Patent Application
20240399398
The invention pertains to spraying apparatuses and methods and, in particular, to spray guns of the type in which a liquid is atomized into finely dispersed droplets via mixing with a pressurized atomization fluid such as air.
There are several industrial processes that employ spray guns to discharge a process liquid at high flow rates as a spray of very fine droplets. Creating small size liquid droplets is important for the processes as it increases contact area, mass transfer rate, reaction rate, combustion efficiency, and/or improves other process parameters that benefit from fine liquid dispersion. Efficient atomization of the liquid with generation of small droplet sizes is thus a required feature for many spray guns.
A typical prior art pressure-atomized spray gun utilized in process industries is depicted in
The ability to control the temperature of the fluids flowing through the spray gun, as well as the temperature of the metal that forms the spray gun itself is a beneficial feature, and often a requirement, in some process applications. Temperature control of the fluids allows for control over their temperature-dependent physical properties that affect the flow and atomization of the fluids, such as viscosity and density. Additionally, for spray guns used in combustion operations or in operations in which the sprayed liquid is at a high temperature, the spray gun can become overheated. An ability to remove some heat via a heat transfer is beneficial in order to avoid deformation of material that forms the spray gun, and avoid undesired physical or chemical changes to the fluid inside the spray gun.
As spray guns are often mounted to vessels in industrial processes, with access to the nozzle restricted since it protrudes into the vessel, servicing the spray gun or performing maintenance can be difficult or time consuming.
Many industrial processes may change their production capacity or process conditions over time, or simply change flowrates through the process depending on external factors such as upstream effects, market demand for the product, etc. Thus, an ability to adjust and customize the geometry and performance of the spray nozzle body and tip to achieve optimal liquid atomization at a wide range of flowrates would be advantageous for a spray gun. Additionally, as the supply of auxiliary or utility streams in industrial processes (e.g., instrument air) is often fixed at certain conditions (e.g., pressure), it would be useful to be able to adjust the flow properties of the atomization fluid entering an internal mixing chamber of the spray gun by adjusting the geometry within the spray gun or nozzle body itself. This could help to achieve optimal liquid atomization regardless of the supply conditions of the fluids.
There remains a need for effective apparatus and methods for spraying atomized liquids which ameliorate at least some of the disadvantages of existing systems.
The invention is directed to spraying devices and methods that involve spraying a liquid as very fine droplets. It is an object of the present invention to provide means to accomplish this operation along with additional functionalities that improve the spray gun's performance, allow for adjustability, improve reliability, and simplify its maintenance.
According to one embodiment of the invention, the spray gun assembly atomizes a liquid by directing flows of liquid and a pressurized atomizing gas into an internal mixing chamber. The atomizing fluid is driven through narrow passages that increase the fluid's velocity before entering the mixing chamber, where it breaks up the liquid into fine droplets before the mixture is discharged from a nozzle tip as a fine mist spray.
The invention accomplishes temperature control of the fluids and the material of construction of the device by feeding a heat transfer fluid (e.g., steam) into a flow passage defined between the passages for the liquid and atomizing fluid, running along the length of the lance.
The spray gun assembly includes a port at the upstream end of the spray gun lance that allows inspection of the main liquid pipe.
The spray gun assembly can be customized to suit a particular spraying operation by reason of its removable nozzle tip and nozzle body as well as its adjustable flow passages which direct the atomizing fluid into the internal mixing chamber. A metallic O-ring seal allows the nozzle body to slide farther into or out of the lance on its threaded connection, exposing more or less flow area, respectively, for the atomization fluid.
Further aspects and example embodiments are illustrated in the accompanying drawings and/or described in the following description.
