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Characteristics of particulate matter emitted from agricultural biomass combustion Wei Yang, Youjian Zhu, Wei Cheng, Huiying Sang, Haiping Yang, and Hanping Chen Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 30 May 2017 Downloaded from http://pubs.acs.org on May 30, 2017
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Characteristics of particulate matter emitted from
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agricultural biomass combustion
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Wei Yang1, Youjian Zhu2, Wei Cheng1, Huiying Sang1, Haiping Yang*1, Hanping Chen1
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1
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University of Science and Technology, Wuhan 430074, PR China
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2
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Henan 450002, PR China
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*
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[email protected]
State key Laboratory of Coal Combustion, Department of Energy and Power, Huazhong
School of Energy and Power Engineering, Zhengzhou University of Light Industry, Zhengzhou,
Corresponding author: Haiping Yang, +86-27-87559358, +86-27-87545526,
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Abstract： ：In this work, the emission of particulate matter from combustion of agricultural
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biomass was investigated in comparison with woody biomass. The mechanism of particulate
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matter emission was studied by means of mass-based particle size distribution, inorganics
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elemental component analysis and morphology at variant combustion temperatures, and different
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biomass feedstocks. The mass-based particle size distributions (PSDs) of PM10 of cotton stalk, rice
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husk and camphorwood exhibits a bimodal distribution, while cornstalk with a unimodal
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distribution. The emission of PM10 of agricultural biomass is much higher than that of woody
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biomass, and it is mainly composed of PM1 in which Na, K are enriched as alkali metal chloride
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and sulfide. On the other hand, Mg and Ca are enriched as the main inorganic compounds in
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PM1-10 for woody biomass. Higher combustion temperature is favorable for the formation of fine
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PM particles against a reduction of PM10. PM1 and PM1-10 formation mechanisms are different for
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different biomass feedstocks, and their formation pathways are hereby proposed for each biomass
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resource.
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Keywords： ：agricultural biomass, particulate matter, combustion, AAEM
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1. Introduction
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In the biomass combustion process, a part of volatile inorganic species, such as alkali metal
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containing compound (KOH, KCl), is released to the gas phase and then form fine particulate
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matters (PM) via complex chemical and physical reactions[1]. PMs could cause serious
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environmental pollution and pose a great threat on human health[2], which is one of key issues
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limiting effective utilization of rich agricultural biomass residues in many countries, particularly
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in China for the deteriorating atmosphere environment on the background of fast economic growth.
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Thus, more and more attention is paid to the PM research recently.
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Previous research[3-6] on PM emission mainly focuses on coal combustion. Minerals as clay
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and pyrite are abundant in coal ash[7, 8] and are transformed into ash particles mainly in the range
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of 1-10 µm via fragmentation and coalescence[3] in coal combustion. The trace elements (Na, Zn,
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etc) in coal also evaporate and subsequently condense to form PM1 (particulate matter diameter
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less than 1 micron) particles[9] in a less content during the combustion process. The biomass fuel,
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on the other hand, differ significantly from coal in properties and result in different PM emission
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characteristics in the combustion. Comparing to coal, more PM is generated in wood
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combustion[10, 11], and also, the physical characteristics and elemental composition of the PM are
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changed significantly[9, 12, 13]. Sippula et al.[14] found that the inorganic components in PM1 during
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Finnish wood combustion were K2SO4, KCl, K2CO3, KOH, and organic species. The PM
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formation pathway was suggested from thermodynamic calculation as follows: K2SO4 in the vapor
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starts to form small particles by homogeneous/heterogeneous condensation at 950-1050 oC,
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followed by the condensation of K2CO3, KOH and KCl as the temperature decreases.
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Agricultural biomass residues are abundant in China and are considered as the potential fuel
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to replace fossil fuel to a certain extent. Different from woody biomass, agricultural biomass has
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higher ash content (especially higher alkali metal content) and leads to different PM emission
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behavior[15]. More PM is generated in the combustion of agricultural biomass than woody
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biomass[16]. Carroll and Finnan[17] found that the total PM emission from wood combustion was in
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22-51 mg/Nm3, while this value increased to 100-399 mg/Nm3 for straw biomass. Garcia-Maraver
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et al.[18] found that the total PM emissions were in the range of 50-100 mg/Nm3 in the case of the
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pine pellets, while the values increased 100-600 mg/Nm3 for the olive biomass pellets. Results
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also indicated that the produced PM was dominated by PM2.5 (particulate matter diameter less than
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2.5 microns) for olive biomass. The ultra-fine particles were formed by homogeneous nucleation
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of alkali vapors, they also pointed out that heterogeneous condensation and particle growth played
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an important roles in the PM1 formation considering the higher particle concentration compared to
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pine wood[18]. On the other hand, both of fragmentation of minerals (rich in Mg, Ca, P, Fe and Si)
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and condensation of alkali vapor and sulfates contributed to the coarse particle formation[18].
