FOSROC International P.O. / Martyn Whitehead
FOSROC Yapı Kimyasalları Sanayi ve Ticaret A.Ş. / Ahmet Erdal
Introduction
The cement industry is a key global industry and demand for cement-based products shows no sign of slowing down. It is well known that the industry is responsible for around 7% of anthropogenic Green House Gas (GHG) emissions [1], but collectively they have been working very hard to address this challenge. The focus of this article will be on the significant contribution FOSROC cement additives and grinding aids can have on reducing the carbon footprint associated with cement production.
Emission Sources
GHG emission sources during the manufacture of cement can essentially be separated into four groups:
- Calcination of the limestone
- CO2 from the production of electrical energy during the various stages of the manufacturing process
- CO2 from the input of thermal energy during clinker production
- CO2 associated with the amount of clinker used in the cement
Reducing the CO2 emission from the calcination of limestone can only be practically achieved by reducing the amount of limestone used in the raw mix. This could be by either using alternative raw materials such as blast furnace slag and/or construction waste or by adjusting the chemistry of the raw mix in order to produce a clinker with a lower Alite content. Aside from this the other mitigation route is via some form of capture and storage.
Since cement additives have almost no ability to impact the emission relating to the chemical conversion of the limestone, this article will look at the way cement additives can be used to reduce the CO2 arising from the associated thermal and electrical energy usage as well as from the ability to reduce the clinker content of the cement.
Grinding Efficiency Improvements
There are three potential applications for cement additives to improve the grinding efficiency and reduce the specific electrical energy consumption. The three applications are:
- Solid fuel preparation
- Raw meal preparation
- Cement grinding
Given that the average emission of CO2 in Europe for the production of electrical energy is 0.296 kg CO2 per kWh (range 0.013 to 0.819 kg CO2 per kWh) [2], the potential for emission reduction is significant.
Solid Fuel Preparation
A number of plants are still using coal and petcoke as their primary fuel sources. Petcoke is much harder to grind than coal and also requires a higher fineness to ensure correct combustion properties due to the lower amount of volatile matter. If the mill was originally sized for coal grinding, the use of petcoke could result in a bottleneck in production. Grinding aids can facilitate the transition from coal to petcoke in order to maximize the benefit from the lower cost fuel. FOSROC’s experience with using Auracem 300 series products in both ball mill and vertical roller mills demonstrated that reductions in specific energy consumption were around 2 kWh/T were achievable.
Raw Meal Preparation
Raw meal with a consistent quality is a crucial factor in the stable operation of kiln during clinker production. FOSROC’s utilized their experience to select and supply FOSROC Auracem 360 RM to a plant in the Southern Caucaus region to improve the grinding efficiency and ensure that the defined residues targets were consistently met. The outcome was around a 10% reduction in specific energy consumption, which equates to a saving of around 2 kWh/T. The supply of a more consistent quality of raw meal to the kiln also has significant benefits for the burning operation, which will be discussed in detail in a later section.
Finish Cement Grinding
The reduction in specific energy consumption during finish grinding has been documented for decades and therefore it will not be discussed in detail. However, the key point to consider when we are looking are reduction in CO2 emissions from the energy supply is that the use of cement additives typically reduces the specific energy consumption by around 10-15% or 5-8 kWh/T for the most common cement types. A specific example is given in table 1 below for an OPC:
Table 1: FOSROC Auracem 415 Effect
Thermal Efficiency Improvements
One of the key factors influencing the thermal efficiency of clinker production is the burnability of the raw meal. The burnability of the raw mix is dependent on a number of factors, but two critical ones that the plant has an ability to control are the contents of coarse quartz and coarse calcite. Using a modified version of our FOSROC Auracem 360RM product we conducted a full-scale industrial trial at a cement plant in Turkey and the results of this were presented in detail at 14th TÇMB International Technical Seminar and Exhibition. In addition to reducing the specific energy consumption during the grinding of the raw meal, the use of the grinding aid resulted in a reduction of the amount of coarse calcite in the mix while maintaining the 90 and 200µm residues. This improved the overall burnability of the raw mix, which resulted in reduction in the specific heat of clinker formation by around 6%.
