Patent Application
20080006225
The present invention is useful in any apparatus wherein a stream of gas, particularly gas at a temperature higher than ambient, is injected at high velocity and high momentum into a workspace or toward a workpiece. Workspaces generally comprise any sort of enclosed or partially enclosed volume, and are usually provided with an outlet that is permanently open or that can be intermittently opened and closed, for allowing gas to leave from the enclosure. Examples of such workspaces include combustion chambers, such as incinerators, furnaces for combusting fuel to generate heat that is converted into steam (which can then be converted into electric power), process heaters wherein combustion is carried out within a chamber to generate heat which is transferred through the walls of the chamber to product contained in or flowing through piping to heat or evaporate the material or to promote chemical reactions carried out within the piping. Other examples of workspaces include furnaces to vaporize or refine metal, and plasma spraying and coating operations.
The present invention is also useful in embodiments in which a gaseous stream is directed toward a workpiece, even if the workpiece is not contained within a workspace. Examples of embodiments wherein the gaseous stream is directed toward a workpiece include refining of steel and other metals, wherein the gaseous stream is directed toward a surface of molten metal (for instance, in the refining of the metal); apparatus wherein a stream of gas is directed toward a slab of metal, such as a slab of metal moving along a conveyor and being heated; and systems wherein a stream of gas is directed toward a pond of wastewater. Other examples of embodiments wherein the gaseous stream is directed toward a workpiece not necessarily enclosed within a workspace include operations wherein a stream is directed toward a surface to remove material from the surface, whether to clean it or for other material removal purposes.
Referring to
Fuel inlet 5 is provided for fuel to enter into chamber 3 from a source of the fuel. Oxidant inlet or inlets 6 permit oxidant to enter into chamber 3 from a source of the oxidant. Preferably, as shown in
Outlet 8 can comprise a single opening, or more than one opening. If outlet 8 comprises more than one opening, the openings can be of the same size and shape or of differing sizes and shapes, and they can all have the same axial orientation (that is, streams passing through them are parallel), or they can have different axial orientations. For example, one preferred outlet 8 would comprise 2 to 12 openings all of whose axes diverge away from a central axis so that gaseous streams passing through the openings form a conical pattern diverging such that its narrow end is at outlet 8.
Suitable fuel fed through fuel inlet 5 for combustion in thermal nozzle 1 includes any combustible hydrocarbonaceous material, preferably liquid or gaseous. Examples include natural gas, methane, and fuel oil.
Suitable oxidants fed through inlet 6 include streams containing less than 21 vol. % oxygen, air, oxygen-enriched air containing more than 21 vol. % oxygen, and oxygen in commercially available purities preferably 90 vol. % or higher.
The process material that is fed into chamber 3 through inlet 4 can be in the solid (preferably in flowable particulate form), liquid, or gaseous state, or can be in any two or all three of such states. The process material fed through inlet 4 can completely comprise material which is inert (not capable of being combusted), it can comprise a mixture of inert material in mixture with combustible material, with oxygen, or with both combustible material and oxygen, and it can completely comprise oxygen, combustible material, or a mixture of oxygen and combustible material. Examples of combustible material that the process material can comprise in whole or in part include the fuels described above that can be fed through fuel inlets 5, as well as gas from other chemical processing refinery operations, from pressure swing adsorption units, steam methane reforming units, and the like.
The amounts of process material fed through inlet 4, the amount of fuel fed through fuel inlet 5, and the amount of oxygen in the oxidant fed through oxidant inlet or inlets 6, relative to each other, are provided so as to attain (as a result of the combustion in chamber 3) the desired composition of the gaseous stream that is provided from the thermal nozzle 1. That is, if stream 11 is to contain oxygen or fuel, as the case may be, in order for instance to participate in combustion in the workspace or near a workpiece, then the amounts of oxygen and fuel that are fed into the thermal nozzle 1 in all feed streams (including in the process material stream 10) must be proportioned so that following the combustion that occurs within thermal nozzle 1 there remains an excess of uncombusted oxygen, or uncombusted fuel as the case may be, that exits in stream 11 and participates as desired in further reaction (such as combustion). Thus, it should be recognized that when the process material is fed into the thermal nozzle, the composition of the gaseous stream 11 that emerges from the thermal nozzle will depend on whether any component of the process material combusts with the combusting fuel and oxidant.
In some embodiments of this invention, the incoming process material is entirely or partially liquid, is entirely or partially solid, or is a mixture of gas and liquid, gas and solid, liquid and solid, or gas and liquid and solid. In any such embodiments, any liquid that is fed will be vaporized in chamber 3, and any solids that are fed will melt and vaporize. Thus, it should also be recognized that in any such embodiments, the determination of the amounts of fuel and oxygen to feed into thermal nozzle 1 must take into account the amount of heat required for melting of solids and for vaporization of liquid (including liquid as fed, and liquid obtained by melting of solids) so that the combustion that occurs within thermal nozzle 1 will produce a gaseous process stream and will provide that stream exiting the outlet at the desired temperature.
The temperature of the stream that exits the thermal nozzle is generally in the range of 100° F. to 3000° F., preferably 300° F. to 3000° F. The velocity of this stream is generally 100 to 3000 feet per second.
Among the many useful advantages of the present invention are those that pertain to the practice of the invention in providing a gaseous stream into a workspace. These advantages include improved mixing and recirculation of the gaseous atmosphere in the workspace, improved staging of combustion carried out in the workspace (which provides improved control to minimize emission of nitrogen oxides (“NOx”)), and enhanced heat transfer between the gaseous stream and the workspace atmosphere, and between the gaseous stream and other gaseous streams fed by auxiliary injectors or burners. These advantages have heretofore been provided by high momentum jets obtained by increasing the mass flow rate and/or the supply pressure of the gaseous stream.
The present invention, on the other hand; provides these advantages by converting thermal energy into kinetic energy to attain high injection velocities even at relatively low gas supply pressure. The injection velocity can be varied at any given supply pressure, permitting control of other properties such as momentum, entrainment ratio, and the like, without changing nozzles or using a variable nozzle. With this invention the gas stream momentum and other characteristics such as the entrainment ratio can be controlled while the process is in operation, by adjustment of the feed rates of the fuel and oxidant into the thermal nozzle and the ratio of those feed rates. There is no need to replace nozzles or other type of injection devices, or to increase the supply pressure of the incoming process material stream, to achieve the desired results.
The present invention is also advantageous in processes wherein the gaseous stream fed from the thermal nozzle is to react with other compounds in the atmosphere within the workspace or near the workpiece, or with other compounds fed by auxiliary injectors (whether or not combustion is taking place). The desired reactivity is increased by the high temperature of the gaseous stream fed from the thermal nozzle.
The present invention can be applied to other processes that do not involve combustion, such as:
hot oxidant injection at high velocity into a tilemaking furnace, to reduce black core formation in refractory and ceramic tile production processes;
hot oxidant injection at high velocity into coke beds;
injection of hot oxidant and/or inert gas at high velocity into molten metal;
injection of hot nitrogen, argon, or other inert gas, or mixtures of inert gases, into heat treating processes;
injection of reactive gases into heat treating processes;
injection of hot oxidant into wastewater treatment processes.
The higher injection velocity and higher temperature of the gaseous stream fed from the thermal nozzle provided by the present invention can bring benefits to the various applications of the invention, such as
enhancing entrainment with the gases within a workspace or adjacent to a workpiece, or with other gases injected into the workspace or toward the workpiece;
enhancing recirculation of the gases within a workspace or adjacent to a workpiece, or of other gases injected into the workspace or toward the workpiece;;
enhancing jet penetration into a body of liquid, such as a pool of molten metal or a wastewater treatment pond, or into a bed of solids such as coke bed;
enhancing reactivity, due to the high temperature and high entrainment and recirculation; and
decreasing the gas stream flow rate to impart the same momentum as a lower temperature stream resulting in comparable process performance with reduced oxygen consumption and thus improved process economics.
