F2 Synthesis Gas

Question 1

Syngas

Answer 1

Mixture of H2 and CO (Colourless, odourless and highly flammamble)

Question 2

Products from syngas

Answer 2

Methane
Transportation fuels (from Fischer Tropsch)
Ammonia
H2 (hydrogen gas)
Methanol
Electricity (from H2?)

Question 3

What raw material can be used for producing syngas?

Answer 3

Natural gas
naphta (nafta är en del av råbensinen - mörk och lättflytande)
coal
waste, etc.
(anything that contains CH - hydrocarbons)

Question 4

Vad beror valet av råmaterial av?

Answer 4

Cost
Availability (good to use waste)
Application (depending on the rawmaterial used you will have different outcomes/structure in the gas)

Question 5

What are the three main processes for producing syngas?

Answer 5

* Steam reforming (natural gas CH4, light hydrocarbons)
–> most common.
* Partial oxidation of heavy hydrocarbons ex diesel (expensive because you need pure oxygen)
* Partial oxidation of coal = coal gasification
–> mostly for power generation

Question 6

General flow scheme of Steam reforming, partial oxidation of heavy hydrocarbons and coal gasification.

Answer 6

Question 7

Methods for removing sulphur from feedstock

Answer 7

* Adsorption - through activated carbon
* Reaction - most common to react with ex ZnO
* Scrubbing - the sulfur reacts with limestone (CaCO3) and water
* Hydrotreatment - if stable sulphur compounds –> let the gas react with H –> the hydrogen will react with the impurities

Question 8

Steam Reforming reaction

Answer 8

CH₄ + H₂O → CO + 3H₂ (endothermic)

Question 9

Water-gas-shift reaction

Answer 9

CO + H₂O → CO₂ + H₂ (exothermic)

Question 10

Steam reforming process

Answer 10

• Temperature > 1000K in order to get good syngas
• Methane is very stable → catalyst is needed (Ni is good)
• Sulphur removal necessary
• Two sections:
  
  • convection section (where you preheat the gas)
  • radiation section (the reforming itself takes place)

Question 11

Effects of externally shaped pellets vs internally shaped pellets.

Answer 11

Externally shaped pellets:

• Lower pressure drop
• better dispersion (spridning) of “the reaction”

Internally shaped pellets:

• higher CH₄ conversion
• higher effectiveness factor

Question 12

Problems with the commercial catalysts

Answer 12

The heat transfer is a limiting step:

Ceramic has low conductivity → the temperature in the middle of the tube will be lower → the reaction will be slower

Endothermic reaction → the wall needs to be capable to handle high temperatures → need stable materials inside as well

Question 13

Why must carbon formation be avoided in Steam Reforming? And how do you prevent this?

Answer 13

Must be avoided for two reasons:
→ Deactivation of catalyst (hinders the methane from the active sites)
→ Blockage of reformer tubes (can increase pressure drop and create hot spots → can cause melting)

Solution: add excess steam! Favour the reaction that doesn’t produce C

Question 14

The affects of high pressure and high temperature?

Answer 14

High pressure:
(-) is thermodynamically unfavourable (SR → more gas molecules)
(-) lower methane conversion
(+) lower syngas compression costs
(+) smaller reformer size

High temperature:
(-) material constraints! (can make the material degrade for ex)
(+) need hight temperatures for the steam reforming - for good quality syngas

Question 15

The predicament of high temperature?

Answer 15

High temperature is needed for a high methane conversion, but will lead to degradation of the tube material. Need more water (steam) for higher methane conversion at lower temperatures.

Question 16

Improvements for the stem reforming process?

Answer 16

• Cost reduction!
• Better materials in the tubes (that can handle heat)
• Better catalysts (sulphur tolerance and less carbon deposition)
• Want to use higher hydrocarbons in the feedstock (forms more carbon) → Use a prereformer (converts higher CH_x to CH₄)
• If you want CO rich syngas → add CO₂ or use autothermal reforming (O₂ addition)

Question 17

What is the coal gasification process?

Answer 17

The coal is heated → the organic matter in the coal melts while gases evolve.

Further heating leads to pyrolysis (char is formed)

There are many reactions in the gas phase

(Gasification can also be used for biomass)

Question 18

Applications for coal gas

Answer 18

Question 19

Reactions in coal gasification

Answer 19

Question 20

What are the three main reactors for coal gasification?

Answer 20

Moving bed gasifier

Fluidized bed gasifier

Entrained flow gasifier

Question 21

Moving bed gasifier

Answer:

What type of coal?

Temperature

Quality of the product gas

Answer 21

Question 22

Pros and cons for moving bed gasifier

Answer 22

(+) Counter-current operation gives high efficiency (all coal is converted but the gas is not of high quality)

(-) Need large excess of steam to keep temp low (lowers efficiency)
(-) Large amount of byproducts
(-) Not for all types of coal

Question 23

Fluidized bed gasifier

Answer:

What type of coal?

Temperature

Quality of the product gas

Answer 23

Question 24

Pros and cons for fluidized bed gasifier

Answer 24

(+) High temp, less impurities

(-) Highly reactive coal is needed
(-) A lot of unreacted carbon → follows with the products gas, lowers the conversion

Question 25

Entraines flow gasifier

Answer:

What type of coal?

Temperature

Quality of the product gas

Answer 25

Question 26

Pros and cons for Entrained flow gasifier

Answer 26

(+) High temp → high conversion
(+) High temp → only CO and H₂
(+) Can handle all types of coal

(-) Short residence time requires very high temp.

Question 27

Usage for product gas from Moving bed vs Fluidized bed vs Entrained flow

Answer 27

Moving bed gasifier: hardly any syngas but good for power generation (CH₄) carries more energy

Fluidized bed gasifier: still better for energy usage

Entrained flow gasifier: the BEST for syngas production

Question 28

Cleaning and conditioning of syngas

Answer 28

Question 29

Conditioning of syngas for ammonia synthesis

Answer 29

WGS: CO + H₂O → CO₂ + H₂

Methanation: 3H₂ + CO → CH₄ + H₂O

Question 30

Biogas to hydrogen

Answer 30