The one benefit of the plastics processing sector being a major user of energy—responsible for 4% of global energy consumption, according to some estimates—is that there’s a lot of scope for reducing its energy use. That, at least, is what the European Commission and the U.S. government think; both of them have introduced initiatives aimed at greatly reducing energy consumption by the plastics sector.
In the USA, the Department of Energy (DOE) has launched the Better Buildings, Better Plants program, which will help manufacturing companies adopt measures intended to enhance their energy efficiency by 25% over a period of ten years. These measures will include developing energy management plans and tracking and reporting energy data annually to the DOE. This program is designed for any manufacturing company, but plastics processors are a definite target, and companies such as Amcor have already become involved.
The European Commission initiative is designed to help meet its target of reducing energy consumption across the EU by 20% by 2020, compared to current projections. As such, in 2011 the European Plastics Converters Association (EPCA), an umbrella group comprising the plastics industry associations for eight countries, including Germany, France, and the UK, established a voluntary agreement on energy efficiency.
Under this agreement, EPCA members pledged to work towards reducing their energy consumption by 20%, compared to their 2007 usage, by 2020. To do this, each national association began by submitting a long-term plan to the EPCA detailing how they will implement the voluntary agreement. They then began monitoring the progress of their own members and reporting back to the EPCA annually.
So it’s a shame that despite these initiatives, and the fact that energy prices remain high even with falling oil prices, energy efficiency is still not a major priority for many plastics processors. “They’ve become accustomed to high energy prices,” says Robin Kent, managing director of Tangram Technology, a British energy management consultancy for the plastics industry. “They’re still concerned about energy efficiency, but [some] of the heat has gone out of it.”
One of the main reasons for this, according to Kent, is that plastics processors simply have so many other things to think about. “People are just overwhelmed with numbers of things to do, and there are competing pressures on their time,” he suggests.
This is unfortunate, because there’s a great deal of scope for processors to reduce their energy consumption, thereby reducing their costs—through simple, straight-forward measures that require little or no financial outlay. Examples of these simple measures and their effects on energy use are detailed in a guide titled Energy Management in Plastics Processing, which was written by Kent and published by the British Plastics Federation ( www.bpf.co.uk) in 2011.
This guide details the benefits of installing variable speed drives (VSDs) on motors, which are the largest single user of energy in most plastics-processing operations. Simply slowing a motor down by 20% with a VSD can reduce energy use by 50%. Compressed air is also a major expense, especially for blow molding operations, accounting for around 10% of energy use—as is cooling water, which can account for 10-15% of energy use.
For compressed air, the most effective way to reduce energy use is to find and fix any leaks, which on an average site can cause the loss of 20-40% of the generated compressed air. In addition, cold air should preferentially be fed to the compressor, as cold air is already denser than warm air.
Where possible, cooling water should be cooled by simply exposing it to cold external conditions, ideally utilizing dedicated cooling towers, rather than by using refrigeration systems. Chilled water pipes should also obviously be insulated to prevent the water warming up.
A Data-Driven Approach
Ensuring that even these simple measures are undertaken effectively, however, requires collecting data on energy use, both before and after instigating the measures. Beforehand, this data is required to determine how and where energy is currently used by the plastics processing plant, in order to identify which measures will be most effective. “The whole process of energy efficiency should be data-driven, and you should go for where the big hits are, and that depends on your process and your factory,” says Kent.
Afterwards, the data is required to determine the effectiveness of those measures, which can help to make the whole energy-saving process self-sustaining. “It’s about being able to go to the decision makers and say, ‘Here’s the data [from when] I changed this motor … and I saved this much money,’” explains Kent. “It’s about using the data to justify current and future purchases.”
Fortunately, obtaining this data is much easier than it used to be. “When we first started trying to wire up factories to understand where we were using energy, we were wiring them up with hard-wire cables, and the whole process was quite difficult to manage,” recalls Kent. “Now we’ve gone from wired networks with poor data handling to wireless networks with great data handling. Instead of trying to look at a machine and download the information, now we can do it all on-screen.”
Cutting Energy in Thermoforming
In addition, many of the latest processing machines come with sensors already built in. Thermoforming is the most energy-intensive of all plastics processing technologies, utilizing 6 kWh of electricity for every kilogram of production, whereas injection molding utilizes just 3 kWh/kg. This high energy usage is due to the large-scale heating required to soften the extruded plastic sheet prior to it being overlaid on a mold, and then the cooling required afterwards.
So to try to manage this energy use as efficiently as possible, the latest thermoforming systems from the Swiss company WM Thermoforming Machines utilize a range of sensors, including temperature, pressure, and water-flow sensors. In addition, these systems, which combine extrusion and thermoforming machines, offer several other ways to reduce energy use. They use highly-efficient, water-cooled AC motors to operate the extruders, and apply cooling more efficiently using a spiral cooling circuit.
This reflects the fact that newer processing machines tend to be much more energy efficient than older varieties. According to Kent, modern plastics processing machinery uses between 20% and 50% less energy than it did ten years ago.
This trend shows no sign of slowing, as new, more advanced sensors generate ever more detailed information about plastics processing. Ceramicx, an Ireland-based developer of heating technologies, has recently developed an analytical instrument to map the heat flux produced by infra-red heating systems during thermoforming. Developed in conjunction with researchers at Trinity College Dublin and known as the Herschel, the instrument combines a radiant heat flux sensor with a six-axis robot. This means the sensor can be positioned anywhere over the heating assemblies, allowing it to build up a detailed map of the heat flux.
According to Ceramicx, this map can be used be used by developers of thermoforming machines to ensure their heating assemblies work as effectively and efficiently as possible. But because Herschel can determine the effect of heat radiation on all kinds of plastic sheets, it can also be employed by thermoforming companies to ensure they are applying the optimum distribution of heat for each different kind of plastic. In this way, they can keep their heating, and thus energy use, to a minimum.
Savings in Other Processes
General technological advances, combined with additional information on plastics processing operations provided by sensors, means that developers of other processing machines have found a variety of ways to make their machines more energy efficient.
For example, German company battenfeld-cincinnati has developed more efficient single- and twin-screw extruders that are able to melt different plastic materials at lower temperatures than previously possible. The company claims that its 75-mm, high-speed single-screw extruders use 25% less energy than conventional extruders of comparable size.
Similarly, the French company Sidel reportedly has achieved substantial energy savings in its new blow molding machines by heating the mold using electrical heat resistance rather than hot oil. According to the company, this offers energy savings of 45% compared to its older blow molding machines. Furthermore, a novel air recovery technology in the machines can reduce consumption of compressed air by up to 45%.
When One Dollar Equals Twenty
So there seems to be no end to the ways in which plastics processors can reduce their energy consumption, from making simple, inexpensive changes to their working practices, to investing in new machinery. And the associated cost savings could prove especially beneficial for processors, many of whom operate on a profit margin of just 5%.
“That means if they save a dollar in energy, that’s equivalent to putting $20 on the sales line,” says Kent. “People get excited by new sales, of putting $200,000 on the sales line, but they don’t get excited about taking $10,000 off the cost line, although it has the same effect on profits.”
As an added bonus, by reducing their costs in this way, plastics processors would also be helping their governments meet their energy-saving targets.