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Tesla expander is a bladeless turbine suited to low power range applications. In this article, a comparison between the performance prediction, as well as the assessment of the main flow characteristics, of a Tesla turbine working with organic fluids obtained through an in-house 2D code developed in EES environment and a simulation run with a computational fluid dynamics commercial software was done. Three working fluids (R404a, R134a and R245fa) were analysed in order to determine the related performance parameters. Various computations were carried out at several speeds of revolution, both with the laminar model and the Langtry-Menter transitional shear stress transport model for turbulence processing. High rotor efficiency was predicted for a small-scale prototype working with all analysed fluids (69% at 3000 rpm). The results obtained by the CFD simulations and by the in-house code showed an excellent matching. Finally, absolute and relative flow path lines were computed in order to determine fluid dynamics inside the channel and to analyse the fundamental flow phenomena.

In this paper, we assess using two alternative allocation schemes, namely exergy and primary energy saving (PES) to compare products generated in different combined heat and power (CHP) geothermal systems. In particular, the adequacy and feasibility of the schemes recommended for allocation are demonstrated by their application to three relevant and significantly different case studies of geothermal CHPs, i.e., (1) Chiusdino in Italy, (2) Altheim in Austria, and (3) Hellisheidi in Iceland. The results showed that, given the generally low temperature level of the cogenerated heat (80–100 °C, usually exploited in district heating), the use of exergy allocation largely marginalizes the importance of the heat byproduct, thus, becoming almost equivalent to electricity for the Chiusdino and Hellisheidi power plants. Therefore, the PES scheme is found to be the more appropriate allocation scheme. Additionally, the exergy scheme is mandatory for allocating power plants’ environmental impacts at a component level in CHP systems. The main drawback of the PES scheme is its country dependency due to the different fuels used, but reasonable and representative values can be achieved based on average EU heat and power generation efficiencies.

Countries that are in the Great Rift Valley have one of the lowest average annual electricity consumption per capita in Africa with a value of 164 kWh per inhabitant. Furthermore, the electrification rate is 34% that is more than fifty percentage points below the world average, which is around 86%. One possible solution to improve the electrification rate is to properly exploit the energy resources present in the territory. One of the most significant energy sources of this region is certainly geothermal energy which has a potential of about 15 GWe, mostly concentrated in Ethiopia. Furthermore, it is possible to find the resource in a wide temperature range, not only to produce electricity, which, nonetheless, has a very limited exploitation rate, as only 900 MWe are installed between Kenya and Ethiopia, but also for direct use. In this study, two geothermal power plants for two different geothermal sites, Corbetti and Arus-Bogoria, respectively in Ethiopia and Kenya, have been hypothesized after analyzing the resource potential. For the first, which has been estimated to be of high enthalpy (~300°C), a flash plant configuration was assumed, and the estimated energy production potential was found to be around 50-100 MWe. While for the second, at medium enthalpy (T

Emissions of contaminants and CO2 are becoming a relevant issue for the development of geothermal energy projects. Organic Rankine (ORC) Cycles present in this light particular appeal in the light of the possibility of total reinjection of the geothermal fluid resource including Non-Condensable Gases (NCGs). The Castelnuovo (IT) case study conditions are considered a saturated vapour resource at 10 bar pressure. The performance of the ORC cycle for power generation from this geothermal resource is evaluated through mass and energy balances, stepping up to exergy, Life Cycle Analysis (LCA) and Exergo-Environmental analyses (EEvA). The applied methodology allows to identify the most critical components of the system and to evaluate the environmental indicators of the system.

The scenarios on the future energy systems invariably point to heat pumps as an emerging technology to reach efficiency goals alongside energy and CO2 reduction targets. Moreover, they may progressively foster the use of chillers and refrigeration units. In this study, a technology that could enhance the efficiency of systems based on inverse cycles is analysed. Particularly, the two-phase flow behaviour of a Tesla turbine is numerically investigated. The main objectives are to clarify the role of the second phase, the actual operating range, and examine the flow mixing. Two computational approaches are developed, relying on a customised home-built mathematical model and CFD analyses carried out with a commercial software. The calculations are performed for two-phase R404a fluid over significant ranges of rotational speed, plate gap size, and plate roughness. All the critical liquid–vapour interactions are determined and discussed utilising the CFD solution of the Eulerian-Eulerian approach with a frame motion technique. The other model is a homogeneous finite-difference solution, and the mass transfer is directly determined based on the phase diagram of the fluid neglecting other phase-interaction parameters. The two approaches are compared to some available experimental results from the literature, revealing an excellent agreement. The results show the average power output of 0.8 W with a delivered torque of 3.6 mN-m at a rotational speed of about 2000 RPM. The numerical analysis explains the different effects of the two-phase conditions on the turbine efficiency, paving the way to an accurate design of boundary layer turboexpanders operating under these conditions.

The Organic Rankine (ORC) and Kalina (KC) Cycles represent two different technologies suitable to exploit low and medium temperature geothermal heat resources. In this work, the performances of KC, CO2 and ORC cycles, the latter using different working fluids, for power generation from two geothermal fluid reservoirs are compared from an energy and exergoeconomic perspective. Two different case studies are discussed: the first one referred to a medium-temperature heat source of 212 °C (Mt. Amiata, Italy), the second one to a low-temperature heat source of 120 °C (Pomarance geothermal basin, Italy). For each case study, cost rate balances and auxiliary equations for all components were evaluated, as well as the flow rate and unit exergy cost for each stream. The results for the medium temperature case study showed that, among the considered cycles, an ORC with R1233zd(E) achieves the best exergoeconomic performance. The cost of the produced electricity was found to be 8.85 c€/kW h, which is 3% lower than that of the KC. On the other hand, for the low temperature case study, the KC shows the best performance, being able to produce 22–42% more net power than the ORC; in this case, the cost of electricity produced by the KC was found at 12.5 c€/kW h, which is 24–34% lower than the typical value for an ORC with different working fluids.

International audience; Geothermal energy could play a crucial role in the European energy market and future scenarios focused on sustainable development. Thanks to its constant supply of concentrated energy, it can support the transition towards a low-carbon economy. In the energy sector, the decision-making process should always be supported by a holistic science-based approach to allow a comprehensive environmental assessment of the technological system, such as the life cycle assessment (LCA) methodology. In the geothermal sector, the decision-making is particularly difficult due to the large variability of reported results on environmental performance across studies. This calls for harmonized guidelines on how to conduct LCAs of geothermal systems to enhance transparency and results comparability, by ensuring consistent methodological choices and providing indications for harmonized results reporting. This work identifies the main critical aspects of performing an LCA of geothermal systems and provides solutions and technical guidance to harmonize its application. The proposed methodological approach is based on experts' knowledge from both the geothermal and LCA sectors. The recommendations cover all the life cycle phases of geothermal energy production (i.e., construction, operation, maintenance and end of life) as well as a selection of LCA key elements thus providing a thorough base for concerted LCA guidelines for the geothermal sector. The application of such harmonized LCA framework can ensure comparability among LCA results from different geothermal systems and other renewable energy technologies.

