Abstract:
A pressure-supercharged fluidized-bed gasification chamber has a pressure-tight lock for supplying the feed materials which are to be gasified. The fluidized-bed gasification chamber is connected to a filter chamber via a connecting channel, with the result that the gas produced can flow over from the fluidized-bed gasification chamber into the filter chamber, where it is directed through the filter layer. An external heat source provides the necessary heat for the allothermic gasification. A heat-pipe arrangement directs the heat from the external heat source into the gasification bed of the fluidized-bed gasification chamber, in order to provide the temperature which is necessary for the gasification.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a facility for the gasification of carbon-containing feed materials, e.g. tar, tar sand, plastics waste, residues from paper and pulp production, residues from the petrochemical industry, electronics scrap and light shredded fractions, and in particular of biogenic feed materials, e.g. harvest waste, energy plants (Mishanthus) or wood chips. The facility serves, in particular, for producing combustible gases with a calorific value of at least 8 000 to 10 000 kJ/m 3 . 
     The energy-related utilization of the abovementioned feed materials, at present, is largely limited to combustion. The gasification technologies are set up predominantly for producing weak gases with a calorific value of below 6 000 kJ/kg. These gases, however, are not suitable for utilization, for example, in gas turbines or fuel cells. 
     In order to produce gases with a calorific value of 8 000 to 10 000 kJ/m 3 , so-called allothermic gasification has to be carried out. For this purpose, it is necessary for the fuel which is to be gasified to be fed sufficient external heat at a high temperature level of 500 to 900 degrees Celsius, which up until now has involved high technical outlay. 
     A significant widely used gasification process is the fluidized-bed process. This process may also be used to operate relatively small installations cost-effectively, but does not produce any high-calorie gases. For allothermic gasification in fluidized beds, essentially the following processes and facilities are currently undergoing testing. 
     Batelle Gasifier 
     In the case of the Batelle gasifier (two-stage fluidized-bed gasification), the reaction heat for the fluidized bed is produced in an external fluidized-bed combustion operation. The heat is transmitted by exchange of the hot sand bed and thus involves high technical outlay, see Peter Jansen, Thermische Vergasung von nachwachsenden Roh-und organischen Reststoffen [Thermal gasification of renewable raw materials and organic residues]; Institutsberichte der Bundesanstalt fur Landwirtschaft. [Reports of the federal institute for agriculture], Brunswick, 1997. 
     DMT Gasifier 
     In the DMT gasifier, a considerable amount of the heat which is necessary for the gasification is to be introduced in that use is made of steam, at a temperature of 750° C., which is superheated for the fluidizing operation. In addition, for the gasification of biomass, the intention is for heat-exchanger pipes to be directed through the fluidized bed, the flue gas with a temperature of 1 150° C. flowing through said pipes. It is barely possible, with the current state of knowledge, to verify that this facility can achieve calorific values of approximately 10 000 kJ/kg. Facilities which operate by this principle are disclosed in U.S. Pat. No. 5,064,444 and U.S. Pat. No. 5,439,491. 
     In order to increase the chemical conversion, attempts have thus been made to increase the introduction of heat into the fluidized bed by the use of pulse combustors, as is disclosed in U.S. Pat. No. 5,306,481. This method basically allows a relatively high level of heat introduction and thus a chemical conversion which is necessary for allothermic gasification. The use of pulse combustors, however, involves relatively high outlay. 
     Furthermore, U.S. Pat. No. 4,160,720 discloses a facility which is intended for the gasification of tar sand and in the case of which heat is transmitted into the reaction chamber by means of heat pipes. In the case of this facility, the tar sand runs through the reaction bed and the combustion zone. Since the pyrolysis gas mixes with the flue gas, there is a reduction in the calorific value of this gas, which is not suitable for direct use for gas turbines or for fuel cells. 
     SUMMARY OF THE INVENTION 
     It is thus an object of the invention to provide a facility for the gasification of carbon-containing and, in particular, biogenic feed materials which ensures a straightforward design and reliable operation and by means of which it is possible to produce combustible gases with a calorific value of at least 8 000 to 10 000 kJ/m 3 . It is also an object of the invention to specify a fluidized-bed reactor which is particularly suitable for such a facility. 
     A pressure-supercharged fluidized-bed gasification chamber has a pressure-tight lock for supplying the feed materials which are to be gasified. The fluidized-bed gasification chamber is connected to a filter chamber via a connecting channel, with the result that the gas produced can flow over from the fluidized-bed gasification chamber into the filter chamber, where it is directed through the filter layer. An external heat source provides the necessary heat for the allothermic gasification. A heat-pipe arrangement directs the heat from the external heat source into the gasification bed of the fluidized-bed gasification chamber, in order to provide the temperature which is necessary for the gasification. 
