Chemical composition and physical properties of filter fly ashes from eight grate-fired biomass combustion plants

For the handling, treatment and utilization of fly ash from biomass combustion its chemical composition and physical properties are important. In this study eight filter fly ashes from different grate-fired biomass combustion plants were investigated. In fly ash from straw combustion high concentrations of（K） were found, whereas in the fly ash from wood combustion the concentrations of Ca and Mg were higher. The average concentration of PO3-4was similar in both types of fly ashes. In all wood fly ashes some measured heavy metal concentrations were above the limits for utilization. The straw fly ashes were much less contaminated and can be utilized. For wood fly ash most parameters showed little variation, except from one fly ash where the dust pre-separator is in poor condition. The average values were： mass median diameter 4.3 ± 0.8 μm, spread of particle size distribution19 ± 11, particle density 2620 ± 80 kg/m^3 and angle of repose 50°± 1°. The density of the straw fly ashes is lower（2260 ± 80 kg/m^3） and the spread of the size distribution is higher（72 ± 24）.For one straw combustion fly ash the values of the mass median diameter and the angle of repose were similar to the values of wood combustion fly ash, for the other straw fly ash the values differed considerably. While the particle size of this fly ash was much smaller,surprisingly the angle of repose was also lower. This can be attributed to the formation of small agglomerates in this fly ash, which were not disintegrated without a certain stress.

Nanosized Carbon Dots from Organic Matter and Biomass

Carbon nanoparticles（C-dots） were prepared by refluxing the combustion soots of candles and corn stalk in nitric acid.The synthesized C-dots were characterized.The results showed a sharp increase in oxygen content and a sharp decrease in carbon content after oxidation.The C-dots had-OH and-CO2H groups introduced which made them hydrophilic.However,their difference was also obvious.The C-dots from candle soot had a 10-45 nm broad particle size distribution,and those from corn stalk soot had a 6-18 nm relatively small and narrow size distribution.The C-dots were mainly of sp2 and sp3 carbon structure different from the C-dots of diamond-like structure from candle soot.Interestingly,two kinds of C-dots all exhibited unique photoluminescent properties.The obtained C-dots have potential applications in a broad range of areas.

Reactivity improvement of ilmenite by calcium nitrate melt infiltration for Chemical Looping Combustion of biomass

Chemical Looping Combustion is a novel process that generates sequestration-ready CO_(2) from the combustion of woody biomass without requiring a gas separation step and without diluting the CO_(2) with N_(2) from air.This is achieved by oxidizing the fuel with lattice oxygen of a metal oxide oxygen carrier.When using cheap and abundant ilmenite ore(FeTiO3)as the oxygen carrier,the rather low reactivity towards volatiles released from the biomass upon devolatilization,as well as detrimental structural changes due to a segregation of Fe and Ti in the material,are of concern.These issues can be addressed by modifying ilmenite with Ca via melt infiltration.In this work,we demonstrate that this modification results in a good distribution of Ca throughout the ilmenite particles that a)prevents detrimental Fe/Ti segregation,b)improves the mechanical stability of the particle compared to materials prepared by solution impregnation and c)improves the reactivity of this material towards hydrogen and wet methane.Moreover,fixed bed experiments showed that the Ca modification not only resulted in increased methane conversion,but also in an increased degree of oxidation of gaseous intermediates CO and H2.We thus conclude that the performance of ilmenite in Chemical Looping processes can be significantly enhanced by Ca modification of ilmenite either prior to use or in-situ during operation of this bed material with Ca-rich fuels such as woody biomass.

