Performance Prediction of Gas Turbine Under Different Strategies

Proceedings of ASME Turbo Expo 2013: Turbine Technical Conference and Exposition GT2013 June 3-7, 2013, San Antonio, Texas, USA

GT2013-96013

PERFORMANCE PREDICTION OF GAS TURBINE UNDER DIFFERENT STRATEGIES USING LOW HEATING VALUE FUEL

Edson Batista da Silva [email protected] Instituto Tecnológico de Aeronáutica São José dos Campos, São Paulo, Brazil

Marcelo Assato [email protected] Vale Soluções em Energia São José dos Campos, São Paulo, Brazil

ABSTRACT Usually, the turbogenerators are designed to fire a specific fuel, depending on the project of these engines may be allowed the operation with other kinds of fuel compositions. However, it is necessary a careful evaluation of the operational behavior and performance of them due to conversion, for example, from natural gas to different low heating value fuels. Thus, this work describes strategies used to simulate the performance of a single shaft industrial gas turbine designed to operate with natural gas when firing low heating value fuel, such as biomass fuel from gasification process or blast furnace gas (BFG). Air bled from the compressor and variable compressor geometry have been used as key strategies by this paper. Off-design performance simulations at a variety of ambient temperature conditions are described. It was observed the necessity for recovering the surge margin; both techniques showed good solutions to achieve the same level of safe operation in relation to the original engine. Finally, a flammability limit analysis in terms of the equivalence ratio was done. This analysis has the objective of verifying if the combustor will operate using the low heating value fuel. For the most engine operation cases investigated, the values were inside from minimum and maximum equivalence ratio range.

HR LHV NGV P PW PZ T V-IGV W WF

Rosiane Cristina de Lima [email protected] Vale Soluções em Energia São José dos Campos, São Paulo, Brazil

Heat Rate Lower Heating Value Nozzle Guide Vane Pressure Power Output Primary Zone Temperature Variable-Inlet Guide Vane Mass flow Fuel flow

Greek Symbols ϕ Equivalence ratio η Efficiency

Subscripts corr corrected value ds design point std standard day, ISO conditions stoic stoichiometric

INTRODUCTION Keywords: Gas turbine performance simulation, Low heating value fuel, Off-design operation, Flammability limit analysis, Fuels from gasification process NOMENCLATURE Abbreviations BDG Biomass Derived Gas BIGCC Biomass Integrated Gasifier Combined Cycles FAR Fuel Air Ratio GGT Generic Gas Turbine

Nowadays, there is a growing demand for new fuel sources, such as ethanol, biodiesel from vegetable sources, and gaseous fuels derived from the gasification process of biomass. Overall, these fuels are cheaper than the higher calorific value fuels. Fuel cost is an important factor from an economic standpoint for ensuring a viable power generation using gas turbines. Together with the technical problems, economic and environmental issues, researchers and engineers are working to develop new gas turbines capable of operating with flexible multi-fuels, and using fuels of low heating value, Ernst [1].

