1,721,004 research outputs found
Analysis of biomass chars thermal decomposition: Experimental tests and modelling in N2 and CO2 atmosphere
No full textChar is a by-product of biomass gasification; nonetheless, it can be valorized in several ways, for wastewater treatment, for instance, or as bio-fertilizer. Char has also been observed to have a high potential for catalytic tar reduction. With a view to designing a char-based gas filtering system for tar cracking applications, it is of key importance to study the behavior of char in terms of mass degradation. For this purpose, the process of char thermal decomposition under different operating conditions has been addressed in the present work. Char samples collected from a local small-scale gasification plant have been studied both under inert (nitrogen) and under reactive (carbon dioxide) atmosphere. Thermogravimetric tests and thermal degradation tests in a lab-scale fixed-bed reactor have been performed. In carbon dioxide, the char mass loss resulted to be much more conspicuous, since many and complex reactions are involved in the kinetics of CO2 gasification. As regards the thermal decomposition of char in inert atmosphere, it has then been modelled by means of a first-order kinetic model coupled with a fluid-dynamic model, thus reproducing the temperature distribution and the mass loss occurring inside the fixed-bed reactor. The developed model predicted the char degradation in a satisfactory way
An efficient numerical scheme for the thermo-hydraulic simulations of thermal grids
No full textRenewable and smart energy systems require district heating and cooling grids able to operate with variable flow rates, to manage different supply temperatures, and to support distributed energy production involving bidirectional flows. Due to these requirements, accurate and effective thermo-hydraulic models are essential to correctly simulate the flow rates, the head drops and the temperature transients for supporting the design, management and optimisation of thermal distribution networks. In this article, an efficient numerical scheme for the simulation of thermal grids based on a thermo-hydraulic model with a quasi-dynamic approach is proposed. Global gradient algorithm of Todini together with a uniformly distributed representation of demand along the pipes is used for steady-state hydraulic simulations of the networks modelled according to the graph theory. The temperature distribution is computed by solving a first order hyperbolic PDE which accounts for heat advection in the flux term and heat dissipation in an algebraic source term. A very efficient second-order Eulerian-Lagrangian finite volume scheme is employed on a staggered mesh, which evolves in time the temperature distribution starting from the velocity distribution given by the hydraulic solver. The usage of a Eulerian-Lagrangian algorithm for the discretisation of the convective terms, allows the proposed model to be unconditionally stable for every time step size. As such, the main advantages of the proposed model are the flexibility due to the admissibility of any spatial-temporal discretisation, the second order accuracy provided by both the demand schematisation and the thermo-hydraulic solver, and the computational efficiency guaranteed by the decoupled modelling approach. The resulting algorithm is extensively validated on four tests consisting of thermal grids of various complexity that have been carefully designed in order to capture different features and behaviours of the model. The accuracy of the results in terms of velocity, pressure and temperature is tested by separately checking the symmetry, the advection term, the heat loss component and, finally, by simulating a complex grid configuration with multiple heat sources. The article aims to present a proof-of-concept concerning a breakthrough numerical scheme for the efficient thermo-hydraulic simulation of pipeline networks, which proves to be suitably implemented in the modelling of district heating and cooling networks
Kinetic Characterization of the Residues from the Pruning of Apple Trees for their Use as Energy Vectors
No full textEnergy and environmental analysis of an innovative system based on municipal solid waste (MSW) pyrolysis and combined cycle
No full textThis paper presents the energy and the environmental impact analysis of an innovative system based on the pyrolysis of MSW which produces solid (char), liquid (tar) and gas (syngas) fuels used in a combined cycle for electric power generation. The syngas, after filtration and compression, feeds two gas turbines. In turn, the exhaust from the gas turbines, after post-combustion with char and tar, drives a steam turbine power plant. Before being discharged, the flue gas is processed in a selective catalytic reduction (SCR) unit to reduce CO, VOC and NOx content and is filtered to remove particulate matter.
