Method for the hydrothermal carbonisation of a biomass and associated device

Abstract

Disclosed is a method for heating a biomass moving along an industrial treatment line including an inlet (91) for the incoming biomass, a pressure pump (93), a heating unit (94) and a treatment station (95). According to an embodiment, steam is injected into the line between the pressure pump (93) and the heating unit (94) such as to pre-heat the biomass by condensing the steam.

Claims

1. A method for heating biomass moving along an industrial treatment line comprising an inlet for incoming biomass, a pressure pump, a heater and a carbonization reactor, said method comprising injecting steam into the line between the pressure pump and the heater and upstream of the heater.

2. The method as claimed in claim 1, wherein the biomass is sewage sludge and said industrial treatment is hydrothermal carbonization.

3. The method as claimed in claim 1, wherein the steam injection and the heater are controlled such that the biomass reaches a preset temperature before reaching the carbonization reactor, the preset temperature being between 165 C. and 205 C.

4. The method as claimed in claim 1, wherein the steam injection is controlled to bring the temperature of the biomass to a value exceeding 70 C. at the inlet of the heater.

5. The method as claimed in claim 1, wherein the steam is injected obliquely or perpendicular to the direction of movement of the biomass on the line, or against the direction of movement of the biomass on the line.

6. The method as claimed in claim 1, wherein the pressure pump increases the pressure of the biomass to a value at which the biomass can be heated to a temperature exceeding 100 C. without boiling.

7. The method as claimed in claim 6, wherein the pressure at the outlet of the pressure pump is greater than 3 MPa.

8. The method as claimed in claim 1, wherein the line also includes a cooling station downstream of the carbonization reactor, and wherein a transfer fluid is heated when moving between the cooling station and the heater.

9. The method as claimed in claim 8, wherein the transfer fluid is heated to a temperature exceeding the temperature of the biomass, said biomass being at the carbonization reactor.

10. The method as claimed in claim 8, wherein a single external heat source is used to heat the transfer fluid and a heat-transfer fluid is used to increase and/or maintain the temperature of the biomass at the carbonization reactor.

11. The method as claimed in claim 1, wherein heat is recovered from the biomass downstream of the carbonization reactor and wherein this recovered heat is transferred to the biomass upstream of the carbonization reactor.

12. The method as claimed in claim 1, wherein heat is recovered from the biomass downstream of the carbonization reactor and wherein this recovered heat is transferred to the biomass upstream of the carbonization reactor using a heat exchanger between the biomass leaving the carbonization reactor and the biomass moving on the line upstream of the carbonization reactor.

13. The method as claimed in claim 1, wherein includes a step in which an additive is injected into the biomass upstream of the heater.

14. The method as claimed in claim 13, wherein the additive is injected into the biomass such that the additive is exposed to the injected steam.

15. The method as claimed in claim 1, wherein a portion of the biomass is removed from the carbonization reactor using a recirculation branch and said portion is returned to the carbonization reactor in order to generate a movement of the biomass in the carbonization reactor.

16. The method as claimed in claim 15, wherein the portion of biomass is removed at a flow rate of between 5 and 15 times the flow rate at which the biomass enters the carbonization reactor.

17. The method as claimed in claim 1, wherein the injected steam and the biomass are mixed on the line between the pressure pump and the heater using a mixer.

Description

DESCRIPTION OF FIGURES AND EMBODIMENTS

(1) Other advantages and details of the invention are set out in the detailed description of non-limiting embodiments and implementations, and the following attached drawings:

(2) FIG. 1 is a schematic view of a hydrothermal carbonization device according to the invention including a cooling station,

(3) FIG. 2 is a schematic view of a hydrothermal carbonization device according to the invention including direct heat exchange means,

(4) FIGS. 3 and 4 are schematic views of mixers according to the invention.

(5) Since the embodiments described below are in no way limiting, variants of the invention including only a selection of the features described are possible, said features being independent of the other features described, even if said other features are described in the same sentence, if said selection is sufficient to afford a technical advantage or to differentiate the invention from the prior art. Said selection includes at least one feature, preferably a functional feature with no structural details or with only some structural details if same are sufficient to afford a technical advantage or to differentiate the invention from the prior art.

(6) FIG. 1 illustrates a preferred embodiment of the invention.

(7) According to this embodiment, the device according to the invention includes an industrial treatment line through which the biomass is circulated.

(8) The incoming biomass, for example dried sewage sludge, enters via an inlet 91 on the line where same enters piping linking the inlet 91 to a mixer 98, said piping having a pressure pump 93 between the inlet 91 and the mixer 98.

(9) The pressure pump 93 increases the pressure of the biomass to a value at which the biomass can be heated to a temperature exceeding 100 C. without boiling. In other words, the pressure pump 93 raises the pressure of the biomass above the saturation pressure, which is typically greater than 1.2 MPa.

(10) The pressure pump 93 circulates the biomass on the line.

(11) More specifically, the pressure pump 93 is able to raise the pressure of the biomass exiting the pump 93 to a value exceeding 3 MPa (piston pump, diaphragm pump or other).

(12) Under the effect of the pressure pump 93, the biomass is routed from the pressure pump 93 to the mixer 98.

(13) The mixer 98 is designed to mix the steam produced by steam generation means 981 with the biomass. The mixer 98 may be a static mixer (means requiring the biomass and the steam to be channeled together for a sufficient time to encourage the steam and the biomass to mix together), or a mixer designed to receive the steam perpendicular to the direction of movement of the biomass in the piping linking the pressure pump 93 and the heating means 94, or have a jet pipe layout.

(14) The steam flow rate is preferably set, for example using control means 9C, to raise the temperature of the biomass (which may have been mixed with an additive) to an optimum operating point both in relation to the size of the different elements of the device, for example the heating means 94, and in terms of the total energy consumption of the device. The steam flow rate is preferably set by adjusting the flow rate of the steam injected.

(15) For example, the steam is injected at a pressure greater than the pressure of the biomass on the line upstream of the pressure pump 93, and consequently at a temperature greater than the temperature of the biomass. However, the steam generation means 981 are controlled to raise the temperature of the biomass such as to optimize the energy recovery implemented in the device.

(16) Typically, the steam injection flow rate may be up to 20% of the flow rate of the biomass moving on the line.

(17) Preferably, an additive is injected into the biomass using any suitable injection means 97, preferably upstream of the heating means 94, in order to further reduce the viscosity of the biomass.

(18) The additive is preferably injected such as to expose same to the action of the steam, thereby encouraging same to mix with the biomass.

(19) Piping also links the mixer 98 to heating means 94.

(20) The heating means 94 are preferably a heat exchanger.

(21) These heating means 94 are used to heat the biomass by thermal exchange between a transfer fluid flowing in the transfer circuit 9T and the biomass passing through the heating means 94. To do so, the transfer fluid, for example oil, is itself heated using a heat source 9T3 by means of a heat exchanger 9T2, this heat source being for example a boiler burner.

(22) Piping also links the heating means 94 to a treatment station 95 towards which the biomass is routed.

(23) The treatment station 95 is preferably a reactor including a chamber designed to receive the biomass and to keep said biomass at a pressure typically between 2 and 3 MPa.

(24) In a preferred embodiment, the sole function of the treatment station 95 is to guarantee a residence time that enables the biomass to undergo chemical reactions, typically hydrolysis. For this reason, the treatment station 95 may alternatively include a reactor, with or without chicanes, with or without pipes, or for example in a pipe long enough to guarantee the required residence time.

(25) Preferably, the biomass coming from the heating means 94 enters the chamber of the treatment station 95 via a lower portion 953, i.e. via a portion of the treatment station 95 at a height that is substantially the lowest in the treatment station 95 within the premises housing the device.

(26) According to the embodiment in FIG. 1, piping also links the treatment station 95 to a cooling station 96.

(27) After a residence time, the (hydrolyzed) biomass exits the chamber of the treatment station 95 via an upper portion 954, from where same is routed towards the cooling station 96. Upper portion 954 means a portion of the treatment station 95 at a height that is substantially the highest in the treatment station 95 within the premises housing the device, opposed to the lower portion 953.

(28) Alternatively, the biomass may also enter the treatment station 95 via an upper portion and exit via a lower portion.

(29) According to another embodiment, the biomass may also enter the treatment station 95 via a lower portion and be routed from this lower portion as far as an upper portion of the chamber via a pipe, the biomass being able to exit the chamber of the treatment station 95 via a lower portion.

(30) The cooling station 96 is preferably a heat exchanger.

(31) The cooling station 96 is used to cool the biomass exiting the treatment station 95 by thermal exchange between the transfer fluid flowing in the transfer circuit 9T and the biomass passing through said cooling station 96.

(32) Thus, the transfer circuit 9T links the heating means 94 to the cooling station 96. It also includes, along with the heating means 94 and the cooling station 96, heat exchange means between the biomass leaving the treatment station 95 and the biomass moving on the line upstream of the treatment station 95.

(33) As shown in FIG. 1, the transfer fluid is circulated in the transfer circuit 9T using circulation means 9T1, typically a pump.

(34) An external heat source 9T3, for example a boiler burner, heats the transfer fluid at the heat exchanger 9T2. The biomass flowing in the heating means is heated by the transfer fluid thus heated, drawing some of the heat from same.

(35) The transfer fluid also recovers some of the heat from the biomass flowing through the cooling station 96.

(36) The transfer fluid is for example heated to a temperature exceeding 220 C.

(37) Alternatively, according to an embodiment shown in FIG. 2, some of the heat of the biomass flowing on the line downstream of the treatment station 25 is transferred to the biomass flowing through a thermal regenerator 94a installed upstream of the heating device 94b. In this case, the heat exchange means exchange heat directly between the biomass leaving the treatment station 95 and the biomass moving on the line upstream of the treatment station 95, using the thermal regenerator 94a.

(38) In a preferred embodiment, the chamber of the treatment station 95 is surrounded by an envelope 952 in which a heat-transfer fluid is circulated.

