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Article

Characteristic Evaluation of Different Carbonization Processes for Hydrochar, Torrefied Char, and Biochar Produced from Cattle Manure

by
Eunhye Song
1,
Ho Kim
1,
Kyung Woo Kim
1 and
Young-Man Yoon
2,3,*
1
Bio Resource Center, Institute for Advanced Engineering, Yongin 17180, Republic of Korea
2
Biogas Research Center, Hankyong National University, Anseong 17579, Republic of Korea
3
Plant Engineering Center, Institute for Advanced Engineering, Yongin 17528, Republic of Korea
*
Author to whom correspondence should be addressed.
Energies 2023, 16(7), 3265; https://doi.org/10.3390/en16073265
Submission received: 2 March 2023 / Revised: 31 March 2023 / Accepted: 4 April 2023 / Published: 5 April 2023
Browse Figures
Versions Notes

Abstract

:
The amount of cattle manure generated accounts for over 40% of the livestock manure in South Korea. Most livestock manure is utilized as a fertilizer and a soil amendment. However, the soil nutrients have exceeded saturation in South Korea. Accordingly, cattle manure, including lignocellulosic biomass, was applied for solid fuel production in this study. The three different types of carbonization process, namely, hydrothermal carbonization, torrefaction, and carbonization (slow pyrolysis), were estimated for a comparison of the hydrochar, torrefied char, and biochar characteristics derived from cattle manure. The processes were performed at temperatures ranging from 190 to 450 °C. The evaluation of the hydrochar, torrefied char, and biochar produced by three processes was conducted by the proximate, ultimate, calorific value, fuel ratio, and energy yield, which were used for the analysis of fuel quality. Additionally, the ash properties, including silicon dioxide, chlorine, and base-to-acid ratio (B/A) on hydrochar, torrefied char, and biochar were investigated to predict ash deposition during combustion. These analyses are essential to stabilize the operation of the combustion chamber. The thermogravimetric analysis represented the upgraded quality of hydrochar, torrefied char, and biochar by three different carbonization processes.

1. Introduction

In South Korea, the level of returning excrement from livestock to farmland as nutrient resources for nitrogen and phosphorus has reached a limit [1]. The generation of phosphorus and nitrogen is 300,000 and 120,000 tons per year, respectively, with a load of 100,000 and 70,000 tons [2]. Additionally, seven of the nine provinces in the country are overloaded with nutrients by over 100%. Accordingly, the Ministry of Agriculture and Forestry promoted the introduction of the total nutrient quota system from 2016 to 2019, which was implemented in 2020 [3,4]. In livestock manure, the liquid portion of pork manure is maintained at an appropriate level through a governmental management system. In the case of cattle manure compost, no such system has been established, and it has been noted as a cause of environmental pollution problems, such as green algae [5]. As a result, several investigations are being conducted in the field of cattle manure energization.
The Ministry of Trade, Industry and Energy signed an agreement with three private power generation companies to stop using imported fuel pellets, or renewable energy certificates (RECs), to expand the utilization of unused domestic biomass [6]. Currently, 94% of the biomass pellets used by the three power generation companies rely on importation, which has the effect of creating a market value of about 240 billion won per year. Therefore, this study analyzed the feasibility of applying a process which produces solid fuels using cattle manure to target the pellet market. Furthermore, we analyzed the annual calorific value of imported wood pellets at three private companies and confirmed that 81% of the imported wood pellets can be substituted for the potential volumes of solid fuel produced from cattle manure [6,7,8].
The cattle manure is resistant to pulverization and accompanied by high transportation costs due to its high moisture and low energy density [9]. To produce solid fuel from cattle manure, three processes were selected: hydrothermal carbonization, torrefaction (mild pyrolysis), and carbonization (slow pyrolysis). The three processes convert biomass to a fuel that is more stable, has a higher energy density, friability, and grindability [10,11,12]. These results overcome the limitations of utilizing raw cattle manure in energy generation. The hydrothermal carbonization process is operated within the temperature range of 180–260 °C in a closed system with subcritical water [13]. In addition to having solid fuels as the final product, a liquid waste is produced which can be utilized as a substrate for anaerobic digestion. No pre-treatment is required for this process, but de-watering and drying are required at the end of the process [14,15,16]. The torrefaction and carbonization processes are performed under inert conditions at atmospheric pressure and are categorized according to temperature zones [17,18,19]. In terms of solid fuel production, the torrefaction process is operated at relatively low temperatures in the 200–320 °C range and produces some liquids and gases as byproducts in addition to solid fuels [20,21]. The torrefaction reaction progresses in the presence of limited devolatilization [22]. The aforementioned study on biomass torrefaction reported that a relatively high temperature and short residence time was more effective in enhancing the torrefied char’s heating value [23]. Both processes were conducted after the drying pre-treatment process of the manure. The moisture content of feedstock should be less than 30% [24]. Additionally, for the efficiency of ignition and energy use, cooling is required after the production of solid fuels. On the other hand, the carbonization is characterized by a relatively high temperature range compared with torrefaction, around 400 °C (generally between 300 and 900 °C) with a slow heating rate, typically below 10 °C/min [25]. The process produces syn-gas, and bio-oils in addition to solid fuels known as biochar. Other studies have shown that the carbon in the final biochar increases with increasing pyrolysis temperatures [26,27]. Meanwhile, the oxygen and hydrogen content decrease. Biochars characteristically have a higher proportion of aromatic C, and condensed aromatic structures [28].
In this study, the hydrochar, torrefied char, and biochars of cattle manure were produced by three different carbonization processes. The physicochemical characteristics of hydrochar, torrefied char, and biochars were analyzed by proximate analysis, ultimate analysis, and heating values. The quality of hydrochar, torrefied char, and biochars were investigated by their fuel ratio, van Krevelen diagram, ash composition, and thermogravimetric analyses. The properties of hydrochar, torrefied char, and biochars that originated from cattle manure were used by applying the basic data on a combustion system and help determine a suitable fuel. The fundamental data in this paper are attributed to the feasibility analysis of different carbonization processes using cattle manure for the construction of a demonstration plant.

2. Materials and Methods

2.1. Cattle Manure

The cattle manure used in this study was obtained from a ranch in Icheon-si, South Korea, as shown in Figure 1. The results of the characterization, including moisture content, proximate analysis, elemental analysis, and calorific value, are listed in Table 1. The moisture content was found to be 66.05%, and the proximate analysis confirmed that the ash content was 20% or more in a dried condition, which is higher than the quality standard for livestock manure solid fuels in South Korea [29]. The elemental analysis also showed a high percentage of carbon and oxygen, 30% or more and 20% or more, respectively. The calorific value was found as an average of 12.55 MJ/kg in a dried condition. According to the Ministry of Environment’s notification on the installation of solid fuel facilities for livestock manure, a moisture content of 20% or less was provided as the standard [29]. When a low calorific value was converted, it was confirmed that all of them were below 12.55 MJ/kg. Therefore, a process to upgrade cattle manure as a solid fuel is required.

2.2. Hydrothermal Carbonization

Experiments were performed using a 3 L lab-scale reactor. The hydrothermal carbonization reaction was carried out by combining 1 Kg of cattle manure with 100 g of distilled water, corresponding to a 10 wt.% of the feedstock. A certain amount of water was injected to offset the high viscosity of the sludge and to enhance the heat transfer effect through the steam. Stirring was performed with a constant torque at 250 rpm throughout the entire reaction process using a magnetic drive in order to supply uniform heat from the reactor’s external heating jacket. Under fully sealed conditions, the reaction temperature conditions were set to 190 and 210 °C to achieve pressure conditions above 15–20 bar without additional gas injection, as previously reported [30,31]. The reaction time was 90 min, including 60 min for the temperature-rising step and 30 min for retention of the major reaction. After the reaction was terminated, the reaction mixture was allowed sufficient time to reach ambient pressure and room temperature. The hydrochar was separated from the liquid using 5 μm filter paper. The hydrochar was then dried at 105 °C for 24 h. The weight change and physical properties of the final reaction products were analyzed for characterization.

