What a block model is? & How can it support the cement production?

October 16, 2018 ptkawalec No comments exist


Raw materials extraction is an essential part of the cement production and contributes significantly to the cost and quality of the final product. This is true in two ways.
First of all, a permanent supply of adequate amounts of raw materials is a precondition of operating a cement plant at all. So, this is the first challenge for mines planning and operation: ensure this steady supply following the mining state of the art, dealing with weather, natural phenomenon’s, environment, biodiversity, communities, OH&S and many more, for the longest possible period of time.
On top of this, qualities do also matter. Plant design is based on average parameters and operation will be optimal if these parameters are always met. But natural raw materials are variable, and if this goes directly into production it will affect cost:

  • High electrical energy consumption for homogenizing the raw material.
  • High and unstable consumption of expensive corrective materials (e.g. bauxite, high-grade limestone etc.).
  • High wear of the vertical roller mill if no attention is paid to quartz, often even as flint.
  • Higher fuel costs and refractories consumption due to fluctuations in the thermal process.
  • Little use of cheaper alternative fuels and raw materials which bring their own variability from other industries, so their usage is extremely risky without proper raw mix control.
  • Need to use “cleaner”, more expensive fuels, like natural gas, to comply with emission limits.

Often cement raw material supply is only understood in terms of limestone, but even the highest-grade limestone has no value without a second component – clay, shale etc. What counts is thus not only limestone but the constant delivery of the right mix of the primary and second component. In many cases, the “lower-grade” limestone is already much closer to the needs of cement production than the very pure “good” material.
Most of the time, additional corrective materials such as high-grade limestone, bauxite, iron ore, sand or others are required as well. But even in small amounts they add considerably to the production cost, so this should be minimized, and suitable inexpensive alternatives need to be permanently evacuated. In the best case, these can be found even in the own quarries – if all the materials have been properly explored and analyzed! It happens too often that exploration only looks at the limestone or second component, considering everything else as “waste”, so opportunities are missed. In some of my projects, I showed that overburden could replace or reduce the use of costly external materials.
Minor elements and oxides (chlorine, magnesium, sulfur, organic carbon etc.) need to be monitored as well because they can either badly affect the process and product quality or lead to emissions above the allowed limits. Controlling them in the quarry is often the only option to do something about them: While main parameters such as silica and alumina ratio can easily be handled with correctives, this is not true for too high amounts of detrimental minor compounds.
Finally, also physical parameters do matter. Depending on geological and climatic conditions, raw materials can be dry or humid and sticky, hard or soft etc. Knowing these parameters in advance is crucial for the plant design – also for the second component: number and type of crushers, bins, weigh feeders, conveyors, preblending piles etc. Plant design issues should, of course, be known before the plant is built.
At the kiln outlet, the results of all previous efforts become evident – with nothing to be done if the results are negative: off-spec clinker cannot be sold, and marginal qualities lead to reputation damage and cost market share.

Quality management at the source is the key to handling all the issues described above, and it starts with exploration, modeling, and planning. And for all these steps, all the materials that exist in the foreseen deposit area should immediately be included – even if at first they do not look like being useful: It was already pointed out that in some cases this impression may be wrong.
The initial exploration steps will be geological desk studies and fieldwork, followed by core drilling and sometimes supplemented with production rig drilling. Drilling is the most expensive part of the exploration process, so it is important to prepare it well by collecting all available geological information in advance and plan the drilling campaign accordingly. Geophysics can also help to complement the geological information.
The resulting database of georeferenced chemical analyses, together with other information, will go into a geological model that represents in 3D the geological units and tectonic structure. Then a block model can finally be calculated. In a block model, the deposited rock volume is divided into rectangular blocks. Qualities and other parameters are assigned to every block and can be visualized with colors. The block model attributes are calculated from the sample database and the geological model using geostatistical methods. A block model approximates the reality in terms of qualities. The reliability of the model depends on input data, the methods used and not the least on the skills and experience of the modeling expert. Doing all this properly costs of course money but saving here in the wrong place costs much more! Thus, in order to save cost:

  • spend enough effort for a good planning of the drilling campaign (desk study and field geology), to minimize the number of required drillings,
  • take care for proper core recovery, and
  • spend money for a high quality, certified laboratory for sample analysis, and invest in the generation of good geological and block models – because otherwise even the most expensive drilling campaign will only deliver unreliable information.

By far the most expensive step is the drilling campaign, but the reliability of the result equally depends on the quality of every single step: the chain is as weak as the weakest link.
The block model is now the base for numerical optimization and scheduling of the quarry production based on quality constraints.
Again, there is a cost related reasoning that easily justifies the efforts done for planning and more selective mining in the quarry according to the plans. The important question is: What is the cost of handling quality deviations at the different stages of the process between the quarry and markets? The answer is clearly: the later the deviations occur the higher the cost for correction or mitigation – up to the loss of production that results from off-spec clinker.


Benefits of the proper deposit management

Once you understand how relatively little efforts in the quarry can generate much higher benefits further down the line you will no longer hesitate to invest in proper deposit exploration and quarry planning.

There is software, like AthosGEO, which can support your efforts in that direction, but the key to making it happen is not a software, but it’s always you and your team! Using the block model for a deeper understanding of the characteristics of your deposit and its potentials is already the first benefit because it means a major change in mindset: miners will stop mining rocks and start mining quality instead. Which may finally trigger a new and better way of working together between plant and quarries – far beyond blaming each other for shortcomings.

The immediate financial benefit depends on the situation. During our careers in Holcim, the top saving estimated amounted to 4 Mio. US$, and in a short time over 1 Mio US$ has been achieved. Which is a rather quick payback for the planning efforts (the major drilling campaign was not included) – and is only one of the positive aspects!

The gain in quarry lifetime, often less emphasized by the managers because mostly not affecting short-term benefits, should not be underestimated: end of quarry lifetime is often also the end of plant production if additional resources cannot be obtained (land, permits etc.).

Finally, do not forget the relative benefit for your surrounding and environment – by reducing emissions and consuming less of the valuable non-renewable natural resources (rocks).


The above post is an abstract of the article of P.Kawalec and C.Bockemühl: “Block Model-Based Cement Quarry Optimization”; Cement and Building Materials Review, No. 73, Sep. 2018 published by Arab Union For Cement and Building Materials

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