Pulverized coal pressurized gasifier system

Abstract

A gasifier system includes a gasifier chamber, a plurality of nozzles or burners injecting and combusting a mixture including coal and oxygen within the gasifier chamber, and an ash bed disposed proximate a bottom of the gasifier chamber. Concurrent flow is generated within the gasifier such that gas and bi-products generated by the combustion of the mixture flow through the ash bed. The ash bed serves as a filter and reducing volume for the trace carbon not gasified during the combustion process. The hot gases exit the gasifier and enter a gas cooler and then a hot gas filter. Ash is unloaded from the gasifier chamber and is transferred into a quench tank, where ash settles and is removed to atmospheric conditions by a progressive pitched dewatering screw press. The dewatering screw press also serves as a seal to prevent excessive water escaping from the high pressure of gasifier operation.

Description

TECHNICAL FIELD

[0002] The present invention relates to a gasifier and more particularly, relates to gasifier system having an ash bed and a concurrent flow there though.

BACKGROUND INFORMATION

[0003] Currently, pressurized coal gasification processes have been either fluidized bed or transport reactor types that are usually oxygen instead of air blown, thus greatly increasing their capital and operating costs. These apparatus utilize various methods, such as cyclones and the like, to trap escaping carbon and reprocess it. These known methods, however, do not have specific reducing zones that can trap trace carbon or char to complete those reactions.

[0004] Moreover, because the known systems utilize pure O2 they suffer from greatly increased parasitic losses that reduce the system's power generating efficiency up to 15% the available electricity when used for power generating purposes. Moreover, the known methods do not provide built-in means to quench ash to recover the energy in the form of steam, or to dewater, isolate, and reject ash residue for both the gasifier and necessary hot gas filter.

[0005] Accordingly, what is needed is a system that is capable of utilizing atmospheric air rather than pure O2. The system should be capable of reducing the parasitic losses, thus increasing the system's efficiency from the current approximate 35% power conversion efficiency to approximately 50% power conversion efficiency.

SUMMARY

[0006] The present invention features a method of combusting and gasifying carbonaceous materials and a gasifier system. The method of gasifying carbonaceous materials comprises combining carbonaceous materials, such as coal and the like, with an oxygen, preferably atmospheric air, and water source to create a mixture that is injected and combusted in a gasifier such that a concurrent flow is generated within the gasifier. During the combustion processes, water, preferably steam, is added to control combustion temperatures, thus gasifying the carbonaceous materials. Carbon monoxide and hydrogen gas and bi-products are generated which then flow through an ash bed that is in fluid communication with the gasifier. In the preferred embodiment, the ash bed is disposed within the gasifier. The ash bed filters and reacts at least some of the bi-products from the gas such as char into carbon monoxide and hydrogen gases.

[0007] In the preferred embodiment, the method also includes controlling the ash bed's porosity such that the gas can flow through the ash bed. The porosity may be controlled by adding an inert material to the ash bed to maintain the ash bed's porosity such that it is sufficient to permit free air flow yet trap char and other bi-products from the gasification/combustion process in the previous entrained combustion volume. Optionally, the carbon dioxide level in the gas within the gasifier is monitored and is used to adjust the air/fuel ratio within the gasifier. Lime may also be added to the air/fuel mixture to reduce sulfur concentration.

[0008] The method also preferably includes maintaining the ash bed's height within the gasifier, and includes removing material from the ash bed. The material removed from the ash bed enters a quench tank wherein energy, in the form of steam, is recaptured. The liquid-soaked material is then removed from the quench tank wherein substantially all of the liquid is removed using a dewatering screw.

[0009] The gas generated by the gasifier is then preferably cooled using a heat exchanger, and is then filtered preferably using a high efficiency 99.99% efficiency filter. Energy, in the form of steam, may also be recaptured from the particulate removed by the filter using the same process described above. The filtered gas may then be used to generate energy, for example by powering a turbine.

