Draft Tube Type Research Articles

СРАВНИТЕЛЬНЫЙ АНАЛИЗ ПУЛЬСАЦИЙ ДАВЛЕНИЯ, ВЫЗВАННЫХ СПИРАЛЬНО-ВИХРЕВЫМИ СТРУКТУРАМИ В ПРОТОЧНОЙ ЧАСТИ МОДЕЛИ ГИДРОТУРБИНЫ

The paper studies the pressure pulsations in the hydraulic turbines flow section arise as a result of vortex structures in non-optimal hydraulic turbine operation regimes. The authors directly compare the approaches to the extraction of synchronous and asynchronous components in pressure pulsation signals, as well as using the decomposition into azimuthal modes. Pressure pulsations were measured using four acoustic sensors while varying the operating regimes of the hydraulic turbine model. The pressure pulsations were compared for the shallow draft tube and the deep draft tube of the hydraulic turbine. It is shown that the level of pressure pul-sations is the same for two types of draft tubes. There is no methodological difference in the application of the two approaches to the extraction of pressure pulsations in the flow. The results shall be applicable in the de-velopment of new methods for suppressing spiral-vortex structures in non-optimal regimes of operation of hydraulic turbines in order to increase their overall efficiency.

Minimum spouting velocity of fine particles in fountain confined conical spouted beds

A novel internal device called fountain confiner has been developed, which stabilizes the system and allows operating with fine particles, even without any type of draft tube. Given the stability this device confers upon the system, lower minimum spouting velocities than in conventional systems are required, and therefore the correlations in the literature overestimate this hydrodynamic parameter. Accordingly, runs have been carried out using this novel device in order to study the hydrodynamics and the influence geometric and operating factors have on the minimum spouting velocity in fountain confined conical spouted beds, with and without draft tubes. The beds are made up of fine sand and sawdust particles. Based on an experimental design, it was ascertained that, although certain factors are influential in given configurations, those of greater influence in all the configurations are the solid properties, static bed height and gas inlet diameter. Therefore, new correlations have been proposed for predicting the minimum spouting velocity in each configuration.

New operation regimes in fountain confined conical spouted beds

The spouted bed regime is an alternative to fixed and fluidized beds due to the excellent gas-solid contact and the high reduction in operating pressure drop. Nevertheless, the most important limitation of this technology lies in its scaling up, since the inlet diameter/particle diameter ratio must be below 20–30 to avoid bed instability. In order to overcome this limitation, a new internal device called fountain confiner has been developed, which stabilises the system and allows operating with fine particles even without any type of draft tube. Runs have been carried out using the fountain confiner in order to analyse the stability of beds composed of very fine particles and the characteristic hydrodynamic curves (pressure drop vs. air velocity) have been obtained. The use of this new device allows attaining highly stable operation regimes, widening the operational range to 4 times that of plain spouted beds, and increasing the inlet diameter/particle diameter ratio from 20–30 to 1000. Moreover, the optimum distance between the bed surface and the lower end of the confiner has been delimited for the range of operating conditions studied, 0.06-0.08m (between 1/2 and 1/3 the confiner diameter), since it is a key parameter for system stability. Finally, the effect of several geometric factors and the scaling up of this technology has been analysed for fine particles of different size and density.

Influence of the fountain confiner in a conical spouted bed dryer

The drying of fine sand particles (below 1 mm) has been studied in a conical spouted bed fitted with a draft tube in order to ascertain the performance of a new internal device to confine the fountain. Accordingly, batch runs have been carried out using three types of draft tubes, with confiner and without it under ambient conditions. Their performances have been compared in order to ascertain the optimum configuration. The results evidence that the systems with the confiner perform much better than those without it. Thus, the drying time decreases considerably and the pressure drop and air flow rate decrease slightly when the confiner is used. The drying performance of the open-sided draft tube is superior to any other configuration, i.e., the drying time required with this tube is the shortest. Nonporous draft tubes are the worst option due to their poor gas-solid contact. Porous draft tubes have an intermediate performance.

