Lab-scale Drop Tube Furnace Research Articles

Comparative radiative property measurements of single biomass and coal particles burning at high reactor temperatures

This research measured the emissivity, temperature and soot loading of pulverized bituminous coal and three types of renewable biomass. Combustion occurred in a laboratory-scale drop tube furnace (DTF), where the fuels experienced high heating rates and ignited and burned in two distinct phases: devolatilization accompanied by volatile matter combustion in envelope flames, and sequential combustion of the char residues. Multi-wavelength spectrometry was used to concurrently determine the emissivity and the temperature of burning particles at discrete points in their history. Three-wavelength pyrometry was used to obtain entire temperature-time histories, and high-speed photography was used to provide both visual observations of phenomena and to obtain two-dimensional temperature distributions. Results showed that soot in volatile matter flames of burning single particles of the bituminous coal and of the three types of torrefied biomass had spectral emissivities in the range of 0.03–0.10, in the wavelength domain of 600–1000 nm. Emissivities were nearly constant with wavelength, i.e., soot mantles in these flames radiated as graybodies. Spectral emissivities of the chars of the bituminous coal and the three types of torrefied biomass were in the range of 0.29–0.5 and varied with wavelength, i.e., they radiated as non-graybodies. The highest measured temperatures of soot in volatile flames for all fuels were between 2150 and 2360 K and maximum temperatures of chars were between 1700 and 2000 K, based on the three measurement techniques. The graybody assumption caused negligible (± 10 K) deviations in volatile matter flame temperatures; however, it caused significant deviations (± 20–100 K) in char temperatures. Envelope flame diameters of torrefied biomass particles were larger than those of coal. To the contrary, soot volume fractions in the envelope flames of coal particles were found to be higher than those in biomass particle flames. Finally, the soot volume fractions in the flames of these fuels were inversely proportional to particle size.

Study on the interaction between inherent minerals of coal with refuse derived fuel (RDF) during co-firing

In this paper, refuse derived fuel (RDF) and bituminous coal were co-fired to investigate the particulate matter (PM) yields and the interaction between the inherit minerals in a lab-scale drop tube furnace (DTF). The PM1-10 yields during the co-firing of coal and RDF dramatically decreased by 16.29 %∼28.5 % of the combustion of coal alone. In addition, methane auxiliary combustion inhibited the PM1 yields by 7.95 % at air atmosphere. The Si-rich minerals in coal interreacted with the organic alkali (earth) metals in RDF, massively generating sticky particles with high liquid amount of K-Al-Si and Ca-Al-Si, promoting the transformation of fine grains into coarser mode. Moreover, it was proved that both methane auxiliary combustion and co-firing can reduce the emission of fine particles. The additional heat accelerated the burn of the char at the early stage of combustion, providing adequate time for the interaction between the inorganic species. Through thermodynamic equilibrium calculations of 1500 ∼ 3000 fly ash grains, it was found that co-firing increased the formation of sticky particles by 64.8 %∼70.3 %, resulting in a significant enhancement in capturing fine particles and Na, K vapor. Therefore, the co-firing of coal with RDF offers a promising approach to realize the harmless and resourceful treatment of municipal solid waste (MSW), and inhibit land resource losses caused by landfill

Carbon black preparation by partial oxidation of spent tyre pyrolysis oil – Influence of temperature, residence time and oxygen to feed ratio

