Advancement in Cement Technology

Indian Cement Industry: A Technology Perspective

 Dripto Mukhopadhyay

Indian cement industry has passed through many ups and down. It was under strict government control till 1982. Subsequently, it was partially decontrolled and in 1989, the industry was opened for free market competition along with withdrawal of price and distribution controls. Finally, the industry was completely de-licensed in July 1991 under the  policy of economic liberalization and the industry industry witnessed spectacular growth in production as well as capacity. Over time, the industry has also witnessed spread of the plants in several regions of the country as presented in Table 1- 2, which were previously concentrated in close proximity to the raw material.

250

   T    M   n    i   n   o    i   t   c   u    d   o   r   p    d   n   a   y   t    i   c   a   p   a    C

200

150

100

50

0 1950

1980

1900

Capacity

2000

2009

Production

Fig 1. Capacity, Production and Capacity Utilization in Indian Cement Industry

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250

200

   T    M   n    i   n   o    i   t   p   m   u   s   n   o    C

150

100

50

0 2003‐04

2004‐05

2005‐06

2006‐07

2007‐08

2008‐09

2009‐10

Fig 2. Cement Consumption in India

100 87

83 74

80

75

67 60

40

20

0 1950

1980

1900

2000

Capacity Utilization

Fig 3. Capacity Utilization in Indian Cement Industry

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2009

Table 1: Distribution of Cement Plants with Installed Capacity above 0.50 MnT State

Installed Capacity above 0.5 Million Tonnes No. of Plants

Percentage Share

Andhra Pradesh

32

21.33

Assam

1

0.67

Bihar

1

0.67

Chhattisgarh

8

5.33

Gujarat

11

7.33

Haryana

2

1.33

Himachal Pradesh

5

3.33

Jharkhand

3

2.00

Karnataka

8

5.33

Madhya Pradesh

11

7.33

Maharashtra

9

6.00

Meghalaya

1

0.67

Orissa

4

2.67

Punjab

2

1.33

Rajasthan

18

12.00

Tamil Nadu

17

11.33

Uttar Pradesh

8

5.33

Uttarakhand

2

1.33

West Bengal

7

4.67

Table 2: Distribution of Cement Plants with Installed Capacity Less than 0.5 MNT Installed Capacity less than 0.5 Million Tonnes State

No. of Plants

Share in %

Andhra Pradesh

3

9.09

Assam

1

3.03

Chhattisgarh

2

6.06

Delhi

1

3.03

Gujarat

3

9.09

Haryana

1

3.03

Himachal Pradesh

1

3.03

Jammu & Kashmir

1

3.03

Jharkhand

2

6.06

Karnataka

3

9.09

Kerala

2

6.06

Madhya Pradesh

1

3.03

Maharashtra

1

3.03

Meghalaya

3

9.09

Punjab

1

3.03

Rajasthan

2

6.06

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Technologies Adopted by Indian Cement Industry

Generally cement manufacturing process involves following stages: 1. Quarrying raw materials 2. Crushing 3. Pre-homogenization and raw meal grinding 4. Pre-heating 5. Precalcining 6. Clinker production in the rotary kiln 7. Cooling and storing 8. Blending 9. Cement grinding 10. Storing in the cement silo India is the second largest cement producing country in the world with a distinction of operating plants with varying capacity and varying technologies. Some of the modern plants can be compared to the best plants in the world in terms of variety, quality and energy efficiency.

Indian

cement

industry

remained

proactive

in

adopting

technological

advancements taking place all over the world. The share of energy inefficient wet process  plants had slowly decreased from 94.4% in 1960 to 61.6% in 1980. Currently, the share of wet process is only about 1% according to industry sources. During the 80's and 90's, major technological advancements took place world over in design of cement plant equipment/systems primarily in the following major areas: a)  b) c) d) e)

Pre-calcination High pressure grinding Automation in process control High efficiency particle separation Clinker cooling

These resulted in significant transformation of the production process globally. The Indian cement industry closely followed the international trend. Energy conservation has been the  prime objective that propelled major technological changes in the industry. A few recent technologies that helped Indian cement industry to consolidate in sustained energy savings are broadly discussed below.

Raw Material Grinding:

Raw material grinding is a critical mechanical operation that

determines the sizing of equipment in cement plant. This process consumes about 20% of

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total energy consumed in the plant. Depending on the raw materials’ physical characteristics, various grinding systems are used in Indian cement industry: a) Ball mills  b) Vertical Roller Mills (VRM) c) Ball mills with high pressure grinding rolls. d) High pressure grinding rolls e) Horizontal roller mills

Vertical roller mills have been widely accepted for combined grinding and drying of moist raw materials due to their excellent drying capacity and low energy consumption. While a number of plants are still using ball mills, many have installed pre-grinders like roller press to improve energy efficiency. Here, the extent to which the roller press is loaded determines the efficiency of the grinding circuit. Use of roller press alone as a finish grinding equipment to give the final product is also a new development. Horizontal roller mill is yet another improvement in grinding systems incorporating the advantages of vertical roller mill and roller press. An additional advantage with the horizontal roller mill is its low space requirement. A compact horizontal roller mill with an in-built separator is now in the process of development. This kind of a mill would eliminate many small conveyors carrying material to separator and from separator. The efficiency of the grinding circuit and power consumption of the mill fan largely depend on the performance of the classifier. Perhaps classifier is the part that has undergone maximum changes and has been the target part for efficiency improvement. A variety of high efficiency classifiers are employed in grinding circuits.

