Cement Manufacturing Process PDF

# Cement ## Introduction Cement is the mixture of the calcerous, argillaceous, siliceous and other substance. Cement is used as a binding material in mortar, concrete and etc. ## Background Joseph Aspdin took out a patent in 1824 for "PortlandCement," a material he produced by firing finely-ground...

# Cement ## Introduction Cement is the mixture of the calcerous, argillaceous, siliceous and other substance. Cement is used as a binding material in mortar, concrete and etc. ## Background Joseph Aspdin took out a patent in 1824 for "PortlandCement," 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. ## What is cement? - Cement: hydraulic binder - Hydraulic: requires water - Binder: a paste that can set and harden to hold other objects in place - Inorganic powder: that when mixed with water forms a paste that sets and hardens with water ## Portland cement raw materials ### Calcareous Material - Such as: Lime stone ($CaCO_3$) - Supply Source of Lime: $CaO$ ### Argillacous Material - Such as: Clay ($Al_2O_3\cdot SiO_2\cdot2H_2O$) - Supply Source of: - $Al_2O_3$ (Alumina) - $SiO_2$ (Silica) - $Fe_2O_3$ (Ferric Oxid) ## Be Attention - (Calcareous + Argillaceous) materials = Clinker - (Clinker + Gypsum (2:3% ) = Cement - Gypsum: act as a retarder (Retardation of setting of cement) ## What is cement? In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. ## Types of cement Cement used in construction is characterized as hydraulic or non-hydraulic. Hydraulic cements (e.g., Portland cement) harden because of hydration, chemical reactions that occur independently of the mixture's water content; they can harden even underwater or when constantly exposed to wet weather. ## History of the origin of cement - John Smeaton made an important contribution to the development of cements when he was planning the construction of the third Eddystone Lighthouse (1755-9) in the English Channel. He needed a hydraulic mortar that would set and develop some strength in the twelve hour period between successive high tides. - In 1824, Joseph Aspdin patented a similar material, which he called Portland cement, because the render made from it was in colour similar to the prestigious Portland stone. ## Joseph Aspdin (Portland Cement) The image shows a plaque commemorating Joseph Aspdin as the inventor of Portland Cement. ## Chemical Composition of Cement | Ingredient | Percentage in cement(%) | | --------------- | ------------------------ | | Lime | 60-65 | | Silica | 17-25 | | Alumina | 3-8 | | Magnesia | 1-3 | | Iron oxide | 0.5-6 | | Calcium Sulphate | 0.1-0.5 | | Sulphur Trioxide | 1-3 | | Alkaline | 0-1 | ## Manufacturing of Cement - Crushing - Mixing (Wet Process) - Mixing (Dry Process) - Grinding (Ball Mill and Tube Mill) - Burning - Drying Zone - Calcination Zone - Clinkering Zone - Grinding - Packaging ## Crushing - Jaw crushers of various sizes are employed for the crushing purpose. - Raw materials are crushed by crushers till the size of the raw material reduces to ¼ of an inch. ## Dry and Wet process ### Dry Process 5) The material are ground into Powder (% moisture 0.07%) - in Horizontal ball mills or in vertical roller mills - The powder is stored in a bin called Silos ### Wet Process 5) The raw material are ground (with the addition of $H_2O$) into Slurry (% water 30 - 40) - Ball or tube mill - The slurry is stored in storage tanks - Raw materials are humid ## Dry Process Manufacturing Diagram The image shows a flowchart for the Dry Process for manufacturing cement. The process includes: 1. Limestone and Shale crushed. 2. Raw material is blended. 3. Raw meal preheated. 4. Raw meal burnt in rotating kiln. 5. Fluidized calciner. 6. Clinker cooler. 7. Gypsum added. 8. Clinker grinded. 9. Cement stored in a silo and then sent for packaging. ## Wet Process Manufacturing Diagram The image shows a flowchart for the Wet Process for manufacturing cement. The process includes: 1. Clay, Chalk and Water are mixed. 