Modelling and Simulation of a Coal-fired Supercritical Power Plant Integrated to a CO 2 Capture Plant

Transcription

1 Energy Technology and Innovation Initiative (ETII) FACULTY OF ENGINEERING UNIVERSITY OF LEEDS Modelling and Simulation of a Coal-fired Supercritical Power Plant Integrated to a CO 2 Capture Plant Elvis O. Agbonghae, Kevin J. Hughes, Derek B. Ingham, Lin Ma, Mohamed Pourkashanian 11/7/2014

2 Introduction (Process Flow Diagram of the Integrated Process) Boiler Steam Cycle Flue Gas pre-treatment CO2 Capture CO2 Compression 11/7/2014 2

3 Introduction (Key Features of the Power Plant) Supercritical once through boiler with a SCR between the economiser and air-heater 2 ppmv NH 3 slip in the SCR Single reheat steam conditions: 241 bar/593 o C/593 o C (3500 psig/1100 o F/1100 o F) Cold reheat pressure: 45.2 bar Steam Cycle Condenser pressure: 0.07 bar Saturation temperature is ~ 38 o C Dedicated turbine (BFWPs) is used to drive the boiler feed water pumps Steam extracted from the IP-LP crossover is used to run BFWPs turbine BFWPs turbine isentropic efficiency is 80% Steam Turbines Efficiencies HP turbine isentropic efficiency is 83.72% IP turbine isentropic efficiency is 88.76% LP turbine isentropic efficiency is 92.56% Generator Efficiency is 98.5% 11/7/2014 3

4 Aim and Objectives 1. To model and simulate an integrated process comprising a supercritical PC-power plant, a CO 2 capture plant and a CO 2 compression train within a single platform (Aspen Plus) 2. To quantifying the impacts of using different types of coal on the overall performance of the integrated process based on simulations. High volatile bituminous coal (Illinois No. 6) Sub-bituminous coal (Montana Rosebud) Lignite coal (North Dakota) 3. To quantify the impacts of important operating parameters of the CO 2 capture plant on the overall performance of the integrated process. Lean MEA solution CO 2 loading and liquid/gas mass ratio Lean MEA solution temperature (absorber inlet) Flue gas temperature (absorber inlet) CO 2 capture level 4

5 An Overview of the Methodology The complete integrated process was modelled with Aspen Plus, V8.4, and dedicated hierarchy blocks were used for sub-processes. Coal-fired boiler, which includes a simple Model for SCR. Steam turbine cycle. a simple model for FGD. CO 2 capture. CO 2 Compression. The CO 2 capture plant was optimally designed based on rate-based calculations. Electrolyte-NRTL model adopted for the liquid phase of the VLE. PC-SAFT equation of state adopted for the gas phase of the VLE. HETPs calculated based on mass transfer theory. The column diameter and height of the absorbers and stripper arrived at systematically using innovative method. CO 2 compression modelled based on parameters in a 2010 US DOE report. PC-SAFT equation of state used for CO 2 Compression Multi-stage Compression with inter-stage coolers and KODs (the sixth stage is a pump) 11/7/2014 5

6 Coal Feed and Combustion Air required (Combustion Calculations) Coal Feed required Combustion Air required 11/7/2014 6

7 Coal Properties Proximate Analysis: As-Received (%) Illinois No. 6 Montana Rosebud North Dakota Moisture Volatile Matter Ash Fixed Carbon Total Ultimate Analysis As-Received C S H H2O N O Ash Cl TOTAL Heating Value As-Received HHV (Btu/Ib) LHV (Btu/Ib) HHV (kj/kg) LHV (kj/kg) /7/2014 Agbonghae E. O. 7

8 Energy Technology and Innovation Initiative (ETII) FACULTY OF ENGINEERING UNIVERSITY OF LEEDS 11/7/2014 Agbonghae E. O. 8

9 Process Modelling Approach The most rigorous and the most complex. Aspen Plus Model! Fig 2: Approaches for modelling reactive absorption processes (Kenig et al., 2001) Reference: Kenig, E. Y.; Schneider, R.; Gorak, A. Reactive absorption: Optimal process design via optimal modelling. Chem. Eng. Sci. 2001, 56,

10 Aspen Plus Model (Key features) Rate-based approach Reaction kinetics Reactions in Bulk liquid Reactions in Liquid Film No concentration gradient in bulk phases Film discretization Electrolyte present only in the liquid phase Charge balance (electrolytes) Equilibrium at V/L Interphase Rigorous VLE Model (Electrolyte-NRTL)

