Electrodeionization Systems

WHITE PAPER: Planning and preparation are the keys to replacing and retrofitting EDI systems

eplacing the electrodeionization, or EDI, system at a power plant may not be as simple as changing the batteries in your smoke alarm or installing new wiper blades on your automobile. With planning Rand preparation, however, technicians can install the latest version of the water purification technology in a matter of days.

Power plants require deionized water as makeup for their high-pressure boilers to produce the steam that drives the turbines that generate electricity. If the dissolved solids in the water are not removed, boiler tubes can experience scaling and fouling, reducing the transfer of heat and the system’s efficiency. To prevent this damage, power producers traditionally used a combination of membrane sepa- ration and ion exchange processes to remove impurities from their feed water. This required the significant use of chemicals, namely acid and caustic; a large footprint; and regular interaction with the systems by workers and sometimes HOW EDI WORKS happened when the management suppliers. EDI combines ion-exchange of a gas-fired plant in the Midwest That all began to change in the membrane technology with contacted MPW Industrial Services late 1980s, however, with the ion-exchange media to provide a for the purchase and installation of introduction of EDI technology. EDI high efficiency demineralization the newest EDI technology through combines ion-exchange membrane process. MPW’s Products Direct arm (https:// technology with ion-exchange Resin beads exchange salts sales.mpwservices.com/), an E-Cell media to provide a high efficiency in cation and anion form for MK-3 from General Electric, now demineralization process. Adoption hydrogen and hydroxide. EDI Suez. Plant management said it of this new technology was slow regenerates the resin beads wanted to switch to the new tech- in many cases because significant continuously using electricity. nology during an upcoming five-day pretreatment was required for early Splitting water at the surface outage. versions of EDI. Today, EDI units of the resin beads creates To ensure the installation of are a common site at power plants hydrogen and hydroxyl ions, the new EDI units went smoothly, because technical advancements which continuously regenerate MPW, General Electric and plant have enhanced the efficiency and the ion-exchange resins. This management engaged in a series simplicity of the water purification eliminates the need for chemicals of planning meetings to define the process. to regenerate the resins, and scope of work as well as the details Nonetheless, the performance of eliminates the batch process that of the assignment. EDI units can gradually and steadily requires traditional ion exchange degrade over time. That’s what (cont.) to be off-line from time to time.

9711 Lancaster Rd. SE • Hebron, OH 43025 www.mpwservices.com 24/7 Customer Support: 800.842.4355 Electrodeionization Systems

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Complicating the switchover, requires traditional ion exchange to the plant. The other pretreatment however, was the fact MK-3 enables be off-line from time to time while process is multimedia filtration. users to eliminate process steps being regenerated, often at off-site As a result, engineers from MPW that were once critical for previous locations. This explains why EDI is a developed detailed drawings for generations of the EDI technology. good choice for remote locations. the installation of pipes from the For example, the brine injection Additionