COMBINATION OF ANAEROBIC TREATMENT OF CARBONACEOUS MATERIAL WITH HYDROTHERMAL GASIFICATION TO MAXIMIZE VALUE ADDED PRODUCT RECOVERY

Abstract

A method for treating carbonaceous material, the method includes a) providing a carbonaceous material CM, b) subjecting the carbonaceous material CM to hydrothermal gasification in a HTG reactor, thereby producing: an inorganic solid residue, a first gaseous fraction G1 comprising CH.sub.4, CO, CO.sub.2 and H.sub.2, and a filtrate F1 containing readily biodegradable carbons such as VFAs, c) subjecting at least part of the filtrate F1 to an anaerobic treatment step in an anaerobic tank, leading to a digestate. An installation for treating carbonaceous material is also provided.

Claims

1. A method for treating carbonaceous material, said method comprising: a) providing a carbonaceous material CM, b) Subjecting subjecting the carbonaceous material CM to hydrothermal gasification operated at a temperature of between 300° C. and 500° C., and at a pressure selected so as to maintain sub- or supercritical conditions, thereby producing: an inorganic solid residue, a first gaseous fraction G1 comprising CH.sub.4, CO, CO.sub.2 and H.sub.2, and a filtrate F1 containing readily biodegradable carbons such as VFAs, c) Subjecting subjecting at least part of the filtrate F1 to an anaerobic treatment step, leading to a digestate

2. The method of claim 1, wherein the HTG step b) is performed at a temperature of between 320° C. and 400° C., and a pressure of between 220 bar and 400 bar, selected so as to maintain sub- or supercritical conditions.

3. The method of claim 1, further comprising a step d) of separating the digestate of step c) into a liquid fraction and a solid fraction.

4. The method of claim 3, wherein the liquid fraction of step d) is subjected to a step e) of recovering the added value compounds such as VFAs.

5. The method of claim 1, to wherein the solid fraction of step d) is combined (step f) with the carbonaceous material CM and the resulting mixture is subjected to the HTG step b).

6. The method of claim 1, wherein the carbonaceous material CM has a dry solid content of between 3% and 25%.

7. The method of claim 1, wherein the carbonaceous material CM has a carbon/nitrogen ratio of 40 or less.

8. An installation for treating carbonaceous material, said installation comprising: a HTG reactor suitable for hydrothermal gasification, having a first inlet (I.sub.cm) and a first (O.sub.s), second (O.sub.g1) and third (O.sub.f1) outlets, the HTG reactor being configured to be fed at the first inlet (I.sub.cm) with a carbonaceous material CM, and to produce: an inorganic solid residue, recovered at the first outlet (O.sub.s), a first gaseous fraction G1 comprising CH.sub.4, CO, CO.sub.2 and H.sub.2 recovered at the second outlet (O.sub.g1), and a filtrate F1, optionally containing readily biodegradable carbons such as VFAs, recovered at the third outlet (O.sub.f1), and an anaerobic tank, suitable for fermentation or anaerobic digestion, having a first inlet (I.sub.l), and a first outlet (O.sub.d), the first inlet (I.sub.l) being in fluid connection with the third outlet (O.sub.f1) of the HTG reactor, the anaerobic tank being configured to be fed at the first inlet (I.sub.l) with filtrate F1, and to produce: a digestate at the first outlet (O.sub.d).

9. The installation of claim 8, further comprising a phase separator having: a phase separator inlet (I.sub.d) connected to the first outlet (O.sub.d) of the anaerobic tank, a first phase separator outlet (O.sub.lf), a second phase separator outlet (O.sub.sf), the phase separator being configured to be fed at the phase separator inlet (I.sub.d) with the digestate, and to separate the digestate into a liquid fraction toward the first phase separator outlet (O.sub.lf) and a solid fraction toward the second phase separator outlet (O.sub.sf).

10. The installation of claim 9, wherein the second outlet (O.sub.sf) of the phase separator is in fluid connection with the first inlet (I.sub.cm) of the HTG reactor, and the HTG reactor is configured to be fed with the solid fraction at the first inlet (I.sub.cm) of the HTG reactor.

