methane, syngas and the lost carbon
At times I really feel like a broken record, but once again all I can say is “Slow down, let’s start from the beginning”.
In this case the culprit was “A Solution to Solar Power Intermittency” i.e. “the article”, which appeared in Technology Review.At the end of the day the comments were on the right track to explaining what the article overlooked. While comments often wind up in all sorts of rat holes, once in a while the conversation does move the discussion forward.
At the moment I do not want to go over the article in detail. Rather, I want to come back to the core concept of reforming methane into syn gas. The article is far from clear how emissions are reduced by 20% when syn gas is combusted compared to the methane from which it was derived. In fact syn gas is presented as “a lower carbon fuel”. If it is a lower carbon fuel, where did the carbon go? It is time to go back to some balances.
At the most basic level the reforming process must adhere to mass/ atom and energy balances. There are no ifs, ands, ors or buts on this point. First, let us go to the mass balance. The reforming reaction that produces syn gas (CO + H2) from methane (CH4) requires water (H2O) as an input. The reaction is
CH4 + H2O => CO + 3H2
All of the atoms are accounted. From this viewpoint syn gas can not be described as a lower carbon fuel, because the carbon from the methane is all still there.
Now we go to the energy balance. The reforming reaction takes place at elevated temperature, which in this case is provided by solar energy. One can think of the elevated temperature as an addition of energy. This thermal energy is “stored” in the syn gas. More energy is produced when combusting the syn gas, as compared to the original methane, because of the stored solar energy. In terms of emissions, it is the input solar energy that is at the root of the reduction in emissions. Less carbon based fuel is required for the same energy. Without going through the numbers this is at the heart of the claim of the a 20% reduction in emissions claim.
A careful read suggests the article did not actually say anything that was not true. It did though miss the opportunity to present information that would allow a broader understanding of the concept. There appears to be some interesting work here, including developments to improve the efficiencies of the system. So, with a bit of additional groundwork one can make sense of less than clear writing.