Experimental investigation on vertical plug formation of coarse particles by a non-mechanical feeder

ABSTRACT Plug flow receives attention due to its advantages of low particle attrition, low pipeline wear and low energy consumption. A novel non-mechanical draft tube type feeder (DTF) for plug formation has been proposed in our previous study for vertical plug conveying of coarse particles. We further investigate the influence of key geometry parameter of the DTF on plug formation for different particle diameter. Furthermore, we attempt to extend the application of PIV technique to evaluate plug velocity in pneumatic plug conveying. Experiments for vertical plug formation are conducted with glass beads of three kinds of particle diameter (i.e. 6 mm, 4 mm and 2 mm). Plug formation characteristics are examined in terms of flow pattern in riser pipe, solids mass flowrate and pressure fluctuation. The experimental results show that four main features of plug flow pattern in the riser pipe are observed. Solids mass flowrate displays good linear relation to superficial gas velocity forthe same particle diameter in the plug flow regime, even with different relative entrainment height. Some interesting phenomena are observed for the pressure fluctuation. Plug velocity is successfully obtained by PIV technique with high temporal resolution. The present study provides a further understanding of the flow pattern and dynamic behavior of coarse particles in vertical plug formation with the draft tube type feeder.

Investigation on vertical plug formation of coarse particles in a non-mechanical feeder by CFD-DEM coupling method

Plug flow attracts continuous interest due to its advantages of low particle attrition, low pipeline wear and low energy consumption. A novel non-mechanical draft tube type feeder (DTF) has been proposed in our previous work for vertical plug conveying of coarse particles. Detailed particle motion behaviors and plug formation mechanisms in the draft tube type feeder are investigated by the combined approach of Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) in the present study. The CFD-DEM method based on local averaging of granular matter is used to deal with fluid cell sizes smaller than particle sizes under the specific conditions. The applicability of the model is verified by comparing the calculated results with the experimental results of vertical plug formation of 6mm glass beads in a draft tube type feeder, in terms of plug flow pattern, pressure drop and solid mass flow rate. Detailed analysis of the particle entrainment in feeder container, flow properties at riser inlet and natural plug formation in riser are then carried out. It is found that both gas and particle flows result in entrainment effect on particles, respectively, through fluid-particle and particle-particle interactions. The linear increase of solid mass flow rate with superficial gas velocity is closely related to the linear increase of particle vertical velocity at riser inlet. Plug formation is achieved in a natural way, which shows the features of self-organization phenomenon. Particle concentration is a key parameter in this self-organization process. This study provides some insights into the natural plug formation of coarse particles in a non-mechanical feeder. The model should be useful to study the gas-solid flow of coarse particles in a confined domain with complex geometry, where the fluid cell size may be smaller than the particle size.

A new fountain confinement device for fluidizing fine and ultrafine sands in conical spouted beds

A study has been carried out on the hydrodynamic performance of a fountain confinement device used in conical spouted beds for the treatment of Geldart A and B type particles. Stability and particle elutriation have been analysed for beds provided only with this device and those provided with this device and two types of draft tubes, namely, open sided draft tube and nonporous draft tube. Stability is greatly improved when only the fountain confiner is used, but the draft tubes are required for significantly avoiding bed elutriation in spouted beds. The modified conical spouted bed has been located in a map of operating conditions together with the remaining gas-solid contact regimes. The fountain confiner provides a dramatic increase in the applicability range of spouted beds. Thus, unlike the traditional use of spouted beds for Geldart D type particles, this device allows operation with Geldart A, B and D particles, with a small fraction of C particles.

Fountain confined conical spouted beds

Particle entrainment is a serious problem in spouted bed contactors when operation is carried out using beds made up of ultrafine particles, irregular ones and fine and coarse particle mixtures. Accordingly, the conventional conical spouted bed has been modified by inserting a fountain confiner in the contactor, and a study has been carried out on the efficiency of the confinement device to avoid fine particle entrainment. Furthermore, the influence of the geometry of the device on the hydrodynamics of conical spouted beds has been studied. The results show that the fountain confiner largely avoids fine particle entrainment, i.e., 60–70% reduction depending on the type of draft tube used. Furthermore, the fountain confiner reduces the operating bed pressure drop and the maximum cycle time of the particles in the contactor, but has no effect on the minimum spouting velocity. Nevertheless, the greatest advantage of the fountain confiner lies in the stabilization of the fountain and the homogenisation of the solid circulation in the bed, which leads to a significant increase in the gas-solid contact in the fountain.