2. The slurry is sent to slurry tank. 3. The slurry burnt in a rotating kiln. 4. Clinker cooler. 5. Gypsum is added. 6. Clinker grinded. 7. Cement stored in a silo and then sent for packaging. ## Dry vs Wet process | Dry process | Wet process | | ------------------------------------------------- | ------------------------------------------------- | | Used when the raw materials are hard | Used for all types of raw materials | | Process is slow | Process is fast | | Fuel consumption is low | Fuel consumption is high | | Lower cost of production | Higher cost of production | | Cement obtained is of low quality | Cement obtained is of high quality | ## Dry Process Manufacturing Diagram The image shows a diagram of cement production by Dry Process. The steps include: 1. Raw grinding 2. Burning 3. Clinker storage 4. Grinding 5. Packaging, storage and dispatch ## Portland Cement Manufacturing Steps 1. Crushing 2. Grinding 3. Calcining in rotary kiln 4. Cooling the resulting clinker 5. Mixing clinker with gypsum 6. Milling 7. Storage 8. Bagging the finished cement ## Grinding ### Grinding Grinding of clinker is done in the large tube mills. After proper grinding gypsum ($CaSO_4$) in the ratio of 0.1-0.4% is added for controlling the setting time of cement. Finally, fine ground cement is stored in storage tanks from where it is drawn for packing. ### Grinding methods #### Ball mill - Consists of cast iron drum containing iron and steel balls of different sizes. - The principle used in ball mill s impact and shear produced by large no. of tumbling and rolling balls. #### Tube Mill - Ball mill grinding is followed by tube mill grinding. - Tube mill is conical at the discharge end with separate inlet and outlet. - Slower is the feeding speed finer is the product coming out of the tube mill. ## Burning Process Corrected slurry is feed to a rotary kiln which is 150-500 ft long, 8-16 ft in diameter and temperature is up to 1500-1650 degree $C$. At this temperature slurry losses moisture and forms into small lumps after that changes to the clinkers. Clinkers are cooled in another inclined tube similar to the kiln but lesser in length. The image shows a diagram of a rotary kiln with different stages of burning. ### Burning Zone Breakdown #### A. Drying Zone - The upper part of the kiln is known as drying zone. - The temperature is about 200-500°C. - Most of the water gets evaporated from the slurry by means of hot gases. #### B. Calcinating Zone - This the middle zone of the kiln with temperature around 1000°C. - Organic matter burns away and $CaCO_3$ decomposes to quick lime and $CO_2$ escapes out. The material forms small lumps called as nodules. #### C. Clinkering Zone - This is lowest portion of kiln with a temperature of about 1400-1600°C. - Lime and clay nodules melts with chemical fusion and gives calcium aluminates and silicates. - These silicates and aluminates then fuse together to form small hard stones called Clinkers which than fall down from lower end of the kiln. - $CaCO_3 \rightarrow CaO + CO_2 \uparrow$ - $2CaO + SiO_2 \rightarrow Ca_2SiO_4$ - $3CaO + SiO_2 \rightarrow Ca_3SiO_5$ - $3CaO + Al_2O_3 \rightarrow Ca_3Al_2O_6$ - $4CaO + Al_2O_3+Fe_2O_3 \rightarrow Ca_4Al_2Fe_2O_{10}$ - Calcium Oxide - Di calcium Silicate - Tri calcium Silicate - Tri calcium Aluminate - Tetra calcium Aluminoferrite ## Packaging The image shows a poster with various packaging options for a company named "PACKAGING+". The ground powder is packed by automatic machines in a 50kg bag. This is then dispatched to the markets where it is sold for constructions of cities. ## Rotary Kiln The powder/slurry is fed into the rotary kiln. - Steel cylinder with refractory bricks. - Generally inclined from 0.5 to 0.75 inch from the horizontal axis. - Rotating at 0.5 – 1 rpm. ## Rotary Kiln Heating Zones 1. Drying zone 2. Calcination zone 3. Burning or clinkering zone 4. Cooling zone ## Rotary Kiln - Steps 1. Up to 100 °C there is evaporation of free water. This step is endothermic. Not required in dry process 2. Drying Zone: At T ≥ 500 °C, the slurry loses all its water content by evolution of water from clay. Also, this step is endothermic. 3. Calcination Zone: At T ≥ 900 °C, limestone ($CaCO_3$) decomposes to $CaO$ and $CO_2$ by an endothermic reaction. 4. Burning (Clinkering) Zone: Between 900 °C < T < 1200 °C, lime and clay combines to form calcium silicates and aluminates called clinker. This is the main reaction and is considered an exothermic reaction. 5. At T ≥ 1250 °C, continuous formation of clinker. 6. Burning (Clinkering) Zone: Between 900 °C < T < 1200 °C - $2\ CaO + SiO_2 \rightarrow Ca_2SiO_4$ (C2S) - $3\ CaO + SiO_2 \rightarrow Ca_3SiO_5$ (C3S) - $3\ CaO + Al_2O_3 \rightarrow Ca_3Al_2O_6$ (C3A) - $4CaO + Al_2O_3 + Fe_2O_3 \rightarrow Ca_4Al_2Fe_2O_{10}$ (C4AF) ## Rotary Kiln - Chemical Reaction 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. ## Rotary Kiln - Temperature Summary | T°C | Reaction | Remarks | | -------- | ---------------------------------------------------------------------------- | ------------------------------------------------------------------------ | | 100 | Evaporation of water | Solid phase reactions, endothermic | | >500 | Evolution of combined water from the clay | Solid phase reactions, endothermic | | 900 | Crystallization of amorphous dehydration products, Carbon dioxide evolution from $CaCO_3$ | Solid phase reactions, endothermic | | 900 - 1200 | Main reactions between lime and clay to form clinker | Fusion reactions, exothermic | | 1250 - 1280 | Beginning of liquid formation | Fusion reactions, endothermic | | 1280 - 1550 | Further liquid formation and final cement formation | Fusion reaction, endothermic | | | The main reactions which give the real strength of cement are as follows: | | | | $2CaO + CaO.SiO_2 \rightarrow CaO + 2CaO.SiO_2 \rightarrow 3CaO.SiO_2$ | | ## Rotary Kiln Finishing Stages 8. The clinker exit the kiln at about 1400 - 1600 °C. 9. Cooling ## Rotary Kiln - Finishing Stage 8. Addition of a retarder (i.e., 2.5 – 3% of gypsum "CaSO4.2H2O") to prevent quick setting of cement paste. 9. Grinding of Portland cement clinker produced. 10.Storage 11.Pagging ## Rotary Kiln - Diagram The image shows a diagram of a rotary kiln with temperatures and stages, highlighting various key chemical processes occurring at different stages. - Exhaust gases. - Raw feed in. - Formation of initial compounds. - Formation of melt. - Dehydration zone. - Calcination zone. - Clinkering zone. - Cooling zone. - Clinker out - Cooling grate. The image captures the temperature gradients within the kiln, as well as the different zones of activity – dehydration zone, calcination zone, clinkering zone, and cooling zone, and the final removal of clinker. ## Rotary Kiln - Clinkering Zone Breakdown 1. Formation of tetra calcium alumino ferrite - $4CaO + Al_2O_3 + Fe_2O_3 \rightarrow 4CaO.Al_2O_3.Fe_2O_3$ (C4AF) - Responsible for Water resistance 2. Formation of tricalcium aluminate - $3CaO +Al_2O_3→ CaO.Al_2O_3$ (C3A) - Responsible for Setting of Cement 3. Formation of dicalcium Silicate - $2CaO + SiO_2 → 2CaO.SiO_2$ (C2S) - Responsible for Final Strength 4. Formation of tricalcium Silicate - $2Cao.SiO_2 + CaO → 3CaO.SiO_2$ - Responsible for Initial Strength ## General Idea of Cement Examples - **Clinker Sample** (Diagram showing the conversion of raw materials into different compound types) - $Fe_2O_3$ (3.1%) -> C4AF - $Al_2O_3$ (4.5%) -> C4AF, C3A - $CaO$ (64.5%) -> C4AF, C3A, C2S, C3S - $SiO_2$ (23.4%) -> C2S, C3S - **Cement Sample** (Diagram showing the formation of different compound types) - $Fe_2O_3$ (3.1%) -> C4AF - $Al_2O_3$ (4.5%) -> C4AF, CJA - $CaO$ (64.5%) -> C4AF, CJA, C3A, C2S, C3S - $SiO_2$ (21.4%) -> C2S, C3S - $SO_(2.3%)$ -> Gypsum