WO2018012968A1

WO2018012968A1 - Installation and process for anaerobic digestion of organic material

Info

Publication number: WO2018012968A1
Application number: PCT/NL2017/050463
Authority: WO
Inventors: Douglas KALKWARF
Original assignee: Seatechenergy Ip BV
Current assignee: Seatechenergy Ip BV
Priority date: 2016-07-15
Filing date: 2017-07-11
Publication date: 2018-01-18
Anticipated expiration: 2019-01-15
Also published as: NL2017177B1

Abstract

The invention relates to an installation for anaerobic digestion of organic material. The installation comprises at least a first hydrolysis reactor and a second anaerobic reactor. Each reactor comprises an inlet for introducing material to be processed inside the reactor, an outlet for removing processed materials from the reactor, at least a gas outlet located close to the top of the reactor and a gas line. The first hydrolysis reactor further comprises at least a gas inlet located close to the bottom of the reactor, wherein the gas lines connect the gas outlets of the reactors with the gas inlet of the first hydrolysis reactor.

Description

Title: Installation and process for anaerobic digestion of organic material

Description The invention relates to an installation for anaerobic digestion of organic material, comprising at least a first anaerobic reactor and a second anaerobic reactor, wherein each reactor comprises an inlet for introducing material to be processed inside the reactor, an outlet for removing processed materials from the reactor, and at least a gas outlet located close to the top of the reactor.

Such an installation is known from WO2015/037989. This installation comprises at least two reactors. Each reactor is equipped with a mixing unit, a liquid/sludge inlet, a liquid/sludge outlet, a solid outlet at the bottom, a gas outlet, connected to gas lines, a pH and/or redox meter, and liquid/sludge lines feeding and discharging the sludge to and from the reactors. The mixing unit comprises a rotatable mixing device inside each reactor. Gas issuing from gas outlets of the various reactors is carried off through lines, and after being combined, passes through a flow meter, which may also contain a unit for assaying the gas composition, and is fed to a biogas collecting unit.

A drawback of the known installation is that the volume of biogas with a relatively high methane content that can be produced with the installation is relatively low.

WO201 1/017420 discloses a multi-phase, gas-lift bioreactor device for digestion and production of biogas or biofuel from organic material. The known bioreactor device comprises reactors, wherein each reactor has a foam chamber for digesting foam. The foam partially goes to a foam separator where half of gas with foam of the bioreactor goes back to the same bioreactor via lower Tesla turbine and the other half goes through an upper Tesla turbine to the gas manipulator.

It is an object of the present invention to improve the installation such that higher volumes of biogas with increased ratios of methane can be obtained.

This object is achieved with the installation as defined in claim 1.

An anaerobic digestion installation is a installation for controlling processes by which microorganisms break down biodegradable material in the absence of oxygen. The anaerobic digestion process starts with bacterial hydrolysis of the feedstock in the first hydrolysis reactor. The feedstock can be biodegradable waste materials, or purpose-grown energy crops, such as maize or seaweed. The anaerobic process produces a biogas which can be used directly as fuel, in combined heat and power gas engines or upgraded to natural gas-quality biomethane. The nutrient-rich digestate also produced can be used as fertilizer. The anaerobic digestion installation according to the invention comprises a first hydrolysis reactor and a second anaerobic reactor. The second reactor can be configured for a second hydrolysis step and/or at least one of the other processes of anaerobic digestion: acidogenesis, acetogenosis or methanogenesis. Each reactor of the installation comprises an inlet for introducing material to be processed inside the reactor, an outlet for removing processed materials from the reactor, at least a gas outlet located close to the top of the reactor and a gas line. In the installation, the first hydrolysis reactor further comprises at least a gas inlet located close to the bottom of the reactor, wherein the gas lines connect the gas outlets of the reactors with the gas inlet of the first hydrolysis reactor. These gas lines connecting the gas outlets with the gas inlet of the first hydrolysis reactor make it possible to select the gas from any reactor, i.e. the first hydrolysis reactor and/or the second anaerobic reactor, to be used to bubble through the first hydrolysis reactor via the gas inlet. Further, it is also possible to directly reintroduce at least a portion of the produced gas in the first hydrolysis reactor or in the second anaerobic reactor via the gas inlet near the bottom of the first hydrolysis reactor without mixing the gas with gas from any other reactor. The gas produced in the first hydrolysis reactor and/or the second anaerobic reactor can be used to produce the most optimal gas composition to bubble through the content of the reactor. Recirculation of the gas in the reactor further allows the contents of the reactor tank to absorb more of the gas that is being bubbled through the reactor tank. It has been found out that the gas bubbling through the content promotes the bacteria processes of transforming the particulate organic substrate into liquefied monomers and polymers i.e. proteins, carbohydrates and fats are transformed to amino acids, monosaccharides and fatty acids respectively. These effects increase the efficiency of the reactor and increase the quality of the end- product, such that higher volumes of biogas with increased ratios of methane can be obtained. The gas released by the gas inlet close to the bottom of the reactor also provides stirring and mixing of the content of the reactor. Hence, it is not necessary to provide separate mixing devices inside the reactor(s) for stirring and mixing. In an aspect of the installation, all the anaerobic reactors of the installation are identical such that each reactor comprises at least a gas inlet located close to the bottom of the reactor, wherein each gas line connects the gas outlet of a reactor with the gas inlet of the same reactor and/or with the gas inlet of another reactor. In this way the above described advantages of the gas reintroduction are applicable for all anaerobic reactors of the installation.

A reactor has at least a bottom portion, a top portion and an intermediate portion between the bottom portion and the top portion. A gas inlet of this reactor is located closer to the bottom of the reactor than to the top of the reactor. The bottom portion may have an inverted pyramid shape which ensures settling of the solid material in the reactor and facilitates collecting of the solid at the lowest part of a reactor for sampling and/or discharging the solid material. The top portion can be dome-shaped which facilitates the gas flow to the top of the dome-shaped top portion, wherein it is advantageous to locate the gas outlet in the top of the dome- shaped top portion. The intermediate portion may have a truncated inverted pyramid shape. Without being bound by theory, it has been surprisingly found that, above the gas inlet, walls of the intermediate portion with an acute angle to the vertical provide a more uniform gas stirring/mixing of the reactor's content than walls extending parallel to the vertical. Instead of the (virtual) vertical it is also possible to use the (virtual) centre line of the reactor to define the acute angle of the walls of the intermediate portion. In a preferred reactor each wall of the bottom portion may define an acute angle a1 with the vertical for collecting the solid efficiently and each wall of the intermediate portion defines an acute angle a2 with the vertical, wherein the angle a1 is different than the angle a2, preferably the angle a1 is larger than the angle a2. The walls of the intermediate portion having the sharp angle a2 with the vertical larger than 0 degrees and smaller than 60 degrees provide uniform stirring/mixing of the reactor's content with the gas from the gas inlet. The angle a2 larger than 15 degrees and smaller than 55 degrees provides even a more uniform stirring/mixing effect, and the best results have been achieved with the angle a2 being larger than 35 and smaller than 50 degrees. The angle a1 is smaller than 75 degrees, preferably smaller than 65 degrees. Such an angle a1 of the walls of the bottom portion provide a relatively large volume for the solid settling in the reactor.

In another aspect, the installation comprises at least four anaerobic reactors, and each reactor is configured for one of the four processes of anaerobic digestion. The anaerobic digestion process is then carried out in a series of at least four reactors, allowing the partial processes of the anaerobic digestion (hydrolysis, acidogenesis, acetogenesis and methanogenesis) to be performed in separate reactors to separate these processes physically from each other such that hydrolysis, acidogenesis, acetogenesis and methanogenesis can be performed under more optimum conditions. In such an installation the outlet of the first hydrolysis reactor is connected to an inlet of an acidogenesis reactor, and/or the outlet of the acidogenesis reactor is connected to an inlet of an acetogenesis reactor and/or the outlet of the acetogenesis reactor is connected to an inlet of a methanogenis reactor.

The acidogenesis reactor, the acetogenesis reactor and/or the methanogenis reactor may comprise a contact area enhancement structure inside the reactor, wherein the contact area enhancement structure provides increased bacterial exposure to reactor content in use. The contact area enhancement structure can be made from a porous material, wherein bacteria are retained in the small pores of this material.

The invention further relates to a system for processing organic material, wherein the system comprises an installation as described in this document and at least an aerobic reactor. There are some applications where it is desired to aerobically digest organic material and this can be achieved by using fresh air to bubble and stir and allow the gas produced within the reactors to escape. The combination of anaerobic and aerobic digestion may provide an odour reduction of the waste. In the system the first stages (the installation) are anaerobic and at least on or some of the last stages may be aerobic under certain circumstances. The at least one aerobic reactor has an inlet for introducing material to be processed inside the reactor, an outlet for removing processed materials from the reactor, and at least a gas inlet for introducing oxygen containing gas to the material processed inside the reactor. The at least one aerobic reactor may have an identical design as the anaerobic reactors.

The invention also relates to a process for anaerobic digestion of organic material by using an installation comprising at least a first hydrolysis reactor and a second anaerobic reactor, wherein each reactor comprises an inlet for introducing material to be processed inside the reactor, an outlet for removing processed materials from the reactor, and at least a gas outlet located close to the top of the reactor, wherein at least the first hydrolysis reactor further comprises at least a gas inlet located close to the bottom of the reactor, wherein at least a portion of the gas collected from the gas outlet or gas outlets is reintroduced through the gas inlet of the first hydrolysis reactor.

The gas reintroduction enhances the bacteria process inside the hydrolysis reactor and provides stirring/mixing of the reactor content. Gas reintroduction can be applied in each reactor used in the process for anaerobic digestion of organic material.

