Process for detecting and monitoring changes in properties...

Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Chemical analysis

Reexamination Certificate

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C702S050000, C422S062000, C422S111000, C422S140000, C700S266000

Reexamination Certificate

active

06301546

ABSTRACT:

1. FIELD OF THE INVENTION
This invention relates to a process for detecting, and monitoring, changes in the properties of a fluidized bed of particulate solids; particularly solids particles agglomeration and/or attrition over a period of time by direct measurement of the magnitude of differential pressure fluctuations at different bed levels which can be directly related to changing particle size.
2. BACKGROUND
Processes are known which utilize fluidized bed techniques wherein a bed of a particulate solid, or solids, for conducting various interactions and/or reactions is contacted with upflow gases the velocity of which exceeds the minimum fluidization velocity, and which may even exceed the free fall velocities of the individual particles causing bed expansion and fluidization of the particles without sweeping significant amounts of the particles from the bed. Fluidized beds are employed in many industrial applications which involve interactions or reactions between a gaseous phase and solid particles.
In a particularly important type of process, now under development, it is known, e.g., to produce synthesis gas (H
2
+CO) from low molecular weight hydrocarbons, primarily methane, reacted in the presence of steam and oxygen at high temperatures within a fluidized bed of catalyst, typically nickel-on-alumina, or a mixture of catalyst and particulate solids diluent used to aid in controlling the heats of reaction. The combination of high temperature and presence of oxygen in such reaction however creates conditions which make careful control, stability, and steady state operation acutely necessary; however difficult. The surface of the particulate catalytic solids thus becomes sticky and tends to agglomerate, leading to lowered catalyst efficiency (lower conversion), and larger particles that are more difficult to fluidize; and/or the production of fine particles due to abrasive impacts and attrition with concomitant loss of catalyst from the reactor, and clogged lines. In some other fluidized bed operations, e.g., gas-phase polyethylene plant reactors, particles grow in size due to the polymerization reaction without any fluidization pathology taking place. Control for such operations is known, or required to maintain conditions so that the growing particles do not become sticky and agglomerate; and devices have been developed and used in the past, with varying degrees of success to maintain the operational stability of such fluidized bed operations.
In accordance with U.S. Pat. No. 5,435,972 to Daw and Hawk, e.g., differential pressure sensing devices have been employed as a means of sensing, and controlling fluid bed operations. Thus, a differential pressure sensing device utilizing a pair of pressure taps is located axially one tap above the other, or at different levels across a fluidized bed to obtain an analog signal. Daw and Hawk employ the analog signal with an electrical circuit and work in real time to control the feed gas velocity to the fluidized bed.
In accordance with U.S. Pat. No. 4,858,144, as in the control method of Daw and Hawk, supra, Marsaly et al likewise generate an analog signal representative of “the time varying pressure drop” across a “segment of the bed”. They employ a differential pressure recording device, digitize the analog signal with an A/D board, collect the data in a PC, and thereafter use a Fast Fourier Transform of the data set to determine recognizable cyclical events present in the fluidized bed. Comparison is then made between a bed which is operating “properly” vis-a-vis one operating “improperly.” Thus, if subsequent data sets examined by Fourier transform exhibit altered states and/or different cyclical events it is apparent that the nature of the fluidization process has changed. These changes are thus considered as indicators of fluidization “pathology”; a type of signature analysis as applied in rotating machinery development. Both Daw and Hawk and Marsaly et al offer processes for analysis of events marked by differential pressure fluctuations, but neither is very effective in tracking changes in particle size, or bubble size; properties which are closer to, and more directly related to variables which affect fluid bed operations; particularly syn gas operations, a process for the better control of which there is a pressing need.
3. STATEMENT OF THE INVENTION
The present invention, which meets this need and others, relates to a process which measures the differential pressure changes across a vertical, or axial, segment of a fluidized bed, particularly the vertical segment of a fluidized bed used in conducting fluid bed synthesis gas operations, analyzes the mean differential pressure to obtain the standard deviation, SD, preferably the normalized standard deviation, NSD, of the pressure fluctuation about the mean value, and repetitively collects and processes the data at time intervals sufficiently short compared to the time period required for particle size growth to lead to process failure. The process requires the use of fast response pressure transducers that are connected to an analog-digital, A/D, board in a personal computer, PC, which can sample and collect the data at speeds of at least 50 Hz for a period of about 1 to 3 minutes. The collection and processing of the data is preferably repeated at time intervals ranging from about 1 minute to about 5 minutes, over a total period of time ranging from about 2 minutes to about 30 minutes. The time record of the SD and NSD, at steady state operation it is found, will initially show a constant value which can be directly related to particle size, and as SD or NSD increases or decreases the change can be directly related to increases or decreases, respectively, in particle size.
The vertical height of the bed, or axial vertical segment of the bed across which a differential pressure measurement is made should generally range from 0.1 of a bed diameter to about 2 bed diameters, preferably from about 0.25 bed diameter to about 1.5 bed diameters to obtain sufficiently large and useful signals for analysis.
The characteristics of a preferred process, as well as the principle of operation of the process, will be more fully understood by reference to the following detailed description, and to the attached drawings to which reference is made in the description. The various features and components in the drawings are referred to by numbers, similar features and components being represented in the different figures by similar numbers.


REFERENCES:
patent: 4336227 (1982-06-01), Koyama et al.
patent: 4755358 (1988-07-01), Voll et al.
patent: 4858144 (1989-08-01), Marsaly et al.
patent: 5043283 (1991-08-01), Endo et al.
patent: 5047209 (1991-09-01), Lenczyk
patent: 5421842 (1995-06-01), Shabaker et al.
patent: 5435972 (1995-07-01), Daw et al.
J. Ruud van Ommen et al, “Monitoring Fluidization Dynamics for Detection of Changes in Fluidized Bed Composition and Operating Conditions”, Proceedings of the ASME Heat Transfer Division, HTD-vol. 361-5, vol. 5, 1998, pp. 395-404, XP000914007.
D. Bai et al, “Characterization of Gas Fluidization Regimes Using Pressure Fluctuations”, Powder Technology, vol. 87, No. 2, May 1996 (1996-05), pp. 105-111, XP000913954, ISSN 0032-5910.

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