Study On Hybrid Composite Reactor For Oxygen-Heatinging Calcium Carbide Production

The technical characteristic of traditional electric-thermal method to produce calcium carbide is high pollution, high emission, high energy consumption, so Liu Zhenyu of Beijing University of Chemical Technology put forward a system for oxygen-heating calcium carbide production, including different reactor design models. Based on the annual output 1000 tons of calcium carbide in a pilot scale, this paper carried out the study of model design. Namely, using method of mechanics of granular media to validate and study solid flow in a stirring hybrid composite reactor, and simulating of pyrolysis and heat transfer characteristics in the reactor by using computational fluid dynamics (CFD) technique, at the same time, utilizing numerical simulation method to study flow characteristics of the combustion zone under different nozzle setting and put forward the optimization design of nozzle.First, using discrete element method to model and calculate the motion of particles under different paddles in the hybrid composite reactor. It was found that the simulation result can correspond with the measurement, which measured using different paddles through a small experimental device. The effect of two kinds of paddles in the process of pilot plant was studied by the model. Specific conclusions are as follows:(1) The velocity distribution of particle s in the reactor is basically same using different paddles. The particle velocity is relatively large in the lower part of the moving bed, the particle velocity reach the maximum value around the blades, and low velocity zone form in the center of the paddle. Disturbance of the blade rotation for particles decrease in the upper bed, showing the obvious bridging phenomenon and particle velocity distribution in upper bed is not uniform.(2) The radial distribution of particles in the reactor takes on the form of "more in the middle and less in the both sides" using flat paddle, while it present opposite form using downward paddle.(3) The fluctuations of radial distribution of particles in the reactor is relatively large when using flat paddle, but radial distribution of particles in the reactor is uniform when using downward paddle. So the downward paddle is preferable.Second, studied the start-up time and steady-state operation state in the reactor under the condition of taking moving bed of the hybrid composite reactor as research object and using 40mm in diameter of composite particle, which is the mixture of pulverized coal and calcium hydroxide. Specific conclusions are as follow:(1) It takes 1200s from cold states to heat state operation in the moving bed.(2)With the increase of time, the flow, temperature and species distribution are significantly different. The flow field development is not sufficient at the beginning of the prolysis, temperature and components distribution in the reactor is relatively uniform. The effort of wall can increase with the increase of time, and velocity, temperature and components distribution in the moving bed present type "W".(3) The reactor can be obviously divided into complete zone, prolysis zone and unreacted zone as the prolysis front moves to the upper bed.(4) Evaporation, coal pyrolsis and calcium hydroxide decomposition happen in turn as rising of the particle temperature. But the three processes is not obvious boundary, volatile begin to overflow in the late stage of the evaporation, and calcium hydroxide decomposition occur in the mid -to-late of the coal pyrolsis.Finally, set up a mathematical model for hybrid composite reactor by the method of modeling, and investigated the different nozzle inlet position, entrance angle and inlet velocity impact on flow distribution and swirling region in the reactor to select suitable design parameters of nozzle. The optimal combination of the parameters including nozzle inlet position is located at a distance of 0.43 meters from the surface of the molten, incident angle is 15 degree, and inlet velocity is 80 meters per second. When using this combination, the flow field distribution and swirling region size were most reasonable.