Use of a heat exchanger, a device and a method for the biosynthesis of methane

Abstract

The invention relates to the use of a low temperature-gradient heat exchanger for controlling the temperature in biotechnological reactors, to a device comprising the heat exchanger and to a method for the biosynthesis of methane using methanogenic microorganisms.

Description

[0001] Use of a heat exchanger, a device and a method for the biosynthesis of methane

[0002] The invention relates to the use of a heat exchanger with a low temperature gradient for temperature control in biotechnological reactors, a device comprising the heat exchanger and a method for the biosynthesis of methane using methanogenic microorganisms.

[0003] Biotechnological reactors in which material transformations are carried out by means of microorganisms or enzymes require compliance with certain temperature ranges in which the intensity of the material transformations can take place at all or are in the economically optimal range.

[0004] For the biological methanation of carbon dioxide and hydrogen, the need for heat removal from the methanation reactor arises due to the release of reaction and condensation enthalpy (Burkhardt et al. 2015), at or in the immediate vicinity of the methane-forming microorganisms immobilized on growth bodies or surfaces, hereinafter also referred to as "methanogens".

[0005] Without the removal of this amount of heat, the temperature in the reactor would rise to such an extent that the microorganisms involved would inhibit themselves and thus the entire methanation process would come to a standstill.

[0006] DE 102011 051 836 A1 relates to a method and a device for producing biogas in a biogas reactor. The bioreactor contains packing elements (growth elements) on whose surface a biofilm containing methane bacteria and optionally accompanying flora is immobilized. The packing elements are sprinkled with a liquid, in particular water and nutrients, (trickling liquid), forming a liquid film on the surface of the packing elements. The method comprises flowing a reactant gas mixture of hydrogen and carbon dioxide through the trickling bed in cocurrent or countercurrent flow with respect to the flow direction of the trickling liquid.

[0007] DE 10 2013 209 734 A1 describes a process for the methanation of gases using trickling bed reactors with a staged addition of carbon dioxide, as well as a device for carrying out the process, comprising a reactor filled with growth media containing methane-forming microorganisms immobilized on the surface of the growth media, which are arranged in the direction of the longitudinal axis of the cylindrical region of the reactor. Carbon dioxide is added in a staged manner. The reactor is preferably designed as a tube. Disadvantageously, cooling via the trickling liquid, in particular an increase in the amount of trickling liquid, leads to an increase in the thickness of the liquid film above the biofilm consisting of methanogens and thus to a significant deterioration in the mass transfer between the biofilm and the reactant and product gases, which leads to a reduction in conversion.Heat dissipation via the reactor wall is successful with small reactor diameters in the range of up to approximately 0.3 m; with larger distances between the reactor interior and the cooled wall, heat transfer is not sufficient and local overheating occurs inside the reactor.

[0008] For temperature control, i.e. heating or cooling, heat exchangers are usually used as recuperators in all designs, power variants and made of a variety of materials, less frequently also regenerators (Wagner 2015).

[0009] DE 29 40 335 A1 discloses a process for chemical-catalytic methanation in which the reaction enthalpy is removed from the reaction gas mixture through a heat exchanger between two reactors connected in series.

[0010] DE 10 2014 011 274 A1 describes a plate heat exchanger for heat removal from a chemical-catalytic methanation comprising an outer shell and a first flow path running within the outer shell from an inlet to a first outlet, as well as a second flow path running within the outer shell, located closer to the first outlet than to the inlet and opening into a second outlet deviating from the first outlet, whereby the plate heat exchanger is intended to have improved thermal contact with the reaction gas on the side facing the reaction medium.

[0011] DE 10 2021 115 881 A1 discloses a multilayer reactor with several structural layers, wherein the various layers are structured in a special way, in preferred embodiments having square recesses to enable improved heat transfer during catalytic reactions. This is intended to achieve heat dissipation while simultaneously ensuring good contact between the reaction medium and the catalysts during chemical-catalytic methanation. DE 20 2021 000 771 U1 discloses a tube-bundle heat exchanger used for chemical-catalytic methanation. The inner surface of the tube-bundle heat exchanger facing the reaction medium is provided with metallic internals ("tube brushes") to prevent axial plug flow. These internals improve heat transfer by generating microturbulent flow and simultaneously support the catalyst.

[0012] DE 10 2020 109 419 A1 describes biological methanation in a tubular reactor, which can be simultaneously cooled. The use of a tubular reactor enables intensive contact between the introduced gas and the microorganisms.

[0013] In recuperators, the heat supply or removal is accompanied by a change in the temperature of the heat-absorbing or heat-removing heat transfer fluid depending on its specific heat capacity and its mass flow, so that a temperature difference occurs between the inlet and outlet of this heat transfer fluid.

[0014] A high heat flow can be achieved either by a high mass flow of the heat transfer fluid or by a high temperature difference between the inlet and outlet, or both; less frequently, by adjusting the specific heat capacity of the heat transfer fluid. Furthermore, a certain temperature difference between the medium to be tempered, i.e., the interior of the biotechnological reactor, and the heat transfer fluid is required to overcome the thermal resistance between the medium to be tempered and the heat transfer fluid. Therefore, in the known temperature control processes, different temperatures occur at different locations in the reaction medium, in particular, a temperature gradient along the flow path of the heat transfer fluid of the recuperator.

[0015] These temperature differences can lead to microorganisms or enzymes in parts of the reactor reaching a temperature range outside their activity optimum, which reduces the turnover in the reactor, e.g. biogas reactor (Vintiloiu et al. 2009).

[0016] In applications where the reaction medium can be stirred or otherwise moved, it is possible to compensate for the temperature differences to a large extent.

