# Study on the Ash Deposition Characteristics for Co-Combustion of Zhundong Coal with Cotton Stalk
## 1 Introduction  
Although the proportion of coal in China's total energy consumption has been declining in recent years, it still accounted for over 53% as of 2024. Consequently, coal will remain a pillar resource in China's energy consumption structure for a considerable period in the future. Xinjiang is rich in coal resources, particularly in the Zhundong coalfield, with an estimated reserve of approximately 390 billion tons, which was the largest integrated coalfield in China [1, 2]. According to the current coal consumption, only the Zhundong coalfield has been able to meet the coal demand of China for nearly a hundred years. Zhundong coal is characterized by high volatile matter, low ash content, and low sulfur content, making it an ideal fuel for power generation [3, 4]. Therefore, the large-scale devellopment and utilization of Zhundong coal is very significant for ensuring the energy security of China. Unlike fossil fuels, renewable energy, as a clean, low-carbon green energy source, will become the primary direction of the global energy transition in the future [5]. Biomass was a renewable energy source and was considered to be the fourth largest energy source globally, following oil, natural gas, and coal [6]. As a major agricultural country, China possesses abundant biomass resources with vast development potential. According to statistics, the annual biomass production in China reaches 3.49 billion tons, which is equivalent to about 460 million tons of standard coal. However, only 13% of biomass resources are used effectively [7]. Under the goals of carbon peaking and carbon neutrality, it is of great significance to strengthen the utilization of biomass energy for the sustainable development of clean energy in China. Direct combustion technology is one of the primary methods of biomass utilization, Due to its low transformation and operation costs, it has been widely used in the fields of power generation and heating [8]. However, the volumetric calorific value of biomass fuels is low, resulting in increased transport and storage costs. In addition, the capacity of the biomass boiler is small, and the combustion efficiency is low, resulting in the poor economy of power plants. Compared with biomass combustion, coal-biomass co-combustion has many advantages [9; 10]. Biomass has low calorific value and high volatile content, while coal has high calorific value and low volatile content. This complementary combination lowers ignition temperatures and enhances fuel ignition. Moreover, by adjusting the ratio of coal to biomass, the effects of seasonal fluctuations in the availability of biomass feedstock can be mitigated. As a promising clean energy method, coal-biomass direct co-combustion technology still has some problems in its application. The content of alkali metal in Zhundong coal is high, which can easily cause slagging and fouling on the heating surface during combustion [11]. Similarly, the abundance of alkali metals in biomass also exacerbates the slagging and fouling problems. This leads to reduced heat transfer efficiency, increased thermal resistance, and possibly even burst pipes [12]. Therefore, investigating the slagging and fouling characteristics during coal-biomass co-combustion is critical to controlling these issues. The ash deposition behavior during the combustion of high-alkali metal fuels plays a critical role in boiler design and fuel selection. Many scholars have carried out a lot of research on ash deposition characteristics during the co-combustion of coal and biomass [13]. [PERSON] et al. [14] studied the sintering and fusion behaviors of Zhundong coal ash blended with three types of biomass ash in a tubular furnace. The results revealed that corn stalk ash and rice husk ash promoted coal ash fusion, while wood chip ash inhibited it. [PERSON] et al.