Presentation of the main results of my PhD thesis. It includes both experimental and numerical analysis.

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

2. 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.

3. INTRODUCTION
Biomass
Energy
environmental
polluFon
energy
security
depleFon
of
fossil
climate
change
3

4. BIOMASS
“plant
material,
vegetaFon,
or
agricultural
waste
used
as
a
fuel
or
energy
source”
4

5. BIOMASS
UTILIZATION
Biodiesel
Ethanol
ETBE
Hydrocarbons
Bio-oil
Producer Gas
Pellets
Transesterification
Combustion
Raw Material Process Intermediate Product Final Product
Vegetal Oil
Sugar & Starch
Lignocellulosics
Wet Biomass
Hydrolysis -
Fermentation -
Destilation
Pyrolysis -
Hydrogenation
Fisher - Tropsh
Gasification
Biogas
Pelletization
Anaerobic Digestion
Chemicals Transport Biofuels
Electricity
Heating
5
GASIFICATION

6. 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

7. TYPES
OF
GASIFICATION
AIR
GASIFICATION
Oxygen
gasificaFon
HydrogasificaFon
PyrolyFc
gasificaFon
Near-­‐
and
super-­‐criFcal
water
7

8. 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
C+CO2↔2CO
C+H2O↔CO+H2
CnHm+nH2O↔nCO+(m/2+n)H2
CnHm+nCO2↔2nCO+m/2H2
REDUCTION
H2O
Tat
CH4
PRODUCER GAS
CO2
H2O
CO
H2
HEAT
dry biomass H2O

9. TYPES
OF
GASIFIER
According
to
the
reactor
design,
there
are
4
different
types
of
gasificaFon.
FIXED
BED
Fluidized
bed
Entrained
flow
Twin-­‐bed
9

10. FIXED
BED
GASIFIERS
DowndraE
gasifier
Co-­‐current
flow
design;
thus,
both
the
biomass
and
the
air
and
producer
gas
follow
a
downward
movement
10

11. 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

12. 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

13. SIMULATION
OF
GASIFICATION
PROCESSES
GASIFICATION
MODELS
CFD
Thermo.
equilibrium
kinecFcs
based
ASPEN
PLUS
neural
network
13

14. ASPEN
PLUS
14

15. PREVIOUS
WORK
KINECTIC
AND
CFD
MODELS
THERMODYNAMIC
EQUILIBRIUM
MODELS
EXPERIMENTAL
15

16. GASIFICATION
EXPERIMENTS
Experimental
study
on
75
kWth
downdraE
(biomass)
gasifier
system
(Sharma
2009)
• Fed
with
woodchips
• Longitudinal
temperature
• Longitudinal
pressure
• Outlet
gas
composiFon
16

17. 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

18. 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

19. THERMODYNAMIC
EQUILIBRIUM
MODELS
Thermochemical
equilibrium
modelling
of
a
gasifying
process
(Melgar
et
al.
2007)
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.
19

20. 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

21. 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

22. CHAR
GASIFICATION
IN
A
CONTINUOUS
FIXED
BED
REACTOR
-­‐
CFIBR
22

23. EXPERIMENTAL
APPARATUS
!1
!3
!4
!5
!6
!7
!8
!9
!!10
thermocouple!/pressure!sensor!and
gas!sampling!probe
volume!flowmeter/controller
23
!M
!M
!V
mass!flowmeter/controller
!V
!M
C3H8
Air
H2O
!2
!12
!!11
!i
a
b
c
d
e
f
g
200mm
1600!mm
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.

24. 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
ceramic#insulator
refractory#concrete#burner#cover
refractory#concrete#disk
burner
200#mm
Reactor#centre

25. CONTINUOUS
FIXED
BED
OPERATION
Charcoal
feeding
systems
Ash
and
residues
removal
system
25
12#cm
!
11#cm
Closed Open
10#cm

26. PRODUCTION
AND
CHARACTERIZATION
OF
THE
BIOMASS
USED
Charcoal
from
woodchips
Granulometric
analysis
and
parZcles
size
distribuZon
26
20#mm 20#mm
(A) (B)
cumula5ve
0 2 4 6 8 10 12 14 16 18
100
80
60
40
20
0
dp)(mm)
mass)(%)
differen5al

27. 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

28. INSTRUMENTATION,
MEASUREMENTS
AND
CALCULATIONS
Gas
composiZon
GC 28
Reactor*wall
Reactor*interior
Filter*and*
dryer
Gas
Temperature*readings
Flow*control/*measurement*(4)
Filter*(2)
Condenser*(3)
Sampling*probe*(1)

