Plastic Products Manufacturer

A Darling Downs-based plastics manufacturer is a large user of liquefied petroleum gas (LPG). Proposed improvements have been identified to drive efficiencies and cost savings, including improvements in the use and insulation of heat throughout the manufacturing process.

Summary of Opportunities

Polymer Pre-Heating

Heating is essential to the plastics manufacturer’s operation, and is a substantial energy cost to the business. It is recommended that the manufacturer pre-heat the polymer using a high shear mixture (known to reduce the heat cycle time by at least 18%) before sending it to the hollow mould. This would reduce the cycle time of heating inside the mould. While this would require new energy into the process, it could be offset with the introduction of an economiser to utilise waste heat from the oven to provide the hot air for pre-heating.  This would result in substantial energy savings – a reduction of 1,221 gigajoules (GJ) per annum and about $36,111 in annual operating cost savings.

Heat Transfer Efficiency via Air Detectors

The largest energy consumers on site are the ovens. To reduce heat cycle times, air directors could be installed in the ovens to focus the airflow and optimise the heat transfer to the polymer inside of the moulds.  This has been known to reduce cycle times by close to 15%. This would deliver an energy saving of 1,018 GJ a year and an estimated $30,092 in annual energy costs.

Mould Arm Holder Insulation

Generally, during the cooling cycle, mist or air is sprayed on the moulds. During the energy assessment, it was noted that mist (not air) was utilised for cooling, which is less efficient. An additional arm insulation, and a move away from water cooling, is recommended in order to:

• Significantly reduce the heat sink of the arms.
• Reduce the required heat input into the process.
• Keep the ambient surroundings cooler due to the insulation on the arms.

Using air only is more effective as it reduces warpage, avoids the challenges associated with collecting and draining excess water, and it can extend the life of the tooling as it avoids shocking the metal components. It’s also an inexpensive option, at a capex of $4,000 with a payback period of 0.4 years, that would deliver energy savings of about 373 GJ a year.

Economiser on Oven Stacks

The site’s four polymer rotomoulding machines, which use LPG as their main energy source and operate in the range of 100-300^oC, currently vent most heat out of their flues into the environment.

It is recommended to instead utilise the wasted energy by installing economisers, which will consume the flue gases in order to pre-heat the combustion air prior to it being used in the oven.

This would deliver about 6.5% in fuel energy saving if the combustion air can be pre-heated to 168^oC, and would produce $32,444 in energy savings annually.

Variable Speed Drives in Shed B

Only two of the four ovens on site are equipped with variable speed drives (VSDs). Retro-fitting VSDs on the main burner fan motors for the remaining two ovens would deliver efficiencies which would result in up to 25% in electrical energy savings, and offer a payback period for the capital investment of 2.1 years.

Insulation on Oven Doors

To maintain the temperature in the ovens and reduce the amount of energy currently consumed for heating, a low-cost option is proposed to close the open holes in the rotomoulding ovens, which draws in cool air, and to install additional insulation on the doors, which would also help to reduce the workshop ambient temperature. This option would see energy savings of 16 GJ a year.