[0017] In applications where this movement or mixing of the reaction medium is not possible due to equipment or process-related reasons, e.g. in fixed-bed or trickle-bed reactors with the fixation of microorganisms or enzymes on carrier materials, this temperature difference between the inflow and outflow of the heat transfer fluid can also be reduced by a high mass flow, which, however, entails higher structural and energy expenditure due to the higher pressure loss.

[0018] The task is therefore to provide a method or device for heat removal in biocatalytic reactors which has a low temperature gradient

[0019] According to the invention, this object is achieved by using a heat exchanger, a device, and a method for the biosynthesis of methane according to the independent claims. Advantageous embodiments of the invention are specified in the dependent claims.

[0020] A first aspect of the invention relates to the use of a heat exchanger with a low temperature gradient for temperature control and as a growth surface for microorganisms in biotechnological reactors, wherein the heat exchanger with a low temperature gradient comprises at least one compartment which is designed to pass a heat transfer fluid, wherein a low temperature gradient is understood to mean a difference of less than 10 K between the minimum and maximum temperature of the heat transfer fluid in the heat exchanger and / or on the surface of the heat exchanger.

[0021] Advantageously, the use of a heat exchanger for temperature control and as a growth surface for microorganisms in biotechnological reactors can maintain the stability of the biological system and the productivity across the entire cross-section of the reactor.

[0022] The term “heat exchanger” refers to a device that transfers thermal energy between at least two materially separate systems, in particular from a heat transfer fluid to a material flow or from a material flow and / or a stationary heat source, for example reaction heat, to a heat transfer fluid.

[0023] The term “temperature gradient” refers to the increase (positive or negative) in temperature depending on the length of the heat transfer fluid in the heat exchanger.

[0024] The term “low temperature gradient” is understood to mean a small difference between the minimum and maximum temperature of a material flow, in particular of a heat transfer fluid, and / or a small difference between the minimum and maximum temperature on the surface of the heat exchanger, in particular on the growth surface for microorganisms, preferably a temperature difference of less than 10 K, particularly preferably a temperature difference of less than 5 K, most preferably of less than 1.5 K.

[0025] The term “compartment” refers to a delimited unit within a device or reactor in which certain processes can take place independently of others, in particular in which a heat transfer fluid can be passed through without coming into material contact with the reactants in the reactor.

[0026] The term "heat transfer fluid" refers to a medium, particularly a gas or liquid, that transports heat from one location to another in a heating or cooling circuit. A heat transfer fluid preferably has a high specific heat capacity, low viscosity, and consistent chemical and physical properties within the operating temperature range.

[0027] In embodiments, the heat exchanger with a low temperature gradient comprises at least two compartments, wherein i. at least one inner compartment has an inlet and an outlet for the heat transfer fluid and ii. at least one outer compartment closed on one side has an outlet for the heat transfer fluid, wherein the diameter of the outer compartment is larger than the diameter of the inner compartment, wherein the inner compartment is at least partially arranged within the outer compartment, and wherein the outlet of the inner compartment is arranged within the outer compartment. Advantageously, a low temperature gradient is achieved by the heat exchanger with at least two compartments, in particular when using different heat transfer fluids, in particular water, and / or mass flows of the heat transfer fluid, in particular even at low mass flows.

[0028] In embodiments, the at least one inner compartment is arranged entirely within the at least one outer compartment. Advantageously, the heat exchanger with a low temperature gradient comprising at least two compartments can be used for heat dissipation and heat supply. In embodiments, a heat transfer fluid, in particular water, flows through the heat exchanger such that the cold heat transfer fluid is guided from the inlet to the outlet of the at least one inner compartment, is redirected or redirected at this point, and is transported in the opposite direction in the gap between the at least one inner compartment and the at least one outer compartment to the outlet, leaving the heat exchanger as a now warm heat transfer fluid.The temperature difference between the incoming cold heat transfer fluid and the warmer heat transfer fluid flowing in the opposite direction on the side facing the reactor causes heat to pass through the inner, heat-conducting compartment, resulting in cooling of the heat transfer fluid in the outer compartment and heating of the heat transfer fluid in the inner compartment. This thermal effect advantageously maintains a nearly constant mixing temperature along the entire heat exchanger.

[0029] In embodiments, a heat transfer fluid, in particular water, flows through the heat exchanger in such a way that the warm heat transfer fluid is guided from the inlet to the outlet of the at least one inner compartment, is redirected or redirected at this point, and is transported in the opposite direction in the gap between the at least one inner compartment and the at least one outer compartment to the outlet, leaving the heat exchanger as a now cold heat transfer fluid. Due to the temperature difference between the incoming warm heat transfer fluid and the colder heat transfer fluid flowing in the opposite direction on the side facing the reactor, heat is transferred through the inner, heat-conducting compartment, resulting in heating of the heat transfer fluid in the outer compartment and cooling of the heat transfer fluid in the inner compartment.

[0030] This thermal effect advantageously results in an almost constant mixing temperature along the entire heat exchanger.

[0031] This mixing temperature can be adjusted to a certain, constant temperature difference between the reactor interior and the outer surface of the heat exchanger by changing the mass flow of the heat transfer fluid or by selecting the temperature of the incoming cold heat transfer fluid or by both.

[0032] In preferred embodiments, the at least one inner compartment and the at least one outer compartment are arranged parallel to one another. In some embodiments, the at least one compartment is an elongated hollow body, preferably a tube or a rectangular hollow body, in particular a square hollow body.

[0033] A “rectangular hollow body” or “square hollow body” is understood to be a hollow body with a rectangular or square cross-section.

[0034] In particularly preferred embodiments, the at least one compartment is a tube.

[0035] A “tube” is a hollow body with a circular or oval cross-section.

