Oxygen Carriers for Chemical Looping Combustion - 4 000 h of Operational Experience
Oil & Gas Science and Technology - Rev. IFP Energies nouvelles, Vol.
Oxygen Carriers for Chemical Looping Combustion - 4 000 h of Operational Experience
A. Lyngfelt 0
0 Chalmers University of Technology , 412 96 Göteborg - Sweden
- Oxygen Carriers for Chemical Looping Combustion - 4 000 h of Operational Experience - Chemical Looping Combustion (CLC) is a new combustion technology with inherent separation of the greenhouse gas CO2. The technology involves the use of a metal oxide as an oxygen carrier which transfers oxygen from combustion air to the fuel, and hence a direct contact between air and fuel is avoided. Two interconnected fluidized beds, a fuel reactor and an air reactor, are used in the process. The outlet gas from the fuel reactor consists of CO2 and H2O, and the latter is easily removed by condensation. Considerable research has been conducted on CLC in the last years with respect to oxygen carrier development, reactor design, system efficiencies and prototype testing. Today, more than 700 materials have been tested and the technology has been successfully demonstrated in chemical looping combustors in the size range 0.3-140 kW, using different types of oxygen carriers based on oxides of the metals Ni, Co, Fe, Cu and Mn. The total time of operational experience is more than 4 000 hours. From these tests, it can be established that almost complete conversion of the fuel can be obtained and 100% CO2 capture is possible. Most work so far has been focused on gaseous fuels, but the direct application to solid fuels is also being studied. This paper presents an overview of operational experience with oxygen carriers in chemical looping combustors.
Chemical Looping Combustion (CLC) has emerged as an
attractive option for carbon dioxide capture because CO2 is
inherently separated from the other flue gas components, i.e.
N2 and unused O2, and thus no energy is directly expended
for the gas separation and no gas separation equipment is
needed. A CLC system is composed of an air and a fuel
reactor, and oxygen is transferred from air to fuel by the use of an
oxygen-carrier. A number of metal oxides have been
proposed and tested for use as oxygen carriers.
Chemical Looping Combustion was invented by Lewis
and Gilliland [
] sixty years ago as a way to produce carbon
dioxide, but long forgotten. Ishida et al. [
] proposed the use
of Chemical Looping Combustion for climate mitigation and
also started laboratory research on oxygen-carrier materials.
Since 2000, the research in CLC has been steadily increasing.
The need to find suitable oxygen-carrier materials for the
process, and comprehensive testing of these under realistic
conditions is a cornerstone in the development of this
technology. Another is to adapt the comprehensive experience from
circulating fluidized bed boilers to this application, in the
design of suitable reactor systems. Thus, the advancement of
the technology is heavily dependent on achieving actual
operational experience with oxygen carriers in well-working
circulating fluidized reactor systems. For the building of
experience and understanding of the process needed in the
further up-scaling of the technology, it is not a disadvantage
if these systems vary in design and size. This paper will
report on such operational experiences.
1 CLC APPLICATIONS
When looking at the requirements for oxygen carriers, as
well as for the process design, it needs to be pointed out that
there are a number of possible applications of chemical
looping technologies, using different fuels. For solid fuels, the
use in large power plants is the expected application, even
though there may be different ways of applying the
technology. One is the partial oxidation to produce hydrogen:
another is direct “combustion” of the solid fuel in the fuel
reactor. In the EU project ENCAP a first design of a 455 MWe
CLC solid fuel power plant was accomplished. This showed
potential of a very low efficiency penalty, 2-3%, as well as a
very low capture cost, around 10 €/ton of CO2 [
For gaseous fuels, again power production would be an
option. However, this should preferably involve a pressurized
system, in order not to lose too much efficiency compared to
presently used combined cycles. Another very attractive
option, chemical looping reforming, is to convert the fuel,
e.g. natural gas, to hydrogen, and thus provide a CO2 free
fuel. Chemical looping steam reforming was proposed by
Rydén et al. [
]. This process is similar to commercial steam
reforming of natural gas, but uses Chemical Looping
Combustion as heat source for the steam reforming and the
off-gas from the hydrogen separation as fuel, thus capturing
all carbon in the fuel. The process was investigated in
EUproject Cachet as a way to produce hydrogen for power
production. This hydrogen might not be competitive as fuel for
base-load power production, as the cost, around 38 €/MWh,
would be similar to crude oil, i.e. at 85 $/barrel. However, it
should be a useful fuel for many other applications and could
emerge as a very important fuel in a CO2-constrained future.
Moreover, there should be a number of applications where
Chemical Looping Combustion of gas could be used for
steam or combined steam/power production, and where
atmospheric operation would not be a major disadvantage
with respect to efficiency. An additional application could be
liquid fuels, e.g. heavy oils .
