Flowback of solids through distribution plates of gas fluidized beds and associated phenomena

This work is concerned with a study of certain phenomena related to the performance and design of distributors in gas fluidized beds with particular regard to flowback of solid particles. The work to be described is divided into two parts. I. In Part one, a review of published material pertaining to distribution plates, including details from the patent specifications, has been prepared. After a chapter on the determination of the incipient fluidizing velocity, the following aspects of multi-orifice distributor plates in gas fluidized beds have been studied: (i) The effect of the distributor on bubble formation related to the way in which even distribution of bubbles on the top surface of the fluidized bed is obtained, e.g. the desirable pressure drop ratio ?PD/?PB for the even distribution of gas across the bed. Ratios of distributor pressure drop ?PD to bed pressure drop at which stable fluidization occurs show reasonable agreement with industrial practice. There is evidence that larger diameter beds tend to be less stable than smaller diameter beds when these are operated with shallow beds. Experiments show that in the presence of the bed the distributor pressure drop is reduced relative to the pressure drop without the bed, and this pressure drop in the former condition is regarded as the appropriate parameter for the design of the distributor. (ii) Experimental measurements of bubble distribution at the surface has been used to indicate maldistribution within the bed. Maldistribution is more likely at low gas flow rates and with distributors having large fractional free area characteristics (i.e. with distributors having low pressure drops). Bubble sizes obtained from this study, as well as those of others, have been successfully correlated. The correlation produced implies the existence of a bubble at the surface of an orifice and its growth by the addition of excess gas from the fluidized bed. (iii) For a given solid system, the amount of defluidized particles stagnating on the distributor plate is influenced by the orifice spacing, bed diameter and gas flow rate, but independent of the initial bed height and the way the orifices are arranged on the distributor plate. II. In Part two, solids flowback through single and multi-orifice distributors in two-dimensional and cylindrical beds of solids fluidized with air has been investigated. Distributors equipped with long cylindrical nozzles have also been included in the study. An equation for the prediction of free flowback of solids through multi-orifice distributors has been derived. Under fluidized conditions two regimes of flowback have been differentiated, namely Jumping and weeping. Data in the weeping regime have been successfully correlated. The limiting gas velocity through the distributor orifices at which flowback is completely excluded is found to be indepnndent of bed height, but a function of distributor design and physical properties of gas and solid used. A criterion for the prediction of this velocity has been established. The decisive advantage of increasing the distributor thickness or using nozzles to minimize solids flowback in fluidized beds has been observed and the opportunity taken to explore this poorly studied subject area. It has been noted, probably for the first time, that with long nozzles, there exists a critical nozzle length above which uncontrollable downflow of solids occurs. A theoretical model for predicting the critical length of a bundle of nozzles in terms of gas velocity through the nozzles has been set up. Theoretical calculations compared favourably with experiments.

Advances towards a pressurised rotating fluidised bed combustor

Rotating fluidised Beds offer the potential for high intensity combustion, large turndown and extended range of fluidising velocity due to the imposition of an artificial gravitational field. Low thermal capacity should also allow rapid response to load changes. This thesis describes investigations of the validity of these potential virtues. Experiments, at atmospheric pressure, were conducted in flow visualisation rigs and a combustor designed to accommodate a distributor 200mm diameter and 80mm axial length. Ancillary experiments were conducted in a 6" diameter conventional fluidised bed. The investigations encompassed assessment of; fluidisation and elutriation, coal feed requirements, start-up and steady-state combustion using premixed propane and air, transition from propane to coal combustion and mechanical design. Assessments were made of an elutriation model and some effects of particle size on the combustion of premixed fuel gas and air. The findings were: a) more reliable start-up and control methods must be developed. Combustion of premixed propane and air led to severe mechanical and operating problems. Manual control of coal combustion was inadequate. b) Design criteria must encompass pressure loss, mechanical strength and high temperature resistance. The flow characteristics of ancillaries and the distributor must be matcheo. c) Fluidisation of a range of particle sizes was investigated. New correlations for minimum fluidisation and fully supported velocities are proposed. Some effects on elutriation of particle size and the distance between the bed surface and exhaust port have been identified. A conic distributor did not aid initial bed distribution. Furthermore, airflow instability was encountered with this distributor shape. Future use of conic distributors is not recommended. Axial solids mixing was found to be poor. A coal feeder was developed which produced uniform fuel distribution throughout the bed. The report concludes that small scale inhibits development of mechanical design and exploration of performance. future research requires larger combustors and automatic control.

Effects of relational policies in export channels

Two key causes of failure for exporters are (1) the availability of adequate resources at the point of entry, and, (2) the quality of the exporter-foreign distributor relationship. Generally, export research has found that, as foreign distributor relationship-specific investments increase and as relational bonds are established, performance improves (e.g., Bello and Gilliland 1997). However, investments and the quality of the relationship are challenged by the foreign distributor’s motivation to participate in the relationship. One way exporters deal with this issue is by developing trade policies, which we refer to as “relational policies,” that are intended to motivate relational behaviors on the part of the foreign distributor.

Marketing resources of actively involved exporters

The purpose of this dissertation is to examine the impact of the market orientation and market based resources of actively involved exporters and their distributors on export venture performance. Previous literature in marketing channels has examined the effect of the market orientation of suppliers and their distributors on supplier-distributor relationships, mainly in a domestic context, as well as the impact of the quality of their relationship on business performance in domestic and international contexts. Little or no research focuses on the interplay between the relevant marketing resources, such as market orientation, proactive market orientation, selling, pricing reputation, and market innovation, of an export venture and their distributor, and consequently on export venture performance. This dissertation is mainly a quantitative study using a mail survey among Greek exporting firms in various industries. The final sample comprised 190 exporting ventures. The survey was enhanced through open interviews with export venture managers and their respective distributors and was pre-tested with a small-scale dyadic survey. Survey data were analysed using structural equation modelling. The main research objective was to assess the impact of marketing support resources, namely market orientation and proactive market orientation, and market-based resources of an export venture and its distributor on export performance. In addition, the relationship of marketing support resources of the export venture and those of the distributor was examined. Some of the relationships examined are a migration of traditional domestic theory (Hooley et al. 2005), to an exporting context, testing whether there are differences in the relationships in a different context. This study contributes to the resource-based view, marketing, and export business literature, as findings indicate that high levels of export venture proactive market orientation lead to distributors with high levels of market orientation. In line with findings of domestic context research, the proactive market orientation of the venture renders its market orientation statistically not significant.

An integrated process for strategic positioning within the value chain

The purpose of this article is to highlight the value of ‘strategic positioning’ as a means of providing competitive edge, and to introduce and describe a novel method of managing this. Strategic positioning is concerned with the choice of business activities a company carries out itself, compared to those provided by suppliers, partners, distributors and even customers. It is therefore directly impacted by, and has direct impact upon, such decisions as outsourcing, off-shoring, partnering, innovation, technology acquisition and customer servicing.

Strategic positioning:an integrated decision process for manufacturers

Purpose – This paper describes research that has sought to create a formal and rational process that guides manufacturers through the strategic positioning decision. Design/methodology/approach – The methodology is based on a series of case studies to develop and test the decision process. Findings – A decision process that leads the practitioner through an analytical process to decide which manufacturing activities they should carryout themselves. Practical implications – Strategic positioning is concerned with choosing those production related activities that an organisations should carry out internally, and those that should be external and under the ownership and control of suppliers, partners, distributors and customers. Originality/value – This concept extends traditional decision paradigms, such as those associated with “make versus buy” and “outsourcing”, by looking at the interactions between manufacturing operations and the wider supply chain networks associated with the organisation.

The right time and place:strategic positioning for competitive manufacture

Increasingly in the UK, companies that have traditionally considered themselves as manufacturers are being advised to now see themselves as service providers and to reconsider whether to have any production capability. A key challenge is to translate this strategy into a selection of product and service-centred activities within the company's supply chain networks. Strategic positioning is concerned with the choice of business activities a company carries out itself, compared to those provided by suppliers, partners, distributors and even customers. In practice, strategic positioning is directly impacted by such decisions as outsourcing, off-shoring, partnering, technology innovation, acquisition and exploitation. If companies can better understand their strategic positioning, they can make more informed decisions about the adoption of alternative manufacturing and supply chain activities. Similarly, they are more likely to reject those that, like off-shoring, are currently en vogue but are highly likely to erode competitive edge and business success. Our research has developed a new concept we call 'competitive space' as a means of appreciating the strategic positioning of companies, along with a structured decision process for managing competitive space. Our ideas about competitive space, along with the decision process itself, have been developed and tested on a range of manufacturers. As more and more manufacturers are encouraged to move towards system integration and a serviceable business model, the challenge is to identify the appropriate strategic position for their organisations, or in other words, to identify their optimum competitive space for manufacture.

Relational incentive policies in cross-border interfirm relationships

How an exporter can effectively craft a distributor agreement that encourages its network of foreign distributors to respond in pro-relational ways? This is an important issue as previous research has shown that relationship quality was linked to export performance. However, research failed to propose managerial tools that allowed exporters to foster relational phenomena in cross-border relationships. In this study, we suggest that exporters can influence importers' attitudes and behaviors with relational incentives policies. We also show that the impact of these policies is impervious to the noise, i.e., psychic distance and information asymmetry, that characterizes international business relationships. Our hypotheses are tested via structural equations modeling with data from a sample of French exporters.

