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close this bookJournal of the Network of African Countries on Local Building Materials and Technologies - Volume 3, Number 4 (HABITAT, 1995, 46 p.)
View the document(introduction...)
View the documentThe aim of the network and its journal
View the documentForeword
View the documentEnergy efficiency in the production of building materials*
View the documentEnergy conservation for cost reduction in Indian cement industry - NCB's initiatives*
View the documentEnergy efficient method of portland slag cement grinding**
View the documentPlant audit and energy management***
View the documentEvents
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Energy conservation for cost reduction in Indian cement industry - NCB's initiatives*

*By J. P. Saxena, Ashwani Pahuja, Pradeep Kumar, National Council for Cement and building materials, New Delhi. This paper was presented to the third National Council for Cement and Building Materials (NCB) International Seminar on Cement and Building Materials, held in January 1991 in New Delhi, India.

SYNOPSIS

The price of energy is a major component of the cost of cement production, being as high as 60 per cent in some of the cement plants. In today's context of energy shortages and its rising prices, energy conservation has assumed high priority in reducing production costs. The paper discusses the initiatives taken by NCB towards energy conservation and cost reduction in cement plants which include energy audit studies with the help of Mobile Energy Diagnostic Unit (MEDU), encouraging use of incentive schemes, energy monitoring, power system management and motivating competitive improvements. The paper also highlights the salient features of MEDU which has proved to be an effective tool for quick on the spot assessment of energy-use pattern with the help of on-board computer process and electrical parameters and brings out some of the case-studies carried out by NCB which has resulted in saving off energy and reduction in the cost of cement production.

1. INTRODUCTION

During the last few years, there has been an increase in cost of production as the prices of various forms of energy viz. thermal and electrical, which constitute a major component of cost of cement production. This coupled with acute shortage of power and reasonable quality fuels has compelled decision-makers in the industry to examine and find new ways and means for energy conservation by minimizing energy wastage and achieving cost reduction in cement manufacture.

Cement Industry in India has followed the principle of co-existence by old and new cement plants and is in a unique situation wherein more and more large capacity plants, have been installed. These plants use dry process with preheaters and precalcinators, but the old wet and semi-dry process plants as well as small vertical shaft kiln plants are also existing simultaneously playing their complementary roles in meeting the country's demand for cement. The industry has been apt to adopt technological developments and upgradings and most of the new installations are coming up with energy efficient systems and equipment. The problem of high ash and variable quality of coals, inconsistent power supply, low grade raw materials, harder to grind raw materials and coals have become part of normal operations in cement plants and results in high energy consumption. Comprehensive approach is necessary to reduce the energy consumption.

2. NCB'S INITIATIVES FOR ENERGY CONSERVATION AND COST REDUCTION

Keeping in mind the various problems of the cement industry, NCB has taken some initiative to reduce the energy consumption levels (Figure 1). These include both short-term and long-term measures and some of these are discussed below.

2.1 Energy

Energy audit has emerged as an important tool for identification, analysis, implementation of energy conservation measures and energy management. The importance of energy audit studies was realized in early 80's when NCB in collaboration with Bureau of Industrial Costs and Prices (BICP) made a survey of 46 cement plants in the country identifying the status of energy consumption levels, potential areas for energy saving and recommendations for short, medium and long-term measures. Subsequently the Advisory Board on Energy (ABE) commissioned NCB to carry out detailed energy audit of six representative cement plants. NCB has since then completed 22 more energy audit studies in cement plants under its own R&D programme as well as studies sponsored by the industry.

Energy audit studies has shown that 'prevention of false air infiltration' (Figure 2) has the maximum impact on the energy savings by operational control in plants. This factor alone has been identified to have about 64 per cent of the total potential thermal and about 35 per cent of the total potential electrical energy cost savings in the plants studied. Process optimization, reducing the preheater exit gas temperature and waste heat utilization are other important areas of thermal energy savings (Figure 3). Reducing the free running of machines and underloading of motors has emerged as one of the most important factors in saving the electrical energy cost. Other factors of saving electrical energy costs as found out from NCB studies are power factor improvement and retrofitting of energy efficient systems.

2.2 Mobile Energy Diagnostic Unit (MEDU)

NCB has taken initiative in modernizing the techniques for energy audit to serve the needs of the industry. NCB's MEDU, a unique facility not only in the cement industry but in the country, is equipped with latest and sophisticated facilities for faster and accurate energy audit studies with various hardware and software capabilities. The MEDU carries out energy data analysis at site including preparation of action plans, calculation of specific energy consumption in each section, target setting and monitoring, calculation of power factor and load factor of the plant, identification of locations of leakages of compressed air and the heat balance of kiln circuit (figure 4).

The instrument facilities in the MEDU measure parameters such as temperature; radiated heat from surfaces; O2, CO2 and CO quantity in gases; ambient humidity; gas velocity; leaks in high pressure lines; voltage, current, kW, kVA, power factor and luminous intensity etc. Apart from the above instruments for instantaneous value measurement, continuous monitoring and recording facilities are available with the microprocessor-based equipment. The on-board computer is equipped with necessary system and application software for real-time data logging and quick data analysis at site.

2.3 Incentive Schemes

NCB has been a prime actor in motivating the plants to take right steps in energy conservation. Based on the techno-economic feasibility of the energy efficient schemes through energy audits, some of the cement plants have already availed the benefit of the incentive schemes from the financial institutions for energy audit and have secured loans for installation of energy efficient equipment. These initiatives have brought out encouraging results.

2.4 Monitoring Energy Use

Having realized the need for monitoring energy use, NCB has brought out Guide Norms for Cement Plant Operations which provide norms for energy usage in various sections of the plant, besides the operational norms. The norms have been in use in cement plants extensively for evaluating the performance of a given section and identifying the areas of improvement.

NCB jointly with DCCI is monitoring the energy use data and has already analyzed the data of 80 cement plants for the year 1988-89. The analysis made by NCB has brought out the specific energy consumption levels of the industry, process and at the regional level; status of energy consumption levels in each section for dry and wet process plants; comparison of these levels with NCB operational guide norms; effect of coal quality on the specific energy consumption in the plant and energy cost trends, process and at the regional level.

Based on the analysis, NCB has also identified plants pertaining to different processes for detailed energy audit studies where either thermal or electrical energy consumption or both have been found to be on the higher side.

2.5 Energy Information System

NCB studies of various cement plants reveal that systematic recording of the data does not exist and there is a need for developing comprehensive data-base keeping in view the ultimate objectives. The data-base thus created would be helpful for individual units as well as for inter-firm comparison and identifying the real problem areas. Keeping the above in view NCB is currently engaged in developing an appropriate computerized energy information system for the Indian Cement Industry. Such an information system shall greatly help in identifying thrust areas, making right decisions at various levels and formulation of policy guidelines.


Figure 1. NCB's initiatives for energy conservation and cost reduction


Figure 2. False air infiltration in kiln section


Figure 3. Impact of areas of energy saving in the potentials of energy savings


Figure 4. Salient features of a mobile energy diagnostic unit

2.6 Power System Management

NCB has developed a comprehensive system for management of power in the cement plants (Figure 5) which includes a software for improvement of load factor through optimized load scheduling thus maximizing the use of available grid power from the electricity board and captive power installed in the plant. Various inputs to the software include grid and captive power availability, power tariff, quality of power, KW load on each equipment in the plant and other operational aspects. The output from the software includes running schedule of each machine at any hour during the day. The software assists in improvement in load factor, reduction in monthly maximum demand, improvement in overall energy efficiency and better production planning.

2.7 Motivation for Competitive Improvement in Energy Performance

NCB realized the need for creating awareness and motivation in cement industry for competitive improvement in energy performance and instituted National Award for Energy Efficiency in Indian Cement Industry in 1986-87 to be given away annually in recognition to the efforts for improving energy performance. The energy award has generated lots of interest and created motivation for energy conservation which is reflected from the analysis of data of the 20 plants which participated for energy award in all the three years from 1987-88 to 1989-90. It is seen that in case of dry process plants in the year 1989-90 as compared to 1987-88, the reduction in specific thermal energy consumption has been 2.4 per cent and in specific electrical energy consumption 7.5 per cent while in case of wet process plants the specific thermal energy consumption has decreased by 3.1 per cent with marginal reduction in specific electrical energy consumption (Figure 6). It is noted that the improvements in the performance of these plants have come as a result of operational control and optimization efforts, retro-fitting of energy efficient equipment, fixation of targets, upgradation of process control instrumentation and manpower training.


