pstarr wrote:I am in no way a chemist, but this just feels craxy. CO2 is reduced. Entropy. What burns in a gasifier is the H2 and the char, ie the carbon, the C. CO2 is a waste product. How can a waste product be a fuel source?Sounds like perpetual energy to me.
There are several types of gasifiers so there are different products you can get out. The earliest systems designed to produce useable gas just roasted coal or wood without letting any air in so the gasses that came out were tar aka pitch used to preserve wood and caulk seams on ship hulls, the flammable gasses were either a bonus or a problem depending on who was roasting the wood or coal. Once the oven stopped putting off gas the remaining mass was charcoal or coke and was a useful fuel.
The next step was to add limited air after all the chemical gas had been produced from the char. By using regular air that was 78% Nitrogen and 21% Oxygen more or less and limiting the amount put through the oven causes the char to form CO2 at first, but because the Oxygen input is limited and the cha is red hot the char robs Oxygen from the CO2 and makes CO. The gas produced by this method is still 78% Nitrogen and it will burn but it has a weak flame because it so diluted.
The next step after that was to make carburated water gas, the coke or charcoal is heated white hot by blowing regular air through it until it is glowing hot, then switch the input from air to steam. The gas produced during the Blow phase is CO2/Nitrogen and just discarded up the smokestack. When steam is blown through glowing carbon the char robs the oxygen from the water vapor because the Carbon-Oxygen bond is stronger than the Hydrogen-Oxygen bond. The CO2 is then robbed by the glowing carbon of half its Oxygen forming CO. The carburated water gas produced is almost half Hydrogen and half CO, but the chemical reaction to break the water vapor robs heat from the char so after a few minutes the reaction stops when the char cools off. In this type of plant as soon as they start getting water vapor out of the production side they switch back to another Blow Cycle pumping air through the oven to heat the carbon mass back up to white hot.
The step after that was to pump pure oxygen into the hot oven instead of air so that the produced gas was CO instead of a mix of CO2/Nitrogen, but Oxygen is expensive. By adding just enough Oxygen to the Steam to replace the energy lost breaking the water vapor into H2 and CO.
The final step so far as I can tell is injecting the steam and Oxygen mixture into deep coal seams that are not mineable by conventional excavation and gasifying the coal before anything else is done too it. The gas produced this way has all the volatile chemicals like Methane, Creosote, Asphalt, Kerosene mixed in with the H2 and CO. In some places the produced gas is sent straight into a gas turbine power station and burned to make electricity. In other places the produced gas is put through a chemical plant and they reformulate it into 'synthetic Natural Gas' and 'synthetic Diesel/Kerosene/Gasoline'. The Chinese seem to be very interested in using underground gasification technique.
Anyhow you can read up on the topic by searching the internet for Carburated Water Gas or click
http://en.wikipedia.org/wiki/History_of ... ctured_gas