Replacement of the Air-lift with Bucket Elevator for Kiln Feed Transport to the Silo

Background

The kiln feed after blending in the silo is conveyed to the top of the pre-heater for further processing. The transport of kiln feed is normally done through pneumatic conveying systems such as air-lift. The pneumatic conveying system consumes more power, nearly 3 to 4 times that of the mechanical conveying system. Also, the pneumatic conveying system adds additional cold air to the pre-heater system, thus reducing the thermal efficiency of the system. Conventionally, the pneumatic conveying system was being preferred as the mechanical system (particularly the Bucket elevator) was not very reliable. In the recent years with the improvement in the metallurgy, bucket elevators that can operate continuously in a reliable manner have been developed. These have been installed in many plants with substantial benefits.

Previous status

In a million tonne dry process pre-calciner plant, the Kiln feed was being conveyed with the help of an air-lift.

Energy saving project

The air-lift was replaced with a bucket elevator. The air-lift was retained to meet the stand-by requirements.

Implementation methodology & time frame

The installation of the Bucket elevator took about 6 months. There was no stoppage of the plant, and the installation of the Bucket elevator was done parallely. The bucket elevator was hooked up during the regular stoppage of the Kiln and a separate stoppage was avoided.

Benefits of the project

The implementation of this project resulted in reduction of power from 146 kW for the air-lift to 51 kW for the Bucket elevator. The air handled by the pre-heater fan also got reduced resulting in pre-heater fan power consumption by 14 kW. The thermal saving was about 3.2 kCal/kg of clinker.

The saving annually amounted to

• Electrical saving - 8.6 lakh units / year
• Thermal saving - 2112 MMkCal / year
  

Financial analysis

The total benefits amounted to a monetary annual savings of Rs. 34.0 lakhs (@ Rs.3.1/unit & Rs.350/mmkCal) The investment made was around Rs. 75.0 lakhs. The simple payback period for this project was 27 months.

Benefits of installing bucket elevator for Kiln feed

• Reduction in conveying energy & PH fan power
• Reduction in thermal energy
  

Cost benefit analysis

• Annual Savings - Rs. 34.0 lakhs
• Investment - Rs. 75.0 lakhs
• Simple payback - 27 months
  

Usage of Cheaper Fuels for Calciner Firing

Background

The Kiln and the Calciner are major consumers of fuel in a Cement plant. The fuel cost amounts to nearly 20 % of the manufacturing cost. The increasing cost of fuel and the competition among the units have made the Cement units to take up many thermal energy saving projects. The plants are also looking for avenues for reducing the cost by replacing the costly fuels with cheaper fuels. The possible fuels that have been tried by the Cement units include Lignite, Rice husk and Ground-nut shell.

Previous status

In a million tonne dry process pre-calciner plant, Coal was being used as fuel for firing in both the Kiln and Calciner. The Coal was having a Calorific value of about 5900 kCal / kg with a cost of about Rs. 2000 / MT.

Energy saving project

A provision was made to utilise Rice husk in the Calciner. With the new system it was possible to replace part of the coal fired in the Calciner with Rice husk.

Implementation methodology & time frame

A hopper was installed by the side of the pre-heater building for storing the Rice husk. The rice husk was fed to this hopper with the help of front end loaders.

The Rice husk was conveyed to the Calciner with the help of a Rotary blower of 32 m³ / hour capacity. The whole system was fabricated with the waste material available in the plant. The system was hooked up with the main system during a brief stoppage of the plant. The system could be operated for about 8 months of non- rainy dry season.

Benefits of the project

The implementation of the project resulted in the reduction of the cost of fuel used in the Calciner. The cost comparison of Coal and Rice husk are as below;

Parameter -- Coal – Rice husk

Cost – Rs.2000/MT – Rs.750/MT

Calorific Value – 5900 kCal/kg – 2900 kCal/kg

Energy Cost – Rs.340/MMKCal – Rs. 260/MMKcal

The rice husk was used for replacing about 10% of the total coal used for firing in the calciners. This resulted in reduction of the total thermal energy cost, with the other conditions such as output, temperature, pressure etc. remaining the same. There was also a marginal reduction of the power consumption in the coal mill, as the rice husk was used directly without grinding. The rice husk becomes wet and handling becomes difficult during the rainy season. Hence, the usage of rice husk was restricted to the non-rainy and dry season (about 8 months in a year).

Financial analysis

The annual benefits (in the form of reduction in thermal energy cost) was about Rs. 35 lakhs. The equipment required for conveying and firing in the pre-heater was fabricated in-house with available material and hence the investment was negligible.

