PETpla.net Insider 05 / 2019

COMPRESSORS PET planet Insider Vol. 20 No. 05/19 www.petpla.net 34 Answers to advances PET bottle blowing Evolving compressed air requirements By Jared Link, Global Product Manager - Large Reciprocating Compressors, and Michael Nicholl, Industry Manager - Plastic Blow Moulding, Ingersoll Rand Over the past two decades several advances have been made in container design, blow- moulding machinery, and bottle processing that have significantly changed the require- ments for high-pressure compressed air in the PET bottle blowing industry. Despite sig- nificant increases to machine cavitation and bottle speeds, high-pressure compressed air consumption has decreased. Firstly, light-weighting efforts aimed at reducing the PET raw material requirements for packaged containers had the unanticipated benefit of allowing for effective blow moulding at reduced pressures. This had an impact on both compressed air flow usage and corresponding energy consumption. In addition to the more obvious benefit associated with the reduced energy consumption to generate lower system pressures, the more impactful benefit was the reduction in actual air flow consumed for the blowing process. This is often referred to as “artificial demand” in which an excessive amount of com- pressed air is utilised to blow and subsequently exhausted as a function of the elevated feed pressure. Secondly, design improvements in blow moulding machinery have eliminated the waste of compressed air and optimised air recovery tech- nologies. As an example, several manufacturers have reduced the ‘dead space’ within their valve blowing blocks and eliminated excess com- pressed air that previously filled larger chambers and was effectively wasted in the process. In another example, air recovery technology improvements allow for the capture of blowing air exhaust at a higher pressure (20 bar) which enables recycled compressed air to be utilised for pre-blow. These developments have further reduced the air flow requirements of high-pres- sure compressed air systems. Lastly, packaging equipment manufacturers have simplified blow moulding machinery and bottle COMPRESSORS manufacturing processes so that more customers are embracing vertical integration and the self-manufacture of PET containers. The trend towards multiple smaller capacity systems, as opposed to larger centralised con- tainer manufacturing operations, has resulted in lower capacity high-pres- sure compressed air systems. This also impacted the financial viability (ROIC) of installed redundancy as a typical design best practice and placed a premium on air compressor uptime availability. Answers to the variability in demand for compressed air Ingersoll Rand’s PET*Star is a 4-stage compression technology that is claimed to provide an inherent efficiency advantage when compared to 3-stage competitive alternatives. Depending on the size of the air com- pressor, the 4-stage design translates into an efficiency benefit of anywhere from 10-15%, states the company. In addition, PET*Star can operate at air discharge pressures ranging from 350 PSIG to 610 PSIG to meet the spe- cific requirements of a given system. Operating at lower pressures directly correlates to reduced energy con- sumption and improved air compres- sor efficiency. With the trend toward smaller capacity systems, there also tends to be greater variability in demand for high-pressure compressed air. There- fore, it is increasingly important for air compression technologies to deliver efficient part load performance. As a result, Ingersoll Rand’s PET*Star tech- nology features 3-step capacity control to achieve optimal performance under any load condition. 3-step capacity control leverages the double-acting stage design coupled with simplified valve controls to allow for unloaded, 50% load, or full load operation without the additional electrical componentry and cost associated with a variable speed drive (VSD). Ingersoll Rand PET*Star-4