Reactor with direct electric heating

Abstract

The present invention relates to a reactor, the reactor comprising a moving bed composed of solid particles, the solid particles moving in the direction of gravity; and a method of heating a reactor for a pyrolysis reaction, the reactor comprising a moving bed.

Description

[0001] The present invention relates to a reactor, which comprises a moving bed composed of solid particles that move in the direction of gravity; and a method for heating a reactor for pyrolysis reaction, the reactor comprising a moving bed.

[0002] As an alternative to the established prior art, for example, US2982622 discloses a method for producing hydrogen and high-quality coke, in which inert solid particles are guided as granular material in the direction of gravity through an elongated reaction zone, hereinafter referred to as a moving bed, and a voltage of 0.1 to 1000 volts per inch is applied across at least a portion of the solid material at both ends in the reaction zone, where the voltage is sufficient to raise the temperature of the solid to 1800°F to 3000°F (980°C to 1650°C). A gas stream composed of hydrocarbons, preferably natural gas, is guided in countercurrent, and the gas stream produces hydrogen via an endothermic pyrolysis reaction and deposits carbon on the previously introduced particles.

[0003] CH4 <-> C(s) + 2H2.

[0004] Due to the countercurrent conditions of the solid and the gas, thermal integration can be achieved, making the method efficient. By direct ohmic heating, when using electricity generated by renewable energy, the carbon dioxide balance of the hydrogen production method can be improved by eliminating fossil heating.

[0005] So far, most of the reactors in the prior art adapted to high-temperature reactions above 900°C are configured as cylinders. The electrodes for heating the reactor are selectively integrated in the cylinder wall or at least axially arranged in the reactor in such a way that the fixed bed packing or the moving bed is not blocked. Such reactors are shown, for example, in US2982622.

[0006] However, the disadvantage of such a pure cylindrical reactor geometry with electrodes as built-in parts is that if there is a central inner rod electrode, the electric field is non-uniform in the radial direction and thus the reaction does not proceed uniformly in the reactor volume. If the electrodes are integrated in the cylinder wall, the carbon deposited at the wall can cause an electrical short circuit, which also hinders the uniform heating of the reactor. The deposited carbon also causes the particles of the moving bed to agglomerate, thereby impairing the particle fluidity and clogging the reactor.

[0007] Therefore, the object of the present invention is to provide a reactor geometry and an electrode arrangement that can overcome the disadvantages of the prior art.

[0008] This object is solved in terms of equipment and process in that the flow cross-section of the reactor changes along the length of the reaction zone and the electrodes are arranged concentrically in a ring in the reaction zone. The moving bed heated by the electrodes passes through the reactor zone.

[0009] Due to the change in the flow cross-section, the particles in the moving bed are forced to undergo relative movement, thereby preventing the particles from caking due to the deposited carbon. The annular concentric electrodes can be arranged continuously or intermittently in an axially symmetric arrangement or arranged in a plane in a conical reactor geometry. In addition, short circuits are avoided because the concentric arrangement of the internal and external electrodes always flows through the packing first.

[0010] Preferably, the electrodes are made of a graphite-containing material and have different electrical conductivities along the length direction.

[0011] The flow cross-section of the reactor preferably changes along the length of the reaction zone such that the reactor has a conical or near-conical shape.

[0012] Preferably, the conical part of the reactor is arranged such that the wider part of the cone is arranged at the feed inlet of the moving bed. In most cases, it is above in the direction of gravity. It is understandable to those skilled in the art that precise radial symmetry cannot always be maintained in the corresponding industrial reactor geometry and the reactor is often constructed as a polygon. Preferably, the reactor is also designed as an annular gap. The annular gap can be technically uniform and straight, but can also expand or contract along the length of the reactor. For this purpose, different internal components can be provided in the reactor, such as a pyramidal geometry. By the implementation of the annular gap design, the annular concentric arrangement of the electrodes can be further optimized, and the above advantages are enhanced.

[0013] The reactor also has inlets and outlets for gaseous reactants and products, so that the reaction stream and product stream can be guided in countercurrent to the moving bed. Further, a further feed inlet for cooling gas can be provided near the product outlet. Preferably, cold product gas or inert gas is used as the cooling gas.

[0014] Preferably, the moving bed is heated to a temperature of 900 °C to 1200 °C.

[0015] The described reactor and the described method are preferably used for methane pyrolysis, where a methane-containing gas stream is used as the reactant.

[0016] In a particular embodiment, the cold moving bed is fed into the reactor from above via a cylindrical inlet. Then, the moving bed is transferred to a further cone with a narrowed diameter via the conical widening of the tube. The moving bed is guided through the reactor in the direction of gravity. In an additional embodiment variant, there can be internal components in the cone, thus creating an annular channel. Through the conical shape strengthened by the annular channel, relative movement occurs between the particles of the moving bed. Thereby, carbon deposits can be deposited on the particles of the moving bed and can be discharged together with the moving bed at the lower end of the reactor at the outlet of the moving bed, which outlet is preferably designed as cylindrical.

[0017] Electrodes are installed inside the conical section of the reactor or in an annular duct, and these electrodes are installed at the reactor wall or the wall of the internal components. The electrodes heat the moving bed passing between them. This avoids short circuits because carbon is deposited only in the hot zones, but electrical contact occurs in the cold zones.

[0018] The electrodes preferably have a circular shape at the ends. Advantageously, the electrical conductivity decreases at the corresponding electrode ends. This is achieved by reducing the electrode area and / or by changing the material composition.

[0019] The flow resistance for the moving bed is reduced by the geometry of the electrodes described. An additional advantage is that deposition or caking of carbon particles is thereby prevented. The emergence of hot zones at the electrode ends is avoided and thus no adverse effects on the reaction are caused.

[0020] The reaction stream and the product stream are guided in countercurrent to the moving bed in the reactor. A cold reaction stream is fed in, and this cold reaction stream is heated by the overflowing hot moving bed. Due to the heat exchange, the cold moving bed can be discharged directly from the reactor and does not have to be further cooled. Due to the countercurrent guidance, the heat in the reactor remains in the heat integration zone, and energy-saving reaction control is possible.

[0021] In order to control the temperature profile of the reactor, if necessary, in a particularly preferred reactor implementation variant, a cooling gas is fed in via a feed port near the product outlet. The cooling gas is preferably the already cooled product gas.

[0022] In addition to methane pyrolysis, this reactor can also be used for other reactions.

[0023] Other features and advantages of the present invention are explained in reference to Figure 1 the description of the embodiments. The drawings show:

[0024] Figure 1 A cross-sectional view of the reactor according to the present invention

[0025] Figure 1 A preferred reactor geometry is shown in the cross-sectional view. The moving bed W is fed into the reactor from above via a cylindrical feed port. The outer wall of the reactor is preferably insulated by masonry.

[0026] The moving bed W is guided into an annular duct, which is implemented as two cones with opposite structures. The annular duct is realized by internal components. Annular concentric electrodes E are installed at the annular duct wall and the internal component wall.

[0027] Preferably, the reactor is used for the pyrolysis of methane. For this purpose, a methane-containing feed stream F is guided in countercurrent to the moving bed W. The feed stream is heated to 900 °C to 1200 °C and converted into hydrogen and carbon or synthesis gas. The product stream P is withdrawn at the upper end of the reactor.

[0028] Effective thermal integration is achieved by this countercurrent method and this does not require expensive devices for cooling or preheating the moving bed or the gas stream.

[0029] To be able to control the temperature profile in the reactor, a cooling gas can be fed in via the feed port Z. In the present example, preferably, the cold product gas is used as the cooling gas.

Claims

1. A method of heating a reactor for a pyrolysis reaction, the reactor comprising a moving bed composed of solid particles moving in the direction of gravity, wherein the flow cross-section of the reactor varies along the length of the reaction zone, such that the reactor has a conical shape, with the wider part of the cone being arranged at the feed inlet of the moving bed, and wherein annular concentric electrodes are arranged in the reaction zone through which the moving bed passes, and the electrodes heat the moving bed, wherein the reactant used is a methane-containing gas stream, and the reactor is for methane pyrolysis.

2. The method according to claim 1, wherein The moving bed is guided in countercurrent to the reaction and product streams.

3. The method according to claim 1, wherein The moving bed is heated to a temperature of 900 °C to 1200 °C.

4. The method according to claim 2, wherein The moving bed is heated to a temperature of 900 °C to 1200 °C.

5. The method according to any one of claims 1 to 4, characterized in that To cool the overflowing product stream, a cooling gas is fed in near the product outlet.

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