Study On The Flow And Heat Transfer Characteristics Of Particles In The Water-cooled Screw Conveyor

Semi coke is the processing of coal products, it is mainly formed by high quality refined Zhuluo coal fired from Shenmu county and Fugu county. At present, most enterprises commonly adopt the way of water quenching to quench and cool the high temperature semi coke particles that discharged by the retort when they use low temperature carbonization furnace to product semi coke. So it caused a lot of waste, for example, a lot of water is wasted, a large amount of energy is costed additionally, the sensible heat of semi coke that discharged by the retort is all wasted. It results in an increase cost of semi coke production and it can also cause environmental pollution. The semi coke waste heat recovery system is particularly suited to conveying and cooling high temperature semi coke particles. It can quench the fired semi coke particles with the method of dry quenching. And it can recycle waste heat in the process of convey semi coke particles. It is significant to energy conservation and emissions reduction and energy sustainable development.Water-cooled screw conveyor is the main component of semi coke waste heat recovery system. In this paper, the flow characteristics of particles in the water-cooled screw conveyor were studied during it conveying particles by using the discrete element method(DEM). The influence of operation parameters, structure parameters and particle parameters on the flow characteristics of particles were analyzed. The heat transfer characteristics of high temperature solid particles along conveyor axial direction and radial direction were studied. And the influence of screw speed and filling rate on the heat transfer characteristics of particles were analyzed. The conclusions are showed as follows:(1) The feed zone of the water-cooled screw conveyor is a small area. The velocity distribution of particles along the conveyor axial direction is uniform and the maximum speed difference is 0.0026m/s when water-cooled screw conveyor full of particles. Along the conveyor radial direction is not uniform and the minimum speed difference is 0.007m/s when water-cooled screw conveyor full of particles. The axial motion of particles is abated with the increase of the filling rate, the axial speed decreased from 0.028m/s to 0.023m/s when the filling rate increase from 60% to 80%. The axial movement of particles is enhanced with the increase of the screw pitch, the axial velocity increased from 0.003m/s to 0.0351m/s when the pitch increase from 100 mm to 300 mm.(2) The time of particles homogeneous mixing decreased with the increase of rotational speed and the time decreased from 200 s to 36 s when the speed increase from 3r/min to 20r/min, small screw pitch is conductive to the mixing movement of particles and the mixing index increase 0.03 when the pitch increased from 100 mm to 300 mm when there is only one type of particles in the water-cooled screw conveyor. And it is also conductive to the mixing movement of particles when the fill rates higher than 80%. The smaller size difference between particles, the better mixing uniformity will get and the mixing index increased from 0.197 to 0.488 When diameter ratio decrease from 3.0 to 1.0, high fill rate is beneficial to the mixture of particles when there is tow types of particles in the water-cooled screw conveyor.(3) The heat recovery efficiency increased with the decrease of the rotational speed and the falling rate slow down gradually. The heat recovery efficiency decreased from 72.1% to 44.9% when the screw speed of water cooled screw conveyor increase from 3r/min to 10r/min. The heat recovery efficiency decreased from 44.9% to 31.4% when the screw speed of water cooled screw conveyor increase from 10r/min to 20r/min. The heat recovery efficiency increased with the increase of the filling rate and the rise rate increased gradually. The heat recovery efficiency are little changed when the filling rate in 60%-80% range. The heat recovery efficiency increased from 62.5% to 66.7% when the filling rate increase from 80% to 90%. The heat recovery efficiency increased from 66.7% to 72.1% when the filling rate increase from 90% to 100%.