Kinetics of redox reactions of ilmenite for chemical-looping combustion

Abad, Alberto; Adánez, Juan; Cuadrat, Ana; Gayán, Pilar; Diego, Luis F. de

doi:10.1016/j.ces.2010.11.010

Cited by 277 publications

(259 citation statements)

References 53 publications

(68 reference statements)

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“…Nevertheless, the intrinsic reactivity of ilmenite particles is higher than the values showed in Fig. 12 [40]. Thus, the reaction rate of ilmenite increases with the temperature, but the resulting increased oxygen transfer was mainly because char was further gasified at higher temperatures and there were more gasification products which were oxidized.…”

Section: T (ºC)mentioning

confidence: 41%

“…When gasifying with higher fraction of CO 2 only CO is produced, whereas when gasifying with H 2 O, H 2 is also generated. Although ilmenite reacts faster with H 2 than with CO, the reaction rate of ilmenite is fast enough and the resulting  comb FR or  T have no substantial change if the gasification products are enriched in H 2 or CO. As it was calculated by Abad et al [40], an inventory of 189 kg/MW th would be enough to fully oxidize the generated CO at 900ºC, and for H 2 the inventory needed would be even lower: 66 kg/MW th . However, in these experiments the solids inventories about 1500 kg/MW th are used.…”

Section: Combustion Efficiency and Oxygen Demandmentioning

confidence: 95%

“…The temperature influences the  comb FR of all types of coals in a similar way as the slopes of the curves are similar. The activation energy of the reaction of CH 4 with ilmenite is higher than with H 2 and CO [40], and a coal with high volatile content could be slightly more influenced by the temperature, but the differences are not relevant. For all the temperatures tested,  comb FR was higher for anthracite, followed by lignite and MV bituminous South African coal.…”

Section: Combustion Efficiency and Oxygen Demandmentioning

confidence: 97%

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Relevance of the coal rank on the performance of the in situ gasification chemical-looping combustion

Cuadrat

Abad

Gayán

et al. 2012

Chemical Engineering Journal

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In this work the CLC process for solid fuels using ilmenite as oxygen carrier was evaluated in a continuous CLC unit. In this process, gasification of solid fuel happens in the fuel reactor which is fluidized by a gasifying agent, i.e, H 2 O. This process has been referred as in-situ Gasification CLC, iG-CLC. The feasibility of using fuels ranging from lignite to anthracite and the effect of the coal rank on the process performance was evaluated. The carbon capture efficiency followed the trend of the coal rank, as it was higher for lignite, then for the bituminous coals and it was lower for anthracite. Special attention was put on the combustion of the volatile matter of the different fuels. In all cases oxygen demands lower than 10% were found; for anthracite the oxygen demand values were 3.5% because of the lower volatile content of this fuel. A temperature increase was proven to be advantageous to reach high carbon capture and combustion efficiencies for all the fuels tested. Also, the feasibility of using H 2 O:CO 2 mixtures as gasification agent with each type of fuel was also assessed and it was seen that in case of bituminous coals and lignite some of H 2 O can be replaced by CO 2 .

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Section: T (ºC)mentioning

confidence: 41%

Section: Combustion Efficiency and Oxygen Demandmentioning

confidence: 95%

Section: Combustion Efficiency and Oxygen Demandmentioning

confidence: 97%

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Relevance of the coal rank on the performance of the in situ gasification chemical-looping combustion

Cuadrat

Abad

Gayán

et al. 2012

Chemical Engineering Journal

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“…Many particles exhibit this kind of behavior (e.g. [19,20]) and this assumption can remain valid up to particle sizes of 1 mm or more [21].…”

Section: 01mentioning

confidence: 99%

Investigation into the effect of simulating a 3D cylindrical fluidized bed reactor on a 2D plane

