Decarbonisation Technology - November 2021

Decarbonisationof steamcrackers A number of technologies are available to reduce the CO 2 emissions fromsteam crackers – fromelectrification and CCUS to electric furnaces

JimMiddleton Technip Energies

Introduction The majority of the worldwide production of petrochemicals (PCs, e.g. ethylene, propylene, butadiene and aromatics) originates from the steam cracking process. As steam cracking is a thermal process, a significant amount of energy is used to manufacture the products. Because of this, steam crackers are a significant emitter of CO 2 in the chemical industry, and chemicals represents the third largest direct source of CO 2 emissions in the industrial sector (after iron & steel and cement). 1 One estimate of worldwide CO 2 emissions from steam crackers 2 shows 198.7 million tonnes of CO 2 in 2015, projected to increase to 264 million tonnes of CO 2 in 2030, or a 33% increase (mid-range of estimate figures are quoted). Clearly, with the global drive to reduce, and then minimise, industrial CO 2 emissions, action is required. The objectives of the industry are twofold: to reduce or capture CO 2 emissions from the conventional steam cracking process and to seek alternative technologies with lower CO 2 footprints. Modern steam crackers are well optimised and integrated, such that almost all the fuel gas fired in the furnaces is generated from the process. In addition, high pressure steam is generated from the waste heat from the furnaces, which is used to drive the main compressors and for process heating. The reduction of CO 2 emissions from the cracker means replacing the methane fuel from the process with alternative lower carbon fuels, such as hydrogen or electrical heating. While the CO 2 emissions from the furnaces can be reduced to zero by using 100% hydrogen or electricity for heating, the CO 2 footprint associated with the generation of the hydrogen or electricity has to be carefully evaluated, as these can exceed the CO 2 footprint from burning the methane fuel.

Waste heat 5%

Generate high pressure steam 20%

Crack the feed 25%

Heat the feed 50%

Figure 1 Fired duty splits

When electricity needs to be relied upon for decarbonisation of steam crackers, additional considerations are the availability, reliability and the actual carbon footprint of the power supply, involving many local factors, not all of which may be clear at the time the project final investment decision (FID) is being made. Reduction of CO 2 from cracking furnaces The furnace fired duty splits approximately as shown in Figure 1 in a liquid cracking furnace. Of this duty, the amount used to crack the feed has to be provided by firing fuel, but the other duties can be reduced by energy optimisation, resulting in minimised fuel firing. The fired duty, and consequently the CO 2 emissions, can be reduced by 20-40%, the maximum reduction being achieved by Technip Energies’ patented 3,4 Low CO 2 Furnace design (see Figure 2 ). Firing hydrogen Complementary to the reduction of firing is increasing the hydrogen content of the fuel gas. As the burning of hydrogen does not generate CO 2 , this is a relatively easy way of reducing the CO 2 emitted from the cracker. The impact on the furnace burners