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29 August 2025

12 Pages

Analysis of Fuel Properties for Fifty Kinds of Typical Alternative Fuels

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1
Sinoma International Environmental Engineering Co., Ltd., Beijing 100102, China
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School of Energy and Mechanical Engineering, Nanjing Normal University, Nanjing 210023, China
3
School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China
*
Author to whom correspondence should be addressed.
Processes2025, 13(9), 2767;https://doi.org/10.3390/pr13092767
This article belongs to the Special Issue Clean Thermal Utilization of Solid Carbon-Based Fuels
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Abstract

With CO2 generation and emissions requirements, the cement industry faces huge pressure for reducing carbon emissions. Choosing alternative fuels instead of coal is a promising approach. However, the fuel properties of the alternative fuels have not been comprehensively studied. In this work, the fifty typical alternative fuels were selected based on the compositions for different classifications, and the basic fuel properties including proximate analysis, ultimate analysis, and low calorific values were analyzed. Most fuels from plastics and clothes have relatively low moisture; the values of as-received basis moisture (Mar) and air-dry basis moisture (Mad) of the others are all lower than 30 wt%. However, the alternative fuels of plastic and cloth all have relatively high contents of air-dry basis volatile compounds (Vad) (>60 wt%), and they all have low contents of air-dry basis fixed carbon (FCad) (commonly <20 wt%) and air-dry basis ash (Aad) (<30 wt%). The air-dry basis carbon contents (Cad) of plastics are higher than 40 wt%, while the Cad values of biomass are lower than 50 wt%. As for air-dry basis hydrogen (Had), the contents are all lower than 14 wt% and relatively stable for different kinds of alternative fuels. As for air-dry basis nitrogen (Nad), the contents are all lower than 9 wt%, and most of them are lower than 3 wt%. In addition, the contents of air-dry basis sulfur (Sad) of different alternative fuels are also lower than 3 wt%, while plastics, biomass, and clothes are all lower than 1 wt%. Also, the low calorific values (Qnet,ar) for the alternative fuels of plastic are commonly high, and the values for biomass are commonly between 500 and 1500 kJ/kg, while Qnet,ar values for the alternative fuels of cloth and others vary. The fuel properties of the fifty typical alternative fuels can guide fuel selection and optimization when they are mixed for combustion with coals in cement decomposition furnaces.

1. Introduction

Nowadays, the CO2 emission amount is continuously increasing with the development of society, and the high CO2 emissions lead to temperature rise [1,2]. The phenomenon results in the melting of glaciers and so on, bringing devastating consequences to the living environment of human beings [3,4]. Under the huge pressure of CO2 emission reductions, many industries face requirements for reducing CO2 generation and emissions [5,6]. Cement production plants are traditional and a key CO2 emission source, where carbon-based fuels such as coals, biomass, and so on are combusted to generate CO2; cement production plants thus also need CO2 reduction and control [7,8].
During the production process of traditional cement, cement raw materials are mixed with coal for combustion, which leads to CO2 emissions. Therefore, in order to reduce the CO2 generation and emission in cement production plants, many studies focus on decreasing coal consumption by adding some other carbon-based fuels [9,10]. The carbon-based fuels used instead of coal in cement decomposition furnaces are named alternative fuels, and they are typically composed by plastics, biomass, and so on [11,12]. The specific contributions of published research on alternative fuels are shown in Table 1. As for the contributions of the alternative fuels, their use in the cement industry can also reduce energy and environmental costs, because alternative fuels are cheaper and can help reduce heavy metals emission [10]. Eugeniusz proposed the usage of alternative fuels in the cement industry and analyzed the specific economic and ecological benefits [13]. Huh studied the effect of fuel price on cement production and proposed guidance for alternative fuel selection [14]. Ali provided a comprehensive analysis of options for future cements and an up-to-date summary of the different alternative fuels and binders that can be used in cement production to mitigate carbon dioxide emissions [15]. In addition, the fuel properties are key for the selection of fuel and combustion optimization; it is thus important to study the fuel properties of alternative fuels. However, there are no comprehensive studies focusing on fuel properties for many kinds of typical alternative fuels.
Table 1. Specific contributions on alternative fuels of published works.
Herein, the fifty typical alternative fuels were selected based on the compositions for different classifications, and the basic fuel properties including proximate analysis, ultimate analysis, and low calorific values were comprehensively analyzed.

2. Experimental and Analysis Methods

2.1. Alternative Fuel Sample Treatment

The alternative fuels were composed mainly of biomass, plastics, waste clothes, and other kinds. Thus, based on the alternative fuel types and production amounts, fifty different typical alternative fuels were collected from Liyang Zhongcai Environmental Protection Co., Ltd. in Changzhou located in China. The collected alternative fuels were firstly cut or ground into uniform sizes based on whether the alternative fuels can be ground, and the samples were stored and labeled as shown in Figure 1 for subsequent usage.
Figure 1. Photos and numbers of alternative fuel samples.
In addition, the specific alternative fuels are named and listed in Table 2. According to compositions of the collected alternative fuels, the fifty samples can be classified into four groups as plastic, biomass, cloth, and others, and the specific classification is also shown in Table 2. The format No.: XXX: A/B/C/D is used to show the name and classification, where No. corresponds to the number in Figure 1, XXX is the name, and A/B/C/D is plastic/biomass/cloth/others.
Table 2. The specific names and classifications of the fifty alternative fuels in this work.

