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Adsorption

, Volume 24, Issue 1, pp 121–133 | Cite as

Modeling and simulation of a pressure–temperature swing adsorption process for dehydration of natural gas

Article

Abstract

Water vapor in a natural gas stream can result in line plugging due to hydrate formation, reduction of line capacity due to collection of free water in the line, and increased risk of damage to the pipeline due to the corrosive effects of water. Therefore, water vapor must be removed from natural gas to prevent hydrate formation and corrosion from condensed water. Molecular sieves are considered as one of the most important materials that are used as desiccant materials in industrial natural gas dehydration. This paper focuses on modeling of pressure–temperature swing adsorption (PTSA) process in a commercial two-layer adsorption system during sequential steps of cyclic operation to remove water from natural gas. The dynamic model equations were constructed from 4 mol balances; model molecule of water vapor in natural gas, a total mass balance, a pressure drop equation and two energy balances of solid and gas phases in the adiabatic column. Results reveal that about 1 m of the bed was overdesigned by vendor and it doesn’t work in optimum condition. The influential parameters of the process were investigated through a parametric analysis of the process efficiency. For the sake of energy saving some suggestions were proposed for upgrading the design conditions with no significant effect on the purification performance. Results show that optimum conditions will be obtained using adsorption time 22 h and regeneration time 9 h with maximum temperature of 240 °C.

Keywords

Natural gas Dehydration Molecular sieve Pressure–temperature swing adsorption process 

Nomenclature

ap

Specific area of adsorbent (1/m)

Bi

Langmuir constant (1/kpa)

B0,i

Pre-exponential factor in the Arrhenius type temperature dependence of B (1/kpa)

Ci

Concentration of species i in the gas (mol/m3)

Cpg

Heat capacity of gas (J/mol/K)

Cps

Heat capacity of adsorbent (J/kg/K)

Dax,i

Effective axial dispersion coefficient of species i (m2/s)

Dm,i

Molecular diffusivity of species i in mixture (m2/s)

DK,i

Knudsen diffusivity of species i (m2/s)

hi

Film heat transfer coefficient between gas and solid (W/m2/K)

∆Hi

Heat of adsorption of species i (J/mol)

Kg

Gas thermal conductivity (W/m/K)

kf,i

Film mass transfer coefficient of species i (m/s)

kp,i

Pore diffusivity of species i (m2/s)

ki

Overall mass transfer coefficient (s−1)

Kax

Effective axial thermal conductivity (W/m/K)

M

Molecular weight (g/mol)

Nu

Nusselt number

ncycle

Number of cycle

n

Number of all component in gas mixture

P

Pressure (kpa)

Pr

Prandtl number

pi

Partial pressure (kpa)

qi

Adsorbed phase concentration of species i (mol/kg)

\({\text{q}}_{{\text{i}}}^{*}\)

Equilibrium adsorbed phase concentration (mol/kg)

qm,i

Saturation capacity (mol/kg)

R

Ideal gas law constant (J/mol/K)

rp

Adsorbent radius (m)

rpore

Pore radius (m)

Re

Reynolds number

Sc

Schmidt number

Sh

Sherwood number

t

Time (s)

T

Gas temperature (K)

Ts

Adsorbent temperature (K)

u

Superficial gas velocity (m/s)

z

Axial coordinate in the bed (m)

Greek letters

ε

Bed porosity

εp

Adsorbent porosity

τ

Tortuosity factor

ρs

Adsorbent density (kg/m3)

ρ

Gas density (mol/m3)

μ

Gas viscosity (kg/m s)

φ

Shape factor

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2017

Authors and Affiliations

  1. 1.Development and Engineering Management DepartmentSouth Pars Gas Complex (SPGC)AssaluyehIran

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