cement industry

For the production of cement, first and foremost a blend of limestone and clay (or marl) is used. In addition, different additives or correction materials, such as quartz sand, materials containing iron oxide, gypsum, schist or similar are applied. As complex and customized is the process of making cement, so are the systems and technologies that are required required. A common factor, however, always remains in place: the basic material must be crushed.

In a vertical roller mill or ball mill, the pre-crushed materials are further ground. The optimum feed grain size for each one of these mills is different; each normally requiring different pre-crushing systems for the production of the correct feed granulation. If not approached correctly, such mistakes can lead to a significant rise in the needed energy costs associated for the comminution or material pulverizing process. 

An important parameter for the production of cement is the LSF (lime saturation factor). The LSF is defined as the rate of the most important chemical component, which has to be kept a constant within narrow limits. By selecting the first stage crushing plant or system the process of influencing the LSF already begins.

Control over the components, such as the limestone and clay (or marl) is indispensable. In many cases, subject to the material characteristics and percent-ages of each, the limestone and clay can be processed together in a single crusher. Under this condition, a certain level of homogenization is already taking place.

The selection of the proper equipment is of vital importance and will further optimize operating costs and the final product. This is ensured by the selection of the complete system, not just a single or individual component. For example, although a compressive type crusher operates with less energy and wear, due to its lower reduction ratio and larger product size, you are faced with the need to include an expensive secondary crushing system to meet the desired product size. Alternatively, under the proper raw material conditions, the flexibility and reduction ratio realized in the primary impactor can produce and offer major advantages. The key is to find that correct solution; at HAZEMAG you will always find what you are looking for – expertise, experience, a trusting partner and the latest proven technology.

A primary pre-crushing plant normally consists of: 

• feed hopper 
• hopper discharge unit
• prescreening stage 
• primary crusher 
• crusher discharge unit

Depending on the characteristics and size of the feed material, these components must be designed in a manner that ensures trouble free operation, reliability and extended service life. These machines must be engineered in a manner that ensures their robust or heavy duty design, allowing them to deal with the possible entry of metallic, foreign materials such as loader teeth, etc. 

The characteristics of the raw material, moisture, inclusions of clays, compressive strength and chemical makeup highly influence not only the selection of aggregates, but also and especially the type of primary crusher that will be utilized. The consideration of mobility for the primary crushing plant is mainly influenced by the raw material resources and the associated transport distances.

The design of the receiving hopper and its discharge unit play an essential and important role in the overall success of the crushing plant. The geometry of the receiving hopper must be in line with its dis-charge unit. The discharge unit, such as the cement industry preferred apron feeder, must be in line and match the flow of the downstream unit. The apron feeder should be designed to convey the material at varying speeds and capable of doing so under varying load conditions.

Prescreening is an excellent way to remove lower quality, unwanted contaminations from the raw material stream. In doing so, benefits such as increased end product quality, reduced crusher wear and reduced energy costs are fully realized. Prescreening can also lead to the reduction and cost savings in regard to the size of the primary crusher, as the volume of material that needs crushed is reduced.

The prescreening stage should work load independent, thus enhancing its success and high efficiency in removing the finer materials, while allowing it to successfully deal with adverse conditions, such as sticky components. When considering the prescreened material, in some cases blending it back together with the crushed material may be desired. However under this condition some level of caution should be taken to ensure that the screening size (opening) is not too large, potentially allowing an excessive amount of oversized slabs to pass. 

Under difficult raw material conditions, such as high levels of contamination, the flexibility of the scalping system can be enhanced and easily fulfilled by the HAZEMAG VARIOwobbler® HVW Roller Screen; which offers hydraulic gap setting adjustment. The benefits of the VARIOwobbler® are easily realized, especially when the raw material contains a high level of variations. Taking everything into account, prescreening and the utilization of the VARIOwobbler® can provide the operating company with a very high level of operating benefits; increased product quality and reduced operating costs.

The main function of the primary crusher is to process the raw material, while reducing it to the desired size so that it can be conveyed and processed downstream in the raw grinding area without any operating problems. Depending on application parameters, feed material and processing requirement, HAZEMAG has developed a range of crushing solutions.

Depending on the selection and design of the primary crusher, the addition of a secondary crusher may be required, as a manner of achieving the correct feed size for the vertical roller mill. Additionally, the secondary crusher can also function on a direct feed basis for the processing of smaller feed sizes. These materials are often found with coal, pozzolana, iron ore, schist, clay and marl. Another consideration for the secondary crusher has been found in its use to increase the overall plant output and efficiency; achieved by a further reduction of the ball mill feed size. In this case, crushing or drying and grinding has resulted in proven benefits associated with the operation and performance of the ball mill.

Depending on the moisture of the raw materials, such as clay, marl, chalk etc., driers are also utilized for reducing the needed drying process in the raw grinding area. If utilized, dryers are positioned after crushing and in front of the raw grinding mill.