Mechanical Process + simple chemistry;PV waste;module delamination

Categories:
Categories:
Unit processes/End-of-life treatment/Other end-of-life services
Location:
CN - China
Reference year: -
Description

Mechanical upcycling that aims to fully recover components. Additional chemical processes are involved, referred as “mechanical recycling” . Several studies have investigated mechanical operations to recover glass and separate it from other parts. We sort these methods as M1, M2, M3, and M4. Inmethod M1, Granata et al. proposed a method to shred the module in atwo-rotor motor followed by hammer milling. Larger fractions (diameter > 0.08 mm) were identified as recoverable glass and smallfractions (diameter < 0.08 mm) were identified to contain Si andmetals that need further pyro/hydrometallurgical treatments. Afterthermal removal of the polymer residue from the glass, this methodproduces recyclable glass at a quantity 80–85%w of the PV module. A follow-up study further improved this process by replacing thecrushing and milling with triple shredding, achieving a glass recoveryrate of 91%w. In method M2, instead of thermal removal of theEVA residue, Yingli Solar developed a cryogenic process to delaminateSi modules. After cooling at sufficiently low temperatures (−196 °C),the interfacial bonding of the sandwich structures are weakened.Then, an abrasive grinding machine can easily peel Si powders fromplastic powders. In method M3, which targets at the unbroken glass pieces, Trina Solar investigated a glass detachment processunder oxidant hydrothermal subcritical conditions to detach the wholeglass sheet from the module. Note that, for M2 and M3 the recycling yield was unclear. Therefore, the viability should be furtherinvestigated and validated. In method M4, another reliable approachwas used: hot knife cutting. The Full Recovery End of Life Photovoltaic(FRELP) project demonstrated a pilot recycling approach that cuts apartthe entire module glass sheet by a high-frequency knife at slightlyelevated temperatures. 98%w of the glass was recovered, and the rest ofthe EVA/solar cell/backsheet sandwiches were sent to an incinerationplant for further treatment. Cutting has a clear advantage to detach glass in a single step to avoid multiple crushing and thermal processes. The hot-cutting concept has been implemented using differentdesigns, such as a heated cutting blade, a fast spinning steel brush, andchisel sheets. Users of this data set should consider the applicability of each recycling method (M1, M2, M3, M4, C1, C2) described for different PV module types and conditions. Attention must be paid to the recycling yields, environmental implications, and technological feasibility of these methods. For methods where recycling yield is not clear (M2, M3), additional research and validation are necessary. The toxicity of fluorine-contained backsheets must also be addressed, potentially altering the treatment process for modules with such backsheets.

Technology

Chemical delamination. The adhesive encapsulation layer can also be dissolved in either inorganic (C1) or organic (C2) solvents to delaminate the module. In method C1, solar glass was firstly separated fromsolar cells by immersing the module in nitric acid (HNO3) for 24 hours. In method C2, Doi et al. reported successfully dissolution of EVAin trichloroethylene at 80 °C for 10 days. The chemical process canbe accelerated with ultrasonic radiation. For example, Kim and Leereported the most effective organic dissolution of EVA in O-dichlorobenzene within 30 minutes to recover damage-free solar cells. Azeumo et al. reported complete dissolution of EVA in less than60 minutes in toluene with the presence of ultrasonic radiation. Insome occasions, the organic solvents could not remove the swollen EVAremaining on the surface, hence a secondary treatment such as pyrolysis is required. This unavoidably adds complexity.In addition to the front glass, fluorine-contained backsheets must beremoved before recycling solar cells because of its toxicity. The backsheet can be peeledoff from the module at elevated temperatures, mechanically removed during scrapping, grinding or milling operations, or thermally combusted in a licensed incinerator. For glass-glass modulesand those with fluorine-free backsheet, this step is unnecessary.

Process type
Unit
LCI modeling approach
Unknown
Multifunctional modeling
NONE
Format
ILCD
Aggregation type
HORIZONTAL
Data provider
TianGong
Review status
Internal
Cost
Free
Contact
Tiangong LCI Data Working Group