Flooding Gas Velocity Research Articles

柱形Pt-SDB催化剂的水–氢交换高处理量工艺

摘要：研究了基于柱形Pt-SDB催化剂的水–氢催化交换工艺, 进行了柱形Pt-SDB催化剂的流体力学性能实验并讨论了填料规格、填料催化剂装填比、反应温度、气液比、处理量等对水–氢交换传质单元高度和传质系数的影响。结果表明，催化活性较低的柱形Pt-SDB催化剂，具有液泛气速高、持液量稳定、单位床层高度压降低等优点；柱形Pt-SDB催化剂水–氢催化交换的高处理量工艺条件为θ环填料与催化剂填装比例1:1、反应温度70℃~75℃、气液比1:1、空塔气速0.3 m/s。 The process conditions are experimentally studied for H2O-H2 liquid catalytic isotopic exchange with Pt-SDB as hydrophobic cylindrical catalyst, and hydrodynamic experiments are conducted for obtaining the correlating expressions of pressure drop △P/Z, flooding gas velocity uF. The results indicate that the Pt-SDB cylindrical catalyst with little catalytic activity has a number of advantages, including low pressure drop, higher flooding gas velocity and stable liquid holdup. The height of transfer unit (HTU) is also changed to be higher with the increasing of the air velocity in empty tower and the packing dimension. The efficiency of catalytic exchange reaction is high with a packing ratio of 1:1 of hydrophilic packing and hydrophobic catalyst in separated layers. The HTU decreases with increasing operating temperature, but the trend is slowed down when the temperature is above 70˚C. The HTU increases with increasing hydrogen flow rate and decreases with increasing diluted heavy water flow rate. When the air velocity of empty tower is 0.3 m/s, the process capacity is higher.

Hydrodynamic and heat and mass transfer performances of novel ceramic foam packing to humidification tower

The humidification tower is the key unit of a humid air turbine cycle. The compactness problem of a humidification tower is crucial to the flexibility and safe operation of the cycles. This research focuses on the potential application of the novel ceramic foam corrugated packing in humidification. The hydrodynamics and heat and mass transfer performances of this packing (type FSC-1) are investigated and compared with those of the traditional structured packing (type TJH-250). The experimental results show that the specific surface area obviously increases with a competitive voidage of 93% for ceramic foam corrugated packing. In comparison with THJ-250, FSC-1 exhibits about 60% pressure drop per mass transfer unit, 50% flooding gas velocity, and no more than 37% height of gas-phase mass transfer unit. Although the ceramic foam packing has relatively low air flux, it is also promising for the compact humidification tower due to its excellent heat and mass transfer performance and low pressure loss.

The Effects of Gap Size on Flooding in Vertical Narrow Rectangular Channels

In this paper, counter-current gas--liquid two-phase flow and onset of flooding in vertical narrow rectangular channels were studied. In order to study the flow pattern, during counter-current flow and determine conditions associated with the onset of flooding, the flow pattern and pressure drop were investigated by visual experiments. The results show that the flow characteristics and the tendency of pressure drop in vertical narrow rectangular channels were similarly with the conventional channels. However, the maximum of pressure drop appeared at the completed carrying up of flooding in vertical narrow rectangular channels, and it appeared at the onset of flooding in conventional channels. Flooding gas velocities decrease as the gap size decreases; The gas velocity required for flooding increases as the gap size increases at the same liquid flow rate.

Comparison of several packings for CO 2 chemical absorption in a packed column

CO 2 capture and storage has gained widespread attention as an option for reducing greenhouse gas emissions. Chemical absorption and stripping of CO 2 with hot potassium carbonate (K 2CO 3) solutions has been used in the past, however potassium carbonate solutions have a low CO 2 absorption efficiency. Various techniques can be used to improve the absorption efficiency of this system with one option being the addition of promoters to the solvent and another option being an improvement in the mass transfer efficiency of the equipment. This study has focused on improving the efficiency of the packed column by replacing traditional packings with newer types of packing which have been shown to have enhanced mass transfer performance. Three different packings (Super Mini Rings (SMRs), Pall Rings and Mellapak) have been studied under atmospheric conditions in a laboratory scale column for CO 2 absorption using a 30 wt% K 2CO 3 solution. It was found that SMR packing resulted in a mass transfer coefficient approximately 20% and 30% higher than that of Mellapak and Pall Rings, respectively. Therefore, the height of packed column with SMR packing would be substantially lower than with Pall Rings or Mellapak. Meanwhile, the pressure drop using SMR was comparable to other packings while the gas flooding velocity was higher when the liquid load was above 25 kg m −2 s −1. Correlations for predicting flooding gas velocities and pressure drop were fitted to the experimental data, allowing the relevant parameters to be estimated for use in later design.

Study on Absorption Performance at High Liquid Loads using a Novel Random Packing: Super Mini Ring

The Super Mini Ring (SMR), a novel random packing, has found wide application in liquefied petroleum gas purification and carbon dioxide absorption as it has particularly good performance at high liquid loads. In this study, the hydrodynamic and mass transfer models for this type of packing were studied and compared over a wide range of liquid loads (LW = 0–220 m3·m−2·h−1). The modified Billet and Schultes pressure equation was found to be superior to other models presented in the literature. Models used to calculate the flooding gas velocity and the height of the mass transfer unit for the SMR have also been presented.

Prediction of flooding gas velocity in gas–liquid counter-current two-phase flow in inclined pipes

The purpose of the experimental study is to investigate the effects of pipe inclination, pipe length, pipe diameter and surface tension of the working liquid on the onset of flooding of gas–liquid adiabatic counter-current two-phase flow in inclined pipes. Flooding in inclined pipes were observed by using the combination of visual observation, measurement of discharged liquid flow rate and time variation of liquid hold-up. And it was defined as the maximum air flow rate at which the discharged liquid flow rate is equal to the inlet liquid flow rate. As a result we proposed a correlation to predict the flooding gas velocity in inclined pipes under a given liquid flow rate, and the predictions agreed well with the experimental observations.

Countercurrent gas–liquid flow in inclined and vertical ducts — I: Flow patterns, pressure drop characteristics and flooding

An experimental investigation into adiabatic gas–liquid counterflow in inclined and vertical rectangular ducts with a square-edged gas inlet is conducted. Water, methanol, propanol, air, argon, helium and hydrogen are used as working fluids. The duct height and width are varied from 50 to 150 mm and 10 to 20 mm respectively. At low gas flow rates the two-phase pressure gradient is gas Reynolds number related while it becomes dependent on the densimetric gas Froude number as the gas flow is increased. The hydraulic diameter is the length dimension required for the gas Reynolds number, while the duct height becomes the characteristic dimension in the Froude number. The flooding gas velocity is found to be strongly dependent on the duct height, the phase densities and duct inclination.

The influence of fluid properties and inlet geometry on flooding in vertical and inclined tubes

Flooding during adiabatic two-phase countercurrent flow in a vertical and 60° inclined (to the horizontal) 30 mm i.d. tube is investigated. Experiments are conducted with air, argon, helium, hydrogen, water, methanol, isopropanol and aqueous methanol solutions. An improved flooding correlation is proposed which accurately correlates the data. In the past, a number of proposed dimensionless groups often only succeeded in correlating their own data. The present correlation excellently correlates the data of three previous investigations. The findings clearly show that some flooding data had been misinterpreted in the past. The fluid densities have the strongest effect on the flooding gas velocity. The effect of the liquid viscosity is relatively stronger than that of the surface tension. Flooding is independent of the gas viscosity.

Experimental study of the effect of pipe length and pipe-end geometry on flooding

The onset of flooding is thought to be highly sensitive to the end geometry of the test channel and its high sensitivity is an important cause of data scattering. In the present work, the effect of end geometry on flooding is experimentally investigated. Observation shows that flooding definition also causes the data scattering and that flooding should be classified into two modes according to the location where it occurs. With the sharp liquid entrance geometry, both entrance flooding and exit flooding are able to take place while only exit flooding does when entrance is smooth. In the range of low liquid flow rates, exit flooding always takes place and flooding gas velocities for the same exit geometry are nearly the same regardless of liquid entrance geometry. When air is injected into the test tube through a nozzle, even if the liquid exit is sharp, flooding gas velocities are nearly the same as those with smooth exit geometry. The present experiments show that the length effect is significantly affected by the pipe-end geometry. It is small in the range of low liquid flow rates but becomes significant as the liquid flow rate increases.