Cement Clinker Factor Reduction
Routes to clinker reduction in cement typically involve the utilization replacement materials such as Limestone, Granulated Blast Furnace Slag (GBFS), Pulverized Fuel Ash (PFA) or natural or calcined pozzolans.
India is perhaps one of the largest producers of Portland slag cement (PSC) and Portland pozzolan cement (PPC) and the results from trials that we conducted there are shown in table 2. The main aim of the trials was to increase the amount of GBFS and PFA that could be incorporated into their cements, while maintaining the same high-quality levels.
In the Portland Slag Cement (PSC) example an experimental additive FOSROC Auracem D-12 is used allows a reduction in the clinker content from 30 to 35%, while maintaining the original strength performance. The second example is Portland Pozzolana Cement (PPC) where another experimental product FOSROC Auracem D-36 is used. In this case the product allows the PFA content to be increased from 31.5 to 34.5%, while maintaining the original strength performance.
Table 2: PSC and PPC Production Examples with FOSROC Auracem Products in India
In India the industry average CO2 emission is around 0.72 ton CO2 per ton of cement and the average clinker factor is 0.72 [3]. Consequently, we can approximate that for each 1% reduction in the clinker factor we will reduce the CO2 emission by around 10kg CO2 per ton of cement. In the two cases above, where the annual production of PSC is around 500,000 tons per annum and PPC production is around 300,000 tons per annum, this equates to potential reduction in the CO2 emission of 25,000 tons for PSC and 9,000 tons for PPC.
Bringing it All Together
The easiest way to understand the potential impact the cement additives can have on the reduction of the CO2 emission is to look at an example. The production parameter details are shown in table 3 and the CO2 savings are shown in table 4.
Table 3: Cement Production Parameters
Assumptions:
- Cement production remains fixed, but clinker and raw meal production are adjusted to reflect the lower clinker factor achieved by using cement
- The reduction in specific energy consumption for grinding is considered to be 10% when using cement additives
Table 4: CO2 Savings T/yr
Assumptions:
- The average CO2 emission for the production of electrical energy is 3 kg of CO2 per kWh
- The fuel split in the cement plant is 70% bituminous coal and 30% alternative fuels, which are considered to be zero emission
- The average heat value of the bituminous coal is 30 MJ/kg and the average CO2 emission is 94,600 kg/TJ
- The average CO2 emission for clinker production is 800 kg/T and the non-fuel elements is simply the total minus the CO2 emission arising from the combustion of the fuel
Conclusion
The use of cement additives across the various stages of the cement manufacturing process can have a significant impact on the CO2 emission associated with it. Using typical values that we have regularly seen during continuous use of cement additives in full scale industrial production, it is possible to reduce the overall CO2 emission by around 4-5%. It is important to note that these savings are over and above the financial savings that are usually attributed to cement additives such as electrical energy cost and the costs of clinker production. Given that the price of CO2 credits in EU Emissions Trading Scheme hit 100 Euro per ton this year, annual savings of over 30,000 tons of CO2 per year not only help the plant reduce the carbon footprint it could also help to save them over 3,000,000 Euros in CO2 credits.
References
- Monteiro, , Miller, S. & Horvath, A. Towards sustainable concrete. Nature Materials, Volume 16, 2017 in Sabbie A. Miller, Guillaume Habert, Rupert J. Myers, John T. Harvey, Achieving net zero greenhouse gas emissions in the cement industry via value chain mitigation strategies, One Earth, Volume 4, Issue 10, 2021
- https://www.rensmart.com/Calculators/KWH-to-CO2, last accessed 29/05/2023, using data from the European Energy Agency (2016)
- Existing and Potential Technologies for Carbon Emissions Reductions in the Indian Cement Industry, A set of technical papers produced for the project ‘Low Carbon Technology Roadmapforthe Indian Cement Industry, Cement Sustainability Published online by the International Finance Corporatation. Retrived from https://www.ifc.org/wps/wcm/ connect/0bd665ef-4497-4d6d-9809-9724888585d2/india- cement-carbon-emissions-reduction.pdf?MOD=AJPERES&C VID=jWEGLpL,last accessed 02/06/2023
