GB2242022A - Analyzer for components in working fluid - Google Patents

Abstract

The working fluid is fed from inlet 28 through a constant level box (18) which provides a constant head of pressure in the apparatus. From the constant level box (18) a fluid sample stream passes through a flow block 26 provided with internal flow passageways to reagent adding passages 56 and path 54 which control mixing time of reagent and fluid. The mixture is then passed to the sampling chamber (86) where an impeller (88) causes it to flow across the working face (84) of an amperometric probe 12 mounted in the block 26. Grit contained in the chamber (86) provides a constant cleaning action on the working face of the probe 12. Backflushing means are provided to periodically clean the apparatus by providing a reverse flow through the reagent addition means, mixing time control and through a sample withdrawal means, but not through the impeller chamber. <IMAGE>

Description

RESIDUAL ANALYZER APPARATUS The present invention relates to a residual analyzer and sampling system for the measurement of residual amounts of specific chemical species in a working fluid. Residual analyzers of this kind are typically used to measure such chemicals as free chlorine, total chlorine, potassium permanganate or chlorine diaxide in a working fluid and may be applied to such commercial applications as drinking water, waste water, and reactor cooling water.

A number of analyticai methods may be employed for the determination of specific chemical species in a working fluid. Three such methods are amperometry, colormetry and potentiometry. Each of these methods has its limitations and advantages for specific applications. For typical commercial applications involving drinking water amperometric or potentiometric methods are usually emploved.

A typical amperometric probe includes two electrodes across which a potential is applied. Under ideal conditions, the current produced bv the probe is proportional to the concentration of the chemical species in the working fluid and which is either at the working electrode. Therefore, zero concentration of the species in the working fluid should result in no current being produced. In actual practice, however, variations in conductivity, pH, temperature, electropotential, interfering substances and electrode and flow fouling may cause significant errors, especial at low residuals (typically below 0.1 mug/1). These errors may be countered by the addition of liquid or gaseous reagents to condition the working fluid.Other methods of minimizing the errors associated with this tvpe analvsis comprise temperature compensation and the use of applied potentials. However, a probe utilizing these various means of compensation for the changing characteristics of the working fluid will still require periodic zero calibration for proper continuous operation.

A mote recent approach in commercial amperometric probes inclll(les the utilization of a membrane to isolate the electrodes from the working fluid. The membrane is positioned between the fluid and the electrodes and protects the electrodes from ionized substances while maintaining a stable electrochemical condition at the electrodes. This type structure typically results in a near true and stable zero calibration. However, due to the reduced sensitivity created by the membrane, varying diffusion rates for different species through the membrane and frequent membrane fouling, this type structure is often considered inadequate for the analvsis of reactor cooling water and waste water.

Sensitivity of the probe is a significant factor in the commercial application of amperometric probes to specific working fluids. Other operational factors, however, must also be considered in evaluating the overall cost of 9 continuous system. A typical residual analyzer probe which includes a membrane, although inaccurate in cooling water and waste water applications, often reduces operating costs since reagents are not required to condition the working fluid.

Reagents are also often required for accurate operation of a probe having exposed electrodes without membrane protection. Additionally, reagents are utilized with non-membrane type probes to maintain electrode cleanliness during its continuous operation. The amount of reagents required as well as their effect on the working fluid are often significant considerations in many commercial applications.

In accordance with the present invention an improved residual analyzer and sampling system is provided for sampling and analyzing a working fluid, preferably by amperometric analysis using an amperometric probe, preferablv but not necessarily of the type described in UR Patent Application no. 8829743.7 (Publication No. GB-A 2211304) from which the present application is divided. In particular the residual analyzer of the present invention is designed to withdraw a continuous sample of the working fluid from a source and to direct this sample towards the probe for analysis while minimizing the amount of any additional reagent required for reliable results.

