There is ample scope for reduction in both thermal and electrical energy consumption
Designers should pay attention to energy consumption implications while carrying out plant layout. Additionally, we recommend that clients consider the provision for waste heat recovery and alternate fuel use to bring down their non- renewable energy use, say Jayanta Saha, Director and Senior Consultant, and Suchismita Bhattacharya, Process Head, Penta India Cement and Minerals, sharing their views with ICR. Excerpts from the interview.
How energy- efficient is the cement industry in India?
The performance of the best cement plants in India are at par with the best in the world. In India, these modern plants coexist with older plants with lower capacities and obsolete technologies. The poor performance of some of the plants brings down the average. The average electrical energy consumption in India is around 97 kWh/tonne cement (OPC) whereas the best achievement is around 77 kWh/tonne cement (OPC). Similarly average thermal energy consumption is around 770 kcal/kg clinker whereas the best figures are around 680 kcal/ kg clinker. There is scope for reduction in both thermal and electrical energy consumption.
Which section/process in a cement industry has the highest scope for improvement in terms of energy efficiency?
The largest consumer of electrical energy is the grinding process and hence, it is grinding technology that has the highest scope for improvement. The correct choice of grinding equipment, proper system engineering, balancing of coupled circuits during operation are all necessary in the achieving the power savings that are promised by various vendors in the market today. This process is set for further improvement as vendors are developing better technology.
The thermal energy requirement of the pyro-processing system can be reduced by effective heat transfer in coolers which is an avenue for technological development.
Waste heat recovery from pre-heater and cooler vent gases can help recover some of the energy that was hitherto lost and improve the overall energy efficiency.
How much can an existing plant improve its energy efficiency through repair or a retrofit job?
The older plants with obsolete technology are poor performers with respect to energy consumption. Some plants still have SP kilns and consume more than 1050 kcal / kg clinker. In some plants, coolers based on old technology are causing cooler losses of about 130 kcal /kg clinker against modern coolers which have losses of only 95 kcal/kg clinker. Apart from that, some of the ball mills are not yet close-circuited while some plants are using old generation separators. In all such kinds of older plants, there is ample scope for improvement without major investments. The exact quantum of gain depends on the plant condition which should be evaluated by a proper process audit. It is obvious that a badly equipped plant can save more energy by retrofitting as compared to plants made timely investment keeping pace with the state of the art technology / equipment. We have helped to bring about reduction of electrical energy consumption of up to 25 per cent in some plants, and up to 20 per cent reduction of thermal energy consumption in others, by taking appropriate measures.
What kinds of energy saving measures/technologies do you recommend to your clients?
For greenfield plants at the design/engineering stage, we recommend that clients choose state- of- the- art technology which will give the best possible energy efficiency. Designers should also pay attention to energy consumption implications while carrying out plant layout. Additionally, we recommend that clients consider provision for waste heat recovery and alternate fuel use to bring down their non- renewable energy use.
For existing plants, the first step for achieving energy savings is carrying out a process audit of the plant. Based on the outcome of the audit, specific improvement areas can be identified and prioritised according to the client`s ability to make investments vis-a-vis expected benefits.
What is your outlook on the PAT scheme introduced by the Bureau of Energy Efficiency?
The PAT scheme in theory is a mandated energy management scheme which has benchmarked energy consumption for designated consumers and is now compelling these plants to undertake continuous improvement. However, its success remains to be seen.
Could you give us with examples where you helped cement companies reduce energy bills?
We are regularly carrying out process audits of plants in India, as well as overseas. Our target is not the reduction of energy bill per se; our thrust is on reduction of specific power consumption per tonne of product. For one of our clients, we were able to reduce thermal energy consumption by 70 kcal/ kg clinker by optimisation of operation alone. Further improvements will be achieved once the retrofits recommended by us are carried out. In another case, electrical energy consumption of the cement grinding circuit was reduced by 5 kwh/tonne cement by us by carrying out a thorough study of the system, identification and improvement of the bottlenecks and making the pre-grinder circuit functional.
Most Common Energy Drainers
- Overdesign of equipment/ motors/ fans which run on low efficiencies at their operating points.
- Low power factor, especially for older plants.
- Improper selection and design of compressed air supply systems.
- Ingress of false air or leakage of ambient air into the system.
- Material handling and transfer related losses due to improper layout.
- Running plants without optimising the various operation parameters.
- Control loops running in manual mode or absence of control loops in older plants.