Fossil-based Hydrogen

On the efficiency page the production of hydrogen from biomass was favoured. But those efficiency and price advantages are not linked only to hydrogen from biomass.  Here hydrogen from fossil fuels is examined, firstly from natural gas.

Production of hydrogen from methane

The efficiency of hydrogen production from biomass and hydrogen from natural gas are very similar.

     Hydrogen can be produced from all carbon containing fuels by means of  thermo-chemical gasification, including natural gas.
     As physical processes are always lossy, there will be waste heat.  A small part of that loss arises at the gasification plant.
     As such installations are predominantly located at chemical industry sites today, which have large heat requirements, 20%-40% of the energy input will be used for heat provision.

Thermo-chemical gasification

Today, nearly all hydrogen is obtained by thermo-chemical gasification of fossil fuels. Worldwide around 500  billion m3/ year of hydrogen are produced. Today the survival of mankind depends on hydrogen, as without nitrogen fertilizers (NH3) most of us would already have starved.  More than 40% of the hydrogen produced is used for the desulphurisation of heating oil and other fuels. Most of the hydrogen is now obtained from natural gas or crude oil.  Its production from coal only continues to achieve some national self-sufficiency.  Thermo-chemical gasification of biomass is still in the early stages of its industrial development. In installations implemented so far the raw gas (synthesis gas: CO  &  H2) is converted directly  to electricity by a gas engine.
     The first step is always the production of synthesis gas, which may be qualitatively explained using methane (natural gas) as an example. The equations for the production of hydrogen from methane are:

CH4 + 2 H2O   =   CO + 3 H2 + H2O   =  CO2 + 4 H2

     Typical reaction conditions for the production of synthesis gas as an intermediate product are 850°C at 25-40 bar. In many cases synthesis gas is used directly for further chemical syntheses, as almost the complete range of chemical products may be produced from synthesis gas. The production of hydrogen is the most simple synthesis.

Source: Linde

     This picture shows an industrial gasification plant for natural gas. On the left side of the picture are the reactors. On the right hand side two rows of cylinders stand upright (PSA installation) each with an upstream pressure tank for different purification tasks.
     These installations are technically mature. They can be bought ready-made.

A hydrogen economy is not expected to begin without the production of hydrogen from carbon containing fuels. The adjacent picture shows a state of the art natural gas reformer. 

Overall efficiency of a hydrogen economy with 70% natural gas and 30% renewable electricity

     There is no formal difference between the production of hydrogen from biomass or from natural gas.  The main difference is that the primary energy at 3.5-4 ct/kWh is almost twice as expensive as from biomass. That may be partially compensated for by the fact that a natural gas gasification plant is cheaper than a biomass gasification plant.  As there are no ash or tar problems with natural gas, natural gas gasifiers may be arbitrarily scaled.

     It is worth noting that the quantity of natural gas needed (2.5 EJ) almost exactly matches Germanys natural gas consumption today. The quantity extracted nationally of 0.4 EJ is hardly significant. Therefore in a hydrogen economy Germany could aim for its entire energy demand to be solely from natural gas and renewable electricity. The import of coal and oil could be dropped. Three problems remain, which are not present if biomass is used instead of natural gas:

  • CO2-Emissions are not reduced by 100% but only by 85%.
  • Import dependency on natural gas continues
  • Prices for fossil energy carriers will continue to rise (from the historical cross-border price, the price increase over the past 15 years has been 10% / year)

The marginally higher energy cost in comparison to biomass could be tolerated. The 2050 goal of the German government to reduce CO2 emissions for electricity by 80% would be easily surpassed with this fossil-based hydrogen. Furthermore this 85% reduction would be for the entire German economy - not only for electricity generation.

Technically and politically a mix of fossil and biomass fuels would be easier to realise. It would be sensible to start the hydrogen economy with natural gas as everything needed for the installation of a hydrogen economy is already technically mature, and can be bought off the shelf. Transport would also benefit from it, because there would then be a mass market for fuel cells.

 

Conclusion

A hydrogen economy is economically and ecologically very attractive for all sources and applications of energy. Sustainable, low energy prices can however only be achieved in the long term by using renewable energy.

COMMENTS:

     Anthracite coal is almost pure carbon.  When that is gasified almost twice as much CO2 will be produced for a given amount of hydrogen.  The 80% reduction target would then be missed.  Other coals, such as brown coal would also produce more CO2 than natural gas.

     It is the features of the hydrogen economy that achieve these huge saving in emissions.  These include the low losses of gasification, fuel cells and transmission together with the use of both the heat and power potential of the primary fuel,  natural gas, oil, coal, or biomass.