[0010] The gasifier system includes a gasifier chamber, a plurality of nozzles or burners, and an ash bed region. The plurality of nozzles inject a mixture including carbonaceous materials and an oxygen, preferably atmospheric air, and water source wherein the mixture is combusted under theoretical air/fuel mixture levels within the gasifier to form a hot gas mixture. In the preferred embodiment, the ash bed region is disposed proximate a bottom of the gasifier chamber and is adapted to contain an ash bed. Alternatively, the ash bed region is disposed in a second chamber that is in fluid communication with the gasifier. A concurrent flow is generated within the gasifier such that gas and bi-products generated by the combustion of the mixture flow through the ash bed and out of the gasifier system.

[0011] The gasifier preferably includes a distributor that distributes the air/fuel mixture to the plurality of nozzles or burners. In the preferred embodiment, the gasifier also includes at least one sensor to determine carbon dioxide levels of the gas and one temperature sensor to determine the steam blast. The carbon dioxide levels are used to adjust the air/fuel ratio within the gasifier chamber and the steam blast is used to adjust the combustion temperature of the incandescent gasification reaction in the entrained flow area of the gasifier chamber.

[0012] The gasifier may also include an unloader to remove material from the ash bed. A liquid bath is preferably used to recover a portion of the energy as steam contained in the material removed from the ash bed. A dewatering screw then preferably removes substantially all of the liquid from the liquid-soaked material and removes the material from the gasifier system.

[0013] The gasifier system also preferably includes a downstream gas cooler, such as a fire tube boiler, and a filter to remove any remaining particulates entrapped in the gas. The filtered gas may then be used to generate power using, for example, a gas turbine. The filter may also include a quench tank to recapture some of the energy of the filtered particulates in the form of steam. The quench tank is preferably the same as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein:

[0015] FIG. 1 is a schematic view of one embodiment according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A gasifier system 1, FIG. 1, according to the present invention, includes one or more fuel tanks 2 (one shown), a distributor 3, a gasifier 4, a gas cooler 5, and a hot gas filter 6. The operating pressure of the gasifier system 1 will depend on many factors, such as the gas turbine used in the integrated gasification combined cycle (IGCC) power system, and is within the knowledge of one skilled in the power systems art. The gasifier system 1 may operate at virtually any pressure greater than, or equal to, atmospheric pressure. In the exemplary embodiment, the gasifier system 1 operates at a relatively high pressure, for example 225 psi or more.

[0017] One or more fuel tanks 2 contain a carbonaceous fuel 13, for example pulverized coal and lime to remove sulfur pollutants by reaction within the gasifier 4. These reactions are well known to those skilled in the art. For simplicity, a single tank is shown containing a mixture of pulverized coal and additives, for example, but not limited to, lime. In the preferred embodiment, multiple fuel tanks 2 are used to allow for more precise control of the fuel 13 and lime ratio, as well as any other fuels or additives such as inert materials to control porosity in the ash bed 31. These inert materials would be used with fuel 13 having very low ash levels, or that generate a very fine ash when burned. According to the preferred embodiment, the fuel tank 2 preferably includes a filling isolation valve 7, a vent valve 8, a lower discharge isolation valve 9, and a feed isolation valve 10, though the exact design of the fuel tank is not a limitation of the present invention.

[0018] When tank 2 is filled, for example after being emptied, isolation valve 9 and a feed isolation valve 10 are closed, and isolation valve 7 and vent valve 8 are open, the reverse being true when tank 2 is unloading into gasifier 4. The tank is filled using pulverized fuel mix and fill conveyor 11. Nitrogen purging for filling and pressurizing operation for pulverized coal tank 2 are not shown, but are well known to those skilled in the art.

[0019] Tank 2 preferably includes an explosion proof sonic level sensor 15 to sense the level 16 of the fuel mix 13. When the level 16 of the fuel mix 13 is low, the level sensor 15 signals the controller (not shown) to switch between tanks 2, for example by gradually closing valves 9 and 10, while opening a comparable valves on the additional tanks 2 (not-shown). As a result, a seamless flow to the same input point on distributor 3 in maintained. The exact size, shape, and operation of the fuel tanks 2 depend on many factors such as, but not limited to, the desired fuel flow rate and refilling parameters, and are within the knowledge of one skilled in the art and are not a limitation of the present invention.

