Thermogravimetric Experimental Study on the Co-Combustion Characteristics of Coal and Salix

Abstract

To study the co-combustion characteristics of coal and Salix, thermogravimetric analysis is adopted to evaluate their co-combustion performance. The effect of blending ratios and synergistic are investigated in detail. Furthermore, kinetic analysis is performed. The results show that the incorporation of Salix into coal enhances combustion performance, with significant improvements observed at higher blending ratios. The ignition temperature decreases notably from 444 °C to 393 °C, highlighting an improvement in ignition properties. The primary weight loss peak shifts from 490 °C at a 15% biomass blend to approximately 320 °C at a 100% blend. Co-combustion demonstrates synergistic effects, with a 15% biomass blend optimizing combustion between 400 °C and 530 °C, while a 30% blend inhibits it. Additionally, temperatures above 600 °C exhibit an inhibitory effect. The activation energy is reduced to 25.38 kJ mol⁻¹ at a 30% blend ratio and further to 23.06 kJ mol⁻¹ at a 15% blend ratio at a heating rate of 30 K min⁻¹. Increasing the biomass blend ratio and heating rate lowers the activation energy, which means facilitating the reaction process.

1. Introduction

In contemporary society, the issues of energy crises and environmental pollution are becoming increasingly severe [1,2]. The energy resources of China are characterized by abundant coal, scarce oil, and limited natural gas. However, the combustion of coal results in significant emissions of CO₂ and other pollutants, which greatly impact the achievement of carbon neutrality and exacerbate environmental issues. Biomass, as the fourth largest energy source following coal, oil, and natural gas, offers the benefit of reducing pollutant emissions [3,4]. Additionally, China is rich in biomass resources, and utilizing these resources could not only mitigate environmental pollution but also address the problem of biomass resource wastage [5,6].

Biomass is an optimal renewable energy source, offering benefits such as renewability, low emissions of sulfur and nitrogen, and nearly net-zero CO₂ emissions—where the CO₂ absorbed during growth approximately equals the emissions during combustion. Additionally, its wide distribution enhances accessibility and utilization [7,8,9]. Salix, a common biomass in the desert regions of Inner Mongolia, is a drought-resistant and salt-tolerant shrub [10]. Salix branches are highly flammable, and the plant is resilient, allowing for multiple harvests, maturing within three years, and thriving with repeated cutting [10,11]. Therefore, utilizing Salix as a dedicated energy crop for fuel presents promising developmental prospects [12]. If biomass resources (especially agricultural and forestry wastes) are coupled with large-scale coal-fired units, it will greatly reduce CO₂ emissions. At the same time, the benefits of large-scale coal-powered units would increase the energy utilization of biomass resources and reduce the pollutants generated during the utilization of biomass resources to the emission level of coal-fired units [13]. The co-combustion of coal and biomass has become an effective method to utilize biomass resources [14]. Biomass exhibits a high volatile content, with pyrolysis occurring between 200 °C and 350 °C. During this process, the combustion of volatile components is vigorous, resulting in a volatile release exceeding 90%. Biomass is characterized by its ease of ignition and combustion. Upon pyrolysis, it produces biochar, which possesses a large specific surface area, high reactivity, and facile combustibility. Blending biomass with pulverized coal enhances combustion performance by facilitating the earlier ignition of the pulverized coal. Moreover, the co-combustion of coal and biomass could also effectively reduce greenhouse gas and pollutant emissions [15].

Numerous scholars have conducted studies [16,17,18,19,20,21] on the combustion performance and process of coal and biomass blends. Si et al. [16] and Liao et al. [17] employed thermogravimetric analysis to explore the burning process of coal blended with different biomasses and obtained that the blended biomasses could reduce the ignition temperature and the burnout temperature and improve the combustion stability index and combustion performance. Liu et al. [18] used thermogravimetric (TG) analyzers to research the combustion characteristics of biomasses and anthracite coals at various ratios and heating rates. The Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods were employed to compute the kinetics, and the interactions between the blended fuels were analyzed. The findings indicated that the combustion characteristics of water hyacinth surpass those of anthracite, primarily due to its higher volatile content. The interactions between water hyacinth and anthracite during the blending process were also examined. Liao et al. [19] explored the co-combustion characteristics, gaseous pollutant emissions, and analysis of the kinetics involved in the co-combustion of coal slurry with camphor wood and wheat straw. Guo et al. [20] conducted a comparative examination of biomass and coal combustion using thermogravimetric analysis. The results indicated that the combustion of biomass pellets (BP) with bituminous coal (BC) occurs in three distinct stages. In contrast, the blend of BP with Xiaolongtan lignite (XL) involves two phases: volatile combustion and the char burning of both BP and XL. The interaction between BP and XL was observed to be more significant than that between BP and BC. The lowest activation energy for biomass blending was achieved with a BP ratio of 30% for BC and 10% for XL. Prayoga et al. [21] employed Thermogravimetric Differential Thermal Analysis (TG-DTA) at heating rates of 5, 10, 15, and 20 K min⁻¹ to evaluate six coal and oil palm biomass blends. The study identified the optimal blend for combustion as comprising 76% low-rank coal, 19% middle-rank coal, and 5% oil palm leaves. Previous studies [16,17,19,20,22] have primarily investigated the co-combustion characteristics of agricultural residues (such as corn stalks) and coal. Salix, as a dedicated energy crop, is characterized by rapid growth, ease of harvest, and high combustibility, making it suitable for a wide range of applications. The understanding of combustion characteristics is considered fundamental to the efficient co-combustion of coal and Salix. However, studies on the co-combustion characteristics of coal and Salix are limited, particularly with regard to the kinetics and synergistic effects of their co-combustion. Therefore, investigating the co-combustion characteristics of coal and Salix could provide valuable insights for their efficient utilization in blended combustion.

In this study, Thermogravimetric analysis, proximate, and ultimate analysis are employed to investigate the co-combustion characteristics of coal and Salix. The effect of blending ratios and synergistic are discussed in detail. Additionally, the Coats–Redfern method is employed to conduct kinetic analysis. The findings of this study could serve as a guide for practical application.

2. Material and Methods

2.1. Material

The coal and biomass (Salix) applied in the study are supplied by Yantai Longyuan Power Technology Co., Ltd., Yantai, China. Before experimentation, both the coal and biomass are crushed. This work carried out ash composition analysis, proximate and ultimate analyses of the samples, and thermogravimetric experiments. The flowchart of the corresponding analysis is illustrated in Figure 1.

The properties of coal and biomass are essential for understanding their combustion and utilization characteristics. In this study, proximate and ultimate analyses of coal and biomass were performed in a fixed-bed reactor system through pyrolysis experiments based on China’s Nation Standards GB/T212-2008 and GB/T31391-2015 [23,24]. The calorific values were measured following GB/T213-2008 [25,26]. The calorific values and proximate and ultimate analysis results of coal and biomass are listed in

Table 1. Calorific value, proximate and ultimate analyses of coal and Salix.

Sample	Proximate Analysis					Ultimate Analysis					${\mathit{Q}}_{\mathbf{net},\mathbf{v},\mathbf{ar}}$
	Mar	Aar	Var	FCar *	Car		Har	Nar	Oar *	St,ar
Salix	8.20	2.75	75.49	13.56	45.00		5.82	0.43	37.72	0.08	17.14
Coal	4.50	18.03	29.66	47.81	61.17		3.93	0.79	10.95	0.63	23.52

* By difference; ar: as received basis.

. The main ash compositions of different samples are detected by X-ray fluorescence (XRF), as shown in

Table 2. Main ash composition analysis of raw coal, biomass, and various fuel blends.

Sample	Ash Composition/%
	Fe2O3	Al2O3	CaO	MgO	SiO2	TiO2	SO3	K2O	Na2O	MnO2
100% C	4.96	14.04	9.16	1.10	54.51	0.85	5.39	2.68	1.32	0.127
100% B	3.27	5.62	31.94	3.06	13.22	0.14	1.85	7.02	0.52	0.225
5% B + 95% C	5.52	16.60	8.71	1.12	53.52	0.80	5.45	2.80	1.38	0.132
10% B + 90% C	5.44	16.64	8.82	1.12	53.20	0.85	4.94	2.69	1.28	0.133
15% B + 85% C	5.60	16.46	9.61	1.14	53.65	0.81	5.04	2.84	1.26	0.13
20% B + 80% C	5.36	16.01	9.83	1.10	54.53	0.85	5.50	2.89	1.19	0.12
30% B + 70% C	5.60	14.51	10.84	1.21	50.58	0.77	4.75	3.17	1.24	0.14

B and C denote biomass and coal, respectively.

.

2.2. Thermogravimetric Experiment

To investigate the co-combustion characteristics of coal and biomass, this study conducted thermogravimetric experiments on blends of coal and biomass. The thermogravimetric experimental system is shown in Figure 2. Labsys Evo Simultaneous Thermal Analyzer manufactured by Setaram Instruments Company, Lyon, France was employed in this study. This instrument comprises components including a recording balance, furnace, programmable temperature control, recording device, gas control unit, support, and computer acquisition system. It is capable of conducting thermogravimetric experiments on solid trace samples over a temperature range from room temperature to 1600 °C. In the experiment, samples weighing 40.00 ± 0.10 mg were placed in an Al₂O₃ crucible, with a total gas flow rate set at 40 mL min⁻¹. The atmosphere was controlled to contain 79% N₂ and 21% O₂. The system was initially purged for 5 min at room temperature. Once stabilized, the temperature was increased from room temperature to 1200 °C at a rate of 10 K min⁻¹, maintained at this peak for 30 min before commencing cooldown.

The biomass ratios in the coal-biomass blends were set at 0, 5%, 10%, 15%, 20%, 30%, and 100%. For the blend with a 15% biomass ratio, the temperature ramp rates were specifically set to 10, 20, and 30 K min⁻¹. Thermogravimetric mass loss (TG), derivative thermogravimetric mass loss (DTG), and differential scanning calorimetry (DSC) measurements were continuously recorded using the analyzer. Blank calibration experiments were conducted before testing, and each experiment was performed three times to ensure repeatability.

2.3. Analytical Method

Ignition and burnout temperature are key indicators applied to evaluate the combustion characteristics of fuel. In this study, the tangent method (as shown in Figure 3) was employed to determine these temperatures. The ignition temperature (T_i) was identified as the point where the tangent line intersects with the baseline at the onset of weight loss [27]. Similarly, the burnout temperature (T_b) was determined by the intersection of the tangent line with the baseline at the end of weight loss. The stable combustion characteristic index (D_w) was employed to assess the ease of ignition and the combustion behavior of coal post-ignition. The flammability index (C_i) reflects the reactivity of the sample during the pre-combustion phase, with higher values indicating greater flammability. The comprehensive combustion characteristics index (S) represents the overall performance of the sample in terms of ignition and burnout, with larger values indicating superior comprehensive combustion performance [28,29,30].

$$D_{\mathrm{w}}={\displaystyle \frac{DT{G}_{\max }}{T_{\mathrm{i}}·T_{\mathrm{b}}}}$$

(1)

$$C_{\mathrm{i}}={\displaystyle \frac{DT{G}_{\max }}{{T_{\mathrm{i}}}^2}}$$

(2)

$$S={\displaystyle \frac{DT{G}_{\max }\cdot DT{G}_{\max }}{T_{\mathrm{i}}^2\cdot T_{\mathrm{b}}}}$$

(3)

where DTG_max is the maximum burning speed (%·min⁻¹), and DTG_mean is the average burning speed (%·min⁻¹).

The synergistic effects of co-combustion are analyzed. The synergistic effects of specific properties are further analyzed by introducing the total weight loss ΔTG by Equations (4) and (5) [17,31,32,33].

$$T{G}_{\mathrm{cal}}={\lambda }_{\mathrm{coal}}T{G}_{\mathrm{coal}}+{\lambda }_{\mathrm{biomass}}T{G}_{\mathrm{biomass}}$$

(4)

$$\Delta TG=T{G}_{\exp }-T{G}_{\mathrm{cal}}$$

(5)

where ${\lambda }_{\mathrm{coal}}$ and ${\lambda }_{\mathrm{biomass}}$ are the contents of coal and biomass in the blends (%), respectively. $T{G}_{\mathrm{coal}}$ and $T{G}_{\mathrm{biomass}}$ are the weight loss of coal and biomass (%), respectively. $T{G}_{\exp }$ and $T{G}_{\mathrm{cal}}$ are the experimental and calculated rates of weight loss (%), respectively.

The energy required to initiate a reaction between molecules in a chemical process is defined as the activation energy (E). A lower activation energy means the reaction can proceed more easily. It accurately identifies the ease or difficulty of a chemical reaction. The pre-exponential factor (A) represents the effective frequency of intermolecular collisions, which influences the rate at which a chemical process occurs.

