1,720,963 research outputs found
Investment and operational optimisation of an energy recovery engineering plant
Get PDFPhD (Business Mathematics), North-West University, Potchefstroom CampusBurnable off-gases generated from operational processes in engineering plants are regularly utilised as energy sources. A common practice is to use this for steam production in boiler houses, where excess steam is allocated to power generation turbines. Fluctuations in off-gas productions may, however, result in turbines shutting down, due to insuficient steam. Some investment models exist, which are typically based on cost minimisations or for the purpose of meeting energy demands. These models do not, however, take into account plant-specific steam flow patterns and typically use average-based pro les for decision making. The operational control of turbines are typically performed by means of a fixed-sequence philosophy. Turbines are loaded in a predetermined order until a fixed set point. This operational philosophy incurs signi cant power generation losses from turbine shut-downs, as a result of the inability to distribute steam dynamically. Such an operating philosophy is easy to implement and, therefore, commonly used in industry. Another philosophy is that of dynamic control where steam distribution between the turbines are computed at each time period by means of an in-time operating control algorithm. In this thesis, a number of novel model formulations are proposed, which addresses optimal power generation and turbine investments under a fixed-sequence philosophy, as well as dynamic control. Seven conceptual formulations are applied to demonstrate basic power generation optimisation. These conceptual formulations are to incorporate either a fixed-sequence philosophy, dynamic control or both. The main contributions of this study entail a further seven formulations where six are optimisation models. Each of these six formulations utilises plant signature steam flow profiles in order to determine, either optimal power generation, or optimal turbine investments in terms of the net present value (NPV), or both. All investment formulations include turbine shut-downs in the decision making process by penalising the NPV with each occurrence. The first three of these model formulations are for turbines operating under a fixed-sequence philosophy, two for optimal power generation and one for optimal turbine investments. For optimal power generation the formulations determine in which fixed order the turbines should operate. Optimal turbine investments, as determined by the third formulation, is the combination that yields the highest NPV. For this combination the optimal fixed turbine order and power generation are determined. Optimal investment results indicate that when future trip costs are taken into account as an NPV penalisation, a single turbine should rather be procured. The final three of these proposed formulations are for turbines operating under dynamic control. The first formulation optimises power generation between any number of turbines. The second formulation optimises turbine investments in terms of NPV. Comparing optimal power generation results, increases between 3.5% and 13.2% are observed for turbines under dynamic control compared to a fixed-sequence philosophy. Optimal NPV's under dynamic control are between 7.3% and 19.3% higher than those of a fixed-sequence philosophy. All optimal outcomes yield that two turbines should be procured. A formulation is proposed that optimises turbine investments, which incorporates the procurement of a supplementary energy resource to assist during low o -gas, and therefore, low steam flow periods. Such a resource is typically very expensive and does not make sense to procure under normal operating conditions. However, in a uctuating steam flow environment it proves to increase the NPV, while safeguarding turbines from shut-down occurrences. Depending on the procurement and projected shut-down costs, results indicate that an investment into a supplementary resource under optimal investments can yield an NPV improvement 10.6% to 118.0% versus a fixed-sequence philosophy, and 3.0% to 82.7% compared to dynamic control. Results further indicate that involuntary turbine shut-downs, owing to low steam flow periods, are reduced up to a 100%.Doctora
A methodology to determine best-suited waiting-time periods for turbine start-up under fluctuating resources
No full text— It is not uncommon for engineering process
plants to comprise energy recovery. When power generation
takes place under such circumstances, the nature of
interlinked processes may result in fluctuating resource
availability. Such fluctuations may, however, result in
turbines tripping due to insufficient availability at times.
Power generation under such conditions typically comprises
turbine protection measurements in an attempt to prevent
unnecessary trip occurrences. One such measurement is to
avoid a possible restart-trip scenario in close proximity, by
enforcing adequate start-up constraints. These constraints
dictate the minimum waiting-time period that needs to be
enforced, where resource availability is sufficient to keep
the turbine(s) operational.
Start-up protection measurements are typically enforced
without changing the time-constraint over time. Although
such a measurement is required it entails time intervals
where potential power generation goes to waste due to a
turbine’s non-operational status. As the enforced waitingtime period increases more power generation potential goes
to waste; however, reduced periods may result in turbines
being restarted, only to trip in near future. A trip does not
only necessitate another waiting-time period, but reduces a
turbine’s life expectancy.
This paper presents two models; the first maximises power
generation amongst two turbines where waiting-time periods
are incorporated as a variable. These results can then be
used in combination of the second proposed model.
The second model is a unique methodology that can be used
to investigate the effect of turbine start-up waiting-time
periods and how it influences the combination of power
generation and turbine trips. This methodology is,
furthermore, incorporated to determine what the ideal startup period should be for an energy recovery plant that
operates under fluctuating resource availability.
A case study is presented that demonstrates the working
ability of the proposed method and results show that by
incorporating this methodology the engineering plant can
generate an additional 0.46 MW per annu
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Implementing an optimisation model for turbine investment selection under fluctuating steam productions
No full textEngineering plants typically have a variety of interlinked production chains, where process flows are dependent on upstream or downstream events. Raw material feeds may fluctuate over time, resulting in fluctuating off-gas and steam productions, and therefore an inefficient energy resource usage. It is common practice to generate steam from burnable offgases, in boiler houses, where excess steam is allocated for power generation after plant usages. Over time fluctuating steam flow may result in turbine trips. A problem is that unused off-gases are flared where the energy potential goes to waste. This paper investigates turbine investment choices under fluctuating steam productions. A mathematical model is used that determines how steam should be distributed between turbines in a fluctuating environment, for optimal power generation. Investment options can be explored regarding which combination of turbines will result in higher power generation for the same combined power generation capabilities and how each turbine configuration will influence the total number of turbine trips due to steam shortages. A number of simulations are performed for various turbine configurations and it was found that an increase in the number of turbines for a fixed maximum total power generation capacity will deliver slightly higher power generation but significant more turbine trips. All simulations are based on real world dat
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