Transcript Imperial College London

Some Aspects of Calcium Looping
Research at Imperial College, London
J. Blamey, N.H. Florin, N. Paterson, D.R. Dugwell and P.S. Fennell*
Department of Chemical Engineering, Imperial College, London
*[email protected]
1st I.E.A. High Temperature Solid Looping Cycles Network Meeting
INCAR, Oviedo, Spain, 17th September, 2009
Overview
• Introduction to calcium looping / using CaO-based sorbents for CO2 capture
• Current projects relating to calcium looping in our group
• Focus on a project related to hydration of spent sorbent
• Focus on a project related to co-precipitation of synthetic sorbents
Introduction to Calcium Looping
• Thank you to the previous speakers on the subject!
Current Projects
• Optimisation of reactivation strategies for exhausted sorbents for CO2, focusing on
hydration [sponsored by EPSRC]
• Design of synthetic sorbents by co-precipitation in a slurry bubble column [sponsored
by the Grantham Institute for Climate Change, Imperial College]
• Applications of the calcium looping cycle to cement manufacture [joint with industrial
partner]
• Morphology changes of limestone sorbent particles during carbonation/calcination
looping cycles in a TGA (also useful for sorbent enhanced H2 production) and
reactivation with steam [joint project with CANMET, Canada, funded by KAUST]
• H2 production via sorbent-enhanced water-gas shift reactions [IC / KAUST]
• UK /China H2 production network (Imperial, Cambridge, Cranfield, Sheffield, Tsinghua,
Taiyuan, NCEPU, TPRI, EPSRC funded)
• Many other projects in the field of CO2 capture, including amines, oxyfuel and
chemical looping, as part of the Imperial College Centre for Carbon Capture and
Storage (IC4S)
Reactivation of Sorbent using Hydration
• If a calcined sorbent is
hydrated, upon calcination an
improved uptake of CO2 can be
observed
• Previous work has focused on
TGA and low temperature
fluidised bed environments
• Investigate reactivation of
‘spent’ sorbents using a small,
bench scale, fluidised bed
reactor
• more realistic conditions
than previously studied
• potential to study attrition
effects
Sorbent reactivated
[Fennell et al, 2007]
Design of Reactor
• Designed, built and tested
for this project
• Small fluidised bed (ID = 21
mm)
• Resistance heated furnace
• Temperature range of up to
1000 °C at ambient
pressure
• Capable of cycling between
two temperatures to allow
carbonation and calcination
within same vessel
• Gas and fines vented to
atmosphere
Experimental Work
Cycling experiments,
varying calcination
temperature
Sorbent hydration
Creation of spent sorbent: Standard cycling
experiments, 15% CO2, atmospheric pressure, 4.3
g Havelock limestone (500-710 µm) in 8 mL bed of
sand (355-425 µm), flow rate ~ 8 U/Umf 13 cycles
of carbonation for 900 s at 700 °C and calcination
for 900 s with variation of calcination temperature.
Tcalc = 840, 900, 950, 1000 °C
Hydration: 38 hrs in a humid vessel at room
temperature. Particles of Havelock limestone
found to be fully hydrated under these
conditions
Further cycling
experiments, constant
calcination temperature
Further cycling experiments: Standard
conditions, with constant Tcalc of 840 °C
Mass measurements: Sample is carefully
weighed before and after each cycling experiment
Effect of Calcination Temperature Before Hydration
Tcalc = 840 °C
after hydration
Increasing
Tcalc
Particles
hydrated after
13th cycle
• Experimental data for Tcalc
= 840 (◆), 900 (◼), 950 (▴)
and 1000 (×) °C
• Fits of data to the Grasa
Equation for the cycles
before hydration of Tcalc =
840 (—) and 950 (---) °C
• After hydration, all
limestones are cycled under
the same conditions
• Error bars shown are one
standard deviation on 5
experiments
Mass Lost As Fines During 26 Cycles
• Note: Typically 10 %
mass lost in 13 cycles
before hydration
• Mass loss is
calculated as mass
loss of sample
(calcined) as a
percentage of
theoretical maximum
• Error bars shown are
one standard deviation
on 5 experiments
Carrying Capacity Normalised for Mass Lost
• When carrying capacity is
normalised for mass loss during
an experiment, similar
deactivation curves are
observed for each sample experimental data shown for
Tcalc = 840 (◆), 900 (◼) and 950
(▴) °C
• It is possible to conclude that:
for particles large enough to
remain within the bed, hydration
has reactivated them to the
same extent, independent of
cycling conditions before
hydration
Analytical Techniques
Pycnometry
• Skeletal (or absolute) density
measured by helium displacement
• Measures density of
particles excluding pores
• Envelope density measured by
fine powder displacement
• Measures density of
particles including pores
Nitrogen adsorption analysis
• Investigation of nitrogen adsorption isotherms varying pressure - yields information about
surface area and porosity of a sample
• From the above isotherm, the following can be
calculated
• Brunauer-Emmett-Teller (BET) surface area
• Barrett-Joyner-Halenda (BJH) pore volume:
yields estimates of pore size distribution
Gas Adsorption and Density Analysis
After
first
calcination
After
cycling
After
hydration
• Separate experiments were ran
for gas adsorption and density
analysis: all results are for
calcined samples
• Tcalc = 840 (▴), 900 (◼), 950 (●)
• Pore volume associated with
small pores decreases upon
cycling and with increasing
calcination temperature
• Pore volume increases after
hydration, hence reactivation
• Densification of particles is
observed upon cycling and to be
greater for samples cycled at
higher values of Tcalc [Manovic et
al, 2009]
• Particles become considerably
less dense after hydration: the
least dense are the most friable
Optical Micrographs Before and After Hydration
• Examples of particles before (left column) and after (right column) hydration.
Two particles cycled at 1113 K show small increase in size upon hydration. One
particle cycled at 1273 K shows larger increase in size upon hydration and mild
fragmentation, whereas the other shatters. Quartz cylinders (diameter 0.48 mm)
used as reference distance.
Stress Distribution in the Growing Hydroxide Layer
Balance on moles of Ca
 Ca (OH )2 (1   Ca (OH ) 2 4
4
3
3  CaO2 1   CaO 
 (r2 3  r13 )
  (r0  r1 )
3
72
3
56


