- Email: [email protected]
Assessment of combustion and emission behavior of corn straw biochar briquette fuels under different temperatures
Journal of Environmental Management 250 (2019) 109399
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Research article
Assessment of combustion and emission behavior of corn straw biochar briquette fuels under different temperatures
T
Ting Wanga, Yuening Lia, Dengke Zhib, Yingchao Lina,∗, Kai Hec,∗∗, Boyang Liud, Hongjun Maoa a Center for Urban Transport Emission Research, State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, College of Environmental Science and Engineering, Nankai University, Tianjin, 300071, China b Key Laboratory of Bioactive Materials, Ministry of Education, College of Life Sciences, Nankai University, Tianjin, 300071, China c Research Centre for Environmental Quality Management, Kyoto University, 1-2 Yumihama, Otsu, Shiga, 520-0811, Japan d QES Department, Novozymes (China) Biotechnology Ltd, Tianjin, 300457, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Corn straw biochar Pyrolysis temperature Solid fuel Combustion characteristics Gas emission
The 350 °C and 700 °C corn straw biochars were used to produce solid fuel briquettes. NovoGro (NG), an industrial by-product, were selected as a binder in the briquetting process. The ratios of the raw material to NG was assumed as 100:1 and 50:1 (denoted as 350NB1, 350NB2, 700NB1 and 700NB2, respectively). The physicochemical and morphological properties, combustion characteristics and gas emissions of the four briquettes were investigated. The results revealed that the biochars and the NG binder performed a good combination. The low temperature biochar briquettes, especially 350NB2, had excellent combustion characteristics, including low H/C and O/C ratios (0.17 and 0.82), low gas emissions (104.06 mg/m3 of CO, 157.25 mg/m3 of NOx and 18.92 mg/ m3 of SO2), optimal resistance to mechanical shock (~90%) and high calorific values (21.48 MJ/kg). Thus, NG is a good binder for the briquetting of biochar. The low temperature biochar was a good feedstock for solid fuel production in the improvement of the combustion and emission quality.
1. Introduction The high demand of renewable energy has been growing nowadays due to shortage of fossil fuels and global warming (Guo and Zhong, 2018). Biomass is considered as a kind of renewable energy resource to replace traditional fossil fuel in the aspect of carbon credit (Jana Růžičková et al., 2019; Tong et al., 2017). Corn is one of the most widely grown cereal crop in the world today. However, most straws are produced annually from farms as agricultural wastes. It is estimated that over three billion tonnes of agricultural wastes were generated worldwide (Yilmaz et al., 2018). Burning in the field is regarded as the common management of straw, due to its convenience and economy for farmers (Yang et al., 2017). However, open crop straw burning is an important kind of primary pollution source, which contributes many pollutants into the atmosphere (Xie et al., 2018; Zhou et al., 2017). Based on the growing shortage of fossil fuels and the environmental pollution problem, the utilization of straw resources is an effective measure to sustainable development. Compared with fossil fuels, crop straw is a scattered resource with lower energy density and less efficient to store and transport (Miranda
∗
et al., 2018; Ji et al., 2018). The energy density of biomass is usually in the range of 14,651–16,744 KJ, which is very less compared to 20,930–29,302 KJ of coal (Balasubramani et al., 2016). Thus, conversion of this bulky biomass into a denser form improves the handling property and reduces the cost of handling, transportation and storage (Sansaniwal et al., 2017). Moreover, zero or negative carbon dioxide (CO2) emission is possible from biomass briquette fuel combustion because released CO2 from the combustion of bio-oil can be recycled into the plant by photosynthesis (Tokimatsu et al., 2017). In addition, it is an attractive clean and environmental friendly fuel as it significantly induces low amount of NOx and SO2 emissions (Boumanchar et al., 2017; Yanik et al., 2018). Pyrolysis technology has the capability to produce bio-fuel with high fuel-to-feed ratios. Therefore, pyrolysis has been receiving more attention as an efficient method in converting biomass into bio-fuel (Azizi et al., 2018). Biochar is a carbonaceous material produced by the pyrolysis of biomass under limited or no oxygen (Dhyani and Bhaskar, 2018). Carbonization of the biomass briquettes will reduce the amount of liquid and gas in the biomass and further increase the carbon content. Hence, the pyrolytic biochars usually have better fuel qualities
Corresponding author. Corresponding author. E-mail addresses: [email protected] (Y. Lin), [email protected] (K. He).
∗∗
https://doi.org/10.1016/j.jenvman.2019.109399 Received 26 February 2019; Received in revised form 4 August 2019; Accepted 12 August 2019 0301-4797/ © 2019 Elsevier Ltd. All rights reserved.
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
2.4. Combustion characteristics and combustion behavior analysis of biochar briquette fuels
than the parent biomass (Weber and Quicker, 2018). Several advantages offered by biochar fuel include higher boiler efficiency due to low moisture and higher density, more uniform combustion, less corrosion effect on boiler equipment due to negligible sulphur content, environment friendly being a pollution free and clean burning fuel, and easy handling and long distance transportation (Boumanchar et al., 2017). Hence, the biochar fuel has a great potential for various applications, such as household heating, industrial steam generation, outdoor barbequing, and so on. Despite of several above advantages, there are only few investigations that have been done on biochar fuel obtained from waste biomass compared to bio-oil and gaseous products (Ramírez et al., 2019). The pyrolysis temperature is one of the vital parameters for biochar fuel production from biomass. It has been reported that the pyrolysis performed at 200–300 °C cannot improve the combustion property of biomass feedstock due to the high decomposition temperature of cellulose (generally higher than 300 °C) (Wei et al., 2019). However, high temperatures favor the liquid and gaseous products, and decrease energy recovery in the biochar (Elkhalifa et al., 2019). Thus, the optimal pyrolysis temperature for maintaining high-energy recovery and desired combustion property should be investigeted. Therefore, in this study, the corn straw biomass was pyrolyzed under different temperature to produce solid fuel biochars with better fuel qualities. The mechanical, thermal and morphological properties of the briquettes were investigated. The bulk and surface element contents, ash content, higher heating value (HHV) and lower heating value (HHV) of the briquettes were measured to evaluate the combustion performance. The surface morphology and the chemical surface structures of the briquettes were investigated with SEM and FTIR spectra, respectively. Moreover, the gas emission test of the prepared briquettes were also conducted to evaluate the emission behavior.
The ash content, volatile matter content, shatter strength, higher heating value (HHV) and lower heating value (LHV) of the four briquettes were determined to systematically evaluate the combustion characteristics of the biochar briquettes. The details of the methods were descripted in the Supporting Information. In order to describe the thermal stability of the four briquettes, the TG and derivative thermogravimetric (DTG) of the four briquettes were investigated by a thermal analyzer (TGA/DSC1, METTLER TOLEDO, Switzerland). The samples were carried out in an air atmosphere. The airflow and heating rate of TG was 30 mL/min and 10 °C/min, respectively. 2.5. Ash analysis The ash fusion temperatures (AFTs) of the briquettes were investigated using an ash fusion analyzer (SDAFDY2000d, Sundy, China) in Ar and H2 atmospheres (Proximate analysis of coal, Chinese National Standards, GB/T 212–2008). The TG and derivative thermogravimetric (DTG) of the briquette ash obtained at 450 °C, 575 °C (ASTM E1755-01, Standard test method for ash in biomass) and 815 °C (GB/T212-2008, Proximate analysis method for coal, China) were investigated by a thermal analyzer (TGA/ DSC1, METTLER TOLEDO, Switzerland). The details of the methods were descripted in the Supporting Information. 2.6. Gas emission in the combustion of the biochar briquette fuels To investigate the emission analysis, the four pellets were combusted in a 210 KWth biomass furnace without gas after-treatment device. The structure diagram of the furnace was shown in Fig. 1. Trace gas emissions were measured using a digital flu gas analyzer, Testo 350 (Testo, Germany) by following a modified protocol of Li et al. (2009). Details of the test parameters were descripted in the Supporting Information.
2. Materials and methods 2.1. Biochar preparation Corn straw stock was collected from a farmland in Zhongyuan District, Zhengzhou, China. The corn straw was air-dried and ground to pass through a 2 mm sieve, then heated at 350 °C or 700 °C in a carbonization furnace under oxygen-limited conditions for 2 h. The biochar produced were ground to pass through the 200 mesh sieves.
3. Results and discussion 3.1. The physical and chemical characteristics of the four briquettes
2.2. Biochar briquetting
The element compositions of the biochar briquettes were listed in Table S1. All tests were carried out in triplicate to ensure reproducibility of the results. The elemental ratios H/C and O/C can offer information about the combustion efficiency of a fuel. Briquettes with low H/C and O/C ratios produce less CO2, water vapor, and smoke when burned, leading to higher combustion efficiency (Abdullah and Wu, 2009). The H/C and O/C ratios of 350NB1, 350NB2, 700NB1 and 700NB2 were listed in Table S1. Although the H/C and O/C ratios tend to decrease with increased pyrolysis temperature. It was due to that the carbon in the char transitions from aliphatic hydrocarbons into aromatic elemental carbon structures (Abdullah and Wu, 2009). Wood chars typically have O/C ratios ranging from 0.01 to 0.35 and H/C ratios from 0.03 to 0.70 (Kearns et al., 2014; Linderholm et al., 2017); coals tend to have O/C ratios of 0.01–0.35 and H/C ratios of 0.06–1.10 (Basu, 2010; Liu and Balasubramanian, 2013; Linderholm et al., 2017). Hence, the four briquettes were acceptable for using as the solid fuel. Besides, the H/C and O/C ratios were further decreased after binding with NG. Hence, NG, as a binder, could enhance the combustion performance of biochar. The remaining primary contents of the briquettes were Ca, K, Si and Cl. The 350NB1 and 350NB2 were typically Ca-rich briquettes. The presence of CaO in low temperature biochar briquettes could make it useful for SO2 capture. The K content of 350NB2 was lowest among the four briquettes. Hence, there was low potential of agglomeration,
The NG, briquetting binder, was a by-product obtained from the centrifuged fermentation broths of the Biological Treatment Plant of Novozymes in Tianjin, China (Wang et al., 2018). The briquette production ratios of the raw material to NG were 100:1 and 50:1. The four biochar briquettes were denoted as 350NB1, 350NB2, 700NB1 and 700NB2, respectively. The moisture of the mixture was adjusted to approximate 15% by adding a predetermined amount of water. Then, the mixtures were stirred to obtain a homogeny mixture. The mixture was briquetted in a flat-shaped granulator under productive capacity of 500 kg h−1 at ambient temperature (25 ± 2 °C). The average diameters and length of the briquettes were 4–5 mm and 15–20 mm, respectively. 2.3. Ultimate analysis and morphological properties of the biochar briquette fuels Seventy-two hours after briquetting, the bulk density and the primary element contents were analyzed. Besides, the morphological and infrared properties of the briquettes were analyzed with SEM microanalysis (QUANTA 200, USA) and FTIR spectroscopy (Tensor 27, Bruker, USA). The details of the methods were descripted in the Supporting Information. 2
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
temperature. Besides, the peaks of 700NB1 and 700NB2 were boarder and sharper than that of 350NB1 and 350NB2. The biochar surface area and total pore volume increased with the rise of pyrolysis temperature, which might be due to the removal of aliphatic and volatile materials at high carbonization temperature. Hence, the roughness and disordered graphite of the biochar improved with increasing pyrolysis temperature (Zhu et al., 2019). The peaks at 2θ = 25–30° (Peak 3 & 4) in 700NB1 and 700NB2 were due to the crystal growth of calcite (Mafu et al., 2016). The calcite has great potential to hinder ash sintering and to mitigate slag formation during biomass combustion (Chi et al., 2019). The peaks at 2θ~36° (Peak 5) were assigned to hemicellulose in 350NB1 and 350NB2 (Nanda et al., 2013), which were much lower in 700NB1 and 700NB2. It was due to that the hemicellulose was decomposed at the high pyrolysis temperature (Chen et al., 2017). In the same condition, the yield of gaseous product of hemicellulose was higher than that of cellulose and lignin (Chen et al., 2018). Hence, the 350NB1 and 350NB2 had the potential of using as the solid fuel. The sharp peaks at ~50° in 700NB1 and 700NB2 samples (Peak 6) indicated the formation of small amounts of silicate (Mafu et al., 2016). The low-temperature eutectic substances of alkali-silicate compounds could cause slagging during the combustion. The K content of 700NB1 and 700NB2 were higher than 350NB1 and 350NB2 (Table S1). Hence, there is a potential of agglomeration, sintering and deposition during the combustion of 700NB1 and 700NB2. 3.2. Combustion properties of the four briquettes The moisture of the fuel has a very significant effect on the ignition and propagation of the fuels. Hence, the total moisture content is one of the vital factors of fuel. Before the briquetting process, 15% (m/m) water was supplied to the raw material. It was considered that the optimum moisture content of briquette was approximately 12%, and higher moisture contents were corresponded with higher bulk densities and durabilities in briquettes (Miranda et al., 2018). As shown in Table 1, the 350NB1 and 350NB2 showed certain advantages of using as fuels. Moreover, the addition of NG further reduced the moisture content of low-temperature biochar briquette but increased that of hightemperature biochar briquette. The ash contents of the700NB1 and 700NB2 were much higher than those of the 350NB1 and 350NB2. It was due to that the increasing pyrolysis temperature increased the formation of biochar ash containing alkaline minerals (Zhao et al., 2018). According to the classification of coals of the International Standard (ISO 11760-2005) and Chinese National Standard (GB/T 15224.1-2010), the 350NB2 was classified as medium ash coal, while the 350NB1 was classified as moderately high ash coal and medium ash coal, respectively. Hence, the 350NB2 could be used as a substitute fuel to relief high-rank fuel shortage. While, the high-temperature biochar briquettes might not suitable for combustion due to the high ash content. The Si content of fuel is relative with the ash content (Daood et al., 2014). According to Table S1 and Fig. 2, the tendency of the Si contents of the briquettes were consistent with that of the ash contents. The 350NB1 and 350NB2 briquettes had relatively higher volatile matter contents than 700NB1 and 700NB2 briquettes. Hence, the low temperature biochar briquettes would show advantages at the initial stage of ignition. The fuel combustion endurance was closely linked with the fixed carbon content of the fuel (Riaza et al., 2014). The fixed carbon contents of the briquettes were followed the order of 700NB2 < 700NB1 < 350NB1 < 350NB2. Thus, the low temperature biochar briquettes also exhibited high combustion persistence. The commercial fuels are usually with excellent resistance to mechanical shock and high calorific value simultaneously. The durability properties fall within the specification of < 10% mass loss during shattering and abrasion tests for CEN/TS 14961, the European standard for solid fuel quality. As shown in Table 1, the 350NB2 and 700NB1 were close to the standard. The HHV and LHV of 350NB1 and 350NB2
Fig. 1. Schematic of the 210 KWth biomass furnace.
sintering and deposition during the combustion. The Si contents of 700NB1 and 700NB2 (4.27% and 3.68%, respectively) were much higher than that of 350NB1 and 350NB2 (1.37% and 0.85%). The volatile silicon compounds could convert into silica particles and cause abrasion damage (Mathison et al., 2010). Besides, during the combustion process, the conversion rates of the fuels could be decreased due to low temperature melting silicate that dominate the ash formation and might partially cover, or totally encapsulate, the remaining fuel (Strandberg et al., 2018). The Cl could cause the formation of low melting point eutectics, which could result in slagging and fouling (Magdziarz et al., 2016). There were large amounts of Cl in 350NB1 and 350NB2. The Cl contents of the briquettes could be ordered as follows: 350NB1 > 350NB2 > 700NB1 > 700NB2. It was revealed that the addition of NG was beneficial to reduce the Cl content of the briquettes. As listed in other literatures, the Cl contents of fuels usually ranged from 0.18% to 4.25% (Febrero et al., 2015; Silva Perez et al., 2015; Zeng et al., 2016; Jin et al., 2017). Hence, the Cl contents of the four briquettes were acceptable for using as the solid fuel. In summary, the low temperature biochar briquettes would exhibit better performance in the combustion process than the high temperature biochar briquettes. Fig. 2 depicts the XRD profiles of the four briquettes. The first obvious peak at 2θ = 21° (Peak 1) is illustrated as the presence of crystal phases of silica like quartz (Niu et al., 2010). The X-ray diffractograms showed the intense peaks for 700NB1 and 700NB2, which resulted from the higher pyrolysis temperature (Ding et al., 2016). This was consistent with the Si content tendency of the briquettes. The sharp peaks at 2θ = 26.6° (Peak 2) for the four briquettes were attributed to the high quality of graphitic basal planes stacking (Mafu et al., 2016). The original peak was at 2θ = 25° (Guerrero et al., 2008). This deviation was attributed to the disordered structure of the briquettes, and the different intensities implied the structural differences in the arrangement of the graphitic planes with the increment of pyrolysis 3
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
Fig. 2. X-ray diffraction patterns recorded for the briquette samples. (1- silica; 2- graphitic plane; 3, 4- calcite; 5- hemicellulose; 6-silicate compounds)
respectively. The total weight loss of the low temperature biochar briquettes were above 60%. While for 700NB1 and 700NB2, there were only two main peaks centered at 460 °C and 650 °C, respectively. And the total weight loss of the two high temperature biochar briquettes were below 20%, which were much lower than that of the low temperature biochar briquettes. It was due to the thermal decomposition of biomass components under the high pyrolysis temperature on production of 700 °C biochar. The high total weight loss are usually due to with high volatile content (Li et al., 2018). This was consistent with the volatile contents results of the briquettes (Table 1). Hence, the low temperature biochar briquettes had high combustion potential.
were 21.48 and 18.62 MJ/kg and 18.85 and 16.56 MJ/kg, respectively, which are much higher than that of 700NB1 and 700NB2 (Table 1). Base on the classification for quality of coal of the Chinese National Standard (GB/T 15224.32010), the HHV and LHV below 16.30 MJ/kg and 12.51 MJ/kg are classified as the low-rank coals. The 350NB1 and 350NB2 were acceptable for using as fuels. Moreover, although the HHV and LHV of low temperature biochar briquettes were a little lower than those of the charcoal (Motghare et al., 2016), they were much higher than the wheat straw, cotton waste, municipal solid waste and wood pellets in others literatures (Johansson et al., 2004; Edo et al., 2016; Motghare et al., 2016), indicating that the low temperature biochar briquettes had the potential to be used as high rank fuel.
3.4. Morphological properties of the four briquettes 3.3. Combustion behavior of the four briquettes The SEM and FTIR spectroscopy were chosen to identify the structural, morphological and infrared properties of the biochar briquettes. The SEM micrographs showed the surface morphology of the four briquettes were homogenous (Fig. 4 a, d, g and j). It revealed that the binder and biochar were mutually substantially evenly mixed together. The NG is produced during the enzyme production process, which is the centrifuged residue of fermentation broth of potato flour, cornstarch and other raw materials, hence containing N, P and K elements, mineral nutrients and organic substances (Wang et al., 2018). These are led to the caking property of NG in the briquetting process. The 350NB1 and 350NB2 particles were mainly composed of fibrous and irregular
The TG and DTG profiles depicting the combustion process of the four briquettes are presented in Fig. 3. In the DTG profile (Fig. 3 b), the peaks (centered at ~70 °C, below 200 °C) attributed to the moisture evaporation of the biochars; the second peak (centered at ~ 450 °C, below 600 °C) corresponded to the decomposition and oxidation of the biochars; and the third peak (centered at ~ 650 °C, below 700 °C) relates to the volatilization of some inorganics including potassium and other inorganics (Guo and Zhong, 2018; Liu et al., 2012; Haykiri-Acma et al., 2013). For 350NB1 and 350NB2, the weight loss of the three peaks were 7.29% and 6.49%, 75.46% and 66.68%, and ~2.5%, Table 1 Combustion characteristics of biochar briquettes. Briquettes
350NB1 350NB2 700NB1 700NB2
Proximate analysis (%)
Calorific value (MJ/kg)
Ash fusion point (oC)
Total moisture
Ash
Volatile matter
Fixed carbon
HHV
LHV
DT
ST
HT
FT
11.5 8.7 4.2 4.9
24.2 17.4 67.8 67.4
26.7 30.8 10.5 10.6
35.0 43.1 21.5 21.1
18.85 21.48 6.96 6.96
16.56 18.62 6.49 6.45
1128 1150 1154 1153
1137 1160 1206 1198
1139 1162 1242 1221
1200 1165 1308 1280
4
Shatter strength (%)
Density (g/cm3)
40.9 89.5 91.4 64.5
1.06 1.12 1.67 1.60
± ± ± ±
1.2 0.3 0.2 0.8
± ± ± ±
0.03 0.06 0.02 0.02
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
Fig. 3. TGA (Thermogravimetric analysis) and DTG (Differential thermogravimetry) plots of the four briquettes of heating in air.
Fig. 4. SEM photography of the pellet samples. (a, d, g, j: × 700; b, e, h, k: × 500; c, f, i, l: × 2000) 5
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
breakdown of the Aphthitalite [K3Na(SO4)2] (Das et al., 2017), respectively. The ash samples obtained at different temperatures had similar variation tendency with the parent briquettes, but the numbers of the peaks decreased with the increased of the ashing temperature (Fig. S2 b, d, f and g). It could be inferred that no matter what the ashing temperature is, when the heating temperature is higher than a certain value, the compositions in the ashes are nearly the same or they contain the same high-temperature molten material.
particles (Fig. 4 b, c, e and f), while the 700NB1 and 700NB2 particles included bulk particles (Fig. 4 h, i, k and l). During the pyrolysis process, the unstable and volatile fractions of the raw materials disappeared. Thus, the low pyrolysis temperature preserved the original morphology of the corn straws. Besides, the particle sizes of 700NB1 and 700NB2 (Fig. 4 c and f) were considerably larger than that of 350NB1 and 350NB2 (Fig. 4 i and l), which were not conducive to the briquetting process. Furthermore, the 350NB1 and 350NB2 particles have rough surfaces (Fig. 4 i and l), while the surface of 700NB1 and 700NB2 particles are relatively smooth (Fig. 4 c and f). Thus, the low temperature biochar briquettes were with well performance in tight formations. These were related to the higher HHV and LHV values of 350NB1 and 350NB2 than 700NB1 and 700NB2. The FTIR spectroscopy was used in the structure analysis of the biochar briquettes. In the FTIR spectra (Fig. S1), the band at ~1650 1/ cm (C]O stretching vibration) was assigned to the hemicellulose component (Mayer et al., 2012). It could be observed that there were small peaks of 350NB1 and 350NB2. It was due to that the hemicellulose was decomposed at the high pyrolysis temperature during the production of 700NB1 and 700NB2. This was consistent with the result of XRD analysis of the briquettes in section 3.1. The band at ~1550 1/cm was resulted of the C]O stretching of lignin (Fierro et al., 2007). The bands at 1100 1/cm and 800 1/cm were due to the C–O stretching and C–H bending of lignin, respectively (Asadieraghi and Daud, 2015). Thus, it was implied that the lignin contents of the 350NB1 and 350NB2 were higher than that of 700NB1 and 700NB2. These constituents led to the high calorific values of the 350NB1 and 350NB2 briquettes. These observed results offered a comprehensive explanation for the high combustion potential of low temperature biochar briquettes.
