Comparison of numerical model-CECO.ppt [兼容模式]

COMPARISON OF NUMERICAL SIMULATIONCOMPARISON OF NUMERICAL SIMULATION METHOD OF COAL GASIFICATION

煤气化数值模拟方法的比较煤气化数值模拟方法的比较

ChangzhengChangzheng EngineeringEngineering Co.,LimitedCo.,LimitedChangzhengChangzheng Engineering Engineering Co.,LimitedCo.,Limited航天长征化学工程股份有限公司航天长征化学工程股份有限公司

中国运载火箭技术研究院中国运载火箭技术研究院China Academy of Launch vehicle TechnologyChina Academy of Launch vehicle Technology

航天工程公司航天工程公司

CONTENTSCONTENTS

The main content of this project is to study numerical simulation methods of the process of coal gasification and compare the different modelsprocess of coal gasification and compare the different models.

1.�Literature�Survey�and�Models�Summary1.�Literature�Survey�and�Models�Summary

2.�Simulation�and�Models�Comparison�2.�Simulation�and�Models�Comparison�



SIMULATION�AND�MODELS�COMPARISONSIMULATION�AND�MODELS�COMPARISON

1.�Physical�and�chemical�process�of�coal�gasification�1.�Physical�and�chemical�process�of�coal�gasification�2 R ti M d l2 R ti M d l2.�Reaction�Models2.�Reaction�Models

3.�Reaction�Rate�Parameters3.�Reaction�Rate�Parameters

4 V l tili ti4 V l tili ti M d lM d l4.�Volatilization4.�Volatilization Model�Model�

5.�Particle�Model5.�Particle�Model

6 T b l M d l6 T b l M d l6.�Turbulence�Model�6.�Turbulence�Model�

7.�Radiation��Model7.�Radiation��Model



LITERATURE�SURVEYLITERATURE�SURVEY

Have retrieved a large number of literatures in CNKI ,SCI, EI database and Japanese NEDO website ,Japanese CRIEPI reports , and finally 50 literatures which consists of 40 references and 10 reduced references are selected.

Language Quantity classification Quantity Aera Quantity Age Quantity Article-level Quantity

Chinese 9 Jonrnal papers 29 Japan 14 1950 1 SCI 22

English 30 Report 6 China 14 1970 1 EI 6

Japanese 11 Web page 6 America 11 1980 2 Chinese 5p p gCore Journals

Conference papers 5 Australia

5 1990 6

Dissertation 3 Taiwan 2 2000 23

Books 1 Italy 1 2010 11

Korea 1 other 6

England 1

Other 1



1.�Physical�and�chemical�process�of�coal�gasification�1.�Physical�and�chemical�process�of�coal�gasification�

Volatilization

Oxidation reaction of carbon particles

Gasification reaction of carbon particles

Gas reaction

Two phase flow of solid particles and gas. Two phase flow of solid particles and gas.

Heat transfer Mainly for the radiation and convection heat

t f

Volatile

Gasification

transfer

In additionThe change of carbon particles size andThe change of carbon particles size and

shape; The deposition and dissolve of ash ;The interactions of particles



2.�Reaction�Models2.�Reaction�Models

Equilibrium model assume that all reactionsEquilibrium model assume that all reactions will eventually be balance, and it can easily predict gas composition and temperature through solving the equilibrium equations. But h ilib i i diffi l hi i i

Equilibrium model

the equilibrium is difficult to achieve in practice so the model can not fully reflect performance in the actual process of coal gasification.

Dynamic model Dynamics model considers the specific dynamic behavior of the reaction It includesdynamic behavior of the reaction . It includes zero dimensional model, one-dimensional model, small room model and multidimensional model. And multidimensional model is usually used in coal gasification simulation.



The reaction models of carbon particles included:

N�order�reaction�model�N�order�reaction�model� LL--H�reaction�modelH�reaction�model

In a high pressure condition, the gasification gas easily gathered around carbon particles to prevent the effect of the gasification reaction. Using the N order model tends to estimate reaction velocity

i l I d t b tt fl t thi ki d f h L H

Random�Pore�reaction�model�Random�Pore�reaction�model�

excessively. In order to better reflect this kind of phenomenon, L-H reaction model can be used.

The model can consider both the reaction constant and the particle structure parameters for different kinds of carbon.



Effective�rate�modelEffective�rate�model

As temperatures rise, main factors dominatingreaction rate move in the "Chemical Reaction",“Pore Diffusion", and “Bulk Diffusion” orderly.Therefore, besides the influence of reaction rateTherefore, besides the influence of reaction rateitself , the reaction rate of carbon particlegasification also will be affected by thesurrounding concentration diffusion (bulkdiffusion) and Pore diffusion. So effectivediffusion) and Pore diffusion. So effectivereaction rate should be the minimum of the three,or using the Effectiveness Factor to integratereaction rate of the three.

Bulk Diffusion Pore diffusion



3.�Reaction�Rate�Parameters3.�Reaction�Rate�Parameters

Summarizing the reaction rates of several literatures, including heterogeneousreaction between solid C with O2 ,H2O, and CO, and homogeneous gasreactions totally eight reactionsreactions, totally eight reactions.

We found great difference, that might because of the various using conditions,as shown in the tables.

3 sets of parameters were selected for the following work.

Literature Pressure Coal Gasifier Type

Article 3 5.9MPa Bitumite Industrial opposed multibuener coal-water slurry entrainerd flow pp ygasifier, The four hedgeing nozzle

Article 10,2 2.0MPa Bitumite A two-stage entrained flow coal gasifier, Dry powder,The four tangential nozzle

Article 13 2 4MPa Lignite coal water slurry entrainer flow gasifier The four tangential nozzle



Article 13 2.4MPa Lignite coal-water slurry entrainer flow gasifier, The four tangential nozzle

Article 17 2.0MPa Bitumite Dry powder, The four tangential nozzle

4.�Volatilization4.�Volatilization Model�Model�

a) Transient evaporation model

b) Simple Reaction Rate Kinetic model

c) One step reaction modelc) One-step reaction model

d）Kobayashi model Reaction Parameter

A ( 1/s) E (kJ/mol)

One-step reaction 2.021x103 3.11x107

Kobayashi model 2x105 1.046x108



5.�Particle�Model5.�Particle�Model

1. Euler-Euler two-phase flow modelWhile this method works and the load is low, but the method is rarely

used in coal gasification. The possible reason might be that the pulverizedcoal gasification is similar to combustion of diesel particle simulation ,somost researchers continue the simulation method.

2. Euler-Lagrange modelBasically most literatures use this method.



6.�Turbulence�Model�6.�Turbulence�Model�

1.RANSIncluding k－epsilon，Realizable k－epsilon, k－omega，SST, RSM etc.Including k epsilon，Realizable k epsilon, k omega，SST, RSM etc.

Throughout most of the literatures, the standard k - epsilon is a betterchoice.

2.LES model In recent years, with the improvement of computer performance, the

usage of LES calculation increased considerablyusage of LES calculation increased considerably



7.�Radiation��Model7.�Radiation��Model

1.P1Generally literatures choose P1 radiation model, this is mainly affectedy y

by the traditional internal engine combustion simulation. Since there areCO2, CH4, and water vapor with high absorption, gas optical thickness isbigger. So using P1 is a reasonable choice.

2.DOIn general the DO model calculation load is high, but it is easy to

consider gray body and absorption spectrum. g y y p p



SIMULATION�AND�MODELS�COMPARISONSIMULATION�AND�MODELS�COMPARISON

1.�Introduction�of�the�object�model1.�Introduction�of�the�object�model

i f hi f h3.�Comparison�of�turbulence�model3.�Comparison�of�turbulence�model2.�Comparison�of�mesh2.�Comparison�of�mesh

5 Comparison of combustion reaction model5 Comparison of combustion reaction model

4.�Comparison�of�4.�Comparison�of�particleparticle--phase�phase�ModelModel

5.�Comparison�of�combustion�reaction�model5.�Comparison�of�combustion�reaction�model



1.�Introduction�of�The�Object�Model1.�Introduction�of�The�Object�Model

A literature with detailed simulation and experimental data are selected as anobject model That is Japanese CRIEPI 2T/d scale gasifier

jj

object model. That is Japanese CRIEPI 2T/d scale gasifier.



The model have four entrances in combustion chamber, and two entrancesff fin reduction chamber. Different components of gas and particles get into the

furnace with different flow rate , and exported from the upper outlet.

C l I lCoal Inlet

Coal Inlet

OutletCoal Inlet

Air Inlet

Air Inlet

Outlet



2.�Comparison�of�Mesh2.�Comparison�of�Mesh

In the mesh comparison part, the cold flow field without reaction andparticle phase was calculated. Specific settings are shown as table 1, eight setsof mesh information are shown as table 2.

T bl 2 G idMesh name Mesh representation Number of

elmentsNumber of nodes

total01 Hex 1126140 1092816

totalless Overall thinning hex 666560 644860

number Unit

Material air

Entrance velocity in A - 28.68 m/s

Table1 Calculation conditions Table2 Grid

totalless Overall thinning hex 666560 644860

addcircle Circumferential encryptedhex

2356380 2300576

addhig Axial encrypted hex 1748940 1698624

yA cross section Entrance velocity in B -B cross section

33.63 m/s

Relative static pressure at outlet

0 Pa

addrad Radial encrypted hex 1999980 1962336

addbou Radial encrypted with add boundary layer addition hex

1999980 1962336

at outletWall No Slip Wall

Turbulence Model Realizable k-ε

totaltra1 Tetra 1209227 385023

totaltra2 Tetra encrypted 4568968 1115953



total01 Totalless

addhig



addcircle

addrad addbou

totaltra1 totaltra2



totaltra2

C i d l i l i di ib i f h i d liComparing and analyzing velocity distribution of the section and centerlineof the section is shown in the following pictures. Conducting qualitative andquantitative analysis according to the calculation results of different mesh size.

Out Section Section Section

Section SectionMiddle Axis

Section Section



Comparison�of�velocity�contour�for�A�- A�section�of�8�kinds�of�mesh�methods.

total01 totalless addcircle addhig

addrad addbou totaltra1 totaltra2


航天工程公司航天工程公司There is no big difference of the hex mesh results, but the tetra mesh results are not very good.

Comparison�of�velocity�contour�for�B�- B�section�of��8�kinds�of�mesh�methods.

totalless addcircle addhigtotal01 totalless addcircle addhig

addrad addbou totaltra1 totaltra2



There is no big difference of the hex mesh results, but the tetra mesh results are not very good.

From velocity results we can see that there is a great difference with between tetra From velocity results, we can see that there is a great difference with between tetramesh and hex mesh, the resolution of tetra mesh is not accurate.

When the number of hex mesh is less, the symmetry of velocity is poor, and theresults become more accurate when hex mesh is encrypted in all directions.yp

The division of boundary layer mesh has little influence on the result of the main flow. Considering the calculation results and efficiency, we choose mesh division method

of radial encryption finally.



3.�Comparison�of�Turbulence�Model3.�Comparison�of�Turbulence�Model

The turbulence models compared are show in table 3 In table 4 it is the calculation

pp

The turbulence models compared are show in table 3. In table 4, it is the calculation conditions.

Table3 Turbulence information Table4 Calculation conditions

Type Turbulence ModelKe-REA Realizable k-ε

number Unit

Material airKe-RNG RNG k-ε

ke-STA Standard k-ε

Kw Standard k-w

Entrance velocity in A - A cross section

28.68 m/s

Entrance velocity in B - B cross section

33.63 m/s

Kw-SST SST k-w

RSM-LPS Linear Pressure-stain Reynolds Stress

LESwale LES WALE

Relative static pressure at outlet

0 Pa

Wall No Slip Wall



C i f l it t f A A ti f 7 ki d f t b l d lComparison of velocity contour for A - A section of 7 kinds of turbulence models.

Ke-REA Ke-RNG ke-STA Kw

Kw-SST RSM-LPS LESwale



C i i f l it t f B B ti f 7 ki d f t b l d lComparision�of�velocity�contour��for�B�- B�section�of�7�kinds�of�turbulence�models.


Kw-SST RSM-LPS LESwale



Comparison�of�velocity�contour��for�outlet�section�of�7�kinds�of�turbulence�models.


Kw-SST RSM-LPS LESwale According to the contours, the symmetry of velocity distribution of Realizable k- ε model

and RSM_LPS model is better The velocity distribution of standard k- ε model shows more gently The velocity distribution of standard k- ε model shows more gently. The result of LES model is good too, but its computational load is big. Overall, realizable k-ε is a more appropriate choice in terms of computational load and

convergence difficulty.



4.�Comparison�of�Particle4.�Comparison�of�Particle--phase�Modelphase�Modelpp pp

DPM��unsteady�model�and�steady�model�are�compared.��The�settings�are�as�below.

number UnitMaterial Carbon particles p

Particle flow at 1.3 entrance on A‐A section

1.792 g/s

Particle flow at 2.4 entrance on A A section

1.157 g/sA-A section

Particle flow at entrance on B-B section

2.719 g/s

Flow velocity at entrance on A-A section

28.68 m/ssectionFlow velocity at entrance on B-B section

33.63 m/s



Unsteady， residence�time�distribution�of�different�particle�size�from�the�entrances�of�the�combustion�chamber.

particle size 0.08mmparticle size 0.04mmparticle size 0.02mm



Unsteady， residence�time�distribution�of�different�particle�size�from�entrances�of the reduction chamberof�the�reduction�chamber


According to the residence time distribution of particles ,we found that the larger particle size is, the longer residence time becomes. The larger particles from the combustor chamber concentrate in the lower part of the furnace, the smaller particles from the reduction chamber are difficult to enter the lower partsmaller particles from the reduction chamber are difficult to enter the lower part of the furnace due to the influence of gravity and airflow direction.



