I remember that as a first-year physics student in 1977 I completed an essay assignment on the hydrogen economy. I don’t remember how this fitted in with the course content, but we students were made aware that oil was a finite resource and expected to run out soon, and that hydrogen was being touted as a useful alternative. Fast forward to 2019, and the use of hydrogen as an energy source is again being pursued. It seems that there is more enthusiasm for it now, especially as it holds great promise as a carbon-free energy source, and one approach to dealing with climate change.
And so it is that in mid-February 2019, a new process trial received environmental approvals to investigate the use of Victorian (Latrobe Valley) brown coal for hydrogen production. According to the proponent’s website, brown coal will be heated to prepare synthesis gas, a mixture of carbon monoxide and hydrogen. (The Victorian Gas & Fuel Corporation attempted this approach in the 1950s as an alternative to manufacturing town gas from New South Wales black coal.) Once hydrogen is separated from the carbon monoxide, further hydrogen can be produced by the reaction of water with the carbon monoxide, via the water gas shift reaction. Carbon dioxide is the other product, and the proposal is that this would then be captured and dealt with by geosequestration.
The chemical reactions are well known, and geosequestration of carbon dioxide is not novel, either. The Norwegian oil and gas industry has been using it in the North Sea oil fields for decades, and it is also being applied in the North West Shelf gas fields. The Latrobe Valley is close to the Bass Strait oil and gas fields, which could be used for sequestration, although the carbon dioxide would still need to be piped a considerable distance, and access agreements negotiated with the operators of those fields. However, something in the EPA’s press release announcing the environmental approvals caught my eye and made me think that there may be other wastes to be managed in full-scale production. The press release stated that up to 160 tonnes of brown coal will be used to produce three tonnes of hydrogen in the trial, along with ‘small amounts of slag and char’.
Before natural gas was introduced in Australian cities in the late 1960s, the gas industry mainly relied on black coal for town gas production, which produced considerable amounts of slag, char and tarry wastes. These wastes found their way to many locations in the urban landscape as cheap filling, and the legacy is still with us today. The use of gasworks waste was so widespread that even now, 50 years after town gas was phased out in some cities, it is routine to analyse uncontrolled fill for the polycyclic aromatic hydrocarbons that were ubiquitous in gasworks waste. So, even if it could be expected that new processes of coal combustion/pyrolysis might generate less solid waste than in the past, it will be interesting to see what the results of the hydrogen production trial tell us in terms of the amount of solid waste per kilojoule of contained energy in the hydrogen product.
This all made me think that, while CO2 emissions in energy production are important, so too are the amounts of solid and other wastes produced. Coal-fired power stations are usually accompanied by large ash ponds, which grow over time, and which present their own environmental issues. For example, selenium in brown coal ash is an issue in the Latrobe Valley, but Australian black coal is known for its high energy and low ash content (hence the large export industry). Radioactive wastes from nuclear energy present a distinct set of issues, and I have written before about Australia adopting a product stewardship approach and taking back the radioactive wastes derived from its uranium exports. Even natural gas is not without its problems, with naturally occurring radioactive materials sometimes extracted in initial processing.
The more I thought about this, the more it became apparent that, while construction of any energy production facility will generate some wastes, the only energy sources that don’t produce wastes (particularly solids) during operation are those that are now referred to as ‘renewables’: solar (photovoltaic), wind, hydroelectricity, geothermal and tidal. I didn’t set out to make a point about renewables, but it is apparent that there is more to consider in the energy debate than just carbon dioxide emissions; other wastes and by-products are important too. Finally, my sense of irony kicked in when I realised that, in 1977, some saw hydrogen as the fuel of the future because we didn’t have enough fossil fuels, whereas, now hydrogen is seen by some as the fuel of the future because we are too reliant on the combustion of fossil fuels.