Apparatus and method for producing a synthesis gas

Abstract

The apparatus described herein comprises a first reaction chamber having an inlet for a hydrocarbon medium, particularly a gas having the composition C.sub.nH.sub.m, and an outlet. Means for decomposing the hydrocarbons into carbon particles and hydrogen by introducing heat are provided between the inlet and the outlet in the first reaction chamber. The apparatus also comprises a second reaction chamber having an elongated configuration and having a first inlet at one end and an outlet at the opposite end, wherein the first inlet of the second reaction chamber is connected with the outlet of the first reaction chamber, and wherein the second reaction chamber comprises a widening flow cross-section (measured perpendicular to the longitudinal dimension of the second reaction chamber) between the inlet and the outlet. In addition, at least one second inlet into the second reaction chamber is provided, wherein the second inlet can be connected to a source for CO.sub.2 and/or H.sub.2O. Preferably, the second inlet is connected with a source of CO.sub.2, and therefore CO.sub.2 is injected therewith during operation. A method for operating this apparatus is also described. The energy balance of a synthesis gas production can be improved with the apparatus and the method for operating compared with known methods.

Claims

1. Apparatus for producing a synthesis gas comprising the following: a source for a hydrocarbon medium; a source for CO.sub.2; a source for H.sub.20; a source for plasma gas; a first reaction chamber having first and second inlets and an outlet, wherein the first inlet of the first reaction chamber is connected to the source for a hydrocarbon medium, and the second inlet of the first reaction chamber is connected to the source for plasma gas; an electric power supply and at least two electrodes connected to the electric power supply, the at least two electrodes being located in the first reaction chamber between the second inlet and the outlet of the first reaction chamber, the electric power supply and at least two electrodes being configured to decompose the hydrocarbon medium into carbon particles and hydrogen by introducing heat; a second reaction chamber having an elongated configuration and having a first inlet at one end and an outlet at the opposite end, wherein the first inlet of the second reaction chamber is connected with the outlet of the first reaction chamber, and wherein the second reaction chamber comprises an enlarging flow cross-section between the inlet and the outlet; the second reaction chamber comprising at least one second inlet connected to the source for CO.sub.2; the second reaction chamber comprising at least one third inlet connected to the source for H.sub.2O; and wherein the second inlet of the second reaction chamber is located in a longitudinal direction of the second reaction chamber between the first and third inlets of the second reaction chamber.

2. Apparatus according to claim 1, wherein the second reaction chamber has a flow cross-section at the outlet end which is at least 20% wider than at the inlet end.

3. Apparatus according to claim 1, wherein the second reaction chamber does not comprise a substantial decrease in flow cross-section between the inlet and the outlet.

4. Apparatus according to claim 1, wherein the second reaction chamber widens conically.

5. Apparatus according to claim 1, wherein the means for decomposing the hydrocarbons are adapted to heat the carbon particles and the hydrogen generated by the decomposition such that they have a temperature higher than 1200 C. at the first inlet of the second reaction chamber.

6. Apparatus according to claim 1, wherein the at least one second inlet into the second reaction chamber is located, measured from the first inlet, in a first third of a longitudinal dimension of the second reaction chamber.

7. Apparatus according to claim 1, wherein the at least one third inlet into the second reaction chamber is located, measured from the first inlet, in a second half of a longitudinal dimension of the second reaction chamber.

8. Apparatus according to claim 1, wherein a plurality of second and/or third inlets is provided which are spaced at least in a longitudinal direction of the second reaction chamber.

9. Apparatus according to claim 1, comprising at least one heating unit which is adapted to heat the second reaction chamber and is located between the at least one second inlet and the at least one third inlet in a longitudinal dimension of the second reaction chamber.

10. Apparatus according to claim 1, comprising at least one heating unit for heating CO.sub.2 or H.sub.2O before injection into the second reaction chamber via the second or third inlets, wherein the heating unit is adapted to heat the respective medium to a temperature of at least 1000 C.

