Abstract:

Coal pyrolysis in thermal plasma opens up a direct means for producing acetylene.This process is operated under ultra-high temperature conditions with the reaction time in milliseconds, where the rapid heating of coal particles and the release of volatile matters from coal particles play the dominant role in the overall reactor performance.A mechanism model was proposed for a deep understanding of the heat transport inside a coal particle under extreme environmental conditions, which incorporated the heat conduction in solid materials and heat resistance due to the outward diffusion of released volatile gases.The predicted yield of volatiles considering the heat transfer inside the particle agreed reasonably with the reported experimental data under different operating conditions, indicating 30%—40% time delay compared with the case without consideration of the heat resistance inside a particle.This effect became more evident for larger particles.Meanwhile, the heating fluid at a higher temperature could speed up and intensify the devolatilization of coal particles.Limited to the milliseconds process of coal pyrolysis, particle size greater than 100 μm or the heating fluid temperature lower than 2000 K is not recommended in the practical application because of the slow release of volatiles in coals.