1. “Problems and Theory for Material Balance of Unsteady state Operations”
Prepared By:
Group.5( to 47)
B.E. Sem-III(Chemical)
Guided By:
Prof. D. R. Gandhi
Prof. S. R. Banker
Chemical Engineering Department
Government Engineering College
Bhuj

2. Classification of Chemical Processes Process Classification
INDEX
Classification of Chemical Processes
Process Classification
General Material Balance Equation
Summary
Balance
General Procedure for Solving Material Balance Calculations
Material Balances on Reactive vs. Nonreactive Processes
Example

3. Classification of Chemical Processes:
1. Batch Processes. 2. Continuous Processes. 3. Semibatch Process.

4. CLASSIFICATION OF PROCESS
Batch Process: Feed is charged at the beginning of the process and the product is collected some time later
Continuous Process: In this type of process, raw materials continuously enter and product continuously leaves the process.
Semibatch Process: A semi batch process does not fall fully under either “batch” or “continuous” classification.

5. PROCESS CLASSIFICATION
Steady-State: Process variables don’t vary with time,
2. Unsteady-State (Transient):Process variables vary with time
Batch and semi batch processes must be transient. Continuous processes may be transient or steady-state.

6. General Material Balance Equation
input + generation – output – consumption = accumulation
Input : enters through system boundaries Generation : is produced within the system Output : exits through system boundaries Consumption : is used up within the system Accumulation : is built up within the system

7. Summary:
All batch processes are considered to be unsteady-state if the changes between the initial and final time is required to determine.
Continuous processes are operated in the unsteady state at the start-up, then it is operated almost at steady state mode.

8. Two types of balances may be written: Differential balance:
Indicates what happens at a certain moment of time
Integral balances :
Indicates what happens between two instants of time

9. 1. If the balanced quantity is the total mass, then:
Special Cases:
1. If the balanced quantity is the total mass, then:
generation = consumption = 0
2. If the balanced substance is a nonreactive species, then: generation = 0 consumption = 0
3. If the system is at steady state, then: accumulation = 0

10. General Procedure for Solving Material Balance Calculations
1). Choose a basis of calculation. 2). Draw and completely label the flowchart. The flowchart is fully labelled if the composition and flowrate (or amount) of each process stream can be expressed in terms of the labelled quantities 3). Express the result (unknown) of interest in terms of the quantities on the flowchart.

11. General Procedure for Solving Material Balance Calculations
4). Perform a degree of freedom analysis If the number of degrees of freedom = 0, the problem is solvable. 5). Write down the equations you will solve. Try to write them in an order that will simplify the calculations. 6). Solve the equations.

12. Material Balances on Reactive vs. Nonreactive Processes
When we earlier considered material balances on nonreactive processes (processes in which no chemical reactions are taking place), we wrote the balance equations in terms of the molecular species flowing through the process.
We will study two ways of solving material balances for reactive processes. The first, which is often the simplest to implement, is the method of atomic species balances.

13. Material Balances on Reactive vs. Nonreactive Processes
Input of atom i – output of atom i = accumulation of atom I
The second approach uses extents of reaction to express flowrates of each reactive species according to the stoichiometries of the reactions taking place.
Which approach one chooses to use does not matter in the sense that both yield the same answers

14. Development of Dynamic Models
Illustrative Example: A Blending Process
An unsteady-state mass balance for the blending system:

15. or
where w1, w2, and w are mass flow rates.
The unsteady-state component balance is:

16. EXAMPLE
In a batch process, the reaction takes place in the presence of an acid medium. The acid is drained from the reaction vessel at the rate of 15ml/s as a result of the density difference of the acid from the reacting component. To avoid wastage of acid, it is recycled to an acid tank which has 1000 L capacity. The acid drained from the rectaion vessel, picks up 50 g/L solids from the reactor.

17. EXAMPLE
Acid is fed once again to the process from acid tank. When the process is started, the acid is almost pure in the tank as a result of filtration. As the reaction proceeds, acid in the tank gets more and more contaminated with the solids. The concentration of the solids should not exceed 100 g/L from the process point of view. The batch time is 16h. Check whether the concentration of the solids will exceed 100g/L during the batch reaction.

18. EXAMPLE

19. EXAMPLE

20. THANK YOU