Methane, a powerful greenhouse gas, is generated via the anaerobic decomposition
ID: 1063101 • Letter: M
Question
Methane, a powerful greenhouse gas, is generated via the anaerobic decomposition of solid waste in landfills. Collecting the methane for use as a gaseous fuel rather than allowing it to be released to the atmosphere provides an alternative to natural gas as an energy source and has a beneficial effect on the environment. If a batch of waste with mass M(tonnes) [1 tonne or 1 metric ton = 1000 kg] is deposited in a landfill at t=0, the rate of generation of methane at a later time t is given by the following equation V CH4 (t) = kL o M waste e -kt where: V CH4 (SCM CH 4 /y) = methane generation rate [SCM = m 3 (STP)] K = rate constant (y -1 ), a measure of how fast the waste decomposes L o = landfill gas yield potential [SCM CH 4 /tonne waste] M waste = tonnes of waste deposited at t= 0
a. Explain in your own words the benefits of reducing the release of methane from landfills and using the methane as a fuel instead of natural gas.
b. Starting with the above equation, derive an expression for the mass generation rate of M CH4 (t)[tonnes CH 4 /y]. Without doing any calculations, sketch the shape of a plot of M CH4 vs t from t=0 to t = 3y, and graphically show on the plot the total masses of methane generated in YEARS 1, 2, and 3 (Hint: Remember your calculus.) Then derive an expression for M CH4 (t)(tonnes CH 4 ), the total methane generated from t =0 to an arbitrary time t.
c. A new landfill has a yield potential L o = 100 SCM CH 4 /tonne waste and a rate constant k = 0.04y -1 . At the beginning of its first year, 48,000 tonnes of waste are deposited. Calculate the tonnes of methane generated from this deposit over a three-year period.
d. A junior engineer solving the problem of Part c calculates the methane produced in three years from the 48,000 waste deposit as M CH4 (t=3) = M CH4 (t=0){tonnes CH 4 /y}x 1y + M CH4 (t=1)x1 + M CH4 (t=2)x1 where M CH4 is given by the first expression derived in Part b.
-- -- -- Briefly state what the engineer is assuming about the rate of methane generation
-- -- -- - Calculate the value she would determine and the percentage error in her calculation, and show graphically what the calculated value corresponds to on another sketch of M CH4 vs t.
-- -- - The answer to Part c is 390 tonnes CH 4 . When one of the text authors first did the calculation of M, the result was 210 tonnes CH 4 . The author immediately knew that something had to be wrong in the calculation. Explain her reasoning.
e. The following amounts of waste are deposited in the landfill on January 1 in each of three consecutive years: Waste (tonnes) Year 1 48,000 Year 2 45,000 Year 3 54,000 Calculate the metric tons of methane generated through December 31 of the third year.
f. One way to avoid the environmental hazard of methane generation is to incinerate the waste before it has a chance to decompose. What problems might this alternative process introduce?
Explanation / Answer
a. In industrialised countries, the development of the LFG (landfill gas) capture and combustion technology has reached the status of deployment of the technology into the market. Activities are focussed on developing the technology to a level of commercial application by making technical improvements and reducing costs. For example, the US Landfill Methane Outreach Program (LMOP) promotes LFG as an important local energy resource by informing local governments and communities about the benefits of LFG recovery and by building partnerships between state agencies, industry, energy service providers, local communities, and other stakeholders.
The most important energy services to be addressed by LFG is generation electricity and heat. For example, in the USA, two-thirds of the currently captured LFG is used for the generation of electricity.
Next to electricity and heat, LFG can also be used for: firing pottery and glass blowing kilns; powering and heating greenhouses; heating water for aquaculture (e.g. fish farming).
more details :
Methane can be caught from landfills, it can be used to deliver power, warm structures, or power dump trucks. Catching methane before it gets into the environment likewise diminishes the impacts of environmental change. The by-products of methane plants incorporate non-vitality items, for example, supplement rich soil changes, pelletized and pumpable composts, and even feedstock for plastics and chemicals. Methane plants give monetary, vitality, and natural advantages for homesteads, organizations, and groups living in rural areas. They enable the capture and utilization of methane while likewise tending to waste administration and supplement nutrient needs. These focal points can be summed up as follows: