Abstract
This dissertation assesses the maintenance techniques employed to clean coal fired boilers used for power generation at SASOL Synfuels Power Station in Secunda, South Africa. Adequate maintenance of boilers used in power plants can result in improved efficiency of the boilers and this ultimately reduces operating cost of the power generation plant over the long term. This research investigates to improve the parameters required for the design of an acoustic apparatus for the online cleaning of these boilers as well as the design of a beam that can withstand the induced vibration from the horn. The theory is that sound energy from a sonic horn is converted to vibrations along the boiler tubes thereby dislodging soot. Using AutoCAD Invertor 2016, parts of the acoustic horn are modelled and simulated against predicted forces and pressures and then compared with calculated results. It was determined that the diaphragm will deflect by 0.5 mm under the action of a 552 kPa pressure. It was also found that the stress acting will be 816 MPa only if the diaphragm does not deflect and bleed out the air, hence the stresses will not reach their expected maximum. The acoustic horn chamber only experiences a pressure of 50 MPa which is acceptable. The acoustic cleaning solution presented in this dissertation is a combination of a horn and a beam which represents the boiler tube. The frequency of the beam used was found to be 70.67 Hz which falls correctly into the real-life limitation of (60 – 75 Hz). This frequency range is the most powerful and enough for cleaning silos and large vessels. A force matching this frequency was found to be 225 N which is also the fracture load and the maximum deflection caused by this force was found to be 26.2866 mm. Thus, there is a range of deflections for which the beam vibrates at close to its natural frequency. In theory the material selected was found to be significant (cast iron) and can reach a maximum deflection of 26.8866 mm and a maximum induced stress of 182.655 Mpa at a force of 820 N. In practice, however, this is not recommended as the beam will not have a long-life span, therefore, one should rather work at a force ranges of 220 N to 300 N as this is the force at which the beam can remove enough soot without undergoing serious damage. Acoustic cleaning technique, therefore, can improve maintenance of boilers which in turn improves the boiler’s efficiency while reducing outages.
M.Tech. (Mechanical Engineering Technology)