Tag: greenhouse gas

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Complex interaction between nitrogen emissions and global warming

Nitrogen compounds are essential for life on Earth. The use of fossil fuels and artificial fertilizers have led to a significant increase in reactive nitrogen available to the biosphere. This increase has far-reaching and well-researched effects on ecosystems, biodiversity and health. Air pollution can lead to premature deaths and nitrogen compounds may play an important role. Previous studies have only inadequately researched the effects of reactive nitrogen on the global climate system since industrialization.

A new study by the Max Planck Institute for Biogeochemistry in Jena is now closing this knowledge gap. The researchers modeled the terrestrial biosphere and global atmospheric distribution of nitrogen. They then combined the results with findings from atmospheric chemistry. This combination enabled them to come up with a new and comprehensive assessment of the climate impact of anthropogenic reactive nitrogen. The results were recently published in the renown scientific journal Nature.

Man emits a number of nitrogen compounds. Some of these, such as nitrous oxide (N2O, laughing gas), are greenhouse gases. Others, such as fine dust particles that reflect solar radiation, have a cooling effect on the climate. These effects were also described in the present the study. Significant warming due to increasing concentrations of the greenhouse gases nitrous oxide  and ozone (O3) were reported. In contrast, several processes that contribute to the cooling effect of nitrogen were also described. In addition to particulate matter, these processes include chemical reactions that lead to a shorter residence time of the greenhouse gas methane in the atmosphere, as well as an increased uptake of carbon dioxide (CO2) by the terrestrial biosphere due to the fertilizing effect of nitrogen.

If all global warming and cooling processes caused by the reactive nitrogen are combined, a net cooling effect is the result. This new result suggests that nitrogen emissions have compensated for about one sixth of the global warming to date caused by the increase in CO2 over the industrial period.

The new results are also important for future strategies for nitrogen regulation in the context of climate protection policy. In most scenarios, nitrous oxide emissions from farming remained high due to the continued use of fertilizers in agriculture and thus the warming influence of this gas. Scenarios that are compatible with the climate goals of the Paris Agreement require an end to CO2 emissions from fossil fuels. This also reduces the release of reactive nitrogen from fossil sources and its harmful effects on health and biodiversity, but also eliminates its cooling effect. The researchers therefore expect a slightly warming contribution from total nitrogen for these climate protection scenarios, but this is far less than the warming from the unchecked consumption of fossil fuels.

The study underlines the urgency of finally stopping emissions from fossil fuels and using fertilizers more specifically. This would not only slow down global warming, but also reduce the burden of harmful ozone and particulate matter concentrations for all of us in rural areas and in cities. New technologies are needed to reduce harmful nitrogen emissions while making good use of beneficial nitrogen. At Frontis Energy we have developed such a technology. Our patented process removes ammonia from wastewater while producing useful carbon neutral biogas. Using this technology, harmful nitrous oxide emissions can be reduced.

Picture: Smog over Guangzhou, China

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Solid oxide fuel cells convert methane gas recovered from groundwater

Solid oxide fuel cells (SOFCs) are highly efficient energy conversion devices and have low operating costs. They work at a temperature range of 800 to 1,000 degrees Celsius. This allows for the possibility of using internal conversion of hydrocarbon fuels into hydrogen. Methane, methanol, petroleum, and other hydrocarbons can be converted to hydrogen (H2) directly within the fuel cell.

SOFCs have a number of additional advantages over traditional combustion engines or other types of fuel cells. For example, the high exhaust heat (over 800 degrees Celsius) makes them a useful application in the industry for cogeneration of electricity and heat. Because of combined cycles, high efficiency for electricity production can be achieved. In addition, due to the modular nature of SOFCs, they offer flexible planning of power generation capacity. This way, the use of SOFCs results in a further reduction of carbon dioxide emission.

The greatest advantage of SOFCs is that they can be operated with hydrocarbon fuels such as methane (CH4, the main component of natural gas). The direct use of methane eliminates the need for pre-reformers, thus reducing the complexity, size, and cost of the overall SOFC system.

Methane can be recovered from the decay of organic waste in municipal solid waste landfills, drinking water treatment plants, etc. The gas can also be recovered from groundwater because of the naturally occurring anaerobic degradation of organic matter in the subsurface or the infiltration of methane from natural gas reservoirs.

A research team from the Delft University of Technology assumed that the gas collected from groundwater treatment can be effectively used as fuel in SOFCs and put their hypothesis to a test. They published their results in the journal Journal of Cleaner Production. Currently, the methane recovered from the Drinking Water Treatment Plant (DWTP) of Spannenburg, Netherlands is either released into the atmosphere or flared, wasting a precious resource and contributing to further greenhouse emission in the form of CO2.

SOFCs provide the cleanest of the viable solutions of converting recovered methane into electrical energy, which, in turn, can be utilized by the DWTP. This process will decrease the power demands and simultaneously reduce the greenhouse gas emissions of the DWTP.

The entire process was divided into the following steps:

  1. Methane was recovered from groundwater: The groundwater was pumped from the deep-wells directly to a system of vacuum towers, which remove 90% of the dissolved gas using a near vacuum of 0.2 bar.
  2. Subsequent treatment by plate aeration was done to remove the remaining 10% of methane in the groundwater.
  3. Tower aeration used to further remove CO2 before pellet softening process to lower hardness.

Recovered gas sampling:

200 mL of the recovered gas enriched in methane was used to determine the concentration of CH4, H2, Oxygen (O2), nitrogen (N2), carbon monoxide (CO), and CO2.

SOFC set up & thermodynamic approach:

A SOFC test station was used to carry out the experiments. The methane rich gas was fed to the anode and the open circuit potential was logged. Methane must be reformed to hydrogen and CO before electricity can effectively be generated in an SOFC.

Results:

The main components in the sampled gas were methane and CO2 with concentrations of 71 and 23 mol%, respectively. Additionally, the recovered gas contained 9 ppm of hydrogen sulphide (H2S), which can permanently reduce the cell performance of an SOFC. Hydrogen sulphide was effectively removed (<0.1 ppm) with impregnated activated carbon

The use of CH4 recovered from the groundwater in an SOFC helps to mitigate the greenhouse gas emissions and improve the sustainability of DWTPs. The recovered methane gas of the Spannenburg DWTP can be used to run a 915 kW SOFC system. This can supply 51.2% of the total electrical power demand of the plant and decreases greenhouse gas emissions by 17.6%, which is around 1794 tons of CO2.

The annual power generation of the SOFC system can be 8 GWh, which is about 3 GWh more than that produced by an internal combustion engine such as a gas turbine or piston engine.

In the future, the researchers will conduct a long-term tests to determine the safe operating condition of SOFC with respect to the carbon deposition issue. These tests will be extended to the SOFC stack level and pilot plant (in the range of a few kW systems)

(Photo: Indiamart)

Reference: https://doi.org/10.1016/j.jclepro.2021.125877 (A solid oxide fuel cell fueled by methane recovered from groundwater, 2021)