SOLIDS-PACKED APPARATUS FOR PERFORMANCE OF ENDOTHERMIC REACTIONS WITH DIRECT ELECTRICAL HEATING

Abstract

The present invention relates to an electrically heatable packed pressure-bearing apparatus for conducting endothermic reactions having an upper (3), middle (1) and lower (3) apparatus section, where at least one pair of electrodes (4, 5) in a vertical arrangement is installed in the middle section (1) and all electrodes are disposed in an electrically conductive solid-state packing (26), the upper and lower apparatus sections have a specific conductivity of 105 S/m to 108 S/m, and the middle apparatus section is electrically insulated against the solid-state packing, wherein the upper and lower apparatus sections are electrically insulated from the middle apparatus section, the upper electrode is connected via the upper apparatus section and the lower electrodes via the lower apparatus section or the electrodes are each connected via one or more connecting elements (10, 16) that are in electrical contact with these sections and the ratio of the cross-sectional areas of the upper and lower electrode to the cross-sectional area of the respective current-conducting connecting element or, without use of a connecting element, the ratio of the cross-sectional area of the upper and lower electrode to the cross-sectional area of the respective current-conducting apparatus section is 0.1 to 10.

Claims

1. An electrically heatable packed pressure-bearing apparatus having an upper apparatus section, a middle apparatus section and a lower apparatus section, where at least one pair of electrodes in a vertical arrangement is installed in the middle apparatus section and all electrodes are disposed in an electrically conductive solid-state packing, the upper and lower apparatus sections each have a specific conductivity of 10.sup.5 S/m to 10.sup.8 S/m, and the middle apparatus section is electrically insulated against the electrically conductive solid-state packing, wherein the upper and lower apparatus sections are electrically insulated from the middle apparatus section, an upper electrode is connected via the upper apparatus section and a lower electrode via the lower apparatus section or each electrode is connected via one or more connecting elements that are in electrical contact with these sections, and a ratio of a cross-sectional area of each of the upper and lower electrodes to a cross-sectional area of the respective connecting element or, without use of a connecting element, a ratio of the cross-sectional area of each of the upper and lower electrodes to a cross-sectional area of the respective apparatus section is 0.1 to 10.

2. The apparatus of claim 1, wherein the ratio of the cross-sectional area of each of the upper and lower electrodes to the cross-sectional area of the respective connecting element or, without use of a connecting element, the ratio of the cross-sectional area of each of the upper and lower electrodes to the cross-sectional area of the respective apparatus section is 0.3 to 3.

3. The apparatus of claim 1, wherein a ratio of the cross-sectional area of the one or more connecting elements to a cross-sectional area of the solid-state packing is 0.001 to 0.2 and/or a ratio of the cross-sectional area of the upper or lower apparatus section to the cross-sectional area of the solid-state packing is 0.001 to 0.2.

4. The apparatus of claim 1, wherein the electrodes are configured as an electrode grid in the form of spokes with 2 to 30 bars arranged in a star shape.

5. The apparatus of claim 1, wherein electrode bars are connected at their outer ends to at least one connecting element or via the upper or lower apparatus section and this connection is the sole fixed support for the positioning of each bar.

6. The apparatus of claim 1, wherein a temperature of the upper electrode is at least 350 C.

7. The apparatus of claim 1, wherein each of the upper and lower apparatus sections is configured as a hood and is removable from the middle apparatus section.

8. The apparatus of claim 1, wherein a current-conducting contact surface between each electrode and the respective connecting element is between 0.1 cm.sup.2 and 10 000 cm.sup.2.

9. The apparatus of claim 1, wherein a vertical distance between an upper edge of the electrically conductive solid-state packing and a lower edge of the electrodes at the upper electrode is from 10 mm to 5000 mm and a vertical distance between an upper edge of the electrodes at the lower electrode and a feed of gaseous reactants is from 10 mm to 5000 mm.

10. The apparatus of claim 1, wherein a cross-sectional blocking of the electrodes is between 1% and 20%.

11. The apparatus of claim 1, wherein electrode bars each have 1 to 100 electrode plates secured thereto and divide a cross section of the apparatus into grid cells, where an equivalent diameter of the grid cells is between 10 mm and 2000 mm.

12. The apparatus of claim 1, wherein the upper and/or lower apparatus section is in a twin-shell design and an inner shell is a current-conducting connecting element and an outer shell is electrically insulated from the inner shell.

13. A process for conducting an endothermic gas phase or gas-solid reaction, the process comprising operating the apparatus of claim 1.

14. The process of claim 13, wherein the electrically conductive solid-state packing is executed as a countercurrent moving bed.

15. The process of claim 13, wherein, at an upper edge of the electrically conductive solid-state packing, a difference between an exit temperature of a gaseous product stream and a feed stream of solid particles is from 0 K to 500 K and, at a lower edge of the electrically conductive solid-state packing, a difference between an exit temperature of a solid product stream and a gaseous feed stream is from 0 K to 500 K.