Many geothermal power plants require systems for steam washing and treatment of non-condensable gases (NGCs). Steam washing is an early-stage unit and the NCG treatment is performed before the reinjection. The paper describes the potential methods for those parts of the process and evaluates the approach of scrubbers and the associated models. The first model is developed for the steam washing scrubber, which eliminates the dissolved solids from the extracted steam. The energy analysis, steam loss, and the efficiency of removal are investigated and potential approaches to the H2S removal process are discussed. The second model is dedicated to the packed-bed acid-gas scrubber, which efficiently reduces the H2S content of NCGs before the reinjection into the reservoir. This model is a rate-based approach that considers all the reactions in parallel. Also, a comprehensive model for the sizing of the scrubbers is proposed. The case study is a binary geothermal power plant, designed for the area of Larderello, in which the extracted steam consists of 25 ppm dissolved solids. The power plant design includes the NCG reinjection system, having about 0.3% of H2S content. The design parameters are found to achieve solid removal efficiency higher than 90%, thus abating the dissolved solids in the steam to less than 3 ppm by the first scrubber. The performance of the selective H2S removal treatment is optimized by identifying the best operating parameters for the effective removal of the H2S and keep the CO2. The selectivity is calculated in various conditions considering recycle-ratio, caustic solution temperature, and caustic solution concentration. The configuration of the second scrubber is optimized with an H2S removal efficiency of about 99.96 percent, with a selectivity index around 10.

Geothermal energy is acknowledged globally as a renewable resource, which, unlike solar, wind or wave energy, can be continuously exploited. The geothermal fluids usually have some acid gas content, which needs to be precisely taken into account when predicting the actual potential of a power plant in dealing with an effective reinjection. One of the key parameters to assess is the solubility of the acid gas, as it influences the thermodynamic conditions (saturation pressure and temperature) of the fluid. Therefore, an enhanced solubility model for the CO2-H2S-water system is developed in this study, based on the mutual solubility of gases. The model covers a wide range of pressures and temperatures. The genetic algorithm is employed to calculate the correlation constants and corresponding solubility values of both CO2 and H2S as functions of pressure, temperature and the balance of the gas. The results are validated against previously published models and experimental data available in the literature. The proposed model estimates the pure gas solubility, which is also a feature of other models. The more innovative feature of the model is the solubility estimation of each CO2 or H2S in simultaneous presence, such as when the binary gas is injected into the pure water of the geothermal reinjection well. The proposed solubility model fits well with the available experimental data, with a mean deviation lower than 0.2%.

Renewable energies are often subject to stochastic resources and daily cycles. Energy storage systems are consequently applied to provide a solution for the mismatch between power production possibility and its utilization period. In this study, a solar integrated thermo-electric energy storage (S-TEES) is analyzed both from an economic and environmental point of view. The analyzed power plant with energy storage includes three main cycles, a supercritical CO2 power cycle, a heat pump and a refrigeration cycle, indirectly connected by sensible heat storages. The hot reservoir is pressurized water at 120/160 &deg, C, while the cold reservoir is a mixture of water and ethylene glycol, maintained at &minus, 10/&minus, 20 &deg, C. Additionally, the power cycle&rsquo, s evaporator section rests on a solar-heated intermediate temperature (95/40 &deg, C) heat reservoir. Exergo-economic and exergo-environmental analyses are performed to identify the most critical components of the system and to obtain the levelized cost of electricity (LCOE), as well as the environmental indicators of the system. Both economic and environmental analyses revealed that solar energy converting devices are burdened with the highest impact indicators. According to the results of exergo-economic analysis, it turned out that average annual LCOE of S-TEES can be more than two times higher than the regular electricity prices. However, the true features of the S-TEES system should be only fully assessed if the economic results are balanced with environmental analysis. Life cycle assessment (LCA) revealed that the proposed S-TEES system has about two times lower environmental impact than referential hydrogen storage systems compared in the study.

Natural refrigeration fluids as CO 2 represent a very promising alternative to hydrofluorocarbons (HFCs) but they generally entail lower COP values. The possibility of recovering the large throttling losses by using an expander could give a substantial contribution to the performance improvement. In this work, a reciprocating expander developed from a hydraulic motor was experimentally analyzed. Despite of the mechanical losses due to the different original application of the machine, the thermodynamic cycles showed very promising results with the adoption of this solution. The machine isentropic efficiency was 19%, while the indicated efficiency was 66%, showing a very interesting potential of the expander. Thus, by considering a reasonable value of mechanical efficiency about 65%, the isentropic efficiency would be around 40%. Consequently, the entailed COP potential improvement, compared to a refrigeration system with simple throttling valve is currently at 7.4%, while it might overcome 20%.

The 3D design and analysis of a 5 kW micro turbo expanders for small, distributed ORC power units is proposed, starting from a recently developed 0D design tool, which was initially applied to 50 kW radial turbines. The turbine was sized referring to R134a as working fluid. At the same time, the main performance parameters, kinematic conditions and the different loss sources were determined. The resulting 0D basic geometry and the related non-dimensional parameters were used as the starting point to define the 3D geometry of the rotor (distribution of the metal blade angles and of the thickness profile) and to refine some design parameters like the number of blades. On the basis of the 3D blade profile and flow channels, a computational grid was generated. The CFD analysis of the rotor was carried out by means of Ansys Fluent ® software, including a real-gas Equation Of State (EOS) model for the working fluid. The design of the rotor was reconsidered as a consequence of the 3D CFD approach. Finally, the comparison between the 0D and 3D results was carried out, showing a good agreement between the two approaches and, thus, verifying the reliability of the combined 0D–3D design tool for micro-size turboexpanders of ORCs.

Geothermal energy is a clean resource, which could significantly contribute to the reduction of greenhouse and other gas emissions by replacing fossil fuels for power generation. In many geothermal sites, the resource contains substantial Non-Condensable Gases (NCGs: CO2 and contaminants), whose emissions can be limited to developing power plant schemes suitable for complete resource reinjection. Organic Rankine or other closed-loop cycles are definitely favored in this light. This work investigates a solution for complete NCG reinjection in the liquid-dominated reservoir conditions typical of the Monte Amiata area (Italy), referring to the specific site of Torre Alfina (IT) which presents a specific attractiveness because of its high pressurization. The solution considered avoids flashing the resource and thus presents an appealing environmental performance. The power plant models include energy and exergy balances, as well as exergo-environmental analysis. The overall environmental performance is evaluated by a simplified (preliminary) Life Cycle Analysis (LCA). Different solutions are compared, considering the possibility of sub- or super-critical power cycles.

Over recent years, the Tesla turbine gained a renewed interest from the scientific community, as its simple structure guarantees low cost and reliability. These are key aspects of the success of an expander suitable for small-distributed energy systems. The reference case for the computational analysis was selected from the available data of an experimental campaign conducted with R1233zd(E) as the working fluid. The analysed turbine has an efficiency of 29% and a power output of 0.57 kW. The fluid dynamics inside the stator, the stator-rotor gap and the rotor was assessed by means of a 3-D computational model. The comprehensive evaluation of the three regions is of paramount importance to determine the machine flow field and the related performance, as they are significantly affected by the interactions amongst the internal components. The effects of the discrete admission to the rotor are relevant in terms of flow field distortion, while the effects on the performance parameters (power and efficiency) are of minor importance. The performance results of the 3-D computational fluid dynamics are in line with those of the analytical 2-D code, which assumes the uniform admission to the rotor. Finally, after that the detailed analysis of the selected test case was conducted, several simulations with different thermodynamic conditions were carried out and compared to the results of the 2-D analytical code and the experiments.

