M.Ing. / Deposition of scale on heating surfaces is a major problem in industry as well as households. The scale that forms on the heating surfaces acts as an insulator and results in decreased heat transfer effectiveness . These are two main approaches to prevent or reduce scaling. Although these approaches are claimed to be efficient, there is a need to evaluate or verify their efficacy. This calls for a method which should preferably enable quantitative and rapid evaluation of these techniques in the laboratory. A reliable, rapid and quantitative measurement method which was comprised of stripping the scale from heat exchanger pipes with a 10% acetic acid solution and measuring the Ca concentration in the acid after stripping, was developed. A total of 11 tests, 7 to test the reproducibility, 2 to test a physical water treatment device and 2 to test the effect of zinc, were conducted. The reproducibility amongst different pipes, and amongst different experiments could not be achieved. Attempts to explain the inconsistency through statistical analysis of the data showed that, the inconsistency in the results could partly attributed to chemical differences, particularly changes in calcium concentration and TDS. Metal contamination, particularly zinc could also be responsible for a part of the inconsistency.

D.Phil. (Chemistry) / The formation ofcalcium carbonate scale is a major problem in industry as well as in households. The scale that forms acts as an insulator, decreasing the effectiveness ofheat exchangers, be it a water cooling systems or a water heating system This raises the energy costs ofthat company and the costs of cleaning are expensive. Physical water treatment has been used for at least 50 years in the treatment ofwater with scale forming potential to reduce the formation ofthis scale. In thisthesis, tests were made on a magnetic and constantelectric field antiscaling device on the effect they have, ifany, on CaC03 scale formation. An attempt will be made to give a mechanism for any effect found. It is hoped that a contribution is made by this research in clearing up the misconceptions that abound in this controversial field ofphysical water treatment. Water with a high calcium bicarbonate content was exposed to the antiscaling devices and then calcium carbonate was forced to precipitate out ofsolution. This precipitation was followed by meauring the pH and the crystal structure ofthe precipitated calcium carbonate was studied. The most important results were that by exposing the calcium bicarbonate solution to an antiscalingdevice, the start ofprecipitation ofthe calcium carbonate was significantly delayed and the crystal structure of the calcium carbonate that formed was predominantly aragonite as opposed to calcite that usually formed.

M.Ing. / Fouling and more specifically scaling is one of the most discussed and not yet well understood problems facing engineers. Scale formation which has enormous economic and environmental consequences does not only influence heat transfer characteristics and pressure drop through tubes, but influence the volumetric flow rate as well. To solve this problem Physical Water Treatment (PWT) devices have been developed which reportedly reduce scale formation. The efficiency of PWT devices is a controversial subject and many contradictions exits in the claimed effect. Researchers have been trying to prove the efficiency of PWT devices but in most cases the results are typically characterised by low reproducibility. An experimental measuring technique is thus required to measure scale formation and the influence PWT devices has on scaling. This technique must also produce reproducible results to clarify the questions surrounding PWT devices. This thesis is an experimental investigation in which an experimental setup and measuring technique is developed. It is used to evaluate a permanent magnet for the decrease of scale formation in tubes. The volumetric flow rate is used as the indicator of scale formation, which relies on the basic principle that the friction pressure drop increases if scaling takes place. The volumetric flow rate is monitored by measuring the time necessary to fill a container of known volume. The test section consists of three soft drawn copper tubes in which water with a velocity of ± 2 m/s flows. One of the tubes is used to evaluate the PWT device and the other two tubes are used as a control. The water temperature is kept at 53°C. The experiments are done in five phases in which the PWT device is placed onto one of the tubes in phase four and removed in phase five. It follows from the results obtained that a very sensitive experimental setup was designed and built which can be used to evaluate the efficiency of PWT devices. It follows from the variation in time necessary to fill the container in phase four and five that a clear conclusion can not be made. More experiments must be done in which reproducible results are obtained.

D.Ing.

Weyerhaeuser's Paper Mill in Albany, Oregon has been experiencing frequent ring formation in the #3 rotary lime kiln. Rings form when lime mud (CaCO₃) or product lime (CaO) particles adheres to the walls of the lime kiln and become resistant to the abrasive action of the sliding motion of product lime particles (Notidis, 1994). Ring formation has resulted in frequent shut downs to remove (blast) the rings and caused a significant loss of productivity and revenue to the company. A careful analysis of the production process in the mill revealed that concentration of sodium was high and that of sulfur low in the lime mud. The high sodium was due to the low sulfur input to the kiln resulting in high sodium to sulfur ratio. The use of natural gas as a fuel source in the kiln partly causes low sulfur levels in the mud. This study examines the effects of burning emulsified sulfur in the #3 rotary lime kiln to reduce sodium enrichment in the solids, and examine its effect on kiln operation and SO₂ emissions from the #3 rotary lime kiln. A four day trial of burning emulsified sulfur to reduce sodium concentration in the #3 rotary lime kiln was planned. Tote bins of 70% solution of emulsified sulfur was fed into the #3 rotary lime kiln. The sulfur feed was controlled to ensure an excess of sulfur by observing the SO₂ concentration in the kiln stack and maintaining a concentration above 100 ppm corrected to 10% oxygen. The results show that while burning emulsified sulfur had no significant effect on kiln operation, it resulted in a high reduction of sodium in the dust caught in the electrostatic precipitator and an increase SO₂ emission from the stack. The reduction of sodium in the dust was 50%, which is an enrichment factor of 2. Although lime can effectively remove SO₂, the removal efficiency decreased from 96.0% to 73.0% when emulsified sulfur was burned in the #3 rotary lime kiln. The results of this trial are promising, since it demonstrates that burning emulsified sulfur significantly lowers the sodium enrichment in the kiln. The reduced levels of sodium can potentially lead to a reduction in ring formation in the #3 rotary lime kiln in the Albany Paper Mill. / Graduation date: 2004

Reproduction de : Thèse doctorat : Chimie physique industrielle : Reims : 2007. / Titre provenant de l'écran titre. Bibliogr. f. 153-178.

No description available.

No description available.

Thesis (Ph.D.)--Ohio University, November, 2004. / Includes bibliographical references (p. 161-171)

Thesis (M.Applied Science(Metallurgical Engineering))--University of Pretoria, 2008. / Abstract in English. Includes bibliographical references.