Energy, exergy, sustainability, environmental emission, and fuel cost analysis of a hot-dip galvanised steel wire process

Hot-dip galvanised steel is a widely used process to protect metals from corrosion. This process is considered an energy-intensive and highly polluting industry. In this context, the present study aims to investigate an energy, exergy, sustainability, environmental emissions and fuel cost analysis of a hot-dip galvanised steel wire process. For this purpose, a real hot-dip galvanised steel wire process belonging to the company Moreda Riviere Trefilerías S.A. (Spain) has been analysed. The parameters necessary to perform the thermodynamic analysis are obtained by means of process models. The methodology used comprises the following steps: a process analysis, an experimental setup, a modelling of the flue gases using the Aspen HYSYS model, a modelling of the galvanising barrel using the computational fluid dynamics model, and a validation of the process. The following conclusions can be drawn from the results: (i) The energy efficiency of the system, burners and galvanising barrel is 62.11%, 42.36% and 34.27%, respectively; (ii) The exergy efficiency of the system, burners and galvanising barrel is 90.84%, 78.90% and 56.60%, respectively; (iii) The sustainability index is 10.92; (iv) The galvanising process emits 72.61 ($\mathrm{kg}/h$) ${\mathrm{CO}}_2$, i.e. 636.06 ($t$) ${\mathrm{CO}}_2$ per year. Therefore, galvanising 1 ($\mathrm{kg}$) of wire in the actual process emits 0.0348 ($\mathrm{kg}$) of ${\mathrm{CO}}_2$; and (v) The natural gas consumption is 25.67 ($\mathrm{kg}/h$), i.e. 224.87 ($t$) of natural gas per year. Therefore, galvanising 1 ($\mathrm{kg}$) of wire requires 0.0123 ($\mathrm{kg}$) of natural gas. These results invite to study, in future work, the possibility of including other technologies, such as cogeneration systems, the use of new burner arrangements, hydrogen-enriched natural gas, solar thermal energy and photovoltaic systems.