downdraft biomass gasification: experimental investigation and aspen plus simulation

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DOWNDRAFT GASIFICATION OF BIOMASS EXPERIMENTAL INVESTIGATION AND ASPEN PLUS SIMULATION By Antonio Oliveira Dr. John Brammer (Supervisor) 1

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Page 1: Downdraft biomass gasification: experimental investigation and aspen plus simulation

DOWNDRAFT  GASIFICATION  OF  BIOMASS    

EXPERIMENTAL  INVESTIGATION  AND  ASPEN  PLUS  SIMULATION  

 By  Antonio  Oliveira  Dr.  John  Brammer  (Supervisor)  

1  

Page 2: Downdraft biomass gasification: experimental investigation and aspen plus simulation

THESIS  OBJECTIVES  

Measure  temperature  and  gas  profiles  in  axial  and  longitudinal  direcFons  in  a  conFnuous  fixed  bed  reactor  fed  with  charcoal;  

Modify  a  commercially  available  throated  biomass  gasifier  to  measure  axial  and  longitudinal  temperature  in  the  reducFon  zone;  

Develop  a  gas  sampling  line  according  to  the  orientaFon  of  European  tar  protocol;  

Apply  restricted  equilibrium  (temperature  approach)  correcFons  to  Aspen  Plus  gasifier  models  to  improve  results  accuracy.  

2  

Study  the  biomass  gasificaFon  process    and  its  behaviour  under  changes  of  operaFonal  parameter  and  feedstock,  with  focus  on  the  reducFon  zone.  As  well  as  developing  a  Aspen  Plus  model  based  on  thermodynamic  equilibrium  able  to  predict  producer  gas  concentraFon.    

Page 3: Downdraft biomass gasification: experimental investigation and aspen plus simulation

INTRODUCTION  

Biomass  Energy  

environmental  polluFon  

energy  security  

depleFon  of  fossil    

climate  change  

3  

Page 4: Downdraft biomass gasification: experimental investigation and aspen plus simulation

BIOMASS  

“plant  material,  vegetaFon,  or  agricultural  waste  used  as  a  fuel  or  energy  source”    

4  

Page 5: Downdraft biomass gasification: experimental investigation and aspen plus simulation

 BIOMASS  UTILIZATION  

Raw Material Process Intermediate Product Final Product

Vegetal Oil

Sugar & Starch

Lignocellulosics

Wet Biomass

Hydrolysis - Fermentation -

Destilation

Pyrolysis - Hydrogenation

Fisher - Tropsh

Gasification

Biogas

Pellets

Producer Gas

HydrocarbonsBio-oil

EthanolETBE

Biodiesel

Pelletization

Anaerobic Digestion

Transesterification

Transport BiofuelsChemicals

Electricity

Heating

Combustion

5  

GASIFICATION  

Page 6: Downdraft biomass gasification: experimental investigation and aspen plus simulation

BIOMASS  GASIFICATION  

“thermochemical  process  in  which  parFal  oxidaFon  of  organic  maYer  at  high  temperatures  results  in  a  mixture  of  products,  but  mainly  consisFng  of  a  gaseous  fuel  that  can  be  uFlized  for  energy  applicaFons”  

6  

Page 7: Downdraft biomass gasification: experimental investigation and aspen plus simulation

TYPES  OF  GASIFICATION  

AIR  GASIFICATION    

Oxygen  gasificaFon  

HydrogasificaFon    

PyrolyFc  gasificaFon    

Near-­‐  and  super-­‐criFcal  water    

7  

Page 8: Downdraft biomass gasification: experimental investigation and aspen plus simulation

GASIFICATION  THERMODYNAMICS    

8  

DRYING

wet biomass

biomass

PYROLYSIS

pyrolysis gas

charcoal

COMBUSTION

C+O2→ CO2 4H+O2→ 2H2O

CnHm+(n/2+m/4)O2→ nCO2 +  m/2H2O

REDUCTION

C+CO2↔2CO

C+H2O↔CO+H2

CnHm+nH2O↔nCO+(m/2+n)H2

CnHm+nCO2↔2nCO+m/2H2

H2O

Tat CH4

PRO

DU

CER

GA

S

CO2 H2O

CO H2

HEAT

H2O dry biomass

Page 9: Downdraft biomass gasification: experimental investigation and aspen plus simulation

TYPES  OF  GASIFIER  

According  to  the  reactor  design,  there  are  4  different  types  of  gasificaFon.    

FIXED  BED  

Fluidized  bed  

Entrained  flow  

Twin-­‐bed    9  

Page 10: Downdraft biomass gasification: experimental investigation and aspen plus simulation

 FIXED  BED  GASIFIERS  

DowndraE  gasifier        Co-­‐current  flow  design;  thus,  both  the  biomass  and  the  air  and  producer  gas  follow  a  downward  movement    

10  

Page 11: Downdraft biomass gasification: experimental investigation and aspen plus simulation

 FIXED  BED  GASIFIERS  

Two-­‐stage  Gasifier  EssenFally  a  downdra`  gasifier.  However,  the  pyrolysis  and  char  reducFon  zones  have  been  separated  into  two  reactors  by  an  intermediate  high  temperature  oxidaFon  zone.    

11  

Page 12: Downdraft biomass gasification: experimental investigation and aspen plus simulation

SIMULATION  OF  GASIFICATION  PROCESSES  

“EssenFally,  all  models  are  wrong,  but  some  models  are  useful”    

(Box  &  Draper  1987)    

Determining  opFmal  operaFng  condiFons  

CreaFng  the  most  appropriate  reactor  design  

Studying  a  wider  range  of  condiFons  that  cannot  be  obtained  experimentally  

Understanding  experimental  results  and  analysing  improper  performance  of  a  gasifier  

Choosing  an  appropriate  feedstock  and  evaluaFng  its  yield  

Scaling-­‐up  a  reactor  

12  

Page 13: Downdraft biomass gasification: experimental investigation and aspen plus simulation

SIMULATION  OF  GASIFICATION  PROCESSES  

GASIFICATION  MODELS  

CFD  Thermo.  

equilibrium  

kinecFcs  based  

ASPEN  PLUS  

neural  network  

13  

Page 14: Downdraft biomass gasification: experimental investigation and aspen plus simulation

