Presence Of Char Research Articles

Post-fire soil emissions of nitric oxide (NO) and nitrous oxide (N2O) across global ecosystems: a review

AbstractWildfires may increase soil emissions of trace nitrogen (N) gases like nitric oxide (NO) and nitrous oxide (N2O) by changing soil physicochemical conditions and altering microbial processes like nitrification and denitrification. When 34 studies were synthesized, we found a significant increase in both NO and N2O emissions up to 1 year post-fire across studies spanning ecosystems globally. However, when fluxes were separated by ecosystem type, we found that individual ecosystem types responded uniquely to fire. Forest soils tended to emit more N2O after fire, but there was no significant effect on NO. Shrubland soils showed significant increases in both NO and N2O emissions after fires; often with extremely large but short-lived NO pulses occurring immediately after fire. Grassland NO emissions increased after fire, but the size of this effect was small relative to shrublands. N2O emissions from burned grasslands were highly variable with no significant effect. To better understand the variation in responses to fire across global ecosystems, more consistent measurements of variables recognized as important controls on soil fluxes of NO and N2O (e.g., N cycling rates, soil water content, pH, and substrate availability) are needed across studies. We also suggest that fire-specific elements like burn severity, microbial community succession, and the presence of char be considered by future studies. Our synthesis suggests that fires can exacerbate ecosystem N loss long after they burn, increasing soil emissions of NO and N2O with implications for ecosystem N loss, climate, and regional air quality as wildfires increase globally.

Effect of aluminum leaching pretreatment on catalytic pyrolysis of metallised food packaging plastics and its linear and nonlinear kinetic behaviour

This research aims to study the effect of aluminum (Al) leaching pre-treatment on the catalytic pyrolysis of metallised food packaging plastics waste (MFPW). The experiments started with removal of Al from MFPW using leaching process to prepare Al-free mixed plastic waste (MPW). The catalytic pyrolysis of MPW over ZSM-5 zeolite catalyst was carried out using thermogravimetric (TG) analysis coupled with FTIR, while GC–MS was used to observe the compounds of the volatile products. The catalytic pyrolysis kinetic behaviour of MPW was studied using the linear and nonlinear isoconversional approaches. The elemental and proximate results showed that MPW is very rich in carbon elements (79 %) and volatile content (99 %). The TG results showed that MPW and ZSM/MPW were fully decomposed in the range of 376–496 °C without any presence of char. Based on TG-FTIR analysis, methane and carboxylic acid residue were the main groups of the synthesized volatile products, whereas nitrous oxide, 1-Butanol, 1-Propene, acetic acid, and formic acid were the major GC compounds. In case of ZSM/MPW, carbon dioxide and acetic acid were the major GC compounds at 5–25 °C/min, triphenylphosphine oxide and Phosphine oxide at 30 °C/min. The kinetic analysis showed that when the activation energies are located in the range 287–297 kJ/mol (MPW) and 153–187 kJ/mol (ZSM/MPW) and KAS, Vyazovkin, and Cai methods are the most suitable models to study pyrolysis kinetic of MPW with R2 > 89. Based on that, leaching and catalytic pyrolysis processes are a highly suggested technology that can be used to convert MFPW into high-added energy and chemical products.

Use of Liquid Scintillation Counting to Study the Fate of C14 Labeled Glyphosate in Entisol Soil System

ABSTRACT Due to reduced tillage practices, glyphosate is widely used as a herbicide in grain farming systems of Australia. Residual glyphosate when mixed with water bodies can be a health concern. Updated information concerning the fate of glyphosate in soil systems with biochar amendment is lacking. For this experiment, different biochars were weighed and premixed in 2 ml Eppendorf tubes. A solution (Mixture of mercuric chloride and radiolabeled C14 glyphosate) having different concentrations provided by the commonwealth scientific and industrial research organization was used. Tubes having solutions were shaken on end over end shaker for 24 h. Tubes were removed from the shaker and centrifuged for 5 min. at 13000 revolutions per minute. Digested, labeled samples after counting disintegration per minute on Tricarb 4810 were used as sorption data. Results showed significant adsorption of glyphosate in the Entisol soil systems in the presence of char. The results have been published, however, the author wants to communicate in detail the role of liquid scintillation counting as a future research method for radiolabeled herbicides to understand the adsorption behavior of herbicides like glyphosate in different soil systems.