Preparation of carbon black (CB) by partial oxidation of the spent tyre pyrolysis oil (STPO) and its heavy residue fraction (HRF) was systematically studied using a lab-scale drop tube furnace. The effect of furnace operating temperature (T: 1100 to 1400 °C), residence time (tr: 5 to 60 s) and oxygen to feed ratio (O/F: 174 to 732) on the yield and quality of CB was examined using the response surface methodology (RSM). T was shown to have the most significant influence on CB yield and properties. While the CB yield was also influenced by tr, the quality was more sensitively dependent on T and O/F. The predicted optimal tr and O/F were approximately the same for both feedstocks (60 s and 174, respectively). However, T was higher for the HRF feedstock (1368 °C) than the STPO feedstock (1331 °C) due to the abundance of more viscous heavy hydrocarbons in HRF. Validation experiments under the aforementioned conditions demonstrated the models’ ability to predict responses accurately. The CB from both feedstocks had low contents of ash (<0.03%), volatiles (∼0.5%), sulphur (<0.7%), and high carbon (≥95%). The BET surface area and average primary particle size for CB from STPO and HRF were comparable to those of commercial CBs from fossil fuel feedstock. The CB from HRF had a higher carboxyl oxygen functional group (18%) compared to the CB from STPO (∼13%) and commercial CB (<5%).

Effects of the addition of RPF and woody biomass on PM emissions during co-firing with coal

Two Cl-free refuse plastic and paper fuels (RPFs) produced by hydrothermal treatment with Ca(OH)2, as well as two biomasses, were co-fired with bituminous coal in a lab-scale drop tube furnace (DTF). The results indicate that the addition of biomass and RPF partially reduced the emission of SO2, which can readily cause corrosion, deposition and pollution. For the biomass co-firing, the particulate matter (PM) emissions from the black pellet (BP) series were 5.0% higher than those from the white pellet (WP) series because more sticky particles were formed with the increment of Ca-Al-Si and K-Al-Si, which absorbed alkali vapor and fine grains in the gas bulk to inhibit the PM emissions. For RPF, the major origins of sticky particles turned into Ca-Al-Si and Ca-K-Al-Si, the proportion of which was dramatically higher than that from the biomass, resulting in a stiffer suppression of PM formation. In general, the promotion of Ca from additives conversely restrained its transformation into PMs during both biomass and RPF co-firing. It can be concluded that the co-firing of RPF with bituminous coal provides an alternative approach to simultaneously control the emissions of greenhouse gases, gaseous pollutants and PM while remediating plastic waste.

Coke evolution during the air- and oxy-firing regeneration of a spent Ni/ZnO sulfur adsorbent

Reactive adsorption desulfurization (RADS) is an effective desulfurization technology in refineries to reduce the sulfur contents in oil products. To ameliorate the desulfurization technology, the evolution of coke was first studied in the air-firing regeneration of a typical spent Ni/ZnO sulfur adsorbent used in RADS. Efforts were made to elaborate the conversion of carbon and sulfur during the oxy-firing regeneration of the spent adsorbent to test the possibility of applying that carbon capture technology – oxy-fuel combustion to the sulfur adsorbent regeneration. A lab-scale drop-tube furnace was employed to conduct the combustion experiments; and the speciation of carbon and sulfur in the regenerated adsorbents was characterized by advanced techniques including near-edge X-ray absorption fine structure (NEXAFS), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The catalytic role of metals (Ni/Zn) in the coke combustion was also verified by acid leaching and temperature-programmed oxidation (TPO) experiments. It has been founded that the carbonaceous materials deposited on the adsorbent comprise five groups, including polyaromatic and graphitic carbon with a fraction of around 27 mol% of the entire carbon, and the other groups which are mostly light aliphatic compounds and oxygen-containing functional groups. During the air-firing regeneration process, most of the light coke species were oxidized into oxygenated intermediates and then desorbed as CO and CO2, with a small portion being polymerized into heavy molecules. Oxy-firing regeneration was verified to improve the efficiency of coke combustion due to the metal-catalyzed CO2 gasification reaction and improved the sulfur conversion under the oxygen-lean condition such as 3 vol% O2 in CO2. The carbon conversion increased from 23% in 3%O2/N2 to 31% in 3%O2/CO2 at 510 ℃. In the meantime, the sulfur conversion was also increased from 50% to 57% at 750 ℃, which is probably due to that the CO2 gasification of coke alleviated the competition of oxygen between carbon and sulfur.

Characterization of Ashes from Co-Firing Biochar with Coal under Pulverized-Fuel Conditions

This contribution presents results on the systematic characterization of the ashes from the co-combustion of biochar or its corresponding raw biomass and coal under pulverized-fuel conditions. A mallee bark (75–90 μm) was subjected to fast pyrolysis at 500 °C to prepare a biochar. The bark and the biochar were then co-fired with a Collie coal of identical size fraction in a laboratory-scale drop-tube furnace at 1400 °C in air, with biomass/biochar shares of 5, 20, and 40% expressed based on lower heating values. The produced ashes were collected using a cyclone and systematically characterized. The results demonstrate that the morphology of the ashes from the bark and the biochar is of irregular shape, whereas the coal ash particles are round. The ash particles follow a unimodal distribution, with an area-equivalent mode diameter of ∼5–12 μm, except for the ash from the bark combustion that also shows two larger peaks at ∼65 and ∼95 μm. The compositions of the ashes from the bark and the biochar are similar, both rich in Ca and Mg, whereas the coal ash contains dominantly Si, Al, Fe, and Ca. Under identical co-firing ratios, replacing the bark with the biochar results in higher contents of Mg and Ca in the ashes because of the enrichment of these elements in the biochar. The major minerals identified in the coal ash include mullite, quartz, and hematite, and those in the bark ash and the biochar ash are portlandite, magnesite, calcite, and lime. Up to ∼56% of Na, ∼41% of K, ∼56% of Mg, and ∼69% of Ca in the ashes can be recycled via water leaching, with negligible environmental concerns. These data are important in developing suitable strategies for the utilization and management of ashes derived from the co-combustion of biochar (or biomass) and coal.

Effect of the optimal combination of bituminous coal with high biomass content on particulate matter (PM) emissions during co-firing

The co-firing of bituminous coal with woody biomass provided an available approach for cutting carbon emissions. In this work, a study on the application of high blending ratios of biomass with coal in co-firing was experimentally conducted in a lab-scale drop tube furnace (DTF) to reduce CO2 emissions and control deposition and corrosion due to the particulate material (PM) yield on the heating surface. Two kinds of woody biomass were blended with two kinds of bituminous coals at dosages of 5 wt%, 15 wt% and 30 wt% to investigate the PM emissions of different combinations during co-firing. With the addition of biomass, the experimental results show that the PM emission during co-firing may greatly increase or remain approximately stable compared with that during the single combustion of coal, which is dominantly determined by the combination of coal and biomass. To quantitively understand this effect, a mathematical method for the prediction and verification of PM yield during co-firing was developed by using a FactSage calculation based on the computer‐controlled scanning electron microscopy (CCSEM) analysis of raw fuel and fly ash. The predicted proportions of sticky particles with a liquid amount of >70 wt% demonstrate a significant difference with the variation in fuel type and biomass dosage during co-firing. According to predictions, 45.3% more sticky particles can be produced due to the diversity of added biomass when co-fired with the same kind of coal, conversely resulting in a 54.8% suppression of particles with an aerodynamic diameter of 2.5 μm or less (PM2.5) emissions. The morphological and elemental distribution of PM further validates that the liquid substance formed can be the decisive factor in generating sticky particles to control the formation of precursors by adsorption of alkali vapor or agglomeration of fine grains, thus inhibiting the PM yield with the addition of woody biomass during co-firing. The optimal combination for the co-firing of coal with high concentrations of biomass can be ascertained to simultaneously realize the reduction of carbon and PM emissions, which could provide a novel approach for the survival and development of coal-fired plants.

