SE542693C2

SE542693C2 - A discharge screw arrangement for discharging lignocellulosic material from a lignocellulosic treatment reactor

Info

Publication number: SE542693C2
Application number: SE1851190A
Authority: SE
Inventors: Örjan Ahlgren
Original assignee: Valmet Oy
Priority date: 2018-10-03
Filing date: 2018-10-03
Publication date: 2020-06-30
Also published as: SE1851190A1

Abstract

A discharge screw (10) for discharging lignocellulosic material (7) from a lignocellulosic treatment reactor (1), where the lignocellulosic material (7) enters into the discharge screw (10) at an outlet end of a reactor vessel (4) in the reactor (1) and is mechanically transported in a longitudinal direction along the discharge screw (10) towards a downstream end (13) of the discharge screw (10), and where the lignocellulosic material (7) is transported from the downstream end (13) of the discharge screw (10) out through an outlet nozzle (20) located downstream of the downstream end (13) of the discharge screw (10) and into a blow pipe (5) located downstream of the outlet nozzle (20), by means of steam (8) flowing along the discharge screw (10), where the discharge screw (10) is at least partially conical with its outer diameter (d) decreasing towards the downstream end (13) of the discharge screw (10).

Description

A DISCHARGE SCREW ARRANGEMENT FOR DISCHARGING LIGNOCELLULOSIC MATERIAL FROM A LIGNOCELLULOSIC TREATMENT REACTOR TECHNICAL FIELD The present invention generally relates to treatment of lignocellulosic material in a reactor, and more particularly to a discharge screw for discharging such material from the reactor.

BACKGROUND The area of the present invention originates in refining of lignocellulosic material for the production of pulp for e.g. paper-making but has in recent years broadened to also include pre-treatment of lignocellulosic material for further processing resulting in biofuel, such as e.g. bioethanol. Lignocellulosic material or biomass is abundant and can provide a sustainable resource for producing e.g. fuels, chemicals and bio-based materials. Lignocellulosic biomass normally comprises primarily cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are natural polymers of sugars, and lignin is an aromatic/ aliphatic hydrocarbon polymer reinforcing the entire biomass network. The hemicelluloses removal is a key step of the pulp production process and is carried out in a steam or water pre-hydrolysis stage. Typically, a horizontal tube reactor is used for pre-hydrolysis of the lignocellulosic material. For higher biomass feed capacities vertical reactors become more cost effective.

The horizontal tube reactor or digester has been adapted to conditions applied in the pre-hydrolysis process. Pre-hydrolysis is sometimes called hydrothermal treatment or just pre-treatment since it is a treatment step before enzymatic hydrolysis. Pre-hydrolysis is typically performed at acid conditions, high temperature and pressure up to 25 bar. The primary application for tube digesters have been processing of agricultural residues such as bagasse and wheat straw or other annual plants for the production of fibers for papermaking.

In a typical horizontal reactor, an internal conveyor screw transports/ feeds the biomass material through the reactor, which gives the biomass a wellcontrolled retention time. Direct steam for heating is added along the reactor. Depending on the feed rate and retention time, several tube reactors can be connected in series.

The discharge or blowing of material from the reactor can be hot or cold depending on the requirements in subsequent steps. With hot blow steam explosion takes place which means disintegration of the biomass into small particles. This may be beneficial e.g. in a subsequent saccharification step since the enzymes used in such a step are given excellent access to the material.

Cold blow, or dilution discharge, is applied when the objective is to separate the sugars dissolved in the liquid phase during the pre-hydrolysis from the remaining solid biomass. It gives the possibility to treat the sugars dissolved in the pre-hydrolysis, mainly from hemicelluloses, separately. Separation of the liquid from the biomass is done in fiber washing equipment.

After treatment in the reactor, the lignocellulosic material is discharged from the reactor for further transport to subsequent processing equipment. In prior art reactors, a large amount of steam is needed in order to discharge the often wet and heavy material from the reactor. This results in a high steam consumption in the reactor. From experience we know that about 1-2 tonnes of steam for every tonne of raw material is required to feed the material from the reactor and out into a subsequent blow pipe. With a more effective outfeed from the reactor, only about 0.3-0.5 tonnes of steam for every tonne of fiber should be required.

Therefore, there is a need for a more effective discharge /blowing of lignocellulosic material out from the reactor.

SUMMARY It is an object to provide a discharge screw which improves the discharge /blowing of lignocellulosic material out from a lignocellulosic treatment reactor, thereby lowering the steam consumption in the reactor.

This and other objects are met by embodiments of the proposed technology.

