subject: Syngas: The fuel generator [print this page] Syngas: The fuel generator Syngas: The fuel generator
Syngas (fromsynthetic gas orsynthesis gas) is the name given to a gas mixture that contains varying amounts ofCOandhydrogen. Examples of production methods includesteam reformingofnatural gasor liquid hydrocarbons to producehydrogen, thegasificationof coal,biomass, and in some types ofwaste-to-energygasification facilities. The name comes from their use as intermediates in creatingsynthetic natural gas(SNG)and for producingammoniaormethanol. Syngas is also used as an intermediate in producingsynthetic petroleumfor use as afuelorlubricant via theFischer-Tropsch processand previously theMobilmethanol to gasoline process.
Syngas consists primarily ofhydrogen,CO, and very often someCO2, and has less than half the energy density of natural gas. Syngas is combustible and often used as a fuel source or as an intermediate for the production of other chemicals.
Production: Gasification
Syngas for use as a fuel is most often produced fromcoal, first by pyrolysis tocoke(impure carbon), aka destructive distillation, followed by alternating blasts of steam and air, or frombiomassor municipal wastemainly by the following simple paths:
C+H2OCO+H2
H298 = 323,1 kJ/mol
C+O2CO2
H298 = -394 kJ/mol
CO2+ C 2CO
H298 = 282,1 kJ/mol
The first reaction, between incandescent coke and steam, is strongly endothermic, producing carbon monoxide (CO), and hydrogen H2 (water gas in older terminology).
When the coke bed has cooled to a temperature at which the endothermic reaction can no longer proceed, the steam is then replaced by a blast of air.
The second and third reactions then take place, producing anexothermic reaction- forming initially carbon dioxide - raising the temperature of the coke bed - followed by the second endothermic reaction, in which the latter is converted to carbon monoxide, CO. The overall reaction is exothermic, forming "producer gas" (older terminology). Steam can then be re-injected, then air etc., to give an endless series of cycles until the coke is finally consumed. Producer gas has a much lower energy value, relative to water gas, due primarily to dilution with atmospheric nitrogen. Pure oxygen can be substituted for air to avoid the dilution effect, producing gas of much higher calorific value.
When used as an intermediate in the large-scale, industrial synthesis of hydrogen (principally used in the production of ammonia), it is also produced fromnatural gas(via thesteam reformingreaction) as follows:
CH4+H2OCO + 3H2
In order to produce more hydrogen from this mixture, more steam is added and thewater gas shiftreaction is carried out:
CO+H2OCO2+H2
The hydrogen must be separated from the CO2 to be able to use it. This is primarily done bypressure swing adsorption(PSA),amine scrubbingandmembrane reactors.
The syngas produced in large waste-to-energy gasification facilities can be used to generate electricity.
Coal gasification processes were used for many years to manufactureilluminating gas(coal gas) forgas lightening, cooking and to some extent, heating, beforeelectric lightingand thenatural gas infrastructure became widely available.
