Mass Balance

A mass balance is also said to be material balance, it is the application of preservation of mass to the analysis of physical systems. Mass flows can be identified by accounting for material entering and leaving a system, without this technique it would be difficult to identify it. Mass balances are widely used in the engineering and environmental analysis. For an example, to design chemical reactors, analyze alternative processes to produce chemicals as well as in pollution distribution models and other models of physical systems mass balance theory is used. Population balance, energy balance and the somewhat more complex entropy balance are closely related and complementary analysis. Why these techniques are required? Because for thorough design and analysis of systems such as refrigeration cycle.  The term budget calculation is used to describe the mass balance equations in the environmental monitoring, where they can estimate the monitoring data.

Mass Recycle

Mass balance can be performed across systems which have cyclic flows. For further reprocessing in these systems output streams are fed back into the input of a unit. In grinding circuit such system is very common, where the materials are first crushed and then filtered to allow certain particles out of the circuit and then larger particles are returned to grinder. However to solid mechanics operations recycle flows are not restricted, they are used in liquid and gas flow as well. For example cooling towers, where the water is pumped through the cooling tower many times, and small quantity of water is drawn off at each pass to prevent solid build up.  The recycle helps in escalating overall conversion of input products, this is very useful for low per pass conversion processes, and the best example is Haber process.

Differential Mass Balance

For generating differential equations, the differential mass balance is used. This is to provide an understanding and effective modeling tool for target system. The concept is the same as for a large mass balance; however it is performed in the context of limiting system.

Usually the differential mass balance is solved in two steps, a set of governing equations must be obtained and then this equation should be solved neither analytically nor numerically for less traceable problems. The good examples of the applications differential mass balance are shown in Ideal (stirred) batch reactor, Ideal tank batch reactor, ideal tank reactor also named as continuous stirred tank reactor and ideal plug flow reactor.

Questions:

• What is mass balance?
• Explain mass recycle?