Alternative Fuels for Combined Cycle Power Plants: An Analysis of Options for a Location in India

: The Sustainable Development Goals 2030 Agenda of United Nations raises the need of clean and a ﬀ ordable energy. In the pathway for more e ﬃ cient and environmentally friendly solutions, new alternative power technologies and energy sources are developed. Among these, the use of syngas fuels for electricity generation can be a viable alternative in areas with high biomass or coal availability. This paper presents the energy, environmental and economic analyses of a modern combined cycle plant with the aim to evaluate the potential for a combined power plant running with alternative fuels. The goal is to identify the optimal design in terms of operating conditions and its environmental impact. Two possible conﬁgurations are investigated in the power plant presented: with the possibility to export or not export steam. An economic analysis is proposed to assess the plant feasibility. The e ﬀ ect of the di ﬀ erent components in its performance is assessed. The impact of using four di ﬀ erent syngases as fuel is evaluated and compared with the natural gas fuelled power cycle. The results show that a better e ﬃ ciency is obtained for the syngas 1 (up to 54%), in respect to the others. Concerning pollutant emissions, the syngas with a GHG impact and lower carbon dioxide (CO 2 ) percentage is syngas 2.


Research Background
Nowadays, the concern for climate change and the limited availability of fossil fuel sources are pushing research to focus on sustainable energy resources. Taken as a reference, 1990 emission limits of Greenhouse Gases (GHGs) concentrations should decrease to 50% until 2050 [1-3]. On this pathway, different policies have been defined in favor of energy production from clean sources [4][5][6] to support Sustainable Development Goals (SDGs) [7].
The optimization of energy production systems including heat, cold and gas, assumes today a fundamental role in the electricity sector [8][9][10][11].
supply to a CHP facility. The optimal working conditions for the production of energy are evaluated and the impact of using syngas fuel in power plant performance is assessed.
Finally, with the aim to highlight the economic benefits of a technical-economic analysis of the plant feasibility, considering an operating plant profile is developed. Several scenarios are discussed, considering different factors of plant utilization, showing the potential interest of the proposed integration.

Location of Geographical Area and Demand Model Definition
Since 2005, an outstanding growth of energy demand has been experienced in India due to several reasons. One of the effects of the fast growth in Indian society has been the increase in electricity demand due to the fact that both industrial and urban areas have grown, and there is an increasing demand of new resources to sustain the economic development.
The potential for production of renewable syngas is strongly linked to the capacity for biomass gasification. The Ministry of New and Renewable Energy of the Government of India has recently reported that the actual availability of biomass in India is about 500 million metric tons per year, estimating a surplus biomass supply of 120-150 million metric tons per annum, referring rural and agricultural traces for a potential of about 18,000 MW [61]. Part of this biomass can be exploited as sustainable raw material for gasification producing alternative fuel for power production. It also can be used as alternative fuel to reduce natural gas supply dependence. In this way, the proper spatial location of biomass can improve the logistic network reducing fuel final costs [62][63][64]. As fossil fuels, biomass energy application will produce pollutant formations, but with adequate application of gasification and power technologies, they will have a lower impact than other fossil fuel sources and power conversion technologies. In this work is studied the installation of a CCPP plant in the city of Gurgaon located at 30 km from the city of Delhi (India) shown in Figure 1a. It is conceived as a Combined Heat and Power plant, where steam is provided to a refinery near the New Delhi area.
Sustainability 2020, 12, x; doi: FOR PEER REVIEW www.mdpi.com/journal/sustainability the production of energy are evaluated and the impact of using syngas fuel in power plant performance is assessed.
Finally, with the aim to highlight the economic benefits of a technical-economic analysis of the plant feasibility, considering an operating plant profile is developed. Several scenarios are discussed, considering different factors of plant utilization, showing the potential interest of the proposed integration.