In more detail, the present invention provides a residual analyzer and sampling system for the residual analysis of a component in a working fluid, wherein the analyzer and sampling system comprises: a means for receiving a flow of working fluid from a source and withdrawing a sample therefrom at constant pressure; means for adding reagent to the sample; means for controlling the reagent reaction time with the sample; means for directing the sample into an impeller chamber into contact with an analyzer probe mounted or mountable in the analyzer; an impeller mounted in the impeller chamber; means for operating the impeller to feed the sample through the impeller chamber and across the analyzer probe at a substantially constant flow rate; means for discharging the sample after passage through the impeller chamber; and means for periodically backflushing the flow through the reagent addition means, the reaction control means and the sample withdrawal means, but not through the impeller chamber.

Preferablv, the analyzer probe is an amperometric probe having a pair of electrodes exposed to the fluid sample as it passes through the impeller chamber.

The backflush mechanism of the sampler system is intended to eliminate build up of materials within the system which may impair operation due to the reduction in the sample flow through the unit.

Also, a build up of organic matter in certain applications within the passageways of the system could cause a residual demand and reduce the accuracy of the analyzer probe measurement or completely block flow into the sampler system. The backflush mechanism periodically energizes to reverse the flow through the system to clean the orifices and passageways through which the flow travels and to remove these materials from the system.

Preferably the impeller chamber contains a quantity of grit which serves to keep the working surfaces of the probe clean.

Further advantages of the invention will become apparent from the following detailed description of the preferred embodiment illustrated in the accompanying drawings, in which: Figure 1 is an isometric view of a complete residual analyzer assembly and sampling system as contemplated by the present invention.

Figure 2 is a top plan view of the residual analyzer assembly shown in Figure 1.

Figure 3 is a cross-sectional view of the working fluid sampler system taken along line 4-4 in Figure 2.

Figure 4 is a cross-sectional view of the working fluid sampler system taken along line 6-6 in Figure 2.

Figure D is a cross-sectional view of the working fluid sampler system taken along line 5-5 in Figure 2.

Figure 6 is a side elevation of the residual analyzer assembly shown in Figures 1 and 2 having its internal structure exposed.

Figure 7 is a cross-sectional view of the working fluid sampler system taken along line 7-7 in Figure 2.

Figure 8 is a cross-sectional view of the residual analyzer probe taken along line 8-8 in Figure 2.

Figure 9 is a plan view of the end face of the cap portion of the probe.

Figure 10 is a cross-sectional view of the working fluid sampler system taken along line 10-10 in Figure 6.

Figure 11 is a cross-sectional view of the working fluid sampler system taken along line 11-11 in Figure 6.

Referring to the drawings, Figure 1 illustrates the complete analyzer assembly 10 which includes a probe 12 and a working fluid sampler system 14. The working fluid sampler system includes a probe block 16 which supports the probe 12 and a flow block 26 which defines the flow passageways of the sampler system 14.

Figure 2 shows a top plan view of the assembly 10 including the probe 12 and illustrating the internal passageways of the working fluid sampler system 14. The sampler system 14, as shown, includes a constant level box 18, a self-cleaning backflush mechanism 20, an adjustable flow delay line 22 and an impeller mechanism 24. All of these structures are supported on or maintained within the flow block 26. The various internal passageways direct a sample of the flow through the system 14 for analyzation and then exhaust the flow back into the working fluid flowpath. The flow block 26 will be described in various sections so as to understand the operational characteristics of the system 14.

As shown in Figures 2 and 10, the flow inlet 28 is positioned on the rear of the flow block 26. Inlet 28 is adapted to r-eceive a flow line (not shown) and direct the full flow through the block 26 into the constant level box 18. The flow line may include a fitting (not shown) supported on the block 26 by internal threads. Valve means 30 is provided to control the flow rate entering the flow block 26 at inlet 28. Valve means 30 as illustrated in Figure 10 includes an adjustment knob 32 which is preferably attached to a needle type valve retained within a first passageway 34 (see also Figure 5).

the flow entering inlet 28 and passing through first passageway 34 is then directed via a second passageway 36 into the constant level box 18 at its base. Second passageway 36 is provided within the flow block 26 via aperture 38. Aperture 38 is required to form the internal intersection of passageway 36 with first passageway 34 within the solid flow block 26. Normally, aperture 38 is plugged after assembly at. the rear of flow block 26 to prevent the flow from exhausting out of the flow block 26. First passageway 34 extends beyond its intersection with the second passageway 36 and terminates adjacent the internal bore supporting the backflush mechanism 20 (see Figure 5).

