RU2803529C1 - Method for producing hydrogen and carbon black from natural gas - Google Patents

Abstract

FIELD: plasma pyrolysis of natural gas.

SUBSTANCE: invention is intended for the production of hydrogen and carbon black. The method for producing hydrogen and carbon black from natural gas includes high-temperature pyrolysis of natural gas in an arc discharge plasma. High-temperature pyrolysis is carried out in a natural gas plasma pyrolysis unit comprising a three-phase AC plasma torch, consisting of three hollow electrodes with magnetic and gas-vortex stabilization of electric arcs in each of the electrodes. The electrodes are joined to a common mixing chamber. The resulting plasma and the additional consumption of natural gas are simultaneously fed into the reactor attached to the mixing chamber of the plasma pyrolysis unit. The plasma enters the reactor through a nozzle to prevent natural gas from being thrown into the mixing chamber area. Natural gas is fed through the reactor's orifice system. The flow rate of natural gas is supplied in such a way as to ensure the mass-average temperature in the reactor at the level of 1400-1600 K during the time τ_P>10 ^-2 s.

EFFECT: invention makes it possible to increase the yield of hydrogen and carbon black with maximum conversion of natural gas and minimum energy consumption.

1 cl, 1 dwg

Description

The present invention relates to the field of plasma pyrolysis of natural gas and is intended for the production of hydrogen (so-called “turquoise” hydrogen) and carbon black (soot).

Currently, there are many technologies for industrial hydrogen production. The cheapest and most common method is steam reforming of natural gas. However, the formation of carbon oxides (CO, CO ₂ ) in the technological process, which require disposal, makes it the least attractive from the point of view of environmentalists and not economically promising due to the tightening of measures aimed at reducing greenhouse gas emissions.

Electrolysis of water is considered the most environmentally friendly way to produce hydrogen. However, there are many factors preventing this method from achieving a leading position, one of which is high cost.

There is a known method for producing hydrogen and carbon black [Decomposition of hydrocarbon to carbon black. Patent Norway 6,068,827, 2000y. Authors: Steinar Lynum, Nils Myklebust, Ketil Hox.], which is a prototype (patent US 6,068,827 C09C 1/48, published 05/30/2000, priority dated 01/10/1997 US No. 08/781,850), in which the main part of natural gas is supplied to cylindrical reactor through a plasma torch installed in its upper part. Natural gas is heated in a plasma torch to form plasma. Through many side holes, natural gas is additionally supplied to the reactor, which interacts with the resulting plasma at temperatures ranging from 1000°C to 1600°C and decomposes into hydrogen and soot. The residence time of the pyrolysis products must be sufficient to completely decompose the natural gas into hydrogen and soot in order to minimize the formation of intermediate pyrolysis products, such as acetylene.

The following disadvantages of this method can be noted. Before mixing the resulting plasma with additional natural gas supplied to the reactor, the resulting plasma of pyrolysis products, which enters the reactor from the plasma torch, does not undergo complete pyrolytic decomposition of the gas into hydrogen and carbon; it may contain pyrolysis products such as ethane, ethylene, acetylene. As a result, the mixing of the resulting plasma with the relatively cold injected natural gas can lead to the hardening of the products of incomplete pyrolysis with the fixation of this composition. Besides:

1) in the volume of the reactor with the described supply scheme it is impossible to ensure uniform mixing and temperature uniformity along the length of the reactor. This leads to a decrease in the yield of target products of natural gas pyrolysis - carbon black and hydrogen.

2) stagnant circulation zones of pyrolysis products can form in the reactor volume with soot settling on the walls of the reactor with subsequent growth of deposits that must be periodically removed.

The technical result of the proposed invention is a significant increase in the yield of hydrogen and carbon black with maximum conversion of natural gas and minimum energy consumption at the level of 12-15 kW⋅h/kg of hydrogen.

The method for producing hydrogen and carbon black from natural gas involves high-temperature pyrolysis of natural gas in an arc discharge plasma, where the resulting plasma and additional flow of natural gas are simultaneously fed into the reactor, while the plasma enters the reactor through a nozzle to prevent the reflux of natural gas into the mixing chamber area , and natural gas is supplied through a system of reactor openings, the flow rate of natural gas is supplied such as to ensure the average mass temperature in the reactor at the level of 1400-1600K over time

The method proposed in this invention is the production of hydrogen from natural gas, the basis of which is methane, without access to oxygen by the method of plasma pyrolysis, that is, the production of pure hydrogen by reaction This technology is attractive due to its low energy intensity (about 12-15 kWh/1 kg of hydrogen) compared to water electrolysis (about 50 kWh/kg of hydrogen) and the absence of harmful emissions (CO, CO ₂ ), which does not require additional costs for their recycling, in contrast to the steam reforming method and some others. In addition, the carbon black obtained in the process is a raw material in demand on the market, which can significantly improve the economic effect of hydrogen production [A. Konoplyanik. Pure hydrogen from natural gas. Corporate magazine "Gazprom", No. 9, 2020].

