A raw mill is an equipment to grind cement raw materials : limestone, clay, silica stone, iron oxide and gypsum. These materials need to be mixed in appropriate proportion.raw mill - cement plant
Blast furnace slag from iron & steel plants, ash from waste incineration plants are also used as cement raw material. In a raw mill these raw materials are ground with roller and then blown up with hot gas drawn from the bottom. This raw material is dried and ground very finely to obtain “raw meal”. Only the materials fine enough can pass through the separator and are carried away toward the next process.
Instrumentation for raw mill :
Electrostatic precipitator is used to remove harmful particles in gas.It removes fine particles, like dust and smoke, from flowing gas using the force of an induced electrostatic charge minimally impeding the flow of gases through the unit.
Because electrostatic precipitators are less troubled by pressure loss and are extensible, they are widely used in large boilers and cement plants. They can treat gases beyond 350°C and highly humid gas. It serves as the final filter which can remove particles of about 0.05 µm.
Instrumentation for electrostatic precipitator :
Stack allow emission of flue gas generated through fuel combustion.
Flue gas is blown an induced draft fan toward stack. Then it is emitted from stack to be diluted into the atmosphere. Height of stack should be determined after considering the effect of weather, geography and neighbouring construction and spread of regulated materials as well.
In this regard air pollution monitoring equipment is indispensable.
Instrumentation for stack and utilities :
Raw meal must be preheated before being introduced into the rotary kiln.
Raw meal is fed into the preheaters heat exchangers aligned vertically. As it passes down through preheater vessels, it is heated to a temperature of 800°C – 900°C with exhaust gas drawn from the rotary kiln.
In this process chemical reaction occurs in the rawmealand it improves calcination efficiency.
Instrumentation for preheater :
A boiler is a closed vessel in which water or other fluid is heated or vaporized to supply steam or hot water to other equipment or facilities. Fire, high temperature gas or electricity are used as a heat source of boilers.
Water-tube boiler : Two drums arranged upper and lower, connected each other by a number of water tubes, through which water is circulated. The tubes are heated by combustion gas to generate steam.
Instrumentation for boiler :
The rotary kiln (a brick-lined metal tube 3-5 meters wide and 30-60 meters long) rotates about 3-5 times per minute, and the raw material flows down through progressively hotter zones of the kiln towards the flame.
Raw meal is heated up to 1450°C while being rotated. It is cooled with cool air to form cement clinker.
The hot air in the cooler is sent back to the preheater to save fuel and energy.
Instrumentation for rotary kiln :
The clinker is then grounded very finely in a cement mill with other additives (ash from thermal power plants, blast furnace slag or gypsum) to obtain different quality of cement. The cement is then stored before delivery.
Instrumentation for cement mill :