Decarbonising gas - a solution to meeting zero-emission targets

News - Energy in Buildings

Tuesday, 10 December 2019

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The UK Government has committed to net-zero carbon emissions by 2050 with the Scottish Government having committed to become net zero by 2045. This includes decarbonising heating and hot water generation, which currently account for around a third of UK's total greenhouse gas emissions. There are two feasible options: full electrification of all homes replacing domestic boilers with heat pumps or replacing natural gas with alternative net-zero carbon gasses.

While electrification involving heat pumps is feasible, there are many technical hurdles to overcome, and the switch would be costly, amounting to around £12,000 a household. While electrification is likely to be part of a combined or hybrid approach, replacing natural gas with a greener alternative has the advantage of maintaining the current infrastructure and would be around two thirds less expensive.

Replacing natural gas with hydrogen
Natural gas is mainly methane; when it burns, it produces the greenhouse gas carbon dioxide and water. When hydrogen burns it produces only water. Currently we produce less than one million tonnes of hydrogen a year, and that would need to be increased to over 8 million tonnes just to satisfy our domestic heating requirements. However, we can manufacture hydrogen from methane and capture and store the carbon at that point. Currently this manufacturing process, known as steam reformation, is not without its challenges, and improvements would be needed, but it is an entirely feasible route.

Apart from scaling up hydrogen production, the main challenges are converting the distribution network to transport hydrogen safely, and to produce domestic boilers capable of burning hydrogen.
Fortunately, much of the low-pressure natural gas pipework has already been changed from iron gas pipes to polyethylene, and work is in hand to convert the remainder. Polyethylene is the ideal material for transporting hydrogen. The high-pressure parts of the network use steel pipes which are likely to be embrittled by hydrogen, and these would need to be replaced by alternative materials. Additionally, as hydrogen is a much smaller molecule than methane, it has a greater potential to leak, primarily through pipe connections. Additionally, network capacity would need to be increased by 20% to account for the increased quantity of hydrogen necessary to produce the same energy output as methane. None of these challenges is insurmountable, and there is adequate time to implement the required changes.

The other main hurdle, producing hydrogen-burning boilers, would require significant research and development. Specifically, new burners might need to be developed, and flame detection would require new technology- hydrogen flames are almost invisible and have no electrical characteristics, so ultra-violet detectors would probably be needed. But none of that is beyond the capabilities of the scientists and engineers. Hydrogen-ready boilers could be installed in advance of the switch over from natural gas.

The other aspect of hydrogen is safety. Within a building, hydrogen ignition is more likely than for natural gas. Just as natural gas, hydrogen has no odour so new odorants would need to be developed to impart a gas smell. Domestic hydrogen detectors would also be required. On the positive side, unlike with natural gas, burning hydrogen does not produce carbon monoxide or other toxic by-products, so the risk of poisoning is eliminated. In the UK, around 60 people a year die from carbon monoxide produced by burning natural gas.

Conclusions
Decarbonising heating and hot water generation by switching over from natural gas to hydrogen is of considerably lower cost than electrification. While there are challenges to be overcome, there is no fundamental reason why this can't be achieved in the timescale. Doing so, however, is critically dependent on the government and the networks to invest in preparing for a national hydrogen conversion program. We have, after all, done it before when, in the 1970s, we converted from poisonous coal gas, a mixture of mainly hydrogen and carbon monoxide. Hydrogen is the next step forward.