HS retention with Ca-based sorbents in a pressurized fixed-bed reactor: application to moving-bed design

Adánez, Juan; Abad, Alberto; Garcı́a-Labiano, F.; DEDIEGO, L; Gayán, Pilar

doi:10.1016/j.fuel.2004.10.004

Cited by 14 publications

(7 citation statements)

References 14 publications

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“…At the beginning of the oxidation period no oxygen could be seen in the produced gas, since it reacted with ilmenite, re-oxidizing it. After this period, the breakthrough curve of oxygen appeared, which is different depending on the reactivity of the bed material [37]. The profiles show that the slope increased significantly with the number of cycles, which was due to the activation process and increase in the reaction rate that was later proven with TGA analysis.…”

Section: Reactivity In Oxidationmentioning

confidence: 84%

Behavior of ilmenite as oxygen carrier in chemical-looping combustion

Cuadrat

Abad

Adánez

et al. 2012

Fuel Processing Technology

225

147

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For a future scenery where will exist limitation for CO 2 emissions, Chemical-Looping Combustion (CLC) has been identified as a promising technology to reduce the cost related to CO 2 capture from power plants. In CLC a solid oxygen-carrier transfers oxygen from the air to the fuel in a cyclic manner, avoiding direct contact between them. CO 2 is inherently obtained in a separate stream. For this process the oxygen-carrier circulates between two interconnected fluidized-bed reactors. To adapt CLC for solid fuels the oxygen-carrier reacts with the gas proceeding from the solid fuel gasification, which is carried out right in the fuelreactor. Ilmenite, a natural mineral composed of FeTiO 3 , is a low cost and promising material for its use on a large scale in CLC.The aim of this study is to analyze the behavior of ilmenite as oxygen-carrier in CLC.Particular attention was put on the variation of chemical and physical characteristics of ilmenite particles during consecutive redox cycles in a batch fluidized-bed reactor using CH 4 , H 2 and CO as reducing gases. Reaction with H 2 was faster than with CO, and near full H 2 2 conversion was obtained in the fluidized-bed. Lower reactivity was found for CH 4 . Ilmenite increased its reactivity with the number of cycles, especially for CH 4 . The structural changes of ilmenite, as well as the variations in its behavior with a high number of cycles were also evaluated with a 100 cycle test using a CO+H 2 syngas mixture. Tests with different H 2 :CO ratios were also made in order to see the reciprocal influence of both reducing gases and it turned out that the reaction rate is the sum of the individual reaction rates of H 2 and CO. The oxidation reaction of ilmenite was also investigated. An activation process for the oxidation reaction was observed and two steps for the reaction development were differenced. The oxidation reaction was fast and complete oxidation could be reached after every cycle. Low attrition values were found and no defluidization was observed during fluidized-bed operation. During activation process, the porosity of particles increased from low porosity values up to values of 27.5%. The appearance of an external shell in the particle was observed, which is Fe enriched. The segregation of Fe from TiO 2 causes that the oxygen transport capacity, R OC , decreases from the initial R OC = 4.0% to 2.1% after 100 redox cycles.

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Section: Reactivity In Oxidationmentioning

confidence: 84%

Behavior of ilmenite as oxygen carrier in chemical-looping combustion

Cuadrat

Abad

Adánez

et al. 2012

Fuel Processing Technology

225

147

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“…In a fixed bed, the reacting gases go through a Fe 3 O 4 layer before they react with fresh Fe 2 O 3 . Syngas reacts with iron oxide in a transition zone. The length of the transition zone in the iron oxide bed could be used to know the iron oxide inventory needed to convert a determined flow of gasified gases.…”

Section: Resultsmentioning

confidence: 99%

“…Syngas reacts with iron oxide in a transition zone. The length of the transition zone in the iron oxide bed could be used to know the iron oxide inventory needed to convert a determined flow of gasified gases. However, there are some difficulties in calculating the reacting zone for the gas concentrations resulting from pyrolysis change, and the tarry material is unknown at present.…”

Section: Resultsmentioning

confidence: 99%

Reduction of Iron Oxide as an Oxygen Carrier by Coal Pyrolysis and Steam Char Gasification Intermediate Products

