US20100313796A1

US20100313796A1 - Biomass gasification in atmospheres modified by flue gas

Info

Publication number: US20100313796A1
Application number: US12/860,759
Authority: US
Inventors: Robert G. Graham; Dejan Sparica
Original assignee: Nexterra Systems Corp
Current assignee: Nexterra Systems Corp
Priority date: 2006-05-18
Filing date: 2010-08-20
Publication date: 2010-12-16
Also published as: BRPI0711715A2; US20070266914A1; US20120137582A1; EP2032503A4; CA2649285A1; WO2007136786A1; EP2032503A1

Abstract

Systems and methods are provided for generating energy from biomass. A gasifier is provided for generating syngas from the biomass. The gasifier comprises a housing for providing a first, oxygen starved environment in which the biomass is sub-stoichiometrically combusted to generate syngas—an effluent comprising gaseous combustibles. An oxidizer is connected to receive the syngas from the gasifier and configured to oxidize the syngas in a second environment distinct from the first, oxygen starved environment and to thereby generate heat energy. An oxidative agent supply mechanism introduces an oxidative agent to the first, oxygen starved environment in the gasifier housing, the oxidative agent comprising a mixture of flue gas and air.

Description

REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No. 11/801,030 filed 8 May 2007, entitled: METHOD FOR GASIFYING SOLID ORGANIC MATERIALS AND APPARATUS THEREFOR. This application claims the benefit under 35 USC §119(e) of the priority of U.S. provisional patent application No. 60/801,574 filed 18 May 2006.

TECHNICAL FIELD

This disclosure relates to the gasification of, and generating of energy from, solid organic materials and to the production of syngas. Particular embodiments provide methods, apparatus and systems for gasifying, and generating energy from, solid organic materials and generating syngas.

BACKGROUND

It has been recognized that many industrial and agricultural solid organic by-products, such as forestry and agricultural residue, and the like, are a potential source of chemical energy. Substantial increases in the cost of traditional fuels, such as fuel, oil and natural gas, have provided corresponding economic incentive to try to develop effective and efficient techniques for recovering the energy in these organic by-products, energy that traditionally was not recovered to any substantial extent. Such organic materials, frequently referred to as “biomass” materials, are now successfully utilized to some extent as fuel in some large industrial systems, for example, in firing the power boiler and the recovery boiler in a pulp or paper mill. However, the high capital cost that has heretofore been associated with biomass energy recovery systems has precluded their successful use in small or even medium-sized energy recovery systems.
Medium-sized energy recovery systems are used in community centers, schools, nursing homes, and small industrial and commercial establishments and, to date, biomass fuels have not been satisfactorily utilized as fuels in heating systems for such facilities. U.S. patents disclosing technology relating to the recovery of energy from wood chips or similar organic materials include, for example: U.S. Pat. No. 5,138,957 that issued to Morey, et al. on Aug. 18, 1992; U.S. Pat. No. 4,184,436 that issued to Palm, et al. Jan. 22, 1980; U.S. Pat. No. 4,312,278 that issued to Smith, et al. on Jan. 26, 1982; U.S. Pat. No. 4,366,802 that issued to Goodine on Jan. 4, 1983; U.S. Pat. No. 4,321,877 that issued to Schmidt, et al on Mar. 30, 1982; U.S. Pat. No. 4,430,948 that issued to Schafer, et al. on Feb. 14, 1984; U.S. Pat. No. 4,593,629 that issued to Pedersen, et al. on Jun. 10, 1986; U.S. Pat. No. 4,691,846 that issued to Cordell, et al. on Sep. 8, 1987; U.S. Pat. No. 4,971,599 that issued to Cordell et al. on Nov. 20, 1990, U.S. Pat. No. 6,120,567 that issued to Cordell et al. on Sep. 19, 2000 and Canadian Patent No. 2,058,103 that issued to Morey et al. on 14 Oct. 1997.
However, it is not known that any of the inventions described in these patents have been successfully adapted to recover biomass energy on a cost-effective basis in small and medium-sized energy recovery systems.

