The Mass Balance

The general balance equation which is the basis for all mass and heat equations is as follows :
MASS IN - RAW MATERIALS CONSUMED + GENERATION = MASS OUT (product & waste)

Using the above process, there are four possible explanations if :
X in != X out

1. There is a loss of X from the process units or pipes
2. X is being consumed as a reactant in the process unit or alternatively being generated as a product within the unit.
3. X is being absorbed on the surface of the process unit causing accumulation.
4. Measurements are incorrect due to human or equipment error.

There are a number of sources of information for the mass balance, some of which are listed below, but it will be necessary to get the input of managers and employees who are familiar with the process :

• Existing flow measurement and analysis of feed stock, products and discharges/emission/waste streams;
• Raw material purchase records;
• Material inventories;
• Batch make-up records;
• Product specifications;
• Design material balances;
• Operating logs; and
• Waste manifestations.

Mass balances have their limitations and are only one tool which can be used in the review process.