Decarbonisation Technology - November 2024 Issue

O-gas

New process unit Adjusted process unit Conventional process unit

Pre- conversion process

Gas fraction processing

Circular plastic

Olen production via steam cracker

Plastic waste

Plastic liqu ef action

Plastic pellets

Pellet mill

Syngas treatment

Methanol synthesis

Methanol to olens

Gasication

Extruder

CO HS

Slag and lter cake

Shell Catalysts & Technologies and Air Products have a strategic alliance in liquid gasification technology. Shell Catalysts & Technologies and Hyundai collaborated on the development of the plastic liquefaction technology

Figure 4 Plastic liquefaction pre-conversion technology can be installed upstream of an existing gasification unit

from industrial biomass processes, to produce low-carbon, bio-based fuels with significant margins. Doing so can help reduce the carbon footprint and circularity of operations and products. Second, operators can produce high- value, circular plastic by leveraging the growing supply of low-value plastic waste. Pre-conversion of waste for gasification Pre-conversion is a key process that can convert a diverse range of materials (such as unsorted plastic waste and biomass) into intermediate feedstocks for gasification units. Shell has developed a range of pre- conversion technologies that offer operators flexibility to use waste feeds that best suit their circumstances: liquefaction for bulk plastic waste, fast pyrolysis for woody biomass, and torrefaction for biomass and agricultural residues (see Figure 2 ). Plastic liquefaction for bulk plastic waste Today, as much as 85% of plastic waste is sent to landfill, incineration, or left unmanaged, largely because current methods, including mechanical recycling and chemical recycling by pyrolysis, require well-sorted, high-purity plastic waste streams, which are costly and resource-intensive to create. Plastic liquefaction, however, can take plastic waste unsuitable for other recycling methods and pre-convert it into gasification feedstock to produce syngas that is equivalent to virgin feedstock (see Figure 3 ). Importantly, when used alongside existing plastic recycling

methods, plastic liquefaction has the potential to play an important role in helping to close the plastic circularity loop. So, how does plastic liquefaction work? The plastic liquefaction technology, developed as part of a strategic collaboration with Hyundai, features a novel liquefaction unit that can be installed immediately upstream of an existing gasifier (see Figure 4 ). With no additional units required, deployment is quick and can be done with relatively little cost. See the Feasibility study overleaf for an example of how a European refiner has evaluated switching to waste gasification to produce high-value circular chemicals.

Conventional

Liquefied plastic

feedstock

C:H ratio Oxygen Sulphur Nitrogen Viscosity

7.7:10.8 <1.5 wt% <7 wt% <1.5 wt%

>1.5 wt% <0.1 wt% <1 wt%

<300 cSt <300 cSt by temperature by temperature

Halides

<75 ppmw <0.2 wt%

>300 ppmv

Ash

>1 wt%

Main ash components

Ni, V, Fe

Al, Ca, Si, Ti, Fe

Ash behaviour

Non-slagging,

Slagging

only soot >38 MJ/kg

+ soot

Higher heating value

>38 MJ/kg

Table 1 Comparison of conventional (hydrocarbon) and plastic liquefaction gasification feeds. Important differences are highlighted in bold