Mathematical modelling of cyclic pressure swing adsorption processes

Golubyatnikov

Dvoretsky

et al. 2020

CI&CEQ

Article Highlights • PSA oxygen production unit is optimized under uncertainty • Optimal modes of the PSA oxygen production unit are studied • A constraint on gas flow velocity in the frontal layer of adsorbent of the PSA unit is introduced • Limiting gas flow velocity provides for resource saving of granulated adsorbent • The fulfilment of gas flow velocity constraint is ensured by controlling the PSA unit's valves Abstract Pressure swing adsorption (PSA) units are widely used for atmospheric air separation and oxygen concentration. However, the efficiency of such installations is reduced due to accidental changes in the characteristics of the atmospheric air to be separated. The article formulates and solves the problem of optimizing the regimes of operation of PSA units with zeolite adsorbent 13X, according to the criterion of oxygen recovery rate in the conditions of interval uncertainty of composition, temperature and pressure of atmospheric air. The optimization problem also takes into account the fulfillment of the requirements on purity of oxygen, productivity of the unit and resource saving of granulated adsorbent from granule abrasion. It is proposed to provide adsorbent saving by limiting the speed of incoming flow in the frontal layer of the adsorbent by means of "soft" stepwise change of the degree of opening of control inlet and outlet valves of the unit. The problem (including the search for time change programs for the degree of opening of control valves) was solved with the use of the developed mathematical model of cyclic heat-and mass exchange processes of adsorption-desorption in a PSA unit and a heuristic iterative algorithm. The comparative analysis of the results of the optimization problem solution, with and without taking into account the constraint on the gas flow velocity in the frontal layer of the adsorbent, is carried out. The influence of the specified requirements for the performance of the PSA unit and the purity of oxygen on the degree of its recovery has been studied.

mentioning

confidence: 99%

Optimization and analysis of pressure swing adsorption process for oxygen production from air under uncertainty

Golubyatnikov

Dvoretsky

et al. 2020

CI&CEQ

“…Математическое описание циклических процессов адсорбционного разделения атмосферного воздуха Технологический процесс концентрирования кислорода методом адсорбционного разделения воздуха осуществляется в двухадсорберной установке КБА с гранулированным адсорбентомсинтетическим цеолитом NаХ и конструктивными параметрами: A D -внутренний диаметр адсорбера, L -высота насыпного слоя адсорбента, gr d -диаметр гранул адсорбента [5]. Входными переменными в установке КБА являются: 1) нагрузка по сырью in G -расход исходной газовоздушной смеси (атмосферного воздуха); 2) возмущающие воздействия -температура in g T Математическое моделированиепроводили при следующих допущениях: 1) атмосферный воздух (состав: 1 -О2 с концентрацией 20,8±1,0 об.%, 2 -N2 с концентрацией 78,2 об.%., 3 -Ar и другие примеси с концентрацией 1,0±1,0 об.%) является 3-компонентной газовоздушной смесью (примеси не превышают 0,001 об.%) и рассматривается как идеальный газ, что вполне допустимо при давлении в адсорбере до 200•10 5 Па [6]; 2) диффузия О2, N2 и распространение теплоты в газовой и твердой фазах осуществляются только в аксиальном направлении движения потока газовоздушной смеси в адсорбере (по длине адсорбента) [7][8][9]; 3) в качестве адсорбента используется гранулированный цеолит NаХ с диаметром гранул 1,6 мм; 4) адсорбционное равновесие (изотерма адсорбции) описывается уравнением Дубинина-Радушкевича [10]; 5) тепловые потери в окружающую среду пренебрежимо малы [11].…”

unclassified

Numerical study of the dynamics and optimization of the modes of air adsorption separation and oxygen concentration

Vestn. Voronež. gos. univ. inž. tehnol.

Голубятников

Дворецкий

et al. 2019

Numerical researches of influence of temperature, composition and pressure changes of the initial gas mixture on the purity, recovery and capacity of the pressure swing adsorption (PSA) unit was made. Air separation dynamics was researches in a wide range of control (pressure at the compressor outlet, the duration of the adsorption – desorption cycle, backflow coefficient, programs of control valves opening degree in time) variables. It was found that the change of regime parameters and the inflow on has a significant impact on the purity and recovery of oxygen. Also was founded that the range of the duration of the adsorption stage and the compressor outlet pressure values should be limited to the intervals of 39-43 s and 2.7–2.8?105 Pa, respectively. The steady-state of the PSA unit mode output time was amount 20-30 cycles of "adsorption-desorption". Formulated and solved the optimization tasks of regime parameters of air separation cyclic processes by criterion of maximum oxygen recovery in 2-bed PSA unit with granular adsorbent zeolite 13X; the optimal values of the control parameters for differential environmental conditions (when the product oxygen concentration not less than 45% vol. and the PSA unit capacity ~2 l/min) are determined. It is shown that the implementation of the optimal of the inlet and discharge valves opening degree changes program in PSA unit allows to provide the set values of the gas flow rate in the "frontal" layer of the adsorbent, in which there is no abrasion of the adsorbent in the cyclic adsorption–desorption processes

Numerical study of cyclic adsorption processes of air oxygen enrichment in dynamics

Golubyatnikov

Dvoretsky

et al. 2019

J. Phys.: Conf. Ser.

The paper discusses the results of numerical analysis of the properties and modes of the adsorption air separation process and oxygen concentration with purity of ∼90% carried out in a double-adsorber PSA unit with a 13X granular zeolite adsorbent with capacity of up to 2 l/min. Calculation experiments have been performed using the developed mathematical model and the influence of perturbations (temperature, composition and pressure of atmospheric air) on the dynamics of the process, the unit performance, the extraction degree and oxygen purity has been investigated. It has been established that the most effective control action is the pressure at the compressor outlet, the increase in which from 2 to 6×105 Pa leads to the increase in the extraction degree and oxygen concentration on average by ∼57% and ∼12 vol.% respectively.