## Some Important Figures

**Current Efficiency**

From the electrochemistry laws we know that, if I is the current (in kA) flowing into a cell, the production of aluminum in 24h is equal to:

Theoretical Amount [in kg] = 8,0533 * I

For example, for a pot with a 200 kA flowing current the daily production should be equal to:

Theoretical Amount = 8,0537 * 200 = 1610.74 kg

But the actual weight of the aluminum produced is always lower than the theoretical amount. This is because together with the alumina reduction reaction:

Is always present a parasite reaction, called “back reaction”:

which reoxidizes to the state of alumina part of the aluminum produced.

The ratio:

Is called current efficiency and is always less than 100%. The best in class aluminum smelters operate with current efficiencies of 95 – 96%, while normal figures for current efficiencies range between 90 ÷ 94%.

**Specific Energy Consumption**

For the current to flow we need to apply a voltage V to the pot. The specific energy consumption, expressed in kWh/kg Al produced, from the electrochemistry laws is equal to:

This equation tell us that to reduce the specific consumption we need either to reduce voltage and/or increase current efficiency. In the aluminum industry specific energy consumption ranges between 13 ÷ 15 kWh/kg Al.

The theoretical amount of energy needed to produce aluminum at 100% current efficiency is equal to 6.34 kWh/kg. The difference between this theoretical and the actual amount in the real world is due to the fact that:

- Current efficiency is never 100%
- More than 50% of the electrical power given is lost as heat escaping from the pot itself

**Specific Carbon Consumption**

As we have seen, in the alumina reduction it is involved also the carbon. Theoretically, at 100% current efficiency, to produce 1 kg of aluminum 0,333 kg of carbon are needed.

The real consumption is higher than the theoretical because current efficiency is always less than 100% and also because of the oxidation of the anodes to the air.

Practically, the specific carbon consumption is equal to: