Design of mixed fuel for heterogeneous reburning

Chen, Wei-Yin; Gathitu, Benson

doi:10.1016/j.fuel.2006.02.010

Cited by 20 publications

(10 citation statements)

References 42 publications

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“…This is a phenomenon that could be of benefit in reducing NO x emissions from coal-fired boilers by enhancing the effectiveness of both reburning and low-NO x burners. Enhanced production of volatile products due to weakened macromolecular structure and increases in pore volume during reburning results in higher NO reduction through homogeneous mechanisms by hydrocarbons and heterogeneous mechanisms on char surface. − Higher nitrogen evolution from coal in reburning also results in higher production of HCN. Although HCN can be recycled to NO in the burnout stage of reburning, we previously discovered that iron oxide can be used as an effective catalyst in converting HCN to N 2 in reburning .…”

Section: Resultsmentioning

confidence: 99%

“…Even when the Fe 2 O 3 is mixed with coal, it still clogs the particle feeder, jamming it. 41 Chen and Tang, 42 Chen and Gathitu, 43 and Su et al 31 have previously demonstrated that the minerals present in lignite can catalyze the conversion of HCN during reburning. Therefore, when conducting consecutive reburn and burnout tests without replacing the ceramic tubes, we were careful to run the bituminous coal samples first and then the lignite samples afterward.…”

Section: Apparatus and Procedures For Oxidation Tests Of Raw And Pret...mentioning

confidence: 99%

“…The same procedure was followed with regard to Fe 2 O 3 ; raw coals were run first before the mixed-fuel runs. To regenerate the tubes' normal (inert) activity, the technique developed previously by Chen and Gathitu 43 was used every time the tube was exposed to lignite and Fe 2 O 3 . The same care was taken when conducting oxidation tests, even though the effect of intermediate conversion might not be as important as it would be during reburning.…”

Section: Apparatus and Procedures For Oxidation Tests Of Raw And Pret...mentioning

confidence: 99%

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Effects of Pretreatment of Coal by CO₂ on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments

Gathitu

Chen

2009

Ind. Eng. Chem. Res.

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Polar solvents are known to swell coal, break hydrogen bonds in the macromolecular structure, and enhance coal liquefaction efficiencies. The effects of the pretreatment of coal using supercritical CO2 on its physical structure and combustion properties have been studied at the bench-scale level. Emphasis has been placed on NO reburning, NO emissions during air-fired and oxy-fired combustion, and loss on ignition (LOI). Pretreatment was found to increase porosity and to significantly alter the fuel nitrogen reaction pathways. Consequently, NO reduction during reburning using bituminous coal increased, and NO emissions during oxidation of lignite decreased. These two benefits were achieved without negative impacts on LOI.

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Section: Resultsmentioning

confidence: 99%

Section: Apparatus and Procedures For Oxidation Tests Of Raw And Pret...mentioning

confidence: 99%

Section: Apparatus and Procedures For Oxidation Tests Of Raw And Pret...mentioning

confidence: 99%

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Effects of Pretreatment of Coal by CO₂ on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments

Gathitu

Chen

2009

Ind. Eng. Chem. Res.

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“…They proposed a heterogeneous NO reduction mechanism that involves multifunctional roles of catalysts on the char surface, and carbon reactive sites. This mechanism has shown technological significance as low-cost, mixed fuels can be designed for effective reburning …”

