DRYING OF SUSPENSIONS IN A MODIFIED SPOUTED BED DRIER WITH AN INERT PACKING

Authors summarize results of drying experiments carried out in aim to investigate effects of operational and process-conditions on the drying output and the product quality. The studies were performed in a laboratory-size spouted bed drier of a new construction with tangentional air inlet and with an inner conveyor screw maintaining the spouted bed recirculation of the inert particles

Effects of parameters assuring intensive gas-solid contact were studied, such as the inlet air-velocity, the recirculation of inert particles as well as chemical and physical properties of the inert material.

Various chemical suspensions (e.g. fine grain inorganic-salt pulps, waste products), biologically active materials (e.g, suspension of yeast) food products were used in preliminary experiments which showed effectiveness of this dryin5 method. On this basis two rode1 materials (cobalt-carbonate suspension and pulp of zinc--carbonate) were chosen for detailed experiments.

As a result cf these studies main optimal operational and process pszramters.have been obtained.     

INFERENTIAL SENSORS FOR ON-LINE MONITORING OF TISSUE MACHINE QUALITY PROPERTIES

There are many processes in a pulp and paper mill where an on-line parameter analyzer cannot be used due to several reasons

•The analyzer is very expensive

•It cannot survive in the environment we want to use it

•It is not operational due to hardware problems, maintenance etc

•Such an analyzer does not exist in the market

In all these situations it would be great for the mill to have an alternative way of measuring those parameters in real-time. Neural network models can serve as virtual sensors that infer process parameters from other variables, which can be measured on-line. One excellent application of inferential sensors in the pulp and paper industry is the on-line prediction of paper properties, like tensile, stretch, brightness, opacity etc. In tissue machines, the most important quality parameter is softness, which is usually measured in a very subjective manner by the touch of a human finger. In this work we examine how neural networks can be deployed in order to build online virtual sensors for softness and other tissue quality properties. The results are promising and show that neural network technology can improve productivity and minimize out of specs production in a tissue machine, by providing accurate real time monitoring ofquality parameters.     

Computational modelling of industrial pulp stock chests

Agitated pulp stock chests are the most widely used mixers in pulp and paper manufacture. Stock chests are used for a number of purposes, including attenuation of high‐frequency disturbances in pulp properties (such as mixture composition, fibre mass concentration, and suspension freeness) and are designed using semi‐empirical rules based largely on previous experience. Tests made on both laboratory and industrial‐scale pulp chests indicate that they are subject to non‐ideal flows, including channelling and creation of dead zones. In the present work, a commercial computational fluid dynamic (CFD) software (Fluent) is used to model two industrial pulp stock chests. The first chest is rectangular, agitated using a single side‐entering impeller, and feeds a mixture of chemical pulps at 3.5% mass concentration (C_m) to a papermachine. The second chest has rectangular geometry, with a mid‐feather wall used to direct suspension flow through a U‐shaped trajectory past four side‐entering impellers. This chest is used to remove latency from a C_m = 3.5% thermomechanical pulp suspension ahead of stock screening. For CFD computations, pulp rheology was described using a modified Hershel–Buckley model. Steady‐state simulations were made corresponding to process conditions during mill tests. The calculated steady‐state flows were then used to determine the dynamic response of the virtual chests and then compared with experimental measurements and found to agree reasonably well. The computed flow fields provided insight into mixing processes occurring within the chests, showing cavern formation around the impellers (which reduced the agitated volume available for mixing). Mass‐less particle tracking, using the steady‐state flow field, gave insight into the stagnant regions and bypassing zones created in the vessels. This paper discusses difficulties encountered in characterising the mixing (both experimentally and computationally) and the limitations of the industrial data.     

THE ELECTRODEWATERING OF SEWAGE SLUDGES

Electrodewatering (EDW), the enhancement of conventional pressure filtration by an electric field, is an emerging technology with the potential to improve dewatering especially for difficult materials. CSIRO has many years of experience in EDW, ranging from bench scale tests to demonstration trials. A recent programme has investigated the applicability of EDW to aerobic wastewater treatment sludges which are particularly difficult to dewater using conventional equipment.