The application of chemical looping will thus be decisive
for the selection of oxygen carrier. Consequently, low cost
oxygen carriers are investigated for solid fuels, whereas
expensive and highly reactive materials have been in focus
for gaseous fuels.
2 OXYGEN CARRIER DEVELOPMENT
For the fluidized bed systems outlined above, important
criteria for a good oxygen-carrier are the following:
– high reactivity with fuel and oxygen, and ability to convert
the fuel fully to CO2 and H2O;
– low fragmentation and attrition, as well as low tendency
– low production cost and preferably being environmentally
The ability of the oxygen carrier to convert a fuel gas fully
to CO2 and H2O has been investigated thermodynamically
and the metal oxide systems of NiO/Ni, Mn3O4/MnO,
Fe2O3/Fe3O4, Cu2O/Cu, CoO/Co were found to be feasible to
use as oxygen carriers . For CoO/Co the thermodynamics
are not so favourable, with maximum 93.0% conversion at
1 000°C, and moreover this oxygen carrier is expensive and
involves health and safety aspects. Copper has the very
interesting ability to release oxygen, which is utilized in the
CLOU process (Chemical Looping with Oxygen Uncoupling)
proposed for solid fuels, e.g. . So far, most work has been
focused on NiO/Ni being the most reactive oxygen carrier.
In addition to the previously mentioned simple
monometallic oxides, also other oxides have potential for being
transferring oxygen. These include for instance various
sulphates, of which CaSO4 is the most studied, as well as a
number of bimetallic oxides. Among the latter the cheap
natural mineral ilmenite, FeTiO3, has received much
attention for use with solid fuels. Very interesting is also the
combination of manganese with a number of other oxides, which
gives oxygen carriers with the ability to release minor
amounts of oxygen [8-9].
Reviews show that there are clearly more than a hundred
publications investigating oxygen carriers [
]. All of the
early oxygen carrier development was made at Tokyo
Institute of Technology. In the last decade important work
has been made for instance at CSIC-ECB in Zaragoza and at
Chalmers, where totally > 700 materials have been
investigated by thermogravimetry or in laboratory fluidized bed. A
number of materials have also been in actual operation as
will be discussed below.
3 OPERATIONAL EXPERIENCE
The following overview summarizes the results from 41
scientific publications, relating more than 4 000 h of
operational experience of 29 materials in 12 different units. Results
from these units are presented in order of year of publication.
Lyngfelt et al. published results from a 10 kW prototype
unit in 2004 [
]. The unit has a circulating Air Reactor
(AR) and a bubbling Fuel Reactor (FR) with overflow
(Fig. 1). Two loop seals separate AR and FR. Here, an
oxygen-carrier based on nickel oxide was operated for 100 h
with natural gas as fuel. A fuel conversion efficiency of
99.5% was achieved, and no carbon dioxide escaped to the
Air Reactor, hence, all carbon dioxide was captured in the
process. Moreover, the attrition of particles was found to be
low, with loss of fines being around 0.002%/h. Later testing
in the same unit involves additional nickel oxide material
 and long term operation, > 1000 h, with a spray-dried
material demonstrating the use of commercial material
Also in 2004, Ryu et al. presented results from a 50 kW
combustor operating with methane as fuel; a nickel oxide
oxygen-carrier was tested during 3.5 h and a cobalt oxide was
tested during 25 h [
]. Also this unit used a circulating
AR and a bubbling FR, and a loop seal after the AR (Fig. 2).
However, outflow from the FR and thus the bed level was
controlled by a slide valve, and particles were returned to the
AR via a horizontal tube. Also in this unit high conversion of
fuel, 98%, was noted. Moreover, it was also verified that no
NO, NO2 or N2O is formed in the Air Reactor.
Later, Adanez et al. [
] operated a 10 kW CLC unit
for 120 h using a copper-oxide based oxygen carrier of two
particle sizes. In this unit both AR and FR are bubbling beds
with overflow exits leading to loop seals (Fig. 3). The
particles from the FR are led to the AR, whereas the overflow
from AR leads to a separate air-blown riser, blowing particles
to an intermediate storage (7). Circulation of particles is
controlled by a solids valve (5) controlling the flow from this
storage to the FR. Operational temperature was lower,
800°C, compared to what is often used with other materials.
Both particle sizes were in operation during 60 h with fuel.
Complete methane conversion was achieved and no
deactivation of the particles was noticed.
10 kW CLC at Chalmers University of Technology. To
facilitate the overview of the unit, some components have
been disconnected and rotated.
A number of oxygen carriers based on Ni, Mn and Fe
have been used in a 300 W CLC reactor at Chalmers with
both syngas and natural gas [
]. Here the FR is bubbling,
and has an outflow to the AR via a fluidized slot (Fig. 4).