A Thermo-Electric Energy Storage (TEES) system is proposed to provide peak-load support (1⁻2 daily hours of operation) for distributed users using small/medium-size photovoltaic systems (4 to 50 kWe). The purpose is to complement the PV with a reliable storage system that cancompensate the produc tivity/load mismatch, aiming at off-grid operation. The proposed TEES applies sensible heat storage, using insulated warm-water reservoirs at 120/160 °C, and cold storage at −10/−20 °C (water and ethylene glycol). The power cycle is a trans-critical CO2 unit including recuperation; in the storage mode, a supercritical heat pump restores heat to the hot reservoir, while a cooling cycle cools the cold reservoir; both the heat pump and cooling cycle operate on photovoltaic (PV) energy, and benefit from solar heat integration at low⁻medium temperatures (80⁻120 °C). This allows the achievement of a marginal round-trip efficiency (electric-to-electric) in the range of 50% (not considering solar heat integration).The TEES system is analysed with different resource conditions and parameters settings (hot storage temperature, pressure levels for all cycles, ambient temperature, etc.), making reference to standard days of each month of the year; exergy and exergo-economic analyses are performed to identify the critical items in the complete system and the cost of stored electricity.

The sustainability of geothermal energy production is analyzed with reference to a production plant located in a specific area (Monte Amiata, Italy). Four solutions combining a flash power plant with an Organic Rankine Cycle in a hybrid configuration are analyzed in terms of production of electricity, exergy balance and emissions level (CO2, H2S, Hg). The different solutions correspond to increasing environmental performance, and for the most advanced case achieve near-zero emissions (complete reinjection of the natural resource, including incondensable gases). The results show that this can be achieved at the price of a progressive reduction of electrical productivity.

In recent years, small-micro power generation was appointed as one of the proper solutions to tackle the increasing energy consumption, while opening the way to distributed energy systems and micro grids. The most interesting solution for small-micro power generation is the ORC technology, however, it still needs further developments especially regarding the design of small and micro expanders. A possible solution for micro-expanders is the Tesla turbine, which is a viscous bladeless turbine. This concept was developed by Nikola Tesla at the beginning of the 20th century, but it went through a long period of indifference due to the run towards large size centralized power plants. Only recently it found a renewed appeal, as its features make it suitable for utilization in small and micro size systems, like ORC applications, where low cost components become very attractive for the exploitation of residual pressure drop. The present study develops a design procedure of a Tesla turbine for ORC applications. A throughout optimization method was performed by evaluating the losses of each component and by introducing an innovative rotor model. Three turbine configurations with different expander size were assessed, in order to show the performance potential of the Tesla turbine, which achieved 64% total-to-static efficiency when working with N-hexane fluid.

Medium temperature (up to 170 °C), water dominated geothermal resources are the most widespread in the world. The binary geothermal-ORC power plants are the most suitable energy conversion systems for this kind of resource. Specifically, combined heat and power (CHP) systems have the potential to improve the efficiency in exploiting the geothermal resources by cascading the geothermal fluid heat carrier to successively lower temperature users, thus increasing first and second law efficiency of the entire power plant. However, geothermal CHPs usually extract heat from the geofluid either in parallel or in series to the ORC, and usually provide only low temperature heat, which is seldom suitable for industrial use. In this paper, a new CHP configuration, called Cross Parallel CHP, has been proposed and analyzed. It aims to provide higher temperature heat suitable for industrial use, allowing the exploitation of geothermal resources even in areas where district heating is not needed. The proposed CHP allows the reduction of the irreversibilities in the heat exchangers and the loss to the environment related to the re-injection of geofluid, thus producing higher electric power output while satisfying, at the same time, the heat demand of the thermal utility for a wide range of temperatures and mass flow rates (80–140 °C; 3–13 kg/s). Several organic fluids are investigated and the related optimizing working conditions are found by a built in procedure making use of genetic algorithms. The results show that the optimal working fluids and conditions vary with the temperature level and heat load of the thermal utility.

The proposed Thermo-Electric Energy Storage (TEES) system addresses the need for peak-load support (1–2 daily hours of operation) for small-distributed users who are often owners of small/medium size PV systems (4 to 50 kWe) and wish to introduce a reliable storage system able to compensate the productivity/load mismatch. The proposed thermoelectric system relies on sensible heat storage: a warm resource at 120/160 °C (a hot water reservoir system), and a cold resource at −10 /−20 °C (a cold reservoir system containing water and ethylene glycol). The power cycle operates through a trans-critical CO2 scheme including recuperation; in the storage mode, a supercritical heat pump restores heat to the hot reservoir, while a cooling cycle (using a suitable refrigerant) cools the cold reservoir. The power cycle and the heat pump benefit from geothermal heat integration at low-medium temperatures (80–120 °C), thereby allowing to achieve a marginal round-trip efficiency (electric-to-electric) in the range from 50 to 75% (not considering geothermal heat integration). The three systems are analyzed with different resource conditions and parameters setting (hot storage temperature, pressure levels for all cycles, ambient temperature…); exergy and exergo-economic analyses are performed to evaluate the economic competitiveness and in order to identify the critical items in the system. A sensitivity analysis on the main parameters affecting the produced power cost of the system per unit electric energy is carried out.

A micro combined heat and power (CHP) plant operating through an Organic Rankine Cycle (ORC) using renewable energy is analysed. The reference system is designed to produce 50 kWe. The heat sources of the system are geothermal energy at low temperature (80–100 °C) and solar energy. The system uses a solar field composed only by evacuated solar collectors, and work is produced by a single turbine. Different working fluids (e.g. R134a, R236fa, R245fa) are considered in the analysis. The aim of this paper is to assess the cost of the proposed CHP plant and to determine the most convenient working fluid through a thermo-economic analysis. The system is sized in base of the weather data of a city in the centre of Italy in three different months (January, March, July), and the main characteristics of the system (i.e. heat exchanger surface, solar collector area) are presented. The results of the thermo-economic analysis show that R245fa allows the lowest price of electricity production and the lowest overall cost of the CHP plant.

Glass heat pipe solar collectors are becoming very popular for heating/sanitary water production. The use of a double glass system, with vacuum in between (Dewar scheme), allows to minimize heat dispersion to the environment, and to reach potentially temperature levels in competition with much more expensive parabolic trough concentrating solar collectors (stagnation temperatures in excess of 200 °C are reported). It opens their use to solar energy conversion (i.e. low-temperature ORC technology). However, in the technical literature there is not much information on the design criteria of these collectors, and of models for evaluating absorbed solar radiation and thermo-fluid-dynamics performance. Starting from the collector’s location weather data and tilt angle, a model to evaluate the absorbed solar radiation is developed. It is based on (I) calculation of the actual angle between solar radiation and the absorbing cylindrical pipe surface; and (II) calculation of the actual absorbed radiation by the heat pipe surface, also including the mutual shading between the different heat pipes, allowing the estimate of the performance in design conditions. Sensitivity to the main design variables is examined. The model includes heat transfer (radiation, forced/natural convection, phase transition) in the different sections of the heat pipe.