The bench scale filtration experiments produced cakes with solids contents of 35-46 wt% using EDW, compared with 24-30 wt% using pressure filtration alone. This paper : • describes how the dewatering results were achieved;

•identifies a relationship between moisture removal limits by EDW and the forms of water within the sludge;

•shows the results of preliminary attempts to mathematically model the EDW process     

Steam Drying - Modelling and Applications

The concept of steam drying originates from the mid of the last century. However, a broad industrial acceptance of the technique has so far not taken place. The paper deals with modelling the steam drying process and applications of steam drying with in certain industrial sectors where the technique has been deemed to hove special opponunities.

In the modelling scction the mass and heat transfer proceases are described along with equilibrium, capillarity and sorption phenomena occurring in porous materials during the steam drying process. In addition existing models in the literslure are presented.

The applications discussed involve drying of fuels with high moisture contcna, cattle feed exemplified by sugar beet pulp. lumber. paper pulp. paper and sludges.

Steam drying is compared to flue gas drying of biofuels prior to combustion in a boiler. With reference to a current insrallation in Sweden. the exergy losses. as manifested by loss of co-generation cupacity. are discussed. The energy saving potentid when using steam drying of sugar beet pulp as compared to other possible plant configurations is demonstrated.

Mechanical vapour recompression applied to steam drying is analysed with reference to reponed dau from industriul plsnts. Finally. environmcntul advantages when using steam drying are presented.     

TREATMENT OF KRAFT PULP AND PAPER WASTEWATERS BY MEANS OF FOAM SEPARATION

The pulp and paper industry is the third largest industrial consumer of fresh water in the United States. The current use rate of over two trillion gallons annually is expected to increase as the demand for paper products continues to rise

Of the various methods of producing paper from wood, the Kraft process is the most widely used. Color, dissolved and suspended organic matter, and dissolved inorganic solids are major pollutants in Kraft processing wastewater. Current federal regulations limit the amount of solids and organic matter that a Kraft facility may dispose into public waters, so most plants have some form of wastewater treatment

In this study, the capacity of a continuous-flow, foam separation system to effect removals of color from a Kraft process wastewater was evaluated. The cationic surfactant, EHDABr, was used to precipitate color bodies in the wastewater and create a foam to carry the precipitates from the wastewater. The effect of pH adjustment was also considered. Color removals in the area of 90% were achieved

Removal of precipitated solids was enhanced by increasing the detention of wastewater in the treatment system.     

R&D Needs-Drying of Sludges

Sludge management is very important subject for the environmental issue in many industrialized countries, because its generated volume is the largest in all generated wastes. In sludge management field, role of drying is becoming more needful as increase of difficulty for sludge disposal and need for sludge drying is expected in the future.

In this paper, the present status of drying of construction sludge, food industry sludge and municipal sludge are mentioned as concrete examples.

To respond these needs, it is necessary to advance further R & D     

CONVECTIVE DRYING OF PAPER CALCULATED WITH A NEW MODEL OF THE PAPER STRUCTURE

Paper drying models are based on the assumption of a rigid solid matrix. Because of the interaction of water molecules and paper fibre the dimensions of the sheet are changing, especially the thickness. These changes influence the moisture transport within the material. A model of the paper structure has been developed taking into account different kinds of pores in the paper.

By the assistance of this model the dependence between water content and thickness or transport parameters as permeability and thermal conductivity can be predicted. The only informations which are needed are sorption isotherms, apparent paper density and permeability of the single phase flow. Further informations as the pore size distribution are useful but not necessary.

The transport parameters are generated in the suggested way for wood pulp. It is shown that in the case of convective drying, the agreement between experimental results and model simulations is good.     

High Intensity Drying of M.G. Paper

The technological properties of paper are strongly influenced by the drying conditions. This is the case in particular with M.G. paper and machine performance is limited largely for quality reasons. Therefore, the question as to which extent the drying conditions influence the process of drying and the paper quality is of major importance for industry.

