Water Addition Rate Research Articles

The controlled crystallisation of a model powder: 1. The effects of altering the stirring rate and the supersaturation profile, and the incorporation of a surfactant (poloxamer 188)

A model drug (ethyl p-hydroxybenzoate) has been crystallised from propanol-water mixtures by the addition of water. The effects of rate of water addition, stirring speed and stirrer type have all been investigated. By consideration of the extent of turbulence and the degree of supersaturation, the process can be assumed to be driven by secondary nucleation mechanisms. A change in habit from plates to prismatic was observed with changes in the rate of addition of the crystallising fluid. The effect of addition of a surfactant (poloxamer 188) was investigated. It was found that the size and habit were altered by the presence of the surfactant, in a concentration-dependent manner. Differential scanning calorimetry (DSC) studies were interpreted to show that it was improbable that the surfactant was incorporated within the crystal lattice. By use of solution calorimetry, it was seen that a more favourable heat of solution was obtained in the presence of poloxamer. If the crystals were washed, however, there was no difference between the heat of solution for crystals which were prepared with or without added poloxamer. This was taken to show that the poloxamer was reversibly bound to the crystal surface. Contact angle measurements revealed that control crystals have a greater contact angle than those produced in the presence of poloxamer after washing of the crystals to remove reversibly adsorbed surfactant, thus the surface remained more hydrophilic if the crystal had been formed in the presence of poloxamer. Consequently, it is argued that the poloxamer is adsorbing and slowing the growth of hydrophilic surfaces of the crystal, thus making the final crystal more hydrophilic. For this to be true, there must be a deviation from the standard view of poloxamers adsorbing to hydrophobic surfaces in a largely irreversible manner. This view relates to adsorption from water, but in this work the adsorption is from a propanol-water mixture. High-sensitivity DSC of the solution showed that there were no phase transitions for the surfactant in the mixed solvent (whereas there are transitions in water). It is proposed that this reveals fundamental information about the conformation of the surfactant in this mixed solvent system, and that this conformational change is the reason for the change in the adsorption profile of the surfactant onto the solid.

Adaptive predictive control of a grinding circuit

This paper deals with distributed adaptive generalized predictive control of a grinding circuit. This multivariable system is commonly used in mineral industries for size reduction. It is characterized by time varying dynamics owing to changes in ore properties and operating conditions. The fresh ore feed rate, the water addition rate, the circulating load and the product fineness are respectively selected as control and controlled variables. The parameters of two single input-single output discrete models are identified using a least-squares algorithm, taking into account the requirements for long-term adaptive control. Numerical results have been carried out using a simulator based on phenomenological models derived from mass balance considerations. The adaptive controller is compared to a fixed parameter controller. These results illustrate the self-tuning ability and the continuous adaptivity of the control strategy. They also highlight that adaptive control is particulary suitable for distributed control.

Column Flotation of a South African Cooking Coal

Abstract The aims of the study reported here were to investigate whether column notation technology could be used to recover a saleable quality coal from a −0.15 mm fines sample obtained from a Natal colliery producing a coking quality coal; and to determine which column cell operating parameters had a dominant effect on the yield and grade of concentrate produced. Seven parameters were investigated namely, froth height, frother concentration, air flow rate, volumetric slurry feed rate, wash water addition rate, sparger type and column height. Tests runs were performed according to a 2-level 27.3 IV fractional factorial design. The test results showed that the column cell was capable of producing a concentrate grade of coking quality. Frother concentration was found to exert the largest effect on yield and grade; followed by air flow rate and slurry feed rate. It was concluded that the high vitrinite (85%) content of the coal sample caused the overall rate of flotation to be determined by froth phase kinetics. Comparative tests showed that, in general, the performance of the column cell was better than conventional flotation but poorer than results obtained from density-based float and sink separations.

Effects of addition rate and pH of water on cordierite powder prepared by complex-alkoxide hydrolysis

In preparation of a cordierite powder by the hydrolysis of complex-alkoxide precursor, the effects of conditions of hydrolysis (i.e, the addition rate and pH of water) on the hydrolysis products were investigated by SEM, ICP, 27Al MAS-NMR and XRD. Drop-wise addition of water gave monolithic gels irrespective of pH values of water added. Rapid addition of a large amount of water was favorable for powder precipitation, preventing gelation. Under such a condition, pH of water had a major influence on the chemical homogeneity of the products. At pH below 11.7, the filtered precipitate deviated from stoichiometric composition (SiO2-poor) and an appreciable fraction of aluminum atoms was in the octahedral coordination, suggesting partial decomposition of the precursor into compounds of separate metals on hydrolysis. By contrast, at pH 11.7 or above, the precipitate was almost stoichiometric and most of the Al atoms occupied tetrahedral Al sites. The precipitate consisted of fine particles of submicrometer size and crystallized to single phase α-cordierite via μ-cordierite without other minor phases at 1050°C for 1 h.