16. The process of claim 13, wherein a temperature of the upper electrode is at least 350 C.

Description

[0163] FIG. 1 shows the diagram of a moving bed reactor of the invention with direct electrical heating. [0164] a. Longitudinal section through the reactor. [0165] b. Cross section of the reactor at the height of the upper electrode. In this view, the cross section of the connecting element 10 is visible. [0166] c. Side view of the unwinding of the skirt of the upper electrode. In this view, the cross section of the electrode 4 is visible.

[0167] FIG. 2 shows the diagram of a moving bed reactor of the invention with direct electrical heating.

[0168] FIG. 3 shows a detail drawing of the middle section of the reactor housing.

[0169] FIG. 4 shows a detail drawing of the upper reactor hood in side view (top) and in top view (bottom).

[0170] FIG. 5 shows a detail drawing of the lower reactor hood in side view (bottom) and in the view from below (top).

[0171] FIG. 6 shows one variant of the reactor of the invention with a twin-shell upper reactor hood.

[0172] FIG. 7 shows a detail drawing of the upper reactor hood in side view (top) and in top view (bottom).

[0173] FIG. 8 shows advantageous longitudinal profiles of the electrode bars in the upper electrode of the invention. Identical profiles in each case are used in the lower electrode.

[0174] FIG. 9 shows advantageous side profiles of the electrode bars in the upper electrode of the invention. The bottom side of the bars is horizontal.

[0175] FIG. 10 shows advantageous side profiles of the bars in the lower electrode of the invention. The top side of the bars is horizontal.

[0176] FIG. 11 shows advantageous cross-sectional profiles of the electrode bars and plates of an electrode of the invention in grid form.

[0177] FIG. 12 shows an advantageous top view of electrodes in grid form. [0178] a. Grid in honeycomb form. The cells may be regular or irregular polygons. Number of sides: 3 to 20. [0179] b. Rectangular grid

[0180] FIG. 13 shows a preferred top view of electrodes in grid form. [0181] a. Grid divided in the form of spokes [0182] b. Grid divided in the form of spokes with lateral bars

[0183] FIG. 14 shows a particularly preferred top view of electrodes in grid form. The dotted lines show the boundaries of the segments. [0184] a. Ring-shaped fractally scaled grid, divided into four segments [0185] b. Ring-shaped fractally scaled grid, divided into six segments

[0186] FIG. 15 shows a segment of an electrode in grid form divided in accordance with the invention, consisting of an electrode bar secured to the skirt of the reactor hood and plates arranged orthogonally thereto. [0187] a) The electrode bar protrudes on the bottom side and the plates protrude on the top side. [0188] b) The electrode bar protrudes upward and downward.

[0189] FIG. 16 shows rod electrodes of the invention. [0190] a) Rod electrode with conical end: front view (left), side view (right), top view (bottom). [0191] b) Rod electrode with wedge-shaped end: front view (left), side view (right), top view (bottom).

[0192] FIG. 17 shows the diagram of a moving bed reactor of the invention with direct electrical heating with rod electrodes.

[0193] FIG. 18 shows a detail diagram of the upper reactor hood with rod electrodes in side view (top) and in top view (bottom).

[0194] FIG. 19 shows a diagram of the bushing of the invention through the outer shell of the upper hood for the entry of the stream of solid particles.

[0195] FIG. 20 shows a diagram of the bushing of the invention through the outer shell of the upper hood for the connection rail for the electrical current.

[0196] FIG. 21 shows the diagram of a fixed bed reactor of the invention with direct electrical heating.

[0197] FIG. 22 shows a hand-drawn sketch of an upper or lower apparatus section of the invention for illustration of the calculation of the ratio of the cross-sectional areas of the upper or lower electrode (A.sub.EI) to the cross-sectional area of the respective current-conducting connecting element (A.sub.VE).

[0198] FIG. 23 shows a hand-drawn sketch of a prototype of the electrode connection analogous to the drawings of U.S. Pat. No. 5,903,591 for illustration of the calculation of the ratio of the cross-sectional areas of the electrode (A.sub.EI) to the cross-sectional area of the respective current-conducting connecting element (A.sub.VE).

