Adsorption based portable oxygen concentrator for personal medical applications

ADSORPTION BASED PORTABLE OXYGEN CONCENTRATOR FOR PERSONAL MEDICAL APPLICATIONS VEMULA RAMA RAO NATIONAL UNIVERSITY OF SINGAPORE 2011 ADSORPTION BASED PORTABLE OXYGEN CONCENTRATOR FOR PERSONAL MEDICAL APPLICATIONS VEMULA RAMA RAO (M. Tech., Indian Institute of Technology, Roorkee) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2011 ACKNOWLEDGEMENT First and foremost, I would like to take this opportunity to express my deepest gratitude to my supervisors Prof. Shumsuzzaman Farooq and Prof. William Bernard Krantz for their continuous encouragement, valuable guidance and constant inspiration throughout this research work and to develop an understanding of the subject. Their enthusiasm, depth of knowledge and patience left a deep impression on me. Their constructive criticism and ingenious suggestions have helped me a lot in getting the thesis in present form. I am very much indebted to my present and past labmates Shima Nazafi Nobar, Shreenath Krishnamurthy, Hamed Sepehr, Shubhrajyoti Bhadra and Sathishkumar Guntuka for actively participating in the discussion and the help that they have provided during this research work. I am also immensely thankful to my laboratory technologists, Madam sandy and Mr. Ng Kim Poi, for their timely cooperation and help while designing and conducting the experiments in the lab. Special thanks also due to my friends Anjaiah Nalaparaju, Vamsikrishna Kosaraju, Satyanarayana PuniRedd, Sundaramurthy Thirunahari, Jayaraman, Sreenivas Srinivasarao Yelneedi, Vempati Sreenivasareddy and Sudhakar Jonnalagadda for their constant support and encouragement to finish this work. I am happy to express my deepest gratitude to my parents Tirupatamma and Veeraiah Vemula, and other family members for their affectionate love, understanding, unconditional support and encouragement in all my efforts. Special words of gratitude to my uncle Bikshamaiah and my late grandfather Kistaiah for i Acknowledgement motivating and encouraging me to boost my confidence and knowledge from my childhood. Finally, I would like to thank National University of Singapore for awarding me the research scholarship and excellent research facilities. ii TABLE OF CONTENTS ACKNOWLEDGEMENT i TABLE OF CONTENTS iii SUMMARY………. ix LIST OF FIGURES .xii LIST OF TABLES .xx NOMENCLATURE .xxii Chapter 1: INTRODUCTION .1 1.1 Overview of the Research 1.2 Chronic Obstructive Pulmonary Diseases and its Treatment 1.3 Air Separation Processes 1.3.1 Adsorption based air separation processes .5 1.3.2 Pressure swing adsorption (PSA) process .7 1.3.3 Vacuum-pressure swing adsorption (VSA and VPSA) processes 11 1.3.4 Rapid cycling pressure swing adsorption (RPSA) process .13 1.3.5 Nitrogen selective adsorbents for oxygen production 17 1.3.6 Zeolite adsorbents (5A, 13X and LSX zeolite) .18 1.3.7 Engelhard titanosilicates (ETS10) 20 1.3.8 Structured adsorbents for RPSA applications .21 1.4 Commercial Medical Oxygen Concentrators for COPD Patients 23 1.5 Miniaturization of Oxygen Concentrators .24 1.6 Objectives of the Current Research .28 iii Table of Contents 1.7 Organization of the Thesis .30 Chapter 2: LITERATURE REVIEW 32 2.1 Overview of the Chapter 32 2.2 Axial Dispersion in Columns Packed with Small Particles .32 2.3 Prior Studies on Pressure Drop in a