NL1016411C2 - Method and device for gasifying biomass. - Google Patents

Description

Method and device for gasifying biomass

The present invention relates to a method for gasifying biomass comprising, in a first step, mixing said biomass with an auxiliary medium and gasifying the biomass, discharging said gas products comprising tar from the first step, and the auxiliary medium, separating said discharge stream into a stream of solid particles and a gaseous stream comprising product gas, discharging said gaseous stream, supplying said solid particles to a second step, burning the solid gasification products in that second step (char ) and supplying that auxiliary medium to that first step

Such a method is known from EP 0239589 A1. This describes the gasification of biomass, whereby sand is used as an auxiliary medium. In the gasifier, biomass is mixed with sand and steam is passed through. At elevated temperature, decomposition takes place in product gas and other components. These other components include charcoal-like material (char) which is burned in a second step. In principle, only auxiliary medium, such as sand, remains which can then be added to the first step. Of course, flue gases are also released in the second step.

It has been found that in all cases with biomass as fuel, tar is formed in the first product gas.

It is proposed in the prior art to remove this tar in a separate step after the process. Tar is here understood to mean substances with long hydrocarbon chains which condense at relatively high temperatures and thereby cause problems.

Due to the method used in the prior art whereby tar is removed in a separate step, it is necessary to supply extra energy, whereby the efficiency of the process decreases. Moreover, the environmentally-friendly nature of gasification of biomass appears to conflict with the environmentally-unfriendly nature of carcinogens such as tar. Transporting and rendering tar harmless poses a health risk.

It is the object of the present invention to improve the method known in the art so that on the one hand the tar can be removed efficiently and without health risks and on the other hand the thermal efficiency of the method increases.

This object is achieved in a method described above in that between said first and second step the discharge flow of the first step in a separate space 5 at a temperature between 700-900 ° C is subjected to an intermediate step for at least 1 second in order to enter the discharge flow to separate tar from the gaseous stream from the first step.

According to the invention it is prevented that tar is present in the product gas which must later be removed with a separate step. Removal of tar 10 according to the present invention can in principle take place according to two mechanisms, whether or not in combination. First, it is possible that tar in the intermediate step is (partially) broken down during the relatively long residence time of more than 1 s. This results in gaseous products that can still be incorporated into the product gas. This process can be promoted catalytically, for example by the solid carbonaceous particles from the first step. It is also possible that (a part of) the tar is adsorbed on the solid particles and in particular the carbon-containing particles and is broken down during the combustion in the second step. This carbonaceous material always comes directly from the gasification in the first step and, unlike the auxiliary medium, is not a recycled material, as a result of which the possible catalytic action or absorbing action is optimal.

In both cases, the energetic content of tar is not lost and fewer harmful components are created. The auxiliary medium that is again supplied to the first step substantially comprises no tar.

According to an advantageous embodiment, the product gas is directly or more particularly separated during this intermediate step. The remainder of the product stream from that first step is subjected to conventional combustion for the purpose of generating electricity and / or heat production or as synthesis gas for, inter alia, the production of methane, methanol, diesel.

According to an advantageous embodiment of the invention, the steps take place in a single reactor housing. Thereby heat losses are prevented as much as possible and the thermal efficiency of the device can increase. The intermediate step is preferably performed in a chamber above the first reactor chamber in which the first reaction is performed. This chamber is preferably also located above the second reactor chamber where the second step, i.e. the combustion, is carried out. In this way an optimum circulation of in particular the auxiliary medium can be obtained, whereby it is not necessary to use special transport means. In the gasifier, transport takes place through the supply of steam and biomass. In the second reactor, transport takes place by air supplied thereto. According to the invention, biomass processing can be integrated into a single reactor which in principle has two outlets, one for product gas and one for flue gas. Such a device is particularly easy to construct.

It will be understood that any other auxiliary medium for the biomass can be used instead of sand. The same applies to the above-mentioned steam and air. Steam is mainly used to provide transport in the first reactor room. Air provides the oxygen demand for the combustion of the solid gasification products (char).

According to an advantageous embodiment, such a single reactor can be isolated.

The time during which the product stream originating from the first step must be subjected to tar reduction is dependent on the amount of tar present which, of course, is again dependent on the gasified biomass. This time is preferably between 1 and 4 seconds and the residence time in the relevant tar reduction space can be controlled by the speed of movement of the product stream and the volume of the space concerned. These are partly determined during the design.

The temperature at which this tar reduction takes place is preferably between 700 and 900 ° C and is more particularly 850 ° C.

The invention will be explained in more detail below with reference to the exemplary embodiment shown in the drawing. Show:

FIG. 1 schematically the various steps of the method according to the invention;

FIG. 2 schematically a device with which the method according to the invention can be carried out; and

FIG. 3 shows the section according to III-III in fig. 2.

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Fig. 1 shows the various steps according to the present invention on the basis of an example. In block 3, biomass, steam and energy are supplied in order to obtain gasification of the biomass. The energy is stored in the auxiliary medium from block 4. Steam is supplied to realize a fluidized bed and to promote gasification.

In block 4, the combustible solid fraction of product stream from block 5 is burned. Also present in this product stream is the auxiliary medium such as sand which is thereby heated. The combustion takes place with the supply of air 10 and flue gas is released thereby.

According to the invention, a block 5 is connected between blocks 3 and 4. Tar reduction takes place there. By subjecting the product stream from block 3 at a temperature of about 850 ° C for at least 1 second, tar present is decomposed into less harmful substances. These less harmful substances are discharged together with the product gas that arises during the gasification for useful use. The necessary residence time is determined by the component in the product stream and the intensity with which carbonaceous matter and tar-containing gas are in contact.

Fig. 2 shows an exemplary embodiment of a device with which the method according to the invention can be realized. This device is indicated in its entirety by 1 and consists of a single reaction chamber 3 which is provided with insulation (not shown). A number of chambers are limited within this housing 2. The first reaction chamber is indicated by 3. As can be seen from the section III-III of Fig. 2, this is a single tube. On the underside, the housing 2 is closed off by a screen plate 15 through which gas but no matter can enter. Steam is supplied to the first reaction chamber 3 via inlet 8. In addition, biomass is supplied to the reaction chamber 3 via inlet 9 and ancillary medium, such as sand, is supplied via inlet 11 at a high temperature. As a result, the auxiliary medium is moved upwards via inlet 11 and comes into contact with the biomass 9 at inlet 9, which is gasified by the high temperature of the auxiliary medium (plus minus 900 ° C). Product gas is thereby produced which leaves the tubular reactor 3 via the outlet 10. The product stream then enters reaction chamber 5. The residence time in chamber 5 is approximately 1-4 seconds. The temperature is around 850 ° C. Various mechanisms may be used to render harmless, during the relatively long residence time, tar formed in reaction chamber 3, i.e., to prevent tar from being entrained with the product gas. Firstly, it is possible to decompose tar (catalytically) and still remove the gaseous decomposition products with the product stream so that they are used effectively. It is also possible that tar is adsorbed on the medium to be burned in the second step and decomposed and burned in this second step. From chamber 5, auxiliary medium and solid products formed after the gasification (charcoal-like products) are fed to reaction chamber 4 via one or more inlets 12 (only one shown). There exists a fluidized bed maintained by the supply of air indicated by 14. The flue gases released thereby are discharged at 13. During the combustion, heat is generated which is stored in the auxiliary medium and which heat is again delivered to reaction chamber 3 in the manner just described by transporting the auxiliary medium.

Moreover, with the method described above, it is advantageous that the nitrogen present in the air introduced at inlet 14 is discharged via the outlet 13 for flue gas. As a result, the calorific value of the product gas obtained at outlet 6 does not decrease and the application possibilities are broadened. Compared to the product gas obtained with a conventional gasifier, that is to say a non-indirect gasifier, the calorific value is about twice as high, that is, about 15 MJ / m3. It has been found that with the present invention a stable equilibrium is set in a particularly simple manner.

Surprisingly, it has been found that a particularly considerable reduction of tar can be obtained in chamber 5. It is believed that the solid mass from the first reactor chamber which is referred to as char has catalytic and adsorbent action. Because new solid mass is always supplied, such a catalytic / adsorbent action is constantly maintained.

With the invention, the tar emissions can be considerably reduced and the efficiency of the gasification of biomass can be considerably increased, and the health risks due to the loss of handling of tar types released can be limited.

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It will be understood that, on the one hand, various of the steps described above can be carried out in a modified manner and that further steps can be switched on, between or after. All such steps are obvious after reading the above description and are within the scope of the appended claims.

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Claims (13)

A method for gasifying biomass comprising in a first step mixing said biomass with an auxiliary medium and gasifying it, discharging said gasification products from the first step, including tar, and the auxiliary medium, separating said discharge stream into a stream of solid particles and a gaseous stream comprising product gas, discharging said gaseous stream, supplying said solid particles to a second step, burning the solid gasification products in that second step and supplying said auxiliary medium to that first step characterized in that between said first and second step, the discharge stream of the first step in a separate space at a temperature between 700-900 ° C is subjected to an intermediate step for at least 1 second in order to be present in the discharge stream of the first step separating the tar from that gaseous stream. 15 The method of claim 1, wherein said separating comprises converting said tar at least partially. 3. Method according to claim 2, wherein said conversion is catalytically supported by the char. The method of any one of the preceding claims, wherein said separating comprises adsorption to said solid particles. The method of claim 4, wherein said separation comprises decomposition on combustion of said solid particles. A method according to any one of the preceding claims, wherein after that intermediate step the product gas is separated. 30 The process according to any of the preceding claims, wherein said steps take place in a single reactor housing. 1016411 Device (1) for gasifying biomass, comprising a first reactor chamber (3) provided with a supply (9) for biomass, a supply (11) of auxiliary medium and a discharge (10) of a first product stream comprising tar and auxiliary medium , a second reactor chamber (4) provided with an inlet (12) for the solid particles from that first product stream and auxiliary medium, a discharge (13) for combustion gases and a discharge for auxiliary medium connected to the feed for auxiliary medium in that first reactor chamber (3), wherein a separation device for gases is provided between said first and second reactor chamber, comprising a discharge (6) for product gas, characterized in that said separation chamber is designed such that the average residence time of said first product stream therein is at least 1 s. Device according to claim 8, wherein said separation chamber comprises a separation device for tar and product gas. Device according to one of claims 8 or 9, wherein said device comprises a housing (2) in which said chambers are arranged. Device as claimed in any of the claims 8-10, wherein said separation chamber is arranged above said first reaction chamber. 20 Device as claimed in any of the claims 8-11, wherein said separation chamber is arranged above a second reaction chamber. 13. Device as claimed in any of the claims 8-12, wherein said first and second reaction chamber are arranged adjacent to each other. 1016411