Cement Manufacturing Page 1 10/12/2005 WP0003

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1 Cement Manufacturing Page 1 10/12/2005 WP0003

2 Is it cement or is it concrete? Does it matter? Cement and concrete might mean the same thing to most of us, but there is a major difference in the two. In common terms, cement is a bonding agent that holds other things together. Today s modern Portland cement is an ultra-fine gray powder whose principle ingredient is limestone. Cement is the bonding agent used in modern concrete mixes. Concrete is a primary stone-like building material found around the world and is made by mixing Portland cement (11%), sand (26%), gravel (41%), air (6%) and water (16%) together to make concrete. Concrete is typically mixed then poured into forms to create buildings, bridges, highways, sidewalks and hundreds of other products. We are all familiar with the concrete trucks with their slowly rotating drums that deliver concrete to a construction jobsite. Annual global production of concrete is approximately 5 billion cubic yards or about 1.25 billions tons. Demand at American plants has increases so far this year at a 7% annualized rate. Cement inventories have fallen from and average 19 days to 3 days, hence the rising prices and tight supplies. Cement, a brief history: In antiquity the Egyptians used a mortar made of lime and gypsum to bind the stones used to build the great Pyramids. The foundation for the Roman Forum, which had depths up to 12 feet, used an early form of concrete. Cement mortar was also used in the Roman Baths (27 B.C.), the Coliseum and the Basilica of Constantine. The art of making cement was lost during the Middle Ages and not rediscovered until 1756 when John Smeaton reinvented a cement mortar that would harden underwater. He successfully repaired a lighthouse in Cornwall, England with this cement. In 1824, Joseph Aspdin, an English stonemason, took out a patent for hydraulic cement that he developed. He called it Portland cement because of its color, which was similar to the stone quarried at the Isle of Portland off the British coast. Today more than 90% of the cement produced worldwide is Portland cement. Its formulation still follows the precise recipe that Aspdin developed using calcium, silicon, iron and aluminum. This report will focus on the manufacturing process for cement. Market Statistics: Three of the four largest players in the U.S. cement manufacturing business are based internationally. The four majors are Cemex (Mexico), Holcim Inc. (Switzerland), Lafarge North America (France) and Texas Industries. Cement manufacturing is a mature industry and closely follows the economic GDP. Construction starts, highway and airport construction also play a major part in this market s growth. Overall in 2003, the United States had 38 companies operating 118 cement plants. The U.S. ranks third in cement production behind China and India. Cement manufacturing is spread fairly evenly across the U.S. The chart below shows that New England has the fewest number of plants and the South East has the most. This would be expected considering the amount of construction spending in these regions. Cement Manufacturing Page 2 10/12/2005 WP0003

3 Percentage of Cement Plants by Region Great Lakes 17% South East 20% Far West 17% New England 3% Rocky Mountains 5% South West 10% Plains 12% Mid East 16% Chart 1: Percent of cement plants per region. The cement manufacturing process: Cement manufacturing requires over 80 separate and continuous process operations, intense heat and lots of motors and controls. Motors are typically totally enclosed and designed for harsh environments. Dust, heat, vibration and shock are enemies #1 for the massive machinery and its motors alike. A modern stationary cement plant may use thousand of electric motors and controls. These include motors for crushers, grinders, mixers, conveyors, fans, explosion proof areas, rotation of kiln and ball mill, bagging equipment and lots of material handling equipment. Controls would include reduced voltage starters, or some type of starter to reduce in-rush current, soft-start starters and VFD s. Cement manufacturing offers an extremely harsh environment for motors and controls. The crushing and grinding of limestone and other materials produces a fine abrasive powder which can clog a motors air intakes, blanket the motor reducing heat dissipation, contaminate the bearings, score the bearing journals and shafts and lead to overheating and mechanical failures. Cement Manufacturing Page 3 10/12/2005 WP0003

4 When evaluating motor replacements be sure to specify components that are suited for harsh environments, have high starting load capacity and can handle shock and vibration. Specify cast iron TEFC or TENV motors. In some application blower cooled motors would be appropriate to prevent overheating. Another possibility often overlooked is the use of premium efficient motors for continuous operations. Not only will the client save operating costs, but these motors generally run cooler and have features conducive of operation in harsh environments. Baldor Premium Efficient Super-E Motor You may find the following two graphics useful during the manufacturing process descriptions throughout the balance of this report. Each step in the process will be briefly described. The modern cement plant has nine major processes. These are: 1. Raw material storage 2. Grinding 3. Blending 4. Preheating 5. Rotary kiln (cooking) 6. Clinker storage 7. Additions (of gypsum, fly ash, etc.) 8. Cement grinding 9. Bulk storage, packaging and loading Cement Manufacturing Page 4 10/12/2005 WP0003

5 Production process in brief: The production of Portland cement begins with the precise blending of the raw materials such as limestone, clay and sand. These materials are heated to 2700 F (1500 C) in a rotating furnace called a kiln. The intense heat causes a chemical reaction converting the partially molten raw materials into pellets called clinkers. After adding additional key ingredients, the mixture is then ground to a fine gray powder called Portland cement. The basic physical layout of a Portland cement plant can be seen in diagram 1. The numbered items refer to the list of processes referred to above. Diagram 1: Basic cement plant layout Cement Manufacturing Page 5 10/12/2005 WP0003