Prediction of thermal ablation in rocket nozzle using CFD and FEA

To protect the structural part of the rocket nozzle, an insulation liner is provided at its inner surface. Charring ablators are used for this purpose. The thickness of the insulation liner is one of the major design considerations of the nozzle. In the present analysis, an attempt has been made to predict thermal erosion (ablation) in the insulation liner through numerical studied CFD and FEA. The problem is modeled in ANSYS software. Fluid flow analysis is performed using the fluent module that works on the finite volume method, and the transient thermal module is used for the thermal analysis that works on the finite element method. Appropriate mesh convergence, residual convergence, and time step convergence exercises are made and the numerical results are verified with the analytical solution wherever possible. The possibility of reduction of thermal load due to the presence of char in ablator liner is considered and the thermal resistance in the region exposed to melting point temperature is altered to permit the propagation of thermal loads to the current pyrolysis front at any instant. The concept of this work is useful in the prediction of thermal ablation in rocket nozzles and in selecting the required thickness of the insulation layer.

Effect of char addition on anaerobic digestion of animal by-products: evaluating biogas production and process performance.

The effect of char addition on the digestion of animal by-products was evaluated as a way for enhancing the performance of the process. Two different types of carbonaceous materials were tested as carbon conductive elements to improve biological treatment. One was derived from a torrefaction process intended for increasing the energy density of lignocellulosic biomass, and the other was obtained from a hydrothermal carbonisation process. In this research, batch digestion systems of animal waste samples were evaluated at a volatile solid (VS) ratio of 1:1 inoculum-substrate (where the content of the substrate in the system was 1.69 ± 0.2g). The system reported a baseline methane yield of 380LCH4kg VS-1 which increased on average to 470LCH4kg VS-1 following to the addition of char. The presence of char allowed a faster degradation of the lipid and protein material, reducing inhibitory interactions. The use of Fourier transformed infrared spectroscopy was applied for elucidating the predetermination of the degradation process and bring an insight into the greater degradation potential attained when carbon materials are used for enhancing microbial performance.

The effect of fire affected Pinus radiata litter and char addition on soil nitrogen cycling

In pine forest litters, decomposition rate is directly affected by the pathway the needle followed to the ground, whether that was via programmed apoptosis and abscission or via stress induced loss through branch damage or tree death. Stress induced losses may occur due to fire damage, which leads to a post-fire litter layer composed of non-senescent debris that fell during or after the event. This study investigates decomposition and nitrogen cycling in soils amended with two litters from Pinus radiata plantations that had different recent fire histories. Litters were incubated in the presence or absence of field collected char for up to 94 days. These soil treatments were analysed for microbial activity (soil respiration) and N pools (microbial, mineral, and potentially mineralisable). Soil and litter treatments were additionally incubated in the presence of ammonium nitrate solution to determine N absorption potential of the litters. Respiration was greatest in soils that received fire affected (FA) litter regardless of the presence or absence of char. Nitrogen pools were largely similar between the control (no litter) treatment and not fire affected (NFA) litter treatments. Measured N pools were exceedingly low (92% of samples <2 μg-N g soil−1 where detected) or not detectable (37% of samples below detection limits) in all FA litter treatments at most times. Char appeared inert throughout and had no effects on microbial activity or nitrogen cycling. This study indicates that fire affected pine litter collected four months post fire has strong N absorption properties with or without the presence of char. The presence of fire affected litter is likely to affect N availability for regeneration of forest growth.