[0020] The fuel mixture 13 is then combined with air 12 in, for example, a rotary feeder isolation valve 14. The air 12 may include pure oxygen O2, but preferably includes atmospheric air containing other gases, for example nitrogen, carbon dioxide, and other naturally occurring gases. The gasifier system 1 preferably operates in a temperature range between about 1600° F. to about 1800° F., though it can operate at higher or lower temperatures. Operating the gasifier system 1 at temperatures above 1800° F. increases maintenance and equipment costs since, for example, the filters need to be capable of withstanding the temperature. The temperature of the gasifier chamber 24 is preferably controlled by adjusting the amount of steam 39 introduced into the gasifier chamber 24.

[0021] The fuel mixture 13 and air 12 then flow into a distributor 3. The distributor 3, for example a high pressure steam-randomized ellipsoid fuel distributor or a chamber with a rotary device to create chaos, is shown with a plurality of fuel inducing randomizing steam jets 17 and 18 that are part of the distributor's 3 inducer 19. The distributor 3 is preferably connected to the gasification chamber 24 within the gasifier 4 using one or more nozzles or burners 20 and 21, and control valves 22 and 23. The number and location (for example elevation) of the nozzles 20 and 21 will depend on the size and flow rate of the gasifier system 1. For exemplary purposes only, gasifier turndown capability can be increased while maintaining high agitation and velocity of steam injected fuel into the gasification chamber 24 with decreased load by shutting off feed valve(s) 22 and leaving 23 open.

[0022] The gasifier 4 preferably includes a refractory coated or lined metallic shell 30, which defines gasifier chamber 24 and ash bed 31. In the preferred embodiment, the shell 30 extends into ash bed 31, but stops short of the ash hearth 32, thus allowing the gas 33 to escape around the base of shell 30 and into annular space 27 having at least one gas outlet 37. The ash bed 31 is preferably disposed proximate the bottom of the gasifier chamber 24 and is formed as combustion ash and unreacted carbon are created from the combustion of the fuel mixtures 13. Inert material such as, but not limited to, volcanic rock material, may be added to maintain the porosity of the ash bed 31. Alternatively, the ash bed 31 may be disposed in a separate enclosure (not shown) that is in fluid communication with the gasifier chamber 24. In this embodiment, the outlet 37 is sized to increase the velocity of the gas to ensure that the bi-products generated by the combustion process exit the gasifier chamber 24 and enter the ash bed 31.

[0023] In the preferred embodiment, the gasifier 4 includes high temperature surfaces and partitions exposed to hot gas water cooled and is insulated and lined inside with refractory (not shown) to maintain uniform temperature conditions of incandescent fire 26 in gasification chamber 24. The gasifier 4 also includes gas exit annulus 27 as well as piping between the gasifier 4, gas cooler 5, hot gas filter 6 to contain and optimize gasification reactions and to minimize NOx formation.

[0024] The gasifier chamber 24 preferably includes one or more gas sensors 29, 38 connected to the main system controller (not shown) that measure a variety of states such as temperature, CO2 concentrations and other gas constituents. As mentioned, in the preferred embodiment the gasifier system 1 operates in the 1600° F. to 1800° F. temperature range. Within this temperature range, the CO2 concentration within the gasifier chamber 24 can be monitored and the air fuel ratio, a/f, adjusted to the optimum ratio, for example the stoichiometric a/f ratio. For any given fuel flow 13 and air flow 12 (air flow measurement method not shown), sensors 29, 38 cooperate to determine final steam blast 39 and 40 of nozzles 20 and 21 respectively to properly control gasification chamber 24 gas temperature.

