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Indian Cement Industry: Scope for Energy Efficiency Improvement

Dr. Suchismita Bhattacharya1, Jayanta Saha1, Sameer Nimkar2, and Gerald L Young3

1PENTA India Cement & Minerals Private Limited, Mumbai, India2Bharathi Vidyapeeth Institute of Technology, Belapur, Navi Mumbai

3PENTA Engineering Corp., St. Louis, USA

SUMMARY

With cement production in India estimated to reach 550 mtpy by the 2017, the cement industry

is poised to face new challenges. There will be serious pressure on the availability of quality raw

materials and fuel. The total emissions to the environment will have to be maintained at todays levels in

absolute terms. The Indian government is also trying to compel the industry to reduce energyconsumption. The Ministry of Power and Bureau of Energy Efficiency (BEE) have introduced the scheme

- Perform, achieve and trade ( PAT ) , a market based mechanism to make improvements in energy

efficiency in energy intensive industries more attractive by certification of energy savings that could be

traded. There will be legal binding for Designated Consumers in the cement industry (the DCs are those

units that consume more than 30,000 mtoe (metric tonnes oil equivalent) of energy) to make targeted

savings of energy both in terms of power and fuel consumption. This will make the cement market more

competetive, too.

In this paper, the different opportunities which exist in Indian Cement plants for improving the

consumption of energy both thermal and electrical will be explored. With the help of case studies, the

necessity to prioritize energy saving projects will be illustrated. Gate to gate energy consumption can

also be reduced by waste heat recovery and substitution of non-renewable fuels like coal with waste

derived fuel. The methods that should be adapted by cement plants in order to meet their energy savingtargets will be discussed.

1.0 INTRODUCTIONThe cement industry is highly energy intensive. The average energy requirement to produce one

tonne of cement is equivalent to the combustion of approximately 120 kg of coal. Thermal energy

required per ton of cement is about 0.80 million kcal and is generally supplied by fuels like coal, pet coke,

gas or fuel oil. Electric power requirement of 100 kWh/tonne of cement can be supplied from the

electricity grid or through captive power plants depending on the location of the cement plant. A one mtpa

(3000 tpd ) cement plant consumes around 90000 mtoe of energy.

This paper focuses on the means that can be adopted by Indian cement plants to improve energy

efficiency. For greenfield cement plants, the exercise is fairly simple and will depend on the choices madeby owners in incorporating energy saving design and equipment. For existing cement plants, this will

entail a thorough appraisal of the existing facilities and carrying out improvements therein. The task of

carrying out improvement projects in existing plants is further complicated by the need to keep the

downtime as low as possible. Change to non-conventional energy sources will also be discussed as it is

being adopted worldwide to reduce the consumption of fossil fuels.


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1.1 Heat Consumption in Cement Manufacturing ProcessThe cement kiln consumes heat in the range of 685 kcal/kg in modern plants to about 800 kcal/kg

or even higher in older plants with low capacities. The actual heat of reaction is around 400-420 kcal/kg.

While radiation losses are to the tune of 50 kcal/kg, around 20 kcal/kg of heat leaves with the clinker,

about 25 % of the total heat is vented from the preheater exhaust and from the cooler exhaust. Heat

consumption in a 6 stage ILC kiln with SF cooler is shown in Figure 1.

Cooler

ILC Kiln

Heat of reaction

400-420 kcal/kg

CPreheaterHeat in smoke and

Dust from preheater

315 C140 kcal/kg cl

Coal Firing

700-720 kcal/kg cl

Heat out with

clinker= 20 kcal/kg

Cooler excess air

250 C

~80 kcal/kg C

Kiln radiation loss

20 kcal/kg cl

60 % calciner

40% kiln

Preheater

Radiation Loss

30 kcal/kg

Heat in with clinker

~ 8 kcal/kg cl

Cooler radiation loss

7 kcal/kg cl

Figure 1: Typical Heat Balance of an ILC Pyro System

(Reference 0 C)

1.2 Electrical Energy Consumption in Cement Manufacturing ProcessTypical electrical energy consumption is between 90 to 110 kwh/ ton OPC. With blended

cements, the consumption will be lower based on the proportion of additives. The contribution of the

respective processes is shown in Table 1.