LEGEND

[0199] 1. middle section of the reactor [0200] 2. upper end section of the reactor/upper reactor hood/upper apparatus section [0201] 3. lower end section of the reactor/lower reactor hood/lower apparatus section [0202] 4. electrode bars of a divided upper electrode [0203] 5. electrode bars of a divided lower electrode [0204] 6. entry of stream of solid particles [0205] 7. exit of the gaseous product stream [0206] 8. connection rail for the electrical current in the upper reactor hood [0207] 9. cone distributor [0208] 10. connecting element/skirt in the upper reactor hood for contact connection of the electrodes [0209] 11. flange to the upper reactor hood [0210] 12. plate distributor for the gaseous reactants stream [0211] 13. ring distributor for the gaseous reactants stream [0212] 14. conical-shaped lower reactor hood [0213] 15. exit of the solid product stream [0214] 16. connecting element/skirt in the lower reactor hood for contact connection of the electrodes [0215] 17. connection rail for the electrical current in the lower reactor hood [0216] 18. flange to the lower reactor hood [0217] 19. channels for the side draw removal of a gaseous substream from the reaction zone [0218] 20. ring collector for the side draw [0219] 21. lining of the reactor shell with a refractory, electrically and thermally insulating brick lining [0220] 22. flange at the upper end of the reactor shell [0221] 23. electrically insulating intermediate ring between the flanges of the upper hood and the reactor shell [0222] 24. flange at the lower end of the reactor shell [0223] 25. electrically insulating intermediate ring between the flanges of the upper hood and the reactor shell [0224] 26. heated zone in the particle bed/in the moving bed [0225] 27. lower heat transfer zone in the particle bed/in the moving bed [0226] 28. upper heat transfer zone in the particle bed/in the moving bed [0227] 29. housing wall of the middle reactor section [0228] 30. housing wall of the lower reactor hood [0229] 31. housing wall of the upper reactor hood [0230] 41. outer shell of the upper reactor hood/upper apparatus section [0231] 42. flange to the upper reactor hood/lower apparatus section [0232] 43. electrically insulating, gas-tight bushings in the outer shell of the upper reactor hood [0233] 44. entry of purge stream for the gap between the inner shell and outer shell of the upper hood [0234] 45. exit of purge stream from the gap between the inner shell and outer shell of the upper hood [0235] 46. bars of an electrode grid in grid form continuously mounted rigidly in the skirt of the reactor hood [0236] 47. plates or lateral bars secured at one end on the electrode bars of a divided electrode [0237] 51. stub on the outer shell with welding flange [0238] 52. connection conduit with welding flange [0239] 53. intermediate ring [0240] 54. stub on the inner shell with compensator and welded-on threaded plate [0241] 55. gaskets for the connection of the flange (51) and (52) to the intermediate ring (53) [0242] 56. gaskets for the connection between the threaded plate (54) and the intermediate ring (53) [0243] 57. sleeves of electrically insulating material [0244] 58. inlet pipe for the stream of solid particles [0245] 61. stub on the outer shell with compensator and welding flange [0246] 62. loose flange [0247] 63. connecting pin for the electrical current from the inner shell of the hood [0248] 64. connecting bush for the electrical current as counterpart to (63) [0249] 65. sleeves of electrically insulating material [0250] 66. gaskets for connection of the flanges (61) and (62) to the sleeve (65) [0251] 67: sleeve of electrically insulating material [0252] 71. upper end section of the reactor housing/upper reactor hood/upper apparatus section in the form of a dished end [0253] 72. catalyst base to support the catalytic fixed bed [0254] 73. entry of the gaseous reactant stream [0255] 74. exit of the gaseous product stream [0256] A.sub.EI: cross-sectional area of the electrode [0257] A.sub.VE: cross-sectional area of the connecting element [0258] VE: connecting element [0259] H: hood [0260] D: sealing and insulation ring [0261] SW: side wall [0262] WD: thermal insulation/lining [0263] F1: flange on the hood [0264] F2: flange on the side wall [0265] El: electrode [0266] T: funnel [0267] ZS: cylindrical shaft

EXAMPLES

Comparative Example (in Analogy to U.S. Pat. No. 5,946,342)

[0268] Methane pyrolysis is to be conducted in a moving bed reactor with direct electrical heating. The volume flow rate of the gaseous reactant is 11 000 m.sup.3 (STP)/h. The stream comprises 65 vol % of methane, 15 vol % of hydrogen and nitrogen at about 20 vol %. The solid reactant stream, which is introduced into the reactor from the top, is 11.45 t/h. The particle stream consists of coke having a carbon content of >99.5%. The diameter of the reaction zone is 3400 mm; the height of the electrically heated zone is 2000 mm. At the upper and lower ends of the heated zone are disposed graphite electrodes in grid form, via which the electrical current is introduced into the solid-state packing of the moving bed. Above the upper electrode is a 1000 mm-long heat transfer zone. Analogously, below the lower electrode, there is a 1000 mm-long heat transfer zone. An electrical current of 70 000 A is to be introduced into the reactor. The introduction of the electrical current is accomplished via twelve cylindrical electrode feeds made of graphite, which are arranged at the level of the respective electrode in a star shape and uniformly across the circumference of the reactor shell. The electrode feeds have a diameter of 100 mm and a length of 1000 mm. In the electrode feeds, 1000 kW are converted to heat. This power corresponds to 12.5% of the process power required. As lost power, it adversely affects the energy balance of the process. In addition, the electrical energy dissipated to heat has to be removed. It is problematic here that the volume-specific development in the electrode feeds is 6.2 MW/m.sup.3. Correspondingly, the heat flow density at the surface of the electrode feed is 154 kW/m.sup.2. This heat flow density, without controlled intensive cooling at the surface of the electrode feed, can cause excess temperatures greater than 1000 K. With these settings, a methane conversion of 94.2% is achieved. The maximum temperature in the reactor is 1230 C. The temperature differential between the solid product stream and the gaseous reactant stream at the lower end of the reactor is virtually zero and the temperature differential between the gaseous product stream and the solid reactant stream at the upper end of the reactor is 315 K. Since the excess heat is obtained at a moderate temperature level, it can be converted to mechanical energy only with a low efficiency.

Inventive Example

[0269] Methane pyrolysis is to be conducted in a moving bed reactor with direct electrical heating. The volume flow rate of the gaseous reactant is 11 000 m.sup.3 (STP)/h. The stream comprises 65 vol % of methane, 15 vol % of hydrogen and nitrogen at about 20 vol %. The solid reactant stream, which is introduced into the reactor from the top, is 13.5 t/h. The particle stream consists of coke with a carbon content of >99.5%. The diameter of the reaction zone is 3400 mm; the height of the electrically heated zone is 2000 mm. At the upper and lower ends of the heated zone are disposed molybdenum electrodes in grid form, by means of which the electrical current is introduced into the solid-state packing of the moving bed. The electrode is designed as a divided grid in the form of spokes with side bars. It comprises 12 electrode bars (spokes) and eight electrode plates (side bars) per electrode bar.

[0270] The side profile of the electrode bars is rectangular with length 1600 mm and height 300 mm. The cross section of the electrode bars is hexagonal, as shown in FIG. 11. The electrode bars are designed as hollow profiles. The shell of the electrode bars consists of a multilayer mesh weave (HAVER & BOECKER POROSTAR STANDARD 6-ply).

[0271] Along the electrode bars, the electrode plates are mounted at equal distances of 200 mm. The electrode plates consist of molybdenum. The electrode plates are secured to the electrode bars straight and to the middle according to FIG. 13b. The length of electrode plates increases from the inside outward. Specifically, the length of electrode plates is (175 mm, 260 mm, 350 mm, 440 mm, 525 mm, 610 mm, 700 mm, 790 mm). The side profile of the electrode plates is rectangular. The height of the electrode plates is a uniform 200 mm. The electrodes are designed as solid profiles. The cross section of the electrode plates is hexagonal as shown in FIG. 11; the thickness of the electrode plates is a uniform 20 mm.

[0272] The electrical current is introduced via the reactor hoods. The upper hood has the shape of a dished end and consists of 1.4541 steel having a wall thickness of 20 mm. Screwed onto the hood is a cylindrical skirt of molybdenum having a length of 1000 mm. The lower hood has a conical shape and consists of 1.4541 steel having a wall thickness of 20 mm. Screwed onto the hood is a cylindrical skirt of molybdenum having a length of 1000 mm. An electrical current of 67 500 A is to be introduced into the reactor. Contact connection via the hood and twelve electrode bars: the heat loss is 19.5 kW, corresponding to 0.2% of the power transferred. This power results in heating of the hoods by about 100 K above the ambient temperature and can be removed to the environment without any special measures.

[0273] The electrode bars function simultaneously as channels for the side draw removal of a substream from the reaction zone. For this purpose, the electrode bars are pushed through the skirt and are open at the outer end. All electrode bars end in a ring channel that functions as collecting channel for the side draw removal. As a result, 15% of the gas stream is drawn off at the upper end of the heated zone of the reaction zone. With these settings, a methane conversion of 96.5% is achieved. The maximum temperature in the reactor is 1320 C. The temperature differential between the solid product stream and the gaseous reactant stream at the lower end of the reactor is 26 K and the temperature differential between the gaseous product stream and the solid reactant stream at the upper end of the reactor is 75 K. As a result, excellent thermal integration is achieved in the reactor. The excess heat is discharged mainly with the sidestream at a temperature level of 1270 C.

SUMMARY

[0274]

TABLE-US-00002 Comparative Inventive example example Power loss in the electrodes 1 MW 0.02 MW Proportion of power dissipated 12.5%.sup. 0.2% in the electrodes based on the effective process power Methane conversion 94.2%.sup. 96.5%.sup. Max. temperature in the reactor 1230 C. 1320 C. Efficiency of the thermal 60% 72% integration in the main stream Efficiency of the thermal 60% 83% integration in the main stream and in the sidestream