Benefits of using cheaper fuel

• Reduction in thermal energy cost
• Marginal reduction in coal mill power consumption
  

Cost benefit analysis

• Annual Savings - Rs. 35.0 lakhs
• Investment – Negligible

Parallel Pre-heater Fan for Increasing the Production

Background

The equipment in a Cement plant are all designed based on a certain load factor of the Kiln. Normally the pre-heaters, coolers and other major equipment are always designed with good margins. Many companies have made use of these margins and achieved higher levels of production with small modifications. In some of the plants all the equipment might have excess capacity and only the PH fan might be the bottle-neck for increasing production. In such cases the pre-heater fan is replaced or modified to increase the output of the plant. The increase in output also aids in reducing the power consumption.

Previous status

A million tonne dry process pre-calciner plant was operating at a capacity of about 3000 to 3100 TPD. The major equipment had additional margin for increasing the capacity by another 10 %, but the pre-heater fan was operating at its full capacity.

Energy saving project

An additional small pre-heater fan equal to about 15 % of the capacity of the existing fan was installed parallel to the existing PH fan. The head of the new fan was the same as that of the existing fan.

Implementation methodology & time frame

The new PH fan was installed parallel to the existing fan. The fan was installed during running of the plant. The new parallel fan was hooked up during a small stoppage of the plant.

Benefits of the project

There was an increase in the output of the Kiln, reduction in pressure drop of the pre-heater, reduction in Kiln section power consumption and reduction in Kiln specific thermal energy consumption. The comparison of the conditions and the energy consumption before and after installation of the Parallel Pre-heater fan are as below:

Parameter Before Implementation After Implementation

Clinker Production 3000 TPD 3200 TPD

DP across Pre heater 880 mmWg 860 mmWg

Pre heater fan Power 12.67 kWh /ton<>

Heat Consumption 790 kCal / kg 780 kCal / kg

The implementation of this project resulted in a power saving of 0.6 units / ton of Clinker, which annually amounted to 10.80 lakh units / year. Additionally there was also the thermal energy reduction of about 10 kCal / kg. The increased output of 200 TPD of clinker also aided in reducing the fixed cost component.

Financial analysis

The total benefits amounted to a monetary annual savings of Rs. 50 lakhs. The investment made was around Rs. 10 lakhs. The simple payback period for this project was 2 months.

Benefits of additional P.H. fans

• Increased clinker production
• Lower P.H. fan (total) power consumption
• Reduction in thermal energy

Cost benefit analysis

• Annual Savings - Rs. 50.0 lakhs
• Investment - Rs. 10.0 lakhs
• Simple payback - 2 months

Replacement of Existing Cyclones with Low Pressure Drop (LP) Cyclones

Background

The Pre-heaters comprising of 4/5/6 stages of cyclones is an important part of the Kiln section in a Cement Plant. In the pre-heaters the waste gas coming out of the Kiln system is used for pre-heating the kiln feed material. With increased focus towards more heat recovery from the waste gas, the number of pre heater stages have been increased from 4 to 5 / 6. The increase in the number of stages however led to increase in the pressure drop across the system and hence higher fan power. This led to the development of cyclones, which have a lower pressure drop. The low pressure drop (LP) cyclones have the advantage of

• Low pressure drop. Hence, lower Pre-heater fan power consumption.
• Higher output rate with the same Pre-heater fan
• Reduction in thermal energy consumption

Previous status

In a million tonne dry process pre-calciner plant, there were 4 stages of conventional cyclones with a twin cyclone at the top. The pressure drop across the top twin cyclone was about 100 – 125 mmWg.

Energy saving project

The existing top stage twin cyclone was replaced with a low pressure drop cyclone.

Implementation methodology & time frame

The top cyclone was at a height of nearly 106 metres. The implementation of this project involved removal of the existing cyclone and fixing of the new LP cyclone. The normal procedure involves the following steps:

• Removal of the bricks inside the existing top cyclone
• Removal of the old cyclone
• Installation of the new cyclone
• Refractory lining of the new cyclones
  

This procedure however needs a stoppage of the plant of more than 90 days. The plant could not afford such a long stoppage and the consequent loss of production.

Hence, the procedure was improvised to reduce the plant stoppage time. The improvised procedure adopted by the plant is as below:

• The entire cyclone was assembled at the ground floor
• The inside brick lining was also done at the ground floor only
• The plant was then stopped and the existing cyclones removed
• The entire twin cyclone along with brick lining was lifted to the top and fixed. A special crane was used for lifting the cyclones of about 150 MT to a height of about 106 metres. In this manner, the project could be implemented with a stoppage of only 20 days.