As shown in Figure 3, second passageway 36 enters and annular chamber 40 within flow block 26 at the base of the constant level box 18. The constant level box 18 comprises an outer cylindrical housing 42 which protects vertically from the upper surface of the flow block 26 and defines the remainder of annular chamber 40.An internal tube 4 having a smaller diameter than thdt of housing 42 is also fixed at the tease of the annular charnbcr 40 and projects rrom the base concentrically with housing 42. The projection of the cylindrical housing 42 is greater than that of the internal tube 44. Tube 44 is connected dt this tease with exhaust passageway 46 to provide an outlet fot the unused portion of the flow entering the constant level box 18 so as to return this flow back into the working fluid stream.

he amount of flow entering the annular chamber 40 through second passageway 3b is preferably regulated to be greater than the amount of flow which will pass through the outlet of the box 18 which is defined bv the cviin(llical housing 42 less tube 44.A pressure head is created by the level which fills the volume defined bv the cylindrical housing 4' ies tube 44. ,\ pressure hcad is created by the level of flutist above !.he outlet 48 of the ariiiul ar chamber 40. the maximum head created is defined by the height of the upper rim of the internal tube 44 above the outlet 48. The fluid level upon reaching the top of internal tube 44 will flow over the upper rim and be exhausted through c.xh.3ust passageway 46. Thus a constant pressure is maintained oil the fluid passing through the first sample passageway 48 and this pressure is tixed bv the height of internal tube 44 within chamber 40.

As shown in Figure 4, the first sample passageway 48 directs the flow from the annular chamber 40 through the flow block 26 to the flow delay line 22. Flow delay line 22 includes a first delay ritting 50 attached at one end to the flow block 26 and having an internal channel 52 which communicates between the first sample passagewav 48 and a delav line 54. Communicating with the firstdelay fitting 62 is means 56 to add reagent to the flow passing through internal channel 77.

Typically, the reagent will be addled at an extremelv low flow rate.

The delay line 54 may be of any size or shape as required for proper mixing of the reagent with the sample flow. The time required for the reagent to properly condition the sample for analyzation determines this length. Delay line 54 is attached at its outlet to a second delay fitting 58 having an internal channel 60. internal channel 60 communicates with a second sample passageway 62 (shown in Figures 2 and 10) which communicates with the backflush mechanism 20 mounted within flow block 26.

A backflush chamber 64 is for-med by the internally mounted structure of backflush mechanism 20 positioned within a steppeci bore thr-ough the flow block 26. As can be seen in Figures 5, 10 and 11, Lhe chamber 64 which is defined by the wdlls of the bore within the flow block '6, orifice member 66 and check vaive retained 68.The sample flows into the backflush chamber 64 through the second sample passageway 62 and is directed into centrdl bore of the orifice member 66 and in which a plunger rod 70 is inserted. Plunger rod 70 on its upper end includes a flat 72 which permits the flow to pass into the centr-al bore of the orifice member 66 then into a transverse slol 74 through the orifice member 66 and which communicates with a circumferential channel 76 in the external surface of the orifice member 66. Circumferential channel 7() is sealed by O-r-ings 78 ancl 80.

The flow entering the slot circumferential channel 76 from the slot 74 passes into a third sample passageway in the flowlock 26 and which directs the flow from there in to the attached pr-obe block 16 (see Figure 11).

The operation of the backflush mechanism 20 has been described only with respect to its function in directing the flow fr-om the flow delay line 22 into the probe block 16. The operation of the backflush mechanism 20 for cleansing the internal passageways of the flow block 26 will be described later in this text.

As shown in Figures 6 and 7, probe 12 is supported on probe block 16 which is attached to and communicates with the internal passageways of flow block 26. The end face 84 of the probe 12 is positioned adjacent un impeller chamber 86 within the probe block 16. Mounted for rotation within the chamber 86 is an impeller 88 adapted to provide a constant sample velocitv adjacent the end face 84 of the probe 12. As shown in detail in Figures 7 and 11, the impeller mechanism 24 includes a motor 90 which rotates a coupling 92 and a permanent magnet 94 supported on the end of the coupling 92 adjacent impeller chamber 86.

