Production Units (production + unit)

Distribution by Scientific Domains

Selected Abstracts

Analysis of the current methods used to size a wind/hydrogen/fuel cell-integrated system: A new perspective

H. G. Geovanni
Abstract As an alternative to the production and storage of intermittent renewable energy sources, it has been suggested that one can combine several renewable energy technologies in one system, known as integrated or hybrid system, that integrate wind technology with hydrogen production unit and fuel cells. This work assesses the various methods used in sizing such systems. Most of the published papers relate the use of simulation tools such as HOMER, HYBRID2 and TRNSYS, to simulate the operation of different configurations for a given application in order to select the best economic option. But, with these methods one may not accurately determine certain characteristics of the energy resources available on a particular site, the profiles of estimated consumption and the demand for hydrogen, among other factors, which will be the optimal parameters of each subsystem. For example, velocity design, power required for the wind turbine, power required for the fuel cell and electrolyzer and the storage capacity needed for the system. Moreover, usually one makes excessive use of bi-parametric Weibull distribution function to approximate the histogram of the observed wind to the theoretical, which is not appropriate when there are bimodal frequency distributions of wind, as is the case in several places in the world. A new perspective is addressed in this paper, based on general system theory, modeling and simulation with a systematic approach and the use of exergoeconomic analysis. There are some general ideas on the advantages offered in this method, which is meant for the implementation of wind/hydrogen/fuel cell-integrated systems and in-situ clean hydrogen production. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Measuring technical efficiency in the stochastic varying coefficient frontier model

Giannis Karagiannis
Stochastic varying coefficient frontier model; Technical efficiency; Nonneutral frontier models; Olive-farms Abstract Due to the assumption that the best practice methods refer to each input separately instead of the whole set of inputs used by a firm, the benchmark technology as defined in the stochastic varying coefficient frontier model may be infeasible and theoretically improper whenever the maximum response coefficients are not coming from the same production unit. To overcome this problem, we propose alternative measures of output-oriented and single-factor technical efficiencies inspired from the maximum likelihood formulation of the nonneutral frontier model. The empirical results indicate that there are significant differences between the two in terms of the estimated efficiency scores but not significant differences we detected in terms of the efficiency ranking. [source]

Economical Feasibility Evaluation of an Ethanol Injection Liposome Production Plant

O. R. Justo
Abstract Over the past few decades liposomes, which are lipid vesicles useful for the controlled release of numerous bioactive compounds, have attracted significant industrial interest. Several techniques have evolved for the manufacture of liposomes on a small scale. However, production on a commercially feasible scale is still somewhat limited. Therefore, this research intends to evaluate the scale-up potential of a liposome production unit using the ethanol injection method, through preliminary economical feasibility estimation, as an addendum to a pre-existing bioactive compound manufacture plant, with the aim of increasing the compound aggregate value. The ethanol injection technique is selected due to its simplicity and low cost, characteristics that make it easily scalable. The preliminary economic evaluation involves the assessment of capital investment, estimation of operating costs, and analysis of profitability. The results of the economic analysis suggest that the process is economically feasible for a plant with a daily production capacity of 288 L of liposomal suspension. [source]

A case of rule-based heuristics for scheduling hot rolling seamless steel tube production

EXPERT SYSTEMS, Issue 3 2006
Jianxiang Li
Abstract: A production scheduling problem for hot rolling seamless steel tube at Tianjin Pipe Corporation of China is studied. Considering the complexity of the problem and the acceptable time for solving it, a rule-based heuristic approach is proposed and implemented. The proposed approach is a bottleneck scheduling method and considers simultaneously all production processes in three production units and ,optimizes' them as a whole. Additionally, the running result shows, on average, that a 3% increase in throughput and a 5% reduction in late deliveries have been achieved since the system implementation. [source]

Applying benchmarking and data envelopment analysis (DEA) techniques to irrigation districts in Spain

