Inside process: System upgrade saves operating costs
The City of College Station runs a groundwater production and wastewater treatment facility with their respective distribution networks in Brazos County, Texas, to serve more than 83,000 people with up to 23 million gallons of water each day at peak demand in the summer.
Pumping groundwater from wells around the county, the City of College Station Water Services (CSWS) cools the water and transports it through water lines to a second pump station for further treatment, and then into the water distribution system and two elevated storage tanks. Raw wastewater travels through a network of over 275 miles of wastewater collection lines to one of two award-winning wastewater treatment plants.
This complex process requires a sophisticated control system to monitor the processes for best efficiency, and to meet the many standards and regulations of the water industry.
Over the past two decades, CSWS has worked to increase city water production and delivery capacity as well as improve water quality and treatment processes. A 2006 capital improvement project earned the city an Environmental Excellence Award from the Texas Commission on Environmental Quality. The treatment facility has also been recognized with consecutive awards for outstanding performance from the National Association of Clean Water Agencies (NACWA).
During that 2006 project, the utility recognized that the existing control hardware was reaching the end of its lifecycle and needed to be upgraded before the system started causing major outages. Keeping it going 24 hours per day was putting a strain on the technical support staff having to work with multiple vendors with few troubleshooting tools.
“With many disparate systems, there can be a lot of finger pointing between suppliers,” says Michael Kellogg, CSWS SCADA systems analyst. “That makes it difficult to just get the issue resolved quickly.”
Specific goals included with the upgrade were to standardize control equipment across all plants, and to improve control, communications, scalability, and flexibility with a comprehensive communication network. CSWS had always used standard digital and analog 4-20 mA I/O but had the foresight to investigate current communication standards such as ControlNet, DeviceNet, EtherNet/IP, Profibus, and HART.
Kellogg says that it was tempting to upgrade what was there piecemeal, but that would not solve the underlying problem. “It would be easy to convert the programs, wire in the existing I/O and keep going with the ‘that’s the way we always did it’ mentality,” he said. “But our calculations on cost per I/O point proved that a networked technology would be very cost effective, especially when you incorporate the cost of conduits, concrete for duct banks, enlarged termination cabinets, and additional terminal blocks.”
In addition to hardware considerations, the utility also tried to factor in how a new control system could benefit maintenance and training, reduce overtime, and prevent regulatory fines and administration costs. The new system would have to provide common programming environments and easy integration with existing and future equipment.
Lastly, city-owned utilities are required by law to take three competitive bids to ensure the best value for citizens’ money. CSWS researched several vendors, looking for one that could support bus technology and the standard I/O. Some vendors could primarily support one method but would have to use third-party vendors for other applications.
CSWS worked with its local electrical distributor, Reynolds Company, of Houston, Texas, and evaluated the cost-benefit of a control system from Rockwell Automation. Its offering could support all the communication methods and provide flexibility to determine the best application solution. It also took into account the opportunities and value of a long-term service and support agreement.
The Rockwell Automation solution included a PlantPAx Process Automation System, motor controllers, and variable frequency drives as well as field services for installation, inspection, calibration, start-up, and commissioning with phone and online support.
PlantPAx integrates all process operation controls and motor controls into one system and uses core integrated architecture technologies through EtherNet/IP, DeviceNet, and ControlNet wireless communication networks. Ethernet is the top-level program for computer networking, replacing conduits and wires for each I/O to help reduce wiring and installation costs, increase reliability, and enable point-to-point management and troubleshooting.
CSWS also standardized on Allen-Bradley ControlLogix programmable automation controllers (PACs) across the treatment plants. ControlLogix PACs are fully integrated with all aspects of the water treatment process and help operators access plant-wide information for better management decision making, and productivity optimization.
Allen-Bradley Centerline 2100 motor control centers (MCCs) with IntelliCenter technology package include soft starting and stopping. “The IntelliCenter software offers the ultimate window into an MCC and allows plant operators to drill into any network-equipped section of the MCC and determine the status of the incoming power, pump performance, and efficiency,” says Kellogg.
Kellogg put his more than 20 years of experience in the water wastewater industry to work and took an active role in the control system design. “Tag-based programming was important to us,” he said. “It enabled us to follow our standards and nomenclature, and provided continuity for operators. Since the first part of the tag identifies the equipment name, for example, TFP01 represents thickener feed pump 01, it was easy for our operators to use and saved valuable programming time.”
CSWS also replaced its two-speed pumps with variable frequency drives (VFDs) on cooling fans, water service pumps, lift pumps, bio-feed pumps, centrifuges, and wasting pumps. Allen-Bradley PowerFlex 700 ac drives now gradually ramp the speed of the motor up and down to help save energy, and to help protect the life of the motor and related equipment. The drives are configured to provide additional data that gather process information at the drive level and automatically disperse it to any part of the plant.
Start-up and commissioning began in May 2009 and the utility now produces an average daily flow of 11.8 million gallons of water, compared to the previous system’s average daily flow of 8.1 million gallons. In the process it has recorded approximately $65,000 in annual energy savings since implementing the new control strategy.
The newly automated plant now only requires five operators instead of 11, allowing CSWS to reallocate its human resources to other critical areas. The control system helps reduce the risk of human error by allowing operators to adjust setpoints while the controller automatically makes related decisions for them. Before the upgrade, the plant operated on a shift schedule, 24 hours a day, seven days a week. Now it runs one shift, from 7:00 am to 3:30 pm, Monday trough Friday, which Kellogg says the operators really appreciate.
The new networked communications make operational functions accessible from remote locations, and programming functions are much simpler. This has allowed improved control in real-time where operators can take proactive action before a problem arises. “The tags and instructions are a lifesaver,” says Kellogg. “It used to take three days to program a water well and test it. Now we can do it in a day to a day-and-a-half.”
Adding VFDs contributed to reduced energy use of the 40 hp cooling tower fans and 450 hp transfer pumps. To maintain a more constant water temperature the CSWS now bases the fan speed on the water temperature, and has estimated a 13%-15% reduction in electrical usage. The preconfigured software wizards facilitate installation of motor controllers, VFDs, and switches to save time. “With the software wizards, I’m up and running, and I don’t have to get IT involved,” Kellogg adds. “It can take as little as 15 minutes to set up a switch, compared to about a week previously.”
Customer service was an important deciding factor for the City. Kellogg was impressed by the products, solutions and services, and the multiple layers of support available. “Every Monday morning I receive an email from Rockwell Automation notifying me of any software updates along with links to the Knowledgebase—an invaluable tool that allows me to search for solutions to specific problems I may encounter,” says Kellogg.
In addition, the city receives one annual invoice for its Rockwell Automation service agreement, making the accounting and tracking process much simpler. The service agreement helps CSWS reduce downtime and extend equipment service life through regularly scheduled inspections and maintenance, vibration and current analysis, harmonics analysis, spare parts surveys, and timely recommendations.
Trish Woznuk is a marketing communication specialist for Rockwell Automation.