The performance of each reactor is analysed by computer analysis and control, wherein dependent of the analysis, the conditions such as the composition of the gas to be reintroduced in at least one of the reactors, the gas flow rate for gas flowing from the gas inlet, the temperature, the pressure and/or the pH can be adapted in each reactor independently and/or the bacteria in the reactor can be enhanced by seeding.

The bacteria in each reactor may be different and the processes performed by the bacteria in a reactor are physically separated from the bacteria in another reactor. The installation used for the process may comprise at least four reactors in series, wherein in the first hydrolysis reactor hydrolysis takes place by means of bacteria for hydrolysis, and/or in the second reactor acidogenesis takes place by means of bacteria for acidogenesis, and/or in a third reactor acetogenosis takes place by means of bacteria for acetogenosis and/or in a fourth reactor methanogenesis takes place by means of bacteria for methanogenesis. The process is a continuous digestion process. In a continuous digestion processes or in a installation for continuous anaerobic digestion, organic matter is constantly added or added in stages to the reactor. In this continuous process or in this continuous installation the end products are constantly or periodically removed, resulting in constant production of biogas.

In addition, the invention relates to a method for processing organic material by using the installation described herein and by using a system with at least one aerobic reactor.

The invention will now be explained in more detail with reference to the drawings and by means of a description of an exemplary embodiment of an installation for continuous anaerobic digestion, wherein: Figure 1 shows a schematic view of an installation for anaerobic digestion of organic material;

Figure 2 shows a perspective view of an alternative embodiment of an reactor which can be used in the installation as shown in figure 1 .

In the following description identical or corresponding parts have identical or corresponding reference numerals.

The anaerobic digestion installation shown in figure 1 enables to enhance the processes of anaerobic digestion to produce higher volumes of biogas with increased ratios of methane. This is achieved in the installation by segmenting the processes of anaerobic digestion. The four main processes are hydrolysis, acidogenysis, acetogenysis and methanogenysis. In the installation as shown in figure 1 it is possible to keep these main processes physically separated and that the feedstock only moves on to the next process in a next reactor once it has been correctly prepared in the reactor.

The installation as shown in figure 1 comprises:

a rinsing section 3

a shredding section 5

a pre-treatment section 7

a reactor section 9

· a biogas section 1 1

an effluent section 13

Depending on the feedstock, it might be necessary to rinse before subjecting the feedstock to mechanical or biological processes. Rinsing will be achieved in the rinsing section 3 by putting the feedstock 14 onto a conveyor belt 15 which passes between over and under shower units 17, 19. The shower units are supplied for example with fresh water 18 or recirculated water from the water recirculation unit 20. The conveyor belt 15 is manufactured in such a way that the under spray of the under shower unit 19 can pass through the conveyor belt 15 to spray the feedstock located on the conveyor belt 15. The feedstock will be dynamically analysed and a computer system (not shown) will control the volume and time of the sprays in order to ensure that the feedstock is in the correct state before passing to the next section, which in the embodiment shown in figure 1 is the shredding section 5. The shredding section 5 comprises a set of rotating blades 21 that will shred the feedstock. By means of the shredding unit 23 it is possible to ensure that the materials to be processed do not exceed the desired maximum size for a feedstock for a hydrolysis reactor B1 . After rinsing and/or shredding, the material moves to the pre-treatment section 7 which may comprise a chopper pump 25, a microniser 27, an electrolysis unit 29 and/or a heating device 31. When the feedstock has been shredded it will be sucked into the chopper pump 25 where all the pieces will be chopped into similar sizes. At this stage, a computer analysis will determine the additional processes (micronisation and/or electrolysis) to be taken if any. If more micronisation and/or electrolysis is required then the feedstock can also be recirculated through loop 34 until all the processes have been completed. Once there are no further pre- treatment processes required, the feedstock will be pumped by pump 32 and collected into a pre-treatment tank (not shown) and heated by the heating device 31 to the desired temperature under computer control in preparation for input via a feed line into the hydrolysis reactor B1 .

The reactor section 9 comprise twelve identical reactors or tanks B1 , B2, B12. Three of these reactors B1 , B2, B12 have only been shown in figure 1 . The reactors are anaerobic reactors and have a standard shape, i.e. these tanks B1 , B2, B12 can be partly cylindrical. Each reactor has a feedstock sample port 41 a, 41 b (not shown for the first reactor B1 ), a feedstock inlet 43a, 43b, 43c, a sludge sample port 45a, 45b, 45c and a sludge outlet 47a, 47b, 47c, a feedstock outlet 49a, 49b, 49c, a gas sample port 51 a, 51 b, 51 c, a gas pump 53a, 53b, 53c, a gas outlet 55a, 55b, 55c, a gas inlet 57a, 57b, 57c, a gas line 58a, 58b, 58c and heating elements (not shown). The sludge/feedstock is transported to and from reactors B1 , B2, B12 by means of lines as shown in figure 1 . As shown in figure 1 , the gas lines 58a, 58b, 58c are connected to each other by bypass gas lines 71 a, 71 b. Further, the gas lines 58a, 58b, 58c are connected to lines for output of methane rich gas 70a, 70b, 70c. These gas transport lines 58a, 58b, 58c, 71 a, 71 b in the biogas section 1 1 can be used by at least one gas sampling unit to select the route of at least a portion of the gas produced in at least one of the reactors. Further, the gas sampling unit can be used to select the portion of the gas produced in at least one of the reactors for reintroduction via a gas inlet(s) in at least one of the reactors, wherein the portion may vary between 0-100% of the gas produced in at least one of the reactors. The gas transport lines are provided with valves. The valves are controlled by the gas sampling unit(s). These valves can also be used to mix gas from at least two reactors to provide a specific gas composition to be reintroduced in a specific reactor via the gas inlet.

The bacterial type in each reactor is analysed in use and enhanced if necessary by the inoculation of the same type of bacteria through the feedstock sample port 41 a, 41 b (not shown for the first reactor B1 ) of each reactor B1 , B2, B12.

The last eleven of the reactors B2, B12 tanks are partially filled with contact area enhancement material 59a, 59b which provides increased bacterial exposure to the contents of the reactor. It is also possible to arrange the contact area enhancement material 59a, 59b in fewer reactors, for example only in the last six final stage reactors.

Flow from a reactor B1 , B2, B12 to the next reactor or section will be under computer control by the automatic opening and closing of the feedstock inlet valve.

The installation for anaerobic digestion of organic material shown in figure 1 has a first hydrolysis reactor B1 . This reactor comprises the inlet 43a for introducing material to be processed inside the reactor, the outlet 49a for removing processed materials from the reactor, the gas outlet 55a located close to the top of the reactor, and the at least one gas inlet 57a located close to the bottom of the reactor, wherein the gas line 58a connects the gas outlet 55a with the gas inlet 57a of the first hydrolysis reactor. The recirculation of at least a portion of the gas from the gas outlet fulfils two functions, one to stir/mix the contents of the hydrolysis reactor B1 and the second to allow the contents of the reactor B2 to absorb more of the gas that is being bubbled through the reactor tank. These two functions of the reintroduced gas increase the quality of the end product such that it is possible to increase the volume of biogas with increased ratios of methane.

The reactors B1 , B2, B12 are identical, i.e. each reactor comprises the at least one gas inlet 57a, 57b, 57 located close to the bottom of the reactor and the gas line 58a, 58b, 58c connecting the gas outlet with the gas inlet of the same reactor B1 , B2, B12.

A number or all reactors B1 , B2, B12 may be provided with a pH meter and/or a redox meter for measuring and by a computer program product for computer analysis and computer control (not shown) control the processes inside the reactors B1 , B2, B12. Each reactor B1 , B2, B12 within the reactor section will be individually heated by means of the heating elements to allow each reactor to be at the correct temperature for the particular bacterial process applicable to that tank. An important aspect of the installation is that the processes in each anaerobic reactor B1 , B2, B12 are physically separated from each other. Further, the performance of each reactor is analysed, wherein dependent of the analysis, the conditions such as the temperature, the pressure and/or the pH can be adapted in each reactor independently and/or the bacteria in each reactor can be enhanced by seeding.

As shown in figure 1 the outlet 49a, 49b, 49c in each reactor is located closer to the top of the reactor B1 , B2, B12 than the inlet 43a, 43b, 43c. In each reactor the sludge outlet 47a, 47b, 47c is located in the lowest section of the reactor B1 , B2, B12. The feedstock inlet 43a, 43b, 43c is located in the lower section of the reactor B1 , B2, B12, but closer to the top of the reactor than the sludge outlet 47a, 47b, 47c. The gas inlet 57a, 57b, 57c is also located in the lower section of the reactor B1 , B2, B12, wherein the gas inlet 57a, 57b, 57c is located closer to the top of the reactor than the feedstock inlet 43a, 43b, 43c. In this way it is normally possible to introduce gas above the level where solid suspensions settle in the reactor such that the gas can more easily bubble through the (more liquid) material in the reactor. In addition, this position of the gas inlet improves the stirring and mixing performance of the (less solids containing) material above the gas inlet. The feedstock outlet 49a, 49b, 49c is located in the intermediate section of the reactor B1 , B2, B12. The feedstock outlet 49a, 49b, 49c is located closer to the top of the reactor B1 , B2, B12 than the feedstock inlet 43a, 43b, 43c and the gas inlet 57a, 57b, 57c. The feedstock outlet 49a, 49b, 49c can also be constructed as overflow pipes (not shown), see for example WO2015/037989. The gas outlet 55a, 55b, 55c is located in the highest position of the reactor B1 , B2, B12, preferably in or close to the top of the reactor B1 , B2, B12.

