WO2021123694A1

WO2021123694A1 - Supercritical water gasification method

Info

Publication number: WO2021123694A1
Application number: PCT/FR2020/052573
Authority: WO
Inventors: Guillaume BOISSONET; Cyril Bourasseau; Thierry Chataing
Original assignee: Syctom L'agence Metropolitaine Des Dechets Menagers; Syndicat Interdepartemental Pour L'assainissement De L'agglomeration Parisienne
Priority date: 2019-12-20
Filing date: 2020-12-18
Publication date: 2021-06-24
Also published as: FR3105253B1; FR3105253A1

Abstract

The invention relates to a method for supercritical water gasification of a co-digestate, the method comprising: - feeding the co-digestate, at a temperature T2, into a supercritical water gasification reactor (10), - discharging, from the reactor outlet, a supercritical flow (FS) comprising water and gaseous species, the reactor being heated by the circulation of a hot air flow (FAC) which is supplied by a boiler and which enters a heating circuit of the reactor at a temperature T5 and leaves the heating circuit via an outlet pipe (21S) at a temperature T6, the method being characterised in that the hot air flow (FAC) at the temperature T6 flows from the outlet pipe (21S) to a first heat exchanger (30) in which an air flow which is intended to be heated by the boiler is pre-heated by heat exchange between the hot air flow (FAC) and the air flow.

Description

Title: SUPERCRITICAL WATER CARBONATION PROCESS TECHNICAL FIELD

The invention relates to the field of the reprocessing of organic waste, and in particular to organic waste of little value such as digestates.

In particular, the present invention relates to a process for the gasification in supercritical water (GESC) of organic or synthetic carbonaceous material, more specifically the gasification in supercritical water of a co-digestate, for example resulting from the methanization of a mixture of FOr (Residual organic fraction), sewage sludge and possibly agricultural waste (eg horse manure).

In particular, the present invention proposes to improve the energy balance of a supercritical water gasification process of a co-digestate.

STATE OF THE PRIOR ART

The supercritical water gasification of wet biomass, comprising for example more than 70% water and today well known to man and is widely described in the literature.

This technique makes it possible in particular to treat sludge from sewage treatment plants, waste, micro-algae, black liquor from paper mills, etc.

In particular, the treatment of these carbonaceous materials by gasification in supercritical water makes it possible to transform the latter into a gaseous mixture, called “syngas”, which comprises in particular the following gaseous species: CH ₄ , H ₂ , CO ₂ , CO. The transformation of the latter, carried out in a dedicated reactor, in the presence or absence of a catalyst, however requires a supply of heat which has a direct impact on the yield, and the energy efficiency associated with the conversion of carbonaceous species into syngas. .

In this regard, the document [1] cited at the end of the description discloses a device for gasification of biomass in supercritical water. It is in particular recalled in this document that the amount of heat necessary to bring a mixture to the gasification temperature in supercritical water is relatively large and constitutes a major limitation to the implementation of this process. This limitation is all the more important in the case of a non-catalytic process for which the gasification temperature is higher. Thus, depending on the nature of the effluent to be treated, the quantity of heat necessary for the gasification of the latter can be 3 times greater than the energy (otherwise called "Superior Calorific Power" or "PCS") that it contains. . Thus, when the effluent considered comprises a relatively low PCS, in particular less than 12 MJ / kg of dry matter, it remains difficult to give the gasification process implemented energy efficiency (defined as the ratio of the energy recovered in the form of of gaseous species on the thermal energy to be supplied) positive without resorting to recovery of the energy exchanged with the effluent.

The digestates or co-digestates resulting from a methanization process have a high content of inorganic matter, which may in particular correspond to more than 40% of the dry matter of said digestate, and consequently have a low SCP.

Improving the energy efficiency of supercritical water gasification processes, in particular non-catalytic, remains a crucial issue when these processes are attributed an energy vocation.

Thus, in a non-catalytic approach described in document [2] cited at the end of the description, it is proposed to preheat the effluent to be treated via heat exchange between said effluent and the supercritical mixture.