The improvement of low temperature exhausts heat recovery network of an industrial textile – drying machine (Stenter/Rameuse) is presented. A complete redesign of the layout of the water – gas heat exchangers network was done. The network was improved changing the original serial configuration of the heat recovery cells to a system with parallel manifolds for the water circuit. The heat transfer layout and the related heat exchangers were modelled with a dedicated thermal design code. The limited heat transfer coefficient of the internal gas side in the original configuration was improved with a “twin barrel” solution, with water in the outer annulus and exhaust gas in the inner duct equipped with internal longitudinal fins, an effective solution allowing easy fabrication and cleaning. A second step refinement design of the heat exchangers modules, realized with an OpenFOAM® CFD procedure, allowed the final definition and optimization of the fins size and layout, which were not continuous on the whole length of the module, but staggered on the inner side and shortened to about 1/3 of the length. Compared to the original version, the new heat exchangers network and the improved thermal design allowed an increase of the heat recovery from the exhausts of about 180%. The adoption of three staggered and segmented fins led to an increase of 97% with respect to the bare pipe. Finally, the results of the models were validated on a test bench reproducing one full-scale section of the drying machine: the tests gave positive issues, confirming the model predictions and the correct operability of the unit. Particularly, the accuracy of prediction of water temperature was very good (less than 0.5 °C difference between simulation and measurements).

Offshore applications allow to exploit different renewable energy sources (wave, wind, solar) that are complementary each other, due to their statistical yearly distributions. In this paper, we discuss an offshore platform for energy production from renewable energy sources coupled with three energy storage systems. The proposed offshore platforms uses a Compressed Air Energy Storage (CAES) to timely shift the electricity production from the demand. The performance of the system related to a north Tyrrhenian Sea location was evaluated by a simulation model developed integrating three different software packages (Matlab, EES, TRNSYS). The system was designed to produce 564 kWh on the 2 h a day where peak electricity demand takes place. The results showed that the system is able to produce 177,000 kWh per year. This offshore power plant is conceived for local users (tourist resorts, villages), especially if placed in small or medium islands, wishing to qualify for extensive use of renewable energy.

Application of a pipeline at the lower side of copper roofs to use them as solar collectors was investigated. An optimized module capable of converting a wide fraction of solar radiation into heat, and at the same time preserving the esthetic quality of the roof, was designed. Exergy analysis, which allowed quantification of the value of collected energy, including temperature effects and friction losses of the heated fluid, was applied. The results allowed suggestion of a rectangular module with four ducts having rectangular cross section. The basic proposed version was the Unglazed Solar Roof (USR), which showed interesting levels of efficiency (30–60%) over the entire working field. Even the glazed version (GSR) was introduced and analyzed, but its performance showed significant improvements only when extensively used during cold seasons. Compared with a commercial reference flat plate collector (FPC) model, the efficiency of USR is reduced by 20% over the whole operating field. The curves of exergy efficiency showed an optimization point at temperatures well above those in flat plate collectors. For this reason, exergy analysis applied to solar collectors is worth only (I) to evaluate the lower limits in cross sectional area of the ducts, to avoid too narrow height or width which may lead to very high friction losses and (II) to manage the flowrate to extract the highest amount of exergy during the variable environmental and fluid conditions. Integration with a domestic hot water system showed a potential achievement of a yearly solar fraction of 53% with USR and 60% with GSR. Considering that both systems are fully integrated within the roof cover, differently from standard collectors, the esthetic appeal of the building roof would not be affected.

This manuscript summarises the results of a project concerning the energy consumption of public buildings and utilities and the evaluation of the most effective and feasible ways to save energy in Certaldo, a small township in Tuscany with approximately 16,000 inhabitants. The energy analysis highlighted a specific partitioning of electric and thermal energy for final use. For example, more than 60% of the electricity consumption of the town is for street lighting, which is still uses obsolete and environmentally problematic lighting technologies, and more than 13% for lighting public schools. With respect to heat utilities, more than 60% of natural gas consumption is for heating public schools and 18% is for heating sport/athletic facilities. The partitioning of energy consumption introduced a list of requalification measures focused on specific areas: each area has an energy saving potential and specific feasible energy requalification technologies in addition to the possible introduction of suitable renewables. The selection of the proposed interventions was based on the results of model simulations, municipal urban regulations and prevailing trends resulting from a survey of municipalities that are the same size as Tuscany. The type and impact of these interventions were also in agreement with the trends found in different international contexts. In the final part of this paper, some instruments and considerations regarding the evaluation of the return on investment (ROI) for investments in energy bill reduction are presented. Although few data are available in the literature about actions to improve energy efficiency in the public sector of small municipalities, the comparison of energy consumption of Certaldo with that of bigger towns with similar climate conditions showed a reasonable proportionality to population and size of the urban area. Thus, the methodology and the examined solutions could be considered a representative case study and a starting point for municipalities with a similar size and number of inhabitants. Finally, a curve of profitability for investments in energy efficiency of the administration was constructed. It can be extended, at least in a first approximation, to similar cases.

Micro combined heat and power (CHP) plants operating through an organic Rankine cycle (ORC) using renewable energy are analyzed. The reference system is designed to produce 50 kWe. The heat sources of the system are geothermal energy at low temperature (80–100 °C) and solar energy. Two different system layouts, a single and a double stage arrangement, are presented. The first uses a solar field composed only by evacuated solar collectors, and work is produced by a single turbine. In the double-stage system, a field of evacuated solar collectors heats the working fluid up to an intermediate temperature. After this first stage, only a part of the working fluid flow rate is heated in a second solar field, composed of direct-steam parabolic through collectors (PTCs), up to the maximum temperature of the cycle. The mechanical work is then produced in two turbo-expanders arranged in series. For the investigations, different working fluids (e.g. R134a, R236fa, R245fa) are considered. The results of the simulation in terms of efficiencies, heat and electricity production and the main characteristics of the system (i.e. heat exchanger surface, solar collector area) are presented and discussed.

Even though textile industry is not considered an energy intensive sector, it comprises a large number of plants consuming and wasting a significant amount of energy that could be, at least partially, conveniently recovered. The objective of this work is to assess the possibilities and convenience of energy recovery from waste heat of different processes of a dry industrial textile laundry. The various thermal wastes from the processes were identified and characterised, in order to estimate their potential recovery and conversion into electricity. A suitable system layout was conceived, in order to exploit the heat deriving from thermal waste of different machinery in the factory, having distinct temperature levels, to an ORC powerplant, which converts the recovered heat into electricity. The ORC cycle was optimized to maximize the thermoelectric efficiency, comparing different possible working fluids. The best fluid was RC318, from which 92.5 kW power output was achieved, at 9.2% efficiency. The economic analysis revealed, conservatively, a payback period of 7 years for the whole system, which is potentially very interesting. The amount of electricity produced by the waste heat recovery equipment is well matched to the company's electrical needs, resulting in a significant reduction of electricity consumption, greatly reducing the electrical withdrawal from the grid and the related costs. The case study, the proposed solutions and the methodology have general aspects and may be extended to a wide range of cases in the sector of industrial textile laundry.

