https://orcid.org/0000-0001-7221-1067
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ABSTRACT
One common application of pressure swing adsorption technology is medical oxygen concentrator (MOC) which directly produces ~ 94% O2 from air. The operating condition determines the separation efficiency of MOC and is varied with practical requirements. A better understanding of performance, mass and heat transfer inside adsorption bed at wide operating conditions is of great importance. The impacts of key operating parameters on the performances, the concentration and temperature distributions of MOC have been numerically investigated. The numerical results demonstrate that high comprehensive performances are achieved at an optimal condition with combination of adsorption pressure, product and feed flowrate and feed temperature. As adsorption pressure increases, the front of gas concentration and temperature becomes sharp, which effectively benefits for improving the performance. It is nearly identical shapes of nitrogen concentration and gas temperature profiles after adsorption and the profiles are pushed forward near production end with increasing of product flowrates and decreasing of feed flowrates. The increasing of feed temperature is beneficial to improve the performance. However, the adverse mass transfer and thermal effects are dominant at very high pressures, flowrates and temperatures conditions and this variation increases the unit power of MOC.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Nomenclature
| Latin letters | = |
|
| bi | = | Langmuir parameter (1/Pa) |
| bi0 | = | Langmuir parameter (1/Pa) |
| c | = | molar concentration (mol/m3) |
| ci | = | component i molar concentration (mol/m3) |
| Cf | = | gas heat capacity (J/(kg·K) |
| Cs | = | solid heat capacity (J/(kg·K) |
| dp | = | particle diameter (m) |
| din | = | bed diameter (m) |
| DL | = | axial dispersion coefficient(m2/s) |
| De | = | effective lumped diffusivity (m2/s) |
| Dm | = | molecular diffusion coefficient (m2/s) |
| DK | = | Knudsen diffusivity (m2/s) |
| L | = | N2 adsorbents loading height (m) |
| m | = | amount of adsorbents (kg) |
| Nu | = | Nusselt number |
| hf | = | gas-solid heat transfer coefficient (W/(m2·K)) |
| hw | = | internal gas-wall convective heat transfer coefficient (W/(m2·K)) |
| ki | = | LDF mass transfer coefficient for adsorbate i (1/s) |
| Kf | = | gas thermal dispersion coefficient (W/(m·K)) |
| Ks | = | solid phase thermal conductivity (W/(m·K)) |
| P | = | pressure (kPa) |
| Patm | = | atmospheric pressure(kPa) |
| Pi | = | gas partial pressure (kPa) |
| PH | = | adsorption pressure (kPa) |
| PL | = | desorption pressure (kPa) |
| PPED | = | pressure at end of PED step (kPa) |
| PPEU | = | pressure at end of PEU step (kPa) |
| PCP | = | pressure at end of CP step (kPa) |
| Pr(=μCf/Kf) | = | Prandtl number |
| q0/c0 | = | dimensionless Henry’s law constant |
| qi | = | adsorbed concentration of the component i (mol/kg) |
| qi* | = | equilibrium adsorption concentration of the component i, mol/kg |
| qs | = | saturation adsorbed concentration (mol/kg) |
| QF | = | feed flowrate (L/min) |
| QP | = | product flowrate (L/min) |
| R | = | gas constant (J/(mol·K)) |
| Re(=dpρfu/μ) | = | Reynolds number |
| t | = | time (s) |
| tAD | = | duration of AD step (s) |
| tCP | = | duration of CP step (s) |
| tPED/tPEU | = | duration of PED/PEU step (s) |
| tPU | = | duration of PU step (s) |
| T | = | temperature (K) |
| Tf | = | gas temperature (K) |
| TF | = | feed temperature (K) |
| TPU | = | purge gas temperature (K) |
| Ts | = | solid temperature (K) |
| Tw | = | wall temperature (K) |
| u | = | interstitial gas velocity (m/s) |
| uin | = | feed velocity (m/s) |
| y | = | oxygen purity of gas |
| yF | = | oxygen purity of feed gas |
| yPU | = | oxygen purity of purge gas |
| z | = | axial position (m) |
| Greek letters | = | XX |
| μ | = | dynamic viscosity (Pa·s) |
| ρf | = | gas density (kg/m3) |
| ρp | = | apparent density (kg/m3) |
| ρb | = | bulk density (kg/m3) |
| εb | = | inter-particle porosity |
| εp | = | particle porosity |
| γ1 | = | axial tortuosity factor |
| τp | = | pore tortuosity |
| ΔHi | = | heat of adsorption (J/mol) |