Location of Geographical Area and Demand Model Definition
Since 2005, an outstanding growth of energy demand has been experienced in India due to several reasons. One of the effects of the fast growth in Indian society has been the increase in electricity demand due to the fact that both industrial and urban areas have grown, and there is an increasing demand of new resources to sustain the economic development.
The potential for production of renewable syngas is strongly linked to the capacity for biomass gasification. The Ministry of New and Renewable Energy of the Government of India has recently reported that the actual availability of biomass in India is about 500 million metric tons per year, estimating a surplus biomass supply of 120-150 million metric tons per annum, referring rural and agricultural traces for a potential of about 18,000 MW [61]. Part of this biomass can be exploited as sustainable raw material for gasification producing alternative fuel for power production. It also can be used as alternative fuel to reduce natural gas supply dependence. In this way, the proper spatial location of biomass can improve the logistic network reducing fuel final costs [62][63][64]. As fossil fuels, biomass energy application will produce pollutant formations, but with adequate application of gasification and power technologies, they will have a lower impact than other fossil fuel sources and power conversion technologies. In this work is studied the installation of a CCPP plant in the city of Gurgaon located at 30 km from the city of Delhi (India) shown in Figure 1a. It is conceived as a Combined Heat and Power plant, where steam is provided to a refinery near the New Delhi area. The position is strategic because the idea is to allow the energy production with low environmental impact near megacities as New Delhi, in a region with a higher availability of  [65]. (b) Biomass energy potential in India (in MWe) [66]. The position is strategic because the idea is to allow the energy production with low environmental impact near megacities as New Delhi, in a region with a higher availability of biomass (crop residues, plantation and manure biomass) and a higher biomass power potential [64]. In Figure 1b, the biomass energy potential in India in year 2016 is reported.

Reference Layout
The reference layout is a CHP combined cycle power plant that provides high pressure steam for processes in an adjacent refinery. It uses the steam to treat crude oil through a series of chemical processes that employ the steam generated. It should be possible to demand up to 80 t/h of steam at a pressure of 102 bars and at a temperature of 445 • C, which can be taken from the high pressure steam just before the entrance to the steam turbine. For the CHP application, the estimated steam demand evolution curve of the steam consumer company is illustrated in Figure 2.

Reference Layout
The reference layout is a CHP combined cycle power plant that provides high pressure steam for processes in an adjacent refinery. It uses the steam to treat crude oil through a series of chemical processes that employ the steam generated. It should be possible to demand up to 80 t/h of steam at a pressure of 102 bars and at a temperature of 445 °C, which can be taken from the high pressure steam just before the entrance to the steam turbine. For the CHP application, the estimated steam demand evolution curve of the steam consumer company is illustrated in Figure 2. The combined cycle rated power is 600 MW with natural gas as main fuel. Figure 3 shows a detailed layout of the CCPP. It has a configuration 2-2-1: 2 gas turbogenerators/2 heat recovery steam generators (HRSG)/1 steam turbogenerator. Gas turbine exhaust gases generate steam at three pressures in the two heat recovery steam generators (HRSG). The boiler configuration also includes two additional evaporators, an intermediate pressure and a low pressure evaporator. Intermediate pressure steam can be mixed with the cold reheating before reheating and the low pressure steam to the turbine after mixing with The combined cycle rated power is 600 MW with natural gas as main fuel. Figure 3 shows a detailed layout of the CCPP. It has a configuration 2-2-1: 2 gas turbogenerators/2 heat recovery steam generators (HRSG)/1 steam turbogenerator.