[0036] In embodiments, the at least one tube is designed as a straight tube, as a bent tube, as a ring or as a flat or spatial spiral.

[0037] In embodiments, the low temperature gradient heat exchanger comprises at least two tubes, wherein i. at least one inner tube has an inlet and an outlet for the heat transfer fluid and ii. at least one outer tube closed on one side has an outlet for the heat transfer fluid, wherein the diameter of the outer tube is larger than the diameter of the inner tube, wherein the inner tube is arranged at least partially within the outer tube, and wherein the outlet of the inner tube is arranged within the outer tube

[0038] In embodiments, the flow cross-section of the inner tube and the flow cross-section of the annular gap between the outer and inner tubes are of equal size.

[0039] In embodiments, the diameter and / or the width of the at least one compartment is in the range of 3 mm to 40 mm and / or the height of the at least one compartment is in the range of 3 mm to 6 mm.

[0040] In embodiments of the heat exchanger comprising at least two tubes, the at least two tubes are designed as straight tubes, as bent tubes, as rings, or as flat or three-dimensional spirals, with a uniform annular gap between the two tubes. Bent tubes advantageously prevent kinking or other deformation of the tubes.

[0041] In embodiments, the at least one compartment consists of a biologically and / or chemically inert, thermally conductive material, preferably steel.

[0042] In embodiments, the at least one inner compartment consists of a thermally conductive material, preferably copper or aluminum, and / or the at least one outer compartment consists of a biologically and / or chemically inert, thermally conductive material, preferably steel.

[0043] In some embodiments, the surface of the at least one compartment comprises a hydrophobic material, preferably polyolefin. Advantageously, the microorganisms grow well on hydrophobic materials.

[0044] In embodiments, the surface of the at least one compartment has a hydrophobic coating, preferably a synthetic resin coating. The coating is preferably applied with synthetic resin as a lacquer in an immersion bath. The hydrophobic coating, in particular the synthetic resin, is preferably non-toxic to microorganisms; in particular, the hydrophobic coating, in particular the synthetic resin, does not contain any organic solvents and / or color pigments containing heavy metals.

[0045] In embodiments, the heat exchanger is an integrated system with plastic constructions, in particular manufactured by block construction.

[0046] In embodiments, the outer compartment has a hydrophobic coating on the surface.

[0047] In embodiments, the at least one compartment is a component of a heat pump system. The heat pump system expediently comprises at least one compressor, a condenser, and an expansion valve, which are arranged outside a reactor vessel. Advantageously, the low-temperature gradient heat exchanger comprising at least one compartment can be used as a component of a heat pump system for heat dissipation. A "compressor" is understood to be a unit that supplies mechanical work to an enclosed gas; compressors are used to compress gases.

[0048] A "condenser" is a unit in which a substance is converted from a gaseous state to a liquid state (condensation). The condenser is advantageously used to liquefy the vaporous heat transfer fluid, thereby enabling a closed cycle in the heat pump system.

[0049] An “expansion valve” is a unit that reduces the pressure of the fluid flowing through it, in particular the heat transfer fluid, by locally narrowing the flow cross-section and thus causes an increase in volume or expansion.

[0050] In embodiments, the expansion valve is arranged upstream of the at least one compartment of the heat exchanger in the flow direction of the heat transfer fluid. Advantageously, the liquid portion of the heat transfer fluid in the at least one compartment absorbs heat from the environment.

[0051] In embodiments, the at least one compartment is a heat pipe. In a heat pipe, heat is advantageously transported by the flow of a fluid evaporated on the warm side and condensed on the cold side. Advantageously, the heat pipe requires minimal design effort.

[0052] In some embodiments, the heat pipe is at least partially filled with a nonwoven and / or woven fabric. Advantageously, the heat transfer fluid is at least partially diffused through the nonwoven and / or woven fabric from the compartment's outlet to the inlet.

[0053] In embodiments, the at least one compartment has an inclination in the range of 10° to 80° starting from the horizontal extent or the cross-sectional planes of the heat exchanger.

[0054] In preferred embodiments, the at least one compartment is arranged along the horizontal axis of the heat exchanger.

[0055] In embodiments, at least one surface-enlarging element is arranged on the surface of the heat exchanger. In embodiments, the at least one surface-enlarging element is selected from the group comprising helical, pore-shaped, rib-shaped, lattice-structured, or spherical structures, in particular ribs, fins, pins, and knobs. Advantageously, the surface-enlarging element enlarges the surface area and / or provides an enlarged growth area for microorganisms. Furthermore, the surface-enlarging element, in particular ribs, fins, pins, and / or knobs, advantageously increases the conversion of a biotechnological reaction comprising a gas-liquid phase transition, in particular methanation.

[0056] In embodiments, the heat exchanger with a low temperature gradient is used for heat dissipation in biotechnological reactors and as a growth surface for microorganisms, whereby thermal coupling occurs.

[0057] “Thermal coupling” refers in particular to the growth of microorganisms on the surface of the heat exchanger and the direct heat dissipation of the heat generated by the microorganisms via the heat transfer fluid of the heat exchanger.

[0058] In embodiments, the heat exchanger with a low temperature gradient is used for heat removal in biotechnological reactors.

[0059] In embodiments, the heat exchanger is used in fixed bed or trickle bed reactors, preferably for the biological methanation of carbon dioxide and hydrogen.

[0060] A further aspect of the invention relates to a device for the biosynthesis of methane comprising at least one reactor vessel having i. at least one heat exchanger with a low temperature gradient, wherein the heat exchanger with a low temperature gradient comprises at least one compartment which is designed to pass a heat transfer fluid, wherein the surface of the heat exchanger serves to colonize methanogenic microorganisms, ii. a unit designed to sprinkle the methanogenic microorganisms with a nutrient solution, iii. a gas inlet designed to introduce the gaseous substrates into the reactor vessel, iv. a gas outlet designed to discharge the methane formed from the reactor vessel.

[0061] The surface of the heat exchanger for the settlement of methanogenic microorganisms is understood to be the surface of the heat exchanger facing the reactor interior.

[0062] In embodiments, the diameter of the reactor is at least 30 cm, preferably in the range of 30 cm to 15 m, particularly preferably in the range of 30 cm to 5 m, in particular in the range of 30 cm to 3 m.

[0063] Advantageously, by using a heat exchanger in a device for the biosynthesis of methane, heat from the exothermic reaction, which cannot escape radially, i.e. via the reactor wall, due to the large diameter of the reactor, can be specifically dissipated and put to use.

[0064] In embodiments, the low temperature gradient heat exchanger comprises at least two compartments, wherein

[0065] - at least one inner compartment has an inlet and an outlet for the heat transfer fluid and

[0066] - at least one outer compartment closed on one side has an outlet for the heat transfer fluid, wherein the diameter of the outer tube is greater than the diameter of the inner tube, wherein the inner tube is arranged at least partially within the outer tube, and wherein the outlet of the inner tube is arranged within the outer tube.

[0067] In embodiments, the at least one heat exchanger is arranged radially in the reactor vessel.

[0068] The term “radial” is understood to mean running in the direction of a radius of the reactor vessel, wherein the reactor vessel is preferably designed as a rotationally symmetrical body, in particular as an upright cylinder. In embodiments, the at least one compartment has an inclination in the range of 10° to 80° starting from the horizontal extent or the cross-sectional planes of the reactor.

[0069] In embodiments, the at least one compartment is arranged along the horizontal extent or the cross-sectional planes of the reactor.

[0070] In embodiments, the at least one compartment is an evaporator as part of a heat pump system, and the heat pump system further comprises at least one compressor, a condenser, and an expansion valve, which are arranged outside the reactor vessel.

[0071] In some embodiments, at least one surface-enlarging element is arranged on the surface of the heat exchanger. In some embodiments, the at least one surface-enlarging element is selected from the group comprising helical, pore-shaped, rib-shaped, lattice-shaped, or spherical structures, in particular ribs, fins, pins, and knobs.

[0072] In embodiments, the reactor vessel comprises at least two heat exchangers, wherein the heat exchangers are arranged in series or parallel.

[0073] In embodiments, the outlet of the first heat exchanger and the inlet of the second heat exchanger are connected.

[0074] In embodiments, the reactor vessel comprises at least two heat exchangers, wherein the heat exchangers are arranged in series or in parallel, wherein at least one surface-enlarging element selected from the group comprising ribs, fins, pins, and knobs is arranged on the surface of each of the at least two heat exchangers. In preferred embodiments, the at least two heat exchangers are arranged horizontally in the reactor, preferably parallel to one another.

[0075] Advantageously, the use of at least two heat exchangers, in particular those arranged in parallel, in the reactor achieves uniform temperature control of the reactor with low temperature gradients throughout the entire reactor volume and avoids local overheating.

[0076] Furthermore, at least two heat exchangers connected in series can advantageously serve to transport heat from the upper levels to the lower levels if the heat dissipation in the lower levels (e.g. heat losses via the reactor wall or through evaporation) exceeds the resulting reaction heat, whereby the temperature is reduced below the optimal process temperature.

[0077] In embodiments, the at least one heat exchanger and / or the at least one compartment has a length of at least 75% of the diameter of the reactor, preferably at least 90% of the diameter of the reactor, particularly preferably in the range of 99% to 100% of the diameter of the reactor.

[0078] In embodiments, the reactor vessel further comprises at least one temperature control device which is designed for heating and / or cooling.

[0079] A further aspect of the invention relates to a method for the biosynthesis of methane using methanogenic microorganisms, comprising the steps: a) inoculating a surface of at least one heat exchanger according to the invention with a low temperature gradient with methanogenic microorganisms in a reactor vessel, wherein the heat exchanger with a low temperature gradient comprises at least one compartment designed to pass a heat transfer fluid, b) introducing a nutrient solution comprising nutrients and water into the reactor vessel, wherein the surface of the at least one heat exchanger with the methanogenic microorganisms comes into contact with the nutrient solution, c) introducing a gaseous substrate comprising carbon monoxide or carbon dioxide and hydrogen into the reactor vessel, wherein the surface of the at least one heat exchanger with the methanogenic microorganisms comes into contact with the substrate,d) heat removal from the reactor vessel by means of the at least one heat exchanger via a heat transfer fluid, and e) discharge of the methane formed from the reactor vessel.

[0080] In embodiments, the method is carried out in the order of steps a), b), c), d), and e). In embodiments, steps b) and c) are carried out after step a), and steps d) and e) are carried out after steps a), b), and c), wherein steps b) and c) and / or d) and e) are carried out simultaneously or sequentially.

[0081] In embodiments, steps b), c), d), and e) are repeated at least once. According to the invention, the at least one heat exchanger with the surface facing the reactor interior serves as a growth surface for the methanogenic microorganisms.

[0082] The passage of a heat transfer fluid is understood to mean the passage through at least one compartment of the heat exchanger, in particular on the side facing away from the reactor interior.

[0083] In embodiments, at least one surface-enlarging element is arranged on the surface of the heat exchanger. In embodiments, the at least one surface-enlarging element is selected from the group comprising helical, pore-shaped, rib-shaped, lattice-shaped, or spherical structures, in particular ribs, fins, pins, and knobs. Advantageously, the surface-enlarging element enlarges the surface area and / or provides an enlarged growth area for microorganisms.

