Pre-Normative Research on Gaseous Hydrogen Transfer

Amongst the key questions: Is pre-cooling to -40°C actually necessary for a 3 minute hydrogen refill of a 70 MPa FCEV?

CFD simulation of the filling of a 531 litre hydrogen tank with hydrogen at -20°C for 25 minutes. As one result, thermocouples for recording temperature during experiments were placed according to this temperature field.  Source: Air Liquide-aT / HyT 2014
CFD simulation of the filling of a 531 litre hydrogen tank with hydrogen at -20°C for 25 minutes. As one result, thermocouples for recording temperature during experiments were placed according to this temperature field. Source: Air Liquide-aT / HyT 2014

Challenge: Overheating and Overcooling during Hydrogen Filling

Hydrogen transfer concerns filling and emptying processes. Filling generates heat which can lead to overheating of composite pressure vessels when filling transportable containers, onsite storage gas vessels or fuelling vehicles. Emptying generates cooling. Excessive cooling may occur during delivery of hydrogen from a trailer.

 

Graphical example of the simulations that are going to be performed as part of HyTransfer. Source: JRC
Graphical example of the simulations that are going to be performed as part of HyTransfer. Source: JRC

Aim: Converting New Filling Approach into RCS Recommendations

HyTransfer aims to develop and experimentally validate a practical approach for optimizing means of temperature control during fast transfers of  compressed hydrogen to meet the specified temperature limit (gas or  material) taking into account the container and system‘s thermal behaviour.

This project aims to create conditions for an uptake of the approach by international standards, for wide-scale implementation into refuelling protocols. The new approach will be thus evaluated and its benefits quantified with regards to performance, costs, and safety. Finally, recommendations for implementation into international standards will be proposed.

 

Approach: Tank Wall Temperature is Critical

As hydrogen vehicle refuelling is the leading application, the project will thus focus on fast filling of composite tanks. To avoid overheating, the speed of transfer has to be limited or the gas to be cooled prior to introduction. Both solutions impact on performance and cost, therefore temperature control is essential for optimization of gas transfer. Temperature limits on hydrogen transfer can be applied to material that must not exceed design temperature (e.g. 85°C), or to the gas that must not exceed a specific limit. A model will be developed for a better understanding of the thermal behaviour of the tanks, the results obtained with this model will be compared with those obtained from experiments to check its accuracy.

 

The two graphs show the influence of the orifice in the inside gas temperature development during a tank filling. With a bigger orifice the gas temperature in the tank is not homogeneous.

Experimental Set Up
Experimental Set Up

The experimental set up on the left will be used. Thermocouples are  distributed throughout the tank volume to identify different temperature zones and inhomogeneity's including hot spots. Test results will be used to verify and improve thermodynamic modelling.