Graz Cycle – A Zero
Emission Power Plant for CCS (Carbon Capture and Storage)
Introduction of closed cycle gas turbines with their capability of
retaining combustion generated CO2 can offer a valuable contribution
to the Kyoto goal and to future power generation. Therefore research and
development at the Institute for Thermal
Turbomachinery and Machine Dynamics (TTM) at Graz
University of Technology since the 90's has lead to the Graz Cycle, a zero emission power cycle of highest
efficiency. It burns fossil fuels with pure oxygen which enables the
cost-effective separation of the combustion CO2 by condensation. The
efforts for the oxygen supply in an air separation plant are partly compensated
by cycle efficiencies far higher than 65 %.
Over the last years the authors have presented a design
solution for this oxy-fuel CO2 retaining gas turbine system which
can by acceptance of international gas turbine industry be put into operation
within a few years. The authors believe, that this system is equal in
thermodynamic performance to any other proposal in the field of Carbon
Capture and Storage (CCS) and is superior in applying gas turbine experience
and research accumulated to our day.
Graz
Cycle power plant of the future ?
History and Continuous Development
The basic
principle of the so-called Graz Cycle has been developed by H. Jericha
and presented at the CIMAC conference in Oslo, Norway, in 1985. Improvements
and further developments since then were presented at many conferences [see publications below].
Any fossil fuel gas (preferable with low nitrogen content) is proposed to be
combusted with oxygen so that mainly only the two combustion products CO2
and H2O are generated. The cycle medium of CO2 and H2O
allows an easy and cost-effective CO2 separation by condensation.
Furthermore, the oxygen combustion enables power cycles which are far more
efficient than current air-based cycles, thus largely compensating the
additional efforts for oxygen production.
ASME Turbo Expo 2004, Vienna, Austria [11]:
At the
ASME IGTI conference 2004 in Vienna a Graz Cycle power plant (High Steam
Content Graz Cycle, S-Graz Cycle) was presented with a cycle efficiency of
nearly 70 % based on syngas firing. The net efficiency including the efforts of
oxygen supply and compression of captured CO2 for liquefaction was
57.7 %. The general layout of the components for a 100 MW prototype plant
showed the feasibility of all components. A concluding economic analysis of the
S-Graz Cycle power plant was performed showing very low CO2 mitigation
costs in the range of 10 $/ton CO2 avoided.
ASME Turbo Expo 2005, Reno-Tahoe, USA [15]:
Due to
this favorable economic data the Norwegian oil and gas company Statoil ASA initiated a cooperation in
order to conduct a feasibility study together with a major gas turbine
manufacturer with the goal of a technical and economic evaluation. In [15] the basic thermodynamic assumptions for component
losses and efficiencies agreed with Statoil for a 400 MW Graz Cycle plant are
shown and the resulting power cycle for natural gas firing is presented. Its
net efficiency of 52.6 % is below the first simulations, but is still above
most alternative CO2 capture technologies.
ASME Turbo Expo 2006, Barcelona, Spain [17]:
In
order to avoid the difficulties of condensation of water out of a mixture of
steam and incondensable gases at very low pressures, at the ASME 2006 [17] a modified cycle configuration was presented with
condensation in the range of 1 bar. It allows a separate bottoming steam cycle
with reasonably high pressures and efficiencies, so that a high net cycle
efficiency above 53 % can be expected. A design concept for a Graz Cycle
plant of 400 MW net output is presented with two shafts. A fast running
compression shaft is driven by the compressor turbine HTTC, whereas the power
shaft comprises the power turbine HPT and the LPST.
ASME
Turbo Expo 2008, Berlin, Germany [21]:
In
2008 the Graz Cycle turbomachinery were changed to higher pressure and
temperatures. A new pre-compressor for the working fluid allows to maintain the
volume flow for the succeeding compressors, so that they remain nearly
identical. The new turbomachinery result in a Graz Cycle power plant of 600 MW
power output. Due to the higher cycle parameters of 50 bar and 1500°C, a net
cycle efficiency above 55 % can be expected.
Economic Analysis
In an
economical analysis the Graz Cycle power plant is compared with a reference
plant. The assumptions for capital costs, fuel costs and O&M costs as well
as the economical parameters are listed in [17].
The resulting mitigation costs are in the range of 20 – 30 $/ton CO2
avoided depending on the costs of the air separation unit (ASU) and thus are
below a threshold value of 30 $/ton CO2 (assumed for future CO2
emission trading). This makes the Graz Cycle an economically interesting
solution for future CO2 capture.
CO2
mitigation costs vs. capital costs
Basic
cycle configuration [15]
Basically the
Graz Cycle consists of a high temperature Brayton cycle (compressors C1 and
C2, combustion chamber and High Temperature Turbine HTT) and
a low temperature Rankine cycle (Low Pressure Turbine LPT, condenser,
Heat Recovery Steam Generator HRSG and High Pressure Turbine HPT).
The fuel (natural gas) together with the nearly stoichiometric mass flow of
oxygen is fed to the combustion chamber, which is operated at a pressure of 40
bar. Steam as well as a CO2/ H2O mixture is supplied
to cool the burners and the liner.
A mixture
of about 74 % steam, 25.3 % CO2, 0.5 % O2 and 0.2 % N2
(mass fractions) leaves the combustion chamber at a mean temperature of 1400
C. The fluid is expanded to a pressure of 1.05 bar and 579 C in the HTT.
Cooling is performed with steam coming from the HPT, increasing the steam
content to 77 % at the HTT exit. The hot exhaust gas is cooled in the
following HRSG to vaporize and superheat steam for the HPT. But after the HRSG
only 45 % of the cycle mass flow are further expanded in the LPT. The LPT exit
and thus condenser pressure is 0.041 bar for a cooling water temperature of
8°C.
Principle
flow scheme of basic S-Graz Cycle power plant
Gaseous
and liquid phase are separated in the condenser. From there on the gaseous mass
flow, which contains the combustion CO2 and half of the combustion
water, is compressed to atmosphere with intercooling and extraction of
condensed water. CO2 is supplied for further use or storage.
After
segregating the remaining combustion H2O, the water from the condenser
is preheated, vaporized and superheated in the HRSG. The steam is then
delivered to the HPT at 180 bar and 549 C. After the expansion it is used to
cool the burners and the HTT stages.
The major
part of the cycle medium, which is separated after the HRSG, is compressed
using an intercooled compressor and fed to the combustion chamber with a
maximum temperature of 600 C.
The cycle
arrangement of the Graz Cycle offers several advantages:
On one hand, it allows heat input at very high temperature, whereas on the
other hand expansion takes place till to vacuum conditions, so that a high
thermal efficiency according to Carnot can be achieved. But only less than half
of the steam in the cycle releases its heat of vaporization by condensation.
The major part is compressed in the gaseous phase and so takes its high heat
content back to the combustion chamber.
Modified
cycle configuration with working fluid condensation at 1 bar [17]
Recent
research shows that difficulties in condensation arise in the formation of
water films on the cooling tubes and in concentration of CO2 forming
a heat transfer hindering layer so that only a low heat transfer coefficient in
condensation will be achieved. This results in excessively large condenser heat
transfer surface and related high costs. Therefore it was suggested to condense
this mass flow at atmosphere, separate the combustion CO2 and
re-vaporize the water at a reduced pressure level using the condensation heat.
The pure steam is then fed to a Low Pressure Steam Turbine LPST, where it can
be expanded to a condenser pressure lower than that for the working fluid
mixture.
In the
novel configuration the process is now split into the high-temperature cycle
and a separate low temperature condensation process as shown in the following
simplified scheme. The high temperature part consists of HTT, HRSG, C1/C2
compressors and HPT. Condensation of the working fluid in the 1 bar range is
proposed in order to avoid the problems of a working fluid condenser at vacuum
conditions as described above. The heat content in the flow segregated after
the HRSG for condensation is still quite high so re-evaporation and expansion
in a bottoming cycle is mandatory.
Principle flow scheme of
modified Graz Cycle power plant with condensation/evaporation in 1 bar range
This
bottoming cycle operates by pure steam with extensively cleaned feed water and
thus allows together with the very low cooling water temperatures of northern Europe
to attain condenser pressures down to 0.02 bar.
For proper
re-evaporation two sections of working fluid condensations are provided, each
following a compressor stage with reasonable increase of flow pressure
resulting in a higher partial condensation pressure of the water content. At
the first pressure level of 1.27 bar about 63 % of the water content can be
segregated, so that the power demand of the second compression stage is
considerably reduced. It compresses up to 1.95 bar, which allows the segregation
of further 25 % of the contained water. Further cooling of the working fluid,
also for water preheating, leads to the separation of additional 11 %, so that
the water content of the CO2 stream supplied at 1.9 bar for further
compression is below 1 %. After segregation of the water stemming from the
combustion process, the water flow is degassed in the deaerator with steam
extracted after the HPT and fed to the HRSG for vaporization and superheating.
This
two-step pre-compressed condensation counteracts the effect of sinking H2O
partial pressure due to condensed water extraction from working fluid and thus
allows a reasonably high constant re-evaporation pressure of 0.75 bar for the
bottoming steam cycle.
TTM
publications on the Graz Cycle
[2] Jericha, H., Fesharaki,
M., 1995, "The Graz
Cycle 1500 C Max Temperature-CO2 Capture with CH4-O2 Firing", ASME
paper 95-CTP-79, ASME Cogen-Turbo Power Conference, Vienna.
[3] Lukasser,
A., 1997, "Graz Cycle, eine Innovation zur CO2 Rückhaltung",
Master thesis, Graz University of Technology.
[4] Tabesh,
H., 1997, "CH4-Graz-Cycle: Optimierung und Auslegung der
Wärmetauscher", Master thesis, Graz University of Technology.
[5] Jericha, H., Fesharaki, M., Lukasser,
A., Tabesh, H., 1998, "Graz Cycle – eine Innovation zur
CO2-Minderung", BWK Bd. 50 (1998), Nr. 10, Seiten 30-34.
[6] Jericha, H.,
Lukasser, A., Gatterbauer, W., 2000,
"Der Graz Cycle für Industriekraftwerke
gefeuert mit Brenngasen aus Kohle- und Schwerölvergasung", VDI
Berichte 1566, VDI Conference Essen, Germany.
[7] Jericha,
H., Göttlich, E., 2002,
"Conceptual
Design for an Industrial Prototype Graz Cycle Power Plant", ASME Paper
2002-GT-30118, ASME Turbo Expo 2002, Amsterdam, The Netherlands (Conference
presentation)
[8] Jericha,
H., Göttlich, E., Sanz, W., Heitmeir, F.,
2003, "Design
Optimisation of the Graz Cycle Prototype Plant", ASME Paper
2003-GT-38120, ASME Turbo Expo 2003, Atlanta, USA. (best
paper award)
[9] Heitmeir, F., Sanz, W., Göttlich, E., Jericha H.,
2003, "The Graz
Cycle – A Zero Emission Power Plant of Highest Efficiency", XXXV
Kraftwerkstechnisches Kolloquium, Dresden, Germany.
[10] Jericha, H.,
Sanz, W., Pieringer, P., Göttlich E., Erroi, P., 2004,
"Konstruktion der ersten Stufe der
HTT-Gasturbine für den Graz Cycle Prototyp“ (in
German), VDI Conference Leverkusen, Germany.
[11] Sanz., W., Jericha, H., Moser, M., Heitmeir, F.,
2004, "Thermodynamic
and Economic Investigation of an Improved Graz Cycle Power Plant for CO2
Capture", ASME Paper GT2004-53722, ASME Turbo Expo 2004, Vienna,
Austria. (Conference
presentation)
[12] Moser,
M., 2004, "Thermodynamische und wirtschaftliche Optimierung des Graz
Cycle", (in German), Master thesis, Graz University of Technology. (nominated
for best TU-Graz Master thesis award of 2004)
[13] Luckel,
F., 2004, "Weiterentwicklung des Graz Cycle und der Vergleich mit
anderen CO2-Rückhaltekonzepten", (in German), Master thesis, Graz
University of Technology.
[14] Erroi,
P., 2004, "Strömungssimulation der ersten Stufe der
Hochtemperaturturbine des Graz-Cycles", (in German), Master thesis, Graz
University of Technology. (nominated for best TU-Graz Master
thesis award of 2004)
[15] Sanz, W., Jericha, H., Luckel, F., Göttlich, E., Heitmeir, F.,
2005, "A Further
Step Towards a Graz Cycle Power Plant for CO2 Capture", ASME Paper
GT2005-68456, ASME Turbo Expo 2005, Reno-Tahoe, Nevada, USA. (Conference
presentation)
[16] Heitmeir,
F., Jericha, H., 2005, "Turbomachinery
design for the Graz cycle: an optimized power plant concept for CO2
retention", Proceedings of the Institution of Mechanical Engineers Part A:
Journal of Power and Energy, Volume 219, Number 2, pp. 147-158(12). (DOI)
[17] Jericha, H., Sanz, W., Göttlich, E., 2006,
"Design
Concept for Large Output Graz Cycle Gas Turbines", ASME Paper
GT2006-90032, ASME Turbo Expo 2006, Barcelona, Spain.
[18] Jericha, H.,
Sanz, W., Göttlich E.,
2006, "Gasturbine
mit CO2-Rückhaltung – 490 MW (Oxyfuel-System Graz Cycle)“ (in German), VDI
Conference Leverkusen, Germany (Conference
presentation)
[19] Jericha, H.,
Sanz, W., Göttlich E.,
2007, "Gas
Turbine with CO2 Retention – 400 MW Oxyfuel-System Graz Cycle“, Paper No.
