Circulating fluidized bed combustion of a high-sulphur eastern canadian coal

Combustion tests were carried out with Minto coal in combination with three different limestones in the University of British Columbia (UBC) pilot scale (152 mm square x 7.3 m tall) circulating fluidized bed combustion (CFBC) unit. Operating conditions were chosen to be typical of those employed in large-scale CFBC power boilers. Recycling of fine particles captured by the secondary cyclone was found to be of considerable importance in increasing sulphur capture, enhancing combustion efficiency and reducing the amount of calcium sulphide in the solids residues. NO_x emissions increased as the Ca:S ratio increased. Local gas concentrations inside the reactor were strongly influenced by the core-annulus solids distribution patterns which characterize circulating fluidized beds.     

An evaluation of autotrophic microbes for the removal of carbon dioxide from combustion gas streams

Carbon dioxide is a greenhouse gas that is believed to be a major contributor to global warming. Studies have shown that significant amounts of CO₂ are released into the atmosphere as a result of fossil fuels combustion. Therefore, considerable interest exists in effective and economical technologies for the removal of CO₂ from fossil fuel combustion gas streams. This work evaluated the use of autotrophic microbes for the removal of CO₂ from coal fired power plant combustion gas streams. The CO₂ removal rates of the following autotrophic microbes were determined: Chlorella pyrenoidosa, Euglena gracilis, Thiobacillus ferrooxidans, Aphanocapsa delicatissima, Isochrysis galbana, Phaodactylum tricornutum, Navicula tripunctata schizonemoids, Gomphonema parvulum, Surirella ovata ovata, and four algal consortia. Of those tested, Chlorella pyrenoidosa exhibited the highest removal rate with 2.6 g CO₂ per day per g dry weight of biomass being removed under optimized conditions. Extrapolation of these data indicated that to remove CO₂ from the combustion gases of a coal fired power plant burning 2.4 × 10⁴ metric tons of coal per day would require a bioreactor 386 km² × 1 m deep and would result in the production of 2.13 × 10⁵ metric tons (wet weight) of biomass per day. Based on these calculations, it was concluded that autotrophic CO₂ removal would not be feasible at most locations, and as a result, alternate technologies for CO₂ removal should be explored.     

Strain Distributions in Adhesive Wood Joints

The influence of overlap length on the strain distribution in a double-lap joint was determined using a computer vision, white light speckle technique. The overlap lengths were 12.7 mm (0.5') and 38.1 mm (1.5'). This range represents a one-tenth scale of overlap lengths in double-lap joints used in adhesive connections in timber trusses. The side members were 50.8 mm (2') long and the center member was 88.9 mm (3.5') long. All joint members were 25.4 mm × 25.4 mm (1' × 1') in cross section. The joint members were yellow-poplar (Liriodendron tulipifera) wood and the adhesive was a resorcinol-formaldehyde.

Even though the connection was loaded in shear, both transverse and shear strains were shown to exist along the gluelines. These strains were significantly intensified at the ends of the overlap. The strain distributions were altered by the degree of overlap and the level of strain concentration was reduced with increased overlap.

The full-field strain distributions as measured with the new computer vision technique revealed progressive failure development, the eventual failure mode and location, and knowledge of the actual distribution of the strains in the entire joint assembly.     

THE INFLUENCE OF COMPRESSION WOOD ON THE DRYING CURVES OF PINUS RADIATA DRIED IN DEHUMIDIFIER CONDITIONS

Measurements of drying rate of Pinus radiata at 55°C and 30% RH are presented. The data, which has been used to establish empirical models for P. radiata under dehumidifier drying conditions, was obtained in four drying runs in a drying tunnel, each yielding detailed drying curves for twelve sample sapwood boards of size 350 × 100 × 50 mm. Compression wood was found to have a significant effect on the drying rate curve, giving lower drying rates at 40-100% MC. This effect is interpreted through the use of a numerical multiple-mechanism two-zone model and quantified by using best-fit diffusion parameters from an isothermal diffusion model. A positive correlation was discovered between the moisture diffusion coefficient and initial moisture content, a strong indicator for the presence of compression wood. In the two-zone model, the compression wood effect was replicated by using a tenfold decrease in permeability to liquid flow. Attributes of compression wood that could cause reduced permeability include an increased proportion of latewood, narrower lumen, and a scarcity of bordered pits on the radial walls of longitudinal tracheids.     

