Hydrogen Refueling Stations: Designing for Efficiency, Safety, and Cost-Effectiveness with Simcenter Amesim

The Complex Reality of Hydrogen Refueling Stations

Despite the clean and seamless appearance of hydrogen refueling stations, their internal systems are intricate. HRS consist of multiple interconnected components, including compressors, valves, tanks, heat exchangers, and advanced control systems. These components must work harmoniously to meet design requirements such as:

• Fast refueling times: 5 minutes for passenger vehicles or 10-15 minutes for large trucks.
• Thermal regulation: Preventing hydrogen temperatures from exceeding safe limits (typically 85°C) to avoid damage to vehicle tanks.
• Safety compliance: Monitoring flows and pressures to prevent risks like explosions.
• Energy efficiency: Minimizing energy consumption for compression and cooling.
• Cost management: Reducing CAPEX and OPEX while ensuring system reliability and performance.

Simcenter Amesim, a comprehensive system simulation platform, provides the capabilities needed to design, analyze, and optimize hydrogen refueling stations. Here’s how it empowers technical teams:

1. Sizing Analysis

Simulate and analyze hydrogen flow, pressure, and temperature in each subsystem.

Accurately size compressors, tanks, pipes, and valves to match operational requirements.

2. Real Gas and High-Pressure Modeling

Utilize advanced equations of state (EoS) for real gas behavior at high pressures.

Predict the effects of rapid hydrogen compression on temperature and pressure.

3. Thermal Management

Design efficient cooling systems to regulate hydrogen temperatures during compression.

Size thermal management components to ensure safe delivery temperatures.

4. Control Strategies

Develop state machines and control logic for optimal system operation.

Test and validate control strategies to reduce refueling time and energy consumption.

5. Virtual Commissioning

Connect simulations to PLCs and hardware devices for automation testing.

Detect and address potential issues before deployment, reducing development time.

Fig. 1: System model

Modeling the refueling station

Hydrogen source

Refueling stations can produce their hydrogen locally, for instance using a combination of solar panels with an electrolyzer. Another alternative is that hydrogen is produced with a larger electrolyzer system to reduce the cost and then transported to the refueling station, for instance using a tube trailer. We will consider this later case in our model with the following assumptions:

• Tube trailer tank volume: 5 m3
• Initial pressure: 200 bar
• Initial temperature: 20°C

In these conditions, the initial quantity of hydrogen in the tube trailer is close to 76 kg.

Fig. 2: Tube trailer

Hydrogen compression system

To fill the hydrogen from the trailer tube pressurized at 200 bar to the vehicle tank expected pressure at 700 bar, the system is using 2 volumetric compressors operating in parallel with the following assumptions:

• Compressor displacement: 150 cm/rev
• Compressor rotary velocity: 120 rpm

Thermal management

To keep the system safe, increase the quantity of hydrogen stored in the tank and avoid high temperatures that would damage the vehicle tank liner, several heat exchangers are integrated in the system. In our case, we assume that heat exchangers are integrated:

1. at the outlet of compressors to cool hydrogen down to 30°C after compression
2. upstream the vehicle tank to supply hydrogen to the vehicle tank at a temperature close to -50°C.

Hydrogen buffer tanks

Low-pressure, medium-pressure and high-pressure tanks are integrated in the system. They can be used to reach several purposes:

• Speed up the vehicle tank refilling
• Downsize compressors or reduce their operating speed
• Reduce the warming up of hydrogen during compressions and then downsize cooling systems

The buffer tanks are fined as follows:

• Low-pressure tank

Initial pressure: 380;  barVolume: 500 L

• Medium-pressure tank

Initial pressure: 580 bar: Volume: 300 L

• High-pressure tank

Initial pressure: 850 bar; Volume: 300 L

Controls

Controls strategies are used to control the compressors and system valves. Strategies are based on a state controller. The state transitions are mainly driven by the value of pressures in the tube trailer, the buffer tanks and the vehicle tank.

Roughly, when the vehicle tank is connected to the refueling system, valves are opened to smoothly equilibrate the vehicle tank pressure with the one of the tube trailer. Then, the compressors can be activated or the buffer tanks can be used.

Fig. 5: Valves and compressors controls: Amesim block and the associated state control logic

First case: refilling the vehicle tank without using the buffer tanks

Using our system model, we can simulate the refilling of the tank, using the hydrogen from the tube trailer and the 2 compressors. The valves of the buffer tanks are remained closed during that process. The simulation is stopped once the vehicle tank pressure reaches the goal pressure (700 bar).

