WO2024023304A1

WO2024023304A1 - Method for the treatment of complex waste

Info

Publication number: WO2024023304A1
Application number: PCT/EP2023/071015
Authority: WO
Inventors: Pierre-Emmanuel Pardo; Safwan AL AYOUBI
Original assignee: Suez International
Priority date: 2022-07-29
Filing date: 2023-07-28
Publication date: 2024-02-01
Also published as: FR3138427A1

Abstract

The invention relates to a method for treating a mixture M1, said method comprising: a) a step of pressurizing the mixture M1 in order to obtain a mixture M1p, b) a step of heating mixture M1p, making it possible to obtain a mixture M2, c) a step of separating mixture M2 in order to obtain a stream M3 enriched in inorganic matter and a stream M4 depleted of inorganic matter, d) a hydrothermal gasification step carried out on stream M4 depleted of inorganic matter in order to obtain a mixture M5, e) a step of cooling and separating at least one fraction of mixture M5 in order to separate the gas from the liquid effluent M5' comprising ammonia, f) optionally a step of enriching at least one fraction of liquid effluent M5' in ammonia in order to obtain an ammonia-enriched stream M5" and an ammonia-depleted stream M8, g) a step of mixing (i) at least one fraction of stream M3 and (ii) at least one fraction of stream M5' or M5" obtained in step f) when it is present, in order to obtain a mixture M6, h) a step of forming struvite from at least one fraction of mixture M6 in a precipitation reactor, i) a step of recovering struvite at the outlet of the precipitation reactor, said method comprising at least one step of injecting at least one magnesium salt into mixture M1 before step a) and/or during step g) and/or during step h) and/or into M6 between steps g) and h), said mixing step g) optionally being carried out in the precipitation reactor.

Description

DESCRIPTION

TITLE: PROCESS FOR TREATMENT OF COMPLEX WASTE

TECHNICAL FIELD OF THE INVENTION

The invention relates to the field of treatment of complex waste, including organic matter and inorganic matter, such as aqueous waste, sludge and sewage sludge.

STATE OF THE ART

Wastewater treatment is necessary for environmental protection. A wastewater treatment plant consists of two main parts, the treatment of waste water and the treatment of sludge resulting from water treatment.

The objective of wastewater treatment is to eliminate pollution, in particular particulate pollution (also referred to as suspended matter), and in particular carbon, nitrogen and phosphorus pollution. A wastewater treatment plant also makes it possible to recover resources - such as phosphorus - or to generate energy, for example through the production of biogas.

Resource recovery is now a concern as many types of elements are close to shortage: it appears more and more critical to recycle them.

This is the case for phosphorus, which is on the European Union's list of critical raw materials due to the progressive depletion of phosphate mines, the increase in demand and the non-substitutable properties of phosphorus. Thus, phosphorus is a fertilizing element, essential to crops and non-replaceable. It is therefore desirable to recycle it as much as possible.

Therefore, emphasis is placed on phosphorus recovery in wastewater treatment plants.

Sludge from wastewater treatment plants has been recognized as an additional phosphorus sink.

Land application is considered the most practical option, but is associated with increased public concerns about pollutants in sludge (e.g., pathogens, heavy metals, persistent organic pollutants, and micropollutants ).

Thermochemical treatment of sludge and especially incineration appears to be an alternative solution to conventional disposal channels. It has significant advantages, such as deodorization, high efficiency, substantial reduction in waste volume (about 90%), destruction of organic pollutants and deactivation pathogens. More importantly, incineration generates solid residue in the form of ash which is concentrated in phosphorus (P) (9-13%) comparable to phosphate rock.

However, the ashes from sludge incineration are made up of a complex matrix of minerals where phosphorus accumulates with heavy metals, which makes the direct reuse of these ashes as fertilizer impossible. Additionally, the bioavailability of phosphorus in ash is restricted due to binding with minerals. Therefore, removing heavy metals and improving phosphorus bioavailability represent economically and environmentally laborious treatments for phosphorus recovery from ash.

There is therefore a real need to propose an alternative process making it possible to recover the phosphorus present in the sludge directly in a bioavailable form such as struvite and containing a restricted concentration of heavy metals thanks to a precipitation step, all with a sustainable approach.

SUMMARY OF THE INVENTION

The invention relates to a process for treating a mixture M1 comprising at least organic matter, said process comprising: a) a step of pressurizing the mixture M1 to a pressure of 150 to 300 bars, preferably between 170 and 210 bars in order to obtain a mixture M1p, b) a step of heating the mixture M1p to a temperature ranging from 250°C to 500°C making it possible to obtain a mixture M2, c) a step of separating the mixture M2 resulting from step b) in order to obtain a flow M3 enriched in inorganic material and a flow M4 depleted in inorganic material, d) a hydrothermal gasification step implemented on the flow depleted in inorganic material M4 in order to obtain a mixture M5 comprising gas and a liquid effluent, e) a step of cooling and separating at least a fraction of the mixture M5 resulting from the hydrothermal gasification of step d) in order to separate the gas from the liquid effluent M5' comprising ammonia, f) optionally a step of enriching in ammonia at least a fraction of the liquid effluent M5' in order to obtain a flow enriched in ammonia M5” and a flow depleted in ammonia M8, g) a step of mixing (i) at least a fraction of the flow enriched in inorganic material M3 obtained at the end of step c) and (ii) at least a fraction of the liquid effluent M5' or at least a fraction of the enriched flow M5” obtained at the end of step f) when it is present, in order to obtain a mixture M6, h) a step of forming struvite from at least a fraction of the M6 mixture in a precipitation reactor, i) a step of recovering struvite at the outlet of the precipitation reactor, said treatment process comprising at least one step injecting at least one magnesium salt into the mixture M1 before step a) of putting under pressure and/or during step g) and/or during step h) and/or in the mixing M6 between steps g) and h), said mixing step g) possibly being implemented in the precipitation reactor.

According to one embodiment of the process of the invention, the magnesium salt is chosen from magnesium hydroxide, magnesium oxide, magnesium chloride, and mixtures thereof, preferably from magnesium hydroxide and magnesium oxide, more preferably the magnesium salt is magnesium hydroxide.

According to one embodiment of the invention, the process comprises, upstream of step a), a step of hydrolysis of the mixture M1 carried out at a temperature ranging from 70 to 165°C and at a pressure ranging from 2 at 8 bars, making it possible to obtain a mixture M1h which will then be put under pressure in step a).

According to one embodiment of the invention, the method comprises a heat exchange between the mixture M5 resulting from step d) and the mixture M1 or M 1 p or M 1 h upstream of the heating step b) .

According to one embodiment of the process of the invention, the mixture M1 comprises from 5 to 50% by weight of solid materials, preferably from 15 to 25% by weight of solid materials, relative to the total weight of the mixture M1.

According to one embodiment of the process of the invention, the stream enriched in salts from step c) comprises phosphorus, preferably in a proportion ranging from 1 to 20% by weight, relative to the total dry weight of the stream enriched with inorganic matter M3.

According to one embodiment of the process of the invention, the liquid effluent M5' comprises from 1 to 20 g/l of ammonia.

According to one embodiment of the process of the invention, the ammonia enrichment step f) is carried out using heat.

Preferably, the heat comes from the M5 mixture resulting from hydrothermal gasification d).

According to one embodiment of the process of the invention, the ammonia enrichment step f) makes it possible to obtain an ammonia concentration in the liquid effluent M5” at least 1.5 times greater than the ammonia concentration in the liquid effluent M5', preferably an ammonia concentration in the liquid effluent M5” at least twice greater than the ammonia concentration in the liquid effluent M5', or even a ammonia concentration in the liquid effluent M5” at least 5 times higher than the ammonia concentration in the liquid effluent M5’.

According to one embodiment of the process of the invention, less than 75% of the volume, preferably less than 50% of the volume, of the liquid effluent M5' from step e) or of the liquid effluent M5” from step f) when it is implemented, is mixed during step g).

The invention also relates to an installation for implementing the treatment method according to the invention, said installation comprising: a pressurization pump 3 supplied by the mixture M1 and comprising an outlet for the mixture M1p,

A heating device 2 comprising an inlet making it possible to introduce the mixture M1p possibly mixed with a magnesium salt Mg and comprising an outlet for the mixture M2,

A separation device 5 supplied with at least a fraction of the mixture M2 and comprising an outlet of flow M3 enriched in inorganic material and an outlet of flow M4 depleted of inorganic material,

A hydrothermal gasification reactor 8 supplied by at least a fraction of the flow M4 coming from the separation device 5 and comprising a mixture outlet M5 comprising gas and a liquid effluent,

A cooling and separation device 9 downstream of the gasification reactor (8), supplied with at least a fraction of the mixture M5 from the reactor 8 and comprising at least one outlet for a gaseous effluent and at least one outlet for a liquid effluent M5', possibly an ammonia enrichment device 10 supplied with at least a fraction of the liquid effluent M5' and comprising an outlet for the enriched flow M5' and an outlet for the depleted flow M8, optionally a mixing device 6 supplied by (i) at least a fraction of the flow M3 coming from the device 5 and by (ii) at least a fraction of the flow M5' coming from the device 9 or at least a fraction of the flow M5” coming from the device 10, and comprising at least minus one output for the M6 mixture,

A precipitation reactor 7 comprising at least one inlet and at least one outlet, said precipitation reactor 7 being able to be supplied: o Either by (i) at least a fraction of the flow M3 coming from the separation device 5 and by (ii) at at least a fraction of the flow M5' coming from the cooling and expansion device 9 or at least a fraction of the flow M5” coming from the enrichment device 10, o Either by the flow M6 coming from the mixing device 6 when it is present,

- At least one injection device located: o upstream of the pressurization pump 3 and/or o in the mixing device 6 and/or o downstream of the mixing device 6 and upstream of the precipitation reactor 7 , and/or o in the precipitation reactor 7.

According to one embodiment, the installation according to the invention further comprises at least one hydrolysis reactor 4 upstream of the pressurization pump 3, said hydrolysis reactor comprising at least one inlet for the mixture M1 and at least one outlet for the hydrolyzate M1h, said hydrolyzate M1h supplying the pressurization pump 3.

The invention makes it possible to recover phosphorus in the form of struvite from sludge resulting from water treatment by a direct process, with optimum efficiency, optimized heat management and reduced generation of deposits in pipes.

The process of the invention also makes it possible to reduce the quantity of heavy metals likely to be recovered with the phosphorus.

BRIEF DESCRIPTION OF THE FIGURES

[Fig. 1] is a schematic representation of a treatment method according to the invention.

[Fig. 2] is a schematic representation of a treatment method according to the invention.

[Fig. 3] is a schematic representation of a treatment method according to the invention.

[Fig. 4] is a schematic representation of a treatment method according to the invention.

[Fig. 5] is a schematic representation of a treatment method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a process for treating a mixture M1 comprising at least organic matter, said process comprising: a. a step of pressurizing the mixture M1 to a pressure of 150 to 300 bars, preferably between 170 and 210 bars in order to obtain a mixture M1p, b. a step of heating the mixture M1p to a temperature ranging from 250°C to 500°C, preferably from 350°C to 450°C, making it possible to obtain a mixture M2, c. a step of separating the mixture M2 from step b) which makes it possible to obtain a flow enriched in inorganic material M3 and a flow depleted in inorganic material M4, d. a hydrothermal gasification step implemented on the flow depleted of inorganic material M4 in order to obtain a mixture M5 comprising gas and an aqueous liquid effluent, e. a step of cooling and separating at least a fraction of the mixture M5 resulting from the hydrothermal gasification of step d) in order to separate the gas from the liquid effluent M5' comprising ammonia, f. optionally a step of enriching in ammonia at least a fraction of the liquid effluent M5' from step e) in order to obtain a liquid stream enriched M5” in ammonia, g. a step of mixing: at least a fraction of the flow enriched in inorganic material M3 obtained at the end of step c) and at least a fraction of the liquid effluent M5' comprising ammonia obtained at the outcome of step e) or at least a fraction of the enriched flow M5” obtained at the end of step f) when it is present, in order to obtain a mixture M6, h. a step of forming struvite from at least a fraction of the mixture of mixture M6 in a precipitation reactor, i. a struvite recovery step at the outlet of the precipitation reactor, said treatment process comprising at least one step of injecting at least one magnesium salt into the mixture M1 before step a) of pressurization and/ or during step g) and/or during step h) and/or in the mixture M6 between steps g) and h), said mixing step g) possibly being implemented in the reactor of precipitation.