2.2. Fuel Property Analysis and Calculation Methods of Alternative Fuels

In order to study the fuel properties, the fifty alternative fuel samples were used to conduct proximate analysis, ultimate analysis, and analysis of low calorific value. As for proximate analysis, the parameters (Mar, Mad, Vad, FCad, Aad; wt%) were studied based on the relevant national standard GB/T 28731 [16]. Proximate analysis results for air-dry basis were automatically determined by a proximate analyzer (Kaiyuan, China, 5E-MAG6700I). Mar was analyzed by Equation (1), where Mf (wt%) was mass percent of external moisture, calculated by Equation (2).
M a r = M f + M a d ( 100 − M f 100 )
M f = m 1 − m 2 m 1 × 100 %
Mf was measured as follows: An appropriate amount of the sample was weighed, and the initial mass was recorded as m1 (g). The sample was spread in a drying oven at 40 °C to dry until the mass was constant (weighed at an interval of 2 h, with a mass change ≤ 0.1%). The mass after drying was recorded as m1 (g).
During ultimate analysis processes, appropriate amounts of the alternative fuel samples were, respectively, placed into an ultimate analyzer (Kaiyuan, China, 5E-CHN2200) to acquire Car, Har, Nar, (wt%) and a sulfur element analyzer (Kaiyuan, China, 5E-AS3200B) to obtain Sar (wt%) based on the relevant national standard GB/T 31391 [17]. In addition, Oar (wt%) was calculated by difference. Low calorific values (Qnet,ar, kJ/kg) of the fifty alternative fuels were recorded and measured by a calorific value analyzer (China Lichen, LC-CV-430) based on the relevant national standard GB/T 30727 [18]. In addition, in order to compare the low calorific values of the fifty alternative fuels, Qnet,ar was also calculated by Mendeleev’s formula, which is shown in Equation (3), and the formula was based on low calorific values from coals and as shown in many books about coal properties. The error was calculated by Equation (4):
Qnet,ar = 339Car + 1030Har − 109(Oar − Sar) − 25Mar
Error = C a l c u l a t e d   v a l u e − E x p e r i m e n t a l   v a l u e C a l c u l a t e d   v a l u e × 100 %

3. Results and Discussion

3.1. Proximate Analysis Results of Alternative Fuels

The proximate analysis experiments of the fifty alternative fuels were measured two times to be averaged to reduce the relative errors, and the results are shown in Table 3. It can be seen that the compositions (Mar, Mad, Vad, FCad, Aad) of different alternative fuels are different, and they were further analyzed based on the classifications; the results are shown in Figure 2A–E.
Table 3. Proximate analysis results (wt%) of alternative fuels.
Figure 2. (A) Mar of different alternative fuels. (B) Mad of different alternative fuels. (C) Vad of different alternative fuels. (D) FCad of different alternative fuels. (E) Aad of different alternative fuels.
Figure 2A,B show Mar and Mad of different alternative fuels based on the classification, respectively, and it can be clearly seen that Mar and Mad show some obvious characteristics. For plastic, most of the fuels have relatively low moisture except for washing material, because it is obtained by washing; for biomass, the moisture is varied since the compositions are different, especially for sludges. For cloth, most of them have relatively low moisture except for wool fabric; Mar and Mad of the others are all lower than 30 wt%. However, the alternative fuels of plastic and cloth all have relatively high content of volatile compounds (higher than 60 wt%), and they all have low contents of fixed carbon (commonly lower than 20 wt%) and ash (lower than 30 wt%). As a whole, the Aad values of clothes and plastics are lowest since there are not many additives in them. The others are composed of inorganic matter, leading to high values of Aad. In addition, the fixed carbon contents of the alternative fuels except for carbon black are all lower than 30 wt%, and they are similar, which can determine the burnout characteristics.