Role of Air Staging in a Batch-Type Fixed Bed Biomass Combustor under Constant Primary Air

Staged combustion of biomass is the most suitable thermo-chemical conversion for achieving lower gaseous emissions and higher fuel conversion rates.In a staged fixed bed combustion of biomass,combustion air is supplied in two stages.In the first stage,primary air is provided below the fuel,whereas in the later stage,secondary air is supplied in the freeboard region.The available literature on the effects of air staging(secondary air location) at a constant primary air flow rate on combustion characteristics in a batch-type fixed bed combustor is limited and hence warrants further investigations.This study resolves the effect of air staging,by varying the location of secondary air in the freeboard at five secondary to total air ratios in a batch-type fixed bed combustor.Results are reported for the effects of these controlled parameters on fuel conversion rate,overall gaseous emissions(CO_(2),CO and NO_x) and temperature distributions.The fuel used throughout was densified hardwood pellets.Results show that a primary freeboard length(distance between fuel bed top and secondary air injection) of200 mm has higher fuel conversion rates and temperatures as well as lower CO emissions,at a secondary to total air ratio of 0.75 as compared to primary freeboard length of 300 mm.However,NO_x emissions were found to be lower for a primary freeboard length of 300 mm as compared to 200 mm.An increase in secondary to total air ratio from 0.33 to 0.75 resulted in higher freeboard temperatures and lower CO as well as NO_x emissions.The outcomes of this study will be helpful in the effective design of commercial scale biomass combustors for more efficient and environmentally friendly combustion.

Compositional and structural study of ash deposits spatially distributed in superheaters of a large biomass-fired CFB boiler

Recognizing the nature and formation progress of the ash deposits is essential to resolve the deposition problem hindering the wide application of large-scale biomass-fired boilers.Therefore,the ash deposits in the superheaters of a 220 t/h biomass-fired CFB boiler were studied,including the platen(PS),the high-temperature(HTS),the upper and the lower low-temperature superheaters(LTS).The results showed that the deposits in the PSs and HTSs were thin(several millimeters)and compact,consisting of a yellow outer layer and snow-white inner layer near the tube surface.The deposits in the upper LTS appeared to be toughly sintered ceramic,while those in the lower LTS were composed of dispersive coarse ash particles with an unsintered surface.Detailed characterization of the cross-section and the initial layers in the deposits revealed that the dominating compositions in both the PSs and the HTSs were Cl and K(approximately 70%)in the form of KCl.Interestingly,the cross-section of the deposition in the upper LTS exhibited a unique lamellar structure with a major composition of Ca and S.The contents of Ca and Si increased from approximately 10%to approximately 60%in the deposits from the high temperature surfaces to the low temperature ones.It was concluded that the vaporized mineral matter such as KCl played the most important role in the deposition progress in the PS and the HTS.In addition,although the condensation of KCl in the LTSs also happened,the deposition of ash particles played a more important role.

Biomass briquette fuel,boiler types and pollutant emissions of industrial biomass boiler:A review

Biomass is considered a renewable and cleaner energy source alternative to fossil fuels.In recent years,industrial biomass boilers have been rapidly developed and widely used in the industrial field.This work makes a review on the fuel types used in industrial biomass boilers,the fuel characteristics and the characteristics of air pollutants emitted from the combustion of industrial biomass boilers and other contents in different studies.However,the existing research still has many deficiencies.In the future,further research on biomass fuel,industrial biomass boiler combustion process and the pollutants emitted by industrial biomass boiler combustion,especially the carbonaceous aerosol emitted by in-dustrial biomass boiler and carbonaceous aerosol optical properties still need to be made.At the same time,the potential harm of carbonaceous aerosols emitted from industrial biomass boiler sources to human health and climate change needs to be studied in depth.This review provides a scientific basis for the accurate evaluation of industrial biomass boilers and the effective prevention and control of various pollutants of industrial biomass boilers.

Emissions from the combustion of eucalypt and pine chips in a fluidized bed reactor

Interest in renewable energy sources has increased in recent years due to environmental concerns about global warming and air pollution,reduced costs and improved efficiency of technologies.Under the European Union（EU）energy directive,biomass is a suitable renewable source.The aim of this study was to experimentally quantify and characterize the emission of particulate matter（PM（2.5））resulting from the combustion of two biomass fuels（chipped residual biomass from pine and eucalypt）,in a pilot-scale bubbling fluidized bed（BFB）combustor under distinct operating conditions.The variables evaluated were the stoichiometry and,in the case of eucalypt,the leaching of the fuel.The CO and PM（2.5）emission factors were lower when the stoichiometry used in the experiments was higher（0.33±0.1 g CO/kg and 16.8±1.0 mg PM（2.5）/kg,dry gases）.The treatment of the fuel by leaching before its combustion has shown to promote higher PM（2.5）emissions（55.2±2.5 mg/kg,as burned）.Organic and elemental carbon represented 3.1 to 30 wt.% of the particle mass,while carbonate（CO3^（2-））accounted for between 2.3 and 8.5 wt.%.The particulate mass was mainly composed of inorganic matter（71% to 86% of the PM（2.5）mass）.Compared to residential stoves,BFB combustion generated very high mass fractions of inorganic elements.Chloride was the water soluble ion in higher concentration in the PM（2.5）emitted by the combustion of eucalypt,while calcium was the dominant water soluble ion in the case of pine.

Physicochemical characterization of forest and sugarcane leaf combustion’s particulate matters using electron microscopy,EDS,XRD and TGA

Physical characteristics and quantitative elemental composition of PM and residual ash produced from sugarcane leaves(SCL)combustion were investigated using TEM-EDS compared with forest leaves(FRL).SEM-EDS was used to analyze the microstructure and chemical composition of biomass raw leaves and PM.XRD analysis was also performed to investigate the characterization of the crystalline nanostructure,structure of PM,and residual ash compared to the TEM image processing method.The oxidation kinetics of biomass raw materials,PM,and residual ash were investigated by TGA.The morphology of fine and ultrafine agglomerate structure of SCL soot and residual ash are not significantly different from the FRL soot and residual ash.The average diameter sizes of single primary nanoparticles of SCL and FRL soot are approximately 37 nm and 35 nm,while the sizes of residual ash are about 18 nm and 22 nm,respectively.The single primary nanoparticles of soot are mainly composed of curve line crystallites of carbon fringes,while residual ash is composed of straightline lattice fringes.The average fringe lengths of SCL and FRL soot are about 1.25 nm and 1.04 nm from the outer shell and 0.89 nm and 0.74 nm from the inner core.The interlayer spacing of curve line carbon fringes of SCL and FRL soot is approximately 0.359 nm and 0.362 nm by the TEM image analysis and it was matched with XRD analysis.The biomass PMs are mainly composed of soot,Si,Ca,and K compounds:SiO_(2),CaCO3,and KCl.

Chemical composition and properties of ashes from combustion plants using Miscanthus as fuel

Miscanthus giganteus is one of the energy crops considered to show potential for a substantial contribution to sustainable energy production. In the literature there is little data available about the chemical composition of ashes from the combustion of Miscanthus and practically no data about their physical properties. However, for handling, treatment and utilization of the ashes this information is important. In this study ashes from two biomass combustion plants using Miscanthus as fuel were investigated. The density of the ashes was 2230 ± 35 kg/m;, which was similar to the density of ashes from straw combustion. Also the bulk densities were close to those reported for straw ashes. The flowability of the ashes was a little worse than the flowability of ashes from wood combustion. The measured heavy metal concentrations were below the usual limits for utilization of the ashes as soil conditioner. The concentrations in the bottom ash were similar to those reported for ash from forest residue combustion plants. In comparison with cyclone fly ashes from forest residue combustion the measured heavy metal concentrations in the cyclone fly ash were considerably lower. Cl-, S and Zn were enriched in the cyclone fly ash which is also known for ashes from wood combustion. In comparison with literature data obtained from Miscanthus plant material the concentrations of K, Cl-and S were lower.This can be attributed to the fact that the finest fly ash is not collected by the cyclone de-dusting system of the Miscanthus combustion plants.