Benefits of the project

There was an increase in the output of the Kiln, reduction in pressure drop of the pre-heater, reduction in Kiln section power consumption and reduction in Kiln specific thermal energy consumption. The comparison of the conditions and the energy consumption before and after installation of the LP cyclones are as below:

Parameter Before Implementation After Implementation

Clinker Production 2650 TPD 2850 TPD

DP across Top Cyclone 100 – 125 mmWg 70 – 90 mmWg

Kiln section Power 30 kWh /ton 28.5 kWh / ton

Heat Consumption 830 kCal / kg 810 kCal / kg

The implementation of this project resulted in a power saving of 1.5 units / ton of Clinker, which annually amounted to 14 lakh units / year. Additionally there was also the thermal energy reduction of about 20 kCal / kg. The increased output of 200 TPD of clinker also aided in reducing the fixed cost component.

Financial analysis

The total benefits amounted to a monetary annual savings of Rs. 240 lakhs. The investment made was around Rs. 220 lakhs. The simple payback period for this project was 11 months.

Benefits of low pressure drop cyclone

• Lower pressure drop across P.H.
• Reduction in P.H. fan power consumption
• Increase in clinker production
• Reduction in thermal energy consumption.
  

Cost benefit analysis

• Annual Savings - Rs. 240.0 lakhs
• Investment - Rs. 220.0 lakhs
• Simple payback - 11 months

Blending Control System for Maintaining Consistent Kiln Feed Quality

Background

The Kiln is the heart of a Cement plant. The steady and continuous operation of the Kiln is essential for producing good quality Clinker, higher level of output and lower energy consumption. To ensure this, consistent quality of kiln feed is a pre-requisite. This can be achieved only if the raw meal fed to the silo is consistent. The raw meal is produced by grinding various raw materials such as limestone, bauxite, iron-ore, etc,. The quality of these raw materials varies from time-to-time. Hence, the quality of the raw meal is analysed every hour and the percentage of the mix is varied to maintain the raw meal quality. In the old plants, the mix percentage is varied manually from hour to hour. This manual method of adjustment is inaccurate and generally leads to fluctuation in the quality of raw meal and hence the kiln-feed.

In the latest plants, the hourly chemical analysis is performed and the data is fed to the computer. A Software included in the system, varies the raw mix proportion so that the required mix quality is maintained. This has been retrofitted in many plants with substantial benefits.

Previous status

In a 3000 TPD dry process pre-calciner plant operating with a VRM and a continuous blending cum storage silo, the raw meal was being produced by grinding Limestone, bauxite and iron-ore. The raw meal was being analysed every hour through an X-ray analyser and the mix varied manually.

Energy saving project

A new blending software based control system was introduced. The new system had a separate PC which could be linked to the existing control system. The X-ray analysis was fed to the blending control system, which automatically varied the raw mix proportion.

Implementation methodology & time frame

The raw mix proportioning was done manually in the initial days and the blending control was put into operation in a phased manner. The system was checked for the extreme conditions (e.g. limestone of maximum and minimum LSF) by both the supplier and the plant team, so that the system is functional at all conditions.

Benefits of the project

There was a marginal increase in the output of the Kiln, reduction in feed cuts on account of quality of kiln feed, better quality of clinker and steady operation of the Kiln.

The benefits achieved are as below.

• Increase in kiln output by 10 to 15 tpd.
• Reduction in LSF variation in Kiln feed from 0.4 % to 0.2 %.
• Reduction in Thermal Energy Consumption
  

Financial analysis

The implementation of this project resulted in an annual saving of Rs. 18 lakhs (Increased Production and thermal energy saving). The investment made was around Rs. 15.0 lakhs. The simple payback period was 10 months.

Benefits of blending control system

• Fine and accurate control of raw mix
• Reduced Kiln feed - L.S.F. variation
• Lower thermal consumption

Cost benefit analysis

• Annual Savings - Rs. 18.0 lakhs
• Investment - Rs. 15.0 lakhs
• Simple payback - 10 months

Cement Process

Raw Materials The main raw materials used in the cement manufacturing process are limestone, sand, shale, clay, and iron ore. The main material, limestone, is usually mined on site while the other minor materials may be mined either on site or in nearby quarries. Another source of raw materials is industrial by-products. The use of by-product materials to replace natural raw materials is a key element in achieving sustainable development. Raw Material Preparation Mining of limestone requires the use of drilling and blasting techniques. The blasting techniques use the latest technology to insure vibration, dust, and noise emissions are kept at a minimum. Blasting produces materials in a wide range of sizes from approximately 1.5 meters in diameter to small particles less than a few millimeters in diameter. Material is loaded at the blasting face into trucks for transportation to the crushing plant. Through a series of crushers and screens, the limestone is reduced to a size less than 100 mm and stored until required. Depending on size, the minor materials (sand, shale, clay, and iron ore) may or may not be crushed before being stored in separate areas until required. Raw Grinding In the wet process, each raw material is proportioned to meet a desired chemical composition and fed to a rotating ball mill with water. The raw materials are ground to a size where the majority of the materials are less than 75 microns. Materials exiting the mill are called "slurry" and have flowability characteristics. This slurry is pumped to blending tanks and homogenized to insure the chemical composition of the slurry is correct. Following the homogenization process, the slurry is stored in tanks until required. In the dry process, each raw material is proportioned to meet a desired chemical composition and fed to either a rotating ball mill or vertical roller mill. The raw materials are dried with waste process gases and ground to a size where the majority of the materials are less than 75 microns. The dry materials exiting either type of mill are called "kiln feed". The kiln feed is pneumatically blended to insure the chemical composition of the kiln feed is well homogenized and then stored in silos until required. Pyroprocessing Whether the process is wet or dry, the same chemical reactions take place. Basic chemical reactions are: evaporating all moisture, calcining the limestone to produce free calcium oxide, and reacting the calcium oxide with the minor materials (sand, shale, clay, and iron). This results in a final black, nodular product known as "clinker" which has the desired hydraulic properties. In the wet process, the slurry is fed to a rotary kiln, which can be from 3.0 m to 5.0 m in diameter and from 120.0 m to 165.0 m in length. The rotary kiln is made of steel and lined with special refractory materials to protect it from the high process temperatures. Process temperatures can reach as high as 1450oC during the clinker making process. In the dry process, kiln feed is fed to a preheater tower, which can be as high as 150.0 meters. Material from the preheater tower is discharged to a rotary kiln with can have the same diameter as a wet process kiln but the length is much shorter at approximately 45.0 m. The preheater tower and rotary kiln are made of steel and lined with special refractory materials to protect it from the high process temperatures. Regardless of the process, the rotary kiln is fired with an intense flame, produced by burning coal, coke, oil, gas or waste fuels. Preheater towers can be equipped with firing as well. The rotary kiln discharges the red-hot clinker under the intense flame into a clinker cooler. The clinker cooler recovers heat from the clinker and returns the heat to the pyroprocessing system thus reducing fuel consumption and improving energy efficiency. Clinker leaving the clinker cooler is at a temperature conducive to being handled on standard conveying equipment. Finish Grinding and Distribution The black, nodular clinker is stored on site in silos or clinker domes until needed for cement production. Clinker, gypsum, and other process additions are ground together in ball mills to form the final cement products. Fineness of the final products, amount of gypsum added, and the amount of process additions added are all varied to develop a desired performance in each of the final cement products. Each cement product is stored in an individual bulk silo until needed by the customer. Bulk cement can be distributed in bulk by truck, rail, or water depending on the customer's needs. Cement can also be packaged with or without color addition and distributed by truck or rail.

Installation of High Efficiency Dynamic Separator for Raw Mill

Background

The Raw Mill is one of the important equipment in the Cement industry used for grinding Limestone into fine raw meal powder. The older plants had Ball Mills for this operation.

Consequently the energy efficient Vertical Roller Mills ( VRM ) came into being. The VRMs have comparatively 30 – 35 % lower energy consumption than the Ball Mills. In the older Cement plants the VRMs had a simple static separator installed for separation of the coarse and fine material. The separator was an integral part of the VRM.

In the conventional separators, the ground material is lifted to the separator by high velocity hot air at the louvres. The separator separates the coarse and fine particles and fine particles are carried away by the airflow to the dust collectors. The coarse material subsides through the raising freshly ground material. This creates additional pressure drop in the VRM and also leads to increased circulation inside the Mill. The particle size distribution is also wider with both very fine and coarse particles present.

The latest trend has been to install cage type high efficiency separator. In these separators, the material enters radially through a cage type separator. The coarse material after separation is collected in a cone just below the separator and is dropped on to the grinding table through a gravity air lock. In this manner the contact between the freshly ground material and the coarse is avoided. The advantages of these separators are as below.

