Principles of material (mass) balance

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Principles of material (mass) balance ACCUMULATION = INPUT - OUTPUT + GENERATION - CONSUMPTION Input – enters through the boundary of the system Output – leaves through the boundary of the system Generation – produced within the system Consumption – consumed within the system Accumulation – build-up within the system

General approach to material balance The general approach for carrying out the material balance on a chemical process can be summarised into the following steps: Step 1

Draw a flow diagram and fill in all the given variables

Step 2

Label unknown stream variables with symbols

Step 3

Decide on a “basis” of calculation (do you need one?)

Step 4

If there are mixed mass and mole units, convert to the same units

Step 5

Write material balance equations using all available information. Write the balance with the fewest unknowns first

Step 6

Check if the equations are solvable or not. You can Degree of Freedon analysis (DOF) to check if the equations are solvable or not. DOF is a powerful tool and used by many chemical engineers.

Step 7

Solve for the unknowns progressively Substitute values on the flow diagram and into other equations as they are found

Step 8

Scale the final values as necessary. Make sure the units are consistent.

Step 9

Check your final answer using dependent equations

Note: Based on the nature of the problem, some of these steps can be avoided.


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Principles of material (mass) balance by SheffieldMZ - Issuu