Showing papers in "Canadian Journal of Chemical Engineering in 1981"

Theoretical studies on the gravity drainage of heavy oil during in-situ steam heating

Abstract: One concept for the in-situ production of oil from the tar sands involves the continuous injection of steam into a growing steam-saturated volume or steam chamber. Steam flow to the boundary of the chamber, condenses and gives up its heat to the surrounding oil sands. The condensate and heated oil flow by gravity to a production well located at the bottom of a chamber and are removed continuously. The well may consist of a horizontal slotted pipe. This paper describes the theory of operation of such a process and an equation is derived which predicts the rate of drainage.

Hydrogen production by the catalytic steam reforming of methanol part 1: The thermodynamics

Abstract: The thermodynamic equilibria involved in the catalytic steam reformation of methanol to produce hydrogen have been examined over the ranges of pressure 101–3040 kPa, temperature 400–700K and water to methanol feed ratio 1.5–0.67. Four models have been considered based upon possible reaction products and the equilibrium composition of each model calculated. The presence of methane and carbon reduce the quantity and quality of hydrogen produced. The best condition for hydrogen production occurs at 500K in the model in which carbon (soot) and methane gas are excluded and where pressures are low, and water is in excess in the feed. To achieve these conditions in practice the reactions for methane formation, which is thermodynamically favoured, and the appearance of carbon (soot) must be inhibited.

Three-phase fluidization: Some knowledge gaps

Abstract: The most recent review by ostergaard — on the fluid mechanics of three-phase fluidized beds — is updated and broadened, and the more manifest knowledge gaps are identified. A systematic classification of the various modes of three-phase fluidization is presented in order to provide some perspective on the research which has been done and on that which has yet to be done. On a mis a jour et elargi la revue de litterature la plus recente, effectuee par ostergaard, sur la mecanique des fluides des lits fluidises a trois phases; on a ainsi identife les trous de connaissance les plus manifestes. On presente une classification systematique des divers modes de fluidisation a trois phases, afin de mettre en perspective la recherche deja faite et celle qu'il reste a faire dans ce domaine.

Local compositions and local surface area fractions: A theoretical discussion

Abstract: The basic constraint for any valid expression for local composition, derived by McDermott and Ashton, is shown to be equivalent to the conservation equation used in Flemr's analysis. A similar constraint for local surface fractions is derived. The applicability of quasi-chemical expressions for local composition or local surface area fractions is extended to different existing (random) models of solutions. Chao's and Kehiaian's treatments appear as special cases. The statistical thermodynamic derivation of UNIQUAC is discussed in the framework of the generalized treatment. A method for solving the quasi-chemical equations for quaternary systems is described. On montre que la contrainte fondamentale etabilie par McDermott et Ashton, relativement a n'importe quelle expression valable de la composition locale, est equivalente a l'equation de conservation employee dans l'analyse de Flemr; on etablit une contrainte semblable pour les fractions locales de surface. On a etendu a differents modeles (aleatoires) de solutions existants, l'applicabilite d'expressions quasi-chimiques pour les compositions locales ou les fractions locales de surface. Les traitements de Chao et de Kehiaian apparaissent comme des cas particuliers. On discute la derivation par thermodynamique statistique d'UNIQUAC dans le cadre du traitement generalise. On decrit une methode pour resoudre les equations quasi-chimiques relatives aux systemes quaternaires.

Laminar falling film flow and heat transfer characteristics on horizontal tubes

Abstract: Knowledge of falling film flow and heat transfer characteristics on horizontal tubes is required in the assessment of certain CANDU reactor accident sequences for those CANDU reactors which use moderator dump as one of the shut-down mechanisms. In these reactors, subsequent cooling of the calandria tubes is provided by falling films produced by sprays. This paper describes an analysis of falling film flow and heat transfer characteristics on horizontal tubes using integral methods. The application of the results to an assessment of the stability of the films on the calandria tubes following a loss-of-coolant accident with impaired emergency coolant injection flow is discussed. La connaissance des caracteristiques de debit et de transfert de chaleur d'un film tombant a la surface des tubes horizontaux est necessaire pour etablir les sequences d'accident du reacteur CANDU, pour les modeles qui utilisent la vidange du moderateur au cours du processus d'arret. Dans ces reacteurs le refroidissement subsequent des tubes de la calandre est effectue grâce a des films tombants obtenus par pulverisation. Cet article decrit une analyse des caracteristiques de debit et de transfert de chaleur du film tombant sur des tubes horizontaux, utilisant des methodes integrales. On discute l'application des resultats obtenus a l'evaluation de la stabilite des films sur les tubes de la calandre, a la suite d'un accident impliquant une perte de caloporteur, et dans le cas d'une alteration du systeme d'injection du caloporteur d'urgence.

