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Title: NUMERICAL SIMULATIONS OF THE EFFECTS OF CHANGING FUEL FOR TURBINES FIRED BY NATURAL GAS AND SYNGAS

Abstract

Gas turbines in integrated gasification combined cycle (IGCC) power plants burn a fuel gas (syngas) in which the proportions of hydrocarbons, H2, CO, water vapor, and minor impurity levels may vary significantly from those in natural gas, depending on the input feed to the gasifier and the gasification process. A data structure and computational methodology is presented for the numerical simulation of a turbine thermodynamic cycle for various fuel types, air/fuel ratios, and coolant flow rates. The approach used allowed efficient handling of turbine components and different variable constraints due to fuel changes. Examples are presented for a turbine with four stages and cooled blades. The blades were considered to be cooled in an open circuit, with air provided from appropriate compressor stages. Results are presented for the temperatures of the hot gas, alloy surface (coating-superalloy interface), and coolant, as well as for cooling flow rates. Based on the results of the numerical simulations, values were calculated for the fuel flow rates, airflow ratios, and coolant flow rates required to maintain the superalloy in the first stage blade at the desired temperature when the fuel was changed from natural gas (NG) to syngas (SG). One NG case was conducted tomore » assess the effect of coolant pressure matching between the compressor extraction points and corresponding turbine injection points. It was found that pressure matching is a feature that must be considered for high combustion temperatures. The first series of SG simulations was conducted using the same inlet mass flow and pressure ratios as those for the NG case. The results showed that higher coolant flow rates and a larger number of cooled turbine rows were needed for the SG case. Thus, for this first case, the turbine size would be different for SG than for NG. In order to maintain the original turbine configuration (i.e., geometry, diameters, blade heights, angles, and cooling circuit characteristics) for the SG simulations, a second series of simulations was carried out by varying the inlet mass flow while keeping constant the pressure ratios and the amount of hot gas passing the first vane of the turbine. The effect of turbine matching between the NG and SG cases was approximately 10 C, and 8 to 14% for rotor inlet temperature and total cooling flows, respectively. These results indicate that turbine-compressor matching, before and after fuel change, must be included in turbine models. The last stage of the turbine, for the SG case, experienced higher inner wall temperatures than the corresponding case for NG, with the temperature of the vane approaching the maximum allowable limit. This paper was published by ASME as paper no. GT2007-27530.« less

Authors:
 [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
Work for Others (WFO)
OSTI Identifier:
932165
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: 2007 ASME Turbo Expo, Montreal, Canada, 20070514, 20070514
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 36 MATERIALS SCIENCE; COMBINED CYCLES; FLOW RATE; FUEL GAS; GAS TURBINES; HEAT RESISTING ALLOYS; NATURAL GAS; POWER PLANTS; THERMODYNAMIC CYCLES; TURBINES; WATER VAPOR

Citation Formats

Sabau, Adrian S, and Wright, Ian G. NUMERICAL SIMULATIONS OF THE EFFECTS OF CHANGING FUEL FOR TURBINES FIRED BY NATURAL GAS AND SYNGAS. United States: N. p., 2007. Web.
Sabau, Adrian S, & Wright, Ian G. NUMERICAL SIMULATIONS OF THE EFFECTS OF CHANGING FUEL FOR TURBINES FIRED BY NATURAL GAS AND SYNGAS. United States.
Sabau, Adrian S, and Wright, Ian G. Mon . "NUMERICAL SIMULATIONS OF THE EFFECTS OF CHANGING FUEL FOR TURBINES FIRED BY NATURAL GAS AND SYNGAS". United States. doi:.
@article{osti_932165,
title = {NUMERICAL SIMULATIONS OF THE EFFECTS OF CHANGING FUEL FOR TURBINES FIRED BY NATURAL GAS AND SYNGAS},
author = {Sabau, Adrian S and Wright, Ian G},
abstractNote = {Gas turbines in integrated gasification combined cycle (IGCC) power plants burn a fuel gas (syngas) in which the proportions of hydrocarbons, H2, CO, water vapor, and minor impurity levels may vary significantly from those in natural gas, depending on the input feed to the gasifier and the gasification process. A data structure and computational methodology is presented for the numerical simulation of a turbine thermodynamic cycle for various fuel types, air/fuel ratios, and coolant flow rates. The approach used allowed efficient handling of turbine components and different variable constraints due to fuel changes. Examples are presented for a turbine with four stages and cooled blades. The blades were considered to be cooled in an open circuit, with air provided from appropriate compressor stages. Results are presented for the temperatures of the hot gas, alloy surface (coating-superalloy interface), and coolant, as well as for cooling flow rates. Based on the results of the numerical simulations, values were calculated for the fuel flow rates, airflow ratios, and coolant flow rates required to maintain the superalloy in the first stage blade at the desired temperature when the fuel was changed from natural gas (NG) to syngas (SG). One NG case was conducted to assess the effect of coolant pressure matching between the compressor extraction points and corresponding turbine injection points. It was found that pressure matching is a feature that must be considered for high combustion temperatures. The first series of SG simulations was conducted using the same inlet mass flow and pressure ratios as those for the NG case. The results showed that higher coolant flow rates and a larger number of cooled turbine rows were needed for the SG case. Thus, for this first case, the turbine size would be different for SG than for NG. In order to maintain the original turbine configuration (i.e., geometry, diameters, blade heights, angles, and cooling circuit characteristics) for the SG simulations, a second series of simulations was carried out by varying the inlet mass flow while keeping constant the pressure ratios and the amount of hot gas passing the first vane of the turbine. The effect of turbine matching between the NG and SG cases was approximately 10 C, and 8 to 14% for rotor inlet temperature and total cooling flows, respectively. These results indicate that turbine-compressor matching, before and after fuel change, must be included in turbine models. The last stage of the turbine, for the SG case, experienced higher inner wall temperatures than the corresponding case for NG, with the temperature of the vane approaching the maximum allowable limit. This paper was published by ASME as paper no. GT2007-27530.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

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  • Gas turbines in integrated gasification combined cycle power plants burn a fuel gas (syngas) in which the proportions of hydrocarbons, H2, CO, water vapor, and minor impurity levels may differ significantly from those in natural gas. Such differences can yield changes in the temperature, pressure, and corrosive species that are experienced by critical components in the hot gas path, with important implications in the design, operation, and reliability of the turbine. A new data structure and computational methodology is presented for the numerical simulation of a turbine thermodynamic cycle for various fuel types. The approach used allows efficient handling ofmore » turbine components and different variable constraints due to fuel changes. Examples are presented for a turbine with four stages. The vanes and blades were considered to be cooled in an open circuit, with air provided from the appropriate compressor stages. A constraint was placed on the maximum metal temperature and values were calculated for the fuel flow rates, airflow ratios, and coolant flow rates for cases where the turbine was fired with natural gas, NG, or syngas, SG. One NG case was conducted to assess the effect of coolant pressure matching between the compressor extraction points and corresponding turbine injection points. It was found that pressure matching is a feature that must be considered for high combustion temperatures. The first series of SG simulations was conducted using the same inlet mass flow and pressure ratios as those for the NG case. The results showed that higher coolant flow rates and a larger number of cooled turbine rows were needed for the SG case to comply with imposed temperature constraint. Thus, for this first case, the turbine size would be different for SG than for NG. In order to maintain the original turbine configuration (i.e., geometry, diameters, blade heights, angles, and cooling circuit characteristics) for the SG simulations, a second series of simulations was carried out in which the inlet mass flow was varied while keeping constant the pressure ratios and the amount of hot gas passing the first vane of the turbine. The effects of turbine matching between the NG and SG cases were increases for the SG case of approximately 7 and 13 % for total cooling flows and cooling flows for the first vane, respectively. In particular, for the SG case, the vane in the last stage of the turbine experienced inner wall temperatures that approached the maximum allowable limit.« less
  • Today`s combustion turbine systems feature high fuel-to-electricity efficiencies. On a lower heating value (LHV) basis, net efficiencies for natural-gas-fired combined cycles are being demonstrated in the 54 to 55% range. Combustion turbines have been introduced that are expected to have combined cycle efficiencies at 58%. Within the U.S. Department of Energy`s Advanced Turbine Systems program, combined cycle net efficiencies are to exceed 60%. Cycle innovations, plus combustion turbine technology advancements are needed to achieve the 60% efficiency. This paper reviews and explores some of the cycle innovations and design improvements that are required to meet and exceed the 60% plateau.more » Hardware and cycle concepts to be discussed include Advanced Turbine Systems, thermochemical recuperation, partial oxidation, solid oxide fuel cell integration and combustion turbines that are fueled with 100% hydrogen. 11 refs., 1 tab.« less
  • Gas turbine manufacturers are driven by the marketplace to continually achieve the optimal balance of output efficiency, cost, flexibility, RAM-D (reliability, availability, maintainability, durability), and environmental performance. Thus, manufacturers must manage the introduction of new technology carefully as the risks to both the manufacturer and customers can be quite large. Advancements in turbine emission control systems must prove to be reliable and cost effective prior to any technology's introduction into the marketplace. Since the commercial availability of dry-low-NO{sub x} systems(lean-premixed combustion) in the early 1990's, achievable NO{sub x} emission levels have steadily declined. Various emission reduction technologies have been developedmore » successfully, after substantial research and development investment. Gas turbine manufacturers will continue to develop combustion systems that result in lower levels of NO{sub x} as long as the economic impact of the systems can be justified. Permitting small natural gas fired turbines continues to become increasingly more challenging, despite the fact that natural gas fired turbines are the most efficient and lowest emitters of all combustion based power generation technology available today. In July, 1997, EPA Region IX, established Lowest Achievable Emission Rate (LAER) for gas turbines at 2 ppmv on a 3-hour average. In May, 1998, the South Coast Air Quality Management District established Best Available Control Technology (BACT) for gas turbines at 2.5 ppmv on a 15-minute average. At the current time, the LAER emission level is only achievable through add-on exhaust gas clean-up controls. While many NO{sub x} control development projects are ongoing, requiring add-on controls regardless of the uncontrolled NO{sub x} emission level will discourage many manufacturers from continuing the development lower NO{sub x} combustion systems.« less
  • Gas turbines in IGCC plants burn syngas that is composed of hydrocarbons, mixtures of H2 and CO, and also handle diluent gases such as N2, CO2, and steam, which may be injected into the combustor in order to increase the turbine mass flow and reduce NOx emissions. Future developments envision the use of syngas and hydrogen in various proportions as an approach to minimizing carbon emissions. In all such fuel scenarios, it is desirable to use the highest possible turbine rotor inlet temperature (RIT) in order to maximize overall efficiency. However, because of the inherently detrimental effects of maximized RITmore » on the lifetime/reliability of the turbine hot gas path components, as well as the associated complications in combustor design for optimum use of such different fuels, it is desirable to know the effects of fuel composition and combustion conditions on the temperatures experienced by the critical components. This study deals with the accurate prediction of hot gas path component surface and interface temperatures as a function of fuel composition and combustion conditions, which have direct implications for component cooling, the rate of strength degradation of structural components and interaction of coatings with those components, hence the service lifetime of protective coatings. The approach involves integration of thermodynamic models of turbine performance (compressor, combustor) with blade cooling models (with and without thermal barrier coatings). The modular structure of a gas turbine allows straightforward implementation of models for various fuel/combustion scenarios, and for the components of interest. Complications include the requirement for detailed analysis that considers the actual geometrical configurations of some components, in order to increase the accuracy of numerical simulations. Several implementation possibilities are discussed, as well as the current status of the computer program development, which is illustrated by some preliminary results.« less
  • Laboratory experiments have been conducted to investigate the fuel effects on the turbulent premixed flames produced by a gas turbine low-swirl injector (LSI). The lean-blow off limits and flame emissions for seven diluted and undiluted hydrocarbon and hydrogen fuels show that the LSI is capable of supporting stable flames that emit < 5 ppm NO{sub x} ({at} 15% O{sub 2}). Analysis of the velocity statistics shows that the non-reacting and reacting flowfields of the LSI exhibit similarity features. The turbulent flame speeds, S{sub T}, for the hydrocarbon fuels are consistent with those of methane/air flames and correlate linearly with turbulencemore » intensity. The similarity feature and linear S{sub T} correlation provide further support of an analytical model that explains why the LSI flame position does not change with flow velocity. The results also show that the LSI does not need to undergo significant alteration to operate with the hydrocarbon fuels but needs further studies for adaptation to burn diluted H{sub 2} fuels.« less