Clinker is the most essential component to make cement a hydraulic binder. Since years, cement producers aim at reducing the so-called clinker factor - the proportion of clinker in the cement - by adding additives.
It can be hydraulically inert additives such as limestone or additives with hydraulic activity such as natural pozzolan, granulated blast furnace slag or fly ash. And this for various reasons:
Reduction of production cost of cement
Cement production volume increase with given clinker production rate
Reduction of CO2 emissions coming from limestone calcination in the clinker production process
Activated clay is a new Supplementary Cementitious Material (SCM) that can contribute to reduce the clinker factor significantly – down to 50% in ternary cement types.
These ternary blends consist of a mixture of clinker, activated clay, limestone and gypsum and give the opportunity to produce green cement.
Reference: First polysius® activated clay plant under construction
thyssenkrupp is currently executing the first flash based activated clay plant for the Dutch-based company Cimpor Global Holdings in Cameroon. The activated clay technology will contribute to savings of 120,000 tons of CO2 emissions per year.
“Our technology is not only eco-friendlier, it also creates cost advantages for our customers such as Cimpor Global Holdings,” says Dr. Luc Rudowski, Head of Product Management and Innovation at the Cement Technologies business unit.
“Our first reference is a very good example that polysius® activated clay leads to both ecological and economical sustainability - this is what we call from #grey2green” says Leo Fit, Product Manager of polysius® activated clay.
Learn more about our first reference.
What is activated clay?
Clay is available in huge quantities worldwide – particularly also in developing countries with growing cement demand such as in Southeast Asia, large parts of Africa and Latin America. In the past, clay has often been discarded as a waste product in the mining industries.
Today this material can be used as raw material to produce a new Supplementary Cementitious Material (SCM) with hydraulic properties to reduce the production costs for cement manufacturing, to increase the production volume and to decrease CO2 emissions.
To produce this new SCM, clay needs to be activated in a thermal process: that’s why we call it activated clay.
CO2 emissions from conventional cement production
For each ton of cement clinker produced, around 790 kilograms of process-related CO2 is emitted. Around two thirds of this results from the limestone used, which releases CO2 in a chemical reaction within the production process. At the same time, the process requires large amounts of energy since limestone has to be processed with temperatures of more than 1,400 degrees Celsius to produce cement clinker, which is the most essential component to make cement a hydraulic binder. Today, cement production accounts to ~7 % of the world’s CO2 emissions.
The role of activated clay for CO2–low cements
Activated clay plays a key role when it comes to CO2-low cements. In a first step the clay minerals have to be activated in a thermal process at temperatures around 800 °C, leading to an active metaphase of the clay which contributes to the strength development of the final activated clay cement. Using the activated clay in the cement allows around one third of the cement clinker to be replaced. For the activation process, less energy input is needed compared to standard clinker production since temperatures are lower. Additionally, there is nearly no CO2 coming from the raw material. Both effects lead to a low CO2 footprint for the production of activated clays, which is around four times lower compared to a standard clinker production.
Low CO2 cement production with activated clay
Advantages at a glance:
Up to 40% lower CO2 emissions compared to Ordinary Portland Cement – reduced CO2 emission costs
Lower energy demand for activated clay production compared to clinker production
Significantly reduced cement production costs
Increased cement production capacity
Superior cement and concrete quality
Reduced clinker factor down to 50%
Up to 70% less CO2 emitted per ton with clay in comparison to standard production of clinker
More self-sufficient operation in terms of raw materials, particularly in regions where clinker limestone and clinker imports are scarce
New business opportunities using widely available residual materials
A significant reduction of the clinker factor leading to highly decreased CO2 emissions as well as lower energy demand. The environmental performance of our activated clay technology is outstanding and a real USP for our customers in the cement industry. And on top of that: our solution leads to a superior cement quality.
polysius® activated clay technology
With its polysius® activated clay technology, thyssenkrupp is providing an innovative solution for the industrial use of clay as an SCM. The technology supports the substitution of conventional fuels by alternative fuels and - if desired - puts an end to the terracotta-color of activated clay cement.
Rotary kiln vs. flash activation
Rotary kiln solution: A strong argument in favour of this type of plant is that it can be retrofitted in a relatively simple way by converting an existing installation. Electrical energy demand is also relatively low, while fuel consumption – by far the most important cost driver – is comparatively high. The choice of feed material and the clay quality require increased attention, with lumpy feed material and pure clays preferred. Compared to the use of a flash dryer, activator/calciner and cooler, this process configuration has a bigger foot print and lower throughput. Controlling the activation temperature and material coloring is challenging and product quality may be inconsistent.
Flash solution: This process configuration achieves the best possible reactivity, leading to maximum clinker substitution rates and superior product quality. Fuel consumption is lower compared to converting an existing installation - such as rotary kiln and cooler plant - and the use of high alternative fuel rates is possible. Color control is also easier to implement. This machine technology is designed for fine materials and prevents dusting issues. A de-agglomeration of the raw material is required. Overall, the flash dryer, activator/calciner and cooler setup has a smaller foot print, a slightly higher electrical demand and a lower thermal demand. The overall OPEX will be lower compared to a rotary kiln solution.
Which technology to apply will be decided on case to case basis. In most cases the flash solution is the preferred option since the activated clay quality is higher and the total cost of ownership (TCO) lower.
Reduce the clinker factor, save money, emit less CO2 – with polysius® activated clay, one-stop solution for raw material changeover.
polysius® activated clay – our approach
thyssenkrupp provides comprehensive business case, clay & activation support. Both the clay and the resulting cement are put through their paces in our R&D centre in Germany. So far, we have tested several tens of different materials for initial feasibility and processing properties and activated them in a muffle furnace, often followed by activation tests in a proprietary pilot (50 kg/hr) or semi-industrial (500 kg/hr) flash activation facility. Finally, the activated clay cement can undergo grinding tests with different technologies and mortar testing in order to determine its optimal composition, workability, water demand, compressive strength and color.
Our approach can be summarized by 5 steps.
Step 1: Find a clay deposit.
First, together with the customer our experts are searching for clay sources in the relevant region. There is a wealth of geological formations worldwide that contains potentially usable clay. If a promising deposit is found, it must be determined whether it is within a reasonable distance from the processing facility, of an adequate size and quality.
Step 2: Review the market.
Once availability and clay quality is assured, the next step is to assess the marketability of potential final products. Ternary blends such as Limestone Calcined Clay Cement, are not yet standardised in all markets. Nevertheless, there are options to use activated clay in the cement portfolio today.
Step 3: Model a business case.
Finally, a business case is designed as basis for the investment decision. The project-relevant parameters include e.g. the cost of clinker, fuels and electricity as well as the supply of clay and other additives.
Step 4: Test the material.
We provide comprehensive raw material testing procedures which we call LAB services. In our R&D centre, both the clay and cement produced from it are subjected to a series of trials to ensure the best product quality at lowest investment and operational costs.
Step 5: Choose the right technology.
We advise interested customers in detail. In most cases, we recommend a plant setup with flash dryer, preheater, activator and cooler. This has some advantages: The energy efficiency is very high due to multi-stage heat utilisation for preheating and coupled drying of the raw clay. Second, a very high degree of clay activation leading to superior product quality with highest substitution rates. Third, a wide range of fuels can be used, including alternative fuels from waste and biomass. polysius® activated clay adapts the technology of flash calcination to the industrial production of activated clay.
polysius® activated clay services
To find out if polysius® activated clay lead to environmental and economic advantages for our customers, thyssenkrupp is offering LAB services.
As we know that both is a prerequisite, we offer cement producers comprehensive support in consulting, project development, implementation and operation. This includes:
Basic analytics & project development including raw material inspection, trial production, mortar tests and a business case calculation
Planning & execution, ranging from EP to EPCM and EPC projects
Operation & maintenance, from assisted start-up to full operation and maintenance
Product portfolio & sales support using high-performance machine technologies and processes, supplemented by warranties regarding substitution rate and/or product performance
Interested in more details? Contact us and walk the path from #grey2green togehter with us!