plants fired by fossil fuels, and the two strategic guidelines of the COORETEC concept by the German Federal
Ministry of Economics and Technology.
First, there are measures to increase efficiency, such as
higher process temperatures and pressures when firing
lignite and hard coal in steam power plants or natural
gas in power plants which combine gas and steam
­turbines (Combined-Cyclepower plants).
Second, technologies which burn coal while capturing
most of the resulting CO2, to store it in subterranean
­repositories, where it cannot affect the climate, are
currently under development. In the oxyfuel power
­
plant version, coal is fired with pure oxygen, without the
nitrogen otherwise present in combustion air, which
causes high CO2 concentrations in the flue gas. Washing
CO2 from the flue gases after conventional combustion is
referred to as “Post Combustion Capture” (PCC or CO2
flue gas scrubbing). CO2 separation after gasification of
coal traps carbon as CO2 before actual combustion, and
is therefore a Pre-Combustion Capture process, which is
based on the Integrated Gasification Combined Cycle
(IGCC).
The oxygen required for the oxyfuel technology is provided
by breaking down the air via low temperature distillation
in cryogenic air separation systems. Air separation processes based on high-temperature membranes were
also considered as an alternative to this. More research
is required into membrane oxygen separation than for
the other separation processes investigated which
should be available by 2020. In their project, the researchers from Harburg studied various versions of
these air separation processes.
The comparability problem
As part of preparatory research for the comparison,
which involved reviewing over 1,700 literature sources,
it was found that most studies to date were performed
with very different assumptions. While some studies
were drawn up for Northern European ambient conditions, others assume higher ambient temperatures
which are thermodynamically less favourable. Others
make different assumptions on the efficiencies of comparable turbines, for example. Therefore, uniform assumptions and constraints had to be specified – in
close cooperation with plant manufacturers and other
research institutions.
Fig. 1 provides a simplified insight into the variety of
definitions used in modelling the overall process of a
power plant. Using the same calculation procedurs for
simulation, their selection influences the range and
Constraints and balance limits
Process topology
Components &
parameters
Material values
Simulation
Result figures
Fig. 1 Composition of the overall process model for power plants by hierarchical
detail level. Source: TUHH
Power plant processes and fuels studied (legend for Fig. 2 and Fig. 3)
RL = raw lignite
PDL = pre-dried liginite
HC = Hard coal
600 = Steam power plant with 600 °C technology (state of the art)
700 = Steam power plant with 700 °C technology
PCC = Post Combustion CO2 Capture (CO2 flue gas washing after combustion)
OXYK = Oxyfuel power plant with cryogenic air separation system
OXY4M = Oxyfuel power plant with high-temperature membrane air separation system in
flue gas flushed 4-end process
IGCC = Integrated Gasification Combined Cycle (coal gasification)
NGCC = Combined-cycle power plant
The models of all power plant processes with CO2 separation (CCS) are based on
hard coal-fired steam power plants using 600° technology (except IGCC).
r­ ealistic nature of the resulting figures. Equivalence of the assumed ambient air temperature and humidity are just as important as the fuel composition or the formula used to calculate the efficiency.
For comparable studies of efficiency and specific CO2 emissions, the researchers at TUHH assumed the same gross output of 1,100 megawatts for
all steam power plant processes and then defined them for uniform comparison via 72 parameters. 30 parameters had to be specified for gas
­turbines. Characteristic temperatures and pressures needed definition, as
did various pressure losses and the auxiliary electricity demand of the
­individual components. This ranges from parameterisation of steam gen­
erators and turbines via pumps, blowers, compressors, electric drives and
generators. For example, the specifications include details like the auxiliary
power demand of the coal mills or the water content of the coal dust and
included even the temperatures and pressure losses for oxygen provision
via high temperature membranes.
Once the researchers had specified the state of the art for coal-fired steam
power plants in basic models with the corresponding parameters, they
­calculated the respective efficiencies and CO2 emissions through process
simulation. This was followed by similar simulations for efficiency-increasing measures such as increasing the fresh steam parameters (pressure and
temperature) and predrying lignite using steam fluidised bed drying which
is heated by the compressed vapor originating form the coal moisture. The
latest gas turbine developments for combined gas and steam turbine power
plants were also simulated. Finally, the power plant processes featuring CO2
separation, subject of current debates, were investigated.
For the studies the researchers modelled the power plant processes with a
low degree of integration, as would likely be initially selected when imple-
Stored
Emitted
Stored
Emitted
Quote of the project leader
Spec. reduction
Spec. reduction
CO2 emissions
CO2 emissions
NGCC
Natural
gas
60
NGCC
OXYK
OXYK
NGCC
PCC
PCC
IGCC
HC700
HC700
IGCC
HC600
HC600
OXY4M OXY4M
RL700
Net efficiency
RL700
0
PDL600 PDL600
10
auxiliary power demand
RL600
40
60
30
50
20
40
10
30
0
20
RL600
Electrical Electrical
efficieny in
efficieny
%
in %
Fig. 2 Comparison of the specific CO2 quantities per kilowatt hour of
CCS
Natural studied.
electric current generated for a selection of power plant processes
gas
Hard coal
Source:Lignite
TUHH
auxiliary power demand
Net efficiency
50
„In order to evaluate new power plant processes simulations must be performed due to the lack of practical
experience. The results produced largely depend on the
constraints and assumptions used. The main goal of
the project was therefore to create the basis for a reliable
and realistic comparison of various power plant processes via generally-applicable definition of identical
constraints and assumptions. Starting with this basis,
new power plant processes can be compared more objectively with one another in future.“
NGCC
IGCC
IGCC
OXY4M OXY4M
OXYK
CCS
Hard coal
OXYK
PCC
PCC
HC600
HC700
HC700
Lignite
HC600
0
RL700
200
RL700
800
1.200
600
1.000
400
800
200
600
0
400
PDL600 PDL600
1.000
RL600
1.200
RL600
Specific CO
Specific
CO2in
quantity
g/kWh in g/kWh
2 quantity
BINE-Projektinfo 05/2011
Fig. 3 Comparison of the heating value-specific efficiencies for a selection of
the power plant processes studied. Source: TUHH
menting the processes, with the result that no highly-optimised processes
were examined. Moreover, when selecting the parameters for the process
models, compromises had to be made between comparability and realism.
Results provide an overview
Figs. 2 and 3 show the results of the study for a selection of ten power plant
processes. The researchers from TUHH have distinguished additional process versions. The above diagrams confirm the current knowledge on the
efficiencies of the technologies studied. The electric efficiencies of natural
gas-fired combined-cycle plants are approximately 15 percentage points
above those of modern coal-fired power plants. If in turn the steam temperature is increased from 600 to 700 °C in a coal-fired power plant, the
results of the simulations reveal with high precision that the efficiency rises
up to approx. three percentage points.
Fig. 2 compares the emitted CO2 mass per kilowatt hour (kWh) of net electricity generated. In processes with CO2 separation, the CO2 quantity to be
stored is shown in a different colour. The difference marked as an example
between the emissions of a hard-coal fired reference steam power process
based on 600 °C technology and the selected CCS technology allows the
specific reduction of CO2 emissions to be seen. This is equivalent to the
­effective decrease in atmospheric pollution if electricity is generated using
CCS. In a direct comparison of electricity generation, this is approx. 670 g/kWh
or roughly 88% in the example entered.
At the same time, the additional CO2 quantity produced as a result of the
decrease in efficiency (8% in the example) due to CO2 separation can also
be seen (approx. 160 g/kWh in the example).
The comparison of electric efficiencies in Fig. 3 clearly shows that all power
Prof. Dr.-Ing. Alfons Kather is Head
of the Institute of Energy Systems
at the Hamburg University of Technology (TUHH) and spokesman for
the COORETEC Initiative of the German Federal Ministry of Economics
and Technology.
plant processes with CO2 separation have significantly
higher auxiliary electricity demands, when compared
with the conventional electricity generation using fossil
fuels. These and other losses of efficiency associated
with CCS technology reduce the net efficiency by approx.
10 percentage points depending on the contrasted coalfired technologies.
Comparison basis for future use
The results of this project by TUHH can be used as a
basis for the implementation of other simulation-based
process studies in research projects pertaining to power
plant technology. This would improve the comparability
of the various power plant processes in future. The approach developed by the Harburg research team allows
other key technologies to be studied in a similar way
and objectively compared with known technologies.
But first, the proposed parameters and simulation processes must prove themselves in a practical environment. If the new comparison method is revealed to be
useful in general, it could form the basis for a directive,
which simplifies the documentation of constraints,
further input parameters and mathematical/physical
­
partial models required for comprehension. The method
can be transferred to any future energy comparison of
power plant technologies based on the familiar basic
processes.