     According to a preferred embodiment of the invention, the external heat is provided by means of combustion, in particular in a fluidized-bed combustion chamber. 
     In order that the filter layer does not grow as a result of the substances filtered out of the combustible gas, some of the growing filter layer is constantly drawn off into the combustion chamber through the solids flow channel. Since the filtered-out substances (ash and residual coke particles) are still combustible in part, they are burned in the combustion chamber. For this purpose, the combustion chamber is preferably connected to the filter chamber via a solids flow channel which is directed upward to the filter chamber. The bottom end section of the solids flow channel has a siphon arrangement in order to deliver material into the combustion chamber from the filter chamber. 
     The filter layer is drawn off, according to a further preferred configuration, via a first blowing-out arrangement at the bottom end section of the solids flow channel. In this case, the solids flow channel is preferably vertical, but always inclined and dimensioned such that, when the bottom blowing-out section of the solids flow channel is blown free, the solid material slides downward of its own accord under the action of gravitational force. 
     A second blowing-out arrangement is preferably provided at the top end section of the solids flow channel. This serves for rearranging and/or loosening the filter layer. 
     Controlling and regulating measures which are known to the person skilled in the art, and specifically the measurement of the gas pressures, determine when and how often the blowing-out arrangement has to be actuated in order to achieve optimum efficiency. 
     The particular advantage of the invention consists in that, depending on the adjustment of the pressure conditions, either more gas or more flue gas (heat) can be produced. The desired gas/flue gas ratio is preferably adjusted by means of a flue-gas-regulating arrangement, e.g. by the cross section of the flue-gas-outlet channel being changed, it being possible for this to be achieved by a flue-gas damper. 
     In an embodiment of the invention, the fluidized-bed gasification chamber is arranged, in spatial terms, above the filter chamber and the filter chamber is arranged above the combustion chamber. This arrangement results in a very compact construction with a good energy balance. 
     In another embodiment of the invention, there is provided an additional heat exchanger, which takes up the waste heat of the drawing-off flue gas and gives it off to the product gas, this likewise improving the energy balance. 
     In another embodiment of the invention, heat-exchanger ribs are arranged on the heat-exchanger sections of the heat pipes. These ribs are formed so as to assume an operative relationship with the streams and vortices of fluid produced by the fluidizing arrangements, such that the fluidized particles are accelerated transversely to their original flow direction. It is thus the case that good transverse mixing of the fluidized bed is achieved, the residence time of the particles in the fluidized bed is increased, gas bubbles are well dispersed, and the heat transfer from the heat-exchanger ribs to the fluidized bed is improved to a considerable extent. This also makes it possible to achieve a compact construction. 
     A fluidized-bed reactor in accordance with the invention is particularly suitable for use in a facility for producing combustible gas from carbon-containing feed materials according to the present invention. A reactor vessel which accommodates the fluidized bed is provided in the fluidized-bed reactor. Fluidizing arrangements for fluidizing a predetermined region of the fluidized bed are provided. In order for additional heat to be introduced or drawn off in this region, use is made of heat exchangers. The better the heat transfer between the heat exchangers and the fluidized bed, the higher is the efficiency of the installation. In order to improve this heat transfer, the heat-exchanger sections of the heat exchanger are designed as special heat-exchanger ribs which are formed and arranged so as to assume an operative relationship with the streams and vortices of fluid produced by the fluidizing arrangements, such that the fluidized particles are accelerated transversely to their original flow direction, as a result of which the transverse mixing of the fluidized bed is improved, the residence time of the particles in the fluidized bed is increased, and the heat transfer from the heat-exchanger ribs to the fluidized bed is improved to a considerable extent. 
     By using such a fluidized-bed reactor, smaller and more cost-effective overall sizes are possible, while maintaining the same output, as a result of the improved heat transfer. Such a fluidized-bed reactor may be used both in the combustion chamber and in the combustible-gas reactor of the facility for producing combustible gas from carbon-containing feed materials. 
     It should be emphasized that it is not possible or expedient to specify specific dimensioning for the special heat-exchanger ribs since the person skilled in the art can only implement such optimization in conjunction with a specific fluidized-bed reactor. It is thus possible, in individual cases, to use very specially designed heat-exchanger ribs which, in certain circumstances, may even be designed to be different, asymmetrical, etc. if this results in the abovedescribed deflection of the particles with the associated positive effects. 
