Dynamic Simulation of a CFB Boiler System

Transcription

1 71th IEA-FBC Technical Meeting Dynamic Simulation of a CFB Boiler System , Seoul, Korea Sang Min CHOI Thermal Engineering Lab Thermal Engineering Laboratory KAIST

2 Introduction

3 Dynamic Performance Prediction of a CFB Boiler System Necessity of a Dynamic Model <External environment changes> Load variation and a change of operating conditions ü ü Dynamically changes mass, energy flow and properties Control system running Dynamic performance prediction is required Modeling Considerations in CFB boiler with drum ü Operation and Performance of a CFB Boiler are determined by SG loop and GS loop ü These loops has to be considered for WS loop SG loop ü exact performance prediction This model considers gas flow, solid flow and water-steam flow 3

4 Model description

5 Modeling description (1) Dynamic sub-models of a 340MWe CFB Boiler Dynamic sub-models Solid-gas circulation loop model <Furnace: 1, 2> <Return part: 3,4,5> Water-steam circulation loop model (drum-downcoomer-riser tube) <2, 2 > Heat exchanger model (Convective heat exchanger) <6,7,8,9,10> The entire CFB boiler is divided into a finite number of dynamic model (Solid-gas circulation loop model, water-steam circulation loop model, heat exchanger model) Relevant theories, Numerical approach and physical conservation rules are applied in each dynamic sub-model. 5

6 ü Each side is connected in terms of heat and mass flow ü Mass-heat flow, heat transfer and heat reaction are dynamically calculated Modeling description (2) Basic concept of heat and mass flow in a discretized heat exchanger + = + : in-out mass flow, mass transfer, generated mass by reaction = + Ø Energy balance: + = + : in-out heat flow, heat transfer, reaction heat Governing equation ( ruf ) rf + = t x S 6 1-D unsteady and no diffusion term

7 Modeling description (3) Transport Phenomena Modules <Solid-gas circulation loop> <Water-steam circulation loop> Hydrodynamics of fluidized bed Solid side behavior Coal combustion reaction Bubbling fluidized Bed (Bubble vs. Emulsion) Core-Annuls model (Core vs. Annulus) Fragmentation, Attrition Solid volume fraction Solid-gas mass transfer Solid circulation rate Devolatilization, Volatile combustion Char combustion, CO combustion Numerical approach ü Convergence condition: Mass and Temperature < 10 ü ü Mass and heat balance of drum and Drum loop model downcommer-riser (Astrom, 1999) Drum level Discharged steam flow rate <Heat transfer coefficient> Furnace Cluster renewal model Cyclone, Loopseal Fitting data from operation data Heat exchanger tube bank Tube bank heat transfer Calculation domain: Furnace (150 2), Heat exchanger (80 1), Downcommer-riser (20 1), Drum and Return part (0-D) Time step : 0.5 sec 7

8 Model Develop and Dynamic Simulation Process Model Develop Process Develop sub-models (Each component) ü Solid-gas circulation loop ü Water-steam circulation loop ü Heat exchanger model Open loop model (CFB Boiler System) ü Each sub model is connected according to mass and heat flow (Model scope) Closed loop model (CFB Boiler System) ü Controller is applied to open loop model Dynamic Simulation Process Transient response of dynamic sub-models Check each model validation! Dynamic behavior of total boiler system (Open loop) Check convergence of total boiler system! Dynamic behavior of total boiler system (Closed loop) Check control! Check with measured data! Operation simulation 8 according to load level

9 Dynamic results

10 Transient response of sub-models (1) Solid-gas temperaure [ C] % Fuel supply (Input condition) Furnace temperature Cyclone temperature +40 C C sec Time [sec] Fuel supply [kg/s] Water temperature [deg C] Heat duty (Input condition) Temperature % C sec Time [sec] Heat duty [MW] Steam Termperature [ C] % Solid-gas circulation loop 24 Heat duty (Input condition) Temperature C sec Time [sec] = Heat duty [MW] 10 Economiz =

11 Transient response of sub-models (1) Water-steam circulation loop Heat duty Steam flow rate Drum pressure Circulation rate ü Validation of water-steam circulation loop model was performed by Astrom model. (small scale 50MWe) ü Astrom model can be applied to a large scale boiler. ü This results show the dynamic behavior of target boiler in this study. ü Dynamic behavior of this boiler is similar to that of the boiler in Astrom. Quality Water level 11

12 Open loop model (2) ü Dynamic sub-models are integrated according to the mass flow and the heat transfer as described in the CFB boiler system of the power plant. 12

13 Open loop model (2) % Fuel Supply Air Flow ü Require controller Furnace Cyclone Mass Flow rate [kg/s] O2 concentration [%] Time [sec] Steam Feed water Time [sec] Water- Steam Temperature [ C] Drum Pressure [MPa] Time [sec] P. SH Drum S. ECO Drum pressure Water Level Time [sec] Water Level [m] ü Disturbance: Fuel supply ü Solid-gas temp. ü Oxygen concentration ü Water steam temp. ü Controller is required in drum pressure, water level and steam mass flow rate. 13

14 Closed loop model (1) ü In order to simulate real operation situation, controller is applied to the open loop model ü Several crucially important parameters are chosen in this model. 14

15 Closed loop model (2) Load [MWe] % 950 sec Drum pressure Set point Fuel supply -0.8MPa -6.3kg/s Time [1,000 sec] Oxygen concentration [%] Oxygen con. Set point Air flow Air flow rate [kg/s] Mass flow rate [kg/s] 795 sec sec Water Level -45 sec 300 Set Level ü It is 796 checked sec that all control variables 200 is controlled to set values ü Response time of drum pressure is larger than other parameters, -1 0 so this 1 parameter 2 dominates 3 4 the 5 6 dynamic behavior of the total CFB boiler system Time [1,000 sec] Time [1,000 sec] Steam Feed Water Set Steam -40 kg/s Water Level [m] 15

16 Operation simulation (1) Operation case (trial operation ü Input Condition: Load data (Set value of drum pressure, steam flow rate) 16

17 Operation simulation (2) Gas Temperature [ C] Tube wall temperature [ C] Fuel supply [ton/hr] FUR out CYC out RH2 in RH1 out SH1 out ECO1 out CYC out RH2 int RH1 out SH1 out ECO1 out time [hr] (a) Gas temperature time [hr] (c) Tube wall temperature Measured data simulation SH3 SH2 SH1 SH3 SH2 SH time 12 [hr] (e) Fuel supply Water-steam temperature [ C] Mass flow [ton/hr] Drum pressure [Mpa] SH3 SH2 SH1 CYC ECO2 SH3 SH2 SH1 CYC ECO (b) Water-steam temperautre time [hr] time [hr] (d) Drum pressure Steam Feed water Steam (f) Mass flow rate time [hr] 17

18 Operation simulation (3) Temperature [ C] RH2 (Gas) ECO2 (Gas) ECO1 (Water-steam) Unmeasured data simulation Boiler circulation rate Spary water flow (c) Temperature time [hr] 18

19 Conclusion Dynamic Simulation of a CFB Boiler System

20 Conclusion ü Through this study, the CFB boiler dynamic model, which is composed of discretized dynamic sub-models considering the water-steam flow, the gas-solid flow and the tube wall, is developed. ü This model is based on physical phenomena, heat and mass balance and numerical approach. Especially, the interaction between the solid-gas circulation loop and the water-steam circulation loop is carefully modeled due to this circulation loops significantly determine the performance of the CFB boiler with the drum loop. ü Model was validated as following process; 1) Each dynamic sub-model (Time constant and reference), 2) Open loop model (Convergence of total boiler system), 3) Closed loop model (Controlled variables), 4) Operation simulation (Measured data in real plant) This model can simulate a real situation relatively well even with its limitations ü Although current model is developed to a particular CFB boiler, the modeling approach and the simulation strategy can be extended to the other CFB boiler system with the drum loop. 20

21 CFB Boiler Dynamic Simulator Thermal Engineering Lab

22 CFB Boiler Dynamic Simulator Ø The dynamic model is developed to a simulator Ø The dynamic simulator is developed by MFC programing in C++ 22

23 CFB Boiler Dynamic Simulator Ø This program can simulate the dynamic behavior of a CFB boiler system according to its load data or operating conditions. Ø Ø Ø Ø These conditions can be defined as the disturbance according to time by user. This program is available to Run/Freeze This program can show visualization :Graph, Result window and Save files This simulation calculates results for a certain time frame, and then it resumes the calculations on a preferred day. Ø Simulation can start from any steady-state, and apply any disturbance. 23

24 CFB Boiler Dynamic Simulator : Main Window, 2: Graph, 3: Time, furnace error, drum error., 4: Input load, 5: Set value, control variables, Manipulated variables 6: Manipulation button 24

25 Input window Furnace and back pass geometry Drum loop geometry Convective HE. geometry Furnace and back pass geometry Drum loop geometry Convective HE. geometry Wall type HE. geometry Coal, Limestone, Sand, Air condition Heat transfer condition and Node Wall type HE. geometry Coal, Limestone, Sand, Air condition Heat transfer condition and Node 25

26 Controller window Ø Ø 1. Controller On: Apply controller, PID value have to input 2. Controller Off: Not apply controller, Input manual have to input 26

27 Simulation Method Ø Ø Ø Simulation method: 1) Auto input, 2) Manual input Auto input can be defined by load data according to time in the text window by user Manual input can be defined by set value and boundary conditions in the set value window Auto input Manual input 27

28 Simulation of CASE 1 28

29 Simulation Results Water-Steam temperature Solid-gas temperature Wall temperature Water-Steam temperature Solid-gas temperature Wall temperature Material Flow Material Flow Drum loop Water-Steam Circulation Water-Steam pressure Water-Steam pressure Gas velocity Water-steam velocity Heat duty Gas velocity Water-steam velocity Heat duty 29