Department % Power Consumption

Raw Material crushing and prehomogenization 3.2

Raw Meal Grinding drying 26.1

Raw Meal Homogenization 1.6

Fuel (coal) grinding 4.4

Clinkerization and Clinker Cooling 24.6

Clinker Grinding- cement production 35

Conveying Packaging Loading 5.1

Total 100

Table 1: Electrical energy consumption of various departments

The performance of the best cement plants in India are at par with the best in the world. In these

cases, incremental improvement in energy consumption is possible by conscious energy management.

The poor performance of most of the plants brings down the average. Refer Table 2 for details. There is

scope for improvement in both thermal and electrical energy consumption.


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Table 2: Comparison of energy consumption

2.0 ENERGY EFFICIENCY IMPROVEMENTWith rising energy costs, plants should continuously be on the look out to reduce energy

consumption. Moreover external agencies like the Bureau of Energy Efficiency have now introduced

reward programs for energy performance.

Typical gate to gate energy consumption for a 5000 tpd plant will be as follows

Heat Consumption kCal/kG Cli. 750 kCal/kG Cement (OPC) 712.5

Power Consumption kWh/t Cement 100 kCal/kG Cement (OPC) 197.6

Gate to Gate Energy Consumption kCal/kG Cement (OPC) 910.1

Gate to Gate Energy Consumption, for 5000 tpd plant MTOE 158078.5

The first step towards energy improvement in a plant is establishment of the baseline. Once the

existing condition is known, it will be possible to identify action areas. As seen above, the contribution of

thermal energy is much higher to the overall energy consumption. A 5% reduction target means a

reduction of 8000 mtoe fuel consumption. This can be brought about by reducing the thermal energy

consumption to 710 kcal /kg or the power consumption to 78 kWh/t cement or a combination of both.

The action plan will differ according the specific situation in a plant. Once the plans are executed, the

results have to be monitored to sustain the improvements.

1. Audit of existing plant

2. Identification action areas

3. Action plan for reduction in thermal and electrical energy consumption4. Implementation, review and monitoring

Department Unit India Average World Best Practice

Raw Materials Preparation

Coal mill kWh/t clinker 8 2.4

Crushing kWh/t clinker 2 1

Raw mill kWh/t clinker 28 27

ClinkerProduction

Kiln & Cooler kcal/kg of clinker 770 680

Kiln & Cooler kWh/t clinker 28 22

Finish Grinding

Cement mill kWh/t cement 30 25

Miscellaneous

Utilities: mining & transportation kWh/t clinker 1.6 1.5

Utilities: packing house kWh/t cement (OPC) 1.9 1.5

Utilities:misc. kWh/t cement (OPC) 2 1.5

Total kWh/t cement (OPC) 95 77


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2.1 Plant AuditInitially it was considered that an energy audit was sufficient to establish the baseline. Now it has

been realized that a thorough technical audit is essential to understand the improvement possibilities for

the plant. The audit should encompass the following

2.1.1 Field inspection of equipment and process flow and plant documentationField inspections are necessary to get to know the existing equipment and their condition.

The equipment name plates have to be compared with the machinery list and with the final supply

documents. In some cases, the plant may not have kept proper records of project documents or the

old documentation may not have not been updated during subsequent modifications. In these

cases, it may be necessary to generate as-is drawings or to contact suppliers to get information

regarding equipment. Records of start-stop can be analyzed to get an idea of the frequently failing

equipment which reduce the run factor.

2.1.2 Evaluation of plant operation methodologySome plants have standardized their operating procedures and an automated PLC system.

