TECHNICAL FIELD

The present invention relates to the field of thatched roofs. More particularly the present invention relates to a method of achieving an extensive and thorough fireproofing through impregnation of the micro-structure of reeds for thatched roof.

BACKGROUND

For centuries, thatched roofs have been used as the conventional type of roof for houses, especially in the North European countries, such as Denmark, Germany, The Netherlands and England.

The most serious draw-back of these thatched roofs is their high content of biomass. If no fire-proofing is carried out, such thatched roofs are very easily inflammable, and therefore the buildings provided with such roofs are subject to particular requirements with respect to fire-proofing, such as a specific minimum distance between the buildings and between the building and the property line.

The fire-proofing of thatched roofs is typically carried out according to one of two principles. According to the first principle, air is prevented from reaching the lower face of the roof, whereas the second principle stipulates a proofing by means of a fire retardant liquid which is sprayed onto the upper and lower face of the roof. Description of these two principles in more detail may be found e.g. in EP 1 779 985, in which is also described different methods of doing this.

In general the most widely used method of treating a thatched roof in prior art is to spray a protective fluid onto the reeds of the thatched roof. Hereby, some degree of fireproofing is obtained for a limited time and regular maintenance is required to maintain the level of fireproofing. Furthermore, even when maintained regularly, this method of fireproofing may not provide fireproofing to a satisfying degree. Accordingly, a demand exists for an improved method of carrying out a fireproofing treatment of reeds for thatching in which the fireproofing is longer-lasting. It is an object of the present invention to provide such a method. SUMMARY OF THE PRESENT INVENTION

The invention relates to a method of carrying out a fire-proofing treatment of reeds for thatching, said method comprising the steps of:

a) placing at least one sheaf of reeds and a sodium silicate solution in a centrifuge, said sodium silicate solution at least partly covering said at least one sheaf,

b) lowering the pressure in said centrifuge to below 0.85 bar and maintaining this lowered pressure for at least 20 seconds,

c) returning the pressure in said centrifuge to at least atmospheric pressure and maintaining this condition for at least 20 seconds,

- d) removing at least part of the sodium silicate solution from the centrifuge by centrifuging said at least one sheaf, and

e) adding C0 ₂ to the centrifuge.

With the obtaining of a markedly improved fire-proofing of the thatching material, at least two advantages are believed to be possible to obtain. Firstly, the insurance expenses today are relatively high for houses with thatched roofs as compared to houses with standard roof. Secondly, according to e.g. Danish regulations, houses with thatched roof must hold a distance of minimum 10 meters to the property line, whereas houses with standard roof only need to hold a minimum of 2.5 meters to the property line. With an improved fire-proofing of thatched roof, there may not be a valid reason for this differential treatment anymore.

Even though the wording of the claim is at least one sheaf, the method will typically be carried out with a plurality of sheaves, such as 50. Furthermore, a sheaf may theoretically comprise almost any number of reeds; however, within the meaning of the present invention, a sheaf is defined by the understanding of a person skilled in the art, namely as meeting a standard diameter.

Theoretically all partial processes may be carried out without the centrifuge. However, by using the centrifuge a number of great advantages are obtained. First of all, all steps may be automatically carried out in the centrifuge which makes the full process faster and easier. Second of all, removal of excess rinsing water is made faster and easier through centrifuging. A final drying of the sheaves may also be performed in the centrifuge even though this step may for some embodiments be performed outside the centrifuge.

The present inventors have performed experiments which have disclosed that it is very important to be able to remove sufficient amounts of liquids during the process, i.e. excess water glass and used rinsing water. Remnants of water glass on the surface of the sheaves, if not sufficiently removed prior to addition of C0 ₂ , will lead to daubing of the sheaves resulting in difficulties in use of such sheaves. It is noted that due to the structure of sheaves, it may be difficult to ensure a sufficient removal of liquid. Therefore, for the purpose of removing liquids in a sufficient amount, the use of a centrifuge is believed to be essential to achieving satisfying results according to the present invention. As such the removal of excess water glass is effectively carried out in a combination between centrifuging and use of rinsing water combined with centrifuging.

The establishment of a negative pressure or a positive pressure is a source of expenses in a process like the one in question. Consequently, the method according to the present invention, where the centrifuge is filled almost fully with the water glass solution prior to establishing a negative pressure ensures that the energy required for lowering the pressure is relatively low due to the low volume of air above the water glass solution. As such the negative pressure level and timing indicated in the claim indicates that a desired result may be achieved by a suitable combination of lowering the pressure and maintaining such lowered pressure for a suitable time. E.g. a negative pressure close to vacuum may decrease the necessary time drastically even down to 20 seconds for some types of reeds; however, a full vacuum is not advantageous for economic reasons. On the other hand, a negative pressure only slightly lower than 1 bar may be sufficient if very long time is used; however, in a process like this time is also a parameter and therefore these two parameters are preferably fine-tuned according to the desired needs. A typical combination may be 0.4 bar for 5 minutes.

When returning the pressure to at least atmospheric pressure, again the timing should be fine-tuned. It is necessary to allow sufficient time for the water glass to enter the pits in the reed; however spending too much time is again here not ideal as it will slow down the full process. Furthermore, too much time with contact between basic water glass solution and the cellulose in the reeds may be a problem as well. Finally, too much time may as well allow for water glass to enter the hollow sections of the reeds, where it does not aid much in the fire-proofing, merely resulting in bigger loss of water glass and undesired weight-gain of the sheaves. Consequently, the time may be within a wide range, e.g. above 30 seconds, above 1, 2, 4, 6, or above 8 minutes depending on a number of factors, mainly the type of reeds being used. Normally it will be atmospheric pressure that will be used; however a pressure of above atmospheric pressure may be useful as well, and may speed up this step as well; however, in this regard the simplest is to use the atmospheric pressure. The step of adding C0 ₂ will last for a suitable time period, typically above 30 seconds, above 1, 2, 4, 6, or above 8 minutes depending on a number of factors, mainly the type of reeds being used.

Upon removal of the majority of the solution by the help of gravity and e.g. a pump such that the level of solution is sufficiently low in the centrifuge, removal of further solution is facilitated by starting the centrifuge. In this regard, therefore, the term "centrifuge" should be taken to cover a centrifuge as well as any equivalent hereto, within the knowledge of the skilled person.

In an embodiment of the invention, the sodium silicate of said sodium silicate solution has a Si0 ₂ :Na ₂ 0 ratio between 2: 1 and 3.75 : 1, preferably between 3 : 1 and 3.4: 1.

In an embodiment of the invention, step a) is divided into two steps:

al) placing at least one sheaf in a centrifuge, and

- a2) adding to said centrifuge a sodium silicate solution.

According to embodiments of the present invention, it is preferred to place the sheaves in the centrifuge before covering them with the solution. Hereby it is much easier to know the amount of solution necessary.

In an embodiment of the invention, step d) is followed by two further steps:

dl) adding rinsing water to said centrifuge, and

d2) centrifuging the reeds to remove at least part of the rinsing water. The steps dl) and d2) are used for removing excess sodium silicate solution from the surface of the sheaves in order to avoid daubing of the sheaves upon further treatment.

In an embodiment of the invention, step e) is followed by two further steps:

- el) adding rinsing water to said centrifuge, and

e2) centrifuging the reeds to remove at least part of the rinsing water.

The steps el) and e2) are used for removing the by-product NaHCC from the sheaves before drying. A reason for ensuring a sufficient removal of NaHCC from the sheaves is that it attracts moisture, which may then be a problem in the long run on a roof if too much moisture enters the sheaves. In general, in order to avoid decomposition of the sheaves, the water content in these must be kept relatively low. Experiments have disclosed that water content above 13% may initiate an undesirable decomposition of the reeds, as all biological material from nature comprises fungi spores ready to grow if the conditions are present, and thereby start to degrade the reeds. Consequently, in preferred embodiments the method also includes the step of drying the sheaves.

In an embodiment of the invention, step e) is followed by a further step:

f) drying said at least one sheaf.

The drying may be performed in the centrifuge or in a separate drying chamber of any kind known to the skilled person, such as by using heating, micro waves, vacuum, IR alone or in a combination. In some cases the drying step may be more time-consuming than the other steps; in this case, it may be advantageous to perform the drying step outside the centrifuge. Furthermore, at least a part of the drying process may be carried out by sufficient time in atmospheric conditions.

According to an embodiment of the invention, step a) further comprises the step of closing the centrifuge with a close-fitting lid.

In an embodiment of the invention, the number of sheaves in the centrifuge during the fire-proofing treatment is at least 10 such as at least 25 sheaves.

In an embodiment of the invention, in step a) said at least one sheaf is placed substantially vertical in the centrifuge with the spikes turning upwards.

In an embodiment of the invention, the ribbon(s) holding the sheaves together is cut open upon placement in the centrifuge. In an embodiment of the invention, in step a) a net is mounted over the spikes of the reeds in order to fixate them. The purpose of a net is to aid in fixation of the reeds/sheaves in each of the following partial processes. The net may be any suitable net known to the skilled person.

In an embodiment of the invention, said at least one sheaf is of the type miscanthus (thatching miscanthus).

Even though any suitable type of reed may be used, the inventors have discovered that the method is in particular suitable with the grass variety miscanthus, in particular miscanthus sinensis and miscanthus tinctorius. The reeds from Thatching Miscanthus looks like the traditionally used reed. Further, they are long and straight reeds which are easy to work with. They give a surface that drains well, and dry out very quickly, which ensures a long lasting roof. As

Thatching Miscanthus is grown on farmland, there is a much better control of the growing process. This is different to traditional reed, which is harvested in lakes and rivers, where e.g. pollution may be a problem. As such it is believed that an impregnation according to embodiments of the present invention may be more uniform and improved with the use of the miscanthus.

In an embodiment of the invention, said at least one sheaf comprises less than 4% reeds with a length below 120cm.

In an embodiment of the invention, said at least one sheaf before being cut open has a circumference between 50 and 70 cm, preferably between 58 and 64cm. In an embodiment of the invention, said sodium silicate solution is a mixture of sodium silicate and water in the range of 2:98 to 98:2, preferably in the range of 5 :95 to 95:5, more preferably in the range of 10:90 to 85: 15, such as 15:85 to 75:25.

The dilution with water serves at least two purposes: partly to lower the viscosity of the liquid in order to facilitate the penetration thoroughly into the pits of the sheaves, and partly to ensure that not more than necessary of the water glass is added to the pits.

The use of a too high amount of water glass obviously results in extra expenses to both water glass and extra C0 ₂ . Consequently, a suitable dilution with water is highly desired, which at the same time ensures a suitable fire-proofing effect.

In an embodiment of the invention, in step a) said sodium silicate solution is added in an amount sufficient to cover said at least one sheaf completely. In an embodiment of the invention, in step b) the pressure in said centrifuge is lowered to below 0.7 bar, preferably to between 0.4 and 0.1 bar, and this lowered pressure is maintained for at least 1 minute, such as for at least 3, at least 5 or at least 7 minutes.

In some embodiments, this lowered pressure is maintained for less than 15 minutes, such as less than 10 minutes.

In an embodiment of the invention, in step c) the pressure in said centrifuge is maintained at atmospheric pressure for at least 1 minute, such as for at least 3, at least 5 or at least 7 minutes.

In an embodiment of the invention, substantially all of the sodium silicate solution is removed from the centrifuge in step d).

After the solution has been allowed to enter the pits of the reeds during negative pressure followed by atmospheric pressure covered by the sodium silicate solution, the part of the solution which has not been trapped in the pits is removed from the centrifuge again. In an embodiment of the invention, in order to make the emptying of the reactor tank faster, the excess sodium silicate solution is removed by the use of a pump. This pump may then be used to pump out the solution until the level of solution is sufficiently low in the centrifuge, upon which the centrifuge is started centrifuging, while continuously pumping excess solution back into the glass water tank. In an embodiment of the invention, in step dl) rinsing water is added to the centrifuge through the hollow axle, wherein said hollow axle is perforated to allow the rinsing water to gain access to said at least one sheaf.

In a preferred embodiment, the hollow axle is perforated in the whole length of the reeds when these are positioned in the centrifuge.

According to an embodiment of the invention, in step dl) the centrifuge rotates by less than maximum speed while adding rinsing water.

The rotation of the centrifuge during addition of rinsing water has the purpose of leading the rinsing water through the reeds from the inner axle to centrifuge wall. Therefore, at this stage high speed is not needed, and instead typically a speed of about half maximum will be appropriate. According to an embodiment of the invention, in step d2) the centrifuge rotates by maximum speed to remove rinsing water after addition of rinsing water is stopped.

According to an embodiment of the invention, in step d2) the used rinsing water is pumped into a first rinsing water tank 9. The water in the first rinsing water tank 9 may be re-used to dilute the sodium silicate solution used in step a) if necessary. Hereby remnants of water glass in the rinsing water are not wasted.

In an embodiment of the invention, in step e) C0 ₂ is added to the centrifuge from a C0 ₂ tank 10 through the hollow axle and a return loop leads the C0 ₂ back into said C0 ₂ tank afterwards, during which preferably the centrifuge is slowly rotating.

The establishment of a loop of C0 ₂ through the sheaves starting from the hollow axle ensures a close contact between the individual reeds and the C0 ₂ , thereby facilitating that the chemical reaction between the water glass and the C0 ₂ may occur to a satisfying degree. According to an embodiment of the invention, the pressure in said centrifuge is lowered prior to adding C0 ₂ to the centrifuge. Hereby less atmospheric air is mixed with the added C0 ₂ if a higher concentration of C0 ₂ . In an embodiment of the invention, gas cylinders are provided to supply fresh C0 ₂ into the C0 ₂ tank corresponding to the amount of C0 ₂ used in the chemical reactions in the centrifuge.

In an embodiment of the invention, in step el) rinsing water is added to the centrifuge through the hollow axle, wherein said hollow axle is perforated to allow the rinsing water to gain access to said at least one sheaf.

According to an embodiment of the invention, in step el) the centrifuge rotates by less than maximum speed while adding rinsing water. As in the previous rinsing water step, the rotation of the centrifuge during addition of rinsing water has the purpose of leading the rinsing water through the reeds from the inner axle to centrifuge wall. Therefore, at this stage high speed is not needed, and instead typically a speed of about half maximum will be appropriate.

The addition of rinsing water is stopped and the reeds are centrifuged, preferably at full speed. The used rinsing water from steps el) and e2), which now comprises NaHC0 ₃ , is led to tank 4.

According to an embodiment of the invention, in step e2) the centrifuge rotates by maximum speed to remove rinsing water after addition of rinsing water is stopped. According to an embodiment of the invention, in step e2) the used rinsing water is pumped into a second rinsing water tank 19.

In an embodiment of the invention, said drying said at least one sheaf in step f) is performed in the centrifuge or in a separate drying chamber. In an embodiment of the invention, said drying in step f) is performed by using heating, micro waves, or vacuum, or a combination thereof.

Said drying may be performed with any kind of suitable technique known to the skilled person in the art.

According to an embodiment of the invention, a lifting means is provided for lifting the sheaves in order for them to be tied together again.

Sometimes it may be desired to tie the sheaves together afterwards, which can be facilitated by a lifting means. Alternatively the sheaves are not tied together but just taken out from the centrifuge as they are.

According to an embodiment of the invention, said centrifuge has a diameter between 1 and 3 m. According to an embodiment of the invention, said centrifuge centrifuges with a speed of at least 60 turns/min, such as at least 100 or at least 200 turns/min.

The rotation speed of the centrifuge should be sufficiently high to ensure the effect of the centrifugation, but at the same time it is very important that the centrifugal forces are not so strong that the reeds are damaged. As this last feature obviously depends on the specific type of reeds, a suitable rotation speed of the centrifuge may be anywhere between 60 turns/min and 600 turns/min, depending on the specific conditions.

Furthermore, the invention relates to a sheaf for thatched roofs, wherein said sheaf comprises a plurality of reeds, and wherein at least 10%, preferably at least 20%, such as at least 40% or at least 60% of the volume of the pits of at least one of said plurality of reeds comprises Si0 ₂ .

Furthermore, the invention relates to a sheaf for thatched roofs, wherein said sheaf comprises a plurality of reeds, and wherein at least one of said plurality of reeds comprises at least one through-going pit, wherein said through-going pit is substantially filled by Si0 ₂ .

Furthermore, the invention relates to a sheaf for thatched roofs, wherein said sheaf comprises a plurality of reeds, and wherein at least one of said plurality of reeds comprises Si0 ₂ in an enclosed hollow section of said at least one of said plurality of reeds.

In an embodiment of the invention, said Si0 ₂ has been inserted into said pits by the use of the method described herein.

Furthermore, the invention relates to a house comprising a thatched roof, wherein said thatched roof comprises at least one sheaf as described herein, wherein said at least one sheaf optionally also comprises a fire-proofing layer applied according to conventional fire-proofing protecting methods.

Furthermore, the invention relates to a system for impregnation of sheaves comprising a reactor tank 1 with a perforated centrifuge 2 and a perforated and hollow main axle 3; wherein said system comprises:

- a tank 8 comprising a solution of water glass and means 12 for providing water glass to said reactor tank,

- a tank 10 comprising C0 ₂ and means 16 for providing C0 ₂ to said reactor tank,

DETAILED DESCRIPTION

The present invention provides an improved impregnation method to use with thatching material in order to obtain an improved fireproofing of the material. This is obtained by implementing in the pits of each reed a lasting, effective and eco- friendly flame-retardant, which is functioning throughout the lifetime of the thatched roof and moreover may possibly prolong the lifetime of the roof with maybe a factor of 2 due to the fact that the impregnation material counteracts microbial growth. In the present context, the terms reeds and sheaves are used to indicate any suitable type of material for thatched roofs. Even though the method as such can be used on a variety of different types of thatching material according to various embodiments of the present invention, a preferred type of thatching material is the grass variety miscanthus (thatching miscanthus).

The water glass mainly used in the experiments in relation to the present invention is highly alkaline, which is the reason for a number of references hereto in the description. Different water glass types may vary in the alkalinity.

A typical reed for thatching is structurally similar to bamboo, with the reed divided into sections along the longitudinal direction, with "knees" marking the division between sections. These knees are the sections where the leaves grow on the reeds before harvesting. The leaves may be removed before use in the present invention or they may fall off by themselves during the processing, or at least some of the leaves may remain on the reeds when used for thatching. Furthermore, the reeds are hollow on the inner side of each section, again with the knees dividing the hollow sections from each other. In all parts of the reed, incl. the knee, the material comprises a large number of pits into/through the material. An important feature of this invention is that the applicant has discovered that fire-proofing of the reeds/ sheaves are markedly improved when these pits are filled with inflammable material. With the present invention, the inventor has developed a method for performing such fire-proofing of reeds as well as fire-proofed sheaves/reeds. The method concerns impregnation of each individual reed (in bundles of typically 50 sheaves), where the impregnation is carried out with a solution of sodium silicate, water glass, reacted with carbon dioxide. Hereby silica (Si0 ₂ ) is released, which is not flammable. The process should be carried out as fast as possible i.a. because a basic solution of sodium silicate may tend to decompose the cellulose and lignin in the reeds if exposed to this solution too long.

In a simple embodiment of the method, the equipment for the method consists of a centrifuge with a vertical, through-going, hollow axle and a number of tanks coupled hereto via valves and pumps.

The equipment may also be divided into a number of parts, where the individual partial processes are carried out. All the partial processes as described here may take place within the centrifuge equipment; however, one or more of the partial processes may in some embodiments be carried out outside the centrifuge, such as in particular the drying process.

The creation of a negative pressure in the centrifuge has the purpose of pulling out air from the interior of the reeds through the pits. Due to the porosity of the material, the interior may hold certain amounts of gas, which is pulled out by the negative pressure. To ensure that sufficient gas is pulled out, the negative pressure should be kept for a while, typically up to 10 minutes.

As the sheaves are enclosed by a diluted solution of water glass, the returning to atmospheric pressure will ensure that the now pressure-reduced pits and hollow regions in the interior of the organic material pulls in water glass to fill up the porous structure/pits. Again, to ensure that sufficient water glass is pulled in, the situation should be maintained for a while, typically up to 10 minutes. Hereafter, rinsing water may be used to remove the water glass solution surrounding the sheaves.

Upon removal of the rinsing water, C0 ₂ is added in circulation between a C0 ₂ tank and the reactor tank, leading to a chemical reaction between the water glass and the C0 ₂ . Hereby, from the diluted water glass within the pits, silica (Si0 ₂ ), which is not flammable, is released and fixated within the organic material in a solid structure. After this process has been allowed to continue for a desired and sufficient amount of time, the resulting by-product sodium bicarbonate may then be removed by another addition of rinsing water. Finally the sheaves are dried and are ready for use.