For the purposes of the present invention, the expression “at least a fraction of X” has the same meaning as the expression “all or part of X”. When it concerns a part of a mixture or a flow or a gas, this expression refers to a certain proportion of said mixture or of said flow or of said gas. For example, in the sense of this expression “each fraction of the mixture” or “each fraction of the flow” or “each fraction of the gas” will have the same composition.

Thus, for the purposes of the present invention, the expression "step intermediate stage of separation between stages X and Y, it being understood that there could be cooling/heating of the flow M between stages X and Y, in particular by heat exchange which could possibly involve an exchange of flows. Mixture M1 comprising at least organic matter

The mixture M1 comprises at least organic matter. Typically, the mixture M1 also comprises inorganic material.

Among the inorganic matter, we can cite salts comprising anions such as phosphates, sulfates, chlorides, carbonates and hydrocarbonates with as counter ions for example sodium, magnesium, calcium, ammonium and metals.

The mixture M1 can for example be chosen from primary, biological, mixed or digested sludge from municipal and industrial wastewater treatment plants.

According to one embodiment, the mixture M1 comprises from 5 to 50% by weight of solid materials, preferably from 15 to 25% by weight of solid materials, relative to the total weight of the mixture M1.

According to one embodiment, at least one magnesium salt is added to the mixture M1 in such a way that the magnesium is in a stoichiometric proportion or in a super-stoichiometric proportion. Thus, preferably the Mg/P molar ratio in the mixture M1 after addition of the magnesium salt ranges from 1/1 to 1.3/1.

Thus, we can provide a measurement of the phosphorus content in the mixture M1 before its implementation in the pressurization step a). Indeed, the measurement of the phosphorus content will typically be done at atmospheric pressure.

The addition of the magnesium salt is preferably carried out upstream of the pressurization step a).

The magnesium salt can be chosen from magnesium hydroxide (Mg(OH)2), magnesium oxide (MgO) or magnesium chloride (MgCI2). Preferably, the magnesium salt is magnesium hydroxide.

The magnesium salt can be added to a mixing device supplied on the one hand by the mixing flow M1 and on the other hand by the magnesium salt flow.

Possible hydrolysis step and possible grinding step

According to one embodiment, the process according to the invention comprises a step of hydrolysis of the mixture M1 upstream of the pressurizing step a).

The hydrolysis step can be carried out at a temperature ranging from 70 to 165°C and at a pressure ranging from 2 to 8 bars.

The hydrolysis step makes it possible to reduce the viscosity of the mixture. Thus, the hydrolysis step makes it possible to obtain a mixture M1 h also called hydrolyzate. The hydrolysis step makes it possible to degrade the organic matter, in particular it makes it possible to break the chemical bonds and to depolymerize the organic matter by the effect of water.

The mixture M1 h will typically have a viscosity at least 2 times lower, preferably at least 4 times lower, more preferably at least 10 times lower than the viscosity of the mixture M1.

Thus, the ratio between the viscosity of the mixture M1 and the viscosity of the mixture M1h is at least 2, preferably at least 4, more preferably at least 10.

The viscosity defined in the context of the present invention is a kinematic viscosity measured at the same temperature (20°C for example) using rheometers adapted to the viscosity to be measured (cylinder - cylinder, plane-plane) and measuring at the same shear (in s ^-1 ) the two viscosities, typically taking care to eliminate the problems of turbulence and to respect the rheological rules (for example spacing between cylinders depending on the particle size).

The hydrolysis step implemented on the mixture M1 can be implemented in one or more hydrolysis reactors in parallel or in series.

Said hydrolysis step makes it possible to hydrolyze the mixture M1 thanks in particular to maintaining an average hydraulic residence time at the desired temperatures and pressures (preferably, temperatures ranging from 70 to 165°C and pressures ranging from 2 to 8 bars), it being understood that if the hydrolysis step is carried out in several hydrolysis reactors, the temperature may be identical or different in the different reactors, likewise, the pressure may be identical or different in the different reactors .

Advantageously, the hydrolysis step will implement an internal energy recovery step, thus making it possible to minimize the thermal consumption of the hydrolysis. For example, there could be an energy recirculation loop from the hot hydrolyzate to the cold product to be hydrolyzed via, for example, production of expansion steam from the hot hydrolyzate and injection into the cold product to be hydrolyzed or heat exchange. .

At the exit of the hydrolysis step, a hydrolyzate M1h is obtained, said hydrolyzate M1h is not necessarily at the desired temperatures and pressures for hydrolysis. Indeed, before leaving the hydrolysis stage, the hydrolyzate could possibly undergo a cooling and/or relaxation stage.

In particular, for example if the hydrolysis is carried out at a high temperature, for example ranging from 100 to 165°C, then it could be desirable to cool the hydrolyzate for example to a temperature below 90°C. , so that the flow M1h has a lower temperature for pressurization in step a) of the process of the invention

The extraction of the M1h hydrolyzate can be controlled by measuring the viscosity. According to one embodiment, a controlled quantity of steam can be injected into the hydrolysis reactor(s) and diffused through the mixture M1. This control can be carried out by measuring the temperature in the hydrolysis reactor. Thus, when the set temperature is reached, the steam injection can be stopped.

The steam can be injected: upstream of the hydrolysis in the inlet with a dynamic mixer type mixer, and/or directly into the hydrolysis reactor, preferably in the lower part in a tangential manner to avoid sludge blockages, and/ or in a hydrolyzed sludge recirculation loop.

According to one embodiment, during hydrolysis, the mixture M1 is mixed, for example it is stirred.

The hydrolysis reactor can be a batch reactor, optionally stirred.

According to one embodiment implementing a hydrolysis step, at least one magnesium salt is added to the mixture M1 to be treated before entering the hydrolysis device.

According to another embodiment implementing a hydrolysis step, at least one magnesium salt is added to the mixture M1h downstream of the hydrolysis device.

Before pressurization, the treatment process may optionally include a grinding step, preferably mechanical grinding.

When present, the step of grinding the mixture M1 can be carried out before, during or after hydrolysis when the latter is present. In the latter case, grinding is then carried out on the M1h mixture.

When the process of the invention implements a hydrolysis step combined with a grinding step, then the process of the invention may possibly comprise a step of recirculating at least a fraction of the hydrolyzate ground with the entry to the hydrolysis stage.

According to one embodiment, the hydrolysis reactor(s) comprise a recirculation loop provided with a grinding device, making it possible to introduce at least a fraction of the hydrolyzate into said grinding device and to return at least a fraction, preferably all, of the hydrolyzate thus crushed, at the entrance to the hydrolysis step. The objective of this grinding step is to reduce the particle size of the mixture M1, typically so that the particle size of the solid fraction is less than 1000 pm, preferably less than 500 pm, preferably less than 100 pm.

A particle size “less than X pm” means the fact that 95% of the solid particles are retained in the square mesh sieve of

In addition to the reduction in particle size which makes it possible to minimize downstream blockages, the grinding step allows homogenization of the M1 mixture and a reduction in viscosity which will allow much better control of the process parameters of the operation of hydrothermal gasification.

In the same way as the hydrolysis stage, grinding and the reduction in particle size also contribute to the homogenization of the biomass.

In reactors using high pressures, it is difficult to have mechanical agitation; the reduction in viscosity implemented thanks to the hydrolysis step and the grinding step also makes it possible to improve turbulence. internal and therefore improve homogenization in pressure reactors.

Pressurization stage a)

The treatment process according to the invention comprises a step of pressurizing the mixture M1 to a pressure ranging from 150 to 350 bars, said mixture M1 having optionally been previously mixed with at least one magnesium salt.

For pressurization, a pump is provided at the start of the line upstream of the heating or at the outlet of the hydrolysis reactor when present.

The pump is provided downstream of the mixing device making it possible to mix the M1 mixture and the magnesium salt.

The M1 mixture under pressure is hereinafter referred to as the M1p mixture.

Heating stage b)

The treatment method according to the invention comprises a heating step at a temperature ranging from 250 to 500°C, implemented on the mixture M1 p.

The heating step can be implemented in a heating device. The device can be a continuous stirred tank reactor (CSTR, continuous stirred tank reactor) or a tubular flow reactor also called plug-flow reactor. This reactor can be equipped with an external heating device or heated via an exchange with a heat transfer fluid. The heating step makes it possible to obtain an M2 mixture.

Thus, steps a) and b) make it possible to obtain a mixture M2 having a pressure ranging from 150 to 350 bars, preferably from 170 to 210 bars and a temperature ranging from 250°C to 500°C, preferably from 350 °C to 450°C.

Separation step c)

The process according to the invention comprises a step of separating the mixture M2 resulting from step b), in order to obtain a flow enriched in inorganic material M3 and a flow depleted in inorganic material M4.

For the purposes of the present invention, the term "flow enriched in inorganic material" means a flow comprising a mass proportion of inorganic material greater than the mass proportion of inorganic material in the mixture M2.

For the purposes of the present invention, the term "flow depleted in inorganic material" means a flow comprising a mass proportion of inorganic material less than the mass proportion of inorganic material in the mixture M2.

The separation step is typically implemented in a separation device comprising a supply line for the mixture M2 from step a) and two outlet lines: (i) a line for extracting the flow enriched in material inorganic material M3 and (ii) a line for extracting the flow depleted of inorganic material M4.

The separation device can be a separation device by gravity or by cyclone type hydraulic effect typically provided in the lower part with a draining system operating continuously or intermittently.

According to one embodiment, the mixture M1 comprises phosphorus and the flow enriched in inorganic material M3 resulting from step c) comprises at least 50% by weight of the total weight of phosphorus present in the mixture M1. In other words, at least 50% by weight of the phosphorus present in the mixture M1 is recovered in the flow enriched in inorganic material M3 resulting from step c).

According to one embodiment, the mixture M1 comprises phosphorus and the stream M3 enriched in salts from step c) comprises phosphorus, preferably in a proportion ranging from 1 to 20% by weight, relative to the total dry weight. of the flow enriched in inorganic matter M3.

Possible pressurization stage and possible heating stage According to one embodiment, the treatment method according to the invention comprises an additional pressurization step implemented on flow M4 upstream of the hydrothermal gasification step.

According to this embodiment, preferably, the pressurization step a) is implemented at a pressure ranging from 150 to 210 bars and the additional pressurization step makes it possible to bring the mixture M4 from the step c) at a pressure greater than or equal to 225 bars.

State-of-the-art hydrothermal gasification processes operate with a single operating pressure. According to an advantageous embodiment of the invention, the method of the invention uses two operating pressures. This two-pressure operation provides multiple advantages.

On the one hand, only a fraction of the installation is put at very high pressure (only the “second part”, after the additional pressurization) so construction costs are reduced as well as installation constraints.

On the other hand, at the time of heat recovery from flow M5 to preheat the mixture M1, M1p or M1h, the pressure difference between the two flows makes it possible to maintain a greater temperature difference (delta T) than in the case where the two pressures would be identical, which favors heat exchange. This makes it possible to have a delta T which is the greater force of heat exchange in the exchanger and therefore a smaller exchanger.

According to one embodiment implemented, the treatment method according to the invention further comprises a step of heating the flow M4, preferably at a temperature greater than or equal to 300°C, more preferably at a temperature ranging from 400°C °C to less than 600°C.

When the process includes an additional pressurization step, then preferably, the process also includes a step of heating the flow M4, preferably to a temperature ranging from 400°C to less than 600°C.

The additional heating step can be implemented in a heating device chosen from electric heating or indirect heating by hot gases resulting from combustion.

Hydrothermal gasification stage d) The treatment method according to the invention comprises a hydrothermal gasification step implemented on the flow depleted of inorganic material M4 in order to obtain a mixture M5 comprising gas and an aqueous effluent.

Hydrothermal gasification (GH) is a thermal depolymerization process used to convert organic material present in a humid environment into a mixture of only small molecules under high to moderate temperature and pressure.

During GH, the carbon and hydrogen of an organic material are converted, thermochemically under near-critical or supercritical conditions. A part is converted into compounds with low molar masses that are soluble in water.

Another part is converted into gas products such as carbon dioxide (CO2), methane (CH4), dihydrogen (H2), carbon monoxide (CO), light hydrocarbons such as ethane (C2H6) and propane (C3H8).

During the stay in the hydrothermal gasification reactor at temperatures below 400°C, the organic matter undergoes, among other reactions, decomposition based on hydrolysis, similar to the reactions occurring in the liquefaction process, but much faster. Indeed, implementation in quasi-critical or supercritical conditions makes it possible to use the unique properties of supercritical water as a solvent, which allow homogeneous solvation and reaction conditions, leading to very high reaction kinetic rates. . As a result, a much shorter residence time and much higher heating rate than those of conventional hydrolysis are used, limiting or even avoiding the secondary condensation and polymerization reactions responsible for the formation of bio-oil and biochar.

When GH operates at a temperature above 400°C, radical decomposition of polymers (involving in particular decarboxylation reactions, deamination by breaking C-N bonds, and C-C or C-O cleavage) is predominant, while reforming Endothermic steam is the primary reaction pathway for converting small molecules with 1 to 3 carbon atoms into carbon oxides and dihydrogen and nitrogen into ammonia.

Methane is also produced by methanation of CO and CO2, using dihydrogen.

Consequently, GH can be considered as a decomposition process transforming the organic residues present in the M4 stream into a more easily biodegradable material and into ammonia dissolved in the liquid phase. The processing conditions (in particular the temperature, pressure, and to a lesser extent the residence time) of the GH can be adjusted to not only produce a gas fraction containing CH4, CO, CO2 and H2 (gas synthesis), but also to produce an aqueous effluent, containing mainly on one side easily digestible compounds, in particular carboxylic acids and on the other side ammonia in the form of ammonium salt of the carbonic acids produced.

It should be noted that GH is different from hydrothermal liquefaction (HTL), particularly in that the conversion rate and level of decomposition of organic matter in HTL are not as high as in GH, even when GH is operated under moderate temperature conditions.

Under HTL conditions, water still contains HO- and H3O+ ions which initiate the hydrolysis of organic matter.

Hydrolysis only takes place on the surface of the cellulose compounds contained in the organic fraction which dissolves very little in the subcritical medium giving fairly low conversions in decomposition.

Condensation reactions (mainly including Aldol condensation, alkylation or Friedel-Craft acylation) of intermediates are an important reaction pathway, leading to the formation of a biocrude which is an oil (also called bio-oil ) which can be used as fuel, i.e. biocrude contains organic molecules containing 5 or more carbon atoms, generally 8 to 16 carbon atoms. In contrast, GH's liquid product mainly contains easily biodegradable compounds.

GH differs from pyrolysis in that it is carried out in a medium containing water, the water being in a supercritical or quasi-critical state.

GH differs from “conventional” gasification of organic materials in that “conventional” gasification reduces the carbon/hydrogen (C/H) mass ratio, which leads to products with increased calorific value, including a gas predominantly composed synthesis gas (mixture of H2 /CO), bio-oil and/or carbonaceous solid (char).

In the treatment process according to the invention, the hydrothermal gasification step is typically implemented in a hydrothermal gasification reactor, fed at the inlet by at least a fraction of flow depleted of inorganic material M4 and comprising an outlet M5, the flow depleted in inorganic material M4 can come directly from the separation device or from the possible additional heating step implemented on at least a fraction of the flow M4.

According to one embodiment, the gasification reactor is a tubular reactor. Preferably, the hydrothermal gasification step is carried out at a temperature below 600°C, preferably at a temperature ranging from 350°C to less than 600°C, more preferably ranging from 450 to less than 600°C. vs.

Preferably, the hydrothermal gasification step is carried out at a pressure greater than or equal to 220 bars, preferably greater than or equal to 250 bars.

Preferably, the (overall) residence time of the flow depleted of inorganic material M4 in step d) of GH typically ranges from 1 min to 20 min, preferably from 2 min to 10 min, more preferably from 3 to 5 min .

According to a preferred embodiment, the hydrothermal gasification step is carried out in the presence of a catalyst. Preferably, the catalyst is chosen from metals on activated carbon, for example of the ruthenium, nickel, palladium or platinum type.

The catalyst can be in the form of a bed of solid particles within the gasification reactor.

Thanks to separation step c) of the process of the invention making it possible to eliminate so-called “poison” compounds, the catalyst possibly used during the hydrothermal gasification step will not be deteriorated by these harmful compounds which can damage, in particular deactivate the catalyst.

Cooling and separation stage e)

The treatment process according to the invention comprises a step of cooling and separating at least a fraction of the mixture M5 resulting from the hydrothermal gasification of step d) in order to obtain a gaseous effluent and a liquid effluent comprising 'ammonia.

The cooling step makes it possible to bring the M5 mixture to a temperature less than or equal to 200°C, preferably less than or equal to 120°C, preferably ranging from 50 to 120°C.

The cooling device can be chosen from a heat exchanger, flash, scrubber, rankine cycle.

The separation step can be implemented in an expansion system making it possible to obtain a liquid effluent M5' on the one hand and a gaseous effluent on the other hand.

According to one embodiment, the liquid effluent M5' comprises from 1 to 20 g/l of ammonia

Possible ammonia enrichment step f) According to one embodiment, the treatment method according to the invention comprises a step of enriching with ammonia at least a fraction of the liquid effluent M5' comprising ammonia from step e) in order to obtain a flow enriched M5” in ammonia and a flow depleted M8 in ammonia.

By “stream enriched in ammonia”, within the meaning of the present invention, is meant a stream comprising a proportion of ammonia higher than the proportion of ammonia in the liquid effluent M5’.

By “ammonia-depleted flow”, within the meaning of the present invention, is meant a flow comprising a proportion of ammonia lower than the proportion of ammonia in the liquid effluent M5’.

According to one embodiment, the ratio between the concentration of ammonia in the enriched stream M5” and the concentration of ammonia in the incoming effluent M5’ is at least 1.5, preferably at least 2, preferably at least 5.

According to one embodiment, the flow enriched in ammonia at the end of step f) comprises from 1 to 20 g/l of ammonia.

According to one embodiment, the ammonia-depleted flow M8 can be sent to a digester for a digestion step.

The enrichment step can be implemented in an enrichment device which can for example consist of a reactor or several evapo-concentration reactors, or of one or more membrane or stripping reactors.

Thus, according to an advantageous embodiment, when an enrichment step is implemented, then preferably, the cooling and separation step e) is implemented so as to bring the liquid effluent M5' to a temperature ranging from 75°C to 200°C, preferably from 100 to 120°C. Indeed, according to this embodiment, it is advantageous to conserve heat to improve the yield during the enrichment step.