Unlike the results already published, tests were carried out with a laboratory machine operating on a continuous basis, with high drying rates, short retention time and application of combined contact/ convectional drying. The kinds of stock used were waste paper containing wood, bleached long-fiber magnefite pulp and unbleached long-fiber sulphate pulp with a basis weight ranging between 37 and 75 g/m2.     

Drop Motion on an Inclined Plane and Evaluation of Hydrophobia Treatments to Glass

Hydrophobic and anti-rain surface treatments are increasingly used to treat various glass articles such as windscreens, windows, headlamps, wing mirrors, optical lenses, sunglasses, etc.

To evaluate the efficiency and durability of these treatments, we determine the smallest volume or critical sliding volume, V _c, of a water drop able to slide down spontaneously under gravity after having been deposited on a vertical treated, glass surface. The property of water repellency is considered to be better when V _c, is smaller. In this paper, a new simplified theory to describe the capillary force retaining the water drops on an inclined plane is proposed and verified practically.

The experimental method allows us to compare the efficiency and durability of a commercial anti-rain and of a Corning Inc. proprietary hydrophobic surface treatment for glass, both being based on silicone derivative chemistry. As defined in this paper, the critical sliding volume appears to be a practical parameter which may be used to characterize quantitatively the hydrophobicity of a solid surface.     

AN EXPLORATORY STUDY OF A COMBINED SONIC AGGLOMERATION AND CROSSFLOW FILTRATION SYSTEM FOR HOT GAS CLEANUP

The Institute or Gas Technology has investigated a combined sonic agglomeration/crossflow filtration system to remove particles smaller than 10 microns from high-temperature, high-pressure gas streams. Sonic energy induces agglomeration so that particles can be removed in a continuously operating cross-flow filler element. Cold-model and preliminary high-temperature, high-pressure results are promising.

The objective of this investigation was to explore the potential effectiveness of sonic agglomeration, crossflow filtration, and a combination of these techniques to remove particles from high-temperature, high-pressure (HTHP) gas streams. The technique of sonic agglomeration has been known since the 1930's, and crossflow filtration has been used successfully in liquid filtration. This investigation is unique in that these two techniques were combined. Sonic energy was used to agglomerate particles to sizes large enough to be separated from the gas stream in a crossflow filter. The crossflow filter has advantages over conventional filters as a paniculate agglomerate removal system because it (1) operates continuously, (2) does not subject the fragile agglomerates to the high stress typical of inertial capture devices, and (3) can control the buildup of a filter cake when properly combined with a sonic agglomerator.

This investigation was supported by the Gas Research Institute and the Institute of Gas Technology Internal Research and Development Fund.

In this preliminary study, we found that—

• A 2-micron porosity filter must be used to achieve 98% paniculate removal from 95% of a dust-laden stream. (In the crossflow operating mode, 5% of the stream bypasses the filter.)

• When sonic agglomeration is combined with crossflow filtration, the same removal efficiency can be achieved with a 10-micron porosity filter.

• Combined sonic agglomeration/crossflow filtration removed particulates smaller than 10 microns in experiments at 265° C and 7000 kPa.

• The pressure drop across a 10-micron filter is about one-half that of a 2-micron filter, which could reduce the energy requirements for filtration.

This method of particulate removal should be applicable to many different coal reactor effluent streams, especially because it can operate at elevated temperatures and avoid gas cooling, liquid condensation, and subsequent liquid-solids separation. Preliminary estimates show that the power requirements of a combined sonic agglomerator/crossflow filter are lower than those of a crossflow filter alone, and that they are lower than or comparable with other particulate removal techniques. Additional tests are needed to establish the degree to which these benefits can be realized.     

DROP DISPERSION IN SUSPENSION POLYMERIZATION

Four models, two based on laminar shear and two based on turbulent flow, are proposed to describe drop dispersion in non-coalescing systems. The models predict the largest surviving drop size _dmax as a function of geometry, speed and physical property variables.

Laboratory data including suspension polymerization runs support the boundary layer laminar shear model for drops larger than approximately 200 microns. Smaller drops support a turbulence model.

The boundary layer shear model was confirmed in scale-up suspension polymerization runs aimed at producing 1000 micron maximum bead sizes. Five approximately geometrically similar polymerizers were used, varying in size from 7.5 to 15000 liters.     