The advantages provided by the present invention follow from the velocity and momentum of the gaseous stream being supplied from the thermal nozzle, and from the ability to adjust the velocity and momentum. These, in turn, are based on the temperature of that stream and from the ability to control that temperature.
The velocity and momentum that the stream produced from the thermal nozzle should have, in order to provide the desired properties in the application for which the invention is being practiced, can be determined by calculations or by experimentation for a given apparatus, by varying the temperature of that stream and varying the rates at which the fuel, the oxidant, and the process material stream are fed to the thermal nozzle, until the gaseous process stream provided by the thermal nozzle exhibits the desired velocity and momentum.
A procedure to determine the conditions for operating a thermal nozzle in a given application, and for sizing the thermal nozzle for the application, is:
determining the velocity and momentum that the gaseous process stream is to have as it passes from the chamber through said outlet,
determining the temperature that the gaseous process stream is to have as it passes from the chamber through said outlet in order to have said velocity and momentum,
determining the amounts of fuel and oxidant that must be combusted in the chamber to generate sufficient heat of combustion to raise the temperature of said process material to the temperature determined in the preceding step, taking into account heat if any that must be provided to vaporize material fed as liquid and/or to melt and then vaporize material fed as solids;
feeding the amounts of fuel and oxidant determined in the preceding step into said chamber, feeding said process material into said chamber, and combusting said fuel with said oxidant and with combustible components, if any, in said process material to form said gaseous process stream, and passing said gaseous process stream through said outlet.
In conventional practice, heat is provided to the combustion chamber from air-fuel burners placed at the bottom of the radiant section of the chamber, but due to the characteristics of the flame promoted by air-fuel burners most of the heat transfer occurs at the upper end of the combustion chamber. When an increase in the throughput rate of material being heated in the aforementioned piping is desired, the overall firing rate at the air-fuel burners has to be increased but increasing the overall firing rate makes the flame much longer and does not promote the desired increase in heat transfer.
The present invention is implemented in this illustrative unit in order to promote a desired throughput increase and to enhance the heat transfer closer to the bottom of the combustion chamber, by providing high momentum injection of oxygen or fuel.
In
Apparatus with which the present invention is useful may contain, in addition to the thermal nozzle employed in the present invention, one or more other injectors of conventional design, such as burners or nozzles, which also emit one or more streams of gaseous material into the workspace or toward the workpiece. The apparatus of
In other embodiments, other nozzles can be provided (instead of or in addition to burners 25) which inject gaseous fluid, whether heated or not, into workspace 22. That is, there is no requirement that gaseous process streams that are fed into a workspace, or toward a workpiece, in addition to the process stream 11 from thermal nozzle 1, must be formed by combustion. Where burners 25 are provided, the fuel and oxidant are provided to each of them in appropriate amounts to enable combustion to occur at the burners, and for the combustion preferably to be maintained at those burners.
In the practice of the present invention, one or more than one thermal nozzle 1 can be added to the apparatus. One or more than one thermal nozzle 1 can replace auxiliary burners or injectors that were already present. Alternatively, the thermal nozzle or nozzles 1 can simply be added to what is already present in the apparatus, without removing any other burner or injector.
The appropriate velocity and temperature and feed rates can be determined by the sequence of steps described above. Here, though, where it is desired that the stream 11 from the thermal nozzle should intersect by entrainment with one or more streams from other injectors such as burners 25, the desired velocity of stream 11 can be determined or derived from correlation of the entrainment ratio (defined as the number of surrounding atmospheres entrained by the stream) against distance from the opening, for different temperatures of the stream 11. With the temperature thus known, the amount of oxygen and fuel required can be determined by straightforward thermodynamic calculations. The particular location of outlet 8, as well as the orientation of outlet 8, are determined based on the geometry and dimensions of the chamber 22 into which the gas is fed, and on the location of the process heating tubes and the location of the burners.
