Energy Management in Plastics Processing - Part 1
A series of energy efficiency worksheets by Dr. Robin Kent for
the Carbon Trust to help the plastics industry reduce costs through efficient
use of energy.
UK Government Environment and Energy Helpline 0800 585 794
The “Climate Change Levy” will increase the cost of electricity by 0.43p/kWh and the base energy generation costs are rising throughout the world. Energy costs are always somebody else’s problem and the plastics processing industry generally regards the energy as an overhead and as a fixed cost. This is untrue and energy is both a variable and a controllable cost. Most processors could easily reduce energy costs (without large investments) and increase profits through simple good energy management practice. This series aims to show you how to reduce energy usage and increase your profits.
Before you can start to reduce your energy costs you need to understand where, when why and how much energy you are using. This information provides the benchmarks and signposts for improvement.
Where you are using energy?
The main electrical energy users are motors and drives, heaters, cooling systems and lighting systems. A simple site energy distribution map will show where energy is being used. If you are using a single meter it may be cost effective to use sub-meters to get further information on the areas of high energy use. Sub metering 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. A first step is to produce an energy map of your site to locate areas for monitoring and improvement.
When you are using energy?
The time at which you are using energy is important and demand plotted versus time will give invaluable information on how to reduce the energy costs (see below). Data for such plots should be available from your supply company. Look for unusual peak variations from day to day and energy use when there is no production. A demand graph also helps you to find the ‘base load’. This is the load used for heating, lighting, compressors and pumps when you have no production at all.
Typical Site Energy Usage over Time
Another way to find the base load is to record the meter readings (in kWh) and production volumes (in kg) at the end of each shift. Plot the amount of polymer processed against the energy consumption. From the graph, the energy use at zero production gives an idea of the ‘base load’. Reducing the base load is a sure way to make savings.
Why you are using energy?
Ideally energy should be used only to produce good product and the most important energy benchmark is the energy used to process good product (in kWh/kg). This is called the specific energy consumption (SEC) and can be found from the slope of the graph produced to find the base load. It can be compared to the industry averages to provide targets for energy reduction.
Is energy being used to keep machines idling when they could be turned off? Are heaters running that are not being used? Are compressors running just to pump air out of leaks? Finding out why you are using energy will reveal a wide range of possible steps for reducing energy use.
How much energy you are using?
Electricity charges are based on a combination of factors (see right) and an initial survey will reveal areas for potential savings, sometimes actions as simple as changing the tariff can reduce costs at no cost! ‘Peak demand lopping’ can be very effective to reduce short peaks in the maximum demand.
Key tips for reducing the cost of electricity
Maximum Power Requirement (MPR) is the maximum current a site can draw at the supply voltage. Reduce the cost by:
- Staggering start-ups.
- Matching the MPR to the requirements.
- Getting the MPR right for new premises to avoid costly charges.
- Negotiating an annually based MD instead of an MPR charge.
Maximum Demand (MD) is the current drawn at the supply voltage averaged over half an hour. Reduce the cost by:
- Staggering start-ups.
- Giving machinery time to stabilise before starting up new processes.
Power Factor (PF) 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.
Load Factor is a measure of the hours per day that the user draws from the supply. Reduce the cost by:
- Running for greater than a single shift.
- Carrying out some operations outside the main shift pattern e.g. regrinding.
Use less energy. See future Worksheets in this series.
Energy management will save money and make you more competitive. Start your energy management programme today and reap the benefits of improved profits by cost effective investment and management.
The Government Energy Efficiency Best Practice Programme (EEBPP) provides free resources for energy management and cost reduction in plastics processing. An initial handbook “Energy in Plastics Processing - a practical guide” (GPG292) gives essential information on how to start reducing your energy costs and signposts further free information.
Get the information, save the money and become more competitive!
The "Energy Management" series is designed to give plastics processors an insight into how to manage a valuable resource.
Download the complete series as an Adobe Acrobat file.Last edited: 11/03/10
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