The integration of E and A offers a more thorough evaluation of the co-combustion reactions occurring within the blend. Thermal conversion processes under experimental conditions are non-isothermal and non-homogeneous. In non-homogeneous processes, the conversion rate (α) is usually employed instead of the reactant concentration [34,35]. k(T), as defined by the Arrhenius equation, is detailed in Equation (7) [36]. A steady rate of temperature rise (β = dT/dt) is selected according to Equation (6).

$$\alpha ={\displaystyle \frac{m_0-m_t}{m_0-m_{\infty }}}$$

(6)

$$k\left(T\right)=A\times \exp \left(-{\displaystyle \frac{E_a}{\mathrm{R}T}}\right)$$

(7)

$$g\left(\alpha \right)={\displaystyle {\int }_0^{\alpha }\frac{1}{f\left(\alpha \right)}}d\alpha ={\displaystyle \frac{A}{\beta }}{\displaystyle {\int }_{T_0}^T\exp \left(-\frac{E_{\alpha }}{\mathrm{R}T}\right)}dT$$

(8)

Since there is no analytical solution, the Coats–Redfern method is employed to solve the equation, which gives [37]

$$\ln \left({\displaystyle \frac{g\left(\alpha \right)}{T^2}}\right)=\ln \left[{\displaystyle \frac{A\mathrm{R}}{\beta E}}\left(1-{\displaystyle \frac{2\mathrm{R}T}{E}}\right)\right]-{\displaystyle \frac{E}{\mathrm{R}T}}$$

(9)

A straight line can be obtained in Equation (9) according to graphing, enabling the values of E and A to be determined from the slope and intercept, and the model of the combustion reaction mechanism [37] can be expressed as

$$f\left(\alpha \right)={\left(1-\alpha \right)}^n$$

(10)

where n is the number of reaction levels; here, the reaction level n = 1 is chosen, then g can be expressed as

$$g\left(\alpha \right)=-\ln \left(1-\alpha \right)$$

(11)

3. Results and Discussion

3.1. Effect of Blending Ratio

Figure 4 shows the TG-DTG plots for coal blended with varying ratios of biomass fuels, while

Table 3. Combustion characteristic parameters of samples.

Sample	Ti (°C)	Tb (°C)	Dw (%·min−1·K−2)	Ci (%·min−1·K−2)	S (%2·min−2·K−3)
100% C	444	571	2.68 × 10−6	3.44 × 10−6	4.36 × 10−10
5% B + 95% C	433	564	2.76 × 10−6	3.60 × 10−6	4.56 × 10−10
10% B + 90% C	429	565	2.51 × 10−6	3.30 × 10−6	4.23 × 10−10
15% B + 85% C	417	561	2.63 × 10−6	3.54 × 10−6	4.64 × 10−10
20% B + 80% C	407	563	2.49 × 10−6	3.44 × 10−6	4.47 × 10−10
30% B + 70% C	393	565	2.25 × 10−6	3.23 × 10−6	4.26 × 10−10
100% B	288	391	1.19 × 10−5	1.62 × 10−5	3.47 × 10−9

B and C denote biomass and coal, respectively.

provides the combustion characteristic indices for the different samples. Analysis of the above experimental results shows that the ignition temperature of coal and biomass blended fuel gradually decreases as the biomass blending ratio increases at a constant rate of temperature rise. The burnout temperature shows a fluctuating trend of reduction, and the stable combustion characteristic index generally tends to decrease, which indicates that the addition of biomass makes the blended fuel easier to ignite, but the stability of combustion reduces. This is attributed to the higher volatile matter and elevated hydrogen and oxygen content in biomass compared to raw coal. It could catch fire and combust rapidly to release heat, accelerate the heating of the coal or biomass, and release the volatile matter in a shorter period, thus promoting combustion. The flammability index (C_i) fluctuates as the biomass blending ratio increases, which shows that with an increase in the biomass blending ratio, the flammability of the blended fuel of biomass and coal is generally enhanced. The comprehensive combustion characteristic index (S) of the blended fuel fluctuates with the increase in biomass blending ratio, which indicates that the addition of biomass is conducive to the improvement of the comprehensive combustion performance of the blended fuel.

All samples exhibit a minor weight loss peak between 50 °C and 100 °C, indicating the release of water from coal and biomass. This weight loss is attributed to water reabsorption by the samples. During thermogravimetric experiments, the gas flow rate is higher than during oven drying, resulting in weaker convective heat transfer and incomplete drying. Consequently, a significant water loss peak is observed between 50 °C and 110 °C during thermogravimetric analysis. With the increase in biomass blending ratios, the TG and DTG curves shift towards lower temperatures, and the slope of the curve becomes steeper. This indicates that the addition of biomass enhances combustion, resulting in easier ignition and burnout of the blended fuel. This effect is due to the higher volatile content of biomass and, after drying, its greater porosity and specific surface area compared to coal. As the ratio of biomass in the blend increases, the ignition temperature and burnout temperature of coal and biomass blended fuels, in general, show a decreasing trend, the stable combustion characteristic index varies irregularly, and the overall combustion performance of the blended fuels is enhanced, which may indicate that the addition of biomass made the blended fuels easier to ignite.

