Abstract

This thesis discusses the results and insights gained from developing a CFD model of a pilot-scale pressurized dry coal-feed system using the Barracuda CFD software and modeling various design concepts and operating conditions. The feed system was required to transport approximately 0.00378 kg/s (30 lb/hr) of pulverized coal from a vertical hopper to a 2.07 MPa (20.4 atm or 300 psi) reactor with a CO2-to-coal mass flow ratio of 1-2. Two feed system concepts were developed and tested for coal mass flow, CO2-to-coal mass ratio, steadiness, and uniformity. Piping system components also were evaluated for pressure drop and coal roping.With the first system concept, Barracuda software model parameters were explored to observe their effect on gas and particle flow. A mesh sensitivity study revealed there exists too fine of a mesh for dual-phase flow with Barracuda due to the particle initialization process. A relatively coarse mesh was found to be acceptable since the results did not change with increasing mesh refinement. Barracuda sub-model parameters that control particle interaction were investigated. Other than the close pack volume fraction, coal flow results were insensitive to changes in these parameters. Default Barracuda parameters were used for design simulations.The gravity-fed system (first concept) relied on gravity to transfer coal from a hopper into the CO2 carrier gas. This design was unable to deliver the required coal mass flow rate due to the cohesion and packing of the particles being greater than the gravity forces acting on the particles. The fluidized bed (second concept) relied on CO2 flow injected at the bottom of the hopper to fluidize the particles and transport them through a horizontal exit pipe. Additional CO2 was added post-hopper to dilute the flow and increase the velocity to minimize particle layout. This concept was shown to decouple the fluidized particle flow and dilution CO2 flow, providing significant design and operating flexibility. A non-uniform mesh was implemented to maintain a high mesh refinement in the 0.635-cm (¼-in) diameter transport pipe with less refinement in the hopper/bed region. The two main hopper diameters evaluated measured 5.08-cm (2-in) and 15.24-cm (6-in). Successful designs were achieved for each with appropriate coal mass flow rates and CO2-to-coal ratios. The particle flow was sufficiently steady for use with a coal burner.A piping system study was performed to test pneumatic transport and the effects of pipe length and bend radius. For a 1-to-1 gas-to-particle mass flow, particle layout occurred after 30 cm of travel. Particle roping occurred to various extents depending on the pipe bend radius. Bend radii of 0.318, 60.96, and 182.88 centimeters were simulated. Roping increased with bend radius and high pressure. Greater gas flow rates increased particle flow steadiness and uniformity. A simple methodology was identified to estimate the pressure drop for different piping system configurations based on the piping components simulated.

Degree

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

Rights

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