2nd cyclone 1st cyclone
The AR has a higher velocity and particles thrown up from
AR come to a widening section where they fall back. Part of
this downflow is led through a downcomer leading directly
into the bed of the FR. In design 2 there is a fluidized loop
seal leading to the FR instead of the downcomer. Moreover
the slot is improved to reduce leakage. In both designs there
is some gas leakage between AR and FR.
The 300 W unit demonstrated the first successful use of
Mn-based and Fe-based particles [
]. Moreover, the unit
has shown the use of combined oxides, i.e. calcium
manganate . Also the unit has demonstrated the option of
partial oxidation of natural gas, giving a methane-free syn-gas
]. Total time of operation is more than 700 h.
Son and Kim used a mixed oxide system of NiO-Fe2O3/
Bentonite in a reactor of about 1 kW [
]. Both AR and FR
are bubbling beds in the form of concentric tubes with the
AR is placed inside the FR (Fig. 5). Both reactors have
outflows in the bottom leading to, and controlled by, loop seals
and from these loop seals the particles are led to risers
recycling the particles to FR/AR. The unit demonstrated
operation of particles mixing two active oxides, NiO and Fe2O3,
using various mixing ratios.
Berguerand used bituminous coal and pet coke in a 10 kW
CLC combustor designed for solid fuels [
demonstrating for the first time the use of solid fuels. The AR
is circulating and similar to Chalmers’ 10 kW unit for
gaseous fuels. The FR (Fig. 6) is a bubbling bed divided in
two sections by an underwear to create a more narrow
residence time distribution in the FR, in order to reduce char loss
to AR. There is also a small carbon stripper, 36 × 44 mm,
after the FR. AR and FR are separated by loop seals. Solid
fuel is fed on top of the Fuel Reactor by a fuel chute. The
operational experience firstly indicates a significant loss of
unconverted char, explained by the very short residence time
of fines in this system. Secondly, the fuel volatiles are
released in the fuel chute and leave the system unconverted as
they have essentially no contact with the oxygen carrier. The
conversion of the syngas produced by the char on the other
hand is around 90% or higher [
]. Lastly the CO2
capture was not complete as some char leaks to the AR. The
CO2 capture could be modelled as function of char reactivity
and circulation flow, using residence time distribution in
Moreover significant testing of Ni and Cu materials have
been performed in a 500 W unit by Adanez et al. [
The unit has a bubbling FR with overflow exit, leading
through a loop seal to the AR (Fig. 7). The AR is also
bubbling but has a narrow upper section through which particles
are entrained by a narrow riser to a container. The container
has a slide valve controlling the return flow to the FR. The
unit has extended the operational experience of fuels by the
study of ethane and propane, indicating that they have similar
reactivities as methane [
]. Moreover the negative effect
of higher concentrations of sulphur on nickel-based material
has been shown .
Vienna University of Technology successfully operated a
140 kW dual circulating fluidized bed system, with natural
gas, H2, CO, using ilmenite and nickel oxides, [
unit has a circulating AR leading the particles to the FR via a
loop seal, and the FR reactor is also circulating, albeit with
the return flow coming back to the FR (Fig. 8). The FR and
the AR have a direct fluidized connection in the bottom. As
material is circulated to the FR, the increased pressure drop
causes a movement of particles through this connection back
to AR. The operational experience include a wide range of
operational conditions, loads of 20-145 kW, temperatures of
O2, CO, CO2
CH4, CO2, CO, H2
1 Fuel reactor
2 Loop seal
3 Air reactor
6 Diverting solids valve
7 Solids valve
8 Water condenser
780-960°C and air ratios of 0.8-1.25. The lower air ratios
were used for syngas production. The unit shows a fuel
conversion up to 95% for CH4 and 99% for H2 and CO.
Shen et al. have operated with coal and biomass using
nickel- and iron-based oxygen carriers in a 10 kW unit [
The unit has a circulating AR leading to a FR also acting as
loop seal (Fig. 9). The FR is a spouted bed, and has an
outflow via a special direct connection to AR. Solid fuel is fed in
the bottom of the FR together with fluidizing gas. The unit
demonstrates the first use of biomass in CLC, using a
nickelbased oxygen carrier under 100 h . Similar testing with
coal, however, showed deterioration of oxygen carriers,
likely due to presence of sulphur [
]. Biomass was also
operated with iron oxide [
Alstom operated with natural gas and different nickel
oxides in a compact highly integrated 15-kW design [
Both AR and FR are circulating and the material is in both
cases led to seal-pots with double outlets, one flow is
recycled and the other is led to the other reactor. Four
nickelbased materials have been operated reaching conversions up
Ryu et al. designed a new 50 kW chemical looping
combustor which was operated with nickel and cobalt oxide
]. Both AR and FR are bubbling beds, Figure 10,
and fluidized by gas flows Q1 and Q2. Both AR and FR
contain an internal riser into which bed material is transferred
from the bubbling beds through holes. These risers are
fludized by the gas flows Q3 and Q4. The gas flow in each of
these risers carries the particles up to the reactor outlet, where
they are transported by the outlet flow to a cyclone which is
placed over the other reactor. The particles then fall down in
a downcomer leading down into the reactor bed. The
downcomers are immersed in the beds which means that both beds
also have the function of being loop seals. With a
nickelbased oxygen carrier 99.2% CO2 and 0.8% CO was attained
in the exit from the Fuel Reactor. Thus, the CO concentration
is a little higher than thermodynamic equilibrium for Ni/NiO
system. The absence of H2 in the exit gas is puzzling, as other
testing with Ni/NiO system always show concentrations at or
above equilibrium concentrations, i.e. above 1-1.5% depending
Wu et al. have presented operational data from a smaller
CLC unit for solid fuels operated with coal and an iron ore as
bed material [
]. Except for the size, and the introduction of
a loop seal in the passage from FR to AR, the unit, Figure 11,
is similar to the 10 kW unit previously described in Figure 9.
The ratio of carbon containing gases from the FR was
typically 1% CH4, 4% CO and 95% CO2. The data indicate that
reasonably high conversion of the gas from FR should be
possible using bottom bed feeding of coal.
In addition to these units a number of units of various
sizes are presently being planned or built, which will likely
provide operational data from new designs.
4 SUMMARY OF REACTOR TESTING
Thus, worldwide results from 12 chemical looping
combustors, in size range 0.3 to 140 kW, have been reported in
the last 6 years, Table 1. Total operational experience in
these units exceeds 4 000 h.
As seen above all units have different designs, some of
which are suitable for testing in smaller scale and giving
opportunities for careful circulation control. Also the sizes
differ, with some units, e.g. Vienna’s 140 kW, also having
designs and sizes more close to what could be expected in
future commercial designs. The dimensions of the units are
summarized in Table 2. All these units are also quite simple
and do not rely on any advanced or complex technology
solutions. Nevertheless, all of the units seem to have worked
well and, at least for the gas-fired units, produced highly
concentrated CO2 without losses to the stream coming from
the AR. Also the results from the units fired by solid fuels
suggest that high concentrations of CO2 and high CO2
capture should be possible given the proper design.
The operational experience also clearly indicates that a
significant number of materials have shown very good
performance. Moreover, the data highlight the availability of
a range of different materials for different purposes, from
highly reactive and expensive NiO materials to cheap natural
minerals which could be a better option for ash-rich solid
fuels. An overview of the materials tested is given in Table 3.
If the number of materials tested in each unit is summarized
the total is 47. However, some materials were tested in more
than one unit, so the total number of different materials tested
is 29. The active oxide in these 29 materials is based on
nickel (13), iron (8), nickel plus iron (3), manganese (3) cobalt
(1), and copper (1). Among the iron and manganese materials
is also found two combined oxides, here meaning that the
active oxide is actually a combined oxide, e.g. a bimetallic
oxide. This is the case for the mineral ilmenite, FeTiO3, and
for CaMn0.875Ti0.125O3. The majority of the materials are
manufactured, but among the materials tested two natural
ores and one industrial waste material are also found. Among
the manufactured materials there are also a significant
number of different production technologies.
Still the number of materials actually tested in operation is
limited whereas there are many interesting materials still
untested. Therefore, it is not unlikely that future results from
operation will include interesting data from a number of new
The work with gaseous fuels like natural gas, using
nickelbased particles has been highly successful. The work has
– nickel materials have very high reactivity, and, as it
seems, rather independent on starting materials and
a Refers to the number of material, i.e. for materials also tested in other units.
– the nickel materials can be manufactured from materials
commercially available in large quantities, at prices
reasonably close to the world market price of nickel;
– the nickel materials have sustained extended operation,
1 000 h, without losing reactivity and showing small loss
of fines, clearly indicating a long lifetime.
Obvious drawbacks with nickel materials are:
– the thermodynamic constraint, with maximum gas
conversions around 99%;
– the price. The expected long lifetime, however, suggests
that low overall costs for nickel materials should be
possible despite the fairly high price of nickel. It is also
expected that spent material, i.e. elutriated fines, can be
recycled for production of new particles;
– the toxicity, which will add to costs for ensuring safety for
health and environment.
As discussed before, nickel materials show high reactivity
with methane-based fuels like natural gas. Based on
measured kinetics and assuming perfect gas-solids contact, a very
small solids inventory of around 10-20 kg/MW would be
sufficient in the Fuel Reactor to reach full conversion, or, to be
more precise, reaching the thermodynamic limit [
However, in fluidized beds, the gas-solids contact is far from
perfect, as there is a by-pass of gas induced by bubbles.
Consequently, predictions based on kinetics and assuming
perfect gas-solids contact will underpredict needed
inventories, and much larger solids inventories would be needed in
reality. This was already observed in pilot unit studies, using
solids inventories of e.g. 133 and 500 kg/MW with
conversions of 89% and 98% . Two-phase modelling indeed
indicates the need of significantly larger solids inventory to
compensate for the imperfect contact between gas and solids
]. Moreover, the actual contact will be highly dependent
on fluidization conditions and reactor design, size, operating
conditions and bed material properties.
Therefore, scale effects may alter performance. As a
consequence, results from a pilot reactor of e.g. 100 kW cannot be
transposed directly to predict safely performance in much
larger units. A large unit could have a riser more than 10 times
higher, thus a freeboard containing large amounts of solids
which would be expected to give improved contact.
Moreover, such a unit would also operate at higher gas
velocities, which might also improve the mixing. On the other
hand, the much larger cross-section area could have negative
effect on the contact.
For other metal oxides the needed solids inventory would
generally need to be higher. The reactivity towards methane
is falling significantly in the order Ni > Cu > Mn > Fe. Here
another approach could be to use so-called CLOU materials,
i.e. oxygen carriers with the ability to release gaseous
oxygen, as these provide a possibility to circumvent the
gassolids contact issue in fluidized beds. For oxygen carriers
using the CLOU principle, the dependence on direct contact
between fuel gas and oxygen carrier particles is less crucial.
For instance, oxygen released in dense regions with
completely converted fuel, may mix with incompletely converted
gas in the upper parts of the riser or in the cyclone.
It can be speculated that the advantages of the oxygen
release of CLOU materials could compensate for a lower
reactivity with CH4 as compared to a nickel material, and that
a good CLOU material could perhaps even need less material
to reach full conversion. Experimental results give some
support for this idea, thus the operation with CuO particles,
known to have a CLOU effect, in the 10 kW unit at CSIC,
achieved complete fuel conversion with a solids inventory
corresponding to 290 kg/MW [
CLC with solid fuels will require a different design of the
Fuel Reactor, as well as oxygen carriers with other properties:
– the ash, normally being part of solid fuels, will make a
very long lifetime of the oxygen carrier unlikely, as this
ash needs to be removed from the reactor system.
Moreover, ash might directly affect the oxygen carrier.
Consequently, low cost materials like ilmenite and iron
ores have been studied;
– solid fuels, after having released volatiles that may react
directly with the oxygen carrier, will form a char residue
that cannot react directly with the oxygen carrier. This char
residue is gasified, e.g. by steam, producing syngas. The
gasification of char is a slow process, which means that the
Fuel Reactor needs a design that provides sufficient
residence time, in order to avoid char particles reaching the Air
Reactor. Char burning in the Air Reactor should be
avoided, as it will produce CO2 that will not be captured;
– in order to achieve high conversion of the volatiles, the
fuel needs to be fed to the Fuel Reactor in a way that
allows good contact between bed material and particles.
An advantage for solid fuels is that most oxygen carriers,
including low-cost iron-based materials, are highly reactive
towards the syngas released from gasification. However, the
syngas produced by the char particles is released inside the
bed, in contrast to gaseous fuels which are introduced from
below. Thus, some of the syngas released, e.g. in the upper
regions, will have insufficient contact with the bed material.
For this reason, complete conversion of the gas in the Fuel
Reactor would be difficult to obtain. The gas conversion in
the 1 kW unit in Nanjing reached approximately 95% [
and batch testing with devolatilized fuels in the Chalmers 10
kW unit, show conversion of the syngas up to 95% [
However, there are several options to reach complete or very
– the downstream introduction of pure oxygen to oxidize the
remaining unconverted gases H2, CO and CH4, i.e. an
‘‘oxygen polishing” step;
– the separation of these unconverted gases from the liquid
CO2 by e.g. distillation and recirculation to the Fuel
– using two Fuel Reactors in series, i.e. leading the
incompletely converted gas from the first Fuel Reactor to a
second Fuel Reactor;
– the use of CLOU oxygen-carriers, i.e. particles able to
release oxygen in the Fuel Reactor – oxygen which can
subsequently convert the remaining gases.
Although more development work is needed, it should be
pointed out that the CLC technology provides unique
advantages for avoiding the large costs and energy penalties
inherent in gas separation. In the case of gaseous fuels, the
technology should be ready to scale up to 1 or 10 MW size. For
the solid fuel application, more work is likely needed to find
the most optimal solution for the Fuel Reactor system.