SUMMARY

Particular embodiments of the invention provide methods, apparatus and systems for gasifying solid organic materials and generating syngas which may be burned to create energy. Particular embodiments provide methods and apparatus that produce high energy, low temperature, and low particulate-laden syngas by controlling the oxygen content in combustion air used for “starved air” combustion of biomass in a gasifier. Recirculated flue gas mixed with an amount of fresh air is utilized for providing the oxygen content therein and for controlling the method.
Particular embodiments provide methods for gasifying biomass materials, such as forestry and agricultural residues, industrial waste materials such as saw mill pulp, paper products, fowl litter, such as chicken litter and turkey litter, and hydrocarbon based plastics and the like.
Particular embodiments provide apparatus used to convert the chemical energy of biomass materials into thermal energy or gaseous products, and specifically, syngas, that is also called production gas. Syngas is a compressible synthetic combustible gas containing very little particulate material. Thus, aspects of this invention can also be viewed as providing methods for producing syngas.
Aspects of the invention provide a method for gasifying solid organic materials, apparatus used in such methods, and systems incorporating such methods and apparatus. One aspect of the invention provides a gasifier for gasifying solid organic materials comprising in combination a housing, wherein the housing has a lower portion and an upper portion and a cylindrical side wall supported by the lower portion and attached to the upper portion.
In particular embodiments, the gasifier comprises a roof for the housing, the roof being supported by and integral with the cylindrical side wall. In some embodiments, there is at least one opening through the roof for exiting syngas effluent and at least one opening for a sensing device. In particular embodiments, the gasifier includes a device for removing the syngas from the gasifier which is located at, and connected to, the roof opening. In some embodiments, the gasifier includes, at the sensing device opening, one or more devices for sensing the elevation of any mass of any solid organic material contained in the housing. In some embodiments, the sensing device is a radar device that is mounted over the sensing device opening and surmounts a non-metallic plate that covers the opening.
Located in the lower housing, particular embodiments of the gasifier comprise one or more openings for supporting a device for determining the amount of non-combustible material (e.g. ash) remaining within the gasifier. In some embodiments, the device is located at, and connected to, the lower portion of the housing, and within the opening for determining the amount of non-combustible material (e.g. ash) remaining within the gasifier.
In particular embodiments, the gasifier comprises one or more openings in the cylindrical wall for supporting one or more devices for providing oxidative gas to the solid organic materials. In some embodiments, the oxidative gas comprises recirculated flue gas containing a predetermined portion of fresh air. In some embodiments, a device for providing the oxidative gas to the solid organic materials is located in, and connected to the oxidative gas opening.
In particular embodiments, a floor is located in the lower portion of the gasifier, the floor having a top surface and a bottom surface, and at least one opening therethrough to allow for the passage of solid organic material into the interior of the gasifier. In some embodiments, the top surface of the floor comprises a retaining wall on the outside of each of the floor openings to form a retention basin to retain the solid organic materials in the lower portion of the gasifier to form a floorless hearth.
Particular embodiments of the gasifier include a device for moving solid organic materials through the floor opening and into the gasifier in an upward motion and a device for providing and retaining a cone structure to the underside of the solid organic materials.
In some embodiments, the gasifier comprises a device for containing the solid organic materials while above the retention basin and one or more openings in the lower portion of the gasifier to allow movement of non-combustibles out of the gasifier, along with a device in the retention basin for removing noncombustible materials from the gasifier.
In particular embodiments, the gasifier comprises a control and monitor for the amount of mass of solid organic material within the gasifier and a control and monitor for the amount of non-combustibles in the gasifier.
Another aspect of the invention provides a square or rectangular “loaf” gasifier for gasifying solid organic materials. In particular embodiments, the loaf gasifier comprises a housing incorporating a lower portion and an upper portion and four side walls supported by the lower portion and attached to the upper portion.
The loaf gasifier has a roof supported by, and integral with, the four side walls. In some embodiments, the loaf gasifier comprises one or more openings through a side wall for exiting syngas effluent and one or more openings through the roof for a sensing device. In some embodiments, the loaf gasifier comprises a device for removing the gaseous effluent from the gasifier which is located at, and connected to, the side wall opening. In particular embodiments, the loaf gasifier comprises a device for sensing the elevation of any mass of any solid organic material contained in the housing which is located at, and associated with the sensing device opening. In some embodiments, the sensing device comprises a radar device that is mounted over any sensing device opening and that surmounts a non-metallic plate that covers the opening.
Located in the lower housing, particular embodiments of the loaf gasifier comprise one or more openings for supporting a device for determining the amount of non-combustible material (e.g. ash) remaining within the gasifier. In some embodiments, the device is located at, and connected to, the lower portion of the housing, and within the opening for determining the amount of non-combustible material (e.g. ash) remaining within the gasifier.
In some embodiments, the loaf gasifier comprises one or more openings in its side walls for supporting one or more devices for providing oxidative gas to the solid organic materials. In some embodiments, the oxidative gas comprises recirculated flue gas containing fresh air. In particular embodiments, a device for providing the oxidative gas to the solid organic materials is located in, and connected to the oxidative gas opening.
The gasifier of particular embodiments comprises a floor located in the lower portion of the loaf gasifier, the floor having a top surface and a bottom surface, and at least one opening therethrough to allow for the passage of solid organic material into the interior of the gasifier. In some embodiments, the top surface of the floor comprises a retaining wall on the outside of each of the floor openings to form a retention basin to retain the solid organic materials in the lower portion of the gasifier to form a floorless hearth.
In particular embodiments, the loaf gasifier includes a device for moving solid organic materials through the floor opening and into the gasifier and a device for providing and retaining a cone structure to the underside of the solid organic materials.
In some embodiments, the loaf gasifier comprises a device for heating the solid organic materials while above the retention basin and one or more openings in the lower portion of the gasifier to allow movement of non-combustibles out of the gasifier, along with a device in the retention basin for removing noncombustible materials from the gasifier.
In particular embodiments, the loaf gasifier comprises a control and monitor for the amount of mass of solid organic material within the gasifier and a control and monitor for the amount of non-combustibles in the gasifier.
In another embodiment, the circular gasifier described above is modified to alter the flow of effluent by providing a constriction in the midsection of the gasifier. This embodiment provides a gasifier for gasifying solid organic materials comprising a housing wherein the housing has a lower portion having a top part and an upper portion having a bottom part. The housing has a cylindrical side wall supported by the lower portion and attached to the upper portion. The cylindrical side wall has a constricted section where the top part of the lower portion and the bottom part of the upper portion meet and join.
In yet another embodiment of this invention, the loaf gasifier described above is also modified to provide a constriction in its side walls. This embodiment provides a loaf gasifier for gasifying solid organic materials comprising a housing wherein the housing has a lower portion with a top part and an upper portion with a bottom part. The housing has four side walls supported by the lower portion and attached to the upper portion. The side walls have a constricted section where the top part of the lower portion and the bottom part of the upper portion meet and join.
Another aspect of the invention provides a method for gasifying solid organic materials to produce a gaseous effluent and a solid residue. The method comprises providing a supply of solid organic material and providing a circular gasifier as set forth in this disclosure. Thereafter, the solid organic materials are introduced into the gasifier upwardly from a lower portion of the gasifier to provide a mass of solid organic materials in the gasifier. The solid organic materials are ignited and then heated in the gasifier while providing an oxidative gas to the gasifier. In particular embodiments, the oxidative gas comprises recirculated flue gas from a flue stack located in a system in which the gasifier is operating. In some embodiments, the oxidative gas comprises a combination of the flue gas and a predetermined portion of fresh air.
In particular embodiments, there is provided an effluent flow path in the gasifier for a portion of the gaseous effluent to migrate, mix, and react through the heated solid organic materials and the syngas formed thereby is transferred outwardly from the gasifier. Non-combustible solids are also transferred out of the gasifier.
Another aspect of the invention provides a method for gasifying solid organic material to produce a gaseous effluent and a solid residue. The method comprises providing a supply of solid organic material and providing a loaf gasifier as set forth in this disclosure. The method also involves introducing the solid organic materials into the gasifier upwardly from a lower portion of the gasifier to provide a mass of solid organic materials in the gasifier. The solid organic materials are ignited and then heated in the gasifier while providing an oxidative gas to the gasifier to provide a gaseous effluent. In some embodiments, the oxidative gas comprises recirculated flue gas from a flue stack located in a system in which the gasifier is operating. In particular embodiments, the oxidative gas comprises a combination of the flue gas and a predetermined portion of fresh air.
In particular embodiments, there is provided an effluent flow path in the gasifier for a portion of the gaseous effluent to migrate, mix, and react through the heated solid organic materials and the syngas formed thereby is transferred outwardly from the gasifier. Non-combustible solids are also transferred out of the gasifier.
Aspects of the invention provide systems that utilize each of the various gasifiers disclosed.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are schematic drawings showing gasifiers, apparatus and methods for gasification of biomass and producing syngas and corresponding portions of systems incorporating such gasifiers according to an example embodiment.

FIG. 2 is a front view of a circular gasifier according to a particular example embodiment.

FIG. 3 is a cross sectional front view of the FIG. 2 gasifier through line A-A.

FIG. 4 is an enlarged front view of a radar sensing device.

FIG. 5 is a perspective view of a segmented, round feed cone which may be used in gasifiers according to particular embodiments of the invention.

FIG. 5A is a perspective view of a unitary, round feed cone feed which may be used in gasifiers according to particular embodiments of the invention.

FIG. 6 is a perspective view of a segmented, square feed cone which may be used in gasifiers according to particular embodiments of the invention.

FIG. 6A is a perspective view of a unitary, square feed cone which may be used in gasifiers according to particular embodiments of the invention.

FIG. 7 is a cross sectional view of the area designated 28 of FIG. 3, showing an example of the detail of the moveable cone feed and the bottom tuyeres according to a particular embodiment.

FIG. 8 is a front view of a square or rectangular, loaf gasifier, according to a particular embodiment.

FIG. 9 is a cross sectional view of the FIG. 8 loaf gasifier through line B-B.

FIG. 10A is a cross sectional view of an example construction of walls having an insulation layer which may be used with particular gasifier embodiments.

FIG. 10B is a cross sectional view of another example construction of walls using air as insulation which may be used with particular gasifier embodiments.

FIG. 11 is an enlarged side view of the roof the FIG. 8 loaf gasifier according to a particular embodiment.

FIG. 12 is a cross sectional view of the FIG. 11 roof according to a particular embodiment.

FIG. 13 is a top view of an ash collection system suitable for use with particular embodiments of the FIG. 8 gasifier.

FIG. 14 is an angled side view of a gasifier according to a particular embodiment, with the sides open to show its ash-removal grate system.

FIG. 15 is a side cross sectional view of the FIG. 14 grate system through the line C-C.

DETAILED DESCRIPTION

FIGS. 1A and 1B (together, FIG. 1) are schematic representations of portions of an apparatus, method and system for gasification of, and generation of energy from, biomass according to an example embodiment. FIG. 2 is a front view of a circular gasifier 1 suitable for use as the gasifier of FIG. 1A. FIG. 3 is a cross sectional front view of the FIG. 2 gasifier through line A-A.
FIG. 1 shows a circular gasifier 1 according to a particular embodiment having an ash removal system 4 and a solid mass feeder 2 comprising a collection bin 5, connected by auger feed 3 to gasifier 1. In the illustrated embodiment, a portion of solid mass feeder 2 runs essentially horizontally 7 beneath gasifier 1 and then turns essentially ninety degrees vertically 8 and thus feeds gasifier 1 from the center of floor 9 of gasifier 1 (as shown in FIGS. 2 and 3). In horizontal run 7, solid mass feeder 2 may be shrouded or may comprise an open trough. In the illustrated embodiment, solid mass feeder 2 is covered by a shroud 6 enclosing auger feed 3 (as shown in FIG. 3).
In some embodiments, the solid mass materials are first comminuted or chopped, if it is forestry product, so that it will flow and be ignited readily. Generally this chopped material is best handled if the pieces are 3 inches or less in any dimension. If the solid mass material is chicken litter or turkey litter, then chopping is not required.
FIG. 2 is an enlarged front view of a circular gasifier, according to a particular example embodiment, showing gasifier 1, auger feed 3, shroud 6, horizontal run 7 and vertical run 8 of solid mass feeder 2. Gasifier 1 comprises a housing 10 that has a cylindrical side wall 11 supported by the lower portion, generally shown as 12, of housing 10. Cylindrical side wall 11 is attached to the upper portion of housing 10, indicated generally as 13. Housing 10 is surmounted by a roof 14, which is supported by, and integral with, cylindrical side wall 11.
In particular embodiments, gasifier 1 is modified to alter the flow of effluent by providing a constriction (not shown) in the mid-section of gasifier 1 (e.g. between the upper part of lower portion 12 and the lower part of upper portion 13). In some embodiments, the constriction is provided in cylindrical side wall 11 and is located where the upper part of lower portion 12 joins the lower part of upper portion 13. Constriction of the gasifier is shown in FIG. 9 with respect to the loaf gasifier 60 described below.
Located in cylindrical side wall 11, particular embodiments may include one or more openings for providing oxidative gas 121 to the solid organic materials. In some embodiments, the oxidative gas comprises recirculated flue gas and fresh air. In some embodiments a device is located in, and connected to, the oxidative gas opening for providing an oxidative gas to the solid organic materials.
In the illustrated embodiment, solid organic materials are introduced upwardly into gasifier 1 from a lower portion (e.g. lower portion 12) of gasifier 1 to provide a mass of solid organic materials in gasifier 1. The solid organic materials are ignited and then heated in gasifier 1, while providing an oxidative gas to gasifier 1, to provide a gaseous effluent. In particular embodiments, the oxidative gas comprises recirculated flue gas from a flue stack located in a system in which gasifier 1 is operating. In particular embodiments, the oxidative gas comprises a combination of recirculated flue gas from a flue stack (e.g. 117 in FIG. 1B) located in a system in which gasifier 1 is operating and fresh air.
An effluent flow path is provided within gasifier 1 for a portion of the gaseous effluent to migrate, mix, and react through the heated solid organic materials. The syngas formed thereby is transferred outwardly from gasifier 1 and any noncombustible solids are transferred out of gasifier 1.
FIG. 3 is a cross sectional front view of gasifier 1 (shown also in FIG. 2). In the illustrated embodiment, syngas exits inner chamber 62 of gasifier 1 through exit port 15 in roof 14. Also shown in FIG. 3 is a sensing device 16 that is positioned over an opening 17. Sensing device 16 is a radar that is used to monitor the top of the solid mass pile 18 shown in FIG. 3. For purposes of illustration, only one such device 16 is shown, but more than one such device 16 may be used. Gasifiers according to particular embodiments use at least three such sensing devices 16. Gasifiers according to other embodiments use at least five such sensing devices 16. As described herein, sensing devices are used to monitor the height of solid mass pile 18. It is generally desirable to maintain an appropriate height of solid mass pile 18 to produce syngas with lower amounts of particulate.
FIG. 4 is an enlarged front view of sensing device 16 shown in FIG. 3. In the illustrated embodiment of FIG. 4, sensing device 16 comprises a radar. FIG. 4 shows details of the construction of sensing device 16 while FIG. 3 shows how sensing device 16 may be positioned on gasifier 1.
FIG. 4 shows a radar sensing device 16 mounted on roof 14 of circular gasifier 1. Sensing device 16 is housed in an open housing 21 and supported by adjustable fasteners 19 and has the capacity to be adjusted angularly on swivelled fasteners 20 so that sensing device 16 can sense the contour of solid mass pile 18 in the interior of gasifier 1. In the illustrated embodiment, sensing device 16, in its housing 21, is mounted over a non-metallic plate 22. Plate 22 is generally non-metallic so that sensing device 16 can direct a radar beam into the interior of gasifier 1 and sense the top of solid mass pile 18. It should be noted that the opening 17 in gasifier 1 is only an opening in the metal cladding of housing 10, and not an opening through the firebrick contained in the interior of housing 10.
Maintaining control of the height of solid mass pile 18 is desirable for combustion control and the release of gaseous combustibles, i.e., the “product gas”. The location of feed cone(s) 25 and vertical auger(s) in vertical run 8 (see FIG. 3) are designed to provide a solid mass pile 18 having a generous depth, and a generally flat upper periphery. In some embodiments, this flat, mesa-like upper surface extends over 60 to 70 percent of the floor area, generally filling the lower portion (e.g. lower portion 12) of gasifier 1, and sharply tapers downward adjacent side wall 11. This downward taper, referred to as the angle of repose, is dependent upon the type of fuel used. A flat fuel pile 18 may help to achieve uniform combustion without bridging. This flat configuration results in an approximately uniform pile depth, which in turn may result in uniform air pressure within pile 18, thus minimizing channeling of pile 18. In addition to the flat shape of fuel pile 18, it may be desirable to maintain a depth of pile 18. Ash may be maintained below the actively burning portion of pile 18 to prevent heat damage to feed cone 25 and ash removal system 4. In an example embodiment, about 6 inches or more of ash is maintained below the actively burning portion of pile 18.
As the solid organic feed material in gasifier 1 moves from feed cone 25 to the center and top of pile 18, it gets hotter and hotter, and volatile components in such material and combustion products begin to dissipate from the surface of pile 18, partly being assisted by the gases that are rising through such material. As the feed material in pile 18 loses more and more of the volatile and pyrolytic ingredients, it will begin to form high molecular weight carbonaceous derivatives and char until, eventually, it is exposed to the full operating temperature inside gasifier 1. This material moves generally horizontally outward and then downward toward the outer wall and lower floor 9 where it is exposed to further oxidation agents via tuyere arrays 32 and 33 for a more complete reaction, at which time further organic constituents of such feed material will gasify, and will pass from gasifier 1 as an incompletely oxidized gaseous effluent of combustibles (syngas). In the illustrated embodiment, the effluent is carried away from gasifier 1 through an insulated exit duct. The velocity of the effluent above fuel pile 18 and through exit port 15 is kept low, reducing particulate carryover.
