Patent Application
20060147853
1. Field of the Invention
This invention relates to feed nozzles, and more particularly to feed nozzles for a variety of gas/liquid reactions, including chemical synthesis reactions and also combustion and other oxidation reactions in which the feed nozzle is part of a burner apparatus.
2. Background of the Art
A variety of related industries employ reaction of a gas/liquid system to effect a desired end result. These include, for example, the waste-reduction industry, the chemical manufacturing industry, the gas manufacturing industry, and energy-related industries that rely upon combustion as the energy source. Each of these industries commonly effects this reaction by means of fine atomization of streams of one or more liquids, frequently within a zone of increased temperature. In the case of gasification reactions, both the atomization and the higher temperature serve to promote the liquid-to-gas phase change that improves mixing at a molecular or near-molecular level, thereby promoting the desired final result. This mixing may be of one or more liquid compounds or compositions with a specific gas, such as air, oxygen, carbon dioxide, steam, an inert gas such as argon or nitrogen, or a combination thereof.
For each of the above types of reactions, the atomization generally takes place within a reactor vessel of some type. One common type of reactor vessel is the refractory-lined, generally cylindrical vessel used for “burning” liquid chemical waste, which is frequently a mixture of halogenated hydrocarbons. Because many of these are chlorinated compounds, the term “R—Cls” is often used to describe them. In essence the same type of combustion reaction is accomplished as in a simple internal combustion engine, for example, where the atomized liquid stream mixes with oxygen in a high temperature zone, and a desirably high conversion results in the final hydrogen, carbon dioxide and carbon monoxide products, with a minimum of residual carbon (“soot”). Other types of reactor vessels are used for a wide variety of chemical synthesis operations, according to the needs of the starting and desired final products.
The cited industries have geared much innovation toward developing appropriate feed nozzles to transport their specific starting liquid streams into the appropriate reactor vessels. They have recognized a number of factors that affect the conversion rates within the reactor, and feed nozzles have been designed to alter velocity, flow dynamics and spray patterns of the liquid. These design options are motivated by essentially one accepted concept: That the drop size of the liquid is an important factor in determining the ultimate outcome, i.e., the performance, of the process. Simply stated, if the drops are too large, the mixing of the liquid stream with a gaseous stream, such as oxygen, will be reduced. If the mixing is reduced (due to the decreased interface between molecules), the conversion of the liquid stream will be likewise reduced. If the conversion is decreased, the result will often be residual unreacted liquid feeds which may either form soot or leave the reactor, which may result in undesirable environmental consequences. This soot can foul equipment, resulting in expensive down-time. Thus, feed nozzle technology has consistently recognized that, to ensure that drop size remains appropriately small, the aperture of the feed nozzle must remain restricted, which limits the throughput of the nozzle. This inherent drop size limitation has heretofore limited the efficiency of operations and resulted in use of either multiple parallel reactor vessels, or single reactor vessels with multiple burner nozzles arranged such that the atomized streams do not converge. This is because those skilled in the art have accepted as common wisdom that convergence of atomized streams tends to result in increased drop size and, therefore, conversion rate losses.
It is important to note that the characteristics of a spray can be expressed in several ways. One common way is to use a spray's drop size average, such as the “Sauter mean diameter” (SMD). The SMD of a spray is the average drop size having the same surface to volume ratio as the overall spray. Alternatively, the spray can be characterized by its “volume median diameter” (“DV”). This method describes a drop diameter which is greater than a given proportion of the spray. For example, if a spray is described as having a “DV90” of a certain diameter, it means that approximately 90 percent of the spray volume is in drops smaller than that diameter. Similarly, a “DV50” of a certain diameter means that approximately 50 percent of the volume of liquid is in drops smaller than that diameter. Because drops follows what is called the “D squared Law” of drop evaporation, where the evaporation time is proportional to the square of the drop size, one of the best indicators of nozzle performance is the spray's DV90. Optimized nozzle systems also exhibit a directly proportional relationship between the spray's DV90 and the SMD of the drops. In view of these relationships, then, the SMD can be used to provide a clear characterization of any spray.
Another problem is encountered where feed nozzles are used as components of so-called “burners”, for example, in the waste-reduction industry. As used herein, the term “burner” refers to an apparatus that comprises both a feed means, such as a nozzle, and a means of mixing the liquid feed stream with a gas, such as oxygen, in a high temperature environment to promote combustion of the feed stream. The combination of the high temperature and the often corrosive nature of the environment surrounding the nozzle, i.e., of the mixture of atomized liquid feed and gases, tends to shorten burner life. This shortening is due to corrosion and/or thermal fatigue of the metals used to construct the burner and its included nozzle.
Still another problem, encountered by the waste reduction industry in particular, occurs when incompatible liquid feed streams are destined for a single reactor. An example of this is streams that contain small amounts of polymerizable monomers that may polymerize once the streams are mixed. Premixing may be impractical in these situations, because the formation of polymeric materials can foul equipment and, in the case of internal mixing burners, even shorten burner life where the polymer/gas reaction results in undesirable products.
In view of these problems, it is desired in the art to identify means to effectively introduce atomized liquid feed streams, having controlled drop size, into a reactor vessel for a variety of types of reactions. It is also desired, where such introduction is intended to accomplish burning of a waste feed stream, to control drop size and also to protect the burner, which includes the feed means, from environmental factors that tend to shorten burner life.
The invention is a feed means designed to ensure maintenance of appropriate drop size while increasing efficiency of a given operation within a single reactor vessel. In one embodiment it is an improvement in a feed means for a gas/liquid reaction system, in which a feed nozzle assembly includes a plurality of feed nozzles, suitable to atomize at least one liquid feed stream to form sprays, the feed nozzles being positioned such that the sprays impinge upon one another. The result of this impingement is that the Sauter mean diameter of the drops of the impinged sprays is substantially less than, or equal to, the Sauter mean diameter of the drops prior to impingement. The arrangement of the nozzles, which includes selection of an appropriate number of nozzles, can be optimized to ensure desired feed volume within a given time period without unacceptable sacrifice of conversion rate.
In another embodiment the invention is a method for reaction of a gas/liquid reaction system wherein the described feed nozzle assembly is employed.
In still another embodiment the invention is an improvement in a burner apparatus for reaction of a gas/liquid reaction system comprising a feed nozzle assembly that is located along a central axis and employs a plurality of feed nozzles suitable to atomize at least one liquid feed stream to form sprays, the feed nozzles being positioned such that the sprays impinge upon one another such that the Sauter mean diameter of the drops of the impinged sprays is substantially the same as, or less than, the Sauter mean diameter of the drops prior to impingement. The inventive burner apparatus also includes a moderator gas feed area, an oxygen feed area, a mixed moderator gas/oxygene feed area, or a combination thereof, located annular to the feed nozzle assembly. An optional annular cooling area may also be included. These annular feed areas may be configured such that the exterior barrier of each annular feed area extends beyond the exterior barrier of the enclosed annular feed area, and the innermost annular area has an exterior barrier extending beyond the centrally-located feed nozzle assembly. This feature ensures that the sprays emitted by the feed nozzles pass first through a cap environment created by the innermost annular feed area.
Finally, in yet another embodiment the invention is a method of gasifying a liquid waste stream using the improved burner apparatus.
The inventive feed nozzle assembly is a simple but extremely effective means to circumvent the problems associated with use of just one feed nozzle, while surprisingly teaching away from the accepted wisdom that convergence of “sprays”, i.e., atomized liquid feed streams, unacceptably and automatically increases drop size, thereby promoting poor conversion and overall process performance. It has now been found that, by appropriate adjustment of the number of feed nozzles and the positioning thereof relative to one another, and taking into account the characteristics of each feed nozzle as to maximum feed velocity, aperture configuration and resulting spray pattern, the sprays can be impinged in such a way so as to balance the impact destruction and coalescence of the drops, and thereby ensure desirable drop size for the given operation while at the same time maximizing potential feed stream input rate.
Impingement obviously requires at least two sprays which overlap at some point in their trajectories within the reactor vessel. For many purposes it is desirable to ensure that this overlap occurs as soon after entry into the reactor vessel as possible, in other words, as close to the feed nozzle apertures as possible. This maximizes the mixing of the liquid feed stream or streams (which may be the same or different) with at least one gaseous feed stream, such as oxygen, and also incidentally reduces the need for a larger reactor vessel. Thus, it is preferred in the present invention that the feed nozzles be located closely proximate or even in some direct contact with one another. Adjustment of the distance is a matter of routine design analysis, to determine the optimum balance of pressure and velocity against any gas phase turbulence which could tend to increase coalescence by increasing the incidence of low velocity collisions.
The relative positions of the feed nozzles can be used to increase or decrease the impingement area. For example, the feed nozzles can be angled toward one another, as in
Those skilled in the art will appreciate that the orientation of the nozzles may, however, desirably take into account the spray pattern of any given nozzle. Each nozzle, according to its aperture and the geometry of the flow conduit leading to the aperture, exhibits a characteristic (and in some cases, adjustable) spray pattern. Such pattern may be a so-called “hollow-cone” or “solid-cone” configuration, or may be described as forming a fan or flattened cone shape, or a hollow or solid cylindrical shape. Other configurations may also be employed. Nozzles may be of the pressure-swirl or other type. While the needs of a given liquid feed stream, including its purity, self-polymerization potential, and other characteristics, may dictate a preference for a particular configuration, a majority of commercially-available industrial pressure-swirl nozzles exhibit the “hollow-cone” pattern, and therefore such is preferred herein as a matter of convenience only. The “cone” diameter will vary according to distance from the feed nozzle, of course, but the angle of the cone at the aperture is, in many commercial models, approximately 80 degrees. Thus, for illustrative purposes only, such is shown in
Those skilled in the art will automatically appreciate that selection of nozzles with cylindrical spray patterns, for example, will require at least some angling of the nozzles toward each other to ensure a desired level of impingement. Conversely, it will also be appreciated that nozzles having broad cone spray patterns may be capable of being positioned even at angles away from one another (i.e., with the aperture of the nozzles being farther apart than the nozzle portions distal to the corresponding apertures, as in
It should be noted that impingement may alter the shape of the impinged spray area(s). For example, it has been found that impingement of a number of fan-shaped sprays, resulting from several nozzles that are annularly arrayed around a central nozzle, with the annular nozzles all angled generally toward the center line, may result in a dense spray having a cylindrical conformation. Thus, the initial shape of a single nozzle's spray pattern will be a factor in determining the initial SMD of the (non-impinged) drops, but may not be visually recognizable in the impinged sprays.
Where multiple feed nozzles are selected, space and overall design preferences will tend to prefer a cluster of nozzles that are closely positioned, enabling the “assembly” of nozzles (which as herein defined does not specifically require that the plurality of nozzles be attached to one another) to be constructed as an “assemblage” (which as herein defined does require physical attachment of the nozzles themselves and/or of at least some of their supporting lines of fluid communication to a liquid feed stream source). Such a cluster is suggested in
It will be appreciated that the exigencies of interior nozzle design are beyond the scope of the invention and therefore need not be discussed in detail herein; however, one potential advantage of the present invention does suggest the basis for an interesting alteration of traditional nozzle design. Simply because the present invention employs a plurality of feed nozzles, which increase output rate and therefore efficiency, rather than the single feed nozzle heretorefore commonly employed for the types of reactions envisioned herein, it is possible to feed two, or more, chemically-different liquid streams into the reactor vessel at one time. Thus, two or more liquid reactants may be fed simultaneously into a synthesis vessel, to produce the desired product in reaction with a gas; or, alternatively, two or more liquid waste streams, that may technically be reactive, can be fed simultaneously into a waste-burner vessel, without encountering a prohibitive level of undesired reaction, if any. With this in mind, then, those skilled in the art will readily see that a single feed nozzle, defined herein to mean the pressure-producing housing containing at least one flow conduit connection that runs from the liquid feed stream source to the aperture, may, when fitted with more than one flow conduit connection and thus more than one aperture, accomplish the same goal. Such is further exemplified in
A particular advantage of the invention is that it may be employed where incompatible liquid feed streams are to be fed into a reactor. As used herein, “incompatible” refers to feed streams that react to produce an undesirable reaction product. An example of this is monomers that polymerize to form a polymer that may foul the equipment in an undesirable manner, or that may produce a product that has an undesirable environmental consequence. Thus, “compatible” refers to feed streams that, though they may react, do not produce a reaction product that is, for any reason, undesirable or that may, in fact, be a desirable reaction product.
A further advantage of the present invention relates to start-up problems. In many cases, conversion rates for single nozzle reactor systems are poor upon start-up because of changes in drop size relating to the necessary pressure ramp-up. As pressure is stabilized at operating levels, drop size likewise stabilizes, but during ramp-up, all of the problems associated with oversized drops, including poor gas/liquid reaction, poor conversion, fouling and the like, may occur. In the present invention, however, the nozzles may be started in a desired sequence, with the effect of the impingement to break up drops used to offset at least a portion of the poorer atomization within a single nozzle that occurs during the pressure ramp-up. In some cases it has been found that using an array of six nozzles surrounding a seventh, central nozzle, and starting the feed through the central nozzle first, followed shortly thereafter by additional feeding through the remaining nozzles, results in improved conversion. Routine engineering analysis and modeling will easily determine the sequencing and pressure ramping profile that will significantly improve performance during the start-up period.
The inventive feed nozzle assembly, described hereinabove, may be incorporated in an inventive burner apparatus. Such apparatuses are particularly suited to use in waste-burning, with the liquids that are destined for destruction being desirably mixed in their atomized, spray condition with one or more gases. Such gas may be air, oxygen, carbon dioxide, steam, an inert gas such as argon or nitrogen, or a combination thereof. The inventive burner apparatus provides a means to effectively accomplish this mixing, by including the inventive feed nozzle assembly in a location that forms a central axis, and with discrete gas feed areas arranged annular thereto. For example, in one embodiment the innermost annular area may be a moderator gas feed area. Such a moderator gas may be any of the above-identified gases, but is frequently steam which conveniently moderates the temperature under which the gasification may take place. In another embodiment there are two or more, outwardly successive annular feed areas, one of which is a moderator gas feed area and the other of which is an oxygen feed area. As the term is used herein, “oxygen feed area” refers to gaseous feeds that include any proportion of oxygen, and thus includes air feeds as well as those that contain generally from 1 to 100 weight percent oxygen.
A particularly desirably feature of the inventive burner apparatus relates to the exterior barriers of the annular areas. As shown in
Finally, in one embodiment some type of exterior cooling means may be employed to further reduce thermal stresses on the burner apparatus and/or on the reactor itself. For example, an annular cooling means, which may be disposed external to any or all of the annular feed areas, may provide desirable temperature control. Such may be, for example, a traditional water jacket, in which cool or cold water is fed into an open or closed loop-type jacketing on a continuous basis, with the water removing heat from the apparatus prior to its being routed away from the apparatus. Such a water jacket may form the final external “layer” of the burner apparatus.
A review of the drawings will assist the reader in understanding the overall concepts of the invention. However, the drawings are intended to be, and should be construed as being, merely illustrative and not indicative of either the scope of the invention or of the inventors' claims appended hereto.
The description, drawings and examples discussed hereinabove are intended to provide to the skilled practitioner the general concepts, means and methods necessary to understand the present invention and, when combined with a level of understanding typical of those skilled in the art, to practice it. It will therefore be understood that not all embodiments deemed to be within the scope of the invention are herein explicitly described, and that many variations of each embodiment, including but not limited to feed nozzle assembly and burner apparatus materials, orientations, constructions, arrangements and applications not described explicitly or in detail herein, will still fall within the general scope of the invention.
