FIELD

The invention relates to biomass steam explosion apparatus and a method for using the same.

BACKGROUND

Steam has been used in the core manufacturing processes of the pulp and paper industries for over 100 years to separate the different elements within wood - cellulose, hemicellulose and lignin. This separation enables a better quality of end-product to be produced to allow the components not utilised in the pulp and paper industries such as sugars and molasses to be used in other industries.

The principles and process methodologies have generally remained unchanged. Woodchips are gravity fed to a reactor prior to the steam being injected. The resulting pulp is then processed accordingly. However, gravity feeding the feedstock is not efficient when using agrifeedstocks (i.e. non-woody biomass) which often have low bulk density and can result in less than 20% of the reactor being loaded.

These inefficiencies in the agri-feedstock steaming process further complicate the continuous process-cycle (filling, steam treating and evacuating), and therefore significantly slow-down the production resulting in low volumes of processed material and consequential increases in operating costs.

The present disclosure seeks to alleviate, at least to a certain degree, the problems and /or address at least to a certain extent, the difficulties associated with the prior art.

SUMMARY OF INVENTION

According to a first aspect of the disclosure, there is provided an apparatus for treating biomass using steam explosion. The biomass steam explosion apparatus comprises at least one feedstock supply means configured to hold feedstock; at least one reactor module; at least one steam reactor chamber; a feedstock filling manifold configured to transfer the feedstock from the feedstock supply means to the steam reactor chamber; a means for transferring the feedstock from the feedstock supply means to the feedstock filling manifold; a means for compressing the feedstock in the steam reactor chamber; a means for evacuating air from the steam reactor chamber; a means for injecting steam to the steam reactor chamber; at least one discharge sump configured to retain processed pulp; a means for regulating the flow of the processed pulp from the reactor chamber to the discharge sump; a means for removing steam from the discharge sump; and a means for evacuating the processed pulp from the discharge sump.

Optionally, the feed hopper comprises a moving floor.

Optionally, the means for transferring feedstock from the feedstock supply means to the feedstock filling manifold is a filling auger.

Optionally, the feedstock supply means is configured to hold between 25 and 60 m ³ .

Optionally, the at least one steam reactor chamber comprises a slide valve to regulate the flow of feedstock into the steam reactor chamber from the feedstock filling manifold.

Optionally, the means for compressing the feedstock in the steam reactor chamber is a hydraulic extending ram.

Optionally, the hydraulic extending ram comprises a convex fluted ram head.

Optionally, the means for compressing the feedstock is configured to compress the feedstock to achieve a steam reactor chamber filling capacity of 90% or over.

Optionally, the means for evacuating air from the steam reactor chamber is a vacuum pump connected to at least one vacuum valve on the steam reactor chamber.

Optionally, the means for evacuating air from the steam reactor chamber is a vacuum pump connected to a plurality of valves on the steam reactor chamber, and preferably between four and twelve vacuum valves.

Optionally, the means for injecting steam to the steam reactor chamber comprises a steam accumulator connected to at least one steam valve on the steam reactor chamber.

Optionally, the means for injecting steam to the steam reactor chamber comprises a steam accumulator connected to a plurality of steam valves on the steam reactor chamber, preferably between eight and twenty-four steam valves. Optionally, the means for regulating the flow of material from the reactor chamber to the discharge sump comprises a depressurising ball valve and a venturi.

Optionally, the at least one steam reactor chamber is cylindrical with a maximum length of 6000mm and an outer diameter of 840mm.

Optionally, there are four steam reactor chambers.

Optionally, the four steam reactors are positioned such that steam may be transferred between the steam reactor chambers via steam transfer valves.

Optionally, the means for removing processed pulp from the discharge sump comprises an auger pump.

Optionally, the apparatus will fit in a shipping container 12.2 metres long, 2.5 metres wide and 2.6 metres high.

Optionally, all the components parts are coated with PTFE.