This preheating is carried out in particular within a heat exchanger, for example an exchanger of the tube-shell type, arranged upstream of the supercritical water gasification reactor.

Document [3] cited at the end of the description also proposes, according to a catalytic approach, preheating of the effluent to be treated essentially according to the same terms as document [2].

The two approaches presented in documents [2] and [3] however require a supply of heat from an external energy source which affects the energy efficiency of the supercritical water gasification process as much. This heat input is provided in particular by a flow of air produced by a boiler and intended to bring the effluent to be treated to the temperature of gasification in supercritical water, and in particular to a temperature above 600 ° C when the approach non-catalytic is considered.

Furthermore, the flow of hot air making it possible to ensure heating to the required temperature of the effluent to be treated must be relatively high, and is consequently a source of additional energy losses.

Thus, whatever the approach considered, the recovery of thermal energy remains limited to a value between 40% and 60%, so that the gasification processes known in the art have a negative energy balance when the co -digestate considered has a low PCS.

An aim of the present invention is therefore to provide a supercritical water gasification process making it possible to achieve positive energy efficiency.

DISCLOSURE OF THE INVENTION

The object of the present invention is achieved by a process for the gasification in supercritical water of a co-digestate forming an aqueous effluent which comprises organic matter, mineral matter, the process comprising:

- injection of the co-digestate, at a temperature T2 in a gasification reactor in supercritical water, heated to a temperature Tr, so as to transform the organic matter into gaseous species,

the flow, at the outlet of the reactor, of a supercritical flow, at a temperature T3 lower than the temperature T2, comprising water and the gaseous species, the heating of the reactor being provided by the circulation of a flow of hot air, supplied by a boiler, entering a heating circuit of the reactor at a temperature T5 and leaving the heating circuit through an outlet pipe at a temperature T6, lower than the temperature T5, the process being remarkable in that the flow of hot air at temperature T6 flows from the outlet pipe to a first heat exchanger in which a Preheating of an air stream, intended to be heated by the boiler, is performed by heat exchange between the hot air stream and the air stream.

According to one embodiment, the hot air flow leaves the first exchanger at a temperature T7 lower than the temperature T6, and is led to a second exchanger in which a preheating of a fuel supplying the boiler is carried out by exchange. thermal between the hot air flow and said fuel.

According to one embodiment, a step of preheating from a temperature T1 to the temperature T2 of the co-digestate prior to its injection into the gasification reactor with supercritical water, the preheating being carried out, in a third heat exchanger, by heat exchange between the supercritical flow flowing from the gasifier reactor in supercritical water and the co-digestate injected into the third exchanger.

According to one embodiment, the third exchanger is a twin-tube type exchanger.

According to one embodiment, prior to its preheating, the co-digestate is injected under pressure into the third exchanger, advantageously at a pressure of between 270 bars and 300 bars.

According to one embodiment, a step of high pressure separation of the gaseous species and of the liquid phase of the supercritical flow at the outlet of the third exchanger is carried out in a high pressure separation module.

According to one embodiment, a step of separating residual gaseous species in the liquid phase coming from the high pressure separation module is performed in a low pressure separation module.

According to one embodiment, the mineral material is extracted from the co-digestate in the third exchanger to form a flow of brine at a temperature T10.

According to one embodiment, the supercritical flow, after the heat exchange step in the third exchanger, and before the high pressure separation step, is injected into a fourth heat exchanger so as to heat a first flow of water. According to one embodiment, a flow of brine leaving the third heat exchanger is injected into a fifth heat exchanger so as to heat a second flow of water.

According to one mode of implementation, the co-digestate results from the methanization of organic materials.

The invention also relates to a supercritical water gasification plant (1) which comprises:

- a supercritical water gasification reactor provided with a heating circuit in which a hot air flow is intended to circulate and provide the thermal energy necessary for the supercritical water gasification of a co-digestate injected into said reactor , said flow of hot air leaving the reactor through an outlet pipe;

- a boiler providing the flow of hot air;

The installation being characterized in that said device also comprises a first heat exchanger within which the air flow intended to be heated by the boiler is preheated by heat exchange with the hot air flow circulating in the heating pipe. exit.

According to one embodiment, said installation further comprises a second heat exchanger intended to preheat a fuel intended to ensure the operation of the boiler by heat exchange with the air flow leaving the first heat exchanger.

According to one embodiment, said installation comprises a high pressure injection module intended to inject a high pressure co-digestate into the supercritical water gasification reactor.

According to one embodiment, a third heat exchanger is arranged between the high pressure injection module and the supercritical water gasification reactor, the third exchanger being arranged to allow preheating of the co-digestate by heat exchange between this last and the supercritical flow from the gasification reactor in supercritical water.

According to one embodiment, said installation further comprises a high pressure separation module intended to collect the supercritical flow at the end of the phase. heat exchange in a third exchanger, and to separate the gaseous species from the aqueous phase.

According to one embodiment, the installation comprises a fourth heat exchanger, arranged between the third exchanger and the high pressure separation module, intended to heat a first flow of water by heat exchange with the supercritical flow.

According to one embodiment, the installation comprises a low pressure separation module intended to collect the aqueous phase coming from the high pressure separation module and to separate residual gaseous species from said aqueous phase.

According to one embodiment, the third exchanger is also intended to separate and extract the mineral matter included in the co-digestate and to evacuate it via an evacuation pipe in the form of brine.

According to one embodiment, said installation comprises a fifth heat exchanger intended to heat a second stream of water by heat exchange with the brine.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages will appear in the following description of a supercritical water gasification process according to the invention, given by way of nonlimiting examples, with reference to the appended drawings in which:

[Fig. 1] is a schematic representation of a supercritical water gasification plant for implementing the supercritical water gasification process of a co-digestate according to the present invention.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

In Figure 1, one can see an example of a supercritical water gasification installation 1 implemented for the supercritical water gasification of a co-digestate formed by an aqueous effluent which comprises organic matter, mineral.

The term “digestate” is understood to mean a residue from the process of methanization of natural organic materials or of organic waste products such as For or sludge from a treatment plant. The term “co-digestate” means a residue from the methanization process of a mixture of natural organic materials or of different organic waste products, such as, for example, a residue of the methanization process of a mixture of For and of sludge. wastewater treatment plant.

The installation 1 comprises in particular a supercritical water gasification reactor 10 in which the organic matter of the co-digestate is transformed into gaseous species dissolved in water, and thus form a supercritical flow Fs delivered at the level of a pipe 11c . A detailed description of such a reactor is given in document [4] cited at the end of the description.

The gasification in supercritical water can be carried out in the presence or absence of a catalyst.

The gaseous species can include methane (CPU), hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), and, in smaller quantities, carbon compounds of the type C _x H _y .

The equilibrium and in particular the relative proportions of the gaseous species in the supercritical fluid is a function of the temperature Tr and the pressure Pr imposed on the effluent in the supercritical water gasification reactor.

The pressure Pr can in this respect be between 270 bars and 300 bars.

The temperature Tr can be between 550 ° C and 700 ° C, for example equal to 600 ° C. The supercritical water gasification reactor 10 may in this regard be of the tube / shell type so as to allow the effluent to be heated to temperature Tr by heat exchange between a hot air flow FAC and said effluent.

For example, according to the present invention, the hot air flow FAC circulates in a heating circuit of the reactor 10 at a temperature T5 and leaves it via an outlet pipe 21s at a temperature T6, lower than the temperature T5.

The temperature T5 is for example between 650 ° C and 800 ° C, for example equal to 700 ° C, while the temperature T6, after heat transfer to the effluent, can be between 550 ° C and 750 ° C. , for example equal to 600 ° C.

The hot air flow FAC is produced in particular by a step of heating a flow of cold air FAF at the level of a boiler 20 supplied with fuel C. According to the present invention, the flow of cold air FAF is nevertheless preheated in a first exchanger 30, for example a tube and shell exchanger or a two-tube plate exchanger. In particular, the preheating of the flow of cold air FAF is ensured, within said first exchanger 30, by a heat exchange between the flow of hot air FAC and the flow of cold air FAF. In this regard, the hot air flow FAC, circulating in the outlet pipe 21 _s , is injected into a heating circuit of the first exchanger 30 at the temperature T6 and leaves it, via an exchange pipe 31 s, at the temperature T7 lower than temperature T6. The temperature T7 can be between 120 ° C and 200 ° C, for example equal to 140 ° C.

In an equivalent manner, the fuel C can be preheated in a second exchanger 40, for example a tube and shell exchanger or a two-tube plate exchanger. In particular, the preheating of the fuel C is ensured, within said second exchanger 40, by a heat exchange between the fuel C and the hot air flow FAC at the temperature T7. In this regard, the hot air flow FAC, circulating in the exchange pipe 31 _s , is injected into a heating circuit of the second exchanger 40 at the temperature T7, and leaves it at a temperature T8, lower than the temperature. T7. The temperature T8 can be between 50 ° C and 120 ° C, for example equal to 70 ° C.

The recovery of energy at the level of the first exchanger 30, and possibly at the level of the second exchanger 40, makes it possible to improve the energy efficiency of the supercritical water gasification process. In fact, the hot air flow FAC circulating in the outlet pipe 21 _s has a relatively high temperature which is advantageously taken advantage of for the preheating of the cold air flow FAF, and possibly of the fuel C. Thus, the quantity of energy supplied by the boiler to bring the flow of cold air FAF to the temperature T5 to form the flow of hot air is thereby reduced.

According to an advantageous embodiment, the method also comprises a step of preheating from a temperature T1 to the temperature T2 of the co-digestate prior to its injection into the gasification reactor with supercritical water 10.

The preheating is carried out in particular in a third heat exchanger 50, for example a two-tube exchanger, by heat exchange between the supercritical flow Fs flowing in line 11c and the co-digestate injected into the third exchanger 50. Following this heat exchange, the flow Fs goes into a subcritical state and has a temperature T4 which can be between 110 ° C and 200 ° C, for example equal to 120 ° C.

The temperature T1 can be between 10 ° C and 50 ° C, and the temperature T2 between 350 and 450 ° C, for example equal to 410 ° C.

Advantageously, the co-digestate is injected under pressure, by a module 60, into the third exchanger 50, for example at a pressure of between 270 bars and 300 bars. The injection can be carried out by means of a piston pump.

Furthermore, the preheating of the co-digestate in the third exchanger 50 can also lead to a separation of the mineral matter from the co-digestate, and an evacuation of the latter in an evacuation pipe 51c in the form of brine at a temperature T10 which can be between 200 ° C and 450 ° C, for example equal to 350 ° C.

The gasification process also comprises a high pressure separation step, carried out in a high pressure separation module 70 at a pressure between 200 bars and 300 bars. This high pressure separation step is intended to separate, at least in part, the ESG gaseous species from the liquid phase. In particular, the gaseous species are evacuated via a first outlet pipe 71s, while the liquid phase, formed of water and traces of gas, in particular traces of CO2, is conveyed, via an intermediate pipe 71i, to a module low pressure separation 80. This module 80 makes it possible in particular to perform a gas-liquid separation step at low pressure, and in particular at a pressure of between 2 bars and 10 bars, of water E and traces of gas TG. The water E and the traces of gas TG thus separated are discharged, respectively, through a second outlet duct 81s and a third outlet duct 82s.

