Patent application title: OXYGEN INJECTION THROUGH A ROOF OR CROWN OF A GLASS FURNACE
Neil Simpson (Edinburgh, GB)
IPC8 Class: AF23C700FI
Class name: Process of combustion or burner operation flame shaping, or distributing components in combustion zone oxidizer added to region of incomplete combustion
Publication date: 2010-09-23
Patent application number: 20100239988
A method is provided to facilitate combustion in a furnace having at least
one burner, an inlet, an outlet, and sidewalls and a crown defining a
combustion chamber for the furnace, the method consisting of identifying
a region of the combustion chamber where a furnace atmosphere therein
requires an increase in oxygen for combustion in the furnace atmosphere,
and providing fresh oxygen to the region at a controlled flow rate for
the combustion, wherein the fresh oxygen provided causes circulation of
the furnace atmosphere for combining existing gases and existing oxygen
of the furnace atmosphere with the fresh oxygen provided to the region
1. A method to facilitate combustion in a glass melting furnace having at
least one burner, an inlet, an outlet, sidewalls and a crown defining a
combustion chamber for the furnace, the method comprising:identifying a
region of the combustion chamber where an atmosphere of the furnace
requires an increase in oxygen for combustion in the furnace
atmosphere;injecting fresh oxygen through an injector in the crown of the
furnace to the region at a controlled flow rate for the
combustion;generating a suction effect for the furnace atmosphere in the
combustion chamber responsive to the fresh oxygen provided, wherein the
furnace atmosphere circulates for combining existing gases and existing
oxygen in the furnace atmosphere with the fresh oxygen provided to the
region for combustion.
3. The method according to claim 1, wherein the fresh oxygen injected is in a gaseous stream containing from 20.9% to 100% oxygen.
4. The method according to claim 1, wherein the injector comprises at least one injection port disposed at the crown of the furnace.
5. The method according to claim 4, wherein the at least one injection port comprises a tubular member having a first end connected to a source for the fresh oxygen, and a second end terminating in the furnace atmosphere for providing the fresh oxygen to the region for combustion with the existing gases and the existing oxygen.
6. The method according to claim 1, wherein the fresh oxygen is provided near the inlet of the furnace proximate the at least one burner.
7. The method according to claim 1, wherein the fresh oxygen is provided to the region in registration with a longitudinal centerline of the furnace.
8. The method according to claim 1, further comprising introducing a fluid with the fresh oxygen to increase a delivery rate of the fresh oxygen into the furnace atmosphere.
9. The method according to claim 8, wherein the fluid is selected from a combustible gas, combustible liquid and combinations thereof.
BACKGROUND OF THE INVENTION
The invention relates to injection of oxygen in furnaces.
Furnaces, such as glass melting furnaces, which require additional tonnage/quality or are operating at reduced tonnage due to damage or degradation of heat recovery devices in the form or regenerators or recuperators, have used oxygen and oxygen burners, and fuel burners to gain additional tonnage/quality or recover lost production.
Oxygen enrichment is typically achieved by introducing oxygen into the combustion air downstream of the forced combustion air fan or blower for the furnace. The required equipment is minimal and therefore is a low cost installation. The oxygen is injected at a location that ensures the oxygen is well blended with the combustion air. Injecting pure 100% oxygen into an air stream means that approximately five times the volume of air can be removed to provide the same amount of oxygen. The actual percentage of oxygen that is possible is determined by local/CGA (Compressed Gas Association) codes and HAZOPs (Hazardous Operation Procedures), but is always less than 29% on a volumetric basis and more typically less than 25%. It should be noted that with respect to enrichment, the point of combustion is indiscriminate. For example, if a first port of a four port cross-fired regenerative furnace is partially blocked, the location at which the oxygen is really required is in the first port area. Since the remaining ports offer a path of lower resistance, there is proportionally more oxygen that goes where it is not required/desired. General enrichment may be the least expensive as far as cost of installation, but it is the least efficient method of using oxygen where it is needed in furnaces.
