High Efficiency in a Large-Scale Power Plant Using the Ultrameter II

Aug. 16, 2012
Find out how Deborah Walker, a plant chemistry and O&M technician with 18 years experience, uses the Ultrameter II to optimize blowdowns and control corrosion, scale, contamination & chemicals

Deborah Walker, an operation and maintenance technician and plant chemistry technician in manufacturing and energy production has been managing water quality in industrial processes for more than 18 years. Through her extensive experience, she has come to rely on the Myron L Co.’s Ultrameter II as a way to monitor control parameters that ensure the functioning of automatic controllers and chemical dosers that optimize cooling tower blowdown schedules; prevent scale, corrosion and microbiological fouling; screen influent and effluent for process parameter control and environmental compliance; as well as directly measuring parameters critical to a total quality assurance plan.

Deborah’s most recent use of the Ultrameter II was in a high output power plant implementing a Heat Recovery Steam Generator (HRSG), gas and steam turbines, all required heat exchangers, cooling towers, and chemical controllers that preserved the life of the equipment and structures in the water circulation loop while minimizing water and energy consumption. Deborah used the UMII as part of quality assurance for all water and steam quality. Make up water for this application was sourced from a massive municipal pipeline with wastewater being discharged into a nearby creek.

Much of the online controllers Deborah monitored featured an online sampling panel. Deborah used the Ultrameter II to draw solution from the panel to ensure the online meters that monitored cooling water throughout the system were functioning properly. Because the Ultrameter II measured all of the parameters critical to her operation, including conductivity, pH, ORP and temperature, she was able to efficiently analyze equipment functioning and chemical dosing quickly and accurately.

The Ultrameter II also features data logging with memory for up to 100 readings, eliminating the need to perform record keeping tasks in the field. This means Deborah could monitor more areas of the plant in less time. Chemicals injected into the system included a cooling water dispersant that consisted of sodium bisulfate and sodium formaldehyde bisulfite. Sodium bisulfate effectively lowered the pH of the system and sodium formaldehyde bisulfite also served as an oxygen scavenger. (Removing oxygen from the system helps to prevent the formation of the hydroxide ion and hence the formation of rust, disrupting the processes of the corrosion cell. Tetrapotassium pyrophosphate is used for water stabilization and disrupts the corrosion process at the cathodic areas by combining with calcium or iron to form a complexed film.) pH monitoring with the Ultrameter II was required to ensure target levels as well as optimum chemical performance.

Deborah also used the Ultrameter II as a quality check to maintain the HRSG. To do this, she tested the purity of the steam by measuring conductivity of steam at the sample panel for boiler chemistry control.

The steam that issued from the HRSG to the turbine had the potential to errode or deposit, which could affect energy efficiency, as well as damage equipment. Any deposits would add mass to the turbine, making it more difficult to turn with greater friction, requiring more energy for the mass with more energy lost as heat. Any increase in conductivity in the steam indicated that either something undesirable was in the water as it was coming in or that there was something wrong with the combustion chemistry—either the dirty water was carried over to the steam or the steam was eroding the boiler and picking up minerals from the metal components. If the steam was corrosive, preventative corrections could be made to stem any equipment damage. If other chemical contamination was evident, additional pretreatment and other chemical controls could be implemented.

Using the Ultrameter II for steam quality control not only increased HRSG energy efficiency and equipment lifecycle, but also decreased its environmental footprint because some of the chemical contaminants that could form deposits could only be removed by other dangerous chemicals with extensive outage during maintenance. The operational target for specific conductivity blowdown identified by Deborah with the Ultrameter II was 1200-1400µS with a goal of 10 cycles of concentration.

Deborah also used the Ultrameter II as part of a disinfection program. Chlorine was used to mitigate biological fouling and corrosion. Chlorine injection occurred at 8 a.m. and 2 p.m. with blowdowns scheduled for once at night and once during the day. Deborah’s target residual level range for system disinfection was 0.2-0.6 ppm free chlorine. The bleach injection used in disinfection, however, not only interfered directly with pH control, but also with the effectiveness of other chemicals used to prevent scaling and corrosion.

Chlorine also had to be kept at a consistent reasonable level at all times to avoid shocking the system with massive doses, which could make the system erratic and difficult to balance. During a shock, biological growth could come loose as well, potentially clogging membranes or small pipes in the sample panel. Spot checking parameters such as pH, ORP and conductivity with the Ultrameter II was critical to ensuring consistent residual chlorine levels, pH, and scale and corrosion inhibitors between blowdowns.

The Ultrameter II was used by Deborah to verify the accuracy of monitors that controlled demineralizer water used in other processes at the power plant. Three trains were employed to remove dissolved solids. The first vessel removed cations. The second vessel removed anions. The third was a mixed bed that removed both types. The Ultrameter II could be used to determine when the trains had become saturated and needed to be regenerated by measuring any increase in conductivity downstream from the beds. Acid injection was used to flush the demineralizer out, which was then rinsed. Deborah used the Ultrameter II to ensure that the brine wastewater that resulted was neutralized and documented its pH and conductivity before it was shipped away.

Deborah also had to mitigate the environmental impact of discharged cooling waters. She used the Ultrameter II to take measurements of pH and temperature of the water from a creek upstream of the plant to establish a baseline for compliance for the wastewater, so that she could get the water as close to the natural conditions of the creek as possible before discharge.

The chlorine injected to kill microbes and prevent fouling while the cooling water was being recirculated also had to be removed from the water before it entered the creek. This is because the chlorine could also kill desirable organisms important to the ecosystem of the creek, either by direct oxidation or accumulation to toxic levels in living tissues. If chlorine residual was above 0.2 ppm, the waste stream was diverted to sodium bisulfite skids. On the discharge side of the skids, Deborah used the Ultrameter II to test that sodium bisulfite was injected and effective at binding with and deactivating the chlorine by measuring the Oxidation Reduction Potential (ORP). ORP measured the total killing power of all sanitizers in solution by measuring the chemical activity, rather than any specific constituent. Deborah also checked the free chlorine level again specifically.

The sodium bisulfite skid itself also caused the pH of the water to vary slightly. So Deborah made a final check of the pH using the Ultrameter II. The pH was controlled to between 6.6 and 8.6 to optimize the efficacy of other chemicals in solution. The cooling tower would typically blow down within this range, but could be as high as the administrative limit, which was set at 8.7—still well within permit discharge limits, but only with special permission.

The outside blowdown line from the cooling tower dumped into a settling basin before it traveled out to the creek. Deborah used the Ultrameter II to test conductivity, pH, ORP and free chlorine before the cooling water was discharged into the settling basin to ensure compliance with the established guidelines.

Part of effluent compliance also included a plan to monitor and control stormwater runoff from the plant. Deborah used the Ultrameter II to monitor and report pH and conductivity following a major rain event.

Ranges for other operational limits include 80-130 mg/L (ppm) Ca, which usually runs at about 60 mg/L; 0-0.5 mg/L iron, which usually runs at about 0.30 mg/L; microorganism plate count of 0-104 cfu/mL, and suspended solids between 0-25 mg/L.

Deborah has also used the Ultrameter II as part of a Quality Assurance plan for a prominent electric semiconductor manufacturer in which she used conductivity measurements to ensure semiconductor chip quality through proper rinsing.

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