Using calcining equipment in the manufacture of cement and lime
The slurry moves from the basins into horizontal basins – each one capable of holding 8000 cubic metres of slurry. The slurry is mixed in the basins, using either a paddle mixing system or compressed air (or possibly a combination of the two, or other methods). This keeps the slurry in a permanent condition in which it is ready and available for baking.
Next, pumps are used to feed the slurry into flurry feeders, which bring it to the rotary kiln. Due to the 3-4% angle of the body of the kiln, and to its rotation, the raw material is moving against a stream of continuous hot convective gases and radiated heat from the gas stream and the heated casing. When this kind of thermo-physical heat is applied – 'baking' – the material which is placed in the kiln dries out, loses its free and bound-in water, after which it changes its structure and chemical make-up. It emerges from the kiln as clinker, at a temperature of 1200-1250° C.
The flue gases from the kiln chamber pass through a dust-settling chamber and an electrofilter, after which the cleaned gas is ducted into the atmosphere through a chimney. The dust which is deposited in the dust-settling chamber and the electrostatic system is fed by a pump back into the system, and ducted once again into the kiln.
The hot clinker emerges from the kiln and is directed into a cooler, where its temperature is reduced by air from fans. The air, which becomes heated as a result of contact with the hot clinker, is fed into the kiln in amounts necessary for burning the fuel, and mixed in with sprayed cold air. The unwanted excess is sucked out of the cooler by suction fans – and once it has passed through a cleaning process of precipitator cyclones is then expelled into the atmosphere.
Once the clinker has cooled to temperatures of 50-80°С, it is fed by conveyers to the clinker store, which is equipped with silos. The clinker moves from the silos through a dispenser system, and once additives have been mixed in, it passes to the mill for cement-grinding.
Cement from the mill is either fed into silos by a pneumatic chamber pump, or sent to the packaging department.
Equipping the production line for dry-line cement production
The raw materials are limestone and clay. The limestone goes through a two-phase crushing-jaw process, after which it is fed into hammer mills. The clay is ground in roller mills and then dried in a rotary tumbler. All of the raw materials which come from the stores are sent to a bunker equipped with shutters and weight-dispensers, and then delivered by conveyor into the feed hopper of the mill.
At the raw material milling section there are two mills for raw materials, capable of accepting materials 4.2 x 10 mm in size. In conditions where the ambient humidity does not exceed 8%, the mill runs using a supply of hot drying gas produced by external heat exchangers. If the humidity level is higher, the raw materials are first fed into a furnace-box, whose hot gas exhaust is reused and fed into the mill.
Both of the two mills operate using a pneumatic discharge system equipped with an air separator. The material filtered by the separator is fed back into the mill for re-milling, while the finished product is fed through cyclones, pneumatic conveyors and size-meters to go as dry raw powder into silos which are equipped with an aerated mixing system. From these silos the cement powder goes through pneumatic conveyors and then on a pneumatic hoist to the cyclone pre-heaters – where it is heated by hot exhaust gases from the kiln to temperatures between 700-750°С and partly decarbonised (up to 20%), after which it is fed into a rotary kiln.
During the normal operating process the gas which feeds out of the heat exchangers is dispatched through a flue into the raw mills, from which a further flue runs through an electro-filter for the de-dusting process, and then using a suction fan into the exhaust chimney. The temperature of the gas coming out of the mill is approximately 50°С. However, if the mills are not running, then the gas which emerges from the cyclone heat-exchangers runs at temperatures of between 300-350°С, and are cooled through a water-spraying process in the gas exhaust until they reach the required temperature.
A notable aspect of the baking process is that the degrading of the raw material and its partial decarbonisation take place in the zone of the external heat exchangers. This makes the baking process shorter, if we compare it to manufacturing procedures using the 'wet' method.
The clinker which emerges from the kilns is sent to coolers, and then fed on slat conveyors into silos. From there a dispenser system takes it by conveyor, mixed with additives, and on to be ground in the cement mill. The cement emerges from the mill and is fed by pneumatic chamber pumps into silos. The re-used hot gases from the chillers are fed into the bunker.
The process described above can be adopted according to need for specific production facilities, factoring in the characteristics of the raw materials being used and the specific end-use to be made of the product. The Strommashina Plant in Samara can carry out a complete audit for the design of a calcining production line. You can purchase a reliable calcining kiln at very attractive prices right now! This will guarantee a top-quality production result from the equipment you purchase! Our many years of experience at Strommashina are based on the continual introduction and development of innovative processes and machinery in manufacturing.