Sustainable Clinker and Cement Production by Using Alternative Fuels and Raw Materials Our expertise

The use of alternative fuels in both combustion and production processes is known as co-processing in cement manufacturing. Waste is now being used to substitute primary fuel sources like coal, petroleum, and gas in the combustion process. They are usually from combustible municipal waste, refuse-derived fuels, biomass, or non-hazardous industrial and commercial waste.

The sourcing of suitable waste as a feedstock, pre-treatment, and technical evaluation are essential preconditions for co-processing. Primary calcium, silica, alumina, iron, and sulfates obtained from the quarry can be replaced by mineral compounds like fly ash, slag, and flue-gas desulfurization gypsum.

Other emerging sources that contain the main elements needed for OPC-clinker mineralization include:

• Rejects from paper recycling contain lime and clay
• Fuller’s earth from edible-oil production and foundry sand supply silica
• Mill scale contains usable iron
• Filter-press cakes precipitated using lime

Waste that contains carbon and/or hydrocarbons can also be used to replace fossil fuels. But precautions must be taken as these materials may be contaminated and require analysis to determine their positive and negative effects on the environment, process, and the end-product. After pre-treatment and quality assurance, shipment, and handling, these can be used as alternative raw materials or alternative fuels in the clinker-burning process.

The quality of cement is mainly indicated through the requirements for mechanical, physical, and chemical properties. These requirements must be met regardless of the type of fuel used or the nature of the raw materials.

The use of waste does not affect these major properties because any potential effects will have been accounted for by making compensatory adjustments to the chemical composition of the raw material fed to the kiln.

For manufacturers, the potential for waste products used depends on the raw materials readily available nearby the cement production plant. High concentrations of silica, alumina, magnesium, or sulfur can affect the large-scale use of alternative decarbonated raw materials. The presence of volatile organic compounds, trace elements content, and variable compositions may also cause further restrictions.

When considering alternative fuels and raw materials, the following variables must be considered:

• Alkali, sulfur, and chloride content: excessive inputs of these compounds may lead to buildup and blockages in the kiln system
• Ash content: the chemical composition of the ash needs to be monitored to ensure that the final composition of the raw mix meets the requirements for clinker production
• Heating (calorific) value: the key parameter for the energy provided to the process
• Water content: moisture content may affect productivity, efficiency, and increase energy consumption
• Organic content: organic constituents are associated with CO2 emissions
• Chloride content: chlorides may combine with alkalis to form fine and difficult to control particulate matter
• Metal content: the non-volatile behavior of most heavy metals allows most of them to pass straight through the kiln system and be incorporated into the clinker. Thallium, mercury, cadmium, lead, selenium, and their compounds are highly volatile
• High sulfur content in raw materials, fuel, and waste may result in the release of sulfur dioxide

All candidate alternative fuels and alternative raw materials should be identified by source before acceptance. This is where elemental and mineralogical analyses of the intermediate, final product, and fuels become even more important.

To achieve this, you need reliable and rugged solutions for steering the process most cost-effectively in manufacturing the highest quality of cement or concrete. The use of X-ray fluorescence, diffraction instruments, and online analyzers will help meet these demands and seamlessly integrate them into the production process.

Among the benefits of these tools:

• Control of mill operation through analysis of composition and fineness of raw mill feed
• Check of mill operation through quality control of raw meal
• Check of composition and material balances (e.g. K, Na, S, Cl) through filter/ESP dust analysis
• Identify causes for coating formation
• Kiln feed analysis through consistency check between raw mill product, kiln feed and clinker analyses, material balances (e.g. K, Na, S, Cl), silo blending efficiency, burnability, and heat consumption
• Analysis of cyclone/hot meal samples to check dust separation efficiencies and degree of calcination, material balances silo blending efficiency, and fuel burn–out
• Check of coal mill operation, fuel consumption, ash absorption in clinker, material balances, burn–out in calciner, and NOx formation
• Check fuel consumption, sulfur absorption in clinker, material balances, and NOx formation
• Clinker analysis to check kiln operation and clinker quality and material balances
• Analysis of finished cement to check mill operation, gypsum and SCM additions as well as the quality of the finished cement (example EN 197, ASTM C150, ASTM C595, and ASTM C1157)