1. Cement history
Throughout history, cementing materials have played a vital role. They were used widely in the ancient world. The Egyptians used calcined gypsum as a cement. The Greeks and Romans used lime made by heating limestone and added sand to make mortar, with coarser stones for concrete.

2. Cement history
After the Romans, there was a general loss in building skills in Europe, particularly with regard to cement. Mortars hardened mainly by carbonation of lime, a slow process. The use of pozzolana was rediscovered in the late Middle Ages.

3. Cement history
Smeaton, building the third Eddystone lighthouse (1759) off the coast of Cornwall in Southwestern England, found that a mix of lime, clay and crushed slag from iron-making produced a mortar which hardened under water. Joseph Aspdin took out a patent in 1824 for "Portland Cement," a material he produced by firing finely-ground clay and limestone until the limestone was calcined. He called it Portland Cement because the concrete made from it looked like Portland stone, a widely-used building stone in England.

4. Cement history
A few years later, in 1845, Isaac Johnson made the first modern Portland Cement by firing a mixture of chalk and clay at much higher temperatures, similar to those used today. At these temperatures (1400 C-1500 C), clinkering occurs and minerals form which are very reactive and more strongly cementitious.

5. Cement history
While Johnson used the same materials to make Portland cement as we use now, three important developments in the manufacturing process lead to modern Portland cement:
- Development of rotary kilns
- Addition of gypsum to control setting
- Use of ball mills to grind clinker and raw materials

6. What is cement and how is it made
What is cement and how is it made? Cement is a fine, soft, powdery-type substance. It is made from a mixture of elements that are found in natural materials such as limestone, clay, sand and/or shale. When cement is mixed with water, it can bind sand and gravel into a hard, solid mass called concrete. Cement can be purchased from most building supply stores in bags and container etc.

7. Cement is usually gray. White cement can also be found but it is usually more expensive than gray cement. Cement mixed with water, sand and gravel, forms concrete. Cement mixed with water and sand, forms cement plaster. Cement mixed with water, lime and sand, forms mortar.

8. Cement powder is very, very fine. One kilo (2
Cement powder is very, very fine. One kilo (2.2 lbs) contains over 300 billion grains, although we haven't actually counted them to see if that is completely accurate! The powder is so fine it will pass through a sieve capable of holding water.

9. An example of how cement can be made
1.) Limestone is taken from a quarry. It is the major ingredient needed for making cement. Smaller quantities of sand and clay are also needed. Limestone, sand and clay contain the four essential elements required to make cement. The four essential elements are calcium, silicon, aluminum and iron.

10. 2.) Boulder-size limestone rocks are transported from the quarry to the cement plant and fed into a crusher which crushes the boulders into marble-size pieces. The limestone as mined is fed to a primary and secondary crusher where the size is reduced to 25 mm. Of late even a tertiary crusher is used to further reduce the inlet size to the mill. The crushed limestone is stored in the stockpile through stacker conveyors. The crushed limestone, bauxite and ferrite are stored in feed hoppers from where they are fed to the raw mill via a weigh feeders in the required proportion.

11. 3.) The limestone pieces then go through a blender where they are added to the other raw materials in the right proportion.
Calsium
Silicon
Iron
Aluminum

12. 4. ) The raw materials are ground to a powder
4.) The raw materials are ground to a powder. This is sometimes done with rollers that crush the materials against a rotating platform.

13. 5.) Everything then goes into a huge, extremely hot, rotating furnace to undergo a process called "sintering". Sintering means: to cause to become a coherent mass by heating without melting. In other words, the raw materials become sort of partially molten.

14. The raw materials reach about 2700° F (1480°C) inside the furnace
The raw materials reach about 2700° F (1480°C) inside the furnace. This causes chemical and physical changes to the raw materials and they come out of the furnace as large, glassy, red-hot cinders called "clinker".
The function of the kiln in the cement industry is to first convert CaCO3 into CaO and then react Silica, Aluminum Oxide, Ferric Oxide, and Calcium Oxide with the free lime to form clinker compounds: C3S, C2S, C3A, and C4AF.

