Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
  • G01N17/02—Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement

Definitions

• the subject of the invention is an apparatus and method or process for providing real time process condi ⁇ tion monitoring and more particularly an apparatus and method or process for real time corrosion monitoring at high temperature.
• Corrosion attack is an inherent problem when operating high temperature combustion equipment. See in this regard, G. A. Whitlow et al. , "On-Line Materials Surveillance For Improved Reliability In Power Generation Systems," NACE 1991 Corrosion Conference, Paper 254. In view of the time over which boilers have been manu ⁇ factured, it would be expected that corrosion problems have been effectively solved. This is not the case because the multiplicity of factors, which include continued upgrading of designs and the utilization of different fuels. The limitations of service materials are quickly revealed if the composition or temperature of the combustion gas is allowed to vary outside narrow operating limits. The consistent trend for improved thermal efficiency demands that combustion temperatures run ever higher and steam temperatures are also steadily increased.
• the volume of the combustion chamber may need to be increased. This frequently causes the gas flow profile to change, especially during periods of reduced load when it is necessary to produce steam at a relatively constant degree of superheat.
• the change from the proven unit produces a new generation of problems to be solved.
• the installation of low N0 ⁇ burners in an existing boiler can produce a similar effect. Staged combustion conditions may promote tube wall sulfidation, wastage or molten salt attack in equipment which previously had not exhibited damage.
• a method of controlling a process parameter to limit the real time material degradation of a component in a process stream operating above 500°F comprises the steps of: providing a sensor having a plurality of spaced apart plates formed from the same material as the com ⁇ ponent, the plates being spaced apart by electrical insulators and being exposed to said process stream; maintaining the sensor generally at or near the temperature of the component; controlling the process or adding a corrosion inhibitor in response to a signal from the sensor indica ⁇ tive of at least one of the following: the electrochemical current noise, the electrochemical potential noise to thereby reduce the real time degradation of the component.
• the apparatus or sensor for monitoring real time corrosion at temperatures above 500°F when made in accordance with this invention comprises three electrodes separated by high temperature insulators.
• the electrodes are disposed in a high temperature environment and have a first loop connecting two of the electrodes with a voltage meter capable of indicating the potential noise between the two electrodes and a second loop connecting the third electrode to an adjacent electrode with an amp meter capable of indicating the current noise between the two electrodes in the second loop.
• Figure 1 is a schematic view of a sensor utilized to determine real time corrosion in a high temperature application
• Figure 2A shows solution resistance vs time
• Figure 2B shows charge transfer resistance vs time
• Figure 2C shows coupling current vs time
• Figure 2D shows potential noise vs time
• Figure 2E shows current noise vs time
• Figure 2F shows temperature vs time
• Figure 3 shows a corrosion circuit with a alternating power source imposed thereon
• Figure 4 is a schematic view of a municipal solid waste incinerator having a high temperature real time corrosion sensor which controls a corrosion inhibitor additive injection system.
• the apparatus or sensor 1 comprises a plurality of electrodes 3a, 3b, 3c, 3d, 3e and 3f generally made of the same material as that used within a high temperature process that operates above about 500°F, for example the outer surface of superheater tubes in a boiler wherein the corrosion is ascribed to processes such as molten salt damage, high temperature sulfidation, oxidation and chlorine or HC1 attack and other high temperature cor ⁇ rosion processes. While superheater tubes are used as an example, the process is applicable to other convection section tubing, radiant section membrane tube walls, high temperature gas turbine components, gasification systems, fuel cells, chemical plant process heaters and similar types of high temperature combustion and process plant installations.
• the electrodes 3a-3f are separated from each other by a temperature resistant electrically insulating material 5.
• a heat transfer conduit 7 or other heat transfer means is provided, if required, to maintain the electrodes 3a-3f at the same metal temperature as the process element by either adding or removing heat Q as required. Material from the process forms a deposit d on the electrodes 3a-3f and corrosion products p form on the surface of the electrodes 3a-3f.
• a thermocouple 9 or other temperature measuring device is installed in one of the electrodes 3a to measure and supply a signal for controlling the temperature T of the electrodes 3a-3f.
• Two electrodes 3e and 3f may have a device 11 for supply ⁇ ing an alternating current electrically connected.
• This circuit also incorporates means for measur ⁇ ing the voltage and current 13 and 15 respectively.
• Three of the electrodes 3b, 3c and 3d are electrically connected to form two parallel circuits or loops with one of the electrodes 3c being common to both circuits or loops.
• One of the circuits or loops has a volt meter 17, which indicates changes in voltage or voltage or potential noise, V n
• the other circuit or loop has an amp meter 19 which indicates changes in current or current noise, I n
• an amp meter 21 which indicates the average current, I, in the circuit or loop.
• the various indications may be in analog or digital form so that they can be sent to a computer 23, which can perform various mathematical operations on the indications to put them in forms which are easily compared with previous indications so the changes in the indica ⁇ tions become apparent and real time corrosion rates or changes in corrosion rates can be determined.
• Figure 3 is an equivalent circuit to the circuit connecting electrodes 3e and 3f, wherein, solution resistance, R s , the resistance of the corrosive compound is the resistance portion of an equivalent circuit and includes the capacitance of the electrodes, C ⁇ ⁇ and the resistance to transfer of the charge, R c t . together with a dilution couplent, W, when an alternating power supply 11 is incorporated in the circuit.
• the solution resistance, R s shown in Figure 2A is plotted against time and is taken from a sensor 1 installed adjacent a superheater tube in a waste heat boiler, wherein the flue gas is the result of burning solid municipal waste. Increases in solution resistance are usually related to an approach of the onset of corrosion.
• Potential noise is the change of potential indicated by the volt meter 17, shown in Figure 1.
• Potential noise is the change in voltage generated by the electrochemical corrosion of the electrodes 3 without applying any external power to the electrodes.
• Figure 2D shows the variation in potential noise over time. Increases and decreases in potential noise are indicative of the onset of corrosion.
• Current noise, I n ,I is the change in current indicated by the amp meter 21 and is generated by the electrochemical corrosion of the electrodes without applying any external power.
• Figure 2E shows the current noise over an extended period of time.
• Increases in current noise, I n are related to an increase in electro ⁇ chemical corrosion activity (rate) on the surface of the sensor elements.
• Resistance noise, R n is the resistance value calculated by Ohms law utilizing simultaneous changes in potential noise, V n , and current noise, I n .
• the resis ⁇ tance noise, R n is inversely proportional to the rate of corrosion in the sensor 1 herein described and provides information similar to charge transfer resistance or polarization resistance when electrolytes are the active corrosive mechanism.
• a decrease in the resistance noise value, R n is indicative of an increase in corrosion rate and this can be related by Faraday's Law to a rate of metal loss.
• One or more of the signals indicative of corrosion can be utilized in conjunction with operating parameters such as temperature, pressure, percent of 0 2 , CO or C0 2 , on line analysis or other operating parameters to control the process and thus maintain the required operating parameters within acceptable limits and minimize the corrosion within the acceptable operating limits reacting in real time thus taking into account real time corrosion and transient conditions which cause the majority of the corrosion.
• operating parameters such as temperature, pressure, percent of 0 2 , CO or C0 2
• Such a control can react to the onset of corrosion, providing a step improvement in control of high temperature processes.
• Figure 4 there is shown a municipal solid waste incinerator 31, wherein solid municipal waste or other combustible material is fed into a rotary combustor 33 and burned.
• the products of combustion pass from the rotary combustor 33 to a waste heat boiler 35 having a superheater portion 37.
• the products of combustion passing over the superheater 37 are not only at high temperature, but often contain such corrosive elements ascribed to processes such as molten salt damage, high temperature sulfidation, oxidation and chlorine or HC1 attack and other high temperature processes.
• corrosion inhibiting additives such as dolomite, lime, limestone, magnesia or other corrosion inhibiting substances are added to the combustible solid waste as it enters the rotary combustor 33.
• the corrosion inhibiting additives are fed to the inlet end of the combustor via a pneumatic line 39 having a valve 41 or other means governing the rate or amount of additives supplied to the combustor.
• the valve 41 is regulated by the indications produced by the sensor 1.
• One or more of the signals indicative of corrosion can be utilized by the computer 23 to operate the valve 41 and govern or control the amount or the rate at which corrosion inhibiting additives are supplied to the combustor 33 to assure that corrosion is maintained at a very low level with a minimum amount of corrosion inhibiting additives being supplied.
• the additives reduce the efficiency of the unit, are expensive and add to the amount of ash so that keeping the quantity added as low as possible substantially reduces operating costs and still protects the components from high temperature corrosion.
• real time corrosion in water cooled and gas cooled nuclear reactors may be monitored.
• real time corrosion may be monitored on-line at nominal temperatures of about 650°F or more in coolant circuits of pressurized water nuclear reactors or at nominal temperatures of about 1000°F or more in boiling water nuclear reactors.

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• 1993
  • 1993-11-19 CZ CZ19941562A patent/CZ291083B6/cs not_active IP Right Cessation
  • 1993-11-19 JP JP6513328A patent/JPH07502830A/ja active Pending
  • 1993-11-19 WO PCT/US1993/011374 patent/WO1994012862A1/en not_active Ceased
  • 1993-11-19 EP EP94901662A patent/EP0643825A1/en not_active Withdrawn

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