PTQ Q3 2024 Issue

Blue hydrogen a low-carbon energy carrier: Part 2

Comparative studies of major hydrogen-producing technologies aid selection of novel and environmentally friendly methods for hydrogen production

Himmat Singh Scientist & Advisor

I nterest in blue hydrogen production technologies is growing. It is produced from fossil fuels, so some or nearly all the CO₂ emissions associated with its production are captured and sequestered. As described in Part 1 ( PTQ Q2 2024 ), there are three primary mature processes to pro- duce blue hydrogen. However, production depends upon important factors such as feedstock availability, technology readiness level, and economic feasibility, which ensure blue hydrogen sustainability. Some researchers have evaluated the environmental and/or economic feasibility of producing blue hydrogen, but a holistic assessment is still needed. 1 Recent studies are briefly reviewed and compared. Comparison based on thermodynamic model Roberto Carapellucci and Lorena Giordano have compared three reforming processes: steam methane reforming (SMR), dry methane reforming, and autothermal reforming (ATR) using a thermodynamic equilibrium model developed and validated via comparison with literature data. The influence of operating conditions on the performance of the reforming options was investigated, addressing chemical and ener- gy-related aspects. The study revealed that moderate pres- sures and oxidant-to-methane ratios find the best balance between H₂ production and process efficiency in all investi - gated reforming options. Under these conditions, SMR per- forms better than dry methane reforming. However, if the reformer operates under autothermal conditions, the perfor- mance of dry methane reforming approaches that of SMR. Comparison based on chemical looping and membrane-assisted ATR Schalk Cloete et al have reported a comparative tech- no-economic study of membrane-assisted chemical looping

reforming (MA-CLR) and that of membrane-assisted ATR (MA-ATR) that inherently avoids a technical challenge faced by the chemical looping reformer. The novelty of MA-ATR lies in replacing the MA-CLR air reactor with an air separa- tion unit (ASU), thus avoiding the need for oxygen carrier cir- culation. The economic study found that H₂ production from MA-ATR is only 1.5% more expensive than MA-CLR in the base case. The calculated cost of hydrogen (compressed to 150 bar) in the base case was 1.55 €/kg with a natural gas price of €6/GJ and an electricity price of €60/MWh. Both con- cepts show continued performance improvements with an increase in reactor pressure and temperature, while an opti- mum cost is achieved at about 2.0 bar H₂ permeate pressure. Natural gas prices represent the most important sensitivity. Comparison based on GHG emissions and cost A. O. Oni et al¹ carried out a comparative techno-economic and greenhouse gas (GHG) emissions assessment for nat- ural gas-based blue hydrogen production technologies: SMR, ATR, and natural gas decomposition (NGD). For SMR based on the percentage of carbon capture and capture (CCS) points, two scenarios – SMR-52% and SMR-85% – were considered. The investigations revealed:  Fuel (energy) and feedstock considerations: • SMR-85% consumes the most natural gas (as fuel and feedstock) and ATR-CCS the least. • SMR-85%, SMR-52%, and ATR-CCS source hydrogen from both steam and natural gas, so they consume less natural gas as feedstock than NGD-CCS. • ATR-CCS uses less fuel than SMR-85% and NGD-CCS. v GHG emissions and cost of producing hydrogen. The environmental implications of blue hydrogen can vary widely, contingent upon a few critical factors: the methane

GHG emission and cost data for different blue hydrogen-producing technologies

Progress name GHG emissions, kg CO₂eq/kg H₂ H₂ production

SMR

ATR 3.91

NTD 4.54

SMR 52%

SMR 85%

ATR-CCS

NGD-CCS

–

8.20

6.60

–

1.22

1.23

2.125

1.695

2.36

1.65

2.55

cost, $/kg H₂

Table 1

PTQ Q3 2024