2013

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Abstract2D planar simulations of 3D cylindrical fluidized bed reactors are routinely carried out in order to reduce computational costs. The error involved in this simplification is largely unknown, however, and this study was therefore conducted to quantify this error over a wide range of reactor operating conditions. 2D and 3D simulations were carried out over a wide range of flow conditions in the bubbling fluidization regime by changing the fluidization velocity, bed mass, reaction temperature and particle size. Detailed comparisons revealed that 2D simulations qualitatively behaved similarly to 3D simulations, but overpredicted reactor performance (measured by the degree of conversion achieved) by about 45% on average. Large systematic variations of this error were also observed with changes in all four independent variables investigated. These large errors were due to two primary factors; incorrect predictions of the gas residence time by misrepresentations of the bed expansion and incorrect predictions of the mass transfer by misrepresentations of bubble formation and the splash zone at the top of the expanded bed. The mass transfer error was found to be most influential and was also confirmed as the most important factor to be correctly predicted by CFD simulations. 3D predictions of the mass transfer resistance were further analysed to identify the particle size as a very influential variable through which the mass transfer characteristics in fluidized bed reactors can be influenced. IntroductionFluidized bed reactors find application in a wide range of process industries dealing with gas-solid or solid catalysed reactions. The fluid-like behaviour of these reactors results in excellent heat and mass transfer performance which is highly favourable for any reactor process. Fluidized bed reactors can be very challenging to design and scale up, however, and commercialisation of processes utilising such reactors therefore typically consists of a large number of incremental scale-up and demonstration steps. For this reason, there is a great need for modelling tools that can be used to reduce the risk of taking larger scale-up steps.The fundamental flow modelling framework of computational fluid dynamics (CFD) is considered in this work to be a viable methodology for achieving this purpose. CFD inherently accounts for the complex and tightly interconnected non-linear interactions between reactor hydrodynamics, heat transfer, species transfer and reaction kinetics. Because of this fundamental basis, it is reasoned that CFD can provide the generality demanded of a modelling tool used for fluidized bed reactor design, optimization and scale-up.CFD simulations face their own challenges, however. The primary challenge is presented by the mesoscale structure formation characteristic of any fluidized bed reactor process. Small clusters of particles are formed within these beds due to the non-linear drag interaction between the gas and solids and have a very large influence on all physics occurring within the reactor...

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“…Furthermore, a reasonable recirculation ratio must be chosen in order to avoid the excessive dilution of the syngas that would lead to a dramatic decrease in the reduction rate. H 2 and/or CO contents lower than 30 vol.% in the feed will significantly reduce ilmenite reactivity [50], and therefore the assumption of narrow reduction fronts during stage (A) would be erroneous. Fig.…”

Section: Reduction Stagementioning

confidence: 99%

Chemical looping combustion process in fixed-bed reactors using ilmenite as oxygen carrier: Conceptual design and operation strategy

Fernández

Alarcón

2015

Chemical Engineering Journal

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A process scheme based on a series of fixed-bed reactors is presented as a possible alternative for carrying out the chemical looping combustion of methane at high pressure with ilmenite as oxygen carrier. The oxygen carrier is stationary and it is alternately exposed to reducing and oxidizing atmospheres by means of the periodic switching of the gas feeds (i.e., methane and air, respectively). Cyclones and filters for the separation of gases and solids are not needed in fixed-beds, which allows a more compact reactor design. Moreover, the operation at high pressure permits the use of highly efficient power cycles. However, more complex heat management strategies and switching valves able to function at very high temperatures are required in these systems. The continuous cyclic operation of a packed-bed chemical looping combustion process is described using a basic reactor model. A sequence of four stages: reduction, steam reforming, oxidation and heat removal ensures the production of a continuous high temperature and high pressure gas stream able to efficiently drive a gas turbine for power generation in combination with a steam cycle. At the same time, a concentrated stream of CO 2 suitable for transport and storage is also produced. The use of suitable recycles of the product gases makes it possible to control the progression of the reaction and the heat exchange fronts, which improves the heat management of the CLC process.The inclusion of steam methane reforming in the process allows the conversion of the ingoing methane to syngas, which enhances the reduction kinetics of the ilmenite and the overall combustion efficiency of the process. A preliminary design for an inlet flow of 10 kg/s of methane (500 MWt) has shown that a minimum of five reactors, 10 m long, with an inner diameter of 6.7 m, would be required to fulfil the overall process assuming cycles of 10 minutes with maximum pressure drops per stage of less than 6 %.These results demonstrate the potential of this novel technology for power generation in combination with CO 2 capture.

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Kinetics of redox reactions of ilmenite for chemical-looping combustion

Cited by 277 publications

References 53 publications

Relevance of the coal rank on the performance of the in situ gasification chemical-looping combustion

Relevance of the coal rank on the performance of the in situ gasification chemical-looping combustion

Investigation into the effect of simulating a 3D cylindrical fluidized bed reactor on a 2D plane

Chemical looping combustion process in fixed-bed reactors using ilmenite as oxygen carrier: Conceptual design and operation strategy

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