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EGA323 - Energy and low carbon technologies > Week 1 - Fossil fuel hydrogen > Flashcards

Week 1 - Fossil fuel hydrogen Flashcards

1
Q

Which is the leading Fossil fuel economy?

Name 3 problems related to it.

A

Oil as a transportation power

  1. Demand is increasing
  2. Supply is limited

3.CO2 emissions

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2
Q

Name 5 gases that are a main cause of air pollution. 2 ideal and 3 non-ideal.

Name 3 main processes that cause environmental pollution and give 3 examples.

A

ideal case - CO2 / H2O as exhaust
Non-ideal - CO / NOx / Unburned hydrocarbons

Process of transporting /
storing oil / minor spills
e.g
Exxon Valdez
BP
Mauritius oil spill

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3
Q

Hydrogen generation is a good way to reduce pollution what is the hydrogen economy?

Describe in 3 steps the process of hydrogen generation

What is an important rule to remember with H2 and energy?

A

Delivering ENERGY using HYDROGEN

  1. Must be generated from other
    energy sources
  2. Steam reforming of natural
    gas, or other methods
  3. Breaking C- hydrogen
    bond in molecules

H2 is a carrier of energy and not a primary energy source!!

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4
Q

4 advantages of the hydrogen economy

A
  1. Elimination of pollution caused by fossil fuel
  2. Elimination of greenhouse gases
  3. Elimination of economic dependence
  4. Distributed and localized production
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5
Q

Name 4 step hydrogen is generated.

How can we achieve a sustainable hydrogen economy?

A
  1. Reforming of hydrocarbons
  2. Reforming biomass
  3. Pyrolysis
  4. Electrolysis of water

Hydrogen must be derived from renewable sources

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6
Q

Name 4 component hydrogen is used for.

A

NH3, HCl, CO(NH2)2, and other commodities

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7
Q

Name 6 ways to create electricity

A
  1. Nuclear power
  2. Hydroelectric dams
  3. Wind turbines
  4. Wave and tidal power
  5. Geothermal power
  6. Solar cells
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8
Q

What is the safety aspect of hydrogen as a fuel and liquid hydrogen spillage? List 8 points

A
  • Colorless and odorless
  • Low ignition energy
  • High flame temperature
  • Invisible flame in daylight conditions
  • Negative Joule-Thompson Coefficient, (i.e. a leak may self-ignite)
  • Small molecular size (2.016 g/mol vs. ~107.0 g/mol for gasoline)
  • Wide range of lower explosive limit to upper explosive limit (4.0-75.0 volume%)

*liquid hydrogen spillage- Burns, explosions

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9
Q

Safety factors are to be considered when designing equipment. List 3 points

How to prevent them. List 5 points

A
  • Catastrophic rupture of the tank
  • Mixture of fuel cells reactant in the cells
  • Leaks due to punctures, faulty controls, stress cracks,
    etc.
  • Testing tanks and equipment (leak prevention)
  • Installing more valves
  • Designing equipment for shocks, vibrations, and wide T ranges
  • Inserting H2, O2, and leak detectors
  • Keeping fuel cells supply lines physically separated
    from other equipment
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10
Q

Methods for producing hydrogen
1. Steam (methane) Reforming (SR)

-Give 2-step equations with 1 equation as heat provider followed by an overall equation of the first two. Give
catalyst, temperature, and endo or exo.

-In the overall equation, how is CO and CO2 removed

-Give the disadvantage of the cost compared to gasoline

A

1) CH4 + H2O > CO + 3H2 endo
T= 700°-1100°; Catalyst: Ni

2) CO+ H2O > CO2 + H2 exo
Water-Gas shift reaction (WGS); catalysts: Fe,
Cr oxides

heat needed in (1) is provided by:
3) CH4 + 2O2 > CO2 + 2H2O

Combining (1) and (2)
4) CH4 + 2H2O > CO2 + 4H2
Efficiency: 65%-75%

CO (traces) and CO2 are removed using adsorption processes

Disadvantages)
Costs: still 2-3 times higher than producing gasoline from
crude oil

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11
Q

Methods for producing hydrogen
2. Methane cracking

-Give the equations
Why does this reaction need a high temperature of the steam?

-CO emission must be low given the equation of carbon contamination and why it needs to be low. What is its ppm allowed?

A
  • CH4 > C + 2H2
    Excess of steam is effective in
    preventing coke formation as Carbon will dispose of the catalyst, destroying it

Carbon contamination
- 2CO > C + CO2
CO is toxic as it deprives oxygen when inhaled
CO: in the range of 10-50ppm!!

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12
Q

Methods for producing hydrogen
3. Partial Oxidation Reforming (POX)
-Give the equations and if it is exo or endo and the names of each equation

A
  1. CH4 + 1/2O2 > CO + 2H2 Partial oxidation Exo
  2. CH4 + O2 > CO2 + 2H2 Partial oxidation Exo
  3. CH4 C + 2H2 Thermal decomposition Endo
  4. CH4 + 2O2 > CO2 + 2H2O(l) Methane combustion Exo
  5. CO + 1/2O2 > CO2 CO combustion Exo
  6. H2 + 1/2O2 > H2O(l) H2 combustion Exo
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13
Q

What product make complete combustion

What product make Incomplete combustion

A

CO2, H2O; no H2, CO, O2 or fuel

H2, CO (in the presence of a catalyst)

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14
Q

Explain and give an example of each case

-Partial Combustion

-COMPLETE COMBUSTION

A

-reactant to produce less than the stoichiometric amount. Unequal equation
e.g C3H8 + 3/2O2 <> 3CO + 4H2

-The number of moles must be
equal on both sides of the equation
e.g C3H8 + 5O2 <> 3CO2 + 4H2O

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15
Q

Methods for producing hydrogen
4. Autothermal Reforming (AR) reaction

-what is this reaction the combination of

-Give the overall equation with stoichiometry as an abbreviation

-what is z/x

-When choosing what should be considered

A
  • (1) Steam reforming (SR) reaction
    (2) The partial oxidation (POX) reaction
    (3) The water gas shift (WGS) reaction
  • CxHy + zH2O(l) + (x-0.5z)O2 <> xCO2 + (z+0.5y)H2
  • z/x = steam-to-carbon ratio
  • should be chosen such that the
    reaction is energy neutral
    (neither exothermic nor endothermic)
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16
Q

Methods for producing hydrogen
5. Coal gasification

-Give the overall equations with stoichiometry as an abbreviation

-give the 3 steps for the reaction

-disadvantages

-Step-by-step equation with names of each equation

A
  • C+ aO2 + bH2O <> cCO2 + dCO + eH2 + “other species”
  • 1) Devolatilisation - From carbon to complex gaseous mixture and porous solid char residue
    2) gaseous mixture - Combination of partial oxidation, SR, and WGS reactions
    3) Char particles - Gasified to CO through partial oxidation of C
  • POLLUTANTS + Solid char
    residues
  • C+ 1/2O2 <> CO Partial oxidation of char

C+ 2H2O <> CO2 + 2H2 Steam reforming (“water gas reaction”) of carbon

CO+ H2O <> CO2 + H2

C+ H2O <> CO + H2 Water-gas shift reaction

17
Q

-Fuel cell catalyst tolerance: CO

-There are two ways to reduce CO yield to extremely low levels. Chemical reaction and physical separation. Give 2 examples for both and
include equations for chemical reaction

A

-CO = ~1-10ppm

  1. Chemical reaction -

Selective methanation of CO
(CO+ 3H2 <> CH4 + H2O
CO2+ 4H2 <> CH4 + 2H2O)
(1) Reduce CO and H2
yield
(2) CO is not reduced; it consumes
even more H2
Therefore need for a catalyst to promote (1) while suppressing (2)

Selective oxidation of CO
(CO+ 0.5O2 <> CO2 over H2+ 0.5O2 <> H2O)

  1. Physical separation -
    Pressure swing adsorption
    Palladium membrane separation
18
Q

Define shale gas

A

is methane (natural gas) which is trapped in impermeable shale rock deep underground.

19
Q

Name 6 Pros and 4 cons of hydrogen fracking

A

Pro
* Energy security
* Job creation
* Lower emissions than
liquified natural gas (if
properly regulated)
* Natural gas is cleaner than
coal and oil: clean coal is
very expensive!
* Horizontal drilling
* Cheaper (?????)

Cons
* Environmental pollution
(aquifer, soil, water, air,
chemicals): Barnett shale:
heavy metals release, Se, Sr,
As .
* Use of huge quantity of water
(but compared to what?)
* Earthquakes
* Impact on habitat, landscape?

20
Q

What is Methane clathrate.

How many are in sediments or reservoir?

Is it economically viable ?

A

Methane trapped into the crystal
structure of water as methane ice
(CH4)·5.75(H2O)

Estimates = 1×1015and 5×1015 m³

low total volume and low
concentration at the sites

21
Q

What is the technique in separating CO2 and CO from H2 with a purity of 99.99%?

What is needed for this separation and what is it based on?

How does the differential loading of adsorption and desorption change with temperature?

A

Pressure swing adsorption

Beds composed of zeolites, silica and carbon

The molecular weight and high pressure

As the temperature is lowered the differential loading increases.

22
Q

How do Palladium membrane hydrogen purifiers operate?

What is the % of H2 separated

Is Pd costly?

A

H2 molecules in contact with the Pd membrane surface dissociates into
monatomic hydrogen and pass through the membrane through diffusion.
On the side of the Pd membrane, the
monatomic hydrogen is recombined into molecular hydrogen. The side where H2 splits is at high pressure and where it joins it is at low pressure.

99.99% of H2

Pd is very expensive (even though less than platinum)

EGA323 - Energy and low carbon technologies (1 decks)

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