June 2006, Vol. 18, No.6

Problem Solvers

Automation Helps Facilitate Peak Flows

Problem: Tourist season causes stress on city’s water treatment plant.
Solution: Controllers to automate processes and streamline workflow and improve safety and security.

Nestled in Tennessee’s Smoky Mountains, Pigeon Forge is home to a variety of special events and entertainment venues, including Dollywood. During weekends in its 9-month tourism season, the town’s population of 5500 swells to upwards of 70,000. While weekend tourism contributes to local business receipts, it also stretches the town’s infrastructure beyond its limits, particularly its water treatment plant.

From daily showers to commercial water rides, water consumption by tourists has challenged the output capacity of Pigeon Forge’s 15,000 m3/d (4 mgd) water treatment plant. On especially high-demand weekends, city officials asked residents to adopt special conservation measures. The problem was not one of supply — the city has an abundance — but rather, the city’s inability to produce enough drinking water. In 2000, the city took action and agreed to triple the existing water plant’s capacity to meet its skyrocketing demands.

In addition to boosting output, city officials sought to streamline the plant’s workflow. During an average shift, workers were responsible for maintaining, inspecting, and operating the raw water intakes, storage tanks, and filters. With the expansion plan, the current staff would be overwhelmed and unable to perform all of the required operations.

The plant needed to incorporate data management technology to comply with new U.S. Environmental Protection Agency (EPA) requirements. EPA mandated that all water production facilities retain a continuous data log of plant processes and continually create backup data files. The district also wanted to improve security for its remote pump house in response to the U.S. Department of Homeland Security’s vulnerability assessments.

Pigeon Forge Water Plant managers partnered with consulting engineers and system integrator Smith Seckman Reid Inc. (SSR; Nashville, Tenn.) and Rockwell Automation (Milwaukee) to meet the city’s goals of tripling water plant capacity, streamlining workflow, meeting documentation requirements, and increasing security. The upgrade solution includes programmable controllers, software, drives, and motor control centers.

To meet reporting requirements, it is important to have immediate access to information at multiple points in the treatment process. SSR recommended upgrading the existing relay panels to intelligent motor control centers (MCCs) and a computer monitoring system. This system would give operators a view of the entire process, including access to predictive-failure information, EPA compliance reports, and monitoring information.

Streamlining Workflow
The new system features an array of operational and electrical information, including predictive-failure alerts. The alerts notify operators of system problems prior to system failures. Motor currents that approach a predetermined excessive value trigger a blinking message on the human–machine interface (HMI). This alert gives operators time to determine the nature and location of problems and correct them before an overload occurs. In some cases, the programmable controller will automatically shut down the system to protect plant assets.

For central processing and remote terminal unit control, Pigeon Forge selected Allen-Bradley ControlLogix® and MicroLogix™ controllers. Installing controls at each blending basin allows plant workers to choose which pump to turn on and gives them the ability to adjust the blending speed as needed. The drives and motor starters located inside networked intelligent MCCs regulate pump and blending speed.

Throughout the facility, HMI software allows operators to monitor all aspects of the process. Operators can monitor basin levels, filter operations, chemical application, flow rates, water turbidity, and chlorine content. Plant workers can run many operations remotely, including controlling the remote water pumps at Douglas Lake.

As plant capacity increased, remote monitoring and control mitigated the need for extra personnel at Pigeon Forge. For example, filter operations at the basin, including scraping floc from basins into the trough and transferring it to the wastewater plant, now can be monitored onsite at the filter station. Staff even can add the flash mix remotely.

“Training on the new system was easy,” said Lynn Light, chief water plant operator at Pigeon Forge. “The graphics walk our personnel through the process, improving comprehension and reducing training time.” The intuitive, easy-to-follow screen designs helped reduce training time by 50%, according to Light.

Data Logging
In the previous system, an operator would spend upwards of 30 minutes walking through the plant, manually checking gauges and pumps. With the new integrated system, operators now spend only minutes monitoring computer screens to get the same operational information. As a result, operators are able to solve problems faster.

Recordkeeping has become much easier. Data files are sent directly to the plant’s server, where they are archived for a year. The stored data can be used for faster troubleshooting and maintenance. When an alert flashes on the screen, plant engineers can quickly reference the stored data to determine when the problem started and how it should be resolved. (After the year has passed, the data files are saved to CDs and stored offline.) As EPA data collection requirements evolve, the water plant will be able to comply by modifying its collection parameters.

Security System
In addition to the controls at the Douglas Lake pump house, the city also integrated a contact-switch-based security system to alert the district of unauthorized entry. By integrating the intrusion detection system into the remote supervisory control and data acquisition system, the district is better prepared to minimize site security vulnerability at these remote sites.

With the automated system in place, the plant has successfully tripled its capacity to 45,400 m3/d (12 mgd) without adding plant personnel — yielding an estimated savings of $200,000 per year.
With higher capacity, the city now meets projected city water demands, which continue to grow 10% annually. The added production capabilities also generate revenue for the city. Pigeon Forge now can sell water to neighboring towns.

Since the newly expanded plant opened — ahead of schedule and under budget — all systems have operated without failure. The operational costs of the facility have dropped $20,000 annually, a 28% operational cost reduction. The new plant also uses fewer chemicals, less water, and less energy, thanks to the new filter system that allows longer filter runtimes between backwash cycles.

“We know more about what is going on at a much more detailed level than before,” according to Light. “The integrated control systems and intelligent motor control centers alert our engineers of problems long before we could have humanly detected them. That helps us maintain uptime and protect assets.”

With the amount of information immediately available from the new system, operator efficiency has increased 20%, according to Pigeon Forge evaluations.

For more information, contact Randy Fordice of Rockwell Automation at (612) 817-9146 or rfordice@gmail.com