Patent Publication Number: US-2016244327-A1

Title: Method and plant for gasifying input material

Description:
The present invention relates to a method and a plant for at least partially gasifying solid, organic input material, in particular biomass, having a low-temperature gasifier and a high-temperature gasifier. 
     PRIOR ART 
     Methods for producing synthesis gas from solid, organic input material, also referred to as gasifying methods, are known. Coal or biomass is advantageously used as the input material for such methods. In biomass gasifying methods, used wood and forest waste wood or what are known as energy woods, but also agricultural wastes such as straw or chaff, are used for example. 
     Gasification of biomass to form synthesis gas with subsequent method steps (what are known as biomass-to-liquid or BTL methods) can be used for example to obtain synthetic biofuel that has similar physicochemical properties to known gas-to-liquid (GTL) and coal-to-liquid (CTL) fuels. One example of a plant for producing Bit fuels is disclosed in Kiener, C. and Bilas, 1.: Synthetic second-generation biofuel. The first commercial Mt production plant in the world. Energy 2.0, July 2008, pages 42-44. 
     Methods and plants for at least partially gasifying solid, organic input material are also known for example from EP 0 745 114 B1, DE 41 39 512 A1 and DE 42 09 549 A1 The present application relates to such methods and plants that have a low-temperature gasifier and a high-temperature gasifier, as explained below. Compared with other methods, these allow, inter alia, lower consumption of input material and have a higher cold gas efficiency. 
     In a low-temperature gasifier, the input material, for example biomass, is converted by partial gasification with a gasifying agent at temperature between approx. 300° C. and 600° C. into coke (in the case of biomass into what is known as biocoke) and pyrolysis gas. 
     The conversion is referred to as “pyrolysis” in the present application. Pyrolysis is known to have an under-stoichiometric oxygen supply and therefore incomplete combustion at comparatively low temperature. 
     The pyrolysis gas is then transferred to a combustion chamber of the high-temperature gasifier and partially oxidised there with an oxygen-containing gas, for example with more or less pure oxygen, but also with air and/or oxygen-containing waste gases, e.g. from gas turbines or internal combustion engines. Heat released by said oxidation causes an increase in temperature to between 1200° C. and 2000° C., for example 1400° C. Under such conditions, aromatics, tars and oxo compounds in the pyrolysis gas are completely decomposed. A synthesis gas that consists substantially of only carbon monoxide, hydrogen, carbon dioxide and steam is formed thereby. The synthesis gas can also be referred to as (synthesis) raw gas at this point. 
     In a further stage, for example in a quenching unit integrated in the high-temperature gasifier or connected downstream thereto, the synthesis gas produced in this manner is brought into contact with coke from the low-temperature gasifier. The coke can be prepared separately beforehand (e.g. by grinding and sieving) and then introduced into the quenching unit. The synthesis gas is cooled to approximately 900° C. by endothermic reactions between the coke and the synthesis gas. This effects a partial conversion of the carbon dioxide into carbon monoxide. 
     The synthesis gas rich in carbon monoxide produced in this manner can then be further conditioned. Conditioning comprises for example further cooling, dedusting, compression and/or removal of residual carbon dioxide. 
     Previously, it had to be ensured when selecting the input materials that the fraction of solid and/or inert foreign materials such as sand did not exceed a certain maximum value, to be able to guarantee that excessive amounts of such foreign materials did not accumulate in the gasifier. In previous plants, it was necessary to shut down the gasifier and remove these solids manually if an excessively large accumulation was found. 
     There is therefore a need for improvements in the operation of such plants. In particular, it should be made possible for such plants to be operated with less strict requirements for the input materials to be free from sand. 
     DISCLOSURE OF THE INVENTION 
     The invention proposes a plant and a method are proposed for at least partially gasifying solid, organic input material, in particular biomass, having the features of the independent claims. Preferred embodiments form the subject matter of the dependent claims and of the following description. 