Non-Destructive characterisation of coke deposit on FCC catalyst and its transient evolution upon Air-Firing and Oxy-Fuel regeneration

In this paper, the regeneration and associated transient evolution of a commercial FCC spent catalyst in both air-firing and oxy-fuel combustion modes (i.e. 0–10% O2 in N2 or CO2, 510–1000°C, and ∼ 4 sec) were studied in a lab-scale drop-tube furnace. A variety of non-destructive techniques including synchrotron NEXAFS, XPS and ATR-FTIR for both non-grounded and grounded spent catalyst and its combustion residues were employed to reveal the speciation, spatial distribution of coke within the catalyst matrix, as well as its evolution upon rapid heart-up and combustion. As have been confirmed, the coke species is highly broad in speciation, covering aliphatic and aromatic compounds as well as graphite that are both physically deposited and chemically adsorbed on acid sites on the catalyst’s exterior surface. The majority of aliphatic hydrocarbons were also embedded deeply within the catalyst matrix, which were presumably caused by the penetration of precursor molecules that are small in size. Irrespective of the combustion mode, upon the initial rapid heat-up, the embedded light hydrocarbons were rapidly volatilised, and diffused outward toward the exterior surface, where it either underwent C-O2/C-CO2 reactions, or simply further recondensed into graphite in the case that oxygen is lean in the air-firing mode. In contrast, in the oxy-firing mode, the coke was confirmed highly reactive for reverse Boudouard reaction and methane drying reaction which were even triggered during the initial particle heat-up stage. Consequently, the initial graphitisation extent of light vapor was mitigated, and the micro-pores of catalysts were opened up to enable a continuous elution of the hydrocarbon vapors to boost the overall coke burn-off. Regarding the competition of the overall C-O2 and C-CO2 reactions on catalyst exterior surface, the former reaction is superior in the case where oxygen is lean (e.g. 3%). In contrast, when the oxygen content is higher (e.g. 10%), the latter one was intensified due to the strong heat feedback from the exothermic C-O2 reactions. As a result, the overall coke including other two species, graphite and aliphatic hydrocarbons were consumed quickly in the O2/CO2 case.

Combustion of distillery sludge mixed with coal in a drop tube furnace and emission characteristics

Co-combustion of coal with distillery sludge waste (DSW) was investigated in a laboratory-scale Drop Tube Furnace (DTF) plant. This study examined the feasibility of combustion of sludge with coal using preliminary testing methods, such as thermogravimetric, ultimate and proximate analysis followed by combustion experiments. These methods helped to identify burnout efficiency, emitted pollutants, and metal constituents in the bottom/fly ash. The ratios of coal to DSW in the feed was 90:10%, 95:5%, 98:2% and 100:0% by dry weight basis. The vibrator feeder and airflow rate were set at the rate of 1.5 kg/h and 150 L/min with slightly negative pressure. The concentration of gases (i.e. nitrogen oxides (NOx), sulphur dioxide (SO2), carbon mono-oxide (CO), hydrocarbon (HC)) and particulate matter (PM) on DSW combustion was measured and compared with the combustion of coal. The pattern of gaseous emission and combustion efficiency showed high degree linear combinations through Pearson’s correlation coefficient. The decrease in the concentration of PM (76.67 ± 10.41 mg/m3 to 91.33 ± 17.62 mg/m3) and SO2 (444 ± 20.63 mg/m3 to 156.60 ± 12.26 mg/m3), increase in the concentration of NOx (136 ± 15.41 mg/m3 to 387 ± 15.2 mg/m3) and CO (26.15 ± 5.36 mg/m3 to 824.32 ± 43.70 mg/m3), unburnt carbon percentage in the fly ash, and clinker formation were taken into account to optimum the sludge proportion in the DTF under a given set of combustion conditions. Most importantly, an increase in sludge quantity (i.e. 2%, 5%, and 10%) showed a decrease in the burnout efficiency (98.41%, 95.91%, and 92.6%, respectively).