Classification of flooding data according to type of tube-end geometry

Flooding data are partitioned according to type of entrance and exit geometry by applying the entropy minimax principle. It is found that the effect of exit geometry on flooding is great in the low liquid velocity region, while that of entrance geometry is great in the high liquid velocity region. Two flooding correlations having second order polynomial form are suggested with ±20% uncertainty bands for smooth exit and sharp exit geometries, respectively. It is found that flooding gas velocities predicted by most previous correlations are close to those predicted by the smooth exit correlation.

Countercurrent Flooding in Pipes Containing Multiple Elbows and an Orifice.

Flooding in three piping systems containing multiple elbows and an orifice was experimentally investigated using a 51mm glass pipe and an air/water system. The vertical-to-horizontal geometry with multiple horizontal sections connected by 90°elbows yielded the most limiting flooding gas velocities due to the prolonged formation of the hydraulic jump caused by the added hydraulic resistance of the multiple elbows. Inclining one of the piping sections downward to 45°from the horizontal or to the vertical in the other two geometries eliminated the hydraulic-jump-induced flooding mechanism and increased the flooding gas velocities for the system at high liquid flow rates. The orifice placed in the horizontal section was seen to generally lower flooding gas velocities, with the greatest effect seen for the smallest orifice tested. A new method based on a superposition principle was also proposed for prediction of flooding in complex piping systems.

COUNTERCURRENT FLOODING IN VERTICAL-TO-INCLINED PIPES

Countercurrent flooding data have been obtained using air and water for vertical-to-downwardly inclined pipes containing elbows of varying angles. Experiments were performed with six different test sections, all having an inner diameter of 51 mm and a 1-m-tong vertical tube connected to an inclined or horizontal tube The flooding data for 112.5° and 135° elbow angles were almost identical and showed that these geometries required the largest gas flow rates for flooding among all the geometries tested. The flooding gas velocities for the 157.5° elbow were slightly less than those of the 112.5° and 135° elbows but greater than those of the vertical pipe without any elbow and vertical-to-horizontal pipes at low to moderate liquid flow rates In all vertical-to-inclined pipes, flooding was initiated in the inclined section at about 15 to 50 cm downstream of the elbow. Due to the countercurrent flow of gas, the liquid stream just downstream of the elbow became highly agitated and a frothy mixture was carried up...

Determination of flooding gas velocity and liquid hold‐up at flooding in packed columns for gas/liquid systems

AbstractA new model of suspended bed of droplets for describing the vaour or gas the vapour or gas velocity at the flooding point in packed of columns for rectification and absorption under vacuum and normal pressure is presented metallic, ceramic and plastic packings with diameters of 8–90 mm as well on sheet metal and gauze packings, in a wide range of liquid and vapour loads. Approximately 650 literature measurements and own data were evaluated. The mean relative error in determining the gas velocity at flooding point is less than ±5%. On the basis of the double layer model, a new equation was derived for the hold‐up at flooding point, which is needed for the calculation of the flooding gas velocity. An example of calculations for sample applications is also included.

Behaviour of liquid films and flooding in counter-current two-phase flow—Part 1. Flow in circular tubes

Experimental results are presented on the flooding gas velocity in tubes over a wide range of parameters—tube diameter, tube length, liquid flow rate, liquid viscosity and surface tension. The flooding phenomenon is caused by interaction between the waves on the liquid film and the upward gas stream. By measuring variation of the maximum height of the wavy liquid films with an increase of the gas flow rate, the complicated effects of tube length and surface tension on flooding are revealed. The data of the flooding velocity are empirically correlated in termes of nondimensional groups for each tube length.