Patent Publication Number: US-2010107493-A1

Title: Bulk fueled gasifiers

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/846,790, filed Sep. 22, 2008, U.S. Provisional Application No. 60/850,944, filed Oct. 11, 2008, and U.S. Provisional Application No. 60/875,483, filed Dec. 18, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to gasifiers. Two types of gasifiers are bulk fuel fed and entrained flow fed. Entrained flow fed gasifiers require more fuel processing such as pulverizers and slurring of coal, for example. Entrained flow also requires other extra equipment such as blowers and bag house. This extra fuel preparation increases the cost and complexity of the gasifier and also lowers reliability. Entrained flow gasifiers also tend to be very large and cumbersome, with present reliability so poor that two gasifiers are frequently supplied to do the job of one. 
     Bulk fuel fed gasifiers are generally simpler than entrained flow gasifiers, but they typically employ counter-current designs that tend to create undesirable tars. Tars that are very undesirable to further process gas either into syncrude or for power plants because cleaning up the tars requires extra processes and coats the inside of gas piping, all of which increases gasification costs and decreases reliability. 
     Down draft gasifiers typically employ a co-current process in which tars are burned off and converted into a gas before exiting the process. However, down draft gasifiers generally have been limited to low fuel moisture levels because there was no method to dry the fuel within the gasifier. Updraft gasifiers can gasify much wetter fuels than downdraft units, because the hot gas exits through the fresh fuel mass. But the upper gas exit temperatures are limited in updraft gasifiers by the blast flow rate and how much heat energy can be pulled upwards. Similarly, downdraft gasifiers maintain a large fresh fuel mass above the fire or incandescent zone that unlike updraft processes has no hot gas continually flowing through it to dry it, and like updraft needs to maintain as hot an average a fuel mass as possible to maximize the output of the gasifier. 
     SUMMARY OF THE INVENTION 
     The above-mentioned problems are overcome by the present invention, one embodiment of which includes a gasifier including a gasifier shell, means for introducing fuel into the shell, and means for introducing oxygenate into the shell. The gasifier also includes means for discharging gas from the shell, which can be located below the means for introducing oxygenate. The gasifier can also include means for re-circulating gas prior to gas being discharged from the shell. 
     The present invention and its advantages over the prior art will be more readily understood upon reading the following detailed description and the appended claims with reference to the accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, however, may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
         FIG. 1  is a side of one embodiment of a gasifier. 
         FIG. 2  is a side of an alternative embodiment of a gasifier. 
         FIG. 3  is a side elevation view of a non-sticking valve useful in the gasifier of  FIG. 4 . 
         FIG. 4  is a partial side of an alternative gasifier. 
         FIG. 5  is a partial side of another embodiment of a gasifier. 
         FIG. 6  is a cutaway view of a portion of the wall of the gasifier of  FIG. 5 . 
         FIG. 7  is a side of yet another embodiment of a gasifier. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows one embodiment of a slagging gasifier as if it is being used in a pressurized operation, say up to thirty bar pressures. Valve details and controls for de-pressurizing and re-pressurizing lock hoppers and controls are well known and are not shown. The upper and body sections are described first and are the same for each ash discharge method. 
     Lock hopper  1  is filled using a conveyor (not shown) that has a much faster capacity than the maximum usage of the gasifier. Undercutting rotating inward helical front edge of self-aligning plate  2  performs the unloading function by pulling material from the outer perimeter of base  3  and under rotating cap  4 . The loose spline drive connection of unloader plate  2  to drive motor  6  allows plate  2  to conform perfectly to base  3  when rotating, reducing friction and eliminating binding forces. Cap  4  prevents free fall of fuel or material  18  into unloader concentric opening  5 . In conjunction with inward rotating helix plate  2 , materials caught in between the bottom of cap  4  and top of base  3  are broken apart by such grinding action. This is useful for unloaders unloading ash that may contain large clinkers. Drive motor  6  is supported by inside braces  7  attached to the inside of the lock hopper  1 . Unloaded material  18  slides down through cone funnel  8  through lower lock hopper valve  9  (typically a sliding disk-type valve such as a higher temperature Everlasting™ valve) into gasifier upper zone  10  to form material level  11 , which surges up and down in level slightly as there is no feed as the hopper  1  is refilled by its high capacity conveyor (not shown). Level  11  is measured by vertical sensor  12 , and the level data is issued to control the speed of the drive motor  6 , including using higher speeds at first after refilling the lock hopper  1  to recover level  11 . 
