Studium expandujícího proudu termického plazmatu s využitím molekulových spekter

Thermal plasmas generated by plasma torches are well-known for their high temperatures and high enthalpies. Therefore optical emission spectroscopy is appropriate diagnostic method because of strong emission of radiation corresponding to the visible light. The decay of excited atoms, ions and molecules causes emission of the light at characteristic wavelengths. Except spectral lines of atoms and ions, also some molecular bands can be seen in the spectra of the plasma jet. Especially expanding thermal plasma jet operated under low pressure conditions offers possibility of observing molecular transitions. Pressure lower than atmospheric may cause the presence of supersonic flow and departures from thermodynamic equilibrium. Spectra of OH radical have been investigated using computer code LIFBASE, which contains a lot of data regarding spectra of diatomic molecules. Radial profiles of rotational and vibrational temperatures have been found in several regions of the jet

Emission Spectroscopy of OH Radical in Water-Argon Arc Plasma Jet

Emission spectra of OH radical are studied in the plasma jet generated by a plasma torch with hybrid water-argon stabilization. Plasma jet is located in a chamber with pressures 4 kPa and 10 kPa. In spite of high temperatures of produced plasma, OH spectra are observed in a large area of the jet. OH spectra are used to obtain rotational temperatures from the Boltzmann plots of resolved rotational lines. Due to line-of-sight integration of radiation, interpretation of the temperatures is not straightforward. It seems that excited OH molecules can be formed by various mechanisms, mainly in the outer parts of the jet, where thermal processes are not as dominant as in the hot central region

Pyrolysis of methane via thermal steam plasma for the production of hydrogen and carbon black

Methane pyrolysis for the production of hydrogen and solid carbon was studied in plasma reactor PlasGas equipped with a DC plasma torch with the arc stabilized by a water vortex. Steam plasma is produced by direct contact of electric arc discharge with water surrounding the arc column in a cylindrical torch chamber. The composition of the gas produced was compared with the results of the equilibrium calculations for different flow rates of input methane. We have found that for the net plasma power 52 kW the optimal flow rate of the input methane was between 200 slm and 300 slm, for which high methane conversions of 75% and 80% are achieved. For the flow rate of 500 slm, the methane conversion is only 60%; however, the output still consists of a mixture of hydrogen, methane and solid carbon, without other unwanted components. For the flow rate of 100 slm, the methane conversion is 88%. For 100 and 200 slm of input methane the energy excess for the reaction with respect to the calculated value is 16 kW and 4 kW. On the other hand, for 300 and 500 slm of input methane we have the energy lack of 10 kW and 38 kW. The solid carbon produced was composed of well-defined spherical particles of the size about 1 μm. Comparison with the steam and dry reforming of methane in the same system shows that the presence of oxygen increases the methane conversion, despite lower available energy produced.</p

Integration of thermal plasma with CCUS to valorize sewage sludge

The presented study addresses the threefold challenges namely, sustainable waste valorization of a difficult waste stream, climate change due to CO2 emissions and clean energy crisis and it is a small step forward to achieve SDG-7. A hybrid DC thermal plasma was employed in a pilot scale facility (∼150 kW) to treat sewage sludge in the presence of waste CO2 (according to the concept of CCUS, Carbon Capture Utilization and Storage) to produce syngas and assess the viability to retrieve phosphorus and other valuable materials from the generated ash. An equilibrium model was also developed to enhance the understanding about the dynamics of process. The H2 generation was around 0.5 m3/kg fuel whereas the amount of char produced was negligible (0–0.013 kg/kg fuel) realizing an efficient transformation of carbon. It was promising to find a high amount of P2O5 in the ash retained in the filter (30 wt %) and reactor (9 wt %) as evaluated by XRF. An average value of 97 % was obtained for CCE (carbon conversion efficiency) depicting almost complete carbon conversion. The results are encouraging to valorize sewage sludge under the CCUS scheme to produce clean energy and reclaim valuable nutrients.</p

Plasma gasification of refuse derived fuel in a single-stage system using different gasifying agents

The renewable evolution in the energy industry and the depletion of natural resources are putting pressure on the waste industry to shift towards flexible treatment technologies with efficient materials and/or energy recovery. In this context, a thermochemical conversion method of recent interest is plasma gasification, which is capable of producing syngas from a wide variety of waste streams. The produced syngas can be valorized for both energetic (heat and/or electricity) and chemical (ammonia, hydrogen or liquid hydrocarbons) end-purposes. This paper evaluates the performance of experiments on a single-stage plasma gasification system for the treatment of refuse-derived fuel (RDF) from excavated waste. A comparative analysis of the syngas characteristics and process yields was done for seven cases with different types of gasifying agents (CO2 + O2, H2O, CO2 + H2O and O2 + H2O). The syngas compositions were compared to the thermodynamic equilibrium compositions and the performance of the single-stage plasma gasification of RDF was compared to that of similar experiments with biomass and to the performance of a two-stage plasma gasification process with RDF. The temperature range of the experiment was from 1400 to 1600 K and for all cases, a medium calorific value syngas was produced with lower heating values up to 10.9 MJ/Nm3, low levels of tar, high levels of CO and H2 and which composition was in good agreement to the equilibrium composition. The carbon conversion efficiency ranged from 80% to 100% and maximum cold gas efficiency and mechanical gasification efficiency of respectively 56% and 95%, were registered. Overall, the treatment of RDF proved to be less performant than that of biomass in the same system. Compared to a two-stage plasma gasification system, the produced syngas from the single-stage reactor showed more favourable characteristics, while the recovery of the solid residue as a vitrified slag is an advantage of the two-stage set-up

Impact of natural gas composition on steam thermal plasma assisted pyrolysis for hydrogen and solid carbon production

Pyrolysis of simulated natural gas (NG) was studied experimentally in the reactor equipped with a steam thermal plasma torch. Simulated NG consisted of 75 % of methane, 15 % of ethane, 5 % of propane and 5 % of butane. Experimental composition of the output gas was compared with the equilibrium calculations corresponding to the gaseous mixture entering the reactor. NG input flow rate 100 slm was considered the best in terms of agreement between the experimental and calculated compositions. Consequently, for this flow rate, the majority of natural gas was reformed into the mixture of hydrogen and solid carbon. For the NG input flow rates of respectively, 200 slm and 500 slm, a non-negligible amount of unconverted methane (from 37 slm to 155 slm) was found to remain in the output gas. On the other hand, the specific energy requirement with respect to the produced hydrogen was better for 500 slm of NG (1.1–1.6 kWh/m3.H2) than for 200 slm (1.8–2.7 kWh/m3.H2) or 100 slm (3.2–3.6 kWh/m3.H2). In all the studied experimental conditions, practically no CO2 was formed, only a small amount of CO corresponding to oxygen from the steam plasma was detected. A comparison with the previously published works, where methane and natural gas were not distinguished, showed that NG composition can play an important role in the pyrolysis process. In particular, the presence of higher hydrocarbons decreased the effectivity of methane conversion and also reduced the specific energy requirement, with respect to the pure methane pyrolysis.</p