Vessels used in the alumina refining process require periodic scale removal, which is presently a very hazardous and costly procedure. High-pressure water jets are currently used for some de-scaling tasks; however, more productive scale removal may be achieved using alternative jet types. This research investigated various configurations of devices that produce cavitating and pulsed water jets to identify effective designs and assess their suitability for industrial use.
Laboratory experiments were conducted with artificially-submerged cavitating jets and externally-interrupted pulsed jets. Stationary and traverse operating modes were used to examine the cutting ability of these jets in simulated scale material. Jet performance was assessed based on the cutting depth after specific exposure periods. To allow comparison of performance, tests were also conducted with the jet type that is currently used for scale removal. A range of variables was investigated, including nozzle size, nozzle design, stand-off distance and exposure time. Each type of device also had its own set of parameters that were altered to affect the jet configuration.
Experiments with artificially-submerged jets operating in a stationary mode demonstrated that a new nozzle design (hom nozzle; 13 degree inlet, 20 degree outlet) was capable of producing a 25 percent more effective jet than the type currently used for de-scaling. Many configurations of the artificial-submergence device provided significantly improved stationary cutting (compared to the jets operating unsubmerged); however, similar performance increases during traversing operation were not realised. Preliminary field testing with an artificially-submerged cavitating jet demonstrated that its performance (scale penetration rate) was unquestionably superior to that of existing water jet devices. Investigation of pulsed jets operating in a stationary mode was limited to small diameter nozzles. The most effective pulsed jet configuration was up to 95 percent more effective than the continuous jet type currently used for de-scaling. This was achieved with a device configuration that allowed less than one-third of the jet to reach the target. Larger pulsed jets are expected to offer similar performance increases. Traverse testing indicated that pulsed jets are less effective than continuous jets for cutting slots in scale material.
With minor modifications, the artificial-submergence and pulsed jet devices could both be used for industrial scale removal operations; however, the pulsed jet device appears to be more suitable for field use. More comprehensive field testing is required with both types of device to allow proper assessment of the potential productivity gains. Further development of the pulsed jet device may dramatically improve its efficiency.
Although more research and development is required to identify optimum device configurations (and ultimately more efficient designs), this study has demonstrated that practical devices can be produced to create cavitating and pulsed high-pressure water jets that may significantly improve de-scaling productivity.