Nov-2023

Using water electrolysis to transform hydrogen production (RI 2023)

There is a global trend toward producing clean hydrogen to achieve the ambitious net zero emissions target by 2050.

Jagadesh Donepudi and Rodolfo Tellez-Schmill
KBC, a Yokogawa company

Article Summary

The US government has made strides in this direction, recently publishing its National Clean Hydrogen Strategy and Roadmap.¹ Underlying this initiative is the goal to reduce greenhouse gas emissions by 50% from 2005 levels by 2030.

Along with this initiative is the need to produce affordable, clean hydrogen, with a target price of 1 USD/kg of hydrogen in one decade. Currently, the estimated production cost of hydrogen via electrolysis ranges between 5 and 7 USD/kg of hydrogen. The US aims to produce 10 million metric tons (MMT) of clean hydrogen per year, mirroring similar targets from the EU across all its member states by 2030.

Within the realm of hydrogen production, the use of alkaline electrolysis is well-established. While it has been applied on a large scale for decades, it also presents technical challenges. These obstacles include high energy consumption, installation costs, and maintenance costs due to corrosive alkali materials. The proton exchange membrane (PEM) electrolyser represents a new technology. It is easy to handle and maintain while generating high-purity hydrogen (99.99% dry basis). PEM, however, also displays some flaws, such as high manufacturing costs for membranes and requiring precious metals for electrodes.

The Government of India announced its Green Hydrogen Mission² to achieve net zero emissions by 2070. This green initiative spans multiple sectors, including refining and petrochemical processes, fertiliser production, mobility, steel manufacturing, and railways. This road map includes manufacturing 5 MMT/year of green hydrogen through green electricity and bioprocesses by 2030, where refineries and fertiliser manufacturers are the major consumers of this resource.

Producing Green Hydrogen
The important aspect of producing green hydrogen involves the electrolyser, which is the technology that splits water into its core elements of hydrogen and oxygen. They are important for efficient and scalable hydrogen production. The estimated cost of producing green hydrogen ranges between 5 and 10 USD/kg compared to grey hydrogen, which costs about 1.5 USD/kg.

Monitoring Water Electrolyser Performance
In this dynamic area, process simulation models have become increasingly important. With a simulator, the user now has the ability to model alkaline, PEM, anion exchange membranes, and solid oxide electrolysers. Users can build digital twins for green hydrogen production processes for design and operation. Furthermore, operation engineers can leverage digital twins to monitor the performance of the water electrolyser. It helps pinpoint potential issues related to asset performance, such as electrode degradation, corrosion, and excessive energy costs.

Process simulator software can be used to build simulations and digital twins of water electrolysers to perform the following activities.
• Design engineering: Process simulation models support critical process and mechanical design activities, including flowsheeting, heat and mass balances, equipment sizing, process optimisation, equipment/instrumentation datasheets, equipment and piping material selection, designing process control strategies, as well as assessing hazards and operability.
• Plant operation: Process simulation models, when connected to plant data, create a digital twin, aiding asset monitoring, data reconciliation, unit monitoring, optimisation, retrofitting, energy management, and emissions monitoring to ultimately enhance profitability and safety.
• Operators training: Dynamic simulations can be incorporated into operators’ training systems to expedite the learning curve of how the system works before the plant is commissioned.
• Real-time optimisation and advanced process control: Process simulation models enable ongoing adjustment to market changes, disturbance accommodation, plant optimisation, retrofitting, and hazard reduction to increase profitability.
• Research and development: Process simulation models facilitate in-depth analysis of current technologies, exploration of future technologies, and identification of potential challenges within the electrolysis domain.
The PEM electrolyser in the Petro-SIM process simulator is shown in Figure 1.

Understanding Voltage Calculations
Voltage calculations provide a solid foundation for understanding the energy requirements and feasibility of electrolysis at standard conditions (25°C and 1 atm) and at different pressure or temperature values. As seen in Figure 2, voltage calculations are a crucial aspect of electrolysis to determine the process’s efficiency and feasibility. These calculations include:
• Electrolysis that requires a minimum supply of electric energy, represented by the reversible voltage from the estimated Gibbs free energy of formation of water:

• The maximum natural amount of energy for electrolysis that corresponds to the thermo-neutral voltage calculated from the heat of formation of water:

Using thermodynamic models, advanced process simulators determine precise estimates of reversible and thermostable voltages based on temperatures and pressures.

System Analysis via Process Simulators
Using digital twin electrolyser models, all system curves for voltage requirements and hydrogen production can be assessed, including the estimation of hydrogen crossover, as shown in Figure 3.

Conclusion: Growing Need for Process Simulators
The demand for computer tools that facilitate engineering design, operations, optimisation and even for research and development is high. With careful planning and diligently applying advanced mathematical and engineering principles, operators can achieve relatively low hydrogen production costs while capitalising on substantial tax credits. According to the US Inflation Reduction Act,³ these tax credits can reach 3 USD/kg of hydrogen when the lifecycle of greenhouse gas emissions (GHG) emissions does not tip 0.45 kg of CO₂e/kg hydrogen.

The water electrolyser unit operation marks a significant milestone. This new unit empowers operators to model many types of electrolysers. Users can build digital twins for green hydrogen production processes for both design and operation. Finally, operation engineers can leverage the digital twin to monitor the  performance of the water electrolyser.

This short article originally appeared in the 2023Refining India Newspaper, which you can VIEW HERE