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Additionally, Bäfver et al.[19] detected certain amount of P in the PM during combustion of oat
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grains.
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These studies, however, are usually conducted in the pellet burner under constant operation
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conditions[17, 20-22]. Researches about the effects of operation parameters on the PM emissions are
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limited. It is imperative to illuminate the PM formation mechanism of different agricultural
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biomass fuels to facilitate a clean and efficient utilization. In this work, the main purpose is to
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further study the formation mechanism of PM from agricultural biomass combustion. Three
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typical Chinese agricultural biomass residues were selected to investigate the effects of the
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feedstock properties on the PM emission characteristics in the combustion. Cotton stalk was
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selected as the representative fuel to investigate the effects of temperature on the PM emission
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characteristics in the combustion.
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2. Experimental
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2.1 Fuel properties
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The biomass fuels used in the experiment include three agricultural biomass residues, rice
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husk, cornstalk and cotton stalk, and one woody biomass, camphorwood. The agricultural biomass
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residues are collected in the rural area of Hubei Province and are selected due to the fact that these
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fuels are abundant in China and are considered as potential biomass fuels for heat and electricity
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production[23-26]. Camphorwood, which is relatively common in the local and is a potential
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renewable energy for heat production, was selected for comparison. The samples were crushed
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and sieved to a particle size of 125-177 µm. The particle size was chosen to ensure complete
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combustion and avoid operational difficulties based on previous results[4, 27, 28]. The proximate and
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ultimate analysis were made by means of the SDTGA-2000 industrial analyzer (Las Navas, Spain)
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and EL-2 type elemental analyzer (Vario, Germany), respectively. The heating value of the
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samples was analyzed using the automatic calorimeter (model: 6300, America). The low heating
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value, proximate and ultimate analysis of the fuels are presented in Table 1. The sample was ashed
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at 823 K and then analyzed using an X-ray fluorescence spectrometer (Jasco FP-6500, Japan) to
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get the chemical composition. The result is presented in Table 2. It can be seen from Table 1 that
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the ash content of camphorwood is the lowest, and the volatile matter is the highest. The contents
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of N and S in three agricultural biomass residues are higher than those in camphorwood. The K
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content in cornstalk is the highest as shown in Table 2, while the Mg/Ca content of cotton stalk
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and camphorwood is relatively high. Rice husk ash is mainly composed of silica.
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2.2 Combustion experiment
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The combustion tests were carried out in a drop tube furnace (DTF) as shown in Fig 1. The
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system is mainly composed of a Sankyo Piotech Micro Feeder (MFEV-10), an electrical heated
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furnace, a tube reactor, a gas supply section, a particulate matter collection section and related
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pipeline. The reactor is made of corundum tube with a height of 2000 mm and an inner diameter
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of 52 mm. The fuel was fed into the reactor at 0.15 g/min together with a primary air (0.5 L/min).
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To ensure complete combustion, a secondary air was fed at 1.5 L/min into the external reactor
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chamber, in which it is heated up and then entered the internal reaction chamber. The residence
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time of the particles in the furnace is about 3.6 seconds.
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The particle size mass distribution was measured by a Dekati low pressure impactor (DLPI)
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(Dekati, Finland). The morphology and chemical composition of the PM was also analyzed to
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provide information on the formation mechanism of PM. The combustion temperature was
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changed from 1073 to 1473 K for study on temperature effect. The burnout rates of the fuels were
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larger than 95% for all the tests. After combustion, the gas sample was firstly diluted by nitrogen
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at 8L/min to prevent secondary condensation reactions and ensure a sufficient sample flow rate for
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the instrument. Then the gas sample went through a cyclone and DLPI to collect fly ash (particles
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larger than 10 µm) and PM10 (particulate matter diameter less than 10 microns) samples,
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respectively. PM10 sample is divided into 13 stages with the corresponding 50% aerodynamic
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cutoff diameters are 0.028, 0.057, 0.094, 0.15, 0.26, 0.38, 0.61, 0.94, 1.58, 2.36, 3.95, 6.6, 9.8 µm,
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respectively[27]. The detailed operating procedures of DLPI have been previously described[4, 29, 30].
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All the sampling devices and related pipelines were kept at 393K to avoid possible acid gas
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condensation and gravitational settling deposition during the sampling process.
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2.3 PM sample
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In this work, each combustion experiment was conducted for three times with aluminum
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membrane to validate the repeatability and for another three times with polycarbonate membrane
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to get samples for the following analysis. The standard deviations indicated that the
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reproducibility of measurement is in acceptable range. The PM collected from the aluminum and
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polycarbonate membranes were used for gravimetric and elemental analysis, respectively.
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For the gravimetric analysis, the collected aluminum substrates were weighed by a
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micro-electrical balance (0.001 mg, Sartorius M2P, Germany) to obtain the mass size distribution
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of the PM. Polycarbonate substrates were used for elemental and morphological analysis. The
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collected sample was digested in a microwave oven with a mixture of HNO3(70% v/v)/H2O2(20%
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v/v)/HF(10% v/v), and then the alkali metal and alkaline earth metal (AAEM) species content was
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analyzed by an inductively coupled plasma mass spectrometry (ELAN DRC-e, America.
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Detection limit: 0.1-10 ppm). Cl was analyzed by ion chromatograph (881 Compact IC pro,
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Switzerland. Detection limit: 0.1-10 ppm) following rinsed in deionized water for 24 hours. For
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the surface morphological and elemental analysis of the PM, samples were mounted on carbon
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tape and then analyzed by an environmental scanning electron microscope with energy dispersive
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X-ray analysis in secondary electron mode (ESEM-EDS, Quanta 200, Netherlands).
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3. Result and discussion
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3.1 Emission of particulate matter from combustion of different biomass fuels
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The particle size distributions (PSDs) of PM10 from the combustion of four fuels at 1273K
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are shown in Fig 2. It is clear that the mass-based particle size distributions (PSDs) of PM10 from
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the combustion of cornstalk presents a unimodal distribution with the peak at around 0.6 µm.
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While for the other three fuels a bimodal distribution is presented with the coarse mode at around
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4 µm and the fine mode at 0.6, 0.3 and 0.2 µm respectively for cotton stalk, rice husk and
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camphorwood. This is consistent with the previous study[31, 32]. The yields of PM0.1, PM1, PM2.5,
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PM10, PM1-2.5, PM2.5-10, PM1-10 from the combustion experiments are presented in Table 3. As can
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be seen, the PM10 emissions of cotton stalk and cornstalk are 45.58 and 88.35 mg/Nm3, which are
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greatly higher than camphorwood (6.10 mg/Nm3). However, the PM10 emission of rice husk is
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quite low (12.37 mg/Nm3) in spite of its high ash content (16.20 wt%). The rice husk ash is
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dominated by SiO2 (96.36 wt%) which has a high melting point and would not evaporate to the
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gas phase under the current combustion temperature[15]. On the other hand, SiO2 could also inhibit
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the evaporation of alkali metal via the formation of silicates[31-33]. This caused the low PM
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emission from rice husk. It can be observed that the particles from agricultural biomass are mainly
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composed of PM1, which is different from camphorwood, which suggests different PM formation
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pathways for agricultural biomass and woody biomass.
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In order to explore the formation pathway of the PM during combustion, the key inorganic
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elements (Na, K, Ca, Mg, Cl) in each particle size range was analyzed and the results are
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presented in Fig 3. As can been seen, Na, K and Cl are enriched in PM1 and depleted in PM1-10 for
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all the agricultural biomass, whereas Ca and Mg are enriched in PM1-10. During the combustion
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process, the volatile alkali chlorides and alkali hydroxides vapors are initially released from the
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fuel[1]. Then ultra-fine-particles are formed when the inorganic vapors reach the condensation
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temperature through homogeneous nucleation[9]. Meanwhile, the inorganic vapors could also
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condense on the newly-formed/existing particles through heterogeneous condensation and
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increase the particle size at the same time[9, 34]. Additionally, agglomeration and coalescence also
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contributes to PM1 formation[9, 35]. On the other hand, it can be observed in Fig 2 and Fig 3 that the
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fine mode peak for cotton stalk and cornstalk situate at 0.6 µm which is higher than that of rice
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husk (0.3 µm) and camphorwood (0.2 µm). This can be explained by the enhanced particle
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agglomeration and coalescence[18] for these two biomass. As indicated earlier, the total PM
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emission of cotton stalk and cornstalk are significantly higher than camphorwood and rice husk.
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This makes heterogeneous condensation on the pre-existing particles, agglomeration and
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coalescence are prevailing during the particle formation process[18], which explains the higher fine
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mode peak for these two biomass.
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The coarse mode peak situates at approximately 4 µm for all biomass fuels if appears as seen
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in Fig 2. However, different formation pathways are suggested based on the elemental
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composition of the PM. Mg and Ca show a unimodal distribution in PM10 for cotton stalk and
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camphorwood and its concentration is under detection limit in PM1. The prevailing existence of
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Mg and Ca in PM1-10 was reported in previous study on combustion of torrefied and spent mallee
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leaf[31, 32]. It is probably attributed to two different formation mechanisms. The first one is the
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direct release of organic bound Ca and Mg during the devolatilization and char combustion
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process[36]. The released Ca and Mg will be oxidized to CaO and MgO[37], and subsequently form
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large Ca/Mg-rich particles through catalyzed sintering[31] and heterogeneous condensation of
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volatile inorganic species (e.g. KCl, K2SO4)[34]. The existence of certain amount K, Na and Cl in
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PM1-10, as seen from Fig 3, confirms the heterogeneous condensation on the existing particles. On
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the other hand, the AAEM compounds could also react with minerals to form silicates and
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phosphates and generate PM1-10 via coalescence and fragmentation[13, 31].
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However, these mechanisms can not be applied to rice husk and cornstalk due to the
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undetectable Mg and Ca contents in the particulate matters. The rice husk ash is dominated by Si
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so that PM1-10 is expectedly composed of Si compounds as SiO2 and silicates. For cornstalk, alkali
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silicates are probably responsible for the PM1-10 formation[38] in light of the high alkali metal and
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silicon content in the ash. Unfortunately, Si is not measured in this work. The PM1-10 formation
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pathway for these two fuels will be discussed later in Section 3.3 with the help of EDX analysis of
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the PM particles.
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3.2 Effect of temperature on the PM emission
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Cotton stalk was chosen to study the effect of temperature on PM emissions considering: 1)
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the dominated roles of AAEM species; and 2) the comparatively alkali and alkali metal content in
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the ash. The PSDs of PM10 at different temperature is shown in Fig 4. Although bimodal
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distributions are presented at all the combustion temperatures, clear differences in the PM1 and
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total PM emission are observed. The total PM10 emission at 1073 K is 90.59 mg/Nm3 and
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decreases to 16.30 mg/Nm3 at 1473 K as seen in Table 3. PM1 emission also decreases. This
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conflicts with the previous studies[39-41] that the total PM1 emission increased along with the
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notably increase of PM0.1 as the temperature increased from 1473 to 1723 K during the
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combustion of Chinese bituminous coal. Generally the enhanced PM1 emission at higher
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temperature results from the higher vaporization of volatile inorganic elements such as alkali
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vapors and chlorides[39-41]. The temperature effect on PM1-10 is much more complicated. Firstly
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higher temperature aggravates the char fragments and leads to the formation of smaller char
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particles[27]. This reduces the possibility of ash particles contact/interaction and thus weakens the
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melting, agglomeration and coalescence effects[27]. The minerals matter (especially these have a
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particle size less than 10 µm) could also release after the burn of char fragment and form PM1-10
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accordingly.
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In our experiment, the PM0.1 tends to increase slightly as the temperature increases. This
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implies the intensified vaporization of alkali vapors and chlorides under high temperature. On the
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other hand, PM10 emission decreases significantly as aforementioned. There are two possible
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reasons for the decrease of PM10. First, the high PM emission at 1073 and 1173 K could be due to
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the incomplete combustion. Thermogravimetric analysis was made to check the combustible
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fraction in the PM samples. Weight losses were found for the PM samples collected at 1073 and
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1173 K. This suggests an incomplete combustion and certain amount of carbon-containing
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compounds such as soot exists in the PM sample. The content of key inorganic elements (Na, K,
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Ca, Mg, Cl) in each range of particle size are presented in Fig 5. It can be observed that the Na and
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K contents in PM decrease notably with a slightly increase of Ca and Mg as the combustion
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temperature increases. Therefore, it is obvious that other reasons are also responsible for the PM
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losses under high temperature. Previous study[42] indicated that alkali hydroxides and chloride
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could react with the corundum tube (consist of high-purity alumina) by reacting with Al2O3 and
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form instable NaAlO2. Alkali chloride could also deposit on the reactor wall through van der
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Waals forces[42]. Therefore, it is speculated that certain amount of alkali compounds react with the
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corundum tube or deposit on the surface of tube under high combustion temperature and
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eventually reduce the K and Na content in PM10 emission. The slightly increase of Ca and Mg
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content in PM1-10 under high combustion temperature could be attributed to the intensified
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particles collision and fragments, which prompted Mg and Ca element to be broken into tiny
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particles and react with other elements to form particle matters[5, 6].