ASPEN  PLUS  

14  

Page 15: Downdraft biomass gasification: experimental investigation and aspen plus simulation

PREVIOUS  WORK  

KINECTIC  AND  CFD  MODELS  

THERMODYNAMIC  EQUILIBRIUM  

MODELS  

EXPERIMENTAL  

15  

Page 16: Downdraft biomass gasification: experimental investigation and aspen plus simulation

GASIFICATION  EXPERIMENTS  

Experimental  study  on  75  kWth  downdraE  (biomass)  gasifier  system  (Sharma  2009)  

•  Fed  with  woodchips  •  Longitudinal  temperature  •  Longitudinal  pressure  •  Outlet  gas  composiFon  

16  

Page 17: Downdraft biomass gasification: experimental investigation and aspen plus simulation

GASIFICATION  EXPERIMENTS  

Experimental  invesZgaZon  of  a  downdraE  biomass  gasifier  (Zainal  et  al.  2002)  

•  Fed  with  wood  furniture  chunks  

•  Several  equivalent  raFo  •  Longitudinal  temperature  •  Outlet  gas  composiFon  

17  

Page 18: Downdraft biomass gasification: experimental investigation and aspen plus simulation

GASIFICATION  EXPERIMENTS  

GasificaZon  of  charcoal  wood  chips:  Isolated  parZcle  and  fixed  bed  (Tagutchou  2008)  

•  Emulates  a  2-­‐stage  gasifier  •  Fed  with  charcoal  from  

woodchips  •  Several  equivalent  raFo  •  Longitudinal  temperature  

and  pressure  and  gas  profile  

18  

Page 19: Downdraft biomass gasification: experimental investigation and aspen plus simulation

THERMODYNAMIC  EQUILIBRIUM  MODELS  

Thermochemical  equilibrium  modelling  of  a  gasifying  process  (Melgar  et  al.  2007)    

19  

Uses  the  approach  equilibrium  constant  together  with  thermodynamic  equilibrium  of  the  global  reacFon.  The  temperature  of  reacFon  is  the  adiabaFc  flame  temperature.  The  system    was  solved  in  EES.  

Page 20: Downdraft biomass gasification: experimental investigation and aspen plus simulation

THERMODYNAMIC  EQUILIBRIUM  MODELS  

Performance  analysis  of  a  biomass  gasifier  (Mathieu  &  Dubuisson  2002)  

Modelled  wood  gasificaFon  in  a  fluidized  bed  using  Aspen  Plus/minimizaFon  of  the  Gibbs  free  energy.    

20  

Page 21: Downdraft biomass gasification: experimental investigation and aspen plus simulation

THIS  WORK  

Char  gasificaZon  in  a  conZnuous  fixed  bed  reactor  -­‐  CFiBR  GasificaZon  in  a  25kW  Throated  fixed  bed  biomass  gasifier  

Modelling  work  –  Aspen  Plus  

 

21  

Page 22: Downdraft biomass gasification: experimental investigation and aspen plus simulation

CHAR  GASIFICATION  IN  A  CONTINUOUS  FIXED  BED  REACTOR  -­‐  CFIBR  

22  

Page 23: Downdraft biomass gasification: experimental investigation and aspen plus simulation

EXPERIMENTAL  APPARATUS  

23  

!M

!M

!V

mass!flowmeter/controller

volume!flowmeter/controller

thermocouple!/pressure!sensor!andgas!sampling!probe

!V

!M

C3H8

Air

H2O

!2

!12

!!11

!!10

!9

!8

!7

!6

!5

!4

!3

!1

!i

a

b

c

d

e

f

g

200mm

1600!m

m

100!mm

Flare

The  CFiBR  was  designed  and  manufactured  by  CIRAD.  It  is  essenFally  of  a  refractory  stainless  steel  tube  of,  surrounded  by  refractory  insulaFon.  At  the  top  of  the  reactor,  there  is  a  conveyor  belt  (a)  that  enables  the  feeding  of  charcoal  to  the  top  of  the  reactor.  A  system  of  two  pneumaFc  valves  (b)  ensures  that  no  air  can  enter  the  reactor  when  the  char  is  introduced.  The  combusFon  (c)  chamber  provides  the  reacFve  atmosphere.    

Page 24: Downdraft biomass gasification: experimental investigation and aspen plus simulation

REACTIVE  ATMOSPHERE  

CombusZon  chamber   Steam  generator  

•  The  steam  generator  is  designed  to  provide  up  to  6  kg/h  of  steam  at  a  temperature  of  up  to  1050  °C.  It  consists  of  a  furnace  and  a  heat  exchanger  equipped  with  a  control  system.  

24  

900#mm

500#mm

refractory#concrete#burner#cover

refractory#concrete#disk

burner

ceramic#insulator

200#mmReactor#centre

Page 25: Downdraft biomass gasification: experimental investigation and aspen plus simulation

CONTINUOUS  FIXED  BED  OPERATION    

Charcoal  feeding  systems   Ash  and  residues  removal  system  

25  

12#cm

!

11#cm

10#cm

Closed Open

Page 26: Downdraft biomass gasification: experimental investigation and aspen plus simulation

PRODUCTION  AND  CHARACTERIZATION  OF  THE  BIOMASS  USED  

Charcoal  from  woodchips  Granulometric  analysis  and  parZcles  size  distribuZon  

26  

20#mm 20#mm

(A) (B)

180 2 4 6 8 10 12 14 16

100

0

20

40

60

80

dp)(mm)

mass)(%)

differen5al

cumula5ve

Page 27: Downdraft biomass gasification: experimental investigation and aspen plus simulation

INSTRUMENTATION,  MEASUREMENTS  AND  CALCULATIONS  

Temperature  •  Fixed  

–  CombusFon  chamber  (T1);  –  Outlet  of  the  steam  generator  

(T2);  –  10  cm  above  the  charcoal  bed  

(T3);  –  Below  the  ash  removal  (T11);  –  Outlet  of  the  cyclone  (T12).  

•  Movable  –  These  thermocouples  (T4  to  T10)    

Pressure  

Two  pressure  sensors  (0-­‐500  mbar)  are  placed  before  and  a`er  the  char  bed,  in  order  to  measure  pressure  drop  across  the  bed.  The  pressure  can  also  be  measured  everywhere  in  the  bed  via  the  thermocouple  probes.    

