Low tar yield and high energy conversion efficiency in a continuous pyrolysis reactor with modified ribbon screw conveyor

Abstract

The high temperature batch and continuous pyrolysis of rice husk, sewage sludge, composite waste, hazelnut and apricot kernel shell were performed at 850 °C in a rotating batch reactor and a continuous reactor with a modified ribbon screw conveyor. Batch results were used in the continuous reactor design and comparison. At the continuous pyrolysis experiments, mixing and conveying efficiency of screw and thermal cracking performance of reactor, heated gas line and cyclone were investigated. Each material was fed into the reactor continuously with a feed rate of 4.5 kg/h for 3.5 h, and then the pipelines and reactor were monitored and collected tar and char were analyzed. The mixing unit and uninterrupted heated system showed excellent performance on tar reduction and tar yields were lower than 1.7 % for all materials. Separation of char dust from the gas without tar condensation in a heated cyclone prevented blocking in gas lines. With the secondary reactions syngas energy conversion efficiency for rice husk, sewage sludge, composite waste, hazelnut shell, and apricot kernel shell were 67.76 %, 59.22 %, 76.35 %, 56.96 %, 61.98 % respectively. With the new design with a modified ribbon screw, different types of materials were decomposed with minimum char yield in less than 15 min without mechanical problems. The high capacity of the installed reactor as 1–10 kg/h moved the technology readiness level (TRL) to 5 and set an example for demonstration in operational environment.