According to a first aspect, the invention relates to a discharge screw arrangement for discharging lignocellulosic material from a lignocellulosic treatment reactor and comprising a discharge screw, a feeder pipe and a blow pipe, the discharge screw being accommodated in and rotatably arranged inside the feeder pipe, where the discharge screw is configured to mechanically transport the lignocellulosic material in a longitudinal direction along the discharge screw and through the feeder pipe towards a downstream, with respect to the material transport direction, end of the discharge screw, and where the discharge screw arrangement is configured to allow the lignocellulosic material to be transported from the downstream end of the discharge screw towards a downstream end wall of the feeder pipe and out through an outlet nozzle formed in the downstream end wall of the feeder pipe, and into the blow pipe located downstream of the outlet nozzle on the outside of the downstream end wall of the feeder pipe, by means of steam flowing through the feeder pipe, wherein the discharge screw is at least partially conical with its outer diameter decreasing towards the downstream end of the discharge screw and the feeder pipe is at least partially conical with its diameter decreasing towards the downstream end wall of the feeder pipe.

According to a second aspect, the discharge screw arrangement is adapted for a horizontal reactor.

According to a third aspect, there is provided a lignocellulosic treatment reactor comprising a discharge screw arrangement as defined above.

An advantage of the proposed technology is that a lower amount of steam is needed to discharge/ blow the lignocellulosic material out from the reactor, which means that the steam consumption in the reactor will be significantly lower.

Other advantages will be appreciated when reading the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which: Fig. 1 is a schematic illustration of a part of a reactor for treatment of lignocellulosic material and a discharge screw for discharging lignocellulosic material from the reactor according to an embodiment of the present disclosure.

DETAILED DESCRIPTION The present invention generally relates to treatment of lignocellulosic material in a reactor, and more particularly to a discharge screw for discharging such material from the reactor.

Throughout the drawings, the same reference designations are used for similar or corresponding elements.

As described in the background section there is continued need in the art to improve the discharge /blowing of lignocellulosic material out from a lignocellulosic treatment reactor in order to lower the steam consumption in the reactor.

As described above, in a typical horizontal reactor, an internal conveyor screw transports/ feeds the lignocellulosic material/ biomass through the reactor. At the end of the internal conveyor screw in the reactor the material falls down vertically through a reactor discharge unit into a second, smaller conveyor screw or discharge screw which runs at a higher speed and transports the material towards an outlet nozzle, e.g. an adjustable hole, which is typically located at the end of the discharge screw. The material is transported from the last part of the discharge screw into and through the nozzle/ hole and out into a blow pipe outside of the discharge screw by means of steam at high velocity. The steam velocity must be very high to be able to transport this often wet and heavy material from the periphery of the screw towards the center of the screw where the outlet nozzle is typically located. If a sudden increase in material flow occurs, there is a possibility that the steam does not provide enough force to transport the material through the nozzle with a risk that the nozzle may get plugged. Therefore, a high amount of steam is needed to transport the material from the last part of the discharge screw into the nozzle. From experience we know that about 1-2 tonnes of steam for every tonne of raw material is required to feed the material from the end of the screw into the outlet nozzle. With a more effective outfeed from the reactor, only about 0.3-0.5 tonnes of steam for every tonne of fiber should be required.

According to the present disclosure, an improved discharge /blowing of lignocellulosic material out from a lignocellulosic treatment reactor can be accomplished by introducing a reactor discharge screw which is at least partially conical with its outer diameter decreasing towards the downstream end of the screw, i.e. the outer diameter is decreasing in the material transport direction. With this design the distance from the periphery of the screw to the center of the screw will be shorter towards the downstream end of the screw, and therefore a lower amount of steam is needed in order to transport the often wet and heavy material from the periphery of the screw towards the center of the screw where the outlet nozzle is typically located.

Fig. 1 is a schematic illustration of a part of a reactor 1 for treatment of lignocellulosic material 7 with a discharge screw 10 for discharging the lignocellulosic material 7 from the reactor 1 according to an embodiment of the present disclosure. As illustrated in the figure, a rotating internal conveyor screw 2 located inside a reactor vessel 4 in the reactor 1 transports the lignocellulosic material 7 through the reactor vessel 4 towards a downstream, with respect to the material transport direction, end of the reactor vessel 4, where the lignocellulosic material 7 enters into the rotating discharge screw 10. The rotations of the internal conveyor screw 2 and the discharge screw 10 are driven by motors (not shown in the figure). In a particular embodiment the discharge screw 10 is located vertically below the reactor vessel 4 at the downstream end of the reactor vessel 4, and the lignocellulosic material 7 falls down vertically from the reactor vessel 4 into the discharge screw 10, possibly via a reactor discharge unit 3 located between the reactor vessel 4 and the discharge screw 10 at the downstream end of the reactor vessel 4.

The lignocellulosic material 7 is mechanically transported by the discharge screw 10 in a longitudinal direction along the discharge screw 10 towards a downstream, with respect to the material transport direction, end 13 of the discharge screw 10. The lignocellulosic material 7 is then transported from the downstream end 13 of the discharge screw 10 out through an outlet nozzle 20 and into a discharge pipe /blow pipe 5 by means of steam 8 flowing along the discharge screw 10. The outlet nozzle 20 is located downstream of the downstream end 13 of the discharge screw 10 and the blow pipe 5 is located downstream of the outlet nozzle 20.

As illustrated in the figure, the discharge screw 10 has a shape that is at least partially conical, such that the outer diameter d of the discharge screw 10 decreases towards the downstream end 13 of the discharge screw 10, i.e. the outer diameter d is decreasing in the material transport direction.

In an embodiment the discharge screw 10 is accommodated in and rotating inside a feeder pipe / screw pipe 11, the discharge screw 10 and the feeder pipe 11 thus forming a discharge screw arrangement 12. The lignocellulosic material 7 is mechanically transported by the discharge screw 10 in a longitudinal direction through the feeder pipe 11 towards the downstream end 13 of the discharge screw 10, and then transported by steam 8 flowing through the feeder pipe 11 from the downstream end 13 of the discharge screw 10 towards a downstream end wall 14 of the feeder pipe 11, out through the outlet nozzle 20 which is formed in the downstream end wall 14 of the feeder pipe 11, and into the blow pipe 5 which is located adjacent to the nozzle 20 on the outside of the downstream end wall 14 of the feeder pipe 11. Furthermore, also the feeder pipe 11 is at least partially conical such that the diameter D of the feeder pipe 11 decreases towards the downstream end wall 14, i.e. its diameter D is decreasing in the material transport direction.

In a particular embodiment the reactor 1 is a horizontal reactor.

Due to the decreasing diameter of the discharge screw 10 the nominal material transport capacity of the screw will also decrease, and therefore the speed of the reactor discharge screw according to the present embodiments will probably have to be increased as compared to prior art discharge screws. Increasing the speed is also beneficial since the material then comes closer to the outlet before the steam transport takes over from the mechanical transport.

With the present embodiments a lower amount of steam is needed to discharge /blow the lignocellulosic material out from the reactor, which means that the steam consumption in the reactor will be significantly lower.

The embodiments described above are merely given as examples, and it should be understood that the proposed technology is not limited thereto. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the present scope as defined by the appended claims. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible.

Claims

1. A discharge screw arrangement (12) for discharging lignocellulosic material (7) from a lignocellulosic treatment reactor (1) and comprising a discharge screw (10), a feeder pipe (11) and a blow pipe (5), the discharge screw (10) being accommodated in and rotatably arranged inside the feeder pipe (11), where the discharge screw (10) is configured to mechanically transport the lignocellulosic material (7) in a longitudinal direction along the discharge screw (10) and through the feeder pipe (11) towards a downstream, with respect to the material transport direction, end (13) of the discharge screw (10), and where the discharge screw arrangement (12) is configured to allow the lignocellulosic material (7) to be transported from the downstream end (13) of the discharge screw (10) towards a downstream end wall (14) of the feeder pipe (11) and out through an outlet nozzle (20) formed in the downstream end wall (14) of the feeder pipe (11), and into the blow pipe (5) located downstream of the outlet nozzle (20) on the outside of the downstream end wall (14) of the feeder pipe (11), by means of steam (8) flowing through the feeder pipe (11), characterized in that the discharge screw (10) is at least partially conical with its outer diameter (d) decreasing towards the downstream end (13) of the discharge screw (10) and the feeder pipe (11) is at least partially conical with its diameter (D) decreasing towards the downstream end wall (14) of the feeder pipe (11).

2. The discharge screw arrangement (12) according to claim 1, characterized in that the discharge screw arrangement (12) is adapted for a horizontal reactor (1).

3. A lignocellulosic treatment reactor (1) characterized in that it comprises a discharge screw arrangement (12) according to claim 1 or 2.

4. The lignocellulosic treatment reactor (1) according to claim 3, further comprising a reactor vessel (4) and an internal conveyor screw (2) located inside the reactor vessel (4), characterized in that the internal conveyor screw (2) is configured to transport the lignocellulosic material (7) through the reactor vessel (4) towards a downstream, with respect to the material transport direction, end of the reactor vessel (4), and in that the discharge screw (10) is configured to receive the lignocellulosic material (7) from the reactor vessel (4) at the downstream end of the reactor vessel (4).

5. The lignocellulosic treatment reactor (1) according to claim 4, characterized in that the reactor ( 1) is a horizontal reactor, and in that the discharge screw (10) is located vertically below the reactor vessel (4) at the downstream end of the reactor vessel (4), such that the lignocellulosic material (7) may fall down vertically from the reactor vessel (4) into the discharge screw (10) at the downstream end of the reactor vessel (4).