1-D dynamic modeling of oxygen fired coal combustion in 30MWth CFB boiler

Transcription

1 3rd Oxyfuel Combustion Conference Ponferrada, Spain, 9th - 13th September D dynamic modeling of oxygen fired coal combustion in 30MWth CFB boiler Jouni Ritvanen*, Jenö Kovacs **, Abraham Fernández *** and Timo Hyppänen * * Lappeenranta University of Technology ** Foster Wheeler Energia Oy *** Fundacion Ciudad de la Energia (CIUDEN)

2 Content Introduction 1-D dynamic CFB simulator CIUDEN TDP Model layout for CIUDEN TDP Description of simulation case Results Conclusions

3 Introduction Current demand is to control the fluidised bed systems with high efficiency also in transient situations Renewable energy sources Wind Solar The role of the dynamic modelling of CFBs with higher efficiencies and in oxy-combustion is growing rapidly In this study the dynamics of OXY combustion with flue gas recirculation at CIUDEN TDP CFB is presented

4 Model frame CFB Boiler main components divided to fully mixed 1D elements Furnace Cyclone(s) / solid separator(s) Solids return channel Fluid bed heat exchanger Main boundary conditions Air/gas fluidizing Fuel feed Surface temperatures at Furnace and fluid bed heat exchanger walls Internal superheater(s)

5 Transient modeling Matlab/Simulink software Pre- and post-prosessing using Matlab Simulations using Simulink Simulink is using explicit iteration scheme Time derivatives for the variables will be got from mass- and energy balances At the CFB there are too many time dependent variables to be simulated and standard Simulink signal-block method is not convenient. At the Simulink the C-coded S-function option is used Option to include dynamic CFB hot-loop model to water/steam-path simulator

6 Main model features Core-annulus model with wall layer Wall layer transfers only energy Semi-empirical hyrdodynamics Solid density profiles based on Johnsson and Leckner (1995) Density at exit region Profile parameters Solid circulation rate Semi-empirical reaction rates Energy diffusion between elements Fully mixed 1D elements

7 Furnace geometry refractory thickness refractory share composition

8 Furnace empirical correlations

9 Time dependent variables at furnace 0D 1D Total solid mass (ash, sand, char, etc.) Total char mass (for each fuel) Density profiles for solid materials Total solids Char (6 size fractions) Concentrations for gas components O 2, N 2, CO 2, H 2 O, SO 2, volatiles Temperature profiles for Core Wall layer Refractories

10 CIUDEN TDP Field instrumentation Process data for determining the model input parameters and mass & energy balances CIUDEN TDP 30 MWth air/oxygen-fired CFB combustor Over 100 test balances during with different fuel mixtures and operating conditions

11 Layout at OXY mode for CIUDEN TDP Fuel feed to furnace Flue gas recirculation Intrex Primary feed Secondary feeds (3) O 2 feed Intrex Primary feed Secondary feeds (3) Boundary temperatures furnace separator loop seal flue gas recirculation Fuel feed Fluid bed heat exchanger

12 CIUDEN TDP model frame Model parameters took from AIR combustion case, without significant tuning

13 CIUDEN TDP fuel reactivity simulation inputs: Fuel feed Preliminary test campain 03/2012 Fuel data. Components Anthracite Ultimate analysis (wt%,dry) C 62.9 H 1.9 N 0.75 O 2.52 S 1.01 Proximate analysis (wt%) Moisture 6.7 Ash (dry basis) Volatiles (dry basis) 6.2 Heat value (MJ/kg) LHV (as received) 21.3 Fuel feed is got from Coal silo weight measurements and analysing the rate of change. Rate of change is correlated to convey belt rotation rate measurement

14 CIUDEN TDP fuel reactivity simulation inputs: Gas feeds Flue gas recirculation flows have been determined based on simulated flue gas composition and measured O 2 flows, and concentrations to hot-loop. Iterative method to obtain recirculating flue gas flows

15 CIUDEN TDP results: Flue gas O 2 and CO 2 concentrations In general, simulated O 2 response is acceptable. Still there are some physical unknown behavior in the system. Further study is needed to improve CO 2 response. CO 2 won t return to expected steady state (1). CO 2 not fully comparable, because of air leakage. - An option to study also air leakage

16 CIUDEN TDP results: Bottom bed and 6.8m temperatures Temperatures at the bottom bed and at 6.8m before marked disturbances has excellent correspondence between measurement and simulation. After disturbances, model fails to capture physical behavior of the system. The system won t return to expected steady state (1)

17 CIUDEN TDP results: Furnace top and flue gas temperatures Temperature at the furnace top before marked disturbances has excellent correspondence between measurement and simulation. After disturbances, model fails to capture physical behavior of the system. The system won t return to expected steady state (1)

18 CIUDEN TDP results: Heat transfer from hot-loop Heat transfer before marked disturbances has excellent correspondence between measurement and simulation. After disturbances, model can still capture most of the physical behaviors of the system. Measured heat transfer returns to expected steady state

19 Conclusions The fuel reactivity test at CIUDEN TPD was successfully studied with 1D dynamic CFB tool In general, simulating the CIUDEN TDP, most of the physical behaviors could be captured There are still some open questions, why the system thermal balance won t behave like expected. Steady state at the beginning? External solid circulation and local material fractions? Comparing the experiments and simulation results, the 1D dynamic simulation tool was verified (more cases is needed to confirm validation), and this simulation tool can be used to study OXY-combustion in different plant layouts. This tool can be used to study OXY-combustion controls and control strategies, to find out highest plant efficiency also in transient situation

20 Thank you for your attention! The research leading to these results has received funding from the European Community s Seventh Framework Programme (FP7/ ) under grant agreement n jouni.ritvanen@lut.fi