METHOD AND APPARATUS FOR TREATING CARBONACEOUS MATERIAL

Abstract

A method for treating carbonaceous material, the method includes a) providing a first carbonaceous material CM1 contaminated with micro-pollutants and/or microplastics, and providing a second carbonaceous material CM2 free of micro-pollutants or microplastics, b) subjecting the first carbonaceous material CM1 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 free of micro-pollutants or microplastics optionally containing readily biodegradable carbons such as VFAs, c) subjecting the second carbonaceous material CM2 together with at least part of the filtrate F1 to an anaerobic treatment step in an anaerobic tank, leading to a digestate free of micro-pollutants or microplastics and optionally a second gaseous fraction G2 containing CH.sub.4 and CO.sub.2. An installation for treating carbonaceous material is also provided.

Claims

1. A method for treating carbonaceous material, said method comprising: a) providing a first carbonaceous material CM1 comprising primary sludge, and providing a second carbonaceous material CM2 comprising biological sludge optionally hydrolyzed and/or hygienized, b) subjecting the first carbonaceous material CM1 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 liquid product F1 optionally containing readily biodegradable carbons such as VFAs, c) subjecting the second carbonaceous material CM2 together with at least part of the liquid product F1 to an anaerobic treatment step, leading to a digestate and optionally a second gaseous fraction G2 containing CH.sub.4 and CO.sub.2.

2. 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, said solid and liquid fractions being free of micro-pollutants or microplastics.

3. The method of claim 2, wherein the solid fraction of step d) is mixed (step e) with the second carbonaceous material CM2 and the liquid product F1 in step c), or returned to an upstream process step.

4. The method of claim 1, wherein the hydrothermal gasification step b) is performed at a temperature of between 330° C. and 500° C., preferably of between 330° C. and 400° C., and at a pressure of between 220 bar and 400 bar, selected so as to maintain sub- or supercritical conditions.

5. The method of claim 1, wherein at least part of the gaseous fraction G1 of step b) is mixed with the carbonaceous material CM2 and liquid product F1, preferably by bubbling (step g) the gaseous fraction G1 into the carbonaceous material CM2 and the liquid product F1, the gaseous fraction G1 being preferably subjected to a biomethanation step (step f) prior to the mixing of the at least part of the gaseous fraction G1 of step b) with the carbonaceous material CM2 and the liquid product F1.

6. The method of claim 1, wherein at least part of the gaseous fraction G1 of step b) is burnt (step h) to produce energy, in particular electricity.

7. The method of claim 1, wherein at least part of the gaseous fraction G1 of step b) is subjected to (step i) a water-gas shift reaction to perform a relative concentration increase in H.sub.2 and/or biomethanation to perform a relative concentration increase in CH.sub.4.

8. The method of claim 2, wherein step c) comprises an anaerobic digestion, and the solid fraction of step d) is suitable for use as fertilizer to be spread on land.

9. The method of claim 1, wherein the first carbonaceous material CM1 comprises primary sludge from a wastewater treatment plant, and is optionally dewatered (step j) prior to being subjected to step b).

10. The method of claim 1, wherein the second carbonaceous material CM2 comprises biological sludge, and is optionally hydrolyzed and/or hygienized prior to being subjected to step c).

11. The method of claim 10, wherein the second carbonaceous material CM2 is thermally and/or biologically hydrolyzed.

12. An installation for treating carbonaceous material, said installation comprising: a HTG reactor suitable for hydrothermal gasification, having a first inlet (I.sub.cm1) 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.cm1) of the HTG reactor with a first carbonaceous material CM1 comprising primary sludge, and to produce: an inorganic solid residue, recovered at the first outlet (O.sub.s) of the HTG reactor, 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) of the HTG reactor, and a liquid product F1, optionally containing readily biodegradable carbons such as VFAs, recovered at the third outlet (O.sub.f1) of the HTG reactor, and an anaerobic tank, suitable for fermentation or anaerobic digestion, having a first inlet (I.sub.cm2), and optionally a second inlet (I.sub.f), and a first (O.sub.d) and second (O.sub.g2) outlets, the second inlet (I.sub.f) of the anaerobic tank and/or the first inlet (Icm.sub.2) of the anaerobic tank 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.cm2) of the anaerobic tank with a second carbonaceous material CM2 comprising biological sludge optionally hydrolyzed and/or hygienized, and to be fed with the liquid product F1 at the first inlet (I.sub.cm2) of the anaerobic tank and/or at the second inlet (I.sub.f) of the anaerobic tank, and to produce: a digestate recovered at the first outlet (O.sub.d) of the anaerobic tank and optionally a second gaseous fraction G2 containing CH.sub.4 and CO.sub.2 recovered at the second outlet (O.sub.g2) of the anaerobic tank.

