WO2019074357A2

WO2019074357A2 - Aerobic acidophilic bio-desulfurization of biogas (hydrogen sulfide)

Info

Publication number: WO2019074357A2
Application number: PCT/MY2018/050068
Authority: WO
Inventors: Hong Wei; Tan Kai Hock FRANCIS; Peck Sai TANG
Original assignee: Unilib Energy Sdn Bhd
Current assignee: Unilib Energy Sdn Bhd
Priority date: 2017-10-13
Filing date: 2018-10-11
Publication date: 2019-04-18
Anticipated expiration: 2020-04-13
Also published as: MY171204A; WO2019074357A3

Abstract

The present invention relates to a method and a system for desulfurization of biogas comprising of hydrogen sulfide. The method comprises the step of preparing a raw biogas and feeding the same to a scrubber tank (100), preparing bacteria and growing the bacteria inside a sphere shaped packing positioned in the scrubber tank (102), deploying bacteria into the aeration tank (103), and supplying oxygen to the aeration tank and the scrubber tank via a pump member (104). The resulting clean purified biogas then exits the scrubber tank (105).

Description

AEROBIC ACIDOPHILIC BIO-DESULFURIZATION OF BIOGAS (HYDROGEN

SULFIDE)

FIELD OF THE INVENTION

The present invention generally relates to desulfurization method of a biogas. More particularly, the present invention relates to an improved method of desulfurizing a hydrogen sulfide biogas. BACKGROUND OF THE INVENTION

When an organic material is broken down in the presence of oxygen, a biogas will be formed by anaerobic microorganisms. Biogas typically refers to a mixture of different gases. Biogas are naturally produced from raw material such as agricultural waste, green waste, food waste, plant material and sewage. Biogas can also be used as an important renewable energy source, together with wave energy, wind energy, anaerobic digestion, geothermal and solar energy. Biogas consists of several components including methane gas, CH₄, carbon dioxide, CO2, hydrogen sulfide, H₂S and hydrogen, H₂.

The presence of hydrogen sulfide, carbon dioxide and water makes biogas very corrosive, thus requiring use of adaptable materials. More particularly, hydrogen sulfide must be eliminated to avoid possible damage to the equipment and hazards to users and the environment. The damages will begin to exhibit to users and environment after the hydrogen sulfide in biogas exceeds 100 ppm. Hydrogen sulfide is toxic and corrosive. The burning of biogas containing hydrogen sulfide will result in production of environmentally hazardous sulfur dioxide, SO2. Desulfurization is a process of removing sulfur from a biogas compound.

The hydrogen sulfide can be removed by using three methods, which are dry method, wet method and biological method. In dry method, the desulfurization is based on absorption on solid solvents, metal oxides or activated carbon, which occurs in a dry state. The wet method involves rinsing biogas with different solution that is capable of absorbing the hydrogen sulfide. On the other hand, the biological method is based on biodegradation of hydrogen sulfide, i.e. removal of the hydrogen sulfide from biogas by using sulfurous bacteria via biochemical processes in a special vessel or bioreactor. See, for example, a European patent publication no. EP 2 767 585 A1 , which discloses a method of purification of a microbiological biogas arising from the methane fermentation of settled organic matter in a fermentation container based on the removal of hydrogen sulfide contaminant. The method includes supplying raw biogas, which contains hydrogen sulfide into a scrubber tank and passing the biogas through a filter bed in a bio filter column.

A need therefore exists for an improved method and a system for providing an efficient distribution of hydrogen sulfide oxidizing bacteria thereby overcoming the problems and shortcomings of the prior art. Although there are method for the same in the prior art, for many practical purposes, there is still considerable room for improvements.

SUMMARY OF THE INVENTION The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

Accordingly, there is provided a method of desulfurizing a biogas having hydrogen sulphide.

The method of the present invention can be characterized by the steps of feeding a biogas having a concentration ranging from 7,000 ppm to 9,000 ppm to a scrubber tank, deploying a bacteria into the scrubber tank and an aeration tank connected thereto, wherein the amount of bacteria deployed to the scrubber tank and the aeration tank are equally distributed between each of the scrubber tank and the aeration tank, growing the bacteria in the scrubber tank, supplying a portion of bacteria from the aeration tank to the scrubber tank through a dispersing member, and feeding oxygen to the scrubber tank and to the aeration tank to allow the bacteria to continuously convert the hydrogen sulfide to elemental sulfur, sulfurous acid, and sulphuric acid. Preferably, the packing is a sphere shaped packing.

Preferably, the bacteria is selected from a group comprising a hydrogen sulfide oxidizing bacteria. In accordance to another aspect of the present invention, there is provided a system for desulfurizing biogas having hydrogen sulfide.

