3rd Oxyfuel Combustion Conference Ponferrada, Spain, 9th - 13th September 2013
1-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)
Content
− Introduction − 1-D dynamic CFB simulator − CIUDEN TDP − Model layout for CIUDEN TDP − Description of simulation case − Results − Conclusions
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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
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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)
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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
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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
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Furnace geometry
composition
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ess
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Furnace empirical correlations
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Time dependent variables at furnace
0D − Total solid mass (ash, sand, char, etc.) − Total char mass (for each fuel) 1D − Density profiles for solid materials
− Total solids − Char (6 size fractions)
− Concentrations for gas components − O2, N2, CO2, H2O, SO2, volatiles
− Temperature profiles for − Core − Wall layer − Refractories
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CIUDEN TDP
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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 2012 - 2013 with
different fuel mixtures and operating conditions
Layout at OXY mode for CIUDEN TDP
− Fuel feed to furnace − Flue gas recirculation
− Intrex − Primary feed − Secondary feeds (3)
− O2 feed − Intrex − Primary feed − Secondary feeds (3)
− Boundary temperatures
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loop seal
Fluid bed heat
exchanger
furnace
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flue
gas
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ircu
latio
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Fuel feed
CIUDEN TDP model frame
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Model parameters took from AIR combustion case, without significant tuning.
CIUDEN TDP fuel reactivity simulation inputs: Fuel feed
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) 31.02 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.
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Preliminary test campain 03/2012
CIUDEN TDP fuel reactivity simulation inputs: Gas feeds
Flue gas recirculation flows have been determined based on simulated flue gas composition and measured O2 flows, and concentrations to hot-loop. Iterative method to obtain recirculating flue gas flows
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CIUDEN TDP results: Flue gas O2 and CO2 concentrations
In general, simulated O2 response is acceptable. Still there are some physical unknown behavior in the system. Further study is needed to improve CO2 response. CO2 won’t return to expected steady state (1). CO2 not fully comparable, because of air leakage. - An option to study also air leakage
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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)
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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)
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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.
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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.
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Thank you for your attention! The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n 239188.
