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What Can Possibly Be New and Exciting About Pressure Swing

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What Can Possibly Be New and Exciting About Pressure Swing Bench-Scale Development and Testing of Rapid PSA for CO2 Capture NETL Meeting, Pittsburg, PA, May 22, 2012 Overall Project Objectives design, develop and demonstrate a bench-scale process for the efficient and cost effective separation of CO2 from flue gas using Pressure Swing Adsorption (PSA) goal to reduce energy consumption, capital costs, and environmental burdens with novel PSA cycle/flowsheet designs applicable to both large (500-1000 MW) and small (5- 50 MW) capacity power plants, and industries with 10 to 100 times less CO2 production Process simulations and experiments, CFDs and experiments and complete flowsheet analyses being used for demonstrating and validating the concepts. PSA Technology Advantages established, very large scale technology for other applications needs no steam or water; only electricity tolerant to trace contaminants; possibly with use of guard or layered beds zeolite adsorbent commercial and widely available increase in COE lower than other capture technologies beds can be installed under a parking lot PSA Technology Challenges energy intensive, but better than today’s amines; possibly overcome by novel designs today, very large beds required implies large pressure drop more power; possibly overcome by structured adsorbents and faster cycling large footprint; possibly overcome by underground installation and faster cycling smaller beds high capitol cost; possibly overcome by faster cycling smaller beds Key PSA Technology Project Challenge although a commercial tri-sieve zeolite could be used today in an efficient PSA cycle, it would only minimize to some extent the pressure drop issues, but not the adsorbent attrition and mass transfer issues so, the key challenge of this project is to develop a structured adsorbent around an efficient PSA cycle that exhibits a high enough packing density to allow the fastest possible cycling rate ( smallest possible beds), while improving pressure drop and mass transfer issues and eliminating attrition issues Today, I would like to answer four questions: How did we get to this point? Where are we now? Where are we going? How are we going to get there? How does pressure swing adsorption work? Aluminosilicate A-Zeolite Molecular Sieve Crystals Aluminosilicate A-Zeolite Molecular Sieve Cage Aluminosilicate A-Zeolite Molecular Sieve Cage Aluminosilicate X Zeolite Molecular Sieve Cage Aluminosilicate Zeolite Molecular Sieve Pellets Adsorption Isotherms for CO2 and N2 on 13X Zeolite 3.0 CO2 @ T = 50 °C CO2 @ T = 75 °C N2 @ T = 25 °C N2 @ T = 50 °C 0.4 2.0 T = 25 °C N2 0.3 T = 50 °C CO2 0.2 n [mol/kg] 0.1 n [mol/kg] 1.0 0.0 0 20 40 60 80 100 Pressure [kPa] N2 0.0 0 5 10 15 20 Pressure [kPa] Pressure and Thermal Swing Adsorption Concepts Based on the Adsorption Isotherm PSA T1 ∆ q TSA T2 > T1 T2 TSA/PSA TSA: long heating and cooling times =>large beds PSA: short pressurizing and blowdown times => small beds Amount Adsorbed, Amount q (mol/kg) Pressure (atm) Behavior of Typical PSA Process Approach to Periodic State Twin-Bed Silica Gel Air Dryer Operating a Simple 4-Step PSA Cycle Same behavior for nearly all PSA systems no matter the application. Periodic PSA Process Behavior Typical loading in a PSA column, for example, at the end of the adsorption and desorption (or regeneration) steps, showing the working capacity of the bed. The loading in the column slowly builds up with time, is never completely regenerated, and after many cycles attains a periodic state. Traditional PSA Cycle Steps six basic steps for conventional PSA pressurization, e.g., with feed or light product high pressure feed with light product production depressurization or blowdown (cocurrent or countercurrent to the feed) desorption at low pressure with light product purge (light reflux), evacuation or both pressure equalization between beds high pressure rinse with heavy product (purge or heavy reflux) following feed Typical Cycle Sequencing for a Four-Bed PSA Hydrogen Purification Plant These cycles can become very complicated, with the state-of-the-art PSA hydrogen purification plant now operating 16 interconnected beds! PSA: UOP Polybed Hydrogen Production Unit How did we get to this point? 1-Bed PSA Experiments to Validate the Dynamic Adsorption Process Simulator VS Typical Cycle Steps for PSA Operation Snapshot of Multi-Bed PSA System CO2 depleted product T P P P P P P H I P L I H H ↓ ↓ L ↓ ↓ PI PL PI PH β α CO rich product Flue gas T 2 Feed Heavy Equalization Counter-current Light Equalization Pressurization Reflux blow down Reflux 1-Bed PSA System Complex PSA Cycle Schedule Analysis 1-Bed PSA System 12 3.8 Liter PT-4 11 To Mass 3.8 Liter PT-5 Spec 3W-3 10 3.8 Liter PT-6 9 18 T/C-9 8 Experimental Setup PT-2 7 1 L-F-1 T/C-8 Pressure Relief 21 • Breakthrough runs Liter Valve 2 T/C-7 L-F-2 T/C-6 • Pure gas cycling Light (L) 3 and L-F-3 F-7 Heavy (H) Component T/C-5 Feed Light Train • PSA cycles (any 4 Product H-F-4 3W-4 T/C-4 3W-5 To Mass Heavy Spec Product possible combination 5 H-F-5 T/C-3 F-8 of cycle steps) T/C-2 6 H-F-6 Pressure Relief Valve 21 Liter PT-1 16 Flow Meter Calibration Vent 17 PT-3 3W-2 15 To Mass Spec 3W-1 T/C-1 Regeneration 16 14 Vent Vent 13 3.8 Liter PT-7 CO2 Breakthrough Experiments on 13X Zeolite 1.0 30% CO2 0.8 70% He 0.6 Flow = 10 SLPM CO2,o y Pressure = 25 psia CO2/ 0.4 y Temperature = 25oC • Mass Transfer 0.2 Coefficient Experiment Model Determination 0.0 1.0 0 20 40 60 80 100 120 • Isotherm 40% CO2 time(min) Validation 0.8 60% He 0.6 Flow = 10 SLPM CO2,o y Pressure = 25 psia CO2/ 0.4 y Temperature = 25oC 0.2 Experiment Model 0.0 0 20 40 60 80 100 120 time(min) N2 Breakthrough Experiments on 13X Zeolite 1.0 20% N2 0.8 80% He 0.6 Flow = 2.55 SLPM N2,o y Pressure = 25 psia N2/ y 0.4 Temperature = 25oC • Mass Transfer 0.2 Coefficient Experiment Model Determination 0.0 1.0 0 5 10 15 20 25 30 • Isotherm 30% N time(min) 2 Validation 0.8 70% He 0.6 Flow = 1.67 SLPM N2,o y Pressure = 25 psia N2/ y 0.4 Temperature = 25oC 0.2 Experiment Model 0.0 0 5 10 15 20 25 30 time(min) Two-Step CO2 and N2 Cycling Experiments P PH H ↑ ↓ P PL L Pure CO2 or N2 Feed Pure CO2 or N2 Effluent Pressurization Counter-Current Blowdown Information Obtained a) Validation of Single Component Isotherms b) Validation Adsorption/Desorption Mass Transfer Coefficients c) Determination of Valve Cv CO2 Cycling Experiments of 13X Zeolite 300 Periodic State 1 Cycle 250 15 sec Desorption 200 150 180 sec Pressure (kPa) Adsorption 100 ExperimentExperiment ModelModel 50 0 60 120 180 240 300 360 420 480 540 600 Cycle time (sec) N2 Cycling Experiments of 13X Zeolite 350 Periodic State Longer Cycle 300 250 30 sec Desorption 200 150 Pressure (kPa) 120 sec 100 Adsorption 50 Experiment Model 0 0 50 100 150 200 250 300 350 400 450 Cycle time (sec) Pure Gas Cycling Experiments on 13X Zeolite Heavy Product Flow Prediction 35 CO2 Cycling Periodic State (1-cycle) 30 25 20 Experiment 15 10 Model 5 Heavy Product Flow (SLPM) Flow Product Heavy 0 0 5 10 15 20 Cycle time (sec) Pure Gas Cycling Experiments on 13X Zeolite Heavy Product Flow Prediction 35 N2 Cycling Periodic State (1-cycle) 30 25 20 Experiment 15 10 Model 5 Heavy Product Flow (SLPM) Flow Product Heavy 0 0 5 10 15 20 Cycle time (sec) Cycle Translation from Multi-Bed to 1-Bed PSA Operation 1-Bed Experimental System CO2 depleted product Pure N2 T T P P P P P P H I P L I H H ↓ ↓ L ↓ ↓ PI PL PI PH Pure CO2 Flue gas T CO2 rich product 15% CO2 85% N2 Feed Heavy Equalization Counter-Current Light Equalization Light Reflux Depressurization Reflux Product Pressurization Typical 1-Bed PSA Experiment Pressure Profile Matching 160 140 120 Model Experiment 100 80 60 Pressure (kPa) 40 20 0 0 100 200 300 400 500 600 700 800 900 Cycle time (sec) 1-Bed PSA Experiment Temperature Profile Prediction 50 50 10% 49% 40 40 C) C) Model o o 30 30 T ( T ( 20 20 Experiment 10 10 50 0 100 200 300 400 500 600 700 800 900 50 0 100 200 300 400 500 600 700 800 900 Cycle time (sec) 23% Cycle time (sec) 62% 40 40 C) C) o o 30 30 T ( T ( 20 20 10 10 50 0 100 200 300 400 500 600 700 800 900 50 0 100 200 300 400 500 600 700 800 900 Cycle time (sec) 36% Cycle time (sec) 75% 40 40 C) C) o 30 o 30 T ( T ( 20 20 10 10 0 100 200 300 400 500 600 700 800 900 0 100 200 300 400 500 600 700 800 900 Cycle time (sec) Cycle time (sec) 1-Bed PSA System: Experimental Results Run CO2 Feed Feed High Π T Cycle CO2 CO2 N2 N2 o Concentration Throughput Pressure (PH) (PH / PL) ( C) Time Purity Recovery Purity Recovery in N2 (%) (L STP/hr/kg) (psia) (sec) (%) (%) (%) (%) 1 15 150 22.3 37 25.2 900 94.1 90.9 93.7 96.0 2 15 150 22.1 44 24.3 900 93.9 92.9 95.1 95.7 3 15 150 22.4 45 25.2 900 91.5 93.2 95.6 94.5 4 15 150 22.0 51 23.6 900 95.9 90.3 93.3 97.2 numerous cycle schedules studied with different relative step times of individual cycle steps CO2 recoveries and purities > 90% various combinations of process parameters and cycle steps giving high CO2 recoveries and purities • understanding of interplay between them becoming crucial Mathematical Modeling and Process Simulation Dynamic Adsorption Process Simulator (DAPS) • multiple absorbent layers and multiple columns • column pressure drop • entering and exiting flows defined by constant flow, valve equations, or choke flow approaches (isentropic, fanno, etc) • valve equations with time dependent coefficients for rotary valves • interaction with other processes: cabin, distillation units, etc • simultaneous feed, exit, pressure varying steps thru multiple ports • ability to handle large P ratios and v’s associated with deep vacuum systems •
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