Oxygen lancing overcomes many of the disadvantages of enrichment by injecting oxygen at the location where it is needed most. Lancing is accomplished by underport, through-port, over-port, side-of-port or from the regenerator target wall. For example, if the first port of a four port cross-fired regenerative furnace is partially blocked, the location at which the oxygen is required is in the first port area and therefore, it is in this area that the majority of the oxygen is injected. A regenerative furnace has a reversal system and therefore, it is necessary in such a furnace to have a relatively complex and expensive control system to feed a correct amount of oxygen to the correct port. Typically, if a lancing system is installed with the furnace it will feed oxygen to at least a plurality of ports. Since the oxygen requirements may vary from one side to the other, there is a requirement for flow control on each side of the furnace. A reversing three-port lancing panel would therefore require six zones of control. There is also a limit to the amount of oxygen that can be injected in the port area. Higher levels of oxygen in the port can cause too much heat release in the port area, thereby causing structural damage. In under-port applications, the flames can become too short and create an imbalance in heat distribution which can cause glass defects.
Oxygen enrichment and lancing have been used to recover up to 10% of lost furnace melt capacity.
When additional capacity is required, there is typically a need for fuel flows beyond the capacity of the installed air fuel system for the furnace. Oxy-fuel boosting involves the placement of at least one and sometimes a plurality of oxy-fuel burners in the zero port (area between charging wall and the first port) or in the hot spot (point of upwell melt area in furnace) of the furnace. Conventional oxy-fuel burners can either recover lost production from a furnace or increase capacity by at least 10%, and occasionally as high as 15%. The furnace design usually determines the capacity that can be obtained and where, if possible, burners can be positioned and installed. Installation is costly, since a dedicated oxygen and fuel control skid is typically required. The overall system capacity is determined by the exhaust capacity of the furnace.
When there are space constraints in the furnace, or capacity in excess of 15% is required, it is possible to install oxy-fuel burners in the crown or roof of the furnace. A significant amount of energy can be injected into the furnace using roof mounted burners. It is possible to block-off existing air-fuel ports and replace the air-fuel ports with oxy-fuel. In extreme cases it is possible to create a 100% oxy-fuel furnace or in a transition phase for the furnace convert to a hybrid furnace with oxy-fuel for melting and air fuel for refining/conditioning.
One of the major disadvantages of oxy-fuel boosting, especially when used with cross-fired regenerative furnaces, is the turndown (reduction in firing capacity) of the burners. This is common to both conventional or crown mounted burners. In order to avoid flame distortion or interaction, there is a minimum flowrate that is required. At certain times due to production or product mix, it is necessary to use more oxygen than is really required.
Mathematical modeling shows that when converting a zero port conventional oxy-fuel boost to roof mounted burners firing with the same amount of oxygen and fuel, there has been a change in distribution of the excess oxygen in the exhaust ports. While providing fuel and oxygen through a burner in the crown provides more oxygen in the first and second ports than with conventional horizontal style burners, there is still the deficiency in known systems of not having enough oxygen to combust as necessary in certain areas of the furnace and for particular melt operations.
Since air is 20.9% oxygen, with the balance being nitrogen and noble gases, replacing air with oxygen provides a reduction in volume of 79.1%. If furnace pressure is a limitation on combustion and flowrate, then replacing air with oxygen, even partially, can solve the problem as discussed below.
SUMMARY OF THE INVENTION
There is provided injection of oxygen through a crown of a furnace, such as a glass furnace, into a selected region of the furnace to enhance the furnace atmosphere convection flow patterns, thereby providing furnace gases with higher concentrations of oxygen. There is provided more efficient combustion in a furnace to recover or provide additional capacity by positioning the oxygen at the point of greatest combustion need; and flexibility to safely inject oxygen into and at increased amounts to specific areas or zones of the furnace.
There is also provided a system, whereby at least one or a plurality of oxygen jets or oxygen injectors are disposed in the roof or crown of the furnace at select positions with respect to the ports of the furnace for injecting oxygen into the combustion atmosphere of the furnace to facilitate a venturi effect of said atmosphere and induce entrained oxygen in the existing furnace atmosphere to areas desired for combustion.
The system of the present invention also reduces NOX (nitrous oxides).
The oxygen (O2) injection and selected flow of oxygen increases the temperature of the furnace and facilitates combustion in the furnace. This is useful for existing furnaces where there is insufficient space for installing additional burners.
