EIGHT YEARS OF PROGRESS IN BURNING TECHNOLOGY

摘要

During the last eight years world cement production has increased by about 450 million t/a (36 %), including a substantial contribution from modernization projects. Numerous plants still operate using the wet, semi-wet and semi-dry processes, but the dry process is used almost exclusively in new plants and conversions. Lower specific energy consumption can be achieved primarily by better efficiency of the clinker cooler, reduced kiln stoppages and more stable kiln operation. The advantages of precalciner technology are now being utilized even for throughputs less than 1 500 t/d. Modern calciners make it possible to use fluctuating mixtures of fuel with a high percentage of secondary fuels. All new calciners are equipped with tertiary air systems; the majority of new kiln lines have five.preheater stages. The plant manufacturers aim to achieve good cyclone collecting efficiencies with low pressure drops in spite of the compact preheater dimensions. Optimized bypass plants are needed to deal with the increased inputs of substances which form recirculating systems when using secondary fuels. The advantages of the kiln on two support stations are recognized and have been implemented in numerous plants. Further developments in the field of kiln mechanics have made it possible to drive the kiln by friction through driven support rollers without the use of girth gears. Further spread of two-support kilns conflicts with the increasing use of secondary fuels in the burning zone which leads to longer flames and the associated tendency to require a longer kiln. Planetary and rotary coolers are in operation in many older plants, but new plants are equipped exclusively with grate coolers. There have been further improvements in grate cooler technology. A new type of cooler characterized by a completely riddlings-free static grate and a separate thrust beam system for conveying the clinker has been used successfully since 1998. Clinker with higher lime saturation factors, increased use of secondary fuels and the abatement of nitrogen oxides have led to modern multi-channel burners with powerful axial momentum which permit stable kiln operation with a short fierce flame. The use of secondary fuels places increased demands on the resistance of the refractory systems to temperature and chemical attack. There has been a continuous trend towards monolithic solutions, in which increasing use is being made of precast and fibre-reinforced elements. 3