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Material Balances Calculation Approach using System Boundary

In this post, I want to share how to calculate material balances using the system boundary approach. This method is especially useful when dealing with a process configuration that involves several types of equipment with a different function, such as reaction, filtration, drying, and recycling.

How to do it?

We need to divide the overall process into several process sub-division or system boundaries. The flows into and out of the system are those crossing the sub-division and must balance with material generated or consumed within the boundary.

There are no rigid rules to use this approach. Selection of the best sub-division for any process is from our judgement and by practice a lot. However, these general rules can be used as a guide to calculate material balance using the system boundary approach:

  1. For complex processes, first thing to do is to take overall complete process and if possible, calculate the flows in and out. Raw materials in, products, and by-products out.
  2. Select the boundaries to sub-divide the process into simple stages and make a balance over each stage separately.
  3. Select the boundary round any stage to reduce the number of unknown streams to as few as possible.
  4. Include any recycle streams within the system boundary.

Let’s see example below to practice. Read More