L7 - Hydrogen

Question 1

Why is hydrogen considered an energy carrier rather than a primary energy source?

Answer 1

Hydrogen must be manufactured from feedstocks that contain hydrogen compounds

Question 2

Main sources of hydrogen

Answer 2

1. Hydrocarbon feedstocks - natural gas, coal, petroleum
2. Cellulosic biomass - through process like coal gasification can produce syngas which is a mixture of h2 and Co, where H2 can be separated from purified
3. Electrolysis of water

Question 3

Hydrogen production by steam methane reforming (SMR)

Answer 3

1. Reformation of natural gas
   - Methane reacts with steam to produce syngas, mixture of h2 and CO at 750-800 C
2. Water gas shift reaction
   - Co reacted with steam over a catalyst to form h2 and co2. Occurs over two stages, high temp shift (HTS) 350 and low temp shift (LTS) 190-210

• SMR used widely in industry
• High efficiency 65-75%
• But more than x2 CO2 produced compared to H2 = sequestration needed = higher costs

Question 4

Hydrogen production by partial oxidation

Answer 4

Reacts hydrocarbon feed with O2 at high temps to produce mixture of H2 and CO

CH1 + 0.5O2 ->< CO + 2H2

• High capital costs
• Used for heavy feedstock
• Produces more H2 than usually required by plant = economically attractive as byproduct.

Question 5

Hydrogen production: electrolysis

Answer 5

• Net energy loss for electrolysis the highest out of all h2 production
• Efficiency of converting electricity to hydrogen = 60-63%
• However need to consider electricity production losses as well thus efficiency of electrolysis is lower

Question 6

Other advanced production tech for hydrogen

Answer 6

1. Nuclear fission
2. Photosynthesis
3. Fermentation
4. Landfill gas recovery
5. Municipal waste reformation

Question 7

Hydrogen delivery methods

Answer 7

1. Compressed gas pipelines - used for large volume hydrogen over short distance eg. to industrial users such as oil refineries
2. Cryogenic, over the road tank trucks, railcars and barges - mid sized quantity of liq hydrogen over longer distance
3. Very small quantities of gaseous liquid hydrogen distributed via high pressure cylinders and tube trailers

Question 8

Hydrogen storage

Answer 8

• One of the most technically challenging barriers to hydrogen use.

1. Physical storage of compressed gas in high pressure
2. Physical storage of liquid hydrogen in insulated freezers - liq hydrogen has highest energy storage density and lowest vehicular weight but requires expensive insulated storage container (dewar) and energy intensive liquefaction process

Question 9

Hydrogen applications

Answer 9

1. Petroleum refining
   - Remove sulfur from crude oil
2. Chemical processing
   - Manufacture ammonia, methanol
3. Pharmaceuticals
   - Produce sorbitol
4. Metal production and fabrication
   - Create protective atmosphere in high temp operations
5. Food processing
   - Hydrogenate oils
6. Lab research
7. Electronics
   - Create special atmosphjere for production of semiconductor circuits
8. Glass manufacturing
9. Power generation
   - Cool turbo generators and protect piping in nuclear reactors

Question 10

Most important hydrogen applications

Answer 10

1. Transportation sector

2. Stationary power applications

Question 11

Hydrogen application in transport

Answer 11

1. Hydrogen internal combustion engine (HICE)
2. Fuel cell vehicles (FCV) - Primary cost component is the fuel cell itself - has life expectancy of x0.5 internal combustion engine so would need to be replaced twice to achieve lifetime equivalent to traditional engine

Question 12

Hydrogen application in power production (stationary power applications - hydrogen fuel cells)

Answer 12

1. Large cogeneration (CHP systems) - fuel cells combined with heat recovery system can meet the needs of commercial buildings or industrial sites as well as providing source of purified water
2. Uninterruptible power supply (UPS) systems - fuel cells used as a backup power supply. Fuel cells have refillable fuel storage system so can provide power for longer time

Question 13

Hydrogen production economics

Answer 13

1. Hydrogen production cost high relative to conventional fuels.
2. Low demand inhibits development of production capacity - little demand for hydrogen as an energy carrier.
3. Hydrogen tech has investment factor of x10 compared to CHP in Lolland hydrogen community

Question 14

Environmental impacts of hydrogen production

Answer 14

1. Current tech produces large amount of CO2 and not optimised for making hydrogen an energy carrier.
2. If H2 produced from electrolysis from fossil fuel powered generators, increased CO2 is emitted in comparison with direct use of the fossil fuel.
   - Using renewable energy to generate H2 by electrolysis requires larger energy input than direct use of the renewable energy directly. Due to extra conversion stages and losses in distribution
3. NOx emissions
4. H2 leakage and ozone depletion - molecular H2 leaks slowly from containment vessel. If more escape, h2 gas may form free radicals in stratosphere due to UV radiation. = act as catalyst for ozone depletion