11. The installation of claim 8, wherein the anaerobic tank is a digester and further comprises a second outlet (O.sub.g2), and the anaerobic tank is configured to further produce a second gaseous fraction G2 containing CH.sub.4, CO.sub.2 and optionally H.sub.2 recovered at the second outlet (O.sub.g2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0107] The accompanying drawings illustrate various non-limiting, exemplary, innovative aspects in accordance with the present description:

[0108] FIG. 1 schematically represents a block diagram with the steps of the method for treating carbonaceous material according to the invention;

[0109] FIG. 2 schematically represents a block diagram with optional steps of the method for treating carbonaceous material according to the invention;

[0110] FIG. 3 schematically represents a first embodiment of the installation for treating carbonaceous material according to the invention;

[0111] FIG. 4 schematically represents another embodiment of the installation for treating carbonaceous material according to the invention;

[0112] FIG. 5 schematically represents another embodiment of the installation for treating carbonaceous material according to the invention;

[0113] FIG. 6 schematically represents another embodiment of the installation for treating carbonaceous material according to the invention.

DETAILED DISCLOSURE

[0114] FIG. 1 schematically represents a block diagram with the steps of the method for treating carbonaceous material according to the invention. The method for treating carbonaceous material comprises a step a) of providing a carbonaceous material CM. The method according to the invention further comprises a step b) of subjecting the carbonaceous material CM to hydrothermal gasification in a HTG reactor 11, thereby producing an inorganic solid residue 12, a first gaseous fraction G1 comprising CH.sub.4, CO, CO.sub.2 and H.sub.2 (i.e. syngas), and a filtrate F1 containing readily biodegradable carbons such as VFAs. And the method according to the invention comprises a step c) of subjecting at least part of the filtrate F1 to an anaerobic treatment step in an anaerobic tank 13, leading to a digestate 14.

[0115] The method according to the invention enables to produce Readily Biodegradable Carbons rather than fully converting the organic matter into syngas, the pressure and temperature operating conditions of HTG are lowered. Furthermore the anaerobic treatment reduces the HTG energy requirements by reducing the need to fully convert all organic matter into syngas, and is improved by the presence of RBCs into the filtrate F1.

[0116] FIG. 2 schematically represents a block diagram with optional steps of the method for treating carbonaceous material according to the invention. The method according to the invention may comprise all the optional steps or only one or some of them.

[0117] Advantageously, the HTG step b) is performed at a temperature of 500° C. or below, preferably of 400° C. or below, so that water in the HTG reactor 11 is exposed to a temperature and a pressure allowing to keep water in a fluid fraction under sub- or supercritical conditions. Pressure in the HTG step depends on the temperature and is chosen so as to maintain sub- or supercritical conditions. To maintain the desired sub- or supercritical conditions and sufficient degradation of the organic matter, the temperature of the HTG step is advantageously of 300° C. or above, preferably of 330° C. or above. This temperature condition enables to promote the separation of the carbonaceous material CM into the various products of the HTG.

[0118] The method of the invention may comprise a step d) of separating the digestate 14 of step c) into a liquid fraction 16 and a solid fraction 17. Advantageously, the liquid fraction 16 of step d) is subjected to a step e) of recovering the added value compounds such as VFAs.

[0119] In an embodiment of the invention, the solid fraction 17 of step d) is combined (step f) with the carbonaceous material CM and the resulting mixture is subjected to the HTG step b).

[0120] Advantageously, the carbonaceous material CM has a dry solid content of between 3% and 25%.

[0121] Advantageously, the carbonaceous material CM has a carbon/nitrogen ratio (C/N ratio) of 40 or less.

[0122] Optionally, the method of the invention may comprise a step of cooling the at least part of the filtrate F1 subjected to the anaerobic treatment step prior to the anaerobic treatment. The step of cooling may be performed with cooling techniques known by the person skilled in the art.

[0123] Optionally, and if the ammonium concentration in the filtrate F1 is too high, the method of the invention may comprise a step of reducing the ammonium concentration in the filtrate F1. This can be done using techniques known by the person skilled in the art, for example diluting the filtrate F1 with water. This enables to reduce the ammonium concentration in the filtrate F1, thus avoiding ammonia toxicity problems in the anaerobic treatment step.