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BINE Projektinfo 01/2010
BINE-Projektinfo
05/2011
Structural change in the electricity market
The market share of electricity generated from renewable energy sources is growing in
Germany. By 2030 more than every third kilowatt hour is to be derived from renewable
energy sources such as wind, biomass and hydroelectricity. Even if this percentage is
twice that of today, the question remains: Where will the remaining electricity come
from? Another objective further complicates this answer: Within the next 10 years,
Germany also intends to reduce emissions of carbon dioxide, the „climate gas“ by
40% compared with 1990.
High-efficiency, low CO2 power plants for fossil fuels such as coal and gas could be a
solution for this. They are a flexible replacement for renewable energy sources when
yield is low due to natural fluctuations. Fossil-fired power plants are often described as
bridge technologies, which can replace old plants and compensate green electricity
supplies.
If we succeed in increasing the average efficiency of German power plants by just 2
percent with constant electricity generation, this is mathematically equivalent to one
tenth of the CO2 emissions caused by road traffic. Since 1985 research has managed to
increase the efficiency of the latest power plant technologies by over 20%. With the
cooperation of industry and science the COORETEC support initiative of the German
Federal Ministry of Economics and Technology has developed a whole range of technologies since 2004 to further increase the efficiency of power plants or to capture CO2 in the
power plant process and store it geologically.
The new power plant technologies are not only intended for German power supply. In the
long term, Germany will fall below 1% of the electricity generated globally. Developing
innovative power plant technologies for the global market not only contributes to the
competitiveness of the export-oriented German economy but also offers a way to reach
the ambitious global climate targets. In order to limit global warming to 2 °C, the CO2
emissions around the world must be reduced rapidly and significantly.
The global population is growing and will probably reach 9 billion people by 2050.
This will increase the demand for energy, in particular for electricity. As long as the
reserves of coal and natural gas are available around the world at low prices, the
percentage of electricity produced by fossil-fired power plants will increase rather than
decrease. Comparative research allows us to make the best choice between energyefficient, economic and flexible technologies.
Project participants
>> Hamburg University of Technology (TUHH), Institute of Energy Systems (M-5),
Prof. Dr.-Ing. Alfons Kather, Imo Pfaff, Hamburg (Germany), Phone +49 40 42878-3243
Links and literature (in German)
>> www.tu-harburg.de/iet | www.kraftwerkforschung.info | www.cooretec.de
>> Kather, A.; Pfaff, I.: Vergleich der in COORETEC verfolgten Kraftwerksprozesse unter
einheitlichen realitätsnahen Randbedingungen. Abschlussbericht. Technische Universität
Hamburg-Harburg (Hrsg.). März 2011. 170 S., FKZ 0327742. Download at TIB Hannover , Germany:
www.getinfo.de | Bundesministerium für Wirtschaft und Technologie, Berlin (Hrsg.): E
­ mpfehlungen
des COORETEC-Beirats zur Förderung von Forschung und Entwicklung CO2-emissionsarmer
­Kraftwerkstechnologien und CO2-Abscheide- und Speichertechnologien, April 2009. Download at:
www.kraftwerkforschung.info | Bundesministerium für ­Wirtschaft und Technologie, Berlin (Hrsg.):
Leuchtturm COORETEC – Der Weg zum zukunftsfähigen Kraftwerk mit fossilen Brennstoffen, Juni 2007.
Forschungsbericht Nr. 566. Download at: www.kraftwerkforschung.info
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Project organisation
Federal Ministry of Economics
and Technology (BMWi)
11019 Berlin
Germany
Project Management Organisation Jülich
Research Centre Jülich
Dr.-Ing. Jochen Seier
52425 Jülich
Germany
Project number
0327742
Imprint
ISSN
0937 - 8367
Publisher FIZ Karlsruhe · Leibniz Institute
for Information Infrastructure
Hermann-von-Helmholtz-Platz 1
76344 Eggenstein-Leopoldshafen
Germany
Author
Peter Horenburg
Cover image
Installation by Vattenfall Europe AG of the
Jänschwalde power plant site with
the planned CCS demonstration power plant
Copyright
Text and illustrations from this publication
can only be used if permission has been
granted by the BINE editorial team.
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