Reference Layout
The reference layout is a CHP combined cycle power plant that provides high pressure steam for processes in an adjacent refinery. It uses the steam to treat crude oil through a series of chemical processes that employ the steam generated. It should be possible to demand up to 80 t/h of steam at a pressure of 102 bars and at a temperature of 445 °C, which can be taken from the high pressure steam just before the entrance to the steam turbine. For the CHP application, the estimated steam demand evolution curve of the steam consumer company is illustrated in Figure 2. The combined cycle rated power is 600 MW with natural gas as main fuel. Figure 3 shows a detailed layout of the CCPP. It has a configuration 2-2-1: 2 gas turbogenerators/2 heat recovery steam generators (HRSG)/1 steam turbogenerator. Gas turbine exhaust gases generate steam at three pressures in the two heat recovery steam generators (HRSG). The boiler configuration also includes two additional evaporators, an intermediate pressure and a low pressure evaporator. Intermediate pressure steam can be mixed with the cold reheating before reheating and the low pressure steam to the turbine after mixing with the turbine intermediate pressure outlet. The boiler has two economizers in parallel to heat water at  Gas turbine exhaust gases generate steam at three pressures in the two heat recovery steam generators (HRSG). The boiler configuration also includes two additional evaporators, an intermediate pressure and a low pressure evaporator. Intermediate pressure steam can be mixed with the cold reheating before reheating and the low pressure steam to the turbine after mixing with the turbine intermediate pressure outlet. The boiler has two economizers in parallel to heat water at high and at intermediate pressure. At degasifier exhaust, the feedwater is distributed by means of two high and intermediate pressure pumps. A recirculation loop is provided to guarantee the conditions of the inlet water to the first economizer and before the degasifier as well as to control exhaust gases' stack temperature at 90 • C. Economizer water inlet temperature is around 55 • C. The generated steam expands in a three pressures and reheating steam turbine. Live steam enters at turbine at 160 bars and 500 • C. Cooling towers are used as water refrigeration system because of the ambient conditions and water availability. Table 1 reports the main characteristics of the CCPP plant. Gas turbogenerator exhaust gases are used to produce steam in the Heat Recovery Steam Generator (HRSG). Figure 4 illustrates layout for modelling the steam turbine (in Aspen Plus), with detail of main flows for the design of the turbine. As indicated in Figure 4, the S83 source is the main steam inlet from the steam generator. FPT1 gives cold stream conditions and the exit conditions will be those of the heated stream. The source S82 represents low pressure stream from the boiler, and S23 refers to turbine discharge. S7 collects the different sealing streams that will be unified before being sent to the gland steam condenser. Gas turbogenerator exhaust gases are used to produce steam in the Heat Recovery Steam Generator (HRSG). Figure 4 illustrates layout for modelling the steam turbine (in Aspen Plus), with detail of main flows for the design of the turbine. As indicated in Figure 4, the S83 source is the main steam inlet from the steam generator. FPT1 gives cold stream conditions and the exit conditions will be those of the heated stream. The source S82 represents low pressure stream from the boiler, and S23 refers to turbine discharge. S7 collects the different sealing streams that will be unified before being sent to the gland steam condenser.    Table 2 shows energy losses, expressed in energy fraction, in the different elements of the Heat Recovery Steam Generator ( Figure 3) for different design conditions and loads: winter design, summer design, annual average and maximum extreme.   Table 2 shows energy losses, expressed in energy fraction, in the different elements of the Heat Recovery Steam Generator ( Figure 3) for different design conditions and loads: winter design, summer design, annual average and maximum extreme.  Figure 6 shows the Temperature Heat Transfer diagram, TQ diagram of the Heat Recovery Steam Generator, HRSG, under design conditions. Red line represents the evolution of the exhaust gases through the HRSG. Blue line represents the steam and water in the different elements.

Operational Curves
In order to maximize CCPP performance, four different gas turbine models were evaluated. They were selected because of their suitability to the global system requirements. The four gas turbines considered are GE 7FA.05 (TG1), Siemens SGT6-8000H (TG2), GE7FA.04 (TG3) and GEM9001E (TG4).
To estimate power cycle performance, the curves of each turbine are implemented in the numerical simulation. The same configurations for the generator and steam turbine have been kept in the analysis of the different gas turbines. In the first analysis, natural gas has been considered as fuel. Natural gas composition is given in Table 3. Additional analyses are performed considering the effect of using alternative syngas fuels. They are obtained through a gasification process that consists of a partial oxidation of a solid fuel. The characteristics of the syngas fuel compositions and features used in this work are given in Table 4.