The main obstacle in the development and commercialization
of the CLC technology, as with all CO2 capture technologies,
is the lack of real incentives. Moreover, large efforts to scale
up more established CO2 capture technologies may divert the
interest from a technology which is quite new, less well
known and which may need a longer time period to reach
commercial size. Nevertheless CLC is rapidly gaining
recognition as a potential break-through technology with respect
to cost and energy penalty, and intensified efforts to develop
the technology can be expected.
Chemical Looping Combustion has successfully been
operated in a number of units of varying designs in the size range
0.3 to 120 kW. This operation includes more than 4 000 h,
using close to thirty different oxygen-carriers. This is clearly
an indication that the technology as such works, although
further work is needed to find optimal scaled-up designs,
especially for solid fuels. A number of suitable oxygen-carrier
materials have been demonstrated, but on the other hand a
vast number of potentially interesting materials have never
been tested, so there should be a potential for finding
improved materials, both with respect to costs and performance.
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19 Adanez J., Gayán P. , Celaya J ., de Diego L., García-Labiano F. , Abad A. ( 2006 ) Chemical Looping Combustion in a 10 kWth Prototype Using a CuO/Al2O3 Oxygen Carrier: Effect of Operating Conditions on Methane Combustion, Ind . Eng. Chem. Res . 45 , 6075 - 6080 .
20 de Diego L., García-Labiano F. , Gayán P. , Celaya J. , Palacios J. , Adanez J . ( 2007 ) Operation of a 10 kWth chemical looping combustor during 200 h with a CuO-Al2O3 oxygen carrier , Fuel 86 , 1036 - 1045 .
21 Johansson E., Mattisson T. , Lyngfelt A. , Thunman H. ( 2006 ) A 300 W laboratory reactor system for chemical looping combustion with particle circulation , Fuel 85 , 1428 - 1438 .
22 Abad A. , Mattisson T. , Lyngfelt A. , Rydén M. ( 2006 ) Chemical looping combustion in a 300 W continuously operating reactor system using a manganese-based oxygen carrier , Fuel 85 , 1174 - 1185 .
23 Johansson E., Mattisson T. , Lyngfelt A. , Thunman H. ( 2006 ) Combustion of syngas and natural gas in a 300 W chemical looping combustor , Chem. Eng. Res. Des . 84 , 819 - 827 .
24 Rydén M. , Lyngfelt A. , Mattisson T. ( 2006 ) Synthesis gas generation by chemical looping reforming in a continuously operating laboratory reactor , Fuel 85 , 1631 - 1641 .
25 Abad A. , Mattisson T. , Lyngfelt A. , Johansson M. ( 2007 ) The use of iron oxide as oxygen carrier in a chemical looping reactor , Fuel 86 , 1021 - 1035 .
26 Rydén M. , Lyngfelt A. , Mattisson T. ( 2008 ) Chemical looping combustion and chemical looping reforming in a circulating fluidized-bed reactor using Ni-based oxygen carriers , Energ. Fuel . 22 , 2585 - 2597 .
27 Linderholm C. , Jerndal E. , Mattisson T. , Lyngfelt A. ( 2010 ) Investigation of Ni-based mixed oxides in a 300-W chemical looping combustor , Chem. Eng. Res. Des . 88 , 5 - 6 , 661 - 672 .
28 Rydén M. , Johansson M. , Lyngfelt A. , Mattisson T. ( 2009 ) NiO supported on Mg-ZrO2 as oxygen carrier for chemical looping combustion and chemical looping reforming , Energ. Environ. Sci. 2 , 970 - 981 .
29 Rydén M. , Lyngfelt A. , Mattisson T. ( 2011 ) CaMn0 . 875Ti0 . 125O3 as oxygen carrier for chemical looping combustion with oxygen uncoupling (CLOU) - experiments in continuously operating fluidized bed reactor system , Int. J. Greenhouse Gas Control 5 , 356 - 366 .
30 Moldenhauer P. , Rydén M. , Lyngfelt A. ( 2010 ) Testing of minerals and industrial by-products as oxygen carriers for chemical looping combustion in a circulating 300 W laboratory reactor , Submitted for publication.
31 Son S.R. , Kim S.D. ( 2006 ) Chemical Looping Combustion with NiO and Fe2O3 in a Thermobalance and Circulating Fluidized Bed Reactor with Double Loops, Ind . Eng. Chem. Res . 45 , 2689 - 2696 .
32 Berguerand N., Lyngfelt A. ( 2008 ) Design and Operation of a 10 kWth Chemical Looping Combustor for Solid Fuels - Testing with South African Coal , Fuel 87 , 2713 - 2726 .
33 Berguerand N., Lyngfelt A. ( 2009 ) Chemical Looping Combustion of Petroleum Coke using Ilmenite in a 10 kWth unit - High Temperature Operation, Energ . Fuel. 23 , 5257 - 5268 .
