Date of Award

Fall 1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering - (Ph.D.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Henry Shaw

Second Advisor

Edward Charles Roche, Jr.

Third Advisor

Howard David Perlmutter

Fourth Advisor

Barbara B. Kebbekus

Fifth Advisor

Norman H. Sweed

Abstract

The use of chlorine (Cl2), sodium hypochlorite (NaClO), and sodium chlorite (NaClO2) as oxidizing agents to promote the absorption of nitric oxide (NO) from gas streams has been investigated in the Gas Scrubbing Laboratory of New Jersey Institute of Technology since 1988. The first step of this project had been to screen out the best scrubbing medium for nitric oxide removal from flue gases. The most successful oxidizing agent was found to be sodium chlorite in acidic aqueous solution. The screening results have been accepted for publication in Chemical Engineering Communications. A sodium chlorite containing aqueous acid solution quantitatively absorbs nitric oxide in a 5.1 cm in diameter by 61 cm long bubble column scrubber. Under the same conditions, 90% removal were achieved with either chlorine gas or sodium hypochlorite aqueous scrubbing.

An analytical instrument train, consisting of a Thermoelectron model 10A NOx analyzer, Beckman model 715 process oxygen monitor, and Rosemount model 890 UV SO2 analyzer, was set up to measure the concentration changes of inlet and outlet flue gas components. A preparatory liquid chromatography equipped with UV/Visible range photodiode array detector was set up for scrubbing solution real time monitoring of oxychlorinated compounds. Chlorine dioxide was found to be the active ingredient in the sodium chlorite aqueous scrubbing, while hypochlorous acid was the key oxidant for both chlorine and sodium hypochlorite scrubbing processes. During the operation, nitric oxide was oxidized to nitrate ion and sulfur dioxide to sulfate ion and were collected in the scrubbing solutions. At the same time, oxychlorine compounds were reduced to chloride ion, which was analyzed by ion chromatography.

To obtain the reaction rate of nitric oxide with sodium chlorite aqueous solution for process design consideration, a droplet surface reaction model was derived to correlate experimental data from spray tower scrubber. The model predicted conversion of NO very well but not absorption because the model does not predict breakthrough of nitrogen dioxide (NO2). Therefore, a model of absorption with chemical reaction was used to study the absorption of NO in a packed bed scrubber to determine the feasibility of controlling all air pollutants in one scrubber. In the model, theoretical height of transfer unit (HTU) was used to evaluate the efficiency of scrubbing solutions. The influence of different variables such as temperature, pH, gas stream flow rate, concentration of sodium chlorite, and other components in the flue gas on height of transfer unit was evaluated.

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