Method for energy supply with a reactor for the release of hydrogen from liquid compounds

Abstract

A method for operating a reactor for the production of hydrogen by dehydrating a liquid, hydrogen-bearing compound by means of an endothermic reaction in tubes or plates of the reactor, which are brought to and maintained at reaction temperature by heat-carrying liquid medium of a heat exchanger, wherein the liquid medium is guided along the tubes or plates of the reactor over a certain distance, wherein the amount of heat to be transferred to the tubes or plates of the reactor is controlled or regulated by reducing the volume flow of the liquid medium, characterized in that the reduction of the heat-transferring volume flow of the liquid medium is effected by withdrawing at least a portion of it from the heat exchanger at at least one point along the path before its end.

Description

[0001] The invention relates to a method for energy supply with a reactor for the release of hydrogen from liquid compounds according to the preamble of the first claim.

[0002] It is already known to integrate hydrogen into an energy supply system by means of an energy transport and storage system. This involves loading a low-energy substance A with hydrogen to form a high-energy substance B, whereby the hydrogen required for this process is provided by the electrolysis of water using preferably renewably generated electrical energy. According to the prior art, this energy loading process typically takes place via a catalytic hydrogenation reaction under pressure in a first reactor. The energy discharge of substance B occurs through catalytic dehydrogenation at low pressures and high temperatures in a second reactor. The hydrogen released in this process can be used, for example, in a fuel cell, an internal combustion engine, or a gas turbine. Hydrogen storage and release can be achieved using LOHC (low-energy hydrogen carriers).The energy storage systems are based on liquid organic hydrogen carriers (LOCs), with a chemical reactor as the first reactor for hydrogenating the hydrogen carrier substance (storage) and a second chemical reactor for dehydrogenating the hydrogen carrier substance (H2 release). Furthermore, the storage technology includes a dual-tank system for the hydrogenated and dehydrogenated hydrogen carrier materials. When there is excess energy in the external electrical grid, as described in DE 10 2011 121 704 A1, or excess regeneratively produced energy, as described in DE 102011 111 565 A1, hydrogen is produced by electrolysis and made available for hydrogenation in the first chemical reactor. This energy is then stored until it is needed for internal use or, in the event of an energy shortage in the external power grid, is converted back into electricity using the second chemical reactor in conjunction with a fuel cell.Another fully autonomous system is shown in DE 10 2012 005 023 A1. US 2007 0 225 532 A1 describes a further method for producing hydrogen.

[0003] Preferably, the LOHC systems known in the art are compound pairs in which the low-energy compound A is a high-boiling, functionalized, aromatic compound that is hydrogenated during the energy charging process. A disclosed, particularly preferred example relates to the use of the compound pair dibenzyltoluene / perhydro-dibenzyltoluene, in which the energy charging can typically be carried out at around 150-200°C and elevated pressures, and the energy discharge at temperatures between 300-350°C. In the aforementioned system, the high-energy compound perhydro-dibenzyltoluene has a hydrogen capacity of around 6 wt% hydrogen. This approach thus represents a technically interesting alternative to other energy storage concepts.

[0004] According to the state of the art, reaction systems for the catalytic release of hydrogen from liquid energy storage molecules consist of fixed-bed reactors or slurry-phase reactors. These consist of countercurrently flowing tubular or plate reactors and are heated using a thermal oil. Due to a locally unvariable and constant thermal oil flow rate within a hydrogen release reactor, the endothermic reaction, acting as a heat sink, results in a temperature profile across the reactor and thus an arbitrary reaction distribution. This does not correspond to the temperature profile required for optimal utilization of the reactor and catalyst for hydrogen release.To establish a temperature profile that enables optimal hydrogen production, the volume flow rate within the reactor must be controlled. This is achieved through the use of multiple heating circuits, intermediate heaters or coolers, and thus additional components. Consequently, the reactor must be larger and therefore more expensive to produce for maximum hydrogen yield.

[0005] Therefore, the object of the present invention is to design a method for releasing hydrogen from liquid compounds by means of a reactor of an energy supply device in such a way as to overcome the aforementioned disadvantages of the prior art.

[0006] The object of the invention is achieved by the process steps and features of the first claim. Advantageous embodiments and further developments are the subject of the dependent claims.

[0007] According to the invention, a method for operating a reactor for the production of hydrogen by dehydrating a liquid, hydrogen-bearing compound by means of an endothermic reaction in tubes or plates of the reactor, which are brought to and maintained at reaction temperature by a heat-transferring liquid medium of a heat exchanger, wherein the liquid medium is guided along the tubes or plates of the reactor over a certain distance, is characterized in that the amount of heat to be transferred to the tubes or plates of the reactor is controlled by reducing the volume flow rate of the liquid medium. The reduction of the heat-transferring volume flow rate of the liquid medium is achieved by withdrawing at least a portion of the liquid medium from the heat exchanger at at least one point along the path before its end.This allows for a simple, section-by-section controlled reduction of the volume flow of the liquid medium along the reactor.

[0008] The method according to the invention also has the advantage that the reactor temperature can be adjusted at various points in the reactor to the optimal temperature profile of the optimal reaction temperature, which depends locally on the degree of hydrogenation.

[0009] Furthermore, for steady-state operation of the reactor, it is easily possible to return the extracted quantity of liquid medium to the heat exchanger circuit for heating. A particularly simple design of the process is achieved by using thermal oil as the liquid medium and / or by operating the heat exchanger in a counterflow configuration.

[0010] This method allows for a simple reduction in the thermal oil flow rate along the reactor by selectively and partially siphoning off the thermal oil. The goal of this measure—optimally adjusting the reactor temperature profile to the optimal reaction temperature, which depends locally on the degree of hydrogenation—is easily achieved. The siphoned-off thermal oil is then directly returned to the thermostat and reheated in a closed loop. This maximizes the reaction rate while simultaneously preventing overheating in the reactor, thus avoiding evaporation or even decomposition of the carrier material. This provides additional degrees of freedom that would not be possible by regulating the total thermal oil flow rate.Controlling the total volume flow rate only allows for variation of the global, passively established temperature profile, but not for section-by-section optimized control of the reaction temperature. These section-by-section control measures are feasible regardless of the reactor design (plate or tubular reactor, etc.) and the heat exchanger design (co-current or counter-current).

[0011] The dehydrogenation of Marlotherm, a hydrogen-containing liquid compound, can serve as an example. The boiling point, or rather the optimal reaction temperature, of Marlotherm increases with increasing degree of dehydrogenation. The boiling point of Marlotherm H18-MSH is approximately 355°C, and that of H0-MSH is approximately 390°C. This means that the curve of the optimal reactor temperature increases progressively from the Marlotherm inlet to the reactor outlet. Accordingly, the heat exchanger integrated into the reactor should be designed as a counterflow heat exchanger, and the reactor temperature should be adjusted to this optimal temperature profile between the different boiling points of the differently dehydrogenated Marlotherm by drawing off the thermal oil.

[0012] This process provides a reactor for the release of hydrogen from a hydrogen-carrying liquid compound, comprising a reactor vessel containing catalyst bodies with a metallic support structure or a packed bed of catalyst spheres, onto which a solid, highly porous coating is applied, containing catalytically active substances for the release of hydrogen from the liquid, hydrogen-carrying compound, wherein the reactor vessel is constructed from parallel tubes or plates, the individual tubes or plates of which, spaced apart from one another, each contain at least one catalyst body around which the hydrogen-carrying compound flows in the respective tube or plate, wherein a heat exchange process between the tube or plate bundle and a heat-carrying liquid medium brings the liquid compound to the reaction temperature of the endothermic reaction for hydrogen release.where the liquid medium is guided along the pipes or plates of the reactor over a certain distance, and the amount of heat to be transferred to the pipes or plates of the reactor is adjusted to the optimal temperature profile (between the different boiling points) of the differently dehydrated hydrogen-bearing liquid compound by reducing the volume flow of the liquid medium through tapping of the liquid medium.

[0013] This optimizes catalyst productivity by generating the optimal reaction temperature distribution for catalyst utilization, thanks to a reaction temperature that can be adapted to the different boiling points of the differently dehydrated hydrogen-carrying liquid compound. The optimized catalyst utilization and productivity allow for minimizing the reactor size and thus the costs of hydrogen release, as no additional components are required for temperature control.

Claims

[1] Method for operating a reactor for the production of hydrogen by dehydrating a liquid, hydrogen-bearing compound by means of an endothermic reaction in tubes or plates of the reactor, which are brought to and maintained at reaction temperature by heat-carrying liquid medium of a heat exchanger, wherein the liquid medium is guided along the tubes or plates of the reactor over a certain distance, wherein the amount of heat to be transferred to the tubes or plates of the reactor is controlled or regulated by reducing the volume flow of the liquid medium, characterized by , that the reduction of the heat-transferring volume flow of the liquid medium is achieved by removing at least a subset of it from the heat exchanger at at least one point along the path before its end. [2] Method according to claim 1, characterized by, that the extracted amount of liquid medium is returned to the heat exchanger circuit for heating. [3] Method according to claim 1 or 2, characterized by that the liquid medium is thermal oil. [4] Method according to any one of claims 1 to 3, characterized by that the heat exchanger operates in a counterflow process.