Fluid sprinkling – spraying – and diffusing – Processes – Including mixing or combining with air – gas or steam
Reexamination Certificate
1999-03-18
2001-03-13
Kashnikow, Andres (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Including mixing or combining with air, gas or steam
C239S590500, C137S896000
Reexamination Certificate
active
06199768
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
FIELD OF THE INVENTION
The invention relates to FCC processes using a high fluid throughput and low pressure drop, liquid atomizing process and apparatus. The process comprises forming a two-phase fluid mixture of the hot feed oil and a dispersion gas, such as steam, dividing the fluid into two separate streams which are simultaneously passed under pressure, through (i) an impingement mixing zone, and then (ii) a shear mixing zone, to form a single stream which passes into (iii) a lower pressure atomizing zone, in which atomization occurs to form a spray of atomized drops of the liquid. The apparatus comprises a nozzle in which the impingement and shear mixing zones comprise a single cavity.
BACKGROUND OF THE INVENTION
Fluid atomization is well known and used in a wide variety of applications and processes. These include, for example, aerosol sprays, the application of pesticides and coatings, spray drying, humidification, mixing, air conditioning, and chemical and petroleum refinery processes. For most applications, a fluid under pressure, with or without the presence of an atomizing agent, is forced through an atomization nozzle having a relatively small orifice. Atomization occurs at the downstream side of the orifice, with the degree of atomization determined by the orifice size, the pressure drop across the orifice, fluid density, viscosity, and surface tension, etc., as is known. Atomization is increased and the droplet size is decreased, with decreasing orifice size and increasing pressure drop. Increasing the degree of atomization of relatively viscous fluids at high flow rates, such as the heavy petroleum oil feeds used in a fluidized catalytic cracking (FCC) process, or fluid cat cracking as it is also called, is particularly challenging. FCC is an established and widely used process in the petroleum refining industry, primarily for converting high boiling petroleum oils to more valuable lower boiling products, including gasoline and middle distillates such as kerosene, jet and diesel fuel, and heating oil. In an FCC process, a preheated feed, often mixed with an atomization promoting fluid, such as steam, is atomized and brought into contact with a particulate, hot cracking catalyst flowing up through a riser which comprises the catalytic cracking reaction zone. Smaller oil feed droplet sizes in the reaction zone result in more feed conversion to valuable products, particularly with the incorporation of heavy feed material, such as a resid, in the FCC feed. Oil that doesn't make contact with the uprising catalyst particles, thermally cracks primarily to methane and coke. As a consequence, efforts continue to try to find economically viable means to decrease the droplet size of the atomized oil, and preferably without either (i) an unacceptably high pressure drop through the atomizer or nozzle or (ii) increasing the amount of steam or other atomization promoting agent. Examples of such efforts are disclosed in, for example, U.S. Pat. No. 5,289,976 and U.S. Pat. No. 5,173,175 which produce an average feed droplet size in the range of about 400-1000 microns. There is still a need for finer atomization of the heavy oil feed for the FCC process and of other fluids for other processes as well. It would be particularly beneficial if the droplet size of the atomized liquid could be reduced to less than 300 microns.
SUMMARY OF THE INVENTION
The invention relates to a process and apparatus for atomizing a liquid, wherein the process includes impingement and shear mixing. The impingement and shear mixing both occur in a cavity longitudinally extending through the interior of a hollow nozzle means, which comprises the impingement and shear mixing apparatus of the invention. The cavity is open at both ends, which are at the respective upstream and downstream ends of the nozzle. In the process of the invention, at least two separate streams of a two-phase, fluid comprising a gas and the liquid to be atomized, are simultaneously and sequentially passed, under pressure, downstream into and through an impingement mixing zone and a shear mixing zone. In the impingement mixing zone, the separate streams are mixed to form a single, mixed stream, by colliding or impinging at least a portion of each stream against the other. By impingement mixing zone is meant a mixing zone in which mixing of the separate streams occurs mostly (>50%) by impingement and by shear mixing is meant that most of the mixing occurs by shear. Impingement mixing between two fluid streams occurs, when the half angle between the streams ranges between at least 15° up to 90°. This means that the total included angle between the impinging streams ranges from 30-180°, with 180° producing the most violent and chaotic mixing. Shear mixing occurs when the half angle ranges from about 0° to 15°. In the practice of the invention, at least a portion (e.g., ≧20%) of each fluid stream in the impingement mixing zone also has a flow component parallel to the downstream flow direction, so that not all mixing in this zone occurs by impingement. In a preferred embodiment, at least the laterally outer, peripheral portion of each fluid stream is directed against the other in the impingement mixing chamber or zone, preferably at an angle of 90°±30° normal to the longitudinal flow direction of the fluid, more preferably 90°±10°, still more preferably 90°±5°, and most preferably 90°±2°. Fluid expansion in the impingement and shear mixing zones is minimized. The impingement mixing zone, the shear mixing zone and the atomizing zone are all in fluid communication. The mixed stream is then passed into and through a shear mixing zone, in which further mixing of the fluid occurs. The impingement and shear mixing zones comprise respective upstream and downstream portions of the single cavity or chamber, within the impingement and shear mixing means or nozzle, with the downstream end of the impingement mixing zone opening into the entrance or upstream end of the shear mixing zone. The kinetic energy imparted to the fluid by the impingement and shear mixing forms a single stream comprising a mixed, two-phase fluid comprising the gas and liquid which, when atomized, produces small droplets of the liquid dispersed in a gas continuous phase. The average size of the liquid drops or droplets dispersed in the gas phase after passing through the nozzle is smaller (e.g., at least 10% smaller and preferably at least 50% smaller) than upstream of the nozzle. The shear mixing zone opens downstream into an atomizing means. The atomizing means typically and preferably comprises or includes an orifice having a smaller cross-sectional area perpendicular to the fluid flow direction through the shear mixing zone, than the smallest cross-sectional area perpendicular to the fluid flow direction in the shear mixing zone. This results in a pressure drop across the orifice and attendant further shear of the two-phase fluid as it enters the lower pressure expansion zone, which comprises the atomizing zone, a portion of which may comprise the downstream portion of the shear mixing zone. This shear results in a further reduction of the size of the atomized liquid droplets. As the fluid passes into the lower pressure expansion or atomizing zone, it rapidly expands, thereby producing a spray comprising atomized drops of the liquid. This rapid expansion and production of a spray of liquid droplets comprises the atomization. Typically and preferably, the downstream fluid exit of the shear mixing zone opens into an adjacent spray distributor, for shaping the spray into the desired shape. The spray distributor forms part of the atomizing zone and may or may not comprise part of the nozzle. This is a preferred embodiment for minimizing coalescence of the liquid phase prior to atomization. However, in another embodiment, the shear mixing zone may open downstream into the upstream end of an atomizing means which includes a hollow fluid conduit open at both ends and having an atomizing orifice and a spray distri
Ito Jackson I.
Koveal Russell J.
Cromwell Michael A.
Exxon Research and Engineering Company
Hughes Gerald J.
Kashnikow Andres
Kim Christopher S.
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