27  

Page 28: Downdraft biomass gasification: experimental investigation and aspen plus simulation

INSTRUMENTATION,  MEASUREMENTS  AND  CALCULATIONS  

Gas  composiZon  

28  GC

Reactor*wall

Reactor*interior

Filter*and*dryer

Gas

Temperature*readings

Flow*control/*measurement*(4)

Filter*(2)

Condenser*(3)

Sampling*probe*(1)

Page 29: Downdraft biomass gasification: experimental investigation and aspen plus simulation

MASS  AND  ENERGY  BALANCES  

Mass   Energy  

29  

The  inlet  reagents  are  charcoal  and  the  reacFve  atmosphere  gases  are  composed  of  O2,  N2,  CO2,  H2O.  The  outlet  products  are  the  producer  gas  (H2,  CO,  CH4,  H2O,  CO2  and  N2)  in  addiFon  to  solid  residues  removed  from  the  boYom.  

There  is  no  mechanical  work  being  produced  by  the  system  and  kineFc  and  potenFal  energy  are  negligible    

CHAPTER 5 – CHAR GASIFICATION ON A CONTINUOUS FIXED BED REACTOR - CFIBR

104

5.3.5 Mass and energy balances

The energy balance is calculated according to the principle of conservation of

energy (1st Law of thermodynamics) as expressed in Eq. 5.10.

0 =   �̇� + �̇� + �̇�   ℎ +

𝑢2 + 𝑔𝑧

− �̇�   ℎ +𝑢2 + 𝑔𝑧

5.10

where Qlost represents the heat lost by the system, Wcv is the variation of the

mechanical work and m, h, u2/2 and gz are respectively the mass flow, enthalpy,

kinetic and potential energy in and out of the control volume (cv).

As there is no mechanical work being produced by the system and kinetic and

potential energy are negligible, Eq. 5.10 can be reduced to

0 =   �̇� + �̇� ℎ  − �̇� ℎ   5.11

The mass balance is given by the difference between inlet reagents and outlet

products (producer gas and residues). It can be mathematically expressed by Eq. 5.12.

0 = �̇�  − �̇� 5.12

The inlet reagents are charcoal and the reactive atmosphere gases are

composed of O2, N2, CO2, H2O. The outlet products are the producer gas (H2, CO, CH4,

H2O, CO2 and N2) in addition to solid residues removed from the bottom.

Therefore,

ℎ �̇� = �̇� ℎ + �̇� ℎ 5.13

and,

ℎ �̇� = �̇� ℎ + �̇� ℎ 5.14

CHAPTER 5 – CHAR GASIFICATION ON A CONTINUOUS FIXED BED REACTOR - CFIBR

105

where h and m are respectively the specific enthalpy and mass flow of each

gaseous compound going in (i) or out (j) of the reactor. The specific enthalpy can be

calculated as:

ℎ , (𝑇) = ℎ , (𝑇) + 𝐶 ( , )(𝑇)𝑑𝑇 5.15

where ℎ , is the standard enthalpy of formation of the component i,j, Cp(j) is

the specific heat and T is the medium temperature.

Combining Eq. 5.11 and Eq. 5.14, the final equation for calculating the energy

balance is:

�̇� ℎ + �̇� ℎ −�̇� ℎ − �̇� ℎ − �̇� = 0 5.16

The heat loss is calculated according to Eq. 5.17

�̇� = ℎ 𝐴𝑑𝑇 5.17

where hc is the convective heat transfer coefficient of the process, A is heat

transfer area of the surface and dT is the temperature difference between the surface

and the ambient.

5.4 Operational parameters

Three experiments were performed. Experiments A and B were performed with

the same conditions. They were intended to provide two set of gas measurements, one

in the wall and another in the centre of the reactor, thus they would allow the study of

the gas variation in the radial direction. Experiment C was performed with a different

atmosphere.

Airflow was constant for all experiments while propane and water vapour flow

were changed.

Page 30: Downdraft biomass gasification: experimental investigation and aspen plus simulation

OPERATIONAL  PARAMETERS  CHAPTER 5 – CHAR GASIFICATION ON A CONTINUOUS FIXED BED REACTOR - CFIBR

108

Table 5.5: Operating conditions of the CFiBR gasification experiments

Experiment A and B Experiment C

Reactants (inlet conditions) Char feeding rate (mC) 2.1 (mol/min) 25 (g/min) 2.1 (mol/min) 25 (g/min) Qair

10 8.031 (mol/min) 235.50 (g/min) 8.103 (mol/min) 237.61 (g/min) QN2 6.494 (mol/min) 181.93 (g/min) 6.553 (mol/min) 183.57 (g/min) QO2

11 1.674 (mol/min) 53.57 (g/min) 1.689 (mol/min) 54.05 (g/min) QC3H8 0.286 (mol/min) 12.59 (g/min) 0.303 (mol/min) 13.35 (g/min) QH2O (added water vapour) 0.67 (mol/min) 12.20 (g/min) 1.02 (mol/min) 18.41 (g/min) Products (attack gases) QO2 235.50 (mol/min) 7.883 (g/min) 0.18 (mol/min) 5.61 (g/min) QCO2 181.93 (mol/min) 37.699 (g/min) 0.91 (mol/min) 39.98 (g/min) QH2O 53.57 (mol/min) 33.238 (g/min) 2.30 (mol/min) 40.73 (g/min) QN2 12.59 (mol/min) 181.928 (g/min) 6.55 (mol/min) 183.57 Total Flux of attack gases 235.50 (mol/min) 260.748 (g/min) 9.94 (mol/min) 269.89 (g/min) Properties (attack gases) Superficial Velocity 0.55 (m/s) 0.57 (m/s) Products Temperature 1060 °C 1080 °C Total Pressure 1.01 atm 1.01 atm

10 Q stands for gas flow. 11 Oxygen is provided in excess of 2.70% in Experiment A/B and 1.78% in Experiment C

30  

Page 31: Downdraft biomass gasification: experimental investigation and aspen plus simulation

DATA  COLLLECTION  AND  PROCESSING  

Temperature  and  pressure  every  10  seconds  

Gases  are  sampled  and  the  condensates  are  stored    

Charcoal  bed  is  cooled  in  an  inert  atmosphere  to  avoid  further  chemical  reacFon  