3.6. Gas emission characteristics of the briquettes In the biomass furnace (Fig. 1), the 350NB1 and 350NB2 exhibited good combustion behavior, and there was little bottom ash discharged during the combustion process. While the 700NB1 and 700NB2 were hardly to ignite in the furnace. The gas emissions of CO, NOx and SO2 of 350NB1 and 350NB2 were 138.3, 149.2, 62.5 and 104.1, 157.3, 18.9 mg/m3, respectively, based on 9% reference O2 at standard conditions (1 atm, 0 °C), where the least CO emissions were obtained. In summary, the CO and SO2 concentrations in the gas of 350NB2 were lower than that of 350 NB1. The NOx emission of 350NB1 and 350NB2 were comparable. The emission standards of biomass boilers in different countries or districts are listed in Table S2. The CO and SO2 emissions of 350NB2 could meet most of the emission standards. In general, all biomass samples have higher nitrogen contents than the coals (Lee et al., 2018). However, the NOx emission of 350NB2 could meet or be close to most of the standards without de-NOx after-treatment device. Hence, pyrolytic biochar was a good strategy to produce clean fuel. In summary, the moisture and AFTs of the four briquettes were all within the limits of the solid fuel acceptability. Low temperature biochar briquettes had higher Ca, lower Si and K contents than high temperature biochar briquettes, which was consistent with the CRD results. The HHV and LHV of low temperature biochar briquettes were much higher than that of high temperature biochar briquettes, and this result was consistent with the XRD, FTIR and TG data. Moreover, the ash contents of low temperature biochar briquettes were much lower than that of the high temperature biochar briquettes. Although the H/C, O/C and Cl contents of high temperature biochar briquettes were lower than that of the low temperature biochar briquettes. Compared to the results in other literatures, these properties of low temperature biochar briquettes were acceptable for using as the solid fuel. These results suggested that the low temperature biochar was a good feedstock for solid fuel production in the improvement of the combustion and emission quality. Besides, 350NB2 had lower H/C and O/C ratios, lower Si, K, Cl and ash contents, lower moisture, and higher HHV and LHV than 350NB1. The CO and SO2 emission of 350NB2 were much lower than that of 350NB1. Furthermore, the SEM micrographs showed that the NG combined well with the biochar feedstock. These analyses revealed that NG is a good binder for the briquetting of biochar. The corn straw biochar briquette fuels may be a promising candidate as the substitute for fossil fuels.
3.5. Ash analysis of the four briquettes The ash fusion temperatures (AFTs) of the briquettes were listed in Table 1. The deformation temperature (DT), softening temperature (ST), hemisphere temperature (HT) and flow temperature (FT) of 700NB1 and 700NB2 were higher than that of 350NB1 and 350NB2. According to the American Society of Mechanical Engineers (ASME) Research Committee, the slagging would be likely to occur when the disparity of FT and DT values of the fuel was above 149 °C. In this study, the disparities of FT and DT values of 350NB1, 350NB2, 700NB1 and 700NB2 were 72, 15, 154 and 127 °C, respectively. It implied that it had a potential for slagging during the combustion process of the low temperature biochar briquettes. However, it is generally required that the coal FT less than 1380 °C in practical industrial application (Li et al., 2019). Therefore, all the four briquettes could meet the standard to use as fuels. The TGA and derivative mass loss (DTG) of the different briquette ashes are shown in Fig. S1. Details of the weight losses of the ash samples of the four briquettes were described in the Supporting Information. The sharp loss in a relatively lower temperature range (600–750 °C) is considered as the high calcium content in ash, and the sharp weight loss is mainly attributed to the decomposition of calcium carbonate (Du et al., 2014). The Ca contents of 350NB1 and 350NB2 were 2.3–2.8 folder higher than that of 700NB1 and 700NB2 (Table S1), which resulted in the weight loss differences of 450 °C and 575 °C ash samples of the four briquettes. KCl, the main volatile composition of corn straw, plays an important role in the process. The intense volatilization of KCl occurs from 750 °C to 950 °C (Nielsen et al., 2000; Lin et al., 2003). The K contents of the four briquettes were comparable, but the Cl contents of 350NB1 and 350NB2 were much higher than that of 700NB1 and 700NB2 (Table S1), which lead to the weight loss variation of the 815 °C ash of the four pellets. Details of the DTG peaks of the ash samples of the four briquettes were described in the Supporting Information. The three peaks were due to the gradual moisture removal, the thermal degradation of hemicellulose and cellulose Slopiecka et al. (2012) and the thermal
3.7. Application and prospect The prospect of the exhaustion of fossil energy and climate change caused by the excessive use of fossil fuel necessitates shifting energy supply from fossil energy to renewable energy in the near future. This study provided a kind of biomass fuel with excellent combustion characteristics, low gas emissions, optimal resistance to mechanical shock and high calorific values, which might be a promising candidate for coal fuel. However, as an alternative technology, many aspects still need to be developed and evaluated due to several variables are correlated to determine the characteristics and applications of biochar fuel. As mentioned above, the ash content of the biochar fuel should be further reduced for using as a high rank fuel. In this study, the gas emissions of the biochar briquettes were 104.06 mg/m3 of CO, 6
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
157.25 mg/m3 of NOx and 18.92 mg/m3 of SO2 without any aftertreatment device. However, the straw nitrogen content was usually higher than that of wood materials. Hence, to achieve the ultra-low NOx emission, it could be coupled with a de-NOx after-treatment device in the practical application.
Dhyani, V., Bhaskar, T., 2018. A comprehensive review on the pyrolysis of lignocellulosic biomass. Renew. Energy 129, 695–716. https://doi.org/10.1016/j.renene.2017.04. 035. Ding, Z., Wan, Y., Hu, X., Wang, S., Zimmerman, A.R., Gao, B., 2016. Sorption of lead and methylene blue onto hickory biochars from different pyrolysis temperatures: importance of physicochemical properties. J. Ind. Eng. Chem. 37, 261–267. https://doi. org/10.1016/j.jiec.2016.03.035. Du, S., Yang, H., Qian, K., Wang, X., Chen, H., 2014. Fusion and transformation properties of the inorganic components in biomass ash. Fuel 117, 1281–1287. https://doi.org/ 10.1016/j.fuel.2013.07.085. Edo, M., Budarin, V., Aracil, I., Persson, P.E., Jansson, S., 2016. The combined effect of plastics and food waste accelerates the thermal decomposition of refuse-derived fuels and fuel blends. Fuel 180, 424–432. https://doi.org/10.1016/j.fuel.2016.04.062. Elkhalifa, S., Al-Ansari, T., Mackey, H.R., McKay, G., 2019. Food waste to biochars through pyrolysis: a review. Resour. Conserv. Recycl. 144, 310–320. https://doi.org/ 10.1016/j.resconrec.2019.01.024. Febrero, L., Granada, E., Patiño, D., Eguía, P., Regueiro, A., 2015. A comparative study of fouling and bottom ash from woody biomass combustion in a fixed-bed small-scale boiler and evaluation of the analytical techniques used. Sustain. Times 7, 5819–5837. https://doi.org/10.3390/su7055819. Fierro, V., Torné-Fernández, V., Celzard, A., Montané, D., 2007. Influence of the demineralisation on the chemical activation of Kraft lignin with orthophosphoric acid. J. Hazard Mater. 149, 126–133. https://doi.org/10.1016/j.jhazmat.2007.03.056. Guerrero, M., Ruiz, M.P., Millera, Á., Alzueta, M.U., Bilbao, R., 2008. Characterization of biomass chars formed under different devolatilization conditions: differences between rice husk and eucalyptus. Energy Fuel. 22, 1275–1284. https://doi.org/10. 1021/ef7005589. Guo, F., Zhong, Z., 2018. Co-combustion of anthracite coal and wood pellets: thermodynamic analysis, combustion efficiency, pollutant emissions and ash slagging. Environ. Pollut. 239, 21–29. https://doi.org/10.1016/j.envpol.2018.04.004. Haykiri-Acma, H., Yaman, S., Kucukbayrak, S., 2013. Production of biobriquettes from carbonized brown seaweed. Fuel Process. Technol. 106, 33–40. https://doi.org/10. 1016/j.fuproc.2012.06.014. Ji, C., Cheng, K., Nayak, D., Pan, G., 2018. Environmental and economic assessment of crop residue competitive utilization for biochar, briquette fuel and combined heat and power generation. J. Clean. Prod. 192, 916–923. https://org/10.1016/j.jclepro. 2018.05.026. Jin, X., Ye, J., Deng, L., Che, D., 2017. Condensation behaviors of potassium during biomass combustion. Energy Fuel. 31, 2951–2958. https://doi.org/10.1021/acs. energyfuels.6b03381. Johansson, L.S., Leckner, B., Gustavsson, L., Cooper, D., Tullin, C., Potter, A., 2004. Emission characteristics of modern and old-type residential boilers fired with wood logs and wood pellets. Atmos. Environ. 38, 4183–4195. https://doi.org/10.1016/j. atmosenv.2004.04.020. Kearns, J.P., Wellborn, L.S., Summers, R.S., Knappe, D.R.U., 2014. 2,4-D adsorption to biochars: effect of preparation conditions on equilibrium adsorption capacity and comparison with commercial activated carbon literature data. Water Res. 62, 20–28. https://doi.org/10.1016/j.watres.2014.05.023. Lee, Y.J., Park, J.H., Song, G.S., Namkung, H., Park, S.J., Kim, J.G., Choi, Y.C., Jeon, C.H., Choi, J.W., 2018. Characterization of PM2.5 and gaseous emissions during combustion of ultra-clean biomass via dual-stage treatment. Atmos. Environ. 193, 168–176. https://doi.org/10.1016/j.atmosenv.2018.09.011. Li, X., Wang, S., Duan, L., Hao, J., Nie, Y., 2009. Carbonaceous aerosol emissions from household biofuel combustion in China. Environ. Sci. Technol. 43, 6076–6081. https://doi.org/10.1021/es803330j. Li, Y., Lin, H., Xiao, K., Lasek, J., 2018. Combustion behavior of coal pellets blended with Miscanthus biochar. Energy 163, 180–190. https://doi.org/10.1016/j.energy.2018. 08.117. Li, M., Li, F., Liu, Q., Fang, Y., Xiao, H., 2019. Regulation of ash fusibility for high ashfusion-temperature (AFT) coal by industrial sludge addition. Fuel 244, 91–103. https://doi.org/10.1016/j.fuel.2019.01.161. Lin, W., Dam-Johansen, K., Frandsen, F., 2003. Agglomeration in bio-fuel fired fluidized bed combustors. Chem. Eng. J. 96, 171–185. https://doi.org/10.1016/j.cej.2003.08. 008. Linderholm, C., Schmitz, M., Biermann, M., Hanning, M., Lyngfelt, A., 2017. Chemicallooping combustion of solid fuel in a 100 kW unit using sintered manganese ore as oxygen carrier. Int. J. Greenh. Gas. Con. 65, 170–181. https://doi.org/10.1016/j. ijggc.2017.07.017. Liu, Z., Balasubramanian, R., 2013. A comparison of thermal behaviors of raw biomass, pyrolytic biochar and their blends with lignite. Bioresour. Technol. 146, 371–378. Liu, Z., Quek, A., Kent Hoekman, S., Balasubramanian, R., 2012. Production of solid biochar fuel from waste biomass by hydrothermal carbonization. Fuel 103, 943–949. https://doi.org/10.1016/j.fuel.2012.07.069. Mafu, L.D., Neomagus, H.W.J.P., Everson, R.C., Carrier, M., Strydom, C.A., Bunt, J.R., 2016. Structural and chemical modifications of typical South African biomasses during torrefaction. Bioresour. Technol. 202, 192–197. https://doi.org/10.1016/j. biortech.2015.12.007. Magdziarz, A., Dalai, A.K., Koziński, J.A., 2016. Chemical composition, character and reactivity of renewable fuel ashes. Fuel 176, 135–145. https://doi.org/10.1016/j. fuel.2016.02.069. Mathison, S., Sattler, A., Lile, R., Guillen, F., Linsley, B., Magers, K., Lee, J., 2010. Determination of siloxanes and other volatile silicon compounds in biogas samples using sample preconcentration with GC-MS and GC-ICP-MS. Proc. Water. Environ. Fed. 2010 (3), 399–424. https://doi.org/10.2175/193864710802768352. Mayer, Z.A., Apfelbacher, A., Hornung, A., 2012. Effect of sample preparation on the thermal degradation of metal-added biomass. J. Anal. Appl. Pyrolysis 94, 170–176.