J. A. Rodríguez Díaz
indicateurs de performance; benchmarking; DEA Abstract In this research, the application of data envelopment analysis (DEA) is proposed as a methodology to overcome the problems related to the lack of methodology to assign the correct weightings for the calculation of indexes and to the subjectivity of the interpretations of results. DEA is a linear programming technique to determine the relative efficiencies of a company when the inputs and outputs of production units within the company are known, but the productive process itself is not. In this way, quantitative efficiencies and the weighting of any performance indicator can be assessed and compared, permitting managers to obtain a well-defined performance ranking. This is especially important when managers dispose of a limited budget. The results of the application of this methodology to Andalusian irrigation districts (Spain) are presented and discussed here. This study was used to select the most representative irrigation districts in Andalusia which were then studied in greater depth by applying the performance indicators selected by IPTRID for use by the benchmarking international program. Copyright © 2004 John Wiley & Sons, Ltd. Dans ce travail, l'utilisation de la méthode de ,,data envelopment analysis (DEA),, est analysée en tant que méthodologie capable de résoudre les problèmes liés au manque de méthodologie pour l'attribution des pondérations dans le calcul d'indices composites et à la subjectivité des comparaisons. La DEA est une technique de programmation linéaire pour déterminer les efficiences relatives d'une compagnie. Les moyens utilisés sont la connaissance des intrants et produits de la compagnie, ignorant les processus de production. De cette façon, les gestionnaires peuvent obtenir un large ensemble d'indices de gestion qui se révèle particulièrement important lorsque le gestionnaire dispose d'un budget limité. Les résultats de l'utilisation de cette méthode pour l'irrigation dans la région d'Andalousie (Espagne) sont présentés et discutés dans ce travail. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Effect of Stocking Weight and Stocking Density on Production of Hybrid Striped Bass (Sunshine) in Earthen Ponds in the Second Phase of a 2-Phase System

Louis R. D'Abramo
Sunshine bass from Phase I or pond production were graded into two weight classes, 3 and 5 g, and stocked into experimental earthen ponds at a density of either 8,649/ha or 11,120/ ha in a 2 × 2 factorial design. After stocking, the fish were fed a commercially manufactured feed (43.0-45.5% crude protein) twice daily to satiation for 17 mo. At harvest, mean survival ranged from 67.4 to 84.8% but was highest for the fish stocked at 5g. Average production Tor ponds stocked at 8,649/ha and 11,120/ha, regardless of stocking weight, was 4,506 kg/ha and 5350 kg/ha, respectively. Production and percentages of assigned weight classes were not significantly different among treatments as a result of wide variation among replicates. Using size-dependent market prices assigned to the different harvest size groups, an economic analysis revealed gross receipts, variable costs, and total costs for the 11,120/ha 5-g treatment. Net returns were not significantly different among the four treatments due to large variation among replicates per treatment. These results confirm that the traditional phase II of pond production can be eliminated in favor of a direct stocking of phase I fish into a single production phase and economically competes very well with traditional three-phase growout management. The potential reduction in turnover time of production units achieved through the direct stock practice is an efficiency trait that should translate into significantly higher returns and a greater profit over the long term. Further reduction of stocking density combined with a stocking weight greater than 5 g should translate into greater proportion of larger, higher valued fish at harvest and a growout period of 18-20 mo, rather than the 24-30 mo traditionally needed for the combined phase II and phase III of production. [source]

POM Forum: Transfer of Changing Production Know-How

Kasra Ferdows
Even with the rich literature on knowledge management, we still don't know enough about how the rate of change in production-know-how affects the choice of mechanisms for its transfer. Codifying tacit know-how helps, but codification becomes more challenging as the know-how changes more frequently. Transfer of tacit know-how becomes much more complicated when it changes often. We need more research in this area, particularly to help production and operations managers who must ultimately use the new know-how and change their companies' production processes. The paper suggests a framework as a step in that direction. The framework focuses on the interplay between the level of codification and the rate of change of production know-how, and identifies four zones for classifying production know-how: "slow and codified," "slow and tacit," "fast and codified," and "fast and tacit." Examples from McDonald,s, Club Med, Intel, and AOL are used to illustrate primary transfer mechanisms for each zone (manuals and systems, people, joint-development, and projects, respectively). Appropriate absorptive capacities in the production units for each zone are also identified. Since the ultimate responsibility of operations managers is to improve (i.e., change) their production know-how as fast as possible, they would be wise to adopt policies that are closer to those suited for the "fast and codified" zone. Intel and Toyota show good models. [source]

Continuous Beer Fermentation Using Immobilized Yeast Cell Bioreactor Systems

Traditional beer fermentation and maturation processes use open fermentation and lager tanks. Although these vessels had previously been considered indispensable, during the past decades they were in many breweries replaced by large production units (cylindroconical tanks). These have proved to be successful, both providing operating advantages and ensuring the quality of the final beer. Another promising contemporary technology, namely, continuous beer fermentation using immobilized brewing yeast, by contrast, has found only a limited number of industrial applications. Continuous fermentation systems based on immobilized cell technology, albeit initially successful, were condemned to failure for several reasons. These include engineering problems (excess biomass and problems with CO2 removal, optimization of operating conditions, clogging and channeling of the reactor), unbalanced beer flavor (altered cell physiology, cell aging), and unrealized cost advantages (carrier price, complex and unstable operation). However, recent development in reactor design and understanding of immobilized cell physiology, together with application of novel carrier materials, could provide a new stimulus to both research and application of this promising technology. [source]