31  

Page 32: Downdraft biomass gasification: experimental investigation and aspen plus simulation

ESTABLISHMENT  OF  STEADY  STATE  

From  start  to  steady  state   Bed  level  

32  

!!!0 1 2 3 4 5 6 7 8 9 10 11

1100

0

100

200

300

400

500

600

700

800

900

1000

Time!(h)

!Tem

perature!(°C)

T2

T3

T5:T10

T11

T12

T4

Hea<ng Steady!state

Cooling!down

12

Bed!level!Thermal!stabilisa<onstabilisa<on !!!0 10 20 30 40 50

1010

750

800

850

900

950

Time!(min)

!Tem

perature!(°C)

T3

T4

T6

T8

T10

60

Page 33: Downdraft biomass gasification: experimental investigation and aspen plus simulation

EXPERIMENTAL  RESULTS  

Over  100  hours  of  gasificaFon    

Every  experiment  could  only  last  a  maximum  of  13h  

The  results  are  analysed  to  provide:  mass  and  energy  balances,    profiles  of  temperature,  pressure,  mole  concentraFon  and  conversion,    both  in  transient  and  steady  states.  

33  

Page 34: Downdraft biomass gasification: experimental investigation and aspen plus simulation

Temperature  

34  !!!0 1 2 3 4 5 6 7 8 9 10 11

1100

0

100

200

300

400

500

600

700

800

900

1000

Time!(h)

!Tem

perature!(°C)

T2

T3

T5:T10

T11

T12

T4

Hea<ng Steady!state

Cooling!down

12

Bed!level!Thermal!stabilisa<onstabilisa<on

REACHING  STEADY  STATE  

Page 35: Downdraft biomass gasification: experimental investigation and aspen plus simulation

STEADY  STATE:  VARIATION  OF  PROPERTIES  ACROSS  THE  REACTOR  

Temperature  Region  1:  Above  bed  level  a  decrease  of  temperature  is  observed  due  to  convecFve  heat  loss  to  the  wall  only.  

Region  2:  Between  T4  and  T6,  reacFve  atmosphere  reaches  the  charcoal  bed  and  the  temperature  drops  rapidly  due  to  the  endothermic  reacFons,  heaFng  up  and  drying  of  the  charcoal.  

Region  3:  Under  T6,  the  temperature  decrease  is  less  pronounced  and  the  longitudinal  gradient  reduces.  The  radial  gradient  becomes  stable.  

35  

Page 36: Downdraft biomass gasification: experimental investigation and aspen plus simulation

STEADY  STATE:  VARIATION  OF  PROPERTIES  ACROSS  THE  REACTOR  

Gas  composiZon  profiles  

36  

200 5 10 15

Inlet

Outlet

T9

T8

T7

T6

T5

T4

T3

333

Concentra9on3(%)

Prob

e3loca9o

ns

CO

H2

O2 CO2 H20

CH43x310

430 5 10 15 20 25 30 35

Inlet

Outlet

T9

T8

T7

T6

T5

T4

T3

333

Species3mass3Flow3(g/min)

Prob

e3locaEo

ns

O2 H20

H2

CO2

CH43x310

CO

Longitudinal  profiles  of  concentraFon  and  species  mass  flow  in  Experiment  A.    

Page 37: Downdraft biomass gasification: experimental investigation and aspen plus simulation

STEADY  STATE:  VARIATION  OF  PROPERTIES  ACROSS  THE  REACTOR  

CHAPTER 5 – CHAR GASIFICATION ON A CONTINUOUS FIXED BED REACTOR - CFIBR

122

Table 5.6: Comparison of concentration on the radial and longitudinal profile of Experiment A/B.

H2 (%) CO (%) CH4 (%)

Centre Wall Diff Centre Wall Diff Centre

Wall Diff

T4 9.47 X

11.05 X

0.93 X

T5 10.91 11.04 -0.13 11.25 11.63 -0.38 0.95 0.97 -0.02 T6 12.97 13.40 -0.43 11.02 12.10 -1.08 0.98 1.00 -0.02 T7 13.30 12.37 0.92 11.65 11.22 0.42 1.94 1.92 0.02 T8 13.23 12.95 0.27 11.77 11.03 0.73 1.95 1.92 0.03 T9 13.38 13.20 0.18 12.10 11.37 0.72 1.98 1.93 0.05 Outlet 13.94 X

11.34 X

1.00 X

Figure 5.18: Comparison of concentration on the radial and longitudinal profile of Experiment A/B. Lines represent samples in the centre of the reactor and larger

symbols represent samples extracted by the wall.

5.6.2.3 Charcoal conversion and bed bulk density

For experiment A/B, It can be seen in Figure 5.19 that in the first 10 cm of the

bed, coal has a conversion rate of about 85%. This conversion rate then slowly evolves

37  

Gas  composiFon  profiles:  Comparison  of  concentraFon  on  the  radial  and  longitudinal  profile  of  Experiment  A/B.    

Page 38: Downdraft biomass gasification: experimental investigation and aspen plus simulation

MASS  AND  ENERGY  BALANCES  

Experiment  A/B   Experiment  C  

38  

7.4$g/min

276.6$g/min

Gasifica'onReac'ons

6.3631$kWTin$=$1060$°C

28$g/min

260.6$g/min

6.252.30$kWTout$=$770$°C

$0.533$kW

Char Gas Enthalpy$flux Heat$lost

9.9#g/min

283.3#g/min

Gasifica'onReac'ons

7.8556#kWTin#=#1080#°C

28#g/min

269.1#g/min

7.1887#kWTout#=#760#°C

#0.533#kW

Char Gas Enthalpy#flux Heat#lost

Mass  balance  error  of  1.6%  and  an  energy  balance  error  of  6%.    

Mass  balance  error  of  1.3%  and  an  energy  balance  error  of  1.9%.    