4. Conclusions The 350 °C corn straw biochar briquette exhibited excellent combustion characteristics, optimal resistance to mechanical shock and high HHV value. An industrial production waste (NG), as a binder in the briquetting process, was excellently combined with the biochar and could improve the combustion property of biomass feedstock. Moreover, the CO and SO2 emissions of the briquettes could meet most of the emission standards, and the NOx emission could meet or be close to most of the standards without de-NOx after-treatment device. Therefore, the corn straw biochar briquette fuels may be a promising candidate as the substitute for fossil fuels. Acknowledgements This work was financially supported by the National Natural Science Foundation of China [21806082], Key Technologies R & D Program of Tianjin [18YFZCNC01410, 16YFZCSF00410] and the Fundamental Research Funds for the Central Universities. The foundation 21806082 provided financial support in the gas emission characteristics of the briquettes. The foundation 18YFZCNC01410 provided financial support in the production of the briquettes. The foundation 16YFZCSF00410 provided financial support in the characteristics analysis of the fuels. The Fundamental Research Funds for the Central Universities provided financial support in the language improvement of the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jenvman.2019.109399. References Abdullah, H., Wu, H., 2009. Biochar as a fuel: 1. Properties and grindability of biochars produced from the pyrolysis of mallee wood under slow-heating conditions. Energy Fuel. 23, 4174–4181. https://doi.org/10.1021/ef900494t. Asadieraghi, M., Daud, W.M.A.W., 2015. In-depth investigation on thermochemical characteristics of palm oil biomasses as potential biofuel sources. J. Anal. Appl. Pyrolysis 115, 379–391. https://doi.org/10.1016/j.jaap.2015.08.017. Azizi, K., Moraveji, M.K., Najafabadi, H.A., 2018. A review on bio-fuel production from microalgal biomass by using pyrolysis method. Renew. Sustain. Energy Rev. 82, 3046–3069. https://doi.org/10.1016/j.rser.2017.10.033. Balasubramani, P., Anbumalar, V., Nagarajan, M.S., Prabu, P.M., 2016. Biomass briquette manufacturing system model for environment. J. Alloy. Comp. 686, 859–865. https://doi.org/10.1016/j.jallcom.2016.06.233. Basu, P., 2010. Biomass gasification and pyrolysis: practical design and theory. Compr. Renew. Energy 25, 133–153. https://doi.org/10.1017/CBO9781107415324.004. Boumanchar, I., Chhiti, Y., Alaoui, F.E.M., Ouinani, A.E., Sahibed-Dine, A., Bentiss, F., Jama, C., Bensitel, M., 2017. Effect of materials mixture on the higher heating value: case of biomass, biochar and municipal solid waste. Waste Manag. 61, 78–86. https://doi.org/10.1016/j.wasman.2016.11.012. Chen, T., Li, L., Zhao, R., Wu, J., 2017. Pyrolysis kinetic analysis of the three pseudocomponents of biomass–cellulose, hemicellulose and lignin. J. Therm. Anal. Calorim. 128, 1825–1832. https://10.1007/s10973-016-6040-3. Chen, D., Gao, A., Cen, K., Zhang, J., Cao, X., Ma, Z., 2018. Investigation of biomass torrefaction based on three major components: hemicellulose, cellulose, and lignin. Energy Concers. Manage. 169, 228–237. https://doi.org/10.1016/j.enconman.2018. 05.063. Chi, H., Pans, M.A., Sun, C., Liu, H., 2019. An investigation of lime addition to fuel as a countermeasure to bed agglomeration for the combustion of non-woody biomass fuels in a 20kWth bubbling fluidised bed combustor. Fuel 240, 349–361. https://doi. org/10.1016/j.fuel.2018.11.122. Daood, S., Ord, G., Wilkinson, T., Nimmo, W., 2014. Fuel additive technology-NOx reduction, combustion efficiency and fly ash improvement for coal fired power stations. Fuel 134, 293–306. https://doi.org/10.1016/j.fuel.2014.04.032. Das, P., Mondal, D., Maiti, S., 2017. Thermochemical conversion pathways of Kappaphycus alvarezii granules through study of kinetic models. Bioresour. Technol. 234, 233–242. https://doi.org/10.1016/j.biortech.2017.03.007.
7
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
185, 1899–1906. https://doi.org/10.1016/j.apenergy.2015.11.077. Tong, Z., Yang, B., Hopke, P.K., Zhang, K.M., 2017. Microenvironmental air quality impact of a commercial-scale biomass heating system. Environ. Pollut. 220, 1112–1120. https://doi.org/10.1016/j.envpol.2016.11.025. Wang, T., Li, Y., Zhang, J., Zhao, J., Liu, Y., Sun, L., Liu, B., Mao, H., Lin, Y., Li, W., Ju, M., Zhu, F., 2018. Evaluation of the potential of pelletized biomass from different municipal solid wastes for use as solid fuel. Waste Manag. 74, 260–266. https://doi.org/ 10.1016/j.wasman.2017.11.043. Weber, K., Quicker, P., 2018. Properties of biochar. Fuel 217, 240–261. https://doi.org/ 10.1016/j.fuel.2017.12.054. Wei, S., Zhu, M., Fan, X., Song, J., Peng, P., Li, K., Jia, W., Song, H., 2019. Influence of pyrolysis temperature and feedstock on carbon fractions of biochar produced from pyrolysis of rice straw, pine wood, pig manure and sewage sludge. Chemosphere 218, 624–631. https://doi.org/10.1016/j.chemosphere.2018.11.177. Xie, M., Shen, G., Holder, A.L., Hays, M.D., Jetter, J.J., 2018. Light absorption of organic carbon emitted from burning wood, charcoal, and kerosene in household cookstoves. Environ. Pollut. 240, 60–67. https://doi.org/10.1016/j.envpol.2018.04.085. Yang, X., Liu, S., Xu, Y., Liu, Y., Chen, L., Tang, N., 2017. Emission factors of polycyclic and nitro-polycyclic aromatic hydrocarbons from residential combustion of coal and crop residue pellets. Environ. Pollut. 231, 1265–1273. https://doi.org/10.1016/j. envpol.2017.08.087. Yanik, J., Duman, G., Karlström, O., Brink, A., 2018. NO and SO2 emissions from combustion of raw and torrefied biomasses and their blends with lignite. J. Environ. Manag. 227, 155–161. https://doi.org/10.1016/j.jenvman.2018.08.068. Yilmaz, E., Wzorek, M., Akçay, S., 2018. Co-pelletization of sewage sludge and agricultural wastes. J. Environ. Manag. 216, 169–175. https://doi.org/10.1016/j. jenvman.2017.09.012. Zeng, T., Weller, N., Pollex, A., Lenz, V., 2016. Blended biomass pellets as fuel for small scale combustion appliances: influence on gaseous and total particulate matter emissions and applicability of fuel indices. Fuel 184, 689–700. https://doi.org/10. 1016/j.fuel.2016.07.047. Zhao, B., O'Connor, D., Zhang, J., Peng, T., Shen, Z., Tsang, D.C.W., Hou, D., 2018. Effect of pyrolysis temperature, heating rate, and residence time on rapeseed stem derived biochar. J. Clean. Prod. 174, 977–987. https://doi.org/10.1016/j.jclepro.2017.11. 013. Zhou, Y., Xing, X.F., Lang, J.L., Chen, D.S., Cheng, S.Y., Wei, L., Wei, X., Liu, C., 2017. A comprehensive biomass burning emission inventory with high spatial and temporal resolution in China. Atmos. Chem. Phys. 17, 2839–2864. https://doi.org/10.5194/ acp-17-2839-2017. Zhu, K., Wang, X., Geng, M., Chen, D., Lin, H., Zhang, H., 2019. Catalytic oxidation of clofibric acid by peroxydisulfate activated with woodbased biochar: effect of biochar pyrolysis temperature, performance and mechanism. Chem. Eng. J. 374, 1253–1263. https://doi.org/10.1016/j.cej.2019.06.006.
https://doi.org/10.1016/j.jaap.2011.12.008. Miranda, M.T., Sepúlveda, F.J., Arranz, J.I., Montero, I., Rojas, C.V., 2018. Analysis of pelletizing from corn cob waste. J. Environ. Manag. 228, 303–311. https://doi.org/ 10.1016/j.jenvman.2018.08.105. Motghare, K.A., Rathod, A.P., Wasewar, K.L., Labhsetwar, N.K., 2016. Comparative study of different waste biomass for energy application. Waste Manag. 47, 40–45. https:// doi.org/10.1016/j.wasman.2015.07.032. Nanda, S., Mohanty, P., Pant, K.K., Naik, S., Kozinski, J.A., Dalai, A.K., 2013. Characterization of north American lignocellulosic biomass and biochars in terms of their candidacy for alternate renewable fuels. Bioenergy. Res. 6, 663–677. https:// doi.org/10.1007/s12155-012-9281-4. Nielsen, H.P., Baxter, L.L., Sclippab, G., Morey, C., Frandsen, F.J., Dam-Johansen, K., 2000. Deposition of potassium salts on heat transfer surfaces in straw-fired boilers: a pilot-scale study. Fuel 79, 131–139. https://doi.org/10.1016/S0016-2361(99) 00090-3. Niu, Y., Tan, H., Wang, X., Liu, Z., Liu, H., Liu, Y., Xu, T., 2010. Study on fusion characteristics of biomass ash. Bioresour. Technol. 101, 9373–9381. https://doi.org/10. 1016/j.biortech.2010.06.144. Ramírez, V., Martí-Herrero, J., Romero, M., Rivadeneira, D., 2019. Energy use of Jatropha oil extraction wastes: pellets from biochar and Jatropha shell blends. J. Clean. Prod. 215, 1095–1102. https://doi.org/10.1016/j.jclepro.2019.01.132. Riaza, J., Khatami, R., Levendis, Y.A., Álvarez, L., Gil, M.V., Pevida, C., Rubiera, F., Pis, J.J., 2014. Combustion of single biomass particles in air and in oxy-fuel conditions. Biomass Bioenergy 64, 162–174. https://doi.org/10.1016/j.biombioe.2014.03.018. Růžičková, J., Kucbel, M., Raclavská, H., Švédová, B., Raclavský, K., Juchelková, D., 2019. Comparison of organic compounds in char and soot from the combustion of biomass in boilers of various emission classes. J. Environ. Manag. 236, 769–783. https://doi.org/10.1016/j.jenvman.2019.02.038. Sansaniwal, S.K., Rosen, M.A., Tyagi, S.K., 2017. Global challenges in the sustainable development of biomass gasification: an overview. Renew. Sus. Energy Environ. 80, 23–43. https://doi.org/10.1016/j.rser.2017.05.215. Silva Perez, D., Dupont, C., Guillemain, A., Jacob, S., Labalette, F., Briand, S., Marsac, S., Guerrini, O., Broust, F., Commandre, J.-M., 2015. Characterisation of the most representative agricultural and forestry biomasses in France for gasification. Waste and Biomass Valorization 6 (4), 515–526. Slopiecka, K., Bartocci, P., Fantozzi, F., 2012. Thermogravimetric analysis and kinetic study of poplar wood pyrolysis. Appl. Energy 97, 491–497. https://doi.org/10.1016/ j.apenergy.2011.12.056. Strandberg, A., Thyrel, M., Skoglund, N., Lestander, T.A., Broström, M., Backman, R., 2018. Biomass pellet combustion: cavities and ash formation characterized by synchrotron X-ray micro-tomography. Fuel Process. Technol. 176, 211–220. https://doi. org/10.1016/j.fuproc.2018.03.023. Tokimatsu, K., Yasuoka, R., Nishio, M., 2017. Global zero emissions scenarios: the role of biomass energy with carbon capture and storage by forested land use. Appl. Energy
8
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Research article
Assessment of combustion and emission behavior of corn straw biochar briquette fuels under different temperatures
T
Ting Wanga, Yuening Lia, Dengke Zhib, Yingchao Lina,∗, Kai Hec,∗∗, Boyang Liud, Hongjun Maoa a Center for Urban Transport Emission Research, State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, College of Environmental Science and Engineering, Nankai University, Tianjin, 300071, China b Key Laboratory of Bioactive Materials, Ministry of Education, College of Life Sciences, Nankai University, Tianjin, 300071, China c Research Centre for Environmental Quality Management, Kyoto University, 1-2 Yumihama, Otsu, Shiga, 520-0811, Japan d QES Department, Novozymes (China) Biotechnology Ltd, Tianjin, 300457, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Corn straw biochar Pyrolysis temperature Solid fuel Combustion characteristics Gas emission
The 350 °C and 700 °C corn straw biochars were used to produce solid fuel briquettes. NovoGro (NG), an industrial by-product, were selected as a binder in the briquetting process. The ratios of the raw material to NG was assumed as 100:1 and 50:1 (denoted as 350NB1, 350NB2, 700NB1 and 700NB2, respectively). The physicochemical and morphological properties, combustion characteristics and gas emissions of the four briquettes were investigated. The results revealed that the biochars and the NG binder performed a good combination. The low temperature biochar briquettes, especially 350NB2, had excellent combustion characteristics, including low H/C and O/C ratios (0.17 and 0.82), low gas emissions (104.06 mg/m3 of CO, 157.25 mg/m3 of NOx and 18.92 mg/ m3 of SO2), optimal resistance to mechanical shock (~90%) and high calorific values (21.48 MJ/kg). Thus, NG is a good binder for the briquetting of biochar. The low temperature biochar was a good feedstock for solid fuel production in the improvement of the combustion and emission quality.