29. mechanical work being produced by the system and kinetic and
negligible, Eq. 5.10 can be reduced to
ℎ௜,௝(푇) = ℎ௜,௝
MASS
AND
ENERGY
BALANCES
଴ is the standard enthalpy of formation of the component the specific heat and T is the medium temperature.
Mass
Energy
− 푄̇௟௢௦௧ = 0 The heat loss is calculated according to Eq. 5.17
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
0 = 푄̇௟௢௦௧ + ෍ 푚̇௜௡
௜௡
ℎ௜௡ − ෍푚̇௢௨௧
௢௨௧
ℎ௢௨௧ 5.11
balance is given by the difference between inlet reagents and outlet
and residues). It can be mathematically expressed by Eq. 5.12.
0 = ෍ 푚̇௜௡
௜௡
− ෍ 푚̇௢௨௧
௢௨௧
5.12
reagents are charcoal and the reactive atmosphere gases are
CO2, H2O. The outlet products are the producer gas (H2, CO, CH4,
addition to solid residues removed from the bottom.
෍ ℎ௜௡푚̇௜௡
௜௡
= 푚̇஼ ℎ஼ + ෍ 푚̇௜
௝
ℎ௜ 5.13
଴ (푇) + න 퐶௣(௜,௝)(푇)푑푇
்బ
where ℎ௜,௝
Combining Eq. 5.11 and Eq. 5.14, the final equation for calculating balance is:
푚̇஼ ℎ஼ + ෍ 푚̇௜
௜
ℎ௜−푚̇ோ஼ ℎோ஼ − ෍푚̇௝ℎ௝
௝
푄̇௟௢௦௧ = ℎ௖퐴푑푇 where hc is the convective heat transfer coefficient of the process, transfer area of the surface and dT is the temperature difference between and the ambient.
5.4 Operational parameters

30. CHAPTER 5 – CHAR GASIFICATION ON A CONTINUOUS FIXED BED REACTOR - CFIBR
OPERATIONAL
PARAMETERS
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
108
30

31. 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

32. ESTABLISHMENT
OF
STEADY
STATE
From
start
to
steady
state
Bed
level
32
Cooling!down
0 1 2 3 4 5 6 7 8 9 10 11 !!!
1100
1000
900
800
700
600
500
400
300
200
100
0
Time!(h)
!Temperature!(°C)
T2
T3
T4
T5:T10
T11
T12
Hea<ng Steady!state
12
Thermal!stabilisa<on Bed!level!
1010
950
900
850
800
750
stabilisa<on 0 10 20 30 40 50 !!!
Time!(min)
!Temperature!(°C)
T3
T4
T6
T8
T10
60

33. 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

34. REACHING
STEADY
STATE
Temperature
34
Cooling!down
0 1 2 3 4 5 6 7 8 9 10 11 !!!
1100
1000
900
800
700
600
500
400
300
200
100
0
Time!(h)
!Temperature!(°C)
T2
T3
T4
T5:T10
T11
T12
Hea<ng Steady!state
12
Thermal!stabilisa<on Bed!level!
stabilisa<on

35. 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

36. STEADY
STATE:
VARIATION
OF
PROPERTIES
ACROSS
THE
REACTOR
Gas
composiZon
profiles
36
O2 CO2 H20
0 5 10 15 20
Inlet
333
T3
T4
T5
T6
T7
T8
T9
Outlet
Concentra9on3(%)
Probe3loca9ons
CO
H2
CH43x310
0 5 10 15 20 25 30 35 43
Inlet
333
T3
T4
T5
T6
T7
T8
T9
Outlet
Species3mass3Flow3(g/min)
Probe3locaEons
O2 H20
H2
CO2
CH43x310
CO
Longitudinal
profiles
of
concentraFon
and
species
mass
flow
in
Experiment
A.

37. STEADY
STATE:
VARIATION
OF
PROPERTIES
ACROSS
THE
REACTOR
CHAPTER 5 – CHAR GASIFICATION ON A CONTINUOUS FIXED BED REACTOR - CFIBR
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 Centr
e 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
37
Gas
composiFon
profiles:
Comparison
of
concentraFon
on
the
radial
and
longitudinal
profile
of
Experiment
A/B.