Experimental study on effects of combustion atmosphere and coal char on NO2 reduction under oxy-fuel condition

Nitrogen oxides (NOx) as the principal air pollutants are mainly from the combustion of fossil fuels. Oxy-fuel combustion is a promising clean coal technology, by which carbon dioxide (CO2) can be captured in large-scale and NOx emission can be reduced significantly. The formation of nitrogen dioxide (NO2) in oxy-fuel combustion exceeds that under traditional air condition. However, the specific studies on NO2 chemistry under oxy-fuel condition are still insufficient and the functional mechanisms of minerals and combustion atmosphere on NO2 reduction have yet to be fully understood. The objective of present study is to experimentally clarify the effects of combustion atmosphere and coal char on NO2 reduction in oxy-fuel combustion using a fixed-bed reactor. Experimental results showed that the decomposition of NO2 had a strong temperature dependence and the NO2 reduction rate showed a positive variation with temperature. The strength of catalytic activity in NO2 reduction to nitric oxide (NO) was Fe2O3 > MgO > CaO > Al2O3 > Na2CO3 > K2CO3 > SiO2. In addition, the increased concentrations of carbon monoxide (CO) and CO2 could promote the reduction of NO2, while the low content of CO2 only established a slight impact on NO2 reduction. However, the increase of oxygen (O2) concentration displayed an inhibition effect on NO2 reduction to a certain extent. The variation of atmosphere in oxy-fuel combustion generated a substantial influence on the creation and reduction of NO2. The char prepared in lower temperature exhibited a higher promotion effect on the consumption of NO2. Higher contents of fixed carbon and basic oxides had more obvious stimulation effects on NO2 reduction. Fixed carbon had a superior activity in NO2 reduction than ash. The kinetic analysis indicated that high content of CO and the presence of char could reduce the apparent activation energy of NO2 reduction. The present study can be helpful to improve the understanding of NO2 chemistry in oxy-fuel combustion.

Interactions between char and tar during the steam gasification in a fluidized bed reactor

The aim of the present work is to understand the different interactions which may occur between the char and a tar model (toluene) in a fluidized bed reactor during biomass char gasification with steam. Experiments are conducted at 850 °C and atmospheric pressure with sand particles as solid medium. The influence of steam and toluene partial pressures on both the char reactivity and the presence of tar in the product gas was investigated in the range of 0.05–0.4 bars and 0.0025 and 0.0075 bars (10.1 and 30.4 g.Nm−3), respectively. Results showed that the presence of char in the fluidized bed reactor leads to toluene polymerization (cokefaction) which produces a carbonaceous deposit (coke) on its surface. This deposit is much less reactive towards steam gasification than the initial char. For the operating conditions used in this study, it was found that the rate of tars polymerization (Rp) is always smaller than the one of coke and char gasification (Rsr+Rg). Finally, a comparison between the different solid catalysts in the fluidized bed reactor revealed that olivine is the best catalyst towards toluene conversion when the ratio PH2/PH2O is higher than 1.5 in the reactive gas atmosphere. Otherwise, for a steam partial pressure higher than 0.2 bars, “olivine + 3% char” and “sand + 3% char” were found to be the best compromise to limit the amount of tar in the product gas.

Biogas to Syngas by Microwave-Assisted Reforming in the Presence of Char

Methane (CH4) and carbon dioxide (CO2), the main components of biomass pyrolysis gasification gas and biogas, are byproduct gases that can be used as energy sources and are also greenhouse gases that contribute to global warming. This study on microwave reforming characteristics was conducted to convert the product gas into high-quality fuel energy. In the case of microwave reforming through carbon receptor application, the carbon was generated by a thermal decomposition, and then it attached on the surface of the receptor, interfering with the catalytic activity. Carbon dioxide reforming, however, cleaned the adsorbed carbon through carbon gasification and thus consistently maintained constant reforming conversion. Therefore, when the mixture of methane and carbon dioxide was reformed at the same time, the catalytic activity could be prevented from deteriorating because of carbon adsorption. When sludge char was used in this study as carbon receptor, the amount of hydrogen and carbon monoxide generated was higher than that generated by the commercial activated carbon receptor because of the former’s relatively high catalytic activity, yielding a gas product with higher heating value. It was also confirmed that the conversion and the product gas yield were high when the receptor bed reforming temperature was high and when the retention time was long.