There is further provided a method for processing biomass using the apparatus, consisting of opening a filling slide valve on a steam reactor chamber; closing an exit ball valve; feeding feedstock to the steam reactor chamber; compressing the feedstock in the steam reactor chamber to a minimum filling capacity of 90%; closing the slide valve on the steam reactor chamber; evacuating air from the steam reactor chamber; transferring steam to the steam reactor chamber at a temperature of between 195 and 220°C and pressure of between 7 and 9 BARG; closing the vacuum valve when steam is detected at the vacuum pump; injecting steam via the steam injection valves to increase the pressure to between 13 and 22 BARG; leaving the steam in the reactor chamber for between 5 and 15 minutes; opening the steam transfer valve and depressurising the steam reactor chamber to a pressure of between 4 and 6 BARG; transferring processed pulp from the steam reactor chamber to a discharge sump; using the compression means to clear the steam reactor chamber of remaining feedstock; and evacuating the processed pulp from the discharge sump.

Optionally, the apparatus is according to the first aspect of the disclosure. Optionally, the apparatus includes any one or more of the optional features presented above in relation to the first aspect of the disclosure.

BRIEF DESCRIOTION OF THE DRAWINGS

The present disclosure may be carried out in various ways and examples of the disclosure will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view of a steam explosion apparatus;

Figure 2 shows a perspective view of a feedstock filling auger and a feedstock filling manifold connected to four separate reactor chambers;

DETAILED DESCRIPTION

A detailed description of an example biomass steam explosion apparatus will now be given.

Figure 1 illustrates a biomass steam explosion apparatus 1. The biomass steam explosion apparatus 1 comprises a feedstock hopper 2 for holding feedstock. The single feedstock hopper may be capable of holding up to 30m ³ of feedstock at any one time. The feedstock hopper may alternatively be sized appropriately to hold any amount of feedstock, for example it may be a double height hopper capable of holding 60m ³ feedstock. The feedstock may be selected from any of the following: a variety of forestry waste, energy crops and agriwaste such as but not limited to: Bagasse, Rice straw, Straw, Corn stalks, Peanut husks, Coconut husks, Miscanthus and Arundo Donax.

The feedstock hopper 2 comprises a moving floor 3 and a motor 4 for powering the moving floor 3. The feedstock hopper further comprises a feedstock filling auger 5 for delivering feedstock to the feedstock filling manifold 6. The feedstock filling auger 5 is driven by a feedstock auger motor 7 and an auger motor gearbox 8. The moving floor 3 is configured to deliver feedstock towards the feedstock filling auger 5 and may, for example, include some form of internal conveyance method i.e. a belt or a vibrating plate. The control system has a series of sensors that measure the flow of materials from the hopper to the feedstock filling manifold and into the reactors. The control system will pause or activate various motors and filling gate actuators to speed up or slowdown the flow of material as required. The feedstock filling manifold 6 connects the feedstock hopper 2 to at least one reactor module 19. The feedstock filling manifold may connect the feedstock hopper to multiple reactor modules 19. The reactor modules in the example shown are configured such that reactor modules 19a, 19b are in a position above reactor modules 19c, 19d.

Figure 2 illustrates the feedstock filling auger 5 and the feedstock filling manifold 6 connecting the feedstock hopper 2 to four separate reactor modules 19a, 19b, 19c, 19d. The feedstock filling manifold 6 comprises a first feedstock feed gate 9a and a second feedstock feed gate 9b.

The reactor modules 19 are cylindrical and are positioned horizontally. Each reactor module 19 comprises an entrance end comprising a feedstock filling casing 21 connected to a centrally positioned reactor chamber 20, which is connected to an exit end of the reactor module 19. Feedstock enters at an entrance end and, after undergoing processing in the reactor chamber, it discharges at an exit end.

Between the feedstock filling manifold 6 and one of the feedstock filling casings 21 is a filling slide valve. The main reactor chamber 20 is attached to the feedstock filling casing 21 , as shown in Figure 1.

Within the reactor module is a hydraulic ram 22 comprising a ram head 23 to both facilitate feedstock flow into the reactor chamber and additionally enable compression of the said feedstock to attain high volumetric capacity levels. The ram head may be a convex fluted ram head. The ram head is configured to extend from an entrance end of the reactor module and pass through the reactor chamber towards an exit end.

The reactor chamber 20 has a smooth inner surface which helps prevent feedstock sticking to the inner edge of the reactor chamber 20.

The reactor chamber is insulated using a suitable material e.g. mineral wool. This helps maintain the reactors inner core operating temperature of approximately 200°C. A series of sensors are used to monitor the temperature, steam volume, BARG and other volumetric parameters within the reactor chamber.

The reactor chamber 20 comprises one or more vacuum valves 24 which may be configured around the outside of the reactor chamber 20. Preferably, the reactor chamber 20 may comprise eight vacuum valves 24 which may be configured in a ring around the outside of the reactor chamber 20. The vacuum valves 24 allow the vacuum pump 25 to remove the air from the filled reactor chamber 20.

The reactor chamber 20 further comprises one or more steam valves 26 which may be configured around the outside of the reactor chamber 20. Preferably, the reactor chamber 20 further comprises two rings of eight steam valves 26 which may be configured around the outside of the reactor chamber 20. The steam valves 26 allow the reactor chamber 20 to be pressurised with steam.

The reactor chamber 20 further comprises a steam transfer valve 27. The steam transfer valve 27 connects a first reactor chamber 20a to a second reactor chamber 20b, for example. The two reactor chambers connected via the steam transfer valves should be run in different phases, such that when steam is removed from one reactor chamber 20a it may be beneficially added to the other reactor chamber 20b. More than two reactor chambers may be connected via steam transfer valves to allow greater transfer of steam between the reactor chambers.

The steam transfer valve 27 comprises a mesh filtered ball valve situated on the side wall of the reactor chamber from which the steam is leaving, and a mesh filtered ball valve on the side wall of the reactor chamber to which the steam is entering. Both valves open at the same time to allow the flow of steam from the higher pressurised reactor chamber to the lower pressure reactor chamber. The mesh filter prevents material from the reactor chambers from entering the ball valves.

A discharge sump 30 is connected to the exit end of each of the reactor modules 19. Between the discharge sump 30 and each of the reactor chambers 20 is an associated ball valve 28 and an associated delaminating venturi 29.

A steam accumulator 32 may be positioned next to the discharge sump 30 and next to the vacuum pump 25.

The discharge sump 30 comprises an auger pump 31 for removing material from the discharge sump 30. The discharge sump 30 further comprises a sump steam transfer valve 33 to transfer steam from the discharge sump 30 into the steam accumulator 32. The discharge sump may have a base which slopes towards the centre of the discharge sump, thereby promoting the processed material towards the auger pump 31 . The reactor modules 19 are connected to the discharge sump 30 using bolts. All of the components of the reactor modules 19 are bolted together to allow for repairs and strip down during maintenance.

The discharge sump 30 and steam accumulator 32 are of a single welded tank construction with a separation baffle wall between both sections. There is a third section at the back of the accumulator that is a storage bin, that contains the vacuum pump and hydraulic pump that operates the extending ram. This storage bin is bolted to the discharge sump 30.

The described apparatus may be configured such that it fits into a standard shipping container of dimensions 12.2 metres long, 2.5 metres wide and 2.6 metres high. This allows the apparatus to be easily moved and installed. If a higher throughput is required, the modular configuration allows another module to be easily added to be run in parallel with the first module and to increase the throughput.

A process of using the apparatus as described above comprising four reactor modules in parallel with each other will now be given.

The process will be explained with reference to four stages:

1. Filling and compressing

2. Pressurising and reacting

3. Exploding

4. Evacuating

Filling and compressing

Before the filling and compressing stage, the ball valve 28a, 28b, 28c, 28d at the exit end of each reactor module 19a, 19b, 19c, 19d being loaded should be closed to prevent feedstock being unwantedly discharged. The filling slide valve 10a, 10b, 10c, 10d of the reactor module 19a, 19b, 19c, 19d being filled should be opened before filling commences. During the filling process, the feedstock filling auger 5 is run to transfer feedstock from the feedstock hopper 2 to the feedstock filling manifold 6. The moving floor 3, powered by the moving floor motor 4, may be run to transfer feedstock internally within the feedstock hopper 2 towards the feedstock filling auger 5 and ensure a continuous supply of feedstock.

Once the feedstock enters the feedstock filling manifold, it may be directed to one of four reactor modules 19a, 19b, 19c, 19d by a first feedstock filling gate 9a and/or a second feedstock feed gate 9b. The first feedstock feed gate 9a is configured to direct feedstock to either reactor module 19a, 19b or to permit the feedstock to pass to the two reactor modules 19c, 19d. If the feedstock is allowed to pass towards reactors modules 19c, 19d, a second feedstock feed gate 9b is configured to direct feedstock to either reactor module 19c or reactor module 19d.

Once the feedstock has entered the reactor chamber 20a, 20b, 20c, 20d, the hydraulic ram 22a, 22b, 22c, 22d is extended along the length of the reactor chambers towards the exit end of the reactor modules 19 such that the feedstock within each reactor chamber is compressed. After the feedstock has been compressed, the hydraulic ram may be withdrawn and more feedstock may be added. The process of adding and compressing the feedstock may be repeated until an adequate filling capacity has been achieved, for example, a filing capacity of above 85%. Preferably, the feedstock may be compressed until a minimum filling capacity of 90% is achieved. Once the desired feedstock is achieved, the filling slide valve 10a, 10b, 20c, 10d is closed thereby sealing the reactor chambers.

Pressurising and reacting

Once the reactor chambers have been sealed, air is withdrawn from each of the reactor chambers through the vacuum valves 24 which are attached to the vacuum pump 25. Prior to a full vacuum being created within the reactor chambers, the steam transfer valve 27 is opened and high-pressure steam is injected into the reactor chamber through the steam transfer valve 27 from another reactor chamber. This means that the steam can be recycled and ensures that the process is not overly energy intensive. The reactor chamber supplying the steam will be in the evacuating stage of the process. When high pressure steam is detected at the vacuum pump, the vacuum valve is closed. The steam transferred via the steam transfer valve will increase the pressure in the reactor chamber to between 7 and 9 BARG. This is not sufficient for the process, and so additional steam will need to be added through the steam injection valves.

Once the desired amount of steam has been transferred from another reactor chamber, the steam transfer valve is closed and the steam injection valves are opened. Preferably, there are sixteen steam injection valves configured in two separate rings around the outside of the reactor chamber. Steam is injected through the steam injection valves to increase the pressure within the reactor chamber to the desired level. The pressure in the reactor chamber is increased to between 13 and 22 BARG. More preferably, the pressure in the reactor chamber may be 16.25 BARG. Once the desired pressure has been achieved, the steam is left in the reactor chamber for a residency time of between 5 and 15 minutes. The steam is injected at a temperature of between 195 and 220°C. On start-up, where it may not be possible to transfer steam from another reactor chamber, all the required steam may be provided by the steam accumulator via the steam injection valves.

Exploding

After the desired residency time, the steam transfer valve 27 is opened and the reactor chamber 20 is depressurised to between 4 and 6 BARG. When the process is running continuously (i.e. not on start-up), steam may also be transferred to another reactor chamber via the steam transfer valve 27. This means that the steam can be recycled and ensures that the process is not overly energy intensive. The reactor chamber receiving the steam will be in the pressurising stage of the process. Once the desired amount of steam has been transferred, the steam transfer valve is closed. The ball valve 28 is then opened. The difference in pressure between the lower pressurised discharge sump 30 and the higher pressurised reactor chamber 20 forces the processed feedstock to explode into the discharge sump 30, passing through delaminating venturi 29. The hydraulic ram 22 with the convex fluted ram head 23 is then extended into the reactor chamber, removing any remaining feedstock from the inside edge of the reactor chamber. At the same time as extending the hydraulic ram, steam may be pulsed into the reactor chamber to aid with the removal of the remaining feedstock. The hydraulic ram is then retracted to its initial position. Once the reactor chamber has been cleared of material, the ball valve 28 is closed.

Evacuating

In the final stage, the auger pump 31 is used to remove the processed feedstock from the discharge sump 30. The processed feedstock may be sent to a downstream processing unit. Any steam remaining in the discharge sump is evacuated to the steam accumulator via the sump steam transfer valve 33.

Each of the four reactor chambers in the apparatus may be in a different stage of the process at any one given time. In this way, two or more reactor chambers may be linked via one or more steam transfer valves in order to recycle the steam.