APPARATUS AND PROCESS FOR PRODUCTION OF SYNTHESIS GAS

Abstract

An apparatus for producing synthesis gas at high capacity is described, wherein particularly fast conversion and operation for a long time without interruption is obtained. The apparatus comprises a reactor (1) having a reactor chamber (2) which comprises at least one first inlet (5) connected to a source of hydrocarbon fluid and at least one outlet (15); further a plasma burner (7) having a burner part (11) which is adapted to produce a plasma; and at least one second inlet (6) connected to a source of CO.sub.2 or H.sub.2O. The reactor chamber (2) defines a flow path from the first inlet (5) to the outlet (15), wherein the burner part is located, with respect to the flow path, between the first inlet (5) for hydrocarbon fluid and the second inlet (6) for CO.sub.2 or H.sub.2O; and wherein the second inlet (6) is located with respect to the flow path such that the second inlet (6) is at a location where between 90% and 95% of the hydrocarbon fluid is thermally decomposed. Further a method for operating an apparatus for producing synthesis gas is described.

Claims

1. Apparatus for producing synthesis gas which comprises: a reactor (1) having a reactor chamber (2) which comprises at least one first inlet (5) connected to a source of hydrocarbon fluid and at least one outlet (15); a plasma burner (7) having a burner part (11) adapted to generate a plasma; at least one second inlet (6) connected to a source of CO.sub.2 or H.sub.2O; wherein the reactor chamber (2) defines a flow path from the at least one first inlet (5) to the at least one outlet (15), wherein the burner part (11) is located, with respect to the at least one flow path, between the at least one first inlet (5) for hydrocarbon fluid and the at least one second inlet (6) for CO.sub.2 or H.sub.2O; and wherein the second inlet (6) is located, with respect to the flow path, such that the at least one second inlet is at a location where between 90% and 95% of the hydrocarbon fluid thermally is decomposed.

2. Apparatus according to claim 1, wherein the at least one second inlet (6) opens into the reactor chamber closer to the burner part (11) than to the at least one outlet (15).

3. Apparatus according to claim 1, wherein the at least one second inlet (6) is located closer to the burner part (11) than the at least one first inlet (5).

4. Apparatus according to claim 1, wherein the at least one second inlet (6) is oriented against the direction of the flow path and is oriented towards at least one the first inlet (5).

5. Apparatus according to claim 1, which comprises a at least one third inlet (8) which is, with respect to the flow path, further away from the burner part (11) than the at least one second inlet.

6. Apparatus according to claim 5, wherein the at least one second inlet (6) is connected to a source of CO.sub.2: and wherein the at least one third inlet (8) is connected to a source of H.sub.2O.

7. Apparatus according to claim 5, wherein a heating element is located between the at least one second inlet (6) and the at least one third inlet (8).

8. Apparatus according to claim 1 wherein the burner part (11) comprises a plasma gas inlet connected to a source of plasma gas and a plasma gas cutlet, wherein the plasma gas outlet opens into the reactor chamber (2); and wherein the inlet (5) of the hydrocarbon fluid is oriented towards the inlet for plasma gas, such that the hydrocarbon fluid and the plasma gas mix closely when entering into the reaction chamber (2).

9. Apparatus according to claim 1, wherein the plasma burner (7) comprises at least two elongated electrodes, wherein each thereof has a base part (9) at one end, the base part being mounted to the reactor wall (3, 3a, 3b), and wherein the burner part (11) is located at the end opposite to the base part and extends into the reactor chamber (2).

10. Method for producing synthesis gas comprising the following steps: supplying a hydrocarbon fluid into a reaction chamber (2) which comprises at least one inlet (5) for hydrocarbon fluid and at least one outlet (15); generating a fluid flow from the inlet (5) to the outlet (15); decomposing the hydrocarbon fluid into carbon particles and hydrogen with the aid of a plasma burner (7) which is located between the inlet (5) and the outlet (15); and mixing the carbon particles and the hydrogen with CO.sub.2 or H.sub.2O in a region of the reactor chamber (2) where between 90% and 95% of the hydrocarbon fluid is thermally decomposed.

11. Method according to claim 10, wherein the step of mixing the CO.sub.2 or H.sub.2O is carried out, with respect to the fluid flow, after the plasma burner (7) in a region of the reactor chamber (2) where the carbon particles have a size of equal to or less than 250 nm and preferably of equal to or less than 100 nm.

12. Method according to claim 10, wherein the step of mixing with CO.sub.2 or H.sub.2O is carried out, with respect to the fluid flow, after the plasma burner (7) in a region of the reactor chamber (2) where a temperature of 1550 to 1800 C. prevails.

13. Method according to on claim 10, wherein the step of mixing with CO.sub.2 and mixing with H.sub.2O are carried out separately and one after another with respect to the fluid flow.

14. Method according to claim 10, wherein the pressure in the reactor chamber (2) is set to 10 to 24 bar.

15. Method according to claim 10, wherein the synthesis gas has an amount of residual or not decomposed hydrocarbon fluid in a range of 1.25 to 2.5 mol % in the region of the outlet (15).

16. Apparatus according to claim 1, wherein the plasma burner (7) is located outside the reactor chamber (2) and is connected to the reactor chamber via an opening in the reactor wail (3, 3a, 3b), wherein the burner part (11) is oriented towards the opening such that the plasma gas is directed into the reaction chamber (2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention as well as further details and advantages thereof are described in the following with the aid of preferred embodiments taken with reference to the figures.

[0021] FIG. 1 shows an apparatus for producing synthesis gas according to the present disclosure according to a first embodiment.

[0022] FIG. 2 shows an apparatus for producing synthesis gas according to the present disclosure according to a second embodiment.

[0023] FIG. 3 shows an apparatus for producing synthesis gas according to the present disclosure according to a third embodiment,

[0024] FIG. 4 shows a plasma reactor for decomposing a hydrocarbon fluid according to the prior art.

DESCRIPTION

[0025] In the following description the terms top, bottom, right and left as well as similar terms relate to the orientations and arrangements shown in the figures and are meant for describing the embodiments. These terms may refer to preferred arrangements but are not meant to be limiting, In the context of this description the term hydrocarbon fluid means a fluid (gas, aerosol, liquid) which contains hydrocarbons.

[0026] FIG. 1 shows an apparatus for producing synthesis gas according to the present disclosure which comprises a plasma reactor 1 and sources for hydrocarbon fluid, for plasma gas and for CO.sub.2 or H.sub.2O which are not shown in detail in the figures. These sources include for instance tubes, storage tanks or other industry equipment.

[0027] The plasma reactor 1 comprises a reactor chamber 2 which is enclosed by a reactor wall 3 which comprises a lower part 3a and a cover 3b. The reactor chamber 2 can be divided also at a location different from that shown in the figures. The reactor chamber 2 is generally cylindrically and has a central axis 4. At the cover 3b of the reactor wall 3, a plasma burner 7 is mounted which comprises elongated electrodes (not shown in detail). The plasma burner 7 has a base part 9 which is fixed to the reactor wall 3 (here particularly at the cover 3b). At the other end thereof, opposite the base part 9, the plasma burner 7 has a burner part 11 which projects into the reactor chamber 2 and is located at the free end 12 of the electrodes. A plasma 13 is formed between the electrodes. At the other end of the reactor chamber 2, opposite the plasma burner 7, the plasma reactor 1 has an outlet 15 through which the substances which are produced inside the reactor chamber 2 can escape. The outlet 15 is located, seen in the direction of the flow, at the opposite end of the reactor chamber 2.