However in some plants it is necessary to engage the operators to determine the specific overrides

and control parameters. In some places the equipment operating manuals are not available or

referred. Hence this step is important before suggesting modifications. Some equipment are

operated at higher than warranted temperatures and this leads to subsequent malfunctions and

lower run times.

2.1.3 Assessment of material and energy balanceOne of the most significant parameters is the clinkerization ratio. Most plants have a

dependable measurement of the kiln feed rate in tph. However clinker production is at best

available as average monthly quantity. The clinker drop test is carried out as a fool proof way of

determining the production rate. Fuel/ Coal consumption can also be determined during this test

to get correct estimate of specific heat consumption. Similar tests can be carried out for the mill

systems. During these tests, the fan flow rates can also be measured along with temperatures and

pressures. Leakages can be estimated based on gas temperatures as well as gas composition

analyses. This is one of the simplest and most accurate ways of establishing the material and

energy balance.

Figure 2: False Air Entry and Detection

2.1.4 Assessing optimum throughputs for the given system based on simulations and comparingwith operation parameters

Simulations of the kiln and raw mill systems are a powerful tool to

Arrive at an optimum throughput and heat consumption for the system.

Estimate the expected operating temperature / pressure.


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Simulations help to estimate leakages in preheaters where gas analysis cannot indicate the

false air entry. Refer Figure 3.

Figure 3: Measurements within boundary of heat balance for Pyro Section

2.1.5 Identification of gap areasOnce a detailed audit is carried out it will be possible to carefully identify the improvement

areas as well as classify them into

Opportunities requiring little no investment- Short term measures

Opportunities requiring some investment- Medium term measures

Opportunities requiring major investment and down time - Long term measures.

The projects for energy efficiency improvement will have to be prioritized based on

possible benefits, funds available and required down time.

3.0 CORRECTIVE ACTIONThe corrective actions can be classified into three types the details of which are listed below.

3.1 Short Term MeasuresThe short term measures are as follows

Training program for operating energy intensive equipment such as crusher, grindingmill, particle size separator, vibrating screen, etc.

Replacement of worn-out parts of crusher and grinding machines

Controlling the combustion air (10% reduction in excess air can save 8-20 kcal/kg of

clinker)


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Controlling the composition of raw materials (the fluctuation encountered in the

composition of the raw materials fed to a cement kiln is generally compensated by an

over-baking which leads to energy losses)

Plugging of all air leakage

Ensuring uninterrupted operation of the kiln

Power factor improvement of electric motors

Turning off motors and heaters when not in effective use

Insulation enhancement

Depending on the case, reduction in energy consumption of 10-15% can be achieved by adopting

these measures.

3.2 Medium Term Measures3.2.1 Measures on processed materials and products

i. Installation of dust collection System

The high velocity gases passing through the kiln system carry along a large portion of dust,

thus losing materials as well as energy due to the extra raw material that has to be processed for

the same amount of output. Larger size dust particles can be removed by cyclones and smaller

size dust can be removed by ESPs, bag filters and cyclones.

ii. Diversification of cement products

The blending of certain materials like granulated slag, fly ash and pozzolans with the cement

makes it possible to produce more cement from the same amount of clinker, and as a result, the

fuel consumption per ton of cement can be reduced. About 30% of clinker can be replaced by fly

ash and upto 55% by blast furnace slag without changing the character of OPC as a general

purpose cement.

3.2.2 Changes and modifications in sub-processesi. Installation of dual firing system

The reaction at the kiln takes place at two stages, firstly at a lower temperature range of 800-

900C (which is called calcination) and then at a higher temperature range of 1300-1500C

(termed as burning). Low grade fuels can be used in the lower temperature range combustion so

that fuels with higher calorific values can be replaced. Depending on the system, 20-25% of the

total fuel can be replaced by low grade fuel being utilized for the calcination phase.

ii. Change in clinker grinding system: vertical roller mills to replace tube and ball mills

Upgradation of equipment such as jaw-crusher to gyratory crusher, ball mill to vertical roller

mill (VRM), worm gears to helical and spiral gears, etc., can increase the efficiency of power

transmission system and reduce specific power consumption. The grinding efficiency of VRM is

more than twice the value for ball mill in coarse size reduction up to a size of 0.5 mm. Thus thepower consumption of VRM is 35% less than the ball mill. Up to 25% electricity may be saved

by replacing ball mills with roller mills. Pregrinders can be installed before existing ball mills to

reduce the power consumption in the totals circuit by 10-15%. In new plants, roller mills are

recommended to be used instead of ball mills.