Operational Curves
In order to maximize CCPP performance, four different gas turbine models were evaluated. They were selected because of their suitability to the global system requirements. The four gas turbines considered are GE 7FA.05 (TG1), Siemens SGT6-8000H (TG2), GE7FA.04 (TG3) and GEM9001E (TG4).
To estimate power cycle performance, the curves of each turbine are implemented in the numerical simulation. The same configurations for the generator and steam turbine have been kept in the analysis of the different gas turbines. In the first analysis, natural gas has been considered as fuel. Natural gas composition is given in Table 3. Additional analyses are performed considering the effect of using alternative syngas fuels. They are obtained through a gasification process that consists of a partial oxidation of a solid fuel. The characteristics of the syngas fuel compositions and features used in this work are given in Table 4. The effects of the different fuels on CO 2 emission are analyzed in the next section.

System Optimization Discussion
The cycle efficiency, η, is defined as the ratio between the net power, .
Wnet between, and the fuel consumption, indicated as C tot : (1) and the Heat Rate: In Table 5 are reported the estimated net power values for the steam turbine, considering the four different gas turbines at full load operation working at different ambient temperatures. Cycle net power, efficiency and Heat Rate as function of temperature are presented in Figure 7. Figure 7a-c show main parameters of the CCPP for the four gas turbines selected, at full load operation conditions and fuelled with natural gas. As ambient temperature increases, the power provided by the gas turbine and the steam turbine drop. It is due to the effect on air density, the decrease in the steam generated in the HRSG and the drop in turbine expansion. Comparing the results obtained for the gas turbines under analysis, Siemens SGT6-8000H gas turbine combined cycle achieves a higher power, with a higher exhaust gas mass flow and a higher steam generation.  7a-c show main parameters of the CCPP for the four gas turbines selected, at full load operation conditions and fuelled with natural gas. As ambient temperature increases, the power provided by the gas turbine and the steam turbine drop. It is due to the effect on air density, the decrease in the steam generated in the HRSG and the drop in turbine expansion. Comparing the results obtained for the gas turbines under analysis, Siemens SGT6-8000H gas turbine combined cycle achieves a higher power, with a higher exhaust gas mass flow and a higher steam generation. Siemens SGT6-8000H (TG2) reaches the highest value in power: an additional share of the 8% compared to the GE 7FA.05 (TG1) and up to 17% in respect to GE7FA.04 (TG3). Table 6 reports net power of the cycle considering the four different gas turbines at full load operations, at different ambient temperatures. Cycle efficiency is evaluated through gross power, flow composition, exhaust gas temperature, fuel features and parasitic power consumption of auxiliaries. Cycle efficiency values at full load operation and different ambient temperature are given in Table 7.  Figure 7b,c show cycle efficiency and heat rate trends obtained from the simulations for the four gas turbines. Siemens SGT6-8000H (TG2) has an efficiency 18% and 35% higher than GE 7FA.05 (TG1) and GE7FA.04 (TG3) respectively. It is also possible to observe how GEM9001E (TG4) is the turbine in which ambient temperature changes have a minor effect on the efficiency.
Additional to these analyses, other aspects must be taken into account, comparing those with a higher efficiency, GE 7FA.05 (TG1) and Siemens SGT6-8000H (TG2). The GE turbine has an annular tube combustion chamber and Siemens gas turbine has an annular design, with a probable less uniform fuel/air mixture. Besides, it has a dry, low NOx system with a lower temperature with reduced NOx emissions with full load operation.