11. Apparatus according to claim 1, wherein the hydrocarbon medium is a gas having the composition C.sub.nH.sub.m.

12. Method for operating the apparatus for producing a synthesis gas according to claim 1, the method having the following steps: decomposing a hydrocarbon medium into carbon particles and hydrogen in the first reaction chamber with addition of heat by means of a plasma; directing at least the carbon particles into the second reaction chamber, the second reaction chamber having the elongated configuration and having the first inlet at one end and the outlet at the opposite end, wherein the first inlet of the second reaction chamber is connected to the outlet of the first reaction chamber, and wherein the second reaction chamber comprises the enlarging flow cross-section between the inlet and the outlet; injecting CO.sub.2 into the second reaction chamber via the second inlet that is in proximity to the inlet end of the second reaction chamber in order to mix the carbon particles with CO.sub.2, wherein the mixture of carbon particles and CO.sub.2 initially has a temperature of at least 1000 C.; converting a portion of the carbon particles and the CO.sub.2 into CO according to the Boudouard reaction; injecting H.sub.2O into the second reaction chamber through a third inlet downstream of the second inlet; and converting at least a portion of the carbon particles and the H.sub.2O to CO and H.sub.2 according to the heterogeneous water gas shift reaction.

13. Method according to claim 12, wherein the carbon particles and the hydrogen generated by the decomposition are supplied conjointly in form of an aerosol and having a temperature of higher than 1200 C. into the second method chamber.

14. Method according to claim 12, wherein the CO.sub.2 is injected via the second inlet in the first third of a longitudinal dimension of the second reaction chamber measured from the first inlet.

15. Method according to claim 12, wherein the amount of the injected CO.sub.2 is regulated.

16. Method according to claim 12, wherein the H.sub.2O is injected via the third inlet in the second half of a longitudinal dimension of the second reaction chamber measured from the first inlet.

17. Method according to claim 12, wherein the second reaction chamber is actively heated in at least one region that is located between the second inlet and the third inlet in a longitudinal dimension of the second reaction chamber.

18. Method according to claim 12, wherein the second reaction chamber is heated to at least 800 C.

19. Method according to claim 12, wherein at least one of the CO.sub.2 and the H.sub.2O is heated to a temperature of at least 1000 C. before injection into the second reaction chamber.

20. Method according to claim 12, wherein the hydrocarbon medium is a gas having the composition C.sub.nH.sub.m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is described in more detail with reference to the drawings; in the drawings:

(2) FIG. 1 is a schematic cross-sectional view of an apparatus for producing a synthesis gas;

(3) FIG. 2 is a schematic cross-sectional view along line II-II in FIG. 1;

(4) FIG. 3 is a schematic detailed cross-sectional view of the inlet area for process gases.

DESCRIPTION

(5) Terms used in the description like above, below, left and right relate to the description in the drawings and shall not be limiting. But these terms can describe preferred embodiments. The term essentially with respect to parallel, perpendicular or angles shall include deviations of +/3 degrees.

(6) In the following, a schematic structure of an apparatus 1 for producing a synthesis gas is described in more detail with reference to FIGS. 1 to 3, wherein FIG. 1 depicts a schematic cross-sectional view of apparatus 1 for producing a synthesis gas. FIG. 2 depicts a schematic cross-sectional view of apparatus 1 along the line II-II in FIG. 1, wherein a special gas injection configuration is shown that is not consistent with the depiction according to FIG. 1. FIG. 3 depicts an enlarged sectoral cross-sectional view of various embodiments of a gas injection region of apparatus 1.

(7) The apparatus 1 consists essentially of a first reaction chamber 3 surrounded by an insulating case 5 as well as a second reaction chamber 7 surrounded by an insulating case 9.

(8) A plurality of first inlets 10 and a plurality of second inlets 12 is formed in the case 5 surrounding the first reaction chamber 3. The inlets 10 and 12 are provided in an upper wall of case 5. The inlets 10 are arranged on a first imaginary circular line and the inlets 12 are arranged on a second imaginary circular line. The two circular lines are concentric to each other. But it is also possible to provide a different arrangement of the first and second inlets 10 and 12. In particular, it is also possible to provide only one inlet 10, which may be circumferential for instance, or one circumferential inlet 12, respectively. The inlets 12 are located further inside.

(9) The case 5 further comprises an outlet 13 located at the bottom. As can be seen in FIG. 1, the case 5 can comprise a tapering in the lower part of the reaction chamber 3. But it is also possible that such a tapering is not provided, and then the case 5 has a cross-section essentially like an upside-down U.

(10) Two circular electrodes 14, 15, which are concentric to each other, are disposed inside the reaction chamber 3, wherein the electrodes are connected to an electric power supply by means of connecting elements (not shown). Here, the electrode 14 is located concentrically inside the electrode 15. The electrodes 14, 15 are attached to an upper wall of the case 5 in such a way that they extend downward. The inlets 12 are aligned with the electrodes 14, 15 such that they open in the space between the electrodes 14, 15. The outlet openings 10 are aligned with respect to the electrodes 14, 15 such that they open towards a region between the outer electrode 15 and a sidewall of the case 5. Alternatively, rod-shaped electrodes can be used.

(11) The second inlets 12 are suitably connected to a source of gas for injecting a plasma gas. Every suitable gas may be selected as plasma gas, which is supplied by an external source or is produced within the hydrocarbon converter. Inert gases, for instance argon or nitrogen, are a suitable plasma gas. On the other hand, hydrogen, CO or synthesis gas may be used as these gases are generated within the present apparatus. The electrodes 14, 15 and the electric power supply connected therewith are coordinated in such a way that when a voltage is applied between electrodes 14, 15 and a plasma gas is injected via the second inlets 12, a plasma is initially formed between the electrodes and can be maintained. In particular, the adjustment can be such that a plasma will burn beyond the free ends of the electrodes 14, 15.

(12) The inlets 10 are connected to a source for a hydrocarbon medium, particularly a gas having the composition C.sub.nH.sub.m. The medium injected through inlets 10 essentially forms a curtain or a layer of gas flowing between the outer electrode 15 and the sidewall of the case 5 in order to shield the sidewall against high temperatures that are generated by the plasma. In addition, the medium absorbs heat and will be decomposed into its base elements by input of heat from the plasma on the medium's way from the second inlet 10 towards the lower outlet 13 of case 5. That means that the medium that is injected through inlets 10, has been decomposed into carbon particles and hydrogen, when it exits through outlet 13 of the first reaction chamber.

(13) The second reaction chamber 7 is essentially shaped like a pipe that widens conically from a first end proximate to the first method chamber 3 to a second end. The second reaction chamber 7 is confined by the case 9 which defines a corresponding conical form. However, a corresponding enlargement can also be provided in a stepwise manner or in another continuous or discontinuous way. Therefore, the process chamber 7 comprises a first inlet 20 that essentially corresponds in form and flow cross-section to outlet 13 of the first reaction chamber and is in direct vicinity thereto. At the other end, a respective outlet 22 is formed.

(14) In the insulating case 9, which has a respective conically enlarging form, a multitude of second gas inlets 24 and third gas inlets 26 are provided.

(15) The second gas inlets 24 are essentially in close proximity to the first inlet 20 of reaction chamber 7, preferably in the first third, especially in the first quarter of the longitudinal dimension of the second reaction chamber measured from the first inlet 20. The second gas inlets 24 can be oriented radially towards the interior and towards the longitudinal axis of the reaction chamber 7 or they may extend at an angle towards the interior of reaction chamber 7 as indicated in FIG. 2. An injection at an angle, as depicted in FIG. 2, results in a circular flow component (perpendicular to the longitudinal axis) of the gas injected by the inlets 24 within the first reaction chamber 7.

(16) The second inlets 24 are connected with a source for CO.sub.2 gas. In particular, the source for CO.sub.2 gas can be the exhaust gases of an industrial method. The respective exhaust gases may have been cleaned an/or filtered in order to provide pure CO.sub.2. For instance, the CO.sub.2 can be frozen out of a respective exhaust gas stream, wherein usually water will be frozen out together with the CO.sub.2 such that not only CO.sub.2 but also water can be injected through the second inlets 24.

(17) In the supply or injection region, the second inlets 24 can be surrounded by a heating device 30 which is adapted to heat the media injected via the respective second inlet 24 to a default temperature. In particular, it is considered to heat the CO.sub.2 (and possibly water) which is (are) injected through the second inlets 24 to a temperature of more than 1000 C. The heating device 30 should be designed accordingly. But it is also possible to use another heating unit that can provide respective pre-heating instead of heating device 30. It is considered to heat the CO.sub.2 (and possibly water) by means of waste heat from the first reaction chamber 3. In this way, the case 5 of the first reaction chamber 3 can be protected from overheating.

(18) The third inlets 26 are located further away from inlet 20 in the longitudinal dimension of reaction chamber 7 than the second inlets 24. In particular, the third inlets 26 are located in the second half, and especially in the last third, of the reaction chamber 7 with respect to the longitudinal dimension of the reaction chamber 7. The third inlets 26 can essentially have the same configuration as the second inlets 24, and they can comprise the same heating device 30 in order to facilitate pre-heating of the medium injected therewith. The third inlets 26 are connected to a source of water or steam, respectively.

(19) A heating unit 34 is provided in a region between the second inlets 24 and the third inlets 26 in the insulating case 9, wherein the heating unit 34 faces the second reaction chamber 7. The heating unit 34 is designed in such a way that it is able to heat the reaction chamber 7 and the substances contained therein to a temperature of at least 800 C., preferably 1000 C. or to maintain this temperature, respectively.

(20) Although a plurality of second and third inlets 24 and 26, respectively, are depicted in FIG. 1 and FIG. 2, wherein the inlets are located in the same plane, it is possible to provide only one inlet which may have different forms. As indicated in FIG. 3, it is also possible to provide several second inlets 24 or third inlets 26 that are spaced in the longitudinal direction of the reaction chamber 7. The inlets 24, 26 can have different forms, wherein FIG. 3 shows two different forms. In the embodiment shown above, three inlets 24 and 26, respectively, are spaced in longitudinal direction along reaction chamber 7, wherein each has a separate feeding line, and optionally has a heating device 30.

(21) In the embodiment shown below, only one feeder having a heating device 30 is provided, and the inlets 24 and 26, respectively, that are spaced in longitudinal direction along reaction chamber 7 are formed by an angled bore through a sidewall of case 9.

(22) In the following, the operation of apparatus 1 is further described referring to the Figures.

(23) A plasma gas, for instance argon, nitrogen, hydrogen H.sub.2, CO or synthesis gas, is injected through the second inlets 12 into the first reaction chamber 3 into the space between the ring electrodes 14, 15. A voltage is applied between the electrodes 14, 15, such that the plasma gas ignites and a plasma is generated. The plasma burns in the space between the electrodes 14, 15 and beyond the free ends.

(24) For instance a methane gas (CH.sub.4) is injected through the first inlets 10 into the annular space between outer electrode 15 and the sidewall of case 5. While flowing in the direction of outlet 13 of the first reaction chamber 3, the methane gas is heated. Thereby it is heated that much that it decomposes into its base elements carbon and hydrogen. These form an aerosol that exits the first reaction chamber 3 through outlet 13. This aerosol also contains components of the plasma gas that are neglected in the following.

(25) The feeding rate of the plasma gas, the voltage between electrodes 14, 15 and the feeding rate of the methane are adjusted with respect to each other such that the methane is fully decomposed and the generated aerosol of carbon and hydrogen has a temperature over 1000 C., particularly over 1200 C., preferably over 1400 C. when exiting through the outlet 13 of the first reaction chamber 3. Further, the process parameters will be adjusted such that the generated carbon particles preferably have a size in the range from 1 to 500 nm, particularly from 5 to 200 nm and preferably from 10 to 100 nm. The particles can occur as single particles or as clusters that decompose to single particles shortly after conversion begins.

(26) The aerosol enters the second reaction chamber 7 via the inlet 20 and is there mixed with CO.sub.2 that is injected into the second reaction chamber through inlets 24. Here, the temperature of the CO.sub.2 is adjusted with respect to the aerosol temperature in such a way that the mixture has a temperature of at least 1000 C., preferably of at least 1200 C. In the resulting mixture, the carbon particles in the aerosol are converted into CO (carbon monoxide) in a reaction with CO.sub.2. The carbon particles that initially loose carbon atoms at the surface, gain heat in this method. The CO.sub.2 gas, however, cools down during this conversion into CO.

