Finish Mill Control with COSMA

Gypsum control

The quality of cement is determined by key performance parameters such as setting time and strength, so it is imperative that contributors to these are controlled carefully during the manufacturing process. Better control of gypsum dehydration leads to better control over cement setting time and strength development, providing a marketing edge over competitors.

In Portland cement manufacture, gypsum or gypsum plus anhydrite is interground with clinker to produce the finished cement product. CaSO4 is required to control setting time; without it the ground clinker would flash set. However, changes that occur when grinding are not just physical as the grinding imparts energy which elevates the temperature causing dehydration of gypsum.

changes over time

Dynamic gypsum states occur at temperatures above 105°C when the partial de-hydration of gypsum produces hemihydrate. Anhydrite begins to form about about 170°C. The ratio of gypsum forms is critical to cement performance in use.

Changes taking place in gypsum states are not readily apparent because to date there has been no way to monitor the phases until it's too late and customers complain of poor performance.

COSMA continuously monitors and reports all three gypsum states from a cement sample stream. For the first time, operators have a live picture of these dynamic states and are able to manage the process to produce a consistent product.

Financial benefits result from the improvements in product quality, especially in competitive markets where the customer demands the best performance characteristics, consistently.

Setting time prediction is the next step after controlling the gypsum dynamics, which has many mineralogical contributors; free lime, clinker minerals and, of course, gypsum states. COSMA provides accurate data on the content of all of these minerals and, over time, correlations between them and setting times enable a control regime to be developed and implemented based on FCT's predictive control model.

What COSMA can do for youWhat COSMA can do for you
  • Controlling gypsum addition to the SO3 target
  • Controlling gypsum dehydration to a hemihydrate target
  • Setting time prediction & control
  • Improved quality
  • Customer satisfaction
  • Competitive edge


Regulations around the world permit the addition of up to 5% limestone in Portland cement. In Europe and North America limestone has been used successfully for decades as an extender in cement, providing equivalent performance to cements without limestone.

Environmental benefit from the use of limestone in cement is a key component of the cement industry's commitment to a reduction in the level of greenhouse gas emissions by the year 2020.

Financial benefits also flow from the substitution of clinker in the cement milling process, as less costly limestone is used instead of valuable clinker.

Cement Mill product XRD analasys

Sold out plants enjoy even more significant benefit as the clinker substituted by limestone is available for additional cement production, maximizing sales whilst demand remains high.

The challenge for cement producers is to maximize the value of clinker production by working as close as possible to the prescribed limit of limestone addition. Traditional control by infrequent spot samples taken from the process for laboratory analysis, which measures the chemistry rather than the limestone mineral itself, do not permit tight control. Thus a target level of addition well below the limit must be adopted to provide large but costly room for error.

Lost opportunity and significant lost revenue will result if limestone addition levels are not able to be accurately and confidently controlled close to the prescribed upper limit, due to inadequacies of analysis.

The solution is COSMA, the first on-line mineral analyser to continuously monitor a sample stream of material for mineral components. The actual amount of limestone in the cement, in per cent, is output from COSMA as a real time trend that is available for manual control actions or may be integrated into process control systems for automatic corrections. It is therefore possible to work at targets close to the 5% limit rather than around 3%.

Contact Us +61 8 8352 9999 now and learn what else COSMA can do for you in real time.

See more details on the benefits .... - view Cement Analysis (see applications/clinker)