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3.3 SEM-EDS analysis of the PM
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The typical SEM images of PM samples are shown in Fig 6, and the corresponding EDS results
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are given in Table 4. Fig 6 a-c shows typical SEM images of PM samples from the combustion of
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cotton stalk. PM particles shown in Fig 6 a and b mainly composed of submicrometer sized
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agglomerates. The EDX analysis indicates that K, Cl, and S are the dominating elements. This
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further confirms that the fine mode of PM1 is formed by homogeneous nucleation, heterogeneous
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condensation of alkali chlorides and sulfates and agglomeration. For Fig 6 c, few fine spherical
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particles are also found except for the irregularly shaped large agglomerate particles. From Table 4,
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it can be seen that the Ca, Mg, Si and P are also present in addition to K, Cl and S. These elements
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generally are less volatile and tend to retained in the residual ash. This further confirms the two
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formation pathways for PM1-10 as proposed in section 3.1: 1）fragments and direct transformation
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of the non-volatile species; and 2) condensation of the alkali compounds on the surface of the
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coarse particles. Elemental composition of typical PM particles from camphorwood combustion is
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presented in Fig 6 j-l. The morphological characteristic is similar to cotton stalk except for the
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diminished agglomeration extent due to the low concentration of PM. Meanwhile, The EDX
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analysis also indicates a similar elemental composition. Thus a similar PM formation mechanism
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to cotton stalk is proposed.
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Fig 6 d-f shows typical SEM images of PM samples from the combustion of cornstalk. It shows
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that PM1 particle shown in Fig 6 d and e mainly composed of particles agglomerates with K and
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Cl as the main elements (Table 3). Irregularly shaped agglomerates and fine spherical particles are
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abundant for Fig 6 f. The EDX analysis indicates that it was mainly composed by K, Cl, Si with a
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less content of P, Ca, Na and Mg. The spherical particles imply the formation of melted alkali
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silicates in PM2.5-10. This confirms our previous speculation and indicates the dominated roles of
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alkali silicates and phosphates in the PM2.5-10 formation.
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SEM images and EDX analysis of typical PM particles from rice husk combustion are presented
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in Fig 6 g-i and Table 4, respectively. It can be seen that PM particle shown in Fig 6 g and h are
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mainly composed of K and Cl suggest as similar PM1 formation mechanism with cotton stalk and
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cornstalk. For the coarse mode particles shown in Fig 6 i, Si and Al are prevailing. Two pathways
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are responsible for this phenomena: 1) Si is oxidized into small particles in the form of silicon
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oxide and form particulate matter with the size of 1-10 µm[43]; and 2) the reaction between SiO2
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and alkali metal leads to the formation of the alkali metal silicate and later forms PM1-10 particle
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through complex physical and chemical effects[9].
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4. Conclusion
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(1) The mass-based particle size distribution of PM10 from the combustion of all biomass
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fuels exhibits a bimodal distribution, except for cornstalk which shows a unimodal distribution.
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The total PM emission of agricultural biomass is much higher than that of woody biomass. The
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PM emitted from agricultural biomass combustion are mostly small particles under 1µm in
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aerodynamic diameter, and mainly composed of Na, K as alkali metal chloride and sulfide.
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Whereas for woody biomass PM1-10 is dominant with Mg and Ca as the main inorganic
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compounds.
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(2) For PM1, vaporization-condensation of alkali compound is the main formation pathway
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for all biomass. However, heterogeneous condensation, agglomeration and coalescence contribute
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significantly in PM1 formation during the combustion of cotton stalk and cornstalk.
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(3) For PM1-10, the following two formation pathways are proposed: 1) direct transformation
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of Ca/Mg and Si-rich particles with subsequent heterogeneous condensation; 2) formation of
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silicates and phosphates. In addition, the formation of alkali silicates and silicon dioxide plays an
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important role during combustion of cornstalk and rice husk.
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(4) The total PM10 emission decreases and PM0.1 emission increases when the combustion temperature increases from 1073-1473 K.
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Acknowledgement
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The authors wish to express sincere thanks for the National Natural Science Foundation of China
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(51476067 and 51622604), the financial support from the National Basic Research Program of
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China (2013CB228102), and the Special Fund for Agro-scientific Research in the Public Interest
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(201303095). The authors are also grateful for the assistance on the experimental studies provided
277
by the Analytical and Testing Center in Huazhong University of Science & Technology
278
(http://atc.hust.edu.cn), Wuhan 430074, China. The authors also would like to express our heartfelt
279
thanks for Professor Wennan Zhang from Mid Sweden University, who put forward many valuable
280
opinions and gave a lot of practical guidance.
281
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[18] A. Garcia-Maraver, M. Zamorano, U. Fernandes, et al., Relationship between fuel quality and gaseous and particulate matter emissions in a domestic pellet-fired boiler. Fuel 2014, 119: 141-152. [19] Linda S. Bäfver, Marie Rönnbäck, Bo Leckner, et al., Particle emission from combustion of oat grain and its potential reduction by addition of limestone or kaolin. Fuel Processing Technology 2009, 90(3): 353-359. [20] Jarkko Tissari, Olli Sippula, Jyrki Kouki, et al., Fine Particle and Gas Emissions from the Combustion of Agricultural Fuels Fired in a 20 kW Burner. Energy & Fuels 2008, 22(3): 2033-2042. [21] L. Limousy, M. Jeguirim, P. Dutournié, et al., Gaseous products and particulate matter emissions of biomass residential boiler fired with spent coffee grounds pellets. Fuel 2013, 107: 323-329. [22] Edvinas Krugly, Dainius Martuzevicius, Egidijus Puida, et al., Characterization of Gaseous- and Particle-Phase Emissions from the Combustion of Biomass-Residue-Derived Fuels in a Small Residential Boiler. Energy & Fuels 2014, 28(8): 5057-5066. [23] Jianmin Chen, Chunlin Li, Zoran Ristovski, et al., A review of biomass burning: Emissions and impacts on air quality, health and climate in China. Science of The Total Environment 2017, 579: 1000-1034. [24] Longjian Chen, Li Xing, Lujia Han, Renewable energy from agro-residues in China: Solid biofuels and biomass briquetting technology. Renewable and Sustainable Energy Reviews 2009, 13(9): 2689-2695. [25] Jorrit Gosens, Biopower from direct firing of crop and forestry residues in China: A review of developments and investment outlook. Biomass and Bioenergy 2015, 73: 110-123. [26] Xianyang Zeng, Yitai Ma, Lirong Ma, Utilization of straw in biomass energy in China. Renewable and Sustainable Energy Reviews 2007, 11(5): 976-987. [27] Xiaowei Liu, Minghou Xu, Hong Yao, et al., Effect of Combustion Parameters on the Emission and Chemical Composition of Particulate Matter during Coal Combustion. Energy & Fuels 2007, 21(1): 157-162. [28] Yoshihiko Ninomiya, Lian Zhang, Atsushi Sato, et al., Influence of coal particle size on particulate matter emission and its chemical species produced during coal combustion. Fuel Processing Technology 2004, 85(8–10): 1065-1088. [29] Chao Wang, Xiaowei Liu, Dong Li, et al., Effect of H2O and SO2 on the distribution characteristics of trace elements in particulate matter at high temperature under oxy-fuel combustion. International Journal of Greenhouse Gas Control 2014, 23: 51-60. [30] Xiangpeng Gao, Hongwei Wu, Effect of Sampling Temperature on the Properties of Inorganic Particulate Matter Collected from Biomass Combustion in a Drop-Tube Furnace. Energy & Fuels 2010, 24(8): 4571-4580. [31] Xiangpeng Gao, Syamsuddin Yani, Hongwei Wu, Emission of Inorganic PM10 during the Combustion of Spent Biomass from Mallee Leaf Steam Distillation. Energy & Fuels 2015, 29(8): 5171-5175. [32] Syamsuddin Yani, Xiangpeng Gao, Hongwei Wu, Emission of Inorganic PM10 from the Combustion of Torrefied Biomass under Pulverized-Fuel Conditions. Energy & Fuels 2015, 29(2): 800-807. [33] Youjian Zhu, Patrycja Piotrowska, P. J. van Eyk, et al., Cogasification of Australian Brown Coal with Algae in a Fluidized Bed Reactor. Energy & Fuels 2015, 29(3): 1686–1700. [34] Olli Sippula, Terttaliisa Lind, Jorma Jokiniemi, Effects of chlorine and sulphur on particle formation in wood combustion performed in a laboratory scale reactor. Fuel 2008, 87(12): 2425-2436.
