ES2299350A1 - Procedure and reactor for the reformation of fuels - Google Patents

Abstract

The present invention relates to a procedure for the reformation of gaseous or liquid fuels in mixtures with water and/or CO2 in a dielectric barrier discharge (DBD) plasma reactor. It is differentiated from other reformation procedures based on plasma techniques in that the design and characteristics of the reactor are conducive to having virtually the entire process lead to the production of mixtures of carbon monoxide and hydrogen, with virtually no contribution from higher hydrocarbons. This process takes place at low temperatures and has low electrical power consumption requirements. Furthermore, the present invention relates to a barrier discharge plasma reactor for the reformation of fuels comprising a power supply source, a cylindrical electrode and a dielectric device.

Description

Procedure and reactor for reforming fuels

Technical Field of the Invention

The application sector of the present invention is framed, within the field of new technologies for the sector energy and chemical technologies, in the development of procedures for converting liquid fuels or gases into hydrogen and / or preparation of "syngas" mixtures (CO mixtures plus H 2). One of the potential applications of technology it relates to its use as a primary source of hydrogen for feed fuel cells or other transformation processes of chemical energy in mechanics (motors) and / or electrical. Other application would be as a generator of "syngas" for purposes synthetic

Object of the invention

The object of the present invention is a procedure and a reactor for fuel reforming liquid or gaseous and its transformation into H2 and CO from  mixtures thereof with water vapor and / or CO2. This procedure is based on the use of plasma technology cold and, in particular, in the use of barrier-type discharges in a cylindrical reactor where the roughness control Micrometric scale surface of one of the electrodes is a determining factor of the effectiveness of the process. The mixtures of fuel and other gas (CO2 or H2O) are passed through the reactor at room temperature (or heated above 100 ° C  in the case of water) to proceed with its activation and conversion into The final desired mixture.

State of the art

The most classical hydrocarbon reforming methods are based on the use of catalysts and run at elevated temperatures (Catalyst for hydrocarbon reforming reaction: United States Patent 6852668). More recently, the use of reforming processes using plasmas has been proposed. These methods have the advantages that they can be carried out at lower temperatures, virtually at room temperature and that require very short stabilization times. The use of various sources of excitation has been proposed, including among the most common the processes of reforming using microwave sources (Maxim Deminsky, Victor Jivotov, Boris Potapkin, and Vladimir Rusanov, Plasma-assisted production of hydrogen from hydrocarbons, Pure Appl. Chem ., Vol. 74, No. 3, pp. 413-418, 2002.) or barrier discharge (DBD) (Kogelschatz U., Plasma Chemistry and Plasma Processing , 18, 375-393 (1998)). In the first case, there are processes that are carried out at pressures below atmospheric and others where the corresponding reactors act at atmospheric pressure. In both cases it is not uncommon for the reaction products to include higher hydrocarbons, the result of uncontrolled hydrocarbon dimerization processes. Another plasma technology widely used to carry out reforming processes with hydrocarbons or alcohols is that based on barrier discharge processes, in which the plasma is generated by high-voltage AC discharges (generally between 5 and 30 kV) and frequencies in the kHz range (Eliasson B., IEEE Transactions on Plasma Science , 19, 1063-1077 (1991); Hammer T., Contributions to Plasma Physics , 39, 441-462 (1999)), although there are results described on the 50 Hz frequency utilization (Aghamir Farzin M., Matin Nasser S., Jalili Amir-hossein and Esfarayeni Mohammad-Ali, Methanol Production in AC Dielectric Barrier Discharge, J. Plasma Fusion Res. Series, Vol. 6 (2004) 696 -698). Again, in this case, it is usually normal to obtain reaction mixtures where, in addition to the desired gases, significant amounts of hydrocarbons and / or higher alcohols are found. (Shigeru Futamura, Hajime Kabashima, and Hisahiro Einaga, Steam Reforming of Aliphatic Hydrocarbons With Nonthermal Plasma, IEEE Transactions on industry applications, vol. 40, no. 6, November / December 2004). In most of all these processes it is normal to add a mixture in the appropriate proportions of the fuel and water or CO2 to the reactor (Shigeru Futamura and Gurusamy Annadurai, Plasma Reforming of Aliphatic Hydrocarbons With CO_ {2 '} IEEE Transactions on industry applications , vol. 41, no.6, November / December 2005). However, there is a recent reference to a process where, through the use of barrier discharge plasmas, the possibility of direct dissociation of methane into carbon (solid) and hydrogen is claimed (David E. Fletcher, United States patent application publication No US 2004/0148860 A1, Aug. 5, 2004). The reactor used in this case integrates a complex mechanism where a screw-shaped conical electrode rotates at high speed in front of a hollow cone of dielectric material where the other electrode is applied. An essential element in the development of barrier discharge plasmas is the type of discharge used and the way in which it is applied. Generally, one of the system's electrodes is activated by high-voltage AC discharge, while the other is usually grounded (Ulrich Kogelschatz, Dielectric-Barrier Discharges: Their History, Discharge Physics, and Industrial Applications, Plasma Chemistry and Plasma Processing , Volume 23, Number 1, March 2003 pages 1-46). Other recent documents (US 2004/0091418 A1 by Carlow et al .) Claim the use of barrier, microwave and radiofrequency discharges to produce hydrocarbon reforming (not alcohol) and for gas purification based on dielectric barrier discharge ( US 2003/0030374 A1 by Deepak Pai). In these documents apart from claiming the method, a detailed analysis of the gases produced is not presented, nor is any performance optimization reported by modifying the microstructural characteristics (for example, porosity in the micron range) of the dielectric material.

Consequently, one of the characteristics differentials of the process of the invention has to do with How to apply external voltage. Other characteristic element present in any of the existing patents on DBD reactors is the use of a porous metal as an active electrode, to through whose pores the gas or mixture of gases used circulates. Apparently a unique nature of micro downloads produced in said pores (conditions similar to those called "hollow cathode") can have an important influence on the process characteristics control (Yun Yang, Alternating-Current Glow and Pseudoglow Discharges in Atmospheric Pressure, IEEE Transactions on plasma science, vol. 31, no. 1, February 2003).

Brief description of the figures

Figure 1.- Connection mode and description schematic of the electrical structure of the reactor

one.

Gas / Vapor Conduction Lines Heated input and output

2.

Source of potential

3.

Electrode (internal cylinder)

Four.

Electrode (metallic layer external)

5.

Tube of dielectric material

Figure 2.- General scheme of the system reaction

one.-

Gas / Vapor Conduction Lines Heated input and output

6.-

Barrier discharge reactor

7.-

Connection to the control system and gas analysis

Figure 3.- General scheme of the reactor

5.-

Tube of dielectric material

8.-

Solid or tubular steel cylinder with surface roughness controlled in the area of the discharge.

9.-

High voltage electrical connections of the active metal electrodes.

10.-

isolation zone dielectric

eleven.-

Arrows indicating the flow of gas

12.-

Metallic layer that acts as electrode

13.-

Heating furnace

Figure 4.- Example about the effectiveness of the process  expressed in terms of percentage decomposition of CH4 in equimolecular mixtures of this gas with CO2 depending on the reagent flow.

Detailed description of the invention

The present invention relates to a procedure for reforming gaseous or liquid fuels  vaporable, in a plasma barrier discharge reactor that It comprises the following stages:

to)

the introduction of a mixture in the form of steam or gas between the fuel and CO2 and / or H2O, in proportions between 1: 1 and 1:10 in the barrier discharge reactor for its continuous and atmospheric pressure treatment.

b)

he adjustment in the reactor of the discharge conditions, particularly the high voltage and frequency value, as well as temperature conditions

C)

the reactor activation once the conditions in the previous stage

The download is done by supplying a high voltage AC potential preferably between 0.5 and 80 kV, more preferably between 15 and 30 kV and frequency preferably between 50 Hz and 70 kHz, plus preferably between 3 and 15 kHz, applied between the two electrodes of the barrier discharge reactor by changing the polarity alternatively, without any of those electrodes being in any grounded moment. When a mixture is introduced fuel / CO2 is used a proportion between preferably 1 and 10. When a mixture is introduced fuel / H2O a proportion is also used preferably between 1 and 10. When a mixture to three, fuel / CO 2 / H 2 O, the proportion is preferably between 1: 0.5: 0.5 and 1: 5: 5.

In the event that fuels are reformed liquid and / or liquid H2O, a previous stage of vaporization by heating.

Additionally, oxygen can be added to the mixing the fuel with CO2 and / or H2O, in a proportion between 0.1 and 0.3% with respect to fuel.

The flow of the reaction mixture is between 1 and 100 standard cubic centimeters per minute (sccm) depending on reactor size, and fuels used are preferably hydrocarbons, alcohols, gas natural or mixtures thereof, more preferably fuels commercial in the form of volatile fluids such as gasoline or gas oil.

The products obtained through the reforming process object of the present invention have a hydrocarbon content of less than 1% and a CO + H_ {2} content corresponding to methane conversions up to 95%.

It is also an object of the present invention, a barrier plasma discharge reactor for the refurbished fuels, comprising the following elements:

a) a power supply that supplies a  high voltage alternating current, between 0.5 and 80 kV, preferably between 15 and 30 kV, and with a frequency between 50 Hz and 70 kHz, preferably between 3 and 15 kHz;

b) a cylindrical steel electrode that incorporates in its exterior a sheet of metal and connected to a high voltage power supply; Y

c) a dielectric geometry device cylindrical placed concentrically outside the electrode  cylindrical.

The surface of the steel electrode presents preferably, a surface roughness characterized by rough motifs of size between 1 and 10 µm and the distance between the cylindrical steel electrode and the device dielectric, corresponding to the discharge zone is comprised between 1 and 10 mm, preferably between 1 and 3 mm.

In a preferred embodiment, the device Dielectric is built in quartz, alumina or ceramic and presents a thickness between 1 and 10 mm.

Optionally, the reactor has some dimensions between 8 and 40 cm long and between 1.5 and 20 cm in diameter

In a preferred embodiment, the reactor includes  temperature control elements of the reaction zone, which They allow its regulation between room temperature and 500ºC.

In the reactor object of the present invention, the power supply does not work between an active electrode and another to ground, but operates alternatively applying the high voltage between the two electrodes that, in this way, both act As active electrodes.

For the realization of the process of reforming fuels through dielectric barrier plasmas, it has built a reactor based on this principle that feeds electrically with a high voltage AC source as described schematically in Figure 1. This figure shows I manifest that, as a novel element with respect to other reactors DBD previously used, in the process developed here none of the two electrodes is grounded; they are activated successively and in the opposite way with positive and negative voltages supplied by the source.

The source of potential built and that constitutes an inseparable part of the reactor for the realization of the reforming process, it is a source of alternating current with variable frequency preferably between 50 Hz and 70 kHz, more preferably between 3 and 15 kHz, and that supplies peak voltages at peak preferably between 0.5 and 80 kV, plus preferably between 15 and 30 kV.

The reactor is integrated into a reaction system general where it is possible to dose controlled quantities of reagents (Figure 2). Both reagent feed tubes As the output products can be heated to temperatures controlled above 100 ° C. It is necessary to proceed to this heating in the case of using water and / or liquid fuels it is necessary to vaporize before feeding the mixture in the reactor. Gas flow control can be done by flow controllers (gases) or flow control systems of liquids in the reactor feed tube system.

The control of the exhaust gases (composition, etc.) can be done through an analysis system directly connected to the outlet gas pipe.

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As can be seen in the schematic drawing of Figure 3, the reactor is formed by a steel cylinder, whose external surface in the discharge zone has been subjected to a controlled abrasion process to produce a surface rugged with defined characteristics. The cylinder connects to the high voltage power supply to the tube and to a steel feed. To avoid that through this tube electrically activate the entire feed pipe system, that is electrically isolated from the pipes, coupling in a intermediate zone a glass tube or other dielectric material. He Steel cylinder is placed concentrically to a tube of a material dielectric (quartz, alumina or any other ceramic) thick between 1 and 10 mm, so that the reaction mixture circulate between the steel cylinder and the ceramic tube. Distance between the two is another of the critical parameters of the process and can vary between 1 and 10 mm. On the outside of the cylinder, it place a sheet of metal that acts as the other active electrode of process. Plasma in the circulation zone of the mixture of gases, is formed coinciding with the surface of the cylinder metallic that has the metallic layer rolled, being able to consequence be varied at will. The whole set is surrounded by a small oven to keep the set above 100ºC in case H 2 O and / or liquid fuels are used in the reaction mixture.

The entire previous reaction system can be integrate into a protective and insulating housing if so considered necessary.

The reactor has dimensions characteristics between 8 and 40 cm long and between 1.5 and 20 cm in diameter

The reactions that can be activated by developed reactor, can be schematized according to:

one

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2

where C_ {n} H_ {m} can indicate a hydrocarbon, hydrocarbon mixtures, an alcohol or mixtures of alcholes and / or hydrocarbons

With the reaction system above described you can perform the reform of the selected fuel (s) changing different process variables, such as the voltage and frequency of the discharge, reactor temperature, total flow of the mixture reaction or the ratio between the hydrocarbon / alcohol and the other selected reagent (H2O or CO2). With the device you it can also induce direct dissociation of the C-hydrocarbon (solid) and H2. Although experiments of this type have been able be carried out for periods of time up to 45 min, its execution  It is not recommended since the carbon produced that remains in the inside the discharge zone can serve as an induction point of unwanted downloads.

Example of embodiment of the invention

An example of application of the procedure is constitutes methane reforming (CH4), using CO2 as the other process gas in a reactor with dimensions of 10 cm  long and 3 cm in diameter. For this reaction mixture has been measured the effectiveness of the process and it has been verified that, depending of working conditions and the characteristics of the source, virtually total conversions of the methane with the formation of a mixture of CO and H2 that can be write, according to the reaction [1] adjusted stoichiometrically, according to:

3

It should be noted that as a product of the reaction only traces of higher hydrocarbons were detected, always below an upper limit of 1%. This absence of higher hydrocarbons can be considered as one of the most unique characteristics of the process developed. At reaction performance [3] influence many parameters as He said previously. An example of how the effectiveness of the reaction depending on process parameters, is presented in the Figure 4 representing the percent conversion of methane for a given frequency and voltage, depending on the total flow of gases through the reactor. As expected, the percentage of conversion varies inversely proportional to the flow of gases, as expected from processes where the time of reactor residence must be a maximum controlling factor importance.