15. 6. ) The clinker is cooled and ground into a fine gray powder
6.) The clinker is cooled and ground into a fine gray powder. A small amount of gypsum is also added during the final grinding. It is now the finished product - Portland cement. The cement is then stored in silos (large holding tanks) where it awaits distribution.

16. Cement is what holds concrete together
Cement is what holds concrete together.  Concrete is just cement mixed with rocks.  The rocks form most of the mass, and the cement holds the rocks in place. Cement is made up mostly of Calcium Silicate (Ca3SiO5 (50% - 70%), Ca2SiO4 (15% - 30%)), Calcium Aluminate (Ca3Al2O4 (5% - 10%)), and Calcium Aluminoferrite (Ca4AlFeO7 (5% - 15%)).  Different combinations determines how fast the cement will set and the color of the cement (which can be changed with other additives).

18. Cement Raw Materials
The main raw materials used in the cement manufacturing process are limestone, sand, shale, clay, and iron ore.
The most common raw rock types used in cement production are: - Limestone (supplies the bulk of the lime) - Clay, marl or shale (supplies the bulk of the silica, alumina and ferric oxide) - Other supplementary materials such as sand, pulverised fuel ash (PFA), or ironstone to achieve the desired bulk composition
A common meal recipe for the production of Portland cement consists of 75% (by mass) CaCO3, 15% SiO2, 5% Al2O3 and 5% Fe2O3. During the final stage of the process, an addition of 5% of gypsum is mixed and ground together with the clinker to form the final product.

19. Examples of raw materials for portland cement manufacture
Calcium
Silicon
Aluminum
Iron
Limestone
Clay
Marl
Shale
Iron ore
Calcite
Sand
Fly ash
Mill scale
Aragonite
Aluminum ore refuse
Blast furnace dust
Sea Shells
Rice hull ash
Cement kiln dust
Slag

20. Mining of Raw Materials
Mining of limestone requires the use of drilling and blasting techniques. The blasting techniques use the latest technology to insure vibration, dust, and noise emissions are kept at a minimum. Blasting produces materials in a wide range of sizes from approximately 1.5 meters in diameter to small particles less than a few millimeters in diameter.
Material is loaded at the blasting face into trucks for transportation to the crushing plant. Through a series of crushers and screens, the limestone is reduced to a size less than 100 mm and stored until required.
Depending on size, the minor materials (sand, shale, clay, and iron ore) may or may not be crushed before being stored in separate areas until required.

21. Storage of raw materials
The need to use covered storage depends on climatic conditions and the amount of fines in the raw material leaving the crushing plant. In the case of a 3000 tonnes/day plant these buildings may hold between and tonnes of material.

22. The raw material fed to a kiln system needs to be as chemically homogeneous as practicable.
This is achieved by controlling the feed into the raw grinding plant.

23. The grinding systems described of the following comminution methods:
Comminution by impact forces
Comminution by compression forces
Comminution by friction / shear forces
Comminution by inter-particle contact forces

24. Raw Materials Grinding
In the wet process, each raw material is proportioned to meet a desired chemical composition and fed to a rotating ball mill with water. The raw materials are ground to a size where the majority of the materials are less than 75 microns. Materials exiting the mill are called "slurry" and have flowability characteristics. This slurry is pumped to blending tanks and homogenized to insure the chemical composition of the slurry is correct. Following the homogenization process, the slurry is stored in tanks until required.

25. Raw Materials Grinding
In the dry process, each raw material is proportioned to meet a desired chemical composition and fed to either a rotating ball mill or vertical roller mill. The raw materials are dried with waste process gases and ground to a size where the majority of the materials are less than 75 microns. The dry materials exiting either type of mill are called "kiln feed". The kiln feed is pneumatically blended to insure the chemical composition of the kiln feed is well homogenized and then stored in silos until required.

26. Typical dry grinding systems used are:
• tube mill, centre discharge
• tube mill, airswept
• vertical roller mill
• horizontal roller mill (only a few installations in operation).
Other grinding systems are used to a lesser extent. These are:
• tube mill, end discharge in closed circuit
• autogenous mill
• roller press, with or without crushers (dryers).

