# Development of a Novel Shaft Dryer for Coal-Based Green Needle Coke Drying Process
## 1 Introduction  
Needle coke, as an important carbon material, can be classified into two types, i.e., petroleum-based needle coke [1] with heavy oil as the raw materials, and coal-based needle coke [2] with coal tar, coal pitch, or their fractions as the raw materials. Initially, petroleum-based needle coke occupies the dominant position, while the production of coal-based needle coke is greatly accelerated due to the high price and lightening production of petroleum in the recent years. Green manufacturing and cleaner production [3] have become one prominent feature of sustainable development. Especially in the context of carbon trade and carbon tax [4; 5], energy conservation and emissions reduction are definitely the key issues of various industrial processes, such as ceramic production [6], ironmaking [7], sintering [8], and power generation [9]; and the needle coke drying process should be no exception. Coal-based needle coke is a perfect material for the manufacturing ofthe ultra-high-power electrode used in the compact steelmaking process. Iron and steel are traditionally produced with iron ores as material inputs and coal-based energies as energy inputs [10], which has a high energy consumption and heavy environmental pollution [11]. Contrarily, the compact steelmaking process using scrap as the main material input and electricity as the main energy source attracts more and more attraction [12]. Coal-based needle coke also serves as anode materials of lithium-ion batteries. The use of ultra-high-power electrode made from coal-based needle coke can reduce the smelting time by 10% to 20%, resulting in the electrode consumption and electricity consumption. In addition, with the rapid development of lithium-ion battery [13], the demand for anode materials increases obviously, which results in the mushroom of green coke of coal-based needle coke [14]. The production of coal-based needle coke consists of three main processes: pretreatment of raw materials, delayed coking [15], and calcining [16]. The coke produced by a delayed coking process is called green needle coke, while called calcined needle coke if produced by a calcining process. For the cooking process, the size of dust emissions is mainly 3.3 to 9.0 \(\upmu\)m, and the main chemical components are C, SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), S, CaO, and TFe, with contents of 76.30%-81.30%, 5.36%-5.91%, 3.96%-4.26%, 1.15%-1.34%, 0.52%-1.59%, and 0.81%-1.34%, respectively [17]. Green coke serves as the material input of the calcining process, and its drying degree directly affects the energy consumption and the quality of the final product of the calcining process. The green coke discharged from the delayed coking unit has a moisture content of 10% to 25%. If the green coke with such a high moisture content enters the rotary kiln to be calcined, the following negative aspects will occur from whole system and life cycle perspectives [18]: (i) the temperature of the kiln tail will be lower, and the parameters such as kiln pressure, air amount, and fuel ratio have to be adjusted frequently, which will cause difficulty in operating the rotary kiln; (ii) more thermal energy will be consumed [19] in the calcining process; and (iii) there is a greater possibility of being exploded to scraps, compared with green coke with low moisture content, resulting in small particle size of calcined coke. To reduce the moisture content of green coke, several standing dehydration tanks are usually used in the real-world production process to maintain the moisture content of green coke below 5% in 5 days. But in winter, the water escapes slower from the coke surface and internal pores [20], then the moisture content may reach 8% due to the low temperature, which results in an unstable operation of the rotary calcining kiln, and further affects the energy consumption and calcined coke quality.