Closer particle size distribution

Less pressure drop across the VRM

Higher output at the same fineness as before or finer product at the same output rate

Previous status

In a million tonne dry process pre-calciner plant, a Vertical Roller Mill ( VRM ) was being used for grinding raw meal. The VRM had a conventional static separator.

Energy saving project

The existing static separator was replaced with a new cage type dynamic high efficiency separator.

Implementation methodology & time frame

The new separator could not be accommodated in the Mill body. So the Mill casings were modified to accommodate the new separator. Hence, to save on time the drawings were prepared and the new separator assembled outside and kept ready for installation.

With all these preparations, the actual installation needed only 21 days of Mill stoppage.

Benefits of the project

There was an increase in the output of the Mill , finer product and reduction in the specific power consumption of the Mill. Additionally, the Mill vibration also got reduced resulting in trouble free operation. The comparison of the conditions and the power consumption before and after installation of the dynamic high efficiency separator are as below:

Parameter	Before Implementation	After Implementation
Feed Rate	200 TPH	225 TPH
Raw Meal Residue
• 90 Microns	18 – 18.5 %	17 – 18 %

• 212 Microns	2.2 – 2.5 %	2.0 – 2.2 %
Mill DP	500 – 520 mmWg	480 – 500 mmWg
Mill Vibration	1.6	0.75
Power Consumption	24.5 units / ton	22.0 units / ton

The power saving amounted to 2.5 units / ton of Raw meal or 3.0 units / ton of Cement which annually amounted to 18 lakh units / year.

Financial analysis

This amounted to an annual monetary saving (@ Rs 3.0 /unit) of Rs 54.0 lakhs. The investment made was around Rs 60 lakhs. The simple payback period for this project was 13 months.

Benefits of high efficiency separator

Closer particle size distribution

Low pressure drop across VRM

Higher output at same fineness (or) same output with finer product.

Cost benefit analysis

Annual Savings - Rs. 54.0 lakhs

Investment - Rs. 60.0 lakhs

Simple payback - 13 months

TECHNOLOGICAL ADVANCEMENTS IN INDIAN CEMENT INDUSTRY

The Indian cement industry is the second largest producer in the world comprising of 130 large cement plants and 206 operating mini cement plants consisting 13 rotary kiln plants and 193 VSK plants. The installed capacity and production during the year 2006-07 are expected to be 180 mn.t and 162 mn.t respectively.

Modernization and technology up-gradation is a continuous process for any growing industry and is equally true for the cement industry. The Indian cement industry today is by and large comparable to the best in the world in respect of quality standards, fuel & power consumption, environmental norms, use of latest technology and capacity. The productivity parameters are now nearing the theoretical bests and alternate means, like alternate fuels and raw materials have to be found to ensure further improvement in productivity and reduce production costs.

Cement industry being energy intensive, the energy conservation and alternate cheaper, renewable and environmentally friendly sources of energy have assumed greater importance for improving productivity. The major challenges confronting the industry today are raging insecurity in indigenous fuel availability, perennial constraints like higher ash content, erratic variations in quality of indigenous coal and inconsistent power supply with unpredicted power cuts. Keeping these challenges in view, the efforts by the industry towards energy conservation and finding alternate cheaper, renewable and environmentally friendly sources of energy are given utmost importance.

Review of Technological Status

Process Profile

The Cement Industry today comprises mostly of Dry Suspension Preheater and Dry-Precalciner plants and a few old wet process and semi-dry process plants. Till late 70’s the Cement Industry had a major share of production through the inefficient wet process technology. The scenario changed to more efficient large size dry process technology since early eighties. In the year 1950, there were, only 33 kilns out of which 32 were based on wet process and only one based on semi-dry process. Today, there are 162 kilns in operation out of which 128 are based on dry process, 26 on wet process and 8 on semi-dry process.

Changing Process Profile of Indian Cement Industry

Item	1950	1960	1970	1983	1995	2001	2006
Wet Process Number of Kilns	32	70	93	95	61	32	26
Capacity (TPD)	9151	25011	38441	39641	25746	13910	11420
% of Total	97.3	94.4	69.5	41.1	12	5	3
Dry Process Number of Kilns		1	18	50	97	117	128
Capacity (TPD)		300	11865	51265	188435	282486	375968
% of Total		1.1	21.5	53.2	86	93	96
Semi-Dry Process Number of Kilns	1	3	8	9	8	8	8
Capacity (TPD)	250	1200	5000	5500	5244	5260	4195
% of Total	2.7	4.5	9	5.7	2	2	1
Total Kilns	33	74	119	154	166	157	162
Capacity (TPD)	9401	26511	55306	96406	219425	310706	391583
Average Kiln Capacity (TPD)	285	358	465	626	1322	1921	2417