Magnet 94 is preferably sealed with respect to the working fluid within the impeller chamber 86 by means of a cup 96. The motor 90 and coupling 99 are scaled by a series of 0-rings 98 positioned around a flange 100. Impeller 88 is mounted on a fixed shaft 102 which projects into the impeller chamber 86 from the wall opposite of the position of the permanent magnet 94. The impeller 88 is free to rotate on shaft 102 and includes a permanent magnet 104 which is paced from coupling magnet 94 by means of a projecting portion of impeller shaft 106.

A grit material is contemplated to be utilized within the impeller chamber 86 for continuous cleaning of the probe end face 84 and chamber 86. A bushing, preferably of polytetrafluoroethylene may be provided adjacent the impeller 88 and the wall of the impeller chamber 86 in which the fixed shaft 102 is mounted. The bushing 108 will prevent grit from impairing the rotation of the impeller 88 or causing the impeller 88 to separate from its magnetic coupling with magnet 94.The impeller shaft 106 anti the protective cup 96 are preferably made ol Hastelloy (Registeled Irade ark) alloy to prevent corrosion due to the reagents as typically utilized in such systems, such as sulfuric or acetic acids or salts.

As also shown in Figures 6 and 8. the impeller 88 is free to rotate directly .jd jacent to the end face 84 of the probe 12. The impeller blades 110 are preferably designed, along with the impeller chamber 86, to create a constant flow velocity directly adiacent the end face 84 of the probe 12. The impeller 88 as shown includes projecting flanges adjacent to the wends of the impeller blades 110 to d.55 LSt in directing the grit material within the chamber 86 to clean the end face 84 of the probe 12. The grit material is continuouslv rotated within the impeller chamber 86 due to the action of the impeller 88 and is preferably not exhausted from the chamber 86 with the normal flow of the working fluid sample.

The impeller chamber- 86 includes an upwardly exten(lirlR channel 112 which is positioned adjacent the portion of the probe 12 projecting into probe block 16. An outlet passageway 114 from channel 112 is located above the inlet of third sample passageway 82 into chamber 86 so that the pressure created by the moving fluid assists in the exhaust of the flow from chamber 86 without causing the grit material to flow along with the sample. As shown in Figure 10, the outlet passageway 114 directs the sample exhaust from chamber 86 into an angled exhaust shaft 116 which communicates with exhaust passageway 46.The pressure head required to raise the level of the fluid sample to the position of outlet passageway 114 is created by the rotation of the impeller- 88 in combination with the head of constant level box 18.

Figure 8 shows in cross-section a preferred embodiment of a probe 12 as contemplated for use within the working fluid sampler system 14.

The end face 84 of the probe 12 is preferably in the form of d cap and is attached by means of a threaded coupling to a shaft 118 which is shown positioned within the probe block 16 adjacent channel 112. The probe shaft 118 is connected at its opposite end to a probe body 120 which includes an internai chamber 122.

As can be seen in Figure 9, the end face 84 of the probe 12 includes a first or working electrode 124 and a second or counter electrode 126. The working electrode is formed in a double spiral helix at the centre of end face 84. The counter etectrode 126 is positioned directly adjacent the working electrode 124 and forms an annular ring or circle surrounding the working electrode 124. It is preferred that both of these electrodes 124, 126 be made of a platinum material. However, the electrode materials may vary depending on the tvpe of analysis that is to be performed.The proximitv of the counter electrode 126 with respect to the working electrode 124 is desired to be close so as to r-educe the ohmic drop between the two during operation. A flexible membrane 128 is positioned dil ectls behind the working electrode 124 and end face 84. The memltane 128, which is preferably made of a hydrophillic polypropylene material, is protected by the working electrode 174 during operation such that the grit which is rotated by impeller 88 does not damage the thin membrane material.

Additionally1 membrane 128 is connected, via a channel 130 within shaft 118, to internal chamber 122. Both the channel 130 and the chamber 122 are filled with an electrolvtic solution. A third or reference electrode 132 is provided within the electrolytic solution. The reference electrode 132 is preferablv formed in a coil and made of silver.

The three electrode configuration, as described above, is preferably operated utilizing a potentiostat circuit (not shown) of the type employed in a variety of electrochemical measurements and laboratory instrumentation. The potentiostat circuit preferably maintains a potential between the working electrode 124 and the reference electrode 132 while allowing current only to flow between the counter electrode 126 and the working electrode 124. Virtually zero current flows through the reference electrode 132 thus rendering insignificant a major portion of the ohmic resistance and impedances between the counter electrode 126 and reference electrode 132.The impedance between membrane 128 and the working electrode 1'4 is minimized bv the placement of the membrane 128 directly behind working electrode 124 and probe end face 84.

The three electrode configuration and its circuitry maintains a fixed electrochemical potential on the working electrode 124 by minimizing the ohmic resistance and impedances between the counter electrode 126 and working electrode 124 and the reference elec rode 132 and working electrode 124. The fixed working electrode potential results in greater selectisity stability, and a near zero celi current at zero concentration.This results in the probe 12 having the ability to measure low resitfuals and eliminates the need for a periodic zero calibration adjustment. Additionally, since the end face 84 of probe 12 is attached to the probe shaft 118 by means of a threaded engagement, replacement of the electrodes 124, 126 and/or the'membrane 128 my be made easily ;)y unscrewing the end face cap 84 antl unplugging the electrode assembly from the electrical connection within shaft 118.

The electrical connection with electrodes 124, 126 are made through the shaft 118 via wires 13 and 136.

The probe 12 on its upper end may also contain a viewing cap 138 which comprises an inser-t into bore 140. The unexposed end of the view plug 138, which is preferably made of a translucent material, pro jets into the electrolytic solution within internal chamber 122 such that when the electrolyte is at its proper level within the chamber 12, the view plug 138 will appear dark. However, ii. the level of electrolytic solution within the chamber 122 is below the end of the view plug 138, the visible end of the plug 138 will appear light or clear. On the radically opposite side of the top of the probe 12 is a second bore 142 which retains a plug 144 having a porous vent within its interior.

Plug 14 is inserted into bore 142 and is sealed by means of an 0-ring 146. Plug 144 preferably includes an internal core of a porous material to permit pressure relief from the internal chamber 122.

Keturning now to Figure 5 which shows the structure of the back flush mechanism 20, a solenoid 148 is shown attached to the flow block 26 via screws 150 and 152. A plunger 154, operated by the solenoid and attached to a piston 156, is biased b a spring 158 so that the plunger 154 in the unactuated position is in its downward or relatively low position. rhe piston 156 is slicleably maintained within a fixed housing 160 with the spring 158 biasing the piston downward with respect to the housing 160. The housing 160 is sealed from exposure to the working fluid sample by gasket 162.Projecting from the piston 156 is plunger rod 70 which extends through the orifice 66 and into chamber 64 as previously described.

The upper or projecting end of the plunger rod 70 extends to a position adjacent the check valve retainer 68. Check valve retainer 68 is inserted through the top of the flow block 5 and is engaged within the upper end of the bore by means of a screw thread. An 0-ring 164 may ne provided so as to further seal the enclosure.Retainer 68 includes a ball check 166, a sliding weight 168 and an internal valve seat 170 all retained within a chamber 172. [n its normal or rest position the ball check 160 is seated on valve seat 170, which is open at its lowest end into back flush chamber 64, with the sliding weight 168 resting on check valve 168 so as to further seal the chamber 172 from chamber 6 Chamber 172 of the retainer 68 includes d number of orifices 174 which are in communication with first passageway 34. During normal operat ion, the ample fluid flow lIoin the flow delay wine 72 moves through the second sample passageway h? into the backflush chamber 64.

The pressure of the sample flow entering from the second sample passageway 62 is less than the full flow moving through the first passageway 34 into the internal chamber 172 of the check valve retainer 68 due to the structure of the constant level box 18. The first passageway 34 is at the same pressure as the flow entering the flow block 26 whereas the pressure through the second sample passageway 62 is dependent upon the head created by the constant level box 18. This pressure differential further maintains the seal of the ball check 166 within the valve seat 170.

Periodically, the internal passageways of the flow block 26 are desired to be cleaned to remove any build up of materials which may have formed. The backf lush mechanism 20 is energized by the solenoid 148 moving its plunger 150, the piston 156 and rod 70 in an upward reaction. The seal created by the ball check 166 is released from the valve seat 170 bv the end of rod 70 and flow is permitted to enter backflush chamber 64 through valve seat 170.Additionally, flat 72 on the plunger rod 70 is moved to a position such that the orifice opening 74 is sealed with respect to the backflush chamber 64. therefore the flow into the third sample passageway 84 an the impeller chamber 86 is prevented during backf lush. Due to the greater flow pressure within the first passageway 62, the first passageway 3i now controls the direction of flow through the flow block 26. This flow moves through second sample passageway 62 opposite the normal sample flow direction through the flow delay line 22 and first sample passageway 48 back into the constant level box 18.Since the third sample passageway 82 is sealed with respect to the backflush chamber 64, the grit and other materials which are retained within the impeller chamber 86 are not removed during backflush. The materials which are bac'flushed through the system are moved into the constant level box 18 and are exhausted through the exhaust passageway 46. Upon deenergization of the solenoid 148, the plunger 154, piston 156 and rod 70 are moveti downward due to the act in of spring 1;8 aid the ball check 166 is returned to the valve seat 170 so as to resume normal flow of the sample into impeller chamber 86.

As also can be seen in Figure 5, orifice 66 includes an axial bore 176 which permits a portion of the flow entering backflush chamber 64 to move into lower chamber 178 adjacent gasket 162. Inuring activation of solenoid 148, the piston 156 moves rapidly into chamber 178 and forces flow back through axial bore 176 to further causes release of ball check 166 from valve seat 170. The back pressure in lower chamber 178 also helps retain orifice 66 in its position within the bore in flow block 26 during this backflush.

In typical operation, the constant level box provides a flow rate substantially less than the full flow entering the flow block 26. The quantity of conditioning reagent required in the system, thereforc, is greatly reduced. However, due to the reduction in the sample flow through the assembly 10, a build up of organic matter could cause a residual demand and affect the accuracy of the residual measurement orcompletelv block flow. Therefore, to minimize this possibility the system, either automatically or manually, periodicaliv energizes the solenoid 148 which raises the plunger rod 70 to open the backflush.

The movement of the plunger rod 70 also removes any material which has been entrained within the orifice 66.

In accordance with this invention, the working fluid sampler system 14, is combined with the probe 12 to result in a substantia1 cost savings in reagent usage and in increased sensitivity, especially for low residual measurement. The backflush mechanism which may be made substantial lv automatic, minimizes operator maintenance and permits utilization in cooling and waste water type svstems where electrode fouling would be frequent.

Claims (3)

CLAIMS:

1. A residual analyzer and sampling system for the residual analysis of a component in a working fluid, wherein the analyzer and sampling system comprises: a means for receiving a flow of working fluid from a source and withdrawing a sample therefrom at constant pressure; means for adding reagent to the sample; means for controlling the reagent reaction time with the sample; means for directing the sample into an impeller chamle' into contact with an analyzer probe mounted or mountable in the analyzer; an impeller mounted in the impeller chamber; means for operating the impeller to feed the sample through the impeller chamber and across the analyzer probe at a substant iallx constant flow rate; means for discharging the sample after passage through the impeller chamber; and means for periodicallv ckflushing the flow through the reaRetIt addition means, the reaction control means and the sample withdrawal means, but not through the impeller chamber.

2. An analyzer and sampling system according to Claim 1, wherein the analyzer probe is an amperometric probe having a pair of electrodes exposed to the fluid sample as it passes through the impeller chamber.

3. An analyzer and sampling system according to Claim 1 or wherein the impeller chamber contains grit, and wherein the impeller means is effective to cause the continuous cleaning of the exposed working surfaces of the probe by said grit as the sample is fd hi-ounh the impeller chamber.