Method and system for separation of particulate material and volatile organic compounds from blow steam involving partial condensation

Abstract

Method for separation of particulate material and at least one volatile organic compound from blow steam obtained from a hydrothermal treatment reactor for hydrolysis and / or steam explosion of lignocellulosic material, the method comprising: feeding (3) the blow steam to a condenser, partially condensing (4) the blow steam using said condenser, collecting (5) the condensate from the partial condensing, withdrawing (6) at least a portion of the collected condensate, said condensate comprising said particulate material, withdrawing (7) a non-condensed fraction of the blow steam from the condenser, and separating (9) at least one volatile organic compound from the non-condensed fraction of the blow steam A corresponding system is also provided.

Description

[0001] METHOD AND SYSTEM FOR SEPARATION OF PARTICULATE MATERIAL AND VOLATILE ORGANIC COMPOUNDS FROM BLOW STEAM

[0002] FIELD OF INVENTION

[0003] The present invention relates to a method and a system for separation of chemicals from secondary steam (blow steam) obtained from hydrolysis and / or steam explosion processes of lignocellulosic materials. More particularly, the invention relates to a method and a system for separation of volatile organic chemicals which comprises separation of particulate material from the blow steam.

[0004] BACKGROUND

[0005] It is known art to process a lignocellulosic material such as wood chips, saw-dust, bark, bagasse, empty fruit bunches and like with steam at elevated temperature in a pressurised vessel for softening of lignin and release of hemicellulose sugar by (pre) hydrolysis reactions. Such processes may be referred to as hydrothermal treatment of the lignocellulosic material. A catalyst, for example sulfuric acid may be added to the hydrolysis process to increase the reaction rate. Such heating under pressure is followed by a rapid discharge of the heated biomass through a valve or an orifice to low (often atmospheric) pressure, so-called steam explosion. The hot and soft hydrolysed biomass will defibrate to small fragments during the rapid and violent discharge providing an excellent raw material for many products, fuel pellets, fibreboard or other mouldable products or alike. The defibrated biomass may also be treated by enzymes for hydrolysis of cellulose. The solubilised carbohydrates may be fermented to ethanol or used as raw material for production of single cell proteins or glycols. Thermal treatment of a biomass in a pressurised vessel followed by rapid discharge to low pressure is in the following referred to as a "steam explosion process”. A typical steam explosion process is described for example in SE 545305 C2.

[0006] The pressure and temperature in the treatment vessel are typically in the range 10-20 bar(a) and 180-210 °C. Therefore, a large amount of steam is released from the biomass at discharging, when the pressure drops to atmospheric and the temperature about to 100 °C. Such steam is here denominated blow steam or secondary steam. Blow steam carries the hydrolysed product to a separation device where it is separated from the blow steam. The separation device is typically one or more cyclones or sometimes a centrifuge. The treatment vessel may also be furnished with one or more vents for inert gases which can be combined with blow steam from the vessel discharge. Blow steam from the separation device is not clean (water) steam. It is a mixture of steam and many biomass-derived condensable compounds. Such condensable compounds are for example furfural, methanol, acetic acid and formic acid. Furfural is a versatile biomolecule with many uses and the amount of it in said blow steam is high making recovery of it interesting. Furfural (and other condensable organic compounds) is normally recovered from blow steam by stripping and rectification. Blow steam is unfortunately contaminated with solid particles such as wood fragments, fibres and lignin particles. These particles are carried with blow steam, or with condensate formed from the blow steam to the stripping and rectification plant. It is a common problem that solid particles clogs trays or packings in strippers, rectifiers and heat exchangers of a fractionation system for furfural or other condensable organic compounds. This means that the fractionation system must be shut down for cleaning, consequently interrupting the recovery of chemicals.

[0007] SUMMARY

[0008] An object of the invention is to reduce the solid particle content of the blow steam / blow steam condensate to reduce the above-described problem of clogging the fractionation system.

[0009] These and other objects are achieved by the present invention by means of methods and systems according to the independent claims.

[0010] According to a first aspect of the invention, there is provided a method for separation of at least one volatile organic compound (and particulate material) from blow steam obtained from at least one hydrothermal treatment reactor configured for hydrolysis and / or steam explosion of lignocellulosic material. The method comprises feeding the blow steam to a condenser, partially condensing the blow steam using the condenser, collecting the condensate from the partial condensing, withdrawing at least a portion of the collected condensate, the condensate comprising particulate material, withdrawing a non-condensed fraction of the blow steam from the condenser, and separating at least one volatile organic compound from the non-condensed fraction of the blow steam.

[0011] In other words, the method comprises partially condensing the blow steam to provide a noncondensed fraction of the blow steam and a condensate comprising particulate material such that the particulate material can be withdrawn as part of the condensate. The non-condensed fraction, which may be described as having a reduced particulate matter content or being substantially particulate free, is withdrawn and is subjected to a separation process for separating at least one volatile organic compound (such as furfural) from the non-condensed fraction of the blow steam. Such separation processes for separating volatile organic compounds are well-known in the art and will not be described in further detail here.

[0012] The partially condensing may comprise condensing up to 50 %, preferably up to 30 % but most preferably up to 20 % of the blow steam entering the condenser. In other words, 50% or less, or 30% or less, or 20% or less of the blow steam may be condensed. The at least one volatile compound may comprise furfural, methanol, diacetyl, 2-3 pentanedione or mixtures thereof.

[0013] The invention is based on the insight that a partial condensation of the blow steam is sufficient to collect a significant portion of the particulate material in the condensate. For example, with a 20% condensation of the blow steam, more than 99% of the particulate material content of the blow steam can be separated as part of the condensate. The invention is furthermore based on the insight that the condensation curve of volatile organic compounds such as furfural is such that it enriches in the vapour phase at partial condensation. For example, only about 2 % of furfural and methanol is condensed at 20 % condensation of the blow steam which means that about 98 % of furfural and methanol can be withdrawn with uncondensed and substantially particulate free blow-steam from the partial condenser. Consequently, an efficient separation of particulate material can be achieved by means of partial condensation of the blow steam.

[0014] In embodiments, the condenser comprises substantially vertically arranged heat exchanger elements (such as tubes or lamellas), wherein the blow steam is fed to an upper portion of the condenser such that condensing blow steam flows downwards through the heat exchanger elements. The method may further comprise recirculating a portion of the collected condensate to the upper part of the condenser and spraying it onto / into said heat exchanger elements. This is advantageous since the condensate sprayed onto / into the heat exchanging elements cleans the heat exchanger elements and prevents, or at least reduces the risk of, clogging of the heat exchanger elements. Furthermore, collection of particulate material in the condensate is improved.

[0015] In other embodiments, the condenser comprises substantially vertically arranged heat exchanger elements, wherein the blow steam is fed to a lower portion of the condenser such that the blow steam flows upwards through the heat exchanger elements. Due to gravity, the condensate formed by the blow steam will flow downwards through the heat exchanger elements, i.e. in the opposite direction to the blow steam. The downwardly flowing condensate cleans the heat exchanger elements and prevents, or at least reduces the risk of, clogging of the heat exchanger elements. In embodiments, the method further comprises subjecting the non-condensed fraction of the blow steam to a further condensation step to obtain a substantially particulate free condensate, wherein said separating comprises separating said at least one volatile organic compound from said substantially particulate free condensate. In other embodiments, the non-condensed fraction of the blow steam is withdrawn directly in gas-phase to a stripping column for separation of said at least one volatile organic compound.

[0016] According to a second aspect of the invention, there is provided a method for treating lignocellulosic material. The method comprises subjecting the lignocellulosic material to hydrothermal treatment in at least one hydrothermal treatment reactor at elevated pressure and temperature by means of adding steam thereto, steam explosion discharge of treated lignocellulosic material and blow steam from the at least one treatment reactor, and separating particulate material from the blow steam using the method according to the first aspect of the invention or embodiments thereof.

[0017] It is understood that elevated pressure and temperature in the hydrothermal treatment reactor refers to that the pressure and temperature in the hydrothermal treatment reactor is above ambient pressure and temperature. The pressure and temperature in the hydrothermal treatment reactor may be within the ranges 10-20 bar(a) and 180-210 °C.

[0018] According to a third aspect of the invention, there is provided a method for separation of particulate material from blow steam obtained from at least one hydrothermal treatment reactor for hydrolysis and / or steam explosion of lignocellulosic material. The method comprises feeding the blow steam to a condenser, partially condensing the blow steam using the condenser, collecting the condensate from the partial condensing, and withdrawing at least a portion of the collected condensate, the condensate comprising particulate material.

[0019] According to a fourth aspect of the invention, there is provided a system for separation of at least one volatile organic compound (and particulate material) from blow steam obtained from a hydrothermal treatment reactor for hydrolysis and / or steam explosion of lignocellulosic material. The system comprises a condenser comprising a steam inlet and a discharge connection for withdrawing a non-condensed fraction of the steam from the condenser, a condensate collection reservoir at a bottom part of the condenser, a cooling liquid control valve connected to the condenser to control a flow of cooling liquid thereto, a control system configured to adjust the aperture of the control valve such that the condenser partially condenses the blow steam, and a separation system connected to the discharge connection of the condenser, the separation system being configured to separate said at least one volatile organic compound from the non-condensed fraction of the steam. The system may furthermore comprise a source of cooling liquid such as cooling water to which the cooling liquid control valve is connected.

[0020] In embodiments, the condenser comprises substantially vertically arranged heat exchanging elements (such as tubes or lamellas), wherein at least one of the blow steam inlet(s) is / are arranged to feed blow steam to an upper part of the condenser, the system further comprising at least one spray nozzle installed in the condenser above said heat exchanging elements and a pump for recirculating condensate from the condensate collection reservoir to the at least one spray nozzle. This is advantageous since the condensate sprayed onto / into the heat exchanging elements cleans the heat exchanger elements and prevents, or at least reduced the risk of, clogging of the heat exchanger elements. Furthermore, collection of particulate material in the condensate is improved.

[0021] In embodiments, the condenser comprises substantially vertically arranged heat exchanging elements, wherein at least one of the blow steam inlet(s) is / are arranged to feed steam to a lower portion of the condenser below the heat exchanging elements. Due to gravity, the condensate formed by the blow steam will flow downwards through the heat exchanger elements, i.e. in the opposite direction to the blow steam. The downwardly flowing condensate cleans the heat exchanger elements and prevents, or at least reduced the risk of, clogging of the heat exchanger elements.

[0022] In embodiments, the control system is configured to adjust the aperture of said control valve to condense up to 50 %, preferably up to 30 % but most preferably up to 20 % of the blow steam entering the condenser.

[0023] According to a fifth aspect of the invention, there is provided a system for treating lignocellulosic biomass material, the system comprising a hydrothermal treatment reactor provided with feeding means for providing lignocellulosic biomass material to the reactor and at least one steam injector for providing steam to the reactor to subject the lignocellulosic material to hydrothermal treatment at elevated pressure and temperature, a steam explosion discharge device configured to discharge treated lignocellulosic material and blow steam from the treatment reactor, a separation device (comprising for example a cyclone or a centrifuge) and a system for separation according to the fourth aspect of the invention or embodiments thereof, wherein the at least one blow steam inlet is connected to the steam explosion discharge via said separation device to receive blow steam therefrom.. The pressure and temperature in the treatment reactor may be within the ranges 10-20 bar(a) and 180-210 °C.

[0024] According to a sixth aspect of the invention, there is provided a system for separation of particulate material from blow steam obtained from a hydrothermal treatment reactor for hydrolysis and / or steam explosion of lignocellulosic material. The system comprises a condenser comprising a blow steam inlet and a discharge connection for withdrawing a noncondensed fraction of the blow steam from the condenser, a condensate collection reservoir at a bottom part of the condenser, a cooling liquid control valve connected to the condenser to control a flow of cooling liquid thereto, a control system configured to adjust the aperture of the control valve such that the condenser partially condenses the blow steam. The system may furthermore comprise a source of cooling liquid such as cooling water to which the cooling liquid control valve is connected.

[0025] The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features. Further, all features and advantages of embodiments described above with reference to the first aspect of the invention may form / be applied in corresponding embodiments of the methods according to the second and third aspects of the invention, and in corresponding embodiments of the systems according to the fourth, fifth and sixth aspects of the invention, and vice versa.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Above discussed and other aspects of the present invention will now be described in more detail using the appended drawings, which show presently preferred embodiments of the invention, wherein

[0028] fig. 1 is a flow chart illustrating an embodiment of the method according to the second aspect of the invention;

[0029] fig. 2 is a schematic illustration of an embodiment of the system according to the fourth aspect of the invention;

[0030] fig. 3 is a schematic illustration of another embodiment of the system according to the fourth aspect of the invention;

[0031] fig. 4 is a schematic illustration of an embodiment of the system according to the fifth aspect of the invention, and

[0032] fig. 5 shows condensing curves for the main components of a typical blow steam. DETAILED DESCRIPTION

[0033] Fig. 1 is a flow chart illustrating an embodiment of the method for treating lignocellulosic material according to the second aspect of the invention. The method comprises subjecting the lignocellulosic material to hydrothermal treatment 1 in a hydrothermal treatment reactor at elevated pressure and temperature by means of adding steam to the reactor, steam explosion discharging 2 of treated lignocellulosic material and blow steam from the treatment reactor. The pressure and temperature in the treatment reactor are typically in the range 10-20 bar(a) and 180-210 °C. The method further comprises feeding 3 the blow steam to a condenser. The condenser comprises substantially vertically arranged heat exchanger elements, and the blow steam is fed to the upper portion of the condenser such that the flow of condensing blow steam flows downwards through the heat exchanger elements. The method further comprises partially condensing 4 about 20% of the blow steam using the condenser and collecting 5 the condensate from the partial condensing, for instance at a lower / bottom portion of the condenser. A portion of the collected condensate is recirculated 10 to the upper part of the condenser and is sprayed into the heat exchanging elements. The method further comprises withdrawing 6 at least a portion of the collected condensate (which comprises particulate material), withdrawing 7 a non-condensed fraction of the blow steam from the condenser, subjecting the non-condensed fraction of the blow steam to a further condensation step 8 to obtain a substantially particulate free condensate, and separating 9 at least one volatile organic compound (such as furfural and methanol) from the substantially particulate free condensate. In other embodiments, the further condensation step is omitted, i.e. the non-condensed fraction is withdrawn directly in gas-phase to the separation of volatile organic compounds.

[0034] Steps 3-9 in fig. 1 also illustrate an embodiment of the method according to the first aspect of the invention.

[0035] Fig. 2 is a schematic illustration of an embodiment of a system 100 according to the fourth aspect of the invention. The system comprises a partial condenser 101 comprising a blow steam inlet 102 and a discharge connection 101b for withdrawing a non-condensed fraction of the blow steam from the condenser, a condensate collection reservoir 101a in a bottom part of the condenser, a cooling liquid control valve 103 connected to the condenser, a control system 104 configured to adjust the aperture of the control valve 103 such that the condenser partially condenses the blow steam, and a separation system 109 connected to said discharge connection 101b of the condenser 101, the separation system being configured to separate said at least one volatile organic compound from the non-condensed fraction of the blow steam. The partial condenser comprises heat exchanging elements 101’ in the form of a bank of vertically assembled tubes. The blow steam inlet 102 is arranged to feed blow steam to the upper part of the condenser 101. Spray nozzles 105 are installed in the condenser above the heat exchanging elements 101’ and a pump 106 is arranged for recirculating condensate from the condensate collection reservoir 101a to the spray nozzles.

[0036] The system operates as follows: contaminated blow steam from a steam explosion process is conducted to the blow steam inlet 102 at the top of a partial condenser 101. The contaminated blow steam enters inside the tubes from the top. The tubes are cooled from the outside with a cooling liquid provided via control valve 103 such that volatile organic compounds and blow steam condense as a film on the inner surface of the tubes. With "contaminated” is here referred to solid biomass derived particles entrained in the blow steam. Blow steam from the steam explosion process always carries a small amount of particles which are harmful in downstream rectification steps for separation / recovery of furfural and other volatile organic compounds.

[0037] The particles will function as condensation nuclei during the condensation process, they get wetted and coalesce to aggregates which sticks to the condensate film draining down the inner wall of the tubes and collect in the condensate reservoir 101a in the bottom of the partial condenser. The partial condenser 101 is provided with a recycle wash to further improve the particle collection effect: condensate from the reservoir 101a is recycled with pump 106 to the top of the partial condenser 101 and is distributed with spray-nozzles 105 (or some other type of liquid distribution device) into the tubes 101’. The cooled condensate spray from nozzles 105 (the condensate from the reservoir is somewhat subcooled) increase heat and mass transfer due to the surface of the droplets and the spray acts as a particle scrubbing stage in the top part of the partial condenser. Furthermore, the recycle wash is washing the condensers top tube sheet clean of particles which otherwise could plug the apparatus. Excess condensate not needed for the recycle wash is discharged via control valve 112 to an effluent handling system, combustion etc.

[0038] The system optionally comprises, as shown in fig. 2, a final condenser 107 followed by a gas cooler 108. The partial condensation is achieved by appropriate distribution of cooling liquid to the partial condenser 101 and to the final condenser 107. The condensers 101 and 107 are advantageously dimensioned such that the hot water temperature from them (the temperature of the cooling liquid leaving the condensers, illustrated as arrows from the condensers at an upper left side thereof) is always close to the condensing temperature of the blow steam. Partial blow steam condensation in 101 and 107 is achieved by proportionating the cooling liquid flows to them by means of the control system 104 controlling the respective control valves 103, 110. Blow steam pressure is an input / control variable of the control system 104. Condensation energy in the partial condenser 101, in the final condenser 107 and in the gas cooler 108 is recovered to the respective cooling liquid.

[0039] Non-condensed, purified blow steam is withdrawn (in gas phase) from the partial condenser 101 through discharge 101b to the separation system 109. In embodiments comprising the optional final condenser 107, a portion (or all) of the purified blow steam is conducted to a blow steam inlet at the top of the final condenser (see fig. 2), and condensate formed from condensed purified blow steam is withdrawn from the bottom of the final condenser 107 via discharge 111 and is conducted (through an optional control valve) to the separation system 109.

[0040] A non-condensed fraction from the final condenser 107 is withdrawn to an optional gas cooler 108. Non-condensed tail-gas from the gas cooler 108 (the dotted line to the left) may be withdrawn to scrubbing or burning. The final condenser 107 and gas cooler 108 are formed with heat exchanging elements in a corresponding manner as described above with reference to the partial condenser 101. It is noted that there is no recirculation of condensate in 107 and 108, though.

[0041] The separation system 109 may comprise at least one stripping and rectification device and at least one decanting device, for example as shown in in W02021167511 or SE545919C2 (which are hereby incorporated by reference in their entirety).

[0042] Fig. 3 is a schematic illustration of another embodiment of the system according to the fourth aspect of the invention. This embodiment corresponds to the embodiment in fig. 2 except that the partial condenser 201 is configured differently. In this embodiment, contaminated blow steam enters inside the tubes / heat exchanging elements via a blow steam inlet 202 at a lower portion of the condenser. Steam flows upwards through the tubes 201' meeting condensate which flows down as a film on the tube inner surfaces. The condensate washes particulate material from the steam and the tube surfaces, ultimately draining in the reservoir 201a at the condenser bottom. The tubes 201a’ are cooled from the outside with a cooling liquid such that condensable compounds of the blow steam condense as a film on the inner surface of the tubes. The noncondensed fraction of the blow steam exits the condenser through a discharge 201b at the top of the condenser 201. Condensate is discharged using pump 206 to an effluent handling system.

[0043] Fig. 4 is a schematic illustration of an embodiment of the system according to the fifth aspect of the invention. Lignocellulosic biomass material is fed to a hydrothermal treatment reactor 301 using a plug-screw 302. The lignocellulose biomass material may for example be in the form wood chips, bark, saw-dust, straw, bagasse, or empty fruit bunches. The plug-screw compresses the biomass to a plug such that the high pressure in the reactor 301 is sealed from the atmospheric pressure. The reactor 301 is provided with means 303 for adding steam into the reactor for thermal treatment of the lignocellulose biomass material at elevated pressure and temperature, and at least one steam explosion discharge device 304 arranged to discharge the thermally treated biomass and blow steam. Collecting means in the form of a separator (a cyclone) 305 is connected to the steam explosion discharge device 304 to separate blow steam from the treated lignocellulosic biomass material.

[0044] Typical operating conditions of the hydrothermal treatment reactor 301 are as follows:

[0045] Temperature in reactor: 140-225°C

[0046] Pressure: corresponding pressure 2 - 30 bar(g)

[0047] Residence time: 1 min - 3 hours, preferably 3-20 minutes.

[0048] The operating conditions are controlled such that prehydrolysis of the material is achieved, i.e. such that lignin is softened, and hemicellulose is broken down. A catalyst, for example sulfuric acid may be added to increase the reaction rate.

[0049] The blow steam is conducted to a system 306 for separation of particulate material and volatile organic compounds such as furfural. The system 306 is a system as shown in fig. 2 or 3, and the description above regarding fig. 2 or 3 applies to system 306.

[0050] Fig. 5 shows condensing curves for the main components of a typical blow steam. In the abovedescribed embodiments of the method and system according to the invention, only a minor fraction of the blow steam is condensed in the partial condenser, only so much which is necessary for blending the entrained particulate material to a dilute and pumpable slurry in the reservoir. In fig. 5, the condensed mass-fraction of furfural (and some other volatile organic compounds) in relation to the mass-fraction of blow steam condensed is shown. Fig. 5 is valid at partial condensation of blow steam mixtures with furfural concentrations staying below its azeotropic point with water. Such conditions are prevailing at partial condensation of blow-steam from a hydrolysis process. Fig. 5 shows condensing curves for the main components in blow steam typically comprising about 93 - 96 mass-% steam, 3 - 5 mass-% furfural and 1 - 2 mass-% acetic acid, balance is many other components in low concentrations. Taking furfural as an example. The condensation curve of furfural is such that it enriches in the vapour phase at partial condensation. Only about 2 % of the furfural condenses, as indicated with a cross, by (partially) condensing 20 % of blow steam. The enrichment of methanol is like that of furfural, only about 2 % of methanol is condensed at 20 % condensation of blow steam. In other word about 98 % of furfural and methanol is withdrawn with un-condensed, particulate free, blow-steam from the partial condenser. The behaviour of carboxylic acids (acetic acid for example) is different to that of furfural and methanol, they are enriched in the (partial) condensate. Thus, the invented method is particularly useful at separation of volatile compounds with a similar vapor-liquid behaviour as furfural and methanol.

[0051] The particles content in condensate from blow steam is normally in the range 1 500-3 000 mg / l. The particles separation efficiency according to the invention using partial condensation is better than 99 %. Thus with 20 % partial condensation, the particle content is reduced to 20-40 mg / l. Such particles content is very low and secures high up-time in downstream furfural rectification systems. The particle content in the condensate from the partial condenser is 8-15 g / l in this example, a concentration level which can be easily handled with a recycle pump and high bore wash nozzles.

[0052] The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, the whole purified non-condensed blow steam from the partial condenser may be conducted directly to a system for separation of volatile organic compounds, i.e. the final condenser may be omitted. Also, the gas cooler may be omitted.

Claims

CLAIMS1. A method for separation of particulate material and at least one volatile organic compound from blow steam obtained from a hydrothermal treatment reactor for hydrolysis and / or steam explosion of lignocellulosic material, the method comprising;feeding (3) the blow steam to a condenser;partially condensing (4) the blow steam using said condenser;collecting (5) the condensate from the partial condensing;withdrawing (6) at least a portion of the collected condensate, said condensate comprising said particulate material;withdrawing (7) a non-condensed fraction of the blow steam from the condenser; andseparating (9) at least one volatile organic compound from the non-condensed fraction of the blow steam.

2. The method according to claim 1, wherein said condenser comprises substantially vertically arranged heat exchanger elements, and wherein said blow steam is fed (3) to an upper portion of the condenser such that condensing blow steam flows downwards through the heat exchanger elements.

3. The method according to claim 2, wherein the method further comprises recirculating (10) a portion of the collected condensate to the upper part of the condenser and spraying it into said heat exchanging elements.

4. The method according to claim 1, wherein said condenser comprises substantially vertically arranged heat exchanger elements, and wherein said blow steam is fed (3) to a lower portion of the condenser such that said blow steam flows upwards through the heat exchanger elements.

5. The method according to any of the preceding claims, wherein said partially condensing (4) comprising condensing up to 50 %, preferably up to 30 % but most preferably up to 20 % of the blow steam entering the condenser.

6. The method according to any of the preceding claims, wherein the at least one volatile compound comprises furfural, methanol, diacetyl, 2-3 pentanedione or mixtures thereof.

7. The method according to any of the preceding claims, further comprising, subjecting the non-condensed fraction of the blow steam to a further condensation step (8) to obtain a substantially particulate free condensate, wherein said separating (9) comprises separating said at least one volatile organic compound from said substantially particulate free condensate.

8. The method according to any of claims 1-6, wherein said non-condensed fraction of the blow steam is withdrawn in gas-phase to a stripping column for separation of said at least one volatile organic compound.

9. A method for treating lignocellulosic material, said method comprising:subjecting the lignocellulosic material to hydrothermal treatment (1) in at least one hydrothermal treatment reactor at elevated pressure and temperature by means of adding steam thereto;steam explosion discharging (2) of treated lignocellulosic material and blow steam from the at least one treatment reactor; andseparating particulate material and one or more volatile organic compounds from the blow steam using the method according to any of the preceding claims.

10. A system (100; 200) for separation of particulate material and at least one volatile organic compound from blow steam obtained from a hydrothermal treatment reactor for hydrolysis and / or steam explosion of lignocellulosic material, said system comprising:a condenser (101; 201) comprising a blow steam inlet (102) and a discharge connection (101b) for withdrawing a non-condensed fraction of the steam from the condenser;a condensate collection reservoir (101a; 201a) in a bottom part of the condenser; a cooling liquid control valve (103; 203) connected to the condenser;a control system (104; 204) configured to adjust the aperture of the control valve (103; 203) such that the condenser partially condenses the blow steam; and a separation system (109; 209) connected to said discharge connection (101b; 201b) of the condenser (101; 201), the separation system being configured to separate said at least one volatile organic compound from the non-condensed fraction of the blow steam,wherein said control system (104, 204) is configured to adjust the aperture of saidcontrol valve (103a, 203a) to provide up to 30 % partial condensation of the blow steam.

11. The system according to claim 10, wherein said condenser (101) comprises substantially vertically arranged heat exchanging elements (101'), wherein at least one blow steam inlet (102) is arranged to feed blow steam to an upper part of the condenser (101), the system further comprising at least one spray nozzle (105) installed in the condenser above said heat exchanging elements (101'), and a pump (106) for recirculating condensate from the condensate collection reservoir (101a) to the at least one spray nozzle.

12. The system according to claim 10, wherein said condenser (201) comprises substantially vertically arranged heat exchanging elements (201'), wherein at least one blow steam inlet (202) is arranged to feed steam to a lower portion of the condenser (201) below said heat exchanging elements (201').

13. A system for treating lignocellulosic biomass material, the system comprising:a hydrothermal treatment reactor (301) provided with feeding means (302) for providing lignocellulosic biomass material to the reactor, and at least one steam injector (303) for providing steam to the reactor to subject the lignocellulosic material to hydrothermal treatment at elevated pressure and temperature;a steam explosion discharge device (304) configured to discharge treated lignocellulosic material and blow steam from the treatment reactor;a separation device (305); anda system for separation (306) according to any of claims 10-12, wherein said at least one blow steam inlet is connected to the steam explosion discharge device via said separation device to receive blow steam therefrom.

Images