PROCESS PRINCESS
INTRODUCTION TO MASS BALANCE
CONSERVATION OF MASS
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Process units & mass cannot be created nor destroyed but it can be converted to other forms by undergoing reaction process.
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Total mass INPUT = Total mass OUTPUT
PROCESS CLASSIFICATION
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batch process
No mass crosses the system boundaries between the time the feed is charged and the time the product is removed
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continuous process
The inputs and outputs flow continuously throughout duration of process
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semi batch
Any process that is neither batch or continuous
STEADY STATE:
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if value of all variables in a process(temperature,pressures,volumes,flow rates, etc) not change with time except possibly for minor fluctuations about constant mean.
TRANSIENT:
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when any of the variable change with time.
MASS BALANCE EQUATION
Balance on Continuous Steady-State Process
Reactive System
Input + Generation - Output - Consumption = 0
Non-Reactive System
Input = Output
Balance on Batch Process
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Input & output = 0
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Generation - Consumption = Accumulation
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Final Output - Initial Input = Accumulation
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Initial Input + Generation = Final Output + Consumption
TYPES OF MASS BALANCES
Differential:
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Analysis in a specific time
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Use of velocity/rate unit: g/s or kg/h, barrel/day
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Use in continuous processes
Integral:
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Occurs between two instants
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Use unit quantities (kg, ton, lb)
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Time elapsed: Tf-Ti
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Use in batch processes
STEPS IN SOLVING MATERIAL BALANCE CALCULATION:
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Read and try to understand on the process description. What type of process unit used and what type of process operation.
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Draw a flowchart for the process description using boxes or other symbols to represent process unit or unit operation and lines with arrows to represent inputs and outputs.
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Write all known stream variables i.e. inputs & outputs, on the flowchart.
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Assign algebraic symbols to unknown stream variables.
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Do the degree of freedom analysis. You must have equal number of equations related to unknown process variables (zero degree of freedom).
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Take basis of calculation.
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Write mass balance equation for the overall system and for specific component using selected Eq [1] to [6].
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Perform mass balance for the process description.
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Always check the overall mass balance for Total Inputs = Total Outputs
try out this question!
