Rodolfo Taccani

Simulation of process for electrical energy production based on molten carbonate fuel cells

Abstract A global molten carbonate fuel cells (MCFC) power plant steady-state simulation is presented. A performance fuel cell numerical model is developed and integrated as a custom block in Aspen plus™for the whole process simulation. The burner/reformer compact unit is built assembling existing Aspen plus™internal blocks. A simulation is obtained with the preliminary input specification to get to the base case and a sensitivity analysis is conducted, in order to find the process parameters whose change improves the global efficiency.

Estimation of a noise level using coarse-grained entropy of experimental time series of internal pressure in a combustion engine

We report our results on non-periodic experimental time series of pressure in a single cylinder spark ignition engine. The experiments were performed for different levels of loading. We estimate the noise level in internal pressure calculating the coarse-grained entropy from variations of maximal pressures in successive cycles. The results show that the dynamics of the combustion is a non-linear multidimensional process mediated by noise. Our results show that so defined level of noise in internal pressure is not monotonous function of loading.

Performance Analysis and Modeling of Different Volumetric Expanders for Small-Scale Organic Rankine Cycles

In the last years one of the main research topics in energy field is represented by Organic Rankine Cycles (ORCs), due to their applicability in energy recovery from waste heat and in distributed combined heat and power (CHP) generation, particularly in small and micro scale systems. One of the key devices of the cycle is the expander: it must have a limited cost (like all the other components, in order to ensure the economic feasibility), but also a high efficiency, since the temperature of the heat source is often low and then the cycle efficiency is inherently scarce. In the first part of this paper a literature review on various positive-displacement expanders is presented, in order to outline their performances and their application field. Then, the numerical model of a volumetric reciprocating expander is implemented. This model, and another one previously developed to simulate scroll expanders, is combined with a thermodynamic model of the whole ORC system, so that a comparison between the two technologies can be carried out. The results confirm the possibility of realizing small scale energy recovery and cogeneration (CHP) systems with acceptable electrical efficiency also adopting low-cost components, directly derived from large scale industrial components.

Experimental Test Facility for the Analysis of Transient Behavior of High Temperature Fuel Cell/Gas Turbine Hybrid Power Plants

Pressurized high temperature fuel cells and gas turbine integrated power systems are receiving growing attention as capable of reaching very high electrical conversion efficiency even in small size power plants. In this system the fuel and the oxidant (air) enter the cell after being compressed. The fuel oxidation reaction occurs predominantly within the fuel cell. The reaction is completed in a combustion chamber and the pressurized combustion products are exhausted through a turbine. The dynamic interdependences related to the integration of the fuel cell and the gas turbine are not completely understood and unexpected complications and dangers might arise. In fact as a consequence of both the relatively large volume of the pressurized portion of the plant and the shape of the stalled characteristic of available compressors, the plant could be affected by the inception of fluid-dynamic instabilities. In particular, surge could be detected in the transient off-design operational conditions occurring during plant regulation, start up and shut down. The paper presents a new experimental fuel cell gas turbine simulation facility that has been constructed at the Mechanical Engineering Department of the University of Trieste, Italy. The facility was designed to examine the effects of transient events on the dynamics of these systems. The theoretical analysis of the plant is completed using a dynamic model of the system purposely developed.

Micro-Organic Rankine Cycle systems for domestic cogeneration

Abstract The Chapter presents the requirements and the main features of a domestic cogeneration unit, based on Organic Rankine Cycle (ORC) technology. The achievable electrical efficiency and proper sizing are discussed in detail, other matters of choice are also taken into account, such as reliability, safety, noise, and the cost of purchasing and operation. To better understand the possible benefits of a cogeneration system, even with low electrical efficiency, the Primary Energy Saving (PES) diagram and the Economic Recovery Index (ERI) diagram are introduced. Then, the claimed performance parameters of existing models and prototypes are discussed and a comparison is outlined with solutions based on Stirling engines. Afterwards, the main technical features of domestic ORC components are presented, with special attention given to the expander and the feed pump. Also the control strategy options for the unit are presented, taking into account the peculiarity of a domestic application. Finally, two possible options are discussed for the integration of a domestic cogeneration unit: a solar thermal system to drive the ORC and an ejector refrigeration cycle to obtain a Combined Cooling Heat and Power (CCHP) system.