Emission Characteristics of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans from the Co-combustion of Municipal Solid Waste in a Lab-Scale Drop-Tube Furnace

Generally, coal-fired incinerators are characterized by a high combustion temperature and a well-equipped flue gas cleaning system. Co-combusting municipal solid waste (MSW) in coal-fired incinerators can reduce the emission of PCDD/Fs and help to enhance the treatment capacity of the MSW; more importantly, this approach provides a new orientation for upgrading and transitioning old coal-fired power plants. In this study, the simulated municipal solid waste (SMSW) is mixed with coal in proportions of 0 (without addition), 7.5, 15, 20, and 25 wt.% and then co-combusted in a drop-tube furnace. The PCDD/Fs emitted in both the flue gases and fly ashes from the combustion tests are well investigated. In the present study, the I-TEQ concentration of the PCDD/Fs in the flue gas can meet the emission limit (0.1 ng I-TEQ/Nm3) when MSW is co-combusted at less than 20 wt.%. The concentration of the PCDD/Fs in the fly ash is much lower than the permitting standard for disposal in sanitary landfill sites (3.0 ng I-TEQ...

Characteristics of high temperature co-gasification and ash slagging for Victorian brown coal char and bituminous coal blends

The low ash and high iron content of Victorian brown coal (VBC) makes it difficult to achieve desirable slagging for entrained-flow gasification. This study investigates the blending of VBC char with a high-ash bituminous coal for entrained-flow gasification. An industrially pyrolyised VBC char, a silica-rich bituminous coal char (BCC), and VBC char with BCC blends in three different blending ratios (20%BCC, 40%BCC and 80%BCC) are selected for high temperature gasification investigation in a lab-scale drop tube furnace (DTF) for temperatures ranging from 1000 to 1300 °C with different CO2 volume fractions. Scanning electron microscopy (SEM) coupled with elemental mapping, advanced synchrotron XANES and Mössbauer spectroscopy (MS) are employed to clarify the slagging propensity and iron transition behaviours during the blend co-gasification. It is found that VBC char, even in large sized particles, achieves a high char conversion and more than 50% CO fraction in syngas at 1300 °C, while BCC shows a lower char conversion and only 15% CO fraction in the same condition, due to only small particles being consumed. The blending of BCC into VBC lowers the char conversion compared to that of VBC alone due to the ash interactions. However, the element (Fe/Ca/Mg) loss during gasification reduces remarkably upon the addition of BCC, showing that the silica from BCC captures these elements. In addition, VBC generates more than 20% metallic iron out of total Fe-species during gasification, and the amount increases when temperature increases, which is undesirable for slag discharge. In contrast, blending 20% BCC with VBC char reduces α-Fe from 15% to about 7%, and reduces Fe3O4 from 12% to less than 6%. This is because the silica in BCC can preferentially capture the iron-bearing compounds before they are reduced into metallic iron. Additionally, the unreacted carbon is covered by the slag, stopping it from reducing the Fe2+ to metallic iron Fe0. The reduction of metallic iron is closely linked to the increase on the ash slagging extent, which is beneficial to slag discharge in entrained-flow gasifiers.

Effect of Pulverized Coal Preheating on NOx Reduction during Combustion

Although various NOx removal technologies have been commercialized, NOx emissions are still so high that they cannot meet the newest standard and endanger the eco-environment and human health. Meanwhile, some NOx reduction technologies suffer from high costs. Recently, a cheap and pending technology called gas-fired coal preheating has surfaced again. This method introduces hot flue gas to heat a coal stream to high temperatures before the coal stream is injected into a utility boiler for combustion, thus resulting in a reduction in NOx. Considering the complex mechanisms during preheating, the effect of the preheating parameters, including temperature, residence time, excess air ratio, and coal type, are studied in a laboratory-scale drop-tube furnace in detail. Meanwhile, by means of Chemkin coupled with the mature NOx reduction mechanisms of GRI-mesh3.0 and Dagaut, as well as a CPD model, a detailed kinetics analysis on NO removal, including the migration and transformation of hydrocarbons and nitrogen...

Nitrogen oxides emissions from the MILD combustion with the conditions of recirculation gas

ABSTRACTThe nitrogen oxides (NOx) reduction technology by combustion modification which has economic benefits as a method of controlling NOx emitted in the combustion process, has recently been receiving a lot of attention. Especially, the moderate or intense low oxygen dilution (MILD) combustion which applied high temperature flue gas recirculation has been confirmed for its effectiveness with regard to solid fuel as well. MILD combustion is affected by the flue gas recirculation ratio and the composition of recirculation gas, so its NOx reduction efficiency is determined by them. In order to investigate the influence of factors which determine the reduction efficiency of NOx in MILD coal combustion, this study changed the flow rate and concentration of nitrogen (N2), carbon dioxide (CO2) and steam (H2O) which simulate the recirculation gas during the MILD coal combustion using our lab-scale drop tube furnace and performed the combustion experiment. As a result, its influence by the composition of recirculation gas was insignificant and it was shown that flue gas recirculation ratio influences the change of NOx concentration greatly.Implications: We investigated the influence of factors determining the nitrogen oxides (NOx) reduction efficiency in MILD coal combustion, which applied high-temperature flue gas recirculation. Using a lab-scale drop tube furnace and simulated recirculation gas, we conducted combustion testing changing the recirculation gas conditions. We found that the flue gas recirculation ratio influences the reduction of NOx emissions the most.

Investigation of reducing ultrafine particulate matter formation by adding modified montmorillonite during coal combustion

Up to now, nearly all sorbents used to reduce the formation of particulate matter (PM) during coal combustion are raw minerals in nature. In this work, a new idea is proposed to improve the control ability by modifying the natural minerals. First, hydrochloric acid (HCl) and hydroxyl polymeric aluminum were selected to modify raw montmorillonite, respectively. Then combustion experiment of pulverized coal alone and that mixed with the raw/modified montmorillonite was performed under O2/N2 atmosphere in a lab-scale drop tube furnace (DTF). The produced PM was collected via a low pressure impactor system (LPI). The results show that the raw montmorillonite reduced the PM0.2 yield by 17.99%. Compared with raw montmorillonite, PM0.2 yield further decreased by 29.00% and 13.11% when acid-treated montmorillonite and aluminum-treated aluminum were added. Further characterization show that the formation of ultrafine PM was reduced mainly because of the chemical reaction between the sorbent and the vaporized alkali metal. More importantly, the modification treatment optimized the surface characteristics of montmorillonite. Moreover, modification treatment increased the number of free oxygen active sites in montmorillonite due to the breakage or formation of certain metallic bonds. These changes promoted the process of capturing alkali metal and thereby the modified montmorillonite showed better performance in reducing PM0.2 formation.

Ignitability and combustibility of Yallourn pyrolysis char under simulated blast furnace conditions

In this paper we have examined the potential of Yallourn brown coal char (collected from an industry-scale pyrolyser) to be used as a pulverized coal injection (PCI) fuel, its size-dependent properties, ignitability and combustibility under the simulated conditions of the blowpipe-tuyere section in a blast furnace. The combustion of individual sizes for Yallourn char was tested in a lab-scale drop-tube furnace (DTF) using pre-heated hot gas with a temperature up to 1000°C, and a particle residence time as short as 0.6s. Computational fluid dynamics (CFD) modelling was further conducted to optimize the char combustion conditions via sensitivity analysis. Irrespective of the pyrolysis condition, Yallourn char is superior over bituminous coal for being used as a top grade PCI fuel, due to its higher calorific value (7500–8110kcal/kg), lower ash content (<10wt%), high ash melting temperatures (>1550°C), and abundance of iron (>40wt% in ash). The performance of Yallourn char is also superior over bituminous coal under the simulated blast furnace conditions, for a rapid ignition and burnout even for a coarse char size of 300μm under the stoichiometric O2/C molar ratio and using low blast temperatures of 800–1000°C. All these are beneficial for reducing the energy consumption related to particle pulverization and the amount of oxygen for the combustion. With regard to the Yallourn char ignition and combustion in the hot gas, a minimum 6wt% volatile content is essential for a stable and rapid ignition of the volatiles at a gas temperature of 1000°C or below, since homogeneous ignition is predominant at low temperatures. However, once the blast temperature rises to 1200°C, the dependence on volatile content turns insignificant due to the dominance of the heterogeneous ignition, high C-O2 reactivity for the solid char, as well as the minimized pore diffusion control due to the large porosity (52.0–63.1%) of the Yallourn char tested here.

Inorganic PM10 emission from the combustion of individual mallee components and whole-tree biomass

This contribution reports the emission of inorganic particulate matter (PM) with an aerodynamic diameter <10µm (PM10) from the combustion of both individual mallee components and whole-tree biomass. Three major components of a mallee tree, namely bark, leaf, and wood, were size-reduced to 75–150µm and mixed at a dry mass ratio of 15% bark:35% leaf:50% wood, which is close to the real mallee's composition, to prepare a whole-tree biomass. The three individual mallee components and the whole-tree biomass were combusted in a laboratory-scale drop-tube furnace at 1400°C in air to produce inorganic PM10 for further quantification and characterization. The results demonstrate that, whereas the particle size distributions of the PM10 from the combustion of the bark, leaf and wood components generally follow a bimodal distribution, the yields of PM0.1, PM0.1–1, PM1, PM1–10, PM2.5, and PM10 from the three mallee components are quite different. On the bases of dry biomass and useful energy input, the yields of the PM of various size fractions studied follow a sequence of the bark>the leaf>the wood, consistent with that of the ash contents in the three components. Oppositely, the ash-based yields of PM0.1, PM0.1–1, PM1, PM1–10, PM2.5, and PM10 from the wood are substantially higher than those from the bark and the leaf. No obvious synergetic effect among different mallee components in PM10 emission is observed during the whole-tree biomass combustion, enabling the prediction of the PM10 yield from the whole-tree biomass combustion based on that from the individual mallee components.

Release Behaviors of Arsenic in Fine Particles Generated from a Typical High-Arsenic Coal at a High Temperature

To make an accurate assessment on transformation behaviors of arsenic in coal at a high temperature, a typical high-arsenic coal collected from southwest China has been chosen in the study and a series of high-temperature experiments in different atmospheres have been conducted with the help of a lab-scale drop-tube furnace. Fine particulate matter were collected by a low-pressure impactor, for obtaining their mass size distributions and further quantifying for arsenic distributions and speciation in fine particles of different sizes. The results indicated that the bleeding ratios of arsenic in air combustion, CO2 gasification, and N2 pyrolysis were 85, 65, and 45%, respectively, at 1300 °C. The ratio was found to remain relatively constant when the temperature increased from 1200 to 1400 °C. Organically associated arsenic would be more inclined to vaporize in N2 pyrolysis, while both organic and inorganic associated arsenic would vaporize in CO2 gasification and air combustion. Pyrite-associated arsenic ...

Advanced subgrid model for the gasification of Athabasca asphaltene in entrained-flow reactors

Recently, heavy bituminous crudes have increasingly being coming into focus as feedstock for synthesis-gas production. One of the heaviest compounds of petroleum is asphaltenes, which are formed during the primary upgrading process of bitumen. One feasible option for asphaltene utilization is their gasification in an entrained-flow gasifier. In this view, modeling can be used as an initial step in the design and optimization of large-scale gasifiers. This work presents a new subgrid model for computational fluid dynamics (CFD) based modeling of the gasification of Athabasca asphaltene particles (median diameter of 207 μm) in an entrained-flow reactor. The model is based on a virtual homogeneous reaction zone (VHRZ) concept (originally developed by [1]). However, in the present formulation the model considers melting, pyrolysis, homogeneous reactions in the particle vicinity and heterogeneous reactions of the char, where the VHRZ thickness is calculated using boundary layer approximation. The model has been verified using preliminary experimental data obtained for Athabasca asphaltene gasified in a lab-scale drop tube furnace (DTF). Experiments have been conducted for two different oxygen ratios, where the experimental conditions are analyzed using CFD. Good agreement between submodel predictions and experiments has been demonstrated. Finally, the results of the subgrid model emphasize the relevance of the energy feedback from the particle vicinity to the particle surface. A sensitivity study of model parameters shows that the ambient temperature and the assumed particle density have a mayor impact on the overall particle conversion.