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Palmer and others in 1993 were already expending efforts to simulate the performance and operational behavior of commercial gas turbines using low heating value fuels. Palmer et al. [2] found a considerable increase of air mass flow and as a result a significant reduction of the compressor surge margin, leaving to the hazardous operation zone. Therefore, they concluded that for a safe operation of the engine, it would be necessary to apply some strategy for recovering the surge margin to safe limits. Following the research with low heating value fuels, but using another commercial gas turbine, Palmer et al. [3] assumed the bleed air as a surge margin recovery approach to recommended limits. For the engine analyzed, 15% of compressed air extraction was required. This way, the efficiency would be slightly increased, and the operational costs would be considerably reduced using the low heating value fuels. Furthermore, the air extracted can be tapped into gasification process in the combined cycles. Malkogianni et al. [4] developed a gas turbine model to analyze the performance at design and off-design conditions using four different gaseous fuels with high, medium and low calorific values. They also found a high augment in the air mass flow increasing the combustion chamber pressure. Hence, they accomplished that some strategy to recover the compressor surge margin should be adopted. Johnson [5] used a gas turbine performance model to analyze the operation conditions when the design fuel is changed by a medium calorific value one. The simulations showed that the turbine inlet section area is blocked forcing the decrease of the compressor surge margin. They investigated five strategies to recuperate the safe operation conditions, as the main strategies can be cited the actuation of the V-IGV and redesign of the turbine inlet section area. As a result, they could achieve an augment of 15% in the output power using a syngas. Rodrigues et al. [6] carried out a performance evaluation of atmospheric BIGCC systems operating under different strategies for the use of gaseous fuel from biomass derived gas (BDG). The analysis showed both advantages and drawbacks in a comparison among the applied strategies, and they displayed that the retrofit of the expander inlet nozzle was the best approach. The present study adopts a generic single shaft gas turbine (named by GGT) designed to operate with natural gas in order to analyze the performance and the operational behavior when the gas natural is converted to a low heating value fuel. A performance model was built using GasTurb 11® (Kurzke [7]) to reproduce the GGT’s design and off-design operation conditions. Two strategies to guarantee the compressor safe operation were compared, (i) air extraction at compressor discharge, and (ii) variable inlet guide vane technique. Beyond, one operational feature of the combustion chamber was evaluated taking into account flammability limits, according to procedure established by Sawyer [8].

2. GAS TURBINE PERFORMANCE The single shaft gas turbine (GGT) used in this work is composed of an axial compressor equipped with a bleed air port in its discharge, an annular combustion chamber and a staged axial turbine with first stage cooled. Figure 1 shows a representative single shaft gas turbine configuration and its thermodynamics stations assumed herein. The nomenclatures are based on the international standard SAE [9].

Sections Descriptions 2 Compressor inlet 3 Compressor exit 31 Combustion chamber inlet 4 Combustion chamber exit 41 Turbine rotor inlet 5 Turbine exit 6 Turbine diffuser exit 8 Exhaust duct Figure 1. Typical single shaft gas turbine, Kurzke [7]. The datasheet parameters of the GGT operating with natural gas and engine’s general specifications are presented in Table 1. Further information such as: compressor and turbine isentropic efficiencies, combustion chamber pressure drop, combustion chamber exit temperature, compressor bleed percentage, mechanical efficiency, reduction drive efficiency and generator efficiency, and others, were assumed to build the computational model in order to achieve the same design point data from GGT. The assumed values will be presented in methodology section. Table 1. Generic Single Shaft Gas Turbine (GGT) data, ISO conditions [10]. Performance Output Power PW 3,515 kWe Heat Rate HR 12,920 kJ/kWe-hr Engine Efficiency ηGGT 27.86 % Exhaust flow W8 19.0 kg/sec Exhaust temp. T8 455.0 °C General specifications Axial Compressor, 11 stages - inlet airflow = 18.4 kg/sec - Pressure ratio = 9.7:1 Axial Turbine, 3 stages - speed = 14,950 rpm

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The relations at design point and off-design conditions of GGT used to adjust the model are shown in Tab. 2. Table 2. Generic Gas Turbine (GGT) off-design data. HR ηGGT WF T2 PW [°C] [kWe] [kJ/kW-h] [-] [kg/s] -7.5 4056 12544.6 0.2870 0.29445 0 3885 12650.1 0.2846 0.28441 8 3694 12787.3 0.2815 0.27336 15 3515 12920.2 0.2786 0.26282 23 3320 13156.5 0.2736 0.25278 30 3152 13388.6 0.2689 0.24422 37.5 2970 13694.6 0.2629 0.23538 43 2820 13990.0 0.2573 0.22831 Note 1: All pressures and temperatures described in the current work represent total (or stagnation) values. For the static values will be mentioned in the text, for example, static pressure (PS) and static temperature (TS). Engine efficiency and fuel mass flow varying with the ambient temperature (T2) were obtained as a function of heat rate and output power as well, equations (1) and (2).

3600 HR [kJ / kW h]

PW [kW ] Fuel flow = WF [kg / s] = ηGGT [−] * LHV [kJ / kg ]

Table 3. Design point: comparison between the reference engine (GGT) and present results. Present Deviations Parameters Units GGT Results [%] T2 [K] 288.15 288.15 PW [kWe] 3515.0 3515.0 0 HR [kJ/kWe-h] 12920.2 12920.2 0 ηnet [%] 0.2786 0.2786 0 WF [kg/s] 0.2628 0.2628 0 T8 [K] 731.15 731.18 -0.03 The current gas turbine model was adjusted at off-design conditions taking into account the variation in ambient temperature, the range adopted was from 265.65 K (-7.5°C) to 316.15 K (+43°C). In Figure 2 are shown the power output and heat rate versus ambient temperature of the current model against the reference engine (GGT). The data in continue lines are from GGT and the points on the lines are the data from the present results; small deviations were found due to the unavailability of the actual performance maps of the compressor and turbine, requiring some adjustments in the generic ones. 4300

(1)

14300

Reference Engine (GGT) Present Results

4100

Power Output [kWe]

Engine Net Efficiency = ηGGT [−] =

to 48,000 kJ/kg at ISO conditions (ISO 2533 [10]) at design point. Table 3 shows a comparison between the reference engine (GGT) and the current results at the design point; negligible deviations can be observed for all compared parameters.

(2)

The fuel composition used in this work is based on Palmer et al. [2], and it is showed below in mole percentage. The lower heating value (LHV) for the Fuel 1 is 4867.4 kJ/kg.

3900

14100 13900

Power Output

3700

13700

3500

13500

3300

13300

3100

13100

2900

12900

Heat Rate

2700

12700

2500

Heat Rate [kJ/kW-hr]

Nominal rating – per ISO, at 15°C, sea level, relative humidity 60% No inlet/exhaust losses; Natural gas with LHV=48 MJ/kg; No accessory losses

12500 265 270 275 280 285 290 295 300 305 310 315 320

Fuel 1: 11.86% H2; 17.69% CO; 11.00% CO2; 4.22% CH4; 0.59% C2H4; 15.43% H2O; 39.16% N2; 0.05% NH3. DESIGN AND OFF-DESIGN MODELS In order to minimize the development costs in an effective manner, it is necessary to develop analytical tools, which permit a study of the engine behavior before its production, preventing possible malfunctions or design problems. The model will provide good approaches as soon as the model calibration process is well performed; therefore this procedure is extremely important. Some values must be initially guessed, and improved by a trial, as part of the procedure to build it. Firstly, for calibration purpose, the computational simulations were conducted using natural gas with a LHV equal

Ambient Temperature [K]

Figure 2. Power output and heat rate. After the calibration process of the design point model and also the adjustments on the “standard” components maps to become the off-design performance model a quite similar of the GGT, the next step is to evaluate the operational behavior in terms of the safety when the fuel is changed by a low heating value. Figure 3 illustrates that, the surge margin is reduced when Fuel 1 is working, compared with the natural gas. In this way, the gas turbine operation becomes hazardous owing to the proximity of the operating line to the compressor surge line. It was noted that the gas turbine operating line is too close the surge line, 5 % of margin, representing an unsafe operation. It

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occurs due to the increasing fuel flow and consequently increases of compressor pressure ratio. Hence, in order to banish the surge margin trouble in all operating points, two control strategies to bring back the surge margin to an adequate limit will be applied and contrasted.

቎

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ೃ೅ ೘ሶ ට ೔೙ ቇ ೛೔೙ ം ವು

ቆ

൥

ቆ

೛ ൬ ೚ೠ೟ ିଵ൰

೛೔೙ ೛ ൬ ೚ೠ೟ ିଵ൰ ೛೔೙ ವು

቏ = ܽ቎

൩ = ܾ൥

ೃ೅ ೘ሶ ට ೔೙ ቇ ೛೔೙ ം

ೃ೅ ೘ሶ ට ೔೙ ቇ ೛೔೙ ം ವು

೛ ൬ ೚ೠ೟ ିଵ൰ ೛೔೙

೛ ൬ ೚ೠ೟ ିଵ൰

ቂሺఎሻ ቃ = ܿ ቂሺఎሻ ቃ ሺఎሻ

ቆ

ቆ

ሺఎሻ

೛೔೙

൩

቏

(3) ௡

(4)

ವು ௡

(5)

ವು ௡

ವು

where: n: refers to original map data performance; DP: refers to data from the design point; a, b, c: correction factors.

Figure 3. Effects over the surge margin when burning Fuel 1.

METHODOLOGY FOR SURGE MARGIN RECOVERING In this work two strategies are investigated for surge margin recovering and, thus, the turbine gas can operate in safe conditions using the low heating value fuel. First strategy adopted consists in extracting a portion of air at the compressor discharge. Palmer et al. [3] used this strategy with extracting of 15% of compressed air. For the present study an air extraction of 12% is sufficient to recovery the surge margin to the same value of natural gas. Second strategy was proposed by Johnson [5] in operating the compressor with the inlet guide vanes partially closed. In this approach the compressor inlet stator vanes are closed slightly in order to decrease the air mass flow through the gas turbine. With the air reduction inside gas turbine, the compressor pressure ratio is reduced; hence, the surge margin is recovered. In our studies, a closing of 9.06 degree of the V-IGV’s led the surge margin approximately equal to that of the natural gas case. For creating performance models of gas turbine that employ compressor variable inlet stator vanes, but not have geometric data available, it is possible to use a method that involves using correction factors that are functions of the geometry variation. This methodology assumes that each new position of V-IGV’s represents a new compressor with a new design point and the characteristics map is shifted to describe this new operating condition. Celis et al. [11] presented equations that can be used to estimate these correction factors:

Note that these correction factors impose the relationship between compressor original map parameters and the obtained ones after varying the component geometry, and that each correction factor relates a map parameter, i.e., the mass flow, pressure ratio and efficiency. Also, the correction factors determine the displacement intensity in the maps with the VIGV’s angles. In Celis et al. [11], the values of a, b and c were adjusted to shift the compressor map and to match with operation available data of a power plant. The correction factors adopted during simulation can be approximated in according to Kurzke [7]: ܽ=

ܾ= ܿ=

ఋ௠ሶሾ%ሿ

ఋ௏ூீ௏ሾ°ሿ

(6)

೛ ఋ൬ ೚ೠ೟ ିଵ൰ሾ%ሿ ೛೔೙


(7)

ఋఎሾ%ሿ


(8)

The efficiency correction is calculated using a quadratic function: ߟ = ߟ௠௔௣ ቀ1 − ߜܸ‫ ܸܩܫ‬ଶ

௖

ଵ଴଴

ቁ

(9)

For this work, no exist operation data from GGT with actuation of IGV, so, it has been assumed the values, a = 1; b = 0.5 and c=0. ANALYSIS OF THE RESULTS FOR FULL LOAD OPERATION VERSUS AMBIENT TEMPERATURE In this section are presented the results obtained using natural gas and low LHV fuel, called by Fuel 1. The simulations for the maximum capacity in generating electric power at several ambient temperatures were done. For the Fuel 1 the strategies for surge margin recovering were used. For the first strategy 12% air extraction at the compressor discharge

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was used, while that for the second strategy a VIGVs closing of 9.06 degree was adjusted during the simulations. Figure 4 shows the increase of the surge margin with increasing of air extraction percentage at compressor discharge. For the air extraction equal to 12% the surge margin achieves the value of 24.8 %.

Figure 6. Output power variation in function of VIGVs closing angle.

Figure 4. Surge margin recovered in function of air extraction percentage at compressor discharge Figure 5 shows the increase of the surge margin with closing of the VIGVs angle. For the VIGVs angle equal to 9.06% the surge margin achieves the same value of the natural gas of 24.05 %. Figure 7. Heat rate variation in function of VIGVs closing angle. Figure 8 shows the surge margin behavior simulated using natural gas and Fuel 1 in function of ambient temperature from 268.15 [K] to 318.15 [K]. Note that in both strategies the surge margin was recovered from 5.3% (without strategy) to approximately the same value that of the natural gas, i.e., 24.8% and 24.05%, respectively, for the first and second strategy.

Figure 5. Surge margin recovered in function of VIGVs closing angle. Figure 6 and Figure 7 present, respectively, the output power and heat rate variation with closing of the V-IGV’s angle. Note that the variation is small for the both parameters investigated, i.e., the penalty is small with variation of the VIGVs angle closing. For the V-IGV’s angle equal to 9.06% the output power and heat rate achieve the values of 4537.4 [kWe] and 11330.4 [kJ/kWe-h], respectively.

Figure 8. Surge margin versus ambient temperature, comparison between natural gas and Fuel 1 with strategies.

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Figure 9 presents the output power values obtained using natural gas and Fuel 1 in function of ambient temperature. It´s possible observe that when the strategies were applied higher output power can be generated using the Fuel 1. Net output power can be increased on the order of 3.6% and 29.1% when firing the Fuel 1, respectively, using the air extraction and VIGV’s closing.

standard day temperature, while fuel consumption increased on the order of 10.7 times and 11.2 times on natural gas value when firing the fuel 1, respectively, using the air extraction and V-IGV’s closing. This significant increase in the fuel flow implies an increase of the net output power due to the advantageous increase in the ratio of the expander-tocompressor mass flow rates.

Figure 9. Output Power using natural gas and Fuel 1 with strategies versus ambient temperature.

Figure 11. Fuel Flow using natural gas and Fuel 1 with strategies versus ambient temperature.

Figure 10 shows the heat rate variation predicted using natural gas and Fuel 1 in function of ambient temperature. As can be noted different heat rate values were obtained using the strategies for the Fuel 1. When firing the low LHV fuel and using the air extraction strategy higher heat rate values were obtained in relation to natural gas, approximately of 4.8% higher at standard day condition. For the VIGVs strategy was observed better results with a decreasing of heat rate of approximately of -12.3% in relation to natural gas at standard day temperature.

FLAMMABILITY LIMIT ANALYSIS In this section, it will be presented analysis of the flammability limits in order to verify if the combustor will operate with the Fuel 1 without redesign. For comparison among fuels with different calorific values, it is recommended to analyze the mixture strength in terms of the equivalence ratio ϕ inside the primary zone (PZ) of the combustion chamber. In this study, it will be applied the methodology described indepth in Sawyer [8]. The equivalence ratio ϕ means: actual fuel/air ratio divided by the stoichiometric fuel/air ratio, equation (10). Thus, for all fuels ϕ = 1 denotes a stoichiometric mixture, whereas a value of ϕ < 1 indicates a lean mixture, finally a value of ϕ > 1 indicates a rich mixture.

φ=

FAR actual FAR stoic

(10)

According to Sawyer [8], the primary zone is designed to use between 14 and 24% of the total air, then the combustor should remain lit at the major operating conditions. Hence, in this work, it will be assumed for all cases 23% of the total air. Figure 10. Heat Rate using natural gas and Fuel 1 with strategies versus ambient temperature. Figure 11 presents the fuel consumption variation simulated using natural gas and Fuel 1 in function of the ambient temperature. Notice that the fuel consumption is expressive when the low LHV fuel is used in comparison with natural gas. The fuel flow using natural gas is of 0.263 [kg/s] at

WF φ PZ =

(0.23 * W 3) = FAR PZ FAR stoic FAR stoic

(11)

where PZ means primary zone. A simplest way to obtain the appropriate value of ϕPZ for most hydrocarbon gases burning in air, examination of the

