Device and method for treating the black liquor resulting from pulping by hydrothermal liquefaction

Abstract

The present invention relates to a paper pulp preparation device comprising a wood component cooking unit and a hydrothermal liquefaction unit. The invention also relates to the use of such a device in a method of treating the black liquor resulting from pulping and a method of preparing paper pulp from wood.

Claims

1. A paper pulp preparation device comprising: a unit for cooking wood components, in which the wood components are separated into two fractions: paper pulp, and black liquor; the unit for cooking the wood comprising a first inlet E.sub.1a for introducing wood, a second inlet E.sub.1b for charging white liquor, a first outlet S.sub.1a, for discharging the paper pulp, and a second outlet S.sub.1b for discharging the black liquor; a hydrothermal liquefaction unit allowing the treatment of at least a part of the black liquor, and comprising: an inlet E.sub.12 for the black liquor connected to second outlet S.sub.1b of the cooking unit; a first outlet S.sub.12a for an organic phase resulting from the hydrothermal liquefaction; a second outlet S.sub.12b for an aqueous phase resulting from the hydrothermal liquefaction and containing organic molecules; a connection line C.sub.1-12 between outlet S.sub.1b and inlet E.sub.12; a separation unit downstream of outlet S.sub.12b of the hydrothermal liquefaction unit, the separation unit allowing the separation of organic molecules contained in the aqueous phase resulting from the hydrothermal liquefaction, and comprising: an inlet E.sub.17 for the aqueous phase resulting from the hydrothermal liquefaction, connected to outlet S.sub.12b of the hydrothermal liquefaction unit; a first outlet S.sub.17a of organic molecules; a second outlet S.sub.17b of aqueous phase; a connection line C.sub.12-17 between outlet S.sub.12b and inlet E.sub.17; a causticizing unit comprising an inlet E.sub.9 for the aqueous phase originating from outlet S.sub.17b and an outlet S.sub.9 for the white liquor, outlet S.sub.9 being connected to second inlet E.sub.1b of the cooking unit; a connection line C.sub.17-9 between outlet S.sub.17b and inlet E.sub.9; a connection line C.sub.9-1 between outlet S.sub.9 and inlet E.sub.1b; an evaporation unit downstream of outlet S.sub.1b of the cooking unit, the evaporation unit allowing to concentrate the black liquor, and comprising an inlet E.sub.5 for the black liquor resulting from the cooking unit and an outlet S.sub.5 of the black liquor concentrated in the evaporation unit; wherein outlet S.sub.1b splits into two separate connection lines C.sub.1-12 and C.sub.1-5; connection line C.sub.1-5 being between outlet S.sub.1b and inlet E.sub.5; a boiler downstream of outlet S.sub.5 of the evaporation unit, the boiler allowing to burn the concentrated black liquor, and comprising an inlet E.sub.6 for the concentrated black liquor and an outlet S.sub.6 for residues of the combustion; a connection line C.sub.5-6 between outlet S.sub.5 and inlet E.sub.6; the causticizing unit downstream of outlet S.sub.6 of the boiler, comprising the inlet E.sub.9 for the aqueous phase originating from outlet S17b and a green liquor containing the residues of the combustion and an outlet S.sub.9 for a white liquor, outlet S.sub.9 being connected to second inlet E.sub.1b of the cooking unit; a connection line C.sub.6-9 between outlet S.sub.6 and inlet E.sub.9; a connection line C.sub.12-6 between outlet S.sub.12a and inlet E.sub.6.

2. The paper pulp preparation device of claim 1, wherein connection line C.sub.12-6 connects outlet S.sub.12a and inlet E.sub.6 via connection line C.sub.5-6.

3. The device of claim 1, wherein connection line C.sub.17-9 connects output S.sub.17b and input E.sub.9 via connection line C.sub.6-9.

4. The device of claim 1, wherein the hydrothermal liquefaction unit successively comprises a heat exchanger, a heating device, and an autoclave.

5. A method of preparing paper pulp from wood, comprising the steps of: cooking the wood; obtaining paper pulp and a black liquor; treating at least part of the black liquor by hydrothermal liquefaction; obtaining an aqueous phase containing organic molecules and an organic phase; treating the aqueous phase resulting from the hydrothermal liquefaction, by separation of the organic molecules, wherein the method is performed by the device of claim 1.

6. A method of preparing paper pulp from wood, comprising the steps of: cooking the wood; obtaining paper pulp and a black liquor; treating at least part of the black liquor by hydrothermal liquefaction; obtaining an aqueous phase containing organic molecules and an organic phase; treating the aqueous phase resulting from the hydrothermal liquefaction, by separation of the organic molecules, wherein the method is performed by the device of claim 2.

7. A method of preparing paper pulp from wood, comprising the steps of: cooking the wood; obtaining paper pulp and a black liquor; treating at least part of the black liquor by hydrothermal liquefaction; obtaining an aqueous phase containing organic molecules and an organic phase; treating the aqueous phase resulting from the hydrothermal liquefaction, by separation of the organic molecules, wherein the method is performed by the device of claim 3.

8. A method of preparing paper pulp from wood, comprising the steps of: cooking the wood; obtaining paper pulp and a black liquor; treating at least part of the black liquor by hydrothermal liquefaction; obtaining an aqueous phase containing organic molecules and an organic phase; treating the aqueous phase resulting from the hydrothermal liquefaction, by separation of the organic molecules, wherein the method is performed by the device of claim 4.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a conventional paper pulp preparation device.

(2) FIG. 2 illustrates a paper pulp preparation device according to a specific embodiment of the invention.

(3) FIG. 3 illustrates a paper pulp preparation device according to a specific embodiment of the invention.

DETAILED DESCRIPTION

(4) The description of the units and connections between units of the devices according to FIGS. 2 and 3 also applies to any embodiment of the invention.

(5) A conventional device (FIG. 1) enabling to prepare paper pulp generally comprises: a cooking unit (1) where the components of the wood or of the prehydrolized wood (2) are separated into two fractions: paper pulp (3), and black liquor (4); an evaporation unit (5) enabling to concentrate the black liquor (4); a boiler (6), particularly of Tomlinson type, where the concentrated black liquor is burnt, thus providing heat and steam to the pulping process; a unit (9) for causticizing the green liquor (8), the green liquor (8) corresponding to the residues (7) of the combustion taking place in the boiler (7), diluted in water (10). The causticizing unit (9) is connected to the combustion unit (1) to inject white liquor (11) formed by the passing of the green liquor (8) in the causticizing unit (9).

(6) Generally, the boiler (6) advantageously is a boiler recovering the thermal energy originating from the combustion of the black liquor, called Tomlinson boiler. As already indicated, it generates steam and heat.

(7) The combustion of the black liquor (4) in the boiler (6) generates combustion residues (7). In an alkaline method, these are molten salts originating from the cooking of the white liquor in the unit (1), particularly alkaline salts of sodium carbonate type. The solubilizing of the residues (7) in water (10) enables to form the green liquor (8).

(8) In the causticizing unit (9), the green liquor (8) is treated to regenerate the cooking reactants in the unit (1). The regenerated reactants may be reinjected into the cooking unit (1), particularly in dissolved form, in the form of the white liquor (11). In an alkaline method, approximately 97% of the sodium initially used in the cooking unit (1) is generally regenerated.

(9) In addition to units (1), (5), (6) and (9), the paper pulp preparation device according to the invention comprises a hydrothermal liquefaction unit (12) and a separation unit (17) (FIGS. 2 and 3).

(10) The paper pulp preparation device according to the invention comprises: a unit (1) for cooking the wood components (2), comprising a first inlet E.sub.1a, a second inlet E.sub.1b, a first outlet S.sub.1a, and a second outlet S.sub.1b; an evaporation unit (5) downstream of outlet S.sub.1b of the cooking unit (1), comprising an inlet E.sub.5 and an outlet S.sub.5; a connection line C.sub.1-5 between outlet S.sub.1b and inlet E.sub.5; a boiler (6) downstream of outlet S.sub.5 of the evaporation unit (5), comprising an inlet E.sub.6 and an outlet S.sub.6; a connection line C.sub.5-6 between outlet S.sub.5 and inlet E.sub.6; a causticizing unit (9) downstream of outlet S.sub.6 of the boiler (6), comprising an inlet E.sub.9 and an outlet S.sub.9, outlet S.sub.9 being connected to second inlet E.sub.1b of the cooking unit (1); a connection line C.sub.6-9 between outlet S.sub.6 and inlet E.sub.9; a connection line C.sub.9-1 between outlet S.sub.9 and inlet E.sub.1b; a hydrothermal liquefaction unit (12) comprising: an inlet E.sub.12 connected to second outlet S.sub.1b of the cooking unit (1); a first outlet S.sub.12a connected to inlet E.sub.6 of the boiler (6); a second outlet S.sub.12b; a connection line C.sub.11-2 between outlet S.sub.1b and inlet E.sub.12; a connection line C.sub.12-6 between outlet S.sub.12a and inlet E.sub.6; a separation unit (17) downstream of outlet S.sub.12b of the hydrothermal liquefaction unit (12), comprising: an inlet E.sub.17 connected to outlet S.sub.12b of the hydrothermal liquefaction unit (12); a first outlet S.sub.17a; a second outlet S.sub.17b connected to inlet E.sub.9 of the causticizing unit (9); a connection line C.sub.12-17 between outlet S.sub.12b and inlet E.sub.17; a connection line C.sub.17-9 between outlet S.sub.17b and inlet E.sub.9.

(11) In this device, inlet E.sub.1a corresponds to the inlet through which the wood is introduced into the cooking unit (1). Inlet E.sub.1a corresponds to the inlet through which the white liquor, recycled or not, is introduced into the cooking unit (1). In an alkaline wood treatment method, the white liquor generally comprises water, soda, and possible a sulfur source, for example, sodium sulfur. As already indicated, such an alkaline wood cooking treatment is generally performed at a temperature in the range from 150 to 180 C., and at a pressure in the range from 7 to 9 bars. According to a preferred embodiment of the invention, the alkaline treatment is carried out in the absence of sulfur.

(12) The paper pulp (3) and the black liquor (4) are respectively discharged from the cooking unit (1) via outlet S.sub.1a and outlet S.sub.1b.

(13) For more clarity, FIG. 2 illustrates connections C.sub.i-j between the different units of the device according to the invention while FIG. 3 illustrates inlets E.sub.n and outlets S.sub.m of the different units of the device according to the invention.

(14) In FIGS. 2 and 3, connection line C.sub.1-12 connects outlet S.sub.1b and inlet E.sub.12 via a branching of connection line C.sub.1-5. Further, connection line C.sub.12-6 connects outlet S.sub.12a and inlet E.sub.6 via connection line C.sub.5-6, and connection line C.sub.17-9 connects outlet S.sub.17b and inlet E.sub.9 via connection line C.sub.6-9.

(15) In FIGS. 2 and 3, the hydrothermal liquefaction unit (12) is in a bypass position, downstream of cooking unit (1) and upstream of the evaporation unit (5). It enables to treat at least part of the black liquor (4), n % by weight, while the other part of the black liquor (4), (100-n)% by weight, is concentrated in the unit (5).

(16) In the hydrothermal liquefaction unit (12), n % by weight of the black liquor (4) are treated. This treatment provides: a fraction (13) corresponding to an organic phase (generally viscous), which is advantageously reinjected upstream of the boiler (6), but downstream of the evaporation unit (5), a fraction (14) corresponding to an aqueous phase containing organic molecules (15).

(17) The organic molecules (15) are then separated from the aqueous phase (14) in the separator (17). Conventional separation techniques may be used, particularly filtering and/or decantation.

(18) The aqueous phase (16) resulting from this separation is advantageously reinjected into the device, for example, upstream of the causticizing unit (9) (FIGS. 2 and 3). The aqueous phase (16) may be directly reinjected into the causticizing unit (9) or into the green liquor (8) or mixed with the residues (7) before the water (10) is introduced.

(19) Generally, the hydrothermal liquefaction unit (12) may successively comprise a heat exchanger, a heating device, and an autoclave.

(20) The heat exchanger enables to preheat the black liquor up to a temperature from 150 to 250 C. The heat exchanger ensures the heat transfer between the incoming fluid (black liquor (4)) and the fluid coming out of the autoclave (aqueous phase (14) and/or organic phase (13)). Thus, the incoming black liquor (4) is heated due to the fluid coming out (14 and/or 13), which is cooled.

(21) The hydrothermal liquefaction unit heating device enables to heat the preheated black liquor to the operating temperature of the autoclave, generally between 200 and 370 C. The heating is generally electric or by combustion.

(22) Due to the heat exchanger, which thus has a double preheating/cooling function, the temperature of the fluid (14 and/or 13) coming out of the autoclave may pass from more than 300 C. to less than 100 C., advantageously between 50 and 80 C. The temperature is selected to keep a sufficient fluidity at the outlet of the autoclave and after the passing through the heat exchanger.

(23) According to an embodiment, only the aqueous phase (14) passes through the heat exchanger. This is especially true when the organic phase (14) is directed towards the boiler (6).

(24) Once treated by hydrothermal liquefaction in the reactor, the black liquor (4) comprises an aqueous phase (14) and an organic phase (13) which is generally viscous.

(25) The aqueous phase (14) is then treated in the separator (17) to isolate the organic molecules (15) that it contains. Such a separation may in particular be performed by decantation.

(26) As already indicated, the aqueous phase (16) resulting from this separation is reinjected, directly or indirectly, into the causticizing unit (9).

Embodiments of the Invention

(27) The following examples relate to the treatment according to the invention of different black liquors. These examples comprise: a) the carbon balance of the hydrothermal liquefaction, b) the sodium balance of the hydrothermal liquefaction, c) the composition of the aqueous phase resulting from the hydrothermal liquefaction, and d) the energy balance of the hydrothermal liquefaction.
a) Carbon Balance of the Hydrothermal Liquefaction,

(28) The black liquor resulting from the cooking of a mixture of prehydrolyzed broadleaf tree wood has been treated by hydrothermal liquefaction according to the invention.

(29) Before this treatment, the black liquor has the following characteristics: solids: 18% by weight, density: 1.09, carbon concentration: 71.8 g.sub.C/L, sodium concentration: 26.5 g.sub.Na/L.

(30) The hydrothermal liquefaction of the black liquor has been performed at 280 C. at a 7 MPa pressure for a 1-hour stage (batch reactor).

(31) 97.7% of the introduced carbon has been recovered, 59.7% being in the aqueous phase and 38% in the organic phase.

(32) b) Sodium Balance of the Hydrothermal Liquefaction

(33) The sodium balance corresponds to the average of the sodium balances of 14 assays carried out at temperatures in the range from 250 to 310 C., for a time period in the range from 5 to 120 minutes, and at different concentrations (initial concentration, dilutions 2 and 4).

(34) Generally, 97.3% of the sodium has been recovered in the aqueous phase originating from the hydrothermal liquefaction.

(35) Accordingly, the sodium balance is not impacted by the integration of the hydrothermal liquefaction step.

(36) c) Composition of the Aqueous Phase Resulting from the Hydrothermal Liquefaction

(37) The organic molecules generated during the hydrothermal liquefaction and present in the aqueous phase have been identified by GCMS analysis (gas phase chromatography coupled to mass spectrometry) and quantified by HPLC (high-pressure liquid chromatography) (table 1).

(38) The molecules with the highest concentration are: phenol, catechol, guaiacol, and syringol.

(39) TABLE-US-00001 TABLE 1 influence of the nature of the black liquor and of the operating conditions on the nature and the quantity of organic molecules contained in the aqueoous phase. phenol catechol guaiacol syringol yield yield yield yield Total Black liquor.sup.(a) Conditions (wt. % of the weight of the introduced black liquor) prehydrolyzed 250 C./5 MPa 0.0% 0.2% 1.2% 1.4% 2.8% broadleaf tree wood 1 hour prehydrolyzed 250 C./5 MPa 0.0% 0.1% 2.0% 0.0% 2.0% resinous tree wood 1 hour non-prehydrolyzed 250 C./5 MPa 0.3% 0.2% 0.8% 1.1% 2.3% broadleaf tree wood 1 hour prehydrolyzed 280 C./7 MPa 0.1% 1.0% 0.7% 0.04% 1.8% broadleaf tree wood 1 hour prehydrolyzed 280 C./7 MPa 0.1% 0.7% 1.0% 0.00% 1.7% resinous tree wood 1 hour non-prehydrolyzed 280 C./7 MPa 0.4% 0.8% 0.4% 0.03% 1.6% broadleaf tree wood 1 hour prehydrolyzed 310 C./10 MPa 0.1% 0.6% 0.2% 0.00% 0.9% broadleaf tree wood 1 hour prehydrolyzed 310 C./10 MPa 0.2% 0.4% 0.2% 0.00% 0.7% resinous tree wood 1 hour non-prehydrolyzed 310 C./10 MPa 0.6% 0.5% 0.0% 0.00% 1.1% broadleaf tree wood 1 hour .sup.(a)black liquors resulting from a process of soda cooking (sulfur-free), preceded or not by a prehydrolysis, from a mixture of broadleaf tree wood or of resinous tree wood

(40) Table 1 shows that the operating conditions and the nature of the black liquor may have a significant influence on the nature and on the quantity of the molecules contained in the aqueous phase. For example, temperature seems to favor the demethoxylation of guaiacol and of syringol. Accordingly, the yield of such compounds can be improved in mild conditions (250 C. vs. 310 C., for example).

(41) d) Energy Balance of the Hydrothermal Liquefaction,

(42) The energy balance has been obtained in the case of a broadleaf wood soda black liquor prehydrolized at 280 C., 7 MPa, and for a 1-hour stage.

(43) Such an energy balance corresponds to the treatment of 1 kg of black liquor: approximately 1,000 kJ are necessary to heat 1 kg of black liquor from 20 C. to 280 C. (considering that the specific heat of the black liquor is equal to that of water); the organic (biocrude) phase originating from the hydrothermal liquefaction of the black liquor contains 40% of humidity and may be directly submitted to a combustion, enabling to recover 1,950 kJ; the evaporation of the residual water of the organic phase requires 60 kJ.

(44) Thus, the combustion of the organic phase resulting from the hydrothermal liquefaction enables to recover a larger amount of energy than that spent during the hydrothermal liquefaction.