Patent Grant
8377155
The invention relates generally to fluidized bed gasifiers and to the production of gasified fuel via and/or in conjunction with the gasification of solid fuels in a fluidized bed gasifier featuring a rotating auger conveyor. More particularly, it deals with improvements to the gasifier that facilitate the continuous controlled movement and gasification of solid fuels in the combustor/gasifier; and facilitate production and enrichment of gasified fuel via and in conjunction with such a gasifier. These and other improvements taught herein in relation to the operation of a gasifier represent significant advances in technology related to the environmentally sound utilization and processing of solid fuel for the production of energy via such fluidized bed gasifiers.
Much of the world's energy needs have been, and continue to be, filled by hydrocarbon fuels. In the past, such fuels provided a convenient, plentiful, and inexpensive energy source. The current rising costs of such fuels and concerns over the adequacy of their supply in the future has made them a less desirable energy source and has led to an intense investigation of alternative sources of energy. The ideal alternative energy source is a fuel which is renewable, inexpensive, and plentiful, with examples of such fuels being the byproducts of wood, pulp, and paper mills, and household and commercial refuse.
The use of such alternative energy sources is not problem-free, however, since there is reason for concern over the contents of the emissions from the combustion of such fuels as well as the environmental ramifications of acquiring and transporting the fuel and disposing of the residue of combustion. Starved-air gasifiers, wherein the air supplied for combustion is controlled in order to control temperature conditions (and the rates of combustion) so as to gasify the fuel as completely as possible, have proved very useful in the utilization of such alternative energy sources while simultaneously maintaining a high degree of environmental quality in emissions. Such starved-air gasifiers are capable of gasifying various types of fuel and producing significant amounts of syngas and heat which can be employed for any number of purposes including the production of process steam for use in manufacturing and in the generation of electricity.
Unfortunately, most starved-air gasifiers, as originally developed and operated, were not entirely satisfactory in processing the gasifiable elements of the fuel at high throughput while not producing noxious emissions. This problem resulted, in part, from the use of such gasifiers to burn a wide variety of fuels, including many which were non-homogeneous, such as household or commercial refuse. While the pollution problem can be solved to a degree by the utilization of scrubbers and other antipollution devices, such mechanisms are very expensive and their cost may militate against the use of alternative energy sources previously described.
Many of the drawbacks of such prior art devices were overcome by the development of the auger gasifier by the inventor and others. See, U.S. Pat. No. 4,009,667 (describing the original auger gasifier utilized in the system); U.S. Pat. No. 4,315,468 (describing a control means for the system); U.S. Pat. No. 4,331,084 (describing a refuse fuel feed mechanism for the system); U.S. Pat. No. 4,331,085 (describing a flame stabilization means for the system); U.S. Pat. No. 4,332,206 (describing an afterburner for the system); U.S. Pat. No. 4,332,206 (describing a hot gas recycle mechanism for use with the system); and U.S. Pat. No. 6,349,658 (describing an auger gasifier with fluidized bed. The auger gasifier technology taught and described in the foregoing patents offers a cost-effective approach to clean, efficient gasification of prepared solid waste and other solid fuels. It employs a starved-air combustion/gasification technique, ideally utilizing only limited combustion in order to gasify solid fuel in a primary chamber (the “combustor” or “gasifier” chamber).
One of the unique features of the auger gasifier system is its auger. Fuel enters the gasifier at a controlled rate and is shaped into a pile by the first auger flight. It is then pushed and tumbled through the gasifier chamber by the auger. As the auger moves the fuel through this horizontal cylinder, it stirs the material to maximize exposure for oxidation and/or gasification. The pitch of the auger can decrease along the path of material flow to accommodate the decrease of fuel bulk and retention time as the material combusts. (The use of an auger to convey fuel through the gasification cycle results in very accurately controlled movement of fuel through the gasification chamber, in comparison to alternative rotary kiln incinerators). This ability to manage fuel-bed configuration permits control of forced-draft combustion air so as to minimize combustion and gasify nearly all the fuel without complete combustion taking place, thereby allowing the gasifier to operate at what is a uniformly moderate temperature from auto-ignition to desired exit gas temperature.
The combination of fuel bed stirring and air injection with precise temperature control gives the auger gasifier system several advantages over prior technology: Reliability and clean operation; high throughput; low gasifier temperature: longer material life (refractory and auger); fully automatic control; and the ability to combust a wide variety of heterogeneous solid fuels. However, several of these advantages are further strengthened by creation of a fluidized bed via the high pressure input of underfire air into the system via a large plurality of input holes. The fluidized bed can be formed in whole or in part by the addition of a substrate of appropriate granular materials or it can be comprised solely of materials in the gasification process. In either case it acts as an “air bearing” in the auger combustor/gasifier chamber, aiding in the diffusion of gasification air through the material being burned as more fully described in U.S. Pat. No. 6,349,658.
Still, while the auger combustor/gasifier described in the foregoing patents offers a cost-effective approach to clean, efficient gasification, I have found that various innovative improvements, as further taught herein, support and facilitate its operations and efficiency. These improvements include provision of a vertically elongated (“oblong”) primary gasifier chamber with an auger that can move up and down, allowing for large amounts of fuel input when necessary. This improvement, in turn, requires and/or is facilitated by provision for simultaneous elevation adjustments of the auger and bed dam to assure that fuel material is processed in degrees from the top downward without sweeping massive amounts of the fluidized bed materials towards the output end of the chamber. Another improvement involves provision for pressurization of the primary gasifier chamber, allowing substantial improvements in the speed of processing materials through the gasifier. Due to issues arising from thermal expansion of the refractory material lining the chamber, I have also made provision for nozzle and refractory imbedded pipe hole thermal expansion capability. To these I have added provision for steam injection into and/or auxiliary heating of the chamber to enhance gasification and the production of syngas. These changes and improvements serve to create an even more efficient and cost effective system which is well adapted to meet the continuing needs of our modern technological civilization for elimination of waste while producing clean environmentally sound sources of alternative energy therefrom.
Turning first to
Extending the length of the gasifier chamber 1 is a rotatable screw conveyor 8 which can be preferably provided by a rotatable auger 8 having a tubular axis 9. The spiral flights 2 of the auger 8 extend from the front wall to the outlet end 10, so that when the auger 8 is rotated, the auger flights 2 will convey and tumble gasifiable refuse entering inlet end 30 from the feed hopper 12 through the gasification chamber 1, and deliver the solid residue to the ash receptacle 13 at outlet end 10 where it can be removed via helical screw conveyor 8. In prior embodiments as well as in the embodiments illustrated, the tubular axis 9 can be raised/lowered and positioned anywhere between the top of chamber 1 (as shown in
Chamber 1 also includes air supply means such as blower 3 for supplying underfire air and overfire air for gasification and provision of a fluidized bed. As is typical of prior embodiments, a plurality of overfire air conduits and underfire air conduits supply air to chamber 1, with underfire air being provided via air distribution pipes 5 from a hot air manifold 15 in a heat exchange relationship with chamber 1. Nozzles 6 in communication with pipes 5 provide an outlet for this air beneath any fuel or non-fuel particle bed in chamber 1 and serve to fluidize such bed. In addition, the underfire air, which is at an elevated temperature due to its pre-heating while passing through manifold 5 and refractory 4, contributes to the gasification of fuel in the bed as well as heating and drying the fuel. A bed dam 27 (with bed dam gap 27A) proximate bottom 7 and outlet end 10 prevents particles of fuel or otherwise forming said fluidized bed from being swept from the chamber 1 when auger 8 is rotated to move and tumble said gasifiable materials from the inlet end 30 to said outlet end 10.
One of the notable improvements embodied herein is, as previously noted, the provision of a chamber 1 that is oblong in cross-section (as illustrated in
The oblong configuration is preferred, but both configurations allow substantial variation in one or both the depth of the fluidized bed in the chamber 1 and the depth of the gasifiable materials in the chamber 1. This is extremely beneficial for a variety of purposes. One reason is because a much greater quantity of fuel can be processed and gasified in chamber 1 at the same time, with the auger 8 (which can be raised and lowered to accommodate fuel bed level variations as necessary) being capable of distributing said fuel throughout chamber 1 and selectively removing fuel residue from the top-most layers thereof selectively. In addition, this along with other features of the invention allow more continuous processing of fuels as the ability of chamber 1 to handle varying amounts of batch loaded fuel enable the system to more easily remain in continuous operations. Finally, in order to better accommodate the aforesaid changes to the cross-section of chamber 1, it is highly beneficial to provide a bed dam 27 that can be raised and lowered in conjunction with the raising and lowering of auger 8 as best illustrated in
Another improvement made, is the addition of at least one additional plurality of sequential supplemental spiral flights 2A disposed around axis 9 proximate inlet end 30 in such manner that supplemental spiral flights 2A likewise form a continuous helix around axis 9 intermediate the previously described spiral flights 2 of auger 8. This allows for (in the case of one additional set of supplemental spiral flights 2A) twice the tumbling of fuel bed material being moved by auger 8 while being moved over the same distance, exposing more of said materials for gasification purposes. This is beneficial to the gasification process overall and particularly assists in the more rapid out-gassing of volatiles (including water vapor) while fuel is still proximate inlet end 30.
