Tangram Technology Ltd. - Reducing Energy Costs

Reducing Energy Costs in Plastics Processing

Increasing energy costs are going to be a feature of plastics processing for the foreseeable future. The "Climate Change Levy" and rising generation costs will ensure that energy becomes an ever more important cost to the plastics processing industry.

Despite this the industry generally regards the energy as an overhead and as a fixed cost. Nothing could be further from the truth. Energy is both controllable and a variable cost. Most processors could easily reduce their energy costs (without substantial investment) and increase their profits. Energy management can save you real money. Energy management is simple. Energy management is good management.

Understanding energy usage

Before you can reduce your energy costs you need to understand the basics of your energy use. You need to understand:

Where you are using energy

The main users of electricity in polymer processing (in rough order of importance) are motors and drives, heaters, cooling systems and lighting systems.

A simple diagram of site energy distribution map will show where energy is being used. If you are using a single meter it may be cost effective to install sub-meters to get further information on the areas of high energy use.

Sub metering will allow 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.

When you are using energy

The time that you are using energy is important in the cost of energy and a simple chart of the demand (at 1/2 hour intervals) plotted versus time will give invaluable information on how to reduce the energy costs.

Peaks of energy usage at the start of the day will increase the energy cost for the complete day. Stagger machine start-ups to reduce the maximum demand and energy costs. A demand graph also allows you assess the 'base load'. The easiest way to find the base load is to note meter readings and production volumes (in kg) at the end of each shift.

Plot the amount of polymer processed against the energy consumption and the energy used when no polymer is processed is the 'base load'. The base load is used for heating, lighting, compressors and pumps. Machines that are idling with no production will also contribute to the base load! Reducing the base load is a sure way to make savings.

Why you are using energy

Knowing when and where you are using energy will start to reveal why you are using energy. Is it being used to keep machines idling when they should be turned off? Are heaters running that are not being used? Are compressors running just to pump air out of leaks?

A key value to calculate is the energy used to process each kg of good product (in kWh/kg). This can be compared to published industry averages to see if you are close to industry best practice and to provide useful targets for energy use and reduction.

How much energy you are using

Knowing how much energy you are using will allow you to start to reduce your energy costs.

Electricity charges are made up of several factors (see box at right) and supply companies vary charges based on these factors. An initial survey of the company will reveal areas for potential savings - sometimes you are simply on the wrong tariff and a change in the MPR or MD can save large amounts of wasted money at no cost!

For some plastics companies the use of 'peak demand lopping' can be a very effective investment.

Electricity purchasing - the key words

Maximum Power Requirement (kVA)

The maximum current that a site can draw at the supply voltage without triggering the main circuit breakers and trips.

Stagger start-ups to avoid exceeding MPR.
Match MPR to real requirements to reduce costs.
Get the MPR right for new premises to avoid costly charges.
Consider negotiating an annually based MD instead of an MPR charge.

Maximum Demand (kVA or kVAh)

A measure of actual current drawn at the supply voltage, usually averaged over half an hour.

Stagger start-ups to avoid exceeding MD.
Give machinery time to stabilise before starting up new processes.

Power Factor

A measure of the phase shift created by machinery. Lightly loaded machinery tends to have a high phase shift, and thus a low power factor.

Run electric motors energy efficiently to get power factors close to 1.

Load Factor

A measure of the hours per day that the user draws from the supply.

Run for greater than a single 8-hour shift to reduce load factors.
Can some operations be run outside the main shift pattern e.g. regrinding.

Practical tips - administration and management

Energy efficiency is not simply turning off lights and investing in new machinery. It is about managing the use of a vital and costly resource. This demands motivation and training to make energy reduction a part of the company culture rather than a 'one time fad'.
The initial purchase cost of a machine will be exceeded by the cost of energy used during the lifetime of the machine. Energy efficient machines and controls may appear to cost more but you will pay less in the long term.
Get your machines set right, record the settings and do not change them unless absolutely necessary. Use SPC to control machine settings and performance. Tweaking of machines by operators causes more lost time and energy than almost any other cause.
Monitor and keep good records of all aspects of performance of each machine for particular product and polymer runs. Process performance records are only one aspect of performance. Monitor and record 'people performance records' as well. Remember, "People do not react as you expect. They react as you inspect"

Practical tips - utilities

Water

Record and monitor water usage. Water may seem cheap but you pay for it twice - once to buy it and once to dispose of it. The total cost can generally be reduced by 10%, this is up to Ł5000 per year and is better on the bottom line than down the drain.

Compressed air

Compressed air is an expensive resource. Minimise the demand, then optimise the supply.
A 3 mm hole in a 7 Bar main will leak about 11 litre/sec, at a cost of about Ł1,000 per year for a 120 hour working week. What is your total leakage? Reduce your costs by sealing the leaks.
The higher the pressure, the more expensive it is to provide the air. Twice the pressure means four times the energy cost. What are your real needs? Remember that the longer the pipeline, the greater the pressure loss over the pipeline and the greater the cost.

Buildings

Buildings are large energy users. A simple site survey can reduce your costs considerably.

Practical tips - machines

Motor and drives

The energy costs of a motor can exceed the purchase cost in just 40 days and 'life costs' are over 100 times the purchase cost. Fit more efficient motors that are matched to the need and use low cost 'soft start' and variable speed drive technology to reduce costs.
Schedule jobs to the most appropriate machines.
Invest in devices that limit peak loads.

Heat transfer

Heat transfer is an essential part of plastics processing. Barrel insulation has a rapid payback and should be a top priority.

Get the free specific advice and help

Energy management can save you 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.

Environment and Energy Helpline - 0800 585 794

The EEBPP provides excellent resources to plastics processors for energy management. "Energy in Plastics Processing - a practical guide" (GPG292) gives essential information on how to start reducing your energy costs. Other detailed publications are available on specific processes and areas of energy efficiency. Get the information, save the money and become more competitive!

GPG292 - Energy in Plastics Processing - a practical guide. (Click here to view an Adobe acrobat copy).

Reducing Energy Costs