Instant Notes: 2. Material Balance Calculations

Mass Balance Equation: \[(\text{input}-\text{output}) + (\text{generation}-\text{consumption}) = \text{accumulation} \tag*{(1)}\] ‘Generation’ and ‘consumption’ are due to any reaction occurring. At steady state, ‘accumulation’ is zero.

Atom Balance:
Since atom can NOT be created or destroyed, for any process, a number of atoms entering the process must be equal to that leaving the process. \[\text{input (of some species of atom)} = \text{output (of the same species of atom)} \tag*{(2)}\] The chemical reactions that take place in a complicated process can be solved by atom balances without knowing the actual chemical reactions taking place in that.

Inert Substance: In most oxidation processes air is used as the source of oxygen. Air is 21 mol% oxygen, and 79 mol% nitrogen. Nitrogen is an inert substance at the temperatures at which most other substances are oxidized.

Tie Substances: Tie material is defined as the material, of necessarily inert or unreactive, which passes through a system from a single input stream to a single output stream, and of course remains completely unchanged during this process.

The term ‘composition on a wet basis’ is commonly used to denote the component mole fraction of a gas that contains water, and the composition on a dry basis signifies the component mole fractions of the same gas without water.