Referring to
The spray gun has three process stream inlets and two process stream outlets. These comprise an inlet 18 for a liquid that is to be atomized, an inlet 20 for a pressurized atomization fluid that breaks up the liquid into fine droplets, an outlet 22 for the atomized liquid and the atomization fluid at the nozzle tip 16, an inlet 24 for a heat transfer fluid, and an outlet 26 for the heat transfer fluid. A flanged connection 28 is provided at the liquid inlet 18 for connecting to the liquid supply. A mounting flange 30 on the lance 12 allows the spray gun to be mounted to a vessel for spraying inside the vessel. An inspection port 32 is provided at the upstream end (the left end in the view of
The spray gun 10 has a pressurized liquid supply passage 36, a heat transfer fluid supply passage 38, a heat transfer fluid return passage 40, and a pressurized atomization fluid supply passage 42. These passages are arranged in concentric pipes. The liquid supply passage 36 is the innermost, in center pipe 44. The heat transfer supply passage 38 is in pipe 46 which is concentric with and outside the center pipe 44. The heat transfer return passage 40 is in pipe 48 which is concentric with and outside pipe 46. The atomization fluid supply passage 42 is in the outermost pipe 50. The liquid supply passage 36 directs the liquid-to-be-atomized from its inlet 18, through the lance 12, to an internal mixing chamber 52 within the nozzle body 14. The atomization fluid passage 42 directs the flow of pressurized atomization fluid from its inlet 20, through the lance 12, to a plurality of annular passages 54 with a small flow area that direct the atomization fluid into the internal mixing chamber 52 at high velocity. The atomization fluid then impacts the liquid at high velocity in the internal mixing chamber 52, which causes the liquid to form a two-phase flow of liquid and air before being discharged out of the nozzle body 14 through a plurality of orifices 56 arranged in the nozzle tip 16. The pressure drop between the internal mixing chamber 52 and the environment (e.g., in a vessel such as a furnace) facilitates primary atomization of the liquid. Additional secondary atomization of the liquid occurs due to the high relative velocity of the liquid-air mixture with respect to a carrier gas in the environment into which the liquid is being sprayed that facilitates further atomization of the liquid.
The heat transfer fluid supply passage 38 directs the heat transfer fluid from its inlet 24, along the length of the lance 12, ending just upstream of the nozzle body 14. The heat transfer fluid then flows through the return passage 40, in the upstream direction of the lance 12, to its outlet 26. This flow path permits the heat transfer fluid to undergo heat transfer with the pipes 44, 50 that house the stream passages 36 and 42 respectively, as well as the fluids they contain. This assists in controlling the temperature-dependent physical properties of the fluids being sprayed as well as maintaining the temperature of the pipes in the lance 12 within an allowable range based on the mechanical properties of their materials of construction, which are typically stainless steel alloys or other materials tolerant to the process conditions.
The pipe 44 forming the liquid supply passage 36 is connected to a pipe tee fitting 60, which directs the flow of the liquid-to-be-atomized from its inlet 18 to the pipe 44 on the central longitudinal axis of the lance 12. An extension 64 of the pipe 44 protrudes from the other end of the pipe tee 60 toward the inspection port 32 at the upstream end of the lance 12. The pipe extension 64 is closed with a removable pipe cap 66. This permits inspection and servicing of the liquid passage 36.
Pipe spacers 68 are spaced along the length of the pipe 50 that defines the atomization fluid passage 42. These are arranged around the pipes 48, 50 to ensure that the flow area for the atomization fluid is symmetrical and equivalent around its circumference and to assist with the mechanical integrity of the assembly. Similarly, there are pipe spacers 70 equivalently spaced along the pipe 48 that defines the heat transfer fluid return passage 40. These also ensure that the pipes are equally spaced and are concentric along the length of the lance 12.
The nozzle tip 16 is connected to the nozzle body 14 by threading or welding 72 on the nozzle body 14, as best seen in
In one embodiment of the invention, a metallic O-ring seal 76 is positioned in an O-ring groove 78 between the nozzle body 14 and the sealing face of the lance 12, as shown in
It will be understood that the mechanical design of the spray gun assembly 10 eliminates the need for expansion joints on the body of the gun or in the equipment internals, which are commonly required on prior art devices. This improves reliability and simplifies the fabrication of the unit.
The spray gun assembly 10 of the present invention is an improvement over prior designs in incorporating features that allow more control and optimization of the extent of atomization of the liquid being sprayed.
As one example of the implementation of the invention, the use of the spray gun assembly 10 as a sulfur gun for the generation of sulfur dioxide (SO2) in a sulfur combustion furnace is now described.
