Grinding is the most important aspect of cement production as the process begins and ends with grinding. First in the process is the grinding of raw materials like limestone; next is the mixture of the grounded raw materials into cement clinker nodules. Lastly, the nodules are ground into fine powdered cement we are familiar with.
The grinding is done at a grinding mill. There are two types of grinding mill technology used for cement grinding. The century-old ball mill and the more recent, Vertical Roller Mill (VRM).
There has been professional, academic, and technical debate as to which grinding mill technology is better. Most claim VRM to be better, yet majority of cement producers still use the BALL MILL FOR CEMENT GRINDING.
For comparing the two, these criteria are usually considered — cost and ease of installation, cost and ease of maintenance, product quality, and product flexibility (versatility). The list is not exhaustive, but we’ll stick to these for our comparison.
A test comparing product quality of cement of the same composition ground in using the two technologies, has shown that there is no significant difference between their qualities, thus, both grinding mill technology can be used if product quality is the sole focus of the operation.
Probably due to current energy saving practices, the VRM consumes 25%-40% less energy than the ball mill. Grinding aid is not required by ball mills for grinding the cement to required fineness, however, it is required by VRM.
Ball mills consume lots of energy and therefore will not need a generator to provide heat for dehydration of the gypsum when grinding OPC. VRM on the other hand, will require the assistance of external heat.
High heat generation of the ball mill makes it a necessity to install water injection for temperature control, while VRM’s low heat production makes it unnecessary for it.
Versatility of the Mill
The VRM is modifiable and flexible, making it more versatile than the ball mill. VRM can easily accommodate several products and materials with just little modifications of the technology, unlike ball mill that has limited adaptation.
Rate of Interest
The upgrade system of ball mill technology (with a pre-grinder) favours low investment. The return on investment (ROI) is high as the upgrade is capable of increasing the efficiency and capacity of the ball mill to up to 100%. Unfortunately, this upgrade system isn’t available in a VRM technology.
Wear and Tear
Generally, the wear rate for the BALL MILL FOR CEMENT GRINDING is higher than that of VRM, however, the replaceable parts of a ball mill are very easy to obtain. Its maintenance is also not as complicated as the VRM. As a VRM wears and tears, its performance level goes down a rapid slope, and it’s replaceable parts are much more expensive and difficult to maintain and obtain.
Cost of setting up a new mill technology (including equipment, civil works, and erection) is 20% lower for the ball mill than the VRM.
It is difficult to arrive at a conclusion on which is better. It is advised one picks that which meets one’s organisational needs after careful considerations.