2.3. Torrefaction and Carbonization

For the torrefaction and carbonization reactions, the cattle manure was dried at 105 °C for 24 h until a constant weight was reached, to exclude the effect of drying on mass flow. Each test was conducted under normal pressures with 250 g of dried cattle manure in a 1 L reactor. Nitrogen was purged until the oxygen concentration in the reactor was less than or equal to 1%, and was continually monitored by a detector. Nitrogen was continuously added at a flow rate of 20 mL/min to maintain inert conditions. Temperature ranges were selected for the torrefaction and carbonization processes based on previous studies [32,33,34,35]. With an electric heater, the temperature was raised to 250 and 300 °C for the torrefaction process and 400 and 450 °C for the carbonization process for 1 h, and then the set temperature was maintained for 30 min. Additionally, the samples were stirred at a speed of 50 rpm to improve the efficient transfer of convective heat supplied from the reactor’s walls by electric heaters. After temperature elevation and temperature hold was complete, and the samples were cooled down to room temperature. Finally, the weight change and physical properties of the torrefaction and carbonized samples were analyzed.

2.4. Mass and Energy Yield

The mass yield was expressed as a percentage of the dry weight of hydrochar, torrefied char, and biochar produced by the three processes based on the weight of cattle manure dried at 105 °C for 24 h, as shown in Equation (1).
Mass   yield = mass   of   dried   biochar   mass   of   dried   raw   material   × 100
The energy densification ratio was the calorific value of the hydrochar, torrefied char, and biochar divided by the calorific value of the feedstock, as shown in Equation (2).
Energy   densification   ratio = LHV   of   char   via   carbonization   processes LHV   of   raw   material
The energy yield, which represents the evaluated energy retained in solid fuels compared with that of the cattle manure [36], was the mass yield times the energy densification ratio, as expressed in Equation (3). Energy yield was utilized as an important performance indicator to compare the energy potential of hydrochar, torrefied char, and biochar produced in each process.
Enegy   yeild = mass   yield   × energy   densification   ratio

2.5. Thermogravimetric Analysis for Pyrolysis Behavior

The thermogravimetric analyses of cattle manure, hydrochar, torrefied char, and biochar were performed in a thermobalance NETZSCH (STA 449 F5) under non-isothermal conditions. A total of about 10 mg of whole dried samples was placed in an alumina crucible. Runs were performed between 100 and 700 °C at a heating rate of 10 °C/min under 100 mL/min of nitrogen. The conversion (α) of the sample in the overall pyrolysis process can be calculated as follows:
α = W 0 − W W 0 − W ∞
where W0, W, and W ∞ represent the instantaneous, initial, and final weights of the sample in the pyrolysis process, respectively.

