Gas–liquid mass transfer in a slurry bubble column operated at gas hydrate forming conditions

Study of the Hydrodynamics and Mass Transfer Coefficient in a 2D Mimicked FT Slurry Bubble Columns for Alternative Clean Energy and Chemical Production

Bubble columns are widely used for contacting gas–liquid and gas–liquid–solid mass transfer/chemical reactions. Gas distributor is the most important accessory because it decides the bubble size/rise velocity and gas distribution. In this study, the effect of distributor design on hydrodynamics and mass transfer coefficient are studied at different operating conditions of height to diameter ratio, solid loading, and superficial gas velocity The overall gas holdup, is studied experimentally using a rectangular slurry bubble column operating at ambient temperature and pressure, using liquid paraffin (C9–C11), three heights to diameter ratios (6, 7.5 and 10) and silica as a solid phase (0 %, 9 % and 25 %) with oxygen as gas phase. Two types of distributor were used, perforated plate and ring type. The results showed that the overall gas holdup increased by increasing gas velocity and decreased by increasing height to diameter ratio and solid loading. Also, it is found that the perforated plate distributor gave a higher gas hold up than ring distributor at gas velocity higher than 0.03 m/sec. The following correlations are obtained:

Plate distributor at presence of silica particles: $$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} =& {\left({1.343{\rm{U}}_{\rm{g}}^{0.0612} - 0.00891{\rm{\varepsilon}}_{\rm{s}}^{- 0.374} - 0.702{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.041}}} \right)^{4.904}}\cr& - 0.0251}$$

Ring distributor at presence and absence of silica particles: $$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} = &{\left({0.216{\rm{U}}_{\rm{g}}^{0.297} - 0.354{\rm{\varepsilon}}_{\rm{s}}^{1.4671} - 0.127{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.147}}} \right)^{1.1206}} \cr&+ 0.058}$$

There is a good agreement between experimental and predicted values with a percent of error less than 2 %.

It has been found that the mass transfer coefficient is higher for ring distributor than the perforated plate and growing higher for heterogeneous flow regime and higher solid loading.

Tetrafluoroethane (R134a) hydrate formation within variable volume reactor accompanied by evaporation and condensation

Vast size hydrate formation reactors with fast conversion rate are required for the economic implementation of seawater desalination utilizing gas hydrate technology. The commercial target production rate is order of thousand tons of potable water per day per train. Various heat and mass transfer enhancement schemes including agitation, spraying, and bubbling have been examined to maximize the production capacities in scaled up design of hydrate formation reactors. The present experimental study focused on acquiring basic knowledge needed to design variable volume reactors to produce tetrafluoroethane hydrate slurry. Test vessel was composed of main cavity with fixed volume of 140 ml and auxiliary cavity with variable volume of 0 ∼ 64 ml. Temperatures at multiple locations within vessel and pressure were monitored while visual access was made through front window. Alternating evaporation and condensation induced by cyclic volume change provided agitation due to density differences among water and vapor, liquid and hydrate R134a as well as extended interface area, which improved hydrate formation kinetics coupled with latent heat release and absorption. Influences of coolant temperature, piston stroke/speed, and volume change period on hydrate formation kinetics were investigated. Suggestions of reactor design improvement for future experimental study are also made.

A new porous material to enhance the kinetics of clathrate process: application to precombustion carbon dioxide capture

In this work, the performance of a new porous medium, polyurethane (PU) foam in a fixed bed reactor for carbon dioxide separation from fuel gas mixture using the hydrate based gas separation process is evaluated. The kinetics of hydrate formation in the presence of 2.5 mol % propane as thermodynamic promoter was investigated at 4.5, 5.5, and 6.0 MPa and 274.2 K. Significantly higher gas consumption and water conversion to hydrate was achieved when PU foam was employed. PU foam as a porous medium can help convert 54% of water to hydrate in two hours of hydrate formation. In addition the induction times were very low (<3.67 min at 6.0 MPa). A normalized rate of hydrate formation of 64.48 (±3.82) mol x min(-1) x m(-3) was obtained at 6.0 MPa and 274.2 K. Based on a morphological study, the mechanism of hydrate formation from water dispersed in interstitial pore space of the porous medium is presented. Finally, we propose a four step operation of the hydrate based gas separation process to scale up.