Editor’s Note: Used to transfer bulk solids at a carefully controlled flow rate, weighbelt feeders are essential pieces of equipment in the cement industry. We spoke to Cesare Riva, bulk weighing and monitoring expert at Thermo Fisher, about the vital role that weighbelt feeders play in cement production.
Weighbelt feeders are essential in cement production. How important is this application?
It sounds incredible to say – but cement is the second most used material on earth after water. The global cement market produced 5.17 billion tons of cement in 2020 and the market is expected to grow by 3.3% each year from 2021 to 2026. This means 6.08 billion tons of cement by 2026.
Weighbelt feeders are essential to the production of every ton of cement. The more cement is being produced, the more important it is to have accurate and reliable weighbelt feeders.
What are the key factors driving the growth we’re seeing in the cement industry?
The main factors are rising disposable incomes and increasing urban populations, which lead to an increase in residential projects and investments in the construction industry. The major regional markets for cement are North America, Africa, Europe, and the Asia-Pacific. China is probably the biggest worldwide; followed by the Middle East and Latin America, where urban population and infrastructures are growing.
Do all of these projects use the same type of cement?
No. The two principal products are blended cement and “ordinary” Portland cement. But cement composition is always based on customers’ specific requests, and different applications require different elemental chemistry in the recipe. A recipe can change depending on the customer’s specification, but also on the local availability of raw materials and even on the season! Weighbelt feeders enable manufacturers to accurately control the proportions of different ingredients in a given cement product.
What steps are involved in producing cement to customer specifications?
There are four main stages of the cement production process that help to maintain consistent quality with minimal chemistry deviation from quarry to silo to customer.
The cement production process begins with the extraction of limestone and clay from the quarry. The material is then transferred to a crusher where the particle sizes are reduced, and the product is pre-blended to reduce variability in composition. Weighbelt feeders help to maintain product consistency during pre-blending, while online analyzers can be used for accurate measurement and storage of the product.
After this, the raw material is transferred to the roller mill and kiln line where it is blended to the current recipe by adding expensive pure additives. Once again, weighbelt feeders are typically used at this stage. Then it is dried, ground and heated into clinker. This phase is fundamental to the final quality of the cement and accurate blending is mandatory. Finally, the clinker is cooled, the elemental composition is determined, and it is ground into fine particle for storage or shipping.
How do cement producers overcome challenges during production?
The main challenge is to maintain the raw material blend and keep quality consistent. This is accomplished by analyzing the product and immediately correcting the production process with reactive machineries such as weighbelt feeders.
The high cost of pure additives presents another challenge. For this reason, it’s critical to manage them in the best way to directly realize savings.
Another challenge is unplanned production downtime – this is a pure loss of revenue. Using reliable equipment is vital to prevent this.
Each of these problems can be addressed by the same pieces of equipment: weighbelt feeders. Weighbelt feeders are reactive conveyor belts which enable producers to carefully control the flow rate of dry bulk solids. Weighbelt feeders are crucial throughout multiple stages of cement production, a role that has earned them the title of “the heart of the plant” in the cement industry.
What are weighbelt feeders and how do they work?
Weighbelt feeders Weighbelt feeders are belt conveyors specifically design for continuous gravimetric metering of bulk solids to a downstream process. The job of weighbelt feeders is to transfer bulk solids from a bin or silo and maintain blend consistency according to a specific recipe. Through continuous weighing of the conveyed solids, weighbelt feeders are able to keep the flow rate constant according to a given percent value. Control is maintained by varying the belt speed, according to the weight of material on the belt.
Weighbelt feeders therefore enable cement producers to precisely adjust recipes and the correct quantities of products to the next process. The capacity of weighbelt feeders to react and adjust the flow rate is fundamental to meet customers’ specifications. Reliable weighbelt feeders play a crucial role in ensuring the quality of the final product and reducing wastage of expensive additives.
Can you talk us through the use of weighbelt feeders in cement production?
First, material is fed onto weighbelt feeders through an inlet feed section, normally equipped with a manually adjustable vertical slide gate. Usually, the gate opening should be at least three times the maximum particle size. Weighbelt feeders are equipped with a weighbridge, which measures the weight of the material and converts this measurement into an electrical output signal that is proportional to belt loading.
Weighbelt feeders then use a controller which integrates the signal from the weighbridge and an input from a speed sensor to provide a true weight and the total weight fed.
Ideally, speed should never exceed 0.5 meter per second. For greater control and blending purposes, weighbelt feeders can provide output signals, improved communication, self-diagnostics and the ability to upload and download information.
What features should manufacturers look for in high-performance weighbelt feeders?
Not all weighbelt feeders are the same. Manufacturers should look for these qualities in reliable weighbelt feeders:
- Weighbelt feeders must provide a consistent flow of material and must be able to properly handle material themselves.
- Good weighbelt feeders should react quickly to material weight variation in order to immediately adjust the flow.
- Weighbelt feeders must be highly sensitive for accurate weighing of raw materials and products.
- Cleaning and maintenance are important considerations when choosing weighbelt feeders. Reliable weighbelt feeders are designed to permit easy cleaning and maintenance: for example, Thermo Scientific weighbelt feeders use a self-supporting frame with cantilever design for easy and fast replacement of the bed without disassembling the entire machine. The construction provides both corrosion resistance and washdown capabilities.
- Finally, weighbelt feeders must be able to maintain a constant bed tension in the presence of variable flow load or strong temperature variation.
In conclusion, weighbelt feeders are critical assets than enable cement producers to ensure product quality and consistency, reduce material waste, minimize plant downtime and therefore maximize profits.
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