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determined flame limit temperatures for weak mixtures (assuming no quenching at the wall) shows that they lie around 1600 K. Thus, the limiting equivalence ratio (weak mixture) corresponding to any condition will be given by a mixture having a temperature rise of (1600 – T3). The corresponding rich extinction value is obtained in a similar way. Following the method above, it was established two correlations to analyze the flammability limits for the Fuel 1, one for ϕmin (equation 12) and other for ϕmax (equation 13) as a function of the compressor exit temperature (T3). These correlations are applicable to the range 200 ≤ T3 [K] ≤ 618 :

φ max = 4.25E - 06 * x 2 + 1.01E - 03 * x + 1.19, where x = T3 [K]

(13)

The equivalence ratio inside the combustor primary zone (ϕPZ) was analyzed for five cases taking into account some extreme operating conditions for both strategies to recovery the surge margin, the air extraction and the V-IGV. The results are presented in Table 4 and Table 5, for the air extraction and VIGV, respectively. In addition, they are illustrated in Figure 12 and Figure 13. As can be seen in Table 4 and Table 5, there is an extremely wide operating range that the gas turbine combustor can operate despite of changing of the fuel by a low heating value one, this leads to the important concept that the gas turbine combustor operates with nearly constant air velocities at all loads. Table 4. Equivalence ratio considering 12 % of air extraction as strategy for surge margin recovering. Cases Operation ϕmin ϕPZ ϕmax 100% load, Case 1: 100% speed 0.1791 1.1991 3.2636 Std day 100% load Case 2: 100% speed 0.1956 1.1913 3.1564 Cold day 100% load Case 3: 100% speed 0.1546 1.1958 3.4325 Hot day 0% load Case 4: 100% speed 0.2112 0.3918 3.0603 Std day 0% load Case 5: 70% speed 0.3241 0.3985 2.4782 Std day

Case 9: Case 10:

100% load 100% speed Cold day 100% load 100% speed Hot day 0% load 100% speed Std day 0% load 70% speed Std day

0.1887

1.1800

3.2006

0.1475

1.1927

3.4838

0.2093

0.2595

3.0717

0.3235

0.2782

2.4809

As pointed up in Figure 12 and Figure 13, the first three cases, which burn with rich mixture, do not present operation trouble, whereas the last two cases require care. Due to lean mixture, in most cases the ϕPZ is quite close to the inferior limit. For the first strategy, air extraction, in all cases analyzed the ϕPZ is between the ϕmin and ϕmax, only the Case 5 inspires care. For the second strategy applied, V-IGV technique, in all cases analyzed the ϕPZ is between the ϕmin and ϕmax, except the last case, Case 10, which presents ϕPZ less than ϕmin, as evidenced for Figure 13. From these analysis, it can be suggested that during the engine startup and accelerating procedures can be used the original fuel (natural gas) and after that the engine reaches the nominal rotational speed (100% speed) the fuel can be switched to low heating value fuel. 4,0 3,5 3,0 2,5

PHI

where x = T3 [K]

(12)

Case 8:

PHI_min PHI_(ZP) PHI_max

2,0 1,5 1,0 0,5 0,0

Figure 12. Equivalence ratio considering 12 % of air extraction as strategy for surge margin recovering. 4,0 3,5 3,0 2,5

PHI

φ min = 6.30E - 07 * x 2 - 1.65E - 03 * x + 0.933,

Case 7:

PHI_min PHI_(ZP) PHI_max

2,0 1,5 1,0

Table 5. Equivalence ratio considering 9.06° V-IGV closing as strategy for surge margin recovering. Cases Operation ϕmin ϕPZ ϕmax 100% load Case 6: 100% speed 0.1719 1.1918 3.3120 Std day

0,5 0,0

Figure 13. Equivalence ratio considering 9.06° V-IGV closing as strategy for surge margin recovering.

