MEC SYSTEM

Abstract

The present invention provides MEC stack with several or multiple MEC cells comprising at least one gas inlet and at least one degassing element as well as methods to improve the bio-electromethanation reaction catalysed by bio catalysts in these MEC stacks.

Claims

1. Method to regulate the gas gradient in a bio-electromethanogenesis process in a Microbial Electrolysis cell (MEC)-stack comprising at least two MEC cells, the method comprising the steps of a. Measuring in the cathode compartments the stack current and/or voltage of the MEC and/or MEC-stack; b. Determine an input gas quantity for at least one gas inlet point based on the information assessed in step a); c. Feeding the determined input gas quantity through at least one gas inlet point, thereby regulating the volumetric requirement for efficient methane production in the system and d. De-gassing the MEC stack through one or more degassing element located after a MEC cell of the MEC stack.

2. Method according to claim 1, wherein step a) further comprises measuring at least one of: (i) the pH value of the catholyte in the catholyte circuit, (ii) the oxidation reduction potential of the catholyte (iii) the temperature of the catholyte thereby regulating in step c) the pH value and/or the temperature and/or the oxidation potential of the catholyte

3. Method according to claim 2, wherein step a) comprises measuring the pH value of the catholyte through a pH measuring system located before and/or after the two or more gas inlets points.

4. MEC stack (1) in a bio-electromethanogenesis plant comprising: at least two MEC cells (10a, 10b), wherein each MEC cell (10a, 10b) comprises a cathode compartment (12a, 12b) and an anode compartment (14a, 14b); wherein the MEC cells (10a, 10b) are fluidly connected parallelly or in series; and wherein the MEC stack comprises at least one catholyte circuit (18), connecting the cathode compartments (12a, 12b) of two or more MEC cells (10a, 10b) of the MEC stack. characterized in that two or more gas inlets (22a, 22b) are located within the at least one catholyte circuit (18).

5. MEC stack (1) according to claim 4, comprising at least one gas inlet (22a, 22b) at one or more individual MEC cells (10a, 10b) of the MEC stack (1).

6. MEC stack (1) according to claim 5 comprising at least one gas inlet (22a, 22b) within the cathode compartment (12a, 12b) of the one or more individual MEC cells (10a, 10b).

7. MEC stack (1) according to any of claims claim 4 to 6, wherein each gas inlet (22a, 22b) comprises a respective flow controller to selectively regulate the gas input from the gas source (20a, 20b).

8. MEC stack according to any of claims 4 to 7, wherein the MEC stack (1) comprises at least one de-gassing element (30) to extract at least a first gas/one of the process gases from the MEC stack (1), wherein one of the de-gassing elements (30) is located after a last MEC cell of the MEC stack.

9. MEC stack according to claim 8 wherein one or more de-gassing element are located after one or more of the other MEC cells.

10. MEC stack (1) according to any of the claims 4 to 9 comprising at least one device selected from of a pH measuring system (32), a ORP measuring system (34), a temperature measuring system, a volume measuring system, a current measuring system.

11. MEC stack (1) according to claim 10 wherein the pH measuring system and/or the ORP measuringsystem and/orthe temperature measuringsystem and/orthe volume measuringsystem and/orthe current measuring system are located before and/or after at least one gas inlet (22a, 22b).

12. A MEC stack (1) in a bio-electromethanogenesis plant comprising: at least two MEC cells (10a, 10b), wherein each MEC cell (1oa, 10b) comprises a cathode compartment (12a, 12b) and an anode compartment (14a, 14b); wherein the MEC cells (10a, 10b) are fluidly connected parallelly or in series; and wherein the MEC stack comprises at least one catholyte circuit (18) for catholyte, connecting the cathode compartments (12a, 12b) of two or more MEC cells (10a, 10b) of the MEC stack. the MEC stack (1) comprising one gas inlet (22a) for an input gas located at a first MEC cell (10a) of the MEC stack characterized in that the MEC stack (1) comprises at least two de-gassing elements (30a, 30b) for extracting at least one output gas, one of de-gassing element (30a, 30b) being located after a last MEC cell (10b) of the MEC stack (1).

13. The MEC stack (1) according to claim 12 wherein at least one de-gassing element (30a, 30b) is located after one or more of the other MEC cells.

14. A MEC module (100) comprising two or more MEC stacks (10a, 10b) according to any of the above claims 6 to 16, the two or more MEC stacks (10a, 10b) being fluidly connected through the catholyte circuit (18).

