Mechanisms Involved in Fly Ash Precipitation in the Presence of Conditioning Agents - A Review
Conditioning agents are usually used to improve the collection efficiency of electrostatic precipitators by causing a reduction in the resistivity of the fly ash. However, certain conditioning agents may have other effects including changing the electrical breakdown strength of the flue gas, space charge enhancement of the collecting field, increasing the mean particle size, changing the adhesion and cohesion properties of the ash, and changing the acid dew point of the flue gas. These mechanisms are reviewed and related to results reported in the literature for ammonia and triethylamine, two conditioning agents which appear able to affect one or more of the mechanisms mentioned above, in addition to the resistivity.
Statistical modelling and optimization of hydrolysis of urea to generate ammonia for flue gas conditioning.
The present study is concerned with the technique of producing a relatively small quantity of ammonia which can be used safely in a coal-fired thermal power plant to improve the efficiency of electrostatic precipitator by removing the suspended particulate material mostly fly ash, from the flue gas. In this work hydrolysis of urea has been conducted in a batch reactor at atmospheric pressure to study the different reaction variables such as reaction temperature, initial concentration and stirring speed on the conversion by using design expert software. A 2(3) full factorial central composite design (CCD) has been employed and a quadratic model equation has been developed. The study reveals that conversion increases exponentially with an increase in temperature, stirring speed and feed concentration. However the stirring speed has the greatest effect on the conversion with concentration and temperature exerting least and moderate effect respectively. The values of equilibrium conversion obtained through the developed models are found to agree well with their corresponding experimental counterparts with a satisfactory correlation coefficient of 93%. The developed quadratic model was optimized using quadratic programming to maximize conversion of urea within experimental range studied. The optimum production condition has been found to be at the temperature of 130 degrees C, feed concentration of 4.16 mol/l and stirring speed of 400 rpm and the corresponding conversion, 63.242%.
Occupational Therapy Graduate Education: The Scientist-Practitioner Model
The development of a scientific based practice is essential if occupational therapists are to defend their practice against scepticism and budget cuts. In order to equip the profession with the skills necessary to develop a scientific basis for practice, it is generally considered that graduate programs in occupational therapy should be initiated. This paper argues that to be most effective a specific kind of graduate program is required — one based on the scientist-practitioner model. This model provides for the dual education of professionals as clinicians and researchers. In occupational therapy the undergraduate curricula already provide excellent education in clinical interventions. Thus, it is the role of the graduate curricula to provide education in methods of scientific inquiry and their application to clinical practice. The composition of such a curriculum is described.