Pyro-processing:

Pyro-processing section in a cement plant comprises pre-heater, rotary

kiln and clinker cooler. This section is considered as the main element of cement plant as cement clinker formation takes place in kiln. This section determines the size of a cement  plant as well as sizes of all other equipment. With the introduction of pre-calciners in 80's, the size of cement plant had considerably increased. With technology upgradation, a kiln size of 7000 tpd is considered as an economic size which was at the level of 600 tpd in 70s. Pre-heaters can be classified into the following 5 categories irrespective of the manufacturer. •

Pre-heater without calciner

•

Inline calciner with air passing through the kiln

•

Inline calciner with external tertiary air duct T3 ‐ 150

•

Separate line calciner

•

Separate line calciner with inline calciner

Cyclones are basic units in a pre-heater system. Efficiency of cyclones depends on pressure drop and change of temperature of gas across each stage. Introduction of Low Pressure drop (LP) cyclones has brought the pressure drop across each stage to around 50 mm WG from around 150 mm WG in conventional cyclones. A typical 6 stage pre-heater with LP cyclones will have a pre-heater exhaust gas temperature of around 2500C and draught of around 500 mm WG. This in turn leads to decrease in pre-heater fan power consumption. The reduced temperatures at pre-heater exhaust contribute to environmental improvement. The burners also play an important role in determining the thermal efficiency of the pyro  processing system. There has been a continuous effort on operating the burners with the least  possible primary air. Multi-channel burners that consume only 5% primary air are being used in many plants. This leads to a direct thermal energy saving of 15 kcal/kg clinker. These modern burners also facilitate easy flame control in the process. Clinker cooler is also critical for the production process. It has dual functions, i.e. reducing the temperature of the clinker to an acceptable level for further transport as well as grinding and recover energy from the heat of the hot clinker by heating the cooling air. Mainly two types of clinker coolers are used at present in cement industry. They are: a) Grate cooler  b) Planetary cooler  Conventional grate coolers are still used by many plants due to comparatively higher thermal efficiency though they account for several bottlenecks. There have been a number of design improvements in grate coolers in recent times, mainly on grate plate to improve the efficiencies simultaneously reducing the cooling air intake. More and more cement plants with conventional grate coolers are retrofitting the coolers with high efficiency coolers. This has resulted in low electrical energy consumption in cooling air fans and also in cooler ID fan.

Cement Grinding:

Cement grinding is another energy intensive operation. Cement

grinding consumes around 25-30% of the total energy consumed in a cement plant. Typical cement grinding systems in use are: • •

Open circuit mills Closed circuit mills T3 ‐ 151

• • • • •

Roller press with open circuit ball mill Roller press with closed circuit ball mill. Roller press in finished mode Vertical roller mill Horizontal roller mill

For many years Ball Mills were in use in open circuit and closed circuit mode. In recent past, roll press as has been introduced and this has led to substantial reduction in energy consumption. Use of vertical roller mill for cement grinding is also very recent and the  performance results are reported to be encouraging. Horizontal roller mills combine the advantages of roll press and vertical roller mill. These mills are reported to be highly energy efficient. Horizontal roller mills are best suited for slag grinding. Separator is crucial equipment in cement mill section as it has direct bearing on production and quality of cement and energy consumption. High efficiency separators are used in modern cement plants and old plants are also going for a retrofit. Apart from these, auxiliary items like mill liners and diaphragms have also been improved continuously over time and these items in different designs are available contributing to energy reduction in cement grinding.

Table 3: Technology of Indian Cement Industry at a Glance Low Technology Plants

Modern Plants

Global Technology

Mining and Material Handling

Conventional

Computer aided

Computer aided

Crushing

Two stage

Single stage

Conveying of Limestone

Dumpers/Ropeway/ Tippers Ball Mills with / without conventional classifier

Grinding

Belt conveyors VRM’s, Roller Presses with dynamic classifier

Wet Semi Dry

Pyro-Processing

Blending & Storage

Dry -4 stage pre-heater - conventional coller - Single channel burner

Batch Blending silos

Dry -5/6 stage pre-heater - High efficiency coller ‐ Multi-channel burner

Continuous Blending silos

In-pit crushing & conveying Pipe conveyors, Belt conveyors VRM’s, Roller Press Dry 6 stage pre-heater ‐ High efficiency coller ‐ Multi-channel burner Co-processing WDF Co-generation of power Low Nox/SO2 emission technology Continuous Blending silos Multi-chamber silos

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Dome silos Bag

Packing & Dispatc

Process ontrol

Relay Logic / Hard Wired / PLC

Bag

Bulk

Bulk

Palleti ing and shri k wrapping

DDC

DDC

Fuzzy lo ic expert system

 Neuro uzzy expert system

Energy consumption level

90-100 kWh t cem.