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iii. Operating the mill in closed loop instead of open loop

Separators can be incorporated in ball mill circuits to improve the grinding efficiency. 2-3

kwh/t reduction in power consumption is observed per pass of circulation. As a result, upto 15-

20% increase in capacity can be obtained from close circuiting of cement mills. A better particle

size distribution is obtained from 3rd generation high efficiency separators and this can improve

the strength of cement.

3.2.3 Recovery of waste heatRecovery of waste heat offers an indirect way of saving energy. For a cement clinker line of

1000 tpd clinker capacity, the amount of waste heat recoverable from various streams can be

By-pass gas: 28-58 kcal /kg of clinker

Cyclone preheater exhaust gas: 92-109 kcal /kg of clinker

Clinker cooler exhaust gas: 82-109 kcal /kg of clinker.

This waste heat that is available after drying of raw materials and/or coal can be used to

produce steam in a boiler which can be used to generate electricity, desalinate sea water and for

other purposes like domestic heating etc. Power generation requires a heat recovery boiler and a

turbine system and can be based on Steam Rankine cycle, Organic Rankine Cycle (ORC) or

Kalina process. Based on the chosen WHR process, 10-12 kWh/t clinker can be produced fromthe cooler waste air and 11-15 kWh/t clinker from the PH gases. Hence up to 25% of the power

consumption of a cement plant can be produced by these technologies without changes in kiln

operation. With suitable modification in kiln operation it may be possible to produce up to 30

kWh/t clinker. Power generation can be further increased by additional co-firing into the boiler.

Some systems report generation of up to 45 kWh /t clinker.

WHR for electricity generation has picked up in a big way in India. From five installations

under operation two years ago, now we have additional six to seven projects underway. The

initial inertia to adopt new technology has now been overcome. There are now more technology

suppliers in the market including some Chinese players.

The following concerns need to be addressed while embarking on a Waste Heat recovery project.

The cement plant exhaust gases are dusty and/or abrasive and hence WHR boilers should be

designed in such a way that the tubes will not get fouled or clogged. Most boiler providers are

coming up with solutions ranging from rapping of tubes to installation of dust collectors

(cyclones) before the boilers.

Variations in waste heat content of the gases with changes in raw material moisture content, or

during operation have to be taken into account while designing the waste heat recovery system.

The design, maximum and minimum conditions need to be determined correctly in order to

achieve smooth running of the WHR generator system. Care should be taken while deciding final

control philosophy.

Financial barriers do exist as WHR project costs are in the range of 8-12 crores per MW

generated. Hence the WHR projects may be financially viable only above a certain scale.

However projected payback periods are in the range of 3-4 years.The implementation of the PAT-BEE scheme will make WHR projects more attractive. The

energy generated from Waste heat will reduce the gate to gate SEC (upto 4-5% reduction in

mtoe) and will assist in reaching the reduction target accordingly.


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3.2.4 Use of renewable energy sourcesAlternate energy sources are gradually becoming popular in the global as well as Indian

Cement Industry. The use of waste as alternative fuels is technically sound as the organic part is

destroyed and the inorganic part, including heavy metals, is trapped and combined in the product.

Cement kilns have a number of characteristics which make them ideal installations in which

alternative fuels can be burnt in safety.

Commonly used alternative fuels are Municipal Solid Waste, Hazardous solid waste,

Hazardous liquid solvent, TDI tar, rice husk, shredded tyre, coconut shell, dorb , waste plastic,

chipped wood araldite, paint sludge and refinery sludge.

The main steps involved in use of alternate fuels are

Clearances from State and Central Pollution Control Boards.

Choosing the technology, exploring the availability of different types of alternative fuels

and subsequent plant scale trials.

Modification in Raw mix chemistry to take care of ash absorption and process balancing

of volatiles such as sulphur, alkalies and chlorides.

Fuel size reduction economics to acceptable levels to ensure complete combustion in the

calciner. Calciner or kiln burner modifications may be necessary.

Modification of material handling system to ensure continuous and free flow of fuel. Theplant will have to incorporate material receiving and storage facility. Size reduction may

have to be carried out using wood chipping machines or plastic shredding machine.

Additional transport systems will have to be incorporated to convey the fuel to the kiln/

calciner.

Special care and facilities for handling hazardous materials. Usually a tie up with and

alternate fuel resource facility ensures that fuel is available in adequate quantity and is of

consistent specifications. Liquid waste will have to be stored in tanks and pumped to the

specially designed burners.

Co-ordination with Regulatory authorities and other Government bodies regularly.

Records of emissions have to be shared with Pollution Control boards to maintain the

permits.

Indian companies have so far achieved only a maximum of 10% heat substitution in kiln

through alternate fuels. Alternate fuels (excluding petcoke) can be substituted in calciners to upto

50%. Some companies are now targeting upto 20% heat substitution in the kiln. The PAT BEE

regulations will also promote the use of alternate fuels as these will not contribute to the gate to

gate specific energy consumption.

3.3 Long Term Measures3.3.1 Replacement with LP cyclones

Cyclones are a basic component of plants with pre-heating systems. The installation of newer

cyclones in a plant with lower pressure losses will reduce the power consumption of the kiln

exhaust gas fan system. Replacement with low pressure drop cyclones can be economicallyreasonable when foundation and tower of preheater are usable without rebuilding. In practice, the

pressure drop is often balanced by higher air volume flow for increase of kiln capacity. The costs

of modifications are usually site specific. Depending on the efficiency of the fan, 0.66 to 0.77

kWh/t clinker can be saved for each 50 mm w.c. reduction in pressure drop. For most older kilns

this amounts to savings of 0.66 to 1.1 kWh/t clinker. Installation of the cyclones can be


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expensive, however, since it may often entail rebuilding or the modification of the preheater

tower, and the costs are very site specific.

3.3.2 Addition or preheater cyclone stageThe preheater cyclone is designed for heat transfer between hot gases from the burning

process and kiln feed. Energy savings can be achieved by reducing the temperature of the hot gasthrough heat recovery with an additional cyclone stage. This will be possible if the moisture in the

raw material is not very high and the drying load of raw mill can be comfortably met by the

preheater exhaust gases. A 6-stage preheater calciner using coal shows exit gas temperatures of

about 280 C, 5-stage preheater 310 C and 4-stage preheater, 350 C. Addition of a cyclone

stage is feasible if the original design was conservative. This may also result in higher pressure

drop across the system and may warrant change of preheater i.d. fan.

The addition of a cyclone stage is a major retrofit and depends on the statics of the tower

which should allow for more structural load. As the upper cyclone stage is normally a twin

cyclone, at least two stages have to be renewed. Addition of 65-80 tons dead load is envisaged.

The energy demand of a 4-stage cyclone preheater would decrease by 20-25 kcal/kg clinker if a

5th stage is added with respect to reduced heat losses. This has to be compared against additional

electrical energy requirement, if any, to decide to add the 5th stage.

3.3.3 Automation of monitoring and control systemHeat from the kiln may be lost through non-optimal process conditions or process

management. Automated computer control systems may help to optimize the combustion process

and conditions. Improved process control will also help to improve the product quality and

grindability, such as reactivity and hardness of the produced clinker, which may lead to more

efficient clinker grinding. Most modern systems use so-called expert control (also known as

'fuzzy logic' or rule-based control strategies). Expert control systems do not use a modeled

process to control process conditions, but try to simulate the best human operator, using

information from various stages in the process.

