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Saturday, January 4, 2014

Fuel Cell Future Unlikely or Inevitable? Part 2 - H2 From Natural Gas

H2 Sources 

Fuel cell advocates often espouse that hydrogen is the most abundant element in the universe. The only problem with that statement, is that here, on Earth, hydrogen is bound to other elements to make things like water and hydrocarbons. To get the isolated H2 that fuel cells need, the hydrogen must be extracted from compounds.

Natural Gas 

H2 can be derived from water (more on this later). Today, however, it is most often produced by a process called Steam-Methane Reforming. In this process, natural gas (Methane) is combined with high-temperature steam (700°C–1,000°C) under pressures that is 3 to 25 times that of standard atmospheric pressure. With this heat, pressure, and a catalyst the natural gas and steam break down and form hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide.

The carbon monoxide is further processed with steam to create more hydrogen and CO2.

Steam-Methane Reforming Reaction
CH4 + H2O (+heat & pressure) → CO + 3H2
CO + H2O → CO2 + H2 

The H2 from this process is captured and the CO2 is vented into the atmosphere.

Generating these pressures and high temperatures requires a lot of energy. Some of the energy used in this process is lost as heat. Overall, the process of generating H2 from natural gas is around a 50 percent efficient process – about 50-60 kWh are need to deliver 1 kilogram of hydrogen. If you could extract 100% of the energy available in the H2, you would get 25-30 kWh back.

Detractors will point out, that using Methane derived H2 is simply moving the transportation sector from one fossil fuel (oil), to another (natural gas) and the energy used by this process generally involves CO2 emissions also, which offsets much of the potential environmental benefit when using H2 produced in this manner.

So let's look at water sourced H2 in our next post.