A comparison of in situ constant and falling head permeameter tests to assess the distribution of clogging within horizontal subsurface flow constructed wetlands

Clogging is the main operational problem associated with horizontal subsurface flow constructed wetlands (HSSF CWs). The measurement of saturated hydraulic conductivity has proven to be a suitable technique to assess clogging within HSSF CWs. The vertical and horizontal distribution of hydraulic conductivity was assessed in two full-scale HSSF CWs by using two different in situ permeameter methods (falling head (FH) and constant head (CH) methods). Horizontal hydraulic conductivity profiles showed that both methods are correlated by a power function (FH= CH 0.7821, r 2=0.76) within the recorded range of hydraulic conductivities (0-70 m/day). However, the FH method provided lower values of hydraulic conductivity than the CH method (one to three times lower). Despite discrepancies between the magnitudes of reported readings, the relative distribution of clogging obtained via both methods was similar. Therefore, both methods are useful when exploring the general distribution of clogging and, specially, the assessment of clogged areas originated from preferential flow paths within full-scale HSSF CWs. Discrepancy between methods (either in magnitude and pattern) aroused from the vertical hydraulic conductivity profiles under highly clogged conditions. It is believed this can be attributed to procedural differences between the methods, such as the method of permeameter insertion (twisting versus hammering). Results from both methods suggest that clogging develops along the shortest distance between water input and output. Results also evidence that the design and maintenance of inlet distributors and outlet collectors appear to have a great influence on the pattern of clogging, and hence the asset lifetime of HSSF CWs. © Springer Science+Business Media B.V. 2011.

Practitioner perspectives on supply chain management and logistics:a study from the United Kingdom

Purpose: The focus of this paper is the evolution of supply chain management (SCM) and logistics, as well as of the relationship between them. Its purpose is to generate deep insights into practice, particularly in relation to the fundamental issue of how practitioners define these key terms and phrases. Research approach: A largely qualitative study which involved in depth interviews with managers from two third party logistics providers (3PLs)/distributors, two retailers and two manufacturers from the United Kingdom. This interview protocol is based on the template used in a previous study published over a decade ago. Findings and originality: The data collected during the focussed interviews in the United Kingdom is contrasted with results from the earlier study. The findings suggest that there is variation between practitioners particularly in relation to what SCM is specifically concerned with. This variation mirrors to a large extent the differing orientations and emphases evident in the many theoretical definitions of SCM that have been proposed in recent decades. Research impact: The authors introduced the concept of refined replication in SCM research. This allows previous research to be built upon in order to test understanding of SCM theory and its practical implementation among SCM professionals in the United Kingdom. Practical impact: A profile of SCM understanding and adoption by firms in the United Kingdom is presented .

A diagnostic framework for demand amplification problems in supply chains

This dissertation delivers a framework to diagnose the Bull-Whip Effect (BWE) in supply chains and then identify methods to minimize it. Such a framework is needed because in spite of the significant amount of literature discussing the bull-whip effect, many companies continue to experience the wide variations in demand that are indicative of the bull-whip effect. While the theory and knowledge of the bull-whip effect is well established, there still is the lack of an engineering framework and method to systematically identify the problem, diagnose its causes, and identify remedies. ^ The present work seeks to fill this gap by providing a holistic, systems perspective to bull-whip identification and diagnosis. The framework employs the SCOR reference model to examine the supply chain processes with a baseline measure of demand amplification. Then, research of the supply chain structural and behavioral features is conducted by means of the system dynamics modeling method. ^ The contribution of the diagnostic framework, is called Demand Amplification Protocol (DAMP), relies not only on the improvement of existent methods but also contributes with original developments introduced to accomplish successful diagnosis. DAMP contributes a comprehensive methodology that captures the dynamic complexities of supply chain processes. The method also contributes a BWE measurement method that is suitable for actual supply chains because of its low data requirements, and introduces a BWE scorecard for relating established causes to a central BWE metric. In addition, the dissertation makes a methodological contribution to the analysis of system dynamic models with a technique for statistical screening called SS-Opt, which determines the inputs with the greatest impact on the bull-whip effect by means of perturbation analysis and subsequent multivariate optimization. The dissertation describes the implementation of the DAMP framework in an actual case study that exposes the approach, analysis, results and conclusions. The case study suggests a balanced solution between costs and demand amplification can better serve both firms and supply chain interests. Insights pinpoint to supplier network redesign, postponement in manufacturing operations and collaborative forecasting agreements with main distributors.^

Benchmarking e regulação do setor de distribuição de energia elétrica nacional: proposta para avaliação dos custos operacionais eficientes

In Brazil, the National Agency of Electric Energy (ANEEL) represents the energy regulator. The rates review have been one of its main tasks, which establish a pricing practice at a level to cover the efficient operating costs and also the appropriate return of the distributors investments. The changes in the procedures to redefine the efficient costs and the several studies on the methodologies employed to regulate this segment denote the challenge faced by regulators about the best methodological strategy to be employed. In this context, this research aims to propose a benchmarking evaluation applied to the national regulation system in the establishment of efficient operating costs of electricity distribution utilities. The model is formulated to promote the electricity market development, partnering with government policies ant to society benefit. To conduct this research, an integration of Data Envelopment Analysis (DEA) with the Stochastic Frontier Analysis (SFA) is adopted in a three stages procedure to correct the efficiency in terms of environmental effects: (i) evaluation by means of DEA to measure operating costs slacks of the utilities, in which environmental variables are omitted; (ii) The slacks calculated in the first stage are regressed on a set of environmental variables by means of SFA and operating costs are adjusted to account the environmental impact and statistical noise effects; and, (iii) reassess the performance of the electric power distribution utilities by means of DEA. Based on this methodology it is possible to obtain a performance evaluation exclusively expressed in terms of management efficiency, in which the operating environment and statistical noise effects are controlled.

Public-Private Partnership Design for Inclusive Cocoa Global Value Chains in Ghana

Within 10 years, there could be a severe global shortage in the supply of cocoa, according to industry practitioners and other experts. Due to global population growth and the emergence of a growing global middle class, by 2025 the cocoa crop would need to increase by nearly 50 per cent to keep up with projected demand. A potential shortage of supply is a direct threat to the business model of lead firms – including cocoa grinders and processors, chocolate confectioners, and retail distributors. But these international firms – the ones that will suffer the most if there is a shortage of cocoa supply – are helping create the market failure that is stifling sustainability. Functioning as a two-tiered consolidated oligopoly with a combined market share of approximately 89%, these firms enjoy the largest portion of value capture in the cocoa-chocolate global value chain (GVC). The smallholder cocoa producers, conversely, are trapped in low value-add segments of the GVC. In fact, most smallholder farmers survive on less than $1.00 per day per capita, on average in many cocoa exporting countries. In Ghana - the second largest producer of cocoa in the world - the government has accomplished little to help these smallholders upgrade and make cocoa an attractive sector for the next generation to inherit. The result – both in Ghana and around the world – is a lack of sustainability of the supply of cocoa. Demand is already beginning to outstrip supply. As a result of these underlying circumstances, the United States Agency for International Development (USAID) has posed the following policy question: "Under what conditions could USAID, as a development agency, support and enhance potential public-private partnerships in order to improve the bargaining power (and financial wherewithal) of smallholder organizations and farmers in the context of the global value chain for cocoa in Ghana?"

International Sales of UK Television Content: Change and Continuity in ‘the space in between’ Production and Consumption

Focusing on the UK, this article addresses key issues facing the international distribution industry arising from over-the-top digital distribution and the fragmentation of audiences and revenues. Building on the identification of these issues, it investigates the extent to which UK distribution has altered over a ten-year period, pinpointing continuities in the destination and type of sales alongside changes in the role and structure of the industry as UK-based distributors adapt to a changing UK broadcasting landscape and global production environment. At one level increasing US ownership of UK-based distributors and the arrival of OTT players like Netflix, highlight the tensions between the national orientations of UK broadcasters and the global aspirations of independent producers and distributors. At another level VOD has boosted international sales of UK drama. Although the full impact of SVOD on content and rights has yet to materialise, significant changes in the industry predate the arrival of SVOD.

Ticking Boxes: (re)constructing the wristwatch as a luxury object

Today the high-price mechanical wristwatch is recognized as a luxury object redolent with notions of adventure, sporting achievement, elevated social status, and technical precision. Through an examination of the segmentation of the current luxury wristwatch market and key moments in the historical development of the wristwatch, this article will explain why these connotations exist. In particular, the article will explain the role that the early development of the wristwatch as a piece of military technical equipment and the mechanical wristwatch’s revitalization as a luxury good in response to the development of commercial quartz timekeeping technology have played in reconstructing the wristwatch as an object type. By utilizing network theory and the analytical tool of complexity, and drawing on fieldwork undertaken in London and Switzerland amongst the manufacturers, distributors, retailers, and consumers of high-value wristwatches, the article will explain how the wristwatch can simultaneously be seen as functional tool, fashion statement, status symbol, and anachronism. This insight into the true nature of the wristwatch as a multivalent and semiotically charged object will also be used to inform reflections on the likely impact of generally perceived current threats to the luxury watch industry: the rise in ethical material sourcing campaigns, the stubborn gender imbalance in watch sales, and the recent appearance of smart watches and similar digital devices.