Effect of Fuel Operation
Based on a criterion of lower emissions, in this section, the effect of using alternative fuels is analyzed. In Figure 8 is presented the degradation curve of the gas turbine considered in this section. Sustainability 2020, 12, x FOR PEER REVIEW 12 of 25       Figure 9 shows the effect of fuel on the net power of the cycle. Using syngas GS1, an additional 11% net power can be obtained, considering full load capacity of the gas turbine for all the fuels and variation range. Depending on the ambient temperature for all the fuels considered, the heat rate evolution gives an idea of the power of the fuel consumed per unit of energy produced. Figure 9b shows the efficiency and Figure 9c shows the Heat Rate. The results show how using syngas fuel Heat Rate can be decreased by 3% with respect to natural gas. Table 9 shows the Heat Rate values at different ambient temperatures for the different fuels.   Figure 9 shows the effect of fuel on the net power of the cycle. Using syngas GS1, an additional 11% net power can be obtained, considering full load capacity of the gas turbine for all the fuels and variation range. Depending on the ambient temperature for all the fuels considered, the heat rate evolution gives an idea of the power of the fuel consumed per unit of energy produced. Figure 9b   Table 10 gives CCPP efficiency operating with the different fuels:  Figure 10 shows the exhaust CO 2 percentage for the analyzed fuels.
shows the efficiency and Figure 9c shows the Heat Rate. The results show how using syngas fuel Heat Rate can be decreased by 3% with respect to natural gas. Table 9 shows the Heat Rate values at different ambient temperatures for the different fuels.

Cycle Heat Rate (kJ/kWh) Natural Gas Syngas 1 Syngas 2 Syngas 3 Syngas 4
Ambient Temperatur  Table 10 gives CCPP efficiency operating with the different fuels:  Figure 10 shows the exhaust CO2 percentage for the analyzed fuels. The proper fuel mixture between natural gas and syngas can generate benefits in terms of lower environmental impact than natural gas, and at the same time, maintain a good combustion performance. The proper fuel mixture between natural gas and syngas can generate benefits in terms of lower environmental impact than natural gas, and at the same time, maintain a good combustion performance.
In previous work [44], authors here have proposed three different cases of operative conditions for the CCPP plant analyzed, changing the percentages of fuel supply between traditional natural gas and syngas. In Table 11, three mixtures are considered for the analysis, based on syngas 2 (GS2), with a low CO 2 value and good efficiency values.