34 Berguerand N., Lyngfelt A. ( 2009 ) Operation in a 10 kWth Chemical Looping Combustor for Solid Fuel - Testing with a Mexican Petroleum Coke , Energy Procedia 1 , 407 - 414 .
35 Berguerand N., Lyngfelt A. ( 2009 ) Chemical Looping Combustion of Petroleum Coke using Ilmenite in a 10 kWth unit - High Temperature Operation, Energ . Fuel. 23 , 5257 - 5268 .
36 Berguerand N., Lyngfelt A. ( 2010 ) Batch Testing of Solid Fuels with Ilmenite in a 10 kWth Chemical Looping Combustor , Fuel 89 , 1749 - 1762 .
37 Markström P. , Berguerand N. , Lyngfelt A. ( 2010 ) The Application of a Multistage-Bed Model for Residence-Time Analysis in Chemical Looping Combustion of Solid Fuel, Chem . Eng. Sci. 65 , 5055 - 5066 .
38 Adanez J., Dueso C. , de Diego L., García-Labiano F. , Gayán P. , Abad A. ( 2009 ) Methane combustion in a 500 Wth chemical looping combustion system using an impregnated Ni-based oxygen carrier , Energ. Fuel . 23 , 130 - 142 .
39 Forero C.R. , Gayán P., de Diego L., Abad A. , García-Labiano F. , Adanez J . ( 2009 ) Syngas combustion in a 500 Wth Chemical Looping Combustion system using an impregnated Cu-based oxygen carrier , Fuel Process. Technol . 90 , 1471 - 1479 .
40 Garcia-Labiano F ., de Diego L., Gayán P. , Adanez J. , Abad A. , Dueso C. ( 2009 ) Effect of fuel gas composition in Chemical Looping Combustion with Ni-based oxygen carriers . Part 1 . Fate of sulphur, Ind. Eng. Chem. Res . 48 , 2499 - 2508 .
41 Gayán P. , Forero C .R., de Diego L.F., Abad A. , García-Labiano F. , Adánez J . ( 2010 ) Effect of gas composition in Chemical Looping Combustion with copper-based oxygen carriers: Fate of light hydrocarbons , Int. J. Greenhouse Gas Control 4 , 1 , 13 - 22 .
42 Dueso C. , García-Labiano F. , Adánez J ., de Diego L.F., Gayán P. , Abad A. ( 2009 ) Syngas combustion in a chemical looping combustion system using an impregnated Ni-based oxygen carrier , Fuel 88 , 12 , 2357 - 2364 .
43 de Diego L.F. , Ortiz M. , García-Labiano F. , Adánez J. , Abad A. , Gayán P. ( 2009 ) Hydrogen production by chemical looping reforming in a circulating fluidized bed reactor using Ni-based oxygen carriers , J. Power Sources 192 , 1 , 27 - 34 .
44 Adánez J., Dueso C. , De Diego L.F., García-Labiano F. , Gayán P. , Abad A. ( 2009 ) Effect of fuel gas composition in chemical looping combustion with Ni-based oxygen carriers. 2. Fate of light hydrocarbons , Ind. Eng. Chem. Res . 48 , 5 , 2509 - 2518 .
45 de Diego L.F. , Ortiz M. , García-Labiano F. , Adánez J. , Abad A. , Gayán P. ( 2009 ) Synthesis gas generation by chemical looping reforming using a Ni-based oxygen carrier , Energy Procedia 1 , 1 , 3 - 10 .
46 Adánez J., Garcá-Labiano F. , Gayán P. , de Diego L.F., Abad A. , Dueso C. , Forero C.R. ( 2009 ) Effect of gas impurities on the behavior of Ni-based oxygen carriers on chemical looping combustion , Energy Procedia 1 , 1 , 11 - 18 .
47 Kolbitsch P , Bolhàr-Nordenkampf J. , Pröll T. , Hofbauer H. ( 2009 ) Comparison of two Ni-Based oxygen carriers for chemical looping combustion of natural gas in 140 kW continuous looping operation , Ind. Eng. Chem. Res . 48 , 5542 - 5547 .
48 Kolbitsch P. , Bolhàr-Nordenkampf J. , Pröll T. , Hofbauer H. ( 2010 ) Operating experience with chemical looping combustion in a 120 kW Dual Circulating Fluidized Bed (DCFB) unit , Int. J. Greenhouse Gas Control. 4 , 2 , 180 - 185 .
49 Bolhàr-Nordenkampf J. , Pröll T. , Kolbitsch P. , Hofbauer H. ( 2009 ) Chemical looping autothermal reforming at a 120 kW pilot rig , Proceedings of the 20th International Conference on Fluidized Bed Combustion , pp. 603 - 607 .
50 Pröll T., Kolbitsch P. , Bolhàr-Nordenkampf J. , Hofbauer H. ( 2009 ) A novel dual circulating fluidized bed system for chemical looping processes , AIChE J . 55 , 12 , 3255 - 3266 .
