Page 395 - Materials Chemistry, Second Edition

Appendix A Solution of Exercises 379

Solution of exercise: Allocation per mass in a process chain (anonymised case
example) (Section 3.3.2.2)

Starting point for the consideration of allocation is the 33 t end product.
• Production end product: no allocation; 154 GJ are fully assigned to the 33 t end
product.
• Production intermediate product: allocation according to mass:
3106 GJ are assigned to 247 t co-product (88.2%) and
415 GJ are assigned to 33 t intermediate product (11.8%).
If no loads would be attributed to the co-product, it would not carry any loads
of the process.
• Steam cracker: One product of the steam cracker is 280 t ethene (37.2% of
products), that is processed in the plant ‘production of intermediate product’.
Of the loads that are allocated by mass in the steam cracker to the 280 t ethene
(2590 GJ) only 11.8% (306 GJ) are to be assigned to the intermediate product. The
remaining 88.2% have to be assigned to the co-product. Otherwise the co-product
would not carry any load of the pre-production.
• Atmospheric distillation: One product of the atmospheric distillation is 935 t
Naphtha (14.7%) that is processed in the steam cracker. Of the loads that are
allocated by mass in the atmospheric distillation to the Naphtha (484 GJ) only
37.2% (180 GJ) are to be assigned to the Ethene. Otherwise the other products of
the steam cracker would carry no loads of the atmospheric distillation. Of this
180 GJ only 11.8% (21 GJ) are to be assigned to the intermediate product. The
remaining 159 GJ have to be assigned to the co-product.
• Consequently the loads for the production of 33 t end product sum up as follows:

Process GJ

Production end product 154
Production intermediate product 415
Steam cracker 306
Atmospheric distillation 21
Sum 896

This corresponds to 27 MJ kg −1 end product.

Solution of exercise: Closed-loop recycling of production scraps (Section 3.3.3)

1. Calculation of raw material and energy consumption without recycling:
In this case the scrap is treated as waste and therefore no load is allocated.