Mineral oils: processes and products – Chemical conversion of hydrocarbons – Solids contacting and mixing
Reexamination Certificate
1999-03-18
2001-01-09
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Solids contacting and mixing
C208S127000, C208S158000, C208S163000
Reexamination Certificate
active
06171476
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to cavitation enhanced liquid atomization. More particularly, the invention relates to atomizing a fluid comprising a solution of the liquid to be atomized and a lower boiling cavitation liquid, by contacting the fluid under pressure and while flowing, with a pressure reducing means to reduce the fluid pressure and thereby produce nucleation and growth of bubbles comprising vapor of the cavitation liquid in the fluid, at a temperature below the bubble point of the solution, and then passing the fluid through an atomizing means into a lower pressure atomizing zone. Bubble nucleation is induced upstream of the atomizing means. This is useful for atomizing a hot FCC feed oil into a catalytic cracking reaction zone, using a lower boiling hydrocarbon as the cavitation liquid.
2. 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 assistance of an atomizing gas, is forced through a pressure reducing orifice in an atomization nozzle. Atomization occurs as the fluid passes through the orifice and into the lower pressure zone downstream. The degree of atomization is 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. Atomizing relatively viscous fluids at high flow rates, such as the heavy petroleum oil feeds used in fluidized catalytic cracking (FCC) processes, 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, the preheated oil feed is mixed with steam or a low molecular weight (e.g., C
4−
) gas under pressure, to form a two phase, gas and liquid fluid. This fluid is passed through a pressure-reducing orifice into a lower pressure atomization zone, in which the gas expands and the oil is atomized, and brought into contact with a particulate, hot cracking catalyst. The atomization is effected primarily by the shearing action between the gas and liquid phases, as the fluid passes through the orifice and into the lower pressure atomization zone. The FCC riser comprises both the feed atomization zone and the cat cracking zone. Steam is more often used than a light hydrocarbon gas, to reduce the vapor loading on the on the gas compression facilities and the downstream products fractionation. However, the use of steam produces sour water, which enhances corrosion. Sour water is also environmentally unfriendly and must therefore be treated before disposal. There is a need therefore, for a process that either reduces or eliminates the amount of steam or low molecular weight gas atomizing agents.
SUMMARY OF THE INVENTION
The invention relates to a liquid atomizing process in which a fluid comprising a solution of the liquid to be atomized and a lower boiling cavitation liquid, is contacted under pressure and while flowing, with a pressure reducing means to reduce the fluid pressure and thereby produce nucleation of bubbles comprising the cavitation liquid vapor in the fluid, at a temperature below the bubble point of the solution, and then passing the fluid through an atomizing means into a lower pressure atomizing zone. Thus, the cavitation bubbles comprise vapor of the cavitation liquid. Nucleation of the cavitation bubbles produces a two-phase fluid comprising the vapor bubbles and the liquid solution. While bubble nucleation is produced upstream of the atomizing means, typically and preferably both nucleation and growth of the cavitation bubbles will occur upstream of the atomizing means. Growth of the cavitation bubbles is produced by one or more pressure reducing means and also by the pressure drop in the fluid, as it flows downstream to the atomizing means. A continued pressure drop, even if only slight, assists in stabilizing the bubbles. Additional growth of the cavitation bubbles occurs as the fluid passes through the atomizing means and into the lower pressure atomizing zone, in which it rapidly vaporizes. Passing the so-formed two-phase fluid through the atomizing means also produces shear between the vapor (the cavitation bubbles) and liquid phases, which increases the surface area of the liquid, as reflected in the formation of ligaments, membranes, smaller globules, etc. The atomization produces a spray of liquid droplets into the lower pressure atomizing zone. This is explained in detail below. By pressure is meant a low pressure reducing means, such as one or more static mixers in the fluid line upstream of the atomizing means. By low pressure is meant that the static mixer(s) or other pressure reducing means produces, in the flowing fluid, a pressure drop less than 50 psi, preferably less than 15 psi and more preferably no greater than 5 psi upstream of the atomizing means, with a typical pressure drop ranging from 1 to 5 psi. Cavitation is a phenomena in which a pressure drop induces bubble formation in a liquid, at a temperature below the bubble point of the liquid. Thus, cavitation occurs by reducing the pressure, while maintaining a constant temperature. This is in contrast to boiling enhanced atomization, in which bubble nucleation is induced by increasing the temperature of the fluid above the bubble point, while maintaining the pressure constant. The cavitation liquid is soluble in the liquid to be atomized at the process conditions and either has a lower boiling point than the liquid to be atomized or contains sufficient material boiling below the boiling range of the liquid to be atomized, to form bubbles which grow and expand for the atomization. Typically this means that at least 0.5 wt. %, preferably at least 1.0 wt. % and more preferably greater than 1.0 wt. % of the cavitating liquid will be vaporized during the initial bubble formation and subsequent atomization of the liquid to be atomized. Thus, the fluid produced by mixing the cavitating liquid with the liquid to be atomized, is preferably a single phase liquid mixture or solution, as opposed to two liquid phases or an emulsion.
The process of the invention is useful for atomizing a wide variety of liquids, including chemical and refinery process liquids, such as atomizing a hot FCC feed oil into a cat cracking reaction zone, using a lower boiling hydrocarbon as the cavitation liquid. In, for example, an FCC process, a two-phase mixture of an FFC oil feed liquid and an atomizing agent comprising steam flows through a feed injector which terminates at its downstream end in an atomizing means comprising an atomizing orifice. The downstream side of the atomizing orifice opens downstream into a spray distributor, as is known. In the practice of the invention, a cavitating fluid, comprising one or more lower boiling hydrocarbons or lower boiling hydrocarbon fractions, is mixed with the hot oil either upstream of the injector or within the injector, to form the fluid solution which, at this point, is a liquid. The injector typically comprises one or more conduits for flowing one or more liquids through and terminates at its downstream end in an atomizing means. The liquid solution of FCC feed oil and the one or more cavitating liquids is maintained at a pressure and temperature, such that cavitation preferably does not occur until the flowing fluid contacts one or more pressure reducing means in the injector, to produce a pressure drop in the fluid and thereby induce nucleation and growth of bubbles compr
Draemel Dean C.
Ho Teh Chung
Nahas Nicholas C.
Cromwell Michael A.
Exxon Research and Engineering Company
Hughes Gerard J.
Myers Helane E.
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