Pyrolysis of solar panels

Mechanical dismantling handles metal and glass well and the polymer badly. EVA or POE encapsulant is designed to bond glass to cells for decades; when a mechanical line tries to separate them it either leaves encapsulant stuck to the glass — which lowers the cullet grade — or it leaves glass and metal fragments in the polymer fraction, which makes that fraction hard to place.

Pyrolysis removes the problem rather than sorting around it. Heated in the absence of air, the polymer does not burn; it decomposes into a condensable oil, a combustible gas and a solid residue. What is left is a cleaner mixture of glass, metals and carbon that can be screened and separated properly.

1. 01

   Feed preparation

   The material must arrive with the frame and junction box already removed, at a controlled particle size and moisture. Oversized or wet feed is the most common reason a reactor under-performs.

2. 02

   Charging

   Batch reactors are loaded in vessels or cages; continuous reactors are fed through a sealed mechanism. The choice is a throughput and labour decision as much as a technical one.

3. 03

   Heating

   The reactor is heated indirectly. Air is excluded, so the polymer decomposes rather than combusts. The temperature profile is set for the feedstock, not by a universal recipe.

4. 04

   Gas and oil recovery

   Vapour leaves the reactor and passes through a condenser. The condensable fraction is collected as oil; the non-condensable gas is typically returned to the burner to heat the reactor.

5. 05

   Solids discharge

   The residue — glass, metals and char — is discharged and cooled under control.

6. 06

   Cooling and screening

   The residue is screened and separated. Metals come out as metals; the fine fraction goes to dust control. This is the step that converts the reactor output into saleable streams.

Oil quality, gas composition and residue characteristics are properties of the feedstock and the operating profile. They are established by assay for a specific project — not read off a process diagram.

• The polymer has no outlet. If the mixed fraction is a disposal cost rather than a product, pyrolysis converts a liability into gas, oil and a cleaner solid.
• A glass buyer rejects encapsulant residue. Thermal removal can get cullet closer to a specification that mechanical separation cannot reach.
• Downstream separation is being blocked. Once the polymer is gone, screening and metal separation work far better on what remains.
• There is permit headroom for thermal treatment. This is the binding constraint in most jurisdictions, and it should be established first.
• The site can run thermal operation safely. Combustible gas, hot solids and fine dust all need procedures, instrumentation and trained operators.

Pyrolysis is not a substitute for dismantling. Feeding whole framed modules into a reactor wastes the aluminium — it ends up in the residue rather than in a clean metal stream — and loads the process with material it was never designed to handle.

It is also the wrong first purchase for a plant that has no separated output to work with. If the front end is not producing a consistent, weighed feed, adding a reactor adds cost without adding control. In our experience the sequence that works is: get the dismantling line right and prove the fractions, then decide whether the polymer fraction justifies a thermal stage.

• Reactor — batch or continuous, indirectly heated
• Condenser and oil collection
• Gas train and burner arrangement
• Discharge, cooling and conveying of the solid residue
• Screening and separation of the cooled residue
• Extraction and dust control at every transfer point
• Instrumentation for temperature, pressure and gas safety