In various embodiments, air-modified flue gas (oxidative gas), steam-modified ambient air or steam-modified pure oxygen is provided to burning piles 18 and 71 through the respective tuyeres fitted on gasifiers 1 and 60. Loaf gasifier 60 and pile 71 are described in more detail below with reference to FIG. 9.
In some embodiments, the feed rate into gasifier 1 is monitored and controlled by monitoring and controlling the height of fuel pile 18 within gasifier 1. Suitable instrumentation, not shown, is provided to control the rate of the delivery of the feed material into gasifier 1 by the feed assembly (e.g. solid mass feeder 2) as a function of the elevation of the top of the feed material in the height of pile 18. The shape and height of feed material pile 18 may thereby be maintained substantially constant.
As solid mass pile 18 burns, it creates ash, which in particular embodiments is removed from gasifier 1. Gasifier 1 of the illustrated embodiment comprises one or more trenches 24 provided in the gasifier floor and one or more devices for removal of ash and combustion residues and for control of the elevation of the “moving bed of ash” hearth described in more detail below. In the illustrated embodiment of FIG. 3, the ash removal system 4 comprises an auger 26. FIGS. 2 and 3 show two trench sections 24, one on either side of a centrally located feed cone 25. Feed cone 25 is described in more detail below. Ash augers 26 in trench sections 24 move the ash toward points of discharge 27 suitably located at the ends or bottoms of trench sections 24. In the illustrated embodiment, trench sections 24 are connected to a bin or a conveyor of suitable design for further disposal of the ash (see ash removal system 4 of FIG. 1A).
Formation of ash creates a floorless hearth 30 in gasifier 1 on which burning solid mass pile 18 is situated. This ash build up, together with intermittent or continuous ash removal, creates a “moving bed of ash”, which provides floorless hearth 30.
In other embodiments, control of the level of the “moving bed of ash” that creates hearth 30 and removal of ash can be accomplished by a conveyor or conveyors moving across the entire floor, or section thereof, from side to side, or end to end of gasifier 1. In other embodiments, a set, or sets, of dump grates can be inserted under “moving bed of ash” hearth 30 to facilitate and control removal of the ash.
In some particular embodiments of the invention, for example, when forestry products are used as the feed, ash removal system 4 comprises a peppermill grate 40 (see FIG. 7 which is a cutaway portion of FIG. 3, section 28). In the illustrated embodiment, peppermill grate 40 comprises a flat metal plate 39 that is perforated with a multiplicity of holes 41 for allowing ash to fall therethrough. Over top of flat plate 39 is a moveable grate 42 that is also perforated with holes 43. Moveable grate 42 may be moved such that it covers part of holes 41 part of the time and can allow holes 43 to be aligned with holes 41, such that ash may fall through aligned holes 43, 41. Grate 42 may be moved in a generally oscillating motion. Ash may then fall through aligned holes 41, 43 and into retention basins 29 below (see FIG. 2). Augers 26 move the ash to discharge point(s) 27 where it is moved out of retention bins 29 into a conveyor portion of ash removal system 4 (see FIG. 1A) for transfer away from gasifier 1.
FIG. 7 further shows a portion of a segment of feed cone 25 surmounting grate 42. Grate 42 is surmounting flat plate 39. At one edge 44 of grate 42 of the illustrated embodiment, there is a pin 45 that attaches grate 42 to flat plate 39. Grate 42 may partially swing around pin 45 such that grate 42 moves in an oscillating motion. The swinging motion of grate 42 moves the ash that piles on grate 42 and flat table 39 and the ash falls through holes 41 and 43 into basin 29 below. Also shown in FIG. 7 are bottom tuyeres 34, which are described in more detail below.
FIG. 14 is an angled side view of a gasifier 1 according to another embodiment with its sides open to show another type of grate system 84, which is similar to peppermill grate 40 of FIG. 7. FIG. 15 is a side cross sectional view of grate system 84 through the line C-C. Grate system 84 comprises two grates 85 and 86 (see FIG. 15) at the bottom of gasifier 1. In the illustrated embodiment, bottom grate 85 is stationary and has openings 87. In particular embodiments, openings 87 are approximately 8 inches wide by 20 inches long. Top grate 86, which also has openings 88, is moveable relative to bottom grate 85. In the illustrated embodiment, top grate 86 is moved by two hydraulic cylinders (not shown). In particular embodiments, the hydraulic cylinders have a stroke maximum of about 8 inches. Because grate ring 86 is round, this stroke rotates grate ring 86. The hydraulic cylinders stroke top grate 86 such that it aligns openings 87, 88 and, on the back stroke, misaligns openings 87, 88.
In the illustrated embodiment of FIG. 15, top grate 86 has wedge plates 89 mounted on top of it. These plates 89 are installed in such a way that when the top grate 86 is rotating, wedge plates 89 push the ash in front of them towards the openings 87 in the bottom grate 85. The movement and height of wedge plates 89 ensure measurable ash removal from the bottom of pile 18, and can prevent the ash bridging above the ash grate openings.
As the bottom layer of ash is discharged, the mixture of ash and unburned carbon from above drops down lower. As the carbon burns, the process temperature in the vicinity of the ash discharge thermocouples (for example, temperature probes 53 described below) becomes higher indicating that the system has to wait for the next ash dump. As the carbon is more and more combusted and disintegrates, the bottom of gasifier 1 becomes colder and colder indicating that only ash is left at the bottom of gasifier 1 and it is time for a new ash dump.
Where the feed material into gasifier 1 is soft, easily combustible material, such as chicken litter, turkey litter, or plastics, and the like, a peppermill grate system (e.g. peppermill grate system 40 of FIG. 7 or grate system 84 of FIG. 14) may not be used.
For circular gasifier 1 of FIGS. 2 and 3, feed cone 25 is also circular—see FIGS. 5 and 5A. As shown in FIG. 3, feed cone 25 is centrally located and arranged along the centerline of the chamber of gasifier 1 and protrudes above the general elevation of the “moving bed of ash” hearth 30. In the illustrated embodiment, feed cone 25 is serviced by a single, or twin set, of vertical fuel feed augers 31 to move feed material through vertical run 8. For the loaf type gasifier 60 of FIGS. 8-9 (described below), which has a rectangular profile, feed cone 25 is also square or rectangular—see FIGS. 6 and 6A. Feed cones 25 may move solid organic material upwardly into gasifier 1 and may provide a cone-like structure to the underside of solid organic material pile 18 or 71.
In particular embodiments, feed cones 25 comprise a single piece, that is a unitary article, for example as shown in FIGS. 5A and 6A, respectively. In other embodiments, feed cones 25 are segmented as shown in FIGS. 5 and 6 so that they can more easily be moved into and out of gasifier 1 or 60 respectively, for servicing, maintenance and repair. The individual segments of segmented feed cones 25 can be simply set in place adjacent each other, or they can be mortared together, or glued together to hold them in place. The segmented feed cones 25 shown in FIGS. 5 and 6 may be used to implement the moveable feed cones 25 described below.
Feed cones 25 may be moveable or non-moveable. In particular embodiments, feed cones 25 may be moved such that they oscillate in a partial circular motion within gasifier 1. A moveable feed cone 25 provides relatively even introduction of oxidative gases through burning solid mass pile 18, which may in turn minimize creation of gas channels. Periodic movement of feed cone 25 also prevents oxidative gas from burning holes between the gas sources and the surface of pile 18.