[0124] The method of the invention makes it possible to lower, or even eliminate, the sludge amount to be disposed of, whereas it maximizes the syngas and biogas production. Furthermore, the syngas and biogas production may be upgraded downstream, for example through electricity production, grid reinjection, NLG production, etc. When the anaerobic treatment is a fermentation, the method of the invention enables to produce a high concentrated, high value liquid. It also removes the need for a dewatering step downstream the fermentation reactor (saving OPEx, in particular by avoiding the use of polymers). Nevertheless, the possibility for land application of sludge (typically either class A or class B sludge) is maintained. Also, the method according to the invention enables the nutrient recovery, in particular phosphorus (P) in the ashes produced in the HTG step.

[0125] FIG. 3 schematically represents a first embodiment of the installation 10 for treating carbonaceous material according to the invention. The installation 10 for treating carbonaceous material according to the invention comprises a HTG reactor 11 suitable for hydrothermal gasification, having a first inlet I.sub.cm and a first O.sub.s, second O.sub.g1 and third O.sub.f1 outlets. The HTG reactor 11 is configured to be fed at the first inlet I.sub.cm with a carbonaceous material CM, and to produce an inorganic solid residue 12, also called ashes, recovered at the first outlet O.sub.s, a first gaseous fraction G1 comprising CH.sub.4, CO, CO.sub.2 and H.sub.2 recovered at the second outlet O.sub.g1, and a filtrate F1 containing readily biodegradable carbons such as VFAs, recovered at the third outlet O.sub.f1.

[0126] The installation 10 further comprises an anaerobic tank 13, suitable for fermentation or anaerobic digestion, having a first inlet I.sub.l and a first outlet O.sub.d. The first inlet I.sub.l is in fluid connection with the third outlet O.sub.f1 of the HTG reactor 11. The anaerobic tank 13 is configured to be fed at the first inlet I.sub.l with filtrate F1, and to produce a digestate 14 recovered at the first outlet O.sub.d.

[0127] The installation according to the invention enables the sludge treatment, which is reduced into syngas, which can be directly used as a fuel, without the need for drying, thickening or dewatering the sludge upstream. No organic matter is left. Ashes are concentrated in both heavy metals and nutrients, which can then be recovered. The major disadvantage of the HTG step is the severe conditions that it imposes such as high temperature and pressure. The HTG reactor should therefore be maintained at a high temperature and pressure level, which is very energy consuming. The advantage of the installation lies in the coupling of the HTG reactor and the anaerobic tank which is fed with the filtrate resulting from the HTG step. Through a digestion or fermentation step in the anaerobic tank, biogas, i.e. an energy source, is produced.

[0128] In other words, the invention couples an energy-consuming HTG step with an energy-producing anaerobic treatment. The HTG step may be performed under a low amount of oxygen to control the formation of specific products, such as easily biodegradable material and to produce energy. Such an HTG step allows the solubilization of suspended carbons in the sludge and enables a phase separation. The resulting RBCs-rich filtrate is fed to the anaerobic tank. RBCs are broken down, thus producing biogas. The other products resulting from the HTG step (inorganic solid residue, gaseous fraction) and from the anaerobic treatment (digestate, gaseous fraction) may be further processed and valued.

[0129] In the figures, the anaerobic tank 3 is represented as one unit (FIGS. 3 to 6) and the step c) of anaerobic treatment is represented as a single step (FIGS. 1 and 2). Nevertheless, the anaerobic treatment of the invention may be a two phase anaerobic digestion (i.e. an anaerobic digestion occurring in two phases: a mesophilic or thermophilic acidogenesis followed by a mesophilic digestion, also known as TPAD or 2PAD) downstream of the HTG step. If the anaerobic treatment is a two phase anaerobic digestion, the anaerobic tank 13 is to be understood as an anaerobic digester configured to operate a two phase anaerobic digestion. This alternative enables to optimize the first fermentation step, as explained below. Indeed heat treatments (such as pyrolysis, gasification, HTL or HTG) generate not only biodegradable molecules (VFA and sugars) but also numerous phenolic derivatives (nearly 50% of the secondary sludge produced). These phenolic derivatives, for example phenols and furans with high inhibitory properties, such as hydroxymethylfurfural or furfural, are known to be toxic to methanogenic populations. Therefore, a standard anaerobic digestion does not seem to be compatible downstream such a heat treatment.

[0130] Despite this toxicity, it was shown that the coupling between digestion and pyrolysis oil reduces the concentration of aromatic compounds (i.e. furfural, phenol, etc.) below the thresholds of detection as a function of the input concentration in digestion. An anaerobic microbial degradation pathway (involving Ruminococcaceae and Peptococcaceae family) could be found for the degradation of aromatic sub-compounds derived from vanillate and syringate.