According to the data in the graph represented in the Figure 4, the temperature is also a large parameter importance that, for values above 120ºC influences decreasing the yield of the reaction.

The present example is introduced by way of illustrative of the operation of the present invention, without being in in any way, limiting its scope.

Claims (20)

1. Procedure for reforming gaseous fuels or vaporable liquids in a plasma barrier discharge reactor characterized in that it comprises the following stages:

to)

introduction of a mixture in the form of steam or fuel gas and, CO2 and / or H2O, in ratios between 1: 1 and 1:10 in a reactor of barrier discharge for continuous and pressure treatment atmospheric;

b)

adjustment in the reactor of the following discharge conditions: high voltage value, the frequency, and temperature;

C)

reactor activation once adjusted the conditions in the previous stage;

so that the download is done supplying a high voltage AC potential applied between two electrodes of the barrier discharge reactor by changing the polarity alternately without any of those electrodes being at no time connected to land. 2. Method for reforming fuels according to claim 1, characterized in that said high voltage AC potential is between 0.5 and 80 kV, and its frequency is between 50 Hz and 70 kHz. 3. Method for reforming fuels according to claim 2, characterized in that said high voltage AC potential is between 15 and 30 kV and said frequency is between 3 and 15 kHz. Method for reforming fuels according to one of claims 1 to 3, characterized in that when a fuel / CO2 mixture is introduced, a ratio between 1 and 10 is used. 5. Process for reforming fuels according to one of claims 1 to 3, characterized in that when a fuel / H2O mixture is introduced, a ratio between 1 and 10 is used. Method for reforming fuels according to one of claims 1 to 3, characterized in that when a fuel / CO2 / H 2 O mixture is introduced, a ratio between 1: 0.5: 0 is used. , 5 and 1: 5: 5. 7. Process for reforming fuels according to one of claims 1 to 6, characterized in that when liquid fuels and / or liquid H2O are reformed, a previous stage of vaporization by heating is included. Method for reforming fuels according to one of claims 1 to 7, characterized in that additionally oxygen is added to the fuel mixture with CO2 and / or H2O, in a proportion between 0.1 % and 0.3% compared to fuel. 9. Process for reforming fuels according to one of claims 1 to 8, characterized in that the flow of the reaction mixture is between 1 sccm and 100 sccm. 10. Process for reforming fuels according to one of claims 1 to 9, characterized in that the fuels used are selected from hydrocarbons, alcohols, natural gas and mixtures thereof. 11. Process for reforming fuels according to claim 10, characterized in that said hydrocarbons are commercial fuels in the form of volatile fluids. 12. Process for reforming fuels according to claim 11, characterized in that said commercial fuels are selected from gasoline or gas-oil. 13. Barrier discharge plasma reactor for the refurbishment of fuels comprising the following elements:

to)

a power supply that supplies a high alternating current voltage, between 0.5 and 80 kV;

b)

a cylindrical steel electrode that incorporates a sheet metal, connected to a high power supply voltage, and that presents a superficial roughness with motifs rough

C)

a cylindrical geometry dielectric device positioned concentric on the outside of the electrode, so that the distance between the cylindrical steel electrode and the dielectric device,  corresponding to the download zone is between 1 and 10 mm

14. Plasma discharge reactor for reforming fuels according to claim 13, characterized in that said high voltage alternating current has a frequency between 50 Hz and 70 kHz. 15. Barrier discharge plasma reactor for reforming fuels according to one of claims 13 or 14, characterized in that said rough motifs of the cylindrical electrode have a size between 1 and 10 µm. 16. Barrier discharge plasma reactor for reforming fuels according to one of claims 13 to 15, characterized in that the power supply supplies an alternating current with a voltage between 15 and 30 kV, and a frequency between 3 and 15 kHz 17. Barrier discharge plasma reactor for reforming fuels according to one of claims 13 to 16, characterized in that said distance between the electrode and the dielectric device is between 1 and 3 mm. 18. Barrier discharge plasma reactor for reforming fuels according to one of claims 13 to 17, characterized in that the dielectric device is constructed of quartz, alumina or ceramic and has a thickness between 1 and 10 mm. 19. Plasma barrier discharge reactor according to one of claims 13 to 18, characterized in that said reactor has dimensions between 8 and 40 cm long and between 1.5 and 20 cm in diameter. 20. Plasma barrier discharge reactor according to one of claims 13 to 19, characterized in that it has temperature control elements of the reaction zone that allows it to be adjusted between room temperature and 500 ° C.