     Advantages of the Invention 
     The invention proceeds from a known method for at least partially gasifying solid, organic input material, for example biomass. A tar-containing pyrolysis gas is produced from the input material by pyrolysis in a low-temperature gasifier. The pyrolysis gas is then converted into a synthesis gas by partial oxidation in a high-temperature gasifier and then by partial oxidation and subsequent partial reduction in an endothermic reactor or gasifier, which can be part of the high-temperature gasifier. According to the invention, it can be ensured in a simple manner for solid (undesirable) foreign materials, which are primarily introduced by the pyrolysis coke, in the synthesis gas to be removed from the synthesis gas flow. This makes it possible to use less pure input materials, in particular, less strict requirements for freedom from sand (that is, tolerance of input materials having correspondingly higher quartz and silicon fractions) can be tolerated while avoiding the accumulation of such foreign materials and in particular the formation of melt phases of alkali silicates. 
     The side offtakes provided according to the invention can be implemented simply in design terms at a desired level or desired different levels in an endothermic gasifier. 
     Advantageously, the at least one level for a side offtake is selected taking into account the cross section of the endothermic reactor at said level and a flow speed produced thereby of the synthesis gas flowing upwards through the endothermic gasifier and a determined or expected size of the foreign particles to be extracted. 
     In particular, the invention exploits the fact that for example undesirable (inert) sand particles have an average particle size (particle diameter). The flow speed of the synthesis gas flowing upwards in the endothermic gasifier decreases towards the top owing to the conical widening of the gasifier. In a lower region of the endothermic gasifier, the (upward) force acting on the foreign particles by the flow is relatively large and exceeds the weight force of the particles. At a certain level of the endothermic gasifier, these two forces cancel each other out, and therefore an increased concentration of said undesirable particles occurs at said level. A side offtake is expediently provided at this level. 
     It is preferred for the at least one side offtake to be operatively connected to a vacuum pump, in particular a jet pump. Such vacuum pumps can be used to extract undesirable foreign materials from the endothermic gasifier in a simple manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of a plant that is designed for carrying out a method according to the invention, and 
         FIG. 2  shows a preferred embodiment of part of a plant according to the invention. 
     
    
    
     EMBODIMENT OF THE INVENTION 
       FIG. 1  shows a plant that is designed to carry out a method according to the invention can is referred to as a whole with  10 . The plant  10  comprises a low-temperature gasifier  1  and a high-temperature gasifier  2 . 
     An input material A, for example biomass such as wood or corresponding wastes as explained above, can be fed into the low-temperature gasifier  1 . Oxygen can be fed in for example via a line  11 . The low-temperature gasifier  1  is designed for pyrolysis of the solid, organic input material A. 
     A pyrolysis gas B can be discharged from the low-temperature gasifier  1  via a line  12  and transferred to the high-temperature gasifier  2 . The high-temperature gasifier  2  is in two parts. It comprises an oxidation unit  21  and an endothermic reactor (quenching unit)  22 . In the oxidation unit  21 , the pyrolysis gas B is partially oxidised with a supplied oxygen-containing gas, producing temperatures of for example 1400° C. to 2000° C., as explained. This produces a synthesis gas, which is referred to with C. 
     The synthesis gas C is transferred to the endothermic reactor  22  via a fluid connection between the oxidation unit  21  and the endothermic reactor/gasifier  22 . Ground coke, in particular pyrolysis coke from the low-temperature gasifier  1 , is introduced into said reactor. A line via which pyrolysis coke is introduced into the endothermic reactor is referred to with  23 . The endothermic reactions resulting therefrom cause the gas temperature to cool rapidly to approx. 900° C.; an at least partial reduction occurs. 
     The obtained gas mixture D, which is still referred to as synthesis gas (now rich in carbon monoxide), is fed to a cooler  3  and cooled there to a temperature of for example 600° C. The synthesis gas D can then be dedusted in a cyclone  4 . The dedusted synthesis gas E, also referred to in the present application as “gas mixture derived from the synthesis gas”, now has a temperature of for example 500° C. and can be cooled in a further cooler  6 . Said gas can then be fed for example to a carbon dioxide removal device  7 . 
     Downstream of the carbon dioxide removal device  7 , a gas mixture received in said device can for example be compressed in a compressor  8 . 
     The gas flow is discharged from the plant  10  via a line  15 . To ensure a sufficient pressure gradient and therefore to prevent back-flow, the plant  10  expediently has a pressure regulator  19  with actuators (not shown). 
     The endothermic reactor (quenching unit)  22  has a shape that widens conically towards the top, as indicated in  FIG. 1  and shown in detail in  FIG. 2 . Said endothermic reactor will now be explained in more detail with reference to  FIG. 2 . It should be noted that the details discussed here can likewise be implemented in the plant according to  FIG. 1 . 
     The synthesis gas flow indicated with C in  FIG. 1  is deflected 90 degrees upwards, i.e. into the vertical, for example in a deflection chamber (not shown). The synthesis gas therefore flows substantially vertically upwards through the endothermic gasifier  22 , which widens conically towards the top. The ground coke from the low-temperature gasifier  1  that is used for the reduction is introduced for example in the lower region  22   a  of the endothermic reactor  22 , for example via a screw conveyor (shown symbolically by arrow  23   a ) operatively connected to the line  23 . Said pyrolysis coke reacts in the described manner with the synthesis gas C, the particle size of the pyrolysis coke particles decreasing with increasing reaction, that is, with increasing dwell time inside the endothermic gasifier  22  (symbolised by two schematically shown particles p, p′). 
     Undesirable foreign particles such as sand grains, which are introduced into the endothermic reactor primarily by the pyrolysis coke, are however inert and substantially do not react inside the endothermic reactor  22 , and therefore retain their particle size. 
     In the lower region  22   a  of the endothermic reactor  22 , said foreign particles are entrained upwards owing to the relatively high flow speed of the raw synthesis gas. However, owing to the conical widening of the endothermic reactor, the flow speed of the synthesis as slows, and therefore a level H inside the reactor  22  can be calculated and/or determined at which the weight force of the foreign particles (sand grains) compensates the upward force exerted by the flow of the synthesis gas. An accumulation or concentration of the foreign particles occurs at said level. 
     The endothermic gasifier is provided with a side offtake  25  at or in the region of said level H. The side offtake  25  is connected to a jet pump  28  via a line (symbolised with arrow  26 ). In this case for example water is used as the pump medium, which is introduced into the jet pump via a line  29  and exits it via a line  30 . The vacuum produced by means of the jet pump causes the particles or foreign particles concentrated at the level H be extracted from the endothermic reactor and removed from the system with the water via the line  30 . 
     It cannot be completely excluded that a small fraction of synthesis gas and also pyrolysis coke particles are extracted together with the foreign particles. The fraction is however very low compared with the synthesis gas fraction that exits the endothermic reactor via the line  24 . The materials extracted via the line  30  can be separated from each other in a suitable manner and fed hack into the system where appropriate. 
     The jet pump  28  expediently carries out a full quench for the extracted mass flow. The amount of the mass flow extracted at the side can be set variably by setting the vacuum produced by the pump  28 . 
     The plant according to the invention can continue operating without interruptions when accumulations of inert solid particles such as sand occur, by corresponding actuation of the jet pump  28 . In particular, such a side offtake prevents the formation of melt phases, such as of alkali silicates. Overall, the requirements for purity of the input material of the gasification are significantly reduced according to the invention. 
     Instead of a jet pump (water jet pump) with water as the drive medium, a jet compressor (gas jet pump) with for example steam or CO2 as the drive medium can be used as the vacuum pump. 
     To prevent melt gases, additives such as kaolin, limestone or dolomite can also be added to the endothermic gasifier. The overall mixture can then be extracted again at the side without sticky particles forming. 
     A side offtake can also be provided on comparable entrained reactors, which are used for endothermic quenching.