# Development of a Novel Shaft Dryer for Coal-Based Green Needle Coke Drying Process
## 2 Design of the Novel Drying System and Shaft Dryer  
To overcome the shortcomings of currently used dryers for drying green coke, this work proposes a novel drying system, as shown in Figure 1. The proposed drying system consists of 10 main components: primary air blower, secondary air blower, combustion chamber, hot stove, belt conveyor, shaft dryer, helical conveyor, bucket elevator, transfer hopper, and exhaust fan. Fuel gas and the air from primary air blower are mixed and fired in the combustion chamber. The generated high-temperature flue gas at 1300 \({}^{\circ}\)C is sent to the hot stove, inside which the high-temperature flue gas is mixed with the low-temperature air from the secondary air blower to get the medium-temperature gas at 450 to 500 \({}^{\circ}\)C. The medium gas is then piped into the bottom of the shaft dryer. A constant feeder discharges the wet green cokes to a belt conveyor, through which the wet green cokes are transferred to the top hopper of the shaft dryer at a constant speed. Next, the wet green cokes are fed into the dryer uniformly to exchange heat with the medium-temperature gas in an energy-efficient, direct-contact, and counter-current way [37]. The discharging unit at the bottom of the shaft dryer controls the discharge speed and loosens the green cokes to prevent blocking the dryer. The discharged final green cokes enter a helical conveyor and are then conveyed to a bucket elevator, which connects the inlet of a transfer hopper. When the temperature of the green cokes is lower than 70 \({}^{\circ}\)C, the final product is packaged. The waste gas from the shaft dryer is treated via a bag filter before emitted into the atmosphere. Figure 2 depicts the layout of the shaft dryer. The shaft dryer is principally based on the moving bed technology [38; 39]. With medium-temperature gas as the heat source, the refractory material can be totally saved, and the over-burnt and pollution caused by the spalled refractory material can be avoided. The wet green cokes are uniformly placed in the shaft dryer and discharged by gravity. Thus, the mechanical transmission unit can be removed, resulting in the low failure of the system. In addition, because no pneumatic conveying of the green cokes occurs inside the shaft dryer, hence there is no need to crush the green cokes to meet a strict limitation of the particle size. A 20,000 t/y shaft dryer is selected as a case analysis. The dryer runs 300 d/y and 24 h/d. The initial moisture is 10%, and the final moisture is 1%. The target temperature of dried green cokes is 80 \({}^{\circ}\)C, and the flow rate of flue gas is 5000 m\({}^{3}\)/h. The average specific heat capacities of green cokes and flue gas are 0.808 and 1.4 kJ/(kg.\({}^{\circ}\)C), respectively. It can be calculated that the energy efficiency is 80%. Given the influence of heat loss, the estimated that an energy efficiency of 65%-75% could be achieved in practice. The corresponding economic and environmental assessment [40] can also be conduction based on the design parameters. The characteristics of the novel shaft dryer can be summarized as follows:  
* It has a simple structure and no mechanical transmission unit, making it easy to maintain, with low noise while operating and low failure rates. Figure 1: Scheme of the green coke drying system. * It is a wholly-sealed system, and thus the energy efficiency can be as high as 65%-75% with no leak of environmental pollutants. * It can be built by using less metal, less land area, lower capital investment cost, compared with other drying methods. * It uses medium-temperature gas as the heat source, which will not cause the over-burnt quality of green cokes. * It does not need liner inside the shaft dryer, ensuring that final green cokes have good quality. * It has a low breakage rate of green coke because of the low-speed flow of green coke inside the shaft dryer, which further reduces the amount of dust and the cost of environmental assets. * It can easily adjust the residence time and the resultant moisture content of green cokes.