THE HYDROGEN CAVALRY SADDLING UP
February 10, 2021 § Leave a comment
A hydrogen economy replacing the current hydrocarbon economy is fanciful at best. But displacing in chunks, that has legs. First the basics on terminology. Energy for our way of life is dominantly produced from fossil fuel, with less than 15% from other sources. That is the basis for defining the current state of affairs as the hydrocarbon economy. Hydrocarbons use results in CO2 and other emissions. Any reasonable expectation of avoiding serious global warming involves one or both of two alternatives: sequester emitted CO2 at source and/or from the air or reduce the use of hydrocarbons. Hydrogen is seen as the route to the second means, but the hydrogen cavalry is at best only just gearing up.
When the cause of hydrogen was advanced in the past, such as in the use of hydrogen as motive power for electric car motors via fuel cells, I had been bearish. Then, as now, 95% of hydrogen was produced from natural gas. The process is known as Steam Methane Reforming (SMR). The first step is partial oxidation of the CH4 to CO plus H2 and then further reacting the CO with water in the water gas shift reaction to CO2 and H2. The net result is the production of hydrogen and CO2. 9.3 kg CO2 are emitted per kg H2 produced.
Each kg H2 contains 34 kWh of energy. A gallon of gasoline also contains about 34 kWh of energy. Combustion of a gallon of gasoline emits about 9.1 kg CO2. What then is the allure of hydrogen to power vehicles? The answer lies in the inherent efficiency advantage of electric motors over internal combustion engines powered by gasoline. The result is that the same 34 kWh in hydrogen will permit a driving distance of 70 miles for a vehicle that would go 25 -30 miles with the same energy content gallon of gasoline. The other factor is that hydrogen powered EV will have zero tailpipe emissions, whereas all the 9.1 kg CO2 per gallon of gasoline will be released at the tailpipe. The CO2 emissions from SMR will be at a location allowing capture and disposition.
Tailpipe capture of CO2 is technically feasible. RTI International invented a process using adsorbents, with the CO2 periodically desorbed for controlled release into a canister. Part of the difficulty is in the management of the canister handling and the logistics of CO2 disposition. This nuisance factor is not unlike the issue of using urea canisters in diesel vehicles as a NOx capture means. The nuisance and expense of that option led to the infamous VW avoidance scheme. In any case, the technology has not been adopted to date.
Traction in the use of hydrogen to displace fossil fuels has been found in the use of hydrogen as a storage means in support of renewable electricity from wind and the sun. Both these forms do not match usage load profiles. Germany, which has a renewable component of 40%, has days on which it is as high as 75% and as low as 15%. This variability dictates the need for storage mechanisms. Batteries are an expensive solution. Hydrogen is increasingly seen as the medium of choice. It may be produced by electrolysis of water using essentially waste electricity during the low load periods. The hydrogen could then be stored for combustion for power during the high load episodes. It could also be converted to ammonia, utilizing nitrogen from the air. Ammonia is more energetically dense, and this is a good option if transport is required. At the receiving end it could be used for a purpose such as fertilizer manufacture, burned for power or cracked to hydrogen (and nitrogen, which is released to the atmosphere) for an industrial use such as hydrogenation of vegetable oil.
Europe is experimenting with putting hydrogen into natural gas pipelines. Hydrogen is a very small molecule and difficult to contain from diffusing away. It also can embrittle steel pipelines. But at 20% dilution of natural gas, the corrosion is tolerable, and the resulting gas mixture is suitable for all purposes designed for plain natural gas. The displacement of 20% natural gas constitutes a nibble at the hydrocarbon economy. The energy giant Engie has piloted this in a town in France.
For a colorless, odorless gas, hydrogen certainly has a lot of color in its classification. Normal hydrogen from fossil fuel sources is considered gray. Electrolytic hydrogen using renewable electricity would be considered green. Hydrogen from natural gas fed SMR would be considered blue, if the CO2 associated were to be sequestered. Hydrogen may be produced from biogas, much as it is from natural gas. If the resulting CO2 is firmly sequestered, the hydrogen is considered green.
Hydrogen will continue to chip away at fossil fuel use. But a wholesale shift to a hydrogen economy remains aspirational *. An interesting wild card is the possibility of copious geologically sourced natural hydrogen. But even this will likely not produce a winning hand.
For more on the topic: https://www.youtube.com/watch?v=5qm3UbUrYWk
February 9, 2021
*Do you believe in magic by The Lovin’ Spoonful (1965), written by John Sebastian