6 To understand what goes on within the cement plant s manufacturing processes, diagram 2, provides a schematic of the manufacturing process. Diagram 2: The production process. Cement manufacturing a step-by-step review: Limestone rock is the principal raw material along with silica sand and clay. Sometimes shells, chalk, blast furnace slag and iron ore are used. Limestone and silica make up 85% of the total ingredients. The first step after quarrying is primary crushing. Truck loads of rock up to the size large oil drums are fed into the primary crushers which reduce the rocks to a maximum size of 6 diameter. These smaller rocks then goes through secondary crushers or hammer mills which reduce the rock to a maximum of 3 diameter. The primary and secondary crushing usually occurs at the quarries. Next these materials are shipped to and stored at the cement mill. The primary crusher may use a 1000 hp motor. Step 1. This bulk material is stored on site. Enough inventories are maintained to assure the continuous flow of the materials. The raw material is analyzed in the laboratory and proportioned onto conveyors that take the material to the raw mill. Cement Manufacturing Page 6 10/12/2005 WP0003

7 Raw Material on its way to the crushers. Step 2. The raw mill is a heavy, wheel type roller that crushes the material against a rotating table. The raw mill grinds the material to a particle size of 90 microns or less. This fine material called meal is sent to the homogenization silos for further blending. Step 3. The homogenization silos complete the blending of the material before it is sent to the preheating process. Step 4. The preheater tower supports a series of vertical cyclone chambers that assist in preheating the materials. Modern cement plants feature towers 200 high with multiple chambers. As the material drops down through these chambers the cyclonic action of the hot gasses rising from the kiln significantly raise the temperature of the materials. Dust is a major problem with this swirling mixture of material and hot gasses. Dust separation and reclamation is often used on these towers as well as pollution control equipment. Massive fans up to 2000 hp, help force the hot gases up the tower. Cement Manufacturing Page 7 10/12/2005 WP0003

8 Preheat homogenization towers with rotary kiln in foreground. Step 5. The raw material now enters an inclined rotating furnace called the kiln. The material slides and tumbles down the kiln through progressively hotter zones. Rotary kiln, drive motor. Cement Manufacturing Page 8 10/12/2005 WP0003

9 The kiln is lined with firebrick and sloped upward toward the preheat tower. The kiln is the heart of the cement making process and rotates from one to three revolutions per minute. It can be 400 long and have a diameter of 10 to hp motors with 200% starting torque rotate the kiln. The kiln my also have external blowers which are used to cool the exterior of the kiln. The raw material is heated to a temperature exceeding 2700 F by a blast of flame that may exceed 3400 F. The heat source is the precisely controlled burning of powdered coal, oil or natural gas plus a forced air draft. As the nearly molten material travels through the kiln, certain elements are driven off in the form of gasses. The remaining materials combine into a new material with new physical and chemical characteristics. This new material is formed in pellets about the size of marbles and is called clinkers. The red-hot clinkers are discharged from the lower end of the kiln into cooling chambers. The clinkers then tumble along an open grate where air is forced over them for cooling. When the clinkers are cool enough they are sent to storage or to the ball grinder. The air from the cooling chambers is sent to the kiln as preheated air. Step 6. A sufficient amount of clinkers are often stored to facilitate the continuous grinding operation. Clinkers are then sent to the storage silos to the mixed with small amounts of gypsum and other materials (note: premium efficient motor opportunity). Step 7. Before the clinkers go to the ball mill small amounts of gypsum are added to control the setting times. Fly ash and other materials can be added to create specialty cement mixtures. Step8. The clinkers, gypsum, fly ash, etc. are feed into the ball mill. The ball mill is a horizontal steel tub filled with steel balls. The steel balls tumble and crush the clinkers to a talcum powder consistency. This is the last process required to make Portland cement. The cement is now sent to the bulk storage and packaging area. The ball mill may use a 3000 hp motor where as the smaller blending mills will use 500 hp motors. Cement Manufacturing Page 9 10/12/2005 WP0003

10 Step 9. The bulk storage and packaging area is the distribution side of the business. Most cement is shipped in bulk form to ready mix plants by truck or rail car. Some is loaded onto boats for export or long distance transport. A small percentage is bagged and sold to Do it Yourself and specialty stores to customers who only need small amounts or need it for mortar mix. The majority of the cement is shipped to ready mix concrete plants. These plants can either be stationary or portable. Portable sites are setup temporarily at jobsites such as road and airport construction sites. Just like cement, concrete is a precise mixture of cement (the glue), aggregate (rocks, gravel), sand, water and air (a byproduct of mixing). Other ingredients can be added for specific strength requirements and physical properties. The mixture is then loaded into the familiar rotating drum trucks, which deliver the concrete to the jobsite. Other types of concrete plants manufacture precast and prestressed concrete products. These products range from concrete construction blocks to bridge spans to decorative birdbaths. As with the ready mix plants, cement is received in bulk and the other ingredients are added as required. Resources: Portland Cement Association Cement Association of Canada ww.cement.ca Various concrete and cement articles from Wikipedia, a free encyclopedia, Definitions from Concrete key dates from Cement Manufacturing Page 10 10/12/2005 WP0003