[0084] Advantageously, the surface of the at least one heat exchanger and the methanogenic microorganisms are in direct thermal contact due to the direct inoculation, thereby enabling direct heat transfer.

[0085] In embodiments, the low temperature gradient heat exchanger comprises at least two compartments, wherein

[0086] - at least one inner compartment has an inlet and an outlet for the heat transfer fluid and

[0087] - at least one outer compartment closed on one side has an outlet for the heat transfer fluid, wherein the diameter of the outer tube is greater than the diameter of the inner tube, wherein the inner tube is arranged at least partially within the outer tube, and wherein the outlet of the inner tube is arranged within the outer tube.

[0088] In embodiments, the at least one compartment is an evaporator as part of a heat pump system, and the heat pump system further comprises at least one compressor, a condenser, and an expansion valve, which are arranged outside the reactor vessel.

[0089] In embodiments, the inoculation of a surface with methanogenic microorganisms in step a) involves immobilization of methanogenic microorganisms, preferably by simultaneously applying accompanying organisms that form adhesive proteins. Advantageously, the accompanying organisms that form adhesive proteins adhere to hydrophobic surfaces.

[0090] The term “adhesive protein” (also adhesive proteins, adhesion molecules) refers to mixtures of proteins and polysaccharides with lipids, phospholipids, glycoproteins, glycolipids, nucleic acids, in particular extracellular DNA and / or lipopolysaccharides, which adhere to surfaces by adhesion as “extracellular polymeric substances (EPS)”.

[0091] In embodiments, the inoculation of a surface with methanogenic microorganisms in step a) is carried out by means of an inoculum, preferably an inoculum comprising methanogenic microorganisms and accompanying organisms which form adhesive proteins, particularly preferably sewage sludge and / or liquid manure.

[0092] In embodiments, the inoculation of a surface with methanogenic microorganisms in step a) is carried out by contacting the surface of at least one heat exchanger with a low temperature gradient with the inoculum.

[0093] By inoculating a surface with methanogenic microorganisms in step a), a biofilm with a layer structure having a thickness in the range of 0.05 pm to 0.1 pm is expediently formed.

[0094] In embodiments, the nutrient solution in step b) further comprises methanogenic microorganisms.

[0095] In embodiments, step b) is repeated at least once, preferably in the range of once to four times a day.

[0096] In embodiments, the gaseous substrate in step c) is passed in cocurrent, countercurrent, crosscurrent or other flow variants relative to the nutrient solution in step b).

[0097] In embodiments, the gaseous substrate comprising carbon monoxide or carbon dioxide and hydrogen further comprises hydrocarbons and / or hydrocarbon compounds optionally containing heteroatoms such as oxygen, nitrogen, sulfur or halogens.

[0098] In embodiments, the gaseous substrate comprises biogas and / or raw biogas as a carrier of the carbon dioxide.

[0099] In embodiments, step c) is carried out by introducing a gaseous substrate, wherein the gases carbon dioxide and hydrogen are not present in a stoichiometric ratio.

[0100] Due to the different solubilities of carbon dioxide and hydrogen in the liquid phase, the proportion of dissolved carbon dioxide is much greater than that of dissolved hydrogen. Furthermore, the dissolution of a large amount of carbon dioxide causes a lowering of the pH value in the liquid through the formation of carbonic acid, thus negatively affecting methanogenic microorganisms.

[0101] In embodiments, step c) is carried out by adding hydrogen and a substoichiometric amount of carbon dioxide such that the gases dissolved in a process liquid (also trickling liquid) are in a stoichiometric ratio. The calculation of the gas concentrations corresponding to the stoichiometric ratio in the liquid can be carried out using the respective sorption isotherms of the two gases hydrogen and carbon dioxide, whereby for simplicity only carbon dioxide needs to be taken into account. Since a large supply of hydrogen but only a small supply of carbon dioxide is inevitably present in the gas phase, and the latter is quickly converted, the described effect of inhibition by the carbonic acid is largely avoided. Advantageously, increased process stability is achieved by avoiding overacidification caused by dissolved carbon dioxide.

[0102] In embodiments, the gaseous substrate, in particular carbon dioxide and / or a carbon dioxide-containing gas mixture, is fed through a control device in each of the individual stages of a trickle-bed reactor and / or along the reaction path. A high methane concentration in the product gas, preferably >99%, is advantageously achieved by a staged addition in a trickle-bed reactor.

[0103] In some embodiments, the process is carried out at elevated system pressure. This advantageously compensates for the low partial pressure or low solubility of hydrogen in the liquid. According to Henry's law, the hydrogen concentration in the liquid then increases, so that a larger amount of hydrogen per unit volume of liquid is available for biochemical methane formation. Within certain limits, the specific conversion is proportional to the partial pressure of hydrogen in the liquid.

[0104] In embodiments, the reactor vessel is operated at a pressure in the range of 0.05 bar to 10 bar and / or at a temperature in the range of 20°C to 90°C, preferably in the range of 35°C to 75°C.

[0105] The heat transfer fluid in step d) is appropriately selected based on the boiling point of the heat transfer fluid, the desired temperature range (target temperature), the non-toxicity with regard to microorganisms (in case of leaks), the ecological harmlessness and / or that the pressure corresponding to the boiling point is as little as possible (maximum a few bar overpressure) above the reactor internal pressure in order to avoid excessive wall thicknesses.

[0106] In embodiments, the heat removal in step d) takes place via a heat transfer fluid selected from water, ammonia, carbon dioxide, or hydrocarbons, in particular ethane, propane, butane, isobutane, or pentane, preferably selected from water or hydrocarbons, particularly preferably water or pentane. Ammonia, carbon dioxide, or hydrocarbons are expediently used as the heat transfer fluid at a pressure in the heat exchanger at which heat transfer takes place at the boiling point of the heat transfer fluid. This advantageously achieves a uniform heat distribution in the heat exchanger. Advantageously, when hydrocarbons are used as the heat transfer fluid, there is no contamination or deterioration of the methane product in the event of a leak. Pentane advantageously has favorable thermodynamic properties as a heat transfer fluid in a temperature range of 40°C to 70°C.

