System for the pulsed pneumatic transport of ash from ash-collector bins

Abstract

Results of investigations of the dependence of the percentage of voids on the shear force of a layer of ash, on the basis of which the design principle of the subassembly for the feed of ash to a transport pipeline is developed, are examined for optimization of ash flows in a pulsed regime. The schematic of a system of pulsed pneumatic transport of ash from the bins of ash collectors, and results of measurements during experimental operation of the system, as well as relationships for the calculation of its dynamic parameters are presented. Conclusions concerning the high reliability of the removal and pneumatic transport of ash over a distance of more than 80 m with minimal air consumption are drawn on the basis of results of the experimental operation.Existing systems for the pneumatic transport of ash have either a short time to overhaul and high air consumption, or an appreciable cost. In these systems, pneumatic transport is restricted by the initiation of deposition of a powdery medium in the pipeline. The velocity of the pneumatic transport should therefore be greater than the velocity, as defined by the initiation of deposition. High pneumatic-transport velocities in certain systems (12 -20 m/sec) cause significant abrasive wear of the walls, which excludes use of a transport pipeline with bends.The method developed for the pneumatic transport of ash in a pulsed-piston regime [1] exhibits high operating characteristics and in-service reliability. To optimize the formation of ash flows (piston-induced) in a pulsed regime, we conducted investigations of the dependence of the percentage of voids (porosity) å on the shear force of the layer of ash using a device in the form of a U-tube. The housing of the device is fashioned from D c -50 and D c -80 pipelines. The following operations were performed during the investigation: a covering of a metered batch of ash, a fluidized bed to an established height, a piston device in the bed of ash, the pulsed effect of the weight of the metered mass on the surface of the piston, and measurement of the displacement of an indicator.The fluidization rate and percentage of voids å were calculated in accordance with [2]where d is the average diameter of the ash particles, m; ñ v , ñ t , and ñ o are the densities, respectively, of the layer of ash, dust particles, and air, g/cm 3 ; ì is the viscosity of the air, g/(cm · sec); and g is the acceleration of free fall, m/sec 2 .Results of the investigations (Fig. 1) indicated the identical character of the dependence of å on the displacement Äh 1 of the ash layer as a result of the pulsed action, and on the force F of the pulsed effect on the layer of ash for D c -50 and D c -80 pipes. It is apparent from Fig. 1 that when å = 0.7 -0.55, an additional pulsed effect is required to displace the layer of ash (to consolidate the layer), and a force several times smaller is required to displace the layer of ash after it has been consolidated to å = 0.45 -0.5.Thus, the ash-feed assembly should form an ash bed with a consolidated structu...