Page 39: Downdraft biomass gasification: experimental investigation and aspen plus simulation

MAIN  ACHIEVEMENTS    

commissioning  of  the  CFiBR  

 Temperature  profiles    

   Irrelevant  variaFon  of  PG  concentraFon  in  the  radial  direcFon  Existence  of  3  disFnct  regions  of  temperature  and  gas  concentraFon    

39  

!M

!M

!V

mass!flowmeter/controller

volume!flowmeter/controller

thermocouple!/pressure!sensor!andgas!sampling!probe

!V

!M

C3H8

Air

H2O

!2

!12

!!11

!!10

!9

!8

!7

!6

!5

!4

!3

!1

!i

a

b

c

d

e

f

g

200mm

1600!m

m

100!mm

Flare

Page 40: Downdraft biomass gasification: experimental investigation and aspen plus simulation

GASIFICATION  IN  A  25KW  THROATED  FIXED  BED  BIOMASS  GASIFIER  

40  

Page 41: Downdraft biomass gasification: experimental investigation and aspen plus simulation

EXPERIMENTAL  APPARATUS  

41  

This  is  the  GEK    Gasifier  Experimenters  Kit  

Reactor

Cyclone

PyroCoil

Auger

Drying2Bucket

Filter

Flare Hopper

Page 42: Downdraft biomass gasification: experimental investigation and aspen plus simulation

GEK  

Reactor  

•  Imbert  type  reactor  •  60-­‐75  kWth  (20-­‐25kWe)  •  20-­‐25  kg/h  of  lignocellulosic  

biomass  

42  

Hopper&Mount&Flange

Air&Inlet

Gas&Exit

Gas&Cowling

Insula8on&Tube

Nozzles5@&0.6&ID&caps

17.8

7.6

10.2

10.2

45.7

19.0

Rotary&Crank/Drive

37.55

15.2

28

Rotary&Support&Grate

Page 43: Downdraft biomass gasification: experimental investigation and aspen plus simulation

INSTRUMENTATION  AND  MEASUREMENTS  

Temperature  

•  Three  k-­‐type  thermocouples  •  16  temperature  points  •  Covers  the  reducFon  zone  •  Error  is  less  than  1%  

43  

Thermocouples Move.ver/cally.

Page 44: Downdraft biomass gasification: experimental investigation and aspen plus simulation

INSTRUMENTATION  AND  MEASUREMENTS  

Pressure  

Fixed  pressure  measuring  points  are  located  at  the  boYom  of  the  reactor  and  a`er  the  filter.    

44  

Reactor

Cyclone

PyroCoil

Auger

Drying2Bucket

Filter

Flare Hopper

Page 45: Downdraft biomass gasification: experimental investigation and aspen plus simulation

INSTRUMENTATION  AND  MEASUREMENTS  

Gas  composiZon  

45  

GC

Massflowmeter

Vacuum0Pump

Condenser0(2)

Sampling0tube

0(3)

Flow0control/0measurement0(4)

Vent

Probe0and0Filtre0(1)

Gas  is  sampled  and  analysed  every  30min  following  the  European  Tar  Protocol.  

Page 46: Downdraft biomass gasification: experimental investigation and aspen plus simulation

INSTRUMENTATION  AND  MEASUREMENTS  

Data  collecZon  Quantity Items 1 Atmel ATmega 1280 processor 16 K-type thermocouple inputs 6 Differential or gauge pressure/vacuum inputs 8 PWM FET outputs 4 Auxiliary analogue inputs 1 Frequency counter input 3 R/C hobby servo outputs 1 Display and four button keypad 1 USB serial host interface 1 SD-card slot 1 CANbus interface 1 Auxiliary RS-232 interface

!

46  

Page 47: Downdraft biomass gasification: experimental investigation and aspen plus simulation

PRODUCTION  AND  CHARACTERIZATION  OF  THE  BIOMASS  USED  

47  

Page 48: Downdraft biomass gasification: experimental investigation and aspen plus simulation

EXPERIMENTAL  PROCEDURES  AND  PARAMETERS  

Commissioning  

•  Cold  and  hot  trials  were  performed  

•  Check  for  leakages  •  Physical  limits    •  OperaFonal  parameters  •  Findings:  

–  Load  with  charcoal  –  Maximum  temperature  

supported  by  TC  and  reactor  –  Control  pressure  drop  –  Setup  of  the  grid      

   

48  

Page 49: Downdraft biomass gasification: experimental investigation and aspen plus simulation

EXPERIMENTAL  PROCEDURES  AND  PARAMETERS  

OperaZonal  parameters  

•  Three  types  of  pellets  comprising  mixed  wood,  Miscanthus  and  wheat  straw    

•  11  experiments  •  Air  inlet  varies  

49  

Page 50: Downdraft biomass gasification: experimental investigation and aspen plus simulation

GASIFICATION  RUNS  

Run Feedstock Airflow (kg/h)

1 100% mixed wood pellets 8.10

2a 75% mixed wood pellets and 25% Miscanthus pellets

10.7

2b 12.8

3a 50% mixed wood pellets and 50% Miscanthus pellets

10.7

3b 12.8

4a 25% mixed wood pellets and 75% Miscanthus pellets

10.7

4b 12.8

5a 100% wheat straw pellets

10.7

5b 12.8

6a 50% mixed wood pellets and 50% wheat straw pellets

10.7

6b 12.8

!

50  

Page 51: Downdraft biomass gasification: experimental investigation and aspen plus simulation

RUN  1:  100%  MIXED  WOOD  PELLETS  

Mass  balance  

Mass  balance   Run  1  

Air  flow  (kg/h)   8.1  

Pellets  flow  (kg/h)   4.6  

Flow  of  unreacted  material  (kg/h)   0.14  

Gas  outlet  flow  (kg/h)   12.2  

Tar  (g/Nm3)   1.5  

ER  –  equivalence  raFo   0.33  

Closure     97.4%  

Temperature  profile  

51  

Page 52: Downdraft biomass gasification: experimental investigation and aspen plus simulation

RUN  2:  75%  MIXED  WOOD  AND  25%  MISCANTHUS  

Mass  balance  

Mass  balance   Run  2a   Run  2b  

Air  flow  (kg/h)   10.7   12.8  

Pellets  flow  (kg/h)   7.4   7.66  

Flow  of  unreacted  material  (kg/h)   0.22   0.38  

Gas  outlet  flow  (kg/h)   17.2   19.2  

Tar  (g/Nm3)   1.30   1.10  

ER  –  equivalence  raFo   0.27   0.31  

Closure     96.5%   95.7%  

Producer  gas  concentraZon  

52  

Species     Run  2a  (vol  %)   Run  2b  (vol  %)  