3. Results

3.1. Comparison of the Properties of the Cattle Manure, Hydrochar, Torrefied Char, and Biochar

Table 2 summarizes the physicochemical properties of hydrochar produced from hydrothermal carbonization (CM-HTC), torrefied chars by torrefaction (CM-TF), and biochars via carbonization (CM-CB). It was found that volatile matter decreased from 56.17% in dry cattle manure (CM) to 11.49–51.37% in the hydrochar, torrefied char, and biochar produced from all carbonization processes, and it decreased in the order of hydrothermal carbonization, torrefaction, and carbonization. Fixed carbon was found to be within the range from 18.43 to 35.35% for all processes compared with 16.34% in cattle manure. It had a maximum increase in the order of hydrothermal, torrefaction, and carbonized by 31.09, 77.93, and 116.91%, respectively, compared with maximum in the raw material. The increase in fixed carbon correlates with the rise in aromatic carbon, which improves fuel quality [37]. Therefore, the rise in fixed carbon involves an increase in the heating value of char [38]. Whereas the reduction in elemental carbon and the heating value from 35.19% to 35.35–35.53%, and from 12.93 MJ/kg to 12.85–12.59 MJ/kg, respectively, was observed from the carbonization process. The reduction signifies a drop in the energy content of the char [39]. Ash content was found to increase from 30.20 to 52.06% compared with 27.49% in the raw material. An increase in the ash content was related to the amplification of the mineral concentration for the release of volatiles from the raw material during the carbonization processes. A rise in the mineral concentration leads to reduction in fuel qualities [38]. Additionally, a preceding study reported that dehydrogenation attributes to a reduction in the heating values at higher temperatures (above 450 °C) [40]. Dehydrogenation ingenerates char with a high percentage of inorganic materials. Thus, the elemental carbon and heating values of biochar produced by carbonization decreased compared with cattle manure.
Through proximate analysis, we estimated the fuel ratio that can be expressed as fixed carbon to volatiles and summarized it as shown in Figure 2. The fuel ratio is used as an indicator of coal quality, with a high volatile fraction being conducive to the ignition behavior of the fuel in a combustor, while high fixed carbon is conducive to stable combustion [41,42]. Low fuel ratios result in a high ignition behavior, which causes spontaneous ignition during storage of the fuels. The high fuel ratios make ignition difficult, but they help maintaining a stable combustion process. The condition of the fuel ratio that maintains stable combustion is known to be in the range of 0.9 to 1.5 [43]. The fuel ratio for hydrochar, torrefied char, and biochar produced from torrefaction was found to be within 0.7–1.09, indicating stable combustion conditions. However, the ash content was found to be somewhat higher, ranging from 39.40 to 44.36%. In the case of the hydrothermal carbonization process, the initial ignition was considered smooth with a fuel ratio of 0.51–0.77, but a slightly higher process temperature was required for stable combustion. The ash content was 30–32.54%, which is considered to satisfy the conditions for stable combustion. The fuel ratio for the carbonization process showed the highest value of 2.71–3.08, indicating some difficulty in the initial ignition, but stable combustion is possible. However, the ash content was the highest, ranging from 53.06 to 53.56%.
Figure 3 presents the extent of the carbonization of hydrochar, torrefied char, and biochar’s solid content in the raw material on the basis of cattle manure utilizing the van Krevelen diagram. The solid content produced by the three different carbonization processes exhibited an obvious drop in the H/C and O/C ratios because of the COOH functional group and H2O leaving via dehydration and decarboxylation compared with that of cattle manure [44,45,46]. The low H/C and O/C ratios indicate the presence of more condensed structures [47,48].
The energy densification ratio and energy yield for the three carbonization processes are shown in Figure 4. For hydrothermal and carbonization processes, the energy densification ratio increased as the reaction temperature increased, but the ratio decreased for torrefaction. Similar to previous studies, we found that severe torrefaction at 300 °C reduced the energy density and is therefore not suitable for cattle manure [33]. The highest energy densification ratio of 1.18 was found for the hydrothermal carbonization process at 210 °C, and a similar value of 1.14 was found for the torrefaction process at 250 °C. For the carbonization process, on the other hand, the energy densification ratio was found to be the lowest at 0.97–0.99. On the other hand, the energy yield considering the calorific value and mass yield showed the highest value of 78.52% in the torrefaction process under 250 °C, and a similar value of 77.56% was found in the hydrothermal carbonization at 210 °C. On the other hand, the energy yield for the carbonization process was found to be 49.69–50.94%, which is considered unfavorable compared with other processes in terms of solid fuel production. The behavior of the three carbonizations is very similar to the findings of previous studies [31,33,34].

3.2. Characteristics of Ash in Cattle Manure, Hydrochar, Torrefied Char, and Biochar

The ash content, a non-combustible material, is one of the quality standards required for hydrochar, torrefied char, and biochar as a solid fuel [49]. Ashes do not burn in the furnace or boiler, and some fine particles move with the flow of the flue gas. When the temperature of the combustion chamber is higher than the melting point of the ash, due to the high flue gas temperature, the ash particles hit the water pipe wall in a molten state and rapidly cool down, agglomerate, adhere, and accumulate on the water pipe wall. This phenomenon is called slagging, and it is called fouling when the ash passes through the convective heating surface with the combustion gases at a relatively low temperature, condenses and adheres to the superheater or reheater, and solidifies [50]. This ash residue reduces heat transfer in the heat exchanger tubes, resulting in a low boiler efficiency and capacity, obstructed flow of internal fluids, mechanical damage, and corrosion. This may even require a shutdown, resulting in energy and economic losses [51].
Various indices have been reported for predicting coal ash adhesion based on basic composition analysis and laboratory-scale experimental data, and are summarized in Table 3 [52,53,54]. The elemental composition of samples for ash in an oxidized atmosphere were obtained by X-ray florescence (XRF) analysis.
Silica is the dominant element in slag and has been confirmed to form a sticky substance in slagging [55,56]. The content of silica in the fuel ash was found to correlate with the degree of slag formation in the burner. As shown in Figure 5, the frequency of slagging, predicted by utilizing SiO2 in the ash of the generated cattle manure-based hydrochar, torrefied char, and biochar in the raw material, was considered as low. Compared with the raw material, a slight improvement in SiO2 was observed in the carbonization process except for the hydrothermal carbonization process at 210 °C. It was found that SiO2 decreased with increasing reaction temperature in the hydrothermal and carbonization processes, but it increased in torrefaction. Previous studies have reported the removal of silicon during hydrothermal carbonization in a specific range from 200 to 230 °C [57,58]. The subcritical conditions of water during the hydrothermal carbonization process characterize a lower density and viscosity than that of water at normal conditions [59]. In these conditions the removal of simple ionic salts in the cattle manure matrix can be enhanced. The increase in the dielectric content, ionic dissociation constant, and decrease in pH of subcritical water are attributable to the removal of ionic-bonded inorganics via ion exchange and the dissolving of inorganic salts [60,61,62]. Accordingly, a pronounced decrease in hydrochar produced at 210 °C was observed.
Chlorine (Cl) plays a role for the reaction of potassium and silica, resulting in the formation of ash fusibility and slag at the operating temperatures of boilers, ranging from 800 to 900 °C [63,64]. Therefore, Cl can be an indicator of the slagging and fouling tendencies in biomass fuels [65,66]. The content of Cl in the ash of the hydrochars, torrefied chars, and biochars produced in this study is shown in Figure 6. The Cl content for both dry cattle manure and the hydrochars, torrefied chars, and biochars was 0.5% or more, categorizing into the extremely high fouling and slagging tendencies. The Cl fraction was analyzed as 7.34% for cattle manure and it increased to 7.54–7.84% for torrefied chars and carbonized biochars, higher than the raw material. On the other hand, hydrochar had a Cl content in the range of 2.59 to 2.77%, representing a 64.69% reduction compared with the dry process. This is due to two main mechanisms in the hydrothermal carbonization process: elimination and substitution reactions [67]. Removal of HCl and substitution of Cl can convert soluble organic chlorine to inorganic chlorine. Thus, the removal of chlorine from the raw material is achieved [68,69]. In particular, the degradation of lignocellulosic components promotes de-chlorination reactions. Lignin, hemicellulose, and cellulose provide many free -OH bonds [70], promoting the substitution of Cl [71].
There are basic components (i.e., Fe2O3, CaO, MgO, Na2O, and K2O) in the ash lower the melting temperature [72]. These groups are categorized as Group B. P2O5 is reported to lower the melting point in fly ash and was, accordingly, added to Group B [53,72]. The acidic components (i.e., SiO2, Al2O3, and TiO2) increase the melting point and are defined as Group A. The base-to-acid (B/A) mass ratio can be expressed by the equation below, and can predict the deposition behavior of ash [53,73,74].
B A   ratio = Fe 2 O 3 + CaO + MgO + Na 2 O + K 2 O + P 2 O 5 SiO 2 + Al 2 O 3 + TiO 2
Figure 7 depicts the B/A ratio in the cattle manure and the hydrochars, torrefied chars, and biochars. For all samples, the maximum basic components were 70% higher than the acidic components in the ash. An additional process for the elimination of basic components in ash is required for stable combustion operation.