75-85 k  h/t cem.

70-80 Wh/t cem.

900-1000 kc l/kg cl.

700-800 cal/kg cl.

675-7 0 kcal/kg cl.

Plant Si e (TPD)

300 –1800

3000 –6000

6000

 – 12000

Outcom of Technological Ch nges

Consequent to grow ing compet tion witnessed in the post de-cont ol era, one of the maj r develop ents has b en the introduction of igher grades of cement . The streng th parameters obtained with mode n technolo ies in India  are far hig er than the  BIS' speci ied standar  s for respective grades of cement.

0.00

0.00

0.00

0.00

0.00 OPC

PPC

SC

Others

Fig . Share in T tal Production (in %)  Note:

OPC - Ordina y Portland Cement, PPC - ortland Pozzolana Cement PSC - Portland S ag Cement

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Concluding Remar s and Poli y Message

Almost ll cement p ants are cu rently equi  ped with high efficienc y dust collection syste s like Electro Static Pr ecipitators. It has been ealized that running the  plant in en ironmentally friendly

ay has dir  ct bearing n the profit  bility and i age of the company.

se of blend d

cement, utilization

f waste he t in cement plant to g enerate ele trical ener  y and use

f

alternate fuels are

  few exa  ples explaining the c ncern of c ement industry not on ly

towards  protection

f environ ent but also ecological balancing.   There hav e been ma y

attempts to recover he heat los  in exhaust gas streams of cement  plants. Wit  the use of 6 stage pr  -heaters, high efficien y coolers nd better r efractory management  practices, t e quantity of heat lost from the ce ment plants has come down signifi cantly. Now technologi es are available to reco er the heat from exhau st gas strea s from pre heater and clinker cool er and gen rate electrical energy.

ore cemen  plants in I dia are exp cted to ado pt such was te

heat rec very syste s mainly o countera t the pow r shortage. As the electrical power generate   from was e heat does  not requir    combustio of any fo sil fuel, su h an attem t would e able the cement plant to significa tly contrib te to the

ovement o   reduction in

greenho se gases.

80

  n   o    i   t   c   u    d   o   r    P    f   o

60

40

   % 20

0

2004

1999

OPC

2009 P C+PSC

Fig 5. Shi t in Production

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Table 4: Comparison of Carbon

mission from Cement OPC

PPC

To ne /t

Calcination Combustion of fuel Use of po er Total

anufacturi g

%

Ton e /t

0.50

60

0.37

58

0.24

29

0.18

28

0.09

11

0.09

14

0.83

1 0

0.64

10

RMs & 30 0 TPD Kilns 1200 TPD 4-ST SP Kilns ow Pressure, PrePC Kilns

Roll r Press &

igh

eater

&

Expert

Effi ienc Se arators Dry Proc ss Kilns High Efficiency Fans, Mechanical Conve ors

K  H/T Cement

Fig 6. Tre d of Electri al Energy Source:

onsumption in Indian C ement Industry

Adopted from R aina, S. J. (20 2), Energy E ficiency Impr  vement in Indian Cement Industry, National Council or Cement & uilding Mate ials, paper pr  pared for IIP C Programme.

T3 ‐  155

1700 120 TPD 4-ST Kilns

PC Kilns

1500  Wet to Dry Conversion

Dry Process Kilns

1300 5-Stage PC Kilns

1100

6-Stage PC Kilns & Multi Channel Burners

900 High Efficiency Coolers

700 1960

1970

1980

1900

2000

KCAL/KG CL Fig 7. Trend of Thermal Energy Consumption in Indian Cement Industry Source: Adopted from Raina, S. J. (2002), Energy Efficiency Improvement in Indian Cement Industry, National Council for Cement & Building Materials, paper prepared for IIPEC Programme.

Production of blended cement is also another outcome of the new researches in theindustry. Blended cements are hydraulic binders in which a part of portland cement is replaced by other hydraulic or non-hydraulic materials. They display some superior properties directly related to durability apart from normal properties of Portland cement. It has been found that fly ash generated in thermal power plants and slag generated in steel plants is suitable for manufacture of blended cements. Fly ash or slag is inter-ground with cement clinker to  produce blended cement. Many developed countries started using such blended cements in large quantities in construction of critical structures such as rocket launch pads, sea water  jetties, large dams etc. Production of blended cements directly increases the plant capacity without any need for creating additional clinker making capacity. This reduces the limestone usage and fuel usage in cement plants and in turn lessens the greenhouse gases emissions. Increasing scarcity of good quality coal and power at an attractive price and an ever increasing energy cost to total production cost are forcing the Indian cement industry to look for alternate fuels. Use of cheap alternate fuels like lignite, pet coke, rice husk, groundnut shells etc. is in practice now. In some European cement plants the cost of fuel is reported to  be zero due to the use of 100% waste fuels. In fact, in many cases the cement plants are paid

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for burning the municipal and industrial wastes in such places. Indian cement industry should also look for such alternatives. However, this requires development of infrastructure at cement plant site as well as waste generation and collection infrastructure.

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