CO   22.3   21  

CO2   8.4   7.7  

CH4   1.7   1.8  

H2   24.4   19  

H2O   8.3   11.4  

N2   34.9   39.1  

Higher  the  ER,  lower  the  HHV  

Page 53: Downdraft biomass gasification: experimental investigation and aspen plus simulation

MAIN  ACHIEVEMENTS    

commissioning  of  the  GEK  

 gas  sampling  line  

 Temperature  profiles  and  beYer  understanding  of  the  behaviour  in  the  reducFon  zone    

53  Reactor

Cyclone

PyroCoil

Auger

Drying2Bucket

Filter

Flare Hopper

Page 54: Downdraft biomass gasification: experimental investigation and aspen plus simulation

SIMULATION  OF  CHAR  GASIFICATION  PROCESS  IN  A  CONTINUOUS  FIXED  BED  REACTOR  USING  ASPEN  PLUS    

54  

Page 55: Downdraft biomass gasification: experimental investigation and aspen plus simulation

The  model  developed  to  simulate  the  CFiBR  is  based  on  Gibbs  free  energy  minimizaFon  (RGIBBS  block  in  ASPEN).  Restricted  equilibrium  parameters  were  used  to  calibrate  the  results  against  experimental.  

55  

Page 56: Downdraft biomass gasification: experimental investigation and aspen plus simulation

PRINCIPLES  OF  RGIBBS  AND  GASIFICATION  MODELLING  

Calculate  phase  equilibrium  and  chemical  equilibrium;  

Restricted  chemical  equilibrium  –  specify  temperature  approach  (or  duty  and  temperature)  of  enFre  system;  

Restricted  chemical  equilibrium  –  specify  temperature  approach  or  molar  extent  for  specified  reacFon  stoichiometry  

Non-­‐stoichiometric  methods  do  not  require  reacFons  to  be  specified,  while  stoichiometric  methods  require  the  specificaFon  of  the  reacFons.  

56  

Page 57: Downdraft biomass gasification: experimental investigation and aspen plus simulation

PRINCIPLES  OF  RGIBBS  AND  GASIFICATION  MODELLING  

Non-­‐stoichiometric  equilibrium  method  (min.  of  the  Gibbs)  

Applies  minimizaFon  of  the  Gibbs  free  energy  to  model  the  equilibrium  of  a  reacFng  system  

NO  reacFons  needed  

Restricted  equilibrium    *Temperature  approach    *Heat  duty  

Stoichiometric  method  (reacZons  enabled)  

Based  on  equilibrium  constant  method.  Mimics  kineFc-­‐controlled  behaviour.  

Needs  chemical  reacFons  

Restricted  equilibrium    *ReacFons  Tapp    *Heat  duty    

57  

Page 58: Downdraft biomass gasification: experimental investigation and aspen plus simulation

ASPEN  PLUS  GASIFICATION  MODEL  

58  

Page 59: Downdraft biomass gasification: experimental investigation and aspen plus simulation

ASPEN  PLUS  GASIFICATION  MODEL  

59  

Yield  reactor  –  converts  the  non-­‐convenFonal  stream  BIOMASS  into  convenFonal  components  (C,  H,  O,  N  and  ash)    

Page 60: Downdraft biomass gasification: experimental investigation and aspen plus simulation

ASPEN  PLUS  GASIFICATION  MODEL  

60  

Separator  –  extracts  a  porFon  of  the  carbon  on  the  feedstock  to  represent  un-­‐

reacted  charcoal  removed  from  the  boYom  of  the  reactor    

Page 61: Downdraft biomass gasification: experimental investigation and aspen plus simulation

ASPEN  PLUS  GASIFICATION  MODEL  

61  

                         Gibbs  free  energy  reactor  –  calculates                                                        the  equilibrium  composiFon  of  the        

                 combusFon  and  gasificaFon  products  

Page 62: Downdraft biomass gasification: experimental investigation and aspen plus simulation

ASPEN  PLUS  GASIFICATION  MODEL  

Non-­‐stoichiometric  equilibrium  method  (minimizaFon  of  the  Gibbs  free  energy);  

Non-­‐stoichiometric  restricted  equilibrium  method  with  system  temperature  approach;    

Stoichiometric  restricted  chemical  equilibrium  method  with  reacFon-­‐specific  temperature  approach.  

Three  soluZons  methods  are  used  to  simulate  the  gasifier,  each  involving  only  a  change  to  the  block  GASIFIER    

62  

Page 63: Downdraft biomass gasification: experimental investigation and aspen plus simulation

SIMULATION  INITIAL  PROPERTIES  

63  

Experiment A and B Experiment C

Reactants flow (g/min) Char feeding rate 25 25 Air 235.50 237.61 Propane 12.59 13.35 Added water vapour 12.20 18.41 Unreacted carbon removed via UC 7.4 8.8 Block temperature (°C) PROP-AIR 25 25 STEAM 1000 1000 BIOMASS 25 25 GAS-ATM 1060 1080 GASIFIER 870 870 Total Pressure (atm) 1.01 1.01

!

Page 64: Downdraft biomass gasification: experimental investigation and aspen plus simulation

NON-­‐STOICHIOMETRIC  EQUILIBRIUM  METHOD  

WITHOUT  temperature  approach:  Gasifier  temperature  is  the  equilibrium  temperature.  

ASPEN Experiment Difference O2 6.75E-18 0.00% 0.00 N2 58.67% 60.67% 2.00 H2O 7.53% 6.35% -1.18 H2 11.76% 13.52% 1.76 CO 14.28% 10.99% -3.29 CH4 3.66E-06 0.10% 0.10 CO2 7.76% 8.37% 0.60 Total Mole 100.00% 100.00%

!

64  

Page 65: Downdraft biomass gasification: experimental investigation and aspen plus simulation

NON-­‐STOICHIOMETRIC  EQUILIBRIUM  METHOD  

WITH  temperature  approach:  Gasifier  temperature  is  the  equilibrium  temperature.  

65  

500#510 #400 #300 #200 #100 0 100 200 300 400

0.2

0

0.04

0.08

0.12

0.16

Tapp.(K)

Concentra9on

CO

H2

CO2

H2O

CH4

#170.K

Page 66: Downdraft biomass gasification: experimental investigation and aspen plus simulation

ASPEN Experiment Difference O2 3.00E-22 0.00% 0.00 N2 58.74% 60.67% 1.93 H2O 6.04% 6.35% 0.31 H2 13.19% 13.52% 0.33 CO 12.63% 10.99% -1.64 CH4 3.99E-04 0.10% 0.06 CO2 9.36% 8.37% -0.99 Total Mole 100.00% 100.0%

!

