The efforts of Indian cement industry moving towards greater sustainability are getting strengthened by the use of increasing clinker substitution, use of alternative fuels and installation of WHR systems.
Energy efficient cement plants in the country are comparable to the best cement plants in the world. In India, these modern plants co-exist with older plants with lower capacities and obsolete technologies, and the poor performance of some of the plants brings down the average. The average electrical energy consumption in India is around 97 kWh/tonne of cement (OPC) whereas the best achievement is around 77 kWh/tonne of cement (OPC). Similarly, average thermal energy consumption is around 770 kcal/kg of clinker, whereas the best figures are around 680 kcal/kg of clinker.
Even in this era of consolidation and acquisitions, the major challenge that dents the healthy growth of the cement industry is the sheer lack of demand; the realty and housing sector which consumes over 67 per cent of the total production is still not out of woods, nor there is a demand pull from the infra sector, as has been expected. The average capacity utilisation is around 70-72 per cent of the total installed capacity. This adversely impacts the energy efficiency drive by the cement manufacturers as running the plants at 70-80 per cent of installed capacity will drive out any of the benefits perceived in installing good equipment or carrying out energy management drives.
Sustained energy efficiency is possible only when plants run continuously with hundred per cent runtime and greater than hundred per cent production factor. Says Jagdish Chandra Toshniwal, Executive Director, Wonder Cement, ´It is absolutely right that the plant runs efficiently when it is operating at its full capacity. Continuous running of a plant is extremely important for energy efficiency as well as for lower maintenance cost. The inefficiency creeps in when it runs below certain optimum level and every plant knows, what its optimum level is. To have lowest cost of operation it is ideal to run the plant between 90 to 105 per cent capacity. Beyond 105 per cent capacity utilisation, the plant starts consuming more power and fuel. Where as anything lower than 90 per cent, your operational cost increases. When we are constrained to operate below 90 per cent, may be because of market conditions, we have to compromise on energy efficiency parameters. Also it is important to note that the maintenance cost is the lowest when we run the plant; under slightly stretched condition, say 105 per cent capacity.´
Says Dr. Suchismita Bhattacharya, Head - Process, Penta India Cement & Minerals, ´State of the art dry process cement plants are designed for specific energy consumption of around 697 kcal/kg clinker and around 90 kWh/tonne of OPC within the boundry of the cement factory from raw material storage to cement despatch. Having said that, achieving such levels in regular operation depends on various factors such as run time and capacity utilisation. Hence it is important to maintain at least 95 per cent of design production levels to take advantages of the new technologies. In some cases, use of variable frequency drives in certain equipment such as process fans may allow one to operate efficiently even at lower capacity levels. In the last few years, as the plants have been running at 60-70 per cent of installed capacity, higher operating costs per unit of production have been observed.´
Says Prashant K Tripathy, Executive Director - Productions & Processes, Dalmia Cement Bharat Ltd, ´Frequent stoppages and restart causes loss of power and fuel, both. Currently the cement demand is sluggish and the industry is awaiting a pickup in cement consumption to operate the plants efficiently at full capacity.´
Another major challenge from the energy efficiency front is the low thermal substitution rate by use of alternative fuels and raw materials (AFR). Even though the Indian cement industry has made a significant improvement in energy efficiency through various measures, use of AFR, a major potential area for improvement, is still in its nascent stage; the present thermal substitution rate by use of AFR being in the range of 0.5 to 1 per cent whereas developed countries achieved as high as 40 per cent TSR.
Says KN Rao, Director, Environment and Energy Conservation, ACC Ltd, ´ACC has been using successfully close to half a million tonnes of alternative fuels and raw materials annually and hope to increase substantially this quantity in the coming years as necessary infrastructure has been created in most of the plants. This initiative is helping the entire country for safe and sustainable disposal of the hazardous waste and non hazardous waste of various industries and municipal solid waste and helping the country to achieve energy security and minimising the GHG footprint of the country.´
Dr. Suchismita adds, ´Alternate fuels and refused derived fuels have considerable scope in India. It is possible to reduce the gate to gate energy consumption of renewable fuels by substituting with such fuels. In India some of the plant owners have achieved 10-15 per cent substitution. However a certain amount of capital investment in fuel handling facilities within the cement plant, fuel firing technology,selection of burner, calciner design, refractory selection and laboratory automation may be warranted. Dealing with the varying nature of the fuel will require expert adjustments in fuel mix. Another hurdle in India is that waste derived fuel is not available from Municipalities in an organised manner. However as Europe has shown the way, over 80 per cent substitution is possible all the variables can be dealt with as long as the management shows the will to use alternate fuel.´
Says Toshniwal, ´In fact the time is ripe to start initiating action in that direction. The leading companies like ACC and Ambuja are the torch bearers. We shall follow them. On the role of regulators, it is changing very fast but there seems to be some confusion. For getting approval we have to go through several layers. The agencies involved are CPCB and State Pollution Board. Sometimes they are not clear as to who will approve what? The procedures have been simplified because even the state officials are realising that waste disposal is a great problem today. There is a positive side, as the mind set of government officials, pollution control board is changing.´ Avers Tripathy, ´Assured long term availability of AFR to justify infrastructure related capex is the main challenge. Requirements of environment permits for each new AFR is a major issue. For small volumes the cost of trials needed is not justified. Land filling is still the preferred option for a large volume of hazardous waste and municipal solid waste.No economic model is available to derive cement quality RDF from MSW for use in cement plants as AFR.´
Optimising clinker content
The cement industry being a highly energy-intensive sector, most of the major players have been adopting the best manufacturing practices right from mining to production to sales and distribution, across all units and disciplines by optimising energy, natural resources and technology. The Indian cement industry, over the years, has employed the best available technology for production; thanks to a high degree of blended cement utilisation, Indian cement producers are at the forefront of fuel and electrical energy consumption on a per tonne- of- product basis. An additional benefit in terms of sustainability is the lower per tonne CO2 emission. Stricter regulatory requirements are leading to greener technologies, and they in turn, lead to further energy efficiency.
