WO2019166620A1 - Anaerobic digestion reactor and plant - Google Patents

Abstract

A continuously stirred reactor (100) for anaerobic digestion of biodegradable organic substrate is provided, comprising a horizontally extended reactor tank (101) with an influent port at an entrance end and at least one effluent port at a discharge end opposite to the entrance end. The reactor (100) further comprises means for continuously stirring the organic substrate within the reactor tank (101), and a temperature regulating system that advantageously comprises a plurality of internal ducts configured to traverse through lateral walls and/or a base of the reactor tank and to convey temperature regulating fluid therealong.

Description

ANAEROBIC DIGESTION REACTOR AND PLANT

FIELD OF THE INVENTION

The present invention generally relates to systems and methods for anaerobic biodegradation of organic substrates accompanied by biogas recovery. In particular, the present invention concerns a continuously stirred horizontal reactor for dry anaerobic digestion of organic substrates and a plant facility comprising said reactor(s).

BACKGROUND

Anaerobic digestion (AD), a complex process of organic matter decomposition by methanogenic bacteria, has been reduced to practice in a variety of biorefinery technologies including agricultural and industrial waste disposal. In all instances, anaerobic digestion is further accompanied by production of biogas, which is further upgraded to yield biofuels.

Two types of anaerobic digestion processes are generally distinguished for management of solid waste with varying dry matter (DM) content, which are referred to as“wet” (DM 5-15 wt-%) and“dry” (DM 30-55 wt-%), accordingly. Dry digesters are generally more compact, with an average capacity 950-1000 m³ upgradable to about 2000 m³, as in comparison to wet ones with an average capacity of 2-4000 m³. Generally speaking, any anaerobic digester may be exploited for wet- and dry processes; however, in practice the equipment is designed to meet specific requirements imposed by choice- and/or availability of feed materials, expected outputs, available premises, etc. Further advantages of dry digestion when used in waste disposal relate to enduring the comparatively impure waste, i.e. containing considerable amounts of non-biodegradable matter; thereby expenditures for pretreatment and conditioning of feedstock prior to digestion can be minimized.

Conventional AD plants include a pre-treatment facility, a digester reactor or reactors, and a number of post-processing facilities, including solid separators and hygienization tanks for digested material and recirculation means for reverting part of digested material into a reaction space as inoculum. Common reactor configurations include fixed dome-shaped tanks comprising, in most instances, wall-integrated mixer or mixers. Dry AD reactors operating at a continuous flow-through basis are generally referred to as plug-flow reactors and are embodied as horizontally extended, narrow tanks with an inlet and an outlet, in where feed is continually decomposed as it advances along the length of the tank. Some plug-flow solutions are complemented with a mixer in the form of a bladed shaft or a mixing screw.

Dry anaerobic digestion, also referred to as dry fermentation, gains more ground for the following reasons. At first, waste fractions become more challenging to process. Some waste management practices prohibit landfilling organic waste; therefore, waste fractions intended for recycling become drier and harder to crush due to the presence of significant amount of impurities, such as stones, sand and mud. Incineration of organic waste is a popular solution, but it gives low energy yields and causes severe flue gas emissions. On the other hand, although dry masses could be handled, to some extent, by wet anaerobic digestion methods, the latter do not tolerate the presence of essentially large amounts of impurities in feedstocks.

However, dry anaerobic digester solutions operating at a continuous flow basis are impacted by a number of common drawbacks. In most instances, biodegradable waste obtained from agrarian and municipal sources contains essential amounts of indigestible solids, such as stones, sand, glass and a variety of plastics, that results in floating layers and massive sediments in the digester. In order to deal with weighty sediments, the United States patent no. 8241869 (Buchner et al) discloses a dry anaerobic fermenter operating at a plug-flow basis and provided in the form of an elongated tubular container with overlapping stirring blades configured to push sediments towards the discharge end, and a suction socket for removing solid sediments from the reactor via an additional outlet. However, the solution does not account for separation of lightweight impurities; thereby provision of a filtration station would be required to handle plastic-rich waste streams.

Additionally, the aforementioned indigestible substrates (sand, stones, etc.) cause friction, therefore, the equipment requires a robust feeding system.

Further challenge concerns raising the capacity of an AD plant without compromising its economic feasibility in terms of capital investment. Conventional solutions include growing the number of reaction tanks per plant, which is not always possible due to limited area, and/or provision of gear that supports stirring and advancement of material through the extremely long reactors. An exemplary solution according to the United States patent no. 7659108 (Schmid) thus concerns means for detecting and compensating sagging of the agitator shaft within horizontal anaerobic fermenters, in particular those, whose length exceeds 50 meters.

Furthermore, according to existing requirements set in the national- and EU standards and regulations imposed on the processes of anaerobic digestion of biodegradable feedstocks, including the Finnish Fertilizer Product Act No. 539/2006, the Finnish Decree on fertilizer products No. 24/11, and the Commission Regulation (EU) No. 142/2011 implementing the Regulation (EC) No. 1069/2009 with regard to animal by-products and derived products not intended for human consumption, decomposition products resulted from AD processes must be sanitized prior to being re-introduced into the ecosystems, in the form of fertilizes, compost or soil amendments. In conventional anaerobic digester plants such sanitization is conducted in separate facilities commonly located downstream the digester reactor(s).

Usually, DM content in feedstocks loaded into dry AD reactors is significantly higher compared to the same in wet processes. Higher DM content accounts for decreased heat conductivity; therefore, the dry reactors must have more powerful heating systems. The latter have high energy consumption and incur high costs onto the recycling process. We note hereby, that although higher DM content in dry fermentation reactors is not indispensable, the benefits of dry fermentation shall be lost if the reactor intended for dry processes shall be loaded with feedstock materials suitable for processing in a (cheaper) wet AD plant.

Provision of AD reactors is often associated with (bio)gas production. In order to maximize said gas production, efficient mixing is required in all types of digestion processes. Due to high solid content of feedstocks, this remains a challenge in dry AD (fermentation) reactors.

In this regard, a revision of technology related to anaerobic digestion in horizontal, continuously stirred reactors suitable for production of biogas is still desired, in view of addressing challenges associated with the application of AD technology as part of a solid waste management system, and in particular, related to unsatisfactory elimination of contaminants, clogging of effluent pathways, inefficient mixing of the material in the digester and/or low biogas yield.

SUMMARY OF THE INVENTION

An objective of the present invention is to solve or to at least mitigate each of the problems arising from the limitations and disadvantages of the related art. The objective is achieved by various embodiments of a reactor arrangement for anaerobic digestion of biodegradable organic substrate and related uses thereof. Thereby, in one aspect of the invention a reactor arrangement for anaerobic digestion of biodegradable organic substrate is provided, according to what is defined in the independent claim 1.

In one preferred embodiment the reactor comprises at least one horizontally extended reactor tank with an influent port at an entrance end and at least one effluent port at a discharge end opposite to the entrance end, at least two longitudinally extending agitators disposed side by side within an interior of the tank, and a temperature regulating system configured to adjust temperature in the reactor tank and comprising a plurality of internal ducts configured to traverse, in a longitudinal direction, through lateral walls and/or a base of the tank and to convey temperature regulating fluid therealong. In an embodiment, the reactor arrangement is configured to convey biodegradable organic substrate along the length of the reactor tank towards the discharge end such, that the digested organic substrate is discharged from the tank through a primary effluent port and the indigestible residue is discharged through an at least one auxiliary effluent port.