Dispersion and hold-up in bubble columns — comparison of rigid and flexible spargers

Abstract: The performance of a new type of bubble generating device, the rubber sheet sparger, is contrasted and compared with rigid spargers. Impulse response tests were analyzed using the weighted‐moments method to determine voidage and dispersion coefficients in counter‐current bubble columns of nominal diameters two, four, six and twelve inches. The flexible rubber sheet sparger produced more uniform emulsions, smaller bubbles and larger voidages than perforated plates, while dispersion coefficients were reduced for a range of superficial gas velocities. The dispersion data seem to fit the isotropic turbulence model, with slight modifications. It is demonstrated that the rubber sheet sparger is self‐regulating, with hole size increasing in direct proportion to pressure drop across the sparger.

Hydrotransport of solids in horizontal pipes: Effects of solids concentration and particle size on the deposit velocity

Abstract: Correlations previously proposed in the literature for the deposit velocity in the flow of settling slurries in horizontal tubes generally predict increasing values with increasing solids concentration. However, the present comprehensive investigation which has drawn on data from a broad geographical base, confirms that the deposit velocity shows a maximum with respect to concentration and decreases above about 15% by volume solids. It is also shown that the presence of fine particles (<75 μm) is particularly significant in determining the degree of the reduction in the deposit velocity for the higher concentrations. This reduction would appear to be due primarily to a significant increase in the drag coefficient for particles settling in a fine particle suspension, i.e. heavy medium. The data are summarized in graphs for a variety of materials including sand, gravel, iron ore and coal. Les correlations proposees anterieurement dans la litterature pour la vitesse de depo't lors de l'ecoulement de suspensions avec decantation dans des tubes horizontaux, prevoient generalement des valeurs croissantes avec la concentration en matieres solides. Toutefois, l'etude poussee presentee ici et basee sur des donnees de provenances geographiques diverses, confirme que la vitesse de depo't atteint un maximum en fonction de la concentration et diminue lorsque la teneur en matieres solides excede environ 15% en volume. On montre egalement que la presence de particules fines (<75 μm) est particulierement importante pour la diminution de la vitesse de depo't dans le cas des concentrations les plus elevees. Cette diminution semblerait due essentiellement a un important accroissement du coefficient de frottement, dans le cas des particules qui se deposent a travers une suspension de fines particules. On resume, sous forme de graphiques, les resultats obtenus pour differents materiaux, dont le sable, le gravier, le minerai de fer et le charbon.

Analysis of fluidized bed catalytic cracking regenerator models in an industrial scale unit

Abstract: Fluidized bed regenerator models, under steady state conditions, have been reconsidered because of recent significant changes in the technology of fluidized bed regenerators. Zeolitic catalysts, temperatures of the dense bed at about 700°C and lower CO/CO2 relationships are the new characteristics of the units. Following these innovations the operating conditions of the industrial catalytic cracking regenerator of Destileria La Plata, Yacimientos Petroliferos Fiscales, Argentina, were significantly modified. As a result, an important improvement in the coke conversion was observed. Five different conventional fluidized bed models using experimental data from the industrial regenerator have been tested. The analysis considers bubbles and grid jet regions, and for each model, the prediction of the regenerator performance is shown. The CSTR model is the most successful in this regard. On a reconsidere les modeles de regenerateurs en lits fluidises en regime stationnaire, en raison des changements importants realises recemment dans la technologie de ces regenerateur. Les nouvelles caracteristiques des regenerateurs sont les suivantes: catalyseurs zeolitiques, temperature du lit dense d'environ 700° C et rapports CO/CO2 moindres. A la suite des innovations mentionnees, on a modifia de maniere importante les conditions operatoires du regenerateur industriel du craquage catalytique de la “Destileria La Plata, acimientos Petroliferos Fiscales, Argentine; il en est resulte une amelioration importante de la conversion du coke. On a examine cinq differents modeles de lits fluidises, en employant les resultats experimentaux obtenus avec le regenerateur industriel. Dans l'analyse on a pris en consideration les regions relatives aux bulles et au jet de grille et l'on a indique pour chaque modele, la prevision de la performance du regenerateur; le modele RHAC est le plus satisfaisant a ce sujet.

Hydrodynamicst axial mixing and mass transfer in rotating disk contactors

Abstract: Correlations for predicting characteristic velocity both above and below the critical rotor speed have been obtained under conditions with and without solute transfer. It has been found that (1) above the critical rotor speed, the characteristic velocity U0 is proportional to g/DrN2, whereas below this value a transition region exists where Uo is proportional to (g/DrN2)0.26; (2) multiple regression analysis of the experimental data of continuous phase axial mixing shows that the axial dispersion coefficient varies not only with the rotor speed and modified velocity of continuous phase but also with the velocity of dispersed phase. With varying RDC operations, the true value of Kod corrected for axial mixing changes continually between the limiting values predicted from stagnant and fully turbulent drop models. However, the highest experimental values were only 30 to 40% of those predicted by the Handlos-Baron model at the same drop Peclet number.

Entrainment of particles from a pilot scale fluidized bed

Abstract: Particles entrained from a pilot scale fluidized bed of sand having a mean size of 102 μm have been captured and analysed at superficial air velocities up to 1.3 m/s. Variation of bed temperature over the range 300 to 445 K and insertion of a tube bundle in the splash zone had little effect on the measured entrainment fluxes. Existing correlations for predicting entrainment from fluidized beds gave widely divergent results, and generally differed markedly from the experimental data. Of the correlations tested, the graphical saturation carrying-capacity correlation of Zenz and Weil gave the best agreement with the experimental data. The size distribution of particles carried over differed widely from the size distribution in the bed at low gas velocities but approached the in-bed distribution at higher velocities. On a collecte et analyse les particules entrai'nees hors d'un lit a l'echelle pilote, flidise de sable, la grosseur moyenne etant de 102 μm aux vitesses superficielles d'air allant jusqu'a 1.3 m/s. La variation de la temperature du lit, sur une gamme de 300 a 445 K, et l'introduction de tubes dans la zone de projection n'ont eu que peu d'effet sur les flux d'entrai'nement mesures. Les correlations qui existent actuellement pour prevoir l'entrai'nement de particules a partir de lits fluidises, ont fourni des resultats tres divergents et leurs donnees different, en general, d'une maniere marquee des resultats experimentaux. Parmi les correlations que nous avons examinees, la correlation graphique de Zenz et Weil, relative a la capacite de transport a saturation, a le mieux concorde avec les resultats experimentaux. La granulometrie des particules entrai'nees differe beaucoup de celles des particules dans le lit, lorsque la vitesse du gaz est faible, mais elle s'en approche lorsque les vitesses du gaz sont plus elevees.

