METHOD AND SYSTEM FOR THE TORREFACTION OF RAW MATERIALS The present invention relates to a method for the production of solids from raw materials using torrefaction, wherein: a) raw material is subjected to an elevated temperature in a reactor in an atmosphere that has a low oxygen content or contains no oxygen, in that b) the raw material is brought into heat-exchanging contact with a gaseous medium at a temperature higher than the torrefaction temperature of the raw material, solid fuel and reaction gas being produced, c) wherein at least part of the reaction gas is fed to a condensation chamber in which said reaction gas is at least partially cooled such that at least some of the condensable components in the torrefaction gas condense and are discharged from said condensation chamber separately from the non-condensed torrefaction gases and at least part of the condensate obtained is combusted by adding gas containing oxygen.

Such a method is disclosed in FR 2 594 135. In this publication a pyrolysis treatment is described where lignocellulose material is treated under a pressure of approximately 800 Pa and at a temperature of approximately 400 °C. This method is used in particular for the production of charcoal.

Compared with the raw material, the solid obtained has, inter alia, a higher calorific value and has better grindability. As a result the solid obtained via the present invention is very suitable as fuel in, for example, gasification and combustion processes.

Possible raw materials consist entirely or partially of organic material and originate, for example, from forestry, agriculture or another branch of industry. These streams can also be entirely or partially of fossil nature or a mixed stream of forms mentioned above.

Examples are biomass (residual) streams such as loppings, cultivated wood, grasses and seeds and raw materials derived therefrom, which, incidentally, can be regarded as product in another preceding process. In the more general sense the raw materials concerned are those that consist entirely or partially of lignocellulose. Possible raw materials are also waste wood originating from, inter alia, the building trade or the wood industry and integral domestic and industrial waste or a separated sub-stream thereof.

The method described in this French patent is unsuitable for large-scale application.

The throughput time is too long, whilst the product obtained is suitable only when very

pure wood-like materials are used.

The aim of the present invention is to avoid these disadvantages.

This aim is realised with a method as described above in that said treatment at elevated temperature comprises a torrefaction treatment at 200 °C-320 °C, the reaction gas comprises torrefaction gas and said raw material is fed continuously to said reactor and product is discharged continuously therefrom. As a result of the use of torrefaction, it is possible to use a wide variety of types of material streams as input product. Moreover, a relatively high yield can be obtained and a hydrophobic product is produced that is easy to grind. As a result of the relatively low temperature it is technically easily possible to carry out this process continuously.

Moreover, the production of contaminated process water is prevented with the present invention.

This process water is produced in the process because the raw material has a certain moisture content and by the thermally induced reactions that take place during the torrefaction process. This water cannot be removed from the torrefaction gases selectively via cooling and partial condensation. Thus, with the condensation of water, other components, such as furans, acids and phenols will condense or dissolve in the water, as a result of which a polluted stream of water is produced that in some cases proves very difficult to purify. This is highly undesirable from the economic standpoint.

According to an advantageous embodiment, the raw material, such as biomass, enters directly into heat-exchanging contact with the gaseous medium.

According to the present invention the pressure under which torrefaction is carried out is essentially the same as atmospheric pressure.

According to a further advantageous embodiment, the removal of components from the torrefaction gas that could otherwise lead to emission problems or to problems in a combustion chamber or a heat exchanger (for example corrosion or deposition) takes place in a highly effective manner. This is applicable in particular to raw materials with a high content of halogens, heavy metals (such as mercury), sulphur or nitrogen. In the present invention halogen-containing components, nitrogen-and sulphur-containing components and components consisting of heavy metals, present in the torrefaction gas, can be removed from the condensate obtained (by cooling of the torrefaction gas) before at least part of this condensate is fed to a combustion step with the addition of oxygen.

According to a further advantageous embodiment, stepwise cooling of at least part of the torrefaction gas takes place, a specific fraction of the torrefaction gas condensing in each step. In this way specific components in the torrefaction gas are prevented from producing contamination at a temperature lower than that at which said fraction has been collected, as a result of which selective removal of water from the condensate obtained by cooling the torrefaction gas is better possible via, for example, membrane separation or liquid/liquid extraction. As a result process water can indeed be removed and discharged without contamination or with minimal contamination.

According to the present invention at least part of the abovementioned condensate is fed to a combustion chamber where this is combusted with the addition of a gas containing oxygen. In this way a significant proportion of the energy contained in the torrefaction gases issuing from a torrefaction chamber is retained for utilisation in the torrefaction process itself. With this procedure at least part of the condensate is optionally vaporised in a vaporisation chamber before it is fed to at least one combustion chamber.

