Jul-2024

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

Article Summary

Interest 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 produce 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 energy-related aspects. The study revealed that moderate pressures and oxidant-to-methane ratios find the best balance between H₂ production and process efficiency in all investigated reforming options. Under these conditions, SMR performs better than dry methane reforming. However, if the reformer operates under autothermal conditions, the performance 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 techno-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 separation unit (ASU), thus avoiding the need for oxygen carrier circulation. 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 concepts show continued performance improvements with an increase in reactor pressure and temperature, while an optimum 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 natural 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:
υFuel (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.

ϖGHG emissions and cost of producing hydrogen. The environmental implications of blue hydrogen can vary widely, contingent upon a few critical factors: the methane emission rate within the natural gas supply chain, the CO₂ removal rate at the hydrogen production plant, and the specific global warming metric employed. Advanced reforming techniques, characterised by high CO₂ capture rates, in conjunction with a natural gas supply featuring minimal methane emissions, result in a substantial reduction in GHG emissions compared to conventional natural gas reforming. Under these optimised conditions, blue hydrogen aligns with low-carbon economies and demonstrates climate change impacts towards the upper spectrum of those associated with hydrogen production from renewable-based electricity.

Typical GHG emissions and the cost of producing hydrogen¹ for 607 tonnes of hydrogen production per day are shown in Table 1. Blue hydrogen from ATR has the lowest life cycle GHG emissions, followed by NGD SMR-85% and SMR-52%, with the longest life cycle GHG emissions of 8.20 kg CO₂eq/kg H₂.

Data relating to blue hydrogen production cost for 607 tonnes of hydrogen production per day, as shown in Table 1, suggest that ATR-CCS and NGD-CCS produce hydrogen with the lowest and highest costs, respectively. ATR-CCS and SMR 52% have lower blue hydrogen production costs and are economically preferable to NGD-CCS and SMR-85%. These cost figures may change with sensitivity analysis involving hydrogen storage and internal rate of return (IRR).

ω Scale factors and the effect of plant capacity on blue hydrogen cost Two plant capacities of 50 to 1,000 tons/day of hydrogen production were investigated by the researchers. The capital cost of each was estimated to determine the plant scale factor using process simulation models for each plant. Figure 1 presents the economic feasibility of increasing plant capacity. It further shows the plots of capital cost vs plant capacity for the four hydrogen technologies. For all the cases considered, the scale factor value indicates that to lower the hydrogen cost, plant capacity needs to be increased.

Figure 2 presents the economic feasibility of increasing plant capacity. Hydrogen costs decrease as plant capacity increases. It is worth mentioning that decreasing ATR-CCS hydrogen production cost is steeper because of its lower operating costs. ATR-CCS and NGD-CCS are more attractive economically for large-scale hydrogen production. Since economies of scale exist for all blue hydrogen technologies, operating the plants at a higher capacity will be beneficial.