(27) A corresponding conversion of carbon particles and CO.sub.2 into CO is also known as Boudouard reaction (CO.sub.2+C->2 CO). The reaction proceeds while the reactants flow along the second reaction chamber 7. Optionally, the area downstream of the second inlets 24 can be kept at a predetermined temperature level using a heating unit 34.

(28) The feeding of CO.sub.2 through the second inlets 24 is preferably controlled in such a way that the entire CO.sub.2 or a certain percentage thereof is converted, but not the entire carbon particles. With other words, CO.sub.2 can be added sub-stoichiometric.

(29) Steam (H.sub.2O steam) is injected through the third inlets 26 into the second reaction chamber 7 downstream from the second inlets 24. The steam and residual CO.sub.2 react with the residual carbon particles. The conversion of carbon particles and H.sub.2O steam proceeds according to the so-called heterogeneous water gas shift reaction (hetWGS-reaction). This reaction is significantly faster than the Boudouard reaction and can proceed at lower temperatures, wherein the temperature should preferably be above 550 C.

(30) The aim is an essentially complete conversion of the carbon particles. At the outlet 22 of the second reaction chamber 7, the carbon particles should essentially be converted completely, wherein essentially means a conversion of at least 90%, preferably at least 95%. Thus, a synthesis gas consisting of a mixture of CO and hydrogen exits through outlet 22, wherein this synthesis gas may contain additionally CO.sub.2 and steam as well as small unconverted carbon particles. Overall, feeding of the reactants should be controlled such that the unconverted components remain below predetermined thresholds, so that they do not interfere with their further processing in for instance a Fischer-Tropsch synthesis. Corresponding adjustments can be performed by the person skilled in the art according to the above disclosure.

(31) As described above, the reaction chamber 7 has a conical pipe shape that widens from the first inlet 20 to the outlet 22. The form is chosen such that the outlet end has an at least 20% larger cross-section than the inlet end. Preferably, the increase of the flow cross-section is between 20 and 25%.

(32) While the operation of the method has been described above with reference to the Figures, further considerations on which the present invention are based are given in the following.

(33) The basic equation of the conversion reaction in the second reaction chamber starting from CH.sub.4 as feed gas in the first reaction chamber 3 is:
3C+6H.sub.2+CO.sub.2+2H.sub.2O->4CO+8H.sub.2,

(34) wherein a stoichiometric ratio of the reactants in a certain relation to each other is assumed.

(35) Accordingly, the number of particles doubles as the proceeds reaction, and the reaction is endothermic. From the general gas equation p V=n R T follows therefore an increase in pressure in a closed system, assuming a constant temperature that can be kept constant using an external heating unit.

(36) If an external heating unit is dispensed with, the temperature decreases in the course of the reaction along the second reaction chamber, and the increase in pressure decreases. With the conical enlargement of the second reaction chamber, the increase in pressure can essentially be avoided or at least reduced, despite an increase in volume, so that the reaction has to work less against an outer pressure. In the present system, a constant temperature within the second reaction chamber is dispensed with, although additional heating can be provided by heating unit 34 in an intermediate region.

(37) The conical design of the second reaction chamber 7 compensates at least partially for an increase in volume that cannot be offset by the decrease in temperature along the second reaction chamber 7.

(38) In the following, two specific examples are given for a method, wherein methane (CH.sub.4) is used as input or starting gas for the first reaction chamber 3. The temperature of the aerosol generated by the decomposition of CH.sub.4 is 2100 C. at the outlet 13, and the temperature of the synthesis gas at the outlet is 1000 C. In a first stage of the second reaction chamber 7, i.e. between the inlet 20 and the inlets 26, 600 units of the aerosol (of carbon particles and hydrogen) and 100 units of CO.sub.2 (1600 C.) are converted into 800 units of fluid. Thereby, the temperature decreases from 2100 C. to 1660 C. In a second stage, i.e. downstream of the inlets 26, 800 units of the fluid are converted with 200 units of steam (1600 C.) into 1200 units of synthesis gas. Thereby, the temperature decreases from 1660 C. to 1000 C. This results in:

(39) TABLE-US-00001 Stage I: T = V = + p = + Stage II: T = V = + p = + Total: T = V = +1 p = +

(40) Therein T refers to the decrease in temperature, A V refers to the increase in volume, and p refers to the increase in pressure.

(41) In a second example, the temperature of the aerosol is 1600 C., and the temperature of the exiting synthesis gas is 500 C. In the first stage, 600 units of the aerosol and 100 units of CO.sub.2 (1600 C.) are converted into 800 units fluid. Thereby, the temperature decreases from 1600 C. to 1080 C. In the second stage, 800 units of the fluid and 200 units of steam (1600 C.) are converted into 1200 units of synthesis gas. The temperature decreases from 1080 C. to 500 C. This results in:

(42) TABLE-US-00002 Stage I: T = V = + p = + 1/12 Stage II: T = V = + p = + 1/10 Total: T = V = +1 p = +
With a lower starting temperature of the aerosol and thus a simultaneously lower exit temperature of the synthesis gas, the pressure increase that needs to be compensated is also lower. The required enlargement of the pipe is given by the equation for the cross-section area A=r.sup.2 as a factor 1.18 (for p.sub.2=1.4 p.sub.1) and as a factor 1.22 (for p.sub.2=1.5 p.sub.1).

(43) The compensation of the increase in volume avoids the Principle of Le Chatelier, and the reaction no longer has to perform work against the outer pressure.

(44) Because of the method above described, heating the second reaction chamber 7 to a constant temperature can be dispensed with, although it can be advantageous to have an additional heating unit for an intermediate region. As a consequence, the exit temperature of the synthesis gas can be made lower than 500 C. and is no longer at 800-1000 C. as with a classic Boudouard reactor as mentioned in the prior art. The corresponding heating energy may be saved.

(45) The reaction gases CO.sub.2 and H.sub.2O can be injected stoichiometric with respect to the carbon particles, wherein however both gases (in total) are used preferably in 10-30% excess. The unconverted reaction gases can be frozen out after the reaction and can be, if appropriate, re-injected into the second reaction chamber. Even if a portion of the synthesis gas is also frozen out, it will not get lost this way. Residual CO.sub.2 and H.sub.2O in the synthesis gas are no hindrance in, for instance, a Fischer-Tropsch method, if certain limits are observed.

(46) However, an excess of carbon particles would reduce the synthesis gas yield and is not economical. Therefore, an excess of CO.sub.2 and/or H.sub.2O is preferred.

(47) The H.sub.2/CO ratio of the synthesis gas can be adjusted by changing the amount of injected CO.sub.2 with respect to the added carbon particles. The more CO.sub.2 is injected, the lower is the relative H.sub.2 content in the synthesis gas, and the higher is the amount of CO.

(48) The reaction gases CO.sub.2 and H.sub.2O can be preheated before being injected into the second reaction chamber. Preheating to a temperature range between 1400 and 1600 C. is considered. Thus, the exit temperature of the aerosol at the outlet of the first reaction chamber can be lowered, for instance to a temperature range between 1200 and 1400 C.

(49) The invention has been described in detail with respect to a specific embodiment without being limited to any specific embodiment. In particular, the design of the first reaction chamber can differ from the design described herein. In particular, the design, arrangement and number of the electrodes can change, and the inlet for hydrocarbons can be arranged differently. In addition, it is not necessary that the decomposition of the starting material is effected with the aid of a plasma. The arrangement and number of the second and third inlets with respect to the second reaction chamber can also differ from the described arrangement and number.

(50) As mentioned above, it is considered that the second reaction chamber has any other form, in particular a constant flow cross-section. In this alternative apparatus, the second reaction chamber has a second and a third inlet that are arranged in the way described above. In operation, CO.sub.2 (and optionally a small amount of H.sub.2O) is injected via the second inlet, and H.sub.2O is injected downstream via the third inlet. All other features of this apparatus and method correspond to the above described statements.