STEADY STATE SIMULATION AND EXERGY ANALYSIS OF SUPERCRITICAL COAL-FIRED POWER PLANT (SCPP) WITH CO 2 CAPTURE

Transcription

1 10 th European Conference on Coal Research and its Application () STEADY STATE SIMULATION AND EXERGY ANALYSIS OF SUPERCRITICAL COAL-FIRED POWER PLANT (SCPP) WITH CO 2 CAPTURE Akeem K Olaleye Process and Energy Systems Engineering Group Department of Chemical Engineering School of Engineering University of Hull Supervisors: Dr. Meihong Wang Gregg Kelsall (BF2RA, UK)

2 CONTENT 1 Background and Motivation SCPP with CO 2 Capture Process Simulation and Integration Exergy Analysis Results and Discussion Conclusions

3 Background and Motivation 2 Coal-fired power plants play a vital role in meeting energy demands Coal-fired power plants are the single largest sources of CO 2 emissions UK Electricity generation by source Global CO 2 Emission Other 2.5% Gas 28.0% Renewables 11.3% Nuclear 19.0% Coal 39.0% (Data Source: DECC,2012) (Data Source: Sustainable aviation CO 2 Roadmap )

4 Background and Motivation 3 Power Generation with CO 2 Capture Post Combustion Technology Air Combustion Power & Heat Flue gas ~14% CO 2 CO 2 Capture CO 2 Fossil Fuel Pre Combustion Technology Gasification O 2 /steam Syngas 20-40% CO 2 CO 2 Capture H 2 Combustion Oxy-Combustion Technology Power & Heat CO 2 CO 2 Compression & Transport for Storage Oxy- Combustion Power & Heat Flue gas >80% CO 2 CO 2 Capture CO 2 Fossil Fuel-fired Power Generation with CCS

5 SCPP with CO 2 Capture 4 Supercritical? Subcritical Coal-fired power plant: Typical coal-fired (subcritical) power plant is based on the rankine cycle. Subcritical plant efficiencies : 30-38% Operating pressure: <22.1MPa economizer Boiler super heater HP, LP Turbines Supercritical Coal-fired power plant : Supercritical is based on an increase in the main steam parameters (T& P), giving rise to a supercritical rankine cycle pump condenser Basic (subcritical) rankine cycles Operating pressure: >22.1MPa There is no generation of steam bubbles within the water, because the pressure is above the "critical pressure" at which steam bubbles can form. Supercritical technology can lead to an increase in efficiency (about 42%) supercritical rankine cycles

6 SCPP with CO 2 Capture 5 Integration of Increase efficiency with emission reduction

7 SCPP with CO 2 Capture 6 Exergy Analysis is useful for system optimization: Exergy Analysis? Need for power plant emission reduction Location of Exergy Destruction Prioritise system/ components for efficiency improvement Compare components or Systems to make Design decisions Need for improvement in efficiency Improvement in components design

8 Process Simulation & Integration 7 SCOPE Model of a reference SCPP Integration of the SCPP model with CO 2 Capture model Estimate Exergy of Individual streams in Aspen Plus (EXERGYML, EXERGYMS and EXERGYFL) Conventional Exergy Analysis to estimate the quantity and location of exergy destruction and losses Advanced Exergy Analysis to Identify optimum option for system Integration Case studies on Exergy Destruction in SCPP with CO 2 Capture REFERENCE SCPP Greenfield coal-fired supercritical steam plant The steam turbine conditions correspond to 24.1MPa/593 C Net plant power, after consideration of the auxiliary power load, is 550 MWe. The plant operates with an estimated HHV efficiency of 39.1 %

9 Process Simulation & Integration 8 FGD & CO 2 Capture Coal mill & Boiler Condensate/Feedwater Heating Turbine & Steam Extraction Hierarchical Model Development in Aspen Plus

10 Process Simulation and Integration 9 Boiler Parameters (NETL, 2007) Description Value Steam cycle (MPa/ o C/ o C) 24.1/593/593 BOILER Hierarchy As received coal (kg/s) Coal Heating value, HHV (MJ/kg) Condenser Pressure (mmhg) 50.8 Boiler Efficiency (%) 89.0 Cooling water to Condenser ( o C) 16.0 Cooling water to Condenser ( o C) 27.0 Ash Distribution, Fly/Bottom ash (%) 98.4 Excess air (%) 20.0

11 Process Simulation & Integration 10 Turbine Parameters (NETL, 2007) Parameters Value HP Turbine efficiency (%) 90.0 IP Turbine efficiency (%) 92.0 LP Turbine efficiency (%) 94.0 TURBINE & Steam Extraction Hierarchy Generator efficiency (%) 98.4 Feedwater Heating Train

12 Process Simulation & Integration 11 CO 2 Capture Hierarchy Design Parameters for the scale-up of the PCC model Description Value Flue gas mass flow rate (kg/s) Flue gas composition (CO 2 ) Flue gas composition (N 2 ) Flue gas composition (H 2 O) CO 2 Capture level (%) 90.0 Estimated flowrate of CO 2 Capture (kg/s) Required MEA flowrate (kg/s) Estimated Lean solvent flow rate (kg/s) Estimated Rich solvent flow rate (kg/s) Lean MEA mass fraction (wt. %) Lean MEA CO 2 loading (mol CO 2 /mol MEA) 0.29 Key Process Parameters of the PCC model Parameter Absorber Desorber Calculation type Rate-based Rate-based Type of packing Sulzer BX 500 Sulzer BX 500 Total Height of Packing (m) Diameter of column (m) Column Number 3 1 No. of Equilibrium stages Operating Pressure (bar)

13 Exergy Analysis 12 Conventional Exergy Analysis Conventional exergy analysis identifies: Main Parameter for Exergy Calculation Parameters Value The location The Magnitude, and The sources of thermodynamic inefficiencies in a thermal system. Environment Temperature (K) Environment Pressure (bar) Fuel Input Exergy factor 1.02 The exergy for the overall SCPP system can be written as Ε F,total = Ε P,total + Ε D,total + Ε L,total (1) whereas for the nth component, Ε F,n = Ε P,n + Ε D,n (2) The exergy efficiency of the nth component ε n = Ε P,n Ε F,n = 1 Ε D,n Ε F,n (3) The exergy destruction ratio of the nth component y D,n = Ε D,n Ε F,total (4) The exergy loss ratio is, y L = Ε L,total Ε F,total (5) Parameter for Estimating Chemical Exergy of MEA Species Parameters (DGAQFM) Value MEA MEAH + (KJ/mol) MEACOO - (KJ/mol) (DGAQFM = Gibbs free energy of formation) Key Ε F= Exergy of fuel Ε P= Exergy of product Ε D= Exergy destroyed Ε L= Exergy loss

14 Exergy Analysis 13 Advanced Exergy Analysis Evaluates: The interaction among components of the overall system, and the real potential for improving a system component and the overall system un = Unavoidable av = Avoidable ex = Exogenous en = Endogenous Splitting the exergy destruction into un/av en/ex Parts

15 Exergy Analysis Advanced Exergy Analysis Conditions for splitting the Exergy Destruction Real (R) Theoretical (T) Unavoidable (U) The splitting combinations can be estimated thus: un, = Ε Ε D,n Ε D,n Ε D,n Ε D,n un,ex = Ε av,ex = Ε av,ex = Ε P,n(Ε D,n/Ε P,n) un (6) D,n un un,en Ε D,n D,n en un,en Ε D,n D,n ex un,ex Ε D,n (7) (8) (9) (Ε D,n/Ε P,n) un,ε P,n en en, and Ε P,n are first determined from the unavoidable and SCPPhybrid Fuel Saving Potential,n R E F,total = E F,total Once-through boiler subsystem for Advanced Exergy Analysis T,n E F,total R where E F,total = fuel exergy consumption of the SCPP under Real condition T,n = SCPP-Hybrid only the component of interest operates Theoretically E F,total Assumptions/Conditions for splitting the Exergy Destruction Components Real (R) Theoretical (TH) Unavoidable (UN) Boiler Subsystem FURN α airfuel = 1.02 α airfuel = 1.02 α airfuel = 1.02 η boiler = 0.89 η boiler = 1.0 η boiler = 1.0 AIR-PRT ΔT min = ΔT min = 0.0 ΔT min = 65.0 SSH ΔT min = ΔT min = 0.0 ΔT min = PSH ΔT min = ΔT min = 0.0 ΔT min = RHT ΔT min = ΔT min = 0.0 ΔT min = ECON ΔT min = ΔT min = 0.0 ΔT min = 50.0 Turbine Subsystem VHP-TURB η isent = 0.90 η isent = 1.0 η isent = 0.92 VHP-TRB2 η isent = 0.89 η isent = 1.0 η isent = 0.96 HP-TURB η isent = 0.87 η isent = 1.0 η isent = 0.98 IP-TURB η isent = 0.92 η isent = 1.0 η isent = 0.96 LP1-TURB η isent = 0.90 η isent = 1.0 η isent = 0.98 LP-TURB2 η isent = 0.94 η isent = 1.0 η isent = 0.96 LP-TURB3 η isent = 0.97 η isent = 1.0 η isent = 0.94 LP-TURB4 η isent = 0.81 η isent = 1.0 η isent = 0.91 BFP-TRB η isent = 0.83 η isent = 1.0 η isent = 0.86 COND ΔT min = 10.0 ΔT min = 0.0 ΔT min = 6.0 BF-PUMP η isent = 0.88 η isent = 1.0 η isent = 0.93 Feedwater Heating Subsystem FWH-1 ΔT min = 2.8 ΔT min = 0.0 ΔT min = 1.5 FWH-2 ΔT min = 2.8 ΔT min = 0.0 ΔT min =1.5 FWH-3 ΔT min = 3.1 ΔT min = 0.0 ΔT min =1.7 FWH-4 ΔT min = 6.3 ΔT min = 0.0 ΔT min = 4.2 DEAERATOR ΔT min = 1.0 ΔT min = 0.0 ΔT min = 0.3 BS-PUMP η isent = 0.87 η isent = 1.0 η isent = 0.91 FWH-5 ΔT min = 5.3 ΔT min = 0.0 ΔT min = 4.3 FWH-6 ΔT min = ΔT min = 0.0 ΔT min = 65.0 FWH-7 ΔT min = 3.0 ΔT min = 0.0 ΔT min = 65.0 FWH-8 ΔT min = 2.8 ΔT min = 0.0 ΔT min =

16 Results and Discussion 15 Results Conventional Exergy Analysis Components E F,n (MW) E P,n (MW) E D,n (MW) y D,n (%) Ɛ n (%) Components E F,n (MW) E P,n (MW) E D,n (MW) y D,n (%) Ɛ n (%) Boiler Subsystem Feedwater Heating Subsystem COALMILL FWH AIR-PRHT FWH DECOMP FWH BURN FWH SSH DEAERATOR RHT BS-PUMP SSH FWH PSH FWH PSH FWH ECON FWH BFP Turbine Subsystem FGD Subsystem VHP-TURB BGS Filter VHP-TRB ID-FAN HP-TURB Desulphurizer IP-TURB MEA-Based CO 2 Capture Subsystem LP1-TURB FG-Cooler LP-TURB BLOWER LP-TURB ABSRBR LP-TURB DESRBR BFP-TRB PUMP COND T-COOLER MHEX Loss (MEA)

17 Results and Discussion 16 Results Conventional Exergy Analysis 3.93% 7.11% SCPP Exergy Destruction and Losses (No CO 2 capture) 1.34% 8.58% 79.04% Boiler Subsytem Turbine Subsystem Feedwater Heating Subsystem FGD Subsystem Losses 3.36% 1.81% 4.14% 4.06% Exergy Destruction in once-through boiler subsystem 2.00% 4.69% 0.88% 3.06% 0.03% 75.97% COALMILL AIR-PRHT DECOMP BURN SSH-1 RHT SSH2 PSH1 PSH2 ECON Exergy Destruction in Turbine subsystem 13.43% 4.29% 2.68% 9.44% 2.02% 1.38% 0.80% 51.77% 8.30% 5.89% VHP-TURB VHP-TRB2 HP-TURB IP-TURB LP1-TURB LP-TURB2 LP-TURB3 LP-TURB4 BFP-TRB COND 7.05% 13.80% 6.02% 12.04% 11.79% Feedwater Heating subsystem 6.76% 11.79% 3.13% 14.15% 12.14% 1.34% FWH-1 FWH-2 FWH-3 FWH-4 DEAERATOR BS-PUMP FWH-5 FWH-6 FWH-7 FWH-8 BF-PUMP Distribution of Exergy losses and Destruction in the SCPP Subsystems

18 Results and Discussion 17 Results Conventional Exergy Analysis Exergy Destruction in MEA-Based CO 2 Capture Exergy Destruction in SCPP with Base Case CO 2 Capture 0.11% 2.59% 5.24% 2.25% 14.60% 13.13% FG-Cooler BLOWER ABSRBR 1.02% 23.59% Boiler Subsytem Turbine Subsystem DESRBR PUMP 3.00% Feedwater Heating Subsystem FGD Subsystem 35.90% 26.17% T-COOLER MHEX Loss 5.43% 66.95% MEA-Based CO2 Capture Subsystem Distribution of Exergy Destruction in (a) CO 2 Capture subsystems and (b) SCPP with CO2 Capture