PSA Column .35 2.4 Pulsed Pressure Swing Adsorption (PPSA) Processes 38 2.5 Ultra Rapid Pressure Swing Adsorption Process .45 2.6 Patents on Portable Oxygen Concentrators 47 2.7 Chapter Conclusion 50 Chapter 3: MODELING AND SIMULATION OF PULSED PRESSURE SWING ADSORPTION PROCESS .51 3.1 Overview of the Chapter 51 3.2 Process Description 51 3.3 Mathematical Modeling .53 3.3.1 General assumptions in PPSA process modeling .53 3.3.2 Model equations 53 3.3.3 Equilibrium and kinetic parameters 58 3.3.4 Numerical simulation 61 3.4 Simulation Results and Discussion 62 3.4.1 Dynamics of adsorption and desorption .65 3.4.2 Optimum in adsorption time and desorption time 67 3.4.3 Effect of particle diameter on process performance .72 3.4.4 Effect of pressure drop on process performance .74 3.4.5 Effect of bed length on process performance .76 3.5 Graphical Design of the Pulsed Pressure Swing Adsorption Process 78 iv Table of Contents 3.5.1 Generalizing the simulation results .78 3.5.2 Correlation for the optimum adsorption and desorption times .83 3.5.3 General design procedure .88 3.5.4 A case study in process miniaturization 88 3.6 Chapter Conclusion 89 Chapter 4: COLUMN DYNAMICS: EXPERIMENTAL DESIGN AND PROCEDURES 92 4.1 Overview of the Chapter 92 4.2 Critical Issues in Experimental Study of PPSA Process 92 4.2.1 Adsorbents 94 4.2.2 Column dimensions 96 4.2.3 Selection of instruments 97 4.2.4 Oxygen sensor, flow meter and pressure sensor .99 4.2.5 Optimum dead volumes and pressure drops .101 4.3 Unary Adsorption Equilibrium Experiments .103 4.3.1 Adsorbent regeneration .105 4.3.2 Experimental procedure 106 4.3.3 Processing of equilibrium data 107 4.4 Experimental Design and Procedure for Pressure Drop and Breakthrough Measurements .109 4.4.1 Experimental set-up 109 4.4.2 Pressure drop characteristics of adsorption column 111 4.4.3 Dynamic column breakthrough experiments. .113 4.5 Sensor Responses .119 4.6 Chapter Conclusion 122 v Table of Contents Chapter 5: COLUMN DYNAMICS: EXPERIMENTAL RESULTS, MODELING AND SIMULATIONS 123 5.1 Overview of the Chapter 123 5.2 Unary Adsorption Equilibrium Experimental Results .123 5.3 Modeling of Pressure Drop along the Adsorption Column .125 5.3.1 Estimation of Darcy's constant .127 5.3.2 Effect of column to particle diameter ratio (Rd) on Darcy's constant .129 5.3.3 Pressure drop across a column packed with 75-90 µm size spherical glass beads 131 5.4 Modeling of Dynamic Column Breakthrough (DCB) Experiments in an Adsorption Column Packed with 63-75 µm Size Binderless 5A Zeolite Adsorbent Particles .133 5.4.1 Modeling of extra column effects at the entrance of the column134 5.4.2 Nonisothermal modeling of breakthrough experiments .138 5.4.3 Axial dispersion in a column packed with very fine zeolite particles .141 5.4.4 Parametric study of breakthrough modeling and simulation 143 5.5 Dynamic Column Breakthrough (DCB) Experiments and Simulation: Results and Analysis 153 5.5.1 Single component breakthrough experiments .155 5.5.2 Binary breakthrough experiments .157 5.5.3 Equilibrium data from dynamic column breakthrough (DCB) experiments .161 5.6 Chapter Conclusion 163 vi Table of Contents Chapter 6: EXPERIMENTAL, MODELING AND SIMULATION STUDY OF A TWO-STEP PPSA PROCESS 164 6.1 Overview of the Chapter 164 6.2 Experimental Study of Pulsed Pressure Swing Adsorption .164 6.2.1 Experimental procedure 164 6.2.2 Parametric study of the PPSA process 166 6.3 Modeling and Simulation of the Experimental PPSA Process 168 6.3.1 Isothermal model 168 6.3.2 Nonisothermal model 170 6.4 Estimation of Power Consumption in the PPSA Process 171 6.5 Experimental and Simulation Results of Pulsed Pressure Swing Adsorption Process 173 6.5.1 Effect of adsorption step duration on PPSA process performance .173 6.5.2 Effect of desorption step duration on PPSA process performance .175 6.5.3 Effect of inlet column pressure on PPSA process performance 177 6.6 Limitations on Current Experimental Study of PPSA Process 179 6.7 A Novel Three-Step Rapid Vacuum Swing Adsorption Cycle for Reducing of Oxygen Concentrator Size 182 6.7.1 Process description .182 6.7.2 Modeling and simulation of three-step vacuum swing adsorption process 183 6.7.3 Simulation results of three-step Rapid VSA processes 186 6.7.4 Estimation of bed size factor 192 vii Table of Contents 6.8 Chapter Conclusion 192 Chapter 7: CONCLUSIONS AND RECOMMENDATION .194 7.1 Overview of the Chapter 194 7.2 Conclusions 194 7.3 Future Recommendations 197 BIBLIOGRAPHY. .199 APPENDIX A: DIMENSIONLESS EQUATIONS IN CHAPTER 208 APPENDIX B: DIMENSIONLESS FORM OF NONISOTHERMAL MODEL EQUATIONS .212 APPENDIX C: EQUILIBRIUM DATA OF NITROGEN AND OXYGEN ON BINDERLESS 5A ZEOLITE 216 viii Bibliography Superior Adsorbent for Air 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US Patent 2008/0134889 A1: 2008. 207 APPENDIX A DIMENSIONLESS EQUATIONS IN CHAPTER Dimensionless equations Equations (3.5)-(3.9) and (3.12)-(3.20) were made dimensionless by introducing the following dimensionless variables.  d p2 q  Pavg RTl A k A P pA qA qB q Ae qBe e e     ; q A   ; qB   ; q A   ; qB   ; k A  ; P  ; pA  60 p PL DM PL PL q q q q   d p2 q  Pavg RTlB k B  d p2 PL t   2  z * 150u z  L    2 k  ; t    ; z  ; uz    L d p2 PL    60 p PL DM 150  L2     Substituting these dimensionless variables in the above equations results in the  B following dimensionless equations:    pA 1  1  0.7  0.5    t 1       1 q A   2  t     4     z     p A      pAu*z P      z P    z  (A1)   P      Pu *z       q A  qB   t z t * P u *z   * z  q A 11 1  k A  q Ae  q A   (1   )   3 t (A3) qB 11 1  k B  qBe  qB   (1   )   3 t (A5) (A4) pA   pA    P  pA  (A6) P  pA   pA    P  pA  (A7) q Ae   qBe   (A2) k A  1   pA    P  pA   k B  1   pA    P  pA   (A8) (A9) 208 Appendix A: Dimensionless Equations in Chapter   pA  P   z   P   P  8  P (   pA )      1   z  1 0.7  0.5 1   4                (A10)  4   4   at z    n    10   t     (n  1)  n10  150    150         pA  2  0  4   4         z  P   at z     (n  1)  n10   t    (n  1)    10  150 150   2      P   (A11)     pA  2  0  4   4        z  P   at z    n    10   t     (n  1)  n10  150    150      P 1  (A12)     pA   2     4   4  z   P      at z     (n  1)  n10   t    (n  1)    10  150    150    P  0  z  (A13)   P*    e qA  qA   pA    e qB  qB   pB   A p  8 at t   0,  z   (A14) The dimensionless groups in the above dimensionless equations are defined as follows: 150 DM     1    d p2 PL    1  2   3  4  RTq  PL dp L b   A PL RT b   B PL RT (A15) (A16) (A17) (A18) (A19) (A20) 209 Appendix A: Dimensionless Equations in Chapter PH PL   y A0 t P 9  a L 7   10  td PL  60 11   (A21) (A22) (A23) (A24) (A25) Hence the oxygen product purity, recovery and productivity will be a function