In addition, 1 have found it very beneficial in terms of the more rapid processing and gasification of fuels in chamber 1 to be able to control the pressure in chamber 1 as necessary for more rapid gasification and processing of various fuel types, and more particularly, to be able to keep chamber 1 at an elevated pressure (requiring chamber 1 to serve as a pressure vessel). Overall, the interior of said chamber will be maintained at a pressure of at least atmospheric pressure, but less than the engineered limits of chamber 1 as a pressure vessel. However, it has been found to be advantageous in the rapid gasification of fuel to be able to maintain chamber 1 pressure at or above approximately 2 atmospheres (i.e., approximately at least 30 psi). Obviously, in order to control pressure in chamber 1, provision must be made to control ingress and egress of gases from chamber 1 via the inlets and outlets for an auger gasifier chamber 1. I have found that this can be accomplished by providing and using, as necessary, rotary lock valves 16 and 18 at, respectively, the waste/ash outlet for chamber 1 and inlet hopper 12, and control valves such as underfired air control valve 20, overfired air control valve 21, flame stabilization duct valve 22, and outlet valve 11, at gas inlets and outlets to chamber 1. However, even when pressure is elevated, proper gasification is facilitated by a starved air environment. Thus, the oxygen content maintained in the chamber 1 interior should be held ideally at the lowest ratio that will maintain stability of the gasification process, but not more than 50% of the oxygen content necessary for combustion of the contents thereof.
A further improvement is based on my finding that thermal expansion of air distribution pipes 5 may displace the openings by which said pipes 5 feed pressurized air to channels 6 into chamber 1 such that the two are no longer aligned, deleteriously effecting the input of pressurized air to chamber 1 necessary for gasification and the production of a fluidized bed. As previously noted, the interior of chamber 1 is lined with a refractory material 4, with air distribution pipes 5 imbedded in said refractory material 4 to form the air distribution conduits in communication with the plurality of openings in the lower side (bottom 7) of chamber 1. Channels 6 through said refractory 4 intermediate air distribution pipes 5 and the interior of the chamber 1 communicate pressurized air to the interior of the chamber 1. In order to handle the aforesaid problem, I have made the apertures of said channels in communication with adjacent apertures in said pipes larger than the adjacent apertures in said pipes 5, allowing for shifts in the location of said pipe apertures due to thermal expansion. In addition, as an added change, channels 6 now form nozzles (being narrowed proximate chamber 1), creating a venturi effect to accelerate a jet of pressurized air issuing from the channels/nozzles into chamber 1.
Finally, I have added additional heat source(s) such as external heater 25 (which may be electric) and provides supplemental heating to the gas stream in chamber 1 (in addition to any heat generated by combustion and gasification of the fuel therein). In addition, I have added a supplemental source of steam such as steam reforming means 26, providing supplemental steam to the gas stream in chamber 1 (in addition to any generated by combustion and gasification of the aforesaid fuel). These both can assist in the production of syngas from said gas stream, with syngas being one of the major products sought through gasification, and serving as a base for further processing by, for example, the Fisher-Tropsch process.
However, numerous variations are possible without deviating from and/or exceeding the spirit and scope of the inventive concept. Moreover, many of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into various other different systems or applications. Also, numerous presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the claims that follow.
Finally, the following parts list for the drawing figures may be found to be of assistance in understanding more fully the concepts of my invention:
| Number | Name | Date | Kind |
|---|---|---|---|
| 611508 | Quinn | Sep 1898 | A |
| 2072721 | Rahm | Mar 1937 | A |
| 4135889 | Mori | Jan 1979 | A |
| 4436588 | Rammler et al. | Mar 1984 | A |
| 6349658 | Tyer | Feb 2002 | B1 |
| 20070043246 | Bridle | Feb 2007 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20090205252 A1 | Aug 2009 | US |
