FLOX COAL II. CFD Modelling of Flameless Combustion at Pilot Scale and Full Scale Applications based on Experimental Investigations.

Transcription

1 Institute of Combustion and Power Plant Technology Prof. Dr. techn. G. Scheffknecht FLOX COAL II CFD Modelling of Flameless Combustion at Pilot Scale and Full Scale Applications based on Experimental Investigations Max Weidmann FLOX-COAL II Workshop 14 th May 2014

2 Outline Gaining Experimental Data Experimental Data s Relation to Simulation Results CFD Modelling at IFK CFD Modelling in the FLOX-COAL II Project Conclusion 2

3 GAINING EXPERIMENTAL DATA 3

4 IFK s 500 kw t Test Rig KSVA 500 kw t pulverized coal testing facility (KSVA) Coal feeding level no Furnace diameter: 0.75 m Furnace length: 7.0 m Combustion air preheating up to 200 C O 2 FD/ RG fan Air / CO 2 Air Stack By-passes APH SCR ESP ID fan Bottom ash

5 Applied PC-FLOX Burners 1 st prototype burner 2 nd prototype burner 2 secondary air nozzles on a PCD 1 central primay air / coal annulus 2 secondary air nozzles on a PCD 2 primary air / coal annuli on a PCD 5

6 Reference Operating Point One operating point was chosen to be simulated as reference case It is characterized by Thermal load of ~ 250 kw Secondary air velocities of ~ 100 m/s Secondary air preheating between 130 C and 150 C Air as coal carrier Burner exit after 1.06 m prototype 1 prototype 2 prototype 1 prototype 2 6

7 Applied Measurement Techniques Laser-Doppler-Velocimetry (LDV) In-flame gas concentration measurement by Fourier-Transform-Infrared-Spectroscopy (FTIR) Non-Dispersive-Infrared (NDIR) Paramagnetic Analyzer In-flame gas temperature measurement by suction pyrometer OH* chemiluminescence imaging Total and radiative heat flux measurement Fly ash sampling 7

8 EXPERIMENTAL DATA S RELATION TO SIMULATION RESULTS 8

9 The Quality of Experimental Data Measurements are afflicted with uncertainties which can arise mainly from the amount of evacuated flue gas from the furnace the relation between probe size and jet diameter the probe location Gas temperature measurement by suction pyrometer close to the burner Measurement error estimation is performed 9

10 The Quality of CFD Simulations Real system Model system Simulation results Model derivation Simulation The derived model is simplified. The ideal solution of the model is always approximated. Sampling technique should be considered when comparing the experimental data and simulation results. 10

11 CFD MODELLING AT IFK 11

12 Program Code AIOLOS Turbulent two-phase flow Heat transfer Chemical reactions Development of mathematical models and methods 3D combustion simulation for the solution of industrial problems Validation of the reliability of modelling assumptions at pilot and full scale High level of detail (number of grid points for numerical discretization up to 10 mio cells) Program code optimized for use of high-end super computers Validation of new modelling approaches with experimental data 12

13 Physical Models in AIOLOS Turbulent two-phase flow k,ε-model and Differential Reynolds Stress model Eulerian approach for the gas phase (Lagrangian approach treating the particle phase) Radiative heat transfer (Semi-stochastic Monte-Carlo model) (Flux method) Discrete Ordinates Method (Discrete Transfer model) Reaction model Global reaction scheme of pulverised coal combustion Consideration of particle size distribution NO x post-processor (fuel NO, thermal NO) SO x post-processor 13

14 CFD MODELLING IN THE FLOX- COAL II PROJECT 14

15 CFD Modelling in AIOLOS Advantages of the in-house developed CFD program code AIOLOS: All sub-models accessible No restrictions in performance optimization Adaptable to different simulation platform like super computers or work stations Applied numerical models and solvers Cartesian coordinates Domain decomposition method Finite Volume approach Solution algorithms: SOR and SIP methods SIMPLE pressure correction scheme Applied physical models Discrete Ordinates Method with gas absorptivity by WSGG approach Eddy-Dissipation -Concept k,e-turbulence model AIOLOS and RWTH NOx sub-model 15

16 Validation of the Existing Models Validation of the flow field Velocity profiles compared to the LDV measurements axial profile furnace axis radial profile near burner IFK AIOLOS, ~610k cells IEn FLUENT, ~840k cells 16

17 Validation of the Existing Models Combustion models are highly dependent on the amount of species respected, the implemented turbulence chemistry interaction and the radiative heat transfer Depending on the applied simulation program code different results can be obtained 17

18 Burner Development Using CFD Different designs of the burner to be evaluated: Central coal nozzle (PT1) Split coal nozzle with minimal diameter (PT2 d PAmin ) Split coal nozzle with medium diameter (PT2 d PAmed ) Split coal nozzle with maximum diameter (PT2 d PAmax ) Evaluation of coal consumption, temperature and NOx by the use of a short (2.2m) and coarse mesh (~400k cells) 18

19 Summary Pilot Scale Simulations Comparability of CFD results and measurements results should be considered. Different CFD program codes can give different detailed results due to the modelling approaches Trends are predicted in good accordance Trends of temperature, coal consumption and NOx formation are correctly predicted Final values to be derived from experimental tests Prototype 1 Prototype 2 CO in mg/m 3 6 vol.-% O NOx in mg/m 3 6 vol.-% O Burnout in %

20 Outlook - Simulation of a 720 MW t Boiler High complexity of streams (coal, carrier / combustion / overfire air) Newly designed burners CFD simulation is the ideal tool to assess the potential of the newly developed burners. Adaptations can be implemented and evaluated relatively fast. First step: efficient mesh PA SA PA SA SA PA SA PA 20

21 CONCLUSIONS 21

22 Conclusions Validation against measurement results are essential. The possible errors and uncertainties of the measurements should be considered when comparing CFD and measurement results. In the course of this comparison, the extraction of results from CFD simulation should take the sampling technique into account. Results from CFD simulations can serve as trends. These trends have to confirmed by measurements. CFD simulations are a suitable tool for the development of new burner designs and the assessment of new combustion technologies at bigger scales. 22

23 FLOX-COAL-II Thank you for your attention! 23