Mechanical degradation of semi‐dilute polymer solutions in laminar flows

Abstract: Mechanical degradation of a semi-dilute solution of non-hydrolyzed polyacrylamide was studied under laminar flow conditions through fine capillary systems. Using a multi-pass device and capillary tubes of the same diameter and of various lengths we have shown that mechanical degradation (i) occurs at a critical value of the wall shear rate, chosen as a reference deformation rate, which is slightly higher than that of the appearance of high pressure losses in the entrance region of the capillary tube; (ii) is independent of the capillary tube length; (iii) increases with the number of passes N up to a maximum value for a limiting number of passes Nlim which is a decreasing function of deformation rates but does not depend on capillary length. The amount of degradation is expressed in terms of loss of viscous dissipation in shear and transient elongational flow. This last point is determined by studying the total end pressure loss through the capillary tube as a function of the pass number. The high pressure loss is related to viscous dissipation on macromolecules stretched by rapid converging flow. A comparison between a fresh and a fully degraded solution indicates that the degradation affects shear viscosity much less than viscous dissipation in rapid converging flow which is related to the properties of extended macromolecules. Both experimental results and theoretical interpretation suggest that, in our capillary system, the mechanical degradation occurs in the entrance region of the capillary where macromolecules are stretched and consequently submitted to extensional forces which can overcome the C–C bonds strength. On a etudie la degradation mecanique d'une solution semidiluee de polyacrylamide non hydrolyse en ecoulement laminaire dans des systemes capillaires fins. En employant un dispositif a passages multiples et des tubes capillaires de meme diametre et de differentes longueurs, on a etabli que la degradation (i) se produit a une valeur critique de la contrainte de cisaillement a la paroi (choisie comme reference de vitesse de deformation), qui est legerement plus elevee que celle de I'apparition de fortes pertes de charge a I'entree du tube capillaire; (ii) est independante de la longueur du tube capillaire; (iii) augmeiite avec le nombre de passages N jusqu'a une valeur maximale pour un nombre-limite de passages N, qui est une function decroissante des contraintes de cisaillenient, mais ne depend pas de la longueur du capillaire. L'ampleur de la degradation s'exprime en termes de diminution de la dissipation visqueuse lors de I'ecoulenient en cisaillciuent et l'ecoulement transitoire d'elongation; on etablit ce dernier point en etudiant la perte de charge totale dans le tube capillaire en fonction du nombre de passages. La forte perte de charge est liee a la dissipation visqueuse sur les macromolecules etirees par un ecoulement rapidement convergent. En comparant une solution fraiche avec une solution totalement degradee, on trouve que la degradation affecte bien moins la viscosite en cisaillenient que la dissipation visqueuse dans un ecoulement rapidement convergent, ce qui est Iie aux proprietes des macromolecules etirees. Les resultats experimentaux et I'interpretation theorique portent a croire que, dans le systeme capillaire precite, la degradation mecanique se produit a l'entree du tube capillaire, ou les macromolecules sont etirees et par consequent soumises a des forces d'extension qui peuvent vaincre la resistance de la liaison C-C.

Flow regime boundaries for an interior subchannel of a horizontal 37‐element bundle

Abstract: A needle contact probe system has been constructed and used to determine flow regime transitions for an interior subchannel in the upper half of a 37-element horizontal bundle (to include the effect of gravity separation) for adiabatic air-water flow. For the experimental range considered (up to ˜15.5 K*s−1, 50% quality), five distinct flow regimes were identified. Using the equivalent hydraulic diameter concept and cross-sectional average superficial velocities, air quality and total mass flux, flow regime maps were constructed. These maps are shown to deviate from pipe flow regime maps. The stratified smooth flow regime was never observed at the lowest flow rate considered due to the periodical disturbance of the flow by the bundle end plates and mid-plane spacers. On a construit un systeme de sonde a contact par pointe, et on l'a employe pour determiner les limites de regimes d'ecoulement pour un sous-canal interieur dans la moitie superieure d'un faisceau horizontal de 37 elements (pour tenir compte de l'effet de la separation par gravite); ce systeme a ete utilise dans le cas d'un ecoulement adiabatique d'air et d'eau. On a identifie cinq regimes d'ecoulement distincts sur la plage experimentale etudiee (allant jusqu'a ˜ 15.5 kg*s−1, qualite 50%). On a etabli des cartes de regime d'ecoulement, en employant le concept du diametre hydraulique equivalent, les vitesses superficielles moyennes dans une section droite, la qualite de l'air et le debit total en masse. On voit que ces cartes different de celles des regimes d'ecoulement dans les tubes. On n'a jamais observe le regime d'ecoulement stratifie et non turbulent au plus faible debit etudie, a cause de la perturbation periodique de l'ecoulement par les plaques d'extremite du faisceau et des espaceurs a mi-plan.

Wet oxidation of glucose

Abstract: Wet oxidation is used to oxidize organic substances at a controlled rate in an aqueous medium at elevated temperatures and pressures. Aqueous glucose solutions were oxidized with pure oxygen at four different temperatures in the range 176.7°C to 260.0°C, and at an oxygen pressure of 2.3 MPa. Three distinct stages of wet oxidation were found — induction, rapid oxidation, and slow oxidation. During the rapid oxidation period the reaction was assumed to be confined to a thin liquid layer next to the gas-liquid interface. The activation energy for the rapid oxidation period was estimated to be 130 ± 20 kJ/mol. Acetic acid was found to accelerate the rate of wet oxidation of glucose only slightly.

