Reduction methane emissions

At some landfills, operators have installed flares to combust the gas without recovering any energy. Typically, these cases arise because electricity seU-back rates are too low to justify generation equipment, and laws require a reduction in methane emissions. 

Chianese, D. S., Rotz, C. A., and Richard, T. L. (2009c). Simulation of methane emissions from dairy farms to assess greenhouse gas reduction strategies. Trans. ASABE 52,1313-1323. 

Kern JS, Gong ZT, Zhang GL, Zhuo HZ, Luo GB. 1997. Spatial analysis of methane emissions from paddy soils in China and the potential for emission reduction. Nutrient Cycling in Agroecosystems 49 181-195. 

It is fair to state that by and large the most important application of structured reactors is in environmental catalysis. The major applications are in automotive emission reduction. For diesel exhaust gases a complication is that it is overall oxidizing and contains soot. The three-way catalyst does not work under the conditions of the diesel exhaust gas. The cleaning of exhaust gas from stationary sources is also done in structured catalytic reactors. Important areas are reduction of NOv from power plants and the oxidation of volatile organic compounds (VOCs). Structured reactors also suggest themselves in synthesis gas production, for instance, in catalytic partial oxidation (CPO) of methane. 

Because of its abundance in anoxic aquatic environments and its importance as a greenhouse gas, methane transformation by anaerobic oxidation has been the subject of numerous studies. The rates of anaerobic methane oxidation and the environments where it has been found were reviewed by Spormann and Widdel (2000). In marine systems, sulfate reduction has been shown to be an important part of the methane oxidation process. Landhlls, however, not hydrocarbon contaminations per se, are the main source of anthropogenic methane emissions in the US and, therefore, methane degradation processes are not discussed further in this chapter (see Chapter 9.16 for a discussion of methane generation from landfills). 

Postformation nitrogen oxide emission control measures include selective catalytic and noncatalytic reduction with ammonia, which between them are used by some 900 power station installations worldwide [51]. The catalytic removal methods are 70-90% efficient at NOx removal, but are more expensive to operate than the noncatalytic methods which are 30-80% efficient. Ammonia or methane noncatalytic reduction of NOx to elemental nitrogen is also an effective method which is cost-effective for high concentration sources such as nitric acid plants (Chap. 11). NOx capture in packed beds is less expensive, but this method is not particularly effective [23]. It is also not a very practical method either for utilities or for transportation sources. Two-stage scrubbing has also been proposed as an effective end-of-pipe NOx control measure. The first stage uses water alone and the second uses aqueous urea. 

In the introduction we mentioned that the two applications for the catalytic methane combustion were in power generation and in the abatement of methane emissions in engine exhausts. In the first application, the amount of NO produced is in fact very small because the presence of a catalyst reduces the operating temperature. However, in the second type of application, the amounts of NO present can be substantial (e.g. several thousand ppm). In addition, the so-called selective catalytic reduction of NO can be effected by using methane as a reductant. In this case, the methane combustion takes place simultaneously with the NO reduction. Therefore, it is important to understand how the presence of NO affects the methane combustion under typical exhaust conditions. In the presence of NO, methane can undergo two different reactions, the reduction of NO and the total oxidation ... 

Stavins and Richards (2005) find that biologic carbon sequestration is also a cost-effective strategy that could be part of a climate mitigation regime. In cases where it may be difficult to measure total mass emissions from these sources but relatively easy to measure emission reductions (e.g., reductions of methane from a landfill) these sources might be captured with project-level offset provisions rather than through inclusion in the cap-and-trade program (U.S. EPA 2003). 

Methane emissions from coastal wetlands are strongly governed by salinity. Decreasing CH emission rates have been demonstrated along a gradient of increasing salinity (fresh, brackish, and saline vegetation types DeLaune et al., 1983) (Table 16.3). The reduction in methane emission is attributed to the effect of SO in seawater, which serves as a more readily available alternate e acceptor, and the formation of SO reduction products, which inhibit CH formation. 

Another application of fumaric acid is as supplement in animal feed. Studies indicate that a large reduction in the methane emissions of cattle can be achieved (up to 70%), if this cattle receives fumaric acid based additives as supplements in their diet (McGinn et al. 2004). Also, fumaric acid increases feed efficiency for pigs and poultry. 

In an in vivo experiment in sheep with tea saponins it has been reported that saponins inhibit protozoa, methane emission and improved rumen fermentation, where the reduction of methane emission was mediated through inhibitory effect on protozoa (Zhou et al. 2010). 

Murrah buffaloes fed on a diet of wheat straw and concentrate mixture (50 50) and supplemented with a feed additive (a mixture of Allium sativum, 1% and Mentha piperita oil, 0.1% of DMI) (Mix 1) on every alternate day resulted in 7% reduction in methane emission (l/kg DMI), but this reduction in methane emission was attributed to reduction in dry matter intake (Verma et al. 2009). There was no adverse effect on rumen fermentation pattern, enzyme and microbial profiles. 

---