Learn why mass balance is the foundation of process engineering and why it's key to every project

“The mass of the ingredients going into the system must equal the mass of the ingredients
coming out of the system. This is the base assumption behind all mass balances.”

Process engineers use the term “mass balance” to refer to the production/usage rates of ingredients throughout a system, but almost everyone – engineers and laypeople alike – use mass balance regularly in our lives.

When using a recipe, you’re following the same principles used to develop the basis of a mass balance. As with a recipe, we need to know how much we’ll produce, how much we need in raw materials to match those production figures, and the steps needed to convert the raw ingredients to the final product. And as with a recipe, there can be complications in a mass balance around when and how items are added. Our clients tend to make either multiple products or several types of the same product using the same or similar processes. We glean information from these end products on how to use and clean the system for production and how to size and operate the system. With a good mass balance, it’s easier to develop process flow diagrams, piping and instrumentation diagrams, and equipment sizing.

The mass balance begins with understanding each step in the process, breaking down where ingredients are added together or removed, heated or cooled, or reacted. With the mass balance, we look at each unit operation or each piece of equipment to determine the inputs and outputs and the time it takes to go through the unit operation. During one unit operation, there can be a variety of combinations of inputs and outputs that balance out. Critically, the mass of the ingredients going into the system must equal the mass of the ingredients coming out of the system. This is the base assumption behind all mass balances.

Once a unit operation mass balance is developed with inputs and outputs, multiple unit operations can be tied together to understand how raw ingredients and materials move through the system to be converted from a raw ingredient to a finished product.

The next step, for systems that create multiple finished products, is to gain an understanding of how multiple products can be created at the same time using the same process, and at what point they’ll need to diverge so additional elements can be added to make the various products destined for grocery store shelving. It’s all part of the process equipment development and layout optimization, so we can understand how to maximize system usage while reducing overall capital investment. With mass balance, we have the building block for not only the rest of the process, but the project in general.