Antonio Piacentino

A methodology for sizing a trigeneration plant in mediterranean areas

Combined heat and power production is an old and well-known technique for the rational use of energy and, thanks to more than fifty years of experience, the state of art can be considered very advanced from a technological point of view. Trigeneration, that is combined electric, heat and cooling energy production, is however a quite recent technology and is becoming economically viable thanks to the commercial spread of absorption chillers. In fact, a well-projected trigeneration plant can achieve better results than a cogenerative one. The CHCP plant benefits over CHP will be underlined, showing the effects of regularisation of annual thermal load curves generated by consumption for feeding the absorption chiller, that leads to a more effective choice of the prime mover. Traditional evaluations of CHP or CHCP plants are finalized to calculate thermodynamic efficiency, and not to examine the primary energy savings that is possible to obtain. However, lack of considerations on the methodology used for plant management can deeply influence the obtained results. It is furthermore recognised that a cogeneration or trigenerative plant must be managed in order to strictly follow thermal demand, since it is possible to sell to the public grid the excess electric energy. This study starts from the results on a energetic consumption research in the hotel sector, and in particular from the complete data on thermal and cooling consumption in several European hotels. The authors propose a general and innovative criterion on plant management and determine, on the base of the examined case-studies, some correlations which allow to size the main components of the plant, using only few data which are easy to obtain.

Energy saving with MSF-RO series desalination plants

Two major techniques are commercially used in different parts of the world: distillation and membrane processes. The dominant distillation process is multi-stage flash (MSF), and the main membrane process is reverse osmosis (RO). Although cost factors vary by site, the total cost of producing potable water from seawater with the RO process is today usually less than thermal desalting processes and the economic advantages of RO vs. evaporation process, such as MSF, are responsible for the rapid increase in use of seawater RO. In many countries both RO and MSF processes are operating. Reduction in product water cost could be achieved when a hybrid MSF-RO system is used, instead of a parallel system to produce drinking water from seawater. An integrated system for the desalination of the seawater is proposed. The plant is composed of reverse osmosis and multistage flash in series. Electrical and thermal energy are supplied by a cogeneration group for the production of electrical and thermal energy connected to the public net. From a first analysis, the proposed plant seems to allow some simplifications and cost reduction for the fresh water, compared to the equivalent systems in parallel.

Salinity gradient engines

Abstract This chapter is devoted to the description of a new class of heat engines based on salinity gradient technology and able to convert low-grade heat into power. The salinity gradient power (SGP) process is employed within a closed loop composed of two different sections: (i) the SGP unit devoted to the energy production, and (ii) a regeneration unit fed by the solutions exiting from the SGP unit and able to restore the initial concentration, thus regenerating the salinity gradient. The main features, limits and perspectives of this novel heat engine are described along with an overview of the state of the art presented in the literature and an example of exergetic analysis of the cycle. Also, additional information on the availability of the low-grade heat and on the economic evaluation of the produced energy is presented..

Assessing the Robustness of Thermoeconomic Diagnosis of Fouled Evaporators: Sensitivity Analysis of the Exergetic Performance of Direct Expansion Coils

Thermoeconomic diagnosis of refrigeration systems is a pioneering approach to the diagnosis of malfunctions, which has been recently proven to achieve good performances for the detection of specific faults. Being an exergy-based diagnostic technique, its performance is influenced by the trends of exergy functions in the “design” and “abnormal” conditions. In this paper the sensitivity of performance of thermoeconomic diagnosis in detecting a fouled direct expansion coil and quantifying the additional consumption it induces is investigated; this fault is critical due to the simultaneous air cooling and dehumidification occurring in the coil, that induce variations in both the chemical and thermal fractions of air exergy. The examined parameters are the temperature and humidity of inlet air, the humidity of reference state and the sensible/latent heat ratio (varied by considering different coil depths). The exergy analysis reveals that due to the more intense dehumidification occurring in presence of fouling, the exergy efficiency of the evaporator coil eventually increases. Once the diagnostic technique is based only on the thermal fraction of air exergy, the results suggest that the performance of the technique increases when inlet air has a lower absolute humidity, as evident from the “optimal performance” regions identified on a psychrometric chart.

Analysis of a Reciprocate Engine–Based Cogeneration Plant With High Temperature Heat Recovery for Industrial Uses

In consequence of the increasing awareness on the future scarcity of fossil energy sources and the global warming impact of energy conversion processes, the European Union has been planning several actions to enhance the efficiency of energy use and reduce the environmental impact. The declared goals of EU actions are synthetized in the 20-20-20 formula, consisting of an expected 20% increase of energy efficiency, a 20% contribution to the total energy supply by renewable sources and a 20% abatement of pollutant emissions. Applications of cogeneration in process industry can significantly contribute to achieve these targets. In this paper a reciprocate engine-based Combined Heat and Power (CHP) plant is presented, serving a pasta factory located in Sicily and installed by an Energy Service COmpany (ESCO) within the context of a national implementation scheme of Energy Saving Certificates (or “white certificates”). The CHP plant, with a 650 kWe capacity, currently covers a relevant fraction of the electric and high-temperature heat loads during peak hours, while it is switched off during off-peak hours because of the much lower electricity price. Heat content of flue gases is recovered by two cascaded gas-diathermic oil and diathermic oil-water heat exchangers; the superheated water obtained is then supplied to the pasta dryers. The first part of the paper provides a detailed plant description and an energetic analysis of historical performance data collected along the last two years of operation. Both the critical analysis of the lay-out and the evaluation of energy saving indicators reveal the current scheme to represent a sub-optimal solution for the particular application. In the second part of the paper a modified solution is simulated, consisting of the same CHP unit equipped with additional heat exchangers for heat recovery from the cooling water jacket circuit. The marginal energetic and economic benefits compared to the current plant setup are calculated; the results are presented in analytic and graphical form, coherently with the provisions of Directive 2004/8/EC and accounting separately for the different cost and revenues (fuel for the CHP unit and the supplementary boilers, electricity purchased from or supplied to the grid, taxes, etc.). The improved solution, designed to increase the thermal efficiency of the CHP unit by allowing a full exploitation of heat cascades, resulted to provide evident benefits and to make the CHP unit to comply with all the current legislative provisions for the assessment of highly efficient CHP plants. Margins for further improvements are also briefly discussed.Copyright

5.18 Energy Management in Geothermal Energy Systems

Authors propose a thermoeconomic analysis of a renewable polygeneration system producing power, desalinated water, heating and cooling and connected to a district heating and cooling network supplying a small district. A comparison between two layouts is performed, a hybrid (solar and geothermal) and a geothermal one, by performing a 1-year dynamic simulation and processing the results on different time bases. A parametric analysis is carried out to assess system performance and its capability to match the time-dependent energy demands. The hybrid configuration provides the best thermodynamic and environmental performances; conversely the geothermal one provides the highest economical profitability, achieving a much lower simple payback time, averaging 4.3 years instead of the 8.4 years of the hybrid configuration.

Trigeneration and Polygeneration Configurations for Desalination and Other Beneficial Processes

Abstract The integration of renewable energy sources (geothermal, biomass, and solar) and desalination systems into novel polygeneration plants is investigated. Two main arrangements are considered: geothermal (GP) and biomass (BP) polygeneration. Both systems include concentrating photovoltaic/thermal solar collectors, a multieffect distillation system for seawater desalination, a single-effect LiBr-H2O absorption chiller, storage tanks, heat exchangers, balance-of-plant devices; a biomass auxiliary heater and geothermal wells are also included, in BP and GP, respectively. The systems can provide electricity and hot water, used for space heating, cooling, domestic hot water production, and drinkable desalted water. Both systems are simulated by means of a zero-dimensional dynamical simulation model. Thermoeconomic, exergy, and exergoeconomic analyses are also presented, aiming at defining the best values of the main design variables. Two case studies are discussed: city of Naples (BP) and Pantelleria island (GP), both characterized by solar and geothermal resources and scarcity of fossil fuels and freshwater.

