Abstract

This paper presents the experimental validation of a thermal treatment technology to recover added-value substances from the plastic matrix of end-of-life wind turbine blades, when these are subjected to a pyrolysis process to recover the glass fibres. The experiments have been carried out in a laboratory installation consisting of two reactors in series, in which pyrolysis and thermal treatment of pyrolysis gases and vapours take place, respectively. The application of this treatment enables a 25 wt.% reduction in the production of pyrolysis liquids, increasing the production of gases in an equivalent way and without compromising the pyrolysis conditions to be used to recover the glass fibres. The two-phase liquids are converted into single-phase aqueous ones, while the hydrogen concentration in the gases increases from 4 % to almost 50 % in volume. This high concentration of hydrogen in the gases allows them to be used as a source of hydrogen for various applications. Consequently, the technology demonstrates that the plastic matrix of wind turbine blades can be valorised in a pyrolysis based recycling process.

Abstract

Pyrolysis is a technically suitable process for recovering fibres from reinforced plastic waste that may also contain other types of materials (wood, foam, lacquer, etc.), such as wind turbine blades at the end of their useful life. The economic profitability of the pyrolysis recycling process depends mainly on the value of the recovered fibres, since pyrolysis liquids currently have no industrial application (and are therefore hazardous waste) and the gases are usually used to partially supply the energy requirements of the process, which is endothermic. Given that the wind turbine blades currently being retired are mainly made of glass fibres, which have low economic value, the profitability of the pyrolysis recycling process for this type of blade is a critical issue.

This paper presents an analysis of the increase in the profitability of a wind turbine blade pyrolysis process that includes a treatment stage to improve the properties of the liquid and gaseous products. To this end, the investment required for this treatment (additional process units) has been defined and the energy costs and liquid waste management costs have been quantified in scenarios with and without treatment, including in the latter case the income from the sale of hydrogen. With this information and the amortisation expense, the incremental income statements derived from carrying out the treatment have been prepared, obtaining the net cash flows (NCF). The NCF has been used to calculate the net present value (NPV) of the investment project, as this is the best criterion from a financial point of view for evaluating a project. Finally, a sensitivity analysis was performed taking into account deviations in the investment to be made, income and costs. The results show that the cost of managing liquid waste is the parameter with the greatest influence on profitability, meaning that implementing the treatment increases the profitability of the recycling process.