How to decarbonise existing steam crackers?

Abstract

According to International Energy Agency (IEA), the demand for high value chemicals (HVC) will increase by 60% to a total of 400 Mt/year by 2050, leading to an increase of 30% in direct CO2 emissions. However, the Paris agreement forces the sector to reduce its emissions by 90-100% in 2050 compared to 1990. This induces the need for a more sustainable character in the petrochemical industry to produce HVC with net-zero emissions by 2050.
Steam cracking is expected to be still the leading production technique for HVC in 2050. Therefore, this research focuses only on petrochemical clusters containing a steam cracker.
Accordingly, the research question to be answered was: How can existing petrochemical clusters containing a steam cracker be transformed to produce
HVC with net-zero emissions in 2050? This thesis aims to look into the potential of alternative feedstocks and combine them with other decarbonisation options for steam cracking to produce HVC with net-zero emissions by 2050 from a cradle-to-gate perspective.
A base model was created of a petrochemical cluster containing a steam cracker capable of serving the global market (3900 kt HVC/year) to answer the research question. The base model was used to develop six models with different decarbonisation options capable of accepting alternative feedstock. Decarbonisation options were based on carbon capture and storage (CCS), both post and pre-combustion, electrification and hydrogen. The alternative feedstock was sourced from the renewable materials: vegetable oils, animal fats, crude tall oil and lignocellulosic biomass. Also, plastic waste (recycled) and synthetic (FT wax and naphtha) feedstock made from captured CO2 and hydrogen were included. The maximum percentage of HVC produced from alternative feedstock was assumed to be 25% due to uncertainties and limitations in the availability of alternative feedstock. The rest of the HVC was yielded from a mixture of fossil feedstock (naphtha, LPG, ethane, gas oil and butene). Different experiments were performed to estimate the emission reduction potential of separate or combined decarbonisation options with HVC yields originating from alternative feedstock ranging from 0% to 25%. The supply chain and associated CO2 emissions of the feedstock were also analysed. Next to determining the emission reduction, the quantitative data from the models were also used to assess the levelized cost of zero emissions HVC and the geographical and infrastructural limitations of decarbonisation options. One problem was the residual fossil fuel gas from the process, possibly leading to unwanted emissions elsewhere if not appropriately handled. In conclusion, the only decarbonisation options capable of dealing with this problem are CCS and auto-thermal reforming combined with CCS. Together with renewable feedstock, from a cradle-to-gate perspective, these options are capable of reaching net-zero emissions or even negative emissions when fossil and renewable feedstock supply chain emissions are drastically reduced. For future research, it is advised to not only focus on producing HVC with steam cracking but also consider other greenfield production method capable of producing HVC with renewable resources. A comparison with the proposed pathways in this research would provide valuable insights.