38. MASS
AND
ENERGY
BALANCES
Experiment
A/B
Experiment
C
283.3#g/min
38
276.6$g/min
7.4$g/min
Gasifica'on
Reac'ons
6.3631$kW
Tin$=$1060$°C
28$g/min
260.6$g/min
$0.533$kW
6.252.30$kW
Tout$=$770$°C
Char Gas Enthalpy$flux Heat$lost
9.9#g/min
Gasifica'on
Reac'ons
7.8556#kW
Tin#=#1080#°C
28#g/min
269.1#g/min
#0.533#kW
7.1887#kW
Tout#=#760#°C
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%.

39. 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
!1
!3
!4
!5
!6
!7
!8
!9
!!10
thermocouple!/pressure!sensor!and
gas!sampling!probe
volume!flowmeter/controller
mass!flowmeter/controller
!V
!M
C3H8
Air
H2O
!2
!12
!!11
!i
a
b
c
d
e
f
g
200mm
1600!mm
100!mm
Flare

40. GASIFICATION
IN
A
25KW
THROATED
FIXED
BED
BIOMASS
GASIFIER
40

41. EXPERIMENTAL
APPARATUS
41
This
is
the
GEK
Gasifier
Experimenters
Kit
Flare Hopper
Reactor
Cyclone
PyroCoil
Auger
Drying2Bucket
Filter

42. 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
Nozzles
5@&0.6&ID&caps
17.8
7.6
10.2 45.7 10.2
19.0
Rotary&Crank/Drive
37.5
15.2 5
28
Rotary&Support&Grate

43. 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.

44. INSTRUMENTATION
AND
MEASUREMENTS
Pressure
Fixed
pressure
measuring
points
are
located
at
the
boYom
of
the
reactor
and
a`er
the
filter.
44
Flare Hopper
Reactor
Cyclone
PyroCoil
Auger
Drying2Bucket
Filter

45. INSTRUMENTATION
AND
MEASUREMENTS
Gas
composiZon
45
Mass
flowmeter
GC
Vacuum0Pump
Condenser0(2)
Sampling0tube0(3)
Flow0control/0measurement0(4)
Vent
Probe0and0Filtre0(1)
Gas
is
sampled
and
analysed
every
30min
following
the
European
Tar
Protocol.

46. 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

47. PRODUCTION
AND
CHARACTERIZATION
OF
THE
BIOMASS
USED
47

48. 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

49. EXPERIMENTAL
PROCEDURES
AND
PARAMETERS
OperaZonal
parameters
• Three
types
of
pellets
comprising
mixed
wood,
Miscanthus
and
wheat
straw
• 11
experiments
• Air
inlet
varies
49

50. 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

51. 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

52. 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

53. MAIN
ACHIEVEMENTS
commissioning
of
the
GEK
gas
sampling
line
Temperature
profiles
and
beYer
understanding
of
the
behaviour
in
the
reducFon
zone
53
Flare Hopper
Reactor
Cyclone
PyroCoil
Auger
Drying2Bucket
Filter

54. SIMULATION
OF
CHAR
GASIFICATION
PROCESS
IN
A
CONTINUOUS
FIXED
BED
REACTOR
USING
ASPEN
PLUS
54

55. 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

56. 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

57. 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

58. ASPEN
PLUS
GASIFICATION
MODEL
58

59. ASPEN
PLUS
GASIFICATION
MODEL
59
Yield
reactor
–
converts
the
non-­‐
convenFonal
stream
BIOMASS
into
convenFonal
components
(C,
H,
O,
N
and
ash)

60. 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

61. ASPEN
PLUS
GASIFICATION
MODEL
61
Gibbs
free
energy
reactor
–
calculates
the
equilibrium
composiFon
of
the
combusFon
and
gasificaFon
products

62. ASPEN
PLUS
GASIFICATION
MODEL
Three
soluZons
methods
are
used
to
simulate
the
gasifier,
each
involving
only
a
change
to
the
block
GASIFIER
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.
62

63. 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
!

64. 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

65. NON-­‐STOICHIOMETRIC
EQUILIBRIUM
METHOD
WITH
temperature
approach:
Gasifier
temperature
is
the
equilibrium
temperature.
65
0.2
0.16
0.12
0.08
0.04
0
CO2
H2
#510 #400 #300 #200 #100 0 100 200 300 400 500
Tapp.(K)
Concentra9on
CO
H2O
CH4
#170.K

66. NON-­‐STOICHIOMETRIC
EQUILIBRIUM
METHOD
WITH
temperature
approach:
Gasifier
temperature
is
the
equilibrium
temperature.
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%
!
66

67. Based on that, the following reactions (Eq. 7.17 to Eq.7.21) calculate the products (H2, CO, CO2, CH4, H2O, O2, N2 and C) that are elements C, H, O. This results in 9 products, 3 elements and 5 reactions.
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
푪 + ퟐ푯ퟐ → 푪푯ퟒ 푪푯ퟒ + 푯ퟐ푶 → 푪푶 + ퟑ푯ퟐ 푪푶 + 푯ퟐ푶 → 푪푶ퟐ + 푯ퟐ 푪 + 푶ퟐ → 푪푶ퟐ 푵ퟐ + ퟐ푶ퟐ → ퟐ푵푶ퟐ Sensitive analysis was applied to every equation, except Eq.

68. SENSITIVITY
ANALYSIS
ReacZon
68
This results in 9 products, 3 elements and 5 reactions.
푪 + ퟐ푯ퟐ → 푪푯ퟒ 7.17
푪푯ퟒ + 푯ퟐ푶 → 푪푶 + ퟑ푯ퟐ 7.18
0.2
푪푶 + 푯ퟐ푶 → 푪푶ퟐ + 푯ퟐ 7.19
CO2 CO
푪 + 푶ퟐ → 푪푶ퟐ 7.20
푵ퟐ + ퟐ푶ퟐ → ퟐ푵푶ퟐ 7.21
0.16
0.12
0.08
0.04
0
"500 "450 "400 "350 "300 "250 "200 "150 "100 "50 0
analysis was applied to every equation, Tapp..".EQ2.(except K)
Eq. 5.7 that has no
results, as N2 is considered inert. This equation was used only to
Mol.Frac:on
."260.K
H2
CH4
H2O
CH4.*10

69. SENSITIVITY
ANALYSIS
ReacZon
69
푪 + ퟐ푯ퟐ → 푪푯ퟒ 7.17
푪푯ퟒ + 푯ퟐ푶 → 푪푶 + ퟑ푯ퟐ 7.18
푪푶 + 푯ퟐ푶 → 푪푶ퟐ + 푯ퟐ 7.19
.#190.K
푪 + 푶ퟐ → 푪푶ퟐ 7.20
0.2
0.16
0.12
H2
CO
푵ퟐ + ퟐ푶ퟐ → ퟐ푵푶ퟐ 7.21
0.08
Mol.Frac:on
CO2 H2O
Sensitive analysis was applied to every equation, except Eq. 5.7 that has no
0.04
results, as N2 is considered inert. This equation was used only to
0
#500 #400 #300 #200 #100 0 100 200 300 400 500
process restriction. A variation of ±500 degrees Tapp..#.EQ3.(K)
was applied to each
turn, while the remaining reactions were kept with no temperature

70. results in 9 products, 3 elements and 5 reactions.
results in 9 products, 3 elements and 5 reactions.
푪 + ퟐ푯ퟐ → 푪푯ퟒ 7.17
OPTIMIZED
METHOD
푪푯ퟒ + 푯ퟐ푶 → 푪푶 + ퟑ푯ퟐ 7.18
Tapp
=
-­‐260
Tapp
=
-­‐170
70
푪푶 + 푯ퟐ푶 → 푪푶ퟐ + 푯ퟐ 7.19
ASPEN Experiment Difference
푪 + 푶ퟐ → 푪푶ퟐ 7.20
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%
analysis was applied to every equation, except Eq. 5.7 that has no
results, as N2 is considered inert. This equation was used only to
!
process restriction. A variation of ±500 degrees was applied to each
푪 + ퟐ푯ퟐ → 푪푯ퟒ 7.17
푪푯ퟒ + 푯ퟐ푶 → 푪푶 + ퟑ푯ퟐ 7.18
푪푶 + 푯ퟐ푶 → 푪푶ퟐ + 푯ퟐ 7.19
푪 + 푶ퟐ → 푪푶ퟐ 7.20
푵ퟐ + ퟐ푶ퟐ → ퟐ푵푶ퟐ 7.21
푵ퟐ + ퟐ푶ퟐ → ퟐ푵푶ퟐ 7.21
analysis was applied to every equation, except Eq. 5.7 that has no
results, as N2 is considered inert. This equation was used only to

71. VALIDATION
Data
of
Van
de
Steene
(2010)
71
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
7.4 8.8 3.1
UC
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
!

72. MAIN
ACHIEVEMENTS
Non-­‐
stoichiometric
with
Non-­‐stoichiometric
Tapp
Stoichiometric
with
Tapp
72

73. GENERAL
CONCLUSION
73

74. 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.
74

75. 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;
75

76. 76