mod 8.3 help (1 Viewer)

[mandemindiguise]

Q: Vikram currently has a cogeneration engine installed at his plant. It is designed to convert natural gas (100% methane) sourced from the grid to electricity. He is considering switching from natural gas to biogas, which is sourced at only 25% price of natural gas from a fermentation reaction of sewage and food waste, however, this method produces methane gas at a concentration of only 60%, with the remainder being co2 and toxic hydrogen sulphide gas.
Evaluate the two methods in terms of the availability of reagants and environmental issues.

 

[mandemindiguise]

bump

 

[Luukas.2]

Q: Vikram currently has a cogeneration engine installed at his plant. It is designed to convert natural gas (100% methane) sourced from the grid to electricity. He is considering switching from natural gas to biogas, which is sourced at only 25% price of natural gas from a fermentation reaction of sewage and food waste, however, this method produces methane gas at a concentration of only 60%, with the remainder being co2 and toxic hydrogen sulphide gas.
Evaluate the two methods in terms of the availability of reagants and environmental issues.

Obviously, you need to compare the energy available per L of gas from 100% methane and the mixture, and also cost per kJ.

Also, what will happen in the mixture to the CO2 and H2S? What are the environmental implications - more greenhouse gas per kJ, other pollutants, what you can do about the CO2 and H2S? This includes considering the source of the mixture and what its environmental implications are?

 

[wizzkids]

H₂S is flammable, so it contributes to the calorific value of biogas; the enthalpy of combustion is -518 kJ/mol of H₂S. However the products of combustion are SO₂ and H₂O so you still have an atmospheric pollution problem to deal with.

 

[Luukas.2]

H₂S is flammable, so it contributes to the calorific value of biogas; the enthalpy of combustion is -518 kJ/mol of H₂S. However the products of combustion are SO₂ and H₂O so you still have an atmospheric pollution problem to deal with.

That's not the only option, though... the H₂S could be removed from the gas stream first. This avoids the need to deal with the oxides of sulfur, but at the cost of reducing the caloric output.

A further option might be to look for an exothermic process that results in a product other than oxides of sulfur.

The different pollution issues with SO₂ as opposed to SO₃ are worth considering too, depending on the number of marks... as is the option of treating the SO₂ not as a pollutant / waste but instead as a raw material for some other process.

The difficulty is that the more deeply you explore, the more issues in modules 6 and 8 arise.

Australia has done quite a bit of work on the issues of desulfurisation because our diesel is naturally high in sulfur but the modern diesel vehicles can't tolerate high sulfur fuels, which is why the maximum sulfur content in diesel was reduced dramatically early this century.

In short, there is a lot that can be discussed in answering this question, which brings with it the danger of losing focus on the question, which is an evaluation of the two methods... so requires evidence supporting a judgement, which needs to include a size / scale aspect.