Physicochemical and toxicological characteristics of nanoparticles in aerosols in southern Thailand during recent haze episodes in lower southeast Asia

Transboundary haze from biomass burning is one of the most important air pollutions in Southeast Asia.The most recent serious haze episode occurred in 2015.Southern Thailand was affected by the haze during September to October when the particulate matter concentration hit a record high.We investigated physical and chemical characteristics of aerosols,including concentration and aerosol size distribution down to sub-micron sizes during haze episodes in 2013 and 2015 and,for reference,an insignificant haze period in 2017.The highest total suspended particulates and PM 10 levels in Hat Yai city were 340.1 and 322.5μg/m^3.The mass fractions were nanoparticles(<100 nm)3.1%-14.8%and fine particles(<1μm)54.6%-59.1%.Polycyclic aromatic hydrocarbon size distributions in haze periods peaked at 0.75μm and the concentrations are 2-30 times higher than the normal period.High molecular weight(4-6 ring)PAHs during the haze episode contribute to about 56.7%-88.0%for nanoparticles.The average values of benzo(a)pyrene toxic equivalency quotient were 3.34±2.54ng/m^3 in the 2015 haze period but only 0.89±0.17 ng/m^3 in 2017.It is clear that particles smaller than 1μm,were highly toxic.Nanoparticles contributed 19.4%-26.0%of total BaP-TEQ,whereas the mass fraction is 13.1%-14.8%.Thus the nanoparticles were more carcinogenic and can cause greater health effect than larger particles.The fraction of BaP-TEQ for nanoparticles during 2017 non-haze period was nearly the same,while the mass fraction was lower.This indicates that nanoparticles are the significant source of carcinogenic aerosols both during haze and non-haze periods.

Emission of organic carbon, elemental carbon and water-soluble ions from crop straw burning under flaming and smoldering conditions

Emissions from major agricultural residues were measured using a self-designed combustion system. Emission factors （EFs） of organic carbon （OC）, elemental carbon （EC）, and water-soluble ions （WSIs） （K＋, NH4＋, Na＋, Mg2＋, Ca2＋, Cl-, NO3-, SO42–） in smoke from wheat and rice straw were measured under flaming and smoldering conditions. The OC1/TC （total carbon） was highest （45.8% flaming, 57.7% smoldering） among carbon fractions. The mean EFs for OC （EFOC） and EC （EFEC） were 9.2 ± 3.9 and 2.2 ± 0.7 g/kg for wheat straw and 6.4 ± 1.9 and 1.1 ± 0.3 g/kg for rice straw under flaming conditions, while they were 40.8 ± 5.6 and 5.8 ± 1.0 g/kg and 37.6 ± 6.3 and 5.0 ± 1.4 g/kg under smoldering conditions, respectively. Higher EC ratios were observed in particulate matter （PM） mass under flaming conditions. The OC and EC for the two combustion patterns were significantly correlated （p 〈 0.01, R = 0.95 for wheat straw; p 〈 0.01, R = 0.97 for rice straw）, and a higher positive correlation between OC3 and EC was observed under both combustion conditions. WSIs emitted from flaming smoke were dominated by Cl- and K＋, which contributed 3.4% and 2.4% of the PM mass for rice straw and 2.2% and 1.0% for wheat straw, respectively. The EFs of Cl- and K＋ were 0.73 ± 0.16 and 0.51 ± 0.14 g/kg for wheat straw and 0.25 ± 0.15 and 0.12 ± 0.05 g/kg for rice straw under flaming conditions, while they were 0.42 ± 0.28 and 0.12 ± 0.06 g/kg and 0.30 ± 0.27 and 0.05 ± 0.03 g/kg under smoldering conditions, respectively. Na＋, Mg2＋, and NH4＋ were vital components in PM, comprising from 0.8% （smoldering） to 3.1% （flaming） of the mass. Strong correlations of Cl- with K＋, NH4＋, and Na＋ ions were observed in rice straw and the calculated diagnostic ratios of OC/EC, K＋/Na＋ and Cl-/Na＋ could be useful to distinguishing crop straw burning from other sources of atmospheric pollution.