13. The installation of claim 12, 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), said solid and liquid fractions being free of micro-pollutants or microplastics.

14. The installation of claim 13, wherein the second outlet (O.sub.sf) of the phase separator is in fluid connection with the first inlet (I.sub.cm2) and/or with the second inlet (I.sub.f) of the anaerobic tank, and the anaerobic tank is configured to be fed with the solid fraction at the first inlet (I.sub.cm2) and/or at the second inlet (I.sub.f) of the anaerobic tank.

15. A method for treating carbonaceous material, said method comprising: a) providing a first carbonaceous material CM1 comprising primary sludge, and providing a second carbonaceous material CM2 comprising biological sludge optionally hydrolyzed and/or hygienized, b) subjecting the second carbonaceous material CM2 together with the first carbonaceous material CM1 to an anaerobic treatment step, leading to a digestate and a second gaseous fraction G2 containing CH.sub.4 and CO.sub.2, c) optionally a step of separating the digestate of step b) into a liquid fraction and a solid fraction, c) subjecting the digestate, and/or the solid fraction of the digestate, to hydrothermal gasification, thereby producing an inorganic solid residue, syngas comprising CH.sub.4, CO, CO.sub.2 and H.sub.2 and soluble and readily biodegradable molecules.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0111] The accompanying drawings illustrate various non-limiting, exemplary, innovative aspects in accordance with the present description:

[0112] FIG. 1 schematically represents a block diagram with the steps of the method for treating carbonaceous material according to the invention;

[0113] FIG. 2 schematically represents a block diagram with optional steps of the method for treating carbonaceous material according to the invention;

[0114] FIG. 3 schematically represents a first embodiment of the installation for treating carbonaceous material according to the invention;

[0115] FIG. 4 schematically represents another embodiment of the installation for treating carbonaceous material according to the invention;

[0116] FIG. 5 schematically represents another embodiment of the installation for treating carbonaceous material according to the invention;

[0117] FIG. 6 schematically represents another embodiment of the installation for treating carbonaceous material according to the invention;

[0118] FIG. 7 schematically represents another embodiment of the installation for treating carbonaceous material according to the invention.

DETAILED DISCLOSURE

[0119] 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 first carbonaceous material CM1 contaminated with micro-pollutants and/or microplastics, and providing a second carbonaceous material CM2 free of micro-pollutants or microplastics. The method according to the invention further comprises a step b) of subjecting the first carbonaceous material CM1 to hydrothermal gasification, thereby producing an inorganic solid residue 12, a first gaseous fraction G1 comprising CH.sub.4, CO, CO.sub.2 and H.sub.2 and a filtrate F1 free of micro-pollutants or microplastics optionally containing readily biodegradable carbons such as VFAs. And the method according to the invention comprises a step c) of subjecting the second carbonaceous material CM2 together with at least part of the filtrate F1 to an anaerobic treatment step in an anaerobic tank 13, leading to a digestate 14 free of micro-pollutants or microplastics and a second gaseous fraction G2 containing CH.sub.4 and CO.sub.2.

[0120] The method according to the invention enables to destroy the fraction of sludge that contains micro-pollutants and/or microplastics contaminants. It produces syngas and biogas. Thanks to step b), the method according to the invention allows for nutrient recovery, in particular phosphorus (P), in the inorganic solid residue (ashes). While contributing to reduce the overall amount of sludge that is produced, the possibility for land application of sludge (typically either class A or class B sludge) is maintained.

[0121] Furthermore, the method of the invention transforms organic micro-pollutants and microplastics into biogas and/or syngas along with the fraction of the carbonaceous material being treated (CM1). In other words, the method of the invention produces energy instead of consuming energy.

[0122] 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.

[0123] The method of the invention may further comprise a step d) of separating the digestate 14 of step c) into a liquid fraction 16 and a solid fraction 17, said solid and liquid fractions 16, 17 being free of micro-pollutants or microplastics.

[0124] Advantageously, the liquid fraction of step d) is mixed in a step e) with the second carbonaceous material CM2 and the filtrate F1 in step c), or returned to headworks of the treatment plant.

[0125] 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 first carbonaceous material CM1 into the various products of the HTG.

[0126] Advantageously, at least part of the gaseous fraction G1 of step b) may be subjected to biomethanation (step f), preferably in a dedicated reactor 21. The process of biomethanation described in WO2018/234058 could for instance be used as biomethanation process.

