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CPOTE2020 logo
6th International Conference on
Contemporary Problems of Thermal Engineering
Online | 21-24 September 2020

Abstract CPOTE2020-1124-A

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The role of hydrogen in microwave plasma valorization of producer gas

Mateusz WNUKOWSKI, Wrocław University of Science and Technology, Poland
Łukasz NIEDŹWIECKI, Wroclaw University of Science and Technology, Poland
Piotr JAMRÓZ, Wrocław University of Science and Technology, Poland

Plasma methods are given significant attention in the context of conditioning the producer gas derived from biomass gasification. These methods include warm plasmas, like gliding-arc or high-power microwave plasma, that provide both the high temperature and production of reactive species. While there are many studies considering applying these types of plasma for producer gas valorization, most of them focus on rather simple gaseous mixtures, rarely including hydrogen in their composition. At the same time, the microwave plasma has been investigated in the context of CO2 reduction and CH4 conversion with the addition of H2, showing that hydrogen may have a great impact on converting both of those compounds - which are also the main compounds in the producer gas. Therefore, the goal of this work is to present the impact of hydrogen on the other producer gas compounds during microwave plasma valorization. These compounds include main producer gas components (CO, CO2, CH4, N2) and minor impurities (tar compounds, H2S and NH3). The results proved a beneficial impact of hydrogen (ca. 20 % v/v) addition on organic compounds conversion. The conversion of CH4 (3.8 % v/v) increased from ca. 68% to 95% while the conversion of toluene (10 g/m3), as a tar surrogate, increased from ca. 97% to 100%, when compared to pure nitrogen plasma. Additionally, the addition of hydrogen changed the distribution of the products, inhibiting soot and aromatics production and promoting C2 compounds creation. In the case of CO2 (ca. 18 % v/v), hydrogen addition resulted in conversion increase as well, from ca. 18% to 63%, when compared to nitrogen plasma, with CO being the resulting product. The presence of hydrogen inhibited H2S (ca. 660 ppm) conversion from 96% (in nitrogen) to 27%. The addition of H2 did not affect CO and NH3. In addition to gas analyses, the optical emission spectroscopy was applied to investigate the plasma. It was proved that with the H2 addition, the H radicals, which are crucial for organic compounds conversion, were present. Moreover, the gas (rotational) temperature within the plasma core zone was estimated at the level of 5600 K, which allows concluding that the processes within the plasma reactor are mostly thermally driven.

Keywords: Hydrogen, Microwave plasma, Biomass gasification, Producer gas, Hydrogen production
Acknowledgment: The work was the result of the research project No. 2017/27/N/ST8/02019 titled "Fate of hydrogen sulfide and ammonia in a warm microwave plasma treatment in the presence of the main syngas compounds" and financed by the Polish National Science Center