Development and optimization of the parameters of processing (firing) of cable scrap with PVC insulation by steam gasification

The process of depletion of ores accompanied by a permanent increase in the production and consumption of nonferrous metals led to the formation of a continuous shortage of copper rolled products and wire rods in the world economy and trade. To compensate this shortage, secondary raw materials, including, in particular, scrap and wastes of the cable and wire production and civil engineering, are now actively introduced in the commercial production. For this purpose, special equipment and installations were created for cable stripping, i.e., for the separation of cables into metal concentrate and plastic waste. However, the existing technologies of cable cutting, parallel with high levels of dust and noise, are characterized by significant losses of the metal (up to 32%) and low quality of finished products (containing at least 7–8% nonmetallic fraction represented mainly by the protective cable insulation). The indicated protective insulation is based on flexible polyvinyl chloride plastics and special admixtures aimed at increasing the ductility of the cable. In a melting furnace, the insulation ignites and releases into the furnace atmosphere H₂, O₂, Cl₂, HCl, H₂O, CO, and CO₂, volatile hydrocarbons, and their chlorinated derivatives (chlorides, oxides, tetrahydride, tetramethyltin, etc.), which dissolve in the melt and may increase the concentration of hydrogen and oxygen in it. For this reason, we think that the concentrate obtained as a result of cable stripping is unsuitable for smelting copper and copper-based alloys. It can be used for smelting rough copper ingots, which requires the procedure of repeated refining remelting.

In this connection, modern environmentally friendly cable-cutting technologies are developed with an aim to increase the degree of extraction of the main product (metal core) and improve its quality. The present work is devoted to the study of environmentally friendly recycling (firing) of cable scrap with polyvinyl chloride (PVC) insulation by the method of steam gasification. It was experimentally established that the indicated method makes it possible to obtain a concentrate, which is practically free of PVC insulation and suitable for smelting branded alloys. The application of the steam gasification method for recycling cable scrap and PVC-insulated wastes guarantees 100% yield of the volatile fraction at the temperatures of firing of raw materials lower than the temperatures corresponding to the pyrolysis mode. At the same time, the minimum losses of metal caused by its oxidation in the course of gasification are guaranteed. By processing the experimental data, it was established that, within the temperature range 475–600 °C, the process of steam gasification of PVC cable insulation is controlled by its duration, temperature, and the flow rate of the steam-air mixture. An empirical dependence that can be used to describe this process is obtained in the form f(Xi) = 3.74∙(−0.1093τ + 63.356)·(−65.594T + 63.356)·(−2.4626η + 35.577). It is experimentally established that the balance efficiency of copper extraction from the PVC insulation by the steam gasification method is not smaller than 99.92%.