Page 396 - Materials Chemistry, Second Edition
P. 396
380 Appendix A Solution of Exercises
Process MJ energy/80 kg product MJ kg −1 product kg raw material/kg product
Punching and moulding 200 2.5
Rolling 300 3.75
Iron production 1000 12.5 5
Sum 18.75 5
2. Calculation of raw material and energy consumption with recycling:
Punching and moulding: In this case the scrap is not waste but a co-product.
Allocation of energy consumption according to mass (product: 160 MJ,
scrap: 40 MJ) must not be conducted because in the case of closed-loop
recycling the scrap remains inside the product system and therefore this
applies also for the loads of the processes in which the scrap material was
processed.
Rolling: Remains unaffected, too, in this process.
Iron production: Because 20 kg of pig iron is substituted by 20 kg of scrap only
80 kg pig iron must be produced from 320 kg iron ore. The resulting energy
demand for the iron production is 800 MJ and 240 kg of slag is generated.
Process MJ energy/80 kg product MJ kg −1 product kg raw material/kg product
Punching and moulding 200 2.5
Rolling 300 3.75
Iron production 800 10.0 4
Sum 16.25 4
3. Savings
energy saving: 2.5 MJ kg −1 product (13%)
iron ore saving: 1 kg/kg product (20%).
