Master of Engineering Science
Chemical and Biochemical Engineering
Vaporization of injected liquid is a key process in many industrial fluidized beds. In Fluid Cokers, for example, quicker vaporization would increase liquid product yield and reduce fouling. A new experimental method was developed to measure the vaporization rate by injecting liquid for a certain duration to reach a constant vaporization rate while monitoring changes in pressure and vapor composition in the exhaust pipe of the fluidization column. Three processes can delay vaporization in a fluidized bed: heat flux from hot-dry particles to wet particles, vapor saturation, and wet agglomerate formation. Operating a spray nozzle at a very high atomization gas flowrate eliminated agglomerate formation, and the heat flux limitation was predominant at bed temperatures well above the boiling point while vapor saturation was predominant at bed temperatures well below the boiling point. Finally, with a practical atomization gas flowrate, bed hydrodynamics and spray characteristics affect agglomerate formation and stability significantly.
Summary for Lay Audience
Fluidization uses a gas flow to impart fluid-like properties to a powder of small particles. Liquid is injected in fluidized beds in industrial processes ranging from oil refining, polymer production and the coating and agglomeration of pharmaceutical powders. In most of these processes, fast vaporization of the injected liquid is essential to ensure reliable operation and high product quality. This thesis developed a new experimental method to measure how quickly a liquid injected into a fluidized bed vaporizes. It identified and characterized three mechanisms that can slow down vaporization. The first, heat flux limitation, is due to the rate at which hot bed particles can provide heat for the vaporization of liquid from wet particles. The second limitation, vapor saturation, is due to the rate at which vapors can be evacuated from the bed. The third limitation results from the formation of wet agglomerates, which cannot dry as quickly as wet individual particles. Practical strategies to speed up vaporization include improving the spray nozzle performance and optimizing its location. Spray nozzle performance can be improved, for example, by increasing the flowrate of atomization gas. The spray nozzle should be located in regions of the bed where the flow of gas and particles entering the spray jet cavity is maximized and where intense agitation promotes agglomerate breakup.
Silitonga, Hansen Mangaranap, "Evolution and Flow of Vapors in a Fluidized Bed" (2020). Electronic Thesis and Dissertation Repository. 7533.
Available for download on Saturday, January 01, 2022