Kinetic analysis of the interactions between calcium ferrite and coal char for chemical looping gasification applications: Identifying reduction routes and modes of oxygen transfer

Chemical Looping Gasification (CLG) is an emerging technology that shows promise for efficient coal gasification by eliminating the need for energy intensive gas separations to achieve a non-nitrogen diluted syngas stream. Oxygen from oxygen carriers, such as CaFe2O4, are used for coal gasification in place of conventionally produced gaseous oxygen from cryogenic separation of air. These oxygen carriers are unique for their ability to selectively oxidize coal to form syngas and show limited reactivity with syngas components (H2, CO). This study was carried out to determine the kinetic model representation and parameters associated with the selective oxidation of coal derived char (Wyodak and Illinois #6) with a metal ferrite (CaFe2O4) of which are needed for advancement of the process concept. Using thermogravimetric analysis (TGA) coupled with mass spectrometry, the selective oxygen release from metal ferrite in the presence of char by proximal contact was examined. The application of model fitting approaches was used to describe controlling resistances during oxygen release. A combination of the modified shrinking core model (SCM) with planar oxygen ion diffusion control and reaction order based models were applied for kinetic parameter determination. CaFe2O4 particle size plays a major role in the prevailing mode of oxygen release. Particle sizes on the range of 40–50µm tend to favor first order kinetically controlled regimes independent of geometric and diffusion controls. The probability for oxygen ion diffusion controlling regimes increased when the particle size range of the oxygen carrier was increased up to 350µm. Char type also impacted the prevalence of the controlling regime. Higher ranked chars react in a slower manner, limiting the gradient for oxygen ion release from the oxygen carrier. Activation energies determined for this process range from 120 to 200kJ/mol and oxygen ion diffusion coefficients are on the order of 10−8cm2/s. It is suggested that oxygen ion movement is regulated by lattice diffusion out of partially reduced phases (Ca2Fe2O5) and through reduced outer layers composed of CaO and Fe. The controlled movement of oxygen ions influences the rate of carbon oxidation in the char and therefore the selectivity towards partial oxidation products, which are desirable in CLG applications.

Catalytic reforming of tar using corncob char and char-supported potassium catalysts

This work aims to investigate the importance of biomass char and the metal oxides in the ash in tar cracking during the volatile–char interactions. Experiments were carried out in a two-stage fixed reactor, and corncob, one typical agricultural biomass rich in potassium, was chosen as raw material. Results showed that char and char-supported potassium catalysts have good activity for tar elimination due to the good absorbability of char and catalytic property of potassium. In particular, tar conversion efficiency can reach 95.8% by using 1.5 K-char catalyst at 700 °C. The reforming reactions can be significantly enhanced during the volatile–char interactions in the presence of char and char-supported potassium catalysts. As a result, the syngas yield increased significantly with increasing temperature and supported K+, particularly the combustible gases including H2, CO and CH4. Physical and chemical structure of char changed due to reforming reactions related to the carbon, while the content of potassium was almost unchanged.

On the Reduction of Gas‐Phase Naphthalene Using Char–Particles in a Packed–Bed Atmospheric Pressure Plasma

AbstractFuel and synthesis gases generated by thermochemical gasification of renewable biomass resources and organic waste fractions are considered to be promising for recent and future energy demands. However, the presence of tar species in the gas mixture is an economic obstacle in the commercialization of this technology. The influence of non‐thermal plasma on gas phase naphthalene which served as tar model compound, in the presence of solids was examined. The naphthalene was evaporated into a N2/H2/CO/CO2 gas atmosphere and led through a packed‐bed, atmospheric plasma reactor operated at a temperature of 350 °C. The influence of two bed materials ‐ glass beads and glass beads mixed with char particles ‐ was studied. The char particles originated from real gasification processes with woody biomass as feedstock. With both reactor fillings, the content of naphthalene in the gas phase was reduced. The characteristic energy β of the naphthalene removal was found to be βno char = 952 ± 77 Jl–1 and βwith char = 232 ± 10 Jl–1, respectively. Consequently, the addition of char material leads to a naphthalene removal efficiency increased by a factor of about four. Furthermore the formation of ammonia (NH3), a by‐product of the plasma reactions, was suppressed in the presence of char. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effects of volatile–char interactions on in-situ destruction of nascent tar during the pyrolysis and gasification of biomass. Part II. Roles of steam

This study aims to investigate the importance of steam to tar destruction during the volatile–char interactions. Steam was supplied in the absence and presence of nascent char during the pyrolysis/gasification of biomass at 850°C. In the absence of char, steam has more significant effects on the reforming of large aromatic ring systems (e.g. >2 fused benzene rings) than small and isolated aromatics. In the presence of char, steam can significantly enhance the reforming of both large and small aromatic ring systems during the volatile–char interactions, especially when the steam–char reactions are also significant. The results indicate that the steam–char reactions are particularly inhibited in a thin char bed by the volatile–char interactions. It is believed that the steam–char reactions can produce additional active sties on the char, such as the radicals/intermediates of char gasification and/or the O-containing groups, to facilitate tar reforming during the volatile–char interactions.

Tar Formation and Destruction in a Fixed Bed Reactor Simulating Downdraft Gasification: Effect of Reaction Conditions on Tar Cracking Products

A lab scale, two stage fixed bed reactor has been used to study the cracking of tars formed during the pyrolysis of biomass, under conditions that are intended to simulate those in the downdraft gasifier. Experiments were done at near atmospheric pressure, with tars being produced at 500 °C under pyrolysis conditions in the first stage and then cracked in the second stage under a range of conditions. These conditions simulated those in the gasification zone of a downdraft gasifier. Both condensable and gaseous products were collected, quantified, and characterized. Cracking in an empty second stage reduced the tar from an inlet value of 33% (of input biomass) to 0.7% under the optimum conditions (temperature 1000 °C, velocity 0.4 ms–1). The presence of char in the second stage decreased the tar to 0.2%. The extent of cracking was not influenced by the source of the second stage char or particle size, within the ranges studied. The addition of a low percentage of O2 to the inlet of the second stage had var...

AlBr3 impact on the thermal degradation of P(S-co-MMA): a study performed by contemporary techniques

Pyrolysis of copolymer, [P(S-co-MMA)], in the presence of AlBr3 was inspected in an inert atmosphere. Five different proportions (copolymer/additive) were chosen. Films were cast from common solvent. It was noticed that copolymer showed more stability on the basis of T 0, however, regions of stability were also observed for the blends. Copolymer showed T 0 at 260 °C, whereas blends started degrading around 70 °C. T max was the same for the copolymer and the blends. Low-temperature decompositions of blends were attributed to the generation of free radicals (Br•) and the zones of stabilizations were assigned to the formation of a “complex type” structure between Al and the carbonyl oxygens of MMA units. Degradation products were collected and identified employing Py-GC–MS technique. Intermediates (solid) at different temperatures (300, 350 and 400 °C) were examined through FTIR spectroscopy. In the light of gathered data, a degradation mechanism was proposed. New products were encountered, viz., bromobenzene, ‘brominated’ anhydride ring, etc., which established the chemical interactions between the constituents of the blends, i.e., copolymer and additive. Anhydride rings were absent when poly (methyl methacrylate) was pyrolyzed in the presence of AlBr3. Oligomers of styrene were not found hinting at the involvement of additive in “targeting” the degrading styrene units. The blends indicate 2–7% residue of original mass; the additive exhibits 9% while the copolymer does not leave residue at the completion of the TG run. The presence of char in the residues of blends suggests that the additive imparts stability to the copolymer. Horizontal burning rate was lowest (6 times less than that of neat copolymer) for [P(S-co-MMA):AlBr3, 87.5:12.5%], thereby revealing the efficiency of the additive as thermal stabilizer. The highest activation energy was calculated for the copolymer (169.46 kJ/mol) and the range of this parameter for the blends was found from 52.72 to 27.14 kJ/mol.

Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction

The eruption of the Siberian Trap flood basalts resulted in the heating and combustion of coals and organic-rich sediments at the time of the Permian mass extinction. The presence of char in distant lake sediments linked to the eruption suggests that fly ash could have been generated by the coal combustion, and then dispersed globally, creating toxic marine conditions.

Tar Formation and Destruction in a Fixed-Bed Reactor Simulating Downdraft Gasification: Equipment Development and Characterization of Tar-Cracking Products

The aim of the present study is to examine operating parameters that would reduce the residual tar content in the fuel gas in downdraft gasifiers and eventually eliminate it altogether. A two-stage fixed-bed reactor has been employed to simulate elements of tar cracking in a downdraft gasifier. In this reactor, tar is generated by pyrolysis in the first stage and cracking and gasification take place in the second stage. Modifications to a previous configuration of this reactor are described, which have enabled the use of smaller char particle sizes in the second stage and the generation of a more complete inventory of the reaction products. In this work, the effect of the temperature and the presence of char on product distributions are reported. Increasing the temperature from 700 to 1000 °C resulted in a decrease in the quantity of tar recovered and an increase in the total amount of CO released. The amount of CH4 released increased between 700 and 800 °C before remaining steady up to 1000 °C. The CO2 content of the gas was relatively constant between 700 and 800 °C and increased as the temperature increased from 800 to 1000 °C. The amount of water and light hydrocarbons (C2−C5 alkanes and alkenes) sharply decreased at 1000 °C. The presence of char in the second stage had significant effects on tar cracking and product distributions. These effects were more obvious on the concentrations of CO, CO2, and H2O, which may be a result of reduction reactions taking place with the carbon in the packed char bed. These reactions appear to be more significant at temperatures between 900 and 1000 °C, where the rates of gasification are expected to increase.

Tar reduction in pyrolysis vapours from biomass over a hot char bed

The behaviour of pyrolysis vapours over char was investigated in order to maximise tar conversion for the development of a new fixed bed gasifier. Wood samples were decomposed at a typical pyrolysis temperature (500 °C) and the pyrolysis vapours were then passed directly through a tar cracking zone in a tubular reactor. The product yields and properties of the condensable phases and non-condensable gases were studied for different bed lengths of char (0–450 mm), temperatures (500–800 °C), particle sizes (10 and 15 mm) and nitrogen purge rates (1.84–14.70 mm/s). The carbon in the condensable phases showed about 66% reduction by a 300 mm long char section at 800 °C, compared to that for pyrolysis at 500 °C. The amount of heavy condensable phase decreased with increasing temperature from about 18.4 wt% of the biomass input at 500 °C to 8.0 wt% at 800 °C, forming CO, H 2 and other light molecules. The main mode of tar conversion was found to be in the vapour phase when compared to the results without the presence of char. The composition of the heavy condensable phase was simplified into much fewer secondary and tertiary tar components at 800 °C. Additional measures were required to maximise the heterogeneous effect of char for tar reduction.

Influence of fire and harvest on soil organic carbon in jack pine sites

Boreal forest soils represent a considerable reservoir of carbon on a global basis. The objective of this study was to compare the response of soil organic carbon (OC) to disturbance along two jack pine ( Pinus banksiana Lamb.) chronosequences of either fire or harvest origin. Total OC stocks were determined for the A and B horizons, and results indicated a recovery to predisturbance levels by 30 years in both chronosequences. To further characterize OC composition at all sites, we used a combination of physical fractionation of soil OC pools, 13C isotopic determination, and cross-polarization magic-angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy. OC within all soils was dominated by a labile pool associated with the coarse-sand fraction. The relative importance of this labile pool increased with time since disturbance along both chronosequences. However, the fire and harvested sites differed in terms of the macromolecular composition of soil OC as determined by NMR. In particular, spectra of the forest floors from the two younger fire sites showed a high aromatic OC intensity that may be attributed to the presence of char. Interestingly, our results also indicated that with increasing time since fire, this char was transferred from the forest floors to the A horizons.

Biogas to Syngas by Microwave-Assisted Dry Reforming in the Presence of Char

The aim of this paper is to study the reforming of CH4 with CO2 using as a catalyst a rich potassium char obtained from biomass pyrolysis. The reaction was carried out at 800 °C by means of two different methods of heating, microwave and electrical heating (MWH and EH, respectively). In addition, the individual reactions proposed for the dry reforming of methane, that is, (i) the decomposition of CH4 to form hydrogen and carbon and (ii) the dissociative adsorption of CO2 followed by reduction to give CO, were also studied with both heating methods at the same temperature. The results showed that MWH produces hot spots (microplasmas located inside the catalyst bed) that favor heterogeneous catalytic reactions. Thus, it was found that the conversion of CH4 and CO2 in the individual reactions was greater for MWH than for EH. An examination of the CH4 decomposition reaction proved the formation of coke deposits, which reduced catalytic activity and CH4 conversion. When a CH4/CO2 mixture was used, this problem...