It is to be mentioned here that instead of a solution of sodium silicate, a solution of potassium silicate may be used instead or in combination therewith in further developments of the present invention.

Drawings

The invention will now be described more in detail with reference to fig. 1 showing a preferred embodiment of an impregnation system suitable for performing the method according to embodiments of the invention.

Example of a preferred embodiment

1. A bundle of sheaves, e.g. 50 sheaves, is placed vertically in the centrifuge 2 with the spikes turning upwards, and the ribbon(s) holding the sheaves together is cut open. A net is mounted over the spikes of the reeds in order to fixate them in the following partial processes. Finally the centrifuge is closed with a close-fitting lid 5.

2. A solution from the water glass tank 8 of commercially available water glass 36°Be diluted with water, e.g. from a fresh water source or from the first rinsing water tank 9, is pumped into the centrifuge 2 in an amount sufficient to cover all the spikes.

3. A negative pressure is created in the centrifuge lowering the pressure to between 0.4 and 0.1 bar and this negative pressure is maintained for up to 10 minutes. 4. The pressure of the centrifuge is returned to atmospheric pressure and this condition is maintained for up to 10 minutes. 5. The remaining sodium silicate solution is pumped back into the water glass tank 8. When the level of solution is sufficiently low in the centrifuge, the centrifuge is started to centrifuge the sheaves. During this centrifugation the pump continuously pumps excess solution back into the water glass tank 8.

6. The valve connecting the centrifuge and water glass tank 8 is closed. Rinsing water is added through the hollow axle 3, which is perforated in the whole length of the reeds, during which the centrifuge rotates by about half speed.

7. The addition of rinsing water is stopped and the reeds are centrifuged at full speed. The used rinsing water is pumped into the first rinsing water tank 9, from which it may be re-used to dilute the sodium silicate solution used in step 2. 8. The valve connecting the centrifuge and the first rinsing water tank 9 is closed. C0 ₂ is led from the C0 ₂ tank 10 to the centrifuge 2 through the hollow axle 3 and a return loop leads the gas back into the CO ₂ tank 10 afterwards. During the full process the centrifuge is slowly rotating. Further, means 17 are provided to ensure that the CO ₂ tank 10 is sufficiently provided with fresh CO ₂ from gas cylinders 1 1 corresponding to the amount of CO ₂ used in the centrifuge 2 for the chemical reactions and loss. Upon completion of the reaction, the connection between the centrifuge 2 and the CO ₂ tank 10 is closed.

9. Rinsing water is added to the hollow axle 3 during which the centrifuge 2 rotates by about half speed.

10. The addition of rinsing water is stopped and the reeds are centrifuged. The used rinsing water from steps 9 and 10, which now comprises NaHC0 ₃ , is led to the second rinsing water tank 19. 11. The valve to the second rinsing water tank 19 is closed, and the reactor tank 1 is opened. A means may be provided for lifting the sheaves in order for them to be tied together again if this is desired. Alternatively the sheaves are not tied together.

Finally the sheaves (or the bundle of sheaves) are dried by a suitable method. This drying may be performed in the centrifuge or in a separate drying chamber of any kind known to the skilled person.

The dried sheaves may ultimately be bundled by means of strings and packed in large rollers, ready for use.

LIST

1 Reactor tank

2 Centrifuge, perforated

3 Hollow main axle, perforated

4 Motor

5 Reactor lid with means 7 for coupling the lid with the main axle 3, and with means 5 A for ensuring a tight fit with the reactor tank 1 and for fixating the centrifuge 2.

6 Water supply

7 Hollow coupling for the hollow main axle 3

8 Water glass tank

9 First rinsing water tank with remnants of water glass

10 C0 ₂ tank for recirculating C0 ₂

11 CO ₂ cylinder

12 Two-way pump for water glass

13 Buffer tank connected to a compressor to establish negative pressure in the reactor tank

14 Valve to neutralize negative pressure

15 Two-way pump for rinsing water with water glass

16 Pump for adding C0 ₂ to the reactor tank

17 Sensor for monitoring use of CO ₂ and for adding fresh CO ₂ from the CO ₂ cylinder 11

18 Pump for removing rinsing water with NaHC0 ₃ from the reactor tank 1

19 Second rinsing water tank for the used rinsing water with NaHC0 ₃