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.

ASME Turbo Expo 2010, Glasgow, UK [23]:

In 2010 the Graz Cycle was adopted for the use of syngas from coal gasification. Syngas containing carbon monoxide, carbon dioxide and hydrogen is fed to the Graz Cycle combustor, the carbon dioxide separation takes place by condensation. Heat of the gasification process is used in the Graz Cycle plant. The oxy-fuel technology of the Graz Cycle is then compared with a pre-combustion plant, where the carbon monoxide is converted to carbon dioxide by shift reaction and separation of the carbon dioxide from the syngas is done by chemical absorption. The comparison shows a higher efficiency for the Graz Cycle plant.

ASME Turbo Expo 2011, Vancouver, Canada [24]:

In order to In order to facilitate construction of a demonstration plant the performance of a near-term Graz Cycle process design based on modest cycle data and available turbomachinery components using a simplified flow scheme is presented at the 2011 ASME conference. Two near-term Graz Cycle plants are presented based on basic and advanced operating conditions of the proposed commercially available turbine. The predicted optimum net efficiency achieved is 23.2 % (HHV).

A near-term zero-emission power plant can only be commercially attractive if it will be deployed in a niche market. Therefore an economic analysis commensurate with an early pre-FEED conceptual study is carried out for the U.S. Gulf Coast where revenue from multiple product streams that could include power, steam, CO2 and water, as well as argon and (potentially) nitrogen from the ASU is provided. The economic analysis suggests that a capital investment of $94 million can secure construction of a 13.2 MWe zero emission oxyfuel power plant and yield a 14.5% (unlevered) return on capital invested.

ASME Turbo Expo 2016, Seoul, South Korea [25]:

A modern energy system based on renewable energy like wind and solar power inevitably needs a storage system to provide energy on demand. Hydrogen is a promising candidate for this task. For the re-conversion of the valuable fuel hydrogen to electricity a power plant of highest efficiency is needed.

In this work presented at the ASME IGTI Conference 2016 the Graz Cycle is proposed for this role. The Graz Cycle is now adapted for hydrogen combustion with pure oxygen so that a working fluid of nearly pure steam is available. The changes in the thermodynamic layout are presented and discussed. The results show that the cycle is able to reach a net cycle efficiency based on LHV of 68.5 % if the oxygen is supplied “freely” from hydrogen generation by electrolysis.

An additional parameter study shows the potential of the cycle for further improvements. The high efficiency of the Graz Cycle is also achieved by a close interaction of the components which makes part load operation more difficult. So in the second part of the paper strategies for part load operation are presented and investigated. The thermodynamic analysis predicts part load down to 30 % of the base load at remarkably high efficiencies.



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

[1]      Jericha, H., Sanz, W., Woisetschläger, J., Fesharaki, M., 1995, "CO2-Retention Capability of CH4/O2-Fired Graz Cycle", CIMAC Conference Paper, Interlaken, Switzerland.

[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) (Conference presentation), Also published in: ASME Journal of Engineering for Gas Turbines and Power, Vol. 126, pp. 733-740, October 2004 (DOI)

[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). Also published in: Journal of Engineering for Gas Turbines and Power, Volume 127, Issue 4, pp. 765-772, October 2005. (DOI)

[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. (Conference presentation). Also published in: Journal of Engineering for Gas Turbines and Power, Volume 130, Issue 1, January 2008. (DOI)

[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)

[22]    Jericha, H., Sanz, W., Göttlich E., Neumayer, F., 2008, "Mit Überschallstufen und ICS-Dampfkühlung zur 600 MW Oxyfuel-Graz-Cycle-Einheit“ (in German), VDI Conference Leverkusen, Germany (Conference presentation)

[23]    Sanz, W., Mayr M., Jericha, H., 2010, "Thermodynamic and Economic Evaluation of an IGCC Plant Based on the Graz Cycle for CO2 Capture“, ASME Paper GT2010-22189, ASME Turbo Expo 2010, Glasgow, UK (Conference presentation)

[24]    Sanz, W., Hustad, C.-W., Jericha, H., 2011, "First Generation Graz Cycle Plant for Near-Term Deployment“, ASME Paper GT2011-45135, ASME Turbo Expo 2011, Vancouver, Canada (Conference presentation)

[25]    Sanz, W., Braun, M., Jericha, H., Platzer, M.F., 2016, "Adapting the Zero-Emission Graz Cycle for Hydrogen Combustion and Investigation of its Part Load Behaviour“, ASME Paper GT2016-57988, ASME Turbo Expo 2016, Seoul, South Korea (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)

-                 Zero Emissions Platform, 2011, “The Costs of CO2 Capture – Post-demonstration CCS in EU”, Report by the European Technology Platform for Zero Emission Fossil Fuel Power Plants (PDF)

-                 Zhang, N., Lior, N., 2008, "Comparative Study of Two Low CO2 Emission Power Generation System Options With Natural Gas Reforming", Journal of Engineering for Gas Turbines and Power, Volume 130, Issue 5, September 2008. (DOI)


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.

Last updated: August 22, 2016