CHALLENGES IN PROCESS
SCALE-UP OF SERPENTINITE
CARBONATION TO PILOT
SCALE
Martin Slotte
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
1
Introduction
 This presentation involves the evaluation of
technical challenges when scaling up a carbon
dioxide sequestration process based on
mineral carbonation from laboratory scale to
pilot scale
 Challenges in process scale-up of serpentinite carbonation to
pilot scale, Slotte et. al. (CAPOTE 2012 proceedings)
 Total lime kiln gas compression for CO2 mineral sequestration
Slotte et. al. (ECOS 2013 under review)
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
2
Background
 Problem: Increasing atmospheric CO2
levels
– (One) option: Carbon dioxide capture and
storage (CCS)
• Underground storage
– Not applicable everywhere, including Finland
• Ocean storage
– Also not applicable in Finland
• CO2 mineral sequestration (a.k.a. CCU)
– An interesting alternative
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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Process
 The process considered is the CCU process under
development at Åbo Akademi University
 The process involves
– the production of magnesium hydroxide, Mg(OH)2,
from magnesium silicate based material using
ammonium sulphate salt, followed by
– carbonation of the Mg(OH)2 in a pressurised fluidised
bed reactor at ~500°C, 20-30 bar CO2 partial pressure
– recovery of the ammonium sulphate salt
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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CO2 mineral sequestration
THE ÅAU ROUTE
Mg-extraction
Mg(OH)2 production
Magnesium silicate mineral
(e.g. serpentinite)
Ammoniumhydroxide
Ammonia
HEAT
NH3
AS* + Mgsilicate
reactor
MgCO3 production
CO2 lean gas
+ H2O
Magnesium(and iron)
extraction
MgSO4 etc.
Mg(OH)2
Pressurised
fluidised bed
> 20 bar, > 500°C
MgCO3
+ MgSO4
AS
Ammoniumsulphate
recovery
Ammoniumsulphate
*Ammonium sulphate
AS
SiO2 m.m.
Iron oxide
(→ iron/steel industry)
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
CO2 rich
flue gas
08/03/2013
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Pilot plant for serpentinite carbonation
 Pilot plant envisioned for a ~200 t/d lime
kiln located in south-western Finland
 Pilot plant intended to process 600 kg/h
kiln gas containing 21 %-vol (dry) CO2
 The process layout needs to be
evaluated with the availability of standard
components taken into account
 Continuous process
 Recycling of chemicals
 Hot kiln gas to be used as heat source
for the endothermic reactions, currently
the gas is quenched from 460°C to
260°C
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
Stream
Serpentinite rock
Ammonium sulphate solution (aq)
Reacted serpentinite
Water
Dissolution slurry (aq)
Solution 1 (aq)
Un-dissolved solids
Precipitation slurry 1 (aq)
Solution 2 (aq)
Precipitation solids 1
Precipitation slurry 2 (aq)
Solution 3 (aq)
Precipitation solids 2
Exhaust gas
Gas solid mixture
Reacted solids
Reacted exhaust gas
Reaction gas
Ammonia solution (aq)
Steam
Water
Ammonium sulfate solution (aq)
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
Flow (kg/h)
550
1000
931.8
900
1832
1531
301
1582
1545
36
2137
1865
272
600
872
381
491
642
642
846
846
1019
08/03/2013
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System layout
14
Precipitate
27
1 Exhaust
Rock silogasfilter
heat1recovery heat exchanger
15
Precipitation
tank
2 (crystallizer)
28
2 Reaction
Serpentinite
gasheater
recovery
fan
16
Precipitate
slurry
2 pump
29
3 Reaction
Ammonium
gas
sulphate
cooler
tank
17
Precipitation
filter
2 solution
30
4 Reaction
Ammonium
gassulphate
condenser
fan pump
18
Magnesium
31
5 Reaction
Water tank
gashydroxide
condenserheater
(scrubber)
19
Magnesium
intermediate silo
32
6 Ammonium
Water pumphydroxide
solution pump
20
Magnesium
feeder silo
33
7 Ammonium
Serpentinite hydroxide
reactor cooler
solution
Reacted serpentinite heat recovery heat
21
gas cooler
34
8 Exhaust
Ammonium
solution dosing pump 1
exchanger
22
Exhaust
gas tank
compressor
withpump
inter 2coolers
35
9 Ammonium
Dissolution
solution dosing
23
Exhaust
gas heater
10 Ammonium
36
Slurry pump
sulphate regeneration
Fluidized
bed sulphate solution
reactor
Regenerated
ammonium
24
11 Solids filter
37
(bubbling/circulating)
pump
25
Particle
separation
12 Steam
38
Precipitation
condenser
tank 1cyclone
(crystallizer)
26
Exhaust
gasslurry
expansion
turbine
13 Water
39
Precipitate
pump
1 pump
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
7
Exergy production and consumption
Exergy consuming
Exergy as heat
Equipment
MJ/kg CO2
Gas compressor
1.52
Serpentinite reactor
5.44
Serpentinite
reactor
5.01
preheater
Exhaust gas heater
0.76
Mg (OH)2 pre-heater
0.25
Exergy producing
Equipment
Expansion turbine
Dissolution tank
Reaction gas cooling
Exergy as heat
MJ/kg CO2
1.01
0.19
6.24
PFB reactor
Reacted serpentinite heat
recovery heat exchanger
Steam condenser
0.07
1.08
2.80
 Several exergy producing and consuming
units
 Waste heat from the lime kiln is needed to
close the exergy balance
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
8
Technical challenges
 Still several variable properties such as:
– Density, viscosity and solid fraction of liquids
– Size, shape and hardness for solids
– Mineral quality
 Material related challenges
–
–
–
–
Corrosive nature of liquids
High temperatures
High pressures
Volumes
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
9
Serpentinite reactor
 Major problems
– Multi-stage reactor
•
•
•
•
Drying of AS solution
Mixing of solid AS with serpentinite particles
Heating of mixture to ~400°C
Reaction stage takes 20-60 min
– Continuous reactor, possibly a rotary kiln
 Minor problems
– Heating to be done with hot exhaust gas from the lime kiln
• Cannot be direct contact heat exchange (gas/solid particle) due to
interference with conversion reaction
– Material transport into and inside reactor
– Reaction gases utilised in later stages » gas tight reactor
Mg3Si2O5(OH)4 + 3(NH4)2SO4
=
3MgSO4 + 2SiO2 + 5H2O(g) + 6NH3(g)
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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Precipitation tanks
 Major problems
– Control of precipitated crystal size
• temperature control
• pH control
– Different optimal conditions for tank 1 & 2
• pH 9 and 50°C in tank 1 and pH 11.5 and 80°C
3MgSO4 + 6NH3(g) + 6H2O(l)
=
3(NH4)2SO4 + 3Mg(OH)2
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
11
Exhaust gas compression
 Major problems
– ~20-30 bar CO2 partial pressure needed leading to
~80 bar total gas pressure
– Compressor intercoolers needed for efficient
compression
– Exhaust gas contains SOx and other impurities that
can cause problems
– Suitable size compressor not commercially
available
– Use of high pressure turbocharger + compressor
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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Exhaust gas compression exergy study
 Exergy analysis is used as the tool for the evaluation
of different compression strategies.
 The goal of the analysis is to find the strategy which
requires the least of external exergy fed to the
process and the one in which the least amount of
exergy is destroyed.
 Several different compressor configurations are
compared and evaluated based on the exergy balance
and financial costs.
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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Full exhaust gas compression model
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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Four-stage compression exergy study
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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Three, four and five-stage compression
comparison
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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Compression strategy comparison based
on temperature
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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Pressurized fluidized bed reactor
 Major problems
– Optimal Mg(OH)2 particle size for efficient
carbonation
– Bubbling vs. circulation bed
– In Finland there several manufacturers of FBR but
no PFBR manufacturers but due to small size a
custom built PFBR is feasible
 Minor problems
– High-pressure reactor in otherwise mostly nonpressurised process
– Pressure vessel regulation
3Mg(OH)2 +3CO2(g) = 3MgCO3 +3H2O(g)
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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Conclusions
 Several component and material related problems still to be
solved
 More lab tests needed to refine the process steps
 Minimising the loss of AS and recovering the AS are important
 Process water balance and treatment needs to be studied
 Heat and energy integration of the process with the lime kiln to
be done
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
19
Acknowledgments
 The authors want to acknowledge the Academy of Finland’s
Graduate School of Energy Efficiency and Systems (20122015) for the financial support for the research
 Experience Nduagu, Inês Romão and Johan Fagerlund of
ÅA are acknowledged their insights into carbon dioxide storage
by mineralization process.
 The authors would also like to acknowledge Nordkalk and in
particular Thomas Nyberg and Matias Erikssson
 Finnish CCSP CLEEN OY motivating this pre-study
Thank you for your attention
Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo
08/03/2013
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