     The gasifier includes a water cooled gasifier shell  13 , and the midsection of the shell  13  has a thick, high temperature refractory  14  penetrated by at least two levels of 3000 F rated gas cooled thermocouple temperature sensors  15  and  16 , steam and oxygenate (e.g., O2 or air) feed tubes  17 , and a final exhaust water cooled and ceramic lined gas exit pipe  19  extending through the shell  13 . A combined sensor  20  mounted under the gas exit pipe  19  includes duplex thermocouples like  15  or  16  plus a CO2 sampling sensor. Refractory  14  is further reinforced with a high temperature rated refractory coating  21  throughout an ash incandescent zone  22  and ash or slag removal zone discussed below. Gas  23  produced in the gasifier exits by cone shaped spaces  24  through underside openings  26  of a water-cooled and lined torus shaped pipe  25  mounted inside the gasifier shell  13  and passes out through the exit pipe  19 , which is in fluid communication with the torus shaped pipe  25 . Intense gasification within incandescent zone  22  feeds gas down through a cone volume  27  formed by an extra high temperature refractory, torus-shaped nose  28  mounted on the torus shaped pipe  25  and a cone solid  29  centered with respect to the torus. The gas  23  passing through this space and up though cone shaped spaces  24  completes the reduction reactions that burn off tars to make a tar free gas for subsequent filtering prior to other operations. The combined reaction time for a given gas flow when combining the incandescent zone  22  with the cone volume  27 , the torus-shaped nose  28  and the torus-shaped pipe  25 , recognizing that raising the position of the steam and oxidizer feed pipes  17  or adding additional feed pipes  17  further increases the volume of the incandescent zone  22 , will be determined by computer simulation and/or experiment but is expected to be about 1 second in duration. It is also possible to make oxidizer and steam feed pipes  17  separate pipes to improve on combustion and then gasification taking place within the perimeter space of the zone  22 , which is also a design detail that would be determined by computer simulation and/or experiment. 
     A lower slag rejection space  30  is defined by the extra high temperature refractory  14  and refractory coatings  21 . The high temperatures achieved in the incandescent zone  22 , which is over the slagging temperature for coal or from about 2350-2700 F, will create a continuously running flow of slag  32  around the torus-shaped nose  28  and the cone solid  29 . The cone solid  29  is located across the top of an inclined, refractory disk  31  (inclined at about three degrees) that is supported on it perimeter at  33  and by posts  34 . Molten slag flow  32  passes through notches  35  molded in refractory disk  31  around support posts  34  to enter a tap hole  36  which at the top has an optional inductive copper coil  37  to melt slag at the tap hole  36  as needed and is fed power and water coolant at  38  and which exits as water and power connection  39 . Coolant flow is constant to insure copper coil  37  doesn&#39;t melt. But inductive power would not be used unless tap hole  36  is plugged which can be determined by the failure of the slag lock hopper  44  to fill. Plugging of the tap hole  36  is also unlikely if the incandescent temperature of zone  22  is maintained sufficient as measured by the temperature sensor  16 . Leaving tap hole  36 , the slag  32  enters a quenching vessel  40  with maintained water level  41  and having an optional slag grinder  42 , which should not be needed if a fast unloader is added to the slag lock hopper. Details of a water system to fill the vessel  40  are not shown but are well known in the art. Slag  32  flows through a valve  43  (such as an Everlasting™ valve) into the slag lock hopper  44 , which will typically have a slag rejection valve (not shown) that is similar to the valve  43 . Steam  45  from quenching the slag  32  rises to combine with exit gas  23 . Water flow control to replenish the water level  41  of the quench vessel  40  is not shown and is well known in the art. 
     To start the gasifier, after preheating refractory, the cone volume  27  is filled with chunk sized stove wood up to the feed tubes  17 , and the shell  13  is then filled with coal to level  11 . An igniter burner (not shown) is inserted into the feed tube  17  to ignite the wood coal area, then oxygenate blast flow is ramped up. Such igniters can be permanently built into the feed tube  17 . By virtue of the exit pipe  19  being located below the feed tubes, and thus below the incandescent zone  22 , the gasifier provides a co-current process that burns off tars before the exit gas  23  is discharged. In other words, the fuel  18  and the gas  23  flow in essentially the same direction through the interior of the shell  13 . 
     Referring to  FIG. 2 , an alternative approach for dry ash removal, that is still capable of pressurized operation, is described. The feed and body of the gasifier is the same as described above, so just the ash removal section will be described here. This is a lower temperature version of the gasifier whereby the temperatures maintained in the incandescent zone  22  are maintained below slagging conditions, or generally under 2300 F. The ash unloader has a raised solid high strength refractory cone  46  around which the gas  23  passes to insure tars are burned off. The design rules of thumb for sufficient incandescent zone plus following volumes and gas retention time for fuel to gasify and burn off tars discussed above in connection with  FIG. 1  also apply to this lower temperature dry ash process. A drive gearhead  47  rotates cone  46  and its supporting disk  49  which will support any ash or clinkered mass that falls within this space and which are broken up by all rotating members. Because of wear and because it is a hot area, cone  49  is coated with high temperature silicon carbide or has other wear and heat resistant inserts on its top surface so as to withstand this severe duty. Also, rotating elements are water cooled which helps prolong their life. Construction of such rotating ash unloading conical structures has the advantage that it is solid and water cooled which should prolong its life even more. Also, a thicker helical front face can be specified which enables the ash unloading assembly to rotate even slower. Ash and/or clinkers  50  accumulate and rest on independently water-cooled support base  51 , cooled by water inflows and outflows  53  and  54 , respectively. A center hole  52  is provided for ash discharge through right angle cone transition piece  55  through a high temperature valve  56  to a lock hopper vessel  57  (partially shown). An ash proximity sensor  58 , such a nuclear gage or air cooled point-type reflective gages, could be used with sample-data control algorithms used to maintain a constant speed to the unloader drive, maintains a nearly constant bed of ash level within the this space. In the case of the nuclear sensors, they are off-side so as to only measure ash or slag materials, but not the center cone  46 . While the lock hopper  57  empties, some ash may accumulate atop closed valve  56 , but also the rotation of unloader helix  64 , which rotates with the disk  49  and the cone  46  respectively, may be momentarily stopped until hopper unloading is complete. The lock hopper  57  may also have an unloader (not shown) to quickly discharge ash to atmosphere. Coolant for drive shaft  61  and support bearing/seal  62  is fed coolant water in at  58  and out at  59  through rotary valve  60 . The same coolant travels up and down shaft  61  and is fed in and out of floating unloading helix  64  through high temperature metallic covered hoses  65 . Water ash quenching in the lock hopper  57  could be used if needed, which adds steam flow to the outlet gas  23 . 
     To start the gasifier, after preheating refractory, ash is filled to the sensor level  58 , and from there to the feed tube  17  is filled with chunk sized stove wood and then filled with wood or coal to level  11  with an igniter burner (not shown) inserted in the feed tube  17  to ignite the wood coal area and then ramp up oxygenate blast flow. Such igniters can be built into tube  17 ; ash rejection is held under manual control until the chunk wood is consumed. 
       FIG. 3  depicts a high temperature disk valve with inductive heating method to unstick the valve in the event it freezes open or shut based on the molten slag that will become deposited on the valve disk surfaces as it operates. The use of this valve is shown in  FIG. 4  as an emergency molten slag flow shutoff valve when discharging high-pressure slag. Generally the valve is open allowing slag to continuously flow out. The valve is constructed around flange  66  with actuator  67  that rotates arm  68  which rotates ceramic disk  69  to open or close discharge opening  81  formed by ceramic cylinder  77  attached to flange  66 . Piston  70  imbedded in disk  69  is also held within cylinder  71  attached to arm  68 . Oil pressure though opening  72  into top of piston space  79  forces disk  69  against tungsten disk  73  to perform the leak-proof shutoff function. “O” ring  74  prevents oil from leaking by piston  70  and cylinder  71  combination. When opening and shutting, disk  73  is heated to insure solidified slag either on disk  69  or disk  73  becomes molten allowing a flush non-leaking seal. To provide high temperature heating, there is a non-conducting cylinder  75  which has induction coil  76  surrounding it which is supported by an inside groove in outer non-conducting cylinder  75 . Conducting tungsten disk  73  is also supported by an inside groove in  75 . Air gap  78  is small to increase the heating effectiveness of coil  76  to disk  73 . When high frequency current is applied to coil  76 , the tungsten disk  73  can get hot enough to melt the slag to unstick the two surfaces of disk  73  and disk  69 , or also melt deposited solidified slag to allow the disk  69  to slide shut and to re-seal as noted previously. A heat shield  80  depicted as dashed line is attached to one side of swinging arm  68  such that when the valve is open, i.e. disk  69  swung away from opening  81 , hot material  82  pouring from opening  81  will not damage actuating parts. 
       FIG. 4  depicts just the lower slag area of  FIG. 1  but shows an alternative direct molten slag discharge method and control thereof without using quenching or lock hoppers. In this instance, the gas discharge area  92  has a constant slag level  83  as measured by a nuclear gage comprised of emitter  84  and receiver  85 . They are located to measure slag depth off-side, i.e. do not detect item  104 . To maintain level  83 , computer control algorithms are designed to manipulate the super chilled water inflow  86  and outflow  87  for upper multiple coil  88  and similarly for lower multiple coil  89  a lower chilled water temperature inflow  90  and with outflow  91  which creates a tapered opening  93  formed as slag solidifies onto the coils, shown as slag coating  94 , such that the duplex coil region (or more if required) acts as a high pressure flow control for the pressure reduction of slag from say thirty bars pressure at level  83  to atmospheric pressure where the slag  95  leaves the emergency shutoff valve  96  described in  FIG. 3  above (in this instance valve  96  shown as maintained open). Further, coolant in feed and out feed copper pipes to copper coils  88  and  89  respectively can also have inductive currents to melt away some of slag build-up  94  should opening  93  become frozen shut, which would cause level  83  to rise to an unacceptable level. From time to time it may be necessary to provide inductive heating to slag mass to maintain molten conditions, thus inductive coil  97  provides the needed energy which has constant coolant in-flow  98  and outflow  99 , which also serve as inductive current carriers. Coolant flow maintains coil  97  protective slag coating  100  and the coil also has electrical back insulation  101  imbedded in refractory  102 . To provide a converging area for co-current gasification to take place, cone shaped riser  103  made form high temperature refractory is attached to the bottom of refractory  102 . Slag  104  flows under notches  105  cast in the base of cone  103  to enter the controlled tap hole opening  93  to leave as molten slag flow  95 . A much longer length to slag opening  93  can be created by adding more coil sections like  88  and  89  as indicated previously, and can be engineered in the base of refractory area  102  by extension of lower gasifier housing  106  such as using a pipe extension before attaching safety shutoff valve  96 . A longer length to opening  93  may be needed such that the viscosity change in the slag to dissipate the pressure energy will enable a lower velocity of slag flow  95  from the exit point of safety shutoff valve  96 . 
     To start the gasifier, after preheating refractory, molten slag is added to reach level  83  and maintained molten with inductive energy to coil  97  while filling the remainder of the gasifier with coal to level  11  (not shown but the same level as in  FIG. 1 ) and with an igniter burner (not shown) inserted in feed tube  17  to ignite the coal and then ramp up oxygenate blast flow. Such igniters can be permanently built into tube  17 . 
       FIG. 5  shows another embodiment of a gasifier that is similar to the gasifier of  FIG. 1  but includes means for hot gas re-circulation. Ash rejection and gas out details can be the same as described in connection with the above embodiments and are thus not described here. This gasifier includes an outer steel shell  5  having an insulation limit  6  and a refractory thickness limit  7 . Referring to  FIG. 6 , an enlarged cross section of the outer steel shell  5  shows the wall thickness details. Item  1  is an outer dimpled wall for a steel pressure shell  2 , which provides for a water cooling method generally comprising a forced water circulating method feeding a steam drum above, details not shown but well known in the art. Item  3  is the insulation next to shell  2 , and item  4  is the thick refractory, up to 14 inches thick. 
     Returning to  FIG. 5 , fresh fuel  8  is fed through a lock hopper valve  9  to a controlled level  10 . The inclined fuel level  10  is measured with a high temperature level sensor  11 , which is preferably a gas purged infrared or radar sensor but other sensors can also be used if able to withstand the temperature of the re-circulating gas  16 . 
     A motorized gearhead  12  drives an agitator  13  located in the fresh fuel zone  17  via a shaft  14 , which is water cooled through a rotary valve  15 . The agitator  13  also levelizes the fuel level  10 . Note that re-circulating gas flow  16  causes gasification of the upper fuel zone  17  to start, including caking. Thus, the agitator  13  operates to break up caking and insure relatively uniform gas flows  16  up through the fuel zone  17 . Extending the length of the shaft  14  and providing multiple agitating bars to the agitator  13  can increase the drying potential for downdraft units. 
     Hot, re-circulation gases  16  are pulled up from the fire or incandescent zone  18  by a rotating blower impeller  19  mounted within the inside gasifier case  20  at or near the top of the shell  5 . In one embodiment, the blower impeller  19  is mounted just inside the gasifier shell  5  within a water-cooled bower case. For example, coolant could be fed through rotary joints (not shown) to cool the impeller vanes, and a separate center pipe (not shown) could periodically feed higher pressure steam to blast clean the surfaces of the vanes. Furthermore, blower pre-filters and tar conversion devices outside the gasifier shell  5  could be provided as well to lessen the particulate and tars loading on the blower impeller  19 . The output of the blower impeller  19  is fed to a hollow, torus-shaped plenum  21  in the upper zone of the gasifier shell  5 , which in turn feeds hot gas down though individual ceramic vertical tubes  22  located in the wall of shell  5  around the circumference of the shell  5 . It should be noted that the pressure needed to re-circulate the gases  16  is relatively low, meaning that the gasifier does not require much energy to re-circulate the gases  16 . Also, the plenum  21  could be rectangular in cross section. 
     The blower impeller  19  forces the gases  16  into the plenum  21  and down though ceramic down-flow tubes  22  to combine as gas  23  in the feed or blast tube  26  which has oxidant blast  25 . This creates the incandescent zone  18 , which can be extended vertically depending on the staggered number of blast tubes  26  (only one is shown with its corresponding ceramic down-flow tube  22 ). By re-circulating the hot gases  16  up through the fuel zone  17 , the fuel is dried. Accordingly, the overall downdraft process now has the advantages of updraft fuel drying plus the steam from the wet fuel is transferred to the incandescent zone  18  where it facilitates gasification reactions, reducing the amount of extra blast steam needed depending on the moisture content of the fuel. Also, since the whole fuel mass is at a higher average temperature, the output capability of the gasifiers will be improved. Furthermore, because the gases  16  are hot, tars and particulates are minimized. Accordingly, the re-circulating gases  16  are not necessarily cleaned prior to re-circulating as gas  23  into the fire zone  18  of the gasifier, although such cleaning could be performed if desired. Note that the plenum  21  has a toroidal shape extending around the upper gasifier inner shell, as depicted by dotted line  24 . The final gas leaves as down-flow  27 , when operating as a co-current or downdraft gasifier ( 27  flow would be upwards when operating as an updraft gasifier), which combine to pass though a cross section restricted lower area (not shown) to finish burning of tars and then exiting the gasifier. As mentioned above ash or slag removal can be accomplished in the manner described above. Note that the blower impeller  19  and the down-flow tubes  22  are located within the gasifier steel shell  5 , which if pressurized more, the upper design horsepower for motor  31  increases and thickness of impeller  19  increases as gases  16  become more dense. 
     While the tar content of the re-circulated gas  16  will be small at these higher temperatures, there may be some particulate matter and tar that could plug the down-flow tubes  22 . To insure the ceramic tubes  22  do not plug from any tars and particulate that may be blown by the impeller  19 , air  29  is periodically injected through valves  30  causing a fire to happen within plenum  21  and the down tubes  22  (like a chimney fire, but the fire is blown downwards) to burn off this material whose ash combines to form a part of gas injection  23 . The valves  30  are purged with nitrogen (not shown) so they will not be damaged when there is no air flow  29 . Also, the speed of the blower impeller  19 , as driven by variable speed motor  31 , is determined by the maximum allowable temperature of the re-circulated gas  16  as measured by thermocouple  32 , which must not exceed the temperature rating of the blower, which is generally about 2000 F. Item  33  is the seal and bearing area of the blower housing  20 ; the arrangement of this is well known in the art, including materials, cooling slingers, gas purging, and any other means to insure a long life for blower impeller  19  and inner case  20 . 
     Referring to  FIG. 7 , yet another embodiment of a pressurized gasifier  16  is shown. In this embodiment, fuel  1  is periodically fed to a holding hopper  4  using a conveyor  2 . A level probe  3  determines when the hopper  4  is full to shut off the conveyor  2 . Another level probe  5  measures material level in a lock hopper  6 . When level probe  5  determines the lock hopper  6  is near empty (as shown), a discharge dome valve  8  is closed and the hopper  6  is decompressed by opening valve  7 , and then dome valve  9  opens to allow fuel  1  from the filled chute hopper  4  to rapidly fill lock hopper  6 . Just enough material is added to chute hopper  4  each fill cycle to refill hopper  6 . Hopper  4  can have air inlets  10  (one shown) to prevent any suction effects from the rapid flow of material out of hopper  4  from flowing through valve  9 , and/or vibrators  11  (one shown) to assist the rapid discharge of hopper  4 . Hopper  4  can also be lined with HDPE plastic sheet to facilitate flow. When the hopper  4  is emptied (and hopper  6  is refilled), valve  9  is closed, hopper  6  is re-pressurized with gas via valve  14 . The gas could be air, CO2, nitrogen, or any other suitable gas applicable to the gasifier design. Then, the valve  8  is reopened so unloader drive  12  can begin to rapidly unload hopper  6  of material  20  to replenish fuel zone  18  inside the gasifier  16 , now at a lower level due to the refill time interval for hopper  6  to reestablish upper level  17  as measured by level probe, which can be a radar probe. 
     Unlike most lock hoppers, hopper  6  has an unloader so as to be able to handle a larger range of material, and it consists of electric motor gear head drive  12  supported by channel iron supports  13 , the speed of drive  12  is controlled by the level probe  15 . The lower the level  17  of upper feed zone  18  of gasifier  16 , the faster the drive  12  is operated to refill zone  18  faster. Drive  12  has a double ended shaft to both drive a top circular disk  19  which orientates material  20  and prevents uncontrolled flow through opening  22 . There is unloader plate  21  with opening  22 , and a lower unloading floating flat plate  23  driven by a loose spline arrangement (not shown) on the lower shaft of drive  12 , plate  23  resting and freely able to orient to plate  21  to eliminate binding forces. Plate  23  has a helical shaped leading edge cut so as to spiral material into the opening  22 . The material  20  flows through a chute  31  into the fuel zone  18 . As noted above, the level of material in zone  18  is allowed to drop while the lock hopper  6  is being refilled by hopper  4 . This simplifies the feed arrangement and takes maximum advantage of the fresh fuel zone  18 , the level surge of which will have no deleterious effects on gasifier operation since this is the fresh fuel zone  18  where essentially no gasification is taking place. 
     The gasifier  16  has a re-circulating blower  23  driven by a variable speed motor  24  and re-circulation tubes  29  and  30  formed in the wall of the gasifier shell and running lengthwise therein. There is constant speed stirrer  25  with blades  26  and  27 , shaft seals not shown. Air injection valves  28  (one shown) enables the re-circulation tubes  29  and  30 , respectively, to periodically be burned free of accumulating soot matter. There is a water cooled chute  31  that creates upper zone  18  in the upper gasifier area but also an empty zone  32 , which is where re-circulating gas  33  enters blower  23 , and empty zone  32  also allows particulate to settle by gravity to level  34  before gas  33  is driven down tubes  29  and  30  respectively. There can be as many tubes as desired to achieve the total gas flow. Level  34  is created by virtue that the gasified material  35  is moving down through the gasifier inner space generally seeking the angle of repose shown due to the chute  31  being offset from the center of the gasifier shell. 
     The temperature of the exit gas  36  is measured by thermocouples  37 , and the speed of blower motor  24  is sufficient to pull hottest lower gases  38  at a rate up though the whole fuel mass  35  such that gases  36  and  33  are of sufficient temperature (generally over 1600 F) to be free of tars. The blower wheel (not shown) of blower  23  is cooled and steam cleaned by flows (not shown) via a double ported rotary valve  27 . The temperature of gas  33  leaving the blower  23  is also measured (sensor not shown) to insure the blower is not overheated, although as noted it is cooled by coolant flows though  27 . Gasifier  16  is generally highly pressurized (although it can be an atmospheric pressure blown gasifier) and gas  36  leaves through tuyeres  39  (only one shown). The temperature of gas  36  can also be influenced or controlled by how much hot gas  33  circulates through bypass three way valves  40  and  41  respectively, thus how much enters lower tubes  44  and  45  respectively to burn in fire zone  46 , increasing the temperature of the hot fire zone  46 . Steam injection  47  (only one shown) can also be used to assist in controlling the temperatures of gases  33  and  36 . 
