OVERVIEW CEMENT PRODUCTION CEMENT PRODUCTION OVERVIEW Cement Plant overview Quarry types Raw material composition Raw Material Grinding Burning-Process in kiln Kiln types Clinker Phases Clinker Cooling Finish grinding Gypsum Conveying Systems 2 CEMENT PRODUCTION „common“ cement plant Preheater Raw material storage and homogenisation Raw material from Quarry Dispatch 3 RAW MATERIAL QUARRY Common quarry Open pit HC, Brevik (Norway) Mine 330 m below see 1.2 Mt cement capacity 4 Limestone: Calciumcarbonat (CaCO3) Clay: Aluminiumoxide and Siliciumoxide (Al2O3, SiO2) Ironoxide (Fe2O3) LH, Lägerdorf (Germany) Chalk (CaCO3), 23% humidity 1.4 Mt cement capacity RAW MATERIAL COMPOSITION CaCO3 Correction materials are added if necessary to achieve the desired composition (CaCO3, SiO2, Al2O3, Fe2O3). Clinker phases Formula Short-cut Tri-Calcium-Silicate 3 CaO SiO2 C3S ø 63 Di-Calcium-Silicate 2 CaO SiO2 C2S ø 16 C4AF ø 8 C3A ø 11 Tetra-Calcium-Alumino-Ferrite 2 CaO (Al2O3, Fe2O3) Tri-Calcium-Aluminate Al2O3, SiO2 5 3 CaO Al2O3 Content [M-%] RAW MATERIAL RAW MATERIAL GRINDING Dry grinding process 1. Homogenization of raw material in special storehouse. 1. Raw material are ground with water in ball mills 2. Raw materials are ground in vertical roller mills or ball mills (< 90µm). 2. Resulting “slurry” is stored in huge basins, where it is continuously mixed before being fed to the kiln. (homogenization). 3. Homogenization of raw meal in silo, before being fed to the kiln. 1 6 Wet grinding process 2 3 1 2 RAW MATERIAL / RAW MEAL HOMOGENIZATION DRY GRINDING PROCESS The main principle is to form layers of the raw material in the longitudinal stockpile from the mix. When the reclaimer slices the pile from the edge, the slice cuts through all the layers and ensures each layer has the right proportion according to the target chemistry. The Homogenizing Silo of raw meal should be at least 50-70% full of material at all times. The aeration at the silo bottom should occur adequately to fluidize the material. The extraction rate and sequence is regulated to bring about maximum mechanical movement of layers of material. http://pecconsultinggroup.com/newsflash/ homogenization-strategy-in-the-cement-industry 7 CLINKER PRODUCTION REACTIONS IN THE KILN 1. Calcination: At approximately 800⁰C, the calcium carbonate (limestone) is burnt to Calcium oxide (lime): CaCO₃ → CaO + CO₂ 2. Clinker formation: The lime and the other raw materials melt and react at temperatures of 1500⁰C to form calcium silicates and calcium aluminates, the main components of clinker. Total 0,8 ton CO2/ton clinker 8 CLINKER PRODUCTION BURNING – PROCESS TYPES Dry process () raw materials are fed to the kiln in a dry state ~ 3’000 MJ thermal energy Wet process () raw material are fed into the kiln in form of a "slurry“. Up to 6’000 MJ thermal energy per ton of clinker per ton of clinker Characteristic sign: Characteristic sign: cyclone preheating tower very long kilns Slurry bassin 9 long kiln CLINKER PRODUCTION OVERVIEW WET PROCESS 10 CLINKER PRODUCTION OVERVIEW DRY PROCESS Hot air from the kiln is used in cyclone pre-heater to drive off moisture and increase temperature of the raw meal. Heated raw meal enters the kiln with a calcination degree of approx. 50%. A higher calcination degree of up to 90% is achieved with pre-calciners (second flame). Kilns are 6-8 m in diameter and 60 m to 100 m long. They are set at a slight inclination 11 and rotate 1 to 3 times per minute. Burner is located at the lower end. Raw materials move toward the flame. CLINKER PRODUCTION BURNING – PROCESS TYPES Lepol kiln (semi-dry) Dry ground raw material is formed with the help of water to pellets The pellets are preheated on the grate preheater with exhaust air from kiln Pellet producer https://www.hc-museum.de/de/video-vomkalkstein-zum-zement 6’15 12 CLINKER PRODUCTION REACTIONS IN THE KILN 13 CLINKER PRODUCTION KILN DUST AND BY-PASS DUST Cement kiln dust is the dust which passes out of the top of the preheater with the exhaust gases, or more typically out of the back of a long wet or long dry kiln. Parts of the raw material, partially processed feed and components of the final product are entrained in the combustion gases that flow countercurrent to the feed. These particulates and combustion gas precipitates are collected in a filter. Alternative fuels Many facilities return all or a significant portion of the CKD to the kiln as a feedstock generate BPD and CKD which is loaded with Bypass dust is the dust that is drawn out of the kiln inlet when some kiln exit gases are extracted Chlorides, Sulfates etc.! between the kiln and preheater to break the cycle of volatile species between the kiln and preheater. The bypass is therefore positioned between the kiln inlet and the preheater. 