Giampaolo Manfrida

An equilibrium model for biomass gasification processes

Energy conversion systems based on biomass utilisation are particularly interesting because of their contribution to the limitation of global CO2 emissions; within the possible methods for energy-based biomass utilisation, thermal gasification appears as the most mature technology. In the first design stage, the designer of these systems, or the user looking for performance predictions under different operating conditions, has advantages of running thermochemical simulations allowing a prediction of the syngas composition and calorific value. The equilibrium model described in this paper is very simple, but it considers chemical species typically encountered by biomass gasifiers, and was tested against published experimental data.

Life Cycle Assessment of electricity production from poplar energy crops compared with conventional fossil fuels

The environmental impact of electric power production through an Integrated Gasification Combined Cycle (IGCC) fired by dedicated energy crops (poplar Short Rotation Forestry (SRF)) is analysed by a Life Cycle Assessment approach. The results are compared with the alternative option of producing power by conventional fossil fueled power plants. The energy and raw materials consumption and polluting emissions data both come from experimental cases. Thermodynamic models are applied for simulation of the energy conversion system. The results establish relative proportions for both consumption and emissions of the two energy systems, in detail. Considerable differences emerge about the environmental impact caused by the different gasification conditions. The evaluation of the environmental effects of residues of the pesticides in ground/surface water and in the soil required a particular care, as well as the characterisation of all chemicals (herbicides, fungicides and insecticides) used for the crops.

Exergy analysis of the semi-closed gas turbine combined cycle (SCGT/CC)

Abstract 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.

SCGT/CC : An innovative cycle with advanced environmental and peakload shaving features

Abstract 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.

Parametric study of HRSG in case of repowered industrial CHP plant

Abstract The case study here presented deals with modernization of an industrial combined heat and power (CHP) plant located in a medium capacity steelworks industrial site. It is proposed to couple the existing power plant with a new gas turbine unit fired with Corex export gas. This fuel is a cold, low Btu by-product of the Corex process for pig iron production. The idea is to select the right distribution of heating surfaces in the heat recovery steam generator (HRSG) connected to a previously selected gas turbine and to the existing bottoming cycle in order to maximize the efficiency and economical profits of the whole plant. The study was performed using several simulation tools: a complete simulation of the system by means of engineering equation solver and a dedicated Fortran language code capable of performing all energy balances. For the correct design of the HRSG, a pinch analysis was applied. The whole set of simulation tools allowed comparing different solutions, of which the most promising ones are presented and discussed.

Thermoeconomic evaluation of the SCGT cycle

Abstract 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.

Exergy analysis of compression and expansion processes

The thermodynamics of compression and expansion processes in turbomachinery are examined. Rational efficiencies are defined and their relation to isentropic and polytropic efficiencies are discussed. Multistage turbines with extractions are optimized. This approach yields expressions that are independent of the concept of thermodynamic irreversibility.

Semi-Closed Gas Turbine/Combined Cycle With Water Recovery and Extensive Exhaust Gas Recirculation

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

Exergy Analysis of Two Second-Generation SCGT Plant Proposals

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.© 1998 ASME

Flow and turbulence Survey for a Model of Gas Turbine Exhaust Diffuser

This paper presents the results of an extensive set of measurements on a model of an exhaust diffuser for gas turbines. The diffuser is of the straight-wall annular-axial type, typically employed in small-to-medium size gas turbines. It features six high-solidity struts, which support, in the real machine, one of the shaft bearings and have piping for oil supply inside.The 35%-scale model has been tested on a special test stand developed at the University of Perugia, using the suction side of a centrifugal-flow industrial fan of suitable capacity. Inlet speed is around 80 m/s, allowing satisfactory accuracy for flow measurements and the similarity in terms of Reynolds number.The instrumentation, the movement of the measurement point and data acquisition system were designed for automatic running of the tests. Both pneumatic and hot-wire or hot-film probes can be used on the same facility. The same wind tunnel, previous a quick replacement of the model with a probe calibration test section, can be used for calibration of both pneumatic and hot-wire/hot-film probes. A three hole directional pneumatic probe was used for stationary flow measurements to determine the global performance parameters of the model and a split-film probe was used to determine the turbulence characteristics.For four test sections, contour plots are produced of average velocity components, flow angle and turbulence quantities as three components of the Reynolds stress tensor.Copyright