of dimensionless groups defined in equations A15 –A25; that is,   Oxygen recovery   f (1 ,  ,  ,  ,  ,  ,  ,  ,  , 10 , 11 ) (A26)  Productivity  Oxygen purity For air separation using a specified adsorbent, operating pressures and temperature, the oxygen product purity, recovery and productivity are only a function of five dimensionless groups; the remaining dimensionless groups are dependent on adsorbent properties, feed gas mole fraction and operation pressure, and temperature. Therefore, for air separation using a specific adsorbent it follows that   Oxygen recovery   f (1 ,  ,  ,  , 10 )  Productivity  Oxygen purity (A27) If the oxygen product purity is maximized with respect to the durations of the adsorption and desorption steps, two additional independent equations are generated that can be used to eliminate the dimensionless groups  , 10 . Hence, the oxygen product purity, recovery and productivity mainly will depend on only three dimensionless groups namely 1 ,  ,  . 210 Appendix A: Dimensionless Equations in Chapter   Oxygen recovery   f (1 ,  ,  )  Productivity  Oxygen purity (A28) Therefore, from the above equation, the effect of process parameters, bed length and particle size, can be studied in terms of dimensionless groups 1 and  for a constant value of the other dimensionless group  , which is only a function of the maximum pressure in the cycle. 211 APPENDIX B DIMENSIONLESS FORM OF NONISOTHERMAL MODEL EQUATIONS The dimensionless forms of Equations (5.15), (5.17)-(5.22) and (3.5)-(3.9) are obtained by introducing the following dimensionless variables: P T q q* u tu P T z ; T  ; Tw  w ; xi  i ; xi*  i ; u z  z ; Z  ;  R PR TR TR qs qs uR L L y A y A x x    y A y A P y A T  T        y A  1 A  y A B  (B1)    uz  Z    Pe  Z P Z Z T Z Z  P P u P uP T  P T  P u   T  x A  xB    Z Z T Z  T  (B2) x  2T T T N    u    5i  i   T  Tw  z  PeH Z Z i 1  (B3)  Tw  2Tw T   1   T  Tw     Tw  a   Z TR   (B4) xi Lk   i ( xi*  xi )  i  i  uR (B5) u z   P Z P xi * T xi  N P   i xi T i 1 i (B6) (B7) 212 Appendix B: Dimensionless Form of Non–isothermal Model Equations Initial conditions y A  y A0   P  1  * xA  xA  yA0   xB  xB*  yB   T  T  TR   T Tw   TR  at   0,  Z  (B8) y A u0   ( y A0  y A )  Pe Z uR     T T   7  T   PeH Z  TR   T  Tw  a  TR  L  a1  VR P  2    1  e   (or )  *  uz uz   u0  at Z  0 ; * in section 6.8.2 (B9) y A   0 Z  T   Z  Tw  Ta   PL  P PR  at Z  L Adsorption (section 5.4.2 and section 6.3.2)  (B10) Desorption (section 6.3.2) 213 Appendix B: Dimensionless Form of Non–isothermal Model Equations y A 0 Z T 0 Z T Tw  a TR          L  a2  P  1    1  e VR  at Z  0 (B11) y A   0 Z  T   Z  Tw  Ta   uz   at Z  L (B12) y A   0 Z  T   Z   P 0  Z  u z   at Z  0 (B13) y A   u ( y Ap  y A )  Pe Z   T0  T      T  PeH Z  TR  L   a1 P  2  2  1  e VR  at Z  L (B14) Reverse Pressurization (section 6.8.2)  The dimensionless equations contain the following dimensionless groups: kL i  i uo i   U  bi PR ; bi  bio e RT Rg TR k p PR uR L 214 Appendix B: Dimensionless Form of Non–isothermal Model Equations PL PR P 2  H PR u L Pe  R DL 1  PeH  uR L Kz   qs RTR  PR  Kw 1  L  wuR c pw 2  2ri hi L  wC pwuo  ro2  ri  3  2ro ho L  wC pwuo  ro2  ri   g c pg      H i qs  5i       TR 4  6  2hi L  ru i R 7   g c pg u0 uR 215 APPENDIX C EQUILIBRIUM DATA OF NITROGEN AND OXYGEN ON BINDERLESS 5A ZEOLITE 0.193069 Nitrogen Amount