14 CLINKER PRODUCTION OVERVIEW COOLING Target cool the material as quickly as possible below 800°C cause solidification of the clinker freeze composition of clinker phases maintain the C3S content (high reactivity + easy grindable) Slow cooling leads to chemical changes: C3S reacts back to C2S discharged from lower end of kiln 15 CLINKER PRODUCTION COOLER TYPES Grate-Cooler most commonly used very quick cooling down to 100⁰C Efficient heat recovery Satellite/Planetary-Cooler cooling tubes around the kiln end higher remaining temperature of clinker (slower cooling) Lower heat recovery CLINKER PRODUCTION GRATE COOLER Clinker Return of heat into kiln ventilation air Adjustable airstream Spread the clinker Initial cooling clinker moves over grating system adjustable cooling fans Fine-adjustment of temperature crusher CLINKER PRODUCTION GRATE COOLER Cross bar cooler CLINKER PRODUCTION VIEW INTO A GRATE COOLER CLINKER PRODUCTION SATELLITE COOLER Hot clinker leaves kiln and falls into the cooling tubes at the kiln end (10 - 11 tubes around the circumference). Increased surface leads to a cooling effect. Lifter pattern in the satellite tubes cause turbulence and promote cooling air contact. For kilns up to 3000 t/day Dis-advantage: only as much cooling air possible as required for burning because all air has to pass the kiln Slow cooling Advantage: no need for de-dusting equipment Airstream Clinker Ambient Air CLINKER PRODUCTION PHASE COMPOSITION Clinker phases Formula Tri-Calcium3 CaO SiO2 Silicate Di-CalciumSilicate 2 CaO SiO2 TetraCalcium- 2 CaO (Al2O3, AluminoFe2O3) Ferrite Tri-Calcium3 CaO Al2O3 Aluminate Free Lime 21 CaO Short-cut C3S C2S C4AF C3A Content [M-%] high 80 average 63 low 45 high 32 average 16 low 0 high 14 average 8 low 4 high 15 average 11 low 7 high 3 average 1 low 0,1 C4AF 10% C3A 10% C2S 20% C3S 60% C4AF 10% C3A 10% C2S 20% C3S 60% Compressive Strength [N/mm²] CLINKER PRODUCTION PHASE COMPOSITION AND STRENGTH C3S C2S C3A C4AF Age [day] 22 CEMENT PRODUCTION FINISH GRINDING Grinding of clinker in a mill to obtain fine powder Addition of: Gypsum (setting regulator) Secondary cementitious materials (SCM) Kiln dust, by-pass dust Chromium reducers CEMENT HYDRATION SET REGULATION WITH GYPSUM Without set regulation: C3A + water → Tetracalciumaluminiumhydrate Big, leaf-shaped crystals. Bridge building microstructure. Immediate reaction and setting With Gypsum: On C3A surface a thin cover of calciumaluminatsulfat (Ettringit) is formed This film delays the reaction of C3A with water High Reactivity of C3A High Fineness of cement High temperature at application 24 → more gypsum CEMENT HYDRATION MAIN TYPES OF GYPSUM Gypsum: CaSO4 ∙ 2H2O Natural or from flue gas desulfuriation FGD Anhydrite: CaSO4 Natural or by dehydration of FGD Hemihydrate: CaSO4 ∙ ½H2O Dehydration of Gypsum at > 120⁰C: CaSO4 ∙ 2H2O → CaSO4 ∙ ½H2O + 1 ½H2O Dehydration can take place in mill Each type of «Sulfate» has different solubility 25 CEMENT HYDRATION SOLUBILITY OF GYPSUM 12 solubility [g CaSO4/l] 10 Optimum for cement: Blend of gypsum and Anhydrit β-hemihydrate 8 6 α-hemi-hydrate 4 anhydrite II 2 gypsum Reality: Availability Economy 0 0 26 20 40 60 80 100 temperature [°C] 120 140 160 180 CEMENT PRODUCTION FINISH GRINDING - OVERVIEW MILL TYPES The cooled clinker is blended with certain additions and ground into a fine powder to make cement. There are mainly 4 different Milling Systems used: Ball mill Roller-Press mill Vertical Roller Mill Horizontal Roller Mill CEMENT PRODUCTION CONVEYING SYSTEMS Air Slide Conveying the cement powder in an air Stream (low pressure) Screw-conveyor Conveying the cement powder in a closed tube with a turning Screw Conveyor-Belt Conveying the cement powder on an open Belt CEMENT PRODUCTION WORKING PRINCIPLE AIR SLIDE Cement conveying in air flow Membrane to separate air & cement flow Air pressure QUESTIONS? • Where can we support the cement plant? • How much CO2 is produced per ton of clinker?