[0131] A 2-phase digestion (TPAD) downstream the HTG step can degrade phenols generated during the HTG step and increase biogas production without suffering apparent inhibition in comparison to a mesophilic digester operating under the same conditions.

[0132] Furthermore, either in the case of a standard anaerobic treatment or in the case of a 2-phase digestion, the invention may also comprise a step of diluting the filtrate F1 produced by the HTG step before being subjected to the anaerobic treatment or the 2-phase digestion. This dilution, performed using techniques known by the person skilled in the art, enables to maintain toxicity below a certain threshold. FIG. 4 schematically represents another embodiment of the installation 20 for treating carbonaceous material according to the invention. The installation 20 for treating carbonaceous material according to the invention comprises the same elements as the installation 10. The installation 20 further comprises a phase separator 15 having a phase separator inlet I.sub.d connected to the first outlet O.sub.d of the anaerobic tank 13, a first phase separator outlet O.sub.lf, a second phase separator outlet O.sub.sf. The phase separator 15 is configured to be fed at the phase separator inlet I.sub.d with the digestate 14, and to separate the digestate 14 into a liquid fraction 16 toward the first phase separator outlet O.sub.lf and a solid fraction 17 toward the second phase separator outlet O.sub.sf.

[0133] The installation 20 represented in FIG. 4 comprises an optional pre-treatment device 45, such as an optional phase separator 45. The optional phase separator 45 is configured to separate the carbonaceous material CM into a liquid fraction 46 and a solid fraction 47, in particular by dewatering, prior to being introduced into the HTG reactor 11. In this embodiment, a phase separation of the carbonaceous material CM is performed upstream the HTG and the HTG reactor is fed with the solid fraction from the phase separation. This optional phase separator enables to concentrate the carbonaceous material CM if it is too liquid. The dry solid content of the carbonaceous material CM is typically between 3 and 25%. But if it is about 3%, it is advantageous to thicken it until its dry solid content becomes about 12%.

[0134] The pre-treatment device 45 is optional and is only represented in FIG. 4, but it could be implemented in each example of the invention.

[0135] FIG. 5 schematically represents another embodiment of the installation 30 for treating carbonaceous material according to the invention. The installation 30 for treating carbonaceous material according to the invention comprises the same elements as the installation 20. In the installation 30, the second outlet O.sub.sf of the phase separator 15 is in fluid connection with the first inlet I.sub.cm of the HTG reactor 11, and the HTG reactor 11 is configured to be fed with the solid fraction 17 at the first inlet I.sub.cm of the HTG reactor 11. This recirculation of the solid fraction 17 in the HTG reactor 11 allows to lower, or even eliminate, the sludge amount to be disposed of. FIG. 6 schematically represents another embodiment of the installation 40 for treating carbonaceous material according to the invention. The installation 40 for treating carbonaceous material according to the invention comprises the same elements as the installation 20 or 30. In the installation 40, the anaerobic tank 13 comprises a second outlet O.sub.g2. The anaerobic tank 13 is configured to produce a second gaseous fraction G2 containing CH.sub.4 and CO.sub.2 and optionally H.sub.2 recovered at the second outlet O.sub.g2. Once recovered, at least part of the second gaseous fraction G2 may be used for burnt to produce energy. The produced energy may be thermal (heat) and/or electrical depending on the converter positioned in the installation 40. Alternatively, at least part of the second gaseous fraction G2 may be used as natural gas, for instance as compressed natural gas or liquefied natural gas, or it is injected into the gas network.

[0136] The installation 40 may comprise further optional elements for further treatments of the first gaseous fraction G1 (comprising CH.sub.4, CO, CO.sub.2 and H.sub.2). The installation 40 may comprise a dedicated reactor for biomethanation of at least part of the first gaseous fraction G1. The installation 40 may comprise a converter to produce energy. Preferably the first gaseous fraction G1, or part of it, is burned using a turbine to generate electrical energy. The installation 40 may comprise a device for bioaugmentation in H.sub.2 or in CH.sub.4 fed with at least part of G1. The relative concentration increase of methane may be performed via biomethanation as described in WO2018/234058 and the bioaugmentation of hydrogen may be performed via water gas-shift reaction, preferably biological water gas-shift reaction.