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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%.

Methane conversion to a rich H2 fuel by reforming reactions is a largely applied industrial process. Recently, it has been considered for applications combined to gas turbine powerplants, as a mean for (I) chemical recuperation (i.e. chemical looping CRGT) and (II) decarbonising the primary fuel and make the related power cycle a low CO2 releaser. The possibility of enhancing methane conversion by the addition of CO2 to the steam reactant flow (i.e. tri-reforming) has been assessed and showed interesting results. When dealing with gas turbines, the possibility of applying tri-reforming is related to the availability of some CO2 into the fluegas going to the reformer. This happens in semi-closed gas turbine cycles (SCGT), where the fluegas has a typical 14–15% CO2 mass content. The possibility of joining CRGT and SCGT technologies to improve methane reforming and propose an innovative, low CO2 emissions gas turbine cycle was assessed here. One of the key issues of this joining is also the possibility of greatly reduce the external water consumption due to the reforming, as the SCGT is a water producer cycle. The SCGT-TRIREF cycle is an SCGT cycle where fuel tri-reforming is applied. The steam due to the reformer is generated by the vaporization of the condensed water coming out from the fluegas condensing heat exchanger, upstream the main compressor, where the exhausts are cooled down and partially recirculated. The heat due to the steam generation is recuperated from the turbine exhausts cooling. The reforming process is partially sustained by the heat recovered from the turbine exhausts (which generates superheated steam) and partially by the auto thermal reactions of methane with fresh air, coming from the compressor (i.e. partial combustion). The effect of CO2 on methane reforming (tri-reforming effect) increases with decreasing steam/methane ratio: at very low values, around 30% of methane is converted by reactions with CO2. At high values of steam/methane ratio, the steam reforming reactions are dominant and only a marginal fraction of methane is interested to tri-reforming. Under optimised conditions, which can be reached at relatively high pressure ratios (25–30), the power cycle showed a potential efficiency around 46% and specific work at 550 kJ/kg level. When the amine CO2 capture is applied, the specific CO2 emissions range between 45 and 55 g CO 2 / kW h .

In this work, a possible way for partial CO2 emissions reduction from gas turbine exhausts by co-firing with biomass is investigated. The basic principle is the recirculation of a fraction of the exhausts (still rich in oxygen) to a gasifier, in order to produce syngas to mix with natural gas fuel. As biomass is a CO2 neutral fuel, the fraction of replaced natural gas is a measure of CO2 removal potential of the powerplant. The investigated solution considers the conversion of solid fuel to a gaseous fuel into an atmospheric gasifier, which is blown with a recirculated fraction of hot gas turbine exhausts, typically still rich in air. In this way, the heat content of the exhausts may be exploited to partially sustain the gasification section. The produced syngas, after the tar removal into the high temperature cracker, is thus sent to the cooling section, consisting of three main components: (I) gas turbine recuperator, (II) heat recovery steam generator and (III) condensing heat exchanger to cool down the syngas close to the environmental temperature before the subsequent recompression and mixing with natural gas fuel into the combustion chamber. The water stream produced within the condensing heat exchanger upstream the syngas compression is vaporised and sent back to the gasifier. If very limited modification to the existing gas turbine has to be applied in order to keep the additional costs limited, only a relatively reduced fraction of the low calorific value syngas may be mixed with natural gas. The analysis at different levels of co-firing has shown that no appreciable redesign has to be applied to the target GE5 machine up to 25–30% (heat rate based) renewable fraction. With an accurate heat recovery from the cooling/cleaning system of the syngas, the same levels of efficiency of the original machine have been achieved, in spite of the relatively large power consumption of the syngas recompression. Very interesting results have been obtained within the 10–30% range of biomass co-firing, with CO2 removal levels between 30% and 50% with reference to the values of the base GE5 gas turbine powerplant. The economic analysis has shown that, in spite of the high investment required for the syngas fuel production chain (gasifier, coolers, cleaners and fuel compressor), approximately at the same level of gas turbine itself, there is an interesting attractiveness due to the possibility of selling high-value green certificates and CO2 allowances, which reduce the payback time to 2–4 years. The uncertainty on the calculated economic parameters are greatly influenced by the uncertainty on actual biomass availability and yearly working time of powerplant, whereas off design operation, which affects mainly the uncertainty of compressor and turbine efficiency, is mainly reflected on the uncertainty of electric power output and efficiency.

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.

Carbon dioxide separation by means of membranes from methane reformed synthesis gas and from semi-closed cycle flue gases has been studied. In the first case, removing carbon dioxide using membrane is more energy consuming than removing it, from the same synthesis gas, using chemical absorption, leading to overall energy conversion efficiency of about 39% for the recuperated-auto thermal reforming (R-ATR) cycle equipped with membrane vs. 45% for the same R-ATR equipped with chemical absorption. With reference to the semi-closed cycle, the net cycle efficiency in the case of membrane removal (42.7%) seems to be not very far from the chemical absorption case (46%). Finally, published data about CO2 membrane separation specific cost have been analysed, showing that the membrane technology for flue gas application can be competitive with respect to chemical absorption if CO2 flue gas concentration is higher than 10%.

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.

A mathematical model of biomass gasification kinetics in bubbling fluidized beds has been developed. It is one-dimensional, as it is capable of predicting temperature and concentration gradients along the reactor axis, and considers two phases, a bubble and a dense phase. In addition to the reaction kinetics in the dense phase, mass transfer between the two phases and a quantitative estimation of local bubble and particle properties are included in the model. A theoretical optimization with respect to ER, pressure, bed height and gas velocity has also been performed. Finally, a comparison with experimental data from the literature was done, which showed a largely satisfactory agreement, though further validation is still required.

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.

The aim of this study is to assess the possibility of reducing CO2 emissions from an Integrated Gasifier Combined Cycle plant, accounting for the entire life cycle.With respect to the basic scheme of a conventional Integrated Gasification Combined Cycle - which already includes H2S removal - a shift reaction section followed by CO2 chemical absorption have been added, before the syngas combustion, in order to obtain a clean and H2-rich synthesis gas.The proposed plant reaches 38.8 % efficiency vs. 46.4 % efficiency of the corresponding IGCC without CO2 removal. The main reason for the efficiency reduction is the complexity due to the addition of shift and CO2 removal sections and, hence, the related losses in the complex heat recovery process.From LCA results, a substantial decrease in the carbon dioxide total production, due to the applied removal technology, is highlighted. In fact, the CO2 equivalent production in the life cycle, per energy unit, is one order of magnitude lower with respect to the parent IGCC.Moreover, the major contribution to CO2 production comes from operation/maintenance phase; likely, in the case of Exergetic Life Cycle Assessment: the major exergy destruction - in term of MJ of destroyed exergy per functional unit - comes from operation/maintenance, which is two orders of magnitude greater than the contributions of the other phases.The whole cycle has been simulated by means of Aspen Plus 10.1-0.

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 goal of the present manuscript is the investigation of two novel systems for partial CO2 capture from the exhausts of fossil fuelled powerplants. These systems should be relatively cheap and easily applicable to existing powerplants with minor modification, in order to make them accessible by a large range of users and favour a significant diffusion of partial CO2 sequestration. Two basic processes were proposed: 1. Absorption with a liquid solution of water and NH3; 2. Absorber/desorber system with a liquid solution of water and phosphates. In the first one, the exhausts react into an absorber column with a liquid sorbent, which is a solution of water and ammonia. The process sequestrates the CO2 in carbammate and bicarbonate and the final product are salt of ammonia, i.e. ammonium carboamate (NH4HCO3) and ammonium bicarbonate (NH4NH2COO). The outgoing streams of this process are the exhaust gas with a reduced content of CO2 and a secondary product formed by salts of ammonium, which have an interesting market potential as fertilizers. The obtained CO2 reduction level was more than 40%, while the amount of secondary products is high enough to get it marketable. In the second process, the exhausts passing through an absorber column react with a liquid sorbent, which is a solution of water and sodium (or potassium) phosphate. The process sequestrates the CO2 in bicarbonate ions by means of the ions phosphate and the outlet stream is a solution of water and phosphate and carbonate ions. This stream is collected in a desorbing column, where the phosphate ions are almost completely regenerated. The CO2 reduction level is always higher than 20% and it can also reach very high values, depending on the parameters of process.

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 natural gas fuel reforming. The 2nd part of the paper is dedicated to the R-REF cycle: the power unit is a Gas Turbine (GT), fuelled with reformed and CO2 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 CO2 and H2 with the addition of water. • CO2 removal unit for the CO2 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 CO2 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 RREF 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 CO2 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 CO2 removal. The effects of the reformed fuel gas composition, temperature and pressure on the amine absorption system for the CO2 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 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.

The results of the investigation of the flow in a transparent (quartz tube) downscaled (≈1:3) model of a lean-premix type gas turbine combustion chamber are presented and discused. The model was tested at atmospheric pressure in reacting conditions; flow measurements were taken by a two-channel fiber-optic laser doppler velocimeter, using Al2O3 seeding of the air flowrate. The measurements cover a wide flow field inside the combustion chamber, including flame development and recirculating regions. Long-time samples (10–20 s) were used in order to achieve a good accuracy in the measurement of average flow conditions over the whole flow field; this involved a limited capability of representation of high-frequency components of turbulence, which could be locally obtained with optimization of the data rate and seeding conditions. Fast measurements were also locally performed where the seeding conditions were favourable. Integral variables and power spectra for reacting conditions show some distinctive aspects for the turbulence structure of reacting turbulent flows in confined spaces. Further measurements cover the outlet throat section of the premix combustor, demonstrating the persistence of a radial flow component on account of wall curvature effects and a certain degree of asimmetry in the inlet velocity distribution.Copyright © 1997 by ASME

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.

An innovative gas turbine cycle is studied, which can offer several advantages from the point of view of environmental friendship and peakload shaving capabilities. The basic idea of SCGT/CC is of cooling down the exhaust to temperatures as low as to allow full condensation of the water vapor; a large part of the exhaust gases is then recirculated to the compressor; the condensed water can be reinjected by means of a pump at compressor delivery. For maximum performance it is convenient not to inject this water flow, but rather to use it for other purposes; however, water injection produces a power boosting effect (at the expense of a small decrease in efficiency) which can be useful for peakload shaving applications. The working gas composition in the GT cycle is that corresponding to stoichiometric combustion, which opens the possibility of applying techniques for CO 2 recycling and general exhaust gas treatment. The cycle guarantees a high level of efficiency, and its adoption should imply minor modifications to existing equipment.

This innovative gas turbine cycle can offer several advantages over conventional cycles from the point of view of environmental friendship. The basic idea of SCGT/CC (Semi-Closed Gas Turbine/Combined Cycle with water recovery) is to cool down the exhaust temperatures to allow full condensation of the water vapor, and recirculate a large part of the exhaust gases to the compressor. The condensed water can then be reinjected by means of a pump at compressor delivery. The working gas composition is thus close to that corresponding to stoichiometric combustion, which opens the possibility of applying techniques for CO2 recycling and general exhaust gas treatment. An increase in work output is connected to water injection, while a high level of efficiency is maintained as the compressor work is reduced and the cycle parameters are tuned for the exhaust of this turbine.Copyright © 1996 by ASME

In the present paper, an exergy analysis of the SCGT/CC cycle is presented. Exergy destruction has been analysed at the component level in order to identify the critical plant devices, considering several operating conditions. The power-plant configuration is similar to that presented in previous works, with the possibility of total or partial water injection in the combustion chamber at peakload conditions. Combustion, heat recovery steam generator (HRSG), water injection/mixing and water recovery system are the main sources of losses, representing globally more than 80% of the overall exergy destruction. The second-law efficiency ranges between 49% and 53%, moving from the fully injected to the not injected condition. These values are close to those of standard open cycles, which means a good potential for the SCGT/CC cycle, which has several advantages from the point of view of containment of emissions and capability of peakload shaving. Peakload operation (with partial or total water re-injection) involves additional waste of exergy, but is attractive as it can be very extended for this plant configuration. Some critical components, such as condensing heat exchanger, show some sensitivity to the operating parameters, which however only marginally affects the cycle performance.

A design of experiment approach was used to solve problems on the new centrifugal compressor stage development test beds at the Nuovo Pignone – GE Oil&Gas premises in Florence, Italy. The company is able to provide centrifugal compressor equipment tailored to the user’s requests, with special reference to the oil & gas market. In order to provide this service, an archive of designs is available which can be adapted to different requirements: CFD is widely used to improve the turbomachinery performance, and on each new stage design extensive fluid dynamics test campaigns are routinely run, in order to confirm the expected performance. Recently inadequacy of the accuracy of the measurements became evident: the cause was traced back to thermal effects which introduced a large uncertainty in the test results, with special reference to machines having large operating Mach number, and low pressure ratio. The present work included: a) The development of a heat transfer model capable of predicting the observed trend of the experimental data. b) The improvement of the accuracy of total temperature measurements, needed to confirm the results of the model. The positive results allow the company to guarantee with increased confidence the expected performance levels.