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Sunday, April 16, 2017

Practical Energy

The requirement statement for practical energy -
The answer is surprisingly simple.

There are 4 or 5 processes that do more-or-less the same thing in slightly different ways. Each was designed with a different purpose in mind, but that doesn't mean they can't be used for other purposes the designers hadn't considered.

Bioenergy, waste-to-energy, renewable energy storage as synthetic natural gas, biogas and synthetic natural gas from coal are different ways of doing the same thing.

Synthetic natural gas can be used to store energy, to generate electricity on demand, and as feedstock in manufacturing processes. Synthetic natural gas can also be manufactured for export in the form of LNG.

It can be made from 100 percent renewable energy, 100 percent fossil fuel energy, or some combination of both renewable and fossil energy. This allows a transition to a 100 percent renewable energy future, achieving the  above requirement statement: ensuring reliable, affordable and clean energy.

The underlying process combines carbon dioxide, water and energy to create methane and oxygen:
CO2 + 2H2O → CH4 + 2O2
  • Photosynthesis by plants and algae to create biomass that methanogenic bacteria convert to methane is one way of doing this with solar energy.
  • Waste-to-energy can use methanogenic bacteria to produce methane using the solar energy embedded in the waste.  
  • Electrolysis of water to produce hydrogen that is reacted with carbon dioxide to make methane is another way of doing this with solar PV systems and wind turbines.
  • Biomass can be converted to methane in high temperature superheated water reactors. The thermal energy to do this can be from concentrated solar thermal energy, or from reaction with either oxygen or hydrogen created by electrolysis of water.
  • Biomass can be converted to methane in very high temperature gasifiers that create carbon monoxide and hydrogen that is reacted in a separate step to create methane. The energy for this high temperature process can be obtained by burning a portion of the feedstock in air. 
In each of the above processes that use biomass to produce methane, coal can be used in place of some or all of biomass.

When there is sufficient solar PV and wind turbine generating capacity, hydrogen can be produced whenever electricity supply exceeds demand. This hydrogen can be reacted with carbon dioxide to make methane for generating electricity whenever demand exceeds the supply.

With sufficient renewable energy generating capacity, synthetic natural gas can be manufactured for export - providing completely renewable energy to importing countries via existing LNG export, transport and import infrastructure.

Curiously, coal is presently being converted to synthetic natural gas in the most environmentally 'unfriendly' option available - burning a portion of the coal in air to create carbon monoxide and hydrogen that is reacted in a separate step to create methane. This technology has been criticised for its high level of carbon dioxide emissions and water usage.

Coal could be converted to methane by reacting it with hydrogen produced by electrolysis of water with electricity from solar PV systems and wind turbines. It can also be converted to methane in high temperature superheated water reactors. The thermal energy to do this can be from concentrated solar thermal energy, or from reaction with hydrogen created by the electrolysis of water.

This is most suitable for low-grade lignite such as that found in Yallourn Valley in Australia that consists of 50 percent or more water. With this process it can be converted to high-value synthetic natural gas, avoiding the need for coal seam gas.

Its use can be gradually phased-out as renewable energy generating capacity increases to the stage where it can completely replace it.
Posted by Askgerbil at 7:50 PM
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