The guiding idea behind oxy-fuel combustion power cycles is guaranteeing a high level of performance as can be obtained by today's advanced power plants, together with CO 2 separation in conditions ready for transport and final disposal. In order to achieve all these goals, oxy-combustion – allowing CO 2 separation by simple cooling of the combustion products – is combined with large heat recovery and staged expansions/compressions, making use of new components, technology and materials upgraded from modern gas turbine engines. In order to provide realistic results, the power plant performance should include the effects of blade cooling. In the present work an advanced cooled expansion model has been included in the model of the MATIANT cycle in order to assess the effects of blade cooling on the cycle efficiency. The results show that the penalty in efficiency due to blade cooling using steam from the heat recovery boiler is about 1.4 percentage points, mainly due to the reheat of the steam, which, on the other hand, leads to an improvement in specific work of about 6%.

The use of heavy fluids (typically refrigerants) for tests on turbomachinery equipment, like centrifugal compressors, under similitude with real working conditions is a common practice in the test facilities of manufacturers. This practice leads to the release of the test gas to the environment, mainly coming from seals, test circuit connections, valve gaskets and from operations of circuit assembling/disassembling necessary to replace or service the machine under test. The spatial distribution and flow of these emissions inside the test building is a complex issue, which depends on the specific circuit features, location of sources, geometry and openings of the building and variable climatic conditions of the location. For a preliminary assessment of the health and safety conditions, a NIST computational package — including a CFD solver — was applied. The aim was to validate the applicability and reliability of this tool, which was developed for other types of buildings; from the industrial side, knowledge of the diffusion scenario is important to define test protocols to guarantee acceptable emissions levels for manpower in working areas. The industrial building is organized in multiple inside workspaces. The concentration of the contaminant in the area of the test benches, determined by the internal fluid dynamics, is calculated with the CFD solver included in the NIST package. In the building, air motion is only affected by natural ventilation. For this reason, the interactions between the outside and the interior climatic and microclimatic parameters must be considered, taking into account also the different possible assumptions about the daily management of the openings of the building envelope. Several cases of release and dispersion of heavy fluid inside the working areas, under different boundary conditions, were considered. The sensitivity of the results to the different seasonal conditions was assessed and discussed. The complex internal geometry of the building was simulated by a combination of single zone models. The results showed an expectable presence of test gas emissions in the neighborhood of the test area and the possibility of buoyancy effects within the large building. A relatively stable concentration of the test gas emissions resulted from the application of the model, which was affected only by substantial variations of the climatic conditions.

The research deals with the possibility of effective exploitation of low temperature geothermal energy resources, which are generally much more widespread worldwide compared to conventional high temperature ones, typically available only in limited areas of the Earth. The basic idea is the application of an advanced binary cycle, only thermally coupled to the primary endogen heat source. The selected reference-power cycle is the well-known Kalina, which gives the possibility of optimizing the matching between heat capacities of the geothermal fluid (i.e. typically hot water or saturated steam) and the cycle working fluid, which is a non azeotropic NH3-H2O mixture with variable vaporization temperature at a fixed pressure. The heat transfer diagrams of the main Kalina heat exchangers, namely the condenser and the evaporator, are analysed with the aim of minimizing the irreversibilities related to the heat transfer. At different fixed NH3-H2O composition and condenser pressures, the evaporator pressure shows an efficiency optimizing value between 40 and 55 bar, generally increasing at higher condenser pressure. At fixed geothermal heat source temperature, condenser/evaporator pressures and working mixture composition, the cycle efficiency increases with increasing evaporator temperature, because of the reduction in the approach temperature difference between the geothermal and the working fluid. Higher efficiencies are found at higher NH3 concentrations. The proposed Water-Ammonia power cycle is further enhanced introducing a chiller (thus making the power cycle a CCP unit), thanks to the properties of the fluid mixture downstream the absorber, through an intermediate heat exchanger between the condenser and the evaporator. Mainly due to the better matching of heat capacities between the geothermal and the working fluid, the proposed power cycle offers the possibility of interesting improvements in electrical efficiency compared to traditionally proposed binary cycles using ORCs, at fixed temperature level of the heat source. In the investigated proposal, values of electric efficiency between 15 and 20% are found. An economic analysis is presented, demonstrating that the CCP system is able to produce electricity at decreased unit cost with respect to the power-only unit.

The possibility of improving the performance of deep well solar pumping systems by using centrifugal pumps with variable rotational speed and modular number of working stages (i.e. Divided Shaft Pump, DSP) was investigated and compared with traditional systems equipped with pumps having a fixed number of stages (i.e Standard Centrifugal Pump, SCP). Starting from commercially available pumps with a given head–mass flow characteristic, a visual simulation tool for the evaluation of the modified DSP pump performance and costs was developed. In principle, it would be possible to use the desired number of modular stages, thus achieving the highest efficiency of the system for all conditions of radiation. In practice, in order to reduce the DSP pump costs to an affordable level, only one shaft breakpoint is suggested (and then two modular blocks of stages), whose optimised position is determined by the simulation program on the basis of insolation curve during the daylight and required head and shaft speed. Referring to a 30 m 2 PV system (about 3000 W peak power) and to a well depth of 100 m and considering a commercial 46-stage submersible pump, it was found that a breakpoint at the 31st impeller produced an increase close to 9% of the yearly pumped water yield with respect to a conventional, non-modular pump. For the above system, assuming that the cost of a modified modular pump is 1.5 times higher than that of a standard pump, the payback time varies from 0.5 to 2.5 years when the water sale price ranges between 1.1 and 0.6 €/m 3 .