     In another embodiment of the invention, the heat-exchanger ribs are connected releaseably to the heat-exchanger sections. This embodiment has a series of advantages: since, for example, fluidized beds in which combustion processes take place, on account of the relatively high temperature in conjunction with the sand of the fluidized bed, have a highly abrasive effect on internals, the heat-exchanger ribs are particularly effected thereby, i.e. they are subject to a high level of wear. The exchangeability of these parts which are subject to wear is thus particularly cost-effective. 
     In yet another embodiment of the invention, heat pipes are used. It is clear to the person skilled in the art that the positive effect provided by the invention is merely achieved by the particular configuration of the heat-exchanger ribs in conjunction with the fluidized bed. The combination of the special heat-exchanger ribs with heat pipes again allows a reduced overall size for maintaining the same output. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained hereinbelow with reference to two exemplary embodiments in conjunction with attached drawings, in which: 
         FIG. 1  shows a sectional illustration of a first embodiment of the invention, 
         FIG. 2  shows a sectional illustration of a second embodiment of the invention, 
         FIG. 3  shows the effect of the top blowing-out nozzle, 
         FIG. 4  shows the effect of the bottom blowing-out nozzle, 
         FIG. 5  shows a perspective illustration of a blade-design eat-exchanger rib on the heat-exchanger section of a heat exchanger, 
         FIG. 6  shows a perspective illustration of a helical heat-exchanger rib, 
         FIG. 7  shows a perspective functional illustration of the heat-exchanger rib according to  FIG. 6 , and 
         FIG. 8  shows heat-exchanger ribs which are arranged on horizontally located heat-exchanger sections. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a first embodiment of the invention. A first tubular vessel  1  has, at its top end section  1   a , a pressure-tight lock  2  for introducing the feed materials  3  which are to be gasified, and are illustrated symbolically by means of the arrow. Provided in the bottom end section  1   b  of the vessel  1  is a fluidized-bed combustion chamber  4 , into which steam- and/or air-mixture feed nozzles project. For starting up, i.e. for heating up, a fuel feed nozzle  6  is arranged within the fluidized-bed combustion chamber  4  in order to blow in combustible gas by means of which the fluidized-bed combustion chamber  4  is heated up. 
     A second tubular vessel  7  is arranged concentrically in the vessel  1  and extends from the top end section  1   a  to the fluidized-bed combustion chamber  4 . At its top end section  7   a , this vessel  7  is connected in a sealed manner to the outlet of the lock  2 . Arranged at the bottom end section  7   b  of the vessel  7  is a combustible-gas outlet  8  for discharging the combustible gas  9  obtained, said outlet not being connected to the interior of the vessel  1 . 
     Arranged in the top section of the vessel  7  is a fluidized-bed gasification chamber  10 , which is described hereinbelow. 
     The fluidized-bed gasification chamber  10  is a tubular vessel  11  which is open at the top. The vessel  11  is arranged such that the feed materials  3  introduced via the lock  2  drop into the vessel  11 . A perforated base  12  is arranged at the bottom end section  11   a  of the vessel  11 , and provided therebeneath is a steam inlet nozzle for the introduction of superheated steam. Arranged above the perforated base  12  is a fuel feed nozzle  15 , which serves for the introduction of fuel which is required for starting up and, if appropriate, for controlling the gasification. 
     The fluidized-bed gasification chamber  10  is arranged concentrically in the vessel  7  such that the remaining annular gap  16  has a predetermined cross section. 
     Arranged in the bottom section of the vessel  7  is a filter chamber  17 , which is described hereinbelow. 
     The filter chamber  17  comprises a wall section  7   c  of the second tubular vessel  7  and a filter-chamber perforated base  18 , which is arranged above the combustible-gas outlet  8 . A solids flow channel  19  is of tubular design and extends from the filter chamber  17 , through the filter-chamber perforated base  18 , into the fluidized-bed combustion chamber  4 , the bottom section  19   a  of the solids flow channel  19  being curved upward. An upwardly directed bottom blowing-out nozzle  20  projects into said section  19   a  and the functioning of said nozzle will be explained at a later stage in the text. A further, upwardly directed top blowing-out nozzle  21  is arranged in the top section  19   b  of the solids flow channel  19 . 
     Heat pipes  22  extend from the fluidized-bed combustion chamber  4 , via the filter chamber  17 , to the fluidized-bed gasification chamber  10 , those end sections of the heat pipes  22  which project into the fluidized-bed combustion chamber  4  taking in heat and the end sections which project into the fluidized-bed gasification chamber  10  giving it off again there, in order to produce the necessary gasification temperature. 
