GB1566981A

GB1566981A - Oxygen sensor system

Info

Publication number: GB1566981A
Application number: GB1437878A
Authority: GB
Original assignee: Combustion Unlimited Inc
Current assignee: Combustion Unlimited Inc
Priority date: 1977-06-22
Filing date: 1978-04-12
Publication date: 1980-05-08
Also published as: JPS549986A

Description

(54) OXYGEN SENSOR SYSTEM (71) We, COMBUSTION UNLI MITED INCORPORATED, a corporation of Pennsylvania, United States of America, whose post office address is P.O. box 8856, Elkins Park Pennsylvania, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an oxygen sensor for flare stacks and vent stacks.

It has heretofore been proposed to provide oxygen sensing systems for flare stacks and vent stacks but the systems heretofore available lacked reliability, were not easily calibrated and had other defects which resulted in their being ignored by operating personnel.

In the present invention an oxygen sensor is provided for flare stacks and vent stacks with provisions for sampling the gas advancing in the stack to determine the oxygen content, provisions also being made for visual indications of the oxygen content of the sample, filter failure, sensor failure and other malfunction with an alarm for excess oxygen content, and with calibrating apparatus for quick and easy checking, the com- ponents being separately removable for replacement.

It is an object of the invention to provide an oxygen sensor for flare stacks and vent stacks which will be reliable in its operation, subject to easy checking and calibration and with which visual indication is available.

It is another object of the invention to provide an oxygen sensor of the character aforesaid in which malfunctioning of com- ponents is utilized to provide visual and/or audible signals.

It is a further object of the invention to provide an oxygen sampling system in which certain of the components can be isolated and removed for replacement.

According to the invention there is provided an oxygen sensor in conjunction with a stack and for connection thereto, and including means for connecting a pipe to the stack for withdrawal of gas therefrom to be sampled, a return fluid connection to the stack, pump means interposed between said connections for effecting fluid flow between said connectons for sampling, an oxygen content sensor interposed between said connections and providing a signal corresponding to the oxygen content of the sampled gas, and an indicating meter responsive to said signal from said sensor.

The invention will now be described by way of example only with particular reference to the accompanying drawings wherein: Figure 1 is a diagrammatic view of the oxygen sensing system of the invention, and Figure 2 is a view showing the visual indications and audible alarm.

In the drawings, a flare stack is shown at 10 carried on a separator 11 and with a gas supply connection 12 connected to the separator 11 for delivery of gas to be advanced upwardly through the stack.

The stack 10 is shown as a flare stack for combustion of waste combustible gas from industrial plants and specifically oil refineries and for this purpose is shown as having a burner 15 at the top end of the stack 10, surrounded by a slotted windshield 16 closed at the bottom. Pilots 17 preferably having gas supplied thereto for combustion are provided interiorly of the wind shield 16 and have ignitors 18 to ignite the pilots 17.

If the stack 10 is a mere vent stack without combustion then the burner 15, windshield 16, pilots 17 and ignitors 18 would not be necessary.

The stack 10, at the lower part thereof, and at the location at which the oxygen content is to be sensed has a gas delivery pipe 20.

The pipe 20 is connected through a shut off valve 22 to a column 24 which is comprised of a number of components to be described and which are removably mounted in the column 24 such as by flanged couplings 25 with the couplings detachably held in engagement in any desired manner.

The column 24 includes a downwardly extending pipe 26 with a condensate tank 27 therebelow. The tank 27 has a level sensing device 28 which may include a float and which transmits a signal through a conductor 29 indicative of high condensate level and provides an indication at an indicating lamp 30 and effects opening of a solenoid controlled drain valve 31 at a predetermined level of condensate in the condensate tank 27.

The column 24, above the pipe 26 has a three way valve 33 for providing a vertical through passageway or a connection to a calibrating connection pipe 34 which is detachably connected to a gas cylinder 35 of conventional type and containing a calibrating gas supply of oxygen and nitrogen preferably in the proportion of 95% nitrogen and 5% oxygen.

The connection pipe 34 preferably has a pressure responsive element 36 connected thereto for making available through a conductor 37 a signal at an indicating lamp 38 if the pressure in the pipe 34 is below a desired operating level.

The column 24, above the valve 33, has a pressure responsive element 40 responsive to the pressure at that location with a conductor 41 extending therefrom for making available a signal at an indicating light 43 when the pressure is above a predetermined level indicating a stoppage beyond the element 40.

The column 24, above the pressure responsive element 40, has a filter 42 for preventing access of dirt thereabove.

The column 24, above the filter 42 has an oxygen sensor 44 which can be of any preferred type, one suitable instrument being available as Series 326 from Teledyne Analytical Instruments, San Gabriel, California. A variable signal, responsive to the oxygen content will be available from the sensor 44 through a conductor 45 and which will be effective at an oxygen indicating meter 46 having a pointer 47 and scale 48 indicating the percentage of oxygen in the gas at the sensor 44.

The column 24. above the sensor 44, has a pressure responsive element 50 responsive to the pressure at that location with a conductor 51 extending therefrom for making available a signal at an indicating light 52 when the pressure is below a predetermined level indicating a stoppage in advance of the element 50 and a vacuum being pulled by the pump 57 referred to below.

The column 24, above the pressure responsive element 50 has a flow sensor 62 for providing a signal of flow or no-flow through a conductor 63 to an indicating light 64.

The column 24, above the flow sensor 62 has a three way valve 53 for providing a vertical through passageway or a connection to a discharge pipe 54 with a venting weather cap 55 for discharge of calibrating gas.

The column 24 is connected to the stack 10 through a pump 56 which is shown as including an expansible chamber 57 such as a bellows, an actuator 58 such as a motor driven crank, an inlet check valve 59 and an outlet check valve 60, with a shut off valve 21 to permit removal of the pump 56 without leakage of dangerous or toxic gases.

The pipe 20, the column 24, and its components, and the pipe 34 can be provided with coils 65 and an outer enclosing jacket 66 for heating or cooling dependent upon the location of use and the ambient temperatures at such location.

The meter 46 can be provided with a continuous strip contact 67 corresponding to a predetermined high oxygen content, say in excess of 6%, activated by movement of the electrically energized pointer 47 for setting up a signal circuit through a conductor 68 to activate an alarm horn 69 to indicate excess oxygen content. A silencer button 70 to break the circuit through the conductor 68 can be provided to discontinue the alarm when desired.

When there is no or low flow of waste gas to the stack 10, the height of the stack along with the high temperature or low molecular weight can, and wind at the top of the stack, can set up a negative pressure in the interior of the stack 10, separator 11 and supply conduit 12 and thus may cause leakage of air into the stack system at various location and connections. Among these are access or man hole openings indicated at 71 or flange couplings indicated at 72.

A twenty-four hour timer clock 75 driven by a motor 76 has a shaft 77 with cam wheels 78 and 79 mounted thereon. The wheel 78 through an operating arm 80, controls a switch 81 and the wheel 79 through an operating arm 82 controls a switch 83.

A source of energy 84 is connected by a main power conductor 85 with branch conductors 86 and 87 extending to the switches 81 and 83, respectively.

The switch 81 is connected by a conductor 88 to the timer motor 76, to indicating lamp 89 indicative that calibration has been effected.

The conductor 88 is connected by a conductor 90 to the winding 91 of a calibration failure relay.

The conductor 85 has a conductor 93 which extends to the sensor and monitors to supply power thereto.

The conductor 85 has a conductor 94 which energizes the pointer 47 which may engage a strip conductor 95 preferably extending from 42 to 521% on the meter The pointer 47 may also engage the strip conductor 67 for excess oxygen alarm activation.

A conductor 96 extends from the strip conductor 95 to join with conductor 88.

The switch 83 has a conductor 97 extending therefrom to the three way valves 33 and 53 for activaton thereof.

A conductor 98 extends from conductor 97 to indicating light 99 to indicate calibration mode.

A conductor 100 extends from conductor 97 through normally closed contact 101 controlled by the winding 91 and moved to open position when the winding 91 is ener pled and through a conductor 102 to an indicating light 103.

The cam 78 has a cut out portion 105 to permit the arm 80 to drop therein to deenergize switch 81.

The cam 79 has a rise portion 106 which is of greater length than the cut out portion 105 to provide an overlap to give sufficient time for the valves 33 and 53 to be activated and start calibration gas flow. Additional time lag must be available to accommodate the sensor 44 and meter 46.

The mode of operation will now be pointed out.

If it is desired to sample the waste gas in the stack 10 to determine the oxygen content, the valves 33 and 53 are positioned for flow through column 24. The pump 56 is actuated to draw through the pipe 20, through the valve 33, past the pressure responsive element 40, through the filter 42, through the oxygen sensor 44, past the pressure responsive element 50, past the flow sensor 62 and through the pump 56 for return of the gas to the system.

