Effects of oxy-fuel conditions on the products of pyrolysis in a drop tube reactor

Heuer, Sebastian; Senneca, Osvalda; Wütscher, Annika; Düdder, Hendrik; Schiemann, Martin; Mühler, Martin; Scherer, Viktor

doi:10.1016/j.fuproc.2016.04.034

Cited by 72 publications

(20 citation statements)

References 37 publications

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“…These results are in agreement with other research on coals of similar rank (Angeles G. Borrego & Alvarez, 2007;C. Wang et al, 2012;Zeng et al, 2008) and they disagree with those obtained by Senneca and Schiemann groups Heuer et al, 2016); However, the differences between experimental conditions are the main cause of results divergence.…”

Section: Impact Of Pyrolysis Atmospheres On Char Reactivitysupporting

confidence: 90%

“…The highest heating rate is evidenced in this environment because of lower energy density (r • Cp) in comparison to the energy density of CO 2 (Kim et al, 2014;Molina & Shaddix, 2007;Tolvanen & Raiko, 2014). Also, the presence of spongy masses of micronic diameter (1 to 2 micrometers), similar to those found by Heuer et al (2016), and characterized in detail by Apicella et al ( 2016) was visible. In agreement with the work of Heuer et al, more of these micronic particles were found in the char obtained under atmosphere of CO 2 than under N 2 .…”

Section: Valdés Betancur López Gómez and Chejnementioning

confidence: 67%

“…Therefore, is important to note, that despite the apparent abundance of reports on the effects of devolatilization in oxy-combustion, the fact is that only recently paper's on the quality of pyrolysis solid products under oxy-fuel conditions, and exclusively for pulverized coal have been published. In this line of research, the works carried out by Senneca and Schiemann groups Heuer et al, 2016;Pielsticker et al, 2016; are highlighted.…”

Section: Introductionmentioning

confidence: 99%

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Effects of pyrolysis atmosphere on the porous structure and reactivity of chars from middle and high rank coals

Valdés¹,

Guerrero²,

López³

et al. 2018

Ing. Inv.

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The influence of a CO 2 or N 2 -based atmosphere on the porous structure and microstructure of the chars obtained from the nonisothermal slow devolatilization (10 °C/min), from room temperature to 900 °C, of two coals of different rank (Semi-Anthracite (SA) and High Volatile Bituminous type C (HVBC)) and different particle size distribution was studied. Physicochemical characterization (ultimate and proximate analysis), structural and morphological characterization by Raman spectroscopy, FE-SEM, BET surface area, and volume and diameter microporous by CO 2 adsorption measurements were carried out for all the chars. It was found that the kinetic parameters, the physicochemical properties, and reactivity of the chars are different, depending on the pyrolysis atmosphere. It was also determined that for the char from SA coal with particle size greater than 0.7 mm, the BET surface area increases when the atmosphere is enriched with CO 2 . This effect appears to be promoted by the interaction of different processes such as intraparticle side reactions (softening, nucleation and coalescence of bubbles, crosslinking, among others), differences in the thermal diffusivity of N 2 and CO 2 , and the reactive effects of the latter. Additionally, tests of oxidative reactivity of chars showed that the char formed in a CO 2 atmosphere is more reactive than that formed in N 2 . With the results of Raman analysis and kinetic parameters quantified, it was concluded that the reaction atmosphere determined the degree of ordering achieved by the char structure and that the thermodiffusive properties of the reaction atmosphere promoted structural differences in the char even at low heating rates.Keywords: Slow pyrolysis, Pore size distribution, large coal particles, Oxy-combustion, reactivity. RESUMENSe estudió la influencia de una atmósfera basada en CO 2 o N 2 sobre la estructura porosa y la microestructura de carbonizados de carbón obtenidos de la pirólisis lenta no isotérmica desde temperatura ambiente hasta 900 °C de dos carbones de diferente rango (Semi-Antracita (SA) y Bituminosos Alto en Volátiles tipo C (BAVC)), y de diferentes distribuciones de tamaño de partícula. Para todos los carbonizados se realizó la caracterización fisicoquímica (Análisis ultimo y próximo), la caracterización morfológica y estructural por combinación de técnicas como espectroscopia Rama, Microscopia electrónica de barrido por emisión de campo (FE-SEM), área superficial (BET -Brunauer-Emmett-Teller) y volumen y diámetro de microporos por mediciones de adsorción en CO 2 (Horvath-Kawazoe (HK) method). Se encontró que los parámetros cinéticos, las propiedades fisicoquímicas y la reactividad de los carbonizados de carbón son diferentes dependiendo de la atmósfera de pirólisis. También se determinó que para el carbonizado de carbón de SA, con un tamaño de partícula mayor de 0,7 mm, la superficie BET aumenta cuando la atmósfera se enriquece en CO 2 . Este efecto parece ser promovido por la interacción de diferentes procesos como las reacciones secund...

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Section: Impact Of Pyrolysis Atmospheres On Char Reactivitysupporting

confidence: 90%

Section: Valdés Betancur López Gómez and Chejnementioning

confidence: 67%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of pyrolysis atmosphere on the porous structure and reactivity of chars from middle and high rank coals

Valdés¹,

Guerrero²,

López³

et al. 2018

Ing. Inv.

View full text Add to dashboard Cite

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“…After heat treatment, the reactivity of the samples was compared by performing combustion or gasification experiments under the same well-defined conditions. Isothermal thermogravimetric analysis (TGA) at fixed temperature and concentration values (for example, 773 or 873 K in air or 1173 K in CO 2 ) has been employed for this scope; − however, also non-isothermal TGA tests have been used ,− ). Notably, the selection of conditions of the pre-pyrolysis step was arbitrary.…”

Section: Introductionmentioning

confidence: 99%

Extension of the Thermal Annealing Concepts Developed for Coal Combustion to Conversion of Lignocellulosic Biomass

et al. 2020

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During the lifetime of coal and biomass particles in a reactor, severe changes in the carbonaceous structure occur. In the early stages of heat treatment, transformations at both the structural and chemical level are dramatic and well-recognized in the literature under the name of pyrolysis. Further heat treatment, even in parallel with heterogeneous reaction, produces less evident changes but is still very impactful on the char reactivity in the late stages of burnoff, which are recognized in the literature under the name of thermal annealing. Thermal annealing of biomass has often been neglected and underestimated. In the present work, a large experimental campaign has been carried out to measure the effects of heat treatment on the reactivity of a lignocellulosic material, namely, walnut shells, and, for comparison, a bituminous coal. The campaign included experiments in a thermogravimetric analyzer, fixed bed reactor, drop tube reactor, heated strip reactor, and flat flame burner, spanning over a very wide range of temperatures (700–2300 K), heating rates (0.1–105 K/s), and residence times (0.02–20 000 s). Results provide a unique set of data useful for testing pyrolysis–annealing models on lignocellulosic materials. Thermal annealing is very relevant also for lignocellulosic biomass and reduces the reactivity of char up to 1 order of magnitude. However, the distinction between pyrolysis and thermal annealing is made complex by the presence of multiple components with different inertia to thermal treatment. The applicability of the concepts developed for thermal annealing of coal to lignocellulosic biomass is therefore open to discussion. It is observed that the boarder line between the stage of pyrolysis and the stage of thermal annealing can be reasonably set when approximately 70–80% of the (ASTM) volatile matter content has been released. The early stages of thermal annealing, involving aromatization and graphitization of the carbon structure, occur in parallel with pyrolysis tails.