[0025] Hot-gas 43 exits down through the ash bed 31 where ash and any free carbon are trapped or filtered. Free carbon or char reducing reactions also take place within the ash bed 31 and change substantially all the free carbon to hydrogen and carbon monoxide that ultimately become part of final gas flow 33. These reactions are well known to those skilled in the art. The ash bed's 31 ability to filter and react the bi-products and gases formed by the combustion process depends on numerous factors, such as, but not limited to, the operating temperature, pressure, as well as the ash bed's density and dimensions. These factors are within the knowledge of one skilled in the art.

[0026] The gas, now referred to by numeral 33, passes around the base of inner ash bed cylinder 30 and passes up annular space 27 as shown. Annular space's 27 cross-section area is designed to maintain exit velocity of final gas 33 to under approximately two feet per second to minimize ash carryover into other following processes. Gas flow 33 is under gas turbine boosted compressor pressure to overcome pressure loses through the system (booster not shown).

[0027] Proximate the bottom of hearth 32 is the ash unloader 44. The ash unloader 44 removes ash from the ash bed 31 as described above, thus maintaining the height 28 of the ash bed 31. The design of the ash unloader 44 is not intended to be a limitation of the present invention, but in the preferred embodiment, the ash unloader 44 is a floating inward helix and includes a loose spline drive 45 disposed on outer shaft 46 driven by a drive motor 47. The inward spiraling helical plate 44 has thicker outer radius than the inner radius, as shown, to maintain a lower ash level in the annular space than the ash bed total thickness 28. The exact dimensions of the inward spiraling helical plate 44 will depend on the particular system, and are within the knowledge of one skilled in the art.

[0028] In one embodiment, the outer helical plate drive shaft 46 includes upper and lower cross beams 50 and 51 with upper bearing 52, all submerged within the a heat exchanger 41, for example a quench tank 53. The bearing of gear head 49 serves the function of bearing 52 on lower bar 51. The inner concentric shaft 54 to outer shaft 46 preferably includes carbon or ceramic bearing assemblies (not shown) that can withstand hot water conditions. The inner concentric shaft 54 is preferably driven by motor 55 through horizontal shaft 56 through liquid/tight bevel gear 57. Continuous rotating stirring bar 58 is disposed on inner shaft 54 and circular unloader hood 59 is disposed on intermittent rotating shaft 46 and is cooled by liquid 61, preferably water. Steam 64 and 65 emendating from passageways within stirrer 58 and circular hood 59 respectively become superheated steam and combine with gas flow 33. Circular hood or disk 59 is designed to overlay the smaller diameter ash outlet opening 66 of the hearth 32 and thus prevent free fall of ash through hearth center circular opening 66 where unloaded ash 60 is seen to pass into quench tank 53. Steam 67 evaporating from quench tank 53 also combines with gas flow 33.

[0029] In the preferred embodiment, unloaded ash 60 is mixed in quench tank 53 having a water level 68 with a mix paddle 69 disposed on outer shaft 46. The paddle 69 mixes the ash 60 and quench water 53, hereinafter referred to as soaked ash 83, whereby ash fines flocculent 70 can be added, if needed, to cause ash fines to agglomerate for the ash screw press 76. A water level sensor 72 is preferably used to determine when to add makeup water 73 to quench tank 53. Agglomerated ash settles to form ash level 74. One or more ash level sensors 75 detect the ash level 74 and control the dewatering screw 76.

[0030] The dewatering screw 76 is preferably operated by turning on motor/gearhead 77, though any means of operating the dewatering screw 76 can be used. The dewatering screw 76 both removes the soaked ash 83 from the quench tank 53 and also removes most, about 50%, of the water from the soaked ash 83 while still maintaining the high pressure within the gasifier system 1. The diameter of the opening of the dewatering screw 76 is preferably smaller than the diameter of the exit of dewatering screw 76. When dewatering screw 76 is operating, ash discharge valve 79 opens to discharge the highly dewatered ash 80 to receiving tank 81.