Model-predictive control use dynamic models of the processes in the kiln. The use of on-lineanalyzers permits operators to keep track of the chemical composition of raw materials being

processed in the plant. This enables rapid changes to be made to the blend of raw materials. A

uniform feed allows for steadier kiln operation, thereby saving fuel. Energy savings from process

control systems may vary between 2.5% and 10%, and the typical savings are estimated at 2.5-

5%. The economics of advanced process control systems are very good and payback periods can

be as short as 3 months.

4.0 NEED FOR ENERGY MANAGEMENTAlthough technological changes in equipment can help to reduce energy use, changes in staff

behavior and attitude may have a greater impact. Staff should be trained in both skills and the companys

general approach to energy efficiency in their day-to-day practices. Personnel at all levels should beaware of energy use and objectives for energy efficiency improvement. Programs with regular feedback

on staff behavior, such as reward systems, have had the best results. Most importantly, companies need to

institute strong energy management programs that oversee energy efficiency improvement across the

corporation and see to it that all employees actively contribute to energy efficiency improvements.

Examples of some simple tasks employees can do include the following:


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Switch off motors, fans and machines when they are not being used, especially at the end of the

working day or shift, and during breaks, when it does not affect production, quality or safety.

Similarly, turn on equipment no earlier than needed to reach the correct settings (temperature,

pressure) at the start time.

Switch off unnecessary lights; rely on daylighting whenever possible. Look for unoccupied areas

being cooled, and switch off cooling.

Report leaks of water (both process water and dripping taps), steam and compressed air. Ensurethey are repaired quickly.

Prevent drafts from badly fitting seals, windows and doors, and hence, leakage of cool air.

Carry out regular maintenance of energy-consuming equipment.

Ensure that the insulation on process heating equipment is effective.

5.0 CONCLUSIONA conscious effort is required throughout the cement industry to improve energy efficiency.

Governments incentives like the BEE- Pat scheme will help to improve the return on investments for the

expenses incurred on energy efficiency improvement projects.

For existing cement plants, plant audits will be the first step towards understanding the status ofthe plant as well as planning the paths for improvement. External audits usually offer an un-biased view

of the operation of the plant as well as the equipment. A plethora of technological improvements are

possible to improve both thermal as well as electrical energy consumption. Once executed in a properly

prioritized manner, these energy saving projects will not just help to lower the cost of production but also

result in sustainable development.

6.0 REFERENCES1. Alternate fuels in Cement Manufacture, CEMBUREAU - The European Cement Association,

April 1997.

2. Analysis of Energy-Efficiency Opportunities for the Cement Industry in Shandong Province,

China, Lawrence Berkeley National Laboratory, October 2009.

3. Assessment of Energy Use and Energy Savings Potential in Cement Sector in India , Asia

Sustainable and Alternative Energy Program (ASTAE), World Bank

http://eetd.lbl.gov/ea/ies/ieua/Pubs.html

4. Cement- A reference book for the Industry, EU-China Energy and Environment Program,

2009.

5. Cement kilns firing hazardous waste, Coordinated by Ms. Ute Karl (Germany) and Ms. Steffi

Richter (Germany), April 2006.

6. Energy auditing and recovery for dry type cement rotary kiln systemsA case study. Tahsin

Engin, Vedat Ari.Energy Conversion and Management46 (2005) 551562.

7. Energy Optimization in Cement Manufacturing, ABB Review 2/2007.

8.

Indias Cement Industry: Productivity, Energy Efficiency and Carbon Emissions, KatjaSchumacher and Jayant Sathaye, Lawrence Berkeley National Laboratory, July 1999.

9. Waste Heat Recovery- Practical Solutions for Cement Plants. G. L Young, N. Jayaraman, J.

Saha and Dr. S Bhattacharya. Presented at the 11th NCB Seminar, 2009.

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