     Three way valve  41  is inserted in rammed refractory  49  (which can alternatively be a water wall) to intersect gas flow though tubes  29  and  30  respectively. Valve  41  has an operator  50  on one end with a shaft  51  stuffing box (not shown) to accommodate the gasifier pressure. The shaft  51  is attached to sliding ceramic block  52  causing it to slide in or out horizontally as needed. Block  52  has a through opening  53  to allow gases  55  to pass through down to the lower tube area  45 , but also has a wedged shaped inner end  54 , which if the block  52  is pushed all the way in by operator  50 , will block off all the upper gas flow  43  and all gas  33  in tube  30  flows at  55  to make a hotter fire in zone  46 . The steam in gas  33  from drying fuel  1  is uniquely positioned whether as flow  43  or  55  to enhance gasification reactions in zone  46  and has the effect to reduce the steam flow  47 . Thus, re-circulating gas flow  33  in this way has the effect of achieving similar gasification efficiency as if fuel  1  were dry since 30-40% of dry fuel mass  1  must be steam addition to gasify properly, and this steam is made from extra dry fuel added. Thus, fuels as wet as 40% will not appreciably affect the overall thermal efficiency of the gasifier or result in any more fuel  1  to be added on a dry measured basis (more weight of fuel  1  is of course added than dry fuel on a wet basis). Valve  40  is designed to operate the same way as  41 . Since the gas is only re-circulating within the inner gasifier itself, there is minimal pressure drop across the valves to control bypass gas flows  43  and  55  respectively. Therefore, valve block  52  does not need to be a tight fit within valve  41  to perform its intended function. Generally, not over thirty to forty inches of water backpressure is expected from fire zone  46  up through hot zone  32 . 
     For some coal fuels, the lower area of zone  18  will be where coal caking occurs, thus the lower stirrer  27  serves to break up this caking. It&#39;s in zone  18  that the volatile compounds are driven off and enter with gas flow  33  whereby temperature in this area  32  are maintained high enough to insure the gas  33  is also free of tars along with the exit gas  36 , i.e. the gas  33  is at least 1600 F or higher in temperature to avoid tars in either gases  33  and  36 . There are ample means to control the upper temperature of these gases  33  and  36 . 
     Gasifier  16  as shown is a slagging gasifier, but it could be non-slagging as well using an ash unloader as described for the feed lock hopper  6  with rotating components water cooled. The slagging discharge lock hopper is not shown. The two oxidant blasts  56  and  57 , respectively, are maintained of sufficient flow to maintain an exit gas  36  having a CO2 concentration to about 5% (CO2 measurement instrument is not shown but would be a pressure reducing gas sampling device to an atmospheric CO2 probe taken near temperature sampling area  37 ) and at the least hot enough temperature in zone  46  such that slag  58  flows around baffle  59  and out tap hole  60  into a slag quenching and lock hopper (not shown). To add another degree of freedom to maintain or control slag as molten, a water cooled copper induction coil  61  is shown mounted around the entrance of the slag hole  60 , getting coolant and high frequency current in through copper tubes  62  and  63  respectively to provide extra heat energy to maintain molten conditions of slag  58 . Note that blasts  56  and  57  cooperate with re-circulating gas blasts  55  to form trajectory burning zones  64  and  65  which projects the hottest fire away from the inner ends of these blast tubes or nozzles, all of which can be water cooled as necessary. The thermocouples  48  (only one shown) in zone  46  would generally be gas-cooled thermocouples with at least two installed, with one as a backup. If zone  46  is not high enough in temperature to maintain molten slag  58  conditions, flux agents can also be added with fuel  1 , or as noted, the induction coil  61  can be designed into the base of the tap hole  60 . The separate tube  66  denoted by a dotted line allows steam flow made from quenching the slag in the quench tank space (not shown) to be separately introduced into the void space  65  which, and due to the suction created by the high velocity flows  57  and  55 , which could have adjustable nozzles, will suction this steam away from the tap hole discharge end. 
     While specific embodiments of the present invention have been described, it should be noted that various modifications thereto can be made without departing from the spirit and scope of the invention as defined in the appended claims.