The reactor section 9 comprises twelve reactors in series which means that the hydrolysis process is subdivided over three or four reactors including reactors B1 and B2. Each hydrolysis reactor B1 , B2 can be optimised for a partial process of hydrolysis. The acidogenesis process, the acidogenesis process and the methanogenis process may each also take place in more than one reactor. Also, the conditions in each of these reactors can be optimised for a partial process of the acidogenesis process, the acidogenesis or the methanogenis process. After finishing the hydrolysis phase under computer analysis and control, the outlet of the last hydrolysis reactor is connected to an inlet of the first acidogenesis reactor. Further, the outlet of the last acidogenesis reactor is connected to an inlet of the first acetogenesis reactor and the outlet of the last acetogenesis reactor is connected to an inlet of the first methanogenis reactor.

In the biogas section 1 1 the biogas is collected from the gas outlets 55a, 55b, 55c and either recirculated through the reactors B1 , B2, B12 or collected as the output methane rich gas 70a, 70b, 70c. The decision of which gas to collect and which to recirculate, and through which reactors the recirculation should occur is automated by computer analysis and control (not shown). The gas line(s) 58a, 58b, 58c is (are) connected to a gas sampling unit in the gas sample port 51 a, 51 b, 51 c for sampling gas in the gas line and the gas line comprises valves controllable by the processor (not shown) of the gas sampling unit deciding which gas to recirculate by gas line 58a, 58b, 58c in the reactor B1 , B2, B12 through inlet 57a, 57b, 57c or which gas to collect as end product in for example a tank (not shown) of the biogas section. The biogas section 1 1 collecting gas from the gas outlet 55a, 55b, 55c uses gas lines 58a, 58b, 58c of the reactors B1 , B2, B12 and the gas lines 58a, 58b, 58c comprise valves as shown in figure 1. The gas lines 58a are further connected to lines for output of methane rich gas 70a. The biogas section 1 1 may also comprise bypass gas lines 71 a, 71 b to transport at least a portion of the gas of the previous reactor to the gas line 58b, 58c of the next reactor or vice versa, i.e. to transport at least a portion of the gas of a reactor (not including reactor B1 ) to a previous reactor (including reactor B1 ). This gas from the bypass gas lines 71 a, 71 b can be introduced via gas lines 58a, 58b, 58c and gas inlet 57a, 57b, 57c to the next or previous reactor B1 ; B2; B12. The gas lines 58a, 58b, 58c, bypass gas lines 71 a, 71 b and the lines for output of methane rich gas 70a, 70b, 70c comprise the gas sampling units and various valves, for example two way valves, to control by means of a computer program product the gas composition of the gas to be reintroduced in a specific reactor, wherein the gas composition to be introduced may comprise gas from the same reactor and/or from any other reactor and/or from at least two reactors and/or external gas. External gas means a gas not being produced by any of the reactors of the installation/system. Further, it is possible to use three way or more way valves to distribute the gas over the gas lines 58a, 58b, 58c, bypass gas lines 71 a, 71 b and the lines for output of methane rich gas 70a, 70b, 70c. The effluent section 13 has a storage tank 65 containing the fully processed digestate where the solids if available will be separated from the liquid. Depending on the composition of the solids, they will either be discarded through exit 73 for example for further treatment or reintroduced via line 75 into the fresh feedstock being input into the shredding section 5 and/or the pre-treatment section 7. In the effluent section 13, the outlet 49c of the last methanogenis reactor B12 is connected by a line to the storage tank 65 of the effluent section 13.

In an embodiment (not shown) the reactor section comprises four anaerobic reactors such that there is always one reactor configured for one of the four processes: hydrolysis, acidogenysis, acetogenysis and methanogenysis. In the first hydrolysis reactor hydrolysis takes place by means of bacteria for hydrolysis, and in the second reactor acidogenesis takes place by means of bacteria for acidogenesis, and in a third reactor acetogenosis takes place by means of bacteria for acetogenosis and in a fourth reactor methanogenesis takes place by means of bacteria for methanogenesis. Segmenting and isolating these four partial processes of anaerobic digestion in separate reactors without interaction between the processes inside the reactors increases the volume of biogas with increased ratios of methane.

Figure 2 shows a reactor 100 that can be used for an anaerobic reactor B1 , B2, B12 of the installation for anaerobic digestion of organic material or for an aerobic reactor (not shown) for a system (not shown) comprising the installation shown in figure 1 .

The shape of the reactor 100 is square with sloping sides and a curved top with an inverted pyramid shaped bottom.

The reactor 100 can be subdivided in an inverted pyramid shape bottom portion 101 , a dome shaped top portion 103 and an intermediate portion 105 between the bottom portion 101 and the top portion 103. The gas outlet 155 is located in the top of the dome-shaped top portion 103. The intermediate portion 105 has a truncated inverted pyramid shape. The height of the intermediate portion is larger than the height of the bottom portion, in the reactor 100 the height of the intermediate portion is at least five times the height of the bottom portion 101 .

