Landfill Gas Generation
Landfill gas generation:
Many factors determine the gases given off by decomposing garbage at landfills. The gases are mainly composed of methane and carbon dioxide. Usually each compound makes up about half the gas. Trace amounts of sulfur, hydrogen, oxygen, and nitrogen gas also are emitted. The composition of the waste in a landfill has the largest impact on gas generation. A landfill with a higher percentage of organic garbage produces gases at a higher rate because inorganic garbage takes much longer to decompose. Organic material in the soil around the landfill also has an impact. More organic soil provides more bacteria and other creatures to decompose the garbage. The weather conditions have a large effect on the rate of gas generation. Increased temperature allows the bacteria to grow faster and increases gas generation. The decomposition of the garbage also produces heat, which can increase the landfill’s temperature further. Moisture also allows the bacteria population to grow. This moisture can be from the soil or precipitation. Increased humidity also appeals to bacteria. Frequent rain and storms can cause a large increase in gas production. Seasonal changes in gas generation can vary. In the summer, the temperature is greater, but there is less moisture. In the winter, temperatures drop but moisture increases, so the seasonal change depends on which factor is stronger in an area. In particular, the West Coast’s mild weather and heavy precipitation make it one on the areas where landfills can produce the most gas.
What to do with the carbon:
The carbon must be removed from the methane to leave only hydrogen for the fuel cell. The only plausible choice for dealing with the carbon in the methane is to convert it into carbon dioxide. A reforming reaction must occur that combines the carbon with oxygen to form carbon dioxide and frees the hydrogen. Extra steps can be added to eliminate carbon monoxide, which can be deadly to humans. The first step is usually a steam reformer that combines the oxygen from steam and the carbon from methane to form carbon dioxide. The rest is hydrogen, which is sent to the fuel cell. Unfortunately carbon dioxide is an unavoidable fact. Since the reformer’s and the fuel cell’s reaction is similar to combustion, only in two steps, carbon dioxide will be given off like in a car. At least we will be getting more energy per unit of carbon dioxide. It is also important to realize that methane is a better greenhouse gas than carbon dioxide by more than 20 times. It is much better to release carbon dioxide than to release methane.
What to do with the sulfur:
Sulfur is a real danger to fuel cells because it can bond to the membranes involved in the fuel cell reaction. Luckily it is not difficult to extract sulfur from the landfill gases because the sulfur comes out as a separate gas rather than included in the hydrocarbons like in gasoline. Using some sort of sulfur scrubber, the sulfur can be removed from the gases. The gas is forced through water. The soluble sulfurs dissolves in the water to form sulfuric acid that can be transported away. The insoluble methane can continue to the reformer or the fuel cell itself. The scrubber can also remove other impurities that will dissolve in water.