Daniele Cocco

Energy and economic analysis of concentrating solar power plants based on parabolic trough and linear Fresnel collectors

This paper compares the performance of 1 MWe concentrating solar power (CSP) plants based on an organic Rankine cycle (ORC) power generation unit integrated with parabolic trough and linear Fresnel collectors. The CSP plants studied herein use thermal oil as heat transfer fluid and as storage medium in a two-tank direct thermal storage system. The performance of the CSP plants was evaluated on the basis of a 1 MWe ORC unit with a conversion efficiency of about 24%. The comparative performance analysis of the two CSP solutions was carried out by means of specifically developed simulation models and considering different values of solar multiple and thermal storage capacity. The results of the performance assessment demonstrate that CSP plants based on linear Fresnel collectors lead to higher values of electrical energy production per unit area of occupied land (about 50–60 kWh/y per m2 vs. 45–55 kWh/y m2 produced by solutions based on parabolic troughs). However, owing to their better optical efficiency, the use of parabolic troughs gives better values of energy production per unit area of solar collector (about 185–205 kWh/m2 vs. 125–140 kWh/m2) and, therefore, better conversion efficiencies (about 10.8–11.9% vs. 7.3–8.1%). The results of a preliminary economic analysis show that CSP plants based on linear Fresnel collectors are still not competitive with those based on parabolic trough owing to their higher energy production cost (about 380 €/MWh vs. 340 €/MWh).

Performance Assessment of Semi-Closed Chemically Recuperated Gas Turbine Systems

The paper is concerned with thermochemical recuperation in semi-closed gas turbine systems. Semi-closed turbines use CO2 as the main working fluid and the combustion process takes place with pure oxygen, allowing the CO2 produced to be easily removed. On the other hand, the exhaust heat recovery through thermochemical recuperation offers interesting capabilities in terms of high conversion efficiency and low polluting emissions.System analysis and performance evaluation of the semi-closed, chemically recuperated gas turbine systems has been conducted and their performance assessed. A comparative analysis of semi-closed and open gas turbine cycles, with and without thermochemical recuperation, has been also carried out.The results of the analysis show that thermochemical recuperation in semi-closed gas turbine systems can allow to remove the CO2 with high cycle efficiency and specific power.Copyright

SOFC-MGT hybrid power plants fuelled by methane and methanol

In this paper the use of methane and methanol in SOFC-MGT hybrid power plants has been compared. As a matter of fact, SOFC-MGT hybrid plants are a very attractive near term option, as they can allow to achieve efficiencies of over 60–65%, even for small power outputs (200–400 kW). The SOFC systems currently developed are fuelled with natural gas, which is reformed inside the same stack at about 800–900 °C. However, the use of alternative fuels with low reforming temperature (for example, methanol reforms at about 250–300 °C) can lead to enhanced hybrid plant performance. In particular, this paper reports a comparative performance analysis of internally reformed SOFC-MGT power plants fuelled by methane and methanol. Moreover, in the case of methanol use, both internal and external reforming have been compared. The performance analysis has been carried out by considering different values for the most important operating parameters of the fuel cell. The comparative analysis has demonstrated that simply replacing methane with methanol in SOFC-MGT power plants slightly reduces the efficiency. However, the use of methanol in SOFC-MGT power plants with external reforming enhances efficiency significantly (by about 4–5 percentage points). The study shows that the use of methanol with external fuel reforming raises stack efficiency thanks to the improved heat management and to the higher hydrogen partial pressure.Copyright

Comparative Performance Assessment of CRGT Power Plants Fuelled by Hydrogen Energy Carriers

