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.
Conditioning of fly ash with ammonia
This paper presents the results of an investigation of the conditioning of fly ash with ammonia in electrostatic pre-cipitators of power plants operated by the Tennessee Valley Authority. It focuses attention primarily on the mechanisms of conditioning encountered under the particular circumstances available for study. No effect of ammonia on the electrical resistivity of fly ash was evident. Instead, the effect of ammonia appeared to be an enhancement pf the space-charge component of the electric field used for charging and precipitating particles of fly ash. In addition, a second effect appeared to be an increase in the cohesiveness of precipitated ash and a reduction in the quantity of ash reentrained during electrode rapping. Data demonstrating the value of ammonia conditioning for lowering the emission pf fly ash during three precipitator studies are presented. Reasons for the ineffectiveness of ammonia conditioning during a fourth precipitator study are discussed. In conclusion, comments are made ab...
Scaffolds Containing Spirulina sp. LEB 18 Biomass: Development, Characterization and Evaluation of In Vitro Biodegradation.
Polymer nanofibers are nanomaterials that can be used as scaffolds in tissue engineering. The objective of this study was to develop, characterize and evaluate the in vitro degradation of a biomaterial consisting of nanofibers produced from biodegradable and biocompatible polymers with potential applications as a scaffold for tissue regeneration and containing Spirulina sp. LEB 18 biomass as the bioactive compound. The polymers used were poly(hydroxybutyrate-co-hydroxyvalerate) and polycaprolactone. The polymeric solutions exhibited sufficiently high viscosity to produce uniform nanofibers with diameters between 335 and 617 nm. The applied conditions were as follows: a voltage of 25 kV, a distance from the capillary to the collector of 120 mm, a capillary diameter of 0.80 mm, and 12% polycaprolactone and a blend of 5% polycaprolactone and 10% poly(hydroxybutyrate-co-hydroxyvalerate). The biomass was incorporated into the nanofibers at a concentration of 3%, and the incorporation was confirmed using confocal microscopy. The nanofibers were characterized using differential scanning calorimetry and thermogravimetric analysis, which showed that the addition of biomass did not alter the thermal properties of the biomaterial. The addition of biomass improved the tensile strength and elongation of the scaffolds compared with those produced with polymers alone. A biodegradation assay showed enzymatic action toward the biomaterial, simulating the behavior of natural tissue. Based on the analysis, it was concluded that the scaffolds that were produced have the potential to be applied in the field of tissue regeneration as biomaterials with pharmacological properties.