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[35] Mook Tzeng Lim, Anh Phan, Dermot Roddy, et al., Technologies for measurement and mitigation of particulate emissions from domestic combustion of biomass: A review. Renewable and Sustainable Energy Reviews 2015, 49: 574-584. [36] Chun-Zhu Li, Importance of volatile–char interactions during the pyrolysis and gasification of low-rank fuels – A review. Fuel 2013, 112: 609-623. [37] Maryori Díaz-Ramírez, Christoffer Boman, Fernando Sebastián, et al., Ash Characterization and Transformation Behavior of the Fixed-Bed Combustion of Novel Crops: Poplar, Brassica, and Cassava Fuels. Energy & Fuels 2012, 26(6): 3218-3229. [38] Liang Wang, Johan E. Hustad, Morten Grønli, Sintering Characteristics and Mineral Transformation Behaviors of Corn Cob Ashes. Energy & Fuels 2012, 26(9): 5905-5916. [39] Lian Zhang, Yoshihiko Ninomiya, Toru Yamashita, Formation of submicron particulate matter (PM1) during coal combustion and influence of reaction temperature. Fuel 2006, 85(10–11): 1446-1457. [40] Sami Zellagui, Gwenaëlle Trouvé, Cornelius Schönnenbeck, et al., Parametric study on the particulate matter emissions during solid fuel combustion in a drop tube furnace. Fuel 2017, 189: 358-368. [41] Simone C. van Lith, Violeta Alonso-Ramirez, Peter A. Jensen, et al., Release to the Gas Phase of Inorganic Elements during Wood Combustion. Part 1: Development and Evaluation of Quantification Methods. Energy & Fuels 2006, 20: 964-978. [42] Xiangpeng Gao, Yuan Chen, Changdong Sheng, et al., Interaction between sodium vapor and reactor wall during biomass combustion and its influence on measurement of particulate matter emission. Fuel 2016, 165: 260-263. [43] Maryori Díazramírez, Christoffer Boman, Fernando Sebastián, et al., Ash Characterization and Transformation Behavior of the Fixed-Bed Combustion of Novel Crops: Poplar, Brassica, and Cassava Fuels. Energy & Fuels 2012, 26(6): 3218-3229.
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394 395
Fig 1. Schematic diagram of the drop tube furnace: (1) feeder and primary air, (2) flowmeter, (3)
396
and (4) secondary air, (5) injection probe, (6) thermocouple and temperature controller, (7)
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sampling probe, (8) dilution air, (9) cyclone, (10) Dekati low pressure impactor, (11)vacuum pump
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20
40 cornstalk
16
32
12
24
8
16
4
8
0
0 1.6
rice husk
3
mg/Nm _raw biomass
cotton stalk
dm/ d log(Dp)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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camphorwood
4 1.2 0.8
2
0.4 0 0.01
0.0 0.1
1
10
0.01
0.1
1
10
398
Aerodynamic diameter (Dp µm)
399
Fig 2. Particle size distributions of PM10 from the combustion of four biomass fuels at temperature
400
1273 K
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0.20
0.8 0.6
0.3
Na
Na
0.15
0.12
Na
Na 0.08
0.2 0.10
3
mg/Nm _raw biomass
0.4 0.1
0.2
K
12
0.04
0.05
0.0
0.0 6
camphorwood
rice husk
corn stalk
cotton stalk
dm/ d log(Dp)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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0.00
K
1.2
0.00
K
0.45
4
8
0.8
0.30
2
4
0.4
0.15
0
0 20
3
Cl
15
0.0 4.5
Cl
0.00
Cl
Cl
0.9
3.0
2
K
0.6
10 1.5
1
0.0 0.15
0 0.15
Mg 0.06
Mg
Not detected 0.05
0.00 0.20
0.00 0.6
0.00 0.6
Ca
Ca
0.00 0.01
0.1
1
10
0.04 0.00 0.6
Ca 0.4
0.4
0.05
Mg 0.08
Not detected
0.05
0.10
0.0 0.12
Mg
0.10
0.10
0.03
0.15
0.3
5
0 0.09
0.2
Not detected
0.0 0.01
0.1
1
Ca
0.4
Not detected 0.2 0.0 10 0.01
0.2
0.1
1
10
0.0 0.01
0.1
Aerodynamic diameter (Dp µm)
401 402
Fig 3. Elemental mass size distribution of Na, K, Mg, Ca, Cl in PM from the combustion of four
403
biomass fuels at temperature 1273 K
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1
10
Energy & Fuels
3
mg/Nm _raw biomass
40
dm/ d log(Dp)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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1073K 1173K 1273K 1373K 1473K 4
2
20 0 2
4
6
8
10
zoom in
0 0.01
404
0.1
1
10
Aerodynamic diameter (Dp µm)
405
Fig 4. Particle size distributions of PM10 from the combustion of cotton stalk at different
406
temperatures of 1073, 1173, 1273, 1373 and 1473 K
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1.5
Na
K
15
1.0 10 5
0.0 0.01 4
0.1
1
10
0 0.01 0.16
Cl
3
0.12
2
0.08
1
0.04
0.1
1
10
0.1
1
10
Mg
3
mg/Nm _raw biomass
0.5
dm/ d log(Dp)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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0 0.01 0.6
0.1
1
10
Ca
0.00 0.01
1073K 1173K 1273K 1373K 1473K
0.4 0.2 0.0 0.01
407
0.1
1
10
Aerodynamic diameter (Dp µm)
408
Fig 5. Elemental mass size distribution of Na, K, Mg, Ca in PM from the combustion of
409
cotton stalk at different temperatures of 1073, 1173, 1273, 1373 and 1473 K
410
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411
412
413
414 415
Fig 6. The typical SEM images of PM from combustion of 4 biomass fuels at temperature 1273K:
416
(a)(b)(c) 0.094, 0.61, 1.58 µm for cotton stalk; (d)(e)(f) 0.61, 1.58, 3.95 µm for cornstalk; (g)(h)(i)
417
0.094, 0.61, 1.58 µm for rice husk; and (j)(k)(l) 0.094, 0.61, 1.58 µm for camphorwood
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418
Table1. Fuel properties samples cotton stalk cornstalk Rice husk camphorwood
419
Proximate analysis (wt.%) Mad 4.55 2.86 3.31 4.03
Adb 2.74 6.58 16.20 0.89
Vdb 78.61 64.49 69.12 87.93
FCdb 18.65 28.93 14.69 11.18
Ultimate analysis (wt.%) Cdb 45.72 39.81 38.20 48.70
Hdb 5.43 5.08 3.15 5.93
Ndb 1.09 0.94 0.89 0.51
Note: M=Moisture; A=Ash; V=Volatile; FC=Fixed Carbon.