[0127] Advantageously, at least part of the gaseous fraction G1 of step b) may be mixed with the carbonaceous material CM2 and filtrate F1, preferably by bubbling (step g) the gaseous fraction G1 into the carbonaceous material CM2 and/or filtrate F1. Preferably the gaseous fraction G1 is subjected to a biomethanation step (step f) prior to the mixing of the at least part of the gaseous fraction G1 of step b) with the carbonaceous material CM2 and filtrate F1. Step g) may be performed directly into the anaerobic tank 13. The anaerobic tank 13 may be a digester or a fermenter.

[0128] Advantageously, the method of the invention may comprise a step h of burning at least part of the gaseous fraction G1 of step b) to produce energy 22, in particular electricity (using a turbine or any other adapted converter).

[0129] Advantageously, at least part of the gaseous fraction G1 of step b) may be subjected to bioaugmentation (step i) in H.sub.2 or in CH.sub.4.

[0130] Advantageously, step c) comprises an anaerobic digestion, and the solid fraction 17 of step d) is suitable for use as fertilizer to be spread on land.

[0131] The first carbonaceous material CM1 may comprise primary sludge from a wastewater treatment plant, and may be optionally dewatered (step j) prior to being subjected to step b).

[0132] The second carbonaceous material CM2 may comprise biological sludge, and may be optionally hydrolyzed and/or hygienized prior to being subjected to step c).

[0133] The second carbonaceous material CM2 may be thermally and/or biologically hydrolyzed.

[0134] The second gaseous fraction G2 may be used for producing combined heated power (CHP).

[0135] 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 in an anaerobic tank 13. The step of cooling may be performed with cooling techniques known by the person skilled in the art. 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.

[0136] FIG. 3 schematically represents a first embodiment of the installation 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.cm1 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.cm1 with a first carbonaceous material CM1 contaminated with micro-pollutants and/or microplastics, 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 free of micro-pollutants or microplastics, optionally containing readily biodegradable carbons such as VFAs, recovered at the third outlet O.sub.f1.

[0137] The installation 10 further comprises an anaerobic tank 13, suitable for fermentation or anaerobic digestion, having a first inlet I.sub.cm2, and optionally a second inlet I.sub.f, and a first O.sub.d and second O.sub.g2 outlets. The second inlet I.sub.f and/or the first inlet I.sub.cm2 are 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.cm2 with a second carbonaceous material CM2 free of micro-pollutants or microplastics, and to be fed with filtrate F1 at the first inlet I.sub.cm2 and/or at the second inlet I.sub.f, and to produce a digestate 14 free of micro-pollutants or microplastics recovered at the first outlet O.sub.d and a second gaseous fraction G2 containing CH.sub.4 and CO.sub.2 recovered at the second outlet O.sub.g2.

[0138] 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 fraction of sludge containing micro-pollutants and/or microplastics contaminants is destroyed. The filtrate is free of micro-pollutants or microplastics. 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.

[0139] 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.

[0140] 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, said solid and liquid fractions 16, 17 being free of micro-pollutants or microplastics. The invention ensures the recovery of a solid fraction and a liquid fraction without any micro-pollutants and/or microplastics. These fractions may be further re-used within the installation as explained below.

[0141] The installation 20 represented in FIG. 4 comprises an optional pre-treatment device 45, such as an optional phase separator 45, a thermal hydrolysis unit or a biological hydrolysis unit. The optional phase separator 45 is configured to separate the second carbonaceous material CM2 into a liquid fraction 46 and a solid fraction 47, in particular by dewatering, prior to being introduced into the anaerobic tank 13. In this embodiment, a phase separation of the second carbonaceous material CM2 is performed upstream the anaerobic tank and the anaerobic tank is fed with the solid fraction from the phase separation. This optional phase separator enables to produce class A or class B sludge prior to be fed to the anaerobic tank. The hydrolysis enables to produce class A sludge.

[0142] The pre-treatment device 45 is optional and is only represented in FIG. 4 but could be implemented in each example of the invention.

[0143] 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.cm2 and/or with the second inlet I.sub.f of the anaerobic tank 13, and the anaerobic tank 13 is configured to be fed with the solid fraction 17 at the first inlet I.sub.cm2 and/or at the second inlet I.sub.f of the anaerobic tank 13. This recirculation of the solid fraction 17 in the anaerobic tank 13 allows to contribute to the thickening of the mass (second carbonaceous material CM2) to be treated in the anaerobic tank 13.

[0144] 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 10, 20 or 30. The installation 40 comprises 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 21 for biomethanation of at least part of the first gaseous fraction G1. The installation 40 may comprise a converter 23 to produce energy 22. 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 24 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. The further treatment of the first gaseous fraction G1 promote the valorization of this gaseous fraction via the production of energy.

[0145] The installation may further comprise a phase separator upstream the anaerobic tank 13. The anaerobic tank 13 is fed with the liquid fraction from the phase separator. The advantage of the phase separator upstream the anaerobic tank 13 is the size reduction of the anaerobic tank 13.

[0146] In another embodiment, the installation may comprise a second anaerobic tank, in particular a digester, preferably a high-rate digester such as an upflow anaerobic sludge digester (UASD), in fluid connection with the third outlet of the HTG reactor 11 and configured to be fed with the filtrate F1. This embodiment enables to reduce the size of the anaerobic tank 13, while treating the same amount of sludge.

[0147] FIG. 7 schematically represents another embodiment of the installation 50 for treating carbonaceous material according to the invention. The installation 50 for treating carbonaceous material according to the invention comprises an anaerobic tank 13, suitable for fermentation or anaerobic digestion, having a first inlet I.sub.cm2, and a first O.sub.d and second O.sub.g2 outlets. The anaerobic tank 13 is configured to be fed at the first inlet I.sub.cm2 with the first carbonaceous material CM1 containing micro-pollutants and/or microplastics and the second carbonaceous material CM2 free of micro-pollutants or microplastics, and to produce a digestate 14 recovered at the first outlet O.sub.d and a second gaseous fraction G2 containing CH.sub.4 and CO.sub.2 recovered at the second outlet O.sub.g2.

[0148] The installation 50 further comprises a HTG reactor 11 suitable for hydrothermal gasification, having a first inlet I.sub.cm1 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.cm1 with the digestate 14 contaminated with micro-pollutants and/or microplastics, and to produce an inorganic solid residue 12, also called ashes, recovered at the first outlet O.sub.s, syngas 52 recovered at the second outlet O.sub.g1, and soluble and readily biodegradable molecules 51 recovered at the third outlet O.sub.f1.

[0149] The installation 50 may comprise a phase separator 15 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 recovered at the first phase separator outlet O.sub.lf and a solid fraction recovered at the second phase separator outlet O.sub.sf. The installation 50 may comprise a dedicated anaerobic tank, in particular an upflow anaerobic sludge digester (UASB type), configured to be fed with the soluble and readily biodegradable molecules 51. The soluble and readily biodegradable molecules 51 may alternatively be redirected toward the anaerobic tank 13. The recirculation of the soluble and readily biodegradable molecules 51 toward a dedicated anaerobic tank or the anaerobic tank 13 enables to treat these soluble and readily biodegradable molecules 51, thus leading to a reduction of the final sludge amount and an increase of biogas production. Ashes 12 contain minerals that can then be returned to the land.

[0150] The installation 50 increases the size of the digester but maximises the redundancy in case of failure of the HTG. Also, it prevents accumulation of sand in the HTG reactor (trapped in the digester), which can be problematic and cause significant abrasion problems. The optional dewatering before the HTG step enables to reduce the HTG reactor size.

[0151] The installation may further comprise a phase separator downstream the anaerobic tank 13, producing a solid fraction and a liquid fraction. The anaerobic tank 13 is then fed with the solid fraction from the phase separator. The presence of the phase separator downstream the anaerobic tank 13 allows to decrease the size of the HTG reactor 11.

[0152] In another embodiment, the installation may comprise a second anaerobic tank, in particular a digester, preferably a high-rate digester such as an upflow anaerobic sludge digester, in fluid connection with the third outlet of the HTG reactor 11 and configured to be fed with the filtrate F1, or at least part of the filtrate F1. This embodiment enables to reduce the size of the anaerobic tank 13, while treating the same amount of sludge.

[0153] The installation according to the invention enables to maximise biogas and/or syngas production as well as hydrogen valorisation, while completely removing micro-pollutants and microplastics. After a contaminated sludge is passed through the installation of the invention, no contaminated sludge/waste leaves the installation. Indeed, even if the sludge produced from a water treatment process is contaminated with the micro-pollutants initially present in water, the method and installation according to the invention avoid the production of sludge contaminated by micro-pollutants and/or microplastics, and still allow to produce syngas and/or biomethane production and also the production of a final safe sludge, suitable for land application. Thanks to the invention, a selective removal of micro-pollutants and microplastics from sludge and organic waste is performed, leading to a final sludge suitable for land application (“back to the land” policy).