NL2020730B1

NL2020730B1 - Biodrying installation

Info

Publication number: NL2020730B1
Application number: NL2020730A
Authority: NL
Inventors: Jan Van De Pol Gerrit
Original assignee: Gmb Bioenergie Zutphen B V
Priority date: 2018-04-06
Filing date: 2018-04-06
Publication date: 2019-10-14

Abstract

The invention provides a biodrying installation, comprising: - a plurality of drying tunnels (11); - a fresh air duct (35) for providing fresh air from an air inlet (40) to at least one of the plurality of drying tunnels; - an outlet air duct (36) for transporting air from at least one of the plurality of drying tunnels to an air outlet (44); - a first interconnecting air duct (37) connecting at least three drying tunnels of the plurality of drying tunnels; - a second interconnecting air duct (38) connecting at least three drying tunnels of the plurality of drying tunnels, wherein the first and second interconnecting air duct (37, 38) are provided with valves (V1-V24);

Description

Field of the invention [0001] The invention relates to a mixing system for a biodrying installation for sludge treatment and to a method for biodrying sludge.

Background of the invention [0002] Biodrying is a technology for removing water from a waste product with a relatively low solid content. An example waste product is the biomass (sludge) which is produced in wastewater treatment. The sludge is an unwanted by-product of the treatment and presents rising challenges since processing the sludge accounts for a significant part of the total cost of a wastewater treatment plant.

[0003] A commonly used technology to handle organic waste is biological composting. Composting aims for the maximal conversion of organic material. Therefore, water is added to the process when the organic matrix reaches certain dryness in order to preserve moisture for optimal microbial activity and hence maximal organic conversion. As a consequence, long residence times of circa 50 days are required, which is less practical for large quantities of sludge.

[0004] Biodrying differs from the conventional composting process and does not aim towards a complete mineralization of the waste. Instead the metabolic heat is used to remove water from the waste matrix at the lowest possible residence time and minimal biodegradation hence preserving most of the gross calorific value of the waste matrix. During this process the organic matrix is both; substrate for microorganisms (which produce heat for drying) and the end product. The end product (fuel/granules) contains a high energy value and can be used as a replacement of coal and for thermal energy generation. Bio-drying of sludge can (in contrast to a conventional way of dealing with waste, such as landfilling) reduce fossil fuel requirements and henceforth greenhouse gas emissions if combusted to produce steam and or power.

[0005] In a biodrying installation, the biodrying process is organized in different stages. For an optimal process, both in terms of speed and resulting increase in solid content fraction, the installation must supply each stage with an optimal mix of sludge, air, and temperature.

Summary of the invention [0006] According to a first aspect, the invention provides a biodrying installation, comprising:

- a plurality of drying tunnels, preferably at least three drying tunnels;

- a fresh air duct for providing fresh air from an air inlet to at least one of the plurality of tunnels;

- an outlet air duct for transporting air from at least one of the plurality of tunnels to an air outlet;

- a first interconnecting air duct connecting at least three biodrying tunnels of the plurality of biodrying tunnels;

- a second interconnecting air duct connecting at least three biodrying tunnels of the plurality of biodrying tunnels, wherein the first and second interconnecting air duct are provided with valves;

[0007] In an embodiment according the invention, the fresh air duct is connected to each tunnel of the plurality of drying tunnels through respective branches, and each branch is provided with a valve.

[0008] In an embodiment according the invention, the outlet air duct is connected to each tunnel of the plurality of drying tunnels through respective branches, and each branch is provided with a valve.

[0009] In an embodiment according the invention, the first air duct is connected to each tunnel of the plurality of drying tunnels through respective branches, and each branch is provided with a valve.

[0010] In an embodiment according the invention, the second air duct is connected to each tunnel of the plurality of drying tunnels through respective branches, and each branch is provided with a valve.

[0011] In an embodiment according the invention, the outlet air duct is provided with one or more of:

- an air scrubber

- a cooling unit; and

- a biofilter.

[0012] In an embodiment according the invention, the outlet air duct is provided with a one way valve configured to let air pass in the direction of the air outlet.

[0013] In an embodiment according the invention, a tunnel of the plurality of tunnels has a volume of at least 500 m³, preferably at least 1000 m³, more preferably at least 1500 m³, or more than 2000 m³. With effective volume is meant the volume that can be effectively used for loading sludge. As a practical example, with tunnels that are 7 meters high, wheel loaders can typically fill the tunnel up to 5.5 meters. The effective volume is then determined by the effective height of 5.5 meters and not the actual height of 7 meters. For example, the effective volume can be about 70% to 80% of the actual volume of a tunnel.

[0014] In an embodiment according the invention, the biodrying installation further comprises:

- a mixing system for mixing sludge material;

- a transport area for transporting sludge between the drying tunnels and the mixing system, wherein the mixing system comprises:

- a fresh sludge inlet

- a composted sludge inlet;

- a mixture outlet

- a fine material outlet, wherein the fresh sludge inlet is connected to an inlet of a mixing unit via a fresh sludge transport means, the composted sludge inlet is connected to a sieve unit via a composted sludge transport means, the sieve unit configured to separate fine material from composted sludge and to provide said fine material via a fine material transport means to the fine material outlet and to provide unseparated sludge to the mixing unit via an unseparated sludge transport means, and an outlet of the mixing unit is connected to the mixture outlet via a mixture transport means.

[0015] The invention further relates to a method for biodrying using a biodrying installation as described above, wherein the valves are configured so that to each biodrying tunnel air is supplied by at least one of the various air ducts in such a manner that the supplied air is suitable for the biodrying phase of the material currently located in each biodrying tunnel.

Brief description of the figures [0016] Embodiments of the present invention will be described hereinafter, by way of example only, with reference to the accompanying drawings which are schematic in nature and therefore not necessarily drawn to scale. Furthermore, like reference signs in the drawings relate to like elements.

[0017] Figure 1 schematically shows a floorplan of a biodrying installation according to an embodiment of the invention;

[0018] Figure 2 schematically shows a mixing system for a biodrying installation according to an embodiment of the invention;

[0019] Figure 3 schematically shows an air circulation system for a biodrying installation according to an embodiment of the invention; and [0020] Figure 4 schematically shows a further air circulation system for a biodrying installation according to an embodiment of the invention.

Detailed description [0021] Figure 1 schematically shows a floorplan of a biodrying installation according to an embodiment of the invention. The biodrying installation comprises a number of drying tunnels 11. In the present example, 9 tunnels labelled T1 through T9 are shown. Each tunnel has a door 12 for loading and unloading sludge. A tunnel can have a volume of at least 500 m³ (cubic meters), preferably at least 1000 m³, more preferably at least 1500 m³, or more than 2000 m³.

[0022] Around the tunnels, a transport zone 13 is provided. The transport zone 13 comprises means, such as wheel loaders (not shown), for loading and unloading the tunnels 11 through the respective tunnel doors 12. Furthermore, a mixing system 14 is provided for mixing various types of sludge.

[0023] While in figure 1 only nine tunnels 11 are shown, practical installations may have a different number of tunnels. Prior to the drying process, the sludge is mixed in the mixing zone 14 with the coarse fraction of already pre-dried sludge. The mixed sludge with a dry solid content of 45% is then loaded by the wheel loaders into one or more tunnels 11. In addition, woodchips are included to the process as structure material to allow a good aeration of the sludge during composting. After sealing the tunnels the sludge is aerated by blowing air through specially designed aeration shafts (spigots) integrated in the concrete floor. The installation can be used with sludge with a dry solid content of preferably above 40%, more preferably above 43%.

[0024] The majority of tunnels (e.g. 6 out of 9) is typically in use for the first drying batch lasting 10 days. Ideally only two tunnels (for re- and unloading) are open at the same time while the remaining tunnels are closed for drying of the sludge. After the first drying batch (10 days) the sludge is taken out of the tunnels and screened. The coarse fraction is used for mixing with fresh sludge and the fine fraction is brought to the second drying batch for further drying. The remaining tunnels (e.g. 3 out of 9) are used for a second drying batch lasting 14 days.

[0025] Figure 2 schematically shows a mixing system 14 for a biodrying installation according to an embodiment of the invention.

[0026] The sludge that can be treated in the installation can be from municipal and industrial wastewater treatment plants with an average total solid content of about 25% (typical range is between 20% and 25%) and with an organic fraction of about 65% (typical range is between 55% and 85%). The fresh sludge is provided to fresh sludge inlet 32 and transported via conveyer belt 31 to the mixing unit 30. Partially composted sludge, which has already been dried in the first batch, is provided via the composted sludge inlet 21. A part of the composted sludge is transported via conveyer belt 24 to the mixing unit 30, while another part of the composted sludge is transported via belt 22 to a sieve unit 26. In the sieve unit, the finer solid material is separated from the composted sludge. The finer material is transported via conveyer belt 28 to the fine sludge outlet 29, for transport to a second batch tunnel. The mixed output of the mixing unit 30 is transported via conveyer belt 33 to mixed sludge outlet 34. The sieve unit can have holes with a diameter of between 4 and 10 mm, preferably between 6 and 8 mm, such as 7 mm.

[0027] The system is not limited to the use of conveyer belts to transport the sludge. Any suitable transport means can be used.

[0028] It is also not required to have two composted sludge inlets. It is possible to have just one sludge inlet connected to the sieve unit 26. Alternatively, a splitting unit (not shown in figure 2) can be provided in the conveyer belt 22 between the sludge inlet and the sieve unit 26 for diverting a part of the composted sludge directly to the mixing unit 30, bypassing the sieve unit 26.

[0029] Figure 3 schematically shows an air circulation system for a biodrying installation according to an embodiment of the invention.

[0030] In figure 3, three tunnels T1 - T3 are shown. In an embodiment according the invention, the biodrying installation uses tunnels that are clustered and each cluster consists of three tunnels. These tunnels are connected to each other by first interconnecting air duct 37 and second interconnecting air duct 38. Each tunnel is connected to each of the interconnecting air ducts 37, 38 through branch lines.

[0031] A fresh air duct 35 is connected to the outside air via a fresh air inlet 40 and to each of the three tunnels T1, T2, T3 via further branch lines. Likewise, an outlet air duct 36 is connected to each of the three tunnels T1, T2, T3 via further branch lines and to an air (acid) scrubber 41, cooling unit 42, biofilter 43, and finally an outlet 44 to the outside air. The process air to be vented to the outside air is thus treated for odour control, heat and nitrogen recovery.

[0032] A plurality of valves V1-V24 are provided in the various branch lines to allow an operator to open or close a connection of a specific tunnel T1 - T3 with a specific air duct 36 - 35. Valves V-3, V-14, V-16, provided in the branch lines leading to the outlet air duct 36, are one-way valves which only allow air to pass in a direction away from the respective tunnels T1, T2, T3. Ventilators 39 may be provided in the various branch lines and air ducts to help move the air along the branch lines and ducts..

[0033] The valves V1-V24 allow the operator of the biodrying installation to set up air flows which are appropriate for the phase of the biodrying batch. That is, by changing the air flow in the tunnels depending on the phase of the biodrying batch, the sludge can remain in the same tunnel throughout the first batch, advantageously removing the need for costly and complex moving around of sludge during a batch period.

[0034] For example, in figure 3 the valves are set so that only the first tunnel T1 takes in fresh air through air duct 36. The valve settings are so that the air from tunnel T1 is carried by a branch line to the third air duct 38, which brings the air from tunnel T1 to tunnel T2. A part of the air from tunnel T1 is carried by the first air duct 36 to the air scrubber 41 and finally the outlet 44. The valves are further configured so that the air from tunnel T2 is carried by the second air duct to tunnel T3. Again, A part of the air from tunnel T2 is carried by the first air duct 36 to the air scrubber 41 and finally the outlet 44. The air from tunnel T3 is also carried by the first air duct 36 to the air scrubber 41 and finally the outlet 44. The sequence is thus that outside air goes through air duct 36 to tunnel T1, then through air duct 38 to tunnel T2 and through air duct 37 to tunnel T3, finally through air duct 36 to the outside. By setting the valves accordingly, the order of tunnels can be adjusted, so that the tunnels T1, T2, T3 can be visited by the fresh air in any order (six permutations in total).

[0035] The configuration of valve settings according figure 3 may be used as follows. The tunnel T1 may be at the end of the biodrying procedure of batch one and hence contain warm dried sludge that needs to be cooled down. The drying process will also heat the air. The heated air (typically 60 degrees Celsius) is then discharged to tunnel T2 where it is used to dry the sludge. From tunnel T2, the hot air is transported to tunnel T3 where the fresh sludge mixture needs to be heated to start the composting process. By using the same air three times the air flow to be cleaned remains as low as possible and odorous components are partly broken down in the biodrying process. By using the system of air ducts 35 - 38 with valves V1 - V24, it is possible to change the air circulation according the phase of the biodrying batch while leaving the sludge in the same tunnel. That is, when the sludge is any given tunnel is ready to be moved to the next phase, the valves are adjusted so that the drying sludge is provided with an appropriate air flow.

[0036] The first biodrying batch takes approximately 10-12 days. The second batch is similar to the first batch, but takes somewhat longer. Heated air from a later phase in the first batch is used. This air is already hot, saturated with water and contains enough oxygen for fast activation of the microbiological process. The second drying batch also acts as a biofilter and was operated for circa 2 weeks until achieving a dry matter content of 65-70%. The end product is cooled with fresh air and the tunnel is emptied by wheel loaders.

[0037] .In the exemplary embodiment according the invention of figure 3, the tunnels are clustered in groups of three, which is practical if a batch drying process is organised in a limited number of phases, which each phase requiring a different air flow. However, it is not necessary to use tunnel clusters of three, other numbers of tunnels in a cluster are also possible.

[0038] Also the fresh air ducts and the outlet air ducts may be connected to each tunnel with a respective branch line, with a valve in each branch line. In other embodiments, the fresh air ducts and/or the outlet air ducts are only connected to a subset of the tunnels, e.g. to every second or every third tunnel.

[0039] In a general biodrying installation, the fresh air duct 35, the outlet air duct 38 is connected to every tunnel. The first and second air ducts 37 and 38 also connect every tunnel through branch lines. This is schematically shown in figure 4.

[0040] Figure 4 shows a series of n tunnels T1, T2, T3 ... Tn. Here n can in principle be any number, and defines the number of tunnels in a cluster. It is possible to have just one cluster, so that the total number of tunnels equals the number of tunnels in a cluster. Typical biodrying installations may use 5 to 40 tunnels or more specifically 10 to 30 tunnels in total. All tunnels T1 - Tn are configurably (through valves, not shown in figure 4) connected to the fresh air inlet 40 via duct 35 and to the outlet 44 via duct 36. Moreover, all tunnels T1 - Tn are configurably (through said valves) connected to each other via interconnecting air ducts 37 and 38. For example, valves can be configured so that air duct 37 connects T1 and T2, air duct 38 connects T2 and T3, air duct 37 again connects T3 and T4, and so on. The sections of air duct 37 which interconnect T1 and T2 and T3 and T4 are separated from each other by a closed valve in air duct 37. In this manner, the operator can set up arbitrary clusters (such as the three tunnel cluster of figure 3) within the larger cluster of n tunnels of figure 4. In this manner, the biodrying installation can cater for various ways of batch processing material in different phases with a minimum amount of moving material between tunnels.

[0041] In the foregoing description of the figures, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the scope of the invention as summarized in the attached claims.

[0042] In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

[0043] In particular, combinations of specific features of various aspects of the invention may be made. An aspect of the invention may be further advantageously enhanced by adding a feature that was described in relation to another aspect of the invention.

[0044] It is to be understood that the invention is limited by the annexed claims and its technical equivalents only. In this document and in its claims, the verb to comprise and its conjugations are used in their non-limiting sense to mean that items following the word are included, without excluding items not specifically mentioned. In addition, reference to an element by the indefinite article a or an does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article a or an thus usually means at least one.

List of reference numbers

10: biodrying installation

T1 - T9, 11: tunnel

12: tunnel door

13: transport area

14: area mixing system

21: composted sludge inlet

22, 24, 25, 27, 28, 31, 33: sludge conveyer belts

26: sieve unit

29: fine materials outlet

30: mixing unit

32: fresh sludge inlet

34: mixture outlet

35: fresh air duct

36: outlet air duct

37: first interconnecting air duct

38: second air duct

V1 - V24: valves

40: fresh air inlet

41: air scrubber

42: cooling unit

43: biofilter

44: air outlet

Claims

Conclusions

A biodrying installation, comprising

- a plurality of drying tunnels (11);

- a fresh air duct (35) for providing fresh air from an air inlet (40) to at least one of the plurality of drying tunnels;

- an air outlet channel (36) for transporting air from at least one of the plurality of drying tunnels to an air outlet (44);

- a first connecting channel (37) connecting at least three drying tunnels of the plurality of drying tunnels;

- a second connecting channel (38) connecting at least three drying tunnels of the plurality of drying tunnels, the first and the second connecting channel (37, 38) being provided with valves (V1-V24), the fresh air channel (35) being connected to each drying tunnel of the plurality of drying tunnels through respective branches, and each branch is provided with a valve, the first connecting channel (37) being connected to each drying tunnel of the plurality of drying tunnels through respective branches, and each branch is provided with a valve, and wherein the second connecting channel (38) is connected to each drying tunnel of the plurality of drying tunnels through respective branches, and each branch is provided with a valve.

The biodrying plant according to claim 1, wherein the air outlet channel (36) is connected to each drying tunnel of the plurality of drying tunnels through respective branches, and each branch is provided with a valve.

The biodrying installation according to any of the preceding claims, wherein the air outlet channel (36) is provided with one or more of:

- an air purifier (41);

- a cooling unit (42); and

- a biofilter (43).

The biodrying installation according to any of the preceding claims, wherein the air outlet channel (36) is provided with a one-way valve adapted to allow air to pass in the direction of the air outlet (44).

The biodrying installation according to any of the preceding claims, wherein a drying tunnel of the plurality of drying tunnels has a volume of at least 500 m ³ , preferably at least 1000 m ³ , more preferably at least 1500 m ³ , or more than 2000 m ³ .

The biodrying plant according to any of the preceding claims, further comprising

- a mixing system (14) for mixing sludge material;

- a transport area (13) for transporting sludge between the drying tunnels and the mixing system;

wherein the mixing system comprises:

- a fresh sludge inlet (32);

- a composted sludge inlet (21);

- a mixture outlet (34);

- a fine material outlet (29), wherein the fresh sludge inlet is connected to an inlet of a mixing unit (30) via a fresh sludge transport means (31), the composted sludge inlet is connected to a screening unit (26) via a composted sludge transport means (22), the screening unit (26) adapted to separate fine material from composted sludge and to supply the fine material via a fine material transport means (28) at the fine material outlet (29) and to provide unseparated sludge at the mixing unit (30), which mixing unit (30) is connected to the mixture outlet (34) via a mixture transport means (33).

7. Biodrying method using a biodrying installation according to one of the preceding claims, wherein the valves are configured such that each biodrying tunnel is provided with air suitable for the biodrying phase of the material occurring through at least one of the various air ducts.

5 is currently located in every biodrying tunnel.

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