Rajpal Singh Shekhawat, Senior General Manager (Production and QC),JK Lakshmi Cement, stresses on the importance of the quality of alternative raw materials in order to maintain the quality of the output.
What are the core raw materials used in the production of cement?
The first step to manufacturing cement is manufacturing the clinker. The principle raw material required to make clinker is cement grade limestone. Other raw material requirements depend upon the quality of limestone and these could be iron ores like red ochre, blue dust, laterite, alumina ores like bauxite, China clay and siliceous materials like Marl and silica sand. As far as cement is concerned for Ordinary Portland Cement (OPC), clinker and
gypsum are used, for Pozzolana Portland Cement (PPC) clinker, gypsum and fly ash are used and for Portland Slag Cement (PSC) clinker, gypsum and slag are used.
What are the alternative raw materials that can be used in the production of cement? How does that impact the process of production?
Waste from the aluminium industry like red mud, waste from the marble industry like marble slurry and marble khanda, waste from the chemical industry like chemical sludge and ETP sludge, waste from the paper industry like paper sludge can be used in clinker manufacturing. For the cement manufacturing process, waste from chemical industry like chemical gypsum, waste from ceramic industry like mould gypsum, waste from zinc industry like jarosite and waste from the salt industry like marine gypsum can be used.
However, the quantity of alternative material or waste to be utilised depends a lot upon the quality of limestone and quality of other raw materials used in cement grinding. It varies from plant to plant and the quality of these alternative materials varies from source to source.
Can cement maintain its quality standard with inclusion of supplementary raw materials as against limestone?
Certainly, the quality of cement can be maintained by including these supplementary raw materials, however, the raw material proportion must be tweaked according to the quality of alternative raw material and the cost benefit analysis.
Explain the impact on carbon emission of the production unit when alternative raw materials are used in various proportions.
Carbon emission in cement manufacturing is mainly because of limestone, fuel burning, and electrical energy consumption. Majority of the CO2 emission in cement industry is from the decomposition of calcium carbonate and if we replace limestone by alternative raw material which contains calcium in any form other than carbonate, carbon emission can be reduced. For example, if we replace 1 per cent of CaO by other raw materials then around 5 kg CO2/ MT of clinker will be reduced.
How can the cost of production be reduced by using alternative or supplementary raw materials in cement production?
Cost of production depends on the plant location, limestone and raw material quality. The source of alternative raw materials for some plants are significant and in some instances because of high logistic cost economics do not work out. For example, if a cement plant is located near the industry where chemical gypsum is generated, there will be a significant gain to that particular cement plant.
What are the major challenges in using other cementitious materials?
Using alternative materials comes with their own set of challenges. Some of the challenges associated with them are high moisture content, material flowability, consistency in the material quality, chloride and sulphur content.
What role does technology play in deciding which materials can be used and incorporating them in the production process?
Certainly, technology plays a vital role in utilising alternative material, for example if drying technology is available at the plant like drier than even high moisture material can be used and handled otherwise only selected material with less moisture content are allowed.
Likewise in case of alternative fuel, if pre-processing facilities like separation of organic and combustion solid fraction, screening and pre-shredding is available then MSW can be directly used. However, when the pre-processing and shredding facility is not available at the plant then the plant requires shredded RDF <80 mm in case of in-line calciner and <40-50 mm in case of separate line calciner. Regarding utilisation of high chloride and high sulphur material if akali/chloride by-pass is installed then even high chloride/sulphur can be accepted based on the cost benefit analysis otherwise chloride input is to be restricted to 200-300gm/tonne of clinker.
Does your organisation manufacture a variant of cement made from alternative raw materials? Tell us more about its performance and use.
Yes, we are utilising various alternative raw materials like chemical gypsum, mould gypsum, ETP and phosphate sludges. Talking about chemical gypsum, its purity is more than natural gypsum. The performance of concrete made by the cement by utilising partial replacement of chemical gypsum is more cohesive than the cement made from natural gypsum. Moreover, the cement made by utilising chemical gypsum improves the workability of cement. Likewise, we utilise various alternative fuels at our premises and their consumption is being optimised looking into process and quality.
By utilising various alternative raw materials and fuels we are saving around 25 kg CO2/Mt of clinker and working on alternative materials and fuels that can reduce carbon footprints further.
How do you foresee future of production?
The per capita capital cement consumption in India is still much lower than the world average. Therefore, there is a huge potential for the industry to grow. There has been a continuous rise in the cost of fuel post covid and post the Russia-Ukraine engagement and still rising.
Owing to this, there is pressure on the industry to maintain the margins. Although, Indian cement industry is co-processing various alternative fuels and alternative raw materials to reduce its carbon footprint, it will in the future also put its focus on utilising alternative materials and fuels to bring down the cost of production.
-Kanika Mathur