There is provided by the present invention a selected region identified in the furnace where the oxygen is needed and therefore injected into the furnace atmosphere near an inlet of the furnace and before a first port or burner of the furnace; the first port being the port closest to the inlet of the furnace. Injection of the O2 may be in registration with, but not be limited to, the longitudinal centerline of the furnace.
A method is provided to facilitate combustion in a furnace having at least one burner, an inlet, an outlet, and sidewalls and a crown defining a combustion chamber for the furnace, the method consisting of identifying a region of the combustion chamber where a furnace atmosphere therein requires an increase in oxygen for combustion in the furnace atmosphere, and providing fresh oxygen to the region at a controlled flow rate for the combustion, wherein the fresh oxygen provided causes circulation of the furnace atmosphere for combining existing gases and existing oxygen of the furnace atmosphere with the fresh oxygen provided to the region for combustion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a longitudinal cross-section of a cross-fired regenerative furnace having an oxygen injector of the invention for facilitating gas flow along an interior of the furnace proximate the crown and toward combustion zones of the furnace.
FIG. 2 shows a lateral cross-section of the furnace of FIG. 1, having a plurality of the oxygen injectors across the furnace width.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1 and 2, there is shown a furnace 10, such as a glass melting furnace, which includes a roof or crown 12. A regenerator 14 or plurality of regenerators are disposed for communication and operational use with the furnace 10. The regenerators 14 are in communication with a furnace atmosphere "A" of the furnace 10. The regenerators 14 each include checkers 15. A batch charging system 16 is in communication with the furnace 10 at an inlet 18 of the furnace for providing batch 20, as in this case glass seed, to the furnace for the melt. A glass bath is shown generally at 22. Exhaust flow from the furnace 10 is shown generally at 24, moving from the furnace 10 combustion atmosphere A to the regenerator 14.
One or a plurality of ports 26 (numbered 1-7) are disposed along opposed sides of the furnace 10. One or a plurality of oxygen injectors 28 are disposed in the crown 12 of the furnace 10. Each one of the oxygen injectors 28 may be formed as a tube constructed from, for example, metal or ceramics. The oxygen injector 28 may be positioned anywhere along the crown 12 of the furnace 10. That is, each oxygen injector 28 can be positioned to be in registration with a corresponding one of the ports 26 or arranged to be positioned between the ports 26. In addition, an oxygen injector 28 can be positioned as shown in FIG. 1, i.e. between the inlet 18 or the batch charging system 16 and the port 26 (#1) of the furnace 10. Similarly, the oxygen injector 28 can be positioned proximate to an outlet 30 (glass discharge section or throat) of the furnace 10, at any location along the crown 12 such as also at a longitudinal centerline "C" of the furnace 10.
The oxygen injector 28 may comprise a pipe or tube having the necessary sealing member or component where the pipe is introduced through the crown 12 of the furnace 10. One end of the oxygen injector 28 is connected to an oxygen source (not shown) while an opposed end of the injector 28 terminates in the furnace atmosphere A as shown in FIGS. 1 and 2. Each injector 28 has its own controllable flow rate to provide its respective oxygen profile 29. A plurality of injectors 28 may have their flow rates adjusted to provide a combined oxygen and burn profile selected for the particular glass bath 22 or melt.
The oxygen injectors 28 may be disposed in the crown 12 of the furnace 10 at a position whereby the oxygen jet is introduced into the furnace vertically (at 90° to the bath 22) and up to an angle 32 as much as 45° with respect to the vertical as shown in FIG. 1. Some furnaces have a throat which is located at an outlet of the furnace below the glass line. The oxygen injectors 28 may be used with existing burners being used in the furnace 10.
Injection of a gaseous oxygen stream through the crown 12 of the furnace 10 generates a venturi (suction) effect in the furnace to draw gases from other parts of the furnace in the form of a circulatory current toward the injected stream for combustion. Such a circulatory current flow is shown generally by arrow 34. Depending on the point of oxygen injection, such will determine what gases are drawn into the oxygen stream. For example, in most cross-fired furnaces there is more oxygen in the downstream ports 26 (such as port #s 5-7) than the upstream ports 26 (port #s 1-4). However, it is desirable to have a sufficient amount of oxygen in the upstream ports 26. Therefore, injecting a gaseous stream in the upstream zone of the furnace draws furnace gas of higher oxygen concentration from the downstream ports 26 (port #s 5-7) toward the upstream ports 26 (for example, port #s 1-4).
In the invention, the injected gaseous stream contains oxygen from 20.9% to 100%. However, due to the entrainment of additional oxygen molecules from an area in the furnace 10 with higher localized oxygen concentration, the total oxygen conveyed to the flame as a result of the venturi effect can be greater than the amount of oxygen injected by the injectors 28, with the combustion air supply shown generally at 36. This is the total of oxygen injected with the oxygen injectors 28 plus the entrained oxygen stream. The entrained stream will comprise compounds of oxygen, nitrogen, carbon monoxide, carbon dioxide, water, noble gases, gases of evolution from the glass, and combinations thereof.
As shown in FIG. 2, having a plurality of gaseous injectors 28 disposed across the crown 12 results in a port fire flame for the furnace being provided with the additional oxygen introduced from the oxygen injector 28 and the flow stream 34 as it crosses the surface of the glass melt 22. This flame injection of furnace gases will reduce overall nitrous oxide (NOx) formation by the increased efficient combustion.
The gaseous oxidant stream flow 34 facilitated by the venturi effect of the injected oxygen resembling the circulatory current will contact the glass batch surface 38 and provide a localized high concentration of oxygen under the flame created by the combustion air supply 36 and burner being used in the furnace 10. This flow 34 will combust the flame and ensure complete combustion prior to exiting through exhaust 24 of the furnace 10. The resulting flame temperature in the furnace 10 will be increased and in turn will increase the localized heat transfer to the glass bath 22.
Utilizing a portable gas analyzer during commissioning and process optimization of the furnace 10 will enable the desired furnace fuel profile and heat release to be achieved with the minimum amount of oxygen to be injected and used.
An important aspect of this invention is to recover unused oxygen in the furnace atmosphere and to reduce NOX (nitrous oxide) of the furnace. To do this, the oxygen stream may be directed down from the lateral centerline of the furnace 10 at an angle so as to sweep under the port 26 (#1). To reduce NOX, the amount of oxygen injected under combustion fire will stoichiometrically complete the combustion of the fuel or exceed the stoichiometric amount of oxygen to complete the combustion of the fuel. Injecting the oxygen toward or at the centerline C of the furnace has the benefits of not overheating the wall of the furnace through which the incoming fuel is passing and avoiding wasting the oxygen by combusting the oxygen with the fuel-gas over the batch rather than at or in the exhaust flow 24 or in the regenerator 14. When the stream of oxygen passes under the path of the fuel-gas, it will pull the fuel-gas down over the batch as it is combusted and reduce the amount of energy that will heat the superstructure of the furnace or the regenerators. This equates to a more efficient process of transferring energy into the bath 22 and accelerating the melting of the batch.
The oxygen injector 28 does not have to provide 100% oxygen. For example, oxygen content injected could be in a range of 70% oxygen and 30% gas. There are advantages to operating the injector 28 with some fuel rather than being 100% oxygen. One advantage is that it would provide thrust to the injected oxygen stream to ensure same will pass under the first port 26 fires. This thrust would be affected by different variables in the furnace operation, such as for example the distance of the crown to the bath 22, the speed of the circulatory flow 34 across the furnace, the amount of the gas in the first port.
In order to have a port firing on the reducing side of stoichiometry, one has to either partially or completely block off that port to limit the amount of combustion air that would pass through that port or add additional fuel through that port that exceeds the stoichiometric amount of oxygen that would be in the combustion air passing through this port. In this case, the amount of air that passes though a port is proportioned by the area of that port relative to the total area of all the incoming ports. This occurs in the regenerator 14 in which all the incoming combustion air passes through a common manifold above the checkers 15 before entering the ports.
The oxygen injectors 28 can be used on the furnace 10 regardless of whether the furnace is providing float, container, lighting, display or specialty glass.
It will be understood that the embodiments described herein are merely exemplary, and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. It should be understood that embodiments described above are not only in the alternative, but may also be combined.
Patent applications in class Oxidizer added to region of incomplete combustion
Patent applications in all subclasses Oxidizer added to region of incomplete combustion