Innovative Air Separation Processes for Oxy-Combustion Power Plants

Transcription

1 2 nd International Oxyfuel Combustion Conference OCC2 12 th -16 th September 2011, Capricorn Resort, Yeppoon, Australia Innovative Air Separation Processes for Oxy-Combustion Power Plants by Chao Fu and Truls Gundersen Department of Energy and Process Engineering Norwegian University of Science and Technology () Trondheim, Norway T. Gundersen Slide no. 1

2 Outline of Presentation Brief Introduction Scenario, Focus, Approach & Background Motivation for our Work Carbon Capture, Energy Penalty & Innovation Ideas for significant Energy Savings in Cryogenic Air Separation Units (ASUs) Patent Application filed 27 July 2011, covering 3 new Process Cycles for ASUs New Vapor Compression Cycle Vapor Compression Cycle with Dual-Reboiler Air bypass Cycle (improved Lachmann Cycle) Performance Comparisons for the Cycles Future Work on the new Concepts T. Gundersen Slide no. 2

3 Introduction (1) Scenario Oxygen Production for Super-critical pulverized Coal based Power Plants using Oxy-Combustion as the vehicle for Carbon Capture Current State-of-the-Art Despite significant OPEX & CAPEX, Cryogenic Distillation still is the only Commercially available Technology for large volume O 2 Production (please welcome Adsorption, Membranes and CLC ) Focus and Approach for our Research Reduce considerably Energy Consumption in ASUs while paying attention to Investment Cost, Operability and Complexity Research Methodology Now: Use Rigorous Simulation and Exergy Analysis to identify the largest Thermodynamic Losses in order to save Energy Later: Use Optimization to handle the inherent Economic Trade-offs in these Plants, and to fine-tune our Design Proposals T. Gundersen Slide no. 3

4 Introduction (2) Our Background Developed and applied Process Integration & Pinch Analysis since1983 working closely with the main architects Bodo Linnhoff and Robin Smith (Univ. of Manchester, UK) Also worked closely with leaders in the field of Numerical Optimization ( Mathematical Programming ), primarily Ignacio Grossmann (CMU) and Paul Barton (MIT) Our more recent History The Group went sub-ambient around 2006 focusing on LNG and later ASU and CPU (Compression & Purification Unit) Methodology is based on Pinch Analysis, Exergy Analysis and Optimization (both Math Programming & Stochastic Search) T. Gundersen Slide no. 4

5 Our Scenario for Oxy-Combustion T. Gundersen Slide no. 5

6 Some key Production Figures Air Coal Mill N2 Air Separation Unit O2 Combustor Steam Turbine HRSG Fan Condenser Electricity Generator ESP Ash Limestone Slurry Fan FGD Fan Gypsum LP Compressor CO2 Drier H2O Inerts CO2 Purification Tower HP Compressor CO2 For Storage Net power output: 567 MW Coal feed: 69 kg/s = tons/day O 2 feed: 161 kg/s (excess O 2 : 19%) = tons/day Efficiency penalty related to CO 2 capture: 10.3% points (ASU: 6.6% points) Power to produce O 2 (95 mol%): 124 MW T. Gundersen Slide no. 6

7 Air Coal Power Plant 1393 MW (HHV) Power 560 MW 560 η without CCS = = % Our Research Motivation 124 MW Air O 2 ASU Coal Exhaust Power Plant 1879 MW (HHV) η Net Power total 567 MW = = 40.5% ηasu = = 6.6% pts ηcpu = = 3.7% pts η with CCS = = 1879 H 2 O 30.2% CPU CO 2 69 MW Improving the ASU by 20% gives 4.4% more Power!! or 1.32% points 9/21/2011 T. Gundersen Slide no. 7

8 Efficiency Penalties for CO 2 Capture ASU Air Coal Mill N2 Air Separation Unit O2 Combustor Steam Turbine HRSG Fan Condenser Electricity Generator ESP Ash Limestone Slurry Fan FGD Fan Gypsum CPU LP Compressor CO2 Drier H2O Inerts CO2 Purification Tower HP Compressor CO2 For Storage Specs on Oxygen: ~ 95 mol%, 1.2 bar Efficiency Penalty (%) , ,6 2,0 1,4 CPU ASU Base case Theoretical Case T. Gundersen Slide no. 8

9 A Double-Column Distillation Cycle An Implementation of the Classical Linde Design 9/21/2011 T. Gundersen Slide no. 9

10 The Double-Column Cycle Our Reference Case 4.9 bar 1.3 bar 5.3 bar The purity of O 2 : 95 mol% The theoretical minimum power consumption vs. the actual value: vs (kwh/kgo 2 ) a factor of 4.7!! T. Gundersen Slide no. 10

