part one: the circular economy - from water to hydrogen and back again
PHC's Senior Fuels Technology Partner Dr. John Buxton begins a series of Insight Features tackling the opportunities and challenges of hydrogen as a net zero fuel for transport. In this first feature, John looks at the "circular economy" and assesses the efficiency of hydrogen as a transport fuel for a net zero carbon future.
Transport and the Climate Emergency
There’s global recognition that the world’s climate is changing. Air and sea temperatures are rising and the greenhouse effect, driven by greenhouse gases (GHG), is causal. GHGs include carbon dioxide (CO2),which is released into the atmosphere by industrial, agricultural and transport activities, and in great quantities. Many of these emissions result from the burning of fossil fuels, but there is growing recognition of the role played by methane (CH4), also released from coal and oil handling, from the agricultural sector and from waste. Methane is a far more potent greenhouse gas, too – around 100 times more potent in its effects than CO2.
Reducing transport’s impact on the climate means lowering GHG emissions, one element in moving from a linear to a circular economy. This can be achieved by reducing consumption, switching to more sustainable biofuels or doing something different, such as harnessing the hydrogen-to-water cycle.
This week’s Insight Feature looks at what hydrogen is and why it’s exciting. It’s the first in our series “Demystifying Hydrogen”: in coming weeks we’ll look at the pros and cons, opportunities and challenges of hydrogen as a transport fuel, helping to figure out a way forward for this important element in transport's journey to net zero operation
Hydrogen – what is it?
Hydrogen is new and yet old, rare and yet ubiquitous, simple and yet complex. With atomic symbol H, it is the first element in the periodic table – and so the lightest – with a molecular weight of 2 (for hydrogen, a molecule means two atoms - or H2). By comparison, methane weighs in at 16, air at around 29 and CO2 at a whopping 44. Hydrogen also has an affinity for oxygen, abundant in air, and the two react to produce water and energy - which can then be harnessed to fuel transport and industrial activity. Hydrogen’s lightness is important: it’s one of the reasons hydrogen is a naturally “good” fuel for transport (lots of energy per unit mass) and why a tonne of hydrocarbon fuel can be replaced by around 1/3 ofa tonne of hydrogen. So far so good.
So why haven’t we used it until now?
In fact, we have. In the UK, until we discovered North Sea gas (which is methane), our gas network delivered ‘town gas’ to our homes. Great cast iron gasometers attached to coking plants abounded: pretty much every townhad one or more. Most have been demolished, some preserved, some converted into swanky flats (see below). But back to chemistry: town gas was a heady mixture of hydrogen (for energy) and carbon monoxide (to reduce explosion risk.) Deadly stuff, but it worked well until natural gas took over.
So why are we now interested in hydrogen as a transport fuel?
Good question, and plenty are sceptical about its future. A short story: when its energy is harnessed, (that is, when it is converted to water, either via combustion with air or in a fuel cell with air), hydrogen generates lots of energy – roughly three times what a hydrocarbon fuel does. Here's a rule of thumb: one kg of hydrogen in a compact vehicle will take you 100km whereas one kg of gasoline will take you 30. So it sounds good for transport.
If hydrogen is introduced into the gas grid, it will raise energy content without increasing CO2 emissions (although the life-cycle CO2 emissions must include how the hydrogen was generated – the convention is to use a colour such as green, blue or brown to identify the CO2 emissions associated with the hydrogen's production method – next week’s Insight Feature addresses this.)
If the numbers stack up, then why the hesitancy?
Getting hold of hydrogen is the problem. It doesn’t occur naturally and so has to be made. The most common way is to start off with methane and ‘reform’ it with water. But this requires hydrocarbons and producesGHGs - so it still has one foot “outside the circle”. But there are other,cleaner, routes to hydrogen production, principally electrolysis, which we will look into inext week.
OK, help me with all this
So, hydrogen has the advantage of low weight, high energy and being free of greenhouse gases when its energy is harvested, but has the disadvantage of a complex GHG story on the production side. Nonetheless, the hydrogen>water>hydrogen cycle can be an important component of our drive towards a circular economy.
Next week we will lookat hydrogen and its colours, and the associated GHG numbers, to help understand its potential contribution to net zero transport and the circular economy, and to bottom out why colour matters. Come back here for more!