Section: Introductionmentioning

confidence: 99%

Stable Oxides on Chars and Impact of Reactor Materials at High Temperatures

2007

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This paper reports our first study on the deactivation of young chars in flame conditions. The quantity and strength of surface oxides on young chars are monitored in situ by temperature-programmed desorption (TPD) up to 1700°C. Young chars contain more abundant surface oxides than old chars over a wide range of temperature. Lignite chars possess more oxides than chars derived from a bituminous coal. Chars oxidized at 629°C show desoprtion products at three distinct temperatures: 725, 1430, and 1700°C. The TPD peaks around 725°C correspond to activation energies in the range of 107-170 kJ/mol and have been well-documented in the literature. CO desorbed at around 1430°C corresponds to activation energies over 300 kJ/mol, signifying the possible roles of strongly bound oxides on the basal planes of carbon. Search of the oxygen source for the huge amount of CO production at 1700°C reveals that commonly adopted alumina tubes and support materials decompose to Al 2 O (g) and emit a notable amount of O 2 at temperatures above 1300°C. Moreover, alumina tube and support materials react with CO and form CO 2 ; they also react with carbon and form CO and aluminum oxycarbides. SiC tube, on the other hand, is oxidized by O 2 , CO 2 , and H 2 O and forms SiO (g) , SiO 2(s) , Si-(OH) 4(g) , and CO above 650°C. Moreover, Si can also form through a secondary reaction of SiC and SiO 2 .Thus, alumina appears suitable for the oxidation part of the experiments, where up to 120 ppm of O 2 emission is acceptable at a temperature of 1700°C. SiC appears acceptable for TPD, though a small amount of SiC may be oxidized by the TPD product, CO 2 , at temperatures above 900°C. Oxidation of SiC prior to TPD should be avoided.

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“…As is well-known, NO reduction reactions with solid fuels (e.g., coal, biomass) include a homogeneous mechanism involving NO reacting with volatiles and a heterogeneous mechanism involving NO reacting with chars. Chen, , Liu, and Lu studied the char contribution to the total NO reduction during coal reburning. Results indicated that coal types have an important influence on NO reduction and char heterogeneous reduction, namely that the char contribution to the total NO reduction increases with the increasing of the volatile matter content in the coal, and heterogeneous mechanisms are more important than homogeneous mechanisms for lignites.…”

Section: Introductionmentioning

confidence: 99%

Study on NO Reduction and Its Heterogeneous Mechanism through Biomass Reburning in an Entrained Flow Reactor

Wang

Huang³

et al. 2011

Energy Fuels

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The effects of biomass types (including cotton stalk, wheat straw, rice husk, and rice straw), the stoichiometric ratio in the reburning-zone (SR2), the reaction temperature in the reburning-zone (t 2), the particle sizes of biomass reburning fuels (d p), and the reburning fuel fraction (R ff) on NO reduction efficiency during biomass reburning were investigated systematically in an entrained flow reactor. The NO heterogeneous reduction mechanism resulting from the reburning of wheat straw and its char was analyzed. The results indicated that cotton stalk has the best performance of NO reduction, wheat straw is in second place, and rice husk and rice straw are less effective. In the range of t 2 = 900–1100 °C NO reduction efficiency increases when the reburning-zone reaction temperature is increased at the same SR2. NO reduction efficiency increases insignificantly with a decrease in the particle size of the biomass with d p < 425 μm. NO reduction efficiency follows a pattern of first increasing and then decreasing with the decreasing of the SR2 or the increasing of the R ff. The higher NO reduction efficiency (more than 50%) can be achieved in the range of SR2 = 0.7–0.8 or R ff = 20–25% during reburning with the four types of biomass. The contribution of NO heterogeneous reduction by wheat straw char to the total NO reduction was in the higher range of 59–68%, whereas the R ff was in the range of 10–26%.

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Design of mixed fuel for heterogeneous reburning

Cited by 20 publications

References 42 publications

Effects of Pretreatment of Coal by CO₂ on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments

Effects of Pretreatment of Coal by CO₂ on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments

Stable Oxides on Chars and Impact of Reactor Materials at High Temperatures

Study on NO Reduction and Its Heterogeneous Mechanism through Biomass Reburning in an Entrained Flow Reactor

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Design of mixed fuel for heterogeneous reburning

Cited by 20 publications

References 42 publications

Effects of Pretreatment of Coal by CO2 on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments

Effects of Pretreatment of Coal by CO2 on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments

Stable Oxides on Chars and Impact of Reactor Materials at High Temperatures

Study on NO Reduction and Its Heterogeneous Mechanism through Biomass Reburning in an Entrained Flow Reactor

Contact Info

Product

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Effects of Pretreatment of Coal by CO₂ on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments

Effects of Pretreatment of Coal by CO₂ on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments