Description:
FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[See section 10, Rule 13]

Title of invention:
A SYSTEM FOR MIXING SLUDGE AND GAS IN A BIODIGESTER

APPLICANT
NUTZEN ENGINEERING SOLUTIONS.

An Indian entity having address:

404, HORIZON WESTONE, VEERBHADRA NAGAR, BANER,
PUNE - 411045, MAHARASHTRA, INDIA.

The following specification describes the invention and the manner in which it is to be performed.

FIELD OF INVENTION
The present invention, in general, relates to a biodigester, and more particularly, relates to a system for mixing sludge and biogas in a biodigester.
BACKGROUND OF THE INVENTION
In nature, organic materials are decomposed biologically by various species of bacteria. Few bacteria live and work in almost any environment, while others are extremely sensitive. Some of them use any type of organic material as food, while others are very selective. Bacteria consume the organic material as food, digest it and convert it into end products consisting of liquids, gases and stabilized solids. Bacterial decomposition can occur with or without air (oxygen). The bacteria that need oxygen are called aerobic bacteria and those live without oxygen are called anaerobic bacteria or anaerobes. Some bacteria can live under either condition are called facultative bacteria. Any treatment system will give desired level of performance only when properly operated in the right environment. The anaerobic digestion process has been used for many years because of its low operating costs, proven effectiveness on high strength wastewater, and production of a combustible biogas, a useful by-product. This biogas has been used as fuel for boilers, gas engines, and power generation and even for domestic purposes. The stabilization of organic wastes by anaerobic digestion must always result in the production of methane gas, which is insoluble in water. Thus, if no methane gas is produced, there can be no waste stabilization. Anaerobic digestion is considered as a three-stage process and shows how organic material as food is changed in two stages by acid forming bacteria to simple organic material, chiefly organic acids. The methane forming bacteria then use these acids as food and produce methane and carbon dioxide gas. No waste stabilization occurs in the first two stages. Real stabilization occurs only in the third stage. One of the major considerations is the type of food available to the acid-forming bacteria. Food may be in two forms, soluble and insoluble. The soluble form can be readily digested (like glucose in water). Insoluble forms, such as fats or complex solids, are more difficult to digest. They are first broken down into a soluble form. This is accomplished in part by enzymes produced by the bacteria. The bacteria can directly use only soluble solids as food since it must be in this form to pass through the cell wall and the membrane.
The cell wall acts as a sieve to screen out the large particles, while the membrane selects and guides material both in and out of the inner cell. Neither all of the organic solids are completely broken down nor does the entire material pass into the cell. The portion of wastewater, which is not degradable, is called inert fraction (not food for bacteria). The bacteria use food for energy and produce organic acid also called volatile acids or fatty acids. The production of these acids completes the first stage of the digestion process and is commonly known as the acid phase. In a normal or healthy digester, the second group consume at the same rate at which acids are produced in the first phase. If the acid phase were the only step occurring in digestion, the process would be incomplete resulting in a continuing drop in pH caused by an overproduction of acids. This does occur for a period of time when the biodigester is first started or when the biodigester has lost a large amount of its methane formers. Digestion can only be completed when the second phase is occurring simultaneously with the acid phase. The second phase in anaerobic digestion occurs because of another bacterial group called the methane formers, which use the volatile acid produced by the acid formers as food. The acids are then converted to methane (CH4) and carbon dioxide (CO2) gases as major end products. This step completes the work of the two principle forms of bacteria and result in stabilizing 80 to 90% of the organic matter in wastewater, (measured as BOD). The methane formers, which are responsible for waste stabilization, grow quite slowly as compared to the acid formers since they get very little energy from their food. This causes the methane formers to be very sensitive to slight changes in loading, pH and temperature. Since the methane formers are obligate anaerobes, they are extremely sensitive to air (Oxygen). The acid formers have a deciding edge over the methane formers since they are rapid growers and are not as sensitive to environmental changes as methane formers. Thus, the operation of anaerobic biodigester depends largely upon keeping methane formers happy. The objective of good biodigester operation is to control food supply, temperature, pH and thus keeping the acid and the methane formers in balance. Waste stabilization cannot occur unless the bacteria are brought in contact with the food.
Thus, there exists a need to expose the bacteria to the maximum amount of food and to distribute the generated or added alkalinity throughout the biodigester. The benefit of mixing speeds up the process of sludge decomposition and increases the amount of biogas production. Further, there is a need of a system for mixing sludge and biogas in a biodigester that can alleviate the problems associated with the existing the biodigester.
SUMMARY OF THE INVENTION
This summary is provided to introduce the concepts related to a system for mixing sludge and biogas in a biodigester, the concepts are further described in the detailed description. This summary is not intended to identify essential features of the claimed subject matter, nor it is intended to use in determining or limiting the scope of the present subject matter.
In one embodiment a system for mixing sludge and biogas in a biodigester is disclosed. The system for mixing sludge and biogas in a biodigester comprising a biodigester tank, a set of mechanical agitators, a sludge recirculating pump, an ejector, and a mixer. The biodigester tank is closed from top by a biogas dome. The set of mechanical agitators are coupled with the biodigester tank. Further, each mechanical agitator from the set of mechanical agitators is configured to agitate sludge stored in the biodigester tank. The sludge recirculating pump is configured to receive sludge from bottom of the biodigester tank and pump a first stream of sludge into the ejector. The ejector is configured to receive the first stream of sludge and biogas from upper portion of the biodigester tank through an inlet pipe and mix the first stream of sludge and biogas to form a sludge-biogas Mixture. The mixer is configured to receive the sludge-biogas mixture. The mixer is held towards the center of the biodigester tank. The mixer is submerged into the sludge stored in the biodigester tank. The mixer comprises a central vertical pipe and a set of vertical branched pipes emerging out from the central vertical pipe. A series of elbow nozzles are attached to each of the set of vertical branched pipes. Each elbow nozzle from the series of elbow nozzles associated with a vertical branched pipe face different direction.
BRIEF DESCRIPTION OF DRAWINGS
The detailed description is described with reference to the accompanying figures. The same numbers are used throughout the drawings to refer like features and components.
Figure 1 illustrates side view of a system for mixing sludge and biogas in a biodigester, in accordance with an embodiment of the present subject matter;
Figures 2 illustrates top view of a system for mixing sludge and biogas in a biodigester, in accordance with an embodiment of the present subject matter;
Figures 3 illustrates a mechanical agitator, in accordance with an embodiment of the present subject matter;
Figures 4 illustrates top view of an ejector, in accordance with an embodiment of the present subject matter;
Figures 5 illustrates front view of the ejector, in accordance with an embodiment of the present subject matter;
Figures 6 illustrates side view of the ejector, in accordance with an embodiment of the present subject matter;
Figures 7 illustrates front view of a mixer, in accordance with an embodiment of the present subject matter;
Figures 8 illustrates top view of the mixer, in accordance with an embodiment of the present subject matter; and
Figures 9 illustrates isometric view of the mixer, in accordance with an embodiment of the present subject matter.
DETAILED DESCRIPTION OF THE INVENTION
Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment” in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. Following is an example which is illustrative only and invention accommodates any and every variation of the example provided below that shall serve the same purpose and is obvious to a person skilled in the art.
The present subject matter relates to a system for mixing sludge and biogas in a biodigester is disclosed. The system for mixing sludge and biogas in a biodigester comprising a biodigester tank, a set of mechanical agitators, a sludge recirculating pump, an ejector, and a mixer.