Figure 5. Module for power system management

NCB INITIATIVES - IMPACT AND ACHIEVEMENTS

The various steps taken in energy conservation such as energy auditing, monitoring the use of energy, creating an information base through energy information system, a systematic power system management and motivation through National Award for Energy Efficiency in Cement Industry have created a healthy structure for energy conservation efforts in the Indian Cement Industry.

The findings from the studies have been revealing and indicating substantial savings of money through both thermal as well as electrical energy savings. The potential annual savings in the various plants studied ranged from Rs 1 million to Rs 19.2 million in dry process plants and Rs 3.3 million to Rs 6.3 million in wet process plants (table 1).


Figure 6. Reduction in energy consumption


Figure 7. Energy and cost of savings by NCB energy audit studies in a 800,000 ton per year capacity plant

In a specific case of a large capacity of dry process cement plant (800,000 tonne/year), suggestions made by NCB were implemented by the plant which resulted in saving 8.5 kWh/t of cement of electrical energy and 27 Kca/kg clinker of thermal energy during the year 1989-90. The total saving of energy cost amounted to Rs 8.6 million that year (figure 7). These results were achieved through implementation of various suggestions made by NCB in different areas such as:

(i) NCB studies indicated false air infiltration in raw mill circuit up to 22 per cent. Plugging of leakages, maintaining optimum feed size, frequent regradation of grinding media, installation of slip power recovery system for raw mill vent fan resulted in overall reduction of about 2 kWh/t clinker.

(ii) Heat and mass balance of kiln circuit indicated 20 per cent false air in preheater string and 15 per cent false air in PC string. Plugging these leakages to the maximum extent and bringing down PC string exit gas temperature through making changes in raw meal and reducing coal firing in PC string resulted in a reduction of heat consumption by 2.6 per cent.

Plugging of leakages and installation of slip power recovery system for PH fan resulted in a saving of 2.5 kWh/t of clinker.

(iii) A significant reduction of electrical energy was achieved in cement mill and packing section by proper selection and frequent regradation of grinding media, prevention of leakages in compressed air lines. These efforts achieved a saving of 4 kWh/t of cement in this section.

(iv) Improvement of power factor resulted in reduction of electrical losses and maximum demand from 18560 KVA in 1988-89 to 16240 KVA in 1989-90.

CONCLUSION

In view of the complex situation, the Indian Cement Industry is confronted with various shortages and poor quality inputs, it is important to increase awareness for energy conservation. The right steps towards this direction would be effective monitoring, better operational control and introspection of energy saving opportunities through energy audit. This would enable the plant management to prioritize the various opportunities. The experience has shown that substantial cost savings can be achieved if the energy conservation efforts are rightly implemented.

ACKNOWLEDGEMENT

The authors have freely drawn upon completed R & D work/status reports of NCB and some of the unpublished work in NCB. This paper is being published with the permission of Director General, NCB.

Table 1. Expected cost savings due to identified potentials for energy saving



Potential Saving in Energy

Process

Plant Capacity (tpd)

Thermal (Kcal/kg cl.)

Electrical (kWh/t cement)

Potential Annual Savings (Rs. million)

Dry

4800

35.3

4.9

11.3

Dry

3000

5.8*

3.1*

3.894

Dry

2500

62

1.8

11.3

Dry

1800**

62.4

2.3

6.658

Dry

1500**

63.8

7.0

6.94

Dry

1800

211

18

19.25

Dry

1200

126.9

6.3

4.588

Dry

600

113

12

4.26

Dry

600

152

9.0

7.79

Dry

300

97.9

14.8

3.802

Dry

300**

71

0.5

1.078

Wet

1800

38

0.8

3.303

Wet

1200

149.5

1.9

6.27

* kWh/t Clinker
** Energy audit studies by Mobile Energy Diagnostic Unit (MEDU)