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“…Improved char burnout in CO2 has been attributed to contribution from CO2 gasification (Gubba et al, 2011;Pohlmann et al, 2016;Wang et al, 2014). Even though the burnout time is high, the release of volatile matter is low under fast heating conditions in drop tube furnace operated under oxy-fuel environment (Heuer et al, 2016;Pohlmann et al, 2016). For entrained flow reactor, Gil et al (2015) observed a high apparent volatile yield during devolatilization of biomass under CO2 environment.…”

Section: Background Of Studymentioning

confidence: 99%

Detailed study of wood combustion in a fixed bed reactor under oxy-fuel condition

Tanui¹

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Biomass fuel is the major source of energy for a significant proportion of the world population. Conventionally, biomass is burned in combustors that use air as oxidizer. The need for efficiency and reduced emissions has led to development of clean combustion technologies such as oxy-fuel combustion. In oxy-fuel combustion technique, fuel is burnt in O2/CO2 environment instead of O2/N2 environment. In spite of biomass being used under oxy-fuel conditions using fixed bed furnaces, there is no detailed study of biomass combustion in fixed bed reactors under oxy-fuel condition. The studies only cover combustion under air-fuel condition. There is no report in the literature on important combustion parameters, viz., flame propagation speed, temperature profiles, ignition time, and species evolution in the fixed bed combustion under oxy-fuel conditions; the studies have been only in air. This work extends the research on biomass conversion to combustion under oxy-fuel conditions. To address these knowledge gaps, this PhD thesis focused on establishing and isolating the role of various CO2 effects on biomass combustion properties using a laboratory fixed bed reactor through experiments and numerical modeling. The fixed bed reactor used in this study was operated in counter-current flame propagation mode. Oxidizer was a mixture of pure O2 and N2 or CO2. Measurement were made for air-fuel condition, oxy-fuel condition of different O2/CO2 mixtures and various initial bed porosity. In this work, all numerical simulations were carried out using a commercial CFD software CD-Adapco (STAR CCM+ version 11.04). Euler-Lagrange (CFD-DEM) approach was used to model biomass conversion in a packed bed. Solid particles and their conversion were modeled using DEM while fluid phase was modeled as a continuous phase using CFD. Biomass conversion was modeled by four sub-models, namely, drying, pyrolysis, gas-phase reactions and char oxidation models. These models were adopted and improved from previous research on wood combustion. To account for oxy-fuel combustion environment, reaction involving CO2 which has been identified as the dominant reaction pathway as well as its associated chain-branching reactions were incorporated in homogeneous reaction sub-model. In order to separate effects of CO2 on wood combustion, four different mixtures of O2 and Ar/CO2/N2 were designed and simulated. Temperature in O2/CO2 combustion environment was adjusted to be equal to that of O2/N2 environment by adding an appropriate amount of Ar while O2 amount remained the same. The results showed that flame front propagation speed in oxy-fuel atmosphere reduced to 78% of that of the air-fuel condition with similar O2 concentration. The CFD-DEM model agreed very well with experimental values for mass loss, propagation speed and flame front positions. However, peak temperatures were poorly predicted at lower oxygen concentrations. The accuracy of temperature prediction improved at higher oxygen concentrations. It was noted that oxy-fuel peak temperature is lower than air-fuel temperature by about 200 K. For oxy-fuel combustion, peak temperature value and propagation speed increases as O2 concentration is increased. The results showed that at any given oxygen concentration, ignition time in oxy-fuel environment is almost twice that of corresponding air-fuel condition. It was established that the packing density affects combustion process by changing the burning conditions and limits. Furthermore, the study revealed that there is an optimum packing density, χ = 0.71, beyond which the efficiency falls due to the onset of quenching in the spaces. It was concluded that dilution effect is the most influential parameter on the burning rate of wood combustion in an oxy-fuel system. In a future study, the model prediction could be improved by including ash inhibition sub-model and using a full chemical kinetic mechanism for hydro-carbon combustion. It was also recommended that a detail analysis of heat transfer in the bed could be investigated in a future study. The findings from this work are important and may be useful when designing burners which operate under oxy-fuel combustion conditions.

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Effects of oxy-fuel conditions on the products of pyrolysis in a drop tube reactor

Cited by 72 publications

References 37 publications

Effects of pyrolysis atmosphere on the porous structure and reactivity of chars from middle and high rank coals

Effects of pyrolysis atmosphere on the porous structure and reactivity of chars from middle and high rank coals

Extension of the Thermal Annealing Concepts Developed for Coal Combustion to Conversion of Lignocellulosic Biomass

Detailed study of wood combustion in a fixed bed reactor under oxy-fuel condition

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