4
3
 r0 3  r13
3
3
 r1 
r r
3
 X  1     0 3 1
4
r0
 r0 
 r0 3
3
(r2  r1 )  X r0
3
3

3

 CaO (1   CaO )
72
 Ca (OH ) (1   Ca (OH ) ) 56
2
2
r0 (1 - X )  r1
3
3
2
3
3
r2   X r0  r0 (1 - X )
3
3
3
3
3
Geometry
r2
 { X  (1 - X )}
3
r0
r2  r0{ X  (1 - X )}1/ 3
r2  r0
r
 { X  (1 - X )}1/ 3  1 
r0
r
r0
Initially CaO,
subsequently
Ca(OH)2
2
Oxide grows
from the inner
boundary
3
(r2  r0 (1 - X ))  X r0 
3
Ca(OH)2
 CaO (1   CaO )
72

 Ca (OH ) (1   Ca (OH ) ) 56
(r2  r1 )  X r0 
3
r2
r1
Stress Distribution in the Growing Hydroxide Layer (2)
 CaO (1   CaO ) 72

 Ca (OH ) (1   Ca (OH ) ) 56
2
porosity of CaO, prior to
hydration.
2
{ X  (1 - X )}
1/ 3
(1   ) 
1 
E


E
{ X  (1 - X )}1 / 3  1  
(1   )
18
16
14
0.4
10
0.5
8
6
relationship between conversion,
stress in growing hydroxide layer
and value 
Shown left is the stress in the growing hydroxide
layer as a function of conversion for three
different initial envelope porosities of CaO
The lower the initial porosity (i.e. the higher the
temperature of calcination), the lower the
conversion before a given stress level is
reached: the more highly stressed the oxide; the
greater the chance of fragmentation
12
Stress (MPa)
 increases with decreasing
0.6
4
2
0
0.00
0.20
0.40
0.60
Conversion
0.80
1.00
Ultimate tensile
stress of concrete
Conclusions of Hydration Work
• Upon hydration, more highly sintered sorbents are reactivated to a
lesser extent
• This is because of their increased friability upon hydration
• A model has been developed that establishes a link between the
porosity of a particle (which decreases upon sintering) and the tensile
strength
• The lower the initial porosity, the lower the conversion before a given
stress level is reached
Design of Synthetic Sorbents by
Co-precipitation in a SBC
• Objective: to create sorbents of high longterm reactivity and better mechanical
stability
• For synthetic sorbents to compete with
natural sorbents, it is necessary for the
synthesis route to be straightforward and the
reactants inexpensive
• Hence, precipitation in a Slurry Bubble
Column (SBC)
• Literature shows that a highly reactive
sorbent powder can be produced by a
precipitation method using a SBC [e.g. Gupta
and Fan, 2002]
• However, although precipitated sorbents
show good short term reactivity, they are very
prone to reactivity decay due to sintering
[Florin and Harris, 2008]
Design of Synthetic Sorbents by
Co-precipitation in a SBC
• Our current work focuses on achieving high
long term reactivity and better mechanical
strength
• Literature shows that a sorbent of high longterm reactivity can be achieved using inert
supports, e.g. mayenite (Ca12Al14O33) and/or
magnesium oxide (MgO) [e.g. Li et al., 2005,
Pacciani et al., 2008]
• Can we use a SBC to co-precipitate