In an embodiment, the lateral walls that define, in a longitudinal direction, the interior of the reactor tank are sloped, thereby a slope element or elements are formed along an entire length of the tank at intersections between the lateral walls and the bottom. In an embodiment, each said lateral wall comprises a substantially flat panel or panels with the slope element provided as a separate module.

In some embodiments, each agitator comprises a drive shaft with a number of blades mounted thereto. In an embodiment, an internal duct configured to convey temperature regulating fluid therealong is arranged inside each the agitator drive shaft.

In some embodiments, temperature regimes within the ducts disposed in the lateral walls of the tank and within the ducts disposed in the base of said tank are adjustable independently.

In an embodiment, the reactor arrangement further comprises a pre-treatment facility with an at least one feed supply appliance configured to adjust the temperature of organic substrate entering the at least one reactor tank such, as to conform to the temperature maintained in said tank.

In some embodiments, the reactor further comprises a hygienization system for thermally sanitizing digested substrate. In an embodiment, said hygienization system is provided in a post-treatment facility arranged downstream the at least one tank.

In an alternative embodiment, the hygienization system comprises an at least one encased conduit configured to traverse through the lateral walls and/or the base of the tank in a longitudinal direction and to receive digested substrate discharged through the primary effluent port.

In an embodiment, the reactor arrangement further comprises a heat recovery and circulation system configured to recover heat produced in the at least one tank during anaerobic digestion and to direct heat thus recovered to the pre-treatment facility.

In some embodiments, said heat recovery and circulation system is further configured to direct recovered heat to the temperature regulating system and optionally to the hygienization system. In an embodiment, the heat recovery and circulation system comprises an at least one heat exchanger unit for mediating heat transfer between the at least one tank and the pre- treatment facility.

In some embodiments, the reactor arrangement comprises a number of reactor tanks disposed next to one another.

In a further aspect, use of the reactor arrangement is provided for anaerobic digestion of organic waste, according to what is defined in the independent claim 16.

In still further aspect, use of the reactor arrangement is provided for production of biogas, according to what is defined in the independent claim 17.

The utility of the present invention arises from a variety of reasons depending on each particular embodiment thereof. At first, the invention provides for a compact reactor solution, whose length is reduced at least twice in comparison to conventional AD reactors of the same type, wherein reduction in length is compensated by provision of at least two reaction sub-zones disposed side-by-side. Absence of a partition wall in between the agitator units allows for efficient mixing of digested substrate. By reducing length of the reactor, imposing of excessive load on stirring agitators and/or a driving engine is avoided, thereby adding stability and reliability to the reactor, enhancing mixing efficiency, reducing energy demand, and allowing for substantial repair- and maintenance cost savings.

Moreover, an efficient effluent/residue sorting- and withdrawal system provided within the reactor allows for processing of a“dirty” feedstock, including organic substrates heavily contaminated with a variety of sediment- and/or lightweight impurities, such as plastic packages and wraps, for example. Efficient sediment withdrawal system further prevents formation of a solid layer on the bottom of the reactor tank and creates prerequisites for a sustained flow dynamics therein.

Due to its prefab construction model, the reactor solution disclosed hereby can be easily and promptly assembled on-site. Additionally, pre-fabricated construction blocks for said reactor are designed, in terms of dimensions thereof, suitable for transportation by a conventional motorized vehicle or a platform, including transportation under the standard bridges (e.g. motorway bridges) and via the road tunnels; thereby, no special transport is required.

The reactor solution disclosed hereby further allows for pre-heating feedstocks such, that when substrate material enters the reaction space, its temperature is close to the temperature required for microbial activity Furthermore, the reactor exploits an integrated heat recovery and (re)circulation concept, whereupon heat obtained during the AD process within the reactor tank is recovered for further storage and/or recirculation towards various facilities upstream and downstream said reaction space. Additionally, heat thus recovered can be further utilized for adjusting temperature within the reactor tank to attain conditions most favorable for bacterial populations residing inside said tank. As a result, the present reactors are fully operable in thermophilic conditions (at 42 - 97 °C, preferably, within 42 - 66 °C and, in some instances, within 43 to 55 °C), in a cost-effective manner, during winter season in Nordic climate.

Provision of a hygienization treatment system integrated inside the walls and/or the base of the reactor tank adds to the compactness of the overall solution and naturally eliminates the need for building a separate sanitization facility. Similarly, integrated system of hollow ducts for circulating temperature-regulating fluid inside the walls and/or the base of the reactor tank further allows for fine-tuning reaction conditions therewithin, thus creating the most favorable environment for biodegrading microorganisms residing in the tank. By adjusting temperature inside the reactor, populations of mesophilic and thermophilic bacteria can be regulated such, as to modify biogas production yields, accordingly.

In overall, the reactor disclosed hereby fulfills, in a cost-effective manner, the requirements indispensable for efficient digestion of (organic) waste fractions in anaerobic conditions, namely: maintenance of constant temperature regime throughout the entire reactor facility (including a feeder); uniform and efficient mixing throughout the entire length of the reactor tank; and uniform supply of feedstock material.

The expression“organic substrate” refers in the present disclosure to substrate materials originating from living beings; whereas the term“biodegradable” refers to (organic) substrates that break down naturally and/or as a result of biological activity of micro organisms. The term“anaerobic” refers in the present disclosure to a biodegradation process that proceeds in an absence of oxygen.

The expression“a number of’ is used in the context of the present document to indicate any positive integer starting from one (1). The expression“a plurality of’ refers hereby to any positive integer starting from two (2), e.g. to two, three, or four.

Different embodiments of the present invention will become apparent by consideration of the detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figs 1A, 1C and 1D schematically illustrate an anaerobic digestion reactor arrangement 100, according to the embodiments. Fig. 1B is a perspective view of the reactor arrangement 100, according to the embodiment. Fig. 1E shows a rooftop assembly for the reactor arrangement 100, according to the embodiment.

Fig. 2A, 2B and 3 show exemplary configurations of the reactor arrangement 100.

Figs. 4A - 4D schematically illustrate a cross-sectional view of the reactor tank 101 for various configurations of the reactor 100.

Fig. 5 A is a longitudinal crosscut view of the reactor arrangement 100 in an exemplary configuration. Fig. 5B is a ground plan of the anaerobic digestion arrangement 100 according to the embodiment, viewed from the top.

Fig. 6 shows the reactor tank 101, according to the embodiment, viewed from the side.

Fig. 7 schematically illustrates heating- and temperature regulating systems within the reactor arrangement 100.

DETAIFED DESCRIPTION OF THE DRAWINGS

Detailed embodiments of the present invention are disclosed herein with the reference to accompanying drawings. The same reference characters are used throughout the drawings to refer to same members. Following citations are used for the members:

100 - an anaerobic digestion reactor arrangement,

101 - a reactor tank,

201 - a post-treatment facility, optionally, with a mechanics section,

202 - a sediment discharge appliance,

203 - a digested substrate discharge appliance,

301 - a feed tank with an (optional) lid 311 ,

302 - a first feed supply appliance,

401 - a pre-treatment facility,

402 - a second feed supply appliance (temperature adjustable),

501 A - a rooftop for the reactor supporting structure(s),

10, 10A, 10B - an interior of the reactor tank,

11, 11 A, 11B - lateral (wall-) profiles,

12, 12A- a base element and its extension, accordingly,

13 - external insulation / lining,

14 - an external foundation element, 15, 501 - a cover and a rooftop above the reaction tank, respectively,

16, 17 - entrance- and discharge ends, accordingly,

18 - an influent port,

19, 20, 21 - effluent ports,

22 - an agitator,

23 - a drive shaft / an axle,

24, 24A, 24B - mixing blades and parts thereof,

25 - separating devices,

26 - depressions for accommodating drive shafts,

27 - drive shaft support elements,

30 - a hygienization system,

31, 32, 33 - a flow conduit, a jacket and an extraction aperture for the hygienization system, according to an embodiment,

40 - a temperature regulating system,

41, 42 - duct(s) inside the walls and the base of the reactor tank,

43 - duct(s) inside the drive shaft,

44 - a heat recovery and circulation system,

50 - a heat exchanger unit,

51 - a central heat distribution and control unit.

Figs. 1A-1C schematically illustrate a concept, underlying, at 100, various embodiments of an anaerobic digestion reactor arrangement 100, hereafter, the“reactor”, in accordance with an aspect of the present invention. The arrangement 100 advantageously comprises at least one reactor tank or a basin 101, a pre-treatment facility 401 and a post-treatment facility 201. The pre-treatment facility advantageously comprises a variety of feeders 302, 402, a number of storage containers 301 for storing feedstock materials, chemical substances, buffers, etc., and a variety of mechanical solutions. The post-treatment facility 201 advantageously comprises discharge means 202, heat recovery- and thermal sanitizing solutions, and optionally mechanical solutions.

Fig. 1B shows an exemplary arrangement 100 configured as an anaerobic (bio)digestion plant, comprising two reactor tanks 101 (see rooftops 501) having common pre-treatment facility 401 and common post-treatment facility 201 with discharge means. A variety of appliances (e.g. 301, 302, 402) configured for pre-treatment and supply of the feedstock material into the tank(s) 101 can be located in a separate“process” hall (Fig. 1B, building on the left, Fig. 5B) and/or in a pre-treatment section disposed upstream the tank(s). The elements indicated by reference numbers 301, 302, 401 and optionally 402 are plant- specific (depend on plant size, substrates, climate conditions, etc.) and may vary within the embodiments. It is preferred that the feed supply appliance 402 configured for thermal treatment of organic feedstock is provided essentially unchanged in each embodiment described hereby and/or perceived by a skilled person based on the present disclosure.

The reactor arrangement 100 advantageously comprises a temperature regulating system configured to adjust temperature in the reactor tank(s) and a heat recovery and circulation system configured to recover heat produced in the tank(s) during anaerobic digestion and to direct heat thus recovered to the pre-treatment facility 401 and optionally to the temperature-regulating system. Mentioned systems are described in details further below.

The reactor arrangement 100 thus comprises a horizontally elongated tank 101 that constitutes a reaction chamber (a reaction space). In some preferred embodiments, the reactor tank 101 has the following dimensions: 2l m x 12 m x 6-7 m, as standing for length x width x height, accordingly.

The reactor tank 101 is defined by a horizontally extended, quadrilateral container with an entrance end 16 for receiving organic feedstock and a discharge end 17 for extracting digested slurry (digestate). For clarity purposes, by the terms“digestate” and“digested substrate” we refer, in present disclosure, to any substantially solid by-product of anaerobic digestion apart from biogas. Feedstock, supplied from the feed tank(s) 301 in the pre- treatment facility 401, is received into the reactor tank 101 through a feed inlet port 18 (influent port) provided at the entrance end 16.

In preferred embodiments, the reactor tank 101 is rectangular at its’ base. In such a case width of the tank is the same at the entrance- and the discharge ends.

In some other embodiments, the reactor tank 101 can be configured as a quadrilateral body, whose width at the discharge end 17 is greater than that at the entrance end 16 (not shown). At its’ base such configuration forms an isosceles trapezoid set upside down (with its narrower base at the entrance end 16).

The reactor tank 101 accommodates, within an interior 10 thereof, at least two agitators or mixers 22 positioned side-by-side and extending in longitudinal direction throughout an entire length of the reactor tank, the latter being defined, in present disclosure, as a distance from the entrance end 16 to the discharge end 17.

As stated hereinabove, the agitator axles should not be extremely long. On the other hand, an AD reactor tank must have volume of at least 800 m³; otherwise stability of reactor conditions is endangered. These two requirements are met by provision of a tank with double mixing axles (i.e. two axles positioned next to one another). The agitators may be disposed strictly in parallel (in case of a“rectangular” tank 101) or deviate from the longitudinal symmetry axis by preferably no more than 45 degrees in each direction (in case of a“trapezoidal” reactor tank 101).

Each agitator 22 comprises a drive shaft 23 configured as an axle with a number of mixing blades 24 mounted thereto. The axle is advantageously provided as a tubular body having wall thickness within a range of 30 - 70 mm, preferably, 50 - 70 mm, still preferably, about 60 - 65 mm. In some embodiments mixing blades 24 are configured as blade paddles (vanes) individually fitted to the drive shaft to follow a substantially radial pattern (Figs. 2 A, 2B) or a substantially helical pattern (not shown). In some alternative embodiments (not shown), each mixing blade can be configured as an open impeller consisting of a series of vanes attached to a central hub, the latter being fitted to the drive shaft 23. The agitators can be further configured as helical ribbon impellers (not shown).

Fig. 1C illustrates an exemplary configuration of the reactor comprising mixing blades 24 configured as paddles made of separate parts 24A, 24B. The innermost part 24A (dashed box) of each paddle is provided as a pair of tubular elements that can be threaded through the axle 23 and fixed by welding, for example, whereby a minimum amount of mechanical stress is caused to the paddles and the entire axle structure is imparted by torsional stiffness. The innermost parts 24A can be secured to the axle(s) 23 already at a manufacturing facility. Attachment of the outermost parts 24B to the innermost parts 24A can be implemented via joint coupling, for example, followed by welding.

To facilitate transportation of the about 20 m long axle(s), the outermost parts 24B may be secured to the innermost parts 24A at a place of assembling the reactor arrangement 100. From Fig. 1C one may observe that otherwise identical mixing blades 24 are mounted on the axle(s) 23 such that each subsequent blade is rotated 45 degrees with regards to the preceding one. These positions are fixed. By the way of an example, the mixing blades 24 indicated on Fig. 1C by Roman numerals (ii) and (iv) point, by their outermost ends, in four cardinal directions, viz. north (N) - south (S) and east (E) - west (W), accordingly; whereas the blades indicated by numerals (i) and (iii) point in four intermediate directions, viz. SW - NE and NW - SE, accordingly. In the example above compass directions are used.

In an event the reactor tank 101 follows a trapezoidal shape, the series of blades 24 are preferably configured such, as to gradually increase in diameter in a direction of the discharge end 17.

The shafts 23 are preferably engine-driven. At least one motor engine, preferably an electric motor (not shown), can be set up within a mechanics section provided in the post-treatment facility 201 and/or in the pre-treatment facility 401. In some instances, at least one additional drive mechanism can be installed outside the tank 101 adjacent to the entrance “front” end 16 thereof to pair the primary motor engine provided on the“rear” of the reactor within the mechanics section. By provision of at least two motors at both ends of the reactor tank, overloading of the agitators can be avoided. The mechanics section can further comprise additional gear, such as a variety of controllers, amplifiers and the like.

It is still preferred that a gearbox and a motor head are disposed at an area within the pre- treatment facility 401. By such an arrangement, seal structures for the agitators can be replaced even when the reaction tank(s) are filled with the substrate material.

In order to provide for a most efficient stirring of the reaction substrate within the reactor tank 101, the agitators 22 are set to rotate in opposite directions (shown by arrows on Figs. 2A, 2B); thereby reaction substrate is directed substantially from the center of the tank 101 towards its sides and back to the center. Preferred rotation model is further shown on Fig. 4A (directions pictured by arrows), wherein the agitator positioned on the right side of the reactor tank 101 (as viewed from the entrance end 16) is set to rotate clockwise and the agitator on the left side is set to rotate counterclockwise, accordingly. In other configurations the agitators 22 can be set rotating towards one another (right side - counterclockwise; left side - clockwise); or, alternatively, rotating in the same direction.

Disposition of blades 24 on the drive shaft 23 for both radial and helical / spiral patterns is preferably such that intervals between the individual blades 24 at the entrance end 16 are superior to that at the discharge end 17. Increase in blades’ density per a unit of distance along the drive shaft 23 allows for efficient handling, aka mixing, of the reaction substrate, whose density, in turn, decreases upon advancing along the length of the tank 101 from the entrance end 16 towards a discharge end 17, as organic substrate solubilizes within the reactor as a result of anaerobic digestion.

The reactor 100 is preferably configured as a horizontal plug-flow reactor (PFR), for continuously stirred anaerobic digestion treatment of organic substrates. The term “anaerobic digestion” refers to, in the present disclosure, to a process or processes of organic matter degradation by microorganisms in an absence of oxygen in a wide range of temperatures and accompanied by production of biogas. Based on said temperature range two sub-processes can be generally identified: mesophilic digestion within a range of 10 - 48 °C, preferably, within 30 to 42 °C and thermophilic digestion within a range of 42 - 97 °C, preferably, within 42 - 66 °C and, in some instances, within 43 - 55 °C. Microorganisms stable and active in the above indicated ranges are referred to mesophilic- and thermophilic microorganisms, accordingly. In fact, according to Brock Biology of Microorganisms, (l2^th Ed., Madigan, Martinko, Dunlap & Clark) thermophilic microorganisms are subdivided to thermophiles, such as Geobacillus stearothermophilus, active within a temperature range of 42 - 66 °C with optimum at 60 °C; hyperthermophiles 1, such as Thermococcus celer, active within a temperature range of 67 - 97 °C, with optimum at 88 °C; and hyperthermophiles 2, such as Pyrolobus fumarii, active at temperatures above 100 °C. For the purposes of the present inventions, the thermophilic temperature range is defined as 42 - 97 °C.

An exemplary representative of mesophilic micro-organisms is Escherichia coli having the temperature optimum at about 39 °C.

The latter demonstrate increased efficiency and yield in biogas production; however, thermophilic microorganisms are also more sensitive to changes in temperature, pH level, redox potential, and the presence of inhibitory factors, such as heavy metals, antibiotics and detergents. The reactor 100 provided hereby can be configured, in terms of adjusting the abovementioned parameters to appropriate values, to operate with mesophilic microorganisms, with thermophilic microorganisms, or both types of microorganisms present in the reactor tank at once. While advancing through the reactor 100, the organic substrate material gradually solubilizes, as a result of microbial activity.

During bacteria-mediated anaerobic digestion biodegradable organic substrate is thus decomposed to yield biogas and substantially solid remnants, generally referred to as digestate. The latter consist of fibrous material (cellulose and lignin), dead bacterial cells and of a sludge-like fraction containing solids and methanogenic liquor. These by-products can be further utilized as fertilizer, compost, low-grade building materials, such as fiberboards, and/or as a feedstock for ethanol production.

Feed input for the reactor 100 is represented primarily by organic waste of plant- or animal origin, such as field (plant) biomass and by-products (bagasse, bran, straw), kitchen- and catering (bio)waste, household- and/or municipal waste, by-products of food industry, forestry, agriculture (farming, animal- and poultry rearing), as well as sewage slurries and wastewater sludge.

It is clear that in terms of purity the abovementioned feedstocks vary greatly. Thus, field biomass and crop by-products, for example, are essentially free of indigestible- or poorly digestible impurities or contains negligible amount thereof in the form of gravel or sand. On the other hand, household- or agricultural bio -waste often contains significant amounts of contaminants represented by indigestible plastics and/or metals, and by a variety of poorly digestible organic by-products, such as wood- and/or lumber processing industry by- products, for example.

In order to effectively deal with these indigestible fractions present in the reaction substrate advancing through the reactor tank 101, in particular, from the entrance end 16 along its’ length towards the discharge end 17, the reactor arrangement 100 further comprises means for sorting and separating digested substrate from indigestible residue and extracting digestate-containing and residue-containing fractions from the tank 101 independently from one another.

The reference is further made to Fig. 3, showing the reactor tank 101 within the reactor arrangement 100 (the post-treatment facility 201 is not shown). The reactor tank 101 thus comprises the feedstock receiving influent port 18 at the entrance end 16 and an at least one effluent port at the discharge end 17 opposite to the entrance end 16. In some configurations, the reactor comprises a number of effluent ports 19, 20, 21 at the discharge end 17. Biodegradable organic substrate containing feedstock (F) supplied from the feed tank (not shown), via the pre-treatment facility 401, enters the reactor tank 101 through said influent port 18. Feedstock (F) comprises a variety of solid, indigestible contaminants suspended therein, as mentioned above.

With an advancement of feedstock (F) along the length of the reactor tank 101, while being continuously stirred by at least two agitators 22, biodegradable organic substrate material contained in feedstock undergoes processes of anaerobic digestion by mesophilic- and/or thermophilic microorganisms. At the same time, weighty, non-buoyant indigestible sediment, such as stone, gravel, sand, glass, metal particulate, etc., settles at the bottom of the tank 101, as dragged down by its own weight, whereas lightweight, buoyant indigestible residue, such as plastics, for example, floats to the surface of the organic substrate material and resides thereat. In conventional digesters, with an inlet and an outlet, such indigestible contaminants must be removed manually upon emptying the reactor(s) to avoid clogging discharge pathways and/or formation of a sediment layer on the bottom of the reactor tank. Formation of the latter causes rising of the base level and thus alters flow dynamics created upon stirring.

The reactor arrangement 100 can be configured to allow for efficient removal of indigestible contaminants from the reaction space 101 continuously during the digestion process. Thus, the digested substrate (digestate), indicated by a capital D on Fig. 3, can be discharged from the reactor tank 101 via a primary effluent port 19, whereas a non-buoyant indigestible residue Rl (sediment) can be discharged via a first auxiliary effluent port 20. The digested substrate D thus obtained is either free of solid, indigestible matter or contains meaningless or negligible amounts of indigestible impurities. In any event, the digested substrate D requires no further purification and/or refinement.

The reactor 100 may further comprise a second auxiliary effluent port 21 configured to receive a lightweight, buoyant indigestible residue R2 (floating matter), such as a variety of non-recyclable plastics (plastic wraps, bubble plastics, etc.). In some instances, said auxiliary effluent ports 20 and 21 can be disposed directly underneath or above the primary effluent port, accordingly (see Fig. 3, port 21). Alternatively, any one of said auxiliary ports 20, 21 can be shifted sideways in a horizontal plane related to a position of the primary port 19 (see Fig. 3, port 20). In some other instances, at least one auxiliary effluent port 20, 21 can be disposed at the same level with the primary effluent port 19.

The reactor arrangement 100 may further comprise a number of appliances configured to mediate separation and sorting of solid, indigestible matter suspended in organic substrate material subjected to anaerobic digestion upon advancing of the latter along the length of the reactor tank 101 towards the effluent ports 19, 20 and/or 21.

In come configurations, the reactor arrangement 100 comprises a sediment discharge appliance 202 (Figs. 1A, 2 A, 2B) configured to convey non-buoyant indigestible residue Rl from the bottom of the tank 101, via the first auxiliary effluent port 20, outside the reaction space. The appliance 202 is disposed at the discharge end 17, optionally within the post-treatment facility 201, and it is configured as at least one conveyor, such as a screw conveyor designed to collect solid sediment, e.g. gravel and sand, that accumulates on the bottom of the tank 101 and advances slowly (as a result of agitator-mediated stirring) towards the discharge end 17. In the embodiments shown on Figs. 2A and 2B the 101 the appliance 202 thus comprises a conveying screw provided within the tank 101 and arranged in a substantially horizontal plane; and a second conveying screw disposed within an ascending tube, thereby sediment residue Rl is conveyed upwards prior to being withdrawn from the reactor 100. After withdrawal from the reactor 100, solid non-buoyant sediment is collected for recovery. Alternative configurations include a single rising- or a non-rising conveyor, such as a screw conveyor, for example. Nevertheless, any other appropriate implementation can be utilized. Provision of the appliance 202 within the reactor arrangement 100 is further shown on Fig. 5 A.

In some configurations, the reactor 100 further comprises an additional residue discharge appliance (now shown) configured to convey the buoyant indigestible residue R2 residing at a surface of the organic substrate material advancing along the length of the reactor tank 101, via the second auxiliary effluent port 21, outside the reaction space. Possible configurations for the additional residue discharge appliance include a conveyor configured to transfer lightweight plastic residue R2 in a horizontal plane and/or downwards for further collection and recovery.

Fig. 2B shows an exemplary configuration, in which the reactor 100 further comprises, within the reactor tank 101, a number of separating devices 25 for promoting separation of indigestible (both buoyant/floating and non-buoyant/sediment) matter suspended in organic substrate. The separating devices 25 may be configured as vertical rods with lower ends fixed to the bottom of tank 101, said rods set to perform vibrational or oscillatory motion. The rods are preferably motor-driven. The separating devices 25 are preferably positioned adjacent to the discharge end 17 of the tank 101 such, as promote separation of the digested (biodegraded) organic products from indigestible solids and to facilitate sorting of the digested products D, and the residue Rl and/or R2 towards the appropriate effluent port 19, 20 and/or 21, accordingly.

In some configurations, the reactor tank 101 comprises a number of optionally identical effluent ports 19, 20, 21 for discharging the (unseparated) digestate D. In such an event separation of indigestible residue occurs elsewhere. Ah effluent ports can be located at the same level or at different levels. It should be noted that more than three effluents ports can be provided per tank.

Reference is further made to Figs. 4A- 4D illustrating, at a cross-section of the reactor tank 101, various embodiments of the reactor arrangement 100. The tank 101 is thus defined, in a longitudinal direction, by lateral walls (side walls). In order to achieve more efficient mixing of the reaction substrate within the reactor tank 101 and to avoid accumulation of sediments in the comers formed at an intersection between (lateral) wall profiles and the bottom, each lateral wall defining, in a longitudinal direction, the interior 10 of said reactor tank 101 is sloped (inclined). Thereby, a slope element, indicated by a capital S is advantageously formed along an entire length of the reactor tank 101, at the comers or intersections where lateral walls meet the bottom.

Fig. 4A shows an exemplary configuration, in which each lateral wall is defined by a number of L-shaped profiles 11; thereby the slope element S is integrated into each L- shaped profile, accordingly. The slope element S is outlined on Fig. 4A by dashed lines.

In configuration of Fig. 4A the L-shaped profiles 11 forming lateral walls are advantageously positioned against each other and joined at the bottom by a base (central) element or elements 12 such, that at least two adjoining subsections 10A, 10B are formed within the interior 10 of the reactor tank 101, wherein each subsection 10A, 10B is configured to receive the agitator 22 (not shown; rotation directions pictured by arrows). Provision of the base element(s) 12 is therefore such, as to form an elevated partition between the subsections 10A, 10B. Said partition may be optionally increased in height by mounting an extension element(s) 12A thereon. In some configurations (not shown) the central base element(s) 12 (as on Fig. 4A) may be provided as essentially flat panel(s), with a separate partition element optionally mounted thereto.

The individual L-profiles 11 are positioned against each other pairwise, as to comply with the principles of mirror- symmetry. L-profiles 11 are configured such, as to externally define the reactor tank 101 as a tank rectangular at its’ base, whereas the internal surfaces of the tank 101 are curved to accommodate at least two agitators 22 within at least two adjoining subsections 10A, 10B, accordingly.

Figs. 4B-4D show preferred configurations for the reactor arrangement 100.

Fig. 4B thus shows a configuration, in which each lateral wall is formed by a substantially flat vertical panel 11 A. The slope element (S) can be provided, for each lateral wall 11 A, as a separate module 11B.

In some configurations, the lateral panels that form side walls are provided about 450 mm thick, whereas the panel that form the head-end (front-end and back-end) walls 16 and 17, accordingly, are provided about 550 mm thick. Mentioned panels are preferably manufactured by casting or molding, such as continuous molding, for example. As shown on Fig. 4C, a number (hereby, two) of holes or depressions 26 are made in each of the end panels 16, 17 to accommodate the axles 23. The axles are further given an additional support by providing support / reinforcement legs 27 at each end 16, 17 of the tank 101 (Figs. 1C, 6). The legs 27 can be provided as about 600 mm thick concrete slabs.

In preferred embodiments, the arrangement 100 includes at least two reactor ranks 101 placed next to one another (Fig. 4D). In such an event, two neighboring reactor tanks advantageously share a lateral wall 11 , which can be addressed as a partition well between two reactor tanks (see Figs. 4D, 5B). Still, provision of more than four reactor tanks disposed side-by-side does not necessarily appear feasible due to heat expansion. In an event when more than four tanks are positioned side-by-side, a moving seal is required.

Slope surface may be curved (Fig. 4 A) or flat (Fig. 4B). Slope (inclination) angle (theta, Q) may vary within a range of about 35 to about 60 degrees; preferably, the slope angle constitutes about 45 degrees. Figs. 4C and 4D show the reactor configuration with separate slope elements 11B having slightly curved slope surface. In configuration shown on Figs. 4B-4D the base element 12 is provided as a substantially flat panel (e.g. 600 mm thick); thereby, at least two agitators 22 are received within the undivided interior 10. In further configurations (now shown), provision of the base element may be implemented in a manner shown on Fig. 4A. Hence, the reactor tank as shown on Fig. 4B may further comprise a separate partition element (not shown) to divide the interior 10 into at least two subsections. Each sloped module 11B is, in turn, provided as an elongated block or as a number of sequential blocks that extend through an entire length of the tank 101.

In order to ensure efficient mixing of material within the reactor tank 101 it configured with an essentially flat bottom, as shown on Figs. 4B-4D.

The reactor 100 further advantageously comprises at least one layer 13 of external lining- and/or insulation (Figs. 4A, 4B). The reactor tank 101 is further placed onto a foundation element 14 and it is sealed from the top by a flexible or rigid cover 15 (Figs. 1C, 1D, 4C, 4D).

While biogas being an ultimate product of bacterial digestion of organic feedstock entering the reaction space, most of biogas is produced during the middle of digestion, thereby, the reactor 100 is advantageously equipped with the inflatable cover and/or a rooftop for storage of biogas. The flexible cover 15 is provided as an expandable layer or a number of layers, which, when inflated, may accommodate in a stationary, rigid dome-shape rooftop structure 501 (Figs. 1A-1E). In some instances the cover 15 may be configured as a rigid, stationary structure (dome-shaped or flat), in which case the reactor is advantageously equipped with a biogas extraction system (not shown).

It is generally preferred that the rooftop structure for the reactor arrangement 100 is configured as a double-membrane structure comprising an inner membrane layer 15 and an outer membrane layer 501. The outer layer 501 is typically inflated by air and is configured to preserve its’ shape even in an absence of biogas production activity in the reactor tank(s) 101. The outer membrane 501 can be configured to cover a number of reactor tanks 101 (each covered with the inner membrane 15) at a time, e.g. one tank at a time (Figs. 1B, 1C) or several tanks at a time (Figs. 1D, 1E). The inner membrane 15 is typically formed by a gas-tight membrane inflatable upon production of biogas inside the reactor tank. The double membrane can be removed from one or more tanks for repair and maintenance. Mentioned actions require removal of both membranes for safety reasons (restoring air- /oxygen-rich atmosphere in a typically anaerobic tank). Other tanks in the reactor arrangement can still function normally when maintenance works are conducted in a single tank (although having the outer membrane 501 removed, in some configurations). In some configurations, a rooftop 501 A of a building or another support structure integrated with- or accommodating the anaerobic digestion reactor tank(s) is provided at an angle (Figs. 1B, 1C). In an example shown on Figs. 1B and 1C the wall on the pre-treatment side 401 (a feeding side) is about 9 m high, whereas the wall on the post-treatment side 201 (an output side) is about 6 m high. In described configuration, each reactor tank 101 is covered by a double membrane (layers 15 and 501). The reactor installation as shown on Figs. 1B, 1C is particularly suitable for geographical locations with essentially mild climate that eliminates the risk of accumulation of snow and rainwater between the rooftops.

Figs. 1D and 1E show a reactor arrangement in which the reactor tanks 101-1, 101-2 are covered by a common rooftop (the outer membrane 501). Such configuration is realized in an absence of the inclined rooftop structure. The reactor installation shown on Figs. 1D, 1E is particularly preferred in Nordic climate, since it allows for avoiding accumulation of snow and rainwater on the rooftop 501 (snow flows down from the rooftop 501).

Lateral profiles 11, 11A and/or 11B, and base (central) elements 12 can be realized as precast blocks (formed and hardened before being brought to the construction site), preferably made of concrete. Typical concrete blocks or slabs comprise of powdered Portland cement, water, sand and gravel. In some instances weighty sand and gravel in said concrete blocks may be replaced with lightweight expanded clay or expanded clay aggregate, for example. In some instances, precast cinder blocks may be utilized, in which the aforesaid gravel and sand are replaced by coal and/or cinders.

The wall- and base structures are preferably made of concrete and are molded on-site (on the site of assembling the reactor).

Additionally or alternatively, the aforesaid profiles can be manufactured from metal. Metal- based configurations include solutions consisting of metal sheets and optionally a core. In some embodiments, the lateral walls 11, llA are concrete slabs, whereas the slope modules 11B are metal-based blocks. Entirely metal-based configurations are not excluded.

In some embodiments (not shown) the reactor tank 101 may comprise a number of base (central) elements 12 positioned side-by-side to form at least two partitions extending, in parallel, in a longitudinal direction, thereby at least three adjoining subsections are formed within the interior 10 of the tank 101. Such configuration allows for accommodating at least three agitators 22, arranged in parallel, within the internal reaction space 10.

It is preferred that the reactor arrangement 100 further comprises a hygienization system 30 for thermally sanitizing digested substrate (Figs. 3, 4A, 4B, 5B). The hygienization treatment system 30 is configured for post-treating digested substrate D via inhibition and/or inactivation (reversible or irreversible deprivation of microbial activity, accordingly) of microorganisms contained in the digested substrate; thereby eliminating or at least reducing epidemiological risks.

The hygienization system 30 is thus configured to deliver heat, as a flow of thermal energy to digested substrate; thereby, attenuation / elimination of microbial activity is thermally- induced. By the way of examples, hygienization treatment has been conducted at a temperature of 70 °C for 1 hour; and at a temperature of 100 °C for 20 minutes; therefore flow rate through the appliances forming said hygienization system has been adjusted accordingly.

In preferred configurations, the hygienization system 30 is provided in a post-treatment facility 201 arranged downstream the at least one tank 101. Said hygienization system 30 can be integrated with a discharge appliance 203 configured to collect digested substrate D from a number of tanks 101 and to convey said digested substrate outside the reactor arrangement 100 (Fig. 5B). In some configurations, the appliance 203 can be configured as a conveyor, such as a scraper conveyor, for example, whereas the hygienization system 30 can be built around said conveyor to establish a heating jacket. Alternatively, the discharge appliance 203 can be configured as a heated conveyor or a conduit for conveying digested substrate from a number of tanks 101 towards exit.

Whether post-processing, viz. hygienization of digested substrate is not required, the appliance(s) 203 configured as a pipework, for example, can be used for heat recovery, via a number of heat-exchanger units 50, for example (Fig. 5B).

In some alternative configurations, the hygienization system 30 may be integrated into the slope elements S formed within the interior of the reactor tank 101 (Figs. 3, 4A, 4B). In such an event, the hygienization system comprises at least one conduit 31 encased in a jacket or a sheath 32. Heat is delivered to the conduit(s) 31 via said jacket(s) 32. The conduit or conduits 31 is/are configured to traverse through the lateral walls and/or the base of the tank 101 in a longitudinal direction and to receive digested substrate discharged through the primary effluent port 19.

The conduit(s) 31 can be configured to traverse through each lateral wall of the reactor tank 101 defined by a number of L-pro files 11 (Fig. 4A). Whether the L-pro files are formed by concrete slabs, in order to house the hygienization system 30 therewithin, each said slab comprises pre-fabricated through-apertures that form, upon assembling the reactor tank, a hollow, tubular duct or a channel. Alternatively, the conduit(s) 31 may be configured to traverse through the slope modules 11B (Fig. 4B). Additionally or alternatively, the conduit(s) 31 may be integrated into the base (central) element(s) 12.

The hygienization system 30 implemented as shown on Figs. 3, 4A, 4B is configured to receive digested substrate D discharged from the reactor tank 101 through the primary effluent port 19, to mediate advancement of said substrate D along the at least one conduit 31 from the discharge end 17 to the entrance end 16, thereupon microorganisms residing in said digested substrate are inhibited and/or inactivated, and to extract post-treated (hygienized) substrate Dl through an least one aperture 33 disposed at the entrance end of the reactor tank 101. Post-treated digested substrate Dl, withdrawn from the reactor 100 at the entrance end 16, is further conveyed elsewhere for storage or transportation.

Figs. 3, 4A, 4B show provision of the hygienization system 30 in the form of a single U- or Y-shaped conduit traversing from the primary effluent port 19 (at the discharge end 17) through both lateral walls, in particular, through slope elements S thereof, towards the apertures 33 arranged at the entrance end 16. Alternatively, the conduits extending through each lateral wall 11 may be provided as separate elements. Hence, as digested substrate D advances along the hygienization system 30 provided as encased conduits 31“piercing” the lateral walls 11 in a longitudinal direction, the digested substrate is sanitized by thermal post-treatment.

The heating jackets or other heating devices provided within the hygienization system 30 (Figs. 3, 5B) advantageously comprise heat transfer means communicating with heat- producing equipment. It is preferred that heat necessary for sanitizing is obtained from a heat recovery and circulation system 44 (Fig. 5B) described further below. Heating can be thus implemented via liquid circulation. Additionally or alternatively, heat transfer can be mediated by means of an external heat exchanger or a heat pump. Exemplary locations for heat exchangers 50 are shown on Figs. 3 and 5B.

The reactor arrangement 100 further comprises a temperature regulating system 40 configured to adjust temperature in the tank or tanks 101. The system 40 comprises a plurality of internal ducts 41, 42 configured to traverse, in a longitudinal direction, through lateral walls 11 and/or the base 12 of the tank, accordingly, and to convey temperature regulating fluid therealong (Figs. 4A-4C). By means of the temperature regulating system 40, temperature within the reactor tank 101 is maintained at a level suitable for the normal functioning of bacterial populations indispensable for anaerobic digestion.

In order to accommodate the temperature regulating arrangement 40 into the reactor tank 101, the elements 11, 11A forming the lateral walls and/or the base element(s) 12 can be provided as preformed, hollow-core concrete slabs with a plurality of hollow, tubular ducts 40. The ducts forming the arrangement 40 are preferably smaller in diameter than those forming the conduits 31. For clarity purposes, a reference number 41 shall further refer to the ducts disposed in the side walls 11, whereas the reference number 42 - to the ducts disposed in the base element 12. The ducts 41 and 42 are provided within the temperature regulating system 40.

In some embodiments, the ducts 41, 42 further comprise (e.g. metal) pipes encased in the concrete slabs forming lateral walls 11, 11A and/or base (central) element(s) 12 or an internal lining / coating to reduce wearing out of the concrete slabs. Coating, such as metal coating, for example, is preferably applied prior to assembling the blocks 11, 11 A, 12.

The temperature regulating fluid is a glycol compound, such as ethylene glycol or propylene glycol, for example. Alternatively, the temperature regulating liquid can be water. By circulating heating fluid through the ducts 41, 42, temperature within the reactor tank 101 is maintained sufficiently high for the mesophilic digestion (10 - 48 °C, preferably, 30 - 42 °C) or for the thermophilic digestion (42 - 97 °C, preferably, within 42 - 66 °C and, in some instances, within 43 to 55 °C).

The ducts 41, 42 forming the temperature regulating system 40 can be arranged into a substantially closed-loop recirculation path, wherein temperature regulating fluid recirculates between the ducts 41, 42 and the heat recovery and circulation system 44, described further below, and optionally at least one external heat source (not shown). To create the recirculation path, in some configurations the head-end wall element or head-end L-profiles may be provided with preformed turns and/or pipe elbows therewithin.

With reference to Fig. 6, in a number of configurations, an internal duct 43 configured to convey temperature regulating fluid therealong is arranged inside each agitator drive shaft 23. As mentioned hereinabove, the agitator axle(s) are provided as tubular bodies hollow from inside. The duct 43 formed inside each said agitator axle is utilized for conveying temperature-regulating fluid, such as glycol or water, along the duct and to provide additional heating to the substrate being stirred in the reactor tank 101.

Temperature regulating fluid (e.g. glycol) is fed into the duct 43 at a discharge side 17. Fluid circulates, via the axle 23, in a direction of the entrance end 16 (marked by arrow, Fig. 6) and returns back. The axles are preferably equipped, at least at the discharge end 17, with rotating couplers to allow directing temperature regulating fluid into the ducts 43 during rotation of the agitator axles 22. Provision of temperature regulating liquid inside the axles allows for equalizing microbial activity throughout the length of the reactor tank.

It is further preferred that temperature regimes within the ducts 41 disposed in the lateral walls of the tank 101 and within the ducts 42 disposed in the base of said tank are adjustable independently via a number of local temperature control units (not shown) and/or via a central heat distribution and control unit 51 (Fig. 7). Provision of the independent temperature controls for each of the walls and the bottom of the reactor tank 101 allows for proper allocation of thermal energy to the sites, within the tank, where material depositions and sediments are most likely to occur, e.g. on the sites, where substrate movement is slower or it is otherwise hindered.

In similar manner, temperature regime within the duct(s) 43 inside the agitator axle(s) can be controlled independently from that in the ducts 41 and/or 42.

The temperature regulating system 40 is preferably set to communicate with the heat recovery and circulation system 44 comprising at least one heat exchanger 50 (Figs. 3, 7). Excessive thermal energy released via the temperature regulating system 40 and/or the hygienization system 30 can be further supplied to the pre-treatment facility 401 and/or extracted for further utilization.

In some configurations, the ducts 41, 42 and 43 establish the temperature regulating system 40 and provide for (internal) temperature regulating fluid circulation within the reactor tank. The reactor 100 further comprises a so called external fluid circulation system, configured to (re)circulate fluid essentially outside the reactor tank, the latter further referred to as a system 44 for heat recovery and (re)circulation / re-use.

The system 44 configured for efficient recovery and re-use of heat produced during anaerobic digestion forms one of the core features of the reactor 100 (Figs. 5B, 7). The system 44 is preferably configured to transfer heat from the output side (facility 201) to the feedstock supply side (facility 401). Additionally, said heat recovery and (re)circulation system 44 is preferably configured to communicate with the “internal” temperature regulating system 40 and to direct heat thus recovered to said system 40 and optionally to the hygienization system 30.

Fig. 7 shows an exemplary configuration for the systems 40, 44 within the reactor 100. The temperature regulating system 40 comprising the ducts 41, 42, 43 and integrating the reactor tanks 101-1, 101-2 is shown in dashed lines. The heat recovery and (re)circulation system 44 is provided as a network of interconnected conduits or pipes configured to communicate heat obtained during anaerobic digestion (17, 201) towards the pre-treatment facility 401 and various appliances 301, 302, 401 therein. As indicated above, heat transfer occurs via liquid circulation.

We note hereby that the systems 40 and 44 form an integrated ensemble for heat recovery, circulation and temperature control. Said systems are referred, in the present disclosure, by distinct reference numerals in order to provide the reader with better understanding of the heat recovery functionality of the reactor arrangement 100.

Each of the systems 40, 44 advantageously comprises a number of local heat exchange units 50 and temperature control units, such as thermostats (not shown), to detect and to regulate temperature regimes in the reactor arrangement 100.

Integrated control over the systems 40, 44 is implemented via the central heat distribution and control unit 51 (Fig. 7). It is preferred, that at least one heat exchanger unit 50 is provided, within the heat recovery and circulation system 44, to mediate heat transfer between the tank(s) 101 (digestate discharge side) and the pre-treatment facility 401 (Fig. 5B). On Fig. 5B heat transfer from the output end (facility 201) to the input end (facility 401) is shown by an arrow (7).

The heat-exchanger unit or units 50 within the system 44 are therefore provided for delivery of thermal energy obtained from the anaerobic digestion process in at least one reactor tank 101 to the pre-treatment facility 401. Via said heat exchanger unit(s) 50 heat transfer can be mediated between the post-treatment facility 201 / the hygienization system 30, the temperature regulating arrangement 40 and the pre-treatment facility 401 (in an indicated order). Heat extracted from the facility 401 can be stored, transferred for further use and/or returned back to the output side (facility 201).

In some instances, the reactor 100 further comprises substrate recirculation means (not shown) for re-introducing a portion of digested substrate back into the reactor tank 101. Separation of this portion (inoculum) occurs before the digested substrate enters the hygienization system 30. It is preferred that at least one third of digested substrate is reversed back into the reactor 100 for maintaining stable bacterial populations in the reactor tank. A conduit or conduits configured for conveying inoculum back into the reactor tank are not subjected to thermal treatment.

The reactor 100 is configured for anaerobic digestion treatment of organic substrate, in which the content of dry matter (solid matter) constitutes 0 - 80 percent by weight (wt-%), preferably, 0 - 45 wt-%. In most instances, the organic substrate inside the reactor tank 101 has DM content within a range of 10 - 35 wt-%; however, the aforementioned range can vary on case-by-case basis. In some embodiments, preferred content of dry matter in feedstock constitutes about 35 wt-%. Organic substrate entering the reactor tank 101 is kept at a solid state, i.e. in the abovementioned range of 30 - 40 wt-% of dry matter. In exceptional cases, with a content of dry matter being equal or exceeding 50 wt-%, the reaction substrate needs to be diluted. Upon advancing along the length of the reactor tank 101 the organic substrate with DM about 35 wt-% solubilizes, thereby the digested product D contains approximately 25 wt-% of dry matter.

In some aspect of the invention, use of the reactor 100 is provided for anaerobic digestion of organic waste.

In some further aspect, use of the reactor 100 is provided for production of bio gas. As mentioned hereinabove the process of anaerobic digestion mediated by microbial activity results in production of biogas. Biogas is a mixture of predominantly methane (50-70%) and carbon dioxide (30-40%) with trace amounts of ammonia (NFU) and hydrogen sulfide (H₂S). Biogas obtained from the reactor 100 is advantageously directed for further refinement, such as for production of biofuels, for example.

Fig. 5 A shows the anaerobic digestion reactor arrangement 100 as a crosscut along an (imaginary) longitudinal symmetry axis, whereas Fig. 5B shows an exemplary layout of the arrangement 100 viewed from top. The reactor arrangement thus comprises at least one reactor tank 101 (three tanks 101-1, 101-2 and 101-3 are shown on Fig. 5B), the post- treatment facility 201 with heat transfer equipment discussed hereinabove and the pre- treatment facility 401, the latter comprising at least one feed tank 301 advantageously equipped with a lid 311, and a number of feed supply appliances 302, 402 configured to convey feedstock in a direction of the tank 101.

The feed tank(s) 301 can be configured to receive entirely unprocessed (“raw”) feedstock or pre-crushed feedstock. Pre-crushing, where applicable, is preferably implemented in a conventional crusher or a grounder prior to loading feedstock into the feed tank(s) 301. It is desirable that size of discrete aggregates, such as feedstock clumps and/or solid residues / inorganic matter, entering the reaction space 101 does not exceed a size of two clenched fists (150 - 200 mm). Whether organic waste to be processed by the reactor 100 contains or can be expected to contain larger aggregates and/or solid pieces (stones, gravel or cattle bones, for example), such waste should be pre-crushed in a manner described above.

On the other hand, whether feedstock to be processed is essentially homogenous and/or contains no outsized aggregates, the reactor 100 can be loaded with the impure substrate containing essential amounts of indigestible residue, such as sand, stone and a variety of plastics contaminants, in view of the embodiments described hereinabove.

Essentially impure feedstock is pre-processed, prior it enters the reactor tank 101, in a first feed supply appliance 302, and in a second feed supply appliance 402. The second appliance 402 that conveys feedstock into the reaction space 101 is preferably configured as a conveyor, such as a scraper conveyor, in the same manner as the discharge appliance 203 discussed hereinabove. It is preferred that said appliance 402 is configured to adjust the temperature of organic substrate entering the reactor tank or tanks 101 such, as to conform to the temperature maintained in said tank. Temperature-adjusted feedstock conveyed into the reactor tank(s) 101 by the feed supply appliance 402 is received into the reaction space through the influent port 18 provided at the entrance end 16.

In most instances, the feed supply appliance 402 is configured to thermally treat organic feedstock by heating, as the temperature maintained inside the reactor tank 101 ( inter alia, primarily by the temperature regulating arrangement 40) is normally higher in comparison to that of unprocessed feedstock. Need in regulation of temperature within the reactor tank 101 arises, in turn, from a necessity to maintain vital functions and activity of resident microorganisms. In some exceptional instances, the facility 401 can be configured to cool down input feedstock.

The appliances 302 configured to convey feedstock towards the storage (feed) tanks 301 towards the heated conveyor 402 are preferably configured as screw conveyors or as piston pumps.

It is clear to a person skilled in the art that with the advancement of technology the basic ideas of the present invention are intended to cover various modifications included in the spirit and the scope thereof. The invention and its embodiments are thus not limited to the examples described above; instead they may generally vary within the scope of the appended claims.

Claims

Claims

1. A reactor arrangement (100) for anaerobic digestion of biodegradable organic substrate, comprising:

at least one horizontally extended reactor tank (101) with an influent port (18) at an entrance end (16) and at least one effluent port at a discharge end (17) opposite to the entrance end (16),

at least two longitudinally extending agitators (22) disposed side by side within an interior (10) of the tank (101), and

a temperature regulating system (40) configured to adjust temperature in the at least one tank (101) and comprising a plurality of internal ducts (41, 42) configured to traverse, in a longitudinal direction, through lateral walls and/or a base of said at least one tank and to convey temperature regulating fluid therealong.

2. The reactor arrangement (100) of claim 1, configured to convey biodegradable organic substrate along the length of the tank (101) towards the discharge end such, that the digested organic substrate is discharged from the tank (101) through a primary effluent port (19), and the indigestible residue is discharged through an at least one auxiliary effluent port (20, 21).

3. The reactor arrangement (100) of any preceding claims 1 or 2, in which lateral walls that define, in a longitudinal direction, the interior (10) of the tank (101) are sloped, thereby a slope element or elements (S) are formed along an entire length of the tank at intersections between the lateral walls and the bottom.

4. The reactor arrangement (100) of any preceding claim, in which each lateral wall comprises a substantially flat panel or panels (11 A) with the slope element (S) provided as a separate module (11B).

5. The reactor arrangement (100) of any preceding claim, wherein each agitator (22) comprises a drive shaft (23) with a number of blades (24) mounted thereto.

6. The reactor arrangement (100) of any preceding claim, wherein an internal duct (43) configured to convey temperature regulating fluid therealong is arranged inside the agitator drive shaft (23).

7. The reactor arrangement (100) of any preceding claim, in which temperature regimes within the ducts (41) disposed in the lateral walls of the tank (101) and within the ducts (42) disposed in the base of said tank are adjustable independently.

8. The reactor arrangement (100), further comprising a pre-treatment facility (401) with an at least one feed supply appliance (402) configured to adjust the temperature of organic substrate entering the at least one reactor tank (101) such, as to conform to the temperature maintained in said tank.

9. The reactor arrangement (100) of any preceding claim, further comprising a hygienization system (30) for thermally sanitizing digested substrate.

10. The reactor arrangement (100) of any preceding claim, in which the hygienization system (30) is provided in a post-treatment facility (201) arranged downstream the at least one tank (101).

11. The reactor arrangement (100) of any preceding claims 1-9, in which the hygienization system (30) comprises at least one encased conduit (31) configured to traverse through the lateral walls and/or the base of the tank (101) in a longitudinal direction and to receive digested substrate discharged through the primary effluent port (19).

12. The reactor arrangement (100) of any preceding claim, further comprising a heat recovery and circulation system (44) configured to recover heat produced in the at least one tank (101) during anaerobic digestion and to direct heat thus recovered to the pre-treatment facility (401).

13. The reactor arrangement (100) of any preceding claim, wherein the heat recovery and circulation system (44) is further configured to direct recovered heat to the temperature regulating system (40) and optionally to the hygienization system (30).

14. The reactor arrangement (100) of any preceding claim, wherein the heat recovery and circulation system (44) comprises an at least one heat exchanger unit (50) for mediating heat transfer between the at least one tank (101) and the pre-treatment facility (401).

15. The reactor arrangement (100) of any preceding claim comprising a number of tanks (101) disposed next to one another.

16. Use of the reactor arrangement (100) as defined in claims 1-15 for anaerobic digestion of organic waste.

17. Use of the reactor arrangement (100) as defined in claims 1-15 for production of biogas.