15. A MEC cell for use in a bio-electromethanogenesis plant comprising one gas inlet for an input gas and two or more degassing elements or comprising two or more gas inlet for an input gas and one or more degassing elements.

Description

SHORT DESCRIPTION OF THE FIGURES AND EXAMPLES

[0129] Specific embodiments of the method and the system will now be disclosed through the following figures, in which:

[0130] FIG. 1a shows a schematic MEC stack with two MEC cells comprising two gas inlets and one degassing element according to one exemplary embodiment of the present invention.

[0131] FIG. 1b shows a schematic of an alternative more compact embodiment of the MEC stack with two MEC cells comprising two gas inlets and one degassing element according to one exemplary embodiment of the present invention.

[0132] FIG. 2 shows a schematic MEC stack with two MEC cells comprising one gas inlets and two degassing elements according to another exemplary embodiment of the present invention.

[0133] FIG. 3 is a graph showing the methane production rate of methane depending on the number and position of gas inlets in the example of FIGS. 1a and 1b. Although for all three experiments the same amount of input gas (CO2 supply) was used already this simple experiment shows that different locations of one or more gas inlets have dramatic consequences on the methane production rate of a MEC stack.

[0134] FIG. 4 shows an exemplary schematic composition of the cathodic compartments of a MEC stack of the prior art with n-MEC cells. The gas inlet is before the first MEC and as it is depicted the total amount of gas is fed into the MEC stack via said inlet, which leads to the above described volumetric problem that in said first MEC the percentage of liquid phase (corresponding to the active area) is quite restricted, while a high percentage of the MEC cathode compartment volume is occupied by the educt (CO2, H2) and product gas (CH4) with the fraction of product gas increasing with increasing cell number.

[0135] FIG. 5 shows an exemplary schematic composition of a MEC stack with n-MEC cell cathodic compartments comprising a gas inlet before each MEC cell and one degassing element at the last MEC cell, according to an exemplary embodiment of the present invention.

[0136] FIG. 6 shows an exemplary schematic composition of a MEC stack with n-MEC cell cathodic compartments comprising a gas inlet before each MEC cell and one degassing element after each MEC cell, according to an exemplary embodiment of the present invention.

[0137] As can be seen in FIGS. 1a and 1b, this exemplary embodiment of a MEC stack 1 comprises two MEC cells 10a, 10b. Each MEC cell 10a, 10b comprises a cathode 12a, 12b and an anode 14a, 14b. The left part of FIGS. 1a and 1b shows the anode side of the MEC Stack which will not be described in detail. The cathode side of the MEC stack 1 comprises a catholyte circuit 18 which fluidly connects the two MEC cells 10a, 10b.

[0138] The MEC stack 1 of FIGS. 1a and 1b comprises two gas inlets 22a and 22b, in which a respective gas source 20a, 20b is used to feed an input gas to the catholyte. The gas sources 20a and 20b comprises carbon dioxide CO2 in this example but are not limited to these. As can be seen, the two gas inlets are arranged before each MEC cell 10a, 10b, respectively.

[0139] On the catholyte circuit 18 and after the second MEC cell 10b, a degassing element 30 is located to degas the catholyte of the catholyte circuit 18. Further, pH measuring systems 32 and ORP measuring system 34 are arranged on the catholyte circuit 18. These measuring systems are in this example encompassed in the degassing element 30. The measurements on the catholyte are hence made after the catholyte has been degassed.

[0140] As can be seen in FIG. 2, this exemplary embodiment of a MEC stack 1 comprises two MEC cells 10a, 10b. Each MEC cell 10a, 10b comprises a cathode 12a, 12b and an anode 14a, 14b. The left part of FIG. 2 shows the anode side of the MEC Stack which will not be described here.

[0141] The cathode side of the MEC stack 1 comprises a catholyte circuit 18 which fluidly connects the two MEC cells 10a, 10b. The MEC stack of FIG. 2 comprises one gas inlets 22a with a respective gas source 20a. In this example the gas source 20a is carbon dioxide. According to this embodiment the MEC stack 1 comprises two degassing elements 30a and 30b both arranged on the catholyte circuit 18. The first degassing element 30a is located after the first MEC cell 10a, while the second degassing element 30b is located after the second (or last) MEC cell 10b.

[0142] Further, pH measuring systems 32 and ORP measuring system 34 are arranged on the catholyte circuit 18. These measuring systems are in this example encompassed in the degassing element 30b. The measurements on the catholyte are hence made after the catholyte has been degassed.