果壳生物质燃烧特性与动力学分析

为充分利用果壳生物质废弃物,采用热重分析对油茶壳、核桃壳、澳洲坚果壳进行了燃烧实验研究,考察了不同升温速率下3种果壳生物质的燃烧特性及动力学参数。结果表明：3种果壳生物质燃烧特性不同,但燃烧特性参数均随升温速率升高而增大;随着升温速率的增加,着火点、燃尽温度、最大燃烧速率、平均燃烧速率及综合燃烧特性指数提高;10℃/min时,油茶壳、核桃壳、澳洲坚果壳综合燃烧特性指数分别为0.56×10^-7、1.18×10^-7、0.88×10^-7;3种果壳生物质的燃烧反应遵循一级反应动力学模型,相关系数（R²）均达0.93以上,低温阶段活化能为30.40~52.41 kJ/mol,高温阶段活化能为18.49~40.62 kJ/mol,低温阶段活化能均大于高温阶段。     

DETERMINATION OF CROSS-GRAIN PROPERTIES OF CLEARWOOD SAMPLES UNDER KILN-DRYING CONDITIONS AT TEMPERATURE UP TO 140° C

Small specimens of Pinus radiata have been tested to determine the creep strain that occurs during the kiln drying of boards. The samples have been tested over a range of temperatures from 20°C to 140°C. The samples, measuring 150 × 50 × 5 mm, were conditioned at various relative humidities in a pilot-plant kiln, in which the experiments at constant moisture content (MC) in the range of 5-20% MC were undertaken to eliminate mechano-sorptive strains. To determine the creep strain, the samples were brought to their equilibrium moisture content (EMC), then mechanically loaded under tension in the direction perpendicular to the grain. The strain was measured using small linear position sensors (LPS) which detect any elongation or shrinkage in the sample. The instantaneous compliance was measured within 60 sec of the application of the load (stress). The subsequent creep was monitored by the continued logging of strain data from the LPS units.

The results of these experiments are consistent with previous studies of Wu and Milota (1995) on Douglas-fir (Pseudotsuga menziesii). An increase in temperature or moisture content causes a rise in the creep straw while the sample is under tension. Values for the instantaneous compliance range from 1.7 × 10^-3 to 1.28 × 10^-7 MPa^-1 at temperatures between 20°C and 140°C and moisture content in the range of 5-20%. The rates of change of the creep strains are in the Order of magnitude 10^-7to10^-8s^-1 for these temperatures and moisture contents. The experimental data have been fitted to the constitutive equations of Wu and Miloia (1996) for Douglas-fir to give material parameters for the instantaneous and Creep strain components for Pinus radiata.     

High temperature desulphurization by fine limestone during staged fluidized‐bed combustion

This paper reviews the SO₂ emission from a 0.3 m² stainless‐steel fluidized‐bed combustor. Fine coal was premixed with fine limestone and fed pneumatically under the bed. The SO₂ emission was found to depend largely on air staging ratio and bed temperature, which agrees with previous observations. The SO₂ emission observed in sorbent‐free tests (reported earlier by Khan and Cibbs, 1995) was found to be proportional to the sulphur content of the fuel when limestone was added, the sulphur capture at a fixed Ca/S molar ratio was dependent on oxygen stoichiometry and bed temperature. Finely sized limestone enhanced the effectivity of the sorbent at low bed temperature and air staging ratio. During staged combustion, the combustion efficiency depended largely on primary air to coal ratio. Around 90% combustion efficiency was observed at 1 m/s fluidizing velocity which was reduced when fluidizing velocity was increased to 1.5 and 2 m/s. This reduction is due to increased elutriation of finer coal particles from the combustor.     