51 Pröll T., Bolhàr-Nordenkampf J. , Kolbitsch P. , Hofbauer H. ( 2010 ) Syngas and a separate nitrogen/argon stream via chemical looping reforming - A 140 kW pilot plant study , Fuel 89 , 6 , 1249 - 1256 .
52 Kolbitsch P. , Pröll T. , Bolhàr-Nordenkampf J. , Hofbauer H. ( 2009 ) Design of a chemical looping combustor using a dual circulating fluidized bed reactor system , Chem. Eng. Technol . 32 , 3 , 398 - 403 .
53 Kolbitsch P. , Proll T. , Bolhàr-Nordenkampf J. , Hofbauer H. ( 2009 ) Characterization of chemical looping pilot plant performance via experimental determination of solids conversion , Energ. Fuel . 23 , 3 , 1450 - 1455 .
54 Kolbitsch P. , Pröll T. , Bolhàr-Nordenkampf J. , Hofbauer H. ( 2009 ) Operating experience with chemical looping combustion in a 120 kW Dual Circulating Fluidized Bed (DCFB) unit , Energy Procedia 1 , 1 , 1465 - 1472 .
55 Bolhàr-Nordenkampf J. , Pröll T. , Kolbitsch P. , Hofbauer H. ( 2009 ) Performance of a NiO-based oxygen carrier for chemical looping combustion and reforming in a 120 kW unit , Energy Procedia 1 , 1 , 19 - 25 .
56 Pröll T., Mayer K. , Bolhàr-Nordenkampf J. , Kolbitsch P. , Mattisson T. , Lyngfelt A. , Hofbauer H. ( 2009 ) Natural minerals as oxygen carriers for chemical looping combustion in a dual circulating fluidized bed system , Energy Procedia 1 , 1 , 27 - 34 .
57 Shen L. , Wu J. , Xiao J . ( 2009 ) Experiments on chemical looping combustion of coal with a NiO based oxygen carrier , Combust. Flame 156 , 3 , 721 - 728 .
58 Shen L , Wu J. , Xiao J. , Song Q. , Xiao R. ( 2009 ) Chemical looping combustion of biomass in a 10 kWth reactor with iron oxide as an oxygen carrier , Energ. Fuel . 23 , 2498 - 2505 .
59 Shen L. , Wu J. , Gao Z. , Xiao J . ( 2009 ) Reactivity deterioration of NiO/Al2O3 oxygen carrier for chemical looping combustion of coal in a 10 kWth reactor , Combust. Flame 156 , 1377 - 1385 .
60 Wu J., Shen L. , Xiao J. , Wang L. , Hao J . ( 2009 ) Chemical looping combustion of sawdust in a 10 kWth interconnected fluidized bed , Huagong Xuebao/CIESC J. 60 , 8 , 2080 - 2088 .
61 Mattisson T., Adanez J. , Proell T. , Kuusik R. , Beal C. , Assink J. , Snijkers F. , Lyngfelt A. ( 2009 ) Chemical Looping Combustion CO2 Ready Gas Power , Energy Procedia 1 1557 - 1564 .
62 Ryu H.-J. , Jo S .-H., Park Y.C. , Bae D .-H., Kim S. ( 2010 ) Long-term operation experience in a 50 kWth chemical looping combustor using natural gas and syngas as fuels , 1st International Conference on Chemical Looping , 17 - 19 March.
63 Wu J., Shen L. , Hao J. , Gu H. ( 2010 ) Chemical looping combustion of coal in a 1 kWth reactor , 1st International Conference on Chemical Looping , 17 - 19 March.
64 Mattisson T., Jerndal E. , Linderholm C. , Lyngfelt A. , Reactivity of a spray-dried NiO/NiAl2O4 oxygen carrier for chemical looping combustion, Submitted for publication .
65 Abad A. , Adánez J. , García-Labiano F. , De Diego L.F. , Gayán P. , Celaya J . ( 2007 ) Mapping of the range of operational conditions for Cu- , Fe- , and Ni-based oxygen carriers in chemical looping combustion , Chem. Eng. Sci . 62 , 533 - 549 .
66 Abad A. , Adánez J. , Dueso C. , García-Labiano F. , De Diego L.F. , Gayán P. ( 2010 ) Modeling of the chemical looping combustion of methane using a Cu-based oxygen-carrier , Combust. Flame 157 , 602 - 615 .
67 Linderholm C. , Cuadrat A. , Lyngfelt A. ( 2010 ) Chemical Looping Combustion of solid fuels in a 10 kWth pilot - batch tests with five fuels , 10th International Conference on Greenhouse Gas Control Technologies, Amsterdam, September 19 -23, (to be published in Energy Procedia).