Abstract
Exergy analysis is one of the useful decision-support tools in assessing the environmental impact related to waste emissions from fossil fuel. This paper proposes a thermodynamic-based design to estimate the exergy quantity and losses during the recycling of copper and other valuable metals out of electronic waste (e-waste) through a secondary copper recycling process. The losses related to recycling, as well as the quality losses linked to metal and oxide dust, can be used as an index of the resource loss and the effectiveness of the selected recycling route. Process-based results are presented for the emission exergy of the major equipment used, which are namely a reduction furnace, an oxidation furnace, and fire-refining, electrorefining, and precious metal-refining (PMR) processes for two scenarios (secondary copper recycling with 50% and 30% waste printed circuit boards in the feed). The results of the work reveal that increasing the percentage of waste printed circuit boards (PCBs) in the feed will lead to an increase in the exergy emission of CO2. The variation of the exergy loss for all of the process units involved in the e-waste treatment process illustrated that the oxidation stage is the key contributor to exergy loss, followed by reduction and fire refining. The results also suggest that a fundamental variation of the emission refining through a secondary copper recycling process is necessary for e-waste treatment.
Highlights
According to Rosen and Dincer [1], “exergy is an ultimate extent of work that can be generated by a flow of heat or work when it reaches an equilibrium state with an environment chosen as a reference”
The suggested technique has been employed to estimate the loss of exergy within the proposed precious metal recovery system, and helps calculate and assess the exergy efficiency for a different percentage of e-waste in the feed material
The results of the two case studies assessed here indicated that the value of emission exergy for exhaust gas (CO, NOx, and SO2 ) is enhanced in the oxidation and fire-refining stages in comparison to the reduction stage for both scenarios (50% and 30% e-waste in the feed)
Summary
According to Rosen and Dincer [1], “exergy is an ultimate extent of work that can be generated by a flow of heat or work when it reaches an equilibrium state with an environment chosen as a reference”.The exergy value is able to disclose the possibility of designing more efficient processes as well as identifying the threshold by which we can achieve these designs. In 1997, Rosen and Dincer indicated that the concept of exergy could be reflected as a gauge for measuring the possible environmental impact of waste emissions [1], and the same researchers further emphasized that exergy characterized in the emission of the waste specifies how far the emissions and the considered reference environment are from each other. This signifies the possible environmental variation as stated by Rosen and Dincer [20]
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