Energy services, Electrical Energy Conservation, Electrical energy audits, Energy Conservation Cement and allied process plants,

Energy Conservation by Power Optimisation in Cement and Allied Process Plants

by E.G. Shankar Managing Director, AGS - Energy Conservation Pvt. Ltd., and CEO-Energy Services Group

In India, the cost of commercial energy is generally high compared to several other countries in the world. Mr. Shankar has to his credit of saving electrical energy through 'zero cost' method, particularly in cement industry. He is also creating awareness for energy conservation through Power Optimisation. - Editor

In any product manufacture, the principal cost is the 'energy cost*, which comprises the power and fuel cost. In India, he cost of commercial energy is generally high compared to several other countries in the world due to spiraling costs and ever increasing taxes and duties. The management has no control over them. However, the management can minimize energy costs by 'energy conservation', which has now become the holy word and panacea for all ills. The management is fully aware of technological developments and the use of computers for the efficient monitoring and on-line control.

For the 'electrical energy conservation', the first step is "energy audit" to find out the actual utilization of electrical power and also to know the scope for Power Optimization without any investment. For Power Optimisation fine-tuning of the voltage (v), current (c) and power factor (PF) are required. The relationship between V, C and PF is complicated and iterative. This makes fine-tuning the system a time consuming exercise. Energy audit is a physician's job and fine-tuning is that of the surgeon gifted with varied experience and exceptional skills

Energy conservation is the wise and effective use of energy that demands efficient, economical and careful use of energy by minimizing wastage. To know the present operating conditions and utilization of energy a detailed data has to be collected, measured and analyzed. This in turn indicates the methods for improving the efficiency of electrical equipment. Power Optimization is also one of the methods of energy conservation that can be done without any investment where On Load Tap Changer (OLTC) facility is provided on the incoming main transformers. All the cement plants have On Load Tap Changer (OLTC) facility and the saving can be achieved without any further investment.

Power Optimisation:

Power Optimisation is utilizing the power to the maximum extent by monitoring operational load parameters of the entire plant. To arrive at the optimum voltage at which the power losses are minimum "Short Term Tests" have to be conducted. These tests are useful to find out the optimum voltage at different sections, individual HT motors so that the final optimum voltage at the main incoming transformer secondary could be arrived. The Power Optimisation can be done, by studying all the equipments in the entire plant and finding-out the common acceptable voltage for minimum consumption. Voltage control helps improvement of efficiency to its design maximum value and also improves power factor.

During 1990-91, while the Power Tariff was frog leaping, a lot of research studies were carried out to identify the saving potential due to voltage reduction to suit the operating conditions of the drive motors. Any research study will yield fruitful results only when implemented successfully. The technical staff,who from their (limited) experience would have some predetermined assumptions, have to be convinced that there is scope for reduction in power and hence cost savings.

"Process Optimisation" has been in practice in recent years, where as 'Power Optimisation' has not been fully practiced, though it could be practically achieved with 'zero cost'. This decades old concept is corning to the light and is being appreciated but slowly. It may take another decade for technocrats in general to get fully acquainted with the uppermost need for Power Optimization. Until that time, an industry may be loosing about 5% of overall power that would be vanishing in thin air as heat / wastage.

Principle of Power Optimisation:

Induction motor has poor efficiency and low power factor (PF) at lightly loaded condition even when it has an energy efficient design. Many induction motors operate at below 50% load for a significantly long duration, whereas replacement by lower capacity motors may not be viable, as the motors would be required to take a full load occasionally. By scientific method, the optimum voltage at different sections of the plant can be found. Optimum voltage operation helps improvement in both efficiency and power factor. Four essentials for Power Optimisation are:

Knowledge about Power Optimisation

Dedicated engineers for monitoring the operational load parameters regularly

Accurate portable measuring instruments for monitoring the load parameters

Overall vision of the operational load parameters to identify any bottleneck that may come in the way of Power Optimisation and persistence to achieve results.

With all the above four essentials, expertise and modern digital measuring, tools for measuring the energy conservation by Power Optimisation can be achieved within a scheduled time frame at 'zero cost' to the client.

Detailed electrical energy audit is the first step for Power Optimization. The audit report indicates the saving potential by Power Optimisation. After Power Optimization, the energy saving can be noticed clearly from:

The daily / monthly power consumption reports

Units / hour consumption

Instantaneous changeover from the tuned parameters to earlier parameters

Power Optimisation improves low load efficiency:

At low load copper, loss is small but the core loss is constant. Core loss is proportional to the square of the voltage at constant frequency. By decreasing the supply voltage, core loss can be decreased significantly so that the efficiency improves. At low voltage, magnetizing component of the stator current decreases and therefore power factor also improves.

A three-phase induction motor has an optimum value of slip at which its efficiency is maximum and it is possible to operate the motor always at this slip by controlling the applied voltage except when the load is closer to the rated one.

With the existing facilities of the plant, energy consumption can be reduced by about 5-7% just by fine-tuning the operational load parameters, which is called "Power Optimisation". As Power Optimisation does not require any investment for achieving the saving, it is called a zero cost method. It has been identified very good potential for electrical energy conservation by zero cost method. The measures to be taken to ascertain the quantum of energy conservation by Power Optimisation are:

Measurement of the running load parameters of all the individual motors

Measurement of HT and LT incomer and distribution network branch loads

Measurement of incoming and outgoing of power transformer load parameters

Study of capacitor distribution for uniform power factor.

Generally continuous process plants drive motors are oversized during the design to take care of any deviations that may defer from the calculations. Once the plant has been commissioned, the oversized motors cause lower efficiency. It is also not practicable to fix all motors to the rated design for high efficiency.

In some plants, the higher rated motors have been replaced by smaller capacity ones to achieve saving by increasing the percentage load on the motor and its efficiency. But in most cases with materials handling equipment viz., belt conveyors, elevators, screw conveyors, one is forced to revert back to original designed motor as the reduced size of the motor was not able to meet the starting torque requirement of the loaded conveyor.

Without replacing with a smaller capacity motor, the efficiency can be improved by effectively tuning the load parameters to the optimum. This has to be done by closely monitoring the characteristics and running load parameters of all the motors in the network distribution. Tuning the load parameters to the optimum reduces energy consumption considerably and also results in prolonged life of the machinery.

Benefits of Power Optimisation:

Considerable amount of energy conservation

Power factor improvement

Improves the life of motors, switch-gear

Noticeable reduction in electrical breakdowns / stoppagesand improved reliability

Conclusion:

Power Optimisation can be done without any investment where automatic OLTC is provided on the incoming main transformer. Optimizing the load parameters reduce energy consumption of the overall plant by about 3-5%. Power Optimization yields full results when implemented by scientific method. Power Optimisation minimizes energy wastage. Due to reduction in energy wastage, the machinery life also increases.