Phase transition phenomena of the adsorbed 1-dodecanol monolayer at the air–water interface

Phase transition phenomenon of the 1-dodecanol monolayer at the air/water interface was studied by the dynamic γ(t) curves and the adsorption isotherm obtained by ellipsometry at 20 °C. The surface-concentration adsorption isotherm clearly showed three abrupt increases at bulk concentration C of 1.3 × 10⁻⁹, 2 × 10⁻⁹ and 3.7 × 10⁻⁹ mol/mL, respectively. The 1st and the 3rd transitions observed herein, that were typical 2D first-order transitions, were consistent with the gas to liquid expanded (G–LE) and the liquid expanded to liquid condensed (LE–LC) phase transitions observed in a previous tensiometry study. The 2nd transition that occurred at C = 2 × 10⁻⁹ mol/mL was not identified from any previous dynamic surface-tension profiles. Judging from the substantial increase in the film thickness of the transition, it was believed that the orientation change of the adsorbed molecule was involved in the LE phase. A LE_h and a LE_v phase, that denoted the “lie-down” and “stand-up” types of adsorption, respectively, was used to describe this transition and a cusp, instead of a constant surface-tension region, was observed in the dynamic γ(t) curves for this transition. This suggested that, since the surface tension varied during the transition process, the newly identified LE_h and LE_v transition might not be the typical first-order type of phase transition.     

TRANSITION TO ANNULAR FLOW IN TWO-PHASE, TWO-COMPONENT VERTICAL FLOW: EXAMINATION OF CORRELATIONS

The available empirical, semi-empirical and analytical correlations and flow pattern maps for predicting the transition to annular flow in upward, two-phase, gas-liquid flow in a vertical tube were tested against a large set of experimental data. These experimental data were taken on the same rig through an observation section (i.d. = 11.7 mm, L = 30.5 cm), preceded by a heated test section ( L/D≃ 52) and a calming length (L/D = 130), all having the same inside diameter as that of the observation section. The total range of variables covered by these data is: 2≤Re_SL≤ 1.3 × 10⁵, 5.6 ≤Pr_L≤ 7000, 0.01 V_SG/V_SL ≤ 7900, 2 × 10^-4≤ρ_G/ρ_Ls0.01, and 19.7 × 10^-3≤ σ ≤72× 10^-3N/m. In total, fifteen correlations and flow-pattern maps were tested with eight liquid-gas combinations covering a very wide range of fluid properties and mass flow rates of both phases. Using the Kutateladze number as the criterion for the transition appears to provide an excellent separation particularly when a lower value than 3.1, as suggested in the model of Taitel et al. (1980) is used (between 1.5 and 2.0). Also using the Weisman and Kang (1981) correlation, the Wallis parameter and the void fraction criteria of Mishima and Ishii (1984) were quite successful in correlating the data.     

Thermoelectric characterization of NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe) polycrystalline materials

Layered -titanate materials, Na_xM_x/2Ti_1−x/2O₂ (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na_0.4Ni_0.2Ti_0.8O₂ were ca. 7×10³ S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm⁻¹ K⁻¹ at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na_0.4Ni_0.2Ti_0.8O₂ and Na_0.4Co_0.2Ti_0.8O₂ was about 1.9×10⁻⁴ and 1.2×10⁻⁴ K⁻¹ around 700 °C, respectively.     

MODELLING OF STRESS DEVELOPMENT DURING DRYING AND RELIEF DURING STEAMING IN PINUS RADIATA LUMBER

A one-dimensional stress model was proposed for drying of radiata pine lumber, which has considered wood moisture shrinkage, instantaneous stress-strain relationships, mechano-sorptive creep, time-induced creep and temperature effects. In addition, wood hardening behaviour in the plastic region and differences between stress increase and decrease have been taken into account. The proposed Stress model can predict stress development and relief in a drying cycle once the required wood mechanical and Theological properties have been quantified.

Drying experiments were performed to dry Pinus radiata sap wood boards of 100×40×590 mm in a tunnel dryer. In the experiment, wood temperature, moisture content gradient and residual stress through board thickness were measured. The drying cycle included HT drying, cooling and final steam conditioning. The measured stress patterns were in agreement with the model predictions. However, more accurate calculations will be made once the detailed experimental data for radiata pine wood mechanical and rheological properties are available.     

Electrochromic properties of chemically prepared polyaniline

The electrochromic properties in non-aqueous medium of chemically prepared polyaniline films proved not to depend on the oxidizing agent used for the synthesis and were very similar to the properties of electrochemically prepared films. These properties were studied by measuring the optical contrast changes at fixed wavelengths in the uv/visible region during cyclic voltammetric scans and by applying 7 × 10³–8 × 10³ redox potential steps.     

