DIGESTER COMPRISING AN INNER WALL HAVING EXPANSIONS AND/OR HOLLOWS

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 comprising the biomass and the gas space, and a means for introducing an oxidizing gas,

characterized in that the portion of the inner wall of the chamber situated at the level of the gas space exhibits expansions and/or hollows.

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 comprising the biomass and the gas space, and a means for introducing an oxidizing gas, characterized in that the portion of the inner wall of the chamber situated at the level of the gas space exhibits expansions and/or hollows.

2. The plant of claim 1, wherein the expansions project towards the interior of the chamber.

3. The plant of claim 2, wherein the expansions project radially.

4. The plant of claim 1, wherein the expansions and/or the hollows are in succession along the perimeter of the chamber.

5. The plant of claim 1, wherein the portion of inner wall of the chamber situated at the level of the gas space exhibits a zigzag shape.

6. The plant of claim 1, wherein the inner wall is composed of a material which is resistant to a humid and corrosive atmosphere.

7. The plant of claim 1, wherein the inner wall is divided into a first wall and a second wall, the two walls being side by side, and the second wall being opposite the interior of the chamber and exhibiting a surface area greater than the surface area of the first wall.

8. Process for producing desulfurized biogas, using a plant according to claim 1, which comprises: injecting biomass into the digester; injecting an oxidizing gas at the top of the digester; and mixing the biomass.

9. The process of claim 8, wherein the biogas is mixed so as to promote transfer of the oxidizing gas to the inner wall of the chamber.

10. The process of claim 8, wherein the oxidizing gas is oxygen or air or enriched air.

Description

BRIEF DESCRIPTION OF THE FIGURES

[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 horizontal schematic section through the chamber of the digester.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The reactions between O.sub.2 and H.sub.2S take place on a surface (not in the gaseous or liquid phase of the digester). The microorganisms needed for the reaction (sulfur-oxidizing bacterial such as Thiobacillus) are in the liquid phase, and the reagents are in the gas phase. The hydrophilic surface is required for contact between the liquid phase, the microorganisms, and the gas phase, the reagents. These surfaces are primarily the inner walls in the gas space, and the gas/liquid interface of the digester or post-digester. If the surface areas available are insufficient, the H.sub.2S abatement reactions do not take place sufficiently, or even not all.

[0026] Expressed alternatively, the solution according to the invention, by increasing the surface area of the inner wall of the chamber, enables an increase in the size of the reaction support and so promotes the more advanced removal of hydrogen sulfide.

[0027] Depending on the case, the plant according to the invention may have one or more of the features below: [0028] the expansions project towards the interior of the chamber, [0029] the expansions project radially, [0030] the expansions and/or the hollows are in succession along the perimeter of the chamber, [0031] the portion of inner wall of the chamber situated at the level of the gas space exhibits a zigzag shape; this zigzag shape is shown in FIG. 1, which is a diagrammatic horizontal section through the chamber of the digester or post-digester. Note that the section is made in the portion of the inner wall of the chamber situated at the level of the gas space. [0032] the inner wall is composed of a material which is resistant to a humid and corrosive atmosphere; examples might include certain stainless steels, PEEK, PTFE, [0033] the inner wall is divided into a first wall and a second wall, the two walls being side by side, and the second wall being opposite the interior of the chamber and having a surface area greater than the surface area of the first wall.

[0034] A further subject of the present invention is a process for producing at least partially desulfurized biogas, using a plant according to the invention, which comprises: [0035] injecting biomass into the digester; [0036] injecting an oxidizing gas at the top of the digester; and [0037] mixing the biomass.

[0038] 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.

[0039] Inside the digester, when hydrogen sulfide reacts with oxygen, the sulfur attaches to the inner wall of the chamber of the digester. After a certain time, the solid sulfur generated falls into the digestate and is removed with said digestate. The solution according to the invention allows a biogas stream to be obtained that comprises less than 200 ppm of hydrogen sulfide.

[0040] 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 on the inner walls of the digester at the level of the gas space, with no need for complex engineering.

[0041] 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.

[0042] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0043] “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”.

[0044] “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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.