A CCSEM study on the transformation of included and excluded minerals during coal devolatilization and char combustion

This study reports the transformation pathways of both included and excluded minerals during coal devolatilization and char combustion. Three Chinese coals of various ranks, namely YQ anthracite, DT bituminous coal and CF lignite, were size narrowed to 45−100μm, devolatilized in nitrogen and combusted in air at 1300°C, using a laboratory-scale drop tube furnace, to prepare chars and ashes. The mineral properties of the coals as well as their derived chars and ashes were analyzed using a computer-controlled scanning electron microscopy (CCSEM). The results demonstrate that, during coal devolatilization, whereas quartz and kaolinite are generally stable for all the three coals, included and excluded Fe-rich minerals (i.e., pyrite and siderite) as well as excluded Ca-rich minerals (i.e., calcite and ankerite) are decomposed and some of the intermediate products are incorporated with aluminosilicates. During char combustion, quartz participates in combustion reactions and forms aluminosilicates. Whereas the mullite-like phase in the YQ and DT chars changes little, that in the CF char absorbs Fe/Ca-rich fine particles and is incorporated into Fe–Ca-aluminosilicate. Most of the Ca/Fe-rich intermediate products react with aluminosilicates to form Fe-, Ca-, and Fe–Ca-aluminosilicates. The interactions between Fe/Ca-rich minerals and aluminosilicates are also observed. Calcium in Ca-rich minerals and iron in Fe-rich minerals of the YQ anthracite and the CF lignite interact with aluminosilicates during both coal devolatilization and char combustion processes. However, for the DT bituminous coal, such interactions between Ca-rich minerals and aluminosilicates only take place during devolatilization. The interactions between excluded Fe/Ca-rich minerals and included aluminosilicates during coal devolatilization are also observed.

Particulate matter emission from bio-oil incomplete combustion under conditions relevant to stationary applications

A raw bio-oil from biomass fast pyrolysis and a filtrated bio-oil, which was prepared from the raw bio-oil via syringe filtration to remove fine char particles, were atomized via an air-assist nozzle set and then combusted in a laboratory-scale drop-tube furnace (DTF) at 1400°C under incomplete combustion conditions. Both air and oxygen (O2) atmospheres were considered to produce PM with aerodynamic diameter of <10μm (PM10). Regardless of experimental conditions, it was found that the particle size distributions (PSDs) of PM10 follow a bimodal distribution. Under such incomplete combustion conditions, the PM10 samples apparently contain substantial amounts of carbonaceous material. Whereas the PSDs of Na, K, Cl and S (in the form of SO42-) exhibit a unimodal distribution, those of Mg and Ca in PM10 are dependent on combustion atmosphere, i.e. a unimodal distribution for air combustion and a bimodal distribution for O2 combustion. The results show that under incomplete combustion conditions, the fine char particles in the raw bio-oil play significant roles in the emission of PM10 as well as Mg and Ca in PM10. The removal of the fine char particles in the raw bio-oil leads to considerable reductions in the mass of PM with aerodynamic diameters of 0.1–10μm as well as that of Mg and Ca in the PM with a size range of 0.372–10μm from the filtrated bio-oil combustion, compared to those from the raw bio-oil combustion. Combustion atmospheres also have significant effects on the emission and chemical composition of PM10 due to incomplete combustion. Switching combustion atmosphere from air to O2 increases the PM1 yield by ∼74.2% due to the increased yields of Na, K, Mg, Ca, SO42- and PO43- in PM1, but decreases the PM1–10 yield by ∼27.2%, apparently as a result of improved burnout and thereby decreased amounts of unburned carbonaceous material in PM1–10.