Each wall of the bottom portion 101 defines an acute angle a1 with the vertical v1 and each wall of the intermediate portion 105 defines an acute angle a2 with the vertical v2 wherein the angle a1 is different than the angle a2. The acute angle a2 with the vertical is 45 degrees and the angle a1 is 35 degrees. The walls of the intermediate portion 105 with the acute angle a2 to the vertical provide above the gas inlet a more uniform gas stirring/mixing of the reactor's content than walls extending parallel to the vertical above the gas inlet.

The gas inlet 157 is located on the transition edge 140 between the intermediate portion 105 and the bottom portion 101 . The reactor 100 may also have a feedstock sample port (not shown), a feedstock inlet (not shown) located below the gas inlet 157, a sludge sample port (not shown) and a sludge outlet 147, a feedstock outlet (not shown) located in the intermediate portion 105 close to the dome shaped top portion 103, a gas sample port (not shown), a gas pump (not shown), a gas line (not shown) between the gas inlet 157 and the gas outlet 155 and optionally heating elements (not shown).

Anaerobic or aerobic reactor (not shown) comprising a reactor wall and at least a gas inlet located closer to a bottom of the reactor than to a top of the reactor, wherein above the gas inlet in the direction to the top of the reactor the inner distance defined by the reactor wall measured in a direction traverse to the centre line of the reactor increases. Such a gas inlet in combination with the reactor wall design increases a uniform stirring of the reactor's content with gas introduced in the reactor by the gas inlet. In this reactor, a gas outlet can be located closer to the top of the reactor than to the bottom of the reactor, wherein the gas outlet is connected to the gas inlet. In this way it is possible to reintroduce at least a portion of the gas leaving the reactor through the gas outlet to the reactor by the gas inlet. The reintroduction of gas provides advantages as described in this document. This reactor design can be implemented in any installation for anaerobic digestion and is not limited to the installation configuration described in this document. The shape of the reactor can be square with sloping reactor walls. In stead of a square design with sloping sides of the reactor, the reactor may also have a curved design such as partial paraboloid or a (truncated) cone reactor wall. A combination of a square wall with sloping sides and a partial paraboloid or a (truncated) cone reactor wall is also possible. The reactor may comprise like the reactor 100 shown in figure 2 a bottom portion, a top portion and an intermediate portion between the bottom portion and the top portion, wherein a gas inlet is provided in the intermediate portion and/or in the bottom portion. The gas outlet can be provided in the top portion. The tangent of a curved reactor wall or the sloping walls of the intermediate portion and/or the sloping walls of the bottom portion at least above the gas inlet define an acute angle with the vertical. The sloping walls of the bottom portion may for example define the acute angle a1 as discussed in this document and/or the sloping walls of the intermediate portion may define an acute angle a2 as discussed in this document. Other features of the reactor discussed in this document can also be applied to the reactor comprising a reactor wall and a gas inlet located closer to a bottom of the reactor than to a top of the reactor, wherein above the gas inlet in the direction to the top of the reactor the inner distance defined by the reactor wall measured in a direction traverse to the centre line of the reactor increases.

Further, it is possible that the installation for anaerobic digestion of organic material comprises at least a first hydrolysis reactor and a second anaerobic reactor, wherein each reactor comprises an inlet for introducing material to be processed inside the reactor, an outlet for removing processed materials from the reactor, and at least a gas outlet located close to the top of the reactor, wherein the first hydrolysis reactor further comprises at least a gas inlet located close to the bottom of the reactor and a gas line, wherein the gas line connects the gas outlet with the gas inlet of the first hydrolysis reactor.

The system/installation shown in the figures allows for a different Hydraulic Retention Time (H RT) and/or Solid Retention Time (SRT). This is achieved by dynamically adjusting the gas flow rate which in turn adjusts the mixing rate resulting in a controlled level of solids in the digestate moving from one reactor tank to the next. A lower gas flow rate provides less mixing which will result in a higher proportion of liquids being transferred. A higher gas flow rate provides increased mixing will result in a higher proportion of solids being transferred. In this way, the relationship between HRT and SRT is controlled to produce the maximum methane in the shortest time.