According to a further advantageous embodiment, part of the abovementioned condensate is combusted in a combustion chamber together with part of the torrefaction gas that originates either from a torrefaction chamber or from a condensation chamber. With this procedure at least one additional auxiliary can optionally be fed in, which is combusted in the same combustion chamber or another combustion chamber. According to a further advantageous embodiment this auxiliary is a raw material, or a raw material in which the moisture content has been lowered, or a solid produced according to the method.

According to a further advantageous embodiment, a raw material is fed to a torrefaction chamber. The requisite energy that is required for the process is introduced into said torrefaction chamber by also feeding a gaseous medium thereto, such that the temperature of this gaseous medium is higher than the temperature that is understood as the torrefaction temperature in said torrefaction chamber. This gaseous medium becomes mixed with gas that is formed in said torrefaction chamber and removed from the torrefaction chamber as torrefaction gas. Torrefaction gas thus at least partially consists of components that have been formed from a raw material and are gaseous at said torrefaction temperature of between 200°C and 320°C.

According to a further advantageous embodiment, this gaseous medium is compressed to compensate for pressure drops over a torrefaction chamber. It can be

advantageous to raise the temperature of the gas beforehand, so that condensation as a result of heat losses before this compression is prevented.

According to a further advantageous embodiment, combustion of both at least part of the condensate and at least part of the torrefaction gas takes place in a common combustion chamber. The solids originating from torrefaction are preferably cooled in order to return the heat contained therein as far as possible to the torrefaction process. This can be done either by means of the gases that are permanently present (on their own or mixed with torrefaction gases) or via an indirect heat exchange with a cooling medium that is present particularly for this.

According to the present invention part of the gaseous medium is discharged mixed with torrefaction gases, but before the discharge the useful energy contained in this gas mixture is used to heat, inter alia, inlet streams to the torrefaction chamber. This is effected by combustion of the gases in a combustion chamber while feeding in oxygen. This produces a flue gas and this flue gas is not returned to the process but is discharged after heat exchange with the material streams introduced into the torrefaction chamber and optional purification.

The heat that is liberated during the combustion of at least part of the torrefaction gas can be used to dry the raw materials fed to the torrefaction and/or can at least partially be used for heating the gaseous medium that is fed to the torrefaction chamber and has to maintain the torrefaction process.

The invention also relates to a system for subjecting raw materials to a torrefaction treatment, comprising a torrefaction chamber with inlet for the raw materials and outlet for solids, which chamber is provided with a feed for heating gases, as well as an outlet for heating gases and gases liberated during torrefaction, wherein said outlet is connected to a combustion chamber, which combustion chamber is provided with an inlet for introducing gas containing oxygen, wherein the outlet of said combustion chamber is connected via heat exchangers to a discharge from a system, which heat exchangers are connected on the other side to the inlet feed of the torrefaction chamber.

The invention will be described in more detail with reference to illustrative embodiments shown highly diagrammatically in the drawing. In the drawing: Fig. 1 shows a block diagram of a first variant of the torrefaction operation according to the present invention; Fig. 2 shows a block diagram of a second variant of the present invention,

Fig. 3 shows a block diagram of a third variant of the present invention; and Fig. 4 shows a block diagram of a fourth variant of the present invention.

In Fig. 1 the system according to the present invention is indicated in its entirety by 1.

There is a central torrefaction chamber 2 with a feed 3 for heating gases that maintain the torrefaction process. Preferably, the torrefaction process is carried out at between 200 and 320 °C, and more particularly between 200 and 280 °C.

The material to be fed to the torrefaction process enters the torrefaction chamber 2 continuously via inlet 4. The torrefaction chamber is provided with an outlet 5 for solid as well as an outlet 6 for gaseous substance. Outlet 6 is connected to the inlet 8 of a condensation chamber 7. The residual torrefaction gases consisting of the gaseous medium originating from the feed 3 as well as the gases produced during torrefaction are discharged via outlet 9. The condensed substances from the torrefaction gases are discharged at 10 and fed to the inlet 12 of a combustion chamber 11. The condensed substance is optionally subjected to a purification step.