NON-­‐STOICHIOMETRIC  EQUILIBRIUM  METHOD  

WITH  temperature  approach:  Gasifier  temperature  is  the  equilibrium  temperature.  

66  

Page 67: Downdraft biomass gasification: experimental investigation and aspen plus simulation

REACTIONS  ENABLED  -­‐  STOICHIOMETRIC  METHOD  

System  of  equaZons   ReacZons  

67  

The  use  of  the  stoichiometric  method  requires  the  specificaFon  of  the  reacFons,  such  that  the  number  of  products  is  equal  to  the  sum  of  the  number  of  reacFons  and  elements.  

(H2,  CO,  CO2,  CH4,  H2O,  O2,  N2  and  C  )  =  8  products.  3  elements  (C,  H,  O)  +  5  reacFons  

CHAPTER 7 – SIMULATION OF CHAR GASIFICATION PROCESS IN A CONTINUOUS FIXED BED REACTOR USING ASPEN PLUS

176

reactions and elements. Furthermore, the equations must be linearly independent

(Schefflan 2011).

Based on that, the following reactions (Eq. 7.17 to Eq.7.21) are used to

calculate the products (H2, CO, CO2, CH4, H2O, O2, N2 and C) that are formed by the

elements C, H, O. This results in 9 products, 3 elements and 5 reactions.

𝑪 + 𝟐𝑯𝟐 → 𝑪𝑯𝟒 7.17

𝑪𝑯𝟒 +𝑯𝟐𝑶 → 𝑪𝑶 + 𝟑𝑯𝟐 7.18

𝑪𝑶 +𝑯𝟐𝑶 → 𝑪𝑶𝟐 +𝑯𝟐 7.19

𝑪 + 𝑶𝟐 → 𝑪𝑶𝟐 7.20

𝑵𝟐 + 𝟐𝑶𝟐 → 𝟐𝑵𝑶𝟐   7.21

Sensitive analysis was applied to every equation, except Eq. 5.7 that has no

influence on the results, as N2 is considered inert. This equation was used only to

satisfy solution process restriction. A variation of ±500 degrees was applied to each

reaction in turn, while the remaining reactions were kept with no temperature

approach.

7.2.3.1 Sensitivity analysis – Reaction 7.17

Figure 7.4 and Figure 7.5 show the results for the sensitivity analysis of

temperature approach in Eq. 7.17. The result shows that this reaction only gives a

variation in the product mole fractions under -350 degrees of temperature approach.

Page 68: Downdraft biomass gasification: experimental investigation and aspen plus simulation

SENSITIVITY  ANALYSIS  

ReacZon    

68  

CHAPTER 7 – SIMULATION OF CHAR GASIFICATION PROCESS IN A CONTINUOUS FIXED BED REACTOR USING ASPEN PLUS

176

reactions and elements. Furthermore, the equations must be linearly independent

(Schefflan 2011).

Based on that, the following reactions (Eq. 7.17 to Eq.7.21) are used to

calculate the products (H2, CO, CO2, CH4, H2O, O2, N2 and C) that are formed by the

elements C, H, O. This results in 9 products, 3 elements and 5 reactions.

𝑪 + 𝟐𝑯𝟐 → 𝑪𝑯𝟒 7.17

𝑪𝑯𝟒 +𝑯𝟐𝑶 → 𝑪𝑶 + 𝟑𝑯𝟐 7.18

𝑪𝑶 +𝑯𝟐𝑶 → 𝑪𝑶𝟐 +𝑯𝟐 7.19

𝑪 + 𝑶𝟐 → 𝑪𝑶𝟐 7.20

𝑵𝟐 + 𝟐𝑶𝟐 → 𝟐𝑵𝑶𝟐   7.21

Sensitive analysis was applied to every equation, except Eq. 5.7 that has no

influence on the results, as N2 is considered inert. This equation was used only to

satisfy solution process restriction. A variation of ±500 degrees was applied to each

reaction in turn, while the remaining reactions were kept with no temperature

approach.

7.2.3.1 Sensitivity analysis – Reaction 7.17

Figure 7.4 and Figure 7.5 show the results for the sensitivity analysis of

temperature approach in Eq. 7.17. The result shows that this reaction only gives a

variation in the product mole fractions under -350 degrees of temperature approach.

0"500 "450 "400 "350 "300 "250 "200 "150 "100 "50

0.2

0

0.04

0.08

0.12

0.16

Tapp..".EQ2.(K)

Mol.Frac:on

."260.K

H2

COCO2

CH4

H2O

CH4.*10

Page 69: Downdraft biomass gasification: experimental investigation and aspen plus simulation

SENSITIVITY  ANALYSIS  

ReacZon    

69  

CHAPTER 7 – SIMULATION OF CHAR GASIFICATION PROCESS IN A CONTINUOUS FIXED BED REACTOR USING ASPEN PLUS

176

reactions and elements. Furthermore, the equations must be linearly independent

(Schefflan 2011).

Based on that, the following reactions (Eq. 7.17 to Eq.7.21) are used to

calculate the products (H2, CO, CO2, CH4, H2O, O2, N2 and C) that are formed by the

elements C, H, O. This results in 9 products, 3 elements and 5 reactions.

𝑪 + 𝟐𝑯𝟐 → 𝑪𝑯𝟒 7.17

𝑪𝑯𝟒 +𝑯𝟐𝑶 → 𝑪𝑶 + 𝟑𝑯𝟐 7.18

𝑪𝑶 +𝑯𝟐𝑶 → 𝑪𝑶𝟐 +𝑯𝟐 7.19

𝑪 + 𝑶𝟐 → 𝑪𝑶𝟐 7.20

𝑵𝟐 + 𝟐𝑶𝟐 → 𝟐𝑵𝑶𝟐   7.21

Sensitive analysis was applied to every equation, except Eq. 5.7 that has no

influence on the results, as N2 is considered inert. This equation was used only to

satisfy solution process restriction. A variation of ±500 degrees was applied to each

reaction in turn, while the remaining reactions were kept with no temperature

approach.

7.2.3.1 Sensitivity analysis – Reaction 7.17

Figure 7.4 and Figure 7.5 show the results for the sensitivity analysis of

temperature approach in Eq. 7.17. The result shows that this reaction only gives a

variation in the product mole fractions under -350 degrees of temperature approach.

500#500 #400 #300 #200 #100 0 100 200 300 400

0.2

0

0.04

0.08

0.12

0.16

Tapp..#.EQ3.(K)

Mol.Frac:on

H2

CO

CO2 H2O

.#190.K

Page 70: Downdraft biomass gasification: experimental investigation and aspen plus simulation

OPTIMIZED  METHOD  

Tapp  =  -­‐260  

Tapp  =  -­‐170  

70  

ASPEN Experiment Difference O2 0.00% 0.00% 0.00 N2 59.30% 60.67% 1.37 H2O 5.98% 6.35% 0.37 H2 12.45% 13.52% 1.07 CO 11.74% 10.99% -0.75 CH4 0.53% 0.10% -0.43 CO2 10.00% 8.37% -1.63 Total Mole 100.00% 100.00%

!

CHAPTER 7 – SIMULATION OF CHAR GASIFICATION PROCESS IN A CONTINUOUS FIXED BED REACTOR USING ASPEN PLUS

176

reactions and elements. Furthermore, the equations must be linearly independent

(Schefflan 2011).

Based on that, the following reactions (Eq. 7.17 to Eq.7.21) are used to

calculate the products (H2, CO, CO2, CH4, H2O, O2, N2 and C) that are formed by the

elements C, H, O. This results in 9 products, 3 elements and 5 reactions.

𝑪 + 𝟐𝑯𝟐 → 𝑪𝑯𝟒 7.17

𝑪𝑯𝟒 +𝑯𝟐𝑶 → 𝑪𝑶 + 𝟑𝑯𝟐 7.18

𝑪𝑶 +𝑯𝟐𝑶 → 𝑪𝑶𝟐 +𝑯𝟐 7.19

𝑪 + 𝑶𝟐 → 𝑪𝑶𝟐 7.20

𝑵𝟐 + 𝟐𝑶𝟐 → 𝟐𝑵𝑶𝟐   7.21

Sensitive analysis was applied to every equation, except Eq. 5.7 that has no

influence on the results, as N2 is considered inert. This equation was used only to

satisfy solution process restriction. A variation of ±500 degrees was applied to each

reaction in turn, while the remaining reactions were kept with no temperature

approach.

7.2.3.1 Sensitivity analysis – Reaction 7.17

Figure 7.4 and Figure 7.5 show the results for the sensitivity analysis of

temperature approach in Eq. 7.17. The result shows that this reaction only gives a

variation in the product mole fractions under -350 degrees of temperature approach.

CHAPTER 7 – SIMULATION OF CHAR GASIFICATION PROCESS IN A CONTINUOUS FIXED BED REACTOR USING ASPEN PLUS

176

reactions and elements. Furthermore, the equations must be linearly independent

(Schefflan 2011).

Based on that, the following reactions (Eq. 7.17 to Eq.7.21) are used to

calculate the products (H2, CO, CO2, CH4, H2O, O2, N2 and C) that are formed by the

elements C, H, O. This results in 9 products, 3 elements and 5 reactions.

𝑪 + 𝟐𝑯𝟐 → 𝑪𝑯𝟒 7.17

𝑪𝑯𝟒 +𝑯𝟐𝑶 → 𝑪𝑶 + 𝟑𝑯𝟐 7.18

𝑪𝑶 +𝑯𝟐𝑶 → 𝑪𝑶𝟐 +𝑯𝟐 7.19

𝑪 + 𝑶𝟐 → 𝑪𝑶𝟐 7.20

𝑵𝟐 + 𝟐𝑶𝟐 → 𝟐𝑵𝑶𝟐   7.21

Sensitive analysis was applied to every equation, except Eq. 5.7 that has no

influence on the results, as N2 is considered inert. This equation was used only to

satisfy solution process restriction. A variation of ±500 degrees was applied to each

reaction in turn, while the remaining reactions were kept with no temperature

approach.

7.2.3.1 Sensitivity analysis – Reaction 7.17

Figure 7.4 and Figure 7.5 show the results for the sensitivity analysis of

temperature approach in Eq. 7.17. The result shows that this reaction only gives a

variation in the product mole fractions under -350 degrees of temperature approach.

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VALIDATION  

Data  of  Van  de  Steene  (2010)  

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Experiment A - B Experiment C Van de Steene (2010)

Reactants flow (g/min) Char feeding rate 25 25 25 Air 235.50 237.61 231.01 Propane 12.59 13.35 11.78 Added water vapour 12.20 18.41 35 Unreacted carbon removed via UC

7.4 8.8 3.1

Block temperature (°C) PROP-AIR 25 25 25 STEAM 1000 1000 1000 BIOMASS 25 25 25 GAS-ATM 1060 1080 1020 GASIFIER 870 870 850 Total Pressure (atm) 1.01 1.01 1.01

!

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MAIN  ACHIEVEMENTS    

   Non-­‐stoichiometric  

   

Non-­‐stoichiometric  with  Tapp  

   Stoichiometric  with  Tapp  

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GENERAL  CONCLUSION  

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The  scope  of  this  was  to  invesFgate  the  reducFon  zone  of  a  downdra`  gasifier,  to  provide  the  necessary  data  for  development  and  validaFon  of  2D  CFD  codes  to  simulate  the  behaviour  of  the  gasificaFon  zone  of  a  downdra`  gasifier,  and  to  develop  an  Aspen  Plus  model  for  char  gasificaFon.    

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SUGGESTIONS  FOR  FURTHER  WORK  

2D/3D  CFD  modelling  of  charcoal  gasificaFon.  This  could  be  validated  with  the  data  presented  in  the  chapter  5;    

2D/3D  CFD  modelling  of  biomass  gasificaFon.    This  could  be  validated  with  the  data  presented  in  the  chapter  6;    

Aspen  modelling  using  reacFon  kineFcs  to  model  fixed  bed  gasificaFon;  

Development  of  technique  to  perform  longitudinal  and  radial  gas  measurements  in  a  GEK;  

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