OCR Text |
Show grinding tools are shown in Figure 7. Aside from the grinding and homogenizing effect, the mill also exhibits a pump characteristic which is utilized to advance the mixture to the storage tank. The fineness of grinding was aimed at 90% smaller than 90 i/*-m. However, for a complete final combustion of the particles in a coal-oil mixture, grain sizes of up to 150 ilm should not present a problem. The actual particle size obtained was in this range. Repeated re-grinding of the mixture in the mill only brought insignificant changes in the fineness of the particles. The grinding tools were subject to a noticeable erosion which essentially related to the hardness and the stone content of the coal. In this regard, the grinding unit leaves room for improvement. -^ ~'<f* ^^ ^^ The transport of the coal-oil mixture from the storage tank to the burner is provided by a variable speed positive displacement pump. Under normal operation the throughput was approximately 1.3 t/h. Combustion of the Coal-Oil Mixture Figure 8 shows the ultrasonic burner installed on the rotary kiln. In the burner a nozzle of the type GOS-Jet with additional concentric pipe was installed, as previously shown in Figure 3. This facilitated the use of heavy oil alone during start-up in bringing the kiln temperature to 1200°C. After this, the system can be switched over to burn C O M. In the actual installation, the COM passes through a pipe of 9.5 mm diameter. It was operated with a mixture temperature at the burner inlet of approximately 90 C. Slightly superheated steam at 3.5 bar absolute was used for atomizing. About 15% of the combustion air was fed through the burner body, while the remaining 8 5% enters the rotary kiln directly at a preheated temperature of about 430°C. The ultrasonic burner produced a long stable flame that is desirable in rotary kiln operation. The fuel atomizing and the intermixing with air was very good. Even under partial load operation, no deterioration of combustion conditions occurred. The high viscosity of the coal oil mixture had no adverse effects on the atomizing process. 16-9 |