Greenfield Water Treatment System Reduces Chemical Handling & Improves Efficiency

The coal-fired Alliant Energy/Interstate Power and Light, Lansing Generating Facility's (LAN) water treatment system was over 40 years old. Nearing the end of its life expectancy, the antiquated water treatment equipment was suffering from excessive corrosion, limited replacement part availability and a variety of retrofit materials. Acid and caustic chemicals were used in the existing ion exchange system, requiring plant operators to handle the chemical on a daily basis. The system operator spent approximately 30% of his time keeping the system operational by manually manipulating valves, adding chemical, and performing maintenance. To eliminate employee hazards, prevent unexpected system failure, and increase environmental responsibility, the plant began its search for upgrade options.

To reduce costs and minimize the project time line, the facility took on many roles themselves, such as project management and commissioning. LAN hired HDR to act as project engineer of record, and HDR's experience with U.S. Water allowed for collaboration during the conceptual stages of the project to develop a complete, integrated water system. Time consuming drawings and multiple revisions were avoided with the use of 3D Building Information Modeling (BIM). BIM allowed engineers to create one visual model that incorporated mechanical, structural, electrical and civil materials, eliminating any potential for interference between the disciplines.

The LAN water system upgrade had three main goals; to operate via a fully automated Distributed Control System (DCS), to reduce chemical usage to increase operator safety, and to obtain the highest overall water recovery rate available. U.S. Water's engineers developed an integrated approach to meet these goals. With the new system, water moved through a media filtration system, two-pass reverse osmosis system and gas transfer membranes to remove carbon dioxide and eliminate the need for caustic chemical. The polishing step was EDI, which produced demineralized water. This design optimized the recovery rate and reduced the chemical requirement to a simple anti-scalant for the RO. Anticipating future water reuse opportunities, the system was designed with the ability to recover media filter backwash and EDI reject streams.

With a base load of 275 MW, it was essential that LAN experienced as little downtime as possible during the transition from old system to new. To ensure this, the plant demolished an existing on-site structure to build the new water treatment plant in its place. This allowed the existing system to remain operational until the new system was ready. The limited footprint for the new building design challenged the engineers to maximize the system's operations in a minimized space. Once the new building and system was complete, LAN was able to switch over to the new system within hours via a by-pass system.

The facility chose to automate the new system by tying into their existing DCS system, verses the traditional option of utilizing Programmable Logic Control (PLC). Connecting the water system to the DCS localized control functions to allow operators to electronically monitor the system. This was the first time U.S. Water had integrated into an existing DCS system, and they worked closely with the facility to provide control narratives that supported DCS control.

Since the new system has been operational, LAN's operator safety and efficiency has increased. Operators no longer have to manually manage the water system due to its DCS platform. The brand new system has eliminated the need for daily remedial maintenance, while the integrated filtration design has relieved operators from handling hazardous chemicals. Working with the LAN team, U.S. Water designed the integrated system to meet the facility's unique needs.

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