Industrial water systems operate under stress. However, excessively high stress causes scale, corrosion and microbial fouling, while low stress that is too low wastes water and chemicals. Maintaining an optimum level of control is crucial to ensuring cooling system efficiency and asset reliability.
Technology has been developed to provide real-time, online monitoring and control. It can save water and energy, and the improved system performance can lead to better efficiency, reliability and productivity. The technology continuously measures the key parameters related to scale, fouling and corrosion. When upsets occur, the technology takes the appropriate corrective action to prevent operational problems.
The technology couples a fluorescent “tagged” high-stress dispersant polymer with an inert fluorescent tracer. The chemical tag reflects the behavior of the dispersant itself while the inert material provides a control reference. Using a sophisticated control algorithm, the technology monitors the decay rates of both the inert tracer and the tag to assess the potential for scale formation. If the potential exists, the technology makes control adjustments to prevent the scale from forming. The technology also can increase system stress by adjusting the cycles of concentration, conserving water and treatment chemicals during periods of low stress.
To monitor and control bio-population, the technology uses a fluorescent “bioreporter” that reacts with an enzyme, dehydrogenase, present in microbial cell walls. The reaction changes the bioreporter's fluorescent signature. The technology monitors changes in the reacted and unreacted bioreporters in real time and automatically adjusts the biocide feed to optimize control.
The technology's controller manages all aspects of scale, corrosion and fouling control, in addition to collecting pH, oxidation-reduction potential (ORP), conductivity and turbidity data. It incorporates two corrosion-sensing probes using linear polarization resistance (LPR) technology and simultaneously calculates system volume, recirculation, makeup, blowdown and heat rejection rates.
Through these and other benefits, the technology is providing improved system efficiency and reduced maintenance costs at numerous facilities with process cooling requirements. Four case histories demonstrate how it might help your facility.
Controlling ScaleWater quality variations at one Gulf Coast refinery made scale inhibition problematic. Because the variations were unpredictable and extreme, refinery personnel simply included heat exchanger cleanings in their regular maintenance duties. Each time a particular exchanger fouled, the financial implications amounted to more than $2,200/day in lost profits.
The refinery decided to install the monitoring and control technology to minimize its maintenance issues. Because the technology measures the key parameters related to scale formation, detects upset conditions and takes appropriate corrective action, it has eliminated the fouling of the critical exchanger and has minimized operating costs, even during periods of high variability and stress.
Controlling CorrosionThe use of five different treatment chemistries and a limited ability to control them caused a lot of stress in a Western utility station. Corrosion protection was often difficult, and the results were occasionally less than optimal (figure 1).
By using the monitoring and control technology, along with a phosphino succinic oligomer (PSO) corrosion inhibitor, the station was able to eliminate two treatment chemicals and provide better corrosion protection over a wider range of operating conditions than with the previous program (figure 2).
Collecting DataAt a Midwestern manufacturing facility, stress on the cooling system was hidden from the engineering staff's view. Oxidizing biocides were applied using ORP control. Although everyone knew that overfeeding oxidants could elevate copper corrosion rates, generating the data to show cause and effect or evaluate the seriousness of the problem was nearly impossible. Then, the facility installed the monitoring and control technology.
Because the controller measures the key system parameters related to stress, it has allowed the facility to collect overfeed data (figure 3). Using ORP control, oxidant levels varied dramatically, and every overfeed resulted in elevated copper corrosion rates. When the new technology was used to control the oxidant feed, the average level of ORP in the system dropped, copper corrosion rates were reduced, and variation was almost eliminated.
Controlling Biological FoulingMonday mornings were a source of stress at one Midwestern commercial building. During the summer, part of the HVAC system was shut down on weekends when the heat load on the building was low. When the employees returned to work on Monday morning, more cooling capacity was needed. During the idle periods, the bio-population increased in the offline equipment because biocides could not circulate through it.
Without the ability to monitor sessile and planktonic bio-populations in real time and respond to changes as they happened, the facility focused its bio-control program on maintaining a sufficient oxidant residual in the system. However, this strategy wasted biocide and adversely impacted other elements of program control.
The facility installed the monitoring and control technology. Because the technology applies biocides based on the rate of change of bio-activity, it detects when an inflection point -- the point where the rate of increase or decrease in the bio-population changes -- has been reached (figure 4). Biocide overfeeds at the facility have been eliminated because only the amount needed for proper bio-control is applied. Changes in bio-population resulting from operational necessity are detected, and responses are made automatically. With the technology, the facility has been able to reduce operating costs and operational problems.
Improving ControlIn addition to automatically monitoring and controlling cooling water systems, the water treatment control technology allows users to monitor all treated systems from one location in a consistent format using Web-based performance summaries, data dashboards and service reports. Additionally, the technology's alarm and notification capabilities can keep key personnel informed of program status and control actions through text messages and e-mail.
With continuous, real-time measurement, automatic control, sophisticated diagnostic capabilities and comprehensive data acquisition and analysis, the new technology is an effective tool that can be used to identify efficiency improvements, solve problems and improve control in cooling water systems.