Numerical and Experimental Analysis of Draft Tubes for Francis Turbine

Objectives: Draft tube is an important component of a hydro turbine (reaction) because it permits a negative head thereby increasing the total head on the turbine. It is located below the runner and allows deceleration of flow at exit. Since, the efficiency of the turbine can be increased by increasing the overall-efficiency of the draft tube, it's important to identify and optimize the design parameters which affect the efficiency of draft tube. Methods/ Statistical Analysis: In the present study, numerical and experimental analysis was done on different draft tubes in Francis turbine. In experimental study, different types of draft tubes were designed, fabricated and tested on a Francis turbine test rig. For conical draft tube, cone angle and cross section (outlet) was varied to understand the flow dynamics. Further, elbow draft tube (rectangular section) was also designed and tested to determine Best Efficiency Point (BEP). Numerical analysis was done using ANSYS CFX for various draft tubes which were designed in ANSYS Design Modeler. Findings/Results: The results of numerical analysis were validated experimentally. High pressure zones were identified in conical and elbow draft tube, although, overall pressure was less than atmospheric pressure. The efficiency of Francis turbine using 8 degree cone angle gives higher efficiency. For angles greater than 8 degree, backflow was observed. For variable discharge conditions (part-load), elbow draft tube can be used because of lesser variations in efficiency at different flow rates. Applications/Improvements: Further, conical draft tube with square section was also analyzed. Higher values of efficiency were obtained at higher speed of the turbine. Hence, it is advisable to further study this type of draft tube.

Experimental study on plug formation characteristics of a novel draft tube type feeder for vertical pneumatic conveying of coarse particles

Plug flow receives attention because of its advantage to reduce particle attrition, pipe wear and energy consumption. A novel non-mechanical draft tube type feeder (DTF) for plug formation is proposed in this study for vertical plug conveying of coarse particles. Particles in the feeder are entrained by gas stream through draft tube direct into the bottom of riser pipe. The plug formation experiments with coarse particles (glass beads particle diameter 4.0mm) are conducted with this novel feeder. Plug formation characteristics are investigated by solids mass flowrate, high frequency pressure fluctuations and high-speed camera measurements. Power spectral density analysis is used to characterize frequency distribution of the high frequency pressure fluctuations. The experimental results show that natural plug formation is successfully achieved by the DTF for the superficial gas velocity ug in the range of 4.86 to 10.16m/s. A “particle cloud” is initially formed by particles entrainment effect in the bottom of riser, then its porosity decreases and length increases by further particles entrainment and pickup to form a plug. The solids mass flowrate shows a good linear relation to the gas mass flowrate. The plug length shows to be stochastic in a certain range around 0.11m, which is mainly attributed to the natural plug formation characteristics of the DTF. This study provides a natural plug formation feeder for vertical plug conveying of coarse particles. The feeder might be used for high temperature and/or high pressure operation environment in which high reliability is required. It might also be used to simplify the feeding device for vertical plug conveying of coarse particles.

Influence of contactor geometry and draft tube configuration on the cycle time distribution in sawdust conical spouted beds

A study has been carried out on the influence the draft-tube configuration has on the solid circulation in conical spouted beds made up of sawdust. Knowledge on the performance of these fine particles of low density and irregular texture is required for the pyrolysis, gasification or combustion of this waste materials in conical spouted beds. Accordingly, particle cycle times have been monitored for contactors of different geometry (angle and gas inlet diameter) provided with draft-tubes of different configuration (nonporous and open-sided tubes). The study has been carried out according to a factorial design of experiments. Particle cycle times follow an almost exponential distribution for both types of tubes and are highly dependent on the type of draft tube and contactor angle, especially in the range from 36° to 45°. On average, cycles times are twice to triple longer when nonporous tubes are used. Therefore, the open-sided internal device provides stability and ensures high turbulence to beds made up of fine and irregular particles, with their behaviour being similar to stable beds made up of coarse particles in which no draft-tube is required.

Operating and Peak Pressure Drops in Conical Spouted Beds Equipped with Draft Tubes of Different Configuration

Operating and peak pressure drops have been studied in conical spouted beds equipped with draft tubes of different configuration using materials of different size. The draft tubes used are nonporous and open-sided ones. Based on an experimental design, the factors of greater influence on both pressure drops have been determined and general correlations valid for fine and coarse materials have been proposed for predicting the operating pressure drop and peak pressure drop with each type of draft tube. The results show that conical spouted beds equipped with draft tubes give way to lower operating and peak pressure drops than those without draft tube. A comparison of draft tube systems reveals that nonporous tubes give way to the lowest values of both pressure drops, but the solid circulation rates and the gas–solid contact efficiency are poorer than those with open-sided draft tube systems.

Particle Cycle Times and Solid Circulation Rates in Conical Spouted Beds with Draft Tubes of Different Configuration

Particle cycle times (average, maximum, and minimum) have been measured in draft tube conical spouted beds for different geometric factors of the contactor (angle and gas inlet diameter), draft tubes (diameter, height of the entrainment zone, and width of the faces) and under different operating conditions (particle density). On the basis of the results, the effects of the type of draft tube and different factors of the contactor/draft tube/particle system have been studied, and those of greater influence have been determined. The results show that particle cycle times and solid circulation rates are highly dependent on the type of draft tube, solid density, and contactor angle. Open-sided draft tubes are the ones with the highest solid circulation rate with stable spouting performance. Therefore, this internal device is a suitable option for scaling up spouted beds with a hydrodynamic performance similar to those without tubes.

Hydrodynamic performance of spouted beds with different types of draft tubes

Hydrodynamic performance of spouted beds with four different types of draft tubes has been investigated experimentally. In this work, irregular and angular particles were used as the spouting solids and the results were compared with those of the previous work in which regular and round particles had been used. It was found that the conical–cylindrical porous draft tube was the best option for solid–gas contact and solids circulation as in the case of round particles. Moreover, by using conical–cylindrical porous draft tube, the gas flow rate through the annulus reached 65–70%, equal to the level of a conventional spouted bed.

Minimum Spouting Velocity of Conical Spouted Beds Equipped with Draft Tubes of Different Configuration

The hydrodynamics and the influence of the geometric and operating factors on the minimum spouting velocity have been studied in draft tube conical spouted beds with materials of different size and density. Two draft tube configurations have been used: nonporous and open-sided tubes. Based on an experimental design, the factors of greater influence have been extracted and the general correlations valid for fine and coarse materials have been proposed for predicting the minimum spouting velocity for each type of draft tube. A comparison of the velocities with and without a tube reveals that the nonporous draft tube requires the lowest minimum spouting velocity. Nevertheless, the solid circulation rate and the gas–solid contact efficiency of the open-sided draft tube outperform any other spouted bed configuration, especially for fine particles. Consequently, open-sided draft tubes allow stable operation with fine particles and high solid circulation rates in conical spouted beds.

Entrainment and Stability of a Horizontal Gas-Liquid Jet in a Fluidized Bed

Fluid coking is a non-catalytic process where heavy hydrocarbon feed, sprayed using jets into a fluidized bed reactor, cracks upon contacting hot coke particles and produces valuable volatile fractions. It is estimated that the Alberta tar sands contain 1.7 trillion barrels of oil, equivalent to 35% of the world’s crude oil reserves, of which the majority is processed using fluid cokers. Important parameters that affect the yield of fluid cokers include the feed jet stability and therefore its ability to entrain and mix the injected feedstock with the fluidized coke particles. To this purpose, this study investigated the effect of the use of various types of draft tubes, placed downstream of the feed jet to enhance mixing, on solids entrainment and jet stability.Specifically, it has been demonstrated with the use of a gas-liquid and gas-only jet that an optimum distance exists between the nozzle and draft tube for entrainment of solids. For both cases, this optimal distance occurs as the jet touches the draft tube wall. However, for a gas-only jet this occurs at a shorter distances due to the increased angle of expansion. The angles of expansion were confirmed using triboelectric probe measurements. It has also been shown that the shape of the inlet to the draft tube will have an effect on the rate of solids entrainment as will the presence of pulsations in the jet.

Removal and recovery of phosphate and ammonium as struvite from supernatant in anaerobic digestion

Removal of phosphorus and nitrogen is required to prevent eutrophication problems in lakes and enclosed coastal seas. And recovery of phosphorus from wastewater has been attracting attention because of lack in phosphorus resources in the near future. In this study, reaction kinetics and design parameters of struvite production are experimentally investigated by using basic reaction type and a draft-tube type reactors. Struvite production rate, which is a very important parameter in reactor design and efficiency estimation, is formulated in an equation consisting of a rate constant (k2), and magnesium, phosphate and ammonium concentrations. The value of k2 is shown to be increased with struvite concentration and mixing intensity in the reactor. The developed equation is applied to the results obtained from the draft-tube type reactor experiments and verified for its applicability. High struvite concentration of 10-25% is maintained in the draft-tube reactor experiments. 92% removal and recovery efficiency with effluent phosphorus concentration of 17 mg/L is achieved under the conditions of 4 minutes reaction time, pH of 8.5 and Mg/P molar ratio of 1.1.

