On the Reduction of Gas‐Phase Naphthalene Using Char–Particles in a Packed–Bed Atmospheric Pressure Plasma

Abstract

Fuel and synthesis gases generated by thermochemical gasification of renewable biomass resources and organic waste fractions are considered to be promising for recent and future energy demands. However, the presence of tar species in the gas mixture is an economic obstacle in the commercialization of this technology. The influence of non-thermal plasma on gas phase naphthalene (C10H8), which served as tar model compound, in the presence of solids was examined. The naphthalene was evaporated into a N2/H2/CO/CO2 gas atmosphere and led through a packed-bed, atmospheric plasma reactor operated at a temperature of 350 • C. The influence of two bed materials -glass beads and glass beads mixed with char particles -was studied. The char particles originated from real gasification processes with woody biomass as feedstock. With both reactor fillings, the content of naphthalene in the gas phase was reduced. The characteristic energy β of the naphthalene removal was found to be β no char = 952 ± 77 Jl −1 and β with char = 232 ± 10 Jl −1 , respectively. Consequently, the addition of char material leads to a naphthalene removal efficiency increased by a factor of about four. Furthermore the formation of ammonia (NH3), a by-product of the plasma reactions, was suppressed in the presence of char.

Tars removal by non-thermal plasma and plasma catalysis

“…in conditions that are less favourable to achieve high NRE. Hubner et al [40] used a DBD reactor packed with glass beads without/with char particles and their NRE did not exceed 35% (at 400 J l −1 ) and 60% (at 220 J l −1 ) at 350 °C, respectively. These results are in agreement with ours and show that glass bead packing is less effective compared to metal-supported and metal-oxide catalysts.…”

“…Tar removal processes that employ NTP have been studied by several research groups in recent years. The majority of studies focused on NTP tar removal processes using pulsed [3,5,[35][36][37] or DC corona discharge [38], DBD [39][40][41] or gliding arc discharge [42][43][44][45][46][47][48]. Pemen et al [3], Devi et al [5] and Nair et al [35,36] used streamer corona discharge powered by a pulsed high voltage power supply and studied the effect of gas temperature (200 °C-500 °C), gas composition (various mixtures of synthetic syngas, including compounds such as CO, CO 2 , H 2 , CH 4 , H 2 O and N 2 , and additives like Ar or air) and discharge energy density (up to 550 J l −1 ).…”

“…The importance of the presence of O 2 for naphthalene decomposition was also confirmed by Wu et al [39], who studied the effect of DBD in O 2 /N 2 mixtures with various O 2 concentrations. Other works used DBD packed with glass beads with and without the addition of char particles in syngas-like mixtures at 350 °C [40] or surface DBD in airlike mixtures at room temperature [41]. A tar decomposition process that employed gliding arc discharge was investigated on several surrogates of biomass tars-pyrene [42], toluene [43], naphthalene [44,45] and toluene and naphthalene [46,47] or benzene and naphthalene [48] mixtures.…”

The Effect of Packing Material Properties on Tars Removal by Plasma Catalysis

“…16% of γAl 2 O 3 [43]. With regard to the effect of glass beads as a packing material, their utilization in naphthalene removal was also studied by Hübner et al [39] and Redolfi et al [42]. They obtained an NRE of 60 and 95%, however, at higher operating temperatures of 350 and 250 • C and at significantly lower naphthalene initial concentrations of 90 and 100 ppm, respectively.…”

“…It summarizes the general knowledge, recent experiments, results, and findings of various authors. Indeed, several discharges have been employed and investigated in the naphthalene removal process by plasma catalysis: corona discharge [35,36], dielectric barrier discharge (DBD) [37][38][39][40][41][42][43], gliding arc discharge [44,45], and even plasma jet [46]. The discharges have been combined with several catalytic materials, most frequently with Ni-based catalysts (Ni/γAl 2 O 3 [37,38,40,44], Ni/ZSM-5, Ni/SiO 2 [41] and Ni/Co-based catalyst [45]) due to their availability and selectivity towards formation of syngas constituents in catalytic processes [23].…”