Within gasifier 1, combustion is carried out sub-stoichiometrically with the application of an oxidizing agent. In particular embodiments, the oxidizing agent comprises flue gas mixed with fresh air. Solid organic materials are transferred continuously or intermittently to gasifier 1 at a rate to maintain a mass of solid organic materials in gasifier 1. The oxidizing agent is continuously added to gasifier 1 to continuously gasify the solid organic materials in solid mass pile 18, and the solid residue (non-combustibles) are transferred out of gasifier 1, for example, as described above. In particular embodiments, the oxidizing agent is administered through a set or sets of suitable ducts connected to nozzles, for example, tuyeres and injection points located within, around and between feed cones 25, and to a row, or line of nozzles and/or tuyeres in the surrounding walls of gasifier 1.
FIG. 3 shows upper tuyeres 32 and lower tuyeres 33 in side walls 11 of gasifier 1 and bottom tuyeres 34 in feed cone 25. Tuyeres 32, 33, 34 are used to facilitate the movement of the oxidizing agent (e.g. air-modified flue gas) to gasifier 1 and into burning solid mass 18. In the illustrated embodiment, upper tuyeres 32 are fed through a common manifold 35 and lower tuyeres 33 are also be fed through a common manifold 36. Tuyeres 32 are linked to manifold 35 by feed tubes 37 and tuyeres 33 are linked to the manifold 36 by feed tubes 38 (see FIG. 2).
In the embodiment shown in FIGS. 2 and 3, manifolds 35 and 36 are fed from a flue gas return system 48 that includes a duct 49 and an air motor 50. Inlet 51 of air motor 50 is attached to system 200 (FIG. 1B) for supplying air-modified flue gas to flue gas return system 48.
Gasifier 1 is equipped with an exit port 15 for the movement of syngas produced therein. In the illustrated embodiment, a fixture 52 is surmounted on exit port 15 for allowing the attachment of components (described below) which may be used to handle the syngas.
In the illustrated embodiment, the lower portion (e.g. lower portion 12) of housing 10 of gasifier 1 includes one or more devices (e.g. probes 53) for determining the amount of non-combustibles (e.g. ash) within gasifier 1. Probes 53 can be used to monitor the level of a moving ash bed defined by the upper elevation of the accumulated ash. As an example, probes 53 may comprise a pair or pairs of thermo elements located one above the other, distanced such that the level of the moving ash bed is in between them, and capable of characterizing the temperature of, and the difference in temperatures between, the material above and below the moving ash bed in operation. This temperature difference can then be used to dictate the degree of movement of ash removal auger(s) 26 and to thereby control the level of the moving ash bed. In particular embodiments, gasifier 1 is equipped with several sets of probes 53, inserted through openings 55, around the perimeter of the gasifier chamber. In such embodiments, an average of probe 53 input data is used determine the desired movement of ash removal auger(s) 26.
Lower portion 12 of gasifier 1 includes a floor having a top surface and a bottom surface. The gasifier floor may have one or more openings through it to allow for the passage of the solid organic material into the interior of gasifier 1. In the illustrated embodiment, the top surface of the floor is provided with a retaining wall on the outside of the floor openings to form a retention basin to retain the solid organic materials in lower portion 12 and to thereby form floorless hearth 30.
To bring gasifier 1 to an operational condition on start up, solid mass feeder 3 is activated to form pile 18 of feed material in gasifier 1 in preparation of development of a “moving ash bed” above gasifier floor 9. Pile 18 of feed material is ignited. To bring pile 18 of feed material up to its normal operating temperature, fuel oil or other readily combustible supplemental fuel may be added to it. As an example, this may be done manually through an opening 54 provided in the wall of gasifier 1.
As the oxidation proceeds and the temperatures elevate, the solid mass in pile 18 pyrolyzes and gasifies. Combustion of the solid mass may take place below the top of pile 18. Gas produced in the starved combustion sifts through burning pile 18 and into the upper portion of burning pile 18, pile 18 acting as a filter for particulate material. The products of combustion rise through pile 18 and cool because the latent heat of water absorbs the energy. As fuel is delivered, it gets pyrolyzed and the fuel moisture and volatile hydrocarbons are separated from the non-volatile components. These processes are driven by the hot gases that result from the combustion of the fixed carbon, which takes place below the top of pile 18.
The moderately slow burning lower portion of pile 18 serves to establish a quiet oxidation zone whereby entrainment of particulate matter and fly ash is minimized or reduced. In particular embodiments, gasifier 1 produces syngas with a maximum of combustible gaseous components and a minimum of particulate matter.
FIG. 8 is a front view of a loaf type gasifier 60, according to another embodiment. FIG. 9 is a cross sectional view of the FIG. 8 gasifier 60, through line B-B. Gasifier 60 is defined by four vertical side walls 61, giving the chamber of gasifier 60 a square or rectangular cross section and forming an enclosure 62 (FIG. 9) which has an irregularly shaped bottom 63. Gasifier 60 includes a roof 64, which in cross section may be vaulted, tapered or flat or any combination thereof.
In particular embodiments, walls 61 are made up of a multiplicity of layers. FIGS. 10A and 10B show cross-sections of walls 61 according to particular embodiments. In the embodiment of FIG. 10A, the innermost layer 65 is an insulating layer of a high-temperature resistant type refractory that is capable of withstanding the elevated temperatures that develop within gasifier 60, for example, temperatures in the range of approximately 2300° F. to approximately 2500° F. Such high-temperature resistant type refractory is capable of withstanding operational temperature variations as well as the corrosive, erosive effects of the gaseous materials produced by the oxidation of biomass feed material that is delivered into gasifier 60. Walls 61 may also include an insulating layer 66 on the outside of wall layer 65 to further prevent loss of heat through walls 61 of gasifier 60. As an example, insulating layer 66 may comprise a single layer of insulating firebrick, block insulation, or blanket insulation. In the illustrated embodiment, the outer casing of the wall 61 is a structural layer or shell 67 comprising sheet metal, for example, plate steel, which is airtight and provides the necessary strength and rigidity for walls 61.
FIG. 10B shows second embodiment of wall 61, wherein insulating layer 66 is not used, and a vacant layer or space 68 is provided between refractory innermost layer 65 and shell 67. The air which fills vacant layer 68 acts as an insulator between refractory layer 65 and shell 67. This warmed air in vacant layer 68 can also be used as a source of preheated air for injection into gasifier 60 and recovery and regeneration equipment 96 and 98 (see FIG. 1) which are described in more detail below.
Referring to FIGS. 8 and 9, the biomass feed material from the storage hopper assembly (not shown) is introduced into gasifier 60 from below gasifier 60 through at least one feed cone 59. In the illustrated embodiment, feed cone 59 is located along the centerline of bottom 63 of gasifier 60. During normal operating conditions, the feed material rises over the top of feed cone(s) 59 and rests on hearth 70 until it forms a pile 71 of such material, which is the normal or equilibrium condition of gasifier 60. Hearth 70 is made up of ash and other solid combustion residues. This self-generated hearth 70 is similar to the “moving ash bed” configuration that was described above in connection with gasifier 1. As primary oxidation progresses, this bed continues to elevate and the ash is removed at essentially the same rate it is formed to maintain the appropriate height of fuel pile 71.
As described above for gasifier 1, the height of pile 71 may be controlled to control combustion and the release of gaseous combustibles. The principles discussed above for the control of pile height in gasifier 1 apply for gasifier 60 and will not be repeated herein.
In the illustrated embodiment (see FIGS. 9, 11 and 12), exit ports 69 are positioned so as to vent gasifier 60 through roof 64. It should be noted that prior art loaf gasifiers required that the exit for the gases produced therein must be through the side wall to minimize the flow of particulate materials along with the gas. In particular embodiments, side walls 61 are provided in a height which allows any air-borne particulate to fall back to pile 71 rather that exit via ports 69. The positioning of exit ports 69 within gasifier 60 can be as shown in FIGS. 9, 11 and 12, may be sloped or vertical, and is selected to be practical and suitable for the specific application.
As in gasifier 1 described above, an oxidizing agent is administered through a set or sets of suitable ducts connected to nozzles, for example tuyeres, and injection points located within, around and between feed cones 59, and to a row, or line of nozzles and/or tuyeres in the surrounding walls 61 of gasifier 60.
FIG. 9 shows upper tuyeres 73 and lower tuyeres 74 in side walls 61 and bottom tuyeres 75 in feed cone 59; all of which, in particular embodiments, are used to facilitate the movement of the oxidizing agent (e.g. air-modified flue gas) to gasifier 60 and into burning solid mass pile 71. In the illustrated embodiment, upper tuyeres 73 are fed through a common manifold 76 and lower tuyeres 74 are also fed through a common manifold 77. In the illustrated embodiment, tuyeres 73 are linked to manifold 76 by feed tubes 78 and tuyeres 74 are linked to manifold 77 by feed tubes 79.
System 200 (FIG. 1) for supplying fresh air-modified flue gas may also be used in conjunction with gasifier 60. Manifolds 76 and 77 of gasifier 60 are fed from a flue gas return system, generally 48 (see FIG. 8), which comprises a duct 49 and an air motor 50. In the illustrated embodiment, the inlet 51 of air motor 50 is attached to system 200 (FIG. 1) for supplying fresh air-modified flue gas to flue gas return system 48. The details of the movement of the fresh air-modified flue gas from flue stack back to gasifier 60 are set forth in detail below.
In the illustrated embodiment of gasifier 60, the upper part of lower portion 12 and the lower part of upper portion 13 (see FIG. 3 for reference to lower portion 12 and upper portion 13) provide a constriction 80 in the interior chamber 62 of gasifier 60. In the illustrated embodiment, constriction 80 is built into layer 65, or it can be formed from a plate that is set at an angle into layer 65. Constriction 80 slows down the upward flow of product gas and thereby assists in reducing the amount of particulate material that tends to reach exit ports 69.
In the illustrated embodiment, feed rate into gasifier 60 is monitored and controlled by monitoring and controlling the height of fuel pile 71 within gasifier 60 using the same sensing devices 16 (e.g. radar sensing devices 16) as described above. Suitable instrumentation, not shown, is provided to control the rate of the delivery of the feed material into gasifier 60 by the feed assembly as a function of the elevation of the top of the feed material in the height of pile 71, in some embodiments to maintain such elevation at a substantially constant value, and thereby to contain the pile 71 of feed material at a substantially constant size.
FIG. 11 is an enlarged front view of roof 64 of loaf gasifier 60. FIG. 12 is a cross sectional view of roof 64, showing the construction of the walls of roof 64. In the illustrated embodiment, roof 64 comprises two exit ports 69 for syngas. Also shown in FIG. 11 is a placement of radar sensing device 16 on roof 64, between exit ports 69. Dotted lines 184 (shown in FIG. 9) illustrate the beam of radar sensing device 16 penetrating into the interior 62 of gasifier 60. In the illustrated embodiment, roof 64 comprises an outer steel wall 67, insulating layer 66 and interior refractory layer 65. In the illustrated embodiment, component 82 is a flange useful for fitting the roof 64 to the side walls 61 of gasifier 60.
FIG. 13 is a cross sectional view showing a number of components of the ash handling system 81 of loaf gasifier 60. Ash handling system 81 of the illustrated embodiment comprises removable grates 42, increasing flight ash removal augers 26 in collection bin and retention bin 29, and castable tuyere panels 83. FIG. 13 also shows the exit of centered feed cone 59.
FIGS. 1A and 1B schematically depict gasifier 1 in use with a system 200 for generating energy from biomass materials. System 200 incorporates one or more methods according to a particular embodiment of the invention.
As discussed above, gasifier 1 is fed a solid mass material using solid mass feeder 2 comprising auger feed 3, and ash is removed from gasifier 1 by ash removal system 4. Syngas 90 that is produced by the pyrolysis and gasification of the solid mass material exits gasifier 1 through exit port 15 into syngas burner 91. Syngas 90 is controlled by draft controls 93. In the illustrated embodiment, syngas burner 91 is aided in combustion using a combustion air blower 94 that provides air 95 to syngas burner 91.
In particular embodiments, syngas 90 is provided to syngas burner 91 at a temperature of about 500° F. to about 600° F. and is in a starved air condition. This contrasts with prior art systems in that the normal temperature of the syngas from prior art devices is in the range of 1200° F. to 1400° F., and in prior art systems, this syngas is not “starved air” and before the prior art syngas can be used, it has to be cooled and compressed, requiring additional and expensive equipment. Syngas burner 91 heats and combusts syngas 90, for example, up to a temperature in the range of 1200° F. to 1400° F. before the syngas is provided to a low NO_xoxidizer 96.
Syngas 90 may be provided to a kiln 98 using syngas blower 99 that moves syngas 90 to a nozzle mix syngas burner 100. Thereafter, syngas 90 is moved through nozzle mix syngas burner 100 into kiln 98. Hot gas stream 107 (about 2200° F.) output from kiln 98 is moved to low NO oxidizer 96 and combined with the oxidation product 97 coming from syngas burner 91.
In the illustrated embodiment, the heating and movement of the gases in kiln 98 is aided by mixing heated air 101 from a heat exchanger 102 (see FIG. 1B) with heated ambient air 105 to form heated air stream 103 which is bled into nozzle mix syngas burner 100 using a preheated combustion air blower 104. A portion 106 of heated air 101 from heat exchanger 102 (FIG. 1B) is also bled directly into kiln 98.
Hot gas stream 107 output from kiln 98 is fed into low NO_xoxidizer 96 and mixed therein with the oxidation product 97 from syngas burner 91 being fed into the top portion of the low NO_xoxidizer 96. Low NO_xoxidizer 96 is fed ambient air 108 using a combustion/tempering air fan 109, through manifolds 110 and tuyeres (not shown) and the flue gas 111 that exits low NO_xoxidizer 96 does so at about 2000° F. and passes to heat exchanger 102 shown in FIG. 1B.
FIG. 1B shows heat exchanger 102 into which flue gas 111 from low NO oxidizer 96 has been passed. Exchanged (cooled) flue gas 112 is then passed to a metal heat exchanger 113, for example, at about 1400° F. Metal heat exchanger 113 is useable because of the relatively lower temperature of cooled flue gas 112 as compared to flue gas 111 input into heat exchanger 102 which is at about 2000° F. Air 114 output from metal heat exchanger 113 becomes the input air to heat exchanger 102. In the illustrated embodiment, the movement of air 114 is aided by the introduction of fresh air 124 using an air blower 125.
Air 101 is the exchanged air output from heat exchanger 102 and has a temperature, for example, in the range of about 400° F. to 1200° F. Air 101 is passed back to kiln 98 (FIG. 1A). In the illustrated embodiment, air 101 is occasionally vented (as shown at 116) to control the temperature and pressure thereof.
Heat-exchanged flue gas 127 from metal heat exchanger 113 (FIG. 1B) is moved to an induction draft fan 115 before it enters stack 117. Prior to exhaust flue gas 122 exiting flue stack 117, a portion of flue gas 120 is withdrawn from stack 117 and moved to a flue gas eductor 118, which is aided by an induced draft fan 119. At this point, fresh air 128 is inducted and mixed with flue gas 120 and it is this flue gas modified with fresh air 121 that is moved back to gasifier 1 as the oxidative gas for use in gasifier 1. Also shown in FIG. 1B is sampling port 129.

Claims

1. A system for generating energy from biomass, the system comprising:

a gasifier comprising a housing for providing a first, oxygen starved, environment in which the biomass is sub-stoichiometrically combusted to generate syngas;

an oxidizer connected to receive syngas from the gasifier and configured to oxidize the syngas in a second environment distinct from the first, oxygen starved environment and to thereby generate heat energy;

an oxidative agent supply mechanism for introducing an oxidative agent to the first, oxygen starved, environment in the gasifier housing, the oxidative agent comprising flue gas.

2. A system according to claim 1 wherein the oxidative agent comprises a mixture of flue gas and air.

3. A system according to claim 2 wherein the flue gas comprises recirculated flue gas generated by the oxidation of syngas in the oxidizer.

4. A system according to claim 3 wherein the oxidative agent consists essentially of a mixture of flue gas and air.

5. A system according to claim 3 wherein the oxidative agent supply mechanism comprises an eductor connected to educe the flue gas from a conduit at a location downstream from the oxidizer and connected to a source of air, the eductor operative to mix the flue gas and the air to provide the oxidative agent.

6. A system according to claim 3 comprising an air supply mechanism connected to introduce air to the second environment of the oxidizer, the introduced air making the second environment an air-enriched environment.

7. A system according to claim 3 further comprising at least one heat exchanger located downstream of the oxidizer, through which the recirculated flue gas is directed prior to being introduced to the first, oxygen starved environment in the gasifier housing.

8. A system according to claim 3 further comprising at least one NO_xoxidizer located downstream of the oxidizer, and through which the recirculated flue gas is directed prior to being introduced to the first, oxygen starved environment in the gasifier housing.

9. A system according to claim 3 wherein the oxidative agent supply mechanism comprises a plurality of conduits arranged to deliver the oxidative agent into the biomass within the gasifier.

10. A system according to claim 9 wherein the housing of the gasifier comprises a side wall and the oxidative agent supply mechanism comprises a plurality of conduits for delivering the oxidative agent through the side walls of the gasifier.

11. A system according to claim 9 wherein the gasifier comprises a feed cone, the feed cone penetrated by a generally vertically oriented feed bore through which biomass may be introduced to the housing of the gasifier and wherein the oxidative agent supply mechanism comprises a plurality of conduits for delivering the oxidative agent through the feed cone and into the biomass within the housing of the gasifier.

12. A system according to claim 11 wherein the feed cone comprises an upwardly facing concave surface surrounding the feed bore and a frustro-conical exterior surface surrounding the upwardly facing concave surface and wherein the plurality of conduits for delivering the oxidative agent through the feed cone comprises a first plurality of conduits located to introduce oxidative agent through the upwardly facing concave surface and a second plurality of conduits located to introduce-oxidative agent through the frustro-conical exterior surface.

13. A system according to claim 12 wherein an interior of the housing of the gasifier is generally rectangularly shaped and the frustro-conical exterior surface comprises a rectangular frustro-conical surface.

14. A system according to claim 12 wherein an interior of the housing of the gasifier is generally circularly shaped and the frustro-conical exterior surface comprises a circular frustro-conical surface.

15. A method for generating energy from biomass, the method comprising:

providing a first, oxygen starved environment;

sub-stoichiometrically combusting the biomass in the first, oxygen starved environment to generate syngas;

oxidizing the syngas in a second environment distinct from the first environment to thereby generate heat energy;

wherein sub-stoichiometrically combusting the biomass in the first, oxygen starved environment comprises introducing an oxidative agent to the first, oxygen starved environment, the oxidative agent comprising flue gas.

16. A method according to claim 14 wherein the oxidative agent comprises a mixture of flue gas and air.

17. A method according to claim 15 wherein the oxidative agent consists essentially of a mixture of flue gas and air.

18. A method according to claim 15 wherein introducing the oxidative agent to the first, oxygen starved environment comprises recirculating flue gas generated by the oxidation of the syngas in the second environment and mixing the recirculated flue gas with air to provide the oxidative agent.

19. A method according to claim 17 comprising recovering heat from the recirculated flue gas prior to introducing the recirculated flue gas into the first, oxygen starved environment.

20. A method according to claim 18 comprising introducing air into the second environment to make the second environment an air enriched environment.

21. A method according to claim 15 wherein introducing the oxidative agent to the first, oxygen starved environment comprises introducing the oxidative agent to the first environment from locations beneath the biomass and from locations beside the biomass.

22. A method according to claim 18 wherein a temperature of the syngas generated by sub-stoichiometrically combusting the biomass in the first, oxygen starved environment is less than about 600° F. and a temperature of an oxidation product resulting from oxidizing the syngas in the second environment is greater than about 1200° F.

23. A method according to claim 18 wherein the temperature of the oxidation product resulting from oxidizing the syngas in the second environment is about 2000° F.

24. A method according to claim 15 wherein a temperature of the syngas generated by sub-stoichiometrically combusting the biomass in the first, oxygen starved environment is less than about 600° F. and a temperature of an oxidation product resulting from oxidizing the syngas in the second environment is greater than about 1200° F.