Abstract
A method for continuous steam explosion discharge of a pressurised reactor for thermal treatment of lignocellulose biomasses. The steam explosion discharge is complete decoupled from the thermal treatment step and the loss of steam from the process is fully controlled without jeopardizing the mechanical disintegration of the lignocellulose material from the process.
Claims
1.-15. (canceled)
16. Method for processing lignocellulose materials, comprising: providing lignocellulosic material to a pressurized vessel; hydrothermally treating lignocellulosic material in said pressurized vessel with saturated or superheated steam; discharging hydrothermally treated lignocellulose material continuously from a pressurized vessel to a discharge chamber using a pressure sealing screw; adding steam to the discharge chamber for pressure control; and discharging lignocellulose material and steam from the discharge chamber through a discharge nozzle at expansion of steam.
17. Method according to claim 16, wherein said treatment in the pressurized vessel is performed at a pressure of 5-30 bar, and at a temperature of 160-240° C. for a duration of 1-20 minutes followed by continuous discharge of said material from said pressurized vessel.
18. Method according to claim 16, further including conveying a mixture of steam and biomass particles from the discharge nozzle to one or multiple cyclones and separating steam and volatile gases from steam exploded material.
19. Method according to claim 16, further including conveying a mixture of steam and biomass particle from the discharge nozzle to a centrifuge and separating steam and volatile gases from steam exploded material.
20. Method according to claim 16, further including adding a mineral acid, for example sulfuric acid, to the hydrothermal treatment process upstream or to the pressurized vessel.
21. System for processing lignocellulose materials, comprising: a pressurized vessel configured to perform hydrothermal treatment of lignocellulose materials using saturated or superheated steam, a pressure sealing screw configured to continuously discharge hydrothermally treated lignocellulose material from the pressurized vessel to a discharge chamber; a control valve configured to add steam to the discharge chamber for pressure control; and a discharge nozzle configured to discharge lignocellulose material and steam from the discharge chamber at expansion of steam.
22. System according to claim 21, wherein the pressurized vessel is configured to perform the treatment at a pressure of 5-30 bar, and at a temperature of 160-240° C. for a duration of 1-20 minutes, and wherein said pressurized vessel is configured to continuous discharge of said material.
23. System according to claim 21, wherein said discharge chamber is furnished with a mixing device.
24. System according to claim 21, where said discharge nozzle has a fixed aperture.
25. System according to claim 21, wherein said discharge nozzle has an adjustable aperture.
26. System according to claim 21, wherein said discharge nozzle is a de Laval nozzle.
27. System according to claim 21, further comprising one or multiple cyclones, wherein a mixture of steam and biomass particles is conveyed from the discharge nozzle and the one or multiple cyclones is configured to separate the steam and volatile gases from steam exploded material.
28. System according to claim 21, further comprising a centrifuge wherein a mixture of steam and biomass particles is conveyed from the discharge nozzle and the centrifuge is configured to separate the steam and volatile gases from steam exploded material.
29. System according to claim 21, where the degassing of the pressurized vessel is connected to the discharge chamber.
30. System according to claim 23, where the mixing device is rotating screw.
31. A method for treating or processing lignocellulose materials in a vessel under pressure with saturated or superheated steam; continuously discharging lignocellulose material continuously from the vessel to a first chamber using a discharge feeder configured to discharge material at a pressure seal; adding steam to the first chamber for pressure control; and discharging lignocellulose material and steam from the first chamber through a discharge opening at simultaneous expansion of steam.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Further objects and advantages of the invention will become apparent from the following description of an apparatus for carrying out the method of the invention shown by way of example in the accompanying figures which form a part of this specification and in which:
[0034] FIG. 1 is a schematic chart illustrating acceleration of wood particles by drag forces caused by pressurized steam at high velocity;
[0035] FIG. 2 is schematic chart comparing steam loss at discharge of a conventional reactor with loss at discharge of a reactor according to the present invention;
[0036] FIG. 3 is a schematic illustration of a plant carrying out the method according to embodiments of the present invention; and
[0037] FIG. 4 is yet another schematic illustration of a plant carrying out the method according to embodiments of the present invention.
[0038] FIG. 5 is a flow chart illustrating a method in accordance to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] The basic idea behind the invention will now be described with reference to FIGS. 1 and 2. FIG. 1 presents how small biomass particles are accelerated by drag forces when a mixture of steam and lignocellulose particles is released from a compartment at elevated pressure through a fixed discharge opening (orifice or nozzle). At sufficient low back pressure (pressure immediately after discharge nozzle), the pressure will drop to the critical pressure, p.sub.C (critical pressure) in the nozzle. FIG. 1 illustrates the acceleration of biomass particles at the critical pressure conditions prevailing for the steam (motive fluid) in the narrow part of the nozzle. The particle velocities in the figure are given at 18 bar(a) and 9 bar(a) discharge pressures, p.sub.D. With discharge pressure p.sub.D is here meant the total pressure at the entrance to the nozzle. The corresponding critical pressures p.sub.C are 9 bar(a) and 5 bar(a) and the steam (motive fluid) velocity at the critical pressures, p.sub.C, is approximately 220 m/s in both cases. The particles are accelerated to high velocity at a very short distance. For example, at 100 mm acceleration distance, the velocity is 80 m/s with p.sub.D=18 bar(a) pressure to the nozzle and 65 m/s at p.sub.D=9 bar(a) pressure to the nozzle. The key observation here is that even though pressure, p.sub.D, is reduced 50% the particle velocity is only reduced about 25%. As said above, the particle disintegration, at steam explosion, is heavily affected by impact and wear. Accordingly, it is surprisingly possible to manipulate the pressure before the discharge nozzle without significantly jeopardizing the steam explosion disintegration effect.
[0040] FIG. 2 presents how the above observations are utilized in the present invention. FIG. 2 is a diagram which presents steam loss with the biomass through a nozzle as a function of nozzle (production) capacity. Steam loss here means the amount of steam which escapes in parallel with biomass at steam explosion discharge through a nozzle. The solid line indicates the steam loss when upstream pressure is kept constant (uncontrolled), for example at 18 bar(a). When the steam explosion discharge is operating at design point for the nozzle 300 kg steam is lost with 1000 kg of biomass. When the production capacity is reduced to 50%, 800 kg steam is lost with 1000 kg of biomass. To avoid such heavy loss of steam (at part load) one may install a control valve in the steam explosion discharge pipe (i.e. prior art) but at the risk of blockage and interrupted production and at the expense of wear on such an expensive control valve. Instead, according to our invention, upstream pressure is controlled, this situation is indicated with the dotted line. The production capacity may vary in the range 50-120% without increasing the steam loss. The steam explosion disintegration effect due to particle velocity and impact remains as demonstrated in FIG. 1.
[0041] From above discussion and FIGS. 1 and 2, the inventors have concluded that there is a good basis to propose a steam explosion system with significantly reduced cost of operation, reduced maintenance need and reduced investment costs due to uncomplicated technical design.
[0042] Preferred embodiments and their advantages are now described by reference to FIGS. 3 and 4. Referring to the figures, reference numeral 101 denotes a feeding container for biomass. Biomass (A) of woody or agricultural origin, such as wood, bark, bagasse, straw and other, or a mixture thereof is fed to the container. From the container 101 biomass is continuously conveyed with screws or stokers 102, to a conical screw 103 for feeding of it into a pressurized vessel 104, e.g. a reactor. The conical screw compresses the biomass to a gas-tight plug which seals the pressure of the vessel 104 to atmospheric. A conical screw is a preferred but not a mandatory solution of feeding material to the vessel 104. It may optionally be replaced with other technical solutions such as a rotary lock feeder or a lock hopper system. Biomass from the screw 103 falls by gravity inside the vessel 104 and piles up inside the vessel 104. The biomass pile slowly moves downwards as it is continuously emptied in the bottom of the vessel 104 with a discharge screw 106. Biomass inside the vessel 104 is preferably heated counter-currently with condensing steam (D) which is added below the biomass pile. The biomass at the exit, in the discharge screw 106, was heated essentially to the temperature which corresponds to condensing temperature of steam at the pressure prevailing in vessel 104. Hydrolysis of hemicellulose sugars takes place in the heated biomass pile and volatile material such as carboxylic acids, furfural, methanol is released to the gas phase. Accumulation of volatile organic compounds in the gas phase of vessel 104 is avoided by degassing it from the top through a valve 110. The processing condition in reactor vessel 104 is determined essentially by retention time and process temperature and these parameters are controlled by adjusting the biomass (pile) level in the reactor 104 and the reactor pressure with steam supply valve 105. The discharge screw 106 continuously empties the reactor. The discharge screw is like the feeding screw 103 gas-tight which means that no steam passes concurrently with biomass to a discharge chamber 107. The discharge chamber is furnished with an exit conductor including a discharge nozzle 108. The pressure in the discharge chamber 107 is controlled by control valve 109 for supply of steam (E) independently of pressure in vessel 104. The discharge nozzle 108 may comprise an orifice plate, a cylindrical nozzle or a de Laval-nozzle. A de Laval-nozzle is a convergent-divergent special nozzle which in comparison to a cylindrical nozzle converts more expansion work to kinetic energy. This is beneficial as the biomass particles can be accelerated to even higher velocity at a short distance. The discharge nozzle may also be replaced with a valve with an adjustable aperture, but such a valve is not used for control of mass flow of steam from the discharge chamber, such a valve is merely used as a kind of adjustable “fixed” orifice. Biomass from discharge screw 106 enters the discharge chamber 107 which is pressurised with steam (E) through a valve 109 and is discharged through the discharge nozzle 108 as a two-phase flow of steam and biomass particles. As said above, the violent blow and expansion of steam disintegrates the particles when passing the discharge nozzle. The mixture of steam and biomass particles (B) is conveyed to a cyclone 111, for separation of steam and volatile gases (G) from steam exploded material (C). The mixture of volatile gas and steam (F) from the rector 104 is conveyed to the cyclone 111. The cyclone 111 is furnished with a pressure lock at the lower exit to avoid gas passing with biomass to downstream process steps. The pressure lock may, for example, be a rotary lock feeder, 112.
[0043] The flow of biomass through the discharge device 107 is controlled by the screws 102, 103 and 106 and the use of steam (E) for steam explosion is determined independently of pressure in the reactor vessel 104. Significant savings in steam usage can be achieved by controlling the pressure in the discharge chamber according to our invention. The particle disintegration during steam explosion can also be controlled independently of the conditions in the reactor vessel 104.
[0044] The discharge system may be applied both to a vertically (FIG. 3) and a horizontally (FIG. 4) assembled reactor vessel. The discharging system is not depending on how the feed of biomass to the reactor 104 is arranged (type of biomass container, feed screws and other) or on how steam is separated from biomass after the discharge. The cyclone 111 may for example be replaced with a centrifuge.
[0045] The nozzle 108 has a fixed opening and is consequently of a technically uncomplicated design. This means that it can be fabricated from a low cost and very hard, for example ceramic material, thereby lowering costs of maintenance.
[0046] With reference to FIG. 5, an embodiment of a method 120 according to the present invention will be described. First, at step 122, lignocellulosic material to a pressurized vessel 104. Then, at step 123, the lignocellulosic material is hydrothermally treating in the pressurized vessel (104) with saturated or superheated steam. At step 124, the hydrothermally treated lignocellulose material is continuously discharged from a pressurized vessel 104 to a discharge chamber 107 using a pressure sealing screw 106. At step 126, steam E is added to the discharge chamber 107 for pressure control. Thereafter, at step 128, the lignocellulose material and steam is discharged from the discharge chamber 107 through a discharge nozzle 108 at expansion of steam.
[0047] 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. The discharge chamber 107, may be furnished with multiple steam inlets (E) or multiple discharge conductor with restrictors (B). It may be of vertical or horizontal design, and it may includes a moving device to promote mixing of steam and biomass. The scope of protection is determined by the appended patent claims.