According to one embodiment, the ammonia enrichment step f) is implemented using heat, preferably the heat is recovered from the M5 mixture resulting from the hydrothermal gasification d).

According to one embodiment, the heat present in the mixture M5 resulting from step d) is recovered, said recovered heat preferably making it possible to at least partially heat the mixture M1 during step a). Preferably, this heat recovery is implemented by heat exchange between the mixture M5 resulting from step d) and the mixture M1 or M1 h upstream of the heating step b).

When hydrolysis is carried out, then the heat exchange can be implemented between the mixture M5 and the mixture M1 to allow the mixture M1 to be heated for the hydrolysis step or between the mixture M5 and the mixture M1h to allow mixture M1h to be heated for heating step b).

Thus, the mixture M1 or M1 h can recover heat from the mixture M5, which will reduce the energy requirements of the process and cool the mixture M5.

Typically, the ammonia requirement for the formation of struvite will generally be less than the quantity of ammonia in the liquid effluent M5' or in the liquid effluent M5", then preferably only a fraction of the liquid effluent flow M5' or enriched liquid effluent stream M5” will be mixed with at least a fraction of the stream M3 during step g). For example, we can use less than 75% of the volume of M5’ or M5”, or even less than 50% of the volume of M5’ or M5” during mixing step g).

Mixing step g)

The treatment method according to the invention comprises a step of mixing at least a fraction of the flow enriched in inorganic material M3 obtained at the end of step c) and at least a fraction of the liquid effluent comprising ammonia obtained at the end of step e) or at the end of step f) when it is present, in order to obtain a mixture M6.

According to one embodiment, the entire flow enriched with inorganic material M3 obtained at the end of step c) is mixed during this step g).

According to one embodiment, all of the liquid effluent comprising ammonia obtained at the end of step e) or at the end of step f) when it is present is mixed during this step g).

This mixing step g) is preferably carried out in a mixing device. The mixing device may be a batch, semi-continuous or continuous reactor, stirred by a blade, propeller, draft tube type stirring system or by recirculation external to the reactor. This reactor is equipped with pH measurement and base and acid injection to control the pH.

Preferably, the pH of the reactor is adjusted such that the pH at room temperature ranges from 7.5 to 10, preferably from 8 to 9.

This mixing step g) is typically carried out at a temperature ranging from 50°C to 250°C and/or at a pressure ranging from 1 to 200 bars. This mixing step can optionally be implemented in the precipitation reactor where the struvite is formed.

Thus, according to this embodiment, at least a fraction of the flow enriched in inorganic material M3 obtained at the end of step c) and at least a fraction of the liquid effluent comprising ammonia obtained at the end of step e) or at the end of step f) when it is present are introduced into the precipitation reactor and the mixture M6 is formed in situ in the precipitation reactor and the step of forming the struvite, step h) takes place.

According to one embodiment, at least one magnesium salt is injected: into the mixture during this step g) and/or into the mixture M6 between steps g) and h) when they are implemented in separate devices and/or during step g) is implemented in the precipitation reactor.

According to one embodiment, at least one magnesium salt is added in such a way that the magnesium is in a stoichiometric proportion or in a super-stoichiometric proportion. Thus, preferably the Mg/P molar ratio in the M6 mixture after addition of the magnesium salt ranges from 1/1 to 1.3/1.

Thus, we can provide a measurement of the phosphorus content in the mixture M1 before its implementation in the pressurization step a). Indeed, the measurement of the phosphorus content will typically be done at atmospheric pressure. This measurement implemented in the M 1 mixture will provide a good estimate of the phosphorus content in the M6 mixture.

A measurement of the phosphate content in the M7 liquid effluent will also make it possible to adjust the magnesium salt content that should be added to the M6 mixture.

The magnesium salt can be added to a mixing device during this step g) and/or downstream of said mixing device in the mixture M6.

Mixing step g) can be done directly in the precipitation reactor.

According to this embodiment, the precipitation reactor is supplied on the one hand by at least a fraction of the flow enriched in inorganic material M3 obtained at the end of step c) and on the other hand by: at least a fraction of the liquid effluent M5' comprising ammonia obtained at the end of step e) or at least a fraction of the enriched flow M5' obtained at the end of step f) when she is here.

According to this embodiment, the mixture will also be called mixture M6.

According to this embodiment, the magnesium salt can be added to the precipitation reactor.

According to one embodiment of the invention, the treatment process comprises: a step of injecting a magnesium salt, preferably chosen from MgO and Mg(OH)2 and their mixtures, into the mixture upstream of the pressurization step a), and a step of injecting a magnesium salt, preferably chosen from MgCI2, into the mixture during step g) and/or during step h) and/ or in the mixture M6 between steps g) and h) when they are implemented in separate devices.

Struvite formation stage h)

The treatment process according to the invention comprises a step of forming struvite from at least a fraction of the M6 mixture of step g) in a precipitation reactor.

The struvite formation step can be carried out at a temperature ranging from 20°C to 250°C and/or at a pressure ranging from 1 to 200 bars.

According to one embodiment, all of the M6 mixture from step g) is used during this struvite formation step i). Of course, when the mixing step g) is implemented in the precipitation reactor, then the entire mixture M6 will necessarily be implemented during this struvite formation step i).

When the mixing step g) is implemented in a device separate from the precipitation reactor, then at least a fraction of the mixture M6, preferably the entire mixture M6, is injected into the precipitation reactor for the implementation of step i).

The precipitation reactor may be an infinitely mixed reactor or a fluidized bed reactor. An example of a commercial precipitation reactor, useful in particular for precipitating phosphorus in the form of struvite, is the Crystal Actor®.

At the end of step h), struvite is recovered after possible decantation. It should be noted that this step h) will produce, in addition to the struvite, another effluent, which will be a liquid effluent M7.

The invention also relates to an installation for implementing the method of the invention.

The installation according to the invention comprises: a pressurization pump 3 supplied by the mixture M1 and comprising an outlet for the mixture M1 p,

A cooling and separation device 9 downstream of the gasification reactor, supplied with at least a fraction of the mixture M5 and comprising at least one outlet for a gaseous effluent and at least one outlet for a liquid effluent M5',

Optionally an ammonia enrichment device 10 supplied by at least a fraction of the liquid effluent M5' and comprising an outlet for the enriched flow M5' and an outlet for the depleted flow M8,

Optionally a mixing device 6 supplied by (i) at least a fraction of the flow M3 and by (ii) at least a fraction of the flow M5' or at least a fraction of the flow M5” and comprising an output for the flow M6,

A precipitation reactor 7 comprising at least one inlet and at least one outlet, said precipitation reactor 7 being able to be supplied: o Either by (i) at least a fraction of the flow M3 coming from the separation device 5 and by (ii) at at least a fraction of the flow M5' coming from the cooling and expansion device 9 or at least a fraction of the flow M5” coming from the enrichment device 10, o Either by the flow M6 coming from the mixing device 6,

- At least one injection device located: o upstream of the pressurization pump 3 and/or o in the mixing device 6 when it is present and/or o downstream of the mixing device 6 when it is present and upstream of the precipitation reactor 7, and/or o in the precipitation reactor 7.

According to one embodiment, the installation further comprises at least one hydrolysis reactor 4 upstream of the pressurization pump 3, said hydrolysis reactor comprising at least one inlet for the mixture M1 and at least one outlet for the hydrolyzate M1h, said hydrolyzate M1h supplying the pressurizing pump 3.

According to one embodiment, the precipitation reactor 7 can be supplied by (i) at least a fraction of the flow M3 coming from the separation device 5 and by (ii) at least a fraction of the flow M5' coming from the cooling device and expansion 9 or at least a fraction of the flow M5” coming from the enrichment device 10.

According to this embodiment, the mixing step g) is implemented in the precipitation reactor 7 where the struvite formation step i) takes place.

According to another embodiment, the installation comprises a mixing device 6 distinct from the precipitation reactor 7. The mixing device 6 is then supplied by (i) at least a fraction of the flow M3 and by (ii) at least one fraction of the flow M5' or at least a fraction of the flow M5” and comprising an output for the flow M6. According to this embodiment, the precipitation reactor 7 is supplied by the flow M6 coming from the mixing device 6.

Figs. 1 to Fig. 3 each illustrate an embodiment of the installation according to the invention and of the method according to the invention, without limiting its scope.

As shown in Fig. 1, the mixture M1 optionally added with a magnesium salt Mg pass is put under pressure using a pressurizing pump 3 then in a heating device 2, where the mixture M1 is typically put under pressure at a pressure ranging from 150 at 350 bars, mixture called M1p, then is heated to a temperature ranging from 250 to 500°C. At the outlet of the heating device 2, a mixture M2 is obtained.

As shown in Fig. 1, the mixture M2 feeds a separation device 5 making it possible to obtain a flow enriched in inorganic material M3 and a flow depleted in inorganic material M4.

As shown in Fig. 1, the flow M4 feeds a hydrothermal gasification reactor 8 in order to obtain a mixture M5 comprising gas and a liquid effluent. The gasification reactor 8 may include a catalyst. As shown in Fig. 1, the mixture M5 feeds a cooling and separation device 9 making it possible to cool the mixture M5 to a temperature less than or equal to 200° C. and to obtain a gas flow and a liquid effluent M5'.

As shown in Fig. 1, the installation comprises a mixing device 6 supplied on the one hand by the flow M3 and on the other hand by at least part of the flow M5' leaving the cooling and separation device 9.

As shown in Fig. 1, the mixture M6 resulting from the mixing device, optionally additive with a magnesium salt (Mg), is then introduced into a precipitation reactor 7.

Struvite is then recovered downstream of the precipitation reactor 7 after possible decantation not shown, as well as a liquid effluent M7.

It should be noted that the installation according to the invention may include other elements not illustrated in the Figures. In particular, the installation according to the invention can include valves and branch pipes, making it possible to introduce only a fraction of flows rather than all of the flows, as illustrated in the Figures for simplicity, in particular for M3 flows , M4, M5 or M6.

It is also possible to provide control elements to control the flow rate.

The Figures illustrate several stages of adding magnesium salt but it should be noted that the installation according to the invention can comprise a single device or several devices allowing magnesium salt to be added. Such a device may include a magnesium salt storage tank and a supply line making it possible to convey the magnesium salt from the tank to the injection site.

The embodiment illustrated in Fig. 2 differs from the embodiment of FIG. 1 in that an enrichment device 10 is present, said enrichment device being located downstream of the cooling device 9 and upstream of the mixing device 6.

The enrichment device 10 comprises an inlet for at least a fraction of the liquid effluent M5' and an outlet for the enriched effluent M5' and an outlet for the depleted effluent M8.

According to this embodiment, the installation according to the invention preferably comprises a diversion valve making it possible to control the quantity of effluent M5” introduced into the mixing device 6. The embodiment illustrated in Fig. 3 differs from the embodiment of FIG. 2 in that a hydrolysis reactor 4 is present, upstream of the pressurization pump 3.

According to one embodiment of the invention, the installation comprises, upstream of the pressurization pump 3, at least one hydrolysis reactor 4.

Indeed, the installation according to the invention can comprise one or more hydrolysis reactors 4 in series or in parallel supplied at the input by a supply line for the mixture M1 and an outlet line for the hydrolyzed mixture M1h at a lower temperature or equal to the hydrolysis temperature. The hydrolysis reactor(s) 4 advantageously comprise(s) a heating and pressurization device and optionally comprise(s) a stirring device, as well as advantageously an internal thermal recovery device.

According to this embodiment, pump 3 is powered by the mixture M1 h.

According to this embodiment, it is possible to provide for the magnesium salt to be injected upstream or downstream of the hydrolysis reactor(s) 4.

The hydrolysis reactor(s) 4 may optionally be preceded by a grinding device or may be provided with a recirculation loop provided with a grinding device or may be followed by a grinding device, upstream of pump 3.

According to an embodiment illustrated in Fig. 4, the precipitation reactor 7 is supplied by (i) at least a fraction of the flow M3 coming from the separation device 5 and by (ii) at least a fraction of the liquid effluent M5' coming from the cooling and expansion device 9. According to this embodiment, a magnesium salt can be injected into the precipitation reactor 7 and/or into the mixture M1 or M1 h (hydrolysis upstream of pressurization via pump 3 is not illustrated in Fig. 4 but forms part of the invention).

According to an embodiment illustrated in Fig. 5, the precipitation reactor 7 is supplied by (i) at least a fraction of the flow M3 coming from the separation device 5 and by (ii) a fraction of the flow M5” coming from the enrichment device 10. According to this embodiment , a magnesium salt can be injected into the precipitation reactor 7 and/or into the mixture M1 or M1 h.

