There are four main ingredients needed to make cement: calcium, alumina, iron and silica. The percentages of each ingredient are 90, 3, 2, and 5, respectively.
How cement is made
In the case of a current customer, calcium, in the form of limestone, is mined from a huge quarry on the plant site. The rock is removed by a large front-end loader with a 6-cubic-yard bucket, and 95-ton haul trucks. In two crushing stages, the three-foot chunks of limestone each are reduced to six inches and then to about three inches. A series of four belt conveyors, approximately 3,000 feet long, carry the crushed rock out of the quarry and into the raw grind area.
Fly ash is one of the residues generated as a combustion byproduct from burning pulverized coal, often in power plants. During combustion, mineral impurities in the coal such as clay, feldspar, quartz and shale fuse in suspension and float out of the combustion chamber with the exhaust gases. Fly ash is the source for alumina in concrete, and is transported by rail to the customer plant and then transferred from the unloading area to storage using an airslide that conveys the material on a cushion of air.
Iron arrives at the plant via barge and is stored in a large enclosed building. It is moved from storage to production by an enclosed belt system. Silica is obtained from sand mined from local quarries.
The raw materials of limestone, fly ash, iron and sand are first combined in proper proportions in the raw grind area. The presses grind the material fine enough so that most of it can be sent directly to the rotary kilns after being mixed and dried. With the fuel source a combination of coal and petroleum coke, inside the kilns the materials are subjected to temperatures of 2,700°F, which causes the materials to combine chemically through a process known as calcining. During calcination, carbon dioxide and water are liberated and the remaining constituents combine to form a new material, commonly called clinker.
The clinker may be stored either in a building for later use or conveyed to the finish grind area. There, it is first mixed with gypsum, and the gypsum and clinker are delivered to roller presses and then ball mills for finish grinding. The discharge from the ball mills is transported to high efficiency separators where it is separated into finished product – cement – and larger particles, which are returned to the mill.
The cement is then transferred to silos prior to being shipped in bulk. Most of the cement manufactured by the customer is shipped by barge to terminals around the Great Lakes, with each barge holding between 10-18 tons of cement. Rail or truck is used to transport the rest.
This customer, like others in the cement industry, has the option of obtaining a cement sample in many forms – slurry, liquid, powder, clinker, slag and finished cement – to ensure product quality and safety. Typical sampling points include raw and finished product, loadout and custody transfer.
Sentry samplers for liquid & slurry and solid & powder designed for the cement industry are ideal for sampling cement from chutes and gravity/freefall applications, air slides, conveyor belts or pneumatic conveyance lines.
While the company already was using auger type samplers to sample product just after the finish grinding mill process, it wanted to confirm the quality of the finished product, so it implemented sampling just as the product was loaded on to the barge. Space was an issue, so auger type samplers could not be used. Another issue was the difficulty the customer was having in obtaining a representative sample from each of its 14 loadout discharge chutes just prior to the material being loaded on to the barge. Taking a sample at the chute was preferable, as it eliminated the need for having an operator on board taking grab samples.
To test the sampling process, different methods of sampling were used to take a “spiked” sample. Because of its accuracy, the Sentry® ISOLOK® SAK automatic point sampler was chosen by the customer as the best solution. The customer now samples finished product from each of its 14 loadout chutes using Sentry ISOLOK SAK automatic point samplers for solid & powder, with a sample size of 18 cc each, just prior to transferring the product to the barges. Samples are removed from the airslide and discharged into a plastic bag. When the bag contains one gallon of sample, the sampler stops and the sample is transported to a lab for analysis.
Testing by the customer company engineers has shown that the Sentry ISOLOK SAK samplers provide incredibly accurate results. The customer feels that the Sentry ISOLOK® SAK sampler has proven to be reliable, compact, and providing samples representative of the process.
Learn more about Sentry sampling solutions for the cement industry here.
This article was originally published on our website.