3.3. Thermogravimetric Analysis of the Cattle Manure, Hydrochar, Torrefied Char, and Biochars during Pyrolysis

Figure 8 and Figure 9 exhibit the TG and DTG curves, respectively, for the cattle manure and the hydrochars, torrefied chars, and biochars in inert atmospheres. Table 4 summarizes the reaction indexes, comprising initial, maximum, final pyrolysis temperatures, maximum degradation rates, and residual fractions. The kinetics parameters and mass fractions were calculated according to the residual mass of the dried samples. The drying process was not included in this study. The main stages of thermal decomposition and the corresponding mass losses of the cattle manure and the hydrochars, torrefied chars, and biochars during the pyrolysis occurred over a wide temperature range. In addition, asymmetrical DTG curves were obtained, which primarily verified the use of heterogeneous materials. Examples of such materials include biomasses obtained between 178 and 696 °C through the decomposition of cattle manure, including general lignocellulosic biomass materials and extractives [75]. Thus, the main components of cattle manure comprise cellulose, hemicellulose, lignin, and partially undigested organic matter. Based on the mass loss profiles of the raw materials, hydrochars, torrefied chars, and biochars all exhibited different behaviors. In the raw material sample, the main weight loss occurred from 185 to 675 °C (approximately 53% of the total weight loss), and the maximum weight loss rate was 0.048 min−1 (approximately at 320 °C).
The main weight loss of the hydrochars was observed to start at approximately 135–140 °C, which is lower than that of the raw materials. As the temperature increased to 315–325 °C, fractional weight loss rates increased, achieving maximum values of 0.0364–0.0438 min−1. For the torrefied chars, two visible peaks can be observed in the DTG curves corresponding to the maximum mass loss. The first peak corresponds to the degradation of cellulose at 309–310 °C, and the second relates to lignin at 419–460 °C. Such a tendency coincides with the findings of other studies [76]. The degradation of the biochars produced via carbonization occurs at temperatures of 370–450 °C, which may imply that most hemicellulose was decomposed.
The deduced data are conformable with the fixed carbon and char obtained through the proximate analyses in Table 1. With respect to the characteristics of solid fuels, hydrochars, torrefied chars, and biochars of the cattle manure exhibit the maximum weight loss. Further, the amount of volatile matter is lower than those associated with the raw materials during pyrolysis, and the maximum pyrolysis temperature shifted to the right as the temperature increased. This can be primarily attributed to the breaking of weak bonds and the subsequent coalification process resulting from a series of reactions during the different carbonization processes [77,78]. Based on the three carbonization processes considered in this study, the maximum weight loss rates and the amount of volatile matter decreased with the increasing reaction temperature.