11 Model Validation (Specific Reboiler duty vs L/G) Sp. Reb Duty (MJ/kg CO 2 ) Exp (A.1) Model (A.1) Exp (A..2) Model (A.2) Exp (A.3) Model (A.3) Exp (A.4) Model (A.4) Pilot plant data from Notz et al. (2012). Experiment sets A.1, A.2 and A.3 correspond to gasfired condition. Experiment set A.4 corresponds to coalfired condition L/G (kg/kg) Reference: Notz, R.; Mangalapally, H. P.; Hasse, H. Post combustion CO 2 capture by reactive absorption: Pilot plant description and results of systematic studies with MEA. Int. J. Greenhouse Gas Control 2012, 6,

12 Model Validation (Profile Results, Experiment set A.4) 70 Absorber 120 Stripper Temperature ( o C) Temperature ( o C) Exp (L/G = 2.0 ) Model (L/G = 2.0) Exp (L/G = 2.6) Model (L/G = 2.6) Exp (L/G = 2.8) Model (L/G = 2.8) Exp (L/G = 3.3) Model (L/G = 3.3) Exp (L/G = 3.6) Model (L/G = 3.6) Exp (L/G = 3.9 Model (L/G = 3.9) Exp (L/G = 4.5) Model (L/G = 4.5) Packing height (m) Packing height (m)

13 Optimal Design of the CO 2 Capture plant The lean amine mass flow rate can be calculated as follows: F Lean Amine = F FGx CO2 Ψ α Rich α Lean M Amine M CO ω Amine ω Amine + α Lean What combination of lean loading, rich loading, liquid flowrate, and stripper pressure will optimise the following? Absorber and Stripper diameters Absorber and stripper heights Reboiler Duty Condenser Duty Pumps Duty Heat Exchanger Area Interested in the design method? A Summary of the design method will be given in the second paper presentation. Details of the design method can be found in our recent journal paper. Agbonghae, E. O.; Hughes, K. J.; Ingham, D. B.; Ma, L.; Pourkashanian, M. Optimal Process Design of Commercial-scale Amine-based CO 2 Capture Plants. Ind. Eng. Chem. Res DOI: /ie /7/2014 Agbonghae E. O. 13

14 Summary of the Optimum Design Results for the Absorber and Stripper Columns Coal: Illinois No. 6 (Supercritical) Flue Gas Flowrate (kg/s) Optimum Lean CO 2 loading (mol/mol) 0.18 Optimum Liquid/Gas Ratio (kg/kg) 2.74 Absorber Number of Absorber 2 Absorber Packing Mellapak 250Y Diameter (m) Optimum Height (m) Stripper Number of Stripper 1 Packing Mellapak 250Y Diameter (m) Optimum Height (m) Specific Reboiler Duty (MJ/kg CO 2 ) 3.69 A lean CO 2 loading of 0.20 mol/mol with a liquid/gas ratio of 2.93 kg/kg is an alternative. 11/7/

15 Energy Technology and Innovation Initiative (ETII) FACULTY OF ENGINEERING UNIVERSITY OF LEEDS 11/7/2014 Agbonghae E. O. 15

16 Optimum Lean CO 2 Loading Reboiler Duty (MW th ) Reboiler Duty (Illinois No. 6) Reboiler Duty (Montana Rosebud) Reboiler Duty (North Dakota) L/G (Illinois No. 6) L/G (Montana Rosebud) L/G (North Dakota) L/G (kg/kg) Net Plant Efficiency (%) with CO 2 Capture only (Illinois No. 6) with CO 2 Capture only (Montana Rosebud) with CO 2 Capture only (North Dakota) with CO 2 Capture & Compression (Illinois No. 6) with CO 2 Capture & Compression (Montana Rosebud) with CO 2 Capture & Compression (North Dakota) Lean CO 2 Loading (mol/mol) Lean CO 2 Loading (mol/mol) 11/7/

