Synthetic Natural Gas (Sng) From Coal and Biomass : a Survey of Existing Process Technologies, Open Issues and Perspectives

Compared with natural gas, HCNG has many advantages when it comes to performance. Research has shown that the brake effective thermal efficiency increases with an increased percentage of hydrogen. Another effect of the addition of hydrogen is that the brake specific fuel consumption is reduced, the cycle by cycle variations are also reduced, and the thermal efficiency is increased. Emissions can also be improved with the addition of hydrogen. Compared to pure natural gas, HCNG reduces the HC emissions, which is in part due to the increased combustion stability that comes with the addition of hydrogen. However, due to the increased temperature and combustion duration that accompanies the hydrogen addition, an increase in NOx emissions is observed. There are many optimization parameters that can be modified to adjust to the HCNG fuel. With the increase of hydrogen addition, the lean operation limit extends which is often used to maximize the thermal efficiency and reduce the nitrous oxide emissions, although due to the increased air running through the engine, at high excess air ratios the combustion becomes more unstable leaving unburned hydrocarbons in the exhaust. Therefore, the excess air ratio should be positioned by finding the best combination of nitrous oxide and the hydrocarbon emissions. Another method to reduce emissions, is to move the spark timing closer to top dead center, however this is greatly dependent on the excess air ratio. The hydrogen ratio can also be increased to extend the lean limit, improve the combustion and reduce the hydrocarbon emissions Synthetic Natural Gas (SNG) from Coal and Biomass: a Survey of Existing Process Technologies, Open Issues and Perspectives Soil-Gas Geochemistry: Significance and Application in Geological Prospectings