The system can be characterized by the system comprising a scrubber tank comprises two layers of containers, wherein the two layers of containers are separated by a biogas redistributor and a spray water distributor, a sphere shaped packing positioned in each of the containers for growing a hydrogen sulfide oxidizing bacteria, an aeration tank for storing a hydrogen sulfide oxidizing bacteria, an inlet pipeline and an outlet pipeline connected to the scrubber tank, a first air pipeline connected to the scrubber tank, a spray water return pipeline connected to the scrubber tank and the aeration tank, a spray pipeline connected to the scrubber tank and the aeration tank for connecting the scrubber tank and the aeration tank, wherein the spray pipeline is attached to the scrubber tank by a dispersing member, a second air pipeline and a discharge pipeline connected to the aeration tank, a first pump member connected to the spray pipeline for transferring a portion of the hydrogen sulfide oxidizing bacteria from the aeration tank to the scrubber tank, and a second pump member connected to the aeration tank and the scrubber tank for supplying oxygen to the hydrogen sulfide oxidizing bacteria. Preferably, the scrubber tank and the aeration tank comprise a fiber- reinforced plastic container.

Preferably, the sphere shaped packing is made of polymer. It is an advantage of the present invention that the method of desulfurization of biogas has an efficiency of up to 98%. The content of contaminants in the biogas treated with the method of the present invention is reducible from a concentration of 8,000 ppm to less than 150 ppm.

It is therefore another advantage of the present invention that the method and system used herein are designed to reduce clogging in the scrubber tank as most of the elemental sulfur in the scrubber tank from the treated biogas is converted into sulphuric acid, sulfurous acid and sulfur by the hydrogen sulfide oxidizing bacteria in the aeration tank.

A proper application of the method and system enables desulfurization of biogas to be more autonomous with little to no intervention from human, thus reducing operational cost and removing needs for chemical dosing.

The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. In the drawings, like numberings represent like elements between the drawings.

BRIEF DESCRIPTION OF THE DRAWING

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Figure 1 is a flow diagram depicting the steps involved in a method for desulfurization of biogas according to the present invention;

Figure 2 is a schematic diagram illustrating a system for desulfurization of biogas according to the present invention; Figure 3 is a diagram depicting cross-sectional view of a scrubber tank according to the present invention; and

Figure 4 is a diagram depicting a cross-sectional view of an aeration tank according to the present invention.

It is noted that the drawing may not be to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention.

DETAILED DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a method of desulfurizing a biogas with an efficiency of up to 98%. The content of contaminants in the biogas treated with the method of the present invention is reducible from a concentration of 8,000 ppm to less than 150 ppm. It also an objective of the present invention, wherein the system and method reduces clogging in the scrubber tank as most of elemental sulfur in the scrubber tank from the treated biogas are converted into sulphuric acid, sulfurous acid, and sulfur by the hydrogen sulfide oxidizing bacteria in the aeration tank. It is yet another objective of the present invention that a proper application of the method and system enables desulfurization of biogas to be more autonomous with little to no intervention from human, thus reducing operational cost and removing needs for chemical dosing.

Accordingly, the present invention provides a method of desulfurizing a biogas having hydrogen sulfide and a system thereof. The present invention provides a method to facilitate removal of hydrogen sulfide, H₂S, from raw biogas via biological approach. The existence of hydrogen sulfide in raw biogas produces corrosive effects to equipment and environment. In order to reduce and eliminate the effect, the removal of hydrogen sulfide, H₂S is therefore essential.

According to an aspect of the present invention, the method can be characterized by the steps of feeding the biogas into a scrubber tank comprising a packing 200, deploying bacteria into the scrubber tank 200 and an aeration tank 300 connected thereto, growing the bacteria in the packing of the scrubber tank 200, injecting an amount of bacteria to the scrubber tank 200 through a dispersing member 206, and feeding oxygen to the scrubber tank 200 and the aeration tank 300.

According to another aspect of the present invention, there is provided a system comprising a scrubber tank 200. The scrubber tank 200 is divided to two layers of containers 200a and 200b, wherein the layer of containers 200a and 200b are separated by a biogas redistributor 200c and a spray water distributor 200d. The layers of containers 200a, 200b contain a sphere shaped packing made of polymer for growing the hydrogen sulfide oxidizing bacteria. The total amount of hydrogen sulfide bacteria provided in the sphere shaped packing is 50% of the total amount of bacteria provided in the system. The scrubber tank 200 is connected to an inlet pipeline 201 , an outlet pipeline 202, a spray water return pipeline 203, a first air pipeline 204b and a spray pipeline 205, wherein the spray pipeline is attached to a dispersing member 206.

Further, the system comprises an aeration tank 300 made of a fiber- reinforced plastic for storing hydrogen sulfide oxidizing bacteria, wherein the total amount of the hydrogen sulfide bacteria is 50% of the total amount of bacteria provided in the system. The aeration tank 300 is connected to a second air pipeline 204 and 204a, the spray water return pipeline 203, the spray pipeline 205, and a discharge pipeline 302, wherein the spray pipeline 205 is attached to the dispersing member 206. The system also includes a first pump member 208a that is connected to the spray pipeline 205, wherein the first pump member 208a act as a means to transfer hydrogen sulfide oxidizing bacteria from the aeration tank 300 to the scrubber tank 200. The system further comprises a second pump member 208b connected to the aeration tank 300 and the scrubber tank 200 for pumping oxygen to the hydrogen sulfide oxidizing bacteria in the scrubber tank 200 and the aeration tank 300.

With reference to Figure 1 , the method 100 begins by preparing the raw biogas containing hydrogen sulfide, H₂S 101 . Raw biogas containing H₂S is produced when a biodegradable material is broken down by anaerobic microorganism in absence of oxygen. The raw biogas can be obtained from several places such as landfills, agriculture production industries, wood waste and waste water from industry and cities. Raw biogas generally comprises several constituents that include methane gas, CH₄, carbon dioxide, CO2, hydrogen sulfide, H2S and hydrogen, H₂. When the raw biogas is prepared, the raw biogas is fed into the scrubber tank 200 through the inlet pipeline 201 that is connected to the scrubber tank 200. In one embodiment, the raw biogas that enters the scrubber tank has a concentration ranging from 7,000 ppm to 9,000 ppm.

The second step 102 is preparing the bacteria inside the scrubber tank 200. More particularly, the bacteria are prepared inside the sphere shaped packing that is placed inside the scrubber tank 200. 50% of total bacteria count provided in the system is placed inside the scrubber tank 200 and another 50% of the total bacteria are placed inside the aeration tank 300. The bacteria are injected into the scrubber tank 200 prior to operation with a preset dosing frequency. A timer and a controller may be installed to the system of the present invention for controlling the dosing frequencies of the H2S oxidizing bacteria. The biological method for desulfurization of H₂S utilizes the bacteria to react with the biogas. There are various kinds of bacteria usable in the system, which can be selected from a group comprising Thiobacillus thiooxidans, Thiobacill utioparus, Thiobasillus ferrooxidans and other bacteria that are capable of oxidizing H₂S.

The next step is to feed the bacteria with oxygen by pumping the oxygen through a pump member 208b to the aeration tank 300 and to the scrubber tank 200 through the second air pipeline 204a and the first air pipeline 204b. The output of the biogas treatment consists of a clean purified biogas that exits the outlet pipeline 202 of the scrubber tank 200. The resulting clean purified biogas with H2S concentration of lower than 150ppm is thus produced when the oxygenized bacteria oxidized the H₂S from the biogas. Figure 2 shows an embodiment of the system of the present invention, whereby in accordance to an embodiment, the system comprises the scrubber tank 200, the aeration tank 300, the inlet pipeline 201 , the outlet pipeline 202, the drainage return pipeline 203, the second air pipeline 204, the spray pipeline 205, the dispensing member 206, an air vent 207, and the pump member 208. The scrubber tank 200 is preferably made of fiber-reinforced plastic (FRP) or Polyethylene (PE) or stainless steel material or other non-reactive material that does not react to the supplied biogas or the bacteria. The aeration tank 300 is also preferably made of fiber-reinforced plastic (FRP) or Polyethylene (PE) or stainless steel material or other non-reactive material that does not react to the supplied biogas, the bacteria, and the by-product of the oxidation of the biogas. In the aeration tank 300, the bio-reaction product of oxidation of the biogas, i.e. elemtnal sulfur and sulfurous acid will be converted into sulphuric acid by the bacteria placed in the aeration tank 300.