A first interesting way to analyze simulation results within Simcenter Amesim is using the Sketch Animation. Sketch Animation makes it possible to visualize on the model sketch the dynamic evolution of pressures or temperature all along the scenario and in the different part of the system (Fig.6 and Fig.7).

Fig. 6: Sketch Animation of the temperature repartition in the system

Fig. 7: Sketch Animation of the pressure repartition in the system

Fig. 8: Evolution of tank pressure and hydrogen mass in the vehicle tank

The maximum power consumed by the 2 compressors is close to 17.3 kW and the energy consumed by these compressors is close to 1.1 kW.h (Fig. 9).

Fig. 9: Evolution of compressors power and energy consumption

The 2 heat exchangers integrated downstream the compressors must be able to extract some heat corresponding to 6.4 kW when the heat exchanger integrated upstream the vehicle tank must be able to extract 26 kW (Fig.10).

Fig.10: Heat flow rate of heat exchangers

These results are interesting and charging our FCEV in 8 minutes is already much faster than recharging batteries of a BEV. However, it is not really satisfying as the purpose is to be able to refill the tank of a passenger car tank in less than 5 minutes.

Different possibilities can make it possible to reach this target:

• We can for instance modify our model and check if a system with 4 compressors with their own heat exchangers would be able to fulfill the requirement. But that would generate a more complex and more expensive system.
• The model can also be used to identify that increasing compressors displacement to 320 cm/rev also make it possible to refill the vehicle tank in less than 5 minutes. But still, we will need to extract more heat with heat exchangers located downstream the compressors (14 kW) and bigger compressors and heat exchangers will be more expensive and will certainly generate more noise.
• Another quite simple alternative would be using buffer tanks. That’s what we will consider in the second scenario.

Second case: Refilling the vehicle tank using the buffer tanks

Using the same system model than previously, it is possible control valves to take benefit of the buffer tanks.

Once the vehicle tank pressure is close to the trailer tube one (200 bar), the control strategy actuates the opening of the valve connected to the low-pressure buffer tank (380 bar). Once the vehicle tank pressure is balanced with the one of this buffer tank, the valve is closed again and it is the turn of the valve of the medium buffer tank (580 bar) to be opened. Finally, when the vehicle tank pressure is balanced with the one of the medium-pressure buffer tank, the valve is closed again and the valve of the high-pressure tank (850 bar) is opened.

When the vehicle tank is filled at 700 bar, the compressors are finally used to re-establish the buffer tank pressures at their initial level.

Fig.11: Sketch Animation of the temperature repartition in the system

Once again, we can use the sketch animation to visualize, all along the scenario, the dynamic evolution of pressures or temperatures in the different parts of the system (Fig.11).

We can also identify that using the buffer tanks, the system is now able to refill the vehicle tank faster than five minutes. So, the target is reached: the FCEV is charged in a time like a conventional gasoline vehicle! Three additional minutes are then used by the system to re-compress the hydrogen in buffer tanks to their initial pressure level.

Fig.12: Sketch Animation of the temperature repartition in the system

However, we can notice that, as a drawback of this case, the compression now requires more power (up to 20 kW) and energy (1.5 kWh). This can mainly be explained by the need to compress hydrogen to 830 bars in the high-pressure buffer tank (Fig.13).

Fig. 13: Compression power and energy using the buffer tanks

On the other hand, there is almost no impact on the sizing of the cooling system as the maximum heat power that will need to be extracted is quite similar (Fig.14).

Fig. 14: Heat flow rate of heat exchangers with buffer tanks

Simcenter Amesim: The Competitive Edge

Simcenter Amesim stands out for its ability to address the unique challenges of HRS design. Key advantages include:

• Predefined libraries: Models for hydrogen components, thermal systems, and controls.
• Multidomain simulation: Integration of mechanical, electrical, thermal, and control systems.
• User-friendly interface: Simplified configuration and validation processes.
• Rapid scenario testing: Simulate and compare various design scenarios in seconds.
• Optimization tools: Fine-tune system performance to reduce costs and improve efficiency.

Conclusion

Hydrogen refueling stations are critical for the widespread adoption of hydrogen vehicles. With Simcenter Amesim, technical teams gain a powerful tool to design systems that are safe, efficient, and cost-effective. From sizing components to validating control strategies, Amesim simplifies the complexities of HRS design, accelerating development and reducing costs.

If you want to download the Simcenter Amesim demo model used to write this blog, click here.