Abstract

"H2 gas" refers to hydrogen gas (H2), which can be used as a clean energy carrier, meaning it can store and transport energy produced and is primarily utilized in fuel cells to generate electricity with only water vapor as a byproduct when combined with oxygen, making it a potential clean energy source.

H2 is primarily used in industrial processes like petroleum refining and ammonia and steel production; it is also increasingly explored as a clean fuel source for transportation due to its potential for low carbon emissions.

An "H2 hub" refers to a regional network of clean hydrogen producers, consumers and the necessary infrastructure to connect them. The primary focus is on developing these hubs to accelerate the production and use of clean hydrogen by creating a nationwide network for clean hydrogen usage.

In a hydrogen hub, a control system plays a critical role in managing and optimizing the entire hydrogen production and distribution process.

Introduction 

An "integrated control system" (ICS) in hydrogen gas production refers to a centralized system that monitors and manages all operations of the hydrogen production process, including the natural gas compressor system, instrument air package, pressure swing adsorption unit and hydrogen gas compressor system.

In figure 1 below, the process control system (PCS) acts as a main PLC that will communicate with various package systems. The PLCs for these packages will act as a slave PLC where the information will be exchanged with the master PLC in STAR network topology over redundant communication.

The signals fetched from master PLC (PCS) will be communicated to the central control room (control building) that will house operator and engineering workstations.

When designing a control system architecture, the below things can be considered:

• Scalability: Whether the system can be easily expanded to handle future growth and changes in requirements. This includes both vertical scalability (increasing the capacity of a single system) and horizontal scalability (adding more systems). 

• Emergency shutdown systems (SIS): Implementing robust emergency shutdown procedures to quickly isolate the system in case of abnormal conditions.

• Security: Protecting sensitive data and ensuring the system can't be manipulated. This may include access controls, encryption and intrusion detection systems. 

• Maintainability: Designing the system so it's easy to update, fix bugs and enhance. This can include breaking the system into modules, using design patterns and following coding standards. 

• Redundancy: Backup components (hardware, software or network paths) should be evaluated ensuring continuous operation even when a part of the system malfunctions.

• Hierarchical structure: Organizing the system into layers, with the supervisory level at the top and control layers below. A control system's architecture defines how its controllers interact with the system, and includes the system under control, sensors, filters and interconnections. 

Figure 1

Results and Observations

Key aspects of an integrated control system include:

• Centralized data access: Collects data from various systems like compressor systems, instrument air package, pressure swing adsorption, selective catalytic reduction unit and more, presenting it on a single interface for comprehensive monitoring and analysis. 

• Improved operational efficiency: By integrating different systems, ICS allows operators to monitor and adjust plant operations from a central location.

• Enhanced decision-making: Real-time data from multiple sources allows operators to make informed decisions based on a holistic view of the system status. 
• Streamlined automation: ICS can automate complex processes by linking different control systems, enabling automated responses to changing conditions.

Figure 2 (below) highlights the overall connectivity between various hydrogen hubs, integrating with the control room over a connected cloud.

Figure 2

Conclusion

In hydrogen production hubs, a control system plays a critical role in managing and optimizing the entire process by controlling key process variables like pressure, temperature and flow rates to run the hubs efficiently.

The control system — through SIS — incorporates safety measures to automatically respond to abnormal conditions like high pressure, temperature excursions or unexpected changes in gas composition, shutting down the process if necessary.

References

• NFPA 2 (Hydrogen Technologies Code)
• International Electrotechnical Commission (IEC), IEC 61511, “Functional Safety: Safety Instrumented Systems for the Process Sector,” Geneva, Switzerland
• International Society of Automation (ISA), ANSI/ISA S84.01, “Application of Safety Instrumented Systems (SIS) for the Process Industry,” Durham, NC
• International Electrotechnical Commission (IEC), IEC 61508, “Functional Safety of Electrical/Electronic/Programmable Electronic Safety Related Systems,” Geneva, Switzerland