Jin Shang* and Lin Zhang*

* School of Energy and Environment, City University of Hong Kong

The greenhouse gas emissions have been rising continuously in Hong Kong since 2000, amounting to over 40 million tonnes of carbon dioxide equivalent in 2012. Hong Kong’s response to the 2015 Paris Agreement is to achieve a reduction in carbon intensity by 50 to 60 percent by 2020 relative to the 2005 level. The government has also set energy saving targets and a new fuel mix for electricity generation posterior 2020. The principal approach is to reduce the use of fossil fuels and switch to the use of renewable energy.

Hydrogen is a renewable energy source and upon use produces zero emissions of carbon dioxide or any other pollutant. It is recognized as a sustainable energy carrier for fuel cell, as a means of storing renewable energy at utility scale, and as a fuel source for backup power. It becomes one of the most prominent players in the new global energy market as research has shown hydrogen is a cost-effective alternative to bioenergy coupled with carbon capture and storage [1]. Mixing hydrogen with natural gas for energy supply can significantly reduce greenhouse gas emissions if hydrogen can be produced from low-carbon or zero-carbon energy sources, such as solar, wind, and biomass. Technically, blending hydrogen into natural gas pipeline network has been proposed as a readily feasible means of supplying hydrogen to markets [2]. It has been or is being considered by many countries in their energy strategy, including Germany, the UK, the USA, Netherland, and Denmark.

The introduction of hydrogen into Hong Kong’s energy mix will contribute to achieving the goal of making Hong Kong sustainable, smart, and green. We believe that, in light of the urgency in tackling the climate change and environmental pollution issues in Hong Kong, the city should not fall behind other countries on green and sustainable city designs. On the other hand, Hong Kong is well-known to be a “l(fā)aboratory” capable of readily experimenting this idea, which will serve as a model for other metropolitan modern cities. While the technology of hydrogen production is progressing rapidly, industrial-scale utilization of hydrogen is limited by the development of hydrogen delivery system [3]. Opting for hydrogen as long-term sustainable solution requires action from now on to help it grow at scale.

Due to the complexity of pipeline network system and the varying composition of natural gas, the appropriate blend concentration may vary significantly from one place to another. A systematic study of the requirements and consequences of hydrogen and natural gas blends in Hong Kong is necessary. Specifically, the study shall encompass analysis in technical, environmental, economic, societal, and political aspects.

The technical considerations include safety, material durability and integrity management, leakage, and downstream extraction. To manage the safety concern, risk assessments need to be conducted for the specific pipeline system; generally the research findings show that adding low-concentration hydrogen (no higher than 20 vol %) into the existing natural pipeline leads to minor increase in ignition risk. Hydrogen can potentially induce the cracking of steel pipelines and thus leakage when operated at high pressure (e.g., up to 2000 psi) and high concentration (e.g., 50%). Although such a risk is low, leak detectors and monitoring sensors should be installed in the pipeline system, together with frequent inspection and maintenance, constituting the material durability and integrity management system. Recovery of hydrogen from the gas mixture at the end point of pipeline can be done using pressure swing adsorption, membrane separation, or electrochemical hydrogen separation. Selection of an appropriate hydrogen extraction technology depends on the local conditions, such as hydrogen concentration and pressure, and availability of land area.

The next step is to overcome the institutional and political barriers that hamper the development of hydrogen infrastructure. Policy makers should provide institutional support to allow for the evolvement of technological transition. To do that, energy policy regulations, business practices, and codes and standards are critical elements to be developed for hydrogen energy. The government must continuously support the innovation and technology development, remove the market barriers, and enforce the compliance of codes. It is important for the government to take action now to design subsidy program, implementation plan for gas companies, supervision and management process, and new charging scheme for users to ensure final success.

[1] J. Yan. Negative-emissions hydrogen energy. Natural Climate Change 8, 560-561 (2018).

[2] M. W. Melaina, O. Antonia, and M. Penev, Blending Hydrogen into Natural Gas Pipeline Networks: A Review of Key Issues. Technical Report, NREL/TP-5600-51995 (2013).

[3] Hydrogen on the rise. Nature Energy 1, 16127 (2016).