Analysis Of Thermal Process For Grate-Kiln Pellet System

As a new-style technology of pelletizing production, the grate-kiln has such advantages as simple device, uniform roasting, single great capacity of production and strong raw material adaptability. When it once came, the world steel industry aroused widespread attention and expanded it widely. During the whole process of pelletizing production, the production is always in a closed system and the monitoring is complex, which leads to the possesses blindness and hysteresis quality of manual operation, as well as the problems of energy waste and large emission of waste gas on the aspect of system technology. This paper is on the background of the pelletizing plant BXsteel’s grate-kiln system and solves the above problem.The main contents of this paper as follows:(1) In allusion to the problems of heated-air circulation system, improvement project is carried up and analyzed. Installing grate plate waste heat recovery room, sensible heat of grate plate can be recovered by62%and energy waste is decreased. Transforming four-parts circular cooler into five-parts circular cooler and reforming parallel connection air feed into series connection air feed, each outlet temperature of circular cooler is increased by80-130℃and high wind temperature is obtained.(2) Based on the analysis of grate, rotary kiln and circular cooler’s heat transfer mechanism, three mathematical models are established and solved with software program, which is programmed by MATLAB. According to field data, validities of the mathematical models are verified(3) Discussing calculation results and analyzing the change regularities of the pelletizing temperature when the operation parameters of the production process, such as output, fuel, blast temperature and speed, changing. Several conclusions are obtained:①With the chain grate’s speed decreased, the thickness of material layer reduced, blast temperature and speed rose, the pellet temperature in the grate increases;②With the rotary kiln’s input quantity, rotate speed and fuel reduced, the pelletizing temperature at the outlet of rotary kiln decreases;③With the circular cooler speed increased and wind speed decreased, the pelletizing temperature at outlet decreases, the gas temperature and thickness of material layer decrease, which leads to the pelletizing temperature at outlet and gas temperature decrease.