Combined Cycle Plant Correction Curves
To analyze into detail the plant behavior, different analyses are performed for different ambient conditions and for the two different considered operating conditions: without and with steam export. The gas turbine GEM9001E (TG4) is used for the analysis. Table 12 shows the estimated outputs of the plant for both cases.  Figure 11 shows the correction curves of the combined cycle as function of temperature in both configurations, as CHP with steam extraction (red line in the graph) and as standalone power plant (black line).
Sustainability 2020, 12, x FOR PEER REVIEW 3 of 13 Figure 11. Effect of ambient temperature on combined cycle performance. Correction factors as function of ambient temperature for a) power and b) heat rate, with (red line) and without (black line) steam export. Figure 11 shows the effect of steam extraction for CHP on the global curves correction factors. It shows that a temperature drop of 10 °C implies a power drop of 4.4% in the standalone power plant operation mode; meanwhile, that in the CHP operation mode power, decrease is 3.2%. This is due to the different reference in both cases. Figure 11 shows how an increase in the temperature clearly  Figure 11 shows the effect of steam extraction for CHP on the global curves correction factors. It shows that a temperature drop of 10 • C implies a power drop of 4.4% in the standalone power plant operation mode; meanwhile, that in the CHP operation mode power, decrease is 3.2%. This is due to the different reference in both cases. Figure 11 shows how an increase in the temperature clearly penalizes combined cycle net power, i.e., an ambient temperature rise of 9.4 • C reduces in 9% the net power. It can be observed an opposite trend for the heat rate (Figure 11b). For the same increase of 10 • C, the heat rate grows by 9% with respect to the reference value. The comparison between the two case results confirms that at low temperatures, the increase in power acquired by not cogenerating is more pronounced. As the ambient temperature increases, this effect becomes less important, and for temperatures around 45 • C, the previous trend is reversed since the power delivered is severely penalized by the maximum extreme conditions.
In Figure 12 are shown the effect of combined cycle parameters as function of relative humidity at different ambient temperatures of 11.5 • C, 17.5 • C, 26.5 • C and 38.4 • C without (Figure 12a,b) and with steam export (Figure 12c,d).
Sustainability 2020, 12, x FOR PEER REVIEW 4 of 13 In Figure 12 are shown the effect of combined cycle parameters as function of relative humidity at different ambient temperatures of 11.5 °C, 17.5 °C, 26.5 °C and 38.4 °C without (Figures 12a and  12b) and with steam export (Figures 12c and 12d). The results obtained show that for a relative humidity lower than the reference, the power decreases and heat rate increases; on the other hand, by increasing relative humidity to values higher than the reference, the inverse trend is observed. It is clear that for high temperatures (38.4 °C), the fluctuation of the corresponding parameter implies a greater variation. Figure 13 shows the effect of ambient pressure on combined cycle performance for both configurations. The results obtained show that for a relative humidity lower than the reference, the power decreases and heat rate increases; on the other hand, by increasing relative humidity to values higher than the reference, the inverse trend is observed. It is clear that for high temperatures (38.4 • C), the fluctuation of the corresponding parameter implies a greater variation. Figure 13 shows the effect of ambient pressure on combined cycle performance for both configurations.  Figure 13 shows how power is increased with higher ambient pressure. This effect is greater with CHP operation, when exporting steam. Power variations of 11% can be obtained depending on ambient pressure. Figure 14 shows the effect of fuel's Low Heat Value (LHV) on combined cycle performance for the two operative conditions proposed. This situation collects the effect of fuel composition variation. In regard to the combined cycle power trend with fuel LHV (Figure 14a), results show that for fuels with LHV lower than the reference, there are not significant variations in power factors. With higher LHV values, in CHP configuration, steam export condition penalizes generation by 2%. Heat rate is not affected by the variation and it is practically an independent condition, as highlighted in Figure 13. Effect of ambient pressure on combined cycle performance. Correction factors with (red line) and without (black line) steam export for (a) power; (b) heat rate. Figure 13 shows how power is increased with higher ambient pressure. This effect is greater with CHP operation, when exporting steam. Power variations of 11% can be obtained depending on ambient pressure. Figure 14 shows the effect of fuel's Low Heat Value (LHV) on combined cycle performance for the two operative conditions proposed. This situation collects the effect of fuel composition variation.  Figure 13 shows how power is increased with higher ambient pressure. This effect is greater with CHP operation, when exporting steam. Power variations of 11% can be obtained depending on ambient pressure. Figure 14 shows the effect of fuel's Low Heat Value (LHV) on combined cycle performance for the two operative conditions proposed. This situation collects the effect of fuel composition variation. In regard to the combined cycle power trend with fuel LHV (Figure 14a), results show that for fuels with LHV lower than the reference, there are not significant variations in power factors. With higher LHV values, in CHP configuration, steam export condition penalizes generation by 2%. Heat rate is not affected by the variation and it is practically an independent condition, as highlighted in Figure 14b. The relative difference of the factors of both conditions represents a discrepancy of 0.05% in the most unfavorable case. In regard to the combined cycle power trend with fuel LHV (Figure 14a), results show that for fuels with LHV lower than the reference, there are not significant variations in power factors. With higher LHV values, in CHP configuration, steam export condition penalizes generation by 2%. Heat rate is not affected by the variation and it is practically an independent condition, as highlighted in Figure 14b. The relative difference of the factors of both conditions represents a discrepancy of 0.05% in the most unfavorable case.
Finally, in Figure 15a,b, the cycle parameters have variations when the power factor of the gas turbine is changed. This has a direct consequence on the power delivered by the gas turbine. The higher the power factor, the greater the active power generated and the lower the reactive power. Finally, in Figure 15a,b, the cycle parameters have variations when the power factor of the gas turbine is changed. This has a direct consequence on the power delivered by the gas turbine. The higher the power factor, the greater the active power generated and the lower the reactive power.

Economic Analysis
For this study, we have assumed that initial investment is divided in 55% provided by the owner and the 45% will be provided by a loan from the World Bank, with a nominal interest rate of 10% without commission, with amortizations and annual liquidations. The construction period of the CCPP can be long and it can go through several years depending on the geographical and commercial circumstances that can be applied to the project. In our case, we have assumed that the start-up will be two years after the start of the civil works. In this way, we have considered those two additional years against the return of the investment in making the investment profitable. We based our analysis on an initial investment cost of €365M that is broken down according to a percentage of the total as considered in Table 13:

Economic Analysis
For this study, we have assumed that initial investment is divided in 55% provided by the owner and the 45% will be provided by a loan from the World Bank, with a nominal interest rate of 10% without commission, with amortizations and annual liquidations. The construction period of the CCPP can be long and it can go through several years depending on the geographical and commercial circumstances that can be applied to the project. In our case, we have assumed that the start-up will be two years after the start of the civil works. In this way, we have considered those two additional years against the return of the investment in making the investment profitable. We based our analysis on an initial investment cost of €365M that is broken down according to a percentage of the total as considered in Table 13: Gas turbines are the most expensive equipment, with the highest fraction of initial investment. Civil works and steam turbines are the other two main parts of Capital Expenditures CAPEX.
To define Operational Expenditures is required an estimation of operational profile of the plant. For this estimation, and due to the difficulty to a more accurate estimation, operational costs have been estimated from a similar plant in terms of relative weights. Total Expenses include fuel expenses, which is the main concept, operation and maintenance, personnel and other general costs. Their estimated proportional weight is presented in Figure 16. Gas turbines are the most expensive equipment, with the highest fraction of initial investment. Civil works and steam turbines are the other two main parts of Capital Expenditures CAPEX.
To define Operational Expenditures is required an estimation of operational profile of the plant. For this estimation, and due to the difficulty to a more accurate estimation, operational costs have been estimated from a similar plant in terms of relative weights. Total Expenses include fuel expenses, which is the main concept, operation and maintenance, personnel and other general costs. Their estimated proportional weight is presented in Figure 16. Fuel price, average price at €0.034/kWh of thermal energy released by the fuel, has been considered.
The profitability of the investment project is quantitatively evaluated considering the Net Present Value NPV. It allows to evaluate short, medium and long-term investments It is defined as: where Vt are the cash flows in period t that will have to be calculated; n is the number of years that we have considered in our time horizon and t in index for each year; k is the discount rate or capital cost and Io is the initial investment. Fuel price, average price at €0.034/kWh of thermal energy released by the fuel, has been considered. The profitability of the investment project is quantitatively evaluated considering the Net Present Value NPV. It allows to evaluate short, medium and long-term investments It is defined as: where V t are the cash flows in period t that will have to be calculated; n is the number of years that we have considered in our time horizon and t in index for each year; k is the discount rate or capital cost and I o is the initial investment. Another parameter considered is the Internal Rate of Return (IRR). When the IRR is equal to the interest rate, the investor is indifferent between making the investment or not. The two necessary conditions to accept the feasibility of the present CCPP examined are that: • the NPV assumes a positive value • that the IRR is greater than the discount rate.
The breakdown of the calculation of the cash flows considered in the NPV formula for the 25 years of our case are developed. As shown in Table 14, in the economic evaluation analysis, four scenarios are considered. To obtain the best options and to understand for which range of plant working the investment should be more profitable, the utilization factor (defined as quotient between the hours of operation considered and the total hours of a year) has been varied from 90% to 50%. In Table 15 are reported the values of the NPV and IRR for the different cases considered. Results obtained highlight that the plant is more profitable the higher the utilization factor. As evident in Figure 17, the most profitable case is the option 1. The cases 2, 3 and 4 are respectively 13%, 41% and 66% less profitable than the first option (considering the NPV value, we can consider about 18, 56 and 90 MM € less NPV). Another parameter considered is the Internal Rate of Return (IRR). When the IRR is equal to the interest rate, the investor is indifferent between making the investment or not. The two necessary conditions to accept the feasibility of the present CCPP examined are that: • the NPV assumes a positive value • that the IRR is greater than the discount rate. The breakdown of the calculation of the cash flows considered in the NPV formula for the 25 years of our case are developed. As shown in Table 14, in the economic evaluation analysis, four scenarios are considered. To obtain the best options and to understand for which range of plant working the investment should be more profitable, the utilization factor (defined as quotient between the hours of operation considered and the total hours of a year) has been varied from 90% to 50%.  Results obtained highlight that the plant is more profitable the higher the utilization factor. As evident in Figure 17, the most profitable case is the option 1. The cases 2, 3 and 4 are respectively 13%, 41% and 66% less profitable than the first option (considering the NPV value, we can consider about 18, 56 and 90 MM € less NPV).  On the other hand, it is very interesting to identify the optimal utilization factor of the plant so that the investment is profitable. On the basis of the established financial model, it is obtained that when the plant operates less than 43% of the year's hours, the investment reaches an NPV negative so the investment is not convenient. In Figure 18 is shown the trend of NPV value considering the working hours of the plant in the year.
On the other hand, it is very interesting to identify the optimal utilization factor of the plant so that the investment is profitable. On the basis of the established financial model, it is obtained that when the plant operates less than 43% of the year's hours, the investment reaches an NPV negative so the investment is not convenient. In Figure 18 is shown the trend of NPV value considering the working hours of the plant in the year. It is clear that the range that makes the investment profitable is between 70% and 43% of the operation of the plant throughout the year. It is also evident that the sale due to the sale of steam assumes a little weight with respect to income from the sale of electricity. In the CCPP, the higher cost is due to the need to purchase fuel. In fact, this cost exceeds, in most cases, both the initial investment and the operation and maintenance costs.