1. Introduction The high demand of renewable energy has been growing nowadays due to shortage of fossil fuels and global warming (Guo and Zhong, 2018). Biomass is considered as a kind of renewable energy resource to replace traditional fossil fuel in the aspect of carbon credit (Jana Růžičková et al., 2019; Tong et al., 2017). Corn is one of the most widely grown cereal crop in the world today. However, most straws are produced annually from farms as agricultural wastes. It is estimated that over three billion tonnes of agricultural wastes were generated worldwide (Yilmaz et al., 2018). Burning in the field is regarded as the common management of straw, due to its convenience and economy for farmers (Yang et al., 2017). However, open crop straw burning is an important kind of primary pollution source, which contributes many pollutants into the atmosphere (Xie et al., 2018; Zhou et al., 2017). Based on the growing shortage of fossil fuels and the environmental pollution problem, the utilization of straw resources is an effective measure to sustainable development. Compared with fossil fuels, crop straw is a scattered resource with lower energy density and less efficient to store and transport (Miranda
∗
et al., 2018; Ji et al., 2018). The energy density of biomass is usually in the range of 14,651–16,744 KJ, which is very less compared to 20,930–29,302 KJ of coal (Balasubramani et al., 2016). Thus, conversion of this bulky biomass into a denser form improves the handling property and reduces the cost of handling, transportation and storage (Sansaniwal et al., 2017). Moreover, zero or negative carbon dioxide (CO2) emission is possible from biomass briquette fuel combustion because released CO2 from the combustion of bio-oil can be recycled into the plant by photosynthesis (Tokimatsu et al., 2017). In addition, it is an attractive clean and environmental friendly fuel as it significantly induces low amount of NOx and SO2 emissions (Boumanchar et al., 2017; Yanik et al., 2018). Pyrolysis technology has the capability to produce bio-fuel with high fuel-to-feed ratios. Therefore, pyrolysis has been receiving more attention as an efficient method in converting biomass into bio-fuel (Azizi et al., 2018). Biochar is a carbonaceous material produced by the pyrolysis of biomass under limited or no oxygen (Dhyani and Bhaskar, 2018). Carbonization of the biomass briquettes will reduce the amount of liquid and gas in the biomass and further increase the carbon content. Hence, the pyrolytic biochars usually have better fuel qualities
Corresponding author. Corresponding author. E-mail addresses: [email protected] (Y. Lin), [email protected] (K. He).
∗∗
https://doi.org/10.1016/j.jenvman.2019.109399 Received 26 February 2019; Received in revised form 4 August 2019; Accepted 12 August 2019 0301-4797/ © 2019 Elsevier Ltd. All rights reserved.
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
2.4. Combustion characteristics and combustion behavior analysis of biochar briquette fuels
than the parent biomass (Weber and Quicker, 2018). Several advantages offered by biochar fuel include higher boiler efficiency due to low moisture and higher density, more uniform combustion, less corrosion effect on boiler equipment due to negligible sulphur content, environment friendly being a pollution free and clean burning fuel, and easy handling and long distance transportation (Boumanchar et al., 2017). Hence, the biochar fuel has a great potential for various applications, such as household heating, industrial steam generation, outdoor barbequing, and so on. Despite of several above advantages, there are only few investigations that have been done on biochar fuel obtained from waste biomass compared to bio-oil and gaseous products (Ramírez et al., 2019). The pyrolysis temperature is one of the vital parameters for biochar fuel production from biomass. It has been reported that the pyrolysis performed at 200–300 °C cannot improve the combustion property of biomass feedstock due to the high decomposition temperature of cellulose (generally higher than 300 °C) (Wei et al., 2019). However, high temperatures favor the liquid and gaseous products, and decrease energy recovery in the biochar (Elkhalifa et al., 2019). Thus, the optimal pyrolysis temperature for maintaining high-energy recovery and desired combustion property should be investigeted. Therefore, in this study, the corn straw biomass was pyrolyzed under different temperature to produce solid fuel biochars with better fuel qualities. The mechanical, thermal and morphological properties of the briquettes were investigated. The bulk and surface element contents, ash content, higher heating value (HHV) and lower heating value (HHV) of the briquettes were measured to evaluate the combustion performance. The surface morphology and the chemical surface structures of the briquettes were investigated with SEM and FTIR spectra, respectively. Moreover, the gas emission test of the prepared briquettes were also conducted to evaluate the emission behavior.
The ash content, volatile matter content, shatter strength, higher heating value (HHV) and lower heating value (LHV) of the four briquettes were determined to systematically evaluate the combustion characteristics of the biochar briquettes. The details of the methods were descripted in the Supporting Information. In order to describe the thermal stability of the four briquettes, the TG and derivative thermogravimetric (DTG) of the four briquettes were investigated by a thermal analyzer (TGA/DSC1, METTLER TOLEDO, Switzerland). The samples were carried out in an air atmosphere. The airflow and heating rate of TG was 30 mL/min and 10 °C/min, respectively. 2.5. Ash analysis The ash fusion temperatures (AFTs) of the briquettes were investigated using an ash fusion analyzer (SDAFDY2000d, Sundy, China) in Ar and H2 atmospheres (Proximate analysis of coal, Chinese National Standards, GB/T 212–2008). The TG and derivative thermogravimetric (DTG) of the briquette ash obtained at 450 °C, 575 °C (ASTM E1755-01, Standard test method for ash in biomass) and 815 °C (GB/T212-2008, Proximate analysis method for coal, China) were investigated by a thermal analyzer (TGA/ DSC1, METTLER TOLEDO, Switzerland). The details of the methods were descripted in the Supporting Information. 2.6. Gas emission in the combustion of the biochar briquette fuels To investigate the emission analysis, the four pellets were combusted in a 210 KWth biomass furnace without gas after-treatment device. The structure diagram of the furnace was shown in Fig. 1. Trace gas emissions were measured using a digital flu gas analyzer, Testo 350 (Testo, Germany) by following a modified protocol of Li et al. (2009). Details of the test parameters were descripted in the Supporting Information.
2. Materials and methods 2.1. Biochar preparation Corn straw stock was collected from a farmland in Zhongyuan District, Zhengzhou, China. The corn straw was air-dried and ground to pass through a 2 mm sieve, then heated at 350 °C or 700 °C in a carbonization furnace under oxygen-limited conditions for 2 h. The biochar produced were ground to pass through the 200 mesh sieves.
3. Results and discussion 3.1. The physical and chemical characteristics of the four briquettes
2.2. Biochar briquetting
The element compositions of the biochar briquettes were listed in Table S1. All tests were carried out in triplicate to ensure reproducibility of the results. The elemental ratios H/C and O/C can offer information about the combustion efficiency of a fuel. Briquettes with low H/C and O/C ratios produce less CO2, water vapor, and smoke when burned, leading to higher combustion efficiency (Abdullah and Wu, 2009). The H/C and O/C ratios of 350NB1, 350NB2, 700NB1 and 700NB2 were listed in Table S1. Although the H/C and O/C ratios tend to decrease with increased pyrolysis temperature. It was due to that the carbon in the char transitions from aliphatic hydrocarbons into aromatic elemental carbon structures (Abdullah and Wu, 2009). Wood chars typically have O/C ratios ranging from 0.01 to 0.35 and H/C ratios from 0.03 to 0.70 (Kearns et al., 2014; Linderholm et al., 2017); coals tend to have O/C ratios of 0.01–0.35 and H/C ratios of 0.06–1.10 (Basu, 2010; Liu and Balasubramanian, 2013; Linderholm et al., 2017). Hence, the four briquettes were acceptable for using as the solid fuel. Besides, the H/C and O/C ratios were further decreased after binding with NG. Hence, NG, as a binder, could enhance the combustion performance of biochar. The remaining primary contents of the briquettes were Ca, K, Si and Cl. The 350NB1 and 350NB2 were typically Ca-rich briquettes. The presence of CaO in low temperature biochar briquettes could make it useful for SO2 capture. The K content of 350NB2 was lowest among the four briquettes. Hence, there was low potential of agglomeration,
The NG, briquetting binder, was a by-product obtained from the centrifuged fermentation broths of the Biological Treatment Plant of Novozymes in Tianjin, China (Wang et al., 2018). The briquette production ratios of the raw material to NG were 100:1 and 50:1. The four biochar briquettes were denoted as 350NB1, 350NB2, 700NB1 and 700NB2, respectively. The moisture of the mixture was adjusted to approximate 15% by adding a predetermined amount of water. Then, the mixtures were stirred to obtain a homogeny mixture. The mixture was briquetted in a flat-shaped granulator under productive capacity of 500 kg h−1 at ambient temperature (25 ± 2 °C). The average diameters and length of the briquettes were 4–5 mm and 15–20 mm, respectively. 2.3. Ultimate analysis and morphological properties of the biochar briquette fuels Seventy-two hours after briquetting, the bulk density and the primary element contents were analyzed. Besides, the morphological and infrared properties of the briquettes were analyzed with SEM microanalysis (QUANTA 200, USA) and FTIR spectroscopy (Tensor 27, Bruker, USA). The details of the methods were descripted in the Supporting Information. 2
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
temperature. Besides, the peaks of 700NB1 and 700NB2 were boarder and sharper than that of 350NB1 and 350NB2. The biochar surface area and total pore volume increased with the rise of pyrolysis temperature, which might be due to the removal of aliphatic and volatile materials at high carbonization temperature. Hence, the roughness and disordered graphite of the biochar improved with increasing pyrolysis temperature (Zhu et al., 2019). The peaks at 2θ = 25–30° (Peak 3 & 4) in 700NB1 and 700NB2 were due to the crystal growth of calcite (Mafu et al., 2016). The calcite has great potential to hinder ash sintering and to mitigate slag formation during biomass combustion (Chi et al., 2019). The peaks at 2θ~36° (Peak 5) were assigned to hemicellulose in 350NB1 and 350NB2 (Nanda et al., 2013), which were much lower in 700NB1 and 700NB2. It was due to that the hemicellulose was decomposed at the high pyrolysis temperature (Chen et al., 2017). In the same condition, the yield of gaseous product of hemicellulose was higher than that of cellulose and lignin (Chen et al., 2018). Hence, the 350NB1 and 350NB2 had the potential of using as the solid fuel. The sharp peaks at ~50° in 700NB1 and 700NB2 samples (Peak 6) indicated the formation of small amounts of silicate (Mafu et al., 2016). The low-temperature eutectic substances of alkali-silicate compounds could cause slagging during the combustion. The K content of 700NB1 and 700NB2 were higher than 350NB1 and 350NB2 (Table S1). Hence, there is a potential of agglomeration, sintering and deposition during the combustion of 700NB1 and 700NB2. 3.2. Combustion properties of the four briquettes The moisture of the fuel has a very significant effect on the ignition and propagation of the fuels. Hence, the total moisture content is one of the vital factors of fuel. Before the briquetting process, 15% (m/m) water was supplied to the raw material. It was considered that the optimum moisture content of briquette was approximately 12%, and higher moisture contents were corresponded with higher bulk densities and durabilities in briquettes (Miranda et al., 2018). As shown in Table 1, the 350NB1 and 350NB2 showed certain advantages of using as fuels. Moreover, the addition of NG further reduced the moisture content of low-temperature biochar briquette but increased that of hightemperature biochar briquette. The ash contents of the700NB1 and 700NB2 were much higher than those of the 350NB1 and 350NB2. It was due to that the increasing pyrolysis temperature increased the formation of biochar ash containing alkaline minerals (Zhao et al., 2018). According to the classification of coals of the International Standard (ISO 11760-2005) and Chinese National Standard (GB/T 15224.1-2010), the 350NB2 was classified as medium ash coal, while the 350NB1 was classified as moderately high ash coal and medium ash coal, respectively. Hence, the 350NB2 could be used as a substitute fuel to relief high-rank fuel shortage. While, the high-temperature biochar briquettes might not suitable for combustion due to the high ash content. The Si content of fuel is relative with the ash content (Daood et al., 2014). According to Table S1 and Fig. 2, the tendency of the Si contents of the briquettes were consistent with that of the ash contents. The 350NB1 and 350NB2 briquettes had relatively higher volatile matter contents than 700NB1 and 700NB2 briquettes. Hence, the low temperature biochar briquettes would show advantages at the initial stage of ignition. The fuel combustion endurance was closely linked with the fixed carbon content of the fuel (Riaza et al., 2014). The fixed carbon contents of the briquettes were followed the order of 700NB2 < 700NB1 < 350NB1 < 350NB2. Thus, the low temperature biochar briquettes also exhibited high combustion persistence. The commercial fuels are usually with excellent resistance to mechanical shock and high calorific value simultaneously. The durability properties fall within the specification of < 10% mass loss during shattering and abrasion tests for CEN/TS 14961, the European standard for solid fuel quality. As shown in Table 1, the 350NB2 and 700NB1 were close to the standard. The HHV and LHV of 350NB1 and 350NB2
Fig. 1. Schematic of the 210 KWth biomass furnace.