According to a particularly advantageous embodiment, a portion of the gaseous species form the fuel C necessary for the operation of the boiler. The installation 1 can also include a fourth heat exchanger 90 within which a first flow of water FE1 is heated. In particular, the heating of the first flow FE1 water is performed by heat exchange with the supercritical flow at the end of the heat exchange in the third exchanger 50. In particular, the supercritical flow at the outlet of the fourth exchanger is at a temperature T9 lower than the temperature T4 at the exit of the third exchanger. The temperature T9 can be between 30 ° C and 80 ° C, for example be equal to 50 ° C.

Equivalently, the flow of brine coming from the third exchanger 50, and at the temperature T6, can be injected into a fifth heat exchanger 100 so as to heat a second flow of water FE2.

The installation described above was the subject of a simulation in order to determine the energy efficiency of a supercritical water gasification process that it implements.

The table given below shows the digital data on the basis of which the simulation is carried out.

[Table 1]

The simulation carried out with the PROSIMPLUS software considers three different configurations and aims to compare the energy yields, carbon yields and heat recovery rates associated with each of these configurations. The energy efficiency is defined as the ratio of the PCS energy of the gas mixture to the thermal energy supplied during the execution of the process.

The carbon yield is defined as the ratio of the quantity of _{net CH 4} to the quantity of carbon in the co-digestate injected. Finally, the heat recovery rate is defined as 1 minus the ratio of the energy supplied by the boiler to the thermal energy to be supplied.

The first configuration only considers heating by hot air of the co-digestate injected into the reactor.

The second configuration, close to what is described in documents [2] and [3], considers a recovery of the thermal energy of the supercritical flow resulting from the gasification in supercritical water in order to preheat the co-digestate before its injection into said. reactor.

Finally, the third configuration takes up most of the terms of the present invention and considers the first, the second, the third and the fourth exchanger. Examination of the table given below shows that the heat recovery rate is much better as the number of exchangers is increased. The result is improved energy efficiency and net carbon return.

[Table 2]

Thus, the complete integration of heat exchangers making it possible to recover the thermal energy of the hot air flow and of the supercritical flow as proposed in the present invention makes it possible to increase in a certain way the overall energy efficiency of the gasification installation considered in the present invention (third configuration).

Such an installation can in particular operate autonomously by using as fuel the methane formed during the gasification. Furthermore, the installation according to the present invention can advantageously treat a co-digestate obtained from a methanization installation.

REFERENCES

[1] Kruse, A., "Hydrothermal biomass gasification", The Journal of Supercritical Fluids, 47, 391-399, 2009; [2] Yukihiko Matsumura et al., “Biomass gasification in near- and super-critical water:

Status and prospects ”, Biomass and Bioenergy 29 (2005) 269-292;

[3] M. Brandenberger, “Producing synthetic natural gasfrom microalgae via supercritical water gasification: A techno-economic sensitivity analysis”, biomass and Bionenergy 51 (2013) 26-34; [4] FR 3072583.

Claims

1. A process for the gasification in supercritical water of a co-digestate forming an aqueous effluent which comprises organic matter, mineral matter, the process comprising:

- injection of the co-digestate, at a temperature T2 in a gasification reactor in supercritical water (10), heated to a temperature Tr, so as to transform the organic matter into gaseous species,

the flow, at the outlet of the reactor, of a supercritical flow (FS), at a temperature T3 lower than the temperature T2, comprising water and the gaseous species, the heating of the reactor being ensured by the circulation of a flow of hot air (FAC), supplied by a boiler, entering a heating circuit of the reactor at a temperature T5 and leaving the heating circuit via an outlet pipe (21S) at a temperature T6, lower than the temperature T5, the method being characterized in that the flow of hot air (FAC) at the temperature T6 flows from the outlet pipe (21S) to a first heat exchanger (30) in which a preheating of a flow air, intended to be heated by the boiler, is performed by heat exchange between the hot air flow (FAC) and the air flow.

2. Method according to claim 1, wherein the hot air flow (FAC) leaves the first exchanger (30) at a temperature T7 lower than the temperature T6, and is conducted to a second exchanger (40) in which a preheating of a fuel supplying the boiler is carried out by heat exchange between the hot air flow (FAC) and said fuel.