Mathematical modelling of rotary cement kilns by the zone method

Abstract: A steady state mathematical model of rotary cement kilns based on the fundamental principles of the physical and chemical processes within the kiln was developed. The zone method of analysis was utilized together with the Monte Carlo method to simulate the radiative interchange within the kiln. Steady state energy balances including the chemical reaction terms for each zone were solved simultaneously to give temperature distributions in gas and solid charge, and composition distribution in solid charge. Predictions of the mathematical model were compared with dry process and wet process rotary cement kiln data.

Batch cultivation of kluyveromyces fragilis in cheese whey

Abstract: Kluyveromyces fragilis was cultivated batchwise in an open pond rectangular bioreactor at 30°C, 2vvm of aeration, under non-sterile conditions and uncontrolled pH. The culture medium contained 7% cheese whey powder, 0.25% KH2PO4, 0.5% (NH4)2SO4 and was adjusted to an initial pH of 4.0 with phosphoric acid. The lactose was almost completely consumed after 16 h and COD reduction attained 80% after 64 h. The maximum suspended solids concentration obtained was 11.7 g/L. The cheese whey which had initially low protein and high lactose contents was converted by this system into a high protein and low lactose carbohydrate product. Une culture en discointinu de Kluyveromyces fragilis est realisee dans un bioreacteur rectangulaire, a 30° C, avec une aeration de 2 vvm, sous la condition non-sterile et sans regulation de pH. Le milieu de culture contient 7% du lactoserum de fromage en poudre, 0.25% KH2PO4, 0.5% (NH4)2SO4 et est ajuste a un pH initial de 4.0 avec de l'acide phosphorique. Le lactose est presque entierement consomme apres 16 h de fermentation et la reduction de DCO atteint 80% apres 64 h. La concentration de la matiere en suspension est de 11.7 g/L. Le lactoserum de fromage contenant initialement une faible teneur en proteine et une forte teneur en lactose, est converti par ce procede en un produit a haute teneur en proteine et basse teneur en lactose.

A simplified driving force model for activated carbon adsorption

Abstract: The use of two simplified driving force expressions are investigated for describing the intraparticle rate behaviour during adsorption onto activated carbon. A previously developed numerical solution to the surface diffusion model is used to compare the linear and quadratic driving force approximation when non-linear isotherms and time variant boundary conditions are present. The results show that while the linear driving force equation is a poor approximation of the exact solution, the quadratic driving force is a good approximation, and its use in a kinetic model of activated carbon adsorption gives as good a description of adsorption behaviour as is given by the more detailed surface diffusion model. The driving force model has the advantage of being easier to solve, and the numerical solution requires significantly less computational effort.

Effect of the physical properties of gas on the volume of bubble formed from a submerged single orifice

Abstract: The effects of the gas properties on the volume of a bubble formed from a submerged single orifice in the presence of pressure fluctuations in the gas chamber are investigated experimentally. The bubble volumes are affected by the specific heat ratio of gas and/or the gas density depending on the dimensionless capacitance number Nc. An extended two stage bubble formation model is proposed by considering the physical properties of gas. The bubble volumes calculated by the present model compare reasonably well with the experimental results.

Measuring and modelling forest evapotranspiration

Abstract: Micrometeorological methods of measuring and modelling forest evapotranspiration are reviewed and evaluated. Measurement methods include eddy correlation, aerodynamic, Bowen ratio/energy balance and stomatal diffusion resistance techniques. Modelling approaches discussed include a model relating evapotranspiration rate to the root zone water content and the net radiation flux, the Penman equation, and vapour diffusion models requiring stomatal resistance characteristics of the stand. Measured and modelled estimates of evapotranspiration from a Douglas-fir stand are compared. On passe en revue et on evalue les methodes micrormeteorologiques pour mesurer et modeliser l'evapo-transpiration de la vegetation forestiere. Ces methodes de mesure incluent la correlation des turbulences, l'aero-dynamique, la relation entre le bilan energetique et le rapport de Bowen et la resistance a la diffusion stomatale. Les methodes de modelisation comprennent a) un modele reliant la vitesse d'evapo-transpiration et la teneur en eau de la zone des racines ainsi que le flux net de rayonnement; b) l'equation de Penman et c) des modeles de diffusion de vapeur d'eau qui exigent les caracteristiques de resistance stomatale de l'arbre sur pied. On compare les estimations de l'evapo-transpiration d'un pin Douglas obtenues par mesure et par modelisation.

