Consideration of Secondary Materials

B, the second educt in Eq. (13.5), gives: mC/MC mol C

YC/A+B is smaller than YC/A and is decreased remarkably if a larger number of primary raw materials is used:

mC/MC

With Eq. (13.7) or Eq. (13.8), only the first of the four points mentioned above can be considered.

Further definitions regarding the kind and amount of the secondary materials N1 and N2 will be introduced which frequently can only be measured using the units of mass instead of moles. Some of these components are often unknown and their number may be high.

For the real balance yield, the result is:

For higher masses of N1 and N2, the result is remarkably low compared to YC/a+b-The relation of both is given by the specific real balance yield:

and indicates the influences of all secondary materials. For 2NP A + B, the specific real balance yield may be for example Yspec = 0.15, influenced by the high amount of secondary raw materials present. From an economical and ecological point of view, a different raw material with a lower amount of secondary substances should be used.

Altogether, there are three important points which should be considered when assessing raw materials: the quality, the price and the cost for environmental protection.

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