Introduction to material balances and basics of mass conservation One of the most basic principles applied in the design and analysis of chemical engineering processes is the law of conservation. This is applied to the following conserved quantities: Mass (material balances) Energy (first law of thermodynamic - energy balances) Linear momentum fluid mechanics (fluid mechanics) Material balances provide a tool for engineers in many fields to grasp and to quantify the factors that determine the behaviour of both man-made and natural systems. Chemical processes are complex and typically involve many interacting factors in non-linear relationships. In this respect, the material balance techniques used by engineers to model industrial processes can be used as both an educational and a predictive tool to deal with complex processes. The principles involved to solve material balance calculations are those you probably learned in secondary school such as: -
The law of conversation Physical quantities Chemical reactions and stoichiometry The ideal gas law The first law of thermodynamics Simple algebra and a little calculus Computer calculations with spreadsheets
Conservation of mass Consider a simple boiler involving two components, A and B, shown below (this could be desalinisation, for example with A being water and B being salt):
Here FT1 is the total mass flowrate of stream 1. The symbols FA1 and FB1 are the mass flowrates of A and B, respectively in stream 1. These have units mass per time.