processes and biomass processes. Figure 1 shows the technologies iden- tified and covered by IDTechEx for blue hydrogen production.2 Al Humaidan et al have also reviewed blue hydrogen in terms of status and future technologies. The bespoke publi - cation highlights the following aspects: “Significant transition is expected in world energy system over the next 30 years, inclusion of blue hydrogen is inevitable for the transition toward hydrogen-economy.” The techno-eco - nomical assessment of many recent studies has indicated that the oxy - gen-based system, such as ATR and partial oxidation, is the most efficient for producing greenfield blue hydrogen. The Shell Blue Hydrogen Process (SBHP) reflects a new way to produce blue hydrogen from natural gas or other hydrocarbon gases (refinery off-gases) that integrates other proven Shell tech - nologies, which is another important route that has been well reported in recent publications.3 Blue hydrogen: Mature production processes Steam methane reforming SMR, a proven catalytic technology, is widely applied for grey and blue hydrogen production, primarily due to its cost effectiveness and ability to obtain high-purity hydrogen. Globally, it is estimated that 75% of all hydrogen supply comes from SMR technology. Initially, natural gas (methane) is des - ulphurised to remove small amounts of sulphur and pretreated to convert higher hydrocarbons to methane, hydrogen, and carbon monoxide (CO) and to prevent coke formation leading to catalyst deactivation. The mixture is then preheated and passed over an alumina-supported nickel catalyst (Ni/ Al 2O3) in the pre-reformer unit, typically operating at a pressure of 35 bars and under high temperature (697-827ºC). At this stage, reacts with the steam, leading to the production of CO and methane, as indicated in Equation 1:
water-gas shift (WGS) reactors, result - ing in additional hydrogen production, as shown by Equation 2:
CO + H2O CO2 + H 2, ΔH°298K = -41.1 kJ/mol (2)
The overall reaction is highly endo - thermic. The reformer consists of catalyst-packed tubes inside a fired industrial furnace that uses a portion of the natural gas feedstock as fuel to pro - vide heat to the endothermic reaction. Finally, the impurities and produced CO2 are captured from the off-gas by different methods depending on the amount of CO2 to enhance the quality of produced hydrogen. More recently, the Shell Cansolv CO2 capture system was introduced to capture nearly all the CO2 (99%) from low-pressure, post-com - bustion flue gas. The system can be retrofitted to convert grey hydrogen production to blue. Autothermal reforming of methane The ATR process4 aims for hydrogen production while saving significant amounts of energy for the reaction com - pared with the SMR endothermic reac - tion. However, an air separation unit (ASU) is required to provide a pure oxy - gen supply for the process. Initially, in the presence of a nickel catalyst, steam, natural gas, and oxygen react in an adiabatic ATR reactor to form syngas, which contains steam, hydrogen, CO, CO2, and some trace gases. The heat generated due to POX is simultaneously used for the endothermic reforming reaction without the need for additional fuel. After that, the resulting syngas is cooled and fed to the WGS unit, where steam reacts with CO over an Fe and Cr catalyst to produce hydrogen and CO2 . CO2 is then separated from the hydro - gen-rich gas using an amine-based syngas purification unit or liquefied nat - ural gas (LNG)-based cold energy sys - tem. Additionally, the hydrogen-rich gas is further purified from any unconverted CO, argon, and other impurities, using a PSA unit, up to 99.9% hydrogen.4 Partial oxidation (POX) In this process,1 methane is partially oxidised as per Equation 3, with oxy - gen typically sourced from a cryogenic ASU. The CO shift reaction, Equation
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CH4 + H 2O CO + 3H2 , ΔH°298K = +241 kJ/ mol (1)
After that, at ~197-247ºC and 347- 547°C, CO undergoes another reform - ing process to convert it to CO2 using
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