Method and system for fuel gas combustion, and burner for use therein

Abstract

Power cycle generation equipment is operated in a more efficient and economical manner by using an uncooled (and potentially uncleaned) fuel gas supplied to the equipment directly from a gasification process, i.e., without first quenching or pressurizing the gas. In one embodiment, a burner used in conjunction with the power cycle generation equipment accepts such fuel gas directly from a syngas generator (or perhaps after particulate removal). The burner preferably operates with fuel gas and oxidizer inputs reversed as compared to existing configuration.

Description

TECHNICAL FIELD

The present invention relates generally to enhancing the efficiency of conventional boilers or steam generators using a non-cooled, non-pressurized fuel gas.

BACKGROUND OF THE RELATED ART

The products generated in high temperature gasification of hydrocarbon materials give high concentrations of carbon monoxide and hydrogen, small quantities of sulfide, fluoride and chloride-bearing compounds, as well as some particulate. To utilize this gas in high efficiency cycles, typically it is cleaned of particulate, acid and condensable gases to a very high efficiency, pressurized, and then supplied to a conventional burner.

BRIEF SUMMARY

Power cycle generation equipment is operated in a more efficient and economical manner by using an uncooled (and potentially uncleaned) fuel gas supplied to the equipment directly from a gasification process, i.e., without first quenching or pressurizing the gas. In one embodiment, a burner used in conjunction with the power cycle generation equipment accepts such fuel gas directly from a syngas generator (or perhaps after particulate removal). The burner preferably operates with fuel gas and oxidizer inputs reversed as compared to existing configuration. In one preferred embodiment, the burner operates with a syngas gas composition, such as 50/50 mixture of carbon monoxide and hydrogen, at a fuel gas temperature in excess of 1500° F. The syngas may be provided from a liquid metal gasifier, although this is not a limitation. The energy content of the fuel gas, excluding heat, preferably ranges from 200-500 BTU's/cubic foot. The oxidizer (air or oxygen) preferably is pressurized from 0.1-5 atmospheres. Although not limiting, an induced draft fan may be used to draw the fuel gas into the burner.

The burner may be implemented as an add-on to existing power cycle generation equipment such as a boiler, a kiln, or a steam generator; alternatively, the burner is built into such equipment anew. Preferably, the burner comprises a set of injectors, with each injector or injectors supporting at one end one or more flame holder wings. Each flame holder wing includes a set of apertures. When positioned in the fuel gas stream, the uncooled, uncleaned fuel gas passes through the apertures in the flame holder wing where it is mixed with an oxidizer (air or oxygen) that is supplied to the burner under pressure and exits one or more openings in each injector. The fuel may auto-ignite, or a separate pilot burner may be used for initial ignition. The flame holder wings create a recirculation zone adjacent the injectors. As compared to the prior art, where the oxidizer is the primary stream and the cooled and pressurized fuel gas is provided through the injectors, the preferred approach here is to invert these inputs to the burner and without any requirement that the fuel gas been cooled or pressurized before being combusted.

The foregoing has outlined some of the more pertinent features of the invention. These features should be construed to be merely illustrative. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention as will be described.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a process flow diagram illustrating a method of energy generation according to this disclosure;

FIG. 2 illustrates plan and elevation views of a first embodiment of a burner for use in the energy generation method;

FIG. 3 illustrates an elevation view of a second embodiment of the burner;

FIG. 4 illustrates a preferred construction of a burner injector and the associated flame holder wings; and

FIG. 5 is a process flow diagram illustrating an embodiment of the gasification stages of a continuous C&D processing facility that produces fuel gas.