sintering and deposition during the combustion. The Si contents of 700NB1 and 700NB2 (4.27% and 3.68%, respectively) were much higher than that of 350NB1 and 350NB2 (1.37% and 0.85%). The volatile silicon compounds could convert into silica particles and cause abrasion damage (Mathison et al., 2010). Besides, during the combustion process, the conversion rates of the fuels could be decreased due to low temperature melting silicate that dominate the ash formation and might partially cover, or totally encapsulate, the remaining fuel (Strandberg et al., 2018). The Cl could cause the formation of low melting point eutectics, which could result in slagging and fouling (Magdziarz et al., 2016). There were large amounts of Cl in 350NB1 and 350NB2. The Cl contents of the briquettes could be ordered as follows: 350NB1 > 350NB2 > 700NB1 > 700NB2. It was revealed that the addition of NG was beneficial to reduce the Cl content of the briquettes. As listed in other literatures, the Cl contents of fuels usually ranged from 0.18% to 4.25% (Febrero et al., 2015; Silva Perez et al., 2015; Zeng et al., 2016; Jin et al., 2017). Hence, the Cl contents of the four briquettes were acceptable for using as the solid fuel. In summary, the low temperature biochar briquettes would exhibit better performance in the combustion process than the high temperature biochar briquettes. Fig. 2 depicts the XRD profiles of the four briquettes. The first obvious peak at 2θ = 21° (Peak 1) is illustrated as the presence of crystal phases of silica like quartz (Niu et al., 2010). The X-ray diffractograms showed the intense peaks for 700NB1 and 700NB2, which resulted from the higher pyrolysis temperature (Ding et al., 2016). This was consistent with the Si content tendency of the briquettes. The sharp peaks at 2θ = 26.6° (Peak 2) for the four briquettes were attributed to the high quality of graphitic basal planes stacking (Mafu et al., 2016). The original peak was at 2θ = 25° (Guerrero et al., 2008). This deviation was attributed to the disordered structure of the briquettes, and the different intensities implied the structural differences in the arrangement of the graphitic planes with the increment of pyrolysis 3
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
Fig. 2. X-ray diffraction patterns recorded for the briquette samples. (1- silica; 2- graphitic plane; 3, 4- calcite; 5- hemicellulose; 6-silicate compounds)
respectively. The total weight loss of the low temperature biochar briquettes were above 60%. While for 700NB1 and 700NB2, there were only two main peaks centered at 460 °C and 650 °C, respectively. And the total weight loss of the two high temperature biochar briquettes were below 20%, which were much lower than that of the low temperature biochar briquettes. It was due to the thermal decomposition of biomass components under the high pyrolysis temperature on production of 700 °C biochar. The high total weight loss are usually due to with high volatile content (Li et al., 2018). This was consistent with the volatile contents results of the briquettes (Table 1). Hence, the low temperature biochar briquettes had high combustion potential.
were 21.48 and 18.62 MJ/kg and 18.85 and 16.56 MJ/kg, respectively, which are much higher than that of 700NB1 and 700NB2 (Table 1). Base on the classification for quality of coal of the Chinese National Standard (GB/T 15224.32010), the HHV and LHV below 16.30 MJ/kg and 12.51 MJ/kg are classified as the low-rank coals. The 350NB1 and 350NB2 were acceptable for using as fuels. Moreover, although the HHV and LHV of low temperature biochar briquettes were a little lower than those of the charcoal (Motghare et al., 2016), they were much higher than the wheat straw, cotton waste, municipal solid waste and wood pellets in others literatures (Johansson et al., 2004; Edo et al., 2016; Motghare et al., 2016), indicating that the low temperature biochar briquettes had the potential to be used as high rank fuel.
3.4. Morphological properties of the four briquettes 3.3. Combustion behavior of the four briquettes The SEM and FTIR spectroscopy were chosen to identify the structural, morphological and infrared properties of the biochar briquettes. The SEM micrographs showed the surface morphology of the four briquettes were homogenous (Fig. 4 a, d, g and j). It revealed that the binder and biochar were mutually substantially evenly mixed together. The NG is produced during the enzyme production process, which is the centrifuged residue of fermentation broth of potato flour, cornstarch and other raw materials, hence containing N, P and K elements, mineral nutrients and organic substances (Wang et al., 2018). These are led to the caking property of NG in the briquetting process. The 350NB1 and 350NB2 particles were mainly composed of fibrous and irregular
The TG and DTG profiles depicting the combustion process of the four briquettes are presented in Fig. 3. In the DTG profile (Fig. 3 b), the peaks (centered at ~70 °C, below 200 °C) attributed to the moisture evaporation of the biochars; the second peak (centered at ~ 450 °C, below 600 °C) corresponded to the decomposition and oxidation of the biochars; and the third peak (centered at ~ 650 °C, below 700 °C) relates to the volatilization of some inorganics including potassium and other inorganics (Guo and Zhong, 2018; Liu et al., 2012; Haykiri-Acma et al., 2013). For 350NB1 and 350NB2, the weight loss of the three peaks were 7.29% and 6.49%, 75.46% and 66.68%, and ~2.5%, Table 1 Combustion characteristics of biochar briquettes. Briquettes
350NB1 350NB2 700NB1 700NB2
Proximate analysis (%)
Calorific value (MJ/kg)
Ash fusion point (oC)
Total moisture
Ash
Volatile matter
Fixed carbon
HHV
LHV
DT
ST
HT
FT
11.5 8.7 4.2 4.9
24.2 17.4 67.8 67.4
26.7 30.8 10.5 10.6
35.0 43.1 21.5 21.1
18.85 21.48 6.96 6.96
16.56 18.62 6.49 6.45
1128 1150 1154 1153
1137 1160 1206 1198
1139 1162 1242 1221
1200 1165 1308 1280
4
Shatter strength (%)
Density (g/cm3)
40.9 89.5 91.4 64.5
1.06 1.12 1.67 1.60
± ± ± ±
1.2 0.3 0.2 0.8
± ± ± ±
0.03 0.06 0.02 0.02
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
Fig. 3. TGA (Thermogravimetric analysis) and DTG (Differential thermogravimetry) plots of the four briquettes of heating in air.
Fig. 4. SEM photography of the pellet samples. (a, d, g, j: × 700; b, e, h, k: × 500; c, f, i, l: × 2000) 5
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
breakdown of the Aphthitalite [K3Na(SO4)2] (Das et al., 2017), respectively. The ash samples obtained at different temperatures had similar variation tendency with the parent briquettes, but the numbers of the peaks decreased with the increased of the ashing temperature (Fig. S2 b, d, f and g). It could be inferred that no matter what the ashing temperature is, when the heating temperature is higher than a certain value, the compositions in the ashes are nearly the same or they contain the same high-temperature molten material.
particles (Fig. 4 b, c, e and f), while the 700NB1 and 700NB2 particles included bulk particles (Fig. 4 h, i, k and l). During the pyrolysis process, the unstable and volatile fractions of the raw materials disappeared. Thus, the low pyrolysis temperature preserved the original morphology of the corn straws. Besides, the particle sizes of 700NB1 and 700NB2 (Fig. 4 c and f) were considerably larger than that of 350NB1 and 350NB2 (Fig. 4 i and l), which were not conducive to the briquetting process. Furthermore, the 350NB1 and 350NB2 particles have rough surfaces (Fig. 4 i and l), while the surface of 700NB1 and 700NB2 particles are relatively smooth (Fig. 4 c and f). Thus, the low temperature biochar briquettes were with well performance in tight formations. These were related to the higher HHV and LHV values of 350NB1 and 350NB2 than 700NB1 and 700NB2. The FTIR spectroscopy was used in the structure analysis of the biochar briquettes. In the FTIR spectra (Fig. S1), the band at ~1650 1/ cm (C]O stretching vibration) was assigned to the hemicellulose component (Mayer et al., 2012). It could be observed that there were small peaks of 350NB1 and 350NB2. It was due to that the hemicellulose was decomposed at the high pyrolysis temperature during the production of 700NB1 and 700NB2. This was consistent with the result of XRD analysis of the briquettes in section 3.1. The band at ~1550 1/cm was resulted of the C]O stretching of lignin (Fierro et al., 2007). The bands at 1100 1/cm and 800 1/cm were due to the C–O stretching and C–H bending of lignin, respectively (Asadieraghi and Daud, 2015). Thus, it was implied that the lignin contents of the 350NB1 and 350NB2 were higher than that of 700NB1 and 700NB2. These constituents led to the high calorific values of the 350NB1 and 350NB2 briquettes. These observed results offered a comprehensive explanation for the high combustion potential of low temperature biochar briquettes.