Thermodynamic, Exergy, and Thermoeconomic analysis of Multiple Effect Distillation Processes

Abstract Multiple effect distillation (MED) is nowadays the preferred technology for the construction of new plants based on thermal processes in the growing desalination market. MED technology, in fact, presents a number of advantages with respect to the more traditional multistage flash technology, among all the lower energy consumption achievable in MED plants. However, a large potential for improvement in terms of lowering production costs still exists, which stimulates further efforts on process optimization from companies and researchers involved in the field. Thermodynamic and exergy analysis provides useful insights regarding the identification of main inefficiencies and the margins for performance improvements. A number of works have focused their attention on these aspects, presenting innovative investigation tools eventually applied to theoretical or real case studies. In the present chapter, the fundamentals of thermodynamic and exergy analysis for MED process optimization are presented. “Exergy costing” is also discussed and proposed as an innovative method capable of reflecting how thermal inefficiencies contribute to a gradual increase in the economic value (to be intended as a cost of generation) of material streams along the process. In order to achieve a more comprehensive view, the aforementioned analyses are carried out for a reference MED plant assumed as the case study.

SETUP OF VIRTUAL EXPERIMENTS AND CRITICAL ANALYSIS OF CONVENTIONAL THERMOECONOMIC DIAGNOSIS OF MULTIPLE FAULTS IN AIR-CONDENSED ROOFTOP SYSTEMS

The diagnosis of soft faults in vapor compression cooling systems is a crucial activity, since malfunctions may provoke heavy degradation in plant performance and increase the power consumption for space cooling. Among the various Faults Detection and Diagnosis techniques developed over the last two decades, thermoeconomic diagnosis has been playing only a marginal role due to the difficulties encountered when applying the conventional thermoeconomic approaches to vapor compression refrigeration plants. In this paper a critical analysis on capabilities and limits of thermoeconomic diagnosis of refrigeration systems is proposed. The reference plant assumed for this study is a 116 kWc air-condensed rooftop systems charged with R407C as refrigerant. A reliable 1-D steady-state simulator is used to calculate thermodynamic and performance data in “off-design” operating conditions; since the simulator has no specific capabilities to simulate faulty systems, literature-derived results were used to adjust the input settings for each specific fault simulated. Among the most common faults in rooftop air conditioners, four different malfunctions are examined: fouling at condenser, fouling at evaporator, refrigerant undercharge (either due to leakage or erroneous charging during service) and extra-superheating along the suction line; the faults are imposed both individually and simultaneously. The thermoeconomic diagnosis is performed basing on the “fuel impact” approach; the need to split physical exergy into its thermal and mechanical fractions and the presence of dissipative components suggested us to formulate some methodological premises, discussed in detail in the paper. The results testify that the adopted conventional approach is not very reliable; although some faults are properly identified, in fact, false fault signals and erroneous causalization eventually resulted, due to the presence of system-level faults (i.e. faults not strictly associated with any specific plant component, like refrigerant undercharge), the subjective assumptions made as concerns the cost allocation of residues and some controversial aspects concerning the productive structure.Copyright

ANALYTICAL PREDICTION OF SPREAD SCENARIOS FOR SMALL-SCALE CHP SYSTEMS

In this paper the potential for penetration of small scale cogeneration is assessed at EU level, starting from an overview of the present CHP market. The new EU Directive, representing a milestone in the EU policy for the growth of cogeneration, requires further provisions and large financial efforts to favour increases in the CHP installed capacity and to contribute in overcoming the main obstacles to the spread of polygeneration. Targeting the incentives to all size plants is verified not to be an effective approach, because of the different obstacles to the spread of CHP systems existing in small and large applications. After identifying the main factors influencing the CHP potential in a liberalized energy market, an original index expressing the opportunity for new profitable CHP installations is introduced. Future scenarios for CHP penetration at EU and national level are presented and the expected effects of different policy actions.