Reduction in the Midrex furnace
Natural gas gives two reducing agents
1. Iron ores and extraction of iron
2. Iron without coke?
Egypt produces natural gas. Can a furnace reduce iron ore with natural gas and no coke at all?
Pick the right answer
Predict: in the Midrex furnace, what reduces the iron oxide?
- A. Methane, CH4, directly
- B. Coke, as in the blast furnace
- C. A mixture of CO and H2 made from natural gas
- D. Oxygen gas
Explanation
In the Midrex furnace a mixture of CO and H2 (water gas), made from natural gas, reduces the iron oxide. Methane is changed into these gases first, no coke is used, and oxygen would add oxygen instead of removing it.
3. Natural gas becomes water gas
Water gas
A mixture of carbon monoxide and hydrogen.
2CH4(g) + CO2(g) + H2O(v) →[Δ] 3CO(g) + 5H2(g)
Natural gas (93% methane) is changed into water gas: 3CO + 5H2.
| Atoms | Left | Right |
|---|---|---|
| C | 3 | 3 |
| H | 10 | 10 |
| O | 3 | 3 |
4. Two reducing agents
2Fe2O3(s) + 3CO(g) + 3H2(g) →[Δ] 4Fe(s) + 3CO2(g) + 3H2O(v)
- CO → CO₂ (gains O)
- H₂ → H₂O (gains O)
Both CO and H2 take oxygen from the ore. So both are reducing agents.
5. Share the oxygen
Two Fe2O3 hold 6 O atoms. Each CO or H2 takes one. Set the mix.
CO molecules 0
H₂ molecules 0
O removed 0
O still on the iron 6
6. Balance it
The reducing gases are given. Fill in the iron oxide and the iron.
Balance the equation
Complete the Midrex reduction equation.
Fe2O3(s) + 3CO(g) + 3H2(g) → Fe(s) + 3CO2(g) + 3H2O(v)
Balanced equation
2Fe2O3(s) + 3CO(g) + 3H2(g) → 4Fe(s) + 3CO2(g) + 3H2O(v)
Explanation
6 O are removed: 3 by CO and 3 by H₂. That is 2 Fe₂O₃, giving 4 Fe.
Need a hint?
- Count the O atoms taken by 3CO and 3H₂.
- Each Fe2O3 gives 3 O atoms. How many Fe2O3 give that many?
7. Blast furnace vs Midrex
| Blast furnace | Midrex furnace | |
|---|---|---|
| Raw material | coke | natural gas (93% methane) |
| Reducing agent | CO | CO + H₂ (water gas) |
| Gases formed | CO₂ | CO₂ + H₂O |
8. Check yourself
Pick the right answer
Exam question: "Explain the role of natural gas in the Midrex furnace." Which answer gets full marks?
- A. Methane reduces Fe2O3 directly to iron.
- B. It is the source of water gas (CO + H2), which reduces the iron oxide.
- C. It burns coke to make CO.
- D. It dries the ore and expels humidity.
Explanation
Natural gas (93% methane) is the source of water gas, CO + H2: 2CH4 + CO2 + H2O → 3CO + 5H2. These two gases reduce the iron oxide: 2Fe2O3 + 3CO + 3H2 → 4Fe + 3CO2 + 3H2O.
Fill in the blanks
New case: NiO + H2 →[Δ] Ni + H2O. The reducing agent is _____.
Explanation
H2 gains oxygen to become H2O: it is the reducing agent.
True or false?
The Midrex furnace uses coke as its source of carbon monoxide.
Explanation
The statement is false: the Midrex furnace uses no coke. Its CO comes from natural gas, together with H2.
9. Summary
- 2CH4 + CO2 + H2O → 3CO + 5H2 (water gas).
- 2Fe2O3 + 3CO + 3H2 → 4Fe + 3CO2 + 3H2O.
- Blast furnace: CO from coke. Midrex: CO + H₂ from natural gas.
Back to the hook: can you explain how the Midrex furnace reduces the ore with no coke?
Reveal
Natural gas is changed into water gas, a mixture of CO and H2: 2CH4 + CO2 + H2O → 3CO + 5H2. Both gases take oxygen from the ore: 2Fe2O3 + 3CO + 3H2 → 4Fe + 3CO2 + 3H2O.