4 - Material Balances

Abstract

One of the simplest concepts in process engineering is the material or mass balance. Because mass in biological systems is conserved at all times, the law of conservation of mass provides the theoretical framework for material balances. In steady-state material balances, masses entering a process are summed up and compared with the total mass leaving the system; the term ‘balance’ implies that masses entering and leaving should be equal. Essentially, material balances are accounting procedures: total mass entering must be accounted for at the end of the process, even if it undergoes heating, mixing, drying, fermentation or any other operation (except nuclear reaction) within the system. Usually it is not feasible to measure the masses and compositions of all streams entering and leaving a system; unknown quantities can be calculated using mass-balance principles. Mass-balance problems have a constant theme: given the masses of some input and output streams, calculate the masses of others.