Chemically Recuperated Gas Turbines (CRGT) perform the exhaust heat recovery through the endothermic steam reforming process of the primary fuel, which produces an H2 -rich fuel. In particular, methanol, ethanol and DME are very suitable fuels for CRGT power plants owing to their low reforming temperature, which leads to a very effective waste heat recovery, especially in comparison with CRGT solutions fuelled by natural gas. This paper reports a comparative performance analysis of CRGT power plants fuelled by methanol, ethanol and DME. The performance analysis has been carried out with reference of two 40 MW class commercial turbines (the aeroderivative GE LM6000 unit and the heavy-duty GE PG6561 one). The best operating conditions have been pointed out by considering different operating parameters for the reforming process (pressure, temperature and water/fuel molar ratio). Thermochemical recuperation in CRGT power plants allows to achieve a significant performance improvement in comparison with the performance of the reference gas turbines without any exhaust heat recovery. In particular, the CRGT solutions here considered show maximum efficiencies in the range 54–57%, according to the primary fuel considered, with a corresponding increase of the power output and a decrease of the specific CO2 emissions.Copyright

Fixed-Bed Coal Gasifiers Integrated With MCFC-GT Hybrid Systems for Distributed Power and Heat Generation

In this paper, a performance assessment of coal gasification processes integrated with molten carbonate fuel cells (IG-MCFC) is reported on. The main aim of the study was to evaluate the performance of small and medium size IG-MCFC systems based on fixed-bed gasifiers for distributed power and heat generation. In particular, the plant configuration considered here was developed on the basis of the 700 kg/h fixed-bed up-draft coal gasifier located in the Sotacarbo Research Centre in Carbonia, Italy. The MCFC section is based on the DFC/T® hybrid system developed by FCE Inc., and includes a MCFC stack integrated with an indirectly heated gas turbine. Two different coals, namely a low and a high sulphur coal, were considered. Moreover, the performance of MCFC hybrid systems fuelled by natural gas and coal gas were also compared. The results of the performance assessment show that the optimum value of the gas turbine pressure ratio is around 3, which is very similar to that used by the DFC/T systems proposed by FCE Inc. and fuelled by natural gas. However, replacing methane with coal gases leads to a significant decrease in MCFC efficiency, on the order of 10–11 percentage points. On the whole, the performance assessment carried out in this paper demonstrates that IG-MCFC systems could be an interesting option for small- and medium-size power generation plants fuelled by coal as they can reach efficiencies of nearly 40%.Copyright

Cardiovascular prevention beyond traditional risk factors: the perinatal programming

It has been long time since “traditional” risk factors for cardiovascular diseases (familial history, smoking habit, diabetes, dyslipidemia, arterial hypertension, ageing, and gender) have been recognized. They are used to provide risk charts to predict the onset of a fatal or non-fatal cardiovascular event (myocardial infarction or stroke) in the next ten years. However, this approach does not explain why a minority of subjects who are not affected by the above mentioned risk factors suffer from heart attack or stroke. Hence, in order to explain these exceptions, researchers have made their efforts to identify other new and previously unmentioned predisposing causes. Prematurity at birth and intrauterine growth restriction, expressed as low birth weight, have been recognized as belonging to these. The aims of this review are to explain the reasons of this recently reported association as well as cite the most recent scientific evidences supporting this theory.

Solar assisted Ultra Supercritical steam power plants with Carbon Capture and Storage

This chapter focuses on the evaluation of the potential benefits arising from the integration of concentrating solar systems into coal-based ultra-supercritical (USC) power plants with post-combustion CO2 capture (PCC). In order to offset the efficiency penalty introduced by CO2 removal, the USC-PCC plant was integrated with a concentrating solar field with direct steam generation based on parabolic trough and linear Fresnel collectors. The performance of the solar-assisted USC-PCC power plant was evaluated by means of specifically developed simulation models by using data sets for a typical meteorological year for the sites of Cagliari (Sardinia, Italy) and the North Western Australia Coast. A preliminary cost analysis was also carried out.

Energy and Cost Analysis of Small Size CHP Coal Gasification Plants Integrated With Syngas Storage Systems

This study evaluates the load modulation capabilities of small and medium size CHP systems based on integrated coal gasification and syngas storage (ICGSS) power plants. ICGSS systems can perform a load-following service since a portion of the produced syngas is stored during periods of low energy demand and used to increase power output during periods of peaking demand. In particular, the main energy and economic performance of ICGSS power generation plants were evaluated with reference to three different prime movers (gas turbines, internal combustion engines and hybrid fuel cell systems) and as a function of the required electrical load curve. Moreover, a preliminary economic analysis was also carried out to evaluate the energy production cost in comparison with base-load energy production cost.The results of the study show that ICGSS power plants offer considerable scope for enhancing operating flexibility and load modulation capabilities of CHP systems based on coal gasification. In comparison to coal gasification power plants designed to produce only base-load energy, ICGSS systems require a more powerful prime mover and a larger coal gasification section. In the field of duty-cycles of more likely interest, the coal gasification section needs to be enlarged by 5–50% and a fraction from 2% to 16% of the produced syngas needs to be stored. ICGSS plants based on hybrid fuel cells performed better in terms of electrical efficiency. Moreover, with respect to the corresponding base-load systems, electrical efficiency decreases by about 2–3 percentage points for ICGSS-GT and ICGSS-ICE, while it increases by about 1–2 percentage points for ICGSS-HFC. Finally, syngas storage can reduce energy costs in CHP systems, especially in the case high peaking electricity requirements, large useful heat productions and by using ICGSS based on ICE as prime movers.Copyright

Integration of Combined Cycle Power Plants and Parabolic Solar Troughs Using CO2 as Heat Transfer Fluid

In this paper, a performance assessment of integrated solar combined cycle systems (ISCCS) is reported on. The main aim of the study was to evaluate the solar conversion efficiency of ISCCS plants based on parabolic troughs using CO2 as heat transfer fluid. The use of CO2 instead of the more conventional thermal oil as heat transfer fluid can allow an increase in the trough outlet temperature and thus in solar energy conversion efficiency. In particular, the ISCCS plant considered here was developed on the basis of a triple-pressure, reheated combined cycle power plant rated at 252 MW. Two different solutions for the solar steam generator are considered and compared. Moreover, the performance of the ISCCS system was evaluated with reference to different values of CO2 maximum temperature, solar radiation and solar share of the power output. The results of the performance assessment show that the solar energy conversion efficiency ranges from 23% to 25% for a CO2 maximum temperature of 550°C. The use of a CO2 temperature of 450°C reduces the solar efficiency by about 1.5–2.0 percentage points. The use of a solar steam generator including only the evaporation section instead of the preheating, evaporation and superheating sections allows the achievement of slightly better conversion efficiencies. However, the adoption of this solution leads to a maximum value of the solar share around 10% on the ISCCS power output. The solar conversion efficiencies of the ISCCS systems considered here are better than those of the more conventional Concentrating Solar Power (CSP) systems based on steam cycles (14–18%) and are very similar to the predicted conversion efficiencies of the more advanced direct steam generation plants (22–27%).Copyright

Comparative Analysis of Hydrogen Combustion Power Plants Integrated With Coal Gasification and CO2 Removal

Two power generation systems with pre-combustion CO2 capture fuelled with hydrogen from coal gasification are analyzed and compared from a thermodynamic and economic standpoint. The first solution, referred as Integrated Gasification Combined Cycle with CO2 Removal (IGCC-CR), is fuelled with hydrogen produced by the integrated gasification section. The second, referred as Integrated Gasification Hydrogen Cycle (IGHC), is based on the oxycombustion of hydrogen, producing steam that expands through an advanced high temperature steam turbine. The two H2 production sections are similar for both power plants, some minor modifications having been made to achieve better integration with the corresponding power sections. System performance is investigated using coherent assumptions to enable comparative analysis on the same basis. The plants have overall efficiencies of around 39.8% for IGCC-CR and 40.6% for IGHC, slightly lower than conventional IGCCs (without CO2 capture) with a CO2 removal efficiencies of 91% and 100% respectively. Lastly a preliminary economic analysis shows an increase in the cost of electricity compared to conventional IGCCs of about 44% for IGCC-CR and 50% IGHC.© 2006 ASME