Geometry of diagonal-effect models for contingency tables

In this work we study several types of diagonal-effect models for two-way contingency tables in the framework of Algebraic Statistics. We use both toric models and mixture models to encode the different behavior of the diagonal cells. We compute the invariants of these models and we explore their geometrical structure.Comment: 20 page

Techno-economic analysis of hydrogen production using biomass gasification. A small scale power plant study

Hydrogen has the potential to be a clean alternative to the fossil fuels currently used. This is especially true if hydrogen is manufactured from renewable resources such as biomass. However, hydrogen from biomass faces techno and economic challenges especially in the small size required for the decentralized hydrogen production. In this purpose, a techno economic analysis was carried out on small scale (100kWth) system. The plant is mainly composed of gasifier (double bubbling fluidized bed reactor) coupled with a Portable Purification Unit (PPS: catalytic filter candles, Water Gas Shift and Pressure Swing Absorption). This work focuses on system costs to identify barriers to the development of this technology. A sensitivity analysis was conducted to study hydrogen production cost as a function of capital cost, operating cost and hydrogen production efficiency. The results showed that although efficiency of the production system is the main factor to fall production cost, it cannot be able to reduce costs to favorable level alone. In other words, PPS cost recognized as the major cost is requisite to go down. Therefore, the 50% reduction of PPS cost and the variation of steam to biomass from 1 to 1.5 allow the special cost to fluctuate between 12.75-9.5 €/kg

Perturbation of matrices and non-negative rank with a view toward statistical models

In this paper we study how perturbing a matrix changes its non-negative rank. We prove that the non-negative rank is upper-semicontinuos and we describe some special families of perturbations. We show how our results relate to Statistics in terms of the study of Maximum Likelihood Estimation for mixture models.Comment: 13 pages, 3 figures. A theorem has been rewritten, and some improvements in the presentations have been implemente

Experimental tests of solar collectors prototypes systems

Solar thermal collectors represent one of the most widely used technologies for heat production from renewable energy sources. To increase efficiency and to not increase too much cost different type of solar collectors, and in particular of evacuated tube collectors have been realized. In order to compare performance, tests at different conditions and in different configurations have to be performed. The aim of this paper is to establish the performance of a new prototype via an experimental evaluation of the performance in different conditions and configurations of three collectors. The prototype is particular owing to his new head configuration that permits an innovative parallel configuration way. Therefore, parallel and series configurations have been analyzed applying the UNI-EN 12975, in a steady-state regime. The efficiencies of the two configurations have been tested for different flow rates and different inflow water temperatures. The experimental results show that, with the same input flow rate to the single collector, the parallel configuration has higher performance than the series one, reaching 15% higher level of efficiency. Thus, it seems that these prototypes in optimized configuration can lead to a systems improvement, thereby increasing the overall energy production or giving the same energy production with smaller collector area. © 2015 Published by Elsevier Ltd

Comparison between 1-D and grey-box models of a SOFC

Solid Oxide Fuel Cells (SOFCs) have shown unique performance in terms of greater electrical efficiency and thermochemical integrity with the power systems compared to gas turbines and internal combustion engines. Nonetheless, simple and reliable models still must be defined. In this paper, a comparison between a grey-box model and a 1-D model of a SOFC is performed to understand the impact of the heat transfer inside the cell on the internal temperature distribution of the solid electrolyte. Hence, a significant internal temperature peak of the solid electrolyte is observed for a known difference between anode and cathode inlet temperatures. Indeed, it highlights the difference between the 1-D model and the grey-box model regarding the thermal conditioning of the SOFC. Therefore, the results of this study can be used to investigate the reliability of the thermal results of box models in system-level simulations

energy analysis of a real grid connected lithium battery energy storage system

Abstract Today, in the grid there are more and more installation of renewable energy plants. The renewable sources are so discontinues and they may affect the stability and efficiency of the grid. Many distribution service operators are experimenting the battery energy storage systems (BESSs) to integrate them on the grid and resolve these problems. This paper analyses the energy performance under real conditions of a BESS prototype. The real BESS under focus has made by a lithium battery pack of 16 kWh, a DC/DC converter of 20 kW and an IGBT inverter of 30 kVA with a direct voltage bus of 600 V. The energy analysis has been performed through an integrated data acquisition system that take data from on-board electronic diagnostic measurements and from smart metering data. This latter using remote devices. The tests have been carried out on the system to monitor the following characteristic parameters: current and voltage of the batteries, current and voltage of the grid and current and voltage of the auxiliaries. The system energy performances have been analyzed in dynamic and real conditions with particular reference to the following quantities: energy consumption for the auxiliary system and overall efficiency of the system in a distributed energy resources microgrid. The entire system has been analyzed until twenty-four hours