Conclusions
In this work are presented the analysis of potential energy, environmental and economic benefits of using alternative fuels for a CCPP located in India, in a region with a potential high availability of biomass.
The main conclusions of the analyses are:  The performance of the combined cycle with operating the four different types of syngas have been estimated and compared with those of the cases of conventional natural gas.
 Among the four syngases analyzed, a better efficiency is achieved for syngas 1 (up to 54%) in respect to the others. The higher efficiencies and lowest CO2 emissions are obtained fuelling with syngas 2.
 Two operation modes have been considered, as CHP plant: considering steam exporting to a refinery and as a standalone power cycle, without exporting steam. Under these two operation modes, operation curves of the combined cycle are estimated for ambient parameters.
 The analysis is closed with an economic analysis to identify the effect of an annual utilization factor in power plant viability, to assess the different effects.
The results of this study can provide useful information to power plant engineers and operators, such as possible performance enhancement modifications to combined cycle power plants. It is clear that the range that makes the investment profitable is between 70% and 43% of the operation of the plant throughout the year. It is also evident that the sale due to the sale of steam assumes a little weight with respect to income from the sale of electricity. In the CCPP, the higher cost is due to the need to purchase fuel. In fact, this cost exceeds, in most cases, both the initial investment and the operation and maintenance costs.

Conclusions
In this work are presented the analysis of potential energy, environmental and economic benefits of using alternative fuels for a CCPP located in India, in a region with a potential high availability of biomass.
The main conclusions of the analyses are: • The performance of the combined cycle with operating the four different types of syngas have been estimated and compared with those of the cases of conventional natural gas.

•
Among the four syngases analyzed, a better efficiency is achieved for syngas 1 (up to 54%) in respect to the others. The higher efficiencies and lowest CO 2 emissions are obtained fuelling with syngas 2. • Two operation modes have been considered, as CHP plant: considering steam exporting to a refinery and as a standalone power cycle, without exporting steam. Under these two operation modes, operation curves of the combined cycle are estimated for ambient parameters.

•
The analysis is closed with an economic analysis to identify the effect of an annual utilization factor in power plant viability, to assess the different effects.
The results of this study can provide useful information to power plant engineers and operators, such as possible performance enhancement modifications to combined cycle power plants.