11 Distribution of Exergy Losses Exergy losses [%] Coolers: 17.6 Compressor: Valves: 2.7 Heat exchanger: 3.0 Condenser/reboiler: 6.3 LP: 14.6 HP: AU1 AU2 AU3 AU4 AU5 AU6 AU1: The main air compressor AU2: The pre-purification unit AU3: The main heat exchanger AU4:The air distillation system AU5: The tail N 2 turbine AU6: The waste N 2 Largest Sources of Exergy Losses Distillation System (28.2%) LP Column Main Air Compressor (38.4%) Interstage Coolers Compression Process itself T. Gundersen Slide no. 11

12 Some Energy reducing Actions Reduce Irreversibilities in the LP Column: Use distributed Reboiling ( reversible distillation) A Dual-Reboiler saves a lot of energy without going crazy on Investment Cost and Plant Complexity Utilize the Compression Heat: Integrate with the Steam Cycle Adiabatic Compression (a kind of Heat Pumping ) Regeneration of Molecular Sieves Moderate amount of Heat Preheat the Recycled Flue Gas and/or Oxygen T. Gundersen Slide no. 12

13 Reducing Compressor Work κ 1 1 p κ out C = p in η is pin W mc T Simplified Equation for Ideal Gas indicates: Increase Compressor Efficiency Responsibility of the Manufacturers Reduce Inlet Temperature Beyond CW requires Refrigeration, thus more Work Reduce Pressure Ratio Limited by Condenser/Reboiler Match, but there are ways around it.!! Reduce Mass Flowrate through the Compressor Do we really need to compress the Oxygen? Our Inventions are based on the last two: Reducing Compressor Flowrate and Pressure Ratio T. Gundersen Slide no. 13

14 Key Features of Air Separation Units Some rather obvious Observations: The main Challenge is to provide liquid Reflux (Nitrogen) to the Distillation Column(s) Heat Exchangers (multi-stream) are very tightly designed, not much Scope for Improvements Distillation is easier at lower Pressures 95 mol% and 1.2 bar O 2 is sufficient in Oxy-combustion Argon only comes into play at higher O 2 Purities Modesty and Respect in proposing new ASUs: The Problem has been extensively studied for Decades Vast number of Scientific Journal Papers & Patents Strong Industrial Players in the Market Excellent Researchers have been involved T. Gundersen Slide no. 14

15 Conventional Cycle with Dual-Reboiler A4-2 A4-1 A4-3 Condenser2 A3-1 A3-2 A3-3 A7-1 Extracted N 2 N 2 waste O 2 Impurities A4-4 A7-3 A5-2 A1-3 PPU MHE A1-4 Condenser1 HP A7-2 A2-1 A2-2 A2-3 LP Reboiler2 Reboiler1 A5-1 A1-5 A1-6 A1-2 A1-1 MAC Air A0 Specific Power Consumption: kwh/kgo 2 9/21/2011 T. Gundersen Slide no. 15

16 Effect of Distributed Reboiling Feed line Feed line y (N2) Equilibrium line Operating line y (N2) Equilibrium line Operating line x (N 2 ) x (N 2 ) Reference cycle Dual-Reboiler cycle Exergy losses, kw Compression process Distillation system Specific power consumption, kwh/kgo Power consumption has been reduced by 10% T. Gundersen Slide no. 16

17 A new Vapor Compression Cycle Specific Power Consumption: kwh/kgo T. Gundersen Slide no. 17

18 The new Cycle with a Single Column Specific Power Consumption: kwh/kgo T. Gundersen Slide no. 18

19 The new Cycle with Dual Reboiler Specific Power Consumption: kwh/kgo T. Gundersen Slide no. 19

20 Performance Comparison Process 1 Conventional double column cycle Process 2 Conventional cycle with dual-reboiler Process 3 Vapor compression cycle with a single column Process 4 Vapor compression cycle with dual-reboiler O 2 purity, % Specification power Consumption, kwh/kgo 2 Power savings Ref. Case % % % OPEX is down; what about CAPEX?? T. Gundersen Slide no. 20

21 Future Work Consider higher Purity Oxygen Production Consider Production of higher Pressure O 2 Are we loosing the Advantage of the Inventions? Optimize TAC (CAPEX vs. OPEX) Quantify the Effects of lower Pressure in the PPU Consider various Heating & Cooling Integration Options between the Sections of the Power Plant CPU Compression Heat integrated with Steam Cycle Use CPU Compression Heat for MolSieve Regeneration Integration between the ASU and the CPU Fine-tune the Cycles using Optimization T. Gundersen Slide no. 21

22 Acknowledgements Technology Transfer As Professor Dag Eimer, Telemark Institute of Technology, Tel-Tek, and D-IDE AS Faculty of Engineering Science and Technology at, Trondheim T. Gundersen Slide no. 22

23 International CCS Research Centre Budget 47 M over 8 years > 20 PhDs and > 10 Post.docs BIGCCS BIGCCS Director: Mona J. Mølnvik BIGCCS Board Chair: Nils A. Røkke SINTEF Energy Research Coordinator: Truls Gundersen T. Gundersen Slide no. 23