Gasification is an advanced thermochemical process that converts carbonaceous feedstock into syngas, a mixture of hydrogen, carbon monoxide, and other gases. However, the presence of tar in syngas, which is composed of higher molecular weight aromatic hydrocarbons, poses significant challenges for the downstream utilization of syngas. This Review offers a comprehensive overview of tar from gasification, encompassing gasifier chemistry and configuration that notably impact tar formation during gasification. It explores the concentration and composition of tar in the syngas and the purity of syngas required for the applications. Various tar removal methods are discussed, including mechanical, chemical/catalytic, and plasma technologies. The Review provides insights into the strengths, limitations, and challenges associated with each tar removal method. It also highlights the importance of integrating multiple techniques to enhance the tar removal efficiency and syngas quality. The selection of an appropriate tar removal strategy depends on factors such as tar composition, gasifier operating and design factors, economic considerations, and the extent of purity required at the downstream application. Future research should focus on developing cleaning strategies that consume less energy and cause a smaller environmental impact.

This work reports the design and characterization of a rotating gliding arc (RGA) reactor developed with novel electrode configuration. This RGA uses gas swirl discs having ‘tangential gas entry ports/holes’ (NH) to achieve arc rotation and does not employ any external magnets. This work investigates the effect of gas dynamics on (1) arc dynamics such as the arc’s rotation and shape; (2) voltage fluctuation pattern; and (3) plasma discharge power for the designed RGA. Experiments were conducted using argon as the plasma forming gas with (a) two gas swirl discs (NH = 3 and 12) and (b) three different gas flow rates (Q = 5, 25 and 50 LPM) as control parameters. Cold flow simulation (CFS) studies using a multidimensional solver were used to understand gas dynamics. The arc rotational frequency (f _arc ) measured from (1) a high-speed camera (HSC) and (2) fast Fourier transform (FFT) analysis of voltage, shows linear dependency on the Reynolds number (Re) calculated from CFS, with an R ² = 0.98. The agreement improves (R ² = 0.99) by applying linear fit only for the cases having turbulent Re. A close match between gas rotational frequency (f _gas ) calculated from CFS and experimentally measured f _arc is seen. The turbulent regime of the gas flow causes: (1) twisting and bending of the arc; (2) sawtooth-like voltage fluctuations with irregular and non-sinusoidal waveform; and (3) arc blow off. The high-frequency voltage fluctuations were reduced/absent when the flow Re reduced from ≈6.0 × 10 ⁴ to ≈1.0 × 10 ⁴ . These findings establish that the gas dynamics, in particular, the bulk flow phenomenon of the gas, has an explicit influence on arc dynamics of the RGA reactor. This novel RGA design has the potential to replace magnetically driven rotating gliding arc systems.

Successful application of plasma-activated water (PAW) as an alternate source of nitrogen for agricultural application requires low specific energy consumption. This work reports on a dielectric barrier discharge (DBD) plasma reactor for the generation of PAW having low specific energy (SE) consumption. The SE to produce N in PAW was 3.26 GJ/kg of N, which is 68% lower than the lowest value reported to date for DBD-PAW systems. The PAW generated was characterized for its physico-chemical parameters, most of which showed a linear increase with activation time (t_a). The concentration of hydrogen ion and that of the nitrate, which is the desired product for agricultural application, remained stable for four weeks in the PAW. The results indicate that minimal reactive oxygen species was formed in the plasma zone and only reactive nitrogen species (RNS) was formed confirming selectivity toward RNS.