Kiln Capacity and Size

The economic unit capacity for cement plants in India till early sixties was about 300 TPD. In mid sixties this was standardized at around 600 TPD for both wet and dry process plants. About a decade later, i.e. from mid seventies, the new plants installed were of 1200 TPD capacity. The advent of precalciner technology in mid eighties provided an opportunity to the industry to modernize and increase the capacity of existing dry process plants, to convert plants from wet to dry process as well as to set up large capacity plants incorporating the latest technological advancements. This led to installation of single line kilns of 3000 TPD (1 MTPA) capacity and more. The present trend indicates the preference of still larger kilns of about 6000 TPD capacity and above. Already there are nine kilns of 8000 tpd capacity in operation and three kilns of capacity 10000 – 12000 TPD are under installation. The green-field plants being installed now are based on most advanced and the best available technology.

Plants with a total capacity of two million tonne and above at a single location, numbering 25, are having a total capacity of 65.6 MTPA accounting for 41% of installed capacity of large plants, whereas plants with a capacity between 1 to 2 million tonnes, numbering 48 are having a total capacity of 68.4 MTPA, accounting for 43% of installed capacity. Balance 57 plants are of capacity less than 1 MTPA, having a total capacity of 25.8 MTPA, accounting for 16% of total installed capacity of large cement plants.

Average annual installed capacity per plant in India is about 1.2 MTPA as against more than 2.1 MTPA in Japan. This is due to blend of small and large plants coming up at various stages and still operating in India as against smaller plants having been decommissioned in Japan.

Present Status of Technology

A comparison of the status of the modernization in equipment and also the technologies absorbed or implemented by the Indian cement industry alongwith status of Global Technology is as under :

Present Status of Technology

	Low Technology Plants	Modern Plants	Global Technology
Mining & Material Handling	Conventional	Computer aided	Computer aided
Crushing	Two stage	Single stage	In-pit crushing & conveying
Conveying of Limestone	Dumpers/Ropeway/ Tippers	Belt conveyors	Pipe conveyors, Belt conveyors
Grinding	Ball Mills with / without conventional classifier	VRM’s Roll Presses with dynamic classifier	VRM’s, Roll Presses, Horo Mills with dynamic classifier
Pyro Processing	Wet Semi Dry Dry - 4 stage preheater - Conventional cooler - Single channel burner	Dry - 5/6 stage preheater - High Efficiency Cooler - Multi Channel Burner	Dry - 6 stage preheater - High Efficiency Cooler - Multi Channel Burner - Co-processing of WDF - Co-generation of power - Low NOx/SO2 emission technologies
Blending & Storage	Batch-Blending Silos	Continuous Blending silos	- Continuous Blending - Multi-Chamber Silos - Dome silos
Packing & Despatch	Bag	- Bag - Bulk	- Bulk - Palletizing & Shrink Wrapping
Process Control	Relay Logic / Hard Wired / PLC	- DDC - Fuzzy Logic expert system	- DDC - Neurofuzzy expert system
Plant Size, TPD	300-1800	3000-6000	6000-12000

The directions in which the modernization activities are proceeding are as illustrated below :

Mining

For rational exploitation of the raw material source, a systematic mine plan is developed by cement plants. Computer-aided techniques for raw material deposit assessment to arrive at proper extraction sequence of mining blocks, keeping in view the blending operational requirements, are envisaged and put to use in number of units.

Crushing

Mobile crushers have come in use in some of the newer plants, keeping in view the split location of limestone deposits and long conveying distances. The mobile crushing plant is stationed at the mine itself and raw material is crushed at the recovery site.

Grinding

Vertical Roller Mills (VRM) have given the real breakthrough in the area of grinding. The VRM draws 20-30 % less electrical energy as compared to the corresponding ball mill system, apart from its ability to give much higher drying capacity. These mills can accept larger feed size and hence mostly be used with single stage crushing. VRMs are now being used in clinker and slag grinding and also as pre-grinder to existing grinding installations.

Another breakthrough that has come with the application of high pressure grinding rolls (HPGR) has been widely adopted in Indian cement industry. The HPGR is being used as pre-grinder for upgrading the existing ball mill systems. Different modes of operating HPGR in open circuit, pretreatment with circulation, pretreatment with de-agglomeration and recirculation and closed circuit are in operation. Such installations could achieve an increase in capacity upto 200% and savings in power consumption to the extent of 30 to 40% as compared to ball mills.