     In the present example, helical heat-exchanger ribs  23  are arranged at those end sections of the heat pipes  22  which project into the fluidized-bed gasification chamber  10 , with the result that transverse acceleration is produced by the upwardly directed steam and bed-material flow, this resulting not just in dispersion of resulting bubbles, but also in transverse mixing in the gasifier bed, by means of which there is an increase in the residence time of the fuel particles in the gasifier bed and thus in the conversion during the gasification. Furthermore, the heat transfer between the heat-exchanger ribs  23  and the gasifier bed is improved to a considerable extent. 
     The gasification process is described hereinbelow: 
     The gasification fluidized bed with the feed materials  3  is fluidized by superheated steam which is introduced via the perforated base  12 , with the result that thorough mixing of the fluidized bed and of the solid fuels introduced via the lock arrangement is ensured. The basic functioning of fluidized-bed gasification is known to the person skilled in the art and will thus not be explained in detail. 
     The high level of heat transfer from the heat-introduction sections  24  of the heat pipes  22  to the fluidized bed guarantees a high level of heat introduction into the fluidized-bed gasification chamber. A high level of superheating of the steam introduced additionally ensures that it is possible to maintain temperatures between 500° C. and 700° C. for the pyrolysis and temperatures up to 800° C. for the gasification in the gasification bed. These high temperatures result, first of all, in the release of volatile constituents of the fuels and, finally, in the conversion of the released hydrocarbons (homogenous steam gasification) and of the residual coke (heterogeneous steam gasification). An excess of steam aids the conversion of the previously formed carbon monoxide with steam into carbon dioxide and hydrogen, as a result of which there is an additional increase in the fraction of hydrogen which is important for utilization in fuel cells. 
     The combustible gases  9  formed in the fluidized-bed gasification chamber  10  are directed, in the directions of the combustible-gas arrows  9 , through the annular gap  16  into the filter chamber  17 , in which first of all particles of coke and ash are separated off. As the combustible gas  9  flows through the filter bed, the combustible gas reacts with not yet converted steam, as a result of which the conversion, assisted by the catalytic action of the residual coke, is further increased. 
     Some of the combustible gas  9  flows into the fluidized-bed combustion chamber  4  via the solids flow channel  19  and some flows directly into the combustible-gas outlet  8  via the filter-chamber perforated base  18  in order to be supplied for external utilization. The division of the two streams of combustible-gas quantities is determined by the pressure loss in the combustible gas in the solids flow channel  19  and also by the pressure levels which prevail in the filter chamber  17 , the line of the combustible-gas outlet  8  and in the fluidized-bed combustion chamber  4 . 
     Particles of ash and of residual coke are transferred from the filter layer of the filter chamber  17  into the fluidized-bed combustion chamber  4  in that filter-bed material is discharged intermittently from the section  19   a  of the solids flow channel  19 . The blowing-out nozzle is activated for this purpose. 
     In order for bed material to be discharged from the solids flow channel  19  into the filter layer of the filter chamber  17 , steam is blown in via the blowing-out nozzle  21 , see  FIG. 3 . This achieves the situation where the bed material covers the deposited ash and the residual coke particles in layers. 
     The combustible gas  9  introduced into the fluidized-bed combustion chamber  4  is burned together with the residual coke fractions and tars separated off in the filter bed. Some of the heat released here is given off to the heat-accommodating sections of the heat pipes  22 , which direct the heat to the fluidized-bed gasification chamber  10 . 
     The rest of the heat is discharged from the fluidized-bed combustion chamber  4  with the flue gas  24  as perceived heat and is used outside the facility for producing superheated steam. This superheated steam is guided back wholly or partially into the facility as a gasification and fluidizing means. 
     In the present embodiment, nozzles  6  and  15  for introducing liquid or gaseous fuels are provided, in addition, in the fluidized-bed combustion chamber  4  and in the fluidized-bed gasification chamber  10 . These nozzles serve, in particular, for heating up the facility during the starting-up process in order for it to be possible to use, for example, liquid biogenic fuels or in order for it to be possible to utilize liquid fuels or combustible gases which occur in external processes. This is expedient, in particular, when, for example during the operation of fuel cells in conjunction with the gasification facility, hydrogen is separated off in intermediate separating processes and the other constituents contained in the combustible gas (carbon monoxide, methane and higher hydrocarbons) are to be guided back for heat production. 