3. The method of claim 1 or 2, wherein a step of preheating from a temperature T1 to the temperature T2 of the co-digestate prior to its injection into the supercritical water gasification reactor (10), the preheating being performed, in a third heat exchanger (50), by heat exchange between the supercritical flow (FS) flowing from the gasifier reactor in supercritical water and the co-digestate injected into the third exchanger (50).

4. The method of claim 3, wherein the third exchanger (50) is a two-tube type exchanger.

5. The method of claim 3 or 4, wherein, prior to its preheating, the co-digestate is injected under pressure into the third exchanger (50), advantageously at a pressure between 270 bars and 300 bars.

6. Method according to one of claims 3 to 5, wherein a high pressure separation step of the gaseous species and the liquid phase of the supercritical flow (FS) at the outlet of the third exchanger (50) is performed in a separation module. high pressure (70).

7. The method of claim 6, wherein a step of separating residual gas species in the liquid phase from the high pressure separation module (70) is performed in a low pressure separation module (80).

8. Method according to one of claims 3 to 7, wherein the mineral material is extracted from the co-digestate in the third exchanger (50) to form a flow of brine at a temperature T10.

9. Method according to one of claims 3 to 7 and claim 6, wherein the supercritical flow (FS), after the heat exchange step in the third exchanger (50), and before the high separation step pressure, is injected into a fourth heat exchanger so as to heat a first flow of water.

10. Method according to one of claims 3 to 9 and claim 8, wherein a flow of brine at the outlet of the third heat exchanger (50) is injected into a fifth heat exchanger so as to heat a second flow of water.

11. Method according to one of claims 1 to 10, wherein the co-digestate results from the methanization of organic materials.

12. Supercritical water gasification installation (1) which comprises:

- a supercritical water gasification reactor (10) provided with a heating circuit in which a hot air flow (FAC) is intended to circulate and provide the thermal energy necessary for the gasification in supercritical water of a co -digestate injected into said reactor, said hot air flow (FAC) leaving the reactor through an outlet pipe (21S);

- a boiler providing the hot air flow (FAC); The installation being characterized in that said device also comprises a first heat exchanger (30) within which the air flow intended to be heated by the boiler is preheated beforehand by heat exchange with the hot air flow (FAC ) flowing in the outlet pipe (21S).

13. Installation according to claim 12, wherein said installation further comprises a second heat exchanger (40) intended to preheat a fuel intended to ensure the operation of the boiler by heat exchange with the air flow leaving the first exchanger ( 30) of heat.

14. Installation according to claim 12 or 13, wherein said installation comprises a high pressure injection module intended to inject a high pressure co-digestate into the supercritical water gasification reactor (10).

15. Installation according to claim 14, wherein a third heat exchanger (50) is arranged between the high pressure injection module and the supercritical water gasification reactor (10), the third exchanger (50) being arranged to allow preheating of the co-digestate by heat exchange between the latter and the supercritical flow (FS) from the supercritical water gasification reactor (10).

16. Installation according to claim 15, wherein said installation further comprises a high pressure separation module (70) intended to collect the supercritical flow (FS) at the end of the heat exchange phase in the third exchanger (50). , and in separating the gaseous species from the aqueous phase.

17. Installation according to claim 16, wherein the installation comprises a fourth heat exchanger, arranged between the third exchanger (50) and the high pressure separation module (70), intended to heat a first flow of water by exchange. thermal with supercritical flux (FS).

18. Installation according to claim 16 or 17, wherein the installation comprises a low pressure separation module intended to collect the aqueous phase from the high pressure separation module (70) and separate residual gaseous species from said aqueous phase.

19. Installation according to one of claims 12 to 18 and claim 15, wherein the third exchanger (50) is also intended to separate extract the mineral matter included in the co-digestate and evacuate it via a pipe. discharge in the form of brine.

20. Installation according to claim 19, wherein said installation comprises a fifth heat exchanger intended to heat a second flow of water by heat exchange with the brine.