Steady， residence�time�distribution�of�different�particle�size�from�the�entrances�of�the�combustion�chamber.




Steady， residence�time�distribution�of�different�particle�size�from�entrances�of�the�reduction�chamber.

particle size 0.08mm

From�residence�time�distribution�is�

particle size 0.04mmparticle size 0.02mm

similar.�And�from�the�average�particle�concentration�of�four�vertical�sections,�we�can�see�that�the�concentration�predicted by unsteady model is largerpredicted�by�unsteady�model�is�larger�than�that�of�steady�model.�

But�which�one�is�better�needs�to�be�validated.Average particle concentration of four vertical sections



5.�Comparison�of�reaction�model�5.�Comparison�of�reaction�model�pp

The equilibrium model and reaction kinetics model are compared.

Physics�Model

Th di i l M d l

coalMoisture(wt%) 4.2

Table Properties of CoalSettings:

Three-dimensional�Model

Steady

Realizable k-ε

( )

Fixed Carbon(wt%) 56.2

Volatile Matter(wt%) 30.9

Ash(wt%) 8 7Realizable�k ε

Standard�Wall�Function

Compressible�Fluid

Ash(wt%) 8.7

HHV(KJ/kg) 30000

C(wt%) 76.3

DPM

DO Model

PDF FR/EDM

H(wt%) 5.31

O(wt%) 7.31

N(wt%) 1.54PDF�or�FR/EDM

S(wt%) 0.46



Settings:



When�using�reaction kinetics model,�chemical�reaction�and�one�set�of�rate�parameters�are�considered�as�follow:p



The temperature distribution of the two models, shows the temperature is lower when equilibrium model is used.

Temperature�distribution�of�A-A�section

Pdf model Reaction model

Temperature�distribution�of�B-B�section

Pdf model Reaction model

Pdf model

Reaction model

Temperature�distribution�of�vertical�center��section



p

Th l i i i ilThe�velocity�distribution is�similar.

Pdf model Reaction model Reaction modelPdf model

Velocity�distribution�of�A-A�section Velocity�distribution�of�A-A�section

Pdf model

Reaction model

Velocity��distribution�of�vertical�center��section



55、、Comparison�of�reaction�models�Comparison�of�reaction�models�

The particle concentration distribution is similar Particles entered from A A section do

pp

The particle concentration distribution is similar. Particles entered from A-A section do rotational motion in the furnace . Particles entered from B-B section smash together and move along with air flow.

Pdf model Reaction model Reaction modelPdf model

Pdf model

Particle�concentration�distribution�of�A-A�section Particle�concentration�distribution�of�A-A�section

Reaction model

Particle�concentration�distribution�of�vertical�center�section



Counting average temperature of horizontal sections along furnace height, thencompare the results with the experimental data.

The temperature variation curves are similar. Temperature increases quickly andp p q yreaches the peak value in the combustion zone, then anther peak in reduction zone,and then temperature decreases quickly after combustion of coal.

But Quantitatively, equilibrium model underestimates the temperature while reactionkinetics model overestimates the temperaturekinetics model overestimates the temperature.

2600

1800

2000

2200

2400

mpe

ratu

re(k

)

Pdf Model

1000

1200

1400

1600

Gas

Tem Reaction Model

Experimental�dataTemperature�variation�curve�along�with�the�height�of�furnace�for�different�combustion�model

0 2 4 6

Gasifier Height(m)



Contrast of syngas compositions at the outlet of gasifier. Reaction kinetics model gives relatively accurate results except water vapor. E ilib i d l i th lt th t l ti l diff t f th Equilibrium model gives the results that are relatively different from the

experimental results.

Comparison�of�product�gas�composition�between�model�and�experimental�result



CONCLUSIONS�/OUTLOOKCONCLUSIONS�/OUTLOOK1. Physical models and parameters which are often used for coal gasification have been researched.

2. Numerical simulation models are compared and studied on the basis of Japanese CRIEPI’s 2T/D gasifer.

3. Mesh comparison is conducted and economical and effective mesh is selected.p

4. Turbulence models and particle models are compared and the suitable turbulence model are selected.

5 C i f ilib i i d l d i ki i d l h h5. Comparison of equilibrium reaction model and reaction kinetics model shows, the temperature variation curves are similar to the experiment, but the temperature value is very different. Equilibrium model underestimates the temperature while reaction kinetics model overestimates the temperature.reaction kinetics model overestimates the temperature.

6. Composition of syngas simulated by reaction kinetics model is less different from the experiment.

7. Other models like volatilization model, radiation model and other reaction models will be compared. And the systemic results of comparison will be used as an guidance for numerical simulation of coal gasifier.



Comparison of numerical model-CECO.ppt [兼容模式]

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