931 research outputs found
Multi-objective Optimization under Uncertainty of Novel CHPC Process
No full textCombined Heat and Power (CHP) and biomethane upgrading plants are the two main processes that use biogas in Europe. The first converts biogas into electric energy and heat while the second consist of the purification of methane, via removal of other components, and its injection into the national natural gas distribution grid. They both are considered to be green technologies but the overall carbon balance is positive for both processes. Use of biogas as raw material in chemical synthesis allows to fix carbon in the chemical molecule and avoid its release as carbon dioxide. This is the basic idea of Combined Heat Power and Chemical plants (CHPC). Starting from biogas, CHPC produces methanol, a valuable and important building block for industrial chemistry. In this work we optimized the entire process by using multiple objective functions (economics and environmental) and considering the uncertainty of the feed composition. The results of mono-objective optimization show that the CHPC plant can be economically feasible with a net consumption of CO2. Multiple objective optimization identified the operating conditions in which payback time is reasonable and CO2 balance negative. Optimization under uncertainty allowed to design a more flexible and realistic process which can accommodate the variations in inlet biogas composition
Present Status of Mixed Plastic Waste Pyrolysis: Plant Simulation through Aspen Hysys
No full textThe widespread use of plastics results in plastic waste generation. After reuse, recycling is the preferred pathway to reduce the need for virgin feedstock. Concerning mechanical recycling, pyrolysis, consisting of heating the feedstock to promote the thermal degradation of polymers, allows to process Mixed Plastic Wastes (MPW) which cannot be easily sorted. Nowadays, chemical recycling through pyrolysis has reached the demonstration scale, but it is still challenging its further scale-up. In this work, a simulation of a MPW pyrolysis plant coherent with the present technology status is presented. The simulation was performed on Aspen Hysys v11. Unit operations composing the system were chosen according to literature and patent reviews. The process flow diagram of the system is composed of 4 lines in parallel, each one constituted by a reactor, one or more condensation (flash) steps, and a water scrubber (ex-situ dehalogenation) for incondensable gases before their combustion to sustain the reactor energy demand. Each line processes 5000 t/y, representing current scalability limits. The MPW feedstock mass composition assumed is the following: 45 % for both polypropylene (PP) and polyethylene (PE), 8 % for polystyrene (PS), and 1 % each for polymethylmethacrylate (PMMA) and polyvinylchloride (PVC). The reactor has been modeled as a conversion reactor which satisfies the conservation of atoms yielding gaseous, liquid, and solid products of 20, 70, and 10 % of the feedstock mass respectively. After the condensing units, a single distillation column collects the oil produced by each line. The influence of changing the number of condensation (i.e., flash) steps has been investigated. The maximum condensate production was observed for one flash unit. Employing fewer flash units allows to obtain more condensate, paying a slightly larger reboiler duty
Assessing Thermodynamic Flexibility Boundaries via Residue Curve Maps
No full textResidue curve maps (RCMs) are a widely exploited tool to assess whether a multicomponent mixture separation by distillation results to be feasible or not. They usually refer to a given feed composition and to the products purities as specifications; sometimes the whole distillation regions can be discussed in order to evaluate all the mixture possible splits (Petlyuk&Danilov (2001), Petlyuk (2004)). All these considerations are nevertheless related to nominal operating conditions, that is for a given and constant feed composition. If feed perturbations are likely to occur (e.g. separation downstream a fermentation process) a flexibility analysis is required to assess the operation feasibility boundaries under uncertain conditions (Swaney& Grossmann (1985)). Moreover, product recovery is often a more appealing specification from an industrial point of view since it is directly related to the process productivity. For all these reasons, this study deals with the use of RCMs to assess the thermodynamic flexibility limits of a simple distillation case study for a given bottom product recovery and purity under uncertain operating conditions. The starting binary mixture is water and n-butanol, a common and well-known mixture whose separation by simple distillation shows an heterogeneous azeotrope. One component at a time is then added up to obtain an ABE/W (acetone, butanol, ethanol and water) mixture. Due to the high nonideality of the mixture, the addition of an organic component substantially affects the equilibria. A thermodynamic flexibility analysis methodology was outlined for both the binary and ternary cases as well as for the quaternary one. After that, the separation feasibility of the binary mixture was compared to the others (Di Pretoro et al. (2019)). Beside illustrating the procedure for thermodynamic flexibility assessment via RCMs, this analysis aims to show how to enhance the separation from a flexibility point of view taking advantage of the mixture nonideality
The Direct Costs for Cover Crops Cultivation: Comparison Between Different Agronomical Practices
No full textHome AIIA 2022: Biosystems Engineering Towards the Green Deal
Conference paper
The Direct Costs for Cover Crops Cultivation: Comparison Between Different Agronomical Practices
Aldo Calcante, Daniele Manenti & Roberto Oberti
Conference paper
First Online: 01 July 2023
25 Accesses
Part of the Lecture Notes in Civil Engineering book series (LNCE,volume 337)
Abstract
As it is known, cover crops are plants that cover the soil between the harvest of the main crop and the seeding of the later. They are herbaceous species that are not cultivated for their commercial value, but to obtain agronomical and environmental benefits. These species are inserted in the production processes with the primary aim to maintain soil covered by vegetation in periods when the same soil would remain lacking in every cultivation, and therefore subject to damaging effect from pedological point of view. The limits of cover crops are due to their nature. Indeed, since they are crops which do not have a commercial value, the most significant aspect is related to their production costs therefore the incidence of costs for the purchase of seed, for seeding and for the termination must be limited.
