Masters Theses

Date of Award

5-1992

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemical Engineering

Major Professor

George Frazier

Committee Members

Wayne Davis, Marion Hansen

Abstract

A novel batch ammonia regeneration system was designed to recover ammonia from a flue gas desulfurization solid waste produced from a pilot plant technology in which a conventional spray dryer is incorporated with calcium hydroxide and ammonia injection to desulfurize high sulfur flue gas. The ammonia regeneration system is needed for this waste because 1) the ammonium products in the waste tend to be soluble, 2) an ammonia odor is given off by the ash, and 3) leaching tests on the waste show a tendency towards selenium leaching. These three characteristics would make the waste difficult to dispose unless an ammonia regeneration system is applied to the waste prior to disposal. This study developed an experimental ammonia regeneration reactor to use on the waste. In the reactor, ammonia is dissolved from the solid waste into an aqueous phase which is then air stripped to recover the ammonia gas. Various parameters affecting this dissolution/stripping process (i.e. pH, temperature, solids loading, and gassing flow rate) are investigated through experimentation using the laboratory scale reactor. The ammonia regeneration process is also modeled using material balance equations for each of the three phases: solid ash, aqueous, and gaseous, in which the ammonia is found during experimentation. The overall results of the experimentation demonstrated that the reactor system can regenerate up to 95% ammonia in no more than 45 minutes with a pH of 11, a temperature as low as 45°C, a solids loading of 100 g/L, and with easily obtained air flow rates of approximately 33 liters/liter-min. The mass transfer model predicts similar ammonia regeneration results and is found to be in relatively good agreement for 12 out of 14 of the experiments modeled. The model is based on the existence of two forms of ammonia in the solid. These two forms include a strongly bound ammonia, believed to be ammonium sulfite, and a weakly bound ammonia, believed to be adsorbed ammonia. The mass transfer model with the best correlation to the experimental data included four stages of the ammonia regeneration process: 1) the conversion of strongly bound ammonia to weakly bound ammonia by a first order reaction, 2) the dissolution of the weakly bound ammonia into the aqueous phase, 3) the stripping of the ammonia from the aqueous phase, and 4) the removal of ammonia in the gas phase from the reactor.

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