Is hydrogen gas the solution to fossil fuel emissions? The City of Leeds thinks so, and potentially so does the South Australian government, but what are the realities for the industry? Enzo Alfonsetti, Energy Services Victoria explains. 

The UK Government has committed to reducing carbon emissions by 80% of 1990 levels by the year 2050. Natural gas (mainly methane) is a much cleaner fossil fuel relative to coal however it still contributes to greenhouse gas emissions through the production of CO2. Hydrogen gas on the other hand emits zero CO2 when it is burnt. As a result the UK Government has committed to converting the City of Leeds to hydrogen in a project referred to as the H21 Leeds City Gate project.

The aim of the project is to determine the technical and economic feasibility of converting the existing natural gas network in Leeds to 100% hydrogen. In the H21 project hydrogen is produced through the steam reforming of natural gas where the carbon is captured during this process and then stored underground using Carbon Capture and Storage Technologies.

Now a “Power to gas” trial has been announced for South Australia where small quantities of hydrogen will be injected into Adelaide’s grid. Wollongong based company Aquahydrex is developing a prototype electrolyser to produce hydrogen from water. The development of the electrolyser is being funded through a $5 million grant from the Federal Government’s Australian Renewable Energy Agency (ARENA). South Australian gas company, Australian Gas Networks, is partnering with Aquahydrex to run this trial.

There are two main differences between the H21 project in Leeds and the South Australian project.

1. Firstly the method by which the hydrogen gas will be produced. The South Australian project will produce hydrogen gas through electrolysis where electricity will be used to split the water molecule H2O into hydrogen and oxygen. Hydrogen production within the H21 Project on the other hand will be by the steam reforming of Natural gas.
2. The South Australian pilot project will focus on blending hydrogen with Natural gas whilst the H21 project involves converting sections of the city at a time to 100% hydrogen. The level of hydrogen injected and blended with Natural gas into the South Australian gas network during the trial will be limited by the ability of currently installed gas appliances to safely burn hydrogen.

Some of the technical challenges that need to be considered include the impact on infrastructure including distribution pipelines. Old steel mains at high pressure are incompatible for transporting hydrogen as embrittlement of the steel can occur. In addition the smaller hydrogen (H2) molecule relative to the methane (CH4) in natural gas increases the probability of gas leaks occurring. The use of polyethylene pipelines addresses these problems.

The impact on infrastructure downstream of household billing meters also needs to be considered. Copper and its alloys such as brass are believed not to be impacted upon. However the eff ect on older downstream infrastructure made of steel may need to be considered.

Hydrogen has a significantly larger (4-75%) flammability range than natural gas (5-15%) and as mentioned earlier is more prone to leakage given its smaller molecule relative to natural gas. Hydrogen also has a higher flame speed which means it is more likely to ignite back at the injector of a burner (commonly referred to as lightback) if the appliance is not designed correctly or if the appliance is not converted to suit.

Type A gas appliances designed for use with natural gas are laboratory tested using a range of natural gas limit gases prior to certifi cation. “Nb” gas is a natural gas limit gas which contains approximately 13% hydrogen. Hence this limitation will have to be taken into consideration when considering the concentration of hydrogen to include in the blend. It is expected that a safety margin would be considered and so therefore the concentration of hydrogen within the natural gas would be considerably less than 13% to ensure satisfactory performance of installed Type A gas appliances. Hence theoretically there should be no need to make any adjustments to the appliances provided the concentration of hydrogen in the natural gas is less than 13%.

Injecting higher concentrations of hydrogen beyond 13% would require for gas appliances to be modified or converted in order to cope with the characteristics of hydrogen. This would typically include a change in the burner head design where burner ports are reduced in size to prevent lightback and also a reduction in primary burner aeration and reduction in operating pressure. An increase in the size of burner injector orifices would also need to be considered to account for the lower heating (calorific) value of hydrogen relative to natural gas.

The success of a project such as this could pave the way one day for a complete conversion of Australia’s gas network to 100% hydrogen and a carbon free gas industry. The other challenge will be to one day produce sufficient quantities of hydrogen to meet demand using renewable energy sources such as solar and wind power.