Additionally, the reduced stacking density and increased surface-active sites improve the capacity of the particles to adsorb oxygen. In the temperature range of 480 to 580 °C, raw coal and blends with a lower biomass ratio exhibit a combustion weight loss peak, signifying the concentrated combustion of volatile matter and fixed carbon, as illustrated by the DTG curves (see Figure 4). Blended fuels with a higher biomass ratio display two distinct weight loss stages: an initial stage between 300 and 350 °C, primarily involving the release and combustion of volatile matter, and a second stage from 450 to 580 °C, dominated by the combustion of fixed carbon. These findings align with previous studies [38,39]. Notably, the combustion peak of fixed carbon in pure biomass occurs earlier, likely due to its higher oxygen content, which enhances combustion. Between 500 and 550 °C, the DTG curve for biomass reveals a minor weight loss peak, indicating the decomposition of CaCO₃ in the ash, corroborated by a higher CaO content detected in pure biomass ash. Table 2 shows that the ash composition of biomass is predominantly CaO (31.94%) and SiO₂ (13.22%), consistent with prior research indicating that CaCO₃ decomposes into CaO and CO₂ within this temperature range [40,41]. When the biomass ratio is low (15%), the DTG curve exhibits a “shoulder” around 250 °C and a “main weight loss peak” near 490 °C, referred to as the “flammable peak” and “refractory peak”, respectively. With a high biomass ratio (100%), the “shoulder” shifts to around 410 °C in the high-temperature zone, while the “main weight loss peak” appears at approximately 320 °C in the low-temperature zone. For medium biomass ratios, the DTG curve reveals two distinct “main weight loss peaks”. This suggests that the “main weight loss peak” reflects the characteristics of the dominant fuel in the blend and aligns closely with the DTG peak of the individual fuel with a similar ratio. As the biomass blending ratio increases, the “main weight loss peak” tends to occur in the low-temperature region, indicating lower ignition points and increased reactivity. Additionally, with higher biomass ratios, the CaCO₃ decomposition peaks in the blends become more pronounced, and weight loss peaks around 700 °C suggest the decomposition of certain minerals in the ash.

The Differential Scanning Calorimetry (DSC) analysis reveals two distinct exothermic peaks. The first peak, occurring between 280 °C and 400 °C, corresponds to the release and combustion of volatile components. The second, more pronounced peak between 400 °C and 600 °C indicates a greater exothermic reaction associated with the combustion of fixed carbon. Pure coal shows the highest exothermic heat at 25 W g⁻¹, over twice that of biomass, which is 12 W g⁻¹. As depicted in Figure 4, the exothermic reaction of pure biomass initiates earlier than that of both the blends and coal but is of lower magnitude due to the lower calorific value and higher volatile fraction of biomass, which facilitate easier ignition. Moreover, the peak during the combustion of volatiles slightly exceeds that of fixed carbon, highlighting the reduced fixed carbon content in biomass.

3.2. The Synergistic Effect of Blended Fuel

Figure 5 presents the ΔTG plots for various blending ratios. ΔTG equals zero solely at 53.2 °C, indicating that coal and biomass are not simply linearly superimposed in the blending combustion but engage with one another during the process of combustion. Following the previously mentioned algorithm, a DTG value below zero suggests that the actual residual combustion mass is smaller than the calculated value. This further suggests that the actual blended combustion weight loss exceeds the proportionally calculated weight loss. This shows that the combustion of the three feedstocks together is not merely a straightforward linear combination; instead, a synergistic enhancement in combustion occurs when the DTG is below zero.

At most blending ratios, the ΔTG peaks for the three fuels are at 330.0 °C and 530.0 °C, respectively, which are not much different from the locations of the final peaks. The primary cause for the peak occurs around 530 °C. The combustion of fixed carbon occurs at 0 °C. At 400.0~530.0 °C, the combustion of fixed carbon finishes sooner, and the absolute ΔTG rises. At this point in the temperature interval from Figure 5, it can be seen that the 15% blending ratio has the largest difference in ΔTG, which also represents the synergistic promotion of combustion at this point is very intense, while 30% of the biomass blending ratio is the state of positive ΔTG, indicating that at this point is in a kind of suppression of combustion situation. As observed in Figure 4, the temperature above 600 °C exhibits a suppression of combustion, potentially due to the coverage by ash and other combustion products, leading to incomplete combustion. As the temperature increases, the inhibitory effect of these products becomes the primary factor influencing the reaction rate, causing the experimental curves to gradually converge with the calculated values.

3.3. Kinetic Analysis

Table 4. Kinetic parameters of blended fuels.

Sample	Rate (K min−1)	α	E (KJ mol−1)	A (mol−1)	R2	f(α)
100% C	10	0.2~0.8	86.94	83,084.38	0.9949	−ln(1 − α)
5% B + 95% C	10	0.2~0.8	77.42	19,963.17	0.9894	−ln(1 − α)
10% B + 90% C	10	0.2~0.8	60.01	1093.26	0.98	−ln(1 − α)
15% B + 85% C	10	0.2~0.8	47.84	144.06	0.95	−ln(1 − α)
20% B + 80% C	10	0.2~0.8	38.81	29.40	0.94	−ln(1 − α)
30% B + 70% C	10	0.2~0.8	25.38	2.53	0.91	−ln(1 − α)
100% B	10	0.2~0.8	34.46	60.48	0.85	−ln(1 − α)
15% B + 85% C	20	0.2~0.8	26.54	2.59	0.91	−ln(1 − α)
15% B + 85% C	30	0.2~0.8	23.06	1.05	0.94	−ln(1 − α)

B and C denote biomass and coal, respectively.

shows the E and A values for the two fuels at various blending ratios and heating rates. Adding biomass reduces the activation energy compared to pure coal, making the fuel easier to burn. As the blending ratio increases, the activation energy exhibits a decreasing trend. For instance, at a 5% biomass addition, the activation energy remains at 77.42 KJ mol⁻¹, whereas at a 30% biomass blending ratio, it decreases significantly to 25.38 KJ mol⁻¹, highlighting the substantial impact of biomass blending on reducing activation energy. With a 15% blending ratio, raising the heating rate further reduces the activation energy, which is observed to be 23.06 KJ mol⁻¹ at a heating rate of 30 K min⁻¹—a reduction by half. Both the increase in heating rate and biomass blending ratio result in a decrease in activation energy, and the pre-exponential factor (A) diminishes correspondingly. This reduction facilitates a faster initiation of the reaction, indicating an overall ease in the reaction process.

4. Conclusions

In this study, thermogravimetric analysis, proximate, and ultimate analysis are employed to study the co-combustion characteristics of coal and Salix. The effect of blending ratios and synergistic are investigated in detail. The Coats–Redfern method is adopted to perform kinetic analysis. The conclusions are as follows:

(1)

As the biomass blending ratio increases from 5% to 30%, both the ignition and burnout temperatures of coal-biomass blended fuels decrease, with ignition temperatures declining from 444 °C to 393 °C and burnout temperatures reducing from 571 °C to 565 °C. Simultaneously, the index of stable combustion characteristics rises, indicating that the incorporation of biomass improves the ignitability and stability of the blended fuel.

(2)

Thermogravimetric analysis reveals that the blending ratio of Salix significantly affects the temperature range of the fuel loss peak. At a lower biomass ratio (15%), the main loss peak is observed at 490 °C, whereas a higher ratio (100%) shifts this peak to approximately 320 °C, indicating an enhancement in combustion characteristics with biomass addition. A synergistic analysis shows that in the temperature range of 400 to 530 °C, a 15% biomass ratio most effectively promotes combustion, whereas a 30% ratio inhibits it. Above 600 °C, the inhibitory effect of combustion products becomes the dominant factor influencing the reaction rate, leading to combustion inhibition.

(3)

Kinetic analysis reveals that the incorporation of Salix reduces the activation energy, thereby facilitating the reaction process. With a 5% biomass addition, the activation energy is 77.42 KJ mol⁻¹. However, as the biomass blending ratio increases to 30%, the activation energy markedly decreases to 25.38 KJ mol⁻¹. At a 15% blending ratio, the activation energy continues to decrease with an increase in the heating rate, reaching 23.06 KJ mol⁻¹ at a heating rate of 30 K/min. Both the increased heating rate and higher biomass ratio contribute to the reduction in activation energy, with the pre-exponential factor A also decreasing under these conditions. This results in a faster initiation of the reaction, indicating improved reaction feasibility. This study provides valuable insights into the co-combustion of coal and Salix in practical applications. Future research could focus on ash accumulation and pollutant emissions resulting from the combustion of coal and Salix.