Study on transient boiling heat transfer of coal with different bedding angles quenched by liquid nitrogen

Abstract

Liquid nitrogen (LN2) cracking is a new waterless cracking technology, and the efficiency of cracking coal from different angles is obviously different. Therefore, the boiling heat transfer of LN2 in contact with media with different stratification angles is studied in this paper. It is found that the longitudinal and transverse wave velocities of ultrasonic waves are positively correlated with the bedding angle of coal samples. With the increase of bedding angle of coal samples, the rate of temperature reduction of coal samples at the initial stage of LN2 quenching first drops and then rises, and the coal temperature decreases fastest in parallel bedding direction. The central temperature of coal samples from different bedding angles has experienced four stages: rapid decline-slow decline-rapid linear decline-slow decline, among which stage 3 lasts the longest and the temperature reduction rate exceeds 50%. The quenching effect parameters are defined, and the quenching effect of four stages is stage 3 > stage 4 > stage 2 > stage 1. Prolonging the time of stage 3 can improve the quenching efficiency of LN2. According to the RPI model, the change of the side wall temperature of coal sample is rapidly decreasing-slowly decreasing, and a low temperature layer with high thermal resistance is formed after rapid decrease, which can inhibit the heat transfer from coal to LN2.

Keywords

• Liquid nitrogen
• Quenching
• Heat transfer
• Bedding direction