(39) This heat-transfer fluid is heated and kept at a temperature designed to keep the biomass contained within the chamber at the temperature of same before entering the treatment station 95, i.e. when the biomass is between the heating means 94 and the treatment station 95, and to compensate for any thermal losses related to the structure of the treatment station 95.

(40) The heat-transfer fluid is preferably heated using the same external heat source 9T3 as the source used to heat the transfer fluid at the heat exchanger 9T2. The transfer fluid and the heat-transfer fluid may therefore be the same fluid, for example oil, flowing in a circuit designed to heat the transfer fluid (flowing in the circuit 9T) and the heat-transfer fluid (flowing in the envelope 952) at the desired temperatures. The differential control of the temperatures of the transfer fluid and the heat-transfer fluid is provided by any appropriate means, for example valves (not shown) mounted on said circuit and control of the opening and closing of said valves as well as of the heat source 9T3.

(41) In order to increase the temperature of the biomass on the line at the heating means 94, the device is controlled, for example using the control means 9C, so that the heat source 9T3 increases the temperature of the transfer fluid to a temperature above the temperature of the biomass contained in the treatment station 95, for example to a temperature close to 210 C.

(42) Thus, a single external heat source 9T3 is used to heat the transfer fluid and the heat-transfer fluid intended to increase and/or maintain the temperature of the biomass at the treatment station 95. In other words, the same external heat source 9T3 is used to heat: firstly the transfer fluid, thereby enabling the biomass to be heated before the biomass reaches the treatment station, and secondly the heat-transfer fluid, thereby enabling the temperature of the biomass to be maintained in the treatment station, preferably at at least 180 C.

(43) To limit the depositing of biomass on the walls of the chamber of the treatment station 95 when using a mechanically passive treatment station 95 (i.e. with no scraper or mixer), the treatment station 95 preferably includes a recirculation branch 9M designed to circulate the biomass inside the chamber. To do so, the biomass is preferably suctioned from the upper portion 954 (where the biomass is more liquid) and reinjected into the chamber via a lower portion 953. Preferably, the flow rate of this recirculation is set such that the biomass circulating in the recirculation branch 9M is removed at a flow rate of between 5 and 15 times the flow rate of the biomass entering the treatment station 95 from the heating means 94. Such recirculation ensures good temperature uniformity in the biomass contained in the treatment station 95.

(44) This biomass is preferably circulated in the recirculation branch 9M using a diaphragm pump 9M1, that is preferably sealed and offset from the treatment station 95. Such a pump 9M1 and thus installed increases the reliability of the device, since this pump 9M1 can for example be repaired and maintained without having to take the entire device out of service.

(45) The different solutions proposed by the present invention help to reduce the viscosity of the biomass and consequently facilitate increasing the temperature of same using smaller means.

(46) The surface of the heat exchangers (heating means 94, 94b and/or cooling station 96), the diameters of the piping and the volume of the treatment station 95 can thus be reduced.

(47) An example mixer 98 according to the invention is shown in FIG. 3. The biomass enters the mixer 98 via a feed channel 21 that is for example linked to the pressure pump 93 shown in FIG. 1. When the biomass reaches the internal volume of the mixer 98, the biomass is exposed to the steam injected by the steam generation means 981 via a nozzle 23. In this example, the steam is injected perpendicular to the feed channel 21. Acid is also injected as an additive into the biomass inside the internal volume of the mixer 98 using the injection means 97, which include an injection head 24. The biomass, steam and acid are thus mixed dynamically in the mixer 98, for example and notably under the effect of the pressure difference between the steam injection and the biomass, which is preferably greater than 0.2 MPa. By way of example, the biomass enters the mixer at a speed of less than 1 m/s and the steam is injected into the mixer 98 at a speed exceeding 130 m/s, preferably between 200 and 250 m/s. The mixture is directed towards the output channel 22, for example towards the heating means 94 shown in FIG. 1. Optionally, the mixer 98 may include a static mixer, for example comprising chicanes 25. In the example in FIG. 3, the steam is injected obliquely or perpendicular to the direction of movement of the biomass in the internal volume of the mixer 98. The steam injection flow rate is 20% or less, and typically between 10% and 20%, of the flow rate of the biomass moving on the line.

(48) Another example mixer 98 according to the invention is shown in FIG. 4. In this example, the mixer 98 includes a wear part 26 designed to limit or prevent erosion of the portion of the mixer 98, in this example a pipe, exposed to the flow of steam generated by the steam injection. This wear part 26 faces the nozzle 23 and is preferably removable. In the example in FIG. 4, the steam is injected perpendicular to the direction of movement of the biomass in the internal volume of the mixer 98, with the biomass moving in the direction 10.

(49) The invention is naturally not limited to the examples described above and numerous adjustments may be made to these examples without thereby moving outside the scope of the invention. Furthermore, different features, forms, variants and embodiments of the invention may be associated with one another in different combinations where same are not incompatible or mutually exclusive.

(50) In the variant shown in FIGS. 3 and 4, the steam is injected in the direction opposite to the direction of movement of the biomass in the internal volume of the mixer 98.