[0028] The plasma reactor 1 comprises one or more first inlets 5 for hydrocarbon fluid which are located near the base part 9 of the plasma burner 7. The first inlets 6 open into the reactor chamber 2 such that, during operation, a hydrocarbon fluid flowing therefrom flows into a space 17 between the reactor wall 3 and the electrodes of the plasma burner 7 in a direction towards the burner part 11. In the figures, the central axis 4 has an arrow head and indicates this direction of the flow. The reactor chamber 2 defines a flow path from the first inlets 6 to the outlet 15.

[0029] In the embodiment of FIG. 1, the plasma reactor 1 comprises one or more second inlets 6 for CO.sub.2 or H.sub.2O which open into the reactor chamber 2 at a location closer to the burner part 11 than to the outlet 15 (in FIG. 1 and 2: distance d1<d2). The second inlets 6 are located closer to the burner part 11 than the first inlets 5 (in FIGS. 1 and 2: distance d1<d3).

[0030] In operation, the second inlets 6 direct CO.sub.2 or H.sub.2O to a location in the reactor chamber where between 90% and 96% of the hydrocarbon fluid has been decomposed into hydrogen and C particles. The one or more second inlets 6 can be oriented in a right angle (as shown in FIGS. 1 and 2) or against the direction of the flow path, i.e. upwards as shown in the figures, towards the first inlets 5.

[0031] In the embodiment of FIG. 2, the plasma reactor 1 additionally comprises of one or more third inlets 8, which are located, along the flow path, further away from the burner part 11 than the second inlets 5 (in FIG. 2: distance d1<d4<d2). In FIG. 2, the second inlets 6 are connected to a source of CO.sub.2 and the third inlets 8 are connected to a source of H.sub.2O. Optionally, a heating element or heat exchanger for heating the reactor chamber 2 is located between the second inlets 6 and the third inlets 8.

[0032] The apparatus shown in FIG. 3 corresponds to the embodiment of FIG. 2, but the plasma burner 7 has a different construction. In FIG. 3, the plasma burner 7 is located outside the reactor chamber 2 and is connected to the reactor chamber 2 via an opening 18 in the reactor wall 3. In this case, the burner part 11 is oriented towards the opening 18, such that hot plasma gas is directed into the reaction chamber 2.

[0033] The electrodes, which are not shown in detail in the figures, are e.g. nested tubular electrodes or tube electrode as known, e.g. from U.S. Pat. No. 5,481,080 A (see above). In the case of tubular electrodes, the introduced hydrocarbon fluid flows along one electrode, i.e. along the outer electrode. For tubular electrodes, the first inlets 5 are located radially outward of the outer tubular electrode. However, it is also envisaged that rod electrodes are used, such as two or more rod electrodes located next to each other. In the case of rod electrodes, the hydrocarbon fluid flows along two or more electrodes towards their free end. Thus, in each type of plasma reactor, the hydrocarbon fluid flows in the space 17 along at least one electrode between the reactor chamber 2 and the plasma burner 7. The plasma burner 7 has an inlet for plasma gas and an outlet for plasma gas which opens into the reactor chamber 2 near the burner part 11. Optionally, at least one of the first inlets 5 is located with respect to the inlet for plasma gas such that the hydrocarbon fluid and the plasma gas mix closely upon entering into the reaction chamber 2.

[0034] The plasma arc 13 is formed between the electrodes, preferably with CO, H.sub.2O or synthesis gas as a plasma gas, since these gases are produced anyway in the apparatus and the method described herein. However, every other suitable gas may be chosen as a plasma gas, such as inert gases as argon or nitrogen, which do not have an influence on or participate in the reaction or decomposition, respectively, in the plasma arc. The inlet for plasma gas is connected with a source of plasma gas, e.g. a storage container. The source of plasma gas may be also the outlet 15 if synthesis gas is used as the plasma gas. If CO.sub.2 or H.sub.2 are used as a plasma gas, these gases may be extracted from the reactor chamber 2 at a suitable location or may be separated from the synthesis gas from the outlet 15.

[0035] One or more sensors may be provided at the plasma reactor so as to sense operation parameters (not shown in the figures). With the aid of pressure sensors, the pressure may be measured inside the reactor chamber 2, at the inlets 5, 6, 8, at the outlet 15 and in the sources for plasma gas, hydrocarbon fluid, CO.sub.2 and H.sub.2O. With the aid of temperature sensors, the temperature of the introduced substances, of the extracted substances and at different locations inside the reactor chamber 2 may be measured. With the aid of gas sensors, the composition of the introduced substances and of the produced synthesis gas may be measured.

[0036] The supply of CO.sub.2 and H.sub.2O can be controlled in a simple way by measuring the composition of the produced synthesis gas. The amount, size, position and orientation of the inlets 6 with respect to the burner part 11 and the operation parameters for introducing CO.sub.2 or H.sub.2O, such as pressure and amount introduced per time, are chosen in one embodiment depending on the amount of residual or not decomposed hydrocarbon fluid in the synthesis gas in the region of the outlet 15. Particularly, the location of the inlets 6 and the operation parameters are chosen such that the synthesis gas comprises an amount of residual or not decomposed hydrocarbon fluid in a range of 1.25 to 2.5 mol-%. This operation is contrary to the prior art, where no residual or not decomposed hydrocarbon fluid in the synthesis gas is desired. Alternatively, the location of the inlets 6 and the operation parameters are chosen such that CO.sub.2 or H.sub.2O is introduced into the reaction chamber 2 where a temperature of 1550 to 1800 C. prevails. With respect to the fluid flow, the inlets 6 are located after the burner part 11 of the plasma burner 7.

[0037] During operation of the apparatus for producing synthesis gas, a plasma 13 is formed in the plasma reactor 1 between the electrodes near the burner part 11. The plasma 13 usually has temperatures between 5.000 C. and 10.000 C. The heat is transferred mainly by radiation to the media (gases) inside the reactor. A hydrocarbon fluid (preferably methane or natural gas) is fed into the reactor chamber 2 via the first inlets 5 for hydrocarbon fluid in a direction towards the plasma 13, wherein oxygen is excluded. In the apparatuses according to FIGS. 2 and 3, the hydrocarbon fluid flows along the plasma burner 7. In the apparatus according to FIG. 3, the hydrocarbon fluid does not flow along the plasma burner 7, but hot plasma gas is introduced into the reactor chamber 2 via the opening 18, wherein the hydrocarbon fluid passes the plasma 13. Catalysts are not provided. In operation, the hydrocarbon fluid is introduced such that a high space velocity (unit 1/hour; volumetric flow rate m.sup.3/h of the hydrocarbon fluid divided by the volume m.sup.3 of the reactor chamber 2) is obtained in the reactor chamber 2. Particularly, a space velocity of 500-1000 1/h is considered. Due to the high space velocity and the corresponding high flow rate of the substances passing through, the risk of deposits of solids on the first inlets 5 and near to them is reduced. The location of the first inlets 5 causes a fluid flow towards the outlet 15 on the opposite end of the reactor chamber 2, which also prevents that hot substances accumulate in the space 17 and lead to problems during operation.

[0038] As soon as the hydrocarbon fluid comes to a region near the plasma 13 where a decomposition temperature prevails, the hydrocarbons contained in the hydrocarbon fluid will be decomposed into C particles and gaseous hydrogen H.sub.2. For instance the hydrocarbon fluid CH.sub.4 is decomposed into C and 2 H.sub.2. The decomposition temperature depends on the supplied hydrocarbons and is e.g. more than 600 C. for natural gas or CH.sub.4. With respect to the direction of the fluid flow after the burner part 11 of the plasma burner 7, the hydrogen H.sub.2 and the C particles are present as a H.sub.2/C aerosol. The H.sub.2/C aerosol is mixed with CO.sub.2 or H.sub.2O coming from the second inlets 6 in a region in the reactor chamber 2 where between 90% and 95% of the hydrocarbon fluid is thermally decomposed. This region is near the burner part 11, so that the ripening zone, which is provided in the prior art, is not present in this case. Near the burner part 11, a high temperature of 800 to 3000 C. prevails in the reactor chamber 2. As soon as CO.sub.2 is supplied via the second inlets 6, the C particles are converted in this temperature range according to the equation C+CO.sub.22 CO. If H.sub.2O is supplied via the second inlets 6, the C particles are converted in this temperature range according to the equation C+H.sub.2O.fwdarw.CO+H.sub.2. The above mentioned reactions are executed without catalysts.

[0039] The above mentioned conversion reactions proceed fast and completely if small C particles are mixed with CO.sub.2 or H.sub.2O. With the prior art plasma reactor 1 shown in FIG. 4, C particles could be produced already with a size of about 350 nm. However, the prior art did not yet disclose how even smaller C particles could be produced. The inventors found that very small C particles having a size of equal to or less than 250 nm to 100 nm are present in a reactor chamber 2 where 90% to 95% of the hydrocarbon fluid is thermally decomposed. Therefore, CO.sub.2 or H.sub.2O is supplied to this region so as to obtain high reaction rates with the present apparatus and method.

[0040] According to one embodiment of the invention, the skilled person can set the supply of CO.sub.2 or H.sub.2O depending on an amount of residual or not decomposed hydrocarbon fluid in the synthesis gas in the region of the outlet 15. The supply of CO.sub.2 or H.sub.2O depends on the number, size, position, and orientation of the second inlets 6 relative to the burner part 11 and from operation parameters such as pressure and supplied mass per time of the supply. Particularly, the location of the inlets 6 and the operation parameters are chosen such that the synthesis gas has an amount of residual or not decomposed hydrocarbon fluid in a range of 1.26 to 2.5 mol-%. This approach is contrary to the prior art, where no residual or not decomposed hydrocarbon fluid is present in the synthesis gas. Alternatively, the skilled person selects the location of the inlets 6 and the operation parameters such that the introduction of CO.sub.2 or H.sub.2O takes place in a region of the reactor chamber 2 where a temperature of 1550 to 1800 C. prevails, which is measured by a temperature sensor or another high temperature measuring method. In the region where CO.sub.2 or H.sub.2O are supplied, the C particles have a size of equal to or less than 250 nm, preferably equal to or less than 200 nm and particularly preferable of equal to or less than 100 nm, which leads to a fast conversion reaction and to a stabile aerosol. Malfunctions and deposits (fouling) can be avoided.

[0041] During operation of the apparatus of FIG. 1, which does not comprise the third inlets 8, CO.sub.2 or H.sub.2O is supplied via the second inlets. Preferably, CO.sub.2 is supplied. When 1 mol CH.sub.4 is supplied, 1 mol C and 2 mol H.sub.2 are generated by the decomposition with the aid of the plasma. The 1 mol C and the 1 mol CO.sub.2 are converted to 2 mol CO. In this case, 4 mol synthesis gas are produced from 1 mol CH.sub.4. If e.g. 10% of the supplied CH.sub.4 is not converted, the synthesis gas has a CH.sub.4 amount of 2.5 mol % at the outlet 15. The skilled person can calculate the corresponding amount of not decomposed hydrocarbon fluid according to the corresponding calculation also for other hydrocarbon fluids, e.g. if the supplied hydrocarbon fluid is natural gas and comprises amounts of other gases (e.g. ethane, propane, butane, ethene and so on).

[0042] During operation of the apparatus of FIG. 2, which comprises both the second inlets 6 as well as the third inlets 8, CO.sub.2 is supplied via the second inlets 6 and H.sub.2O is supplied via the third inlets 8, and both are mixed with the aerosol of C particles and H.sub.2 or CO/H.sub.2 respectively. In the course of the flow path from the burner part 11 to the outlet 15, there is a temperature decrease of about 1000 C.: The CO.sub.2 supplied via the second inlets 6 is less than would be necessary for a complete conversion of the C particles into CO. The CO.sub.2 is supplied in such an amount that about 25 to 40%, preferably one third, of the mass of a C particle is converted into CO. During the conversion of C and CO.sub.2 into CO (Boudouard reaction), there is a temperature decrease of about 500 C. (50% of the total temperature decrease). Since the C particles in the region of the introduction of CO.sub.2 are smaller than in the known plasma reactor of FIG. 4 (about 350 nm), the aerosol of C particles, CO, H.sub.2 and the residual hydrocarbon fluid remains stable despite the substantial temperature decrease of about 500 C. Such an amount of H.sub.2O is supplied via the third inlets 8 that the rest of the C particles (75 to 60%, preferably two thirds) is converted into CO (hetWSR or heterogene Watergas-Shift-Reaction: C+H.sub.2O.fwdarw.CO+H.sub.2). Here a further temperature decrease of about 500 C. occurs. Thus, the temperature at the outlet 15 is lower than during operation of the apparatus in FIG. 1.

[0043] The operation of the apparatus of FIG. 3 is basically the same as described above for FIG. 2. Different from FIG. 2, the hydrocarbon fluid does not flow along the plasma burner 7 but passes the plasma burner. The plasma gas is supplied to the plasma burner 7 with such a pressure and such a flow rate that the plasma 13 is blown into the reactor chamber 2. The pressure of the supplied plasma gas is preferably higher than the pressure of the supplied hydrocarbon fluid.

[0044] The following features can independently be applied for all apparatuses of FIGS. 1 to 3. The supply of CO.sub.2 or H.sub.2O through the one or more second inlets 6 can be carried out based in a measured temperature. The temperature measurement can be used alternatively to the above mentioned method where the amount of residual hydrocarbon fluid is measured, or the temperature measurement can be used in addition so as to improve the accuracy. The pressure in the reactor chamber 2 is set to 10 to 25 bar. In one case, the plasma burner 7 is generally inside the reactor chamber 3. Alternatively, the plasma burner 7 is outside the reactor chamber 2, and the plasma gas heated by the plasma burner 7 flows during operation into the reactor chamber 2 via a tube. The one or more second inlets are at a location of 0-3 m and preferably at a location of 0-1 m downstream of the location where at least 90% of the hydrocarbon fluid has been decomposed into C particles and hydrogen. Therefore, mixing of CO.sub.2 or H.sub.2O takes place at a location of 0-3 m and preferably at a location of 0-1 m downstream of the location where at least 90% of the hydrocarbon fluid has been decomposed into C particles and hydrogen. The step of mixing the CO.sub.2 or H.sub.2O begins in a region of the reactor chamber where the carbon particles have a size of equal to or less than 260 nm, preferably equal to or less than 200 nm and particularly preferably equal to or less than 100 nm in diameter. Both CO.sub.2 and H.sub.2O can be supplied into the reactor chamber 2, and the introduction of CO.sub.2 and the introduction H.sub.2O are carried out separately and one after the other.

[0045] It may be summarized that the following benefits can be obtained by the above described apparatus and method: deposits of C particles can be avoided; a stabile aerosol can be obtained also at substantial temperature decreases; fast conversion and reduced reaction time; compared to the prior art, lower temperature of the produces synthesis gas.

[0046] The invention has been described based on preferred embodiments, wherein individual features of the described embodiments may be combined freely and/or may be substituted as far as these features are compatible. Furthermore, individual features of the described embodiments may be omitted as long as these features are not essential. Thus, those skilled in the art will appreciate that various modifications and practical implementations are possible and obvious without departing from the full and fair scope of the present invention.