DIGESTER COMPRISING A POROUS INNER WALL

Abstract

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 is at least partly porous.

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, wherein the portion of the inner wall situated at the level of the gas space is at least partly porous.

2. The plant according to claim 1, wherein the porosity of the portion of the inner wall of the chamber situated at the level of the gas space is between 75% and 95% of the volume.

3. The plant according to claim 1, wherein the portion of the inner wall of the chamber situated at the level of the gas space comprises wall sub-portions having a porous surface.

4. The plant according to claim 1, wherein the portion of the inner wall of the chamber situated at the level of the gas space 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 at least part of its surface porous.

5. The plant according to claim 1, wherein the porous part of the portion of the inner wall of the chamber situated at the level of the gas space is composed of a material which is resistant to a humid and corrosive atmosphere.

6. The plant according to claim 1, wherein it comprises a mixing means which promotes transfer of the oxidizing gas to the inner wall of the chamber.

7. A process for producing at least partially 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.

8. The process according to claim 7, wherein the biomass is mixed so as to promote transfer of the oxidizing gas to the inner wail of the chamber.

9. The process according to claim 7, wherein the oxidizing gas is oxygen or air or enriched air.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0021] 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 drawing, in which like elements are given the same or analogous reference numbers and wherein;

[0022] FIG. 1 is a horizontal schematic section through the chamber of the digester.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0023] FIG. 1 is a horizontal schematic section through the chamber of the 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. It highlights the porous part 1.

[0024] The reactions between O.sub.2 and H.sub.2S take place on a surface (not in the gas or liquid phase of the digester). The microorganisms needed for the reaction (sulfur-oxidizing bacteria such as Thiobacillus) are in the liquid phase, and the reagents are in the gas phase. A 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, the gas/liquid interface of the digester or post-digester, and any other surface available in the gas space, e.g. fillets. If the surface areas available are insufficient, the H2S abatement reactions do not take place sufficiently, or even not at all.

[0025] In other words, the solution according to the invention is to increase the surface area of reaction between the liquid phase and the gas phase, by adding one or more porous parts to the surface of the inner wall of the chamber. This addition of porous mass allows an increase in the size of the reaction support and so promotes the greater removal of the H2S.

[0026] Depending on the case, the plant according to the invention may have one or more of the features below: [0027] the porosity of the portion of the inner wall of the chamber situated at the level of the gas space is between 75% and 95% of the volume, [0028] the portion of the inner wall of the chamber situated at the level of the gas space comprises wall sub-portions having a porous surface. [0029] the portion of the inner wall of the chamber situated at the level of the gas phase 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 at least part of its surface porous. [0030] the porous part of the portion of the inner wall of the chamber situated at the level of the gas phase is composed of a material which is resistant to a humid and corrosive atmosphere, for example certain stainless steels, PEEK, PTFE. [0031] the plant comprises a mixing means which promotes transfer of the oxidizing gas to the inner wall of the chamber.

[0032] 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: [0033] injecting biomass into the digester; [0034] injecting an oxidizing gas at the top of the digester; and [0035] mixing the biomass.

[0036] The biomass is preferably mixed so as to promote transfer of the oxidizing gas to the inner wall of the chamber.

[0037] 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.

[0038] 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 evacuated with the latter.

[0039] The solution according to the invention produces a biogas stream containing 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] 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.

[0042] 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.