Development of fragmentation models for solid fuel combustion and gasification as subroutines for inclusion in CFD codes

This work arises from substantial problems found in the modelling of the gasification and combustion of solid fuel, both coal and biomass in the following different systems:

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Coal fired non-slagging cyclone combustors.

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Pre-calciners on cement plant.

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Fuel rich inverted cyclone combustors used to simulate the time temperature history of large utility boilers.

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Cyclonic gasifiers for sawdust and direct firing of small gas turbines.

•

Deposition studies for slagging and fouling in large utility boilers.

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Prediction of final carbon in ash from pulverised coal systems.

Commercial CFD codes such as Fluent are well developed and have well proven routines for lagrangian tracking of burning particles through complex flow fields. However what has become apparent in numerous studies is that existing models for solid fuel combustion can be adjusted to predict the initial flow field aerodynamics, sometimes the temperature, but fall down when particles have to be followed completely through a system. This is manifested with cyclone combustors and gasifiers via enhanced retention of burning particles in centrifugal force fields, which can only be resolved by changes in the particle size distribution and thus fragmentation as the particle gasify or burn. This problem also becomes apparent in studies of processes in pre-calciners and in deposition in large utility boilers and furnaces.The paper will review the literature of the fragmentation of pulverised coal and biomass during gasification, devolatilisation and combustion and relate it to observed phenomena in the type of system under consideration. The difficulties of incorporating models of fragmentation in CFD codes such as Fluent are discussed. Then the implementation of such a model in Fluent is described, together with results from a number of different systems. It is concluded that the model so implemented shows improved prediction in many difficult areas, but still needs development to better reflect actual fragmentation conditions in different experimental systems.It is concluded that the model needs to be further extended beyond the single step fragmentation at present used, especially to include many of the fine particles known to be generated in such systems.     

In-situ monitoring the inhibiting effect of polyphosphinocarboxylic acid on CaCO3 scale formation by synchrotron X-ray diffraction

The formation of calcium carbonate mineral scale is a persistent and expensive problem in oil and gas production. The aim of this paper is to further the understanding of scale formation and inhibition by in-situ probing of crystal growth by synchrotron radiation wide angle X-ray scattering (WAXS) in the absence and presence of polyphosphinocarboxylic acid (PPCA) scale inhibitor. This technique offers an exciting prospect for the study of scaling.It has been shown that the nucleation and growth of various calcareous polymorphs and their individual crystal planes can be followed in real-time and from this the following conclusions are reached:

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The process of scale depositing on the surface can be divided into an unstable phase and a stable phase.

•

PPCA lengthens the induction time of the surface deposition process.

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PPCA suppresses calcite formation and results in vaterite-dominated scale.

•

PPCA causes a change of lattice parameter for both calcite and vaterite crystals. The c-axis of unit cell increases and the a-axis and b-axis of unit cell decrease.

     

Studies of fluid bed granulation in an industrial R&D context

Following a brief overview of recent developments in laundry powder processing by comparison with other areas of industrial application, and current drivers and trends, a review is presented of collaborative research between Unilever R&D and Sheffield University on fluidised bed granulation using melt binders.These fall apart into 4 areas:

1.

Contact zone studies;

2.

Growth similarity for non-ideal systems;

3.

Growth and breakage decoupled;

4.

Scale-up rules based on similarity of growth kinetics.

The emphasis of the paper is on the identification and relative quantification of the dominant mechanisms, which are found in the balance of fluxes of solids and binder, together with heat transfer and conduction, not so much binder viscosity. These mechanisms allow for the control of the growth kinetics and rapid scale-up.Together, this lays the broad ground-work for fluidised bed granulation. Some concluding remarks provide pointers for the future of research in this area:

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There is a strong requirement for multi-dimensional phase volume distribution based population balances.

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Many processes require pre-granulation, and liquid-liquid contact in the spray-zone is scarcely investigated.

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Simple combined Lagrangian-Eulerian modelling implemented in commercial code environment can be especially useful to investigate the effects of the relations between material properties and process conditions on growth kinetics.

     

Measurement of the size, shape and orientation of convex bodies

Different types of solid bodies (particles) with specific shape and size are needed for industrial processes. For spherical particles, ‘sizer’ measurements are usually reported as sphere diameters. For non-spherical particles, particle shape and especially orientation must be taken into account. Particles of a specific shape will present different views when looked at from different directions.We have employed a Camsizer^® instrument to measure the distribution of projected area under different physical conditions for solid cylindrical particles:

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Under ‘ideal’ conditions, corresponding to a uniform distribution of particle orientation, measurements agreed with predictions. The celebrated theorem of Cauchy applies only to this case.

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For two other situations, measured and predicted results differed. However, from the experimental data it was possible to infer the particle orientations and hence theoretically predict the projected area distribution. Excellent agreement between theory and practice was then restored.

     

Sustainable management of Agiasma Lagoon-River Nestos delta—Using R.E.MO.S. daily monitoring data of water quality and quantity parameters : Trends, assessments, and natural hazards for the years 2000-2002

Three R.E.MO.S. (Remote Environmental MOnitoring System) telemetric networks have been installed in the catchment area of River Nestos, by research team PERSEAS. The first network has been installed in Nestos Delta. This network consists of two Remote Stations (R.S.):

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The first one is called R.S. “Nestos” and is settled in Nestos Delta in Chrysoupoli and

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the second one is called R.S “Agiasma” and is settled in the homonymous Lagoon.

This paper deals with R.S. “Agiasma”, which operates in Agiasma Lagoon, an area of great environmental importance in the west part of River Nestos Delta. The gradients of the water quality and quantity monitored parameters are very important for the ecological preservation of the lagoon. Moreover, this case can be an excellent example of how the real-time monitoring data can work as an alarm system to prevent environmental hazards.The scientific issues this paper is focused on are:

1.

The three years systematic daily electronic monitoring data (1/1/2000-31/12/2002). The monitored parameters are Water level—H (cm), Salinity—Sal (‰), Redox Potential—RP (mV), Dissolved Oxygen—DO (mg/l), Water Temperature—T_w (^oC) and Air Temperature—T_a (^oC).

2.

The assessment of water quality and quantity parameters and the aquatic environment of Agiasma lagoon.

3.

The detection of trends, using the non-parametric Spearman's criterion. This trend analysis proved the existence of trends for the parameters H, Sal and RP.

4.

The necessity of real-time monitoring, which can prevent and confront possible natural hazards and disasters and work as an alarm system for the local authorities.

     

In brief

DSM Composite Resins

JEC Composites Show 2004

EPTA

Composites Processing Association

Rhodia Engineering Plastics

Ashland Distribution Co

Hypercar

Fiber-forge

Aldila Inc

Carbon Fiber Technology LLC

SGL Carbon Fibers and Composites Inc

HK Research

     

In brief

Magnum Venus Products

Atofina

DuPont Engineering Polymers

Health and Safety Executive

Johns Manville Slovakia AS

PPG Industries

ITW Irathane

Futura

DuPont Automotive

     

Multiple hydrodynamic states in trickle flow: Quantifying the extent of pressure drop, liquid holdup and gas-liquid mass transfer variation

It is well established that pressure drop and liquid holdup under trickle flow conditions are functions of the flow history. However, the extent of possible variation of these and other critical hydrodynamic parameters has not been fully quantified. In this study, specifically defined prewetting procedures are used as limiting cases for hydrodynamic hysteresis. These are:

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Non-prewetted.

•

Levec prewetted: the bed is flooded and drained and after residual holdup stabilisation the gas and liquid flows are introduced.

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Kan_L prewetted: the bed is operated in the pulse flow regime (by increasing liquid velocity) after which liquid flow rate is reduced to the desired set point (all at the desired gas flow rate).

•

Kan_G prewetted: the bed is operated in the pulse flow regime (by increasing gas velocity) after which gas flow rate is reduced to the desired set point (all at the desired liquid flow rate).

•

Super prewetted: the bed is flooded and gas and liquid flows are introduced once draining commences.

It is shown that the upper limiting case for pressure drop is the Kan_L mode of operation. The lower limiting cases are the non-prewetted and Levec prewetted modes (these coincide). Pressure drop may vary by as much as 700% even for prewetted beds. Liquid holdup is different in all five prewetting modes. The upper limiting case is the Kan_G mode of operation, while the lower limiting case is the non-prewetted mode (Kan_G holdup is approximately 160% that of non-prewetted mode holdup at ). At low gas velocities the Kan_L holdup can be 400% of that of the non-prewetted beds. Importantly, the lower limiting case for prewetted beds is the Levec mode. Holdup in the Kan_G mode may be as much as 130% of the holdup in the Levec mode (at ).The effect of hydrodynamic multiplicity of the volumetric mass transfer coefficient is measured by the desorption of oxygen from water into nitrogen. In this case the different prewetting procedures result in three distinct regions, the upper region being the Kan and Super prewetted beds, the intermediate region being the Levec prewetted bed and the lower region being the dry bed. Mass transfer coefficients in the upper region can be as much as 600% of that of the lower region and 250% of that of the intermediate region. Evidently, prewetting (and even pulsing flow prewetting) does not guarantee that the bed is operating at the maximum values of pressure drop, holdup and mass transfer coefficient. Evidence of operation in between the limiting cases is presented. These non-limiting cases can be reached in multiple ways.     

In brief

Strongwell Corp

Dow Chemical's

Interplastic Corp's

SP

McFarland-Cascade

Powertrusion International

CTG

     

In brief

Huntsman Advanced Materials

The German Composite Federation AVK-TV

1st Euro Trade 2004

Reichhold

Röchling Engineering Plastics KG

Owens Corning

     

Damage mechanisms analysis of a multi-scale fibre reinforced cement-based composite subjected to impact and fatigue loading conditions

For several years, Laboratoire Central des Ponts et Chaussées (LCPC) has worked on the development of new cement composites in order to obtain materials sufficiently tough and ductile to be used in structures or structural elements without any other reinforcement that fibres.Then a multi-scale fibre reinforced cement-based composite (MSFRCC) has been developed and patented. It is principally characterized by a high percentage of fibres, percentage equal to 11% per m³.Three fibre dimensions are used in this composite.In the present article, a qualitative analysis of damage mechanisms of this material under impact and fatigue loadings is proposed.Concerning impact loading condition, the main conclusions are:

•

Apparent fibre-matrix adherence, which increases with the loading rate, leads to an increase in material modulus of rupturel, an increase much greater than for all existing cement-based materials due to high percentage of fibres used;

•

Mechanical homogenization of composite with loading rate is the result of cracks delocalization during cracking process. This delocalization results from viscous effects generated within the matrix and around the fibre-matrix interfaces.

Concerning fatigue loading condition, the main conclusions are:

•

Intermediate fibre length (high percentage of meso-fibres) that is highly and positively involved in material static tensile strength, corresponds to scale of fibre that is sensitive to fatigue loading. As a matter of fact, meso-fibres become rapidly inactive and composite can no longer behave as a multi-scale reinforcement material. Material strength is then greatly affected.

•

If the initial cracking state of the material before fatigue loading corresponds to a state of tensile strain that is less than or equal to 1.27 10^− 3, meso-fibres perfectly play their role with respect to relevant cracks (i.e. meso-cracks whose opening corresponds to their mechanical efficiency domain, that means less than 100 μm), material fatigue behaviour being then good (fatigue rupture after 2 millions of cycles).

•

Specimens that did not break before 2 millions of cycles have better residual bending behaviour (gain of 6.5%) than reference specimens (specimens which were not previously loaded in fatigue) This result is the consequence of a morphological modification of cracks due to fatigue loading. Indeed, fatigue cycles lead to a gradual “blunting” of crack tips, cracks that subsequently become less dangerous with respect to their potential propagation.

     

In brief

Disc filter orders in pulp & paper sector

Environmental cleanup expands market

Pannevis belt filters now made in Australia

     

In brief

water treatment expansion at Indian refinery

PGI announces relocation of coporate office

UK supplier for HVAC drives

water treatment expansion at Indian refinery

PGI announces relocation of coporate office

UK supplier for HVAC drives

     

Biomass steam gasification in fluidized bed of inert or catalytic particles: Comparison between experimental results and thermodynamic equilibrium predictions

In order to improve the understanding of biomass gasification in a bed fluidized by steam, the thermochemical equilibrium of the reactive system was studied. The equilibrium results were compared to LGC experimental results, obtained by the gasification of oak and fir in a laboratory-scale fluidized bed of different catalysts: sand, alumina, and alumina impregnated with nickel.The research was completed by a study of the influence on the equilibrium of additional parameters such as the quantity of steam, the pressure or the kind of biomass. Those results of simulation may be used for evaluating the limits of actual reactors.The following conclusion may be drawn from all the results:

The thermodynamic equilibrium state calculated is far away from the experimental results obtained on sand particles.

The steam to biomass ratio, between 0.4 and 1 kg_steam/kg_{dry biomass}, has a strong influence on the gas mixture composition.

The temperature increase and the use of catalyst allow producing a gas mixture with a high content of hydrogen and carbon monoxide. The H₂:CO ratio may reach values greater than 3.

The use of catalyst allows the system to get closer from the equilibrium, especially for the nickel based catalyst.

     

Chemical vapor infiltration of C/C composites: Fast densification processes and matrix characterizations

Fast densification processes have been developed to improve the fabrication of C/C composite materials. In this work, a comparison is made between two techniques: the film boiling technique with a liquid reagent and the gas infiltration method. In both methods, the same home-made reactor was used. For the film boiling technique, the preform is either wrapped or not with a porous thermal barrier.Two different substrates have been densified, a carbon felt (RVC-2000^® from Le Carbone-Lorraine), and a 3D carbon cloth (Novoltex^® from Snecma). In situ temperature gradients and their temporal changes during the infiltration process have been recorded together with the delivered power necessary to maintain a constant deposition temperature. From these experiments, we have concluded about the following main points:

•

the analysis of in situ parameters, powers and temperatures, and the associated profiles of the pyrocarbon deposits,

•

the matrix quality with their associated microstructures as characterized by helium density, optical microscopy and Raman scattering experiments,

•

the key role of the evolutive preforms as heat and mass exchangers during the process, and the assisted thermal fluxes inside the reactor.

This paper presents results which should allow to control automatically the process at an industrial scale.     

RP Asia 2004

www.rpasia.com

Thai Composites Association

Conference programme

Help for UK firms to exhibit

     

In brief

Porex focuses on filtration

Filter/strainer sales venture

Plant expansion in US

Sieve Calibration Partners

     

People

PPG Industries

Nida-Core

HITCO Carbon Composites

     

Patents+technologies

Commercialization of innovative classifier

Advancing the HEPA filter concept

New biomass technology for MTBE removal