The installation according to the invention can of course include one or more of the characteristics described in the context of the method according to the invention.

Claims

CLAIMS Process for treating a mixture M1 comprising at least organic matter, said process comprising: a) a step of pressurizing the mixture M1 to a pressure of 150 to 300 bars, preferably between 170 and 210 bars in order to obtain a mixture M1p, b) a step of heating the mixture M1p to a temperature ranging from 250°C to 500°C making it possible to obtain a mixture M2, c) a step of separating the mixture M2 resulting from step b ) in order to obtain a flow M3 enriched in inorganic material and a flow M4 depleted in inorganic material, d) a hydrothermal gasification step implemented on the flow depleted in inorganic material M4 in order to obtain a mixture M5 comprising gas and a liquid effluent, e) a step of cooling and separating at least a fraction of the mixture M5 resulting from the hydrothermal gasification of step d) in order to separate the gas from the liquid effluent M5' comprising ammonia , f) optionally a step of enriching in ammonia at least a fraction of the liquid effluent M5' in order to obtain a stream enriched in ammonia M5” and a stream depleted in ammonia M8, g) a mixing step ( i) at least a fraction of the flow enriched in inorganic material M3 obtained at the end of step c) and (ii) at least a fraction of the liquid effluent M5' or at least one fraction of the enriched flow M5” obtained at the end of step f) when it is present, in order to obtain a mixture M6, h) a step of forming struvite from at least a fraction of the mixture M6 in a precipitation reactor, i) a struvite recovery step at the outlet of the precipitation reactor, said treatment process comprising at least one step of injecting at least one magnesium salt into the mixture M1 before step a ) pressurization and/or during step g) and/or during step h) and/or in the mixture M6 between steps g) and h), said mixing step g) possibly being implemented in the precipitation reactor. Treatment method according to claim 1, in which the magnesium salt is chosen from magnesium hydroxide, magnesium oxide, magnesium chloride, and mixtures thereof, preferably from magnesium hydroxide and magnesium oxide, more preferably the magnesium salt is magnesium hydroxide. Treatment method according to any one of claims 1 to 2, comprising upstream of step a), a step of hydrolysis of the mixture M1 carried out at a temperature ranging from 70 to 165°C and at a pressure ranging from 2 to 8 bars, making it possible to obtain an M1h mixture which will then be put under pressure in step a). Treatment method according to any one of claims 1 to 3, comprising a heat exchange between the mixture M5 resulting from step d) and the mixture M1 or M 1 p or M 1 h upstream of the heating step b). Treatment method according to any one of claims 1 to 4, in which the mixture M1 comprises from 5 to 50% by weight of solid materials, preferably from 15 to 25% by weight of solid materials, relative to the total weight of the M1 mixture. Treatment method according to any one of claims 1 to 5, in which the stream enriched in salts from step c) comprises phosphorus, preferably in a proportion ranging from 1 to 20% by weight, relative to the weight total dry flow enriched in inorganic matter M3. Treatment method according to any one of claims 1 to 6, in which the liquid effluent M5' comprises from 1 to 20 g/l of ammonia. Treatment method according to any one of claims 1 to 7, in which the ammonia enrichment step f) is carried out using heat. Treatment method according to claim 8, in which the heat comes from the M5 mixture resulting from hydrothermal gasification d). Treatment method according to any one of claims 1 to 9, in which the ammonia enrichment step f) makes it possible to obtain an ammonia concentration in the liquid effluent M5” at least 1.5 times greater than the concentration of ammonia in the liquid effluent M5', preferably an ammonia concentration in the liquid effluent M5' at least twice the concentration of ammonia in the liquid effluent M5', or even an ammonia concentration in the liquid effluent M5” at least 5 times higher than the ammonia concentration in the liquid effluent M5’. Treatment method according to any one of claims 1 to 10, in which less than 75% of the volume, preferably less than 50% of the volume, of the liquid effluent M5' resulting from step e) or from liquid effluent M5” from step f) when it is implemented, is mixed during step g). Installation for implementing a treatment process according to any one of claims 1 to 11, said installation comprising: a pressurization pump (3) supplied by the mixture M1 and comprising an outlet for the mixture M1 p ,

A heating device (2) comprising an inlet making it possible to introduce the mixture M1p possibly mixed with a magnesium salt Mg and comprising an outlet for the mixture M2,

A separation device (5) supplied with at least a fraction of the mixture M2 and comprising an outlet of flow M3 enriched in inorganic material and an outlet of flow M4 depleted of inorganic material,

A hydrothermal gasification reactor (8) supplied by at least a fraction of the flow M4 coming from the separation device (5) and comprising a mixture outlet M5 comprising gas and a liquid effluent,

A cooling and separation device (9) downstream of the gasification reactor (8), supplied with at least a fraction of the M5 mixture from the reactor (8) and comprising at least one outlet for a gaseous effluent and at least one outlet for a liquid effluent M5',

Optionally an ammonia enrichment device (10) supplied with at least a fraction of the liquid effluent M5' and comprising an outlet for the enriched flow M5' and an outlet for the depleted flow M8,

Optionally a mixing device (6) supplied by (i) at least a fraction of the flow M3 coming from the device (5) and by (ii) at least a fraction of the flow M5' coming from the device (9) or at least a fraction of the flow M5” coming from the device (10), and comprising at least one outlet for the mixture M6,

A precipitation reactor (7) comprising at least one inlet and at least one outlet, said precipitation reactor (7) being able to be supplied: o Either by (i) at least a fraction of the flow M3 coming from the separation device (5) and by (ii) at least a fraction of the flow M5' coming from the device cooling and expansion (9) or at least a fraction of the flow M5” coming from the enrichment device (10), o Either by the flow M6 coming from the mixing device (6) when it is present,

- At least one injection device located: o upstream of the pressurization pump (3) and/or o in the mixing device (6) and/or o downstream of the mixing device (6) and in upstream of the precipitation reactor (7), and/or o in the precipitation reactor (7). Installation according to claim 12, further comprising at least one hydrolysis reactor (4) upstream of the pressurization pump (3), said hydrolysis reactor comprising at least one inlet for the mixture M1 and at least one outlet for the hydrolyzate M1h, said hydrolyzate M1h supplying the pressurization pump (3).