Technological possibilities of using natural gas in shaft furnaces for limestone roasting

Abstract

One of the ways to improve the technology of limestone roasting in shaft furnaces is associated with improvement of conditions of combustion with natural gas when burning it directly in the layer. To implement this technology, it is necessary to ensure the development of two parallel processes: preparatory, in which the initial gas-air mixture is formed and heated to the ignition temperature, and the main one, during which a layer of combustion of gaseous fuel occurs. At air-blast tuyere feed and at coaxial jet supply of gaseous fuel under increased pressure when there are gas permeable nozzles in the path, a more powerful gas flow (natural gas) flows out of the nozzle at high speed into the external environment. It creates conditions for air flow ejection. Inside the annular space between the streams, a combustion zone is formed, on the inner and outer side of which there are circulating vortices directed along the axis of the jet to the nozzle. It improves stability of the gas-air mixture ignition. The considerable range of turbulent jets (at elevated pressures of the gaseous medium), as well as the possibility of sufficient complete mixing in the boundary layer, opens up the possibility of forming a gas-air mixture of a given composition along the front of the flare process, the movement of gas jets. To ignite the gas flow in the layer, it is necessary to ensure its preheating at least to a temperature of 800-1050 °C using a heat source located near its entrance. Energy efficiency of this direction is confirmed by experimental studies on a shaft furnace with a working space with diameter of 3 m. According to the results of experimental sounding of the heated zone of a limestone shaft furnace (in the mode of layer burning of natural gas), regularities were established in changing the temperature field of the burning layer with the formation of maximum temperature of 1200 °C at a distance of 200mm from the nozzle section. The depth of formation of the combustion zone was limited to the level of 110mm with the spread of the region of high temperatures over a distance of up to 1000 mm. Technological possibility of forming a region of high temperatures of 1100-1600 °C with a length of the high-temperature zone up to 2000mm was established. © 2020 National University of Science and Technology MISIS. All rights reserved.