A mass and energy balance is the guiding document for any chemical effort. It accounts for all the various inputs and outputs of every unit. Values can easily be assigned to track losses and tie the financial performance of the system to the process control data. The mass and energy balance is a tool by which to guide the engineers and operators so that the most financial productivity can be extracted from the system. All lab scale, pilot scale and commercial scale plant units, systems and equipment testing, evaluation, and operation should be based on constituent level mass and energy balances.
These balances shall be compiled from the mass based (not volume disguised as mass) measurements of composition from the analytical lab combined with the mass based flow measurements from the on line systems or by collection and weighing of the batch run materials. Temperature measurements can be used to determine and resolve the energy balances for all systems. In cases where the direct mass flow measurement is impractical equivalent volumetric flow measurements combined with a density measurement will be used to determine the calculated mass flow.
The composition measurements shall focus on the needed constituents of concern. The analytical test methods used in the compilation of the mass balances shall be validated using accepted statistical methods. The error in the measurement shall be displayed as part of the reported values in any mass balance. For example: the total flow shall be reported as 1.0 +/- 0.1 lb/hr. Another example at the constituent level would be the total Ca concentration in that flow shall be reported as 250 +/- 10 mg/kg. The mass flow of the Ca in the stream would be calculated using the combination of the analytical composition measurement and the total mass flow measurement. The correct methods should be used to propagate the error through the calculation.
All commercial runs, test plans and experimental orders should include mass balance sampling plans and energy balance sample plans. Key learnings reports should issue the mass balance and energy balance according to the corresponding sample plan as the basis for the work.