Detection of dynamic fluidized bed level in a fluidized bed polymerization reactor using ultrasonic waves or microwaves

• US 6,460,412 B1
• Filed: 10/27/2000
• Issued: 10/08/2002
• Est. Priority Date: 10/27/2000
• Status: Expired due to Fees

• Current Assignee: Univation Technologies LLC (Dow, Inc.)
• Original Assignee: Union Carbide Chemicals & Plastics Technology Corporation (Dow, Inc.)
• Inventors: Cai, Ping, Lee, Kiu Hee
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): WILSON, KATINA M
• Application Number:
  US09/698,425
• Time in Patent Office: 711 Days
• Field of Search: 735/97, 736/02, 736/28, 736/29, 73/7, 732/90.V, 735/98, 250/357.1
• US Class Current: 73/290.00V
• CPC Class Codes: B01J 2208/00256 in a heat exchanger for the heat exchange medium separate from the reactor
• CPC Class Codes: B01J 2208/00274 involving reactant vapours
• CPC Class Codes: B01J 2208/0061 Controlling the level
• CPC Class Codes: B01J 2219/00247 Fouling of the reactor or the process equipment
• CPC Class Codes: B01J 8/1809 Controlling processes
• CPC Class Codes: C08F 10/00 Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
• CPC Class Codes: C08F 2/00 Processes of polymerisation
• CPC Class Codes: C08F 2/34 Polymerisation in gaseous state
• CPC Class Codes: C08F 210/08 Butenes
• CPC Class Codes: C08F 210/16 Copolymers of ethene with alpha-alkenes, e.g. EP rubbers
• CPC Class Codes: C08F 2400/02 Control or adjustment of polymerization parameters
• CPC Class Codes: C08F 2500/12 Melt flow index or melt flow ratio
• CPC Class Codes: C08F 2500/18 Bulk density
• CPC Class Codes: C08F 2500/24 Polymer with special particle form or size
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01F 23/2962 Measuring transit time of reflected waves
• CPC Class Codes: G01N 22/00 Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more G01N3/00 - G01N17/00, G01N24/00 take precedence
• CPC Class Codes: G01N 2291/02433 Gases in liquids, e.g. bubbles, foams
• CPC Class Codes: G01N 2291/0255 (Bio)chemical reactions, e.g. on biosensors
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 2291/02854 : Length, thickness
• CPC Class Codes: G01N 29/024 : by measuring propagation velocity or propagation time of acoustic waves

Abstract

The dynamic fluidized-bed level in an olefin polymerization reactor is determined by radar or ultrasound waves. Echoes are processed to take into account the turbulence caused by bubbles, which can be as large as four meters in diameter, bursting on the surface, expelling resin particles into the freeboard above the dynamic fluidized-bed level.

Claims

1. Method of measuring a dynamic fluidized-bed level in a fluidized-bed olefin polymerization reactor, said reactor having a top wall and said fluidized bed having a superficial gas velocity of 0.3 to 3.5 feet per second and including bubbles bursting at said fluidized-bed level, said bubbles having an average diameter of 0.05 meter to 4 meters, comprising transmitting a series of short pulses of ultrasonic waves or microwaves from said top wall toward said fluidized-bed, receiving from said fluidized-bed level reflections of at least 0.01% of said ultrasonic or microwave pulses, calculating the times between said transmission and reception of said pulses, and calculating said bed level from said times.

2. Method of claim 1 wherein said transmitting and said receiving are performed by the same instrument.

3. Method of claim 1 wherein said waves are ultrasonic and said transmitting and receiving are performed on the exterior of said top wall.

4. Method of claim 3 wherein said waves are ultrasonic waves having a wavelength from 2.6 to 8 times the thickness of said top wall.

5. Method of claim 3 wherein said receiving takes place over an area on said top wall having a diameter 7 to 15 times the thickness of said top wall.

6. Method of claim 1 wherein said pulses are ultrasonic, and said calculating of said bed level includes a factor representing at least one of the composition, temperature and pressure of said fluidized-bed.

7. Method of claim 1 wherein each of said pulses has a duration from one millisecond to one second and from 10 to 500 pulses are transmitted at intervals from 2 milliseconds to 10 seconds.

8. Method of claim 1 wherein said waves are ultrasonic waves having a frequency of from 20 kHz to 10 MHz.

9. Method of claim 1 wherein said waves are microwaves at a frequency from 4 to 30 GHz.

10. Method of claim 1 wherein said waves are microwaves at a frequency between 5 and 25 GHz.

11. Method of claim 1 including the step of determining which of said at least 0.01% of said received waves is received from said dynamic fluidized bed surface.

12. Method of monitoring dynamic fluidized-bed level in a fluidized-bed olefin polymerization reactor having a top wall comprising fixing an ultrasonic transceiver to the exterior of said top wall, emitting ultrasonic waves having wavelengths of about 2.8 to about 8 times the thickness of said top wall from said transducer through said top wall and toward said dynamic fluidized-bed level, receiving ultrasonic waves reflected from said dynamic fluidized-bed level in a receiver having a diameter about 7 to about 15 times the thickness of said top-wall, and computing said bed level from the difference in time between said emission and said reception of said ultrasonic waves.

13. Method of claim 12 wherein said computing includes a factor representing at least one of temperature, pressure or temperature of the gaseous atmosphere in said reactor.

14. Method of claim 12 wherein 20 to 200 pulses are transmitted.

15. Method of claim 12 wherein said computing includes a factor representing superficial gas velocity in the reactor.

16. Method of claim 12 wherein said dynamic fluidized bed level is characterized by the substantially continuous bursting of bubbles of 0.05 to 4 meters in diameter.

17. Method of determining a magnitude of fluctuation of a dynamic fluidized-bed level comprising receiving reflections of waves emitted from a wave transmitter to said dynamic fluidized-bed level, calculating one or more averages of at least one characteristic of said reflections, and analyzing deviations from said average or averages to determine said magnitude of fluctuation.

18. Method of claim 17 including the step of comparing a statistical analysis of said deviations to a base representing a normal dynamic fluidized bed.

19. Method of claim 18 wherein said dynamic fluidized-bed level is characterized by the substantially continuous bursting of bubbles of 0.05 to 4.0 meters in diameter.

20. Method of claim 17 wherein said dynamic fluidized-bed level is characterized by the substantially continuous bursting of bubbles of 0.05 to 4.0 meters in diameter.