The filter 42 is effective to remove undesired solid material and the oxygen sensor 44 will provide a signal at the meter 46 corresponding to the oxygen content. If the filter 42 or the oxygen sensor 44 are clogged, this will result in a high pressure drop thereacross so that a signal is available through the conductor 41 and at the indicat ing lamp 43. Similarly if there is high vacuum in the gas advanced by operation of the pump 56, because of interruption in flow, a signal is available from the pressure responsive element 50, through the conduc tor 51 and at the indicating light 52. The level of condensate from the gas in the condensate tank 27 is indicated at the indicating lamp 30 and when the level rises to the point desired for discharge the solenoid control valve 31 is actuated to discharge condensate.

If it is desired to check the operation of the meter 46 the valves 33 and 53 are moved respectively to their calibrating positions.

This is effected once in each twenty-four hour time period by the clock 75 and the mechanism operated thereby and will require approximately three minutes. The valve 33 permits the delivery of calibrating gas into the column 24, below the pressure responsive element 40, from which it passes upwardly through the filter 42 and to and through the oxygen sensor 44 for delivery through the valve 53 and pipe 54 for discharge. The pressure of the calibrating gas in the tank 35 is utilized for the advance of the calibrating gas in the path just described.

The meter 46 should respond to the oxygen content of the gas from the tank 35 and give a proper reading.

If the pressure of the calibrating gas in the pipe 34 is low a signal from the pressure responsive element 36 through the conductor 37 gives an indication on the indicating light 35 so that a replacement cylinder 35 may be provided.

Upon completion of the checking of the meter 46 the valves 33 and 53 are preferably returned to their positions for normal operation.

In the event that the oxygen content in the stack 10 as determined by the sensor 44 exceeds a fixed predetermined limit, such as 6%, the pointer 47 is effective through the strip contact 67 and conductor 68 to activate the alarm horn 69. If it is desired to discontinue the horn operation, this may be effected by operation of the button 70.

WHAT WE CLAIM IS: 1. An oxygen sensor in conjunction with a stack and for connection thereto, and including means for connecting a pipe to the stack for withdrawal of gas therefrom to be sampled, a return fluid connection to the stack, pump means interposed between said connections for effecting fluid flow between said connections for sampling, and oxygen content sensor interposed between said connections and providing a signal corresponding to the oxygen content of the sampled gas, and an indicating meter responsive to said signal from said sensor.

2. An oxygen sensor as claimed in claim 1 in which a filter is interposed between said connections for filtering the gas advanced to said oxygen content sensor.

3. An oxygen sensor as claimed in claim 2 in which pressure responsive means is provided between said fluid connections responsive to the pressure conditions at said filter.

4. An oxygen sensor as claimed in claim

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The conductor 85 has a conductor 93 which extends to the sensor and monitors to supply power thereto. The conductor 85 has a conductor 94 which energizes the pointer 47 which may engage a strip conductor 95 preferably extending from 42 to 521% on the meter The pointer 47 may also engage the strip conductor 67 for excess oxygen alarm activation. A conductor 96 extends from the strip conductor 95 to join with conductor 88. The switch 83 has a conductor 97 extending therefrom to the three way valves 33 and 53 for activaton thereof. A conductor 98 extends from conductor 97 to indicating light 99 to indicate calibration mode. A conductor 100 extends from conductor 97 through normally closed contact 101 controlled by the winding 91 and moved to open position when the winding 91 is ener pled and through a conductor 102 to an indicating light 103. The cam 78 has a cut out portion 105 to permit the arm 80 to drop therein to deenergize switch 81. The cam 79 has a rise portion 106 which is of greater length than the cut out portion 105 to provide an overlap to give sufficient time for the valves 33 and 53 to be activated and start calibration gas flow. Additional time lag must be available to accommodate the sensor 44 and meter 46. The mode of operation will now be pointed out. If it is desired to sample the waste gas in the stack 10 to determine the oxygen content, the valves 33 and 53 are positioned for flow through column 24. The pump 56 is actuated to draw through the pipe 20, through the valve 33, past the pressure responsive element 40, through the filter 42, through the oxygen sensor 44, past the pressure responsive element 50, past the flow sensor 62 and through the pump 56 for return of the gas to the system. The filter 42 is effective to remove undesired solid material and the oxygen sensor 44 will provide a signal at the meter 46 corresponding to the oxygen content. If the filter 42 or the oxygen sensor 44 are clogged, this will result in a high pressure drop thereacross so that a signal is available through the conductor 41 and at the indicat ing lamp 43. Similarly if there is high vacuum in the gas advanced by operation of the pump 56, because of interruption in flow, a signal is available from the pressure responsive element 50, through the conduc tor 51 and at the indicating light 52. The level of condensate from the gas in the condensate tank 27 is indicated at the indicating lamp 30 and when the level rises to the point desired for discharge the solenoid control valve 31 is actuated to discharge condensate. If it is desired to check the operation of the meter 46 the valves 33 and 53 are moved respectively to their calibrating positions. This is effected once in each twenty-four hour time period by the clock 75 and the mechanism operated thereby and will require approximately three minutes. The valve 33 permits the delivery of calibrating gas into the column 24, below the pressure responsive element 40, from which it passes upwardly through the filter 42 and to and through the oxygen sensor 44 for delivery through the valve 53 and pipe 54 for discharge. The pressure of the calibrating gas in the tank 35 is utilized for the advance of the calibrating gas in the path just described. The meter 46 should respond to the oxygen content of the gas from the tank 35 and give a proper reading. If the pressure of the calibrating gas in the pipe 34 is low a signal from the pressure responsive element 36 through the conductor 37 gives an indication on the indicating light 35 so that a replacement cylinder 35 may be provided. Upon completion of the checking of the meter 46 the valves 33 and 53 are preferably returned to their positions for normal operation. In the event that the oxygen content in the stack 10 as determined by the sensor 44 exceeds a fixed predetermined limit, such as 6%, the pointer 47 is effective through the strip contact 67 and conductor 68 to activate the alarm horn 69. If it is desired to discontinue the horn operation, this may be effected by operation of the button 70. WHAT WE CLAIM IS:

1. An oxygen sensor in conjunction with a stack and for connection thereto, and including means for connecting a pipe to the stack for withdrawal of gas therefrom to be sampled, a return fluid connection to the stack, pump means interposed between said connections for effecting fluid flow between said connections for sampling, and oxygen content sensor interposed between said connections and providing a signal corresponding to the oxygen content of the sampled gas, and an indicating meter responsive to said signal from said sensor.

4. An oxygen sensor as claimed in claim

3 in which visual indicating means is provided responsive to the condition of said pressure responsive means.

5. An oxygen sensor as claimed in claim 1 in which flow sensing means is provided between said connections and responsive to flow through said oxygen content sensor.

6. An oxygen sensor as claimed in claim 5 in which visual indicating means is provided responsive to a signal from said flow sensing means.

7. An oxygen sensor as claimed in claim 1 in which a condensate receiver is provided for collection of water between said fluid connections.

8. An oxygen sensor as claimed in claim 7 in which valve means is provided for discharge of liquid condensate from said receiver.

9. An oxygen sensor as claimed in claim 8 in which said valve means is controlled by the level of liquid in said condensate receiver.

10. An oxygen sensor as claimed in claim 9 in which visual indicating means is provided responsive to the level of the liquid in said condensate receiver.

11. An oxygen sensor as claimed in claim 1 in which means is provided responsive to oxygen content at said sensor in excess of a predetermined value for activating an audible alarm.

12. An oxygen sensor as claimed in claim 1 in which valve members are provided between said fluid connections and on opposite sides of said sensor for cutting off the flow between said fluid connections.

13. An oxygen sensor as claimed in claim 1 in which means is provided for applying a gas of predetermined content to said oxygen sensor.

14. An oxygen sensor as claimed in claim 13 in which said means includes a source of gas of predetermined content, valve means for connecting said source to an inlet side of said sensor, a discharge connection, and valve means for connecting said discharge connection to a discharge side of said sensor.

15. An oxygen sensor as claimed in claim 14 in which pressure responsive means is provided responsive to the pressure of said source.

16. An oxygen sensor as claimed in claim 15 in which said pressure responsive means provides a visual signal indicative of low source pressure.

17. An oxygen sensor as claimed in claim 14 in which said first mentioned fluid connection is shut off from communication with said sensor by one of said valve means, and said return fluid connection is shut off from communication with said sensor by the other of said valve means.

18. An oxygen sensor as claimed in claim 12 which comprises members for activating said valve members for isolating said sensor from communication with said stack.

19. An oxygen sensor as claimed in claim 12 in which a timer is provided for periodically positioning said valve members to connect said sensor to said stack and for isolating said sensor.

20. An oxygen sensor as claimed in claim 1 in which a timer is provided for periodically isolating said sensor from said stack.

21. An oxygen sensor as claimed in claim 1 in which a contact is provided associated with said indicating meter for activation of an alarm.

22. An oxygen sensor as claimed in claim 1 in which means is provided for applying a gas of predetermined content to said oxygen sensor, and a timer is provided for controlling said last mentioned means.

23. An oxygen sensor substantially as hereinbefore described and as shown in the accompanying drawing.