The inlet pipeline 201 and the outlet pipeline 202 are preferably connected to the scrubber tank 200. A metal or PE or polyvinyl carbon (PVC) are preferably used as the spray water return pipeline 203, which is also connected to the scrubber tank 200 to return any excess of bacteria to the aeration tank 300.The dispensing member 206 is attached to scrubber tank 200 for dosing a required portion of the H₂S bacteria from the aeration tank 300 to the scrubber tank 200 through a pipeline 205, depending on the amount of H₂S bacteria required in the scrubber tank 200. A controller or timer or any device utilizable to assist in the process may be used, such as a computer or a smartphone device. The air vent 207 is attached to the aeration tank 300 to reduce any pressure or exchange air inside the aeration tank 300. The pump member 208 is coupled to the second air pipe 204 and the spray pipeline 205. The pump member 208 is used to provide oxygen to the bacteria inside the scrubber tank 200 and the aeration tank 300. With reference to Figure 3, another embodiment of the system of the present invention is provided. The scrubber tank 200, which comprises the inlet pipeline 201 connected to the first air pipeline 204b, the outlet pipeline 202, and the dispensing member 206 are shown in Figure 3. The scrubber tank 200 is divided to two layers of containers, which is an upper container 200a and a lower container 200b. In between the containers, a separator or redistributor is placed to separate the layers, wherein the separator or redistributor comprises the biogas redistributor 200c and the spray water redistributor 200d. The advantage of the scrubber tank 200 having two layers of containers include reduction or elimination of any channeling effects. At least one sphere shaped packing is placed in each of the layers of the containers 200a and 200b. The sphere shaped packing is used as a medium to grow the H₂S oxidizing bacteria supplied to the sphere shaped packing in the scrubber tank 200, i.e. 50% of the total H₂S oxidizing bacteria supplied to the system. Figure 4 depicts an embodiment of the aeration tank 300, which comprises a spray water return pipeline 203, the second air pipeline 204, the air vent 207, a spray water outlet pipeline 209, a bacteria separator 301 , the discharge pipeline 302 and an air diffuser 303. The aeration tank 300 may be made of FRP or PE or stainless steel to eliminate any chance of unwanted reaction between the container and the bacteria. The aeration tank 300 is used to store 50% of the total H₂S oxidizing bacteria used in the system of the present invention. A bacteria separator 301 is preferably attached in the aeration tank 300 to ensure only H₂S oxidizing bacteria are transferred to the scrubber tank 200. The bacteria that do not contribute to the system will be kept inside the aeration tank 300 and will be discharged from the system through a discharged pipeline 302 that is attached to the aeration tank 300. An air diffuser 303 is preferably attached to the aeration tank 300 to provide oxygen to the H₂S oxidizing bacteria. The air vent 207 on the other hand is attached to the aeration tank to regulate the air flow and to exchange air inside the aeration tank 300.

The terms "a" and "an," as used herein, are defined as one or more than one. The term "plurality," as used herein, is defined as two or more than two. The term "another," as used herein, is defined as at least a second or more. The terms "including" and/or "having," as used herein, are defined as comprising (i.e., open language).

While this invention has been particularly shown and described with reference to the exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

A method of desulfurizing a biogas having hydrogen sulfide, characterized in that, the method comprising the steps of:

feeding a biogas having a concentration ranging from 7,000 ppm to 9,000 ppm to a scrubber tank (200);

deploying a bacteria into the scrubber tank (200) and an aeration tank (300) connected thereto, wherein the amount of bacteria deployed to the scrubber tank (200) and the aeration tank (300) are equally distributed between each of the scrubber tank (200) and the aeration tank (300);

growing the bacteria in the scrubber tank (200);

supplying a portion of bacteria from the aeration tank (300) to the scrubber tank (200) through a dispersing member; and

feeding oxygen to the scrubber tank (200) and to the aeration tank (300) to allow the bacteria to continuously convert the hydrogen sulfide to elemental sulfur, sulfurous acid, and sulphuric acid.

The method according to Claim 1 , wherein the packing is a sphere shaped packing.

The method according to Claim 1 , wherein the bacteria is selected from a group comprising a hydrogen sulfide oxidizing bacteria.

A system for desulfurizing biogas having hydrogen sulfide, characterized in that, the system comprising:

a scrubber tank (200) comprises two layers of containers (200a and 200b), wherein the two layers of containers (200a and 200b) are separated by a biogas redistributor (200c) and a spray water distributor (200d);

a sphere shaped packing positioned in each of the containers (200a and 200b) for growing a hydrogen sulfide oxidizing bacteria;

an aeration tank (300) for storing a hydrogen sulfide oxidizing bacteria; an inlet pipeline (201 ) and an outlet pipeline (202) connected to the scrubber tank (200);

a first air pipeline (204b) connected to the scrubber tank (200); a spray water return pipeline (203) connected to the scrubber tank (200) and the aeration tank (300);

a spray pipeline (205) connected to the scrubber tank (200) and the aeration tank (300) for connecting the scrubber tank (200) and the aeration tank (300), wherein the spray pipeline (205) is attached to the scrubber tank (200) by a dispersing member (206);

a second air pipeline (204 and 204a) and a discharge pipeline (302) connected to the aeration tank (300) ;

a first pump member (208a) connected to the spray pipeline (205) for transferring a portion of the hydrogen sulfide oxidizing bacteria from the aeration tank (300) to the scrubber tank (200); and

a second pump member (208b) connected to the aeration tank (300) and the scrubber tank (200) for supplying oxygen to the hydrogen sulfide oxidizing bacteria.

The system according to Claim 4, wherein the scrubber tank (200) and the aeration tank (300) comprises a fiber-reinforced plastic container.

The system according to Claim 4, wherein the sphere shaped packing is made of polymer.