Many processes of chemical production are relatively complex, so the material balance should be carried out according to certain steps to give a clear calculation process and correct results. The following steps are usually followed.
1. Draw a block diagram of the process to select the accounting system
The graphic expression should be simple, but the content represented must be accurate, and there must be no omission of incoming and outgoing materials, otherwise the balance calculation will cause errors.
2. Write the chemical reaction equation and balance it
If the reaction is too complicated, or the reaction is not clear enough to write the reaction formula, the atomic balance algorithm should be used for calculation at this time, and there is no need to write the reaction formula.
3. Select the accounting benchmark
The accounting benchmark is the starting material quantity selected for material accounting, including material name, quantity and unit. Other material quantities obtained from the accounting result are relative to the benchmark. The selection of accounting benchmark is based on the principle of convenient calculation. Any stock of materials or a certain amount of a component related to the accounting system can be selected as the benchmark. For example, a certain amount of raw materials or products (1kg, 100kg, 1mol, 1m3) can be selected as the benchmark, or the unit time (1h, 1min, 1s, etc.) can be selected as the benchmark. The unit amount of raw material is used as the benchmark to facilitate the calculation of yield; The unit time is used as the benchmark to facilitate the calculation of consumption indicators and equipment production capacity. It is a technical problem to select the balance calculation benchmark. In the calculation, we should pay attention to training. Proper selection of the benchmark can greatly simplify the calculation.
4. Data collection
The calculations can be greatly simplified by collecting or calculating the various data necessary.
5. Set up unknowns, list equations, and solve them simultaneously
If there are several unknowns, several independent equations should be listed. In addition to the material balance calculation, these equations sometimes need other relational expressions, such as composition relation constraints, chemical balance constraints, phase balance constraints, material volume ratios, etc.
6. Calculate and check
7. Report the calculation results
The known calculation results are usually listed as a material balance sheet, which can be in different forms, but it should fully reflect the absolute and relative contents of various materials and components that are imported and exported.