The air membrane-auto thermal reforming (AM-ATR) gas turbine cycle combines features of the R-ATR power cycle, introduced at the University of Florence, with ceramic, air separation membranes to achieve a novel combined cycle process with fuel decarbonisation and near-zero CO2 emissions. Within this process, the natural gas fuel is converted to H2 and CO through the auto thermal reforming process (ATR), i.e. combined partial oxidation and steam methane reforming, within the air separation membrane reactor. In a subsequent process unit, the H2 content of the reformed fuel is enriched by the well known CO–CO2 shift reaction. This fuel is then sent to an amine based carbon dioxide removal unit and, finally, to two combustors: the first one is located upstream of the membrane reformer (in order to achieve the required working temperature) and the second one is downstream of the membrane to reach the desired turbine inlet temperature (TIT). The main advantage of the proposed concept over other decarbonisation processes is the coupling of the membrane and the ATR reactor. This coupling greatly reduces the mass flow of syngas with respect to the air blown ATR contained in the previously proposed R-ATR, thus lowering the size of the syngas treatment section. Furthermore, as the oxygen production is integrated at high temperatures in the power cycle, the efficiency penalty of producing oxygen is much smaller than for the traditional cryogenic oxygen separation. The main advantages over other integrated GT-membrane concepts are the lower membrane operating temperature, lower levels of required air separation at high partial pressure driving forces (leading to lower membrane surface areas) and the possibility to achieve a higher TIT with top firing without increasing CO2 emissions. When compared to power plants with tail end CO2 separation, the CO2 removal process treats a gas at pressure and with a significantly higher CO2 concentration than that of gas turbine exhausts, which allows a compact carbon dioxide removal unit with a lower energy penalty. Starting from the same basis, various configurations were considered and optimised, all of which targeted a 65 MW power output combined cycle. The efficiency level achieved is around 45% (including recompression of the separated CO2), which is roughly 10% less than the reference GT-CC plant (without CO2 removal). A significant part of the efficiency penalty (4.3–5.6% points) is due to the fuel reforming, whereas further penalties come from the recompression units, loss of working fluid through the expander and the steam extracted for the ATR reactor and CO2 separation. The specific CO2 emissions of the MCM-ATR are about 120 kg CO2/kWh, representing 30% of the emissions without CO2 removal. This may be reduced to 10–15% with a better design of the shift reactors and the CO2 removal unit. Compared to other concepts with air membrane technology, such as the AZEP concept, the efficiency loss is much greater when used for fuel de-carbonisation than for previous integration options.

Two relatively innovative gas turbine (GT) based power cycles with high CO2 removal potential have been proposed and discussed in terms of exergy analysis. Fuel decarbonisation is applied by the means of auto thermal reforming (R-ATR) and simple reforming (R-REF), in order to convert the primary natural gas into a highly H2 and CO2 concentrated fuel. Thus, CO2 is captured with amine chemical absorption into a specific unit and, finally, the decarbonised fuel is sent to the GT combustion chamber. No bottoming steam cycle is included, which should promote the size flexibility of the powerplant. The heat content of GT exhausts is employed partially to sustain the endothermic reforming reactions and partially for cycle recuperation. Moreover, the possibility of steam blade cooling has been investigated. The efficiency is optimised at low pressure ratios (7–10) in the steam cooled R-ATR, whereas higher values have been found in air cooled version (16–17). Generally, the R-ATR solution shows higher efficiency levels, mainly due to the reduced combustion chamber and CO2 capture exergy destruction and higher cycle recuperation degree. The exergy analysis showed a relatively limited influence of combustion chamber losses on the primary fuel exergy input (20–23%). The relative loss of CO2 removal unit is limited as well (5–7%) when compared with values of semi-closed GT configurations. The exergy destruction of R-ATR and R-REF CO2 removal sections is greatly reduced if steam blade cooling is adopted. Generally, all the proposed cycles showed satisfactory values of efficiency (43–46% under optimised conditions) taking into account that they do not involve combined power plants.

The relatively innovative gas turbine based power cycles R-ATR and R-REF (recuperative-auto thermal reforming GT cycle and recuperative-reforming GT cycle) here proposed, are mainly aimed to allow the upstream CO 2 removal by the natural gas fuel reforming. The second part of the paper is dedicated to the R-REF cycle : the power unit is a gas turbine (GT), fuelled with reformed and CO 2 cleaned gas, obtained by the addition of several sections to the simple GT cycle, mainly: ○ reformer section (REF), where the reforming reactions of methane fuel with steam are accomplished: the necessary heat is supplied partially by the exhausts cooling and, partially, with a post-combustion, ○ water gas shift reactor (WGSR), where the reformed fuel is, shifted into CO 2 and H 2 with the addition of water, and ○ CO 2 removal unit for the CO 2 capture from the reformed and shifted fuel. No water condensing section is adopted for the R-REF configuration. Between the main components, several heat recovery units are applied, together with GT cycle recuperator, compressor intercooler, and steam injection into the combustion chamber. The CO 2 removal potential is close to 90% with chemical absorption by an accurate choice of amine solution blend: the heat demand for amine regeneration is completely self-sustained by the power cycle. The possibility of applying steam blade cooling (the steam is externally added) has been investigated: in these conditions, the R-REF has shown efficiency levels close to 43-44%. High values of specific work have been observed as well (around 450-500 kJ/kg). The efficiency is slightly lower than that found for the R-ATR solution, and 2-3% lower than CRGTs with CO 2 removal and steam bottoming cycle, not internally recuperated. If compared with these, the R-REF offers higher simplicity due to absence of the steam cycle, and can be regarded as an improvement to the simple GT In this way. at least 5-6 points efficiency can be gained, together with high levels of CO 2 removal. The effects of the reformed fuel gas composition, temperature, and pressure on the amine absorption system for the CO 2 removal have been investigated, showing the beneficial effects of increasing pressure (i.e., pressure ratio) on the specific heat demand.

The relatively innovative gas turbine based power cycles R-ATR and R-REF (Recuperative-Auto Thermal Reforming GT cycle and Recuperative-Reforming GT cycle) here proposed are mainly aimed to allow the upstream CO 2 removal by the way of natural gas fuel reforming. The power unit is a gas turbine (GT), fueled with reformed and CO 2 cleaned syngas produced by adding some basic sections to the simple GT cycle: ○ auto thermal reforming (ATR) for the R-ATR solution, where the natural gas is reformed into CO, H 2 , CO 2 , H 2 O, and CH 4 ; this endothermic process is completely sustained by the heat released from the reactions between the primary fuel (CH 4 ), exhausts and steam. ○ water gas shift reactor (WGSR), where the reformed fuel is, as far as possible, shifted into CO 2 and H 2 by the addition of water. ○ water condensation, in order to remove a great part of the fuel gas humidity content (this water is totally reintegrated into the WGSR). ○ CO 2 removal unit for the CO 2 capture from the reformed fuel. Among these main components, several heat recovery units are inserted, together with GT cycle recuperator, compressor intercooler, and steam injection in combustion chamber. The CO 2 removal potential is close to 90% with chemical scrubbing using an accurate choice of amine solution blend: the heat demand is completely provided by the power cycle itself. The possibility of applying steam blade cooling by partially using the water released from the dehumidifier downstream the WGSR has been investigated: in these conditions, the R-ATR has shown an efficiency range of 44-46%. High specific work levels have also been observed (around 450-550 kJ/kg). These efficiency values are satisfactory, especially if compared with ATR combined cycles with CO 2 removal, more complex due to the steam power section. If regarded as an improvement to the simple GT cycle, R-ATR shows an interesting potential if directly applied to a current GT model; however, partial redesign with respect to the commercially available version is required. Finally, the effects of the reformed fuel gas composition and conditions on the amine CO 2 absorption system have been investigated, showing the beneficial effects of increasing pressure (i.e., pressure ratio) on the thermal load per kg of removed CO 2 .

In this paper, a zero-dimensional model for the design of radial turbo-expanders for ORC applications is discussed, with special reference to the estimation of losses and efficiency; a comparison between different fluids (R134a, R1234yf, R236fa, R245fa, Cyclohexane, N-Pentane) is presented and discussed, referring to a typical small-size application (50 kW). In the model, different methods for the design of radial turbines are screened, with special attention to the estimation of losses, for which correlations from literature are used. Real Equations Of State (EOS) are applied to the expansion process in place of the traditionally adopted Mach relationships for ideal gas, which is a significant advancement for modeling organic fluids in ORC, often operating near to critical conditions. The results show that the total to total efficiency of the designed machines range between 0.72 and 0.80, depending on the considered fluid. Generally, higher efficiency (1.5–2.5% points) can be achieved adopting backswept-bladed rotors. The most significant losses come from the rotor secondary flows, due to the high curvature of blade profiles combined to the large pressure gradient. The best performing fluids are R236fa and R245fa, followed by R134a and R1234yf. Finally, starting from the developed design tool, an off-design analysis of turbo-expanders is presented. Once the design data are available, the characteristic curves of the expander at variable temperature, pressure and fluid mass flowrate at the expander inlet for different values of the specific speed are built. It is thus possible to evaluate the performance of the radial expanders when working far from design point. This analysis, demonstrated for R134a, shows that the total to static efficiency has a relatively modest sensitivity to the off design of the expansion ratio, especially at corrected speed below the design value.

The potential performance of optimized gas-steam combined cycles built around latest-generation gas turbine engines is analyzed, by means of energy/exergy balances. The options here considered are the reheat gas turbine and the H-series with closed-loop steam blade cooling. Simulations of performance were run using a well-tested Modular Code developed at the Department of Energy Engineering of Florence and subsequently improved to include the calculation of exergy destruction of all types (heat transfer, friction, mixing and chemical irreversibilities). The blade cooling process is analyzed in detail as it is recognized to be of capita] importance for performance optimization. The distributions of the relative exergy destruction for the two solutions — both capable of achieving energy/exergy efficiencies in the range of 60% — are compared and the potential for improvement is discussed.

The analysis of the SCGT (Semi-Closed Gas Turbine cycle) is extended to the treatment of acid condensation (sulphur compounds) at the exit of the separator (SEP), with reference to different possible configurations already studied from the thermodynamic and environmental points of view. This detailed analysis was considered necessary because the natural gas fuel can contain a small amount of H 2 S which, reacting with air, can form SO 2 and finally sulphuric acid. This can represent a problem (mainly from the economic point of view) because of the possibility of sulphuric acid condensation at the exit of the separator, where the temperature can reach values below the acid dew point of the mixture. The data obtained from ENI publications were used for the natural gas composition, and a 0.005% H 2 S molar fraction was additionally hypothesized. With these assumptions, about 0.1% SO 2 can be found in the exhaust gases at the separator inlet. Aspen Plus was used in order to evaluate the chemical effects of the acidity of the condensate produced in the separator. An evaluation about costs of the devices to be used for condensation of the recirculated flue gas humidity has been performed, considering use of the special materials necessary for reducing the aggressive effects of acid water condensation. A final evaluation of the overall conversion system plant is also produced, showing the economic balance in terms of resulting cost of the unit of electrical energy produced and of inlet power in terms of fuel. The results are also evaluated in terms of CO 2 emissions, considering the ratio between the global cost of the power generation plant and the global carbon dioxide emissions, compared to other types of energy conversion open cycle solutions.

In this work, a new Semi-Closed Gas Turbine Cycle (SCGT) configuration is presented, named Semi-Closed Gas Turbine/Regenerative Combined Cycle (SCGT/RCC). The SCGT/RCC is an hybrid combination of the SCGT/CC and SCGT/RE cycle concepts, including both partial regeneration of the gas turbine and coupling to a bottoming steam cycle by a small-size Heat Recovery Steam Generator (HRSG). An energy and exergy analysis is carried out for several configurations and operating conditions. A preliminary analysis of the RHE size, CO 2 absorption potential and related effects on the cycle performance is presented, at several operating conditions and investigating three possible plant operation modes. The performance of the SCGT/RCC is very interesting at optimized operating conditions (specific power exceeding 550 kJ/kg of compressor inlet flow rate, efficiencies close to 50% including a 80% CO 2 removal). This plant is a promising solution that combines the positive features of semi-closed gas turbines, allowing a drastic reduction of size and capital costs for both HRSG and RHE and maintaining high values of performance.

An advanced cycle for the thermodynamic conversion of energy, which is particularly relevant in applications involving the use of cryogenic fuels and oxidants, is analysed by an exergy balance approach. This allows a check on which components are responsible for the largest irreversibilities and opens the way to further plant optimisation.

The aim of the present paper is to study the gasification and combustion of biomass and waste materials. A model for the analysis of the chemical kinetics of gasification and combustion processes was developed with the main objective of calculating the gas composition at different operating conditions. The model was validated with experimental data for sawdust gasification. After having set the main kinetic parameters, the model was tested with other types of biomass, whose syngas composition is known. A sensitivity analysis was also performed to evaluate the influence of the main parameters, such as temperature, pressure, and air-fuel ratio on the composition of the exit gas. Both oxygen and air (i.e., a mixture of oxygen and nitrogen) gasification processes were simulated.

Exergy analysis is a powerful and systematic tool for the improvement of energy systems, with many possible applications in both conversion and utilization of energy. Here we present selected applications, with a special attention to renewable energy systems (solar), covering both design and operation/control. After these applications to non-reactive systems, potential ways of reducing the large irreversibilities connected to reactive systems (combustion) are considered, with special reference to chemically-recuperated gas turbine cycles and topping high-temperature fuel cells.

Some hybrid methanol fuelled SOFC-GT power cycles including a few innovative features are analyzed, compared and discussed. The low reforming temperature of methanol allows high heat recovery from the exhaust of hybrid fuel cell gas turbine cycles, which produces high overall efficiency. Different layouts of hybrid SOFC-GT cycles are presented and discussed, including the possibility of coupling the GT to a bottoming steam plant to further improve the overall performance. A target 10 MW GT size is taken as a reference, coupled to different possible SOFC sizes. The modeling of power cycles, reactors and SOFC is done with author-developed codes. The results show that the most efficient solutions are those considering pressurized fuel cells, which partially replace the GT combustor. Cycles with atmospheric fuel cells placed downstream of the gas turbine are also investigated. In both cases, very interesting levels of efficiency are achieved, ranging from 55 to more than 73%.Copyright © 2008 by ASME

The Semi Closed Gas Turbine Cycle (SCGT) was introduced as a short to medium term solution for applying existing CO2 removal techniques to current production gas turbine powerplants. Thus, one of the main goals is the adaptability to existing turmomachinery, with only minor changes to the equipment. In this manuscript, the off–design analysis of two previously proposed and thermodynamically assessed configurations was carried out: the first one is the combined cycle (SCGT/CC), related to an heavy duty gas turbine, whereas the second one is the recuperative–evaporative cycle (SCGT/RE). Both of them may be equipped with intercooled or, either, aftercooled compression, which is done with spray water injection. The analysis was carried out with special reference to the off design conditions of the compressor and to its coupling with turbine when the partial exhausts recirculation is applied to originally open cycle GTs. In the SCGT/CC configurations, the steam pressure levels are increased due to the increased GT exhausts temperature with respect to the open cycle. When no water injection is applied, the working point of the compressor due to the different gas composition and temperature are largely within the operating margins, thus the semi closed configuration may be applied even to compressors with reduced stall bounds and no large decays in compressor efficiency were found compared to the design operation. On the contrary, when water injection is applied, heavy variations of the compressor working point were found, which make the effects of exhausts recirculation comparatively marginal and leads to unavoidable compressor efficiency drop. It suggests that the application of water injection may be suitable only for the short peakload times, whereas current technology allows the shifting to SCGT.Copyright © 2006 by ASME

The relatively innovative gas turbine based power cycles R–ATR and R–REF (Recuperative – Auto Thermal Reforming GT cycle and Recuperative–Reforming GT cycle) here proposed are mainly aimed to allow the upstream CO2 removal by the way of natural gas fuel reforming. The power unit is a Gas Turbine (GT), fuelled with reformed and CO2 cleaned syngas produced by adding some basic sections to the simple GT cycle: • Auto Thermal Reforming (ATR) for the R-ATR solution, where the natural gas is reformed into CO, H2 , CO2 , H2 O and CH4 ; this endothermic process is completely sustained by the heat released from the reactions between the primary fuel (CH4 ), exhausts and steam. • Water Gas Shift Reactor (WGSR), where the reformed fuel is, as far as possible, shifted into CO2 and H2 by the addition of water. • Water Condensation, in order to remove a great part of the fuel gas humidity content (this water is totally reintegrated into the WGSR). • CO2 removal unit for the CO2 capture from the reformed fuel. Among these main components, several heat recovery units are inserted, together with GT Cycle recuperator, compressor intercooler and steam injection in combustion chamber. The CO2 removal potential is close to 90% with chemical scrubbing using an accurate choice of amine solution blend: the heat demand is completely provided by the power cycle itself. The possibility of applying steam blade cooling by partially using the water released from the dehumidifier downstream the WGSR has been investigated: in these conditions, the R-ATR has shown an efficiency range of 44–46%. High specific work levels have also been observed (around 450–550 kJ/kg). These efficiency values are satisfactory, especially if compared with ATR combined cycles with CO2 removal, more complex due to the steam power section. If regarded as an improvement to the simple GT cycle, R-ATR shows an interesting potential if directly applied to a current GT model; however partial redesign with respect to the commercially available version is required. Finally, the effects of the reformed fuel gas composition and conditions on the amine CO2 absorption system have been investigated, showing the beneficial effects of increasing pressure (i.e. pressure ratio) on the thermal load per kg of removed CO2 .Copyright © 2002 by ASME

A model of the vaned intake of a centrifugal compressor was instrumented and tested for the investigation of aero-acoustic excitation modes for specific flow conditions, in order to check the possibility of damage to the Inlet Guide Vanes (IGV). The tests demonstrate that several acoustic modes occur for such complex geometries, and that their frequencies and amplitudes should be verified in order to avoid the excitation of forced vibration of the blades.Copyright © 2002 by ASME

This new power cycle is derived from a simplified HAT cycle, with a partial recirculation of the exhaust gases added with respect to the traditional HAT configuration. The basic idea of applying recirculation to the HAT cycle stems from the interesting performance levels and general environmental advantages obtainable applying this technique to combined-cycle (SCGT/CC) and regenerative GT solutions (SCGT/RE); these power plants all share the integration with CO2 chemical scrubbing of the exhaust stack in order to reduce greenhouse effects. A relevant advantage of the proposed configuration over the original HAT solution is the possibility of complete water recovery from the separator before the recirculation node; here the temperature level is necessarily very low, allowing thus condensation of water produced by the natural-gas combustion process. This allows the self–sustainement of the HAT cycle, from the water consumption point of view, without any external supply. For the water separator, two thermodynamic models were developed (respectively simulating a single- and a multiple temperature condensation process), which have provided similar results. The whole cycle is modeled using a modular code, thoroughly tested against the performance of a large set of existing GTs. The layout is derived from an existing HAT configuration, with suppression of the economizer section in the regenerator and the possible practice of external (non-recuperative) intercooling between the two compressors. The first choice is imposed by the presence of an additional low-temperature heat load for the CO2 removal plant, while the second is sometimes necessary depending on the compressor pressure ratios and the possibility of including inside the cycle low-temperature internal cycle regeneration. The expected performance of the plant is relatively high and close to those typical of HAT, SCGT/RE and SCGT/CC cycles: a LHV-based efficiency level exceeding 50% inclusive of CO2 separation and delivery at ambient pressure and temperature; the specific work levels — in the range of 680 kJ/kg for the basic configuration — are lower than those of the HAT cycle but larger than for SCGT/CC and SCGT/RE solutions; the cycle requires relatively high overall pressure ratios (35–40). A notable improvement in specific work can be obtained with reheat.

Heat pumps are becoming more and more applied for heating, due to their possibility of working as cooling systems in the summer period. However, up to now, recovery of expansion work in small system has not been considered as a viable solution, because of the limited amount of recoverable energy and of difficulties in designing and operating a two-phase flow expander. The idea here presented is to investigate the application of a radial piston machine, adapted from oleodynamic motor designs, as an expander that will be coupled with the compressor motor shaft; the consequent power reduction goes directly to COP improvement. First, heat pumps working conditions (pressures, mass and volume flows) are defined, and the possible power recovery is calculated. Then, a model for the performance calculation of the radial piston motors used as expander is presented; the model considers the kinematics of the mechanical system and uses real fluid properties. The results indicate that such a machine could be developed from existing units with limited modifications, encourage to develop a test rig, and to run preliminary experimental work in order to measure the real performance.

Two different power plant configurations based on a Semi-Closed Gas Turbine (SCGT) are analyzed and compared in terms of First and Second Law analysis. SCGT plant configurations allow the application of CO2 separation techniques to gas-turbine based plants and several further potential advantages with respect to present, open-cycle solutions. The first configuration is a second-generation SCGT/CC (Combined Cycle) plant, which includes inter-cooling (IC) between the two compression stages, achieved using spray injection of water condensed in a separation process removing vapor from the flue gases. The second configuration (SCGT/RE) combines compressor inter-cooling with the suppression of the heat recovery steam generator and of the whole bottoming cycle; the heat at gas turbine exhaust is directly used for gas turbine regeneration. The SCGT/CC-IC solution provides good efficiency (about 55%) and specific power output figures, on account of the spray inter-cooling; however, with this configuration the cycle is not able to self-sustain the CO2 removal reactions and amine regeneration process, and needs a substantial external heat input for this purpose. The SCGT/RE solution is mainly attractive from the environmental point of view: in fact, it combines the performance of an advanced gas turbine regenerative cycle (efficiency of about 49%) with the possibility of a self-sustained CO2 removal process. Moreover, the cycle configuration is simplified because the HRSG and the whole bottoming cycle are suppressed, and a potential is left for cogeneration of heat and power.