1. Wet production: the raw meal is made into slurry with water content of 32%-36%, and the raw meal slurry is dried in a rotary kiln until it is mature. Wet preparation of slurry, grinding energy consumption is low, about 30%, slurry is easy to mix, raw material composition is stable, which is conducive to firing high-quality clinker. However, the steel consumption in the wear-prone parts of the ball mill is high, the unit heat consumption of clinker in rotary kiln is 2093 ~ 2931kt/kg (500 ~ 700 kcal/kg) higher than that in dry kiln, and the outlet temperature of clinker is low, so it is not suitable to burn clinker with high silicic acid rate and alumina rate.
2. Semi-dry production: dry raw meal powder is added with 65,438+00% ~ 65,438+05% water to make pellets, which are calcined in a kiln, which is called semi-dry production. Rotary kilns with grate heaters, also known as Libor kilns and shaft kilns, are all semi-dry production. There is also a semi-wet production abroad. The slurry prepared by wet method is filtered and dehydrated by mechanical method, made into mud section with water content of about 19%, and then calcined in Lipol kiln. The moisture content of materials entering the kiln by semi-dry method is reduced, and the unit heat consumption of clinker in the kiln is also reduced by 837 ~1675 kj/kg (200 ~ 400 kcal/kg) compared with that by wet method. Because the grate heater is used to dry pellets instead of a part of the rotary kiln, the efficiency is higher, and the rotary kiln can be shortened, for example, the output per unit volume of the kiln can be increased by 2-3 times. However, the semi-dry method requires that the raw materials must have certain plasticity before pellets can be formed, which limits its application. There are many mechanical failures of heaters, and the calcination temperature in China is generally low, which is not suitable for firing high-quality clinker. Vertical kiln is semi-dry production, and it is the earliest calcining kiln used in cement industry. It evolved from a lime shaft kiln in the middle of 19th century, and developed into a mechanized shaft kiln in 19 10. Vertical kiln has small production scale, simple equipment and relatively low investment, which is most suitable for areas with relatively small cement market demand, inconvenient transportation and relatively low industrial technology level.
3. Dry production: The dry method is to directly send raw meal powder into the kiln for calcination, and the moisture content of raw materials in the kiln is generally only 1% ~ 2%, which saves a lot of heat needed for drying raw meal. In the past, the hollow rotary kiln was used in dry production, and the heat transfer efficiency in the kiln was low, especially in the decomposition zone with high heat consumption, and the thermal efficiency of the dry hollow kiln was not improved much. The raw meal powder prepared by dry method is not easy to mix evenly, which affects the quality of clinker. Therefore, wet production was dominant in the 1940s and 1950s. In 1950s, air stirring technology and suspension preheating technology of raw meal powder appeared. Pre-decomposition technology, raw material pre-homogenization and raw material quality control technology were born in the early 1990s, and now dry production can completely prepare raw materials with uniform quality. The new precalcining kiln moves the preheating of raw meal powder and carbonate decomposition to the suspended state outside the kiln, which has high thermal efficiency and reduces the load of the rotary kiln. Low heat consumption not only improves the thermal efficiency of rotary kiln from about 30% to over 60%, but also expands the production capacity of kiln. At present, the standard kiln type is 3000 t/d, and the largest is 10000. There are several specifications of 700t/d, 1000t/d, 2000t/d and 4000t/d in China, which are gradually developing to large scale. The invention has the advantages of good pre-combustion of raw materials, high temperature in the kiln, fast cooling speed of clinker, high silicic acid rate, high saturation rate and aluminum-oxygen ratio, and high clinker strength. Therefore, suspension preheating and precalcining kilns are now collectively called new dry kiln or new dry production line, and new dry production is the future development direction. The new dry kiln has a large scale, relatively high investment and high requirements for technical level and industrial supporting capacity. If the conditions are not met, it will be difficult to develop normally.