High efficiency separators are now widely used for better classification of product and help in increasing the mill capacity besides reducing the specific power consumption. The new classifier designs include two stage separation integrating primary and secondary separation. High efficiency separators are also used now with VRM’s for further improvement in their performance.

A new mill system called Horizontal roller mill has been developed which is capable of producing uniform raw meal and have advantages in processing raw materials containing higher percentage of quartz.

Pyro-processing

The introduction of precalciner technology has increased the production from the kiln by 2.0 to 2.5 times and enabled utilization of high ash coals with lower calorific value, as well as various agricultural and industrial combustible wastes. Systems have been developed to use fuels like lignite and petcoke and various alternate fuels.

The advantages of economy of scale are fully exploited by the cement industry through the precalciner technology. Many single kilns capable of producing more than 6000 tpd capacity have already been installed and are operating with state-of-the-art technology and kiln capacities in the range of 10000-12000 tpd are under installation.

Many cement plants have some excess capacity at both upstream and downstream, which could be utilized economically if the kiln output can be increased at modest costs. Traditionally, the kilns have been designed with specific volumetric loading of 1.5 to 2.2 tpd/m³ for SP kilns and 3.0 to 4.0 tpd/m³ for precalciner kilns. The corresponding thermal loads in burning zone for such kilns have remained between 3.5 to 4.5 x 10⁶ Kcal/m²/hr. Many cement plants have gradually increased the specific volumetric loading upto 7-7.5 tpd/m³, ensuring much higher than originally designed output.

The introduction of high efficiency and low pressure-drop-cyclones have led to conversion of conventional 4-stage cyclone preheaters to 5-stage and even 6-stage cyclone preheaters with improved thermal efficiency.

The latest development like controlled flow grate clinker cooler system and cross bar cooler ensure better clinker distribution, increase in cooler heat recuperation efficiency, decrease in clinker exit temperature and reduced maintenance costs.

The limitations of the conventional straight pipe burner have been overcome by use of highly flexible multi-channel burner. The multi-channel burner enables easy and sensitive flame shape adjustments as well as gives rise to better entrainment of secondary air.

High Alumina refractory bricks which were mostly used in pre-heating / precalcining zone in the past, are now replaced by light weight high strength insulating bricks. The Aluminum-Zirconium-Silicate bricks with coating repellent properties are also in use now in transition zones. With the new improved refractory bricks it is possible to increase the refractory lining life and reduce the radiation losses in the kiln. Greater use of monolithic refractories in preheater, precalcinator, cooler, kiln outlet zone etc. is in practice now.

Conventional analog instrumentation is gradually being replaced with digital instrumentation. The large mimic diagrams used of late are being replaced by cathode ray tube (CRT) display. Motor control by relay sequence is being changed to programmable logic controllers. Analog PID controllers are being replaced with multi-loop digital controllers. Due to the advent of microprocessors, a variety of advanced control concepts like adaptive control, self-tuning control, feed forward control, etc. have been introduced in the Indian cement industry.

As a corollary to automation, quality is also maintained by continuous monitoring of the raw mix composition with the help of X-ray analyzer and automatic proportioning of raw mix components. New type of on-line bulk material analyzers have also been developed based on Prompt-Gamma-ray Neutron Activation Analysis (PGNAA) for giving maximum control over raw mix. The analyzer quickly and reliably analyses the entire flow-on-line providing real time results. The latest trends in on-line quality control include computers and industrial robots for complete elemental analysis by X-ray fluorescence, on-line free lime detection and particle size analysis by latest instrumental methods and x-ray diffraction techniques respectively.

It is also important to phase out the manual sampling systems especially so when the super high capacity plants are being installed. Auto sampler technology should be dovetailed into the plants for ensuring disciplined sampling and control.

Upgradation of Technology of Low Technology Cement Plants

The technological spectrum in the industry is very wide. At one end of the spectrum are the old wet process plants, while at the other end, are the new state-of-the-art technology plants presently being built by the Industry. In between these two extremes, are the large number of dry process plants built during the period 1965-90. These plants could not fully modernize or upgrade side by side with advent of newer technologies and had thus remained at intermediate technology level. Also, the level of technology is not same at all the plants built during the same period.

Majority of the cement plants in the country in the capacity range of 0.4 to 1.0 MTPA were set up more than 15-20 years ago i.e. before 1990’s. They were based on state-of-art technology at that time. Since then, numerous developments have taken place in the cement manufacturing technology.

Though some of the old plants have been modernized to a limited extent by retrofitting the new technologies, substantial scope still exists for adopting the state-of-art technologies and bringing the old plants at par with world-class plants in terms of productivity, energy efficiency and environment friendliness, leading to cost competitiveness.

