Yves Marc Schade, stela Laxhuber, explains in the latest issue of World Cement the role of low-temperature belt dryers in facilitating the increased use of alternative fuels.
As a leader in technology for low-temperature belt dryers, stela Laxhuber Drying Technology regularly brings its team of engineers together, covering the different relevant fields. In recent years, the drying of alternative fuels (AFs) and fractions of high-calorific waste (RDF), has been an increasingly important topic, particularly in the cement industry.
As part of one of the company’s training days earlier this year, stela invited an established expert in the industry, Dip-Ing. Wolfgang Schwörer, where he provided insights from his many years of experience working at cement plants. The resulting synergies, particularly in the design and application of belt dryer technology in an industrial setting, can be used by operators.
Firstly, it must be questioned what types of AF are currently used in the cement industry. Various types of AF are being used to replace traditional fossil fuels like coal, natural gas and oil. These AFs come from different sources and can be divided into different categories, such as:
- Biomass fuels (such as wood waste, agricultural waste, as well as biogenic waste from the food industry).
- Secondary fuels (such as old and used tyres, non-recyclable plastics, industrial waste).
- Municipal waste (household waste, processed waste, municipal sewage sludge).
- Industrial by-products (sewage sludge, oil sludge from oil processing and refineries).
- Other fuels (‘meat & bone’, solvents, etc.).
The environmental benefits
The environmental benefits of using AF in cement production have been discussed in depth.
Refuse-derived fuels are a substitute for fossil fuels and therefore help to conserve resources from limited fossil sources. Substitute fuels sometimes contain significant proportions of biomass and other CO2-neutral fuels. As the amount of CO2 released during combustion corresponds to the amount absorbed by the plants during their growth, they are considered CO2-neutral. This significantly reduces the relevant carbon dioxide emissions. Many other AF come from waste that would otherwise be disposed of in landfill sites. By using this type of AF in cement production, the volume of waste is reduced, lowering the environmental impact of landfills, and increasing their lifespan. By substituting fossil fuels, the limited fossil resources are replaced, contributing to the conservation of resources. Using waste as fuel supports the concept of the circular economy by reusing and recycling materials rather than disposing of them. This promotes the sustainable use of resources and minimises waste.
The challenges
Switching to AF in the cement process brings various challenges and risks, which can be of a technical, economic and ecological nature. Existing cement plants may need to be upgraded with suitable storage, dosing and transportation equipment in order to be able to use AFs efficiently. The combustion properties of AFs differ from those of fossil fuels. This may require adjustments to combustion technologies and processes.
The quality of AFs can vary greatly, which can affect the consistency and stability of cement production, and drying of AFs plays a key role in this.
This therefore links to stela’s drying technology, which has a modular design and uses waste heat to homogenise the material’s combustion properties. Some AFs can lead to higher emissions of certain pollutants, which may require additional emission control measures. Additionally, the combustion of AFs causes fuel ash or other residues to enter the kiln process. These ash components must be considered in the operating mode and the chemical control of the clinker process.
In addition, the prices and qualities of AFs can be volatile, particularly if they are in demand from other industries or are subject to seasonal fluctuations. Competition for certain waste materials or biomass can lead to bottlenecks and price increases.
To achieve the desired cement quality, adjustments must be made to the production process and the fuels, whilst carefully monitoring and controlling the production parameters. The drying of AFs plays a central role in this again and highlights the importance of efficient and reliable drying technology. AFs are cheaper than traditional fossil fuels such as coal or natural gas. Waste materials that would otherwise have to be disposed of are often made available at a lower cost, free of charge or, depending on demand and quality, even at an additional cost.
Although substitute fuels often come from international markets, they become available locally after their original material use and after processing, they are therefore ideally not subject to high dependencies on the international fuel market. The conversion of existing cement plants to AFs requires investments in flexible and modular plant engineering or technologies. Maintenance and operating costs must also be considered, as the plant technology is more complex and requires more frequent maintenance. Looking back on over 100 years of history, including nearly 500 installations worldwide in all different applications, stela can contribute to the critical process benchmarks.
The importance of alternative fuels
The implementation of AFs in cement production has resulted in different experiences worldwide over the last 10 years. Some countries and producers have achieved remarkable successes and gained relevant experience in successful day-to-day operation.
Germany is leading the use of AFs in the cement industry. Many cement plants already use a high proportion of refuse derived fuels (RDF) such as used tyres, plastic waste and biomass. This switch has led to significant reductions in CO2 emissions and less of a dependence on fossil fuels. According to the national trade organisation VDZ in its latest report, the proportion of AFs in Germany is over 70% higher than the average.1 Successful plants achieve annual average substitution rates of up to and over 95%.
The use of substitute fuels must always be considered with the aim of meeting climate, political and corporate targets. In particular, the cement industry will play a significant role in leading the sustainable transition, having the potential to conserve resources, implement the circular economy concept and reduce CO2 emissions.
These possibilities with parallel optimisation of fuel costs and reduction of international dependencies make the use of substitute fuels (in developed markets) the logical conclusion. The adjustments to be made in terms of both plant technology and operating methods are tasks that should not be underestimated, but which can be successfully and profitably mastered. The success of the German cement industry, in particular, is proof of this.
To ensure the successful use of substitute fuels, availability and uniformity of the materials used are essential. As substitute fuels often have very varied properties, the technology used must be able to react flexibly to these variations. One parameter that is often subject to major fluctuations is the material moisture content. As the moisture has a direct influence on thermodynamic processes and the calorific value, it has a direct impact on the operation of the kiln. It is therefore very important that the material moisture is as low and uniform as possible. Again, the drying of AF plays a central role in this, demonstrating the importance of sufficient, efficient and reliable drying technology. It is often not possible to actively influence the qualities of available material, as they are supplied ready-made by the upstream supplier. One very successful way of exerting influence is to dry the material directly in the factory. The cement process, with its many possibilities for using existing waste heat, is perfect for this. The quality of the available fuel can be considerably improved without the need for additional primary energy, with the aim of significantly increasing the overall substitute fuel rate. Depending on the framework conditions, even previously unusable fuel streams can be processed and used in the cement process. The successful implementation of suitable drying systems in an existing plant is required in the existing processes. In addition to the dimensioning of the system, the available waste heat potential and restrictions are also evaluated and the exact system setup, including material feed and removal, is defined. Stelas’ engineering team of more than 50 experts and its competence in industrial manufacturing of customised modular drying systems based on more than 200 motivated and experienced workers, are proof for these kinds of applications.
Case study: Latvia
A project implemented by Schwenk Latvia, Broceni, is an example of a successful application of a drying system. This project made it possible to reduce material moisture to an optimum level by using waste heat. In addition to the technology from stela, the project was aided by the comprehensive consulting services of Mr. Schwörer to ensure a comprehensive analysis of the existing processes, the identification of optimisation potential and support in the implementation of the drying systems, guaranteeing maximum efficiency and sustainability.
References 1.
‘Zementindustrie im Überblick 2023/2024’, Verein Deutscher Zementwerke e.V., Hrsg., Stand Oktober 2023. Berlin, 2023, p. 19.
About the author
M.Sc./Dipl.-Ing.(Fh) Yves Marc Schade is an alumni of University of Applied Sciences Rosenheim (2000) & Technical University Munich (2005), graduating with a Master’s of Science Sustainable Resource Management. He has 20 years of experience in industrial drying systems specialised in biomass and renewable energy, and has worked for 15 years at stela Laxhuber Drying Technology, working with industrial applications of low-temperature drying systems.
Source: World Cement Reprinted from September 2024
