Having crossed several milestones in energy efficiency and sustainability, Indian cement industry is set to achieve the pinnacle.
Increasing competitive pressures, rising energy prices, coupled with stricter regulations for environmental protection are making energy efficiency and sustainable use of resources a top priority for the manufacturers in the recent years, and the cement industry is no exception.
Indian cement industry has already crossed several milestones on energy efficiency ans sustainability parameters. It has emerged as one of the most energy-efficient industry globally with the lowest carbon footprint in the world and it is among few large scale modern industries that do not produce any hazardous solid or liquid discharge, according to Cement Manufacturers’ Association (CMA).
But the icing on the cake has come from the Cement Sustainability Initiative (CSI) an initiative of the World Business Council for Sustainable Development (WBCSD). In 2015 itself CSI had said, “The member companies from India are more efficient.
They emit less CO2 than the companies in Europe and the US. Their energy consumption is also less.” The distinction between Indian firms from those in the US and Europe is technology. Indian companies use the latest technology since many of the cement plants are relatively new, CSI had said. CSI was then a 23-member organisation including nine Indian cement companies, including UltraTech Cement and Dalmia Bharat, and seven global companies with operations in India.
Since then the industry is taking a number of measures aimed at further improving its performance on parameters like specific heat consumption, setting up of waste recovery systems and use of alternate fuels. In fact, all these measures help the companies attain the GreenCo rating, where the core focus is on energy efficiency. For example, the industry has increased the Thermal Substitution Rate (TSR) through use of alternative fuels and raw materials to 4 per cent in 2017, from a meagre 0.6 per cent in 2014.
The cement production process is quite energy intensive, both in terms of electrical and thermal energy consumption (E&TEC). There are plants in India that have achieved energy efficiency figures which are considerable to the world’s best. However, the presence of old plants with high specific energy consumption (SEC) brings down the average figures. Cement production involves the heating, calcining and sintering of blended and ground materials to form clicker. As a result, cement manufacturing is the third largest cause of man-made CO2 emissions due to the production of lime, the key ingredient in cement. Therefore, energy savings during cement production could lead to lower environmental impact.
Improvement in the cement industry’s energy efficiency and reduction of CO2 emissions could be mainly achieved through two procedures:
(i) By changes in the manufacturing and production processes, and
(ii) By adjusting the chemical composition of cement.
Improvement in manufacturing and production processes can be achieved by changing energy management processes and by investing in new equipment and/or upgrades. The same way, changes in the chemical formulation of cement have proved to save energy and reduce CO2 emissions. The same holds good for cement industry, which is a highly capital intensive and competitive sector with long economic lifetimes, making changes in the existing capital stock difficult.
“The average electrical energy consumption in India is around 90-95 kWh/tonne cement (OPC) whereas the best achievement is around 80 kWh/tonne cement (OPC). Similarly, average TEC is around 760 kcal/kg clinker, whereas the best figures achieved are around 680 kcal/ kg clinker. There is scope for reduction in both E&TEC in many of the cement plants in India,” says PK Ghosh, Group Managing Director, Ercom Engineers.
The best achievable figures are generally observed for the larger scale plants in India using the state of the art technology when operating at or higher than design levels, Ghosh added.
The contribution of the various departments to power and heat consumption is given in the Table-1.
Perform, Achieve & Trade (PAT) scheme of the Bureau of Energy Efficiency (BEE), a market-based mechanism focused on reducing specific energy consumption - energy used per unit of production - in large industries, has managed to save a whopping Rs 47,185 crore in three years between 2012 and 2015 in the form of energy savings achieved on the back of robust implementation of energy efficiency measures. The scheme facilitates these large, energy-intensive industries to achieve their legal obligation under the Energy Conservation Act of 2001, while also motivating them with market-based incentives to reduce their energy use and surpass their individual energy saving targets.
A Government of India initiative, PAT’s first cycle covered 478 designated industries from 8 energy-intensive sectors - Aluminium, Cement, Chlor-alkali, Fertilizer, Iron and Steel, Pulp and Paper, Textiles and Thermal power plant. Together, these sectors account for around one-third of India’s primary energy consumption.
“The scheme resulted in saving of energy equivalent to 8.67 million tonnes of oil, exceeding the target of 6.86 million tonnes by about 30 per cent. This also resulted in avoided generation of about 5,635 MW of power, resulting in monetary savings of
Rs 37,685 crore. At the same time Rs 9,500 crore has been saved due to reduction in energy consumption,” according to BEE.
The third PAT cycle was also notified from April 1, 2017 for 3 years including 116 new units with a reduction target of 1.06 MTOE.
The energy efficiency achieved is the result of optimisation between capital expenditure and reducing operating expenses.
Adoption of alternative fuels as a means of increasing cost competitiveness is gaining ground. But the industry has a long way to go before achieving 25% TSR. The Thermal Substitution Rate (TSR) in India has shown a very positive trend year on year, reaching a level of around 4 per cent in 2017. As indicated in the CII approach paper, India plans to achieve 25 per cent TSR by 2025. “In comparison to global standards, we are far behind as in many countries the substitution is in the range of 60-100 per cent,” says Milind Murumkar, Advisor AFR, Vicat India.
Another way to reduce energy and process emissions in cement production is to blend cements with increased proportions of alternative (non-clinker) feed stocks, such as volcanic ash, granulated blast furnace slag from iron production, or fly ash from coal-fired power generation. Indian cement plants consume a quarter of the fly ash produced in the country annually, according to CMA. For the long run, cement industry lacks a viable carbon-free alternative, and the IEA suggested scenarios imply a heavy reliance on Carbon Capture and Storage (CCS) cement kilns with xy-fuelling. Waste heat recovery systems are expected to play a much bigger role as more of it gets tapped. “In case of specific heat consumption, approximately 20 per cent losses are through preheater exhaust gases, 12 per cent are through cooler exhaust gases and around 4-5 per cent are radiation losses (for 6 stage preheater - precalciner system with the state-of-the-art cooler), says Ghosh.
The cement grinding department and the raw material grinding are the major consumers of electrical energy. The material transport systems have also to be looked in to ensure that the power consumption is lowered.
Ghosh of Ercom says, “The implementation of MIS (management Information systems) like SAP helps in keeping track of key performance indicators. Management is able to monitor both plant operations and the productivity in a continuous manner for achieving energy efficiency targets.”
When comparing the state of the art technologies in terms of sustainability, suitability, performance, robustness, cost-efficiency, patent restrictions (availability), and competence requirements, it can be expected that at least in the short term cement companies are going to be based on pyro processing and grinding mills.
Having tasted the fruits of energy efficiency measures over the recent years, and development of a host of case studies highlighting several achievements and sustainable development, the Indian cement industry is set to reach the pinnacle in energy efficiency in the world.
Underutilisation and Energy Efficiency
Consider a Cement manufacturing unit which is designed for clinkerisation capacity of 5000 tpd (tonnes per day) and correspondingly OPC of 5250 tpd for the sake of this discussion.
The specific heat consumption of this precalciner kiln will lie in range of 695-700 kcal/ kg clinker at the design capacity. The operating temperatures for calcination (900-950oC) and clinkerisation (1350-1400oC) will be the same irrespective of the operating level. The gas and material temperatures in the preheater stages will also to be maintained at similar levels. As a result, the total heat loss due to radiation will remain the same at all production levels. This will cause a higher specific heat consumption for lower than design operating levels as depicted in Figure 1.
The specific electrical energy consumption is around 90 kWh/t of Cement (OPC). The electrical drives, the fans and the HT motors are also designed to have maximum efficiency at their design operating levels. As a result, they will have suboptimum energy consumptions at lower than design production levels. This is depicted in Figure 2.
One of the ways to take care of underutilisation is by operating at design capacities and keeping the plant idle for extended periods of time. This may be feasible for those plants with multiple Pyro processing lines. At 80% annual production, the plant can be shut down for a total of 2 more months, and at 70% there are 3 extra months of shut down. However, the clinker storage section will be a constraint for this mode of operation.
Increased number of kiln shutdowns leads to wastage of heat during kiln cool down and start-up. The refractory life also reduced even though these shutdowns are planned. There are maintenance issues if the equipment has extended idle times.
Hence most plants settle for a production level which helps them meet the demands of the market while continuing to keep the kiln under operation for extended levels of time. However, it is important to note that there is a minimum turndown level, below which gas velocities in cyclones will reduce to a value which will not support the efficient heat transfer in the preheater and affect the gas-solid reaction in the calciner.
- P. K. Ghosh, Group Managing Director,
- BS Srinivasalu Reddy