Mineral oils: processes and products – Chemical conversion of hydrocarbons – Solids contacting and mixing
Reexamination Certificate
1999-07-14
2002-03-19
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Solids contacting and mixing
C208S113000, C208S120010, C208SDIG001, C422S145000, C700S266000
Reexamination Certificate
active
06358401
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to apparatus and procedures for replenishing particulate materials (e.g., bulk catalysts, catalyst additives, particulate raw materials, etc.) for industrial processes (e.g., fluid catalytic processes used to refine petroleum, polymer manufacturing processes, etc.). More particularly, this invention relates to those apparatus and methods calling for injection of particulate materials into industrial processes using streams of high pressure gas (e.g., air, nitrogen, hydrocarbons, etc.) in which the particulate material is entrained.
2. Description of the Prior Art
Particulate materials are employed in many chemical and petrochemical manufacturing processes. Requirements for more closely controlling and adjusting use of such materials can be engendered by any number of anticipated and/or unanticipated changes in such processes, e.g., (1) changing product requirements, (2) changing character of feedstock(s) and/or (3) changing pollution control regulations. Moreover, the ability to more closely control and adjust introduction of particulate materials into most industrial processes serves to minimize the use of, and hence the costs associated with, raw materials, catalysts and energy. The ability to more closely control and adjust industrial processes also usually serves to reduce perturbations to such processes when those pressurized vessels holding raw materials, catalyst, diluents, etc. for use in said processes have to be taken out of service in order to refill them.
Many of those devices and procedures used to replenish particulate materials stored in pressurized vessels that feed into industrial processes call for use of a stream of pressurized gas (usually air) to transfer the particulate material from an unpressurized storage tank to a pressurized process vessel. These materials are then injected into the process by entraining them in another stream of pressurized gas (e.g., air, nitrogen, light hydrocarbon gases, etc.) that feeds into said process.
Unfortunately, significant errors and/or maladjustments were frequently introduced into many industrial processes employing such streams of pressurized gas. Such errors and/or maladjustments generally follow from a combination of two factors: (1) many particulate material delivery systems are controlled by timed meters or clocks and (2) plant air supply systems supplying the streams of pressurized gas may, and often do, operate over a rather wide range of operating pressures. For example, an “assumed” 60 psi plant air supply system would, in fact, operate at pressures ranging from about 30 to 80 psi at any given point in time. Such pressure differences caused timed particulate material injection devices using these air streams to deliver differing amounts of particulate material in different time periods in which plant air pressures varied.
The prior art has addressed this problem in several ways. For example, U.S. Pat. No. 5,389,236 (“the '236 patent”) discloses a catalyst addition system wherein a pressurized catalyst vessel is continuously weighed in order to determine how much catalyst is actually added to a fluid catalytic process in any given time period. In other words, this catalyst injection system operates on the basis of the weight of material actually leaving the vessel and injected into the process—regardless of the pressure of the air stream used to deliver the material to that process. The apparatus and methods of the present patent disclosure build upon the weighing procedures taught in the '236 patent; hence said patent is incorporated herein by reference.
The advances made through use of the apparatus and processes of the present patent disclosure revolve around the fact that the pressurized vessels used in such processes are typically operated under pressures ranging from about 30 psi to about 150 psi. Therefore, they must be depressurized before new particulate material supplies (e.g., catalysts, raw materials, diluents, etc.) can be loaded into them. Those skilled in this art will appreciate that this reloading is a time-consuming process. For example, using those vessel venting devices and procedures on the catalyst addition systems taught by the '236 patent, a typical refilling operation (comprised of [1] depressurizing the vessel from an operating pressure ranging from about 30 to about 150 psi, [2] refilling the vessel with particulate material and [3] repressurizing the vessel back to a 30-150 psi operating pressure) may take from about 60 to about 120 minutes for vessels having a capacity for about 10-15 tons of particulate material.
Such rather lengthy time requirements follow, in large part, from the fact that the depressurization process, and especially the first part of that depressurization process, must proceed very slowly. Otherwise, any particulate material still remaining in the vessel (and there usually is some) when it is vented will be entrained in the departing air and lost from the system. This will be especially likely if the initial phase of the vessel depressurization process proceeds too quickly (i.e., so quickly that any significant amount of particulate material in the vessel is, in effect, sucked out of said vessel along with the pressurized gas being vented). Particulate material losses of this kind have at least two bad consequences. First, valuable materials such as catalysts will be wasted; and second, any particulate material entrained in a stream of rapidly released gas through the vessel's venting system may clog or otherwise interfere with operation of equipment “downstream” of that venting system (e.g., gas silencers, electrostatic precipitation units, dust-catching bag units, etc.).
There is, however, a competing drawback to venting these pressurized vessels too slowly. This drawback follows from the fact that while such a vessel is being depressurized, refilled with fresh particulate material and again repressurized, it is no longer capable of injecting its particulate material contents into the industrial process it serves. In short, the vessel is “down” while it is being resupplied with particulate material. Consequently, if the process using the particulate material is scheduled to receive a shot or stream of the particulate material during the 60-120 minutes that the vessel is down for its resupply routine, injection of scheduled shot(s) or stream(s) of the material must be deferred until the vessel is again put back into service. Likewise, if the process needs an unscheduled shot or stream of the particulate material, this unscheduled addition also must be deferred until the vessel is again brought back into service. Those skilled in the chemical engineering arts will of course appreciate that the longer a scheduled or needed injection of catalyst or raw material is deferred, the greater the perturbation to most ongoing chemical processes. Hence, there is an ever pressing demand to shorten the time needed to recharge a pressurized vessel whose normal duty is to feed an industrial process with a particulate material at time intervals that are shorter (e.g., every 10 minutes) than the down time (e.g., 45-60 minutes) associated with replenishing the vessel with fresh particulate material. In many cases, if these refill times can not be shortened, very expensive duplicate pressure vessel systems must be employed.
Heretofore, the depressurization aspect of these vessel replenishing operations has been carried out in one of two ways. The first way involves the use of a single “on/off” type valve (such as a so-called ball type valve) having a very small opening. The second way employs valves that are capable of producing proportional or variable sized openings (“proportional valves”). Use of a single, ball type, valve in such venting operations has the advantage of simplicity of operation and maintenance. Such valves must, however, have a very small vent opening so that an initial, large volume, surge of escaping air does not suck parti
Griffin Walter D.
Intercat Equipment, Inc.
Lillie Raymond J.
Olstein Elliot M.
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