So many flavors and colors of gas these days. They are all problematic.
There is so much hype about hydrogen these days, particularly in the UK right now, where a third of carbon emissions come from heating and cooking with gas. A pilot project at Keele University, near Stoke-on-Trent, is pumping out a mix of 80 percent natural gas and 20 percent hydrogen made by electrolysis in a shipping container sized unit from ITM, who writes:
Heating for domestic properties and industry accounts for half of the UK’s energy consumption and one third of its carbon emissions, with 83% of homes using gas to keep warm. The 20% volume blend means that customers can continue to use their gas supply as normal, without any changes being needed to gas appliances or pipework, while still cutting carbon emissions. If a 20% hydrogen blend was rolled out across the country it could save around 6 million tonnes of carbon dioxide emissions every year, the equivalent of taking 2.5 million cars off the road.
Unsurprisingly, this is being promoted by a gas company, Cadent. All the gas companies love hydrogen because they still will have something to put in their pipes in a decarbonizing world. But there are different colours and flavours of hydrogen:
Brown hydrogen is made from coal; this is what used to be called town gas before natural gas took over. It has a very high carbon footprint and is not too common anymore.
Grey hydrogen is made from the steam reformation of methane, which separates the hydrogen from the carbon; On molecule of CH4 reacts with H20 to form 4H2 and 1 CO2, plus whatever CO2 is made generating the 1000 degree steam. This is what about 98 percent of the hydrogen being made right now is.
Blue Hydrogen is what the oil and gas companies will be trying to sell us on, where they take the CO2 from the Grey Hydrogen process and store it somewhere, or use it in synthetic fuels or other products.
Green Hydrogen is the holy grail, where it is made by electrolysis using renewable electricity. Solar and wind power doesn't always happen when you need it most, so using surplus renewables to make green hydrogen does make some sense. It's the argument being used to run hydrogen trains and cars.
[출처] treehugger, 2020.01.06