In the polymer recycling sector, the demand for high-quality compounds is increasing, while the supply of well-sorted, clean post-consumer waste (PCW) flakes is limited. This scarcity results in energy-intensive pre-processing steps, particularly due to the wet and thin flakes. This then increases the energy input and embodied carbon into the final product.
To address these challenges, Luxus partnered with the Technology Research Centre to undertake Project Microdry, in collaboration with the Department for Energy Security and Net Zero (DESNZ, formally BEIS). This DESNZ funded project began in September 2021, with the aim to produce an end-to-end energy efficiency improvement, from raw materials handling to the final product.
The project was divided into four objectives over a period of three years;
Build and demonstrate a pilot flake drying system to process 2 tph of wet flake at 3 wt% water, as efficiently as possible.
Build and demonstrate a pilot system for low grade heat recovery and re-use from extruded pellets into wet flake.
Build and demonstrate a pilot novel extruder for direct feed of dry PCW flake (100%) into extruder with higher output than the current process.
Monitor and present the energy requirements of existing processes and proposed pilot systems to demonstrate the overall energy reduction in PCW flake processing.
The project was successfully completed in March 2024, with the implementation of two systems designed to meet the above objectives as efficiently as possible.
The first is a process which can dry, filter, and blow material to silo ready for production. The feed system for this handles material straight from the bulk bags on arrival, and after processing blows it to silo ready to be used in production. After loading, this process requires no manual intervention, increasing efficiency. This step has a ‘fines’ filter, taking out the smallest fraction of powder-like polymer. This mitigates material flow issues through the pipework by preventing blockages caused by a build-up of dust and moisture within the pipework. The processing mechanism also improved the bulk density of the material, which has proven to be of huge benefit to the gravimetric feed systems, as the mass flow was improved from silo to extruder.
A spiral cooling tower was designed to recover heat from extruded pellets. It was noted that a considerable amount of heat energy was lost to the atmosphere from our finished product. Polypropylene pellets typically come off the production line at around 40°C, are placed into a tonne bag and then left to cool in our warehouse. One of our objectives was to capture this residual heat and re-use it within the process. The first insulated meter of the tower is designed to capture and transport warm air, with the rest of the tower used to further cool pellets to ambient temperatures.
Another potential benefit of this system is that cooled pellets in FIBC’s can be wrapped at the end of line, without the need to transport and wait in the warehouse. This reduction in bag handling equates to 130 less fork truck movements per average batch, which is 3.25km less travelled. This equals approximately 2 litres of diesel, and using the conversion factor, 4.95 kg CO2 e.
During the project, the energy data loggers that were used to monitor energy consumption were upgraded. This upgrade included access to the MW2 software, which has comprehensive energy analysis capabilities to aid with Scope 2 emissions for carbon footprint analysis.
The technology in place so far has already provided improvements to the energy efficiency of our processes, and there are ongoing plans to further improve this.
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