Figure 1 and 2 illustrates side view and top view of a system for mixing sludge and biogas in a biodigester, in accordance with an embodiment of the present subject matter. The system (100) may comprise a biodigester tank (102), a set of mechanical agitators (104a, 104b, 104c, 104d), a sludge recirculating pump (110), an ejector (106), and a mixer (112). The biodigester tank (102) may be closed from top by a biogas dome (104). The biodigester tank (102) may be made of any suitable material including but not limited to glass, ceramic, specialty thermoplastic, thermoset plastic, high chemical and heat resistant elastomer, nickel-molybdenum alloy, mild steel, stainless steel, reinforced concrete cement etc. The set of mechanical agitators (104a, 104b, 104c, 104d) may be coupled with the biodigester tank (102). Each mechanical agitator from the set of mechanical agitators (104a, 104b, 104c, 104d) may be configured to agitate sludge (118) stored in the biodigester tank (102). The sludge recirculating pump (110) configured to receive sludge (118) from bottom of the biodigester tank (102) and pump a first stream of sludge into an ejector (106). The ejector (106) may be configured to receive the first stream of sludge and biogas from upper portion of the biodigester tank (102) through an inlet pipe (116) and mix the first stream of sludge and biogas to form a sludge-biogas mixture. The mixer (112) may be configured to receive the sludge-biogas Mixture. The mixer (112) may be held towards the center of the biodigester tank (102). The mixer (112) may be submerged into the sludge (118) stored in the biodigester tank (102). The mixer (112) may comprise a central vertical pipe (112a) and a set of vertical branched pipes (112b) emerging out from the central vertical pipe (112a). A series of elbow nozzles (112c) may be attached to each of the set of vertical branched pipes (112b). Each elbow nozzle from the series of elbow nozzles (112c) may be associated with a vertical branched pipe (112b), face different directions. The system (100) further comprises may a sludge heat exchanger (108) and a foam breaker (114). The sludge recirculating pump (110) may be configured to receive sludge (118) from bottom of the biodigester tank (102) a second stream of sludge into the foam breaker nozzle (114). The foam braker nozzle (114) may be configured to eject the sludge on foam formed on top of the sludge stored in the biodigester tank (102) thereby breaking the foam.
In one embodiment, the set of vertical branched pipes (112b) and the set of mechanical agitators (104a, 104b, 104c, 104d) are aligned in such a way that the mixing inside the digester tank (102) is in the same pattern in clockwise direction. The mixer (112) may be installed at center with connecting each vertical branched pipe of the set of vertical branched pipes (112b) at 1200 and the set of mechanical agitators (104a, 104b, 104c, 104d) are placed at 900 , 1800 , 2700 , 3600 respectively.
In another embodiment, method for mixing sludge and gas in a biodigester is disclosed. The method comprises various steps.
In first step, sludge may be received in a biodigester tank (102). The biodigester tank (102) is closed from top by a biogas dome (104);
In second step, the sludge may be mixed using a set of mechanical agitators (104a, 104b, 104c, 104d). The set of mechanical agitators (104a, 104b, 104c, 104d) may be coupled with the biodigester tank (102). Each mechanical agitator from the set of mechanical agitators (104a, 104b, 104c, 104d) may be configured to agitate sludge (118) stored in the biodigester tank (102).
In third step the sludge may be pumped by a sludge recirculating pump (110). The sludge recirculating pump (110) configured to receive sludge (118) from bottom of the biodigester tank (102) and pump a first stream of sludge into an ejector (106). The ejector (106) may be configured to receive the first stream of sludge and biogas from upper portion of the biodigester tank (102) through an inlet pipe (116) and mix the first stream of sludge and biogas to form a sludge-biogas Mixture.
In fourth step the mixture of sludge- biogas may be received at a mixer (112) The mixer (112) configured to receive the sludge-biogas Mixture. The mixer (112) may be held towards the center of the biodigester tank (102). The mixer (112) is submerged into the sludge stored in the biodigester tank (102). The mixer (112) may comprise a central vertical pipe (112a) and a set of vertical branched pipes (112b) emerging out from the central vertical pipe (112a). A series of elbow nozzles (112c) may be attached to each of the set of vertical branched pipes (112b). Each elbow nozzle from the series of elbow nozzles (112c) may be associated with a vertical branched pipe (112b), face different directions.
In last step, the sludge-biogas mixture may be sprayed through the series of elbow nozzles (112c), in the biodigester tank (102).
Figures 3 illustrates a mechanical agitator, in accordance with an embodiment of the present subject matter. The system (100) may comprise a biodigester tank (102), a set of mechanical agitators (104a, 104b, 104c, 104d), a sludge recirculating pump (110), an ejector (106), and a mixer (112). The mechanical agitator of the set of mechanical agitators (104a, 104b, 104c, 104d) may comprises a motor (202), a gearbox (204), a shaft (206), and an impeller (208). The mechanical agitator of the set of mechanical agitators (104a, 104b, 104c, 104d) may be configured to mix various process media together. The media include all liquid types, gases & sludge solids. The mechanical agitator may work by rotating the impeller (208) to impart energy to the media which interact and mix. The mechanical agitator may be used for mixing different process media – liquids, gases and solids. The mechanical agitator imparts energy through mechanical mean by rotating the shaft (206) on which there may be the impeller (208) designed specifically for the duty. This could be axial pumping, gas induction, flocculating, high viscosity products, high & low shear mixing etc. The gearbox (204) may be coupled with the motor (202) with various speed ratios. The set of mechanical agitators (104a, 104b, 104c, 104d) are coupled with the biodigester tank (102). Each mechanical agitator from the set of mechanical agitators (104a, 104b, 104c, 104d) may be configured to agitate sludge (118) stored in the biodigester tank (102). The shaft (206) may be connected to the drive unit (motor (202) & gearbox (204)) and where the impeller (208) may be used for the mixing are welded or bolted onto. The set of mechanical agitators (104a, 104b, 104c, 104d) may be magnetic driven where there is a hermetic seal as opposed to mechanical. Mixing of sludge is the most important part of the process, without which the entire process of obtaining biogas would not commence. In fermentation processes, agitation is crucial for mixing and shearing. It not only facilitates mass, but it also ensures that the medium maintains homogeneous chemical, physical & microbial conditions. The set of mechanical agitators (104a, 104b, 104c, 104d) play very important role for a proper functioning of the biodigester.
Figures 4, 5 and 6 illustrates top, front and side view of an ejector, in accordance with an embodiment of the present subject matter. The system (100) may comprise a biodigester tank (102), a set of mechanical agitators (104a, 104b, 104c, 104d), a sludge recirculating pump (110), an ejector (106), and a mixer (112). The sludge recirculating pump (110) configured to receive sludge (118) from bottom of the biodigester tank (102) and pump a first stream of sludge into an ejector (106). The ejector (106) may be configured to receive the first stream of sludge and biogas from upper portion of the biodigester tank (102) through an inlet pipe (116) and mix the first stream of sludge and biogas to form a sludge-biogas Mixture. The ejector (106) may comprise a sludge input port (106b), a biogas input port (106a), and a sludge-biogas mixture output port (106c). The sludge input port (106b) may be configured to receive sludge (118) from bottom of the biodigester tank (102) by the sludge recirculating pump (110). The biogas input port (106a) may be configured to receive the biogas from upper portion of the biodigester tank (102) through an inlet pipe (116). The sludge-biogas mixture output port (106c) may be configured to send the sludge-biogas mixture to the mixer (112). The ejector (106) may comprise a nozzle shape geometry (106d) such that the biogas is sucked from the upper portion of the biodigester tank (102) through the biogas input port (106a). The ejector (106) may work by accelerating a high-pressure first stream (the ‘motive’) of the sludge (118) through a nozzle, converting the pressure energy into velocity. Around the nozzle tip, where velocity is highest, a low-pressure region is created. This results into a suction chamber of the ejector (106), where the pressure in this region is lower than the pressure of the suction fluid connected to the biogas input port (106a) or ejector side-inlet or ‘suction branch”. The two fluid streams namely the biogas and the sludge (118) then travel through the diffuser section of the ejector (106), where velocity is decreased as a result of the diverging geometry and pressure is regained. Importantly, the low-pressure suction stream experiences a pressure increase/compression, whilst the motive stream sees a decrease in pressure, as some of its energy has been used to ‘do work’ on the suction stream. The resultant discharge pressure is therefore somewhere between the motive and suction pressures, ejectors (106) are pipeline mounted devices and can be manufactured in almost any material to suit the process conditions, it has 3 connections: Motive (the sludge input port (106b)), Suction (the biogas input port (106a)) and Discharge (sludge-biogas mixture output port (106c)). The Ejectors are simple, static devices that use the energy within a high-pressure motive fluid (Gas or Liquid) to entrain and compress a low-pressure suction fluid to an intermediate discharge pressure.
Figures 7, 8 and 9 illustrates front, top and isometric view of a mixer, in accordance with an embodiment of the present subject matter. The system (100) may comprise a biodigester tank (102), a set of mechanical agitators (104a, 104b, 104c, 104d), a sludge recirculating pump (110), an ejector (106), and a mixer (112). The mixer (112) may be configured to receive the sludge-biogas Mixture. The mixer (112) may be held towards the center of the biodigester tank (102). The mixer (112) may be submerged into the sludge stored in the biodigester tank (102). The mixer (112) may comprise a central vertical pipe (112a) and a set of vertical branched pipes (112b) emerging out from the central vertical pipe (112a). A series of elbow nozzles (112c) may be attached to each of the set of vertical branched pipes (112b). Each elbow nozzle from the series of elbow nozzles (112c) may be associated with a vertical branched pipe (112b), face different directions.
In one embodiment, the mixing flowrate of the sludge using the set of mechanical agitators (104a, 104b, 104c, 104d) and the mixer (112) is less than 60 minute to ensure the liquid / sludge homogenization in the biodigester (10).
The system for mixing sludge and biogas in a biodigester of the present subject matter has, but are not limited to, following benefits/advantages:
• To avoid and destroy swimming and sinking layers of the sludge;
• To improve the activity of bacteria through release of biogas and provision of fresh nutrients;
• To mix fresh and fermenting substrate in order to inoculate the former;
• To arrive at an even distribution of temperature thus providing uniform conditions inside the biodigester;
• To breakdown the organic material;
• To homogenize mixing of bacteria and sludge;
• Ejector based continuous stirred biodigester; and
• Improved efficiency of biogas production.
, Claims:WE CLAIM:
1. A system (100) for mixing sludge and biogas in a biodigester (10), the system (100) comprising:
a biodigester tank (102), wherein the biodigester tank (102) is closed from top by a biogas dome (104);
a set of mechanical agitators (104a, 104b, 104c, 104d), wherein the set of mechanical agitators (104a, 104b, 104c, 104d) are coupled with the biodigester tank (102), wherein each mechanical agitator from the set of mechanical agitators (104a, 104b, 104c, 104d) is configured to agitate sludge (118) stored in the biodigester tank (102);
a sludge recirculating pump (110) configured to receive sludge (118) from bottom of the biodigester tank (102) and pump a first stream of sludge into an ejector (106), wherein the ejector (106) is configured to receive the first stream of sludge and biogas from upper portion of the biodigester tank (102) through an inlet pipe (116), and mix the first stream of sludge and biogas to form a sludge-biogas Mixture; and
a mixer (112) configured to receive the sludge-biogas Mixture, wherein the mixer (112) is held towards the centre of the biodigester tank (102), wherein the mixer (112) is submerged into the sludge stored in the biodigester tank (102), wherein the mixer (112) comprises a central vertical pipe (112a) and a set of vertical branched pipes (112b) emerging out from the central vertical pipe (112a), wherein a series of elbow nozzles (112c) are attached to each of the set of vertical branched pipes (112b), wherein each elbow nozzle from the series of elbow nozzles (112c), associated with a vertical branched pipe (112b), face different direction.
2. The system (100) as claimed in claim 1, wherein the system (100) further comprises a sludge heat exchanger (108) and a foam breaker (114).
3. The system (100) as claimed in claim 1, wherein the sludge recirculating pump (110) is configured to receive sludge (118) from bottom of the biodigester tank (102) and pump a second stream of sludge into the foam breaker nozzle (114), wherein the foam braker nozzle (114) is configured to eject the second stream of sludge on foam formed at the top of the sludge stored in the biodigester tank (102) thereby breaking the foam.
4. The system (100) as claimed in claim 1, wherein each mechanical agitator, from the set of mechanical agitators (104a, 104b, 104c, 104d), comprises a motor (202), a gearbox (204), a shaft (206), and an impeller (208).
5. The system (100) as claimed in claim 1, wherein the ejector (106) comprising a sludge input port (106b), a biogas input port (106a), and a sludge-biogas Mixture output port (106c).
6. The system (100) as claimed in claim 1, wherein the ejector (106) comprising a nozzle shape geometry (106d) at the intersection of the biogas input port (106a) and sludge input port (106b), such that the biogas is sucked from the upper portion of the biodigester tank (102) through the biogas input port (106a), wherein the ejector (106) is configured to mix the biogas and the sludge.
7. The system (100) as claimed in claim 1, wherein the set of vertical branched pipes (112b) and the set of mechanical agitators (104a, 104b, 104c, 104d) are aligned to enable the mixing inside the digester tank (102) in the same pattern in clockwise direction.
8. A method for mixing sludge and gas in a biodigester, the method comprising steps of:
receiving sludge in a biodigester tank (102), wherein the biodigester tank (102) is closed from top by a biogas dome (104);
mixing the sludge using a set of mechanical agitators (104a, 104b, 104c, 104d), wherein the set of mechanical agitators (104a, 104b, 104c, 104d) are coupled with the biodigester tank (102), wherein each mechanical agitator from the set of mechanical agitators (104a, 104b, 104c, 104d) is configured to agitate sludge (118) stored in the biodigester tank (102);
pumping the sludge by a sludge recirculating pump (110), wherein the sludge recirculating pump (110) configured to receive sludge (118) from bottom of the biodigester tank (102) and pump a first stream of sludge into an ejector (106), wherein the ejector (106) is configured to receive the first stream of sludge and biogas from upper portion of the biodigester tank (102) through an inlet pipe (116), and mix the first stream of sludge and biogas to form a sludge-biogas Mixture; and
receiving the mixture of sludge- biogas mixture at a mixer (112) wherein the mixer (112) configured to receive the sludge-biogas Mixture, wherein the mixer (112) is held towards the centre of the biodigester tank (102), wherein the mixer (112) is submerged into the sludge stored in the biodigester tank (102), wherein the mixer (112) comprises a central vertical pipe (112a) and a set of vertical branched pipes (112b) emerging out from the central vertical pipe (112a), wherein a series of elbow nozzles (112c) are attached to each of the set of vertical branched pipes (112b), wherein each elbow nozzle from the series of elbow nozzles (112c), associated with a vertical branched pipe (112b), face different direction.
spraying the sludge-biogas mixture through the series of elbow nozzles (112c), in the biodigester tank (102).
9. The method as claimed in claim 8, wherein the mixing flowrate of the sludge using the set of mechanical agitators (104a, 104b, 104c, 104d) and the mixer (112) is less than 60 minute to ensure the liquid / sludge homogenisation in the biodigester (10).

Dated 13th Day of May 2022

Priyank Gupta
Agent for the Applicant
IN/PA-1454