Energy

Energy is required to fix nitrogen from air and convert it to a reactive and useful nutrient and biological building block. Fossil fuels have been the backbone of this industry for close to hundred years. The technology is tailored for this energy source. The greenhouse gas issue, peak oil and the lack of abundant stranded gas is going to change the basis for this industry dramatically over the next 20 years. Local initiatives are already being taken to find more sustainable alternatives for the future.

The technological developments in the 20th century have reduced the energy consumption down towards a practical and theoretical minimum.
Steam reforming of methane has a stoichiometric minimum of  26 GJ/tN

Industrial Nitrogen fixation is best done in an oxygen free atmosphere with the help of an iron catalyst.  It can also be done by applying high temperature plasma gereration in air. In both cases energy is required for eighter cracking the N2 bond in plasma  to produce NO, or to produce pure Hydrogen for catalytic Ammonia process.

When oxygen is present the active catalyst site is blocked by the O2 and no practical catalytic process is realized yet.  It is interesting to note that also Biologocal Nitrogen fixation  is creating oxygen free conditions for the enzyme to be active.

The electric arc plasma process is reacting nitrogen with oxygen according to the equation:

N2  +  O2  =  2NO                                    dHf = 6,4   GJ/tN

 

The ammonia process reacted nitrogen with hydrogen as:

3H2O(l) = 3H2(g)  +  1,5O2(g)                                                      dHf   =     30,62 GJ/tN

+    N2(g)   +  3H2(g)    =  2NH3(l)                                              dHf   =      -5,77 GJ/tN

=     3H2O(l) + N2(g)  =  1,5O2(g)  + 2NH3(l)              dHf   =    24,85 GJ/tN

The modern steam reforming process however, is using the energy in the methane to split water to get the perfect process with the right hydrogen to nitrogen ratio at minimum energy input.  The in-process stoichiometry is:

7 CH4  +  10 H2O  +  8 N2  +  2 O2 = 7 CO+  16NH3            26 GJ/tN  LHV   Stoichiometric  minimum

The stoichiometric minimum energy consumption is not commercially viable, but best industrial practice is able to come down to 36 GJ/tN.  Coal based ammonia plants has an energy consumption of 75GJ/tN, and as all the energy is comming from the carbon, the CO2 emission per tonne of ammonia produced is 4-5 times higher than for the methane based process.

The methane steam reforming process is the dominating process for producing ammonia due to its low energy consumption, and because natural gas has been found stranded and cheap for the last 40 years.  The global warming issue and peak oil will change this in favor of more sustainable energy sources and recycling of nitrogen.

Renewable energy will be realized in distributed systems depending on the local source being wind, sun or waterfalls.  The N-fix technology will be able to adjust to the economy of small scale local solutions.  The future will be fusion farming.

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