The gases issuing from the outlet 9 are fed in part to a heat exchanger 16, to be discussed below, fed in part to chamber 26 and fed in part to the inlet of the combustion chamber 11. Air is also fed to this combustion chamber 11 via inlet 14. Apart from air, an auxiliary can also be fed in to promote the combustion. This can be used both at start-up and during the maintenance stage. Such an auxiliary fuel can be either liquid, gaseous or solid. The solid obtained in the torrefaction operation is mentioned as an example of a solid. Combustion of part of the torrefaction gas and all products liberated during the condensation takes place in the combustion chamber 11. The flue gas thus produced is fed via outlet 15 to heat exchanger 16 and more particularly the inlet 17 thereof. After cooling, this flue gas is fed to the inlet 22 of a dryer 21. After further cooling, the gas is discharged into the environment via outlet 23 after optional intermediate purification steps.

Raw material is fed to the dryer via inlet 24. The gaseous medium (which contains some torrefaction gas) is fed into heat exchanger 16 and after heating is introduced into inlet 3 of the torrefaction chamber.

The device described above functions as follows: The raw material is fed continuously to the inlet 24 of a dryer 21. Depending on the percentage moisture in the material fed in, a drying step is or is not necessary. In the dryer a large proportion or all of the water is removed by heating. The material thus obtained is then fed to the torrefaction chamber 2 and subjected to torrefaction treatment with a

gaseous medium that enters through the inlet 3. The continuous solid stream issuing from the outlet 5 is fed to the inlet 27 of a cooler 26 and subjected to a cooling step and discharged at 28. By means of this cooling part of the gas originating from the torrefaction and introduced at inlet 29 is heated and discharged at 30. This gas is then mixed with the gas issuing from the outlet 6 of the torrefaction chamber 2.

After cooling in chamber 26 a solid is produced that can be used, for example, as fuel for power stations. The torrefaction gases released at the outlet 6 consist of the gaseous medium and gases produced in the torrefaction chamber 2. As already described above, following a condensation step part of this gas is fed to the combustion 11 and discharged into the environment after utilising the heat. Another fraction is circulated to the torrefaction chamber. A further fraction is used for cooling solids liberated during torrefaction.

In Fig. 2 a variant of the present invention is shown, which is indicated in its entirety by 31. All components corresponding to the components described above have been given the same reference numerals increased by 30. That is to say, the torrefaction chamber is indicated by 32, the feed of which chamber with a heating gas is indicated by 33 and the inlet for raw materials is indicated by 34.

In contrast to the embodiment of the cooler 26 described above, the cooler 56 that is now used is not incorporated in the stream of the gaseous medium, but a separate cooling medium is fed through it. That is to say, a separate cooling medium passes through the inlet 59 and outlet 60. Moreover, with this embodiment only a small fraction of the gases released from the outlet 39 after the condensation is fed to the combustion chamber 41.

This is indicated by a line 43.

Instead of connecting the heat exchanger 16 and drying chamber 21 in series as above as far as the gas stream issuing from the outlet 15 of the combustion chamber 11 is concerned, the gas issuing from the combustion chamber 41 is now distributed between heat exchanger 46 and dryer 51.

In Fig. 3 a further variant of the present invention is shown, which is indicated in its entirety by 61. All components corresponding to those in Fig. 1 have been given the same reference numerals increased by 60.

The gases liberated during torrefaction are fed via line 68 to the condensation step 67.

However, in contrast to the previous embodiments, a fraction of the torrefaction gases is fed directly to the combustion chamber 71. This separate feed is indicated by 89. An

ancillary advantage of this possible embodiment is that the torrefaction gas is not cooled unnecessarily, since it has to be burned anyway. The same applies for a fraction of the torrefaction gases that is fed directly to the heat exchanger 76 via feed 79. Cooling of solids obtained during torrefaction takes place at 86 in a manner that is not shown in more detail.

In Fig. 4 a further variant of the invention is indicated in its entirety by 91. Compared with the embodiment in Fig. 1, all components corresponding to the embodiment in Fig. 1 have been provided with a reference numeral that has been increased by 90. Reference is made explicitly to Figure 1 for a description of the mode of operation. With this embodiment, as in the case of the embodiment described with reference to Fig. 3, a fraction of the torrefaction gases is not subjected to the condensation process but is fed directly to the combustion chamber 101. In contrast to Figure 2 and 3 and corresponding to Figure 1, the cooled gas is used to cool the solids in block 116. This gas is then returned to the torrefaction unit via heat exchanger 106. As a result the heat that is liberated during cooling of the solids in 116 is recovered and employed to maintain the torrefaction treatment. At the same time only one recycle of gases is needed.

Further variants will be immediately apparent to those skilled in the art after reading the above. These fall within the scope of the present application and more particularly of appended claims.