The gas from any reactor can be used to bubble through any other reactor. Gasses from multiple reactors can be bubbled through a single reactor or selectively divided among multiple reactor sections, including the one that the gas has come from. The rate of flow of the gas is individually controlled in each reactor by means of a processor or a computer system using a computer program product to control the processes of the installation/system described in this document. The processes within the reactor may be measured and analysed by a computer system with the computer program product in real time, real time adjustments are being made to all the controllable elements of the process in order to optimise the output of methane. The parameters that may be controlled independently from each other by the computer system with the computer program product are:

- salinity of the material to be introduced to the hydrolysis reactor by controlling the rinsing of the material before introduction in the reactor;

- particle size of the material to be introduced to the hydrolysis reactor, by controlling the shredding, chopping, micronizing, electrolysis and cooking of the material before introduction in the reactor;

- temperature of the material to be introduced to the hydrolysis reactor;

- percentage of total solids (TS) and/or percentage of volatile solids (VS) of the material to be introduced to the hydrolysis reactor, by regulating the amount and type of dilutant being applied to the material;

- loading rate of the material introduced to the hydrolysis reactor by regulating the feed rate;

- the temperature of the material being processed inside each reactor;

- the composition of the gas to be introduced into each reactor, by analysing the gas being produced in each reactor by the gas sampling unit and then recirculating the gas and/or blending gasses from different reactors before introducing the gas to a particular reactor;

- the rate of gas flow in each reactor tank, preferably to control the Solid Retention Time (SRT) and/or the Hydraulic Retention Time (H RT) for each reactor;

- the transfer rate between the outlet and the inlet between two reactors; and/or

- the Solid Retention Time (SRT) for each reactor, this is achieved by adjusting the gas flow rate and hence the mixing rate.

Claims

1 . An installation for anaerobic digestion of organic material, comprising at least a first hydrolysis reactor and a second anaerobic reactor, wherein each reactor comprises an inlet for introducing material to be processed inside the reactor, an outlet for removing processed materials from the reactor, at least a gas outlet located close to the top of the reactor and a gas line, wherein the first hydrolysis reactor further comprises at least a gas inlet located close to the bottom of the reactor, wherein the gas lines connect the gas outlets of the reactors with the gas inlet of the first hydrolysis reactor.

2. The installation of claim 1 , wherein each reactor comprises at least a gas inlet located close to the bottom of the reactor, wherein the gas line of each reactor connects the gas outlet with the gas inlet of the same reactor and/or with the gas inlet of another reactor.

3. The installation of claim 1 or 2, wherein the gas line is connected to a gas sampling unit for sampling gas in the gas line and the gas line comprises a valve controllable by the gas sampling unit, preferably the valve is a 3-way or more way valve.

4. The installation of claim 1 , 2 or 3, wherein the at least one gas outlet is located in a top section of the reactor and the gas inlet is located in a bottom section of the reactor.

5. The installation according to any one of the preceding claims, wherein the at least one gas inlet in each reactor has a position such that the reintroduced gas provides stirring of the reactor content in use.

6. The installation according to any one of the preceding claims, wherein at least the hydrolysis reactor has at least a bottom portion, a top portion and an intermediate portion between the bottom portion and the top portion, preferably the bottom portion has an inverted pyramid shape.

7. The installation according to claim 6, wherein the reactors of the installation are identical.

8. The installation of claim 6 or 7, wherein the top portion is dome- shaped, preferably the gas outlet is located in the top of the dome-shaped top portion.

9. The installation of claim 6, 7 or 8, wherein the intermediate portion has a truncated inverted pyramid shape.

10. The installation according to any one of the preceding claims 6-9, wherein at least two walls of the bottom portion define an acute angle a1 with the vertical and/or at least two walls of the intermediate portion define an acute angle a2 with the vertical, preferably the angle a1 is different than the angle a2.

1 1 . The installation of claim 10, wherein the acute angle a2 with the vertical is larger than 0 degrees and smaller than 60 degrees, preferably the angle a2 is larger than 15 degrees and smaller than 55 degrees, most preferably the angle a2 is larger than 35 and smaller than 50 degrees.

12. The installation of claim 10 or 1 1 , wherein the angle a1 is smaller than 75 degrees, preferably smaller than 65 degrees.

13. The installation according to any one of the preceding claims 6-12, wherein the height of the intermediate portion is larger than the height of the bottom portion, preferably the height of the intermediate portion is at least three times the height of the bottom portion.

14. The installation according to any one of the preceding claims 6-13, wherein the gas inlet is located close to the transition of the intermediate portion to the bottom portion, preferably the gas inlet is located on or adjacent the transition between the intermediate portion and the bottom portion.

15. The installation according to any one of the preceding claims, wherein the installation comprises at least four anaerobic reactors, wherein the outlet of the first hydrolysis reactor is connected to an inlet of an acidogenesis reactor, and/or the outlet of the acidogenesis reactor is connected to an inlet of an acetogenesis reactor and/or the outlet of the acetogenesis reactor is connected to an inlet of a methanogenis reactor.

16. The installation of claim 15, wherein the acidogenesis reactor, the acetogenesis reactor and/or the methanogenis reactor comprise a contact area enhancement structure inside the reactor, wherein the contact area enhancement structure provides increased bacterial exposure to reactor content in use.

17. The installation according to any one of the preceding claims, wherein the processes in each reactor are physically separated from each other.

18. The installation according to any one of the preceding claims, wherein the installation comprises more than four reactors, wherein at least one of the processes: hydrolysis, acidogenysis, acetogenysis and methanogenysis uses more than one reactor.