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Still, according to Sawyer [8], to design for minimum smoke, CO, and HC, it is desirable that the primary zone equivalence ratio never be richer than 1.5 at any single operating condition. Considering the criteria even above, all analyzed cases are inside the flammability limits. CONCLUSIONS Procedures were described to simulate the performance of a gas turbine originally designed to fire natural gas and then evaluate it working with a low heating value fuel. It was found as a primary difficult an expressive surge margin reduction indicating a dangerous operation condition when the low heating value fuel is used. Thus, two strategies for surge margin recovering were adopted. For the first strategy was assumed an air extraction of 12% at the compressor discharge. The second strategy used in this study was to rotate the V-IGV’s up to a closing angle of 9.06°. The obtained results have shown that using the strategies, the surge margin has been recovered and the gas turbine combustor could operate inside of the flammability limits for the Fuel 1. Therefore, according to the performed analysis the gas turbine can operate, and further the simulation results have indicated that when firing the Fuel 1, the output power can be increased of 3.6% using the air extraction strategy and 29.1% applying V-IGV’s closing. This occurs due to the advantageous increase in the ratio of the expander-to-compressor mass flow rates. Also, it is possible to obtain advantages in relation to heat rate where the results showed a decreasing of approximately 12.3% in relation to natural gas at standard day temperature using V-IGV’s technique. Considering the flammability limit analysis, all analyzed cases have an extremely wide operating range. Two cases, Case 4 and 5, of air extraction inspire care, because they are fairly close to the ϕmin. Despite the V-IGV technique to represent the best strategy in terms of performance, it was identified a ϕPZ out of range, Case 10, which works with 0% load and 70% speed at a standard day condition. In these cases, which request attention, it may be required a start–up fuel.

Gas Turbine Utilizing Low Heating Values Fuels,” ASME Cogen Turbo Power, pp. 1-10. [4] Malkogianni, A. K., Tourlidakis, A., and Polyzakis, A. L., 2009, “Single and Two Shaft Gas Turbine Configurations Performance Analysis, Using Different Types of Fuels.” ASME Turbo Expo, GT2009-59805, pp. 1-7. [5] Johnson, M. S., 1992, “Prediction of Gas Turbine On - and Off-Design Performance When Firing Coal-Derived Syngas.” International Gas Turbine: international journal of Engineering for Gas Turbine and Power, ASME, 114, pp. 380 - 385. [6] Rodrigures, M., Walter, A., Faaij, A., 2006, “Performance evaluation of atmospheric biomass integrated gasifier combined cycle system under different strategies for the use of low calorific gases.” Elsevier, pp. 1289-1301. [7] Kurzke, J., 2007. Gas Turb 11, Design and Off-Design Performance of Gas Turbine, Germany. [8] Sawyer, J.W., 1985, Sawyer’s Gas Turbine Engineering Handbook, 1, Theory & Design, Turbomachinery International Publications, Connecticut. [9] SAE AS755D, 2009, (R) Aircraft Propulsion System Performance Station Designation and Nomenclature. [10] ISO 2533, International Organization for Standardization, Standard Atmosphere. [11] Celis, C., Ribeiro Pinto, P, Barbosa, R. S., Ferreira, S. B., “Modeling of variable inlet guide vanes affects on a one shaft industrial gas turbine used in a combined cycle application”. In: ASME TURBO EXPO, GT2008-50076, 2008, Berlin.

ACKNOWLEDGMENTS VSE (Vale Soluções em Energia S.A.), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and CAPES (Coordenação do Aperfeiçoamento do Pessoal de Nível Superior) are acknowledged for their support to the research carried out at the Center of Reference on Gas Turbines (ITA). REFERENCES [1] Ernst, Y., 2011, “BP Statistical Review of World Energy.” BP, London, Review 2010, pp. 45. [2] Palmer, C. A., Erbes, M. R., and Pechtl, P. A., 1993, “Gatecycle Performance Analysis of the LM2500 Gas Turbine Utilizing Low Heating Value Fuels,” ASME Cogen-Turbo Power, IGTI, 8, pp. 1-8. [3] Palmer, C. A., and Erbes, M. R., 1994, “Simulation Methods Used to Analyze the Performance of the GE PG6541B

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