1,720,968 research outputs found
Scale-up of photo-bioreactors for microalgae cultivation by π-theorem
No full textRobust microalgae cultivation at industrial scale needs complex scale-up of photobioreactors since the same yields obtained at lab-scale are hardly reached during pilot or industrial production. In this paper we propose a procedure based on Buckingham π-theorem to perform the scale-up of photobioreactors used to cultivate Chlorella Vulgaris fed by CO2 and wastewater rich in glycerol. This theoretical approach is usually overlooked in favor of the synergy of modeling tailored on the process and piloting, but it grants excellent generalizability. An experimental campaign at three levels was designed and carried out to evaluate the characteristic dimensionless numbers individuated by the theoretical formulation. Since scale-up regards both geometrical dimensions and type of reactor, passing from lab-scale stirred tanks (STRs) to pilot scale tubular and airlift, particular attention was devoted to defining characteristic lengths inside the dimensionless numbers. Moreover, since scale-up also regards the operating mode, scaling from discontinuous to semi-continuous to continuous, some interesting dimensionless numbers arise other than Re, Sh ,Da. They are mainly related to the type of biological process and its operating mode and are the ratios O2/CO2 and T/Topt, the ratio between the incident light intensity and the saturation constant, the absorbance, the ratio between the final and the initial concentration c/c0, the ratio between the maximum increase in cell population and its initial concentration, the ratio between the estimated specific kinetic constant and a variable representing the characteristic time of mixing inside the chosen reactor. Preliminary outdoor tests confirmed the operability of the scaled-up airlift reactors reaching c/c0 = 5.3 – 7.5, with c = 1.15 g L-1 at extraction intervals of 5 days. They were operated under optimal light conditions of incident light greater than Chlorella v. saturation constant and absorbance A = 40 and at incipient churn flow (Re = 10000 - 11000) with dimension of fluegas bubbles around 5 mm, apt to guarantee Sh = 1500-2500; and with a calculated Da around 25
Multiscale mathematical models for simulation and scale-up of green processes in the perspective of industrial sustainability
No full textThe present work presents research studies aimed at developing tools useful to design
engineering solutions moving in the direction of industrial sustainability. The investigations
hereinafter discussed regard an extraction process of active compounds – polyphenols – from
agro-food industry wastes (olive and grape pomaces) and a biorefinery exploiting waste
frying oil, solid organic wastes and algal biomass to produce biofuels. In particular, for the
former topic, a procedure aimed at the evaluation of the technological feasibility at pilot scale
of said process is discussed. The proposed approach takes into consideration the extended
kinetic route coupled with mathematical simulation. Detailed physically-based dynamic
mathematical models, taking into account mass and energy balance equations, are adopted
to describe both the lab-scale and the pilot-scale reactors. Chemical physical parameters
appearing in the models are estimated from the experimental data at lab-scale or are partially
taken from literature. Different heating systems are designed for the pilot scale reactor and
their performance is tested by simulation. Characteristic times are evaluated also during
start-ups and different control loops are analyzed in order to set-up the best process and
operating variables. Average yields in polyphenols are finally evaluated for both the batch
and the continuous operated pilot reactor, by considering feed variability and fluctuations of
process parameters.
For what concerns the biorefinery, special attention was devoted to the modeling of the
airlift reactor, its most delicate and complex component. In fact, to optimize this interesting
microalgae cultivation system, a precise description of the moving interfaces formed by the
liquid and gas phase is critical. In this study, coupled front capturing methods (standard and
conservative level set methods) and finite difference method are used to simulate gas bubbles
dynamics in a pilot-scale external loop air-lift photobioreactor in which microalgae are used
to capture CO2 from flue gas and to treat wastewater. Numerical simulations are carried out
on rectangular domains representing different sections of the vertical axis of the riser. The
data employed was either acquired from previous experimental campaigns carried out in the
airlift reactor or found in the literature. The rise, shape dynamics and coalescence process of
the bubbles of flue gas are studied.
Moreover, for each analyzed applications, a procedure based on Buckingham π-theorem
to perform a rigorous scale-up is proposed. In this way, scale-invariant dimensionless
groups describing and summarizing the considered processes could be identified. For the
research focused on the scale-up of photobioreactors used to cultivate Chlorella Vulgaris,
an experimental campaign at three levels was designed and carried out to evaluate the
characteristic dimensionless numbers individuated by the theoretical formulation. Since
scale-up regards both geometrical dimensions and type of reactor, passing from lab-scale
stirred tanks to pilot scale tubular and airlift, particular attention was devoted to define
characteristic lengths inside the dimensionless numbers
Airlift photo-bioreactors for Chlorella vulgaris cultivation in closed-loop zero waste biorefineries
No full textThis study aims to set up the operating conditions of a battery of airlift photo-bioreactors (AL-PBRs) for Chlorella vulgaris cultivation integrated into a pilot-scale Biowaste-to-Biofuels (BtB) production plant, producing both biodiesel by transesterification of waste frying oils and syngas by wood chips gasification. Microalgae are fed with both wastewater rich in glycerol and flue gas. Mixing, mass transport, kinetics, and light conditions inside the AL-PBRs are chosen by keeping some dimensionless numbers (Re, Sh, Da, and A) fixed around the values found at lab-scale (11000, 1550, 23, 35, respectively).
pH, T, nutrient-related ratios, and light intensity are adjusted inside the optimal ranges found at indoor conditions. The number of AL-PBRs, feeding/extraction time intervals, and flowrates are designed by mass balancing the entire pilot-plant in order to operate in continuous quasi-zero waste.
Outdoor tests confirmed that 12–15 AL-PBRs with a total volume of 125–155 L reuse 28.8 L d−1 of wastewater by-produced from the biodiesel units providing 228 L d−1 of biodiesel and reuse the total of about 90 m3 h−1 of flue gas in exit from the syngas combustion unit with power generation of 9–9.5 kW. The battery works at an initial concentration for each cycle of around 0.5 g L−1 and concentration at extraction of around 1.05 g L−1
A Low-Cost Monitoring System and Operating Database for Quality Control in Small Food Processing Industry
No full textThe use of completely automated systems for collecting sensor data with the aim of monitoring and controlling the quality of small-scale food processes is not widespread. Small and micro-enterprises usually do not carry out their own precompetitive research or prototype development as regards to automation technologies. This study proposes a web-based, low-cost monitoring and supervisory control and data acquisition (SCADA) system whose kernel is available for free, as a possible solution that could be adopted by these food producers. It is mainly based on open SW/HW so as its configuration is adaptable to the application and type of plant. It presents a modular architecture and its main functionalities encompass the acquisition, management, aggregation and visualization of process data, providing an operating database. It also provides food tracking and process quality control: The time series are browsable due to QR-Code generation and different early warning detection strategies are implemented. A tool for solving migration problems based on Fick’s equation is offered as a packaging decision support system
Sustainable Biodiesel Production by Transesterification of Waste Cooking Oil and Recycling of Wastewater Rich in Glycerol as a Feed to Microalgae
No full textThe amount of solid and liquid organic waste and wastewater is continuously increasing all over the world. The necessity of their reuse and recycling is, therefore, becoming more and more pressing. Furthermore, the limited fossil fuel resources, in conjunction with the need to reduce greenhouse gas emissions, advocate the production of renewable fuels. In this work, we analyze a sustainable second-generation process to produce biodiesel by transesterification of waste cooking oil, coupled with a third-generation process in cascade for recycling the incoming wastewater. Since this latter is rich in glycerol, it is used as a feed for microalgae, from which oil can be extracted and added to the waste cooking oil to further produce biodiesel and close the cycle. We studied the influence of different factors like temperature, catalyst load, and reactants ratio on the kinetics of transesterification of the waste oil and estimated the kinetic parameters by different kinetic schemes. The obtained values of activation energies and pre-exponential factors at chosen conditions of T = 60 °C and catalyst load of 0.6% w/w in methanol are: Ea,direct = 35,661 J mol−1, Ea,reverse = 72,989 J mol−1, k0,direct = 9.7708 [dm3 mol−1]3 min−1, and k0,reverse = 24,810 [dm3 mol−1]3 min−1 for the global fourth-order reversible reaction scheme and Ea = 67,348 J mol−1 and k0 = 2.157 × 109 min−1 for the simplified pseudo-first-order irreversible reaction scheme; both in strong agreement with literature data. Furthermore, we designed very efficient conditions for discontinuous and continuous operating mode, both at lab-scale and pilot-scale. The quality of the biodiesel produced from waste cooking sunflower oil is compared with that of biodiesel produced by different kinds of virgin vegetable oils, showing that the former possesses acceptable quality standards (Cetane number = 48 and LHV = 36,600 kJ kg−1). Finally, the recycling of wastewater rich in glycerol as a nutrient for mixotrophic microalgae nurturing is discussed, and microalgae growing kinetics are evaluated (k1 about 0.5 day−1), endorsing the possibility of algae extraction each 4–5 days in a semi-continuous operating mode. The experimental results at the pilot scale finally confirm the quality of biodiesel, and the obtained yields for a two-stage process prove the competitiveness of this sustainable process on the global market
Extraction of polyphenols from olive pomace: Mathematical modeling and technological feasibility in a high temperature and high pressure stirred reactor
No full textA procedure to evaluate the technological feasibility at pilot scale of the extraction process of polyphenols from olive pomace is presented in this work. The proposed approach takes into consideration the extended kinetic route coupled with mathematical simulation. Detailed physically-based dynamic mathematical models, taking into account mass and energy balance equations, are adopted to describe both the lab-scale and the pilot-scale reactors. Chemical physical parameters appearing in the models are estimated from the experimental data at lab-scale or are partially taken from literature. Different heating systems are designed for the pilot scale reactor and their performance is tested by simulation. Characteristic times are evaluated also during start-ups and different control loops are analyzed in order to set-up the best process and operating variables. Average yields in polyphenols are finally evaluated for both the batch and the continuous operated pilot reactor, by considering feed variability and fluctuations of process parameters
Modeling in environmental interfaces
No full textThis chapter focuses on the use of different modeling approaches for the study of the dynamic behavior of environmental interfaces. It provides an overview of the main recent simulation schemes to deal with multiscale physically based models, with particular reference to both moving interfaces and moving environmental compartments. The chapter also provides a brief review of the most commonly used phenomenological bottom-up modeling approaches, state-space and black-box models, data-based mechanistic models. Two case studies in the field of wastewater treatment/biofuel production and groundwater contamination are presented to illustrate the application of some recent techniques described in the chapter
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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