Yang¹,

Cai²,

Li³

2007

Energy Fuels

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The feasibility of the reduction of oxygen carrier Fe 2 O 3 in chemical-looping combustion using solid fuel (lignite) provided a gasifying agent like steam was introduced into the reactor was investigated with a fixedbed reactor. The X-ray diffractometer and scanning electron microscope were used for the characterization of the Fe 2 O 3 and its reduction residue. Results strongly supported the feasibility of Fe 2 O 3 reduction by lignite and obtaining pure CO 2 from the off-gases. Fe 2 O 3 can be fully converted to Fe 3 O 4 by pyrolysis and gasification intermediates primarily H 2 and CO, which was confirmed by both the off-gas concentrations and X-ray diffractometer analysis. A 0.75 g portion of Fe 2 O 3 can be completely reduced to Fe 3 O 4 by the volatile matter released from 0.1 g coal, and Fe 2 O 3 can be fully reduced to Fe 3 O 4 by steam char gasification products provided that the molar ratio of carbon in char to Fe 2 O 3 is 1:6. The purity of CO 2 in the outlet gases was higher than 85% when Fe 2 O 3 was reduced by intermediate products during coal pyrolysis, and the purity of CO 2 in the off-gases was higher than 95% when Fe 2 O 3 was reduced by intermediate products resulting from steam char gasification, making CO 2 sequestration disposal desirable for high purity CO 2 . The char gasification reaction rate was slow compared with the reactivity of the iron oxide with the char gasified intermediates, indicating that char gasification was the rate-limiting step in the reduction process. In the steam char gasification process, the times it took to reach 90% carbon conversion for K-10-char and Ca-10-char were 15 and 30 min, respectively, at 1123 K, but the time for the raw char was 50 min at 1173 K.

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“…Among the different approaches that can be taken for sulfur abatement is the use of dolomite, a well-known desulfurization agent − especially suitable for application in fixed-bed reactors. Furthermore, it also shows significant tar cracking activity. , Finally, nickel-containing catalysts have been widely studied for tar reforming of the product gas from coal or biomass gasification. ,, In this work, the effectiveness of these two materials for hot gas conditioning has been tested for the specific case of co-gasification of sewage sludge and coal blends.…”

Section: Introductionmentioning

confidence: 99%

Desulfurization and Catalytic Gas Cleaning in Fluidized-Bed Co-gasification of Sewage Sludge–Coal Blends

García

Μοnzόn²,

Bimbela³

et al. 2013

Energy Fuels

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Energy recovery from digested sewage sludge can be achieved by means of co-gasification with coal in a fluidizedbed system. In this regard, one of the main hurdles in developing a feasible process is the need for gas cleaning, with special emphasis on desulfurization and minimization of the tar content of the product gas. In this work, high-temperature catalytic gas cleaning was investigated by means of two fixed beds placed in series downstream of the gasification system: the first containing dolomite for desulfurization and primary tar cracking and the second containing a nickel-based catalyst for additional gas reforming. The effect of the temperature on the performance of the Ni catalyst bed (800−900 °C) was assessed. The use of dolomite in a secondary bed at 800 °C allowed for a significant reduction in both tar [15−0.21 g/m 3 standard temperature and pressure (STP)] and H 2 S (to less than 0.01%) and an increase in the heating value of the gas [lower heating value (LHV) from 2000 to 2800 kJ/m 3 STP]. The use of the Ni catalyst decreased the tar content of the gas to undetectable levels. The best results were obtained with the Ni-based catalyst at 800 °C, in terms of enhanced LHV (increasing from 2000 to 3300 kJ/m 3 STP), gas production, which increased from around 2.40 to 2.75 m 3 STP/kg on a dry and ash-free basis (daf), and energy requirements for the process. However, some evidence of Ni catalyst deactivation was found when operating under these conditions.

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HS retention with Ca-based sorbents in a pressurized fixed-bed reactor: application to moving-bed design

Cited by 14 publications

References 14 publications

Behavior of ilmenite as oxygen carrier in chemical-looping combustion

Behavior of ilmenite as oxygen carrier in chemical-looping combustion

Reduction of Iron Oxide as an Oxygen Carrier by Coal Pyrolysis and Steam Char Gasification Intermediate Products

Desulfurization and Catalytic Gas Cleaning in Fluidized-Bed Co-gasification of Sewage Sludge–Coal Blends

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