DETAILED DESCRIPTION

FIG. 1 is a basic process flow diagram illustrating how the burner is used as an add-on (or adjunct) to an existing boiler or steam generator. In this example, it is assumed that the fuel gas is provided to the burner from a molten metal gasification unit (or “gasifier”), although this is not a limitation as the fuel gas source may be quite varied. In this example, the syngas generated in the gasifier 100 (e.g., a molten iron bath) entrains iron oxide particulate, which is very abrasive and preferably is removed close to the source. A preferred method of removing this particulate is by means of a conventional cyclone 102 (or a dust collector, an electrostatic precipitator, or the like) designed to resist abrasion. The cyclone typically does not provide fine cleaning of the particulates. There also may be carbon particulate entrained in the syngas but, due to the differences in aerodynamic diameter (resulting from iron density), typically the iron-based particulate can be removed while allowing the majority of the carbon particulate to pass to the burner 104. Preferably, the burner 104 uses the syngas in a non-traditional oxidizer design. In particular, the syngas is delivered to the burner by the boiler or heat generator-induced fan 106, while an oxidizer (air or oxygen) is delivered to a flame holder burner under pressure. These burner inputs are thus inverted (or reversed) as compared to the prior art. As also illustrated, the burner may receive a primary oxidizer, and a secondary oxidizer, although the latter is not strictly necessary. In this staged combustion embodiment, the primary oxidizer injection system is designed to minimize NO_x generation, while the secondary oxidizer injection is designed to produce complete combustion. The secondary oxidizer injection system can be multiple sequential injection points.

FIG. 2 illustrates plan and elevation views of an embodiment of a burner 200 of this disclosure. The hot and dirty fuel gas (e.g., syngas) is directly ducted to the burner 200 via refractory-lined duct and burner inlet section 202. The refractory is designed to operate at temperatures to 3000° F. with hydrogen concentrations up to 50% by volume. The burner is designed to operate with fuels being introduced from negative to positive pressures (3 atmospheres). The flame holder-oxidizer injector 204 is constructed of high temperature alloys. Air or oxygen is injected at less than stochiometric amounts in the burner to reduce the formation of nitrogen oxides. As seen above, the injector 204 comprises a set of individual free-standing injectors 206, with each injector 206 supporting at one end one or more flame holder wings 208. A preferred construction for each injector is illustrated in FIG. 4, described below.

In another embodiment, illustrated in FIG. 3, secondary oxidizer injection is injected downstream of the primary oxidizer injector and may have water added. The oxidizer injectors typically operate at pressures 1-2 atmospheres above the fuel gas pressure. In one embodiment, there are different injection pressures for the oxidizer, although this is not a requirement.

As noted above, preferably the burner injector comprises flame holder “wings” that are perforated metal especially designed to minimize thermal stresses in their attachment to the main oxidizer header. A preferred construction is illustrated in FIG. 4, which shows the wings with the paths for syngas and oxidizer. The burner or inlet ducting may have a natural gas feed header that augments the BTU content of the syngas or that is otherwise capable of operating the burner at its rated value even without syngas.

The burner illustrated above may be retrofitted to existing boilers, kilns or other such equipment, or it may be built into such equipment originally. The burner may be used with any fuel gas source, such as syngas, and it is preferred that the fuel gas be provided to the burner directly as opposed to being first cooled, pressurized and/or cleaned. As such, the fuel gas is a “hot” (uncooled) and/or “dirty” (uncleaned) fuel source that is drawn through the burner, preferably using an induced draft fan, while the oxidizer is provided to the burner under pressure. As compared to the prior art, the burner inputs are inverted, and it has been found that this structural and process arrangement provides energy efficiencies and reduced emissions as compared to the prior art.

In one preferred embodiment, the fuel gas is provided by a liquid metal gasifier. It is known in the prior art to provide gasification systems that convert municipal solid waste (MSW) and construction and demolition waste (C&D) into clean energy. As described in U.S. Publication No. 2006/0228294, which is representative, these systems may comprise a refractory, induction furnace that receives the feed material into a molten metal bath, wherein a mix of organic and non-organic material is treated resulting in metal recovery and efficient production of synthesis gas (syngas). The syngas can be used to fuel a combined-cycle generator to provide municipalities with clean, renewable electricity.

FIG. 5 illustrates a representative process flow for the gasification process, although this is not a limitation of the described technique. The processing assumes material (as indicated by reference numeral 201) having a moisture content between about 20-50% due to the flotation tank processing. At this point, the material is about 1-250 mm in size. At step 203, the material is supplied to the fluid bed dryer, which reduces the moisture content to between about 0-10% by weight. In this embodiment, the fluid bed dryer is driven by heated air 205, and the output of dryer is supplied to an air pollution control system 207. In this embodiment, where an average gasification rate measured in hours is acceptable, the dried material is then supplied to a gravimetric weigh feeder at step 209. An auxiliary solid fuel feeding step 210 may be used to supplement the gravimetric weigh feeder if necessary. The output of the gravimetric weigh feeder is supplied to an injection system at step 212, such as a bucket elevator and a series of conveyors (mechanical or pneumatic). In this manner, the feed is delivered to a multiple piston feed system, as indicated at step 214. A multiple piston feed system supplies the material to a gasifier, such as a molten metal furnace, at step 216. In one embodiment, the molten metal bath is located within a refractory-lined vessel. Preferably, the vessel is not over-pressurized (i.e., operated above ATM pressure); alternatively, the techniques described herein may be carried out in a pressurized vessel. In one embodiment, the feed enters the vessel through a top-loaded feed tube, which injects the feed at a given submergence depth below the surface of a molten metal bath having a vitreous slag top layer. Other techniques for introducing the feed into the gasifier may be used as well. Upon entry into the metal bath, the waste material particles are exposed to elevated temperatures in excess of 1550° C., and as a consequence the material rapidly disassociates into elemental hydrogen and carbon. Carbon is oxidized to carbon monoxide by the oxygen content in the waste; thus, the primary reaction in the vessel is that the organic compounds in the waste should break down into C, CO and H₂. The residual carbon dissolves into the bath. This excess carbon is leached out of the bath by secondary O₂ injection, which is indicated by step 218. Gasification products include, for example, synthesis gas (a mixture of hydrogen and carbon monoxide). Collection of the off-gas is shown at step 220, and step 222 indicates that the slag and excess metal can be removed from the furnace and recovered as well.

While the above describes a particular order of operations performed by certain embodiments of the invention, it should be understood that such order is exemplary, as alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, or the like. References in the specification to a given embodiment indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Further, while given components of the system have been described separately, one of ordinary skill will appreciate that some of the functions may be combined or shared in given systems, machines, devices, processes, and the like.

In operation, the burner accepts fuel gases preferably directly from fuel gas generator without a requirement of significant cleaning and pressurization. The burner has the ability to utilize gases with gas compositions, such as 50/50 mixtures of carbon monoxide and hydrogen, at fuel gas temperatures in excess of 1500° F. The energy content of the fuel gas, excluding sensible heat, preferably ranges from 200-500 BTU's/cubic foot. Existing combustion systems would require cooling, cleaning and compressing of the fuel gas and injecting into the combustor under pressure. The oxidizer (air or oxygen) source would normally be at very low pressures. In contrast, a preferred combustor accepts fuel gases directly from the syngas generation process without significant cleaning and pressurization. The oxidizer (air or oxygen) is pressurized from 0.1-5 atmospheres.

Claims

1. A method of releasing energy, comprising:

receiving a fuel gas from a fuel source;

drawing the fuel gas through a burner while simultaneously injecting an oxidizer at a higher pressure relative to a pressure of the fuel gas;

wherein the fuel gas is drawn through the burner without first cooling, pressurizing or fine cleaning.

2. The method as described in claim 1 wherein the fuel gas is syngas.

3. The method as described in claim 2 further including separating particulates from the syngas prior to the drawing step.

4. The method as described in claim 1 wherein the fuel gas is drawn through the burner using an induced draft fan.

5. A burner, comprising:

a refractory-lined duct and burner inlet section that receives fuel gas directly from a gas source without first cooling, pressurizing or fine-cleaning the fuel gas; and

an oxidizer injector operating downstream of the burner inlet section.

6. The burner as described in claim 5 wherein the oxidizer injector comprises at least one free-standing injector comprising one or more flame holder wings.

7. The burner as described in claim 6 wherein each flame holder wing comprises one or more apertures through which the fuel gas is drawn.

8. The burner as described in claim 5 further including a secondary oxidizer injector downstream of the oxidizer injector.

9. The combustor as described in claim 5 wherein air or oxygen is injected by the oxidizer injector at less than stochiometric amounts to reduce formation of nitrogen oxides.

10. A method of energy generation, comprising:

retrofitting or providing energy generation equipment with a burner having first and second input sources;

receiving, as the first input source, a fuel gas; and

injecting, as the second input source, an oxidizer, where the oxidizer is injected at a higher pressure relative to a pressure of the fuel gas;

wherein the fuel gas is received from a fuel source without first cooling, pressuring or fine cleaning the fuel gas.