3.6. Gas emission characteristics of the briquettes In the biomass furnace (Fig. 1), the 350NB1 and 350NB2 exhibited good combustion behavior, and there was little bottom ash discharged during the combustion process. While the 700NB1 and 700NB2 were hardly to ignite in the furnace. The gas emissions of CO, NOx and SO2 of 350NB1 and 350NB2 were 138.3, 149.2, 62.5 and 104.1, 157.3, 18.9 mg/m3, respectively, based on 9% reference O2 at standard conditions (1 atm, 0 °C), where the least CO emissions were obtained. In summary, the CO and SO2 concentrations in the gas of 350NB2 were lower than that of 350 NB1. The NOx emission of 350NB1 and 350NB2 were comparable. The emission standards of biomass boilers in different countries or districts are listed in Table S2. The CO and SO2 emissions of 350NB2 could meet most of the emission standards. In general, all biomass samples have higher nitrogen contents than the coals (Lee et al., 2018). However, the NOx emission of 350NB2 could meet or be close to most of the standards without de-NOx after-treatment device. Hence, pyrolytic biochar was a good strategy to produce clean fuel. In summary, the moisture and AFTs of the four briquettes were all within the limits of the solid fuel acceptability. Low temperature biochar briquettes had higher Ca, lower Si and K contents than high temperature biochar briquettes, which was consistent with the CRD results. The HHV and LHV of low temperature biochar briquettes were much higher than that of high temperature biochar briquettes, and this result was consistent with the XRD, FTIR and TG data. Moreover, the ash contents of low temperature biochar briquettes were much lower than that of the high temperature biochar briquettes. Although the H/C, O/C and Cl contents of high temperature biochar briquettes were lower than that of the low temperature biochar briquettes. Compared to the results in other literatures, these properties of low temperature biochar briquettes were acceptable for using as the solid fuel. These results suggested that the low temperature biochar was a good feedstock for solid fuel production in the improvement of the combustion and emission quality. Besides, 350NB2 had lower H/C and O/C ratios, lower Si, K, Cl and ash contents, lower moisture, and higher HHV and LHV than 350NB1. The CO and SO2 emission of 350NB2 were much lower than that of 350NB1. Furthermore, the SEM micrographs showed that the NG combined well with the biochar feedstock. These analyses revealed that NG is a good binder for the briquetting of biochar. The corn straw biochar briquette fuels may be a promising candidate as the substitute for fossil fuels.
3.5. Ash analysis of the four briquettes The ash fusion temperatures (AFTs) of the briquettes were listed in Table 1. The deformation temperature (DT), softening temperature (ST), hemisphere temperature (HT) and flow temperature (FT) of 700NB1 and 700NB2 were higher than that of 350NB1 and 350NB2. According to the American Society of Mechanical Engineers (ASME) Research Committee, the slagging would be likely to occur when the disparity of FT and DT values of the fuel was above 149 °C. In this study, the disparities of FT and DT values of 350NB1, 350NB2, 700NB1 and 700NB2 were 72, 15, 154 and 127 °C, respectively. It implied that it had a potential for slagging during the combustion process of the low temperature biochar briquettes. However, it is generally required that the coal FT less than 1380 °C in practical industrial application (Li et al., 2019). Therefore, all the four briquettes could meet the standard to use as fuels. The TGA and derivative mass loss (DTG) of the different briquette ashes are shown in Fig. S1. Details of the weight losses of the ash samples of the four briquettes were described in the Supporting Information. The sharp loss in a relatively lower temperature range (600–750 °C) is considered as the high calcium content in ash, and the sharp weight loss is mainly attributed to the decomposition of calcium carbonate (Du et al., 2014). The Ca contents of 350NB1 and 350NB2 were 2.3–2.8 folder higher than that of 700NB1 and 700NB2 (Table S1), which resulted in the weight loss differences of 450 °C and 575 °C ash samples of the four briquettes. KCl, the main volatile composition of corn straw, plays an important role in the process. The intense volatilization of KCl occurs from 750 °C to 950 °C (Nielsen et al., 2000; Lin et al., 2003). The K contents of the four briquettes were comparable, but the Cl contents of 350NB1 and 350NB2 were much higher than that of 700NB1 and 700NB2 (Table S1), which lead to the weight loss variation of the 815 °C ash of the four pellets. Details of the DTG peaks of the ash samples of the four briquettes were described in the Supporting Information. The three peaks were due to the gradual moisture removal, the thermal degradation of hemicellulose and cellulose Slopiecka et al. (2012) and the thermal
3.7. Application and prospect The prospect of the exhaustion of fossil energy and climate change caused by the excessive use of fossil fuel necessitates shifting energy supply from fossil energy to renewable energy in the near future. This study provided a kind of biomass fuel with excellent combustion characteristics, low gas emissions, optimal resistance to mechanical shock and high calorific values, which might be a promising candidate for coal fuel. However, as an alternative technology, many aspects still need to be developed and evaluated due to several variables are correlated to determine the characteristics and applications of biochar fuel. As mentioned above, the ash content of the biochar fuel should be further reduced for using as a high rank fuel. In this study, the gas emissions of the biochar briquettes were 104.06 mg/m3 of CO, 6
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
157.25 mg/m3 of NOx and 18.92 mg/m3 of SO2 without any aftertreatment device. However, the straw nitrogen content was usually higher than that of wood materials. Hence, to achieve the ultra-low NOx emission, it could be coupled with a de-NOx after-treatment device in the practical application.
Dhyani, V., Bhaskar, T., 2018. A comprehensive review on the pyrolysis of lignocellulosic biomass. Renew. Energy 129, 695–716. https://doi.org/10.1016/j.renene.2017.04. 035. Ding, Z., Wan, Y., Hu, X., Wang, S., Zimmerman, A.R., Gao, B., 2016. Sorption of lead and methylene blue onto hickory biochars from different pyrolysis temperatures: importance of physicochemical properties. J. Ind. Eng. Chem. 37, 261–267. https://doi. org/10.1016/j.jiec.2016.03.035. Du, S., Yang, H., Qian, K., Wang, X., Chen, H., 2014. Fusion and transformation properties of the inorganic components in biomass ash. Fuel 117, 1281–1287. https://doi.org/ 10.1016/j.fuel.2013.07.085. Edo, M., Budarin, V., Aracil, I., Persson, P.E., Jansson, S., 2016. The combined effect of plastics and food waste accelerates the thermal decomposition of refuse-derived fuels and fuel blends. Fuel 180, 424–432. https://doi.org/10.1016/j.fuel.2016.04.062. Elkhalifa, S., Al-Ansari, T., Mackey, H.R., McKay, G., 2019. Food waste to biochars through pyrolysis: a review. Resour. Conserv. Recycl. 144, 310–320. https://doi.org/ 10.1016/j.resconrec.2019.01.024. Febrero, L., Granada, E., Patiño, D., Eguía, P., Regueiro, A., 2015. A comparative study of fouling and bottom ash from woody biomass combustion in a fixed-bed small-scale boiler and evaluation of the analytical techniques used. Sustain. Times 7, 5819–5837. https://doi.org/10.3390/su7055819. Fierro, V., Torné-Fernández, V., Celzard, A., Montané, D., 2007. Influence of the demineralisation on the chemical activation of Kraft lignin with orthophosphoric acid. J. Hazard Mater. 149, 126–133. https://doi.org/10.1016/j.jhazmat.2007.03.056. Guerrero, M., Ruiz, M.P., Millera, Á., Alzueta, M.U., Bilbao, R., 2008. Characterization of biomass chars formed under different devolatilization conditions: differences between rice husk and eucalyptus. Energy Fuel. 22, 1275–1284. https://doi.org/10. 1021/ef7005589. Guo, F., Zhong, Z., 2018. Co-combustion of anthracite coal and wood pellets: thermodynamic analysis, combustion efficiency, pollutant emissions and ash slagging. Environ. Pollut. 239, 21–29. https://doi.org/10.1016/j.envpol.2018.04.004. Haykiri-Acma, H., Yaman, S., Kucukbayrak, S., 2013. Production of biobriquettes from carbonized brown seaweed. Fuel Process. Technol. 106, 33–40. https://doi.org/10. 1016/j.fuproc.2012.06.014. Ji, C., Cheng, K., Nayak, D., Pan, G., 2018. Environmental and economic assessment of crop residue competitive utilization for biochar, briquette fuel and combined heat and power generation. J. Clean. Prod. 192, 916–923. https://org/10.1016/j.jclepro. 2018.05.026. Jin, X., Ye, J., Deng, L., Che, D., 2017. Condensation behaviors of potassium during biomass combustion. Energy Fuel. 31, 2951–2958. https://doi.org/10.1021/acs. energyfuels.6b03381. Johansson, L.S., Leckner, B., Gustavsson, L., Cooper, D., Tullin, C., Potter, A., 2004. Emission characteristics of modern and old-type residential boilers fired with wood logs and wood pellets. Atmos. Environ. 38, 4183–4195. https://doi.org/10.1016/j. atmosenv.2004.04.020. Kearns, J.P., Wellborn, L.S., Summers, R.S., Knappe, D.R.U., 2014. 2,4-D adsorption to biochars: effect of preparation conditions on equilibrium adsorption capacity and comparison with commercial activated carbon literature data. Water Res. 62, 20–28. https://doi.org/10.1016/j.watres.2014.05.023. Lee, Y.J., Park, J.H., Song, G.S., Namkung, H., Park, S.J., Kim, J.G., Choi, Y.C., Jeon, C.H., Choi, J.W., 2018. Characterization of PM2.5 and gaseous emissions during combustion of ultra-clean biomass via dual-stage treatment. Atmos. Environ. 193, 168–176. https://doi.org/10.1016/j.atmosenv.2018.09.011. Li, X., Wang, S., Duan, L., Hao, J., Nie, Y., 2009. Carbonaceous aerosol emissions from household biofuel combustion in China. Environ. Sci. Technol. 43, 6076–6081. https://doi.org/10.1021/es803330j. Li, Y., Lin, H., Xiao, K., Lasek, J., 2018. Combustion behavior of coal pellets blended with Miscanthus biochar. Energy 163, 180–190. https://doi.org/10.1016/j.energy.2018. 08.117. Li, M., Li, F., Liu, Q., Fang, Y., Xiao, H., 2019. Regulation of ash fusibility for high ashfusion-temperature (AFT) coal by industrial sludge addition. Fuel 244, 91–103. https://doi.org/10.1016/j.fuel.2019.01.161. Lin, W., Dam-Johansen, K., Frandsen, F., 2003. Agglomeration in bio-fuel fired fluidized bed combustors. Chem. Eng. J. 96, 171–185. https://doi.org/10.1016/j.cej.2003.08. 008. Linderholm, C., Schmitz, M., Biermann, M., Hanning, M., Lyngfelt, A., 2017. Chemicallooping combustion of solid fuel in a 100 kW unit using sintered manganese ore as oxygen carrier. Int. J. Greenh. Gas. Con. 65, 170–181. https://doi.org/10.1016/j. ijggc.2017.07.017. Liu, Z., Balasubramanian, R., 2013. A comparison of thermal behaviors of raw biomass, pyrolytic biochar and their blends with lignite. Bioresour. Technol. 146, 371–378. Liu, Z., Quek, A., Kent Hoekman, S., Balasubramanian, R., 2012. Production of solid biochar fuel from waste biomass by hydrothermal carbonization. Fuel 103, 943–949. https://doi.org/10.1016/j.fuel.2012.07.069. Mafu, L.D., Neomagus, H.W.J.P., Everson, R.C., Carrier, M., Strydom, C.A., Bunt, J.R., 2016. Structural and chemical modifications of typical South African biomasses during torrefaction. Bioresour. Technol. 202, 192–197. https://doi.org/10.1016/j. biortech.2015.12.007. Magdziarz, A., Dalai, A.K., Koziński, J.A., 2016. Chemical composition, character and reactivity of renewable fuel ashes. Fuel 176, 135–145. https://doi.org/10.1016/j. fuel.2016.02.069. Mathison, S., Sattler, A., Lile, R., Guillen, F., Linsley, B., Magers, K., Lee, J., 2010. Determination of siloxanes and other volatile silicon compounds in biogas samples using sample preconcentration with GC-MS and GC-ICP-MS. Proc. Water. Environ. Fed. 2010 (3), 399–424. https://doi.org/10.2175/193864710802768352. Mayer, Z.A., Apfelbacher, A., Hornung, A., 2012. Effect of sample preparation on the thermal degradation of metal-added biomass. J. Anal. Appl. Pyrolysis 94, 170–176.