     In order to produce hot water, saturated steam or superheated steam, it is also possible for steam-generator pipes to be integrated, e.g. as ribbed pipes or immersion heating surfaces, wholly or partially in a fluidized-bed combustion chamber. 
     It should also be mentioned that the fluidized-bed combustion chamber has a conventional ash-discharge arrangement. 
       FIG. 2  shows a further embodiment of the invention. In this embodiment, the fluidized-bed gasification chamber  10 , the filter chamber  17  and the fluidized-bed combustion chamber  4  are arranged one beside the other and are likewise coupled thermally via the heat pipes  22 . The same functional elements are provided with the same designations. In the case of functioning which corresponds to the first embodiment, the explanation is not repeated and you are thus referred to the explanation relating to  FIG. 1 . 
     The feed materials  3  which are to be gasified are introduced through the pressure-tight lock  2  and gasified as in the first embodiment. The combustible gas  9  passes, via the channel  16 ′, into the filter chamber  17 , flows through the latter and passes out of the combustible-gas outlet  8  in the filtered state. Some of the combustible gas is directed through the solids flow channel  19  and burned in the fluidized-bed combustion chamber  4 . 
     As in the first embodiment, blowing-out nozzles  20  and  21  are arranged in the end sections  19   a  of the solids flow channel  19 . 
       FIG. 3  shows the functioning of the top blowing-out nozzle  21 . The arrows show how the material is fluidized and rearranged. 
       FIG. 4  shows the functioning of the bottom blowing-out nozzle  20 . The arrows show how filter material is drawn off from the filter chamber and is fed to the combustion chamber for combustion purposes. 
     Finally, it should also be mentioned that it would be possible for the specific way of discharging material by means of the blowing-out nozzles  20  and  21  to be replaced by a mechanical discharge arrangement. Such a discharge arrangement, e.g. conveying screws, however, is/are more expensive than blowing nozzles and is/are susceptible to malfunctioning under the prevailing operating conditions, with the result the solution with the blowing nozzles is preferred. 
     Different embodiments of heating or cooling ribs on the heat-exchanger sections of the heat pipes are described hereinbelow with reference to  FIGS. 5 to 8 . These heating and cooling ribs are particularly suitable for the fluidizing-bed reactor according to the present invention and thus also for the fluidized-bed gasification chamber  10  and the fluidized-bed combustion chamber  4 . 
       FIG. 5  shows an end section  24  of a heat exchanger, in particular in the form of a heat pipe  22 , on which blade-design heat-exchanger ribs  25  are arranged. 
       FIG. 6  shows an end section  24  of a tubular heat exchanger or of a heat pipe  22  on which helical heat-exchanger ribs  23  are arranged. 
       FIG. 7  shows the tubular end section  24  of a heat exchanger  22  with helical heat-exchanger ribs  23  (such as in  FIG. 6 ) in a fluidized bed  26  which consists, for example, of fuel particles  28  and in which gas bubbles  30  are rising. The arrows  32  show the direction in which the fuel particles  28  and the gas bubbles  30  are deflected. The fluidized bed  26  is assigned to a reactor vessel which corresponds to the tubular vessel  7  in  FIG. 1 . The outer vessel  1  from  FIG. 1  is also illustrated laterally.  FIG. 7  thus constitutes a detail of  FIG. 1 . 
     The fluidized bed is homogenized by said lateral deflection. At the same time, the fuel particles  28  remain in the fluidized bed longer, with the result that they are burned in their entirety. A longer residence time of the feed materials is also desirable in other reactions, e.g. gasification. The lateral deflection gives the particles very good heat contact with the heat-exchanger ribs  23 , as a result of which the heat transfer is improved to a considerable extent and the efficiency is thus increased. 
       FIG. 8  shows part of a fluidized-bed reactor with horizontally located heat-exchanger pipes  22  with heat-exchanger sections  24 , on which heat-exchanger ribs  34  are arranged. The heat-exchanger sections  24  project horizontally into the fluidized bed  26 , which is arranged in a reactor vessel  36 . The reactor vessel  36  comprises a base plate which is designed as a perforated base  38  with holes  40 . A fluidizing arrangement is illustrated by way of the holes  40  together with arrows  42 . 
     In this embodiment, the heat-exchanger ribs  34  are inclined, the direction of inclination of the heat-exchanger ribs  34  having been changed in the heat-exchanger section  24  located above. The particles  28  and the steam bubbles  30  are thus deflected alternatively to the left or right, which results in good transverse mixing. It is thus clear to the person skilled in the art that the heat-exchanger ribs  34  according to the teaching of the invention are to be provided in the case of heat-exchanger sections  24  which are located obliquely.