Moreover, the emission norms are likely to become more stringent in future and at the same time, the cement plants will be required to utilize waste derived raw materials and fuels to a large extent. The modifications of old plants to comply with these future requirements will also become inevitable. Therefore, there is a need to carry out a comprehensive assessment of all the earlier generation plants in the country to identify the extent of modernization required to improve their all round efficiency and enable them to meet the future criteria of viability, competitiveness and compliance with regard to energy consumption enabling them to comply with the provision of the Energy Conservation Act 2001.

Perceived Benefits of Technology Upgradation

It is envisaged that the technology upgradation measures for the Pre-1990 era cement plants would result in :

Increase in capacity : 25-30 MTPA

Reduction in thermal energy consumption : 15-20 kcal/kg clinker

Reduction in electrical energy consumption : 5-10 units/t

Reduction in cost of production of cement : 5-10% because of above initiatives

Reduction in energy costs through co-processing : 10–15%

Reduction in the CO₂ emissions : 20%

(through blended cements & energy conservation)

Future Modernization Needs of the Indian Cement Industry

Although the industry has largely set up plants with energy efficient equipment, there are still some areas for further improvements like:

Appropriate pre-blending facilities for raw materials

Fully automatic process control and monitoring facilities including auto samplers and controls.

Appropriate co-processing technologies for use of hazardous and non hazardous wastes

Interactive standard software expert packages for process and operation control with technical consultancy back-up

Energy efficient equipment for auxiliary/minor operations

Mechanized cement loading operations, palletization/shrink wrapping

Bulk loading and transportation, pneumatic cement transport

Low NO_x/SO₂ combustion systems and precalciners

Standards for making composite cement so that all the flyash and other industrial wastes viz. slag are fully used.

Co-generation of power through cost-effective waste heat recovery system (only one demonstration unit in operation)

Horizontal roller mills (Horo Mills) for raw material and cement grinding

Advanced computerized kiln control system based on artificial intelligence

Fuel Requirements and Alternate Sources of Energy

Fuel

Coal continues to be the main fuel for the Indian cement industry and will remain so in the near future as well. The industry is mainly using coal from various coalfields in the country. It is also procuring coal through open market and direct imports. Lignite from deposits in Gujarat and Rajasthan is also being used by cement plants. Pet coke has also been successfully utilized by some cement plants, mainly in Gujarat, Rajasthan and MP, thereby substituting main fossil and conventional fuel coal upto 100% in some plants. In the recent past, waste derived fuels including hazardous combustible wastes have also been tried due to economic pressures in cement manufacturing process owing to tough competition in domestic and global markets as well as ecological reasons on account of waste disposal and co-processing in cement rotary kilns being most effective mode of waste treatment.

Use of Industrial Wastes

i) Cement plants in India utilized about 19% of flyash generated by power plants and 100% of granulated slag generated by steel plants (year 2005-06), as compared to almost 100% flyash and 84% of granulated slag in the Japanese cement industry.

ii) Recycling of Industrial wastes in manufacture of cement is highest in Japan followed by India.

Use of Alternate Fuels

i) Use of hazardous and refuse derived combustibles and Municipal Solid Waste (MSW) as fuel is common in countries like Canada, EU, Japan and Korea, but regulations do not yet permit in India.

ii) CPCB is actively engaged in plant level trials in respect of wastes viz. used tyres, refinery sludge, paint sludge, Effluent Treatment Plant (ETP) sludge and Toluene Di-Isocyanite (TDI) tar waste from petroleum industries and in formulation of guidelines for use of these wastes as fuel by cement industry.

Energy Management

The industry’s average consumption in 2005-06 was 725 kcal/kg clinker thermal energy and 82 kWh/t cement electrical energy. It is expected that the industry’s average thermal energy consumption by the end of Year 2011-12 will come down to about 710 kcal/kg clinker and the average electrical energy consumption will come down to 78 kWh/t cement.

The best thermal and electrical energy consumption presently achieved in India is 667 kcal/kg clinker and 68 kWh/t cement which are comparable to the best figures of 650 kcal/kg clinker and 65 kWh/t cement in a developed country like Japan.

The improvements in energy performance of cement plants in the recent past have been possible largely due to :

Retrofitting and adoption of energy efficient equipment

Better operational control and Optimization

Upgradation of process control and instrumentation facilities

Better monitoring and Management Information System

Active participation of employees and their continued exposure in energy conservation efforts etc.