Temperature Pressure adsorbed (K) (bar) (mmol/cc) 0.151855 0.209244 298.15 0.10454 0.38461 0.289946 0.390078 0.23609 0.530086 0.811152 0.457453 0.69988 0.519025 0.616811 0.312302 0.39915 1.074729 1.408884 0.844639 1.111145 0.749906 0.967031 0.525311 0.572481 1.78652 2.200515 1.304989 1.556072 1.104799 1.450567 0.715246 0.882355 2.614234 3.128463 3.62458 4.479461 5.354113 6.206091 6.810736 1.767938 2.036482 2.265822 2.597247 2.87591 3.099844 3.459963 1.828548 2.302822 2.819953 3.317799 3.798363 4.276023 4.802487 1.117743 1.314365 1.519809 1.666559 1.835183 2.092303 2.240618 7.391256 3.641195 5.303996 2.386569 8.005164 8.736448 3.808507 3.972636 5.787878 6.158255 2.59152 2.698084 9.14913 9.586006 4.056964 4.189503 6.553794 7.104245 2.726056 2.885693 10.09892 4.310645 7.531167 8.11777 8.539439 9.068253 9.594301 10.0768 3.03106 3.10353 3.246185 3.353279 3.40032 3.504771 Temperature Pressure (K) (bar) 288.15 Amount adsorbed (mmol/cc) 216 Appendix C: Equilibrium Data of Nitrogen and Oxygen on Binderless 5A zeolite Oxygen Temperature Pressure (K) (bar) 288.15 Amount adsorbed (mmol/cc) 0.20238 0.080372 0.446332 0.657049 Temperature Pressure (K) (bar) 298.15 Amount adsorbed (mmol/cc) 0.20558 0.03312 0.128662 0.195122 0.69184 0.955902 0.136185 0.229263 0.823456 0.974358 0.238521 0.273234 1.229641 1.466121 0.24079 0.294658 1.197497 1.349713 0.287817 0.349425 1.81417 2.543795 0.336387 0.477292 1.57769 2.033438 2.517251 0.358526 0.422813 0.49345 3.047378 3.502918 4.089107 0.538927 0.605908 0.691736 3.018069 3.466835 0.607155 0.648677 4.67412 5.317821 0.809684 0.891829 3.984243 4.463631 0.748372 0.832204 5.987307 6.50907 0.977225 1.044202 4.956362 0.93608 6.979472 1.125507 5.543449 5.970786 1.014029 1.11065 7.50082 7.95484 1.184115 1.201328 6.509554 6.977606 1.204639 1.246 8.484138 8.981845 1.253044 1.362499 7.439229 7.986085 8.520775 1.342837 1.420502 1.506544 9.433929 10.00007 1.400042 1.46104 9.078621 9.555591 10.00214 1.583438 1.640814 1.706001 Single component Langmuir isotherm parameters Adsorbate qs (mol/cc) bo(cc/mol) ∆U (Kcal/mol) Nitrogen (N2) 7.98 x 10-3 0.498 4.912 Oxygen (O2) 6.77 x 10-3 14.533 2.288 217 [...]... also require special care for storage and handling Therefore, these options are not safe and economically viable for personal medical applications of COPD patients In contrast, an oxygen concentrator generates oxygen using ambient air as the feed and continuously delivers oxygen to patients Therefore, these units have a widespread use for home oxygen therapy and portable personal oxygen Further details... life for those people who need oxygen therapy to overcome their lung insufficiency The adsorption columns and the compressor are the two principal contributing factors to the size and weight of an oxygen concentrator designed based on Pressure Swing Adsorption (PSA) technology The principal focus in this study was reduction of the adsorption column size in an oxygen concentrator for personal medical applications. .. swing adsorption VPSA vacuum pressure swing adsorption (or PVSA) URPSA ultra rapid pressure swing adsorption xxix Chapter 1 INTRODUCTION 1.1 Overview of the Research Use of oxygen- enriched streams produced from air spans from classical chemical engineering to biological and medical applications There is a significant demand for portable oxygen supply for personal use by people needing oxygen therapy Medical. .. methodology had also been proposed for the sizing of an oxygen concentrator for personal medical applications In the next step, an experimental set-up was designed with minimum dead volume and pressure drop at the entrance and exit of the column for the experimental verification of the proposed simple two-step PPSA process for reduction of adsorber size in an oxygen concentrator and also to verify the... have similar adsorption capacities on zeolite molecular sieves Consequently, the maximum oxygen purity that can be attained using adsorption based air separation processes is limited to less than 95% Nonetheless, the zeolite adsorbents are typically used for adsorption based oxygen production from air for small scale applications However, because the zeolite adsorbents have a high capacity for the other... processes are still developing for producing high purity oxygen from air streams Since, the invention of synthetic zeolites for air separation, the adsorption based air separation process contribute to more than 30% of the world oxygen demand in comparison to cryogenic distillation processes for small scale applications [Thorogood (1991)] A detailed overview of adsorption based gas separation processes... following section 1.3.1 Adsorption based air separation processes In an adsorption based air separation process for oxygen, the air fractionation into its primary components is based on selective adsorption of N2 over O2 and Ar on zeolite adsorbent materials The preferential adsorption of N2 on zeolites is due to the quadrupole moment of N2 molecules under the influence of a non-uniform charge distribution... enhanced due to particle clustering have been proposed for the size reduction of the oxygen concentrator This study demonstrated that the 3-step VSA process using binderless 5A zeolite and superior Ag-Li-X adsorbent for air separation has a potential to significantly reduce the adsorber size and compressor size in an oxygen concentrator for personal medical applications xi LIST OF FIGURES Figure 1.1: Comparison... tp=6s, ta=3s and td=8 s Thick lines for 5A zeolite and thin lines for Ag-Li-X Solid lines for purity and productivity, and dash lines for recovery and power .191 xix LIST OF TABLES Table 1.1: Comparison of commercially available oxygen therapy options 4 Table 1.2: Commercially available portable oxygen concentrators 26 Table 3.1: Equilibrium isotherm parameters for 5Aa and Li-Ag-X (Li94.2Na0.7Ag1.1-X-1.0)b... Safest way for oxygen and not safe supply Maintenance required Requires extreme care Liquid oxygen Oxygen concentrators (Instant use) Onsite, unlimited supply of oxygen; requires electricity Less maintenance Cryogenic air separation is the most cost effective and efficient technology currently used for production of large quantities of oxygen and nitrogen with high purity and recovery It is based on . ADSORPTION BASED PORTABLE OXYGEN CONCENTRATOR FOR PERSONAL MEDICAL APPLICATIONS VEMULA RAMA RAO . NATIONAL UNIVERSITY OF SINGAPORE 2011 ADSORPTION BASED PORTABLE OXYGEN CONCENTRATOR FOR PERSONAL MEDICAL APPLICATIONS VEMULA RAMA RAO ( M. Tech., Indian. conducted to investigate the performance of the PPSA process for an oxygen concentrator for personal medical applications. The experimental results showed that the maximum oxygen product purity attained