Future power plants will require some type of carbon capture and storage (CCS) system to mitigate carbon dioxide (CO 2 ) emissions. The most promising technologies for CCS are: oxyfuel (O-F) combustion, pre-combustion capture, and postcombustion capture. This paper discusses the recent work conducted by Siemens Power Generation, Florida Turbine Technologies, Inc. (FTT) and Clean Energy Systems, Inc. (CES) in adapting high temperature gas turbines to use CES's drive gases in high-efficiency O-F zero emission power plants (ZEPPs). CES's O-F cycle features high-pressure combustion of fuel with oxygen (O 2 ) in the presence of recycled coolant (water, steam or CO 2 ) to produce drive gases composed predominantly of steam and CO 2 . This cycle provides the unique capability to capture nearly pure CO 2 and trace by-products by simple condensation of the steam.An attractive O-F power cycle uses high, intermediate and low pressure turbines (HPT, IPT and LPT, respectively). The HPT may be based on either current commercial or advanced steam turbine technology. Low pressure steam turbine technology is readily applicable to the LPT. To achieve high efficiencies, an IPT is necessary and efficiency increases with inlet temperature. The high-temperature IPT's necessitate advanced turbine materials and cooling technology. O-F plants have an abundance of water, cool steam ~200ºC (400ºF) and CO 2 that can be used as cooling fluids within the combustor and IPT systems.For the "First Generation" ZEPP, a General Electric J79 turbine, minus the compressor, to be driven directly by CES's 170 MW t high-pressure oxy-fuel combustor (gas generator), has been adapted. A modest inlet gas temperature of 760ºC (1400ºF) was selected to eliminate the need for turbine cooling. The J79 turbine operating on natural gas delivers 32 MW e and incorporates a single-stage free-turbine that generates an additional 11 MW e . When an HPT and an LPT are added, the net output power (accounting for losses) becomes 60 MW e at 30% efficiency based on lower heating value (LHV), including the parasitic loads for O 2 separation and compression and for CO 2 capture and compression to 151.5 bar (2200 psia). For an inlet temperature of 927ºC (1700ºF), the nominal value, the net output power is 70 MW e at 34% efficiency (LHV).FTT and CES are evaluating a "Second Generation" IPT with a gas inlet temperature of 1260ºC (2300ºF). Predicted performance values for these plants incorporating the HPT, IPT and the LPT are: output power of approximately 100-200 MW e with an efficiency of 40 to 45%.The "Third Generation" IPT for 2015+ power plants will be based on the development of very high temperature turbines having an inlet temperature goal of 1760ºC (3200ºF). Recent DOE/CES studies project such plants will have LHV efficiencies in the 50% range for natural gas and HHV efficiencies near 40% for gasified coal [ ] 1 .

In Aug 2004 the Zero Emission Norwegian Gas (ZENG) project team completed Phase-1: Concept and Feasibility Study for a 40 MW Pilot & Demonstration (P&D) Plant, that is proposed will be located at the Energy Park, Risavika, near Stavanger in South Norway during 2008. The power plant cycle is based upon implementation of the natural gas (NG) and oxygen fueled Gas Generator (GG) (1500°F/1500 psi) successfully demonstrated by Clean Energy Systems (CES) Inc. The GG operations was originally tested in Feb 2003 and is currently (Feb 2005) undergoing extensive commissioning at the CES 5MW Kimberlina Test Plant, near Bakersfield, California. The ZENG P&D Plant will be an important next step in an accelerating path towards demonstrating large-scale (+200 MW) commercial implementation of zero-emission power plants before the end of this decade. However, development work also entails having a detailed commercial understanding of the techno-economic potential for such power plant cycles: specifically in an environment where the future penalty for carbon dioxide (CO2) emissions remains uncertain. Work done in dialogue with suppliers during ZENG Project Phase-1 has cost-estimated all major plant components to a level commensurate with engineering pre-screening. The study has also identified several features of the proposed power plant that has enabled improvements in thermodynamic efficiency from 37% up to present level of 44–46% without compromising the criteria of implementation using “near-term” available technology. The work has investigated: i. Integration between the cryogenic air separation unit (ASU) and the power plant. ii. Use of gas turbine technology for the intermediate pressure (IP) steam turbine. iii. Optimal use of turbo-expanders and heat-exchangers to mitigate the power consumption incurred for oxygen production. iv. Improved condenser design for more efficient CO2 separation and removal. v. Sensitivity of process design criteria to “small” variations in modeling of the physical properties for CO2/steam working fluid near saturation. vi. Use of a second “conventional” pure steam Rankine bottoming cycle. In future analysis, not all these improvements need necessarily be seen to be cost-effective when taking into account total P&D program objectives; thermodynamic efficiency, power plant investment, operations and maintenance cost. However, they do represent important considerations towards “total” optimization when designing the P&D Plant. We observe that Project Phase-2: Pre-Engineering & Qualification should focus on optimization of plant size with respect to total capital investment (CAPEX); and identification of further opportunities for extended technology migration from gas turbine environment that could also permit raised turbine inlet temperatures (TIT).

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