27. Whether the process is wet or dry, the same chemical reactions take place. Basic chemical reactions are: evaporating all moisture, calcining the limestone to produce free calcium oxide, and reacting the calcium oxide with the minor materials (sand, shale, clay, and iron). This results in a final black, nodular product known as "clinker" which has the desired hydraulic properties.

28. In the dry process, kiln feed is fed to a preheater tower, which can be as high as meters. Material from the preheater tower is discharged to a rotary kiln with can have the same diameter as a wet process kiln but the length is much shorter at approximately 45.0 m. The preheater tower and rotary kiln are made of steel and lined with special refractory materials to protect it from the high process temperatures.
For dry classification, air separators are used. The newest generation, rotor cage type separators, have several advantages. These are:
• lower specific energy consumption of the grinding system (less over-grinding)
• increased system throughput (efficiency of particle separation)
• more favourable particle size distribution and product uniformity.

29. In the wet process, the slurry is fed to a rotary kiln, which can be from 3.0 m to 5.0 m in diameter and from m to m in length. The rotary kiln is made of steel and lined with special refractory materials to protect it from the high process temperatures. Process temperatures can reach as high as 1450oC during the clinker making process.
The fineness and particle size distribution of the product leaving a raw grinding system is of great importance for the subsequent burning process. The target given for these parameters is achieved by adjusting the separator used for classifying the product leaving the grinding mill.

30. Regardless of the process, the rotary kiln is fired with an intense flame, produced by burning coal, coke, oil, gas or waste fuels. Preheater towers can be equipped with firing as well.

31. This sequence of events may be conveniently divided into four stages, as a function of location and temperature of the materials in the rotary kiln.
1. Evaporation of uncombined water from raw materials, as material temperature increases to 100°C (212°F);
2. Dehydration, as the material temperature increases from 100°C to approximately 430°C (800°F) to form oxides of silicon, aluminum, and iron;
3. Calcination, during which carbon dioxide (CO2) is evolved, between 900°C (1650°F) and 982°C (1800°F), to form CaO; and
4. Reaction, of the oxides in the burning zone of the rotary kiln, to form cement clinker at temperatures of approximately 1510°C (2750°F).

32. Clinkering
This is the step which is characteristic of Portland cement. The powder from the dry process doesn't contain much moisture, so can be dried in a preheater tower. As it falls through the tower (which takes 30 seconds) it is heated from 70 to 800oC. The moisture evaporates, up to 20% of the decarbonation (loss of CO2) occurs and some intermediate phases such as CaO•Al2O3 begin to appear. The mixture is then fed into the kiln.

33. Clinkering
The kiln shell is steel, 60m long and inclined at an angle of 1 in 30. The shell is supported on 3 roller trunions and weighs in at over 1100 T. The kiln is heated by injecting pulverised coal dust into the discharge end where it spontaneously ignites due to the very high temperatures. Coal is injected with air into the kiln at a rate of T hr-1.

34. Clinkering

35. Zone 1: min, oC
Decarbonation. Formation of 3CaO•Al2O3 above 900oC. Melting of fluxing compounds Al2O3 and Fe2O3.
heat
CaCO3 → CaO + CO2

36. Zone 2: min, oC
Exothermic reactions and the formation of secondary silicate phases as follows:
heat
2CaO + SiO2 → 2CaO•SiO2

37. Zone 3: min, oC
Sintering and reaction within the melt to form ternary silicates and tetracalcium aluminoferrates:
heat + time
2CaO•SiO2 + CaO → 3CaO•SiO2
3CaO•Al2O3 + CaO + Fe2O3 → 4CaO•Al2O3+Fe2O3

38. Zone 4: min, oC
Cooling and crystallisation of the various mineral phases formed in the kiln.

39. The cooler
Immediately following the kiln is a large cooler designed to drop the temperature of the clinker (as the fused material is now called) from 1000oC to 150oC. This is achieved by forcing air through a bed of clinker via perforated plates in the base of the cooler. The plates within the cooler slide back and forth, shuffling the clinker down the cooler to the discharge point and transport to a storage area.

40. The cooler

41. The cooler
Immediately following the kiln is a large cooler designed to drop the temperature of the clinker (as the fused material is now called) from 1000oC to 150oC. This is achieved by forcing air through a bed of clinker via perforated plates in the base of the cooler. The plates within the cooler slide back and forth, shuffling the clinker down the cooler to the discharge point and transport to a storage area.

42. The cooler
At this point in the process the materials have been formed into all the required minerals to make cement. Like cement, the clinker will react with water and harden, but because it is composed of 1-3 cm diameter fragments it is too coarse to be used.

43. Cement milling
To produce the final product the clinker is mixed with gypsum (CaSO4•2H2O), which is added as a set retarder, and ground for approximately 30 minutes in large tube mills. The cement flows from the inlet to the outlet of the mill (a rotating chamber), being first ground with 60 mm then 30 mm diameter steel balls.

44. Cement milling
The first grinding breaks up the material and the second grinds it to a fine powder. The amount of grinding is governed by the volume of cement fed into the mill: the greater the volume the coarser the grind. This has practical limits, with too much cement clogging up the mill and not enough actually increasing the particle size.

45. Cement milling
The particle size is measured by laser diffraction analysis, and the quantity of material entering the mill adjusted accordingly. Over time the charge (steel grinding balls) wear out, so when they reach a certain size they fall through a seive and then are replaced.

46. Cement milling
The cement grinding process is highly energy intensive. The largest mill at Golden Bay Cement is some 11 m in length, weighs over 230 T, is driven by a 2100 kW motor and can produce over 60 T hr-1. The rotating mill generates significant quantities of energy and water is added to both the inlet and outlet ends of the mill to cool the product and the mill itself.

47. Portland cement is a fine powder, gray or white in color, that consists of a mixture of hydraulic cement materials comprising primarily calcium silicates, aluminates and aluminoferrites.
Gray portland cement is used for structural applications and is the more common type of cement produced.
White portland cement has lower iron and manganese contents than gray portland cement and is used primarily for decorative purposes.

48. Main Clinker Phases: Tri-calcium silicate 3 CaO x SiO2 C3S Alite
Di-calcium silicate 2 CaO x SiO2 C2S Belite
Calcium aluminate 3 CaO x Al2O3 C3A Aluminate
Calcium ferrite 4 CaO x Al2O3 x Fe2O3 C4AF Ferrite

49. MINERAL ADDITIONS PREPARATION
Mineral additions used in the manufacture of blended cements require separate installations for storage, preblending, crushing, drying and feeding.
Commonly used mineral additions include natural materials such as volcanic rocks, limestone or calcined clay, and materials originating from industrial sources such as granulated blast-furnace slag, pulverised fly ash from power stations, or microsilica.

50. The black, nodular clinker is stored on site in silos or clinker domes until needed for cement production. Clinker, gypsum, and other process additions are ground together in ball mills to form the final cement products. Fineness of the final products, amount of gypsum added, and the amount of process additions added are all varied to develop a desired performance in each of the final cement products.

51. IDENTIFICATION OF ENVIRONMENTAL SIGNIFICANCE
The main environmental impacts in the manufacture of cement are related to the following categories:
Dust (stack emissions and fugitive sources)
Gaseous atmospheric emissions (NOx, SO2, CO2, VOC, others)
Other emissions (noise and vibrations, odour, process water, production waste, etc.)
Resources consumption (energy, raw materials).

52. CEMENT INDUSTRY
Depending on climatic conditions and the amount of fines in the raw material coming from the crushing plant, it is usual for the raw material to be kept in covered stores. For a 3000 t/d plant these buildings may hold between 20,000 and 40,000 tons of material.

53. CEMENT INDUSTRY
The raw material fed to a kiln system needs to be as chemically homogeneous as practicable. This is achieved by control of the feed into the raw grinding plant. When the material from the quarry varies in quality, initial preblending can be achieved firstly by stacking the material in a manner which lays the material in rows or layers along the length (or around the circumference) of the store and secondly by cross sectional extraction across the material pile.