modeling small scale solar powered orc unit for standalone application

When the electricity from the grid is not available, the generation of electricity in remote areas is an essential challenge to satisfy important needs. In many developing countries the power generation from Diesel engines is the applied technical solution. However the cost and supply of fuel make a strong dependency of the communities on the external support. Alternatives to fuel combustion can be found in photovoltaic generators, and, with suitable conditions, small wind turbines or microhydroplants. The aim of the paper is to simulate the power generation of a generating unit using the Rankine Cycle and using refrigerant R245fa as a working fluid. The generation unit has thermal solar panels as heat source and photovoltaic modules for the needs of the auxiliary items (pumps, electronics, etc.). The paper illustrates the modeling of the system using TRNSYS platform, highlighting standard and "ad hoc" developed components as well as the global system efficiency. In the future the results of the simulation will be compared with the data collected from the 3 kW prototype under construction in the Tuscia University in Italy

Hydrogen-rich gas production by sorption enhanced steam reforming of woodgas containing TAR over a commercial Ni catalyst and calcined dolomite as CO2 sorbent.

The aim of this work was the evaluation of the catalytic steam reforming of a gaseous fuel obtained by steam biomass gasification to convert topping atmosphere residue (TAR) and CH 4 and to produce pure H 2 by means of a CO 2 sorbent. This experimental work deals with the demonstration of the practical feasibility of such concepts, using a real woodgas obtained from fluidized bed steam gasification of hazelnut shells. This study evaluates the use of a commercial Ni catalyst and calcined dolomite (CaO/MgO). The bed material simultaneously acts as reforming catalyst and CO 2 sorbent. The experimental investigations have been carried out in a fixed bed micro-reactor rig using a slipstream from the gasifier to evaluate gas cleaning and upgrading options. The reforming/sorption tests were carried out at 650 °C while regeneration of the sorbent was carried out at 850 °C in a nitrogen environment. Both combinations of catalyst and sorbent are very effective in TAR and CH 4 removal, with conversions near 100%, while the simultaneous CO 2 sorption effectively enhances the water gas shift reaction producing a gas with a hydrogen volume fraction of over 90%. Multicycle tests of reforming/CO 2 capture and regeneration were performed to verify the stability of the catalysts and sorbents to remove TAR and capture CO 2 during the duty cycle

Thermodynamic modeling of hydrogen refueling for heavy-duty fuel cell buses and comparison with aggregated real data

Abstract The foreseen uptake of hydrogen mobility is a fundamental step towards the decarbonization of the transport sector. Under such premises, both refueling infrastructure and vehicles should be deployed together with improved refueling protocols. Several studies focus on refueling the light-duty vehicles with 10 kgH2 up to 700 bar, however less known effort is reported for refueling heavy-duty vehicles with 30–40 kgH2 at 350 bar. The present study illustrates the application of a lumped model to a fuel cell bus tank-to-tank refueling event, tailored upon the real data acquired in the 3Emotion Project. The evolution of the main refueling quantities, such as pressure, temperature, and mass flow, are predicted dynamically throughout the refueling process, as a function of the operating parameters, within the safety limits imposed by SAE J2601/2 technical standard. The results show to refuel the vehicle tank from half to full capacity with an Average Pressure Ramp Rate (APRR) equal to 0.03 MPa/s are needed about 10 min. Furthermore, it is found that the effect of varying the initial vehicle tank pressure is more significant than changing the ambient temperature on the refueling performances. In conclusion, the analysis of the effect of different APRR, from 0.03 to 0.1 MPa/s, indicate that is possible to safely reduce the duration of half-to-full refueling by 62% increasing the APRR value from 0.03 to 0.08 MPa/s

techno economic analysis of in situ production by electrolysis biomass gasification and delivery systems for hydrogen refuelling stations rome case study

Abstract Starting from the Rome Hydrogen Refuelling Station demand of 65 kg/day, techno-economics of production systems and balance of plant for small scale stations have been analysed. A sensitivity analysis has been done on Levelised Cost of Hydrogen (LCOH) in the range of 0 to 400 kg/day, varying capacity factor and availability hours or travel distance for alkaline electrolysers, biomass gasification and hydrogen delivery. As expected, minimum LCOH for electrolyser and gasifier is found at 400 kg/day and 24 h/day, equal to 12.71 €/kg and 5.99 €/kg however, for operating hours over 12 and 10 h/day the differential cost reaches a plateau (below 5%), for electrolyser and gasifier respectively. For the Rome station design, 160 kWe of electrolysers 24 h/day and 100 kWth gasifier at 8 h/day, LCOH (11.85 €/kg) was calculated considering the modification of the cost structure due to the existing equipment, which is convenient respect the use of a single technology, except for 24 h/day gasification