Decarbonisation Technology - November 2021

and performance is being developed and studied (burning hydrogen is likely to result in shorter, hotter, flames, which, combined with a reduced flue gas flow rate, results in reduced steam production from the furnaces and lower radiant section inlet temperatures). Also, some types of burners are not well suited to burning high hydrogen fuels. Hydrogen can either be generated from the fuel gas generated in the cracker by reforming or imported from outside the cracker. Hydrogen from outside the cracker would normally be generated by electrolysis. Currently, the most mature electrolysis technology is alkaline electrolysis (AE). Taking the AE technology as an example, Table 1 provides a comparison between hydrogen from electrolysis and hydrogen from SMR reforming the cracker fuel gas. The data is for a 1,500 kTA ethylene liquid cracking plant. The AE estimated figures are based on the data from Reference 8, supplying 100% pure hydrogen to provide the same heat duty as the hydrogen from an SMR reformer converting the fuel gas. It can be seen from the figures in Table 1 that: • By all measures (Opex, Capex, CO 2 emissions, power consumption) reforming provides a better solution than currently available electrolysis technology • Electrolysis consumes a large amount of electricity, which can represent a considerable operating cost

Figure 2 Technip Energies’ Low CO 2 Furnace Design

• The Capex for electrolysis is currently very high; however, this is predicted to decrease in the period 2021-2050 • For electrolysis, the CO 2 footprint of the cracker

Source of hydrogen

Parameter

Alkaline electrolysis

SMR (blue H 2 )

Quantity of hydrogen, t/h (Nm 3 /h) Technical cost of hydrogen, $/kg

29.9 (332,500)

29.9 (332,500) a

3.6 1.6 1.7

0.33 0.02 0.11 0.04 0.4

Electrical power, GWh

Capex, $bn

CO 2 from electricity @ 376 tCO 2 e/GWh, MMt/year CO 2 from electricity @ 26 tCO 2 e/GWh, MMt/year

4.70 0.33

Parameter

Cracker + AE

Cracker + SMR

Tonnes of CO 2 /t HVC @ 376 tCO 2 e/GWh electricity Tonnes of CO 2 /t HVC @ 26 tCO 2 e/GWh electricity

b , tCO

2 e/tHVC

1.72 0.21

0.24

c , tCO 0.12 Notes: a. Figure given is for the contained hydrogen in the SMR product. Total heat value of SMR product is the same as that of the hydrogen from electrolysis. b. 376 tCO 2 e/GWh electricity is the basis used for the calculation of cracker CO 2 footprints for comparison with the benchmark in the European Emissions Trading Scheme (ETS) c. 26 tCO 2 e/GWh electricity is the average value for electricity generated from wind or hydroelectric 9 2 e/tHVC

Table 1 CO 2 , Capex and Opex figures for hydrogen from electrolysis and reforming