168, CIMAC Conference 2007, Vienna, Austria (Conference
presentation)
[20] Sanz, W.,
Jericha, H., Bauer, B., Göttlich E.,
2007, "Qualitative
and Quantitative Comparison of Two Promising Oxy-Fuel Power Cycles for CO2
Capture“, ASME Paper GT2007-27375, ASME Turbo Expo 2007, Montreal, Canada (Conference
presentation). Also published in: Journal of Engineering for Gas Turbines
and Power, Volume 130, Issue 3, May 2008. (DOI)
[21] Jericha,
H., Sanz, W., Göttlich E., Neumayer, F., 2008,
"Design Details of a 600 MW Graz Cycle
Thermal Power Plant for CO2 Capture“,
ASME Paper GT2008-50515, ASME Turbo Expo 2008, Berlin, Germany (Conference
presentation)
Third party publications
citing the Graz Cycle
The list
below is by no far an exhaustive list of publications mentioning the Graz
Cycle. We only recently thought that it could be of interest to visitors of
this web page and the list can be considered work in progress. We will add
links on an occasional basis. As we do not regularly check the availability of
the linked pages below, some of them might disappear over time. Please let us
know if you find outdated links, so we can remove them. Also, if you are one of
the authors of the papers listed below and want a link amended or if you want
to make us aware of a new related paper, just contact the maintainer of this
web page.
-
Mori, H., Sugishita, H., Uematsu, K.,
1998, "A Study of 50MW Hydrogen Combustion Turbines", XII World
Hydrogen Energy Conference. (HTML)
-
Bolland, B., Kvamsdal, H.M., Boden,
J.C., 2001, "A Thermodynamic Comparison of the
Oxy-Fule Power Cycles, Water-cycle, Graz-Cycle and Matiant-Cycle",
International Conference on Power Generation and Sustainable Development,
Liège, Belgium. (PDF)
- Celano A., 2002, "Comparison of near Zero CO2 Emission Power Plants on CO2/H2O Mixture", Doctoral Thesis, Padova, Italy
-
Kail, C., Haberberger, G., 2002,
"Kohlendioxid-Rückhaltung und Wirkungsgraderhöhung durch interne Zusatzfeuerung
bei Dampfkraftwerken", (in German), VDI Berichte 1714. (PDF)
-
Miller, A., Lewandowski, J., Badyda, K., Kiryk,
S., Milewski, J., Hama, J., Iki, N., 2003,
"Off-Design Analysis of the GRAZ Cycle Performance", Proceedings of
the International Gas Turbine Congress 2003, Tokyo, Japan. (PDF)
-
Mathieu, P., 2003,
"Zero Emission Technologies: An Option for Climate Change Mitigation",
Third Nordic Minisymposium on Carbon Dioxide Capture and Storage, Trondheim. (Conference
presentation)
-
Gupta, M., Coyle, I., Thambimuthu, K.,
2003, "CO2 Capture Technologies and Opportunities in Canada", 1st
Canadian CC&S Technology Roadmap Workshop, Calgary, Alberta, Canada. (PDF)
-
Ito, S., Saeki, H., Inomata, A., Ootomo,
F., Yamashita, K., Fukuyama, Y., Koda, E., Takehashi, T., Sato, M., Koyama, M.,
Ninomiya, T., 2005,
"Conceptual Design and Cooling Blade Development of 1700°C Class
High-Temperature Gas Turbine", Journal of Engineering for Gas Turbines and
Power, Volume 127, Issue 2, pp. 358-368. (DOI)
-
Anheden, M., Yan, J., De Smedt, G.,
2005, "Denitrogenation (or Oxyfuel Concepts)", Oil & Gas Science
and Technology – Rev. IFP, Vol. 60 (2005), No. 3, pp. 485-495. (PDF)
-
Gou, C., Cai, R., Hong, H., 2006, "An Advanced Oxy-Fuel Power Cycle with High
Efficiency", Proceedings of the Institution of Mechanical Engineers Part
A: Journal of Power and Energy, Volume 220, Number 4, pp. 315-325(11). (DOI)
-
ENCAP, 2006,
“Second Newsletter of ENCAP Project” (PDF)
-
Franco, F., Mina, T.,
Woolatt, G., Rost, M., Bolland, O., 2006, “Characteristics of Cycle Components for CO2 Capture”,
Proceedings of 8th
International Conference on Greenhouse Gas Control Technologies, Trondheim,
Norway. (PDF)
-
Kvamsdal, H.M., Bolland, O., Maurstad, O.,
Jordal, K., 2006, "A Qualitative Comparison of Gas
Turbine Cycles with CO2 Capture", Proceedings of 8th
International Conference on Greenhouse Gas Control Technologies, Trondheim,
Norway (PDF)
Third party publications related to
the Graz Cycle
-
VGB PowerTech Service GmbH,
" CO2
Capture and Storage – VGB Report on the State of the Art", VGB PowerTech
Service GmbH, August 2004. (PDF)
This web page is maintained by
Wolfgang Sanz,
Professor at the Institute for Thermal
Turbomachinery and Machine Dynamics (TTM), Graz University of Technology.
Contact: wolfgang.sanz@TUGraz.at
Last updated: July 18, 2008.