While plastic has many valuable uses, not all types of plastic are recyclable, and there currently lacks an effective circular economy strategy for these polymers. Most of the commonly used plastics are not biodegradable and need up to 500 – 1000 years to decompose. Therefore, any solution that has a significant impact on this situation and helps to reduce the volume of plastic waste is being encouraged.
Addressing two environmental issues with one act
One promising alternative has been recently developed by Quantafuel, a Norwegian start-up whose mission is turning non-recyclable waste into fuel. The company’s innovative feedstock recycling process converts plastic polymers into hydrocarbons, which can then be used by different downstream industrial processes that currently rely on fossil fuels. By using recycled hydrocarbons to produce fuels and other petroleum-based products, including new plastic materials, it is possible to lessen waste whilst reducing the depletion of natural oil and gas resources.
Quantafuel’s Plastic-to-Liquid (PtL) process starts with a thermal depolymerisation, i.e. pyrolysis or gasification, of polyolefin-based plastic, such as polyethylene (PE) and polypropylene (PP). The reaction produces alkanes, which can then be used to distil liquid fuels, as well as secondary products, namely alkenes (or olefins), aromatic compounds and carbon black.
Following this first step, a catalytic process hydrogenates and cracks the secondary products, turning them into useful alkanes. This proprietary catalytic system allows Quantafuel to carefully control the reaction, obtaining over 90% w/w alkanes whilst avoiding any thermal degradation of the substances and production of large volumes of polluting CO2.
The last stage resembles refinery vacuum distillation operations. The alkanes are separated into different hydrocarbon fractions, i.e. diesel (approximately 70% w/w), gasoline (circa 15% w/w) and fuel oil (approximately 5% w/w), that can be used by a number of industries.
Uniting two companies with one goal
The feasibility of this process was first tested in a pilot plant located in Mexico under batch conditions and it proved to be successful. Therefore, Quantafuel decided to set up its first of many full-scale plants for continuous processing in Skive, Denmark. To do so, it required a reliable partner that would supply suitable fractionation equipment whilst allowing Quantafuel to focus on other aspects of its business; Sulzer was selected.
Speed to market was particularly crucial for Quantafuel, therefore Sulzer needed to ensure responsiveness and time efficiency, despite the long manufacturing lead times for different pieces of separation equipment. To succeed in this challenge, Sulzer mobilised its manufacturing sites around the world and adopted a skid-mounted design for the distillation unit. Thanks to its expertise in this practice, Sulzer was able to complete the installation in less than 10 months.
Due to the quick turnaround time and positive reception of the skid-mounted system, Quantafuel decided to continue the collaboration with Sulzer for its future PtL plant reactors that are planned around the world.
The anatomy of a winning distillation solution
The fractionation unit that Sulzer developed for Quantafuel consists of a feed distribution system that supplies alkanes to a distillation column structured over four beds. More precisely, the feedstock enters the column in two phases – liquid and gaseous – and is then separated into three different fractions: heavy vacuum gas oil (HVGO), diesel, and light vacuum gas oil (LVGO). While the solution provided is very similar to a vacuum distillation unit typically used by refineries, it incorporates some key modifications that allow the system to maximise its efficiency and performance within the PtL plant.
Firstly, compared to traditional downstream operations, Quantafuel’s process presents a lighter feed and maximises diesel recovery. Therefore, Sulzer designed a strong diesel side draw that could support a high-volume stream.
Secondly, the unit’s top pressure, at 100 mbar (1.45 psi), is higher than conventional vacuum distillation units (VDUs), yet it still results in low vacuum conditions. Therefore, the structured packings used for the different beds were adapted to cope with the different operating pressure whilst maintaining low pressure drops.
Thirdly, the recovery of HVGO, diesel and LVGO required a large temperature gradient. This spanned from 90°C (194 °F) at the top of the column to 280°C (536 °F) at the bottom. To address this, Sulzer developed a distillation unit design that would resist these temperature variations.
“Most importantly, Sulzer built an extremely flexible fractionation unit,” explains Akbar Farshori, Senior Process Engineer at Sulzer. “In this way, Quantafuel can always obtain maximum yield, independently of the type of plastic being processed. Also, it is possible to modify the operating parameters in order to vary the relative percentages of HVGO, diesel and LVGO recovery. As a result, Quantafuel can address specific industrial needs and customer requests.”
A new plastics industry
The resulting PtL plant in Skive culminated in a unique, fully integrated solution that will be able to recycle 66 tpd of plastic to generate 53 t of hydrocarbon feed that can be used as fuel or to produce a wide range of chemicals.
Olav Stadaas, Chief Operating Officer at Quantafuel, comments: “Quantafuel aims to expand globally, installing PtL plants in various locations. To do so, we have decided to work with Sulzer and look forward to our continued collaboration. The company has been a very reliable partner and we are extremely satisfied with their services and technologies.”
Miguel Peña, Head of Process Plants for Sulzer Chemtech, concludes: “Quantafuel’s concept is an innovative solution and we are pleased to be involved in realising it. We’ve helped Quantafuel build its first PtL plant in record time. Even more, our success in this first collaboration has offered a unique platform to develop further similar sites around the world. Sulzer is involved in a number of sustainable projects that are revolutionising the way we recycle and reduce emissions. Our role can support new players, such as Quantafuel, in establishing these new processes.”
Read the article online at: https://www.hydrocarbonengineering.com/petrochemicals/01112019/sulzer-and-quantafuel-collaborate-for-sustainable-downstream-plant/