[0031] In the preferred embodiment, the dewatering screw 76 includes four “zones”. The first “zone” includes the inlet zone 82 for soaked ash to 83 be dewatered. The second “zone” includes a screened inner housing zone 84 through which typical dewatered water flow 87 passes to combine with water 53. The third and fourth “zones” include the seal zone 85 and the ash rejection/outlet section 86. The seal zone 85 is preferably a short section of housing prior to the discharge section 86 to prevent water from leaking by into the ash outlet 79. Dewatered ash 80 is then introduced onto takeaway conveyor 89, and any remaining water 88 (for example water 88 that leaks by the seal zone 85) accumulates in tank 81 and is recirculated back to the quench tank 53.

[0032] Gas 33 passes flows into gas cooler 5, preferably through isolation valve 96, which reduces the temperature of the gas 33. The cooler 5 is currently necessary because the cost associated with designing the filter 6 and turbines (not shown) that can operate at the gasifier system's 1 temperature are extremely high. For optimum efficiency, however, the cooler 5 should be removed. Optionally, a vent pipe 97 and valve 98 may be provided that can divert start-up gas through valve 98 when valve 96 is closed to flare burner 99 until the gasifier 4 is producing a reliable hot gas.

[0033] The cooler 5 includes known heat exchanger such as, but not limited to, cooling coils, pipes, fire tube boiler, or the like 101. In a preferred embodiment, the cooler 5 uses water 100, though other means known to those skilled in the art of cooling the gas, such as evaporation chillers, atmospheric coolers, and the like, may also be used. Within the cooler 5, the water 100 is converted to steam 102 which may be combined with other steam operations which is well known to those skilled in the art of integrated gasification combined cycle (IGCC) design or the steam 102 may be used for injection into the gasifier for combustion temperature control. Cooled gas 103, and any blow-down, passes from the base of cooler 5 and is transported into gas filter 6 through pipe 104 and isolation valve 105. The gas filter 6 removes any particulates that pass through the ash bed 31, and typically would have 99.99% particulate removal metalized candle filter array 106. Other filter designs and efficiencies are also contemplated depending on environmental concerns as well as downstream equipment requirements.

[0034] Filtered gas 108 passes from the gas filter 6, for example through top pipe 109, for use downstream. Periodically, high-pressure nitrogen back pulses (system not shown) may be utilized to blast away ash 110 from the candle filter surfaces of array 106. When such blasting occurs, flapper-valve 111 (for example having a built-in rotary actuator) opens to quench tank 112, and typical vibrating wall units 113 are activated to facilitate ash flow into quench tank 112. After nitrogen back pulsing of filters ceases, the flapper valve 111 closes. Valve 111 does not have to be tight fitting since it serves to insulate the lower quench water volume 114′ from the hot gas stream above to slow down steam evaporation 114 from water level 115 which quickly becomes superheated steam. Such superheated steam 114 is not harmful to filter elements 106. The small amount of evaporated water 114 becomes superheated and combines with the final filtered gas 108 as shown. Water level sensor 116 determines make-up flow 117 through double check valve 118 from pump 119 as in gasifier 4. Also, as with the gasifier 4 ash quench tank, there is settled ash interface rotating paddle level sensor 120 in the filter quench tank 112. Flocculent 121 is added to quench water 114′ by combination ash flocculent pump and stirrer 122, which has shaft and agitator 123. The remaining parts of the filter ash dewatering and discharge to atmosphere are identical in function to the gasifier, and so are not be described again here.

[0035] Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims.

Claims

1. A method of combusting carbonaceous material comprising the acts of: combining carbonaceous material with an oxygen and water source to create a mixture; injecting said mixture into a gasifier such that a concurrent flow is generated within said gasifier; gasifying said mixture within said gasifier to generate a gas and bi-products; and passing said gas and said bi-products through an ash bed.

2. The method as claimed in claim 1 wherein said ash bed is disposed within said gasifier.

3. The method as claimed in claim 1 wherein said ash bed is in fluid communication with said gasifier.

4. The method as claimed in claim 1 wherein said act of passing said gas through said ash bed filters at least some of said bi-products from said gas.