19 Results and Discussion 18 Case Study: CO 2 Capture Absorber Intercooling Configuration (AIC) Split-flow Configuration (SF)

20 Results and Discussion 19 Case Study: CO 2 Capture Performance Indicator of the SCPP and the CO 2 Capture Cases Description Performance Summary Reference SCPP SCPP- Base Case CO 2 Capture SCPP-AIC SCPP-SF SCPP (AIC+SF) Total (steam turbine) power (MW) Auxiliary load (MW) Gross plant power (MW) Generator loss (MW) Net power output (Mw e ) Unit efficiency, HHV (%) CO 2 Capture Performance Summary Reboiler Duty (MW) Energy penalty (%) Efficiency penalty (%) Exergetic Performance Exergy Destruction, y D (%) Exergy Losses, E L (%) Exergetic efficiency, Ɛ (%)

21 Results and Discussion 20 Case Study: CO 2 Capture Case 1: Exergy Destruction in SCPP with Absorber Intercooling 21.40% 1.05% 3.09% 5.59% 68.87% Case 2: Exergy Destruction in SCPP with Splitflow 21.06% Case 3: Exergy Destruction in SCPP with Absorber Intercooling and Split-flow 19.36% 1.06% 3.10% 1.08% 3.17% 5.61% 5.73% 69.17% 70.66% Exergy Destruction in SCPP with three cases of MEA-Based CO 2 Capture

22 Results and Discussion 21 Results Advanced Exergy Analysis Fuel Saving potential & Advanced Exergy Destruction of the SCPP Components E T,n F,tot ΔE*,n F,tot E T D,n E R D,n E un D,n E av D,n E en D,n E ex D,n E en D,n E ex D,n E un,en D,n E av,en D,n E av,ex D,n E un,ex D,n Boiler subsytem FURN AIR-PRT SSH PSH RHT ECON Turbine subsystem VHP-TURB VHP-TRB HP-TURB IP-TURB LP1-TURB LP-TURB LP-TURB LP-TURB BFP-TRB COND Feedwater heating subsystem FWH FWH FWH FWH DEAERATOR BS-PUMP FWH FWH BF-PUMP FWH FWH FGD Subsystem BGS Filter ID-FAN Desulphurizer Endo/Exo-genous Exergy destruction Subsystems Exo(%) Endo(%) Boiler Turbine Feedwater heaters Subsystems Avoidable/Unavoidable Exergy destruction Subsystems av (%) un (%) Boiler Turbine Feedwater heaters Fuel Saving potential Value (MW) Boiler Turbine Feedwater heaters FGD 6.03

23 Results and Discussion 22 Results Advanced Exergy Analysis (a) (b) (c) Splitting the Exergy destruction of Boiler Subsystem into (a) AV/UN (b) EN and EX (c) AV,EN and UN,EN (a) (c) (b) Splitting the Exergy destruction of Turbine Subsystem into (a) AV/UN (b) EN and EX (c) AV,EN and UN,EN

24 Results and Discussion 23 Results Advanced Exergy Analysis (a) (b) (c) Splitting the exergy destruction of Feedwater Subsystem into (a) AV/UN (b) EN and EX (c) AV,EN and UN,EN

25 Conclusions 24 Conventional Exergy Analysis Boiler Subsystem: The most exergy destruction occurs in the furnace combustion chamber (76%). Turbine Subsystem: The maximum exergy destruction occurs in the steam condenser (52%). Feedwater Heating: The HP feedwater heaters accounts for most of the exergy destruction (43.65%). CO 2 Capture: The absorber (26%) and the desorber (36%) are the main sources of exergy destruction. Advanced Exergy Analysis Fuel saving potential: The turbine subsystem are almost double that of the boiler subsystem. The feedwater heater almost has no influence on fuel consumption Exo/Endo/-genous exergy destruction: Most exergy destruction of SCPP components is endogenous (over 70%). Un/Avoidable exergy destruction: 30 50% of exergy destruction in the turbine subsystem is generally avoidable.

26 Thanks 25

27 Acknowledgement 26 Biomass and Fossil Fuel Research Alliance (BF2RA) EU FP7 Marie Curie Multiphase Flow Measurement Research Group, South East University, Nanjing, China

28 Questions 27