A new clay calcination project by FLSmidth in Ghana marks a key milestone in the green transition of cement production.
FLSmidth will deliver equipment to replace cement clinker with environmentally friendly clay, cutting up to 20 per cent of CO2 emissions compared to current practices on site. The order includes the world’s largest gas suspension calciner system and acomplete grinding station adding another 120 per cent grinding capacity. Using calcined clay to minimise the need for traditional, carbon-intensive clinker is a key technology in eliminating the environmental footprint from cement production. “Calcined clay cements are the most sustainable alternative to traditional clinker-based cement. With the support from FLSmidth, we will be able to operate clay calcination in a large scale,” said Frédéric Albrecht, CEO, CBI Ghana Ltd.
Supplementary cementitious materials are changing the way and the speed at which cement manufacturing is moving on the spectrum of environment sustainability. With large stakes on the line for achieving net zero targets, how is the Indian cement industry rising up to the challenge, finds out ICR.
Across the globe, cement is one of the most consumed and important materials for building all infrastructure. From homes, to factories, roadways or tunnels, everything would require cement in one form or the other. India especially is moving towards becoming infrastructurally strong with new projects in the works across the sub-continent. All infrastructural projects demand the consumption of concrete and cement, which has led to the rise of concrete requirement, thus, increasing the production of cement.
India is the second largest producer of cement. Limestone is at the core of its production as it is the prime raw material used for production. The process of making cement involves extraction of this limestone from its quarries, crushing and processing it at the cement plant under extreme temperatures for calcination to form what is called a clinker (a mixture of raw materials like limestone, silica, iron ore, fly ash etc.). This clinker is then cooled down and is ground to a fine powder and mixed with gypsum or other additives to make the final product, cement.
Limestone is a sedimentary rock composed typically of calcium carbonate (calcite) or the double carbonate of calcium and magnesium (dolomite). It is commonly composed of tiny fossils, shell fragments and other fossilised debris. This sediment is usually available in grey, but it may also be white, yellow or brown. It is a soft rock and is easily scratched. It will effervesce readily in any common acid. This naturally occurring deposit, when used in large volumes for the cement making process is also depleting from the environment. Its extraction is the cause of dust pollution as well as some erosion in the nearby areas.
The process of calcination while manufacturing cement is the major contributor to carbon emission in the environment. This gives rise to the need of using alternative raw materials to the cement making process. The industry is advancing in its production swiftly to meet the needs of development happening across the nation.
Aligning Sustainability Goals
In one of its recent bulletins, owing to India’s announcement at the Glasgow Climate summit to reach net-zero by 2070, the RBI noted that with India aiming to reach half of its energy requirements from renewables and reduce the economy’s carbon intensity by 45 per cent by 2030, it ‘necessitates a policy relook across sectors, especially where carbon emission is high’ and ‘cement industry is one of them.’ However, it said, recent developments in green technologies, particularly related to reverse calcination, offer ‘exciting opportunities’ for the cement sector.
The RBI report noted that India’s cement production is expected to reach 381 million tonnes by 2021-22 while the consumption is likely to be around 379 million tonnes, in the light of the country’s renewed focus on big infrastructure projects like the National Infrastructure Pipeline, low-cost housing (Pradhan Mantri Awas Yojana), and the government’s push for the Smart Cities mission is likely to drive demand for the cement in future. On similar lines, according to the Eco-Business news portal report of April 2022, the India Energy Outlook 2021, which notes that most of the buildings that will exist in India in 2040 are yet to be built. Their projection suggests that urbanisation in the near future will demand an increase in infrastructure, which will ultimately lead to increase in the cement consumption.
With these forecasts in mind, RBI has recommended that there is a need to align India’s economic goal with its climate commitments by implementing emerging green tech solutions. It has also recommended an increase in finance towards green sustainable solutions through subsidised interest loans, proactive engagement with the leading research institutes and countries involved with green tech-related innovation in the cement industry.
“When clinker is blended with other supplementary cementitious materials like fly ash, slag or both, products are called Portland Pozzolana Cement (PPC), Portland Slag Cement (PSC) and composite cement (CC) respectively. Blended cement products have a much lower carbon footprint than OPC. Since clinker manufacturing is the phase where most thermal energy is consumed and CO2 is emitted, reducing clinker factor in cement not only results in lowering the process CO2 but also the thermal energy and electrical energy requirements,’’ says Manoj Kumar Rustagi, Chief Sustainability and Innovation Office (CSIO), JSW Cement.
Alternative Raw Materials
Alternative cementitious materials are finely divided materials that replace or supplement the use of portland cement. Their use reduces the cost and/or improves one or more technical properties of concrete. These materials include fly ash, ground granulated blast furnace slag, condensed silica fume, limestone dust, cement kiln dust, and natural or manufactured pozzolans.
“Each material has its own composition and behaves differently during the burning process. In order to maintain the consistent clinker quality and stable clinkerisation process, we need to analyse these materials with respect to quality (during raw mix design) and also impact on the environment (if any harmful gases are released). There are certain materials which come in both ARM and cement additives like Ashes from coal fired thermal plants and slag from steel plants that have to be looked at from various angles,” says Gulshan Bajaj, Vice President (Technical), HeidelbergCement India.
The use of these cementitious materials in blended cements offers advantages such as increased cement plant capacity, reduced fuel consumption, lower greenhouse gas emissions, control of alkali-silica reactivity, or improved durability. These advantages vary with the type of alternative cementitious material.
Cement manufacturers are moving towards incorporating these supplementary cementitious materials in their raw material:
Fly Ash: Containing a substantial amount of silicone dioxide and calcium oxide, fly ash is a fine, light, glassy residue generated during ground or powdered coal combustion.
Ground Granulated Blast-furnace Slag (GGBS): It is a by-product of the iron and steel industry. In the blast furnace, slag floats to the top of the iron and is removed. GGBS is produced through quenching the molten slag in water and then grinding it into a fine powder. Chemically it is similar to, but less reactive than, Portland cement.
Silica Fume: It is a by-product from the manufacture of silicon. It is an extremely fine powder (as fine as smoke) and therefore it is used in concrete production in either a densified or slurry form.
Slag: It is a by-product of the production of iron and steel in blast furnaces. The benefits of the partial substitution of slag for cement are improved durability, reduction of life-cycle costs, lower maintenance costs, and greater concrete sustainability. The molten slag is cooled in water and then ground into a fine powder.
Limestone Fines: These can be added in a proportion of 6 to 10 per cent as a constituent to produce cement. The advantages of using these fines are reduced energy consumption and reduced CO2 emissions.
Gypsum: A useful binding material, commonly known as the Plaster of Paris (POP), it requires a temperature of about 150OC to convert itself into a binding material. Retarded plaster of Paris can be used on its own or mixed with up to three parts of clean, sharp sand. Hydrated lime can be added to increase its strength and water resistance.
Cement Kiln Dust: Kilns are the location where clinkerisation takes place. It leaves behind dust that contains raw feed, partially calcined feed and clinker dust, free lime, alkali sulphate salts, and other volatile compounds. After the alkalis are removed, the cement kiln dust can be blended with clinker to produce acceptable cement.
Pozzolanas: These materials are not necessarily cementitious. However, they can combine chemically with lime in the presence of water to form a strong cementing material. They can include – volcanic ash, power station fly ash, burnt clays, ash from burnt plant materials or siliceous earth materials.
Dr Sujit Ghosh, Executive Director – New Product and R&D, Dalmia Cement (Bharat), says, “Blended cements made using supplementary raw materials, have ‘additional’ activated silica (SiO2) and/or activated lime (CaO), which when co-processed with cement clinker, provide ‘additional’ cementitious gel paste (complex calcium-silica-oxide-hydrates) when mixed with water, that renders improved strength and durability to the cement-concrete structure.”
He adds, “With specialised processing and with the use of performance enhancers, blended cements using supplementary raw materials, provide acceptable rate of strength gains, comparable to pure-clinker cement and top-class long-term durability, with lower carbon footprints and at the same time effectively finding value-solution to other industry wastes!”
Besides having the advantage of lower emissions and better environmental conditions, use of supplementary cementitious materials also has a cost benefit. “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,” says Rajpal Singh Shekhawat Senior General Manager (Production and QC), JK Lakshmi Cement.
Researchers at the Indian Institute of Technology, Madras, are finding ways to use bacteria to develop bio-friendly cement and reduce carbon dioxide emission, as per a report in The Hindu earlier this year.
Professor GK Suraishkumar and assistant professor Nirav Bhatt in the Department of Biotechnology and Subasree Sridhar, a research scholar, are conducting the research. They have developed a mathematical model to produce an alternative to current cementation process. They have suggested the use of bacteria like S Pasteurii, which will microbially-induced calcite precipitation.
This bio cement will require temperatures in the range of 30 to 40 degrees as opposed to the traditional process that would require over 900 degrees for the calcination process. The emitted carbon dioxide will be negligible in this case and industrial waste like lactose mother liquor and corn steep liquor can be used as the raw materials for the bacteria, thus making the manufacturing of this cement more economical.
One of the most important ways of reducing carbon emission in cement manufacturing is the use of alternative raw materials from various other industries. This gives way to a circular economy, utilising waste from other industries and bettering the environment with reduced emission of harmful gases, especially carbon dioxide. It also helps the avoidance of landfills or ocean pollution, as waste of industries is utilised in manufacturing cement. Overall, new compositions of cement are the future.
EU states agree on a carbon border adjustment system for cement
The European Union’s ‘Fit for 55’ package includes a carbon border adjustment system for cement, which is one of the major aspects.
This environmental measure’s main goal is to prevent carbon leakage. It would also urge partner countries to implement carbon pricing measures in order to combat global warming. CBAM does so by focusing on carbon-intensive product imports in full compliance with international trade rules, in order to avoid offsetting the EU’s greenhouse gas emission reduction efforts with imports of products made in non-EU countries with less ambitious
climate change policies than the European Union.
Harnessing Heat Energy
Renewable energy resources and waste heat recovery are measures that are paramount for cement players to minimise the impact of cement manufacturing on the environment. We explore waste heat recovery systems and its processes that cement makers are utilising in a bid to reduce their carbon footprint.
Concerns about global warming, rising fuel and material costs are challenging industries to reduce their greenhouse gases emission and to improve efficiency on their sites. Waste Heat Recovery (WHR), as an alternative source of energy, plays an important role in this regard for industry processes that are targeting the reduction of fuel consumption and harmful emissions.
By definition, ‘Waste Heat Recovery’ is the process of ‘heat integration’, that is, reusing heat energy that would otherwise be disposed of or simply released into the atmosphere. Industrial waste heat is the energy generated out of a chemical process that otherwise is lost or dumped in the environment. By recovering waste heat, plants can reduce energy costs and CO2 emissions, while simultaneously increasing energy efficiency.
Sources of waste heat can be heat loss during transfers, conduction, convection or combustion processes. This lost heat can be classified as high temperature, medium temperature and low temperature grades. High temperature waste heat goes greater than 400 degree Celsius medium temperature waste heat ranges from 100 degree to 400 degree Celsius while low waste heat is for temperatures below 100 degree Celsius. A different kind of waste heat recovery system is applicable for each grade of waste heat.
The method of waste heat recovery includes transferring the waste heat from a process with a gas or liquid to derive an extra source of energy. Conventionally, higher the temperature of the heat wasted or recovered, the better quality of an energy source it is. The waste heat power plants installed in cement plants use heat generated from the rotary kilns preheaters and exhaust gases for the generation of power.
According to a study conducted by Kawasaki Heavy Industries in Japan, the waste heat recovery system in cement industries can cover approximately 30 per cent of the total electric consumption of the plant. The Japanese have spearheaded the introduction of waste heat recovery plants in their cement industry since as early as the 1980s and are the leaders in this technology instalment.
Cementing the impact
Cement manufacturing is an energy intensive process. It requires a large amount of energy to function which is primarily derived from coal. That however, is a non-renewable source of energy as well as a large contributor towards carbon emission. Energy consumption also contributes to approximately 40 per cent of the cement manufacturing costs. The industry as a whole is fighting these challenges and that is where the waste heat recovery plants come as a saviour.
According to Sanjay Kumar Khandelwal, Head – Power Plants, JK Cement Ltd., “WHRS utilises hot gases emitted both from preheater as well as clinker cooler to generate power without the usage of any additional fuel. In other words, we are able to generate power without utilising any fossil fuels; which not only reduces overall carbon footprints but also restricts hot gases from entering into the atmosphere.”
“This system results in reducing the overall cost of production by reducing Overall Power Consumption cost followed by a reduction in cost through optimum power mix (maximum usage of WHRS and renewable power sources and least usage of grid and CPP power) through effective power management,” he adds.
Processing heat energy
Globally in cement plants there are three processes for functionality of Waste Heat Recovery plants, namely, Steam Rankine Cycle System (SRC), Organic Rankine Cycle System (ORC) and Kalina-based system. The mostly widely used system in India is the SRC.
“There is a vast potential for power generation from waste heat across the world. The installation of cement WHR based power plants in China is over 80 per cent, much ahead of India. Similarly, Europe, the USA, and Latin America plan to implement WHR in their cement plants. It is observed that waste heat recovery-based power plants are emerging as an excellent value addition to the existing captive power plants. Other than reducing energy costs significantly, it can also be a reliable source of power,” says Arun Mote, Executive Director, Triveni Turbine Limited.
The most common raw material used for cement manufacturing is limestone. Depending on the type of cement that needs to be produced, other raw materials like fly ash, clay etc., are added to limestone and are then ground in a fired rotary furnace to form the clinker. Once the clinker production process is complete, it is transferred to coolers and the exhaust gases and hot air are left outside of it. According to a study published in the International Journal of Engineering Research and Technology (IJERT), these exhaust gases from the preheater are on average at 361 degree Celsius and the temperature of the air discharged from the cooler stack is 268 degree Celsius. They are then passed to the waste heat recovery boiler. Water is circulated through the waste heat recovery boiler. Latent heat from the hot gas is transferred to the water and it is converted to steam. This steam is then expanded in the turbine and is condensed. The condensed water is passed through the WHRG and the process repeats. The electricity generated in this process, offsets a portion of the purchased electricity, thereby reducing the electrical energy demand in cement plants.
With the results obtained from these processes, the efficiency of the waste heat achieved is 22.7 per cent of the total power generation which results in a large amount of costs being saved in the long run for cement plants.
Other renewable sources
India ranks third, behind the US and China, among 40 countries with renewable energy focus, on the back of strong focus by the government on promoting renewable energy and implementation of projects in a time bound manner.
The annual energy consumption by the cement industry contributes close to 10 per cent of the total energy consumed in the entire industrial sector. According to the Cement Manufacturers’ Association, modern cement plants consume 68-93 units to produce a ton of cement while the older ones use up 110-120 units of electrical energy.
Most cement plants in India are located in hot and dry areas and are subjected to high heat and solar radiations. This presents an opportunity of utilising solar power as an energy source for the cement manufacturing process. Solar plants have a lifetime of 25 years and that is a one-time cost for cement plants to expense. By installing these panels, they can not only substitute energy cost, but can also lower their carbon footprint. Major players in the market such as Dalmia Cement, Birla Cement, UltraTech Cement are using solar energy to meet their sustainability goals.
Researchers Aristeides Tsiligiannis and Christos Tsiliyannis in their study for Anion Environmental Ltd. have found solid biofuel, derived from household food waste (food residue biofuel, FRB) as a potential bioenergy source in cement manufacturing. Some of the key issues in cement plant operations issues have been quantitatively assessed by them where the findings have resulted in showing that food residue biofuel can substitute 20 per cent of the thermal energy requirement of a cement plant. This finding can greatly impact waste food disposal as well as make a positive impact on the environment where carbon footprint is concerned for cement plants.
To secure and safeguard the environment and to bring out the cement production costs, it has become imperative for cement manufacturing plants to make an investment in the renewable energy sources and systems that allow the cement plants to harness that energy, which is readily available and does not emit carbon dioxide. Reducing their carbon footprint is a challenge every cement organisation has taken up. This can be a major step in achieving the same and fulfilling the sustainability goals determined by the policy makers of the country.
– Kanika Mathur