It is an undeniable fact that the world is now proceeding with fast steps towards an energy crisis that comes shoulder-to-shoulder with the depletion of fossil fuel reserves. The only way to survive this crisis is the integration of renewable energy with synthetic replacements of fossil fuel, both put together to secure the world energy demand. On top of these synthetic replacements is what we call “synthetic gas”.
Synthetic gas is a mixture comprising of carbon monoxide, carbon dioxide, and hydrogen; sometimes it is referred to as “synthesis gas” or simply “syngas”. Syngas is produced by gasification of a carbon containing fuel to a gaseous product that has some heating value.
The name syngas is derived from the use, as an intermediate, in generating synthetic natural gas and to create ammonia or methanol. Syngas is also an intermediate in creating synthetic petroleum to use as a lubricant or fuel. Synthetic fuel or “synfuel” is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, basically carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass, or by reforming of natural gas.
To produce syngas for use as a raw material in fuel production by the gasification of coal or municipal waste, a series of chemical reactions take place. In these reactions, carbon combines with water or oxygen to give rise to carbon dioxide, carbon monoxide, and hydrogen.
To use syngas as an intermediate in the industrial synthesis of ammonia and fertilizer, a process called “steam reforming” is conducted. During this process, methane—from natural gas—combines with water to generate carbon monoxide and hydrogen.
The general raw materials used for the gasification process are coal, petroleum-based materials, or other materials that would be rejected as waste. From these materials, a feedstock is prepared; this is inserted to the gasifier in dry or slurry form. In the gasifier, this feedstock reacts in an oxygen starved environment with steam at elevated pressure and temperature. The resultant syngas is composed of 85% carbon monoxide and hydrogen, and small amounts of methane and carbon dioxide.
The syngas may contain some trace elements of impurities, which are removed through further processing and either recovered or redirected to the gasifier. For example, sulfur is recovered in the elemental form or as sulfuric acid, and both of these can be marketed.
If syngas contains a considerable quantity of nitrogen, the nitrogen must be separated to avoid production of nitric oxides, which are pollutants and contribute to acid rain production. Both carbon monoxide and nitrogen have similar boiling points, so recovering pure carbon monoxide requires cryogenic processing, which is very difficult.
If the syngas is to be put to use to generate electricity, then it is generally used as a fuel in an Integrated Gasification Combine Cycle (IGCC) power generation configuration. The energy is then utilized by the factory that originally produced the syngas, thereby lowering operating costs.
The economics of synthetic fuel manufacture vary greatly depending on the feedstock used, the precise process employed, site characteristics such as feedstock and transportation costs, and the cost of additional equipment required to control emissions.
A central consideration for the development of synthetic fuel is the security factor of securing domestic fuel supply from domestic biomass and coal. Nations that are rich in biomass and coal can use synthetic fuel to off-set their use of petroleum derived fuels and foreign oil.
The environmental footprint of a given synthetic fuel varies greatly depending on which process is employed, what feedstock is used, what pollution controls are employed, and what the transportation distance and method are for both feedstock procurement and end-product distribution.
In many locations, project development will not be possible due to permitting restrictions if a process design is chosen that does not meet local requirements for clean air, water, and increasingly, lifecycle carbon emissions.
References
clarke-energy.com
biofuel.org.uk