The goal of this study is to experimentally evaluate and analyze in details the fuel consumption, the main operative parameters (i.e. workability and hours necessary to carry out every single mechanized activity per hectare) and costs per unit of area for fuel, labor and agrochemical required for the cover crops cultivation, as a function of different agronomical practices applied. In particular, the study takes into account the following agronomical practices: 1) conventional tillage, 2) minimum tillage, 3) direct seeding and 4) no-tillage and, to destroy cover crop, the mechanical and the chemical termination
Mountain protected areas as refuges for threatened freshwater species: the detrimental effect of the direct introduction of alien species
No full textOne of the main threats to native European crayfish species is presented by the spread of invasive ones, which are vectors of the crayfish plague Aphanomyces astaci. In particular, the Austropotamobius pallipes complex is suffering extensive decline in its whole distribution range. In this paper, we describe a case of extinction of a native population of the A. pallipes complex driven by the direct human introduction of the alien species Orconectes limosus, in a mountain protected area in northern Italy. The local extinction event of the native crayfish population is reported, and the factors that drove it are reconstructed. Our results help to better understand the threats to native crayfish species occurring even in protected areas, as well as to establish proper prevention and management actions
The 3-D Supply Chain Management
No full textIncreasing in market competitiveness for the worldwide energetic demand and the raw materials supply, in primis natural gas and crude oil, even more constrained by contract clauses and trade agreements, is pushing main enterprises and both National and European energetic corporations to be interested in the supply chain management as a valid support for decision-making processes and strategic optimization.
This paper remarks the importance of a strategic coordinator, which can decide when and especially what to produce. It is placed on the top of the widespread tactical coordinators (model predictive controls, dynamic optimizations ...), which can decide how to produce. The strategic coordinator has the aim to (i) reduce the energetic consumption; (ii) fulfil final users’ market demand; and (iii) transform process transients, demand volatilities, and market price fluctuations into interesting opportunities to improve enterprise-wide benefits.
Specifically, the paper wants to introduce the commercial hierarchy in the multifaceted problem of the enterprise-wide optimization of decentralized-production societies, going beyond horizontal (process flow) and vertical (process control) hierarchies, which characterizes the traditional supply chain. It strictly deals with the business supply chain, by discussing the business strategies adopted by large-scale societies and main energy-intensive production sites as well as contract clauses defined by National organizations, including the National (Italian) electric energy suppliers (TERNA, GRTN)
Heat and mass transfer in roast beef cooking. Temperature and weight loss prediction
No full textThe development of food processes, ingredients and formulations is a daily topic for the food industries. Model-based product, process and equipment design are getting increasing industrial attention, due to the high potential in matter of time and money saving. Bringing these advantages to the consumers’ table by the application of this approach is one of the ultimate challenges of food and bioprocess engineering. This work aims to consider roast beef cooking as a practical, widespread, case study. A computational model, which correlates temperature, time and weight loss for a standard piece of meat cooked in oven, is developed and validated with experiments. The thermal properties are derived with a general approach, applicable to other food. The heat and mass transport equations are based both on conservation laws and on the cooking conditions
Processo per operare su un fluido di lavoro secondo un ciclo termodinamico frigorifero
No full textProcesso per operare su un fluido di lavoro secondo un ciclo termodinamico frigorifero
comprendente le fasi cicliche di:
5 a) evaporare un fluido di lavoro allo stato liquido in una unità di evaporazione (10)
generando un flusso di vapore; il fluido di lavoro presentando condizioni iniziali di
temperatura e pressione;
b) comprimere almeno una porzione del flusso di vapore proveniente dalla fase a)
in una unità di compressione (20) aumentando temperatura e pressione del flusso di vapore;
10 c) condensare cedendo calore verso un ambiente esterno almeno una porzione del
fluido di vapore compresso proveniente dalla fase b) mediante una unità di condensazione
(30) generando un flusso di condensato;
d) laminare almeno una porzione del flusso di condensato proveniente dalla fase c)
mediante una unità di laminazione (40) abbassando temperatura e pressione del flusso di
15 condensato per ottenere il fluido di lavoro sostanzialmente alle condizioni iniziali di
temperatura e pressione;
e) inviare il fluido di lavoro proveniente dalla fase d) alla fase a);
la fase a) prevede surriscaldare il flusso di vapore mediante dissoluzione di almeno un
soluto non volatile nel fluido di lavoro e riscaldamento della soluzione ottenuta fino a
20 raggiungimento della temperatura di ebollizione della soluzione e conseguente produzione
di vapore surriscaldato essenzialmente costituito dal fluido di lavoro, detta soluzione
presentando una temperatura di ebollizione superiore alla temperatura di ebollizione del
fluido di lavoro
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