17 Optimum Lean CO 2 Loading (Continuation) Pumps Duty (kw e ) Lean Pumps (Illinois No. 6) Lean Pumps (Montana Rosebud) Lean Pumps (North Dakota) Rich Pumps (Illinois No. 6) Rich Pumps (Montana Rosebud) Rich Pumps (North Dakota) L/R Heat Exchanger Duty (MW th ) Exchanger Duty (Illinois No. 6) Exchanger Duty (Montana Rosebud) Exchanger Duty (North Dakota) 1.35x x x x x x10 5 L/R Heat Exchanger Area (m 2 ) Lean CO 2 Loading (mol/mol) /7/ Exchanger Area (Illinois No. 6) Exchanger Area (Montana Rosebud) Exchanger Area (North Dakota) Lean CO 2 Loading (mol/mol) 1.05x x10 5

18 Impact of Flue Gas Temperature on Performance Sp. Reb Duty (Illinois No. 6) Sp. Reb Duty (Montana Rosebud) Sp. Reb Duty (North Dakota) Reboiler Duty (Illinois No. 6) Reboiler Duty (Montana Rosebud) Reboiler Duty (North Dakota) CO 2 Capture Efficiency (Illinois No. 6) CO 2 Capture Efficiency (Montana Rosebud) CO 2 Capture Efficiency (North Dakota) Sp. Reb Duty (MJ/kg CO 2 ) Reboiler Duty (MW th ) CO 2 Capture Efficiency (%) Inlet Temperature of Flue Gas ( o C) Inlet Temperature of Flue Gas ( o C) 11/7/

19 Impact of Lean Amine Temperature on Performance Sp. Reb Duty (Illinois No. 6) Sp. Reb Duty (Montana Rosebud) Sp. Reb Duty (North Dakota) CO 2 Capture Efficiency (Illinois No. 6) CO 2 Capture Efficiency (Montana Rosebud) CO 2 Capture Efficiency (North Dakota) Sp. Reb Duty (MJ/kg CO 2 ) CO 2 Capture Efficiency (%) Inlet Temperature of Lean Amine ( o C) Inlet Temperature of Lean Amine ( o C) 11/7/

20 Impact of CO 2 Capture Level L/G (Illinois No. 6) L/G (Montana Rosebud) L/G (North Dakota) Sp. Reb Duty (Illinois No. 6) Sp. Reb Duty (Montana Rosebud) Sp. Reb Duty (North Dakota) 3.72 L/G (kg/kg) Sp. Reb Duty (MJ/kg CO 2 ) CO 2 Capture Level (%) CO 2 Capture Level (%) 11/7/

21 Summary: Overall Energy Performance Illinois No. 6 Montana Rosebud North Dakota Fuel heat input, HHV (MWth) Steam turbine thermal input, (MWth) Steam turbine power, without steam extraction (MWe) Steam turbine power, with steam extraction (MWe) Power plant auxiliary loads (MWe) Other auxiliary loads (MWe), estimated based on a US DOE report CO 2 capture plant auxiliary loads (MWe) CO 2 Compression loads (MWe) Power output without CO 2 capture and compression (MWe) Power output with CO 2 capture only (MWe) Power output with CO 2 capture and compression (MWe) Efficiency without CO 2 capture and compression (%), HHV Efficiency with CO 2 capture only (%), HHV Efficiency with CO 2 capture and compression (%), HHV US DOE "Cost and Performance Baseline for Fossil Energy Plants. Volume 1: Bituminous Coal and Natural Gas to Electricity," US Department of Energy, Revision 2, November /7/

22 Conclusions The design of the CO 2 capture plant can easily handle different coal types without operational issues. Fractional approach to flooding velocity was fairly constant. No flooding! The performance order of the different types of coal investigated is as follows: Illinois No. 6 (bituminous) > Montana Rosebud (sub-bituminous) > North Dakota (lignite) The Optimum lean CO 2 loading lies between 0.18 and 0.22 for all the coal types investigated. A lean CO 2 loading of 0.18 was adopted gave about the same performance! The temperature of the lean MEA solution at the absorber inlet has minimal effect on the overall performance. There is no need to over-cool! The flue gas temperature up to 45 o C has a very slight effect on the overall performance. However, its effect becomes slightly more pronounced above 45 o C. Do not over-cool! Specific reboiler duty increases slightly with capture level up to about 90% and it increases sharply above 90%. The same L/G per CO 2 capture level can be used for 75% to 90% CO 2 capture level with minimal loss of performance. This is a plus for power plant flexibility! 11/7/

23 Energy Technology and Innovation Initiative (ETII) FACULTY OF ENGINEERING UNIVERSITY OF LEEDS 11/7/