Ministry study on boosting resource efficiency in manufacture of PET bottles

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First results of the research project

Deniz Ulutürk*
Matthias Gernhuber**

Boosting energy and resource efficiency in production processes is a topic that is of great interest to researchers, consumers, and trade and industry alike.  We are nowadays just as concerned with saving on resources and fulfilling our social obligations to future generations as we are with the issues of sustainability and economy. Year in, year out, the German Federal Ministry of Education and Research (BMBF) sponsors industrial projects within a specific area and scope.  In 2009, various experts in the stretch blow molding process chain submitted grant applications with the aim of increasing energy and resource efficiency in the manufacture of PET bottles.  Applicants included a team comprising KHS Corpoplast, the Institute for Plastics Processing (IKV), the company AdPhos Innovative Technologies, and Okertaler Mineralbrunnen, a mineral water bottling plant.  The project group was awarded a grant to implement the proposed project that will be sponsored using money from the federal ministry's small and medium-sized business initiative production research program and supervised by the Research Center of Karlsruhe until its completion in 2011.  This article aims to highlight the various measures that have led to an optimization in the manufacture of PET bottles in full accordance with the abovementioned concerns.  The process initially entailed defining specific parameters, followed by finding possible ways of improving the characteristics of the PET material, assessing the energy a stretch blow molder consumes, examining new technologies used to heat plastics, and incorporating a stretch blow molder in an energy management system established throughout a company. 

Four project partners with a clear distribution of tasks

There is a clear distribution of tasks among the project partners, with the IKV responsible for the coordination and scientific supervision of the various research activities. 

*Graduate Engineer, Process Engineering, KHS Corpoplast GmbH & Co. KG, Hamburg, Tel: +49 (40) 67907-450
*Product Manager, Bottles & Shapes™, KHS Corpoplast GmbH & Co. KG, Hamburg, Tel: +49 (40) 67907-442


The IKV also supports the project by providing ongoing simulation of all of the process stages.  As a specialist for the manufacture of PET bottles, KHS Corpoplast contributes its manifold expertise on machine technology, operational procedure, materials characteristics, and optimization of PET bottle designs.  AdPhos Innovative Technologies, who specialize in thermal processes and have developed an NIR heating technique, is working on various approaches to increasing the energy efficiency of preform heating.  Practical tests of the latest findings are being performed, analyzed, and optimized on a KHS Corpoplast InnoPET Blomax Series III at Okertaler Mineralbrunnen. 

500 billion PET bottles produced worldwide each year

The enormous number of PET bottles that pass through the hands of consumers each year shows just how important the above project is.  Each year, around 25 billion PET bottles are made in Germany alone, with the figure at 500 billion worldwide.  This alone specifically raises issues concerning our responsibility towards the environment, as the material PET, the molecules of which primarily consist of oxygen, hydrogen, and carbon, is extracted from oil.  To make one kilogram or around two pounds of PET, approximately 1.9 kilos (4.2 lbs) of oil and 23 kWh of energy are required.  

Consumers question environmental friendliness

Consumers and also retailers are increasingly questioning the environmental friendliness of the products they buy.  It is thus quite feasible that in the future products whose environmental friendliness is explicitly extolled have a better chance of being sold.  The result is that the less energy and the fewer resources that are ploughed into PET manufacture, the more likely this type of packaging is to have good prospects for the future – especially as the characteristics of this material justify a further use.  The use of less energy and fewer resources in the manufacture of PET bottles also results in lower CO2 emissions.  This is not only relevant to the protection of the environment; here, one could also envisage the allocation of a climate or CO2 label that describes the product's carbon footprint.  The first CO2 label in the world was developed in Great Britain in 2006.  Such labels are not yet used in most countries but this could change very quickly – and here provision must be made. 