[0107] In embodiments, the boiling point of the heat transfer fluid is designed to be less than 5 K below the target temperature of the desired temperature optimum for the biosynthesis of methane, in particular for the methanogenic microorganisms.

[0108] In embodiments, the boiling point is controlled by regulating the working pressure in the at least one compartment (evaporator) via the expansion valve.

[0109] In some embodiments, the mass flow of the heat transfer fluid is high enough to maintain the target temperature in the reactor vessel within + / - 1.5 K. The mass flow of the heat transfer fluid is advantageously adjusted based on the reactor size and geometry, the geometry of the heat exchanger, the type of biotechnological reaction, and the amount or rate of reactant addition. It is advantageous to measure the temperature in the reactor vessel and control the mass flow of the heat transfer fluid accordingly.

[0110] In embodiments, heat removal occurs in step d) so that the surface inoculated with methanogenic microorganisms is kept constant at a temperature in the range of 20 °C to 80 °C.

[0111] In embodiments, the heat removal g in step d) takes place via a heat transfer fluid selected from water or pentane having a temperature in the range of 20 °C to 80 °C, preferably in the range of 30° to 50°.

[0112] In embodiments, heat removal in step d) is achieved by adjusting the temperature of the heat transfer fluid. The temperature of the heat exchanger is expediently dependent on the selection of the heat transfer fluid. The temperature of the heat transfer fluid is expediently set to a range of 1 K to 5 K lower than the temperature in the reactor.

[0113] In embodiments, the substrate and gas are guided via at least one heat exchanger.

[0114] In embodiments, the heat removal from the reactor vessel in step d) is carried out by additional removal of a warmer heat transfer fluid or supply of a colder heat transfer fluid, by changing the mass flow of the heat transfer fluid, by additional cooling or by a combination of these measures.

[0115] In some embodiments, the gaseous substrate is discharged from the bottom of the reactor vessel. In other embodiments, the discharged gaseous substrate is fed back into the reactor vessel from the top.

[0116] The invention is not limited to the embodiments illustrated and described, but also encompasses all embodiments having the same effect within the meaning of the invention. Furthermore, the invention is not limited to the specifically described combinations of features, but can also be defined by any other combination of specific features of all the individual features disclosed as a whole, provided that the individual features are not mutually exclusive or a specific combination of individual features is not explicitly excluded.

[0117] The invention will be explained in more detail below using an exemplary embodiment. This exemplary embodiment is intended to describe the invention without limiting it.

[0118] The invention is explained in more detail with the aid of drawings.

[0119] Fig. 1 is a diagram of a heat exchanger according to the invention with a low temperature gradient and a diagram showing the temperature profile and heat exchange.

[0120] Fig. 2 is a diagram of a heat exchanger according to the invention with a low temperature gradient comprising surface-enlarging elements, in particular fins, wherein the fins are used as a growth surface for the biofilm.

[0121] Fig. 3 is a diagram of another heat exchanger according to the invention with a low temperature gradient comprising surface-enlarging elements, in particular fins, wherein the fins are used as a growth surface for the biofilm.

[0122] Fig. 4 Series connection of three heat exchangers according to the invention in a methanation reactor.

[0123] Fig. 5 is a diagram of another heat exchanger according to the invention with a low temperature gradient comprising surface-enlarging elements, in particular fins, wherein the fins are used as a growth surface for the biofilm, designed as an evaporator as a component of a heat pump system.

[0124] A heat exchanger (see Fig. 1), consisting of an outer tube 1 and an inner, very good heat-conducting tube 2 made of copper, with the inner tube ending in front of the closed end of the outer tube 3, is pushed into a reactor 4 on one side and is intended to dissipate a heat flow 5. For this purpose, a heat transfer fluid, in particular water, flows through the heat exchanger in such a way that the still cold heat transfer fluid from the inlet

[0125] 6 to the end point of the inner pipe 3, is deflected at this point and in the opposite direction in the gap between the inner and outer pipe to the exit

[0126] 7 and leaves the arrangement as a now warm heat transfer fluid. Due to the temperature difference between the incoming cold heat transfer fluid and the warmer heat transfer fluid flowing in the opposite direction on the side facing the reactor, heat transfer occurs through the inner, heat-conducting tube 2, resulting in a cooling of the warmer heat transfer fluid and a heating of the colder heat transfer fluid. Since the heat transfer fluid in the inner tube and in the tube gap has exactly the same mass flow with the same material properties, this thermal effect results in a nearly constant mixing temperature along the entire heat exchanger.This mixing temperature can be adjusted by changing the mass flow of the heat transfer fluid or by selecting the temperature of the incoming cold heat transfer fluid or by both to a specific temperature difference between the reactor interior and the outer surface of the heat exchanger, which is conducive to the methanation process and constant along the heat exchanger and sufficient to dissipate the heat flow 5.

[0127] The heat transfer is qualitatively expressed by the direction and length of the arrows. On the inlet side, the right side in Fig. 1, the heat transfer fluid in the tube has a first temperature, which corresponds to that of the incoming heat transfer fluid, and a second temperature in the tube gap, which is opposite to the first temperature, whereby the first temperature is lower than the second temperature. Due to the equicaloric heat exchange, the incoming heat transfer fluid, flowing from right to left here, heats up to the same extent as the outgoing heat transfer fluid cools, resulting in a constant and gradient-free mean temperature over the entire effective length.