Optimal control of a ball mill grinding circuit—I. Grinding circuit modeling and dynamic simulation

Mineral grinding circuits can be controlled with a set of proportional—integral (PI) controllers or alternatively by specialized controllers which make use of optimal control theory. The latter control strategy is superior in the sense that feed solid and water addition rates are manipulated in concert to achieve a specified control objective. A dynamic model is needed for PI control the model can be used for off-line tuning. Off-line tuning circumvents the problem of on-line tuning during which transients persist for a long time, resulting in lost production. The key elements of the full dynamic model are the population balance model of the ball mill and an empirical model of the hydrocyclone. The model development and its verification for both steady- and unsteady-state responses are shown. On-line computations with the full dynamic model require the solution 37 differential equations at every sampling instant. In addition, optimal control calculations may overburden the control computer. Therefore, a simplified model using just three state variables is shown to be adequate for dynamic predictions. In Part II the full dynamic model is used in off-line tuning and the simplified model is used in the optimal controller. Both model predictions and pilot scale ball mill circuit responses are shown.

WATER ADDITION EFFECTS ON HEAT EXCHANGER PERFORMANCE IN AN UNSATURATED SOIL

ABSTRACT A heat transfer and water movement model was developed to study heat exchanger performance in an unsaturated Sharpsburg silty clay soil. Heat exchanger performance was simulated, without water addition, for different soil water contents and exchanger operating temperatures. Soil drying reduced exchanger performance in all but the highest soil water content cases. Water addition was modeled by maintaining an elevated soil water content adjacent to the exchanger surface. Water addition increased heat transfer for all soil water contents studied, with up to a 24% increase for the driest conditions simulated. Predicted water addition rates ranged from 0.0012 to 0.0314 L/m of heat exchanger length per hour, depending on heat exchange temperature, soil water content, and water content at the exchanger surface. Implications for the design of water addition systems are discussed.

The effect of rate of water addition on the response of wheat roots to added nitrogen in a leaching environment

Wheat was grown under a range of leaching regimes in columns of a loamy sand soil to which nitrogen had been added as calcium nitrate. Rates of water addition up to depths of 4.5 cm per week were found to have little effect on the amount of nitrogen taken up at 6 weeks after seeding, but higher rates of water addition progressively reduced uptake. Distributions of root length in the soil profiles varied markedly with leaching intensity, and were found to be related to the distributions of mineral nitrogen that had existed in the soil as the roots were growing.

Studies on combustion and exhaust emissions in a high speed diesel engine. (2nd report. Combustion, vibration and noise of water-in-oil type emulsiied fuel).

This paper deals with quantitatively the influence of water emulsified fuel on combustion, engine vibration and noise, and the effect of ignition improver on the reduction of vibration and noise. The main conclusions obtained are as follows : (1) With an increase in the water addition rate, ignition delays and the maximum pressure rise rate increases. As a result, engine vibration and noise increase, in proportion to the pressure rise rate. (2) An increase in ignition delay with the addition of water is closely related to the heat quantity required to evaporate water in the fuel spray under a high temperature and high pressure condition. (3) Increases in engine vibration and noise due to the addition of water can be reduced by adding a small amount of ignition improver without aggravating engine performance.

Kinetics and mechanisms of the reactions of ketenes with water and alcohols in dioxane solutions

The spontaneous addition of water to diphenyl- and to dimethyl-ketene in dioxane–H2O and dioxane–D2O mixtures is third order in the stoicheiometric water concentration, [H2O]s, when [H2O]s≲ 1.5M. At higher water concentrations (up to 19M) the observed order falls, and the patterns of the results for the two ketenes are similar, but differ in detail. The isotope effect kH2O/kD2O= 1.7–2.3 for all the systems studied. The addition of ethanol to diphenylketene in dioxane–ethanol mixtures has a kinetic pattern very similar to that for addition of water to this ketene, except that the change to a lower order occurs when [EtOH]S≃ 5M. The variation of the activation parameters with medium composition is also very similar for all these spontaneous additions: at low water or ethanol concentrations Ea= 1 ± 1 kcal mol–1, and ΔS‡=–60 ± 8 cal K–1 mol–1; at higher concentrations Ea rises somewhat, and ΔS‡ becomes less negative. The results are considered in the light of previous work. It is concluded that water and alcohol add to ketenes by a common mechanism in non-hydroxylic solvents of low dielectric constant, and that this involves a cyclic, hydrogen-bonded transition state such as (1). Hydroxide ions (ca. 5 × 10–3M) have no effect on the rate of water addition in dioxane, but hydrogen ions have powerful effects: the addition to diphenylketene is inhibited, that to dimethylketene is catalysed. These observations are explained. The isotope effect kH3O+/kD3O+≃ 1.9 for the catalysis. We propose a catalytic mechanism with a cyclic transition state (3) involving a dominant slow proton transfer to the ketene β-carbon atom.

