Measurement of mixing time and holdup of solids in gas–solid fluidized bed using radiotracer technique

Mixing times and holdup of solids were measured in a gas–solid fluidized bed using radiotracer technique. Sand and air were used as solid and gas phase, respectively in the fluidized bed. Gold-198 labeled sand particles were used as radiotracer for mixing time measurement at different operating conditions and ¹³⁷Cs sealed source was used for holdup measurement at different axial and radial positions. The experiments were conducted at different operating conditions. The measured mixing times ranged from 1.4 to 21 s at different conditions. It was observed that at a particular bed height, the mixing time initially decreases with increasing gas velocity and tend to become constant at higher gas velocities. However, mixing time increases with increasing bed height. The holdup fraction of solid was found to be more towards the wall compared to the centre of the column. The study provided inputs to improve the existing design, design of a new system and scale-up of the process.     

Residence time distribution study in a pilot-scale gas–solid fluidized bed reactor using radiotracer technique

This paper describes a radiotracer study carried out to measure residence time distribution (RTD) of coal particles in a pilot-scale gas–solid fluidized bed reactor (FBR). Gold-198 labelled on coal particles was used as radiotracer. RTD measurements were conducted for selected operating conditions and mean residence times (MRTs) of the coal particles were determined. Gamma function model was used to simulate the measured RTD data and mixing of coal particles in the reactor was investigated. Based on the results, the performance of the air distributor used in the reactor was evaluated.     

Investigation of hydrodynamic behaviour of a pilot-scale trickle bed reactor packed with hydrophobic and hydrophilic packings using radiotracer technique

A radiotracer study was carried out in a trickle bed reactor (TBR) independently filled with two different types of packing i.e., hydrophobic and hydrophilic. The study was aimed at to estimate liquid holdup and investigate the dispersion characteristics of liquid phase with both types of packing at different operating conditions. Water and H₂ gas were used as aqueous and gas phase, respectively. The liquid and gas flow rates used ranged from 0.83?×?10^?7?C16.67?×?10^?7?m³/s and 0?C3.33?×?10^?4?m³ (std)/s, respectively. Residence time distribution (RTD) of liquid phase was measured using ⁸²Br as radiotracer and about 10?MBq activity was used in each run. Mean residence time (MRT) and holdup of liquid phase were estimated from the measured RTD data. An axial dispersion with exchange model was used to simulate the measured RTD curves and model parameters (Peclet number and MRT) were obtained. At higher liquid flow rates, the TBR behaves as a plug flow reactor, whereas at lower liquid flow rates, the flow was found to be highly dispersed. The results of investigation indicated that the dispersion of liquid phase is higher in case of hydrophobic packing, whereas holdup is higher in case of hydrophilic packing.     

Radiotracer investigation in a rotary fluidized bioreactor

A rotary fluidized bioreactor (RFBR) designed for treatment of wastewater was required to be investigated for its hydrodynamic behaviour and validation of design. A radiotracer investigation was carried out to measure residence time distribution (RTD) of wastewater in the RFBR using ⁸²Br as a radiotracer. The radiotracer was instantaneously injected into the inlet feed line and monitored at the inlet and outlet of the reactor using collimated scintillation detectors connected to a data acquisition system. The measured RTD data was treated and simulated using a tanks-in-series model and model parameters i.e. number of tanks describing the degree of mixing was obtained. The results of the investigation showed no flow abnormalities and the reactor behaved as an ideal continuously stirred-tank reactor at all the operating conditions. Based on the results, the design of the reactor was validated.     

Measurement of discharge rate in a canal using radiotracer dilution technique

Measurement of discharge rates of fluids and solids is an essential requirement in industrial and environmental systems. Radiotracer techniques are widely used for measurement of fluids/solids in situations where conventional techniques cannot be applied. The present paper describes application of radiotracer dilution technique to measure the discharge rate of water in a canal with an objective to validate efficiency of the Concrete Volute Pump used for pumping water in the canal. ¹³¹I radioisotope having activity of 55.5 GBq was used as radiotracer. The discharge rate of water was measured to be 20.6 m³/s.     

First use of millicurie levels of172Hf−172Lu in the industrial sector

The first use of the¹⁷²Hf–¹⁷²Lu generator system in industry is reported. Millicurie quantities of¹⁷²Lu have been utilized for radiotracer studies of oil pipeline flow rates, refinery column residence times, and the performance of a coal liquefaction pilot plant.     

CaF2对CaO-CaF2-B2O3-SiO2：Sm2O3玻璃的光致发光增强效应

用高温熔融法制备了掺杂Sm₂O₃的CaO-CaF₂-B₂O₃-SiO₂(CFBS:Sm)发光玻璃材料, 并借助X射线衍射(XRD)谱、傅里叶变换红外(FTIR)光谱以及光致发光(PL)光谱等分析手段研究了玻璃基体中CaF₂的摩尔分数及其结构、红外透过性能以及荧光性能的关系. XRD和FTIR测试表明, 玻璃基体中引入CaF₂并未引起非晶结构的变化但其红外透过峰发生移动. 光谱学测试表明, CFBS:Sm发光玻璃在404 nm波长激发下出现对应于Sm³⁺离子位于566、603和650 nm的特征荧光峰, 其发光颜色为橙红色(x=0.531, y=0.371). 此外, 随着玻璃基体中CaF₂摩尔分数的增加, CFBS:Sm发光玻璃的荧光发射强度、荧光寿命(Sm³⁺的⁴G_5/2能级)和荧光量子效率也表现出增大的趋势. 这种CFBS:Sm发光玻璃中荧光发射强度和荧光寿命的提高主要是由于玻璃基体中的CaF₂替代CaO引起基体相互作用和声子能量降低、无辐射跃迁减弱造成的.     

Effect of heating rate on the thermal properties and devolatilisation of coal

The apparent specific heat of coal was measured by employing a computational calorimetric technique during continuous pyrolysis at heating rates of 10, 25 and 100°C min^-1. For all of the examined heating rates, the apparent specific heat was found to be approximately 1.4 kJ kg^-1 K^-1 at room temperature. When the sample reached decomposition temperature (~410°C), the specific heat increased to 1.9 kJ kg^-1 K^-1. From this point, the apparent specific heat was greatly influenced by the coal reaction mechanism. For this purpose a detailed gas analysis was carried out for the three examined heating rates. It was found that with increased heating rates, the devolatilisation reactions were shifted to higher temperatures, as reflected in the measured apparent specific heat. This revised version was published online in July 2006 with corrections to the Cover Date.     

New In-Situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors in a rf Thermal Plasma Reactor. Part 2: Analysis of CeO<Subscript>2</Subscript> Powders,Fuel Addition,and Image Analysis

A novel reactor design, sampling probe and wet collection system were used to investigate the combined effects of plasma operating parameters and particle collection mechanisms on the synthesis of CeO₂ particles from liquid precursors. The sampling of particles in-flight and the collection of particles at several reactor regions were used to provide experimental evidence of particle size at different reactor locations at various plasma operating conditions, i.e., power and plasma gas flow rates. This information provided a picture of how CeO₂ particles were formed and how these particles were collected in various locations. The effect of adding water-soluble fuels (alanine and glycine) to the original cerium nitrate solutions was also investigated. Fuel addition decreased the temperature of CeO₂ formation by acting as a local heat source as a result of fuel auto-ignition. Photographs of the particles in-flight were taken using a fast speed CCD camera.     

Solubility of particulate cadmium sulfide at pH=1–14: A radiotracer study

Cadmium sulfide particles were prepared by precipitation from acid solution. A radiotracer technique with¹⁰⁹Cd was applied to measure the solubility of cadmium sulfide at various pH's. Filtration, centrifugation, ultracentrifugation, and dialysis were used to separate the particles from the solution. Only the last two techniques proved to be successful. The solubility of cadmium sulfide in water (pH=7) is found to be: 7.9·10^–5 mol·l^–1 in contrast with the literature value of 9.0·10^–6 mol·l^–1. At low pH (1–4), the solubility agrees fairly well with the solubility calculated on the basis of generally accepted values for the solubility product and for the various complex formation constants, while at high pH (4–14) the solubility is higher than expected.     

Urea and CaCl2 as inhibitors of coal low-temperature oxidation

Thermal analysis was used to study the influence of CaCl₂ and urea as possible chemical additives inhibiting coal oxidation process at temperatures 100?C300?°C. Weight increase due to oxygen chemisorption and corresponding amount of evolved heat were evaluated as main indicative parameters. TA experiments with different heating rates enabled determination of effective activation energy E _a as a dependence of conversion. In the studied range of temperatures, the interaction of oxygen with (untreated) coal was confirmed rather as a complex process giving effective activation energies changing continuously from 70?kJ?mol^?1 (at about 100?°C) to ca. 180?kJ?mol^?1 at temperatures about 250?°C. The similar trend in E _a was found when chemical agents were added to the coal. However, while the presence of CaCl₂ leads to higher values of the effective activation energies during the whole temperature range, urea causes increase in E _a only at temperatures below 200?°C. Exceeding the temperature 200?°C, the presence of urea in the coal induces decrease in activation energy of the oxidation process indicating rather catalysing than inhibiting action on coal oxidation. Thus, CaCl₂ can only be recommended as a ??real?? inhibitor affecting interaction of coal with oxygen at temperatures up to 300?°C.     

Exchange of mercury between mercuric ions and methylmercuric nitrate

The rate constant for the exchange between Hg²⁺ and CH₃Hg⁺ ions in a Cl-free 1NH₂SO₄ solution at 25°C was measured with²⁰³Hg as a radiotracer and separation of the two compounds by liquid extraction of the organic species into benzene from a NaCl- or NaI-solution.     

Determination of radioactivity concentration in the primary coolant channel of a Pressurized Heavy Water Reactor

CdZnTe detector was used to monitor the radioactivity at several locations of primary heat transport (PHT) system of the Tarapur Atomic Power Station-III & IV reactor during shut down as well as operating condition of the reactor. Dose measurements at the same locations were also carried out using a teletector. MCNP code was used to simulate the detector efficiency for the required counting geometry. The efficiencies were then used to convert the experimental count rates (cps) to corresponding activity concentration (Bq/mL) of different radionuclides in coolant water. The total dose rates in these locations were also calculated by summing up the simulated dose rates of individual γ ray energy. The simulated and the measured total dose rates were found to be in reasonably good agreement.     

Combined effects of Ca2+ and humic acid on colloid transport through porous media

We report the separate and combined effects of humic acid and Ca²⁺ ions on the transport of colloidal particles through a sand-packed column. Polystyrene latex particles with a sulfate functional group were used as model colloids. The concentrations of both the inlet solution and the effluent solutions were measured during each experimental run. Breakthrough curves were obtained by taking the ratios of each effluent sample concentration to the inlet solution concentration. In the absence of humic acid, the results indicate that increasing the concentration of Ca²⁺ increases particle attachment to the sand, thus causing decreased transport rates of latex particles through the porous bed matrix. Once 4 mg/l humic acid was added to the system, changes were observed in the effect that Ca²⁺ has on latex particle breakthrough. In a system containing calcium, increasing the humic acid concentration was shown to reduce particle attachment and increase transport rates. In the absence of calcium, the ratios for the outlet-to-inlet concentrations were similar for each concentration of humic acid. The electrophoretic mobility was also measured in order to determine the role of electrostatic repulsion in the latex particle transport. The electrophoretic mobility of the latex particles was found to be dependent on humic acid concentration in the absence of Ca²⁺ but not in its presence. Received: 2 February 2001 Accepted: 6 2001     

Use of radiotracer in adsorption studies of copper on peat

In this work copper adsorption by peat was studied using ⁶⁴Cu as tracer considering kinetic and thermodynamic aspects of the process. The study was carried out in agitated batch experiments with copper ion solutions with different initial concentrations at pH 4.5. Adsorption isotherms determined from equilibrium experiments by fitting experimental data to the Langmuir equation showed good correlations. Data obtained from kinetics experiments were fitted to a pseudo-second order model and also in this case a good correlation was obtained. Some parameters calculated from these studies such as rate constant or peat sorption capacity can be used in the development of a waste treatment process based on peat adsorption in batch or in column. The use of the ⁶⁴Cu radiotracer is presented as a simple, rapid and efficient technique to assess the copper adsorption by the peat. This revised version was published online in August 2006 with corrections to the Cover Date.     

The potentiality of microcalorimetry as a rapid method for monitoring the microbiological quality of raw meat and fish

The exothermic heat production rates (HPRs) of ground meat and cod suspended in culture media were measured at different operating temperatures using a LKB BioActivity Monitor and correlated to bacterial numbers determined by plate colony counts at varying tims/tenperature incubation conditions. Significant correlation between peak HPRs and colony counts were obtained with all experimental conditions. Bacterial levels in the range of 10⁴-10⁸g^?1 could be estimated in < 24h. Peak HPR-times were also related to sensory quality scores (0–10) for cod samples. By using a cut-off tine of 11h it was possible to differentiate between fish of high (scores > 6) and inferior quality.     

Pyrolysis kinetics and chemical composition of Hazro coal according to the particle size

Summary The relationship between particle size and chemical composition of Hazro coal (origin: SE Anatolia, Turkey) has been examined by elemental analysis and by thermogravimetric pyrolysis. The chemical composition of the coal was determined by grinding sample particles physically and separating according to their size in mm by sieving. Particle size distribution of the coal and chemical composition of these fractions were given. The coal has been non-isothermally pyrolyzed in a thermogravimetric analyzer to determine the kinetic factors. Thermal gravimetric (TG/DTG) experiments were performed from ambient temperature to 800°C under a nitrogen atmosphere at heating rate 10 K min^-1 with five different particle size ranges. Kinetic parameters of the samples were determined using a Coats and Redfern kinetic model, assuming a first-order reaction. Depending on the particle size of the coal samples, the mean activation energy values varied between 49.1 and 84.6 kJ mol^-1. The results discussed indicate that activation energies increase as the particle size decreases.     

循环流化床煤燃烧/热解双反应器压力分布的实验研究

实验测量了一种新型的循环流化床煤燃烧/热解冷模反应器中提升管及立管内的压力分布，其中提升管的内径为100 mm、高为6 m;立管内径为44 mm、高为3 m，热解室的截面为200 mm×200 mm、高为770 mm。分别考察了提升管内的表观气速Ur、循环量Gs、加到热解室内的松动气量Qa以及初始装料量G等对系统压力分布的影响。结果表明，在立管底部阀门开度不变的情况下随着Ur的增加，提升管及立管内的压力梯度都趋于减小；在提升管内表观气速一定的情况下随着循环量Gs的增加，提升管及立管内的压力分布也随之增大；加到热解室内的松动气对立管内的压力分布影响较大，而对提升管内的压力分布影响相对较小；在立管底部阀门开度及Ur一定的情况下，随着初始装料量的增加提升管及立管内的压力分布也趋于增大。     

Influence of biomass on hydrodynamics of an internal loop airlift reactor

The effect of the biomass presence on the overall circulation velocity, the linear velocities both in the riser and the downcomer and the overall gas hold-up was studied in a three-phase internal loop airlift reactor (ILALR). The measured data were compared with those obtained using a two-phase system (air—water). All experiments were carried out in a 40 dm³ ILALR at six different biomass concentrations (ranging from 0 g dm⁻³ to 7.5 g dm⁻³), at a temperature of 30°C, under atmospheric pressure. Air and water were used as the gas and liquid model media, respectively. Pellets of Aspergillus niger produced during the fermentation of glucose to gluconic acid in the ILALR were considered solid phase. In addition, liquid velocities were measured during the fermentation of glucose to gluconic acid using Aspergillus niger. All measurements were performed in a bubble circulation regime. At given experimental conditions the effect of the biomass on the circulation velocities in the ILALR was negligible. However, increasing of the biomass concentration led to lower values of the total gas hold-up. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

多元醇法合成具有不同长径比的棒状LiFePO4/C材料

以三价铁盐为铁源,采用多元醇还原法在低温下制备出了具有不同长径比的棒状LiFePO₄材料. 通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、循环伏安(CV)、交流阻抗谱(EIS)和恒电流充放电测试等手段分析了不同回流反应时间下制备出的前驱体和最终的LiFePO₄/C 样品. 结果表明：回流反应时间对LiFePO₄的形貌和特性有明显的影响. 通过把回流反应时间从4 h延长至16 h,材料的形貌由不规则的短棒状颗粒变为规则的长棒状颗粒,且棒的直径明显变小. 当回流反应时间为10 h 时,样品复合了多种形貌,有利于电子的传输,在低倍率下具有优秀的性能,0.1C放电比容量为163 mAh·g^-1;当回流反应时间为16 h 时,样品具有最大的长径比,有利于锂离子的扩散,在高倍率下具有良好的性能,1C、3C、5C、10C、20C倍率下放电比容量分别为135、125、118、110、98 mAh·g^-1,循环性能良好,几乎无衰减.