Solubility of acetylene in several polar and non‐polar solvents and solvent mixtures

Abstract: Solubilities of acetylene in pure solvents, hexane, cyclohexane, hexadecane, benzene, carbon disulfide, carbon tetrachloride, methanol, butanol and ethylene glycol, and mixtures, hexane-hexadecane and butanol-ethylene glycol, are reported at atmospheric pressure and temperatures ranging from 0 C to 50 C. Hydrogen bonding (H-bonding) factors expressed by a simplified Margules equation were found useful to correlate the solubilities of gases in the pure solvents as well as the solvent mixtures.

Heat transfer from cylinders in unsteady flow

Abstract: The paper is concerned with the experimental determination of the forced convective heat transfer from heated cylinders when the approaching flow has low frequency oscillations in the magnitude of the free stream velocity. Initial tests showed that at very low reduced frequency values, based on the cylinder diameter and the mean flow speed, up to values of .01, a reduction in the Nusselt Number value of up to 12% below the Nusselt Number for uniform approaching turbulent flow was recorded. For reduced frequency values above .03, an increase in the Nusselt Number to the original value when the flow was steady was measured. Le present travail a trait a la determination experimentale du transfert thermique en convection forcee a partir de cylindres chauffes, lorsque le debit qui s'en approche est anime d'oscillations de faible frequence de l'amplitude de la vitesse du courant principal. Des essais initiaux ont indique qu'a des tres faibles valeurs de la frequence reduite rapportees au diametre des cylindres et a la vitesse moyenne du debit, allant jusqu'a 0.01, on a enregistre une diminution de la valeur du nombre de Nusselt jusqu'a 12% au-dessous de celle correspondant a un debit turbulent uniforme. On a mesure, pour des valeurs de la frequence reduite superieures a 0.03, un accroissement du nombre de Nusselt par rapport a sa valeur originale correspondant a un debit stationnaire.

Void fraction and pressure drop in two phase stratified flow

Abstract: A procedure for computing the void-fraction and pressure drop in two-phase stratified flow over the whole range of flows from turbulent-turbulent to laminar-laminar, has been put forth. The results are in excellent agreement with those of previous investigators in flow situations where data are available. Simple curve fits of the theoretical results have been developed to compute the required quantities, as functions of the Lockhart - Martinelli parameters.

The plug flow model for mass transfer in three-phase fluidized beds and bubble columns

Abstract: The plug flow model (PFM), overwhelmingly used to describe mass transfer in bubble columns and three-phase fluidized beds, has never been critically tested. This study analyzes the PFM single parameter, KLa, to quantify mass transfer in the forementioned systems. Particular attention is paid to the mass transfer features of the zone near the distributor (grid zone) largely ignored until now. This study, carried out under the largest gas and liquid flow rates ever published, for similar types of systems, indicates the presence of two well defined mass transfer zones. These features invalidate, for design purposes, the use of the PFM. However, it still can be used as a qualitative mass transfer indicator. This has permitted a comparison between the mass transfer efficiency of bubble columns and three-phase fluidized beds with the conclusion that three-phase fluidized bed of 0.5 cm particles can compete successfully with bubble columns. On n'a jamais teste de maniere critique le modele d'ecoulement piston employe systematiquement pour ecrire le transfert de masse dans des colonnes a bulles et des lits fluidises a trois phases. On analyse, dans la presente etude, l'unique parametre de ce modele (KLa) pour quantifier le transfert de masse dans les systemes precites. On a porte une attention particuliere aux caracteristiques du transfert de masse au voisinage du distributeur, dont on a peu tenu compte jusqu'a maintenant. L'etude a ete faite, en ayant recours aux plus grands debits de gaz et de liquide qu'on ait encore utilises pour de tels systemes, a indique la presence de deux zones bien definies de transfert de masse; ce point indique que l'emploi du modele d'ecoulement piston pour les calculs de reacteurs n'est pas valable. Il peut cependant ětre utilise comme indicateur qualitatif du transfert de masse. Cette constatation a permis d'etablir une comparaison entre l'efficacite relative des colonnes a bulles et des lits fluidises a trois phases, comprenant des particules de 0.5 cm peuvent concurrencer avantageusement les colonnes a bulles.