Modern cities are made possible by cement and concrete, with buildings from skyscrapers to low-income housing using large amounts of this stuff. Even if a structure is built using brick, steel, stone, wood, or other materials, these almost exclusively rest on concrete foundations, a vital ingredient of cement. Processing cement is, in fact, integral to making concrete.
Yet cement and concrete are used for far more than buildings and their foundations.
Contemporary societies use concrete—and, by association, cement—for myriad things: airport runways, bridges, dams, city streets, country roads, highways, parking lots, piers, power plants, sidewalks, storm drains, subway systems, tunnels, water pipes, wind turbine foundations, and other aspects of today’s cities. Cement processing equipment is needed for all of these structures.
Cement Processing & Its Role in Making Concrete
In a cement plant, equipment used for making concrete must endure a rigorous manufacturing process. It begins with machinery used for mining and processing the raw ingredients that go into it. These materials include clay and limestone, which are crushed and ground by particle reduction equipment into what’s known as raw meal. The meal is then heated in a cement kiln to temperatures reaching up to 1450°C (2642°F).
These high temperatures break down the raw meal’s chemical bonds before they’re recombined into what’s known as clinker. This is ground raw meal that’s been reduced to rounded particles from 1 mm to 25 mm (about .04 to .98 inch) in size. Specialized mills then grind the clinker into a fine powder before blending gypsum and other additives into the mixture to make cement. This powdered cement is then mixed with aggregates and water, making concrete used for construction.
Cement processing generally goes through the following stages:
- Extraction: Raw material like limestone and clays are mined from quarries.
- Crushing: Rocks are broken down into smaller bits.
- Grinding: These smaller rocks are then ground down into smaller particle sizes.
- Burning: This ground raw material is heated in a kiln to produce clinker.
- Second grinding: Additives like gypsum and fly ash are mixed with the clinker, which is ground together into cement.
- Packaging and storage: Cement is packaged and/or stored for delivery.
Cement plant equipment consists of particle size reduction machinery and supporting mechanisms like rotary valves, all of which work together to process the raw materials and blend them into cement. Processing involves mainly limestone, clay, and gypsum, which include aluminum, calcium, iron, and silicon. Blast furnace slag, chalk, fly ash, iron ore, seashells, shale, silica, and slate are also sometimes used when processing cement.
How Modern Construction Depends on Making Concrete
For each person in the world, three tons of concrete are used per year, double that of all other construction materials combined. In fact, concrete is the second most consumed material by humans only after water. So, it’s a pretty reliable bet that making concrete for construction will continue far into the future. But why is concrete used so extensively?
Concrete is the most used building material globally due to properties that include:
- Acoustic insulation: Concrete insulates against sound, reducing the noise between different areas within a building.
- Adaptability: Capable of being molded into various forms and sizes, it offers considerable versatility, extending even to unique aesthetics in architecture.
- Cost: When compared to other materials like steel, making concrete in large quantities is fairly economical, especially for larger building projects.
- Recyclability and reusability: While it has an extraordinarily long lifespan, as evidenced by ancient Roman concrete structures made thousands of years ago, concrete can also be reused and recycled.
- Resistance: Once set, it offers durability and strength, allowing it to handle heavy loads, which is why it’s used for foundations, pillars, slabs, walls and other supporting structures.
- Thermal insulation: Insulating against both heat and cold, concrete helps maintain temperatures within a comfortable range when used in buildings.
- Toughness: It resists chemicals, fire, impacts, weathering and other adverse conditions well.
In addition to all these benefits, making concrete requires less energy to produce than other materials used in construction.
Ease of Use
With all these benefits, perhaps the one trait it has that differentiates concrete from other building materials most is its ease of use. Making concrete structures is relatively easy and quick, whether it needs to be poured, mixed, shaped or otherwise worked. Concrete can even come prefabricated from the factory, which can reduce construction timelines. But making concrete depends on cement processing, as it’s cement that binds all the aggregates together.
Essentially, cement acts like paste, hardening in a process known as hydration, which sometimes takes years and, in this process, also making concrete stronger the longer it sets. The ratio of cement to water determines its strength. Making concrete is a balance between strength and flexibility, with less water producing higher quality concrete. However, with too little water it loses malleability, which is what makes concrete so easy to use.
Making Concrete from Recycled Building Materials
Another aspect is recyclability. Reutilizing concrete debris conserves the energy making concrete from scratch would use, while also saving space in landfills. Recycling concrete lowers costs and reduces environmental impact, making it a much more sustainable material.
Equipment Used for Cement Processing & Making Concrete
Cement plant equipment needs to be robust enough to handle the raw materials used while also being sufficiently efficient. As noted earlier, cement processing starts with the mining and preparation of raw materials like limestone. Initially, limestone is blasted out of the rock with explosives, with the resulting boulders carried away by a dump truck then loaded onto a tipple for transport.
Cement processing can be either a dry or wet process, though for simplicity’s sake the cement plant equipment described below are those from the dry process. In a cement plant, equipment used for dry cement processing generally performs the following tasks in this order.
Stack
Once crushed, limestone is piled lengthwise, which takes place at either the quarry or in the cement plant. Equipment known as a stacker performs this role, dealing with piles up to 300 meters (about 984 feet) long and up to 10 meters (about 34 feet and 8 inches) high. Another piece of cement plant equipment called a reclaimer cuts the pile uniformly from top to bottom. These two pieces of cement plant equipment work together to prepare limestone as it’s made into cement. Processing at this point will affect the quality of clinker produced later.
Weigh Feeder
A specialized piece of cement plant equipment called a weigh feeder conveys the crushed limestone while simultaneously weighing it. Weigh feeders deal not only with limestone but also with other raw materials that go into cement. Processing of bauxite, clay, iron, and other materials begin with transporting the material along the weigh feeder’s conveyor belt into their respective hoppers, which rotary valve feeders often feed. Appropriate amounts of these raw materials – known as raw meal – are then fed into a silo where processing continues.
Raw Meal Silo
An array of cement plant equipment is used at this point to blend the raw ingredients together within the silo, where it’s blended with compressed air. At this stage of processing cement, plant equipment will normally consist of a blower to introduce air into the silo and sometimes a rotary airlock valve to maintain proper pressure before the raw meal is sent to the kiln via a conveyor belt.
Preheater
Normally, the raw meal goes through four to six stages in a piece of cement plant equipment called a preheater, which is fed from the top via pressurized air. Hot gas from within the kiln enters the preheater from below, while raw meal slips downwards through the preheater. At this stage of cement processing, also known as calcination, temperatures will reach between 900°C and 1000°C (1652°F and 1832°F). During preheating, about 90 percent of the carbon dioxide is removed from the calcium carbonate found in calcite, the main component of limestone. This prepares the material and then moves on to be heated within a rotary kiln.
Rotary Kiln
A rotary kiln is a huge piece of cement plant equipment, usually measuring from 50 to 60 meters (about 164 to 197 feet) long and about 3 to 3.5 meters (about 10 to 11.5 feet) in diameter. It’s positioned horizontally, though it inclines to ensure movement of the raw mixture within the kiln, with the preheated material entering at the opposite end to where the burner is positioned.
Rotary kilns usually revolve from one to three times per minute. The raw mixture within the kiln melts until it liquifies, with the rotating kiln producing nodules as it turns. This mixture moves from the preheating or calcining zone into the burning zone, where temperatures reach from 1350°C to 1450°C (2462°F to 2642°F). What comes out of the kiln is known as clinker.
Cooler
The kiln discharges the heated clinker, where cement plant equipment – typically a grate cooler – quickly reduces the temperature of the material. The cooler blows air across the clinker to reduce material temperatures quickly to around 50°C (122°F), where the material is sent to another storage container. For quality clinker, it’s vital this cooling happens quickly, as slower cooling adversely affects its stability, resulting in lower strength cement. Processing throughout the heating and cooling treatments are largely automated, but managed closely from a centralized control room with the help of computerized controls.
Cement Processing Mill
Clinker is next transported from the hopper in which it’s stored via a conveyor belt as are gypsum, fly ash and other additives conveyed from their respective siloes. Electronic weigh feeders add proportionate amounts of clinker, gypsum and other additives. Both clinker and gypsum come already crushed with a roller press or similar type of cement plant equipment before they’re fed into specialized mills for fine grinding.
Packaging & Transport
Once finished, rotary packers efficiently weigh bags of cement. Plant equipment for packaging these days is completely automated, including electronic weighing machines that release bags of cement once fully filled. In the last stages of processing, cement in these packed bags is transported via conveyor belts, after which they’re loaded on trucks and shipped to distributors for use by the construction industry.
Cement Plant Equipment from Prater
Prater Industries makes cement plant equipment that can handle individual ingredients and additives as well as finished cement. Processing cement and making concrete can involve a great many different ingredients, with special properties provided to it from optional additives. Many of Prater’s machines are used to reduce the particle size of ingredients and additives prior to the final stages of processing cement. Processing systems for making concrete and cement require versatility, depending particularly upon the desired properties of the finished product.
In a cement plant, equipment made by Prater could include:
- Air classification mills: Used in cement processing and making concrete, Prater air classification mills can handle activated carbon, calcium carbonate, clays, coal, gypsum, iron oxide, limestone, magnesium hydroxide, phenolic resin, sodium bicarbonate and other ingredients or additives.
- Air classifiers: Used in cement processing and making concrete, Prater air classifiers can handle aluminum oxide, calcite, carbon black, coal dust, diatomaceous earth, ground glass, gypsum, iron oxide, kaolin clay, lime, magnesium oxides, manganese dioxide, mica, perlite, phenolic resin, quartz, silica in various forms, sodium bicarbonate, sodium phosphate, zeolite and other ingredients or additives.
- Fine grinders: Used in cement processing and making concrete, Prater fine grinders can handle activated carbon, calcium carbonate, clays, coal, diatomaceous earth, gypsum, iron oxide, limestone, magnesium hydroxide, perlite, phenolic resin, soda ash, sodium bicarbonate and other ingredients or additives.
- Hammer mills: Used in cement processing and making concrete, Prater hammer mills can handle activated carbon, activated charcoal, calcium carbonate, calcium chloride, calcium stearate, chalk, clays, coal, crumb rubber, diatomaceous earth, oyster shells, plastic scrap, potassium sulfate, salt cake, sodium carbonate, sodium hydroxide, sodium nitrate, sodium phosphate, sodium tripolyphosphate, vermiculite and other ingredients or additives.
- Lump breakers: Used in cement processing and making concrete, Prater lump breakers can handle aluminum silicate, barium sulphate, bentonite, borates, calcium carbonate, clays, fly ash, melamine, phenolic resin, potassium, sodium tripolyphosphate, sulfur and modified for other ingredients or additives.
- Rotary valves: Used in cement processing and making concrete, a diverse assortment of Prater rotary valves can handle activated carbon, aluminum oxide, bauxite, calcium carbonate, carbon black, cement, coal, fly ash, gypsum, hydrated lime, kaolin clay, limestone, pebble lime, petroleum coke, polymer resin, potash, potassium carbonate, silica, soda ash, sodium bicarbonate, sodium sulfate, sulfur, titanium dioxide, vermiculite, zinc oxide and other ingredients or additives.
Processing of various ingredients or additives is possible with modifications of our standard models as well, with systems for processing cement and making concrete that can be honed in our test lab. To learn more about our cement plant equipment, contact the material handling experts at Prater.
