Computational Fluid Dynamics Modelling of Dispersion of Hydrogen Pipeline

Introduction

Hydrogen is viewed as a carrier of energy with the potential of helping to overcome issues like air pollution, greenhouse gas emission and the security of the supply of energy (Leeth, 2018). With this, it is necessary to access all safety aspects that are related to the practical use of hydrogen other than just doing an assessment of the safety aspects of the production and use of hydrogen (Fekete, Sowards and Amaro, 2015). Hydrogen has the potential of becoming the main source of energy that would replace fossil fuels. Additionally, as a result of the higher dispersion effect of hydrogen. Its transportation via pipelines is more feasible. Dispersion is the process whereby gases mix with the surrounding air and consequently create new molecules that are hazardous to the environment. The release of hydrogen into the atmosphere would for a hydrogen-air cloud which could also be flammable (Dadashzadeh, Ahmad and Khan, 2016). The strength of the explosion that may occur is evident in the condition of hydrogen-air cloud, for example, its flow field. There was a massive hydrogen gas explosion in Polysar, Canada which killed three people in 1984 and led to the death of three people and injury of scores.

Today, gaseous hydrogen is transported through pipelines just the same way natural gases are transported. There are however technical concerns related to pipeline transmission of hydrogen which include;

• Hydrogen`s potential to embrittle the welds and steel used in the fabrication of the pipelines.
• The need to have a control on permeation of hydrogen and leaks.

Aim of the study

In the area of industrial safety and particularly in explosion and gas dispersion issues, CFD application is not very well advanced. This study will seek to develop a firm computational fluid dynamic model for the dispersion of hydrogen pipelines. The established predictive qualities of CFD codes in the field of hydrogen fuel safety are not very firm and as such, scatter results characterise benchmark exercises like those conducted on the HYSAFE Network of excellence.

Objectives of the study

• To study and compare the effect of hydrogen gas dispersion process in an underground pipeline.
• Develop a Computational Fluid Dynamics model for dispersion of hydrogen pipeline.

It is worth noting that hydrogen has problems with both hydrogen corrosion and embrittlement. Hydrogen contains an active electron which makes it to behave like a halogen. For such a reason, it is necessary that hydrogen pipes are capable of resisting corrosion. What compounds this problem is the potential of hydrogen to migrate into most metals crystal structures. The preferred piping for process metal piping at pressures of up to 7,000 psi (48 MPa) is high-purity stainless steel piping with a 80 HRB maximum hardness.

Small hole leakage in pipes as a result of perforation and erosion is a major form that leads to leakages. Leakage rates are an important premise and foundation for evaluation of risk and computation of consequences. Whenever leakage happens for gas pipelines acoustic waves generated at the point of leakage would propagate to the both ends of the pipe which would be measured and then subsequently processes to locate where the leakage specifically happened. Propagation of acoustic waves in the gas leads to attenuation of the amplitude and the waveform spreads. That decides the distance of installation of acoustic sensors.

One of the key components of analysis of risk of systems for storing fuels is development of an understanding of the behaviour of fuel releases in scenarios that are realistic, be they intentional or unintentional. With such knowledge, it would be possible to develop measure that would aid in the minimisation of the probabilities of accidents and of methods for mitigating consequences in the event an accident happened (Giannissi and Venetsanos, 2018). The accuracy of a procedure for leak detection would be dependent on the leak and flow parameters in any given pipeline. A numerical simulation would be more efficient for provision of a better understanding of pipeline internal flows and the additional consequences of pipeline leaks in scales that are different. Risk is in the context of safety defined as the combination of probabilities of harm occurrence and such harms severity (Rui et al., 2017).

Problems with modern fluid dynamics could not be possibly solved without using computational fluid dynamics (CFD). There exists a rather limited scope of analytical solutions within fluid dynamics, as such, whenever a difficult set of geometry is encountered, to obtain a solution, it becomes necessary to choose a given numerical method. The term CFD is used in reference to a spectrum of numerical methods that is wide used for solving time-dependent and three dimensional flow problems (Moukalled, Mangani and Darwish, 2016). Originally, the scientific field developed from the early approaches that were used to numerically solve the Navier-Stokes equation which up to date remains to be one of the most challenging problems.

Mainly, CFD is used for design of systems and enhancement of performance and high levels of confidence are generally attached to such calculations mainly because of;

• The increased awareness of best practice guidelines in setting up and carrying out CFD calculations.
• CFD codes benefit from a validation for flows that is complete and thorough and that is representative of the industrial applications (Blazek, 2015).

Before the advent of computers, fluid mechanical problems` numerical solutions were restricted to cases that were simple where, for example, methods of simplification that were used on the method of characteristics were used. Among the first methods to be relied upon more heavily were the relaxation schemes as there were several simplifications to the schemes that were manual which made calculations easier.

Using computational fluid dynamics, it can be possible to detect leakages in the transportation of hydrogen gas. The use of CFD is with no doubt the most effective and efficient means of studying the leakages of hydrogen gas as there are low costs involved in the process in comparison construction of pipeline networks that would test such situations. The use of computational fluid dynamics (CFD) modelling for safety purposes has been increasing as a result of the high costs attached to undertaking experimental hydrogen combustion and release in real-scale configurations. Additionally, CFD modelling also provides an opportunity for investigation of releases in real world environments.

Based on the FLUENT software, Xu et al (2018) established a CFD simulation model of hole leakages in pipes. They studied the impacts of crack geometric forms on small hole leakage rates of mid-low-pressure pipes and the existing aerodynamic characteristics of leakage holes. To obtain the velocity of distribution on the interface of the leakage hole, the study carried out simulation of leakage modules and further explored the impacts of pressure and pipe flow rates on distribution of velocity.

Methodology

The methodology is based on four main stages;

1. Identification of release scenarios.
2. Release source calculations.
3. Dispersion calculations.
4. Analysis of results.

The release boundary calculations that are required to calculate the dispersion calculations are obtained from the release calculations. The ADREA-HF code will be used for release and dispersion calculations.

Research Plan

References

• Blazek, J., 2015. Computational fluid dynamics: principles and applications. Butterworth-Heinemann.
• Dadashzadeh, M., Ahmad, A. and Khan, F., 2016. Dispersion modelling and analysis of hydrogen fuel gas released in an enclosed area: A CFD-based approach. Fuel, 184, pp.192-201.
• Fekete, J.R., Sowards, J.W. and Amaro, R.L., 2015. Economic impact of applying high strength steels in hydrogen gas pipelines. international journal of hydrogen energy, 40(33), pp.10547-10558.
• Giannissi, S.G. and Venetsanos, A.G., 2018. Study of key parameters in modeling liquid hydrogen release and dispersion in open environment. International Journal of Hydrogen Energy, 43(1), pp.455-467.
• Leeth, G.G., 2018. Transmission of gaseous hydrogen. Hydrogen: Its technology and implications, pp.3-10.
• Moukalled, F., Mangani, L. and Darwish, M., 2016. The finite volume method in computational fluid dynamics. An Advanced Introduction with OpenFOAM and Matlab, pp.3-8.
• Rui, Z., Han, G., Zhang, H., Wang, S., Pu, H. and Ling, K., 2017. A new model to evaluate two leak points in a gas pipeline. Journal of Natural Gas Science and Engineering, 46, pp.491-497.
• Xu, T., Chen, S., Guo, S., Huang, X., Li, J. and Zeng, Z., 2018. A small leakage detection approach for oil pipeline using an inner spherical ball. Process Safety and Environmental Protection.