Energy-efficiency opportunities in plastics manufacturing

New research supports pre-heating stage and its impact on primary energy requirements

Author: Jamie Zachary

In previous blog posts, we’ve discussed the opportunity of putting industrial waste heat to work.

For example, many of the intermediate processing steps within the ceramic industry generate heat from free-flowing granular solids streams that’s traditionally been “thrown away.”

In these cases, a vertical tube configuration of our moving bed heat exchange technology (VT-MBHE) can transfer that heat from solids to other fluids such as water or air. Then, for example, the hot air generated can be used to produce electricity through different technologies such as gas turbines or Organic Rankin Cycle (ORC) machines.

We’ve also discussed similar applications within the fertilizer industry. Here, a vertical plate configuration can take the hot transfer fluid that comes out of the cooling process, and convert it into low-grade thermal energy. Combined with a heat pump, this stream of recovered heat offers significant value.

For example, the recovered heat can then be used upstream in the production process to pre-heat combustion air in equipment such as a fluid bed or rotary drum dryer – and, in turn, materially reduce the amount of primary energy used for drying.

Are there other applications where we are seeing opportunities to put otherwise wasted heat to good use? Let’s take a closer look at plastics manufacturing.

Plastics and waste heat recovery

In a recent blog post, Jill Caskey, Global Sales Director at Solex, detailed the process of converting polymer chains into finished products, which primarily involves the following steps:

• Heating: Transitioning a stiff solid to a softer material that’s more pliable.
• Shaping/forming: Done either through an extrusion or injection molding process.
• Cooling: So that it can retain its shape. This is often referred to as crystallization.

Yet for this blog, we’ll be focusing on the pre-heating stage, which is in the spotlight following new research that shows opportunities to re-use waste heat.

In 2021, German plastics institute SKZ published findings from a two-year study that determined a pre-heating step – for example, with a plate-based MBHE – that uses energy from process-related waste heat could result in a considerable reduction in primary energy requirements at the subsequent extrusion stage.

Backed by funding from the German federal government, the OptiHeat project found savings in the drive power of the extrusion motor ranged from seven to 19% in the tests SKZ carried out.

As part of its findings, SKZ also published an online tool that provides plastics manufacturers with an opportunity to calculate their potential savings.

Using an example that involves pre-heating 500 kg/h of polypropylene granules from a storage temperature of 23°C to 80°C before passing them through an extruder, the expected savings works out to €1.03/kg. Based on 6,000 operating hours of the extruder and electricity costs of €0.40 per kWh, the annual savings due to pre-heating work out to €39,948.62 ($59,019.84 Cdn).

So, where is this waste heat coming from? Depending on the shaping process, it could be available at the cooling stage.

Let’s use the example of a vertical plate MBHE. Much like the fertilizer example noted above, a hot working fluid is an output after cooling the polymers. That hot fluid would normally be discharged to atmosphere. Yet instead, it can be “upcycled” into useful energy that’s then used to pre-heat the polymers. The polymers would then go through the typical extrusion or injection molding process and back to the cooling stage where the process of recovering the waste heat would repeat.

Learn more

Want to learn more?  Let’s talk! Our team is available to discuss your polymer process. Contact us today.

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This entry was tagged Heating, Cooling, and last updated on 2023-5-10

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