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Reducing energy costs: The first steps (Part 1 of 6 in a series)

Rising energy costs are a worldwide concern and companies around the world are both complaining and appealing to their governments about these. Despite this, most companies have failed to carry out even the most basic actions to reduce their energy consumption.

It appears that many would rather talk the talk than walk the walk. This series shows that for many companies a simple walk around of the factory will reveal that processors are wasting a good percentage of the energy they purchase.

There are two ways to reduce the cost of energy

  • Reduce the amount paid for the energy (the euros or cents/kWhr approach).

  • Reduce the amount of energy used in the factory and the process (the kWhr/kg approach).

    The second approach is more productive because a kW saved is a total saving whereas a kW at a reduced price is only a partial saving.

    The plastics processing industry generally regards energy as a fixed and uncontrollable overhead cost. This is untrue. Energy is a variable and controllable cost and most processors can reduce energy usage by up to 30% and increase profits by up to 3% through management action, maintenance action, and intelligent investment. This series aims to show you the way forward. Instead of complaining about things that are mostly beyond your control, why don''t you actually take the actions within your control to reduce costs?

    Energy is a variable and a controllable cost. Before you can start to reduce your energy usage you need to understand where, when, why, and how much energy you are using.

    Where are you using energy?

    The main electrical energy users are motors and drives, heaters, cooling systems, and lighting. A simple site energy-distribution map will show where energy is being used. The site electrician generally can easily prepare one of these.

    If you are using a single meter it may be cost effective to use submeters to get further information on the areas of high energy use. Submetering allows you to start to calculate the cost of energy for each operation and to identify areas of high energy usage-a key factor in reducing energy costs. Produce an energy map of your site to locate areas for monitoring and possible improvement.

    When are you using energy?

    The time you are using energy is important, and a graph of demand versus time gives invaluable information on how to reduce your energy costs (see Box 1). Data for such a plot should be available from your energy supplier-look for unusual peak variations (spikes) and energy use during nonproduction periods (waste). These are potential areas for improvement.

    Why are you using energy?

    Energy use in plastics processing is a combination of two components:

    Total energy use = (production volume x SEC) + base load

    The SEC is Specific Energy Consumption and is a measure of the amount of energy used to process each kilogram of good finished product. This is an excellent benchmark figure to check competitiveness and to provide targets for improvement.

    The base load is incurred regardless of whether production is taking place or not-it does not change as output changes. This is the load used for heating, lighting, compressors, and pumps when you have no production at all.

    The best way to find the SEC and the base load is to record the meter readings (in kWh) and the related production volumes (in kg). Plot these (see Box 2) and find the equation of the best-fit line. The SEC is the slope of the line and the base load is the intersection of the line with the vertical axis (the energy use at zero production).

    There are two methods of reducing the total energy use:

  • Reduce the SEC to reduce the variable costs-this involves improving production efficiency and is something we should always be trying to do. No excuses allowed. Later articles in this series concentrate on this area.

  • Reduce the base load to reduce the fixed costs-this mainly involves switching something off and is a sure way to make savings because the energy used is not production related. Some examples are: idling machines, heaters running with no production, compressors running even as no production occurs, and so on.

    How much energy you are using?

    Electricity charges are based on a combination of factors and an initial survey will reveal areas for potential savings, sometimes actions as simple as changing the tariff can reduce costs at no cost! Hints for actions are given in the side bar.

    Start now!

    Energy management will save you money and make you more competitive. Start your energy management program today by discovering the source of the costs, making the users responsible for them and giving them the authority to reduce them. It will prove far more productive than simply complaining about rising energy costs!

    Key tips for reducing the cost of electricity

    Maximum Power Requirement is the maximum current a site can draw at the supply voltage without tripping the circuit breakers and cutting supply to the site.

    Reduce by:

  • Staggering startups.

  • Matching the MPR to the requirements.

  • Getting the MPR right for new premises.

    Maximum Demand is the peak current drawn at the supply voltage (generally over every

    half-hour). Reduce by:

  • Staggering start-ups.

  • Giving machinery time to stabilize before starting new processes.

    Power Factor is a measure of the phase shift created by machinery. Lightly loaded machinery tends to have a high phase shift, and a low power factor. Improve the power factor by running electric motors efficiently to get power factors close to 1, and by using PF correction equipment.

    Load Factor is a measure of the hours per day that energy is used. Reduce by:

  • Running for more than a single shift.

    About the author

    Robin Kent is managing director of Tangram Technology, a team of consulting engineers for energy management in plastics processing. He has been involved in plastics processing since 1971, has a materials engineering degree and a Ph.D. in polymer physics, and avers to MPW that he never met a processor whose energy costs he couldn''t help reduce.

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