Tar Reforming under a Microwave Plasma Torch

Abstract

Because of the scarcity of nonrenewable natural resources, such as petroleum and natural gas, the use of biofuel is needed. Gasification is a major process used to obtain renewable fuels from biomass; however, the gas cleaning system is a constraint for its broad utilization. During the pyrolysis process, a mixture of organic compounds in the gas phase is produced and must be removed from the gases before it is used in the most practical applications. In order to remove such organic compounds, which are known as tar, large, sophisticated, problematic, and expensive gas cleaning systems are added to the gasifier gas exit. Previous papers have shown that the plasma torch has the potential to destroy produced tar, being a simpler and less-expensive system than traditional gas cleaners. This work presents a qualitative and quantitative evaluation of a microwave plasma system running on tar destruction and its reforming. In order to evaluate a 1 kW microwave plasma system performance, an apparatus was developed and installed at ITA Laboratory of Plasmas and Processes (LPP-ITA). The system runs at atmospheric pressure with nitrogen and argon as carrier gas under a large range of flow rates. Experiments were performed using a gas mixture of N 2 , H 2 O, ethanol, and tar at controlled concentration in order to simulate the gases produced by a gasifier. The injected tar was obtained from pine pyrolysis and characterized for energy purposes. In order to reduce tar viscosity, it was diluted in commercial ethanol (92.5% ethanol and 7.5% water) and its concentration varied from 0.8 g tar /Nm gas 3 to 4.2 g tar / Nm gas 3 . Species formed in the microwave plasma torch were identified using an optical spectrometer. The reactor exit gases had their composition evaluated on tar content as well as for noncondensable gases. As a result, this paper shows that no tar content was detected at the reactor outlet, indicating that all supplied tar was destroyed in the plasma reactor. The main detected products were CO and solid carbon (C (s) ). Furthermore, neither NO nor CO 2 were detected, and an indication of H 2 formation was obtained. This paper concludes that the microwave plasma system is capable of destroying and reforming tar efficiently and produces mainly H 2 , CO, O 2 , and C (s) as byproducts.

Green chemistry, sustainable agriculture and processing systems: a Brazilian overview

“…This low supply of oxidative agents hinders complete combustion of carbon and hydrogen into CO 2 [54] used a mathematical model to predict the performance of a feasible biomass-to-energy conversion process, which was optimized by Brazilian researchers [55][56][57].…”

Sewage Sludge-Derived Producer Gas Valorization with the Use of Atmospheric Microwave Plasma

“…The principle of work of all atmospheric, electrodeless MWP reactors is identical [28, 39,41,42]. The plasma discharge is initiated and sustained due to absorption of microwave radiation.…”

“…The plasma gas is introduced into the reactor tangentially, what increases the stability of the plasma discharge and protects the reactor's walls from contact with the plasma. Practically, most of the electrodeless, atmospheric plasma reactors have very similar construction [28, 39,41,42] but some differences may occur in the geometry of the reactor, the generator's power and the presence of additional auxiliary devices. The major difference in the case of presented results was using four MW generators in series.…”

“…Many plasma techniques have been investigated in terms of tars conversion, e.g. corona discharge [31,32], dielectric barrier discharge [33,34], arc plasma [12,35], gliding arc plasma [36][37][38], and microwave plasma (MWP) [28, [39][40][41]. The previous research of the authors proved that MWP might allow high conversion of tar compounds, while at the same time it influences gas composition increasing the content of H 2 and CO at the cost of CO 2 and hydrocarbons [28,40].…”

Preparation, modification and development of Ni-based catalysts for catalytic reforming of tar produced from biomass gasification

“…Considering the properties of the complex tar and the challenges of tar for syngas application, the removal of tar has been extensively studied. Generally, tar is removed or destructed after a gasifer, using mechanical separation (cyclone, wet scrubber, filter, and electrostatic precipitator) and thermal-chemical methods (thermal destruction [42,43], catalytic steam reforming [44,45], plasma reforming [24,26,46], partial oxidation [47,48] and miscellaneous reforming [25]). The mechanical method can remove tar from flue gas, however, the secondary pollution and the loss of chemical energy in tar make it unattractive [34].…”