54. CEMENT STORAGE
For the storage of cement usually various silos are required. However new silo designs allow the storage of more than one type of cement in the same silo.
Nowadays for cement storage the silo configurations described below are used.
There are four type of cement storages in use:
Single Cell Silo with Discharge Hopper (SCSDH)
Single Cell Silo with Central Cone (SCSCC)
Multi-Cell Silo (MCS)
Dome Silo with Central Cone (DSCC)
Compressed air is used to initiate and maintain the cement discharge process from these silos via aeration pads located at the silo bottom.

55. CONVENTIONAL FUELS STORAGE
Three different types of conventional or fossil fuels are used in cement kiln firing in decreasing order of importance:
pulverized coal and petcoke;
(heavy) fuel oil;
natural gas.

56. Conventional fuels are today increasingly substituted by non-conventional, nonfossil (gaseous, liquid, pulverized, coarse crushed) alternative (or secondary) fuels for resource efficiency and economical reasons.

57. COAL AND PETCOKE FIRING
Raw Coal Storage
Raw coal and petcoke are stored similarly to raw materials (see Chapter 6.1) in (covered) storage halls. In the case of (strategic) long term stocks, outside storage in large, compacted stockpiles is used. To prevent rainwater and wind erosion such stockpiles may be seeded with grass.
Fine Coal Storage
Pulverized coal and petcoke is exclusively stored in silos. For safety reasons (explosions triggered by smouldering fires and static electricity spark-overs) these silos have to be of the mass flow extraction type and have to be equipped with standard safety devices.
Coal Preparation
Coal and petcoke are pulverized to about raw meal fineness in grinding plants comprising equipment similar to raw grinding. Special features have to be incorporated to protect the equipment from fires and explosions.

58. FUEL OIL FIRING Fuel Oil Storage
Fuel oil is stored in vertical uninsulated steel tanks equipped with heatable suction
points to maintain the oil locally at pumpable temperature (50 to 60° C).
Fuel Oil Preparation
In order to facilitate metering and combustion the fuel is brought to 120 to 140° C
resulting in a viscosity reduction to 10 to 20 cSt. Additionally the pressure is increased to 20 to 40 bars.
Fuel Oil Firing
At adequate viscosity and pressure the fuel oil is discharged via an atomizer nozzle
into the kiln in order to form e.g. the main flame. As with coal firing flames, shaping is mainly accomplished via multi-primary air channel burners with the oil atomizer head at central location.

59. NATURAL GAS FIRING Natural Gas Storage
There is no gas storage equipment in a cement plant. The international high
pressure gas distribution network acts as a gas storage facility.
Natural Gas Preparation
Prior to combustion the gas pressure has to be brought from the pipeline pressure of 30 to 80 bar down to plant network pressure of 3 to 10 bar and then further to the burner supply pressure of around 1 bar (overpressure).
The first pressure reduction step is accomplished in the gas transfer station where also consumption metering takes place. To avoid freezing of the equipment due to the Joule-Thompson effect the natural gas is preheated prior to passing through the pressure reduction value.
Natural Gas Firing
Kiln burners for natural gas, too, are designed according to the multi-channel principle, the gas thereby replacing the primary air.

60. ALTERNATIVE FUELS STORAGE
Alternative fuels can be subdivided into five classes:
Gaseous alternative fuels
Examples: Coke oven gases, refinery waste gas, pyrolysis gas, landfill gas, etc.
Liquid alternative fuels
Examples: Low chlorine spent solvents, lubricating as well as vegetable oils and fats, distillation residues, hydraulic oils, insulating oils, etc.
Pulverized, granulated or fine crushed solid alternative fuels
Examples: Ground waste wood, sawdust, planer shavings, dried sewage sludge, granulated plastic, animal flours, agricultural residues, residues from food production, fine crushed tyres, etc.
Coarse crushed solid alternative fuels
Examples: Crushed tyres, rubber/plastic waste, waste wood, reagglomerated organic matter, etc.
Lump alternative fuels
Examples: Whole tyres, plastic bales, material in bags and drums, etc.