Dilute solution properties of carboxymethylchitins in high ionic-strength solvent

The hydrodynamic characteristics in aqueous solution at ionic strength I=0.2  of carboxymethylchitins of different degrees of chemical substitution have been determined. Experimental values varied over the following ranges: the translational diffusion coefficient (at 25.0°C), 1.1<10⁷×D<2.9 cm² s⁻¹; the sedimentation coefficient, 2.4<s<5.0 S; the Gralen coefficient (sedimentation concentration-dependence parameter), 130<k_s<680 mL g⁻¹; the intrinsic viscosity, 130<[η]<550 mL g⁻¹. Combination of s with D using the Svedberg equation yielded ‘sedimentation–diffusion' molecular weights in the range 40 000<M<240 000 g mol⁻¹. The corresponding Mark–Houwink–Kuhn–Sakurada (MHKS) relationships between the molecular weight and s, D and [η] were: [η]=5.58×10⁻³ M^0.94; D=1.87×10⁻⁴ M^−0.60; s=4.10×10⁻¹⁵ M^0.39. The equilibrium rigidity and hydrodynamic diameter of the carboxymethylchitin polymer chain is also investigated on the basis of wormlike coil theory without excluded volume effects. The significance of the Gralen k_s values for these substances is discussed.     

NATURAL CONVECTION MASS TRANSFER INSIDE HORIZONTAL SQUARE DUCTS

Rates of free convection mass transfer inside horizontal square ducts were measured by electrochemical technique. Physical properties of the solution and duct side length were changed to provide Sc.Gr range of 7.38 × 10⁸ - 1.4 × 10¹¹. Under these conditions the data were correlated by the equation Sh= 0.382(Sc.Cr)^0.278 A comparison between the measured overall rate of mass transfer with that calculated by summing the rates of mass transfer at the separate sides of the duct showed that the measured value is higher than the calculated value owing to convective interaction between adjacent surfaces.     

Zeta potential of coal fine-particles in aqueous suspension

The relation between the zeta potential of coal fine-particles and pH value of suspension in aqueous suspension for different kinds of coal samples was determined by using a rectangular micro-electrophoresis cell.

The empirical equation of the relation between the zeta potential of the particles and the chemical components of coal samples was determined in aqueous suspension of different pH values. The equation is represented as follows: Z = B_C × (C) + B_H × (H) + B_O × (O) + B_N X × (N) + B_S × (S) + B_A × (A) where Z is the zeta potential of the particles, (C), (H), (O), (N), (S) and (Ash) are weight percent of carbon, hydrogen, oxygen, nitrogen, sulphur and ash, respectively, and B_C, B_H, B_O, B_N, B_S and B_A are coefficients of each of the respective components of coal samples.

The above coefficients were calculated numerically by the least-square method in suspensions with different pH values. The values of the coefficients, B_C, B_H, etc., (mV/%), indicate the zeta potential of each respective single component; viz. carbon, hydrogen, etc., of the coal samples. When the chemical components of a coal sample are known, the zeta potential of the coal fine-particles can be determined by the equation with the coefficients obtained in suspensions with different pH values.     

THERMAL CONDUCTIVITY OF GASEOUS AMMONIA IN THE TEMPERATURE RANGE 358-925 K.

Thermal conductivity of research grade pure ammonia gas has been measured by the column method at pressures of 12.9, 26.5, and 45.0 kN/m² over the temperature range 358 to 925 K. The maximum probable error of measurement is 1.5% at 874 K and it increases in magnitude as the temperature decreases. At 405 K, it is about 4.8%. The experimental data are correlated by the following cubic polynomial in temperature:

k(T)=5.237× 10^-3 + 5.179 × 10^-4 T + 8.404 × 10^-7 T² + 1.557 × 10^-10 T³.

Here k is in mW/cm-K and T is in K.

The experimental values are compared with three kinetic theory expressions for thermal conductivity of polyatomic gases in conjunction with the Stockmayer (12-6-3) potential. It is concluded that none of the theories can accurately predict the thermal conductivity of ammonia and probably of polar gases in general. The diffusion coefficient characterizing the transport of vibrational energy is computed as a function of temperature and on the basis of experimental data and the theory due to Ahtye. It has been long known that the transfer of energy by polyatomic and polar molecules is quite complex because of the presence of internal degrees of freedom and the possibility of resonant energy transfer in the latter (Hirschfelder, Curtiss and Bird, 1964).     

