DIGESTER COMPRISING A DESULFURIZATION NET COMBINED WITH PENDENT ROPES

Abstract

Plant for producing at least partially desulfurized biogas, comprising a biomass digester and/or post-digester, the digester and/or post-digester comprising: a chamber (1) in which an anaerobic digestion of the biomass takes place, leading to the production of biogas (2) and of digestate (3), a means for introducing an oxidizing gas, a desulfurization net (4) placed horizontally and fastened in the upper part of the chamber, and ropes (5) attached to said desulfurization net and which hang down to the biogas-digestate interface.

Claims

1. A plant for producing at least partially desulfurized biogas, comprising a biomass digester and/or post-digester, the digester and/or post-digester comprising: a chamber (1) in which an anaerobic digestion of the biomass takes place, leading to the production of biogas (2) and of digestate (3), a means for introducing an oxidizing gas, a desulfurization net (4) placed horizontally and fastened in the upper part of the chamber, and ropes (5) attached to said desulfurization net and which hang down to the biogas-digestate interface.

2. The plant according to claim 1, wherein the ropes are made of polyethylene.

3. The plant according to claim 1, wherein the ropes have a diameter of between 1 and 50 mm, preferably between 2 and 10 mm.

4. The plant according to claim 1, wherein the ropes have a tensile strength of between 50 and 50 000 kg, preferably between 100 and 500 kg.

5. The plant according to claim 1, wherein the ropes withstand temperatures of between −30° C. and 70° C., preferably between 10° C. and 60° C.

6. The plant according to claim 1, wherein the net-rope assembly occupies between 0.1% and 3% of the gas space located between the digestate and the top end of the chamber.

7. The plant according to claim 1, wherein porous blocks are attached to the net and/or the ropes.

8. The plant according to claim 7, wherein the porous blocks comprise iron oxide and/or biochar and/or an activated carbon.

9. A process for producing at least partly desulfurized biogas, using a plant according to claim 1, which comprising: injecting biomass into the digester; injecting an oxidizing gas at the top of the digester; and mixing the biomass.

10. The process according to claim 9, wherein the oxidizing gas is oxygen or air or enriched air.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0024] FIG. 1 is a diagram of a cross-sectional view of the inside of the chamber of the digester.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0025] FIG. 1 is a diagram of a cross-sectional view of the inside of the chamber of the digester.

[0026] On the inside of the chamber of the digester, when the hydrogen sulfide reacts with oxygen, sulfur attaches itself in particular to the desulfurization net and to the ropes at the gas-liquid interface.

[0027] The ropes make it possible to offer an additional surface to the sulfur-oxidizing bacteria, e.g. Thiobacillus, in order to remove sulfur at the location where the hydrogen sulfide is most concentrated, i.e. close to the gas-liquid interface. A better sulfur removal is thus obtained.

[0028] Depending on the case, the plant according to the invention may have one or more of the features below: [0029] the ropes are made of polyethylene. [0030] the ropes have a diameter of between 1 and 50 mm, preferably between 2 and 10 mm. [0031] the ropes have a tensile strength of between 50 and 50 000 kg, preferably between 100 and 500 kg. [0032] the ropes withstand temperatures of between −30° C. and 70° C., preferably between 10° C. and 60° C. [0033] the net-rope assembly occupies between 0.1% and 3% of the gas space located between the digestate and the top end of the chamber. [0034] porous blocks are attached to the net and/or the ropes. [0035] the porous blocks comprise iron oxide and/or biochar and/or an activated carbon. Generally, the porous blocks may comprise any known hydrogen sulfide adsorbent. [0036] the ropes are made of polyethylene.

[0037] The net could be of octagonal shape. It could also be fastened in the chamber by attaching the net to hooks fastened to the internal wall of the chamber.

[0038] A further subject of the present invention is a process for producing at least partially desulfurized biogas, using a plant according to the invention, comprising:: [0039] injecting biomass into the digester; [0040] injecting an oxidizing gas at the top of the digester; and [0041] mixing the biomass.

[0042] Note that the oxidizing gas might be oxygen or air or enriched air. Enriched air refers to air having a higher oxygen content than the oxygen content normally present in air.

[0043] As explained above, the sulfur attaches itself to the net and the ropes. After a certain period of time, the solid sulfur generated falls into the digestate and is discharged therewith.

[0044] The solution according to the invention makes it possible to obtain a biogas stream comprising less than 200 ppm of hydrogen sulfide.

[0045] The invention makes it possible to reduce the costs of purifying biogas by removal of hydrogen sulfide effectively, by increasing the reactivity of the oxygen already injected with the sulfur-containing products, by creating an additional reaction surface within the gas space of the digester, with no need for complex engineering.

[0046] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0047] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0048] “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”.

[0049] “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0050] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0051] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0052] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

[0053] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.

[0054] While embodiments of this invention have been shown and described, modifications thereof may be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and not limiting. Many variations and modifications of the composition and method are possible and within the scope of the invention. Accordingly the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims.