Gas Volumetric Mass Transfer Coefficient Research Articles

Simultaneous absorption of H2S, MM and COS into a novel SRSG absorbent using a rotating packed bed

In industries, many gases are required to remove hydrogen sulfide (H2S) and organic sulfur. However, it is still a huge challenge to achieve the efficient and simultaneous removal using a single process. Herein, a novel simultaneous removal sulfide gas (SRSG) absorbent is developed to simultaneously absorb H2S, methyl mercaptan (MM) and carbonyl sulfide (COS). The absorption mechanism between the SRSG absorbent and H2S, MM, COS is explored by quantum chemistry calculations (QCC) and controlled experiments in a rotating packed bed (RPB). Results indicate that the interaction between SRSG and H2S, MM belongs to physical absorption while COS absorption in SRSG obeys two molecule reaction mechanism. Furthermore, the effect of different operating conditions, including rotating speed (N), liquid flow rate (L), gas–liquid ratio (G/L) and temperature (T), on the absorption efficiencies (η) and gas volumetric mass transfer coefficient (KGa) of H2S, MM and COS is systematically investigated. It can be found that both η and KGa are dependent on those operating conditions. The optimal η value for H2S, MM and COS is up to 99.99%, 100%, 100%, respectively. Moreover, nondimensional equations for Sherwood number (Sh) are established, and the calculated and experimental values of Sh(H2S), Sh(MM) and Sh(COS) are in agreement with a deviation within ±13%, ±13%, and ±20%, respectively. These results will provide a valuable potential technique for simultaneously removing acidic gas components from industrial gases.

Selective absorption process intensification of ammonia from melamine exhaust gas using a counter airflow shear-rotating packed bed

The molar ratio of ammonia to carbon dioxide (NH3/CO2) in melamine exhaust can reach up to (2.0–2.4):1, and its direct emission will aggravate the greenhouse effect and waste of resources. Therefore, there is an urgent need to separate and recycle ammonia from the gas mixture in a more economical and efficient way. As an effective process intensification equipment, the counter airflow shear-rotating packed bed (CAS-RPB) has the advantages of high gas-liquid mass transfer efficiency, milliseconds of residence time and enhanced gas turbulence，which could enhance the absorption rate of ammonia in the gas mixture, inhibit the absorption of carbon dioxide caused by chemical absorption, and realize the selective absorption of ammonia.In this study，the CAS-RPB was adopted as an absorption device and the water was used as absorbent, the effects of the gas-liquid (G/L) ratio and high gravity factor (β) on absorption process were investigated. It was found that under suitable operating conditions, NH3/CO2 was close to 1:1 or 2:1 after absorption, which meet the requirement for the co-production of ammonium hydrogen carbonate or urea, the selectivity of ammonia was above 94 %, and the ammonia concentration in the absorption liquid were not less than 8.87 wt%. To compared with Cross-flow rotating packed bed (RPB), the absorption efficiency, selectivity, and gas volumetric mass transfer coefficient of ammonia are increased by 3.34 %, 8.83 %, and 7.02 % in CAS-RPB, respectively. The results show that the CAS-RPB can significantly enhance the selective absorption process of ammonia from melamine exhaust, therefore ammonia and carbon dioxide with potential high-added value can be obtained and utilized, and the zero-emission of ammonia and carbon dioxide can be realized.

Enhanced gas-liquid mass transfer coefficient by bulk nanobubbles in water

Liquid-gas operation explores the widespread applications in multiple chemical processes industries. For an instance, the inclusion of fermentation, dissolved air flotation, paper and pulp processing, sludge decomposition, aeration, ozonation, etc. are majorly covered. Liquid-gas contacting devices are primarily employed to perform their mixing, and the conventional contacting devices envelopes the fine bubble diffusers, jet aerators, surface aerators, static mixers, ejectors, etc. The gas transfer into the liquid is done by bubble formation, and the bubbles furthermore diffuses into the bulk liquid. The bubble size plays an important role in the transfer of gas, lower the size of bubbles, more is the rate of gas transfer, such as the mass transfer coefficient is remarkably enhanced by microbubbles when compared with milli-bubbles. In this work, we created O2 nanobubbles by sparging oxygen gas into nanopores, and during the production of nanobubbles, we examined the oxygen gas volumetric mass transfer coefficient (kLa) into the water. Nanoparticle tracking analysis was used to determine the population and size of nanobubbles, and we found that the population of nanobubbles is in the order of 107 bubbles/mL, with a mean diameter of 100–200 nm. The gassing out technique determines the volumetric mass transfer coefficient (kLa), and the influence of gas flow rate on the volumetric mass transfer coefficient (kLa) has been demonstrated to be positive. The volumetric mass transfer coefficient (kLa) in the case of nanobubbles is found significantly larger than that of microbubbles, ranging from 2.2 to 3.8 min−1.