The sulfur-atomization gun 10 is mounted to a furnace 82 by the mounting flange 30 so that the lance 12 protrudes into the furnace 82. The gun is connected to a hot liquid sulfur supply line at inlet 18 with the flanged connection 28. A supply of pressurized air is connected to the gun at inlet 20, with the supply pressure of the air being greater than that of the sulfur. A steam supply line is connected to the gun at inlet 24 and a condensate return line is connected to the gun at outlet 26.
Molten sulfur(S) is fed to the inlet 18 at a temperature between about 130-145° C., preferably 140° C. At this temperature range, the viscosity of the sulfur is lowest.
Increasing the temperature of the sulfur above 155° C. causes the viscosity to increase asymptotically, which leads to inadequate atomization and possible plugging. Low temperature leads to solidification of sulfur and plugging. The steam fed to the gun can be used to ensure the sulfur remains in the desired temperature-range for optimal flow conditions. The steam can also re-melt any sulfur that may cool and solidify in the gun during downtime.
Atomization air is fed to the inlet 20 of the spray gun and flows through the annular passages 54 having small cross-sectional areas so that the air impacts the molten sulfur at a high velocity in the internal mixing chamber 52. This causes the sulfur to become partially atomized before being discharged through the angled orifices 56 on the nozzle tip 16. The pressure drop between the inside of the gun and the inside of the furnace 82 causes the sulfur to further atomize as a mist of fine droplets. The high relative velocity between the drops and furnace carrier gas causes the sulfur to undergo secondary atomization, resulting in a mist of find droplets. The small size of the sulfur droplets helps to improve the combustion efficiency and inhibits the accumulation (or pooling) of unburned molten sulfur at the bottom of the furnace.
A stream of excess air 99 is also fed to the combustion furnace as a source of oxygen (O2). The atomized liquid sulfur is then combusted with oxygen to produce sulfur dioxide (SO2). The combustion reaction in a combustion chamber 97 is typically operated in the temperature range of 800-1500° C., with 800-1200° C. being the preferred temperature. The combustion furnace can be of a variety of materials, and the most preferred is a combination of a steel shell with high-temperature resistant brick-lining and castable materials 96. At such high temperatures, the metal of the sulfur gun has the potential to become warped or suffer other defects.
Therefore, the steam flowing through its passage 38 may be used as a means to cool the lance 12 to avoid deformation from the high temperatures in the furnace.
The resulting combustion gas has a high concentration of SO2, typically in the range of 8-20% on a molar/volumetric basis, and exits the furnace via a gas outlet 98. This SO2-rich gas can be used directly in various applications such as food preservation or as a reducing agent for bleaching or other purposes. More commonly, however, the SO2-rich gas is fed to a sulfuric acid plant for the production of sulfuric acid (H2SO4) via the contact process. This process involves the catalytic conversion of SO2 to SO3 by reaction with O2. Thus, in this application, operators must ensure the O2:S ratio in the combustion furnace is sufficiently high for both the combustion and conversion reactions or add excess O2 at some point downstream of the furnace and upstream of the converter. The conversion process is exothermic, so it is performed in stages (typically three to five) with interstage cooling to shift the reaction to favor product (SO3) formation.
The SO3-rich gas is fed to one or two absorption towers, where it is absorbed into an aqueous solution of sulfuric acid via reaction with water (H2O). This creates the product H2SO4. In single absorption sulfuric acid plants, the gas passes through all stages of the converter before going to one absorption tower. In a double absorption plant, however, the gas will typically pass through three or four conversion stages, undergo absorption in an intermediate absorption tower, pass through the final conversion stage, and then undergo absorption again in a final absorption tower.
Sulfuric acid is used in great quantities and in many industries. The application of the present invention as a sulfur gun allows the first step in the production process of this valuable chemical to be performed efficiently and be optimized based on the feed conditions of the process fluids.
Specific examples of systems, methods, and apparatus have been described herein for purposes of illustration. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the person skilled in the art, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.
Throughout the foregoing description and the drawings, specific details have been set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense. The scope of the invention is to be construed in accordance with the following claims.