5. The method as claimed in claim 1 wherein said act of passing said gas through said ash bed reacts at least some of said bi-products from said gas to form other materials.

6. The method as claimed in claim 1 further comprising the act of controlling said ash bed's porosity such that said gas can flow through said ash bed.

7. The method as claimed in claim 6 further comprising adding an inert material to said ash bed to maintain said ash bed's porosity.

8. The method as claimed in claim 1 further comprising the act of maintaining said ash bed's height.

9. The method as claimed in claim 8 further comprising the acts of removing material from said ash bed and recapturing a portion of the heat energy from said material.

10. The method as claimed in claim 9 wherein said act of recapturing heat energy from said material includes quenching said material in a quench tank.

11. The method as claimed in claim 10 further comprising the act of removing substantially all of said liquid from liquid-soaked material and removing said material from said gasifier.

12. The method as claimed in claim 11 wherein said act of removing said liquid from said liquid-soaked material and removing said material from said gasifier includes using a screw-dewater.

13. The method as claimed in claim 1 wherein said act of injecting said mixture into said gasifier further includes distributing said mixture into a plurality of nozzles using a distributor.

14. The method as claimed in claim 1 further comprising powering a turbine with said gas.

15. The method as claimed in claim 14 further including the act of removing substantially all of said remaining bi-products from said gas before said act of powering said turbine in a filter.

16. The method as claimed in claim 15 wherein further comprising cooling said gas prior to said act of filtering said filtering said gas.

17. The method as claimed in claim 16 wherein said act of removing substantially all of said remaining bi-products from said gas includes cooling said bi-products in a quench tank.

18. The method as claimed in claim 17 further comprising the act of removing substantially all of said liquid from liquid-soaked bi-products and removing said cooled bi-products from said filter.

19. The method as claimed in claim 18 wherein said act of removing said liquid from said liquid-soaked bi-products and removing said bi-products from said filter includes using a screw-dewater.

20. A gasifier comprising: a gasifier chamber; a plurality of nozzles, said plurality of nozzles injecting and combusting a mixture including carbonaceous mixture and an oxygen and water source within said gasifier chamber to cause gasification; and an ash bed region in fluid communication with said gasifier chamber, said ash bed region adapted to contain an ash bed wherein said a concurrent flow is generated within said gasifier such that gas and bi-products generated by said gasification of said mixture flow through said ash bed.

21. The gasifier as claimed in claim 20 wherein said ash bed region is disposed proximate a bottom region of said gasifier chamber.

22. The gasifier as claimed in claim 20 wherein said ash bed region is disposed in a second chamber.

23. The gasifier as claimed in claim 20 further including a distributor, said distributor distributing said mixture to said plurality of nozzles.

24. The gasifier as claimed in claim 20 further comprising an unloader to remove material from said ash bed.

25. The gasifier as claimed in claim 24 further comprising a quench tank to recapture a portion of the energy contained in said material removed from said ash bed region.

26. The gasifier as claimed in claim 25 further including a dewatering screw to remove substantially all of said liquid from said liquid-soaked material and to remove said material from said ash bed region.

27. The gasifier as claimed in claim 20 further including a mixer disposed within said ash bed region.

28. The gasifier as claimed in claim 20 further comprising a heat exchanger in fluid communication with said ash bed region, said heat exchanger reducing the temperature of said gas generated by said gasifier.

29. The gasifier as claimed in claim 28 further comprising a filter in fluid communication with said heat exchanger for removing any particulates in said gas.

30. The gasifier as claimed in claim 29 further comprising a quench tank in fluid communication with said filter.

31. The gasifier as claimed in claim 30 further including a second dewatering screw to remove substantially all of said liquid from said liquid-soaked particulates and to remove said particulates from said filter.

32. The gasifier as claimed in claim 20 further comprising a turbine in fluid communication with said gasifier wherein said gas generated by said gasifier rotates said turbine.