- How to read, set up, and solve a material balance problem on processes that don't include reactors.

This page encompasses all the basic Mass Balance problems, as well as processes that have recycle and bypass streams, but not for processes that include reactors.
In general, a typical solution process for these types of mass balance problems are as followed: **read**problems statement- re-read and write
**flow chart** - re-write flow chart: if
a-the first flow chart is messy, or b-if the problems presents a unit conversion exercise, that is, if given information is in several unit systems, convert all to a consistent unit system on this re-written flow chart **Draw boundaries**on flow chart.**Make a table**and write balances next to it**Solve:**Fill out table, and if necessary, you may need to do one or more of the following: a-**solve simultaneous equations** b-**choose a basis**if the requesting a ratio for an answer (eg. mass fraction) c-**scale**to get subsequent answers- Is your answer reasonable?
**The Mass Balance Equation**gives In = Out for all boundaries.- Remember
**the rules for drawing boundaries**on flow chart, draw a boundary around each of the following:- Components (eg. distillation column)
- Junction Points
- The Total Process
- In
**making a table**- The top row labels a column for total material in addition to a column for each component (and of course, the far left column labels a row for each stream.
- We can do either mass or mole balances, which ever is more convenient.
- Solving simultaneous equations
- Choosing a Basis
- Scaling the answer
- For processes that have
**Recycle and Bypass streams**, the solution process is the same, the only new concept is in drawing the stream correctly on the flow charts (and remember, draw a boundary around each junction point).
Example #2:
Here, we are given the flow chart. PLACE "MBINTROEX1" HERE. Determine all unknown stream variables, given that the molar flow rate in stream 1 = 1/5 * molar flow rate of stream 2.
- i. Calculate the percentage of benzene in the process feed that emerges in the overhead product stream from the second column.
- ii. Calculated the percentage of toluene in the process feed that emerges in the bottoms product of the second distillation column.
Fresh air containing 4.00 mole% water vapor is to be cooled and dehumidified to a water content of 1.70 mole % H
A steam containing 5.15 wt% chromium, Cr, is contained in the wastewater from a metal finishing plant. The wastewater stream is fed to a treatment unit that removes 95% of the chromium in the feed and recycles it to the plant. The residual liquid stream leaving the treatment unit is sent to a waste lagoon. The treatment unit has a maximum capacity of 4500 kg wastewater/h. If wastewater leaves the finishing plant at a rate higher than the capacity of the treatment unit, the excess (anything above 4500 kg/h> bypasses the unit and combines with the residual liquid leaving the unit, and the combined stream goes to the waste lagoon. Waste water leaves the finishing plant at a rate m-dot = 6000 kg/h. Calculate the flow rate of liquid to the waste lagoon, and the mass fraction of Chromium in this liquid. |

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