Study On Resistance Properties Of Inclined Pipe In High-pressure Dense-phase Pneumatic Conveying

Coal is one of the main primary energy resources in China. Direct combustion of coal leads to many environmental problems. Coal pressurized gasification technology can realize clean utilization of coal resources. As one of the key techniques in gasification, high-pressure dense-phase pneumatic conveying technology is significant to the performance of the whole gasifier. Inclined pipe is inevitable to be applied in the feeding system of the pulverized coal gasifier, while the solids concentration is high and the flow characterisitics is complex in high-pressure dense-phase pneumatic conveying. Investigation on resistance properties of the inclined pipe is few reported. Experimental study, theoretical analysis and numerical simulation are utilized to study the resistance properties of the inclined pipe in high-pressure dense-phase pneumatic conveying.Experiments of pneumatic conveying of anthracite coal and petroleum coke were carried out using nitrogen. First of all, powder physical properties of the experimental materials were precisely examined including the industrial analysis of the materials, true density, bulk density, moisture content, particle size distribution and surface morphology. Results show that total moisture contents of all experimental materials are below 3%, which means the materials are very dry. Ash content of petroleum coke is smaller than that of anthracite while fixed carbon content of petroleum coke is higher. The bulk density and true density of petroleum coke are smaller than those of anthracite, respectively. The surface morphology of anthracite is quite different from that of petroleum coke of the similar particle size. The surface of anthracite is smooth and compact while the surface of petroleum coke is rough with pellets and plates attached on the surface. Shear tests were carried out using ShearTrac-II shear tester for different materials to investigate the flowability of the experimental materials. Results show that flow functions of the experimental materials all distribute in two to four, that is to say, all experimental materials are cohesive materials. The flowability of coarse material is better than fine material for the same catergory and the flowability of anthracite is better than that of petroleum coke of the similar particle size.Conveying characteristics of high-pressure dense-phase pneumatic conveying in bottom-discharge system is investigated. The effects of operating conditions and powder physical properties on conveying characteristics are charactered. Results show that under the same pressure differential, mass flow rate and solid-gas ratio firstly decreases and then increases with increasing fluidizing gas flow rate. The mass flow rate increases with increasing pressure differential, while the increasing trend decreases under high pressure differential. Flow stability appears better as the pressure differential increases. The mass flow rate and solid-gas ratio of coarse material are smaller than those of fine material under the same pressure differential, respectively. Conveying capacity and flow stability of anthracite are better than those of petroleum coke under the same conveying pressure and pressure differential.Phase diagram is used to study effects of different parameters on resistance properties of the inclined pipe. Results show that the pressure drop through the inclined pipe at a fixed angle firstly decreases and then increases with increasing superficial gas velocity. The pressure drop of coarse material is larger than that of fine material under the same superficial gas velocity. The pressure drop through the inclined pipe conveying anthracite is larger than that of petroleum coke of the similar particle size. The pressure drop through inclined pipe increases with increasing inclination angle under the same superficial gas velocity. Empirical correlations based on Barth’s Theory using dimensional analysis are derived from experimental data. The predicted values show good agreement with experimental data and a critical inclination angle of about 63° is deduced.Numerical simulation was carried out to investigate the flow characteristics in the inclined pipe in high-pressure dense-phase pneumatic conveying. Two-fluid model and k-ε-kp-εp turbulent model were applied. Two kinds of interaction between solid phase and gas phase were taken into account:(1) drag force between gas phase and solid phase due to the difference of velocity of two phases; (2) turbulent kinetic energy exchange due to pulsation of solid velocity and gas velocity. Results show that with increasing superficial gas velocity solids centralized region rises towards the center of the pipe. Coarse particles seem easier to settle on the bottom of pipe. Solids concentration of the coarse particles is higher than that of fine particles in the lower half of the pipe cross-section. As the inclination angle increases, materials tend to settle on the bottom of pipe.