Investigation of the effects of operating parameters on the local mass transfer coefficient and membrane wetting in a membrane gas absorption process

One of the most important components of an absorption air-conditioning/heat pump system is the absorber, where the refrigerant water vapour is absorbed into the liquid solution. While absorption systems have been in use for several years, the complex transport phenomena occurring in the absorber are not fully elucidated yet. Thus, an attempt is made to model the absorption process of water vapour in aqueous solutions of lithium bromide considering a falling-film, vertical-tube absorber. The proposed analysis is based on the formulation of four differential equations describing the spatial variation (parallel to the tube-axis) of solution mass, temperature, mass fraction and coolant temperature. The system of ordinary differential equations is numerically solved using a non-stiff numerical method. Thermophysical properties and especially, heat and mass transfer coefficients are calculated using widely-accepted and reliable relationships, which are extracted from the literature using recently published information on wavy-laminar flows. In the present study, the questionable assumption of treating the water vapour as an ideal gas is heavily modified utilizing. Consequently, the hypothesis of saturated water vapour at the steam-solution interaction surface is revised by introducing an energy difference between the superheated steam and the liquid water within the binary solution. The last correction encouraged us to compare theoretical results for solution temperature, mass fraction and mass flow rate, which were obtained using both assumptions. It was proved that the initial treatment causes an underestimation of the absorbed steam mass and correspondingly, an underestimation of solution temperature and mass fraction at the mass exchange interface. An attempt is made also to identify the effect of mass transfer coefficient on the effectiveness of the absorption process and on the energy differences between the superheated steam and the liquid water either as pure substance or as component of the binary mixture. It was shown that the increase of mass transfer coefficient leads to an increase of steam mass transfer rate and to a corresponding decrease of solution temperature slope at the entrance of a tube. Correspondingly, the increase of mass transfer coefficient results in an increase of heat of absorption and heat of dilution at the same variation range of the solution mass fraction.

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ABSORBSI H2S MENGGUNAKAN LARUTAN Fe-EDTA DALAM PACKED COLUMN

EKUILIBIUM ◽

10.20961/ekuilibrium.v10i2.2236 ◽

2011 ◽

Vol 10 (2) ◽

Author(s):

Endang Kwartiningsih ◽

Arif Jumari

Keyword(s):

Mass Transfer ◽

Liquid Phase ◽

Transfer Coefficient ◽

Mass Transfer Coefficient ◽

Gas Phase ◽

Reaction Rate ◽

Packed Column ◽

Reaction Rate Constant ◽

Absorption Process ◽

Edta Solution

Abstract: Gas purification from the content of H2S using Fe-EDTA (Iron Chelated Solution) gave several advantages. The advantages were the absorbent solution can be regenerated that means a cheap operation cost, the separated sulfur was a solid that is easy to handle and is save to be disposal to environment. This research was done by simulation and experimental. The simulation step was done by mathematical model arrangement representing the absorption process in packed column through mass transfer arrangement such as mass transfer equations and chemical reaction. The experimental step was done with the making of Fe-EDTA solution from FeCl2 and EDTA. Then Fe-EDTA solution was flown in counter current packed column that was contacted with H2S in the methane gas. By comparing gas composition result of experiment and simulation, the value of mass transfer coefficient in gas phase ( kAga), mass transfer coefficient in liquid phase (kAla) and the reaction rate constant ( k) were found. The values of mass transfer coefficient in liquid phase (kAla) were lower than values of mass transfer coefficient in gas phase (kAga) and the reaction rate constant (k). It meant that H2S absorption process using Fe-EDTA absorbent solution was determined by mass transfer process in liquid phase. The higher flow rate of absorbent, the higher value of mass transfer coefficient in liquid phase. The smaller packing diameter, the higher value of mass transfer coefficient in liquid phase.From analysis of dimension, the relation of dimensionless number between Sherwood number and flow rate of absorbent, packing diameter was Keywords: chemical reaction, Fe-EDTA, H2S absorption, mass transfer

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Study on Mass Transfer Characteristics of Hydrate-based Gas Absorber

MATEC Web of Conferences ◽

10.1051/matecconf/202133304002 ◽

2021 ◽

Vol 333 ◽

pp. 04002

Author(s):

Shun Takano ◽

Ryosuke Ezure ◽

Yusuke Takahashi ◽

Hiroyuki Komatsu ◽

Kazuaki Yamagiwa ◽

...

Keyword(s):

Mass Transfer ◽

Transfer Coefficient ◽

Mass Transfer Coefficient ◽

Gas Separation ◽

Bubble Column ◽

Hydrate Formation ◽

Continuous Operation ◽

Gas Absorption ◽

Volumetric Mass Transfer Coefficient ◽

Type Apparatus

Hydrated-based gas separation is a method capable of selectively separating and recovering greenhouse gases. Although a conventional hydrate-based gas separation apparatus is a batch or a semi-batch system, continuous operation is preferable to increase the throughput of gas without changing the apparatus volume. Recently, we proposed a flow type apparatus to allow continuous operation of hydrate formation (absorption) and subsequent decomposition (desorption). The aim of this study is to investigate the mass transfer characteristics of the continuous apparatus using the HFC134a-N2 mixed gas system. The volumetric mass transfer coefficient was calculated especially during a steady state of gas absorption. Besides, we compared mass transfer performance between the hydrate-based gas absorber and a conventional bubble column. Sodium dodecyl sulfate was used as a hydrate dispersant. In the flow type apparatus, the gas-liquid contact was good and the hydrate slurry state was observed during hydrate formation. In the surfactant solution, the volumetric mass transfer coefficient increased in comparison with that in water. The volumetric mass transfer coefficient with hydrate was higher than that of the bubble column. These results suggest that hydrate formation improves gas absorption performance.

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