4. Conclusions The 350 °C corn straw biochar briquette exhibited excellent combustion characteristics, optimal resistance to mechanical shock and high HHV value. An industrial production waste (NG), as a binder in the briquetting process, was excellently combined with the biochar and could improve the combustion property of biomass feedstock. Moreover, the CO and SO2 emissions of the briquettes could meet most of the emission standards, and the NOx emission could meet or be close to most of the standards without de-NOx after-treatment device. Therefore, the corn straw biochar briquette fuels may be a promising candidate as the substitute for fossil fuels. Acknowledgements This work was financially supported by the National Natural Science Foundation of China [21806082], Key Technologies R & D Program of Tianjin [18YFZCNC01410, 16YFZCSF00410] and the Fundamental Research Funds for the Central Universities. The foundation 21806082 provided financial support in the gas emission characteristics of the briquettes. The foundation 18YFZCNC01410 provided financial support in the production of the briquettes. The foundation 16YFZCSF00410 provided financial support in the characteristics analysis of the fuels. The Fundamental Research Funds for the Central Universities provided financial support in the language improvement of the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jenvman.2019.109399. References Abdullah, H., Wu, H., 2009. Biochar as a fuel: 1. Properties and grindability of biochars produced from the pyrolysis of mallee wood under slow-heating conditions. Energy Fuel. 23, 4174–4181. https://doi.org/10.1021/ef900494t. Asadieraghi, M., Daud, W.M.A.W., 2015. In-depth investigation on thermochemical characteristics of palm oil biomasses as potential biofuel sources. J. Anal. Appl. Pyrolysis 115, 379–391. https://doi.org/10.1016/j.jaap.2015.08.017. Azizi, K., Moraveji, M.K., Najafabadi, H.A., 2018. A review on bio-fuel production from microalgal biomass by using pyrolysis method. Renew. Sustain. Energy Rev. 82, 3046–3069. https://doi.org/10.1016/j.rser.2017.10.033. Balasubramani, P., Anbumalar, V., Nagarajan, M.S., Prabu, P.M., 2016. Biomass briquette manufacturing system model for environment. J. Alloy. Comp. 686, 859–865. https://doi.org/10.1016/j.jallcom.2016.06.233. Basu, P., 2010. Biomass gasification and pyrolysis: practical design and theory. Compr. Renew. Energy 25, 133–153. https://doi.org/10.1017/CBO9781107415324.004. Boumanchar, I., Chhiti, Y., Alaoui, F.E.M., Ouinani, A.E., Sahibed-Dine, A., Bentiss, F., Jama, C., Bensitel, M., 2017. Effect of materials mixture on the higher heating value: case of biomass, biochar and municipal solid waste. Waste Manag. 61, 78–86. https://doi.org/10.1016/j.wasman.2016.11.012. Chen, T., Li, L., Zhao, R., Wu, J., 2017. Pyrolysis kinetic analysis of the three pseudocomponents of biomass–cellulose, hemicellulose and lignin. J. Therm. Anal. Calorim. 128, 1825–1832. https://10.1007/s10973-016-6040-3. Chen, D., Gao, A., Cen, K., Zhang, J., Cao, X., Ma, Z., 2018. Investigation of biomass torrefaction based on three major components: hemicellulose, cellulose, and lignin. Energy Concers. Manage. 169, 228–237. https://doi.org/10.1016/j.enconman.2018. 05.063. Chi, H., Pans, M.A., Sun, C., Liu, H., 2019. An investigation of lime addition to fuel as a countermeasure to bed agglomeration for the combustion of non-woody biomass fuels in a 20kWth bubbling fluidised bed combustor. Fuel 240, 349–361. https://doi. org/10.1016/j.fuel.2018.11.122. Daood, S., Ord, G., Wilkinson, T., Nimmo, W., 2014. Fuel additive technology-NOx reduction, combustion efficiency and fly ash improvement for coal fired power stations. Fuel 134, 293–306. https://doi.org/10.1016/j.fuel.2014.04.032. Das, P., Mondal, D., Maiti, S., 2017. Thermochemical conversion pathways of Kappaphycus alvarezii granules through study of kinetic models. Bioresour. Technol. 234, 233–242. https://doi.org/10.1016/j.biortech.2017.03.007.
7
Journal of Environmental Management 250 (2019) 109399
T. Wang, et al.
185, 1899–1906. https://doi.org/10.1016/j.apenergy.2015.11.077. Tong, Z., Yang, B., Hopke, P.K., Zhang, K.M., 2017. Microenvironmental air quality impact of a commercial-scale biomass heating system. Environ. Pollut. 220, 1112–1120. https://doi.org/10.1016/j.envpol.2016.11.025. Wang, T., Li, Y., Zhang, J., Zhao, J., Liu, Y., Sun, L., Liu, B., Mao, H., Lin, Y., Li, W., Ju, M., Zhu, F., 2018. Evaluation of the potential of pelletized biomass from different municipal solid wastes for use as solid fuel. Waste Manag. 74, 260–266. https://doi.org/ 10.1016/j.wasman.2017.11.043. Weber, K., Quicker, P., 2018. Properties of biochar. Fuel 217, 240–261. https://doi.org/ 10.1016/j.fuel.2017.12.054. Wei, S., Zhu, M., Fan, X., Song, J., Peng, P., Li, K., Jia, W., Song, H., 2019. Influence of pyrolysis temperature and feedstock on carbon fractions of biochar produced from pyrolysis of rice straw, pine wood, pig manure and sewage sludge. Chemosphere 218, 624–631. https://doi.org/10.1016/j.chemosphere.2018.11.177. Xie, M., Shen, G., Holder, A.L., Hays, M.D., Jetter, J.J., 2018. Light absorption of organic carbon emitted from burning wood, charcoal, and kerosene in household cookstoves. Environ. Pollut. 240, 60–67. https://doi.org/10.1016/j.envpol.2018.04.085. Yang, X., Liu, S., Xu, Y., Liu, Y., Chen, L., Tang, N., 2017. Emission factors of polycyclic and nitro-polycyclic aromatic hydrocarbons from residential combustion of coal and crop residue pellets. Environ. Pollut. 231, 1265–1273. https://doi.org/10.1016/j. envpol.2017.08.087. Yanik, J., Duman, G., Karlström, O., Brink, A., 2018. NO and SO2 emissions from combustion of raw and torrefied biomasses and their blends with lignite. J. Environ. Manag. 227, 155–161. https://doi.org/10.1016/j.jenvman.2018.08.068. Yilmaz, E., Wzorek, M., Akçay, S., 2018. Co-pelletization of sewage sludge and agricultural wastes. J. Environ. Manag. 216, 169–175. https://doi.org/10.1016/j. jenvman.2017.09.012. Zeng, T., Weller, N., Pollex, A., Lenz, V., 2016. Blended biomass pellets as fuel for small scale combustion appliances: influence on gaseous and total particulate matter emissions and applicability of fuel indices. Fuel 184, 689–700. https://doi.org/10. 1016/j.fuel.2016.07.047. Zhao, B., O'Connor, D., Zhang, J., Peng, T., Shen, Z., Tsang, D.C.W., Hou, D., 2018. Effect of pyrolysis temperature, heating rate, and residence time on rapeseed stem derived biochar. J. Clean. Prod. 174, 977–987. https://doi.org/10.1016/j.jclepro.2017.11. 013. Zhou, Y., Xing, X.F., Lang, J.L., Chen, D.S., Cheng, S.Y., Wei, L., Wei, X., Liu, C., 2017. A comprehensive biomass burning emission inventory with high spatial and temporal resolution in China. Atmos. Chem. Phys. 17, 2839–2864. https://doi.org/10.5194/ acp-17-2839-2017. Zhu, K., Wang, X., Geng, M., Chen, D., Lin, H., Zhang, H., 2019. Catalytic oxidation of clofibric acid by peroxydisulfate activated with woodbased biochar: effect of biochar pyrolysis temperature, performance and mechanism. Chem. Eng. J. 374, 1253–1263. https://doi.org/10.1016/j.cej.2019.06.006.
https://doi.org/10.1016/j.jaap.2011.12.008. Miranda, M.T., Sepúlveda, F.J., Arranz, J.I., Montero, I., Rojas, C.V., 2018. Analysis of pelletizing from corn cob waste. J. Environ. Manag. 228, 303–311. https://doi.org/ 10.1016/j.jenvman.2018.08.105. Motghare, K.A., Rathod, A.P., Wasewar, K.L., Labhsetwar, N.K., 2016. Comparative study of different waste biomass for energy application. Waste Manag. 47, 40–45. https:// doi.org/10.1016/j.wasman.2015.07.032. Nanda, S., Mohanty, P., Pant, K.K., Naik, S., Kozinski, J.A., Dalai, A.K., 2013. Characterization of north American lignocellulosic biomass and biochars in terms of their candidacy for alternate renewable fuels. Bioenergy. Res. 6, 663–677. https:// doi.org/10.1007/s12155-012-9281-4. Nielsen, H.P., Baxter, L.L., Sclippab, G., Morey, C., Frandsen, F.J., Dam-Johansen, K., 2000. Deposition of potassium salts on heat transfer surfaces in straw-fired boilers: a pilot-scale study. Fuel 79, 131–139. https://doi.org/10.1016/S0016-2361(99) 00090-3. Niu, Y., Tan, H., Wang, X., Liu, Z., Liu, H., Liu, Y., Xu, T., 2010. Study on fusion characteristics of biomass ash. Bioresour. Technol. 101, 9373–9381. https://doi.org/10. 1016/j.biortech.2010.06.144. Ramírez, V., Martí-Herrero, J., Romero, M., Rivadeneira, D., 2019. Energy use of Jatropha oil extraction wastes: pellets from biochar and Jatropha shell blends. J. Clean. Prod. 215, 1095–1102. https://doi.org/10.1016/j.jclepro.2019.01.132. Riaza, J., Khatami, R., Levendis, Y.A., Álvarez, L., Gil, M.V., Pevida, C., Rubiera, F., Pis, J.J., 2014. Combustion of single biomass particles in air and in oxy-fuel conditions. Biomass Bioenergy 64, 162–174. https://doi.org/10.1016/j.biombioe.2014.03.018. Růžičková, J., Kucbel, M., Raclavská, H., Švédová, B., Raclavský, K., Juchelková, D., 2019. Comparison of organic compounds in char and soot from the combustion of biomass in boilers of various emission classes. J. Environ. Manag. 236, 769–783. https://doi.org/10.1016/j.jenvman.2019.02.038. Sansaniwal, S.K., Rosen, M.A., Tyagi, S.K., 2017. Global challenges in the sustainable development of biomass gasification: an overview. Renew. Sus. Energy Environ. 80, 23–43. https://doi.org/10.1016/j.rser.2017.05.215. Silva Perez, D., Dupont, C., Guillemain, A., Jacob, S., Labalette, F., Briand, S., Marsac, S., Guerrini, O., Broust, F., Commandre, J.-M., 2015. Characterisation of the most representative agricultural and forestry biomasses in France for gasification. Waste and Biomass Valorization 6 (4), 515–526. Slopiecka, K., Bartocci, P., Fantozzi, F., 2012. Thermogravimetric analysis and kinetic study of poplar wood pyrolysis. Appl. Energy 97, 491–497. https://doi.org/10.1016/ j.apenergy.2011.12.056. Strandberg, A., Thyrel, M., Skoglund, N., Lestander, T.A., Broström, M., Backman, R., 2018. Biomass pellet combustion: cavities and ash formation characterized by synchrotron X-ray micro-tomography. Fuel Process. Technol. 176, 211–220. https://doi. org/10.1016/j.fuproc.2018.03.023. Tokimatsu, K., Yasuoka, R., Nishio, M., 2017. Global zero emissions scenarios: the role of biomass energy with carbon capture and storage by forested land use. Appl. Energy
8