This innovative approach to energy recovery from MSW combines high energy effciency with a low level of polluting emissions. The estimated global effciency of the plant, referred to the LHV of the MSW, is around 28–30%, a much higher value than ordinarily obtained in traditional waste incineration plants. The environmental analysis includes a study of the polluting emissions and the simulation of their concentration in the area surrounding the plant: the emissions of the plant have a negligible influence on the original polluting levels of the settlement are
Valorization of Biomass Gasification Char as Filler in Polymers and Comparison with Carbon Black
No full textChar, the solid residue produced during biomass gasification, is usually treated as a waste with high environmental and economic costs associated to its disposal. However, char shows remarkable properties that make it suitable for a plethora of different applications. In particular, this study aims at investigating the feasibility of using char as filler in polymers for boosting polymer thermal stability and electrical conductivity, and comparing its performances with carbon black (CB), a more traditional carbonaceous filler. Char residues were collected from a commercial biomass gasifier, thoroughly characterized, and compared with CB. Both materials were used in combination with a styrene-ethylene-butylene-styrene (SEBS) matrix for the production of two different compounds, deeply characterized as well. An addition of 44 wt% of char increases the thermal stability of the compound and its electrical conductivity up to 2 x 10(-3)S cm(-1), without interfering with its structure and mechanical properties. Less CB (20 wt%) was needed for obtaining composites with the same electrical conductivity. The findings of this study pave the way for new valorization routes for large amounts of char in cutting-edge applications and present the opportunity to the polymer manufacturing to use a high-available and low-cost substitute for carbon-based fillers
Valorization of Biomass Gasification Char as Filler in Polymers and Comparison with Carbon Black
Full text linkProcess analysis of an MCFC power plant fed with a biomass syngas
No full textThe coupling of renewable energy sources and innovative power generation technologies is of topical interest to meet demands for increased
power generation and cleaner environmental performance. Accordingly, biomass is receiving considerable attention as a partial substitute for fossil
fuels, as it is more environmentally friendly and provides a profitable way of disposing of waste. In addition, fuel cells are perceived as most
promising electrical power generation systems. Today, many plants combining these two concepts are under study; they differ in terms of biomass
type and/or power plant configuration. Even if the general feasibility of such applications has been demonstrated, there are still many associated
problems to be resolved. This study examines a plant configuration based on a molten carbonate fuel cell (MCFC) and a recirculated fluidized-bed
reactor which has been applied to the thermal conversion of many types of biomass. Process analysis is conducted by simulating the entire plant
using a commercial code. In particular, an energy assessment is studied by taking account of the energy requirements of auxiliary equipment and
the possibility of utilizing the exhaust gases for cogeneration
Experimental Investigation and RSM Modeling of the Effects of Injection Timing on the Performance and NOx Emissions of a Micro-Cogeneration Unit Fueled with Biodiesel Blends
Full text linkThe (partial or total) substitution of petro-diesel with biodiesel in internal combustion engines (ICEs) could represent a crucial path towards the decarbonization of the energy sector. However, critical aspects are related to the controversial issue of the possible increase in Nitrogen Oxides (NOx) emissions. In such a framework, the proposed study aims at investigating the effects of biodiesel share and injection timing on the performance and NOx emissions of a diesel micro combined heat and power (CHP) system. An experimental campaign has been conducted considering the following operating conditions: (i) a reference standard injection timing (17.2° BTDC), an early injection timing (20.8° BTDC), and a late injection timing (12.2° BTDC); (ii) low (0.90 kW), partial (2.45 kW), and full (3.90 kW) output power load; and (iii) four fuel blends with different biodiesel (B) shares (B0, B15, B30, and B100). Experimental data were also elaborated on thanks to the response surface modelling (RSM) technique, aiming at (i) quantifying the influences of the above-listed variables and their trends on the responses, and (ii) obtaining a set of predictive numerical models that represent the basis for model-based design and optimization procedures. The results show: (i) an overall improvement of the engine performance due to the biodiesel presence in the fuel blend —in particular, B30 and B100 blends have shown peak values in both electrical (29%) and thermal efficiency (42%); (ii) the effective benefits of late SOI strategies on NOx emissions, quantified in an overall average NOx reduction of 27% for the early-to-late injection, and of 16% for the standard-to-late injection strategy. Moreover, it has emerged that the NOx-reduction capabilities of the late injection strategy decrease with higher biodiesel substitution rates; through the discussion of high-prediction-capable, parametric, data-driven models, an extensive RSM analysis has shown how the biodiesel share promotes an increase of NOx whenever it overcomes a calculated threshold that is proportional to the engine load (from about 66.5% to 85.7% of the biodiesel share)
Building Simulation Applications BSA 2013 - Proceedings of 1st IBPSA Italy conference
Full text linkBuilding Simulation application 2013 was the first IBPSA Italy regional conference on building performance simulation. The two-day event focused on three main subjects: simulation of building performance, actual perspectives in building physics and simulation tools. The principal mission is to promote and advance the practice of building performance simulation in order to improve the design, construction, operation and maintenance of new and existing building
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