Detection of distillation column flooding

• US 8,216,429 B2
• Filed: 06/17/2009
• Issued: 07/10/2012
• Est. Priority Date: 06/18/2008
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Pihlaja, Roger Kenneth, Miller, John Philip
• Primary Examiner(s): Hopkins, Robert A
• Application Number:
  US12/486,076
• Publication Number:
  US 20090314623A1
• Time in Patent Office: 1,119 Days
• Field of Search: 202/160, 203/2, 700/270
• US Class Current: 202/160
• CPC Class Codes: B01D 3/4211 of columns
• CPC Class Codes: Y10S 203/19 Sidestream

Abstract

A method comprises sensing a differential pressure signal, filtering the differential pressure signal, generating a flooding indicator as a function of the filtered differential pressure signal, and indicating the onset of flooding. The differential pressure signal is sensed along a distillation flow path. The filtered differential pressure signal is responsive to a phase inversion along the flow path, and the flooding indicator is responsive to an onset of a flooding condition, based on the phase inversion. The onset of the flooding condition is indicated based on a change in the flooding indicator.

Claims

1. A system comprising:

a pressure sensor for sensing differential pressure across a vertical height of a distillation column;

a filter for filtering the differential pressure as a function of frequency to produce a filtered differential signal emphasizing high-frequency components in the differential pressure and suppressing low-frequency components in the differential pressure;

a processor for generating an indicator function based on the filtered differential pressure signal, wherein the indicator function comprises a standard deviation of the filter output and is indicative of a flooding condition in the distillation column;

an indicator for indicating onset of the flooding condition in the distillation column based on a change in the indicator function; and

a controller for controlling the distillation column based on the change in the indicator function, wherein the controller is configured to control a mass transfer rate between liquid and vapor phases within the distillation column to encourage condensation and separation without runaway flooding.

2. The system of claim 1, further comprising packing materials in the distillation column, wherein the pressure sensor is configured for sensing the differential pressure in a frequency range that is responsive to bubble formation and collapse in void regions between the packing materials.

3. The system of claim 2, wherein the change in the indicator function is indicative of a phase inversion between continuous and discontinuous vapor and liquid phases in the void regions between the packing materials.

4. The system of claim 3, further comprising a transmitter configured to house the pressure sensor, the filter, the processor and the indicator.

5. The system of claim 4, wherein the filter is configured for filtering the differential pressure signal by means of a difference filter.

6. The system of claim 4, wherein the pressure sensor is configured for sensing the pressure at a rate of at least 10 Hz and wherein the transmitter is configured for operation on a two-wire control loop having a current of about 20 mA or less.

7. The system of claim 1, wherein the sensor samples the differential pressure at a sampling rate of 10 Hz or higher, corresponding to a Nyquist frequency of about 5 Hz or more, such that the Nyquist frequency is above a frequency of bubble formation along the distillation column.

8. The system of claim 1, wherein the indicator function further comprises a variation of the filtered differential pressure signal.

9. The system of claim 1, wherein the indicator function further comprises a skewness of the filtered differential pressure signal.

10. The system of claim 1, wherein the indicator function further comprises a kurtosis of the filtered differential pressure signal.

11. The system of claim 1, wherein a relative gain of the indicator function is scaled so that the change in the indicator function is indicative of onset of the flooding condition in a local region of the distillation column before runaway flooding spreads across the distillation column.

12. The system of claim 11, wherein the controller is configured to regulate a reboiler duty to increase or decrease a vapor flow rate in the distillation column based on the change in the indicator function.

13. An apparatus comprising:

a sensor configured to sample differential pressure;

means for connecting the sensor across a vertical height of a two-phase liquid and vapor phase counter-current flow distillation column;

means for generating a frequency-filtered signal emphasizing high-frequency components in the differential pressure and suppressing low-frequency components in the differential pressure, such that the frequency-filtered signal is responsive to foaming within the vertical height of the distillation column;

means for generating an indicator function comprising a standard deviation of the frequency-filtered signal, such that the indicator function is indicative of a phase inversion in the two-phase liquid and vapor phase counter-current flow;

means for indicating a flooding condition in the distillation column based on a change in the indicator function; and

means for controlling a mass transfer rate between the liquid and vapor phases within the distillation column based on a change in the indicator function, in order to encourage condensation and separation without runaway flooding.

14. The apparatus of claim 13, wherein means for generating the frequency-filtered signal is responsive to noise signals associated with bubble formation and collapse in the distillation column.

15. The apparatus of claim 14, wherein means for generating the frequency-filtered signal includes a difference filter for generating the frequency-filtered signal.

16. The apparatus of claim 13, wherein means for generating the indicator further utilizes a sampling window of about five minutes or less, and wherein the standard deviation is generated within the sampling window.

17. The apparatus of claim 13, wherein the sensor samples the differential pressure at a sampling rate of about 22.2 Hz or higher, corresponding to a Nyquist frequency of about 11.1 Hz or more.

18. The apparatus of claim 13, wherein the indicator function further comprises a variation of the filtered differential pressure signal.

19. The apparatus of claim 13, wherein the indicator function further comprises a skewness of the filtered differential pressure signal.

20. The apparatus of claim 13, wherein the indicator function further comprises a kurtosis of the filtered differential pressure signal.

21. The apparatus of claim 13, wherein a relative gain of the indicator function is scaled so that the change in the indicator function is indicative of onset of a flooding condition in a local region of the distillation column before runaway flooding spreads across the distillation column.

22. The apparatus of claim 21, wherein means for controlling the mass flow rate comprises means for regulating a reboiler duty to increase or decrease a vapor flow rate in the distillation column based on the change in the indicator function.

23. A transmitter comprising:

a differential pressure sensor;

a housing for the differential pressure sensor, the housing having differential pressure ports configured to connect the differential pressure sensor to a distillation column;

a filter connected to the pressure sensor, the filter configured to generate a filter output emphasizing high-frequency components in the differential pressure and suppressing low-frequency components in the differential pressure;

a processor connected to the filter, the processor configured to generate an indicator function comprising a standard deviation of the filter output, wherein the indicator function is indicative of a flooding condition in the column; and

an interface connected to the processor, the interface configured to indicate onset of the flooding condition based on a change in the indicator function; and

a controller for controlling the distillation column based on the change in the indicator function, wherein the controller is configured to control a mass transfer rate between liquid and vapor phases within the distillation column to encourage condensation and separation without runaway flooding.

24. The transmitter of claim 23, wherein the indicator function further comprises a variation of the filtered differential pressure signal.

25. The transmitter of claim 23, wherein the indicator function further comprises a skewness or kurtosis of the filtered differential pressure signal.

26. The transmitter of claim 23, wherein the differential pressure sensor senses the differential pressure at a sampling rate corresponding to a Nyquist frequency that is above a frequency of bubble formation in the distillation column.

27. The transmitter of claim 23, wherein a relative gain of the indicator function is scaled so that the change in the indicator function indicates onset of a flooding condition in a local region of the distillation column before runaway flooding spreads across the distillation column.

28. The transmitter of claim 27, wherein the controller is configured to regulate a reboiler duty to increase or decrease a vapor flow rate in the distillation column based on the change in the indicator function.