[0128] Further heat exchangers according to the invention are shown in Figs. 2 and 3. The heat exchangers comprise surface-enlarging elements, in particular fins, which serve as growth surfaces for the biofilm. These surfaces are coated with suitable low-thickness materials, in particular hydrophobic polyolefins, to promote growth and ensure a high and stable colonization by methanogenic microorganisms and their accompanying microorganisms.

[0129] The heat exchanger designed in this way removes the reaction heat generated, in particular from methane synthesis, directly from the heat-generating biofilm and from the surrounding fluids in a trickle-bed reactor, i.e. from the trickle liquid and the gas mixture of reactant and product gas.

[0130] To generate a low temperature gradient in the heat exchanger according to the invention, a high heat flow is achieved either by a high mass flow of the heat transfer fluid, by a high temperature difference of this mass flow between inlet and outlet, or both, and more rarely by setting a specific heat capacity of the heat transfer fluid (Fig. 2). To further reduce the temperature differences, the heat exchanger in Fig. 3 (as in Fig. 1) consists of an outer tube 1 and an inner, very thermally conductive tube 2 made of copper, wherein the inner tube ends before the closed end of the outer tube 3 and is pushed into a reactor 4 on one side. For this purpose, a heat transfer fluid, in particular water, flows through the heat exchanger in such a way that the still cold heat transfer fluid is led from the inlet 6 to the outlet of the inner tube 3, at which point it is turned over oris deflected back and transported in the opposite direction in the gap between the inner and outer tube to the outlet 7 and leaves the arrangement as a now warm heat transfer fluid.

[0131] A reactor 4 is equipped with three heat exchangers according to the invention connected in series on three levels, with an immobilized biofilm of methanogens on their fins (see Fig. 4).

[0132] The reactor is fed with a reactant gas mixture of carbon dioxide and hydrogen. The highest material conversion occurs at the top level (as shown in Fig. 4), and consequently, heat generation is also highest there. Because the conversion decreases with the reaction progress, heat generation is also lowest at the bottom level, and therefore significantly less heat needs to be removed there.

[0133] The three heat exchangers are connected in series, meaning the output of the upper heat exchanger forms the input for the heat exchanger below. Due to the decreasing heat release, the output temperature of the heat transfer fluid increases after the heat exchange process at each level. However, due to the decreasing heat release towards the bottom, this increase becomes increasingly smaller.

[0134] As a result, the increasing temperatures of the heat transfer fluids in the individual heat exchangers also lead to a smaller temperature difference between the reactor interior and the average temperature of the heat exchanger surface at each level. Consequently, the cooling effect decreases, which corresponds to the decreasing heat generation in the reactor.

[0135] The heat exchanger can also advantageously be used to transport heat from the upper levels if the heat dissipation in the lower levels (e.g. heat losses via the reactor wall or through evaporation) exceeds the resulting reaction heat, whereby the temperature is lowered below the optimal process temperature.

[0136] Fig. 5 shows a heat exchanger according to the invention corresponding to Fig. 2 as a component (namely, the evaporator) of a heat pump system. The selection of a suitable heat transfer fluid is based on its boiling temperature, which is slightly below the desired temperature range (target temperature) of the methanogenic microorganisms located on the biofilm-covered surface of the heat exchanger 8.

[0137] This achieves a virtually constant temperature across the entire length of the heat exchanger. Upon leaving at least one compartment, the heat transfer fluid is predominantly in a gaseous state or is separated into a gas phase and a liquid phase in a separation device 14 due to density differences.

[0138] As the heat transfer fluid continues its flow, the gas phase is directed to a compressor 15, which is driven by electrical energy 16. The compression process increases the pressure and temperature of the heat transfer fluid. After the compression process, the heat transfer fluid releases heat energy to an external thermal system in a condenser 17. At least the return temperature of this external thermal system is lower than the condensation temperature of the heat transfer fluid Sj at the pressure prevailing in the condenser 17, so that the heat transfer fluid condenses. The useful heat 21 released in the condenser to the external thermal system approximately corresponds to the sum of the reaction heat 11 absorbed in at least one compartment of the heat exchanger and the electrical energy 16 supplied to the compressor.

[0139] The heat transfer fluid condensed and cooled in the condenser 17 is returned to the evaporator via an expansion valve 20, thus closing the circuit. The expansion valve 20 is responsible for reducing the pressure in the heat transfer fluid back to the boiling pressure in the evaporator.

[0140] Cited non-patent literature:

[0141] Burkhardt M, Koschack T, Busch G (2015) Biocatalytic methanation of hydrogen and carbon dioxide in an anaerobic three-phase system. Bioresource Technology 178, 330-333. DOI: 10.1016 / j.biortech.2014.08.023.

[0142] Vintiloiu A, Brue M, Lemmer A, Oechsner H, Jungbluth T, Jurcoane S, Israel-Roming F (2009) Influence of temperature and pH on enzyme activity in the biogas process. Landtechnik 64(1), 22-24.

[0143] Wagner W. (2015) Heat Exchangers; Vogel Business Media, ISBN 978-3-8343-3361-2. Reference

[0144] 1 at least one outer compartment closed on one side

[0145] 2 at least one inner compartment

[0146] 3 closed end of at least one outer compartment

[0147] 4 reactor

[0148] 5 Heat flow

[0149] 6 Entrance

[0150] 7 Outlet

[0151] 8 at least one compartment

[0152] 9 surface-enlarging element, rib

[0153] 10 methanogenic microorganisms

[0154] 11 Heat of reaction

[0155] 12 gaseous substrate

[0156] 13 Nutrient solution

[0157] 14 Separation device

[0158] 15 compressors

[0159] 16 Electrical energy

[0160] 17 Capacitor

[0161] 18 Flow useful heat

[0162] 19 Return useful heat

[0163] 20 Expansion valve

[0164] 21 Useful heat

Claims

Patent claims 1. Use of a heat exchanger with a low temperature gradient for temperature control and as a growth surface for microorganisms in biotechnological reactors, wherein the heat exchanger with a low temperature gradient comprises at least one compartment which is designed to pass a heat transfer fluid, wherein a low temperature gradient is understood to mean a difference of less than 10 K between the minimum and maximum temperature of the heat transfer fluid in the heat exchanger and / or on the surface of the heat exchanger.

2. Use of a heat exchanger for temperature control in biotechnological reactors according to claim 1, wherein the heat exchanger with a low temperature gradient comprises at least two compartments, wherein i. at least one inner compartment has an inlet and an outlet for the heat transfer fluid and ii. at least one outer compartment closed on one side has an outlet for the heat transfer fluid, wherein the diameter of the outer compartment is larger than the diameter of the inner compartment, wherein the inner compartment is arranged at least partially within the outer compartment, and wherein the outlet of the inner compartment is arranged within the outer compartment.

3. Use of a heat exchanger for temperature control in biotechnological reactors according to claim 1 or 2, characterized in that the at least one compartment is a tube.

4. Use of a heat exchanger for temperature control in biotechnological reactors according to claim 3, characterized in that the flow cross-section of the inner tube and the flow cross-section of the annular gap between the outer and the inner tube are of equal size.

5. Use of a heat exchanger for temperature control in biotechnological reactors according to one of claims 2 to 4, characterized in that the inner compartment consists of copper or aluminum and / or the outer compartment consists of steel.

6. Use of a heat exchanger for temperature control in biotechnological reactors according to one of claims 2 to 5, characterized in that the outer compartment has a hydrophobic coating on the surface.

7. Use of a heat exchanger for temperature control in biotechnological reactors according to one of claims 1 to 6, characterized in that the at least one compartment is an evaporator as a component of a heat pump system 8. Use of a heat exchanger for temperature control in biotechnological reactors according to one of claims 1 to 7, characterized in that at least one surface-enlarging element selected from the group comprising ribs, fins, pins and knobs is arranged on the surface of the heat exchanger.

9. Use of a heat exchanger for temperature control in biotechnological reactors according to one of claims 1 to 8 in fixed bed or trickle bed reactors, preferably for the biological methanation of carbon dioxide and hydrogen.

10. Device for the biosynthesis of methane comprising at least one reactor vessel having i. at least one heat exchanger with a low temperature gradient, wherein the heat exchanger with a low temperature gradient comprises at least one compartment which is designed to pass a heat transfer fluid, wherein the surface of the heat exchanger serves to colonize methanogenic microorganisms, ii. a unit designed to sprinkle the methanogenic microorganisms with a nutrient solution, iii. a gas inlet designed to introduce the gaseous substrates into the reactor vessel, iv. a gas outlet designed to discharge the methane formed from the reactor vessel.

11. Device for the biosynthesis of methane according to claim 10, characterized in that the heat exchanger with a low temperature gradient comprises at least two compartments, wherein - at least one inner compartment has an inlet and an outlet for the heat transfer fluid and - at least one outer compartment closed on one side has an outlet for the heat transfer fluid, wherein the diameter of the outer tube is greater than the diameter of the inner tube, wherein the inner tube is arranged at least partially within the outer tube, and wherein the outlet of the inner tube is arranged within the outer tube 12. Device for the biosynthesis of methane according to claim 10 or 11, characterized in that the at least one compartment is an evaporator as a component of a heat pump system and the heat pump system further comprises at least one compressor, one condenser and one expansion valve, which are arranged outside the reactor vessel.

13. Apparatus for the biosynthesis of methane according to one of claims 10 to 12, characterized in that the reactor vessel comprises at least two heat exchangers, wherein the heat exchangers are arranged in series or in parallel.

14. A process for the biosynthesis of methane using methanogenic microorganisms, comprising the steps of: a) inoculating a surface of at least one heat exchanger with a low temperature gradient with methanogenic microorganisms in a reactor vessel, wherein the heat exchanger with a low temperature gradient comprises at least one compartment designed to conduct a heat transfer fluid, b) introducing a nutrient solution comprising nutrients and water into the reactor vessel, wherein the surface of the at least one heat exchanger with the methanogenic microorganisms comes into contact with the nutrient solution, c) introducing a gaseous substrate comprising carbon monoxide or carbon dioxide and hydrogen into the reactor vessel, wherein the surface of the at least one heat exchanger with the methanogenic microorganisms comes into contact with the substrate,d) heat removal from the reactor vessel by means of the at least one heat exchanger via a heat transfer fluid, and e) discharge of the methane formed from the reactor vessel.

15. A process for the biosynthesis of methane using methanogenic microorganisms according to claim 14, characterized in that the heat exchanger with a low temperature gradient comprises at least two compartments, wherein - at least one inner compartment has an inlet and an outlet for the heat transfer fluid and - at least one outer compartment closed on one side has an outlet for the heat transfer fluid, wherein the diameter of the outer tube is greater than the diameter of the inner tube, wherein the inner tube is arranged at least partially within the outer tube, and wherein the outlet of the inner tube is arranged within the outer tube 16. A process for the biosynthesis of methane using methanogenic microorganisms according to claim 14, characterized in that the at least one compartment is an evaporator as a component of a heat pump system and the heat pump system further comprises at least one compressor, one condenser and one expansion valve, which are arranged outside the reactor vessel.

17. The method according to any one of claims 14 to 16, characterized in that the heat removal in step d) takes place via a heat transfer fluid selected from water or pentane.

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