Tar destruction using non-thermal plasma technology-a critical review

Tar, a by-product of gasification, is a complex mixture of high molecular weight hydrocarbons that can cause significant damage to downstream equipment and reduce the efficiency of gas utilization. Effective tar destruction is therefore essential for producing clean syngas. Non-thermal plasmas (NTP's) technology offers a promising solution for gas cleaning by effectively destroying tar. This review explores various plasma sources and experimental approaches for using NTP's in tar destruction. It evaluates the performance of different plasma sources on the destruction of toluene and naphthalene, the most prevalent tar compounds in gasifier product gas, and discusses the chemical mechanisms and modeling approaches involved in their destruction. The most common modeling approach includes reaction kinetics, demonstrating how chemical reactions occur and behave in the NTP's system. This approach, known as the plasma global model, simplifies plasma modeling by focusing on reaction rates to predict the production and loss of species without needing to model plasma's bulk properties. The works that investigated plasma-catalysis for tar destruction were considered. A comparison of literature works reveals that the best performance for naphthalene destruction is achieved by corona plasma and reverse vortex flow gliding arc reactors, with the destruction efficiency (eta d) of 99% and 99.8% at concentrations of 5 g m-3 and 10.3 g m-3, respectively. For toluene, the gliding arc discharge and rotating gliding arc combined with the catalyst demonstrate the highest efficiency, achieving 99% and 99.9% destruction at 22.9 g m-3 and 4 g m-3, respectively. The synergy between plasma and catalysts offers key benefits, including higher energy efficiency, faster reactions, and lower operating temperatures compared to traditional thermal methods. The review suggests that NTP's technology shows strong potential for removing biomass tar from gasification. It could be a promising solution for biomass tar cracking and upgrading product gas in real gasification applications. Several pilot and small-scale plasma plants have been developed, but the technology is still emerging and faces various technical and economic challenges.