Holdup Profile and Bubble Size Distribution of Flotation Column Froths

Wash water is added at the top of flotation columns to eliminate fine hydrophilic particle recovery. It helps create a deep packed bubble bed (loosely termed “froth”) with a well defined froth/pulp interface. Common industrial practice is to maintain a constant froth depth (about 1–2 m) by regulating the wash water addition rate. This practice is being examined through a systematic study of the froth zone.A two-dimensional Plexiglass column was used with a two-phase (gas-liquid) froth. Gas holdup and bubble size distribution through the froth were measured as a function of gas rate, water rate and frother dosage. Wash water dramatically increased froth stability and depth. Gas holdup increased with increasing height above the interface; the rate of increase is highest close to the interface. The liquid holdup at the top of the froth column was found to increase significantly with increasing gas or wash water flowrate, and increasing frother concentration.Mathematical models are developed to describe liquid entrainment and drainage throughout the froth.

Holdup Profile and Bubble Size Distribution of Flotation Column Froths

Wash water is added at the top of flotation columns to eliminate fine hydrophilic particle recovery. It helps create a deep packed bubble bed (loosely termed “froth”) with a well defined froth/pulp interface. Common industrial practice is to maintain a constant froth depth (about 1–2 m) by regulating the wash water addition rate. This practice is being examined through a systematic study of the froth zone.A two-dimensional Plexiglass column was used with a two-phase (gas-liquid) froth. Gas holdup and bubble size distribution through the froth were measured as a function of gas rate, water rate and frother dosage. Wash water dramatically increased froth stability and depth. Gas holdup increased with increasing height above the interface; the rate of increase is highest close to the interface. The liquid holdup at the top of the froth column was found to increase significantly with increasing gas or wash water flowrate, and increasing frother concentration.Mathematical models are developed to describe liquid entrainment and drainage throughout the froth.

A Model System for Curd Formation and Melting Properties of Calcium Caseinates

ABSTRACTA lipid‐free model system was developed to aid in the study of melting and other functional properties of calcium caseinates in their application to imitation processed cheese. The model system was formed by the controlled addition of water to an alcohol suspension of the protein. At a critical water concentration, a curd was formed spontaneously. The recovered curd was melted and the area of the melt determined (melt area index). The amount of water added, rate of water addition and the source of caseinate affected the melt area index. A protein fraction, recovered from the supernatant, was rich in γ‐casein and also contained minor amounts of β‐, αs‐ and k‐caseins.

Emulsion Paint of Aromatic Petroleum Resin. I. Emulsification of Aromatic Petroleum Resin Solution in Water

Industrial emulsification of an aromatic petroleum resin solu tion in bodied linseed oil was investigated using an emulsion inversion process. It was found that the preferred surfactant had the best match in solubility parameter between olefinic group and resin solution A slight variation was found in optimum H LB for emulsification, depending on the chemical family of surfactants chosen, but independent on resin molecular weight. The average particle size of the emulsion obtained showed an ordi nary tendency to be dependent on speed of agitation, rate of water addi tion, resin viscosity, and surfactant concentration.

A novel method for the hydrolysis of ethyl and isopropyl silicates

AbstractThe hydrolysis of ethyl and isopropyl silicates without the use of an acid or base catalyst is described. The silicate and an alcohol which is a mutual solvent for water and the silicate are treated with water, preferably under reflux. For ethyl silicate the reaction temperature can be as low as 40°C. A liquid hydrolysate is obtained when the rate of water addition is carefully controlled. This hydrolysate will form a rigid coherent gel capable of binding refractory materials. Liquid hydrolysates prepared in this way have been used to make refractory shapes, also foundry moulds and cores for precision piece moulding work and an ethyl silicate hydrolysate can be used to prepare an anti‐corrosion paint based on zinc. It would be expected that other lower alkyl silicates can be treated similarly to form hydrolysates which give a rigid coherent gel capable of binding refractory materials and which can also be used to prepare anti‐corrosion paints based on zinc.

A novel method for the hydrolysis of ethyl and isopropyl silicates

The hydrolysis of ethyl and isopropyl silicates without the use of an acid or base catalyst is described. The silicate and an alcohol which is a mutual solvent for water and the silicate are treated with water, preferably under reflux. For ethyl silicate the reaction temperature can be as low as 40°C. A liquid hydrolysate is obtained when the rate of water addition is carefully controlled. This hydrolysate will form a rigid coherent gel capable of binding refractory materials. Liquid hydrolysates prepared in this way have been used to make refractory shapes, also foundry moulds and cores for precision piece moulding work and an ethyl silicate hydrolysate can be used to prepare an anti-corrosion paint based on zinc. It would be expected that other lower alkyl silicates can be treated similarly to form hydrolysates which give a rigid coherent gel capable of binding refractory materials and which can also be used to prepare anti-corrosion paints based on zinc.