calcium carbonate and aluminum
hydroxide?
• Thermodynamic studies performed within
the group suggest that yes, we can
Design of Synthetic Sorbents by
Co-precipitation in a SBC: Exptl.
•Main hypothesis: Better distribution of CaO
achievable via co-precipitation vs. wet mixing
or hydrolysis methods
• Experiments performed in a SBC, varying:
Ca(OH)2 loading and derivation
amount of Al(NO)3.9H2O solution
presence of dispersant (propan-2-ol)
presence of inorganic additives
• carbonation initiated by bubbling through
CO2 – precipitating CaCO3 seeded on finely
dispersed Al(OH)3
•Preliminary results indicate high capture
capacity on a g-CO2/g- sorbent basis
compared to Havelock; and method suited to
using Ca2+ dissolved from natural limestone
Co-precipitation of CaCO3 and Al(OH)3
Figure 1 (left) Weight change associated with CO2 capture-and-release for PCC with 15 wt. %
mayenite through 30 cycles – calcination 5 min at 900 °C, carbonation 10 min at 650 °C (15
% CO2); Figure 2 (right) Carrying capacity of four synthetic sorbents compared to Havelock
Optimisation and scale-up
Figure 1 (left) slurry bubble column;
Figure 2 (centre) preliminary extrusion experiment;
Figure 3 (right) bench-scale FBR
Acknowledgements
Engineering and Physical Sciences Research Council (EPSRC), UK
King Abdullah University of Science and Technology (KAUST), Saudi Arabia
National Resources, Canada
The Grantham Institute for Climate Change, Imperial College
Prof. Ben Anthony
Prof. Rafael Kandiyoti
Dr. Yinghai Wu
Charles Dean
Kelvin Okpoko
References
Fennell, P.S., Davidson, J.F., Dennis, J.S., and Hayhurst, A.N., Regeneration of sintered
limestone sorbents for the sequestration of CO2 from combustion and other systems.
Journal of the Energy Institute, 2007. 80(2): p. 116-119.
Florin, N.H. and Harris, A.T., Screening CaO-based sorbents for CO2 in biomass gasifiers.
Energy and Fuels, 2008. 22(4): p. 2734-2742.
Gupta, H. and Fan, L.S., Carbonation-calcination cycle using high reactivity calcium oxide
for carbon dioxide separation from flue gas. Industrial & engineering chemistry research,
2002. 41(16): p. 4035-4042.
Li, Z.-S., Cai, N.-S., Huang, Y.-Y., and Han, H.-J., Synthesis, experimental studies, and
analysis of a new calcium-based carbon dioxide absorbent. Energy & Fuels, 2005. 19(4):
p. 1447-1452.
Manovic, V., Charland, J.-P., Blamey, J., Fennell, P.S., Lu, D.Y., and Anthony, E.J.,
Influence of calcination conditions on carrying capacity of CaO-based sorbent in CO2
looping cycles. Fuel, 2009. 88(10): p. 1893-1900.
Pacciani, R., Muller, C.R., Davidson, J.F., Dennis, J.S., and Hayhurst, A.N., Synthetic Cabased solid sorbents suitable for capturing CO2 in a fluidized bed. The Canadian journal of
chemical engineering, 2008. 86(3): p. 356-366.