4. Conclusions

The characteristics of hydrochar, torrefied char, and biochar derived from cattle manure were analyzed to ascertain the adequacy of different carbonization processes. The main focus concerned comparing the extent of solid fuel quality and energy densification.
For the three carbonization processes, with increasing temperature, the volatile content reduced, while the fixed carbon increased compared with the cattle manure. These results imply an improved fuel quality. For all processes, the fuel ratio increased, and the O/C and H/C ratios decreased. The findings also demonstrate the conversion of cattle manure into a coal-like solid fuel. The heating value increased for hydrochars and torrefied chars, while for biochars, it decreased, caused by an increase in the mineral concentration. Concerning energy densification and energy yield, the hydrothermal carbonization at 210 °C and torrefaction at 250 °C showed the highest values and were considered optimal processes for the efficient production of solid fuels derived from cattle manure.
The ash composition of hydrochars, torrefied chars, and biochars was analyzed to predict the slagging and fouling tendencies in the combustion process as solid fuels. With respect to the silica content, the hydrochars, torrefied chars, and biochars tended to have low slagging occurrences. Conversely, based on the Cl and B/A ratios, hydrochars, torrefied chars, and biochars were considered in this study to have high probabilities of slagging and fouling occurrences. Hence, eliminating chlorine and basic oxide in the ash is required for stable combustion operation in industrial boilers.
The pyrolysis behaviors of hydrochars, torrefied chars, and biochars were distinct via thermogravimetric analysis. The solid fuels of the cattle manure were improved by the different carbonization processes demonstrating that the maximum degradation and the amount of volatiles were lower than those of the cattle manure in the pyrolysis process. It can thus be concluded that chars produced by the three different carbonization processes have appropriate characteristics to be used for incineration and boiler operations.