Effect of Selected Geometry Aspects in the DTM Crystallizer on Power Input and Pumping Capacity

This paper deals with the effect of draft tube shape on pumping capacity, as well as power input in a typical crystallizer with inner suspension circulation forced by means of propeller. The common theoretical relationship between the main factors affecting pumping capacity has been derived. Four types of draft tubes were considered including cylindrical and conical-cylindrical draft tube with inner and outer baffles. The investigations substantiating the theoretical considerations, were carried out for a wide range of independent variables: unit power input 0.1–1.5 Wkg −1 ; d r /d m ratio 0.8–0.95; h r /d r ratio 0.15-0.6. The experimental data proved to be consistent with the theoretical predictions. The results make it possible to determine the best shape and the optimum location of the draft tube in the apparatus for generating the maximum pumping effect at minimum power input.

Volumetric Mass Transfer Coefficient of Oxygen in An Internal Loop Airlift Reactor with a Convergence-Divergence Draft Tube

Experimental measurements of hydrodynamics and the volumetric mass transfer coefficient of oxygen (VMTCO) in an internal loop airlift reactor with different types of draft tubes are reported for the two-phase systems, air/water and air/carboxyl methyl cellulose (CMC) solution, and a three-phase system, air/water/resin particle, respectively. The properties of convergence-divergence draft tubes with three different structural parameters are compared with those of the conventional column draft tube. The results indicate that gas holdups in convergence-divergence draft tubes are higher than those in conventional draft tubes, the volumetric mass transfer coefficient of oxygen increases with increasing superficial air flow rates. The convergence-divergence draft tubes all show higher mass transfer capacity than the traditional ones. A 10% higher mass transfer coefficient is observed for the three structural parameters. In the air/CMC system, the volumetric mass transfer coefficient of oxygen decreases with increasing bulk viscosity, while in the three-phase system VMTCO increases with the resin particle loading. The correlation equation of the volumetric mass transfer coefficient with the operating conditions and structural parameters is established.

Comparison of biotin production by recombinant Sphingomonas sp. under various agitation conditions

Biotin production by fermentation of recombinant Sphingomonas sp./pSP304 was investigated. A complex medium containing 60 g/l of glycerol and 30 g/l of yeast extract was suitable for biotin production. Biotin was produced in the late logarithmic or stationary phase after glycerol starvation. The optimum pH value for biotin production was 7.0. When the dissolved oxygen concentration (DO) was controlled at a constant level, the biotin concentration produced after 120 h was significantly lower than that obtained in a test tube culture. Therefore, a batchwise jar-fermentor culture with a constant agitation speed and without DO control was conducted for investigating the effect of agitation conditions on biotin production. Six types of impeller were tested: turbine-blade type, turbo-lift type, rotating mesh type (EGSTAR ®), screw with draft tube type, Maxblend ®type, and anchor type. With some impellers, agitation speed was also changed. Both the maximum cell concentration and biotin production varied depending on agitation conditions. Relatively high cell concentrations were attained with four of the impeller types, turbine-blade type, rotating mesh type, Maxblend ® type, and anchor type. Among these impellers, the turbine-blade impeller with sintered sparger was suitable for biotin production. After 120 h, the cell concentration reached an OD 660 of 43 and a biotin concentration of 66 mg/l was obtained, which was comparable with the results from the test tube culture. Morphological variation was also observed depending on the agitation conditions: oval-shaped, rod-shaped, and elongated-shaped cells. Biotin production was relatively high in slightly long rod-shape cells but low in elongated cells. The difference in morphology appeared to depend on the shear stress. It was found that biotin production was strongly correlated with cell length and the oxygen transfer coefficient ( k L a); cell lengths in the range 4–7 μm and k L a values in the range 1.5–2.0/min were found to be suitable for biotin production in jar-fermentor culture.