From the energy efficiency perspective, consistent availability of quality fly ash is another constraint as it impacts optimisation of clinker component per tonne of cement produced by using fly ash. According to Rao, there is a greater scope of using fly ash and other cementitious materials in cement manufacturing by actively promoting blended cements and composite cements. Present Indian Standards for PPC allows 35 per cent absorption of flyash in cement manufacturing process. Similarly Indian Standards for Portland Slag Cement (PSC) which allows 65 per cent absorption of slag in cement manufacturing process. Composite cement standards which are currently under draft stage are expected to permit higher usage of pozzolona materials in cement manufacturing. The above initiatives will result in lower consumption of clinker in cement manufacturing. Since the clinker manufacturing involves huge amount of thermal energy, electrical energy consumption and CO2 emissions, any reduction in the clinker content in cement will reduce specific thermal energy, electrical energy and CO2 emission in cement manufacturing.
Says Rao, ´The cement industry is the biggest consumer of fly ash in India and ACC is the leading manufacturer of blended cements. ACC is consuming 4.4 million tonne of fly ash and 2.8 million tonne slag annually for production of blended cement. Use of slag and fly ash in cement manufacture helps the steel industry and power plants to dispose of their waste in an environment friendly manner while reducing the GHG emission from the cement industry and also minimising the use of limited resources like limestone.´
Following the global Cement Technology Roadmap in 2009 developed in a partnership between WBCSD CSI and the International Energy Agency (IEA), nine CSI members in India again joined hands with IEA to develop a Technology Roadmap: Low-Carbon Technology for the Indian Cement Industry. The initiative in India is supported by the International Finance Corporation (IFC), a member of the World Bank Group. The India roadmap, launched in February 2013, outlines a low-carbon growth pathway for the Indian cement industry that could lead to carbon intensity reductions of 45 per cent by 2050. It proposes that these reductions could come from increased clinker substitution and alternative fuel use; further improvements to energy efficiency, and the development and widespread implementation of newer technologies.
Says Rao, ´We have developed many products which have a low carbon footprint and energy foot print aligning with our sustainable development road map. Our blended cement CDM project is the biggest CDM project in the cement sector in the country with annual CO2 emission reduction potential of approximately of 200,000 tonne of CO2/year.´
Says Prashant, ´In all our units we have taken the initiative to maximise the use of AFR as it is a key lever to reduce CO2 emissions. We are proud member of Cement Sustainability Initiative (CSI) and are tackling all challenges to use AFR as per CSI guidelines/charter.´
Waste heat recovery
According to Sunil Kumar Singh, Director - Metals, Mining & Minerals, Schneider Electric India, even though the investment is high for WHR applications, it is the major energy efficiency project on thermal side. He says, ´Power generation using WHR results in considerable savings and also Indian cement industry can take the advantage under PAT cycle.´
Speaking about the scope of WHR Dr. Suchismita had this to say. ´WHR projects were adopted by Indian owners in a big way during the last four years. However there are mixed experiences regarding the successful implementation of these projects. This is dissuading some of the owners who were on the fence from going ahead and finalising their planned WHR projects. In some of the WHRS projects, the process design basis was not selected properly and as a result, there were over promise of power generation. Moreover, equipment selection has to be made properly and workmanship has to be perfect when it comes to boiler tubes, etc. Steam Rankine cycle based power generation is a fairly mature technology and the technology providers have suited their designs for the exhausted gas of the cement plants. Newer technologies based on the Organic Rankine cycle and the Ammonia-based Kalina cycle may take a while to pick up as they are the more costly options. Says Rao, ´Typically, clinkerisation lines, in all cement plants, have a potential to generate power by utilising the waste heat from pre-heater and cooler gases using low pressure boilers and turbine. A 7.5 MW WHR system has been installed at our Gagal plant in Himachal Pradesh in 2014. We have plans to implement similar projects in other cement plant of ACC.´ Speaking about the challenges of installing WHR system, Chander K, Technology Manager, India Operations Center, Process Automation, ABB India, says, ´High initial capital investment is almost always a deterrent to employing WHR systems. However, the benefits realised over a longer term in terms of utilising waste heat for generating power will pay off the high initial costs.´
Plant & equipment
The amount of energy saving varies on a case-to-case basis depending on the actual selection of process and equipment, quality and consistency of fuel, raw material characteristics, etc. However, it is important to understand here that long-term plant energy efficiency cannot be guaranteed based on the mere selection of the most efficient individual equipment alone. Rather, over a long term, energy (fuel and power) efficiency is largely driven by uniformity of the kiln feed chemistry, mastery of the burning zone which is primarily a kiln operation, and plant reliability factor i.e, avoiding stoppages due to incidents; all this in turn, relates to plant preventive maintenance.
Says Chander, ´The energy efficiency of cement production strongly depends on the process used to produce the clinker, the main component in cement manufacturing and the type of kiln. Dry kilns with pre-heaters and pre-calciners are the most efficient. The most efficient technologies used to produce cement are found in Japan, Mexico and in European countries, whereas the technologies used in Asian and North American countries are less efficient. Pre-heater, kiln and cooler section, raw mill, cement mill and coal mill are areas where tremendous scope is available in terms of energy savings.´
According to Singh on electrical side most of the cement plants have installed updated technology and process equipments. It is mainly grinding mill circuits, process fans and material conveying method which will determine the energy efficiency of the plant. Singh explains, ´The plants are considered to be energy efficient if they adopt the following:
Using vertical roller mills with full capacity utilisation and a high efficiency separator, ensuring minimum air ingress and pressure drop in circuit
Using process fans of high operating efficiency and using drives for flow control
Using mechanical conveying for material transport.
Utilising a vertical roller mill or roll press circuit in finish grinding mode for raw material grinding is the industry norm today, and this makes for a significant energy cost reduction when compared to the traditional closed circuit ball mill system. Likewise, for coal grinding, a vertical mill is used, and for the energy- intensive finish grinding process, the ball mill plus roll press system is widely popular. In specific cases where slag grinding is involved with high per centage moisture, the VRM technology for finish grinding is used. High efficiency separators are the standard today for all milling systems.
As regards the pyro-processing area, Indian cement producers continuously strive to achieve the lowest specific fuel consumption along with high power savings. High efficiency fourth- generation grate coolers are being widely used; they provide high recuperation efficiency along with lower maintenance interventions. As the total cooling air requirement reduces from the earlier 2.2 Nm3/kg clinker to say, 1.8 Nm3/kg clinker, there is a lot of savings through reduced exhaust air and fans` power consumption. To achieve lower fuel consumption, six stage pre-heater systems are the popular choice, along with in- line calciners. Advanced low NOx technologies are used in many cement plants. As regards process fans, a static efficiency = 82 per cent and use of variable speed drives reduces power consumption.
Sustainability awareness has picked up momentum in recent years in the cement industry, and several efforts are on by both cement manufacturers and major plant and machinery and auxiliary equipment manufacturers to integrate sustainability issues, essentially in energy conservation, resource optimisation and environmental planning, with business plans and reviews. For the cement industry, the major focus areas for sustainability are improving thermal energy efficiency and process technology, optimising fuel composition, including the use of waste as fuel, waste heat recovery, reduction in clinker factor, especially through increased rates of blending, and renewable energy. It is heartening to note that most of the cement companies have developed specific initiatives and road maps to reduce their organisational carbon footprint.
AGITH G ANTONY
ENERGY SAVING MEASURES
CASE STUDY: ABB
We received the first major order in the energy efficiency domain from Holcim in India, to improve specific power consumption of their cement plants. The solution offered included ACS 5000 and ACS 2000 range of 6.6 kV medium voltage (MV) drives that enhance energy efficiency at three plants, replacing existing damper controls. There is a huge potential to further enhance the efficiency by providing the MV drives for other process critical applications like preheater fans, mill separator fans, cooler fans in cement production area and also extend it to captive power plants to cover boiler feed pump (BFP), primary air and secondary air (PA/SA) fans and induced draft (ID) fans. Fans in the cement industry are usually large and consume a major part of electrical energy. Traditionally, Indian cement producers use cascade converters û also called Slip Power Recovery Systems (SPRS) - to control the speed of process fans. However, due to inherent limitations of SPRS, such as operation in weak networks and higher harmonics, they are now considering the variable speed drive (VSD) solution. With the use of VSDs, the energy consumption can be reduced from 90 kWHs/tonne to about 70 kWHs/tonne of cement produced.
- Chander K, Technology Manager, India Operations Center, Process Automation, ABB India