[0143] FIG. 3 shows the methane conversion rate of the system of FIG. 1a with two different CO2 feed configurations.

[0144] The first column shows the methane conversion with just one gas inlet 22a of FIG. 1athis represents the prior art. The second column shows the methane conversion with two gas inlets 22a, 22b, according to the exemplary embodiment of the present invention in FIG. 1. As can be seen from the graph, the methane conversion is at its highest when two gas inlets 22a, 22b have been arranged in the MEC stack 1. As described before, this is due to the better physico-chemical conditions for the strains through a distributed and targeted input gas supply.

[0145] FIG. 4 shows the distribution of gases and catholyte (liquid phase) in the MEC cells of a MEC stack of the prior art. As can be seen from this illustration, the input gas (in this example CO2) is fed at a single gas inlet 22a point before the first MEC cell. The first MEC cell has further a liquid phase which is of limited volume and shows also the hydrogen produced through electrolysis. In the first MEC cell a portion of the CO2 is converted into methane (CH4) and the methane as well as the remaining CO2 is transferred by the catholyte in the catholyte circuit to the second MEC cell catholyte compartment 12b.

[0146] In the second MEC cell further reactions occur, and further methane is produced, which with the remaining CO2 is transmitted to the third MEC cell catholyte compartment 12c. This process continues until the last MEC cell catholyte compartment 12n in which most of the gas is the produced methane and there is enough CO2 for at least one more reaction in the last MEC cell catholyte compartment 12b to produce methane. The produced methane 97 is then degassed after the last MEC cell through the degassing element 30a. The remaining catholyte is then send back through the circuit to the first MEC cell, where it is enriched with input gas again.

[0147] As can be seen, in this system of the prior art, the MEC cells are confronted with big quantities of input gas (e.g. CO2) and quite some energy and efficiency is wasted transporting both the produced methane and the remaining CO2 through all MEC cells.

[0148] The liquid phase in this figure represents the active area of a respective MEC cell.

[0149] FIG. 5 shows the distribution of gases and material in the MEC cells of a MEC stack according to an exemplary embodiment of the present invention in which a respective gas inlet is located before each MEC cell. The MEC cell catholyte compartment s 12a to 12n are connected by a catholyte circuit 18, but this time before each MEC cell a gas inlet 22a to 22n is located before the respective MEC cell catholyte compartments 12a to 12n. As can be seen from the distribution in the first MEC cell, the average liquid phase is substantially bigger than in the example of FIG. 4. Therefore, the active area in the MEC cells of FIG. 5 is increased and more efficient reactions with less power consumption can be achieved.

[0150] Through the gas inlet 22a the required quantity of CO2 for the methanation process in MEC cell catholyte compartment 12a is fed to the MEC cell catholyte compartment 12a. Through the gas inlet 22b the required quantity of CO2 for the methanation process in MEC cell catholyte compartment 12b is fed to the MEC cell catholyte compartment 12b. Same applies for the remaining MEC cells. As such the methane portion in the second MEC cell is bigger than the methane portion in the second MEC cell of the FIG. 4.

[0151] In FIG. 5, the liquid phase in the MEC cell is decreasing between MEC cells. The last MEC cell catholyte compartment 12n has the complete amount of methane produced 98 in the MEC cell catholyte compartment s before 12a to 12n-1, the input carbon dioxide required for the last reaction of the MEC cell catholyte compartment 12n and the lowest amount of liquid phase of all MEC cells in the MEC stack. In this embodiment due to the overall increased liquid phases and hence the larger active areas, energy consumption is minimized compared to the example according to FIG. 4. Accordingly, the whole MEC stack is more efficient.

[0152] FIG. 6 shows a further development of an exemplary MEC stack according to the present invention. The MEC stack of FIG. 6 is similar to the one of FIG. 5 with the exception, that further to several gas inlet before various MEC cell, the MEC stack comprises several degassing elements after various MEC cell. In this way, as can be taken form the figure, the liquid phase is nearly constant at a high level in each MEC cell catholyte compartment therefore increasing the active area constantly. In this example power consumption is less than in the MEC stack of FIG. 5 and methane production 99a to 99n is still more efficient.

[0153] It has surprisingly found that even with an energy consumption, which is less for the whole MEC stack compared with the sums of the energy consumption of all individual MEC cell a more efficient methanation rate and a higher methane production per unit energy can be upheld.