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Sdb 0.24 0.23 0.19 0.17
Odb 44.77 47.37 41.38 43.80
LHV （MJ/kg） 15.97 13.49 11.66 17.56
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420
421
Page 26 of 28
Table2. XRF results of different sample ash (wt.%) Samples
MgO
Al2O3
SiO2
P2O5
SO3
Cl2O
K2O
CaO
Fe2O3
cotton stalk cornstalk Rice husk camphorwood
9.06 4.59 12.96
2.24 -
3.87 18.18 96.36 10.38
11.59 7.55 8.72
11.74 2.51 0.55 5.32
2.37 12.68 -
30.51 46.73 1.80 7.99
27.94 7.12 0.88 53.77
0.58 0.39 0.24 0.59
Note: “-”, not detected.
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Table3. Yields of PM0.1, PM1, PM2.5, PM10, PM1-2.5, PM2.5-10, PM1-10 from the combustion of the
423
samples (mg/Nm3)
PM0.1 PM1 PM2.5 PM10 PM1-2.5 PM2.5-10 PM1-10 424 425 426 427
CS 1273K
CSK 1273K
RH 1273K
CW 1273K
CS 1073K
CS 1173K
CS 1373K
CS 1473K
0.38±0.03
1.32±0.06
0.66±0.16
0.45±0.16
0.49±0.01
0.52±0.30
1.00±0.14
0.86±0.07
39.84±0.05
78.12±1.22
8.67±1.55
2.55±0.73
81.89±8.30
68.90±13.41
14.02±0.80
14.07±1.14
43.47±0.25
87.36±3.57
10.14±1.68
4.08±0.55
87.07±8.90
73.13±14.46
15.87±0.93
14.96±1.27
45.58±0.40
88.35±3.89
12.37±1.89
6.10±0.62
90.59±9.00
75.41±15.21
18.20±0.93
16.30±1.23
3.63±0.20
9.24±2.35
1.47±0.12
1.53±0.22
5.18±0.60
4.23±1.05
1.86±0.12
0.89±0.13
2.11±0.15
0.99±0.33
2.23±0.24
2.01±0.14
3.51±0.10
2.29±0.75
2.32±0.01
1.34±0.04
5.74±0.35
10.23±2.67
3.70±0.30
3.54±0.29
8.69±0.70
6.52±1.80
4.18±0.12
2.23±0.09
Note: PM0.1, PM1, PM2.5 and PM10 mean the yield of particles of aerodynamic cutoff diameters less than 0.1, 1, 2.5 and 10 µm, respectively. PM1-2.5, PM2.5-10 and PM1-10 mean the yield of particles of aerodynamic cutoff diameters between 1-2.5, 2.5-10 and 1-10 µm, respectively. CS: cotton stalk; CSK: cornstalk; RH: Rice husk; CW: camphorwood.
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428
Table4. The elemental composition of spots presented in the SEM images (at%).
a b c d e f g h i j k l 429
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Na
K
Mg
Ca
Si
Al
Cl
S
P
4.59 29.19 3.83 47.47 44.30 -
48.16 54.05 12.52 46.99 21.40 22.71 50.32 49.32 10.76 26.68
13.12 3.12 2.23 3.71
44.14 4.96 3.67 18.37
4.37 35.16 46.69 1.41
1.89 36.65 1.24
51.84 18.04 3.68 53.01 49.41 19.45 49.68 47.67 50.52 53.38 25.80
23.32 11.63 3.01 2.01 2.32 21.02
-
Note: “-”, not detected.
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8.65 10.77 1.77
