Fluid atomization process

Details Fluid atomization process Fluid atomization process

2001-04-02

2002-09-24

Griffin, Walter D. (Department: 1764)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

Cracking

C208S153000, C208S157000, C239S008000

Reexamination Certificate

active

06454933

ABSTRACT:

BACKGROUND
The invention relates to liquid atomization, in which atomizing gas is heated by indirect heat exchange with the hot liquid to be atomized. More particularly, the invention relates to a liquid atomization apparatus and process in which atomizing steam is heated to a superheat temperature and a high velocity, by indirect heat exchange with the hot liquid to be atomized. This is useful for atomizing the hot feed oil in an FCC process.
Atomizing hot, 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 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 fluid comprising the steam or gas phase and the liquid oil phase. This fluid is passed through an atomizing means, such as an orifice, into a lower pressure atomizing zone, to atomize the fluid into a spray of oil droplets which contact a particulate, hot cracking catalyst. Feed atomization is initiated immediately downstream of the atomizing orifice or means, and may continue into the downstream riser reaction zone. Steam is more often used than a light hydrocarbon gas, to reduce the vapor loading on the gas compression facilities and the downstream products fractionation. With the trend toward increasing the fraction of the very heavy and viscous residual oils used in FCC feeds, more and hotter steam is needed for atomization. However, many facilities have limited steam capacity and the steam is typically saturated, which constrains their ability to effectively process heavier feeds.
SUMMARY
The invention relates to a fluidized cat cracking (FCC) process in which the hot feed oil is atomized with an atomizing gas, and wherein at least a portion of the atomizing gas has been heated by indirect heat exchange with the hot oil feed. The heat exchange takes place upstream of the atomizing means, in at least one heat exchange means which may comprise, for example, a heat conductive apparatus or body having a plurality of fluid passage means therein, with each fluid passage means having at least one fluid entrance and exit, to permit the gas and the hot oil to flow separately into and through, in indirect heat exchange, during which the hot oil heats the gas. By atomization is meant that the liquid feed oil is formed into a spray comprising discrete and dispersed, small drops or droplets of the oil. Atomization is achieved by conducting the fluid through at least one atomizing means, into a lower pressure atomizing zone. When more than one atomizing means is used, they may be in a series or parallel flow arrangement, preferably parallel. The heated atomizing gas preferably comprises steam, which may or may not be in admixture with one or more other gases, such as hydrocarbon gases and vapors. Thus, the term “steam” as used herein is not meant to exclude the presence of other gases in admixture with the steam. However, the atomizing gas preferably comprises at least 95 volume % steam and more preferably all steam. In the practice of the invention, the steam is heated to a superheat temperature and, in a preferred embodiment, the superheated steam exits the heat exchange means and is injected into the flowing, hot, oily fluid at a high velocity. By high velocity is meant a steam Mach number of preferably greater than 0.5, more preferably greater than 0.8, and still more preferably greater than 0.9. The hot oil flowing through the heat exchange means may be a single-phase fluid comprising the hot feed oil or a two-phase fluid comprising gas, as in preferably steam, and the hot oil. Hereinafter, the term “fluid” as used herein is meant to include both a single liquid phase, and a two-phase mixture comprising a gas phase and a liquid phase. The superheated steam, preferably at a high velocity, is injected into the flowing fluid to increase the surface area of the liquid phase. Increasing the velocity reduces the amount of steam required and increases the kinetic energy available for increasing the liquid surface area (e.g., e=mv
2
), which is ultimately manifested by smaller droplet sizes of the atomized oil spray. The superheated steam may be injected into the flowing hot fluid either inside, outside, upstream or downstream of the heat exchange means. The superheated steam injection results in either (i) a two-phase fluid comprising the steam and hot feed oil or (ii) a two-phase fluid in which the surface area of the liquid phase has been increased. That is, if the hot fluid into which the steam is injected is a single-phase liquid, injecting the steam into the liquid produces a two-phase fluid comprising a steam phase and a liquid phase. If the fluid into which the steam is injected is a two-phase fluid comprising steam (or gas) and the hot liquid oil, injecting the steam into the fluid increases the surface area of the liquid phase of the fluid. The two-phase fluid is passed into and through an atomizing means and into a lower pressure atomization zone, in which the steam expands and forms a spray comprising atomized droplets of the oil. The atomizing means typically comprises a pressure reducing and velocity increasing orifice, as is known, but it may also comprise a pressure reducing and velocity increasing region or zone, just upstream of the lower pressure atomizing zone, in which the steam expands sufficiently to form the spray of oil droplets. The atomizing means may or may not comprise part of the heat exchange means, as is described in detail below. If it comprises part of the heat exchange means, it will typically be located proximate to its fluid exit. In another embodiment, all or a portion of the superheated steam formed in the heat exchange means may be directed as “shock steam” into the two-phase fluid, as it exits the atomizing means and enters the lower pressure atomizing zone, to provide a more uniform drop size distribution of the atomized oil.
In an FCC process in which at least a portion of the atomizing steam is heated to a superheat temperature according to the practice of the invention, the hot feed oil will typically be injected or mixed with a portion of the atomizing steam to form the two-phase fluid, prior to being injected with the superheated steam produced in the heat exchange means. This will typically occur upstream of the heat exchange means. A portion of this prior or upstream steam may be superheated, but is more typically all saturated steam. In one embodiment, the heat exchange means may include atomizing means such as an orifice. In another embodiment it will include means for mixing the two-phase fluid formed upstream to increase the surface area of the liquid feed oil phase. In the practice of the invention, the temperature drop incurred by the hot oily fluid flowing through the heat exchange means, as it heats the steam to a superheat temperature, will be typically less than 6° C. If saturated steam is passed into the heat exchange means, then passage of the steam through this means superheats the steam and this superheated steam is injected or impacted into the flowing hot fluid. If superheated steam is passed into the heat exchange means, its superheat temperature will be increased. In either case, the superheated steam heated or formed in the heat exchange means is directed into the flowing hot fluid as atomizing gas. Both the heat exchange and atomizing means will typically comprise part of a feed injection unit, which sprays the hot, atomized oil droplets into a cat cracker reaction zone, in which they contact hot catalyst particles which catalytically crack the hot oil into more valuable, and generally lower boiling, material. The injection unit will generally comprise a feed conduit in

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