Three criteria: the consumption of materials, electricity, and compressed air

The project entitled Increasing Energy and Resource Efficiency in the Manufacture of PET Bottles began by determining which key data was to be collected.  It was decided that the first and foremost criterion was the weight of the PET material used in the production of a PET bottle.  As a rule, 70% of the cost of a PET bottle is attributable to the material used.  Preform manufacture and the actual production of the PET bottle account for a further 15% of costs respectively.  Reducing energy consumption in the manufacture of PET bottles is always equal to a reduction in cost.  This means that cutting down on the weight of a PET bottle is not only important for its economic weighting but at the same time is the most important consideration in bringing about an improvement in figures for energy consumption. 

The second decisive factor was the amount of energy required to heat one kilogram or about two pounds of PET.  One important consideration here is the fact that the preform mouth is not heated in the stretch blow molder and thus not altered, meaning its weight can be deducted from the weight of the overall preform when calculating the total weight to be heated.  If a preform weighs 25 grams, for example, and its mouth 5 grams, only 20 grams need to be included in the calculation when computing the amount of PET to be processed.

The third criterion was the amount of compressed air needed to inflate the PET bottles.  This was to split into two areas: firstly, the amount of compressed air needed to blow mold the PET container itself, and secondly, the quantity of compressed air supplying what are known as dead space volumes.

Recording the actual state of play and exploiting optimization potentials on an InnoPET Blomax Series III at Okertaler Mineralbrunnen

The next stage in the project was to record the defined parameters on the InnoPET Blomax Series III stretch blow molder installed at the Okertaler Mineralbrunnen bottling plant.  Following this, the researchers wanted to exploit to the full the potential for optimizing the entire system.  The final challenge was to find classifications which earmark both an especially good stretch blow molder and an outstanding PET bottle in terms of energy consumption in both cases. 

The InnoPET Blomax Series III in operation at Okertaler Mineralbrunnen has 14 blow stations and produces 25,000 PET bottles per hour.  The company's yearly volume of 1.5-liter disposable PET bottles designed to hold carbonated soft drinks is approximately 100 million.  Each bottle weighs 31 grams. 

Fast stretching increases strength

First, let's look at the factor of materials, which holds the greatest potential for energy savings and cost reductions.  Here, the team tested how the properties of the Okertaler PET bottle reacted when the biaxial stretch of the PET material was altered (the material is stretched in both an axial and radial direction).  One part of the project was to try and stretch the PET as fast as possible, as experience has shown that the material's orientation is highest when stretched at speed.   This means that the strength of the PET material increases when it is stretched rapidly.  This greater strength and higher orientation enable lighter PET bottles to be designed.  Experiments were also explicitly conducted to ascertain whether these lighter PET bottles behaved as normally expected and required under these new conditions with regard to their top load (stackability), resistance to pressure and temperature, and expansion. 

First results showed that faster stretching results in an improved PET strength of around 10% for the Okertaler bottle.  Within the project tests were carried out to determine at which stretch speed the highest possible orientation and thus the highest possible PET material strength can be obtained.  This increase in bottle strength is measured using what is known as the modulus of elasticity (E modulus).  An elastic modulus is usually greater the larger the resistance of the material to its deformation.  The E modulus of the PET bottles fabricated at Okertaler Mineralbrunnen was tested in the lab.  Samples of PET bottles stretched in various different ways were examined on a test bench set up to investigate the tensile strength of the PET material. 

30 grams instead of 31 grams of PET per 1.5-liter bottle

If the tests at Okertaler prove that the 10% increase in strength expressed by the modulus of elasticity is indeed given when PET bottles are stretched at speed, this would mean that the plant's 1.5-liter PET bottles could become 3% lighter in the future.  The weight of each PET bottle would thus drop from the current 31 grams to 30 grams.  One gram less material per PET bottle would lead to a considerable saving of 100,000 kilograms (roughly 220,500 lb) of PET material per annum, assuming that approximately 100 million PET bottles are produced a year.  At a market price of €1.20 for one kilogram (2.2 lb) of PET, the amount saved per year would be €120,000. 

If Okertaler's PET bottles were 3% lighter, then the CO2 emissions given off during manufacture would also fall by 3%, creating another key benefit that is especially kind to the environment and also prepares for possible restrictions.

Bottles & Shapes™ program in use

Besides the correlation between the modulus of elasticity and the bottle weight, in the use of material the contours of the PET bottle are also of tantamount importance, as the specific shape can help to reduce the amount of material even further than that expressed by the elastic modulus increase.  In this project, like the E modulus the shape of the Okertaler PET bottle was developed according to the principles of the extremely successful Bottles & ShapesTM program employed at KHS Corpoplast for many years now.  (To date, KHS Corpoplast has optimized around 9,000 PET bottles using the program.)  In its Bottles & Shapes™ program KHS Corpoplast first clarifies which products are to be filled and which forms of stress are expected to be exerted on the container before suggesting designs for PET bottles.  The contours of the container are developed by computer simulation.  Using finite element analysis, all known influences are simulated and applied to the virtual packaging.  If the features of the simulated PET container meet customer requirements, KHS Corpoplast begins producing prototypes.  The next step is to then manufacture the PET bottles on a lab machine that works just like the stretch blow molder used in practice.  Only when lab results confirm all given specifications does KHS Corpoplast release the plastic container for production and initiate the ensuing practical  tests.  In the project we are dealing with here, the Bottles & Shapes™ procedure described above was applied in identical form to the Okertaler PET bottle.  

Projecting results on the new InnoPET Blomax Series IV generation of stretch blow molders

At the time the project was launched, Okertaler Mineralbrunnen was running an InnoPET Blomax Series III stretch blow molder that achieved the lowest energy consumption per stretch blow molded container of all the stretch blow molders used in the beverage industry.  This is partly brought about by the use of a pulsed heating system and the lowest possible preform spacing.  Other features of the InnoPET Blomax Series III stretch blow molder include precision production of lightweight PET bottles, optimum process stability, and a high level of availability.  With the InnoPET Blomax Series IV, KHS Corpoplast recently introduced a new generation of stretch blow molders that manages to trump its predecessor when it comes to satisfying market demands for sustainability and reduced overall operating costs. 

Let's take the strength of the material, for example.  In the InnoPET Blomax Series III, the stretch blow molding process in the blow stations was controlled mechanically; in the InnoPET Blomax Series IV, this is now controlled by servo motor.  As a result, the stretch speed responsible for the strength of the PET material can now be more flexibly and accurately controlled than in the previous generation of machines.  If the speed of the blow molder is reduced, the stretching motion can still be carried out at the same rate as at the high machine speed – despite the slower machine rotation speed.  The previously mentioned dependence of the material hardening on the stretch speed does thus not depend on the output speed of the machine.  The results pertaining to increased material strength obtained on the InnoPET Blomax Series III can thus be directly applied to the new generation of stretch blow molders and further perfected here on the tide of even higher stretch speeds.

Optimized energy consumption for preform heating of between 15 and 20%

A change in the amount of material used per PET bottle always also has an effect on the variables energy and compressed air consumed by the stretch blow molder.  A lighter preform, for example, therefore needs less heating energy and compressed air during inflation. 

On the InnoPET Blomax Series III installed at Okertaler Mineralbrunnen a heater module is in use that operates with classic infrared radiation.  The area of the project pertinent to heating technology sets out to analyze and optimize the temperature profile generated in the preform wall during heating.  The variables used to asses the heating process were the energy content of the preform and its axial temperature profile.  An optimum thermal profile for a preform can be achieved by applying various doses of infrared thermal radiation and an adjustable flow of air to cool the outer surface of the preform.  Tests carried out to date have revealed that in the preform preheating process the consumption of energy can be optimized by between 15 and 20%.  Applying this information, the amount of electricity needed to preheat preforms would then drop from 0.15 kWh/kg PET to 0.12 kWh/kg PET.  Based on the assumption that electricity costs €0.10 per kWh, this would yield an annual saving of €7,800.
 