Author Contributions

Conceptualization, E.S.; methodology, E.S. and Y.-M.Y.; validation, E.S. and H.K.; formal analysis, K.W.K. and E.S.; investigation, K.W.K., H.K. and E.S.; resources Y.-M.Y. and E.S.; data curation, H.K. and E.S.; writing—original draft preparation, E.S.; writing—review and editing, E.S.; supervision, H.K. and Y.-M.Y.; project administration, H.K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry and Energy (MOTIE) of the Republic of Korea (No. 20183010092750).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest. The funding agencies had no role in the design of the study; in the collection analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Sampling site (a) and collecting procedure (b) for cattle manure in Icheon-si, South Korea.
Figure 1. Sampling site (a) and collecting procedure (b) for cattle manure in Icheon-si, South Korea.
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Figure 2. The fuel ratio of the cattle manure, hydrochar, torrefied char, and biochar.
Figure 2. The fuel ratio of the cattle manure, hydrochar, torrefied char, and biochar.
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Figure 3. The van Krevelen diagram of the cattle manure, hydrochars, torrefied chars, and biochars.
Figure 3. The van Krevelen diagram of the cattle manure, hydrochars, torrefied chars, and biochars.
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Figure 4. Energy densification ratio and energy yield of the hydrochar, torrefied char, and biochar derived from cattle manure.
Figure 4. Energy densification ratio and energy yield of the hydrochar, torrefied char, and biochar derived from cattle manure.
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Figure 5. Silicon dioxide content in the cattle manure, hydrochar, torrefied char, and biochar.
Figure 5. Silicon dioxide content in the cattle manure, hydrochar, torrefied char, and biochar.
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Figure 6. Chlorine content in the cattle manure, hydrochar, torrefied char, and biochar.
Figure 6. Chlorine content in the cattle manure, hydrochar, torrefied char, and biochar.
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Figure 7. B/A ratio in the cattle manure, hydrochar, torrefied char, and biochar.
Figure 7. B/A ratio in the cattle manure, hydrochar, torrefied char, and biochar.
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Figure 8. Experimental pyrolytic TG curves of the cattle manure, hydrochar, torrefied char, and biochar.
Figure 8. Experimental pyrolytic TG curves of the cattle manure, hydrochar, torrefied char, and biochar.
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Figure 9. Experimental pyrolytic DTG curves of the cattle manure, hydrochar, torrefied char, and biochar.
Figure 9. Experimental pyrolytic DTG curves of the cattle manure, hydrochar, torrefied char, and biochar.
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Table
Table 1. The characteristic properties of cattle manure.
Table 1. The characteristic properties of cattle manure.
PropertiesCattle Manure
Moisture (wt. %, ar 1)66.05
Proximate analysis (wt. %, db 2)
Volatile matter56.17
Fixed carbon16.34
Ash27.49
Ultimate analysis (wt. %, db 2)
Carbon36.19
Hydrogen4.36
Oxygen29.12
Nitrogen1.87
Sulfur0.97
Calorific analysis (MJ/kg, db 2)
Lower heating value12.93
1 as received, 2 on dry basis.
Table
Table 2. Proximate, ultimate, and calorific analysis of the feedstock, hydrochar, torrefied char, and biochar samples.
Table 2. Proximate, ultimate, and calorific analysis of the feedstock, hydrochar, torrefied char, and biochar samples.
DescriptionsCM
(Raw)		CM-HTC
(190 °C)		CM-HTC
(210 °C)		CM-TF
(250 °C)		CM-TF
(300 °C)		CM-CB
(400 °C)		CM-CB
(450 °C)
Proximate analysis (wt.%, d.b. 1)
Volatiles56.1746.37 38.04 35.59 26.56 12.50 11.49
Fixed carbon16.34 23.43 29.42 25.00 29.08 33.94 35.45
Ash27.49 30.20 32.54 39.40 44.36 53.56 53.06
Ultimate analysis (wt.%, db. 1)
Carbon36.1937.5241.1337.637.9735.3535.53
Hydrogen4.363.884.463.132.671.751.41
Oxygen29.12 20.718.5616.87 12.21 6.93 7.77
Nitrogen1.872.572.82.081.841.511.27
Sulfur0.970.520.710.920.950.90.96
Calorific value (MJ/kg, d.b. 1)
LHV12.93 13.35 15.23 14.77 13.77 12.59 12.85
1 A dry basis.
Table
Table 3. Slagging and fouling indices.
Table 3. Slagging and fouling indices.
IndexSlagging and Fouling Indices
LowMediumHighExtremely High
SiO2 (%)<2020~25>25-
Cl (%)<0.20.2~0.30.3~0.5>0.5
B/A ratio<0.50.5~11~1.75>1.75
Table
Table 4. Characteristics of the cattle manure, hydrochar, torrefied char, and biochar during pyrolysis.
Table 4. Characteristics of the cattle manure, hydrochar, torrefied char, and biochar during pyrolysis.
SampleTi
(°C)		Tpk
(°C)		Tf
(°C)		Rpk
(min−1)		Mf
(g/g)
CM 185 320 675 4.80 × 10−20.47
CM-HTC (190 °C)140 315 675 4.38 × 10−20.51
CM-HTC (210 °C)135 335 675 3.64 × 10−20.59
CM-TF (250 °C)190 419 675 8.84 × 10−30.72
CM-TF (300 °C)200 460 675 6.71 × 10−30.74
CM-CB (400 °C)370 610 675 4.03 × 10−30.85
CM-CB (450 °C)450 635 680 4.02 × 10−30.88
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Song, E.; Kim, H.; Kim, K.W.; Yoon, Y.-M. Characteristic Evaluation of Different Carbonization Processes for Hydrochar, Torrefied Char, and Biochar Produced from Cattle Manure. Energies 2023, 16, 3265. https://doi.org/10.3390/en16073265

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Song E, Kim H, Kim KW, Yoon Y-M. Characteristic Evaluation of Different Carbonization Processes for Hydrochar, Torrefied Char, and Biochar Produced from Cattle Manure. Energies. 2023; 16(7):3265. https://doi.org/10.3390/en16073265

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Song, Eunhye, Ho Kim, Kyung Woo Kim, and Young-Man Yoon. 2023. "Characteristic Evaluation of Different Carbonization Processes for Hydrochar, Torrefied Char, and Biochar Produced from Cattle Manure" Energies 16, no. 7: 3265. https://doi.org/10.3390/en16073265

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