3.2. Ultimate Analysis Results of Alternative Fuels

The ultimate analysis experiments of the fifty alternative fuels were also analyzed two times and averaged to reduce the relative errors, the results of which are listed in Table 4. Cad, Had, Nad, and Sad were analyzed by an experimental instrument, and Oad was calculated by the differences. It can be found that the element compositions for the alternative fuels are different. Furthermore, they are also analyzed based on the classification, and the results are shown in Figure 3A–D. The figure for Oar of different alternative fuels is not shown, because the parameter was calculated, rather than measured.
Table 4. Ultimate analysis results (wt%) of alternative fuels.
Figure 3. (A) Cad of different alternative fuels. (B) Had of different alternative fuels. (C) Nad of different alternative fuels. (D) Sad of different alternative fuels.
Figure 3A shows the Cad of different alternative fuels, and it can be clearly seen that carbon contents of plastics are higher than 40 wt%, while the carbon contents of biomass are lower than 50 wt%. In addition, the alternative fuels for cloth and others varied in carbon content. Hydrogen content values are all lower than 14 wt% and are relatively stable for different kinds of alternative fuels: Had of plastics is commonly higher since they are composed by organic polymers, while Had of the others is lowest since their main component is inorganic matter. As for nitrogen content, the values are all lower than 9 wt%, and most of them are lower than 3 wt% which is lower than most coals, suggesting the alternative fuels can produce fewer nitrogen oxides when they are reasonably blended for combustion. In addition, Sad of different alternative fuels are also lower than 3 wt%, while plastics, biomass, and clothes are all lower than 1 wt%. The results of sulfur contents also directly show that the alternative fuels can be blended before the combustion process to reduce sulfur when the sulfur content of coal is high, which is beneficial for gas pollutant control.

3.3. Low Calorific Value Results of Alternative Fuels

The low calorific value (Qnet,ar) experiments of the fifty alternative fuels were still repeatedly analyzed two times, and the results were averaged to reduce relative errors. The experimental values of Qnet,ar are shown in Table 5. In addition, the calculated values of Qnet,ar were calculated based on Equation (3), where the proximate and ultimate analysis results were transformed to as-received basis. Moreover, the errors were calculated by Equation (4), and the results are listed in Table 5.
Table 5. Low calorific value results (Qnet,ar, kJ/kg) and errors of alternative fuels.
Figure 4 shows the relationship of low calorific values by experimental and calculated methods, and it can be seen that the as-received basis low calorific values calculated by Mendeleev’s formula are generally close to the experimental values, which also verifies the rationality of the experimental detection results. Furthermore, the deviation rates of the low calorific value of the 50 alternative fuels are mostly below 10%, and the rest are mainly between 10% and 20%. This is primarily due to the following reasons: (1) the complexity and non-uniformity of the components of the alternative fuel samples; (2) Mendeleev’s formula is mainly derived from coals and is relatively less adaptable to alternative fuels. The average deviation rate of the 50 samples was calculated to be 6.1%, which was relatively small, indicating the reliability of the experimental results.
Figure 4. The correlation between Qnet,ar-Exp. and Qnet,ar-Cal.
Also, Qnet,ar values of different alternative fuels for the specific classification are shown in Figure 5. It can be found that the alternative fuels of plastic commonly have high values, and biomass has commonly low values between 500 and 1500 kJ/kg, while the alternative fuels for cloth and others have varied values as for different alternative fuels. The low calorific values of the fifty alternative fuels can guide fuel selection and optimization when they are mixed for combustion with coals in cement decomposition furnaces.
Figure 5. Qnet,ar of different alternative fuels.

4. Conclusions

The fifty typical alternative fuels were selected based on the compositions for different classifications, and the basic fuel properties including proximate analysis, ultimate analysis, and low calorific values were comprehensively analyzed.
Most alternative fuels from plastics and clothes have relatively low moisture; Mar and Mad of the others are all lower than 30 wt%. However, the alternative fuels of plastic and cloth all have relatively high contents of volatile compounds (>60 wt%), and they all have low contents of fixed carbon (commonly <20 wt%) and ash (<30 wt%). The carbon contents of plastics are higher than 40 wt%, while the carbon contents of biomass are lower than 50 wt%. As for hydrogen content, they are all lower than 14 wt% and relatively stable for different kinds of alternative fuels. As for nitrogen content, they are all lower than 9 wt%, and most of them are lower than 3 wt%. In addition, Sad values of different alternative fuels are also lower than 3 wt%, while plastics, biomass, and clothes are all lower than 1 wt%. Also, Qnet,ar values for the alternative fuels of plastic are commonly high, and biomass commonly shows values between 500 and 1500 kJ/kg, while Qnet,ar values for the alternative fuels for cloth and others are varied.
The work provided abundant basic fuel properties of typical alternative fuels, which can be used to analyze actual applications by coupling with AI.

Author Contributions

Conceptualization, J.Y. and H.W. (Hao Wu); data curation, Q.R.; formal analysis, Y.G.; funding acquisition, H.W. (Hao Wu); investigation, Y.G., J.Y., W.R. and Q.R.; project administration, H.W. (Hao Wu); supervision, H.W. (Hao Wu); validation, H.W. (Hewei Wang); visualization, Y.Z. and J.J.; writing—original draft, J.Y. and Q.R.; writing—review and editing, Y.G. and H.W. (Hao Wu). All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available because they are part of an ongoing study.

Acknowledgments

The assistance from School of Energy and Mechanical Engineering of Nanjing Normal University is acknowledged. Also, the authors would like to acknowledge the ultimate analysis provided by zkec (www.zkec.cc, accessed on 1 August 2025).

Conflicts of Interest

Authors Yanpeng Guo, Jinhui Yu, Wenjie Rui, Hewei Wang and Yanlong Zhang were employed by the company Sinoma International Environmental Engineering Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The companies 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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