Gas‐phase mass transfer characteristics in a counter airflow shear rotating packed bed

The gas‐phase mass transfer characteristics in a counter airflow shear rotating packed bed (CAS‐RPB) were studied. The gas volumetric mass transfer coefficient (kyae) was characterized with the physical absorption system NH3‐H2O and the effective interfacial area (ae) was determined by the chemical absorption system CO2‐NaOH, and then the gas‐phase mass transfer coefficient (ky) was obtained. The gas‐phase mass transfer characteristics in the CAS‐RPB were compared with those in the rotating packed bed with split packing (SP‐RPB) under the same operating conditions. The experimental results indicated that the kyae, ae, and ky for counter‐rotation of adjacent packing rings in the CAS‐RPB and SP‐RPB were larger than those for co‐rotation, and the kyae, ae, and ky for counter/co‐rotation in the CAS‐RPB were respectively greater compared with those for counter/co‐rotation in the SP‐RPB. This confirmed that the CAS‐RPB can further intensify the gas‐phase mass transfer process compared to the SP‐RPB. Moreover, the correlative expressions for the kyae, ae, and ky in the CAS‐RPB and SP‐RPB were obtained and were in close agreement with the experimental results.

Mass transfer characteristics in a rotating packed bed with split packing

The rotating packed bed (RPB) with split packing is a novel gas–liquid contactor, which intensifies the mass transfer processes controlled by gas-side resistance. To assess its efficacy, the mass transfer characteristics with adjacent rings in counter-rotation and co-rotation modes in a split packing RPB were studied experimentally. The physical absorption system NH3–H2O was used for characterizing the gas volumetric mass transfer coefficient (kyae) and the effective interfacial area (ae) was determined by chemical absorption in the CO2–NaOH system. The variation in kyae and ae with the operating conditions is also investigated. The experimental results indicated that kyae and ae for counter-rotation of the adjacent packing rings in the split packing RPB were higher than those for co-rotation, and both counter-rotation and co-rotation of the split packing RPB were superior over conventional RPBs under the similar operating conditions.

Effects of flow field on the metabolic characteristics of Streptomyces lincolnensis in the industrial fermentation of lincomycin

In this work, the flow field in the existing fermentor with radial-flow impellers (C1) was studied using the computational fluid dynamics (CFD) software package Fluent, then the fermentor with radial-axial flow impellers (C2) was constructed and was compared with the C1 fermentor by CFD and experimental research. The simulation results revealed that the flow field in C2 fermentor had characteristics such as higher turbulent kinetic energy, gas holdup and shear rates. Metabolic variables of Streptomyces lincolnensis in the two fermentors such as carbon and nitrogen source consumption rates, specific growth rates (μ), hyphae morphologies, and lincomycin productivities were further explored. The correlation analysis between the experimental measurements and the simulation results indicated that the hyphae clustering and dry cell weight (DCW) decreasing at production stage were eliminated in C2 fermentor, which had higher gas volumetric mass transfer coefficient (K(L)a), dissolved oxygen (DO) concentration and consumption rates of nutrient materials. When C2 was employed in the fermentor, the specific growth rate of S. lincolnensis at growth stage was higher, and the maintenance metabolism together with secondary metabolism at production stage was kept at higher levels. As a result, the yield of lincomycin was achieved 7039 μg ml(-1) when the 60 m(3) industrial fermentor was equipped with C2, which was increased by 46% compared to that obtained in the C1 fermentor.