THE ELUTRIATION OF FINE AND COHESIVE PARTICLES FROM GAS FLUIDIZED BEDS

Experimental work on the entrainment of an FCC powder was carried out in 76  mm and 152  mm glass columns. Fluidization tests were carried out batchwise and continuously at velocities between 0·2 m/s and 0· 8 m/s. Non-cohesive fine powders and cohesive superfine powders were added to a coarse base FCC powder in proportions which ensured that the mixture remained within Geldart's Group A. The entrainment rale constant, K_i∞^*, is found to depend slightly on the fines concentration in the bed. Our work has confirmed that there is a critical particle size at which K_i∞^* no longer increases as particle size decreases, and may even decrease. Several mechanisms are postulated to explain this but from the experimental results it is concluded that interparticle adhesion forces between the very fine particles play an important role. An empirical correlation to predict K_i∞^*, below the point where levelling off occur is proposed.     

The condensation/polymerisation of dimethyl siloxane fluids in a three-phase trickle flow monolith reactor

For the production of siloxane fluids, the viability of using a multi-channel monolith as a catalyst support system in a three-phase reactor has been studied. The catalyst was tripotassium phosphate (K₃PO₄). Experiments were performed in a single-channel flow reactor (15 mm i.d. and 500 mm catalyst coated length). The rate of reaction was followed by monitoring the disappearance of the hydroxyl group (–OH). Reaction experiments were performed at a hydroxyl group concentration range from 150 to 170 mol m⁻³, T=373–413 K and P=7.9 kPa with a nitrogen purge. The maximum temperature of operation was restricted to 413 K to avoid the formation of undesirable by-products. In the regime controlled by chemical kinetics, reaction was of an apparent first order with respect to –OH concentration, and in the apparent rate constant, the pre-exponential factor was 4.19×10⁻⁴ ms⁻¹, and the apparent activation energy was 16.1 kJ mol⁻¹. These are only valid for the operating pressure and purge gas flowrate used, as both of these are shown to affect water removal from the liquid phase and, hence, reaction rates. Mass transfer coefficients from the liquid to the catalyst surface were estimated and these increased rapidly with flowrate and were higher than expected for a falling liquid film.     

MASS TRANSFER AND DIFFUSION COEFFICIENT DETERMINATION IN THE WET AND DRY SALTING OF MEAT

Dehydrated salted meat is widely used in Brazil as a very important source of animal protein. The main objective of this kind of processing is water removal. initially by osmotic pressure changes and then by drying, resulting in a product with intermediate moisture levels.

In this work, mass transfer and salt diffusion in pieces of meat submitted to wet and dry salting were studied. Slabs of beef m. trapezius with an infinite plate geometry were salted in a NaCl saturated solution or in a dry salt bed, at two temperatures (10 and 20°C) and different time exposures (120 min and 96 hours). Equilibration studies were extended up to six days.

It was observed that water loss increased with salt uptake, for increasing periods of times. At 20°C the moisture loss was higher than it was at 10°C in both salting processes. On the other hand, the kinetics of salt uptake and moisture loss were of greater importance in the process of dry salting than in that of wet salting.

The salt diffusion coefficient for wet salting was 0.26 × 10^-10m²/s at20°C and 0.25 × 10^-10 m²/s at 10°C and for the dry salting the values were 19.37 × 10^-10 m²/s at 20°C and 17.21 × 10^-10 m²/s at 10°C.     

Electrical conductance of KI in anhydrous acetonitrile

The electrical conductivity of KI solutions in anhydrous acetonitrile has been determined at 0, 25 and 35°C in the concentration range 0·9– 600 × 10⁻⁴ mole/l. The values of Λ₀, K and a calculated from the results are, respectively: 145·9 mho/cm, 0·95 × 10 ⁻² and 1·72 Å at 0°C; 186·2 mho/cm, 8·98 × 10⁻² and 4·6 Å at 25°C; and 204·8 mho/cm, 5·17 × 10⁻² and 3·5 Å at 35°C. The phoreograms at all the three temperatures are catabatic at lower concentration, but become anabatic at 0·017, 0·022 and 0·024 respectively, at 0, 25 and 35°C.