cement manufacturing process flow chart
The following section discusses the cement manufacturing process in detail, with specific reference to the PPC Port Elizabeth (PE) factory, including process flow diagrams and photographs from the PE kiln program and operational equipment.
The Cement Generating Process
PE manufactures Ordinary Portland Cement (OPC) and Surebuild Cement. PE’s production is supplemented with clinker and / or cement from Slurry when necessary.
PE presently has 1 operating kiln, PEK four. The kiln is really a long dry kiln, which was commissioned in 1966. The kiln is 132m lengthy and 3.75m in diameter, and isn’t equipped with a preheater. The clinker from the PE kiln is cooled in a planetary clinker cooler. The kiln will not have a conditioning tower; however the exit gases from the kiln are cooled by direct water injection. All the exhaust gas streams at PE (from the raw mill, finishing mill and kiln) pass through ESPs to minimise the dust emissions from the factory.
Cement clinker is made by crushing, blending and fine milling of limestone (calcium carbonate) and other materials containing silica, alumina and iron oxides, which are then heated to temperatures as high as 1,450°C in a kiln exactly where the compounds react chemically to form clinker. The clinker is then cooled and ground with little quantities of gypsum and other additives to create cement. The heating method is performed in a rotary kiln, that is inclined at 3 – 4 towards the horizontal. The length and diameter from the kiln is dependent on the type of manufacturing procedure.
Primary Raw Materials
Limestone employed at PE is mined from Grassridge Quarry aapproximately 40 km north of the plant.
The limestone is passed by means of multiple-stage crushers in the Grassridge quarry, exactly where it’s decreased to much less than 19mm in diameter. Sand, shale/clay and haematite are also used as raw supplies. The raw supplies are milled together in a raw mill, to a fine powder and sent towards the blending silo for homogenisation. The homogenised powder, referred to as kiln feed, is stored in silos before use. Roughly 1.5 – 1.6 tons of kiln feed is necessary to generate one ton of clinker.
The main fuel employed in South African cement kilns is coal. It’s transported to PE by rail, exactly where it is ground to fine dust in a coal mill, and stored in a silo. The fine coal dust is accurately metered into the kiln firing program. The coal has a calorific value of 24-26MJ/kg, hence to produce 100 tons of clinker, 15-18 tons of coal are burned per 100 tons of clinker.
Secondary Raw Materials
According to availability and chemical composition, additional components could be added towards the raw mix. These are referred to as “Secondary” raw supplies. Examples are coal fly ash from power stations, steel slag, foundry sand, lime sludge, FCC catalysts from oil refineries, and many much more.
Apart from raw supplies, extra fuel sources could be added for the coal to fire the kiln. Examples consist of Spent Pot Lining (SPL) and tyres.
Only refractory SPL is currently utilized as a secondary material at PE. It’s received from BHP Billiton, Richards Bay, and stored in the quarry. It is crushed and transported for the factory, exactly where it’s included using the coal for the firing in the kilns.
The rotary kiln is a cylindrical steel vessel, that is inclined for the horizontal at 2.5% to 4.5%. The kiln slowly rotates at 0.5 – 4.5 revolutions per minute to allow the material to tumble by means of the kiln to ensure adequate residence time in the kiln to accomplish the needed thermal conversion processes.
The finely ground coal is fed for the firing end of the kiln exactly where it really is burned to create a gas temperature of around 2,000°C.
A preheater consists of several stages contained in a tall preheater tower, which utilizes the heat produced by the flame at the firing end from the kiln to preheat the raw supplies as they move by means of the various stages of the tower. Kiln systems with preheaters are a lot more fuel effective than extended kilns, making use of up to 50% less energy. Long dry kilns, like at PE, have no preheater.
The prepared raw mix, now referred to as kiln feed, is fed towards the kiln method, directly into the long dry kiln. Extended dry kilns are not equipped with preheaters and as a result, the initial heating in the kiln feed occurs within the kiln itself. To make sure sufficient heating for the thermal processes, the kiln is created to become a lot longer. Lengthy dry kilns represent an older less power effective cement manufacturing technology, and are being phased out as more cement manufacturing plants alter towards the newer shorter kilns with multi-stage preheaters.
Once the clinker has formed, and has arrived in the firing end from the kiln, it drops into a planetary cooler, exactly where the clinker is cooled to roughly 100°C above ambient. It’s then transported to the clinker storage silos.
The properties of clinker (and therefore, in the cement produced from it) are mainly determined by its mineral composition and its structure (silicates, aluminates and ferrites of the element calcium). Some components within the raw materials such as the alkalis, sulphur and chlorides are volatilized at high temperature inside the kiln system resulting in a permanent internal cycle of vaporization and condensation (“circulating elements”). A large component of these components will stay within the kiln system and will finally leave the kiln incorporated in the clinker. A tiny component will be carried using the kiln exhaust gases and will primarily be precipitated with the particulates in the dedusting program.
Milling and Final Product (Cement)
Portland cement is created by grinding clinker, with a small proportion of gypsum (or calcium sulphate di-hydrite) and an extender, like limestone, slag or fly ash. Gypsum is utilized to manage the setting times of the final cement items. The materials are milled together in a finishing mill. The final cement product is stored in silos by product sort.
PE manufactures OPC and Surebuild; each and every cement kind is defined by the proportion of materials added throughout the above milling method.
Cement is dispatched either in bulk or in 50kg bags and distributed from the manufacturing plant by way of rail or road. The 50kg bags are palletised, with 40 bags per pallet and loaded via forklifts onto road trucks.
Summary of inputs and outputs
The cement manufacturing method has several inputs and outputs. Raw materials and fuel items (inputs) are converted to clinker (item), emissions and Cement Kiln Dust (CKD) (outputs) within the cement kiln.
It ought to be noted that there is no continuous method waste generated from the cement manufacturing method.
The main constituents of fuel ash are silica and alumina compounds which combine with the raw materials to turn out to be component of the clinker. As the cement manufacturing process is really a thermal method, you will find resultant pollutants emitted via the stack. Under typical operating conditions, emissions that will be expected from the stack consist of:
a) Cement Kiln Dust (CKD)
b) Sulphur Dioxides (particularly SO2)
c) Nitrogen Oxides
d) Carbon Dioxide and Carbon Monoxide
e) Trace Metals
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