Decarbonisation Technology - November 2021

for electric motor drives for the compressors, as the steam generation from the cracking furnaces is much reduced. 560 MW is approximately equivalent to the power consumption of 276,000 average EU households. It is clear that start-up and shutdown of the plant represents a significant impact on the power demand local to the site, unless the site is provided with its own dedicated power supply. As the fuel gas generated in the ethylene plant is not used in the furnaces, another use has to be found for this. Carbon capture and storage/carbon capture and utilisation (CCS/CCU) Carbon capture (CC) has been proven in the power industry and can be applied to steam crackers. Apart from the use of high hydrogen content fuels, CC is the only currently commercially proven technology which can achieve very high levels of reduction of CO 2 emissions from steam crackers. Typically, CC can achieve 90-95% CO 2 removal. The CO 2 would be removed from the furnaces and, if required, the auxiliary boilers. From studies carried out by Technip Energies, it is feasible to operate the steam cracker without the CC plant, therefore the operation and start-up of the steam cracker should not be affected by the addition of the CC plant. It is straightforward to design a new steam cracker with future provision for installation of CC. The main requirements are: • Provision of tie-in connections on furnace and boiler stacks • Provision of plot space for the CC plant, as close as possible to the furnaces and boilers, to minimise the length of the flue gas ducting • Provision of space for the flue gas ducting and support on furnace and boiler structures In addition to the above points, the utilities requirements of the CC unit should be considered when the cracker is designed. Whether or not pre- investment is made in the cracker, to allow for the future utilities requirements of the CC unit, needs to be decided on a case-by case basis. Where such investments can be made for relatively low incremental Capex, and future expansion could be very expensive or disruptive to operations (e.g. cooling water intakes and water treatment plants), then pre-investment may be justified. The conventional routes for captured CO 2 are for

oilfield recovery or storage. These routes are only accessible to certain plants, generally those located close to the sea and/or a now unused oil pipeline. An alternative for captured CO 2 is conversion to saleable products, 6 such as methanol and ethanol (which can be converted to olefins) and methane (for export as fuel). Technip Energies anticipates that these routes will be of most interest to cracker operators, as these produce green products which fit with their existing product portfolios, customer base and infrastructure. The technologies are all at early stages of development and only certain parts are currently commercialised. It should be noted that one of the main Capex and Opex items associated with a conventional CCS plant is the compressor to raise the CO 2 to over 100 bar(g) for discharge to a pipeline for oilfield recovery or storage. When the CO 2 is used to make product, much lower pressures are required and both Capex and Opex can be reduced. It should be noted that CC does not rely on having low CO 2 electricity available to reduce the CO 2 emissions from the cracker, although the increased utility demand for the CC plant should be met with as low a carbon footprint as possible. Application of CC does not result in an increase in surplus fuel gas from the cracker. Associated with CC is oxycombustion, which is the firing of the cracker fuel with oxygen rather than air, in the furnaces and possibly the boilers. The advantage of oxycombustion is that it can eliminate the need for the carbon capture plant, as most of the nitrogen is removed from the flue gas. Some purification of the CO 2 is required to meet typical specifications for CO 2 used for oilfield recovery. In order to fit oxycombustion into conventional cracking furnace designs, it is necessary to re-circulate flue gas to the furnace burners, to reduce the high flame temperature and provide an adequate volume of flue gas for heat transfer in the furnace convection sections. Consideration also has to be given to the start-up of the furnaces and the cracker, when a transition will need to be made between ambient combustion air and oxygen. Use of oxycombustion requires an air separation plant to produce the oxygen. The air separation plant has a significant Capex and its own CO 2 footprint. Application of oxycombustion requires the development of burner designs to fire oxygen, and the associated modifications to the furnace design.