19. The installation according to any one of the preceding claims, wherein the installation comprises a feedstock conditioning unit for conditioning the organic material to be processed in the first hydrolysis reactor, the feedstock conditioning unit comprises at least one of the following sections: a rinsing section, a shredding section and a pre-treatment section.

20. The installation according to any one of the preceding claims, wherein the installation comprises a biogas section.

21 . The installation according to any one of the preceding claims, wherein the installation comprises an effluent section, preferably at least the outlet of the last reactor being connected to a storage tank of the effluent section.

22. The installation according to any one of the preceding claims, wherein in each reactor the outlet is located closer to the top of the reactor than the inlet.

23. A reactor for an installation according to any one of the preceding claims.

24. System comprising an installation according to any one of the preceding claims 1 -22, wherein the system further comprises at least an aerobic reactor.

25. System according to claim 24, wherein the at least one aerobic reactor has an inlet for introducing material to be processed inside the reactor, an outlet for removing processed materials from the reactor, and at least a gas inlet for introducing oxygen containing gas to the material inside the reactor.

26. System according to claim 24 or 25, wherein the at least one gas inlet is located close to the bottom of the reactor.

27. System according to claim 24, 25 or 26, wherein the at least one aerobic reactor comprises a gas outlet located close to the top of the reactor.

28. System according to any one of the preceding claims 24-27, wherein the at least one aerobic reactor further comprises a gas line, wherein the gas line connects the gas outlet with the gas inlet of the at least one aerobic reactor.

29. A process for anaerobic digestion of organic material by using an installation comprising at least a first hydrolysis reactor and a second anaerobic reactor, wherein each reactor comprises an inlet for introducing material to be processed inside the reactor, an outlet for removing processed materials from the reactor, and at least a gas outlet located close to the top of the reactor, wherein at least the first hydrolysis reactor further comprises at least a gas inlet located close to the bottom of the reactor, wherein at least a portion of the gas collected from the gas outlet or gas outlets is reintroduced through the gas inlet of the first hydrolysis reactor.

30. The process according to claim 29, wherein for each reactor the gas outlet is connected to the gas inlet for recirculating gas through the reactor.

31 . The process according to claim 29 or 30, wherein a gas sampling unit decides which gas or which portion of the gas to recirculate in at least one of the reactors through a gas inlet or which gas or which portion of the gas to collect as end product.

32. The process according to claim 29-31 , wherein at least a portion of the gas from the gas outlet of the second anaerobic reactor is supplied to the at least one gas inlet of the first hydrolysis reactor.

33. The process according to any one of the preceding claims 29-32, wherein the performance of each reactor is analysed, wherein dependent of the analysis, the conditions such as:

- the composition of the gas to be reintroduced in at least one of the reactors

- gas flow rate for gas flowing from the gas inlet,

- the temperature,

- the pressure and/or

- the pH can be adapted in each reactor independently and/or the bacteria in the reactor can be enhanced by seeding.

34. The process according to any of the preceding claims 29-33, wherein the first hydrolysis reactor has bacteria for hydrolysis and the second reactor has bacteria for one of the other processes of anaerobic digestion, wherein the bacteria in each reactor are different and the processes performed by the bacteria in a reactor are physically separated from the processed performed by the bacteria in another reactor.

35. The process according to any of the preceding claims 29-34, wherein the installation comprises at least four reactors in series, wherein in the first hydrolysis reactor hydrolysis takes place by means of bacteria for hydrolysis, and/or in the second reactor acidogenesis takes place by means of bacteria for acidogenesis, and/or in a third reactor acetogenosis takes place by means of bacteria for acetogenosis and/or in a fourth reactor methanogenesis takes place by means of bacteria for methanogenesis.

36. The process according to any of the preceding claims 29-35, wherein the outlet of the first hydrolysis reactor is connected to the inlet of the second anaerobic reactor.

37. The process according to any of the preceding claims 29-36, wherein the process is a continuous digestion process.

38. The process according to any of the preceding claims 29-37, wherein the gas reintroduction provides stirring of the reactor content

39. The process according to any of the preceding claims 29-38, wherein the process is configured to control at least one the following parameters:

- temperature of the material to be introduced to the hydrolysis reactor;

- the temperature of the material being processed inside each reactor;

- the composition of the gas to be introduced into each reactor, by analysing the gas being produced in each reactor and then recirculating the gas and/or blending gasses from different reactors before introducing the gas to a particular reactor;

- the transfer rate between the outlet and the inlet between two reactors;

40. A method for processing organic material by using an installation according to any of the preceding claims 1 -22 and by using a system according to any of the preceding claims 24-28.

41 . Use of an installation according to any of the preceding claims 1 -22 for anaerobic digestion of organic material.

42. Computer program product, comprising a readable storage medium, comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the process according to any of the claims 29-30.