Classic infrared radiation versus near infrared (NIR)

The new InnoPET Blomax Series IV generation of stretch blow molders modifies the Series III by using near infrared (NIR) technology to heat preforms.  The advantage of this particular technique is that only shortwave or near infrared is used, resulting in a substantially higher energy density.  With NIR, the penetration of the preform wall is extremely intense – a feature further increased by feeding the preform through a closed heating chamber with all-round reflection.  If NIR heating technology is applied, a further potential saving in electricity of up to 30% can be made as opposed to the Series III.

Further research into completely new heating technologies

The project not only examines possible ways of optimizing the preform heating process in Okertaler's stretch blow molders or assessing how much electricity can be saved using NIR technology; completely new heating technologies for preforms are also being taken into account.  Researchers are thinking about using laser power to heat preforms, for example.  Heating preforms with diode lasers would possibly provide new ways of profiling temperature both in the axial preform direction and across the entire circumference of the preform. 

Optimized compressed air consumption through new designs, intelligent ventilation, and recycling

The third major factor to play an important role in the project is the amount of compressed air a stretch blow molder uses.  Looking at the amount currently consumed by the Okertaler stretch blow molder, the project participants began weighing up how this could be optimized.  The compressed air involved in the inflation of a PET bottle is split between the amount need to blow mold the PET container and the losses in compressed air caused by the machine construction.  New bottle designs and integrating intelligent ventilation systems could help to reduce the amount of compressed air required to inflate a PET bottle, for example.  Tests also focused on the aspect of compressed air recycling through Airback systems.  The Okertaler mineral water bottling plant uses two air recycling systems.  In Airback System 1 some of the compressed air in the newly inflated bottles is extracted and used to blow mold new bottles in other blow stations.   Airback System 2 regulates the recirculation of residual compressed air back into the compressed air system at the plant.  The team are presently investigating how they can get the most out of compressed air recirculation.  To date they are reckoning with a possible 31% reduction in compressed air.  A further 5% saving can be assumed in addition to this, brought about by a change in the shape of the bottle; in total, this would result in 36% less compressed air being consumed.  This in turn generates a yearly cost cut of €26,000 if we assume that one kilowatt hour costs €0.10.  CO2 emissions would also be much lower in conjunction with this.

With the InnoPET Blomax Series III KHS Corpoplast is a leader in the field of stretch blow mold technology when it comes to compressed air consumption.  In the new InnoPET Blomax Series IV this figure has been improved upon; depending on the bottle size, an additional 5 to 15% less compressed air is used.  One reason for this is that the dead space volume has been reduced. 

Checking the inline behavior of the stretch blow molder

In order to paint a fuller picture during the Okertaler project, the team decided to investigate the inline behavior of the stretch blow molder in varying complete system setups.  Their objective was to check how much current was used under certain machine conditions.  Various systems of measurement connected up to the KHS plant information system in the stretch blow molder recorded consumption figures for individual, defined states within the stretch blow molder.  These values were then again closely examined with a view to further optimization. 

Investment in particularly energy-efficient stretch blow molders made simple

All told, the research project sponsored by Germany's Federal Ministry of Education and Research on increasing energy and resource efficiency in the manufacture of PET bottles long-term invests in the future for the next generations.  First results show that considerable savings in materials, electricity, and compressed air can be made.  To date criteria and characteristics have been defined, the current state of the stretch blow molder at Okertaler Mineralbrunnen has been recorded, the Okertaler machine has been equipped with state-of-the-art measurement systems, and consumption has been minimized.  The remaining project objectives are to continue to assess and optimize the amount of material, energy, and compressed air used for PET bottles, and to also research new heating technologies.  The final results will be published at the end of 2011.  These can be used as a general form of classification for PET bottles and stretch blow molders.  In the future, they can also help companies seeking to invest to easily single out those stretch blow molders that are particularly efficient in their consumption of energy. 

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