VISCOMETRIC FLOWS OF NEUTRALLY BUOYANT SUSPENSIONS IN SECOND-ORDER FLUIDS

The local volume averages of the equations of motion as well as the appropriate boundary conditions for neutrally buoyant suspensions of spheres in second-order fluids (Li and Slattery, 1989a) are employed to analyze both the cone-plate viscometer and the parallel-plate viscometer. The predicted results are compared with measurements of apparent viscosity and of the primary normal stress difference. Predictions of measured apparent viscosities are in excellent agreement with the experimental data up to 20% solids by volume; the average error is no more than 5%. Predictions of apparent viscosities for the limiting case of a very dilute suspension are restricted to less than 10% solids by volume. The primary normal stress difference is predicted to be independent of the volume fraction of solids, in approximate agreement with previously reported data.

Both theory and experiment have demonstrated that a neutrally buoyant suspension of uniform spheres in an incompressible second-order fluid behaves like a single-phase second-order fluid in these two viscometers.     

GAS CHROMATOGRAPHIC DETERMINATION AND CORRELATION OF WEIGHT-FRACTION HENRY'S CONSTANTS FOR HYDROCARBON GASES AND VAPORS IN MOLTEN POLYMERS

In the polymer industry, separation equipment is required to separate unreacted monomers and solvents from polymers. In order to design such equipments, solubilities of gases and vapors in molten polymers are needed as fundamental data. It is very helpful if the weight-fraction Henry's constant, which gives solubilities of a solute at concentrated regions of a polymer, can be estimated by a predictive method.

In the present study, a new expression for the free volume term has been derived and is coupled with the UNIFAC model. The present UNIFAC-FV model was applied to common polymer systems. The weight-fraction Henry's constants were calculated for several volatile hydrocarbons and the calculated results were compared with the experimental data determined by a gas chromatographic technique.

The present UNIFAC-FV model with a new free volume expression was found to be helpful in predicting the weight-fraction Henry's constants of hydrocarbon solutes in molten polystyrene, in polypropylene, and in low-density polyethylene. It is advantageous that our model is applicable both supercritical gases and subcritical vapors with no adjustable parameters.     

DELIQUORING BY EXPRESSION - PART 2 VARIABLE-PRESSURE EXPRESSION

Expression processes under variable-pressure condition are analyzed in view of the flow through compressible porous media. It has been demonstrated that the expression mechanism of slurry consists of two flow phenomena and these types of phenomena can be analyzed first by filtration theory and second by the so-called consolidation theory.

By assuming that the continuous screw expression process con- sists of a succession of batch processes, the basic equations ex- pressing the relationship between the dehydration rate, the feed rate, and the expression pressure distribution are derived.     

FIBROUS MEDIA PLUGGING MODELLING FOR LIQUID FILTRATION

The aim of this work is to model the plugging curve of fibrous media for depth and surface filtration. The model links the evolution of pressure drop versus the injected mass of pollutants to structural properties of the media. Furthermore, thanks to the model, it is possible to predict the fibrous composition of a medium, which conforms to given filtration properties

First, a review of the typical fibrous media for engine oil filtration formed in our Laboratory is proposed, and, the measured filtration properties as well as the methods used for the characte rization of structural properties of the media during plugging are presented. Then, an explanation of the evolution of structural properties is proposed

In the second part, the results of the structural property characterization during plugging are used to develop a model of the pressure drop evolution as a function of the injected mass of pollutants. Then, correlation laws linking the model parameters to the structural properties of the medium are given and the model is used to predict the plugging curve of two typical filtering media.     

DEVELOPMENT AND TESTING OF THE INTERNAL ROTARY COMPRESSION PRESS

The Internal Rotary Compression (IRC) press is based on a concept patented by Anderson Metal Industries, Inc. (AMI) in which one dewatering roll is configured internally and eccentrically to the other. The press can simultaneously apply severe mechanical compression and shear forces to the material being dewatered. This design permits a larger no-slip entry volume for dewatering than that obtainable from conventional external roll presses of the same size.

Bench-scale tests of the IRC press have been conducted at IGT with several different materials including peat, wood fines, and paper waste. Significant dewatering was achieved for each material tested. Dewatered peat moisture contents in the range of 40 to 50 weight percent have been achieved. These results represent a significant improvement over those achievable by conventional continuous presses.

Tests have also been conducted in an IRC prototype press designed to produce 45 kg/h of dewatered peat. Tests with moderately and slightly decomposed peats have achieved pressed peat moisture contents as low as 50 weight percent. This paper presents the results of tests conducted with peat in the bench-scale and IRC prototype presses.     

Improving deposition tester to study adherent deposits in papermaking

Conventional methods used for the quantification of adherent material contained in a pulp suspension propose either filtration of the sample, which may lead to loss of sticky material in the filtrate, or dilution of the pulp, which may cause destabilization of the dissolved and colloidal material; thus, leading to unreliable results. In 1998, the Cellulose and Paper Group of University Complutense of Madrid developed a deposition tester which aimed to quantify the adherence of material (microstickies and secondary stickies from dissolved and colloidal material) that was present in white waters generated during papermaking processes. In this paper, an improved deposition tester capable of directly studying the deposition tendency of total stickies in pulps without dilution is described and validated. The design of this device prevents the rotor system from being clogged and blocked by pulps, hence, being able to quantify deposits without having to apply any filtration and/or dilution stages. In addition, the study provides determination of the equipment optimum operating conditions as well as comparison between the improved deposition tester and the one previously developed. Results show that this deposition tester can determine the adherent material contained in pulps with a consistency up to 1%. The comparison of results obtained after applying both deposition quantification methods shows that the quantities of deposits that were measured with the improved tester are slightly lower than those obtained with the application of the conventional method; however, they are in the same order of magnitude. Therefore, it is possible for the improved tester to determine total stickies in all cases, including cases that it is not convenient to apply a filtration and/or a dilution stage.     

EXPERIMENTAL DETERMINATION OF THE PERMEABILITY AND RELATIVE VISCOSITY FOR FINE LATEXES AND YEAST SUSPENSIONS

The specific cake resistances of thin layers of fine latexes and of yeast cells have been determined from flux data for pressure drops of up to 100 kPa in a static filtration device. A single correlation has been developed that relates the cake resistance to particle diameter for monodisperse rigid latex spheres with diameters between 1.0 and 6.7 μm. The specific resistance of the yeast cell layers was found to be almost 50 times larger than that of the rigid latex spheres of the same median diameter

The relative viscosities of a 7.3 μm latex and yeast cell suspensions have been measured in a cone-and-plate viscometer. Empirical correlations relating the relative viscosity to the solids volume fraction were developed from linear regression of the data for each suspension. A correlation was also developed that relates the relative viscosity of the yeast cell suspension to the cell count. The effective shear-viscosities were not observed to exhibit a significant shear-rate dependence. However, an apparent viscosity increase with time was observed. This is attributed to radial migration of the particles as a result of interactions with the surface of the cone.     

THE FLOODING CAPACITY OF PERFORATED PLATES IN ROTATING LIQUID-LIQUID-SYSTEMS†

Centrifugal extractors found wide applications in the industry, but up to now very little is known about what happens inside and how to calculate fluid-dynamic and mass transfer. For the basic research of dispersed liquid-liquid-systems in centrifugal fields a model centrifuge was built which is resistant to the high loads produced by rotation and which enabled us to observe the flow mechanism at the flooding points.

The processes inside have been measured and photographed by a high-speed-camera.

The calculation of centrifugal extractors is based mainly on the contact surfaces of the phases and the contact times. The maximum flow or flooding capacity is determined by three limits. Two of them are determined by the interface locations inside, controlled from the back pressure. The third limit is given by the maximum combined flow. This limit is dependent on the set of internals, the rotor speed and the physical properties of the liquid system. The experimental results will be shown and compared with new theories for the flooding capacities of perforated cylindrical plates in rotating liquid-liquid-systems.

The results predicted using the mathematical model for calculating the capacities are in fair agreement with the measurements.