To ensure the technical result, an installation for plasma pyrolysis of natural gas is proposed, containing a three-phase alternating current plasma torch, consisting of three hollow electrodes with magnetic and gas vortex stabilization of electric arcs in each of the electrodes. The electrodes are joined to a common mixing chamber, and the arcs are closed at the zero point of the mixing chamber. Natural gas is supplied to each of the electrodes through a swirler - an insulator. A reactor is attached to the mixing chamber for additional supply of natural gas.

In fig. Figure 1 shows an installation for producing hydrogen and carbon black. The installation consists of three electrodes 1, connected through confusers 2 to a common mixing chamber 3. Magnetic coils are installed on the electrodes to rotate the arc 4, in addition, the rotational movement of the arc is ensured by the tangential supply of natural gas 5 through the swirler - insulator 6.

A reactor 7 is docked to the mixing chamber for additional supply of natural gas through a system of holes 8. The outflow from the mixer into the reactor occurs through a nozzle 9. A cooling and separation unit 11 is docked to the reactor through a nozzle 10.

As an example, consider the implementation of the method. Natural gas is supplied to the plasma torch and, when a certain pressure is reached in the electrode channels, the three-phase plasma torch is switched on, during which gas breakdown occurs between electrodes 1 and confusers 2 and an arc discharge occurs. Since the gas supply is carried out through tangentially located nozzles (with flow swirl), the arc discharge is centered along the axis of the electrode - the arc chamber, that is, vortex stabilization of the arc discharge occurs. Gas heating occurs in arc discharges and adjacent axial areas, so that in mixing chamber 3 the average mass temperature is established at the level of 3000-4000K. This temperature significantly exceeds the required temperature required for energy-efficient pyrolysis of natural gas and is therefore not optimal. By mixing additional gas into the docked reactor 7, it is possible to reduce the temperature to the required values (1400-1600K).

The mass of gas mixed into the reactor can significantly exceed the mass of gas supplied to the plasmatron. To prevent the gas supplied to the reactor from refluxing into the mixing chamber of the plasmatron and negatively affecting arc discharges, the reactor and the mixing chamber are separated by a nozzle. A similar nozzle 10 separates the reactor 7 and the cooling and separation unit 11. Cold methane supplied to the reactor is heated by plasma from a mixing chamber consisting of hydrogen and carbon particles, which become nuclei for further growth due to pyrolysis of the gas supplied to the reactor.

The dimensions of the electrodes and the mixing chamber are calculated from the condition of ensuring the residence time in accordance with the ratio τ _p >10 ^{-2 s.} This ensures that there are no pyrolysis intermediates in the mixing chamber. Based on the same requirement, the dimensions of the reactor are calculated.

This invention was implemented at the Keldysh Center. The efficiency of the method is shown under the following parameters. The electric power of the plasma torch is 1.5 MW, the total consumption of natural gas is 400 kg/hour, while about 1/3 of the total gas consumption is supplied to the electrodes - 130 kg/hour, and 2/3 of the total gas consumption is supplied to the reactor - 270 kg/hour. The average mass temperature in the mixing chamber is set at 3000K, and the temperature in the reactor is 1500K. The total volume of the electrodes and mixing chamber is about 4000 cm ³ , and the residence time is ~25 ms, which exceeds the required time to ensure complete pyrolysis of the gas. The reactor volume is about 5000 cm ³ and the residence time is ~30 ms. Sampling of pyrolysis products after the reactor showed that the gas phase consists predominantly of hydrogen (98% by volume), and the solid phase is soot with a characteristic nanoparticle size from 20 to 100 nm. In this case, the specific energy consumption is 15 kW⋅h per 1 kg of hydrogen.

Claims (1)

A method for producing hydrogen and carbon black from natural gas, including high-temperature pyrolysis of natural gas in an arc discharge plasma, characterized in that high-temperature pyrolysis of natural gas is carried out in a plasma pyrolysis installation of natural gas containing a three-phase AC plasmatron consisting of three hollow electrodes with magnetic and gas vortex stabilization of electric arcs in each of the electrodes, while the electrodes are docked to a common mixing chamber, the resulting plasma and the additional flow of natural gas are simultaneously fed into the reactor docked to the mixing chamber of the plasma pyrolysis installation, while the plasma enters the reactor through a nozzle to prevent the overflow of natural gas into the mixing chamber area, and natural gas is supplied through a system of reactor openings, and the flow rate of natural gas is supplied in such a way as to ensure the average mass temperature in the reactor at the level of 1400-1600 K for a time τ _p >10 ^-2 s.

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