Patent Application
20200124567
The present application discloses apparatuses and methods for detecting chloride concentration of water.
A chloride concentration measuring device is provided which includes a first portion configured to hold a reference solution. The first portion comprises a reference electrode configured to contact the reference solution. The measuring device also includes a second portion, adjacent the first portion, and configured to receive sample water at a flow rate. The second portion includes a measuring electrode configured to contact the sample water. When a constant voltage is received across the reference electrode and the measuring electrode, a current is produced in the sample water which is proportional to an amount of chloride ions in the sample water.
An apparatus for determining water chloride concentration is provided which comprises a chloride concentration measuring device, a power supply and a processor. The measuring device comprises a first portion configured to hold a reference solution. The first portion includes a reference electrode configured to contact the reference solution. The measuring device also comprises a second portion, adjacent the first portion, which is configured to receive sample water at a flow rate. The second portion includes a measuring electrode configured to contact the sample water. The processor is configured to control the power supply to apply a constant voltage across the reference electrode and the measuring electrode, receive an indication of a current, produced in the sample water in response to the constant voltage, which is proportional to an amount of chloride ions in the sample water and determine a chloride concentration of the sample water based on the current.
A method of detecting chloride concentration of water is provided which includes receiving, at a flow rate, sample water at a portion of a chloride concentration measuring device. The method also includes controlling a constant voltage to be applied across a measuring electrode, disposed in the portion and electrically connected to the sample water flowing in the portion and a reference electrode disposed in another portion of the chloride concentration measuring device which is adjacent the portion and holds a reference solution contacting the reference electrode. The method further includes determining a chloride concentration of the sample water based on a current in the sample water, produced in response to the constant voltage, the current being proportional to an amount of chloride ions in the sample water.
A more detailed understanding can be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:
Chloride ions (Cl—) are recognized as harmful contaminants in applications that require ultrapure water and steam systems, such as power plants. For example, relatively low levels of Chloride ions present in the steam have been shown to be directly related to stress corrosion cracking of high energy components in the low pressure sections of steam turbines. This corrosion can reduce the life of the components, such as turbines, and in some cases, can cause failure of the components. Efforts to prevent such failures have led to the formation of groups, such as EPRI (Electric Power Research Institute), ASTM (American Society of Testing Materials), ASME (American Society of Mechanical Engineers), ISO (International Standards Organization) and others to establish strict standards for water and steam contaminants. These efforts have been hampered, however, by the lack of reliable and efficient direct measurement equipment for real-time monitoring of chloride contamination in ultrapure water systems.
Conventional techniques for detecting chloride concentration of water include titration, ion chromatography, degassed conductivity and techniques using ion selective electrodes. For example, titration techniques involve incrementally adding a titration mixture (e.g., silver nitrate mixture), of a known quantity and volume, to water until an indicator has a reaction. These titration techniques do not have sufficient sensitivity, however, to measure chloride at low levels required by the standards.
Ion chromatography techniques include detecting ions based on their electrochemical charge in comparison to other analytes. Ion chromatography can detect chlorides at levels of 100 ppb or less. Ion chromatography has not, however, been adapted to power plant steam sampling systems. In addition, the equipment is very costly and difficult to maintain.
Degassed conductivity includes measuring the electrical conductivity of the sample after cations and conductive gases have been removed. The amount of chloride ions in ultrapure water systems is indirectly estimated. Degassed conductivity measures the total anions in water, however, which typically includes other anions such as sulfates, nitrates, amines, and other species. Accordingly, degassed conductivity techniques do not accurately measure the chloride concentration of the water.
Attempts to build chloride analyzers based on ion selective electrode techniques have been unsuccessful, due in part, because these analyzers are extremely complex, requiring precise temperature controls and buffering chemicals which are very toxic and difficult to use.
Some conventional techniques for detecting chloride concentration of water include measuring the concentration of another contaminant, such as sodium to indirectly measure the concentration of chlorides. For example, the level of sodium is proportional to the level of chlorides due to the common chemical pair of sodium chloride (i.e., table salt). There are, however, other more serious chemical species that can be present in water, such as HCl (hydrochloric acid), which can be present at low concentrations, even in an apparently alkaline environment.
The present application discloses apparatuses and methods for efficiently and accurately detecting low level amounts (e.g., <100 parts per billion (ppb)) of chloride concentration of water. The apparatuses and methods described herein provide an automated electrochemical process which determines the chloride concentration of the sample water in real time. That is, continuous and analogous readings (e.g., output current of the sample water passed by the counter electrode 124 to processor 116) of the chloride concentration are provided for the sample water as it flows through the measuring device. The readings are determined substantially instantaneously, with a signal constant buffering of up to about 20 seconds. The present application discloses cost efficient, easy to operate, low maintenance analyzers useful for monitoring steam and water systems in power plants.
An electrochemical process is used in which a constant voltage (i.e., voltage is maintained within a threshold voltage range) is applied between a reference electrode, which contacts a solution in a first portion of a measuring device, and a measuring electrode, which contacts sample water in a second portion of a measuring device. An output current is produced in response to the constant voltage. Based on the chemical reaction between the analyte (i.e., chloride) and the measuring electrode, as described below, the output current, which is proportional to the amount of chloride ions in the water, is determined. The chloride concentration of the water is measured according to the output current, the flow rate of the sample water and the temperature of the sample water.
The chloride concentration measuring device 102 includes a first portion 106 and a second portion 108, adjacent the first portion. The second portion 108 is, for example, disposed below the first portion 106 relative to ground during operation. The second portion 108 may not be disposed below the first portion 106, however, during operation. The first portion 106 is configured to hold a reference solution (e.g., a copper sulfate solution). The first portion 106 includes a reference electrode (e.g. copper) 110 configured to extend within the first portion 106 and contact the reference solution.
The second portion 108 is disposed below the first portion 106 relative to ground. The second portion 108 is configured to receive, via inlet 112, sample water at a flow rate. As described in more detail below, the sample water can be received at a constant flow rate or a variable flow rate. The second portion 108 also includes a measuring electrode 114 configured to extend within the second portion 108 and contact the sample water that is received via inlet 112. A surface of the measuring electrode 114 comprises a material reactive with chloride such that a measurable current is produced when an electric potential is applied. For example, the surface of measuring electrode 114 may include silver (e.g., silver chloride (AgCl)).
Electronics housing 104 is configured to house electronic and processing components used to control operation of the components and to communicate between the components described herein. Electronic and processing components include, for example, one or more processors 116 (hereinafter “processor”), user interface 118, power supply 120 and other components (not shown) such as memory (e.g., RAM), storage (e.g., removable storage device) circuitry, wires, buses, transmitters, receivers and network interfaces. The electronic and processing components may be configured to communicate (wired or wirelessly) with components of analyzer 100. Additionally one or more electronic and processing components, such as one or more additional control processors (not shown), can be located at one or more of the components of the analyzer 100 and configured to communicate with the electronic and processing components housed at electronics housing 104. The processor 116 is configured to process instructions (e.g., from user input and predefined programmed instructions).
As shown in
Power supply 120 is used to apply a constant voltage (i.e., electric potential) across the reference electrode 110 and the measuring electrode 114. For example, the processor 116 controls the power supply 120 to maintain a constant voltage within a target voltage range (e.g., about 130 mV to about 250 mV) such that the working potential of the measuring electrode 114 is reached under the following two conditions: 1) in the absence of chloride ions the counting electrode reads zero; and 2) linearity is achieved over the target measuring range and the reading from the counting electrode.
As described in more detail below, when the constant voltage is applied, an output current is produced, via counter electrode 124, based on the electrochemical half reaction between the material (e.g., silver chloride) on the surface of the measuring electrode 114 and the chlorides in the sample water. The output current is proportional to the amount of chloride ions in the water. The proportion is determined according to the temperature of the sample water, the surface area of the measuring electrode 114 and the flow rate of the sample water. The output current of the sample water flowing, via outlet 122 from the second portion 108, is provided by the counter electrode 124 to the processor 116. The processor 116 determines the chloride concentration based on the output current.
Second portion 108 includes a wall 216 (e.g., comprising stainless steel or another conductive metal material) defining a sample water flow chamber configured to hold the sample water flowing within. Second portion 108 includes sample water inlet 112, configured to receive the sample water into the flow chamber, and sample water outlet 122, configured to provide the sample water from the sample water flow chamber of the second portion 108.
Second portion 108 also includes measuring electrode 114, comprising a measuring electrode base 114a (e.g., comprising silver) and a measuring electrode surface (plating) 114b. The measuring electrode surface 114b is disposed within the second portion 108 such that the surface 114b contacts the sample water flowing through the second portion 108. Measuring electrode surface 114b comprises a material (e.g., silver chloride) configured to react with the chlorides in the sample water and produce a current in the sample water. The measuring electrode also includes a protective material comprising an electrochemically inert, hydrophobic elastic, for example acetate, disposed on the electrode surface 114b to extend the life of the electrode surface 114b. Measuring electrode 114 is electrically connected to power supply 120 via electrically conductive material housed by wire 212. The wire 212 enters lower sealing assembly 214 and is electrically connected to a second portion 114c of measuring electrode 114.
The chloride concentration measuring device 102 also includes diaphragm 218. As shown in
Counter electrode 124 is electrically connected to the sample water (e.g., directly connected to the water or indirectly connected to the water via a part of the second portion (e.g., to the metal wall defining the second portion 108). Counter electrode 114 is also electrically connected to power supply 120 via electrically conductive material housed by wire 210. Counter electrode 124 is configured to receive an output current resulting from a half reaction of the chlorides in the sample water and, for example, the silver of the measuring electrode surface 114b. An indication (e.g., amperage value) of the output current is provided from the counter electrode 124 to processor 116. The processor 116 receives an indication of the output current and determines the chloride concentration of the sample water based on the output current.
The determination of the chloride concentration of the sample water is also based on the temperature of the sample water flowing through the measuring device 102. The processor 116 may scale the output current derived from the reaction according to a sensed temperature.
For example, as shown in
A temperature of the sample water is determined from a temperature sensor (e.g., temperature sensor 220 in
Alternatively, a constant temperature provider, such as a heat exchanger (not shown), which controls the temperature of the sample water provided to the measuring device 102 can be used to provide the sample water at a predetermined constant temperature (e.g., a temperature within a predetermined temperature range). Accordingly, the processor 116 may then determine the chloride concentration without scaling the output current according to the predetermined temperature.
The determination of the chloride concentration of the sample water is also based on the flow rate of the sample water flowing through the measuring device 102. The sample water may flow through the measuring device 102 at a constant rate or a variable rate. When the flow rate is variable, the processor 116 may scale the output current derived from the reaction according to a determined flow rate. Alternatively, the processor 116 determines the chloride concentration of the sample water according to a constant flow rate.
For example,
Arrows are used in
The sample water flows from the flow meter 302 through outlet conduit 306 to the measuring device 102. The sample water is received into the second portion 108 of the measuring device 102 via sample water inlet 112. The sample water flows through the second portion 108 and exits the second portion 108 at water outlet 122.
Processor 116 controls a constant voltage to be applied across the measuring electrode 114 and the reference electrode 110. When the water contacts the measuring electrode surface 114b at the applied voltage, the material on measuring electrode surface 114b reacts with the chlorides in the sample water and produces a current in the sample water. For example, if the material on measuring electrode surface 114b is silver chloride, a reaction between the silver chloride and the chlorides in the sample water at the applied voltage produces the current in the sample water, as shown below in the half reaction equation.
Cl−+Ag→AgCl+e− Equation (1)
The current in the sample water is passed by the counter electrode 124 to the processor 116. In response to receiving the indication of the current, the processor 116 determines an unscaled chloride concentration (e.g., a ratio of the chlorides to the sample water) of the sample water according to the current, which is proportional to the amount of chloride ions in the water. The proportion is calculable from the temperature of the sample and the flow rate. The processor 116 scales the determined unscaled chloride concentration of the sample water according to the determined flow rate.
Alternatively, the flow rate of the sample water can be controlled such that sample water flows into the measuring device 102 at a constant rate. For example,
As shown in
The sample water is received at inlet conduit 404 and is provided to the constant flow provider 402. The sample water flows from the constant flow provider 402 through outlet conduit 406 to the measuring device 102. The sample water is received into the second portion 108 of the measuring device 102 via sample water inlet 112. The sample water flows through the second portion 108 and exits the second portion 108 at water outlet 122.
As described above in
As shown at block 504 of
As shown at block 506 of
As shown at block 508 of
In one embodiment, determining the chloride concentration of the sample water also includes determining an unscaled chloride concentration and scaling the chloride concentration based on a sensed variable temperature.
In another embodiment, determining the chloride concentration of the sample water also includes determining an unscaled chloride concentration and scaling the chloride concentration based on a determined variable flow rate.
The methods provided can be implemented in a general purpose computer, a processor, or a processor core. Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. Such processors can be manufactured by configuring a manufacturing process using the results of processed hardware description language (HDL) instructions and other intermediary data including netlists (such instructions capable of being stored on a computer readable media). The results of such processing can be maskworks that are then used in a semiconductor manufacturing process to manufacture a processor which implements features of the disclosure.
The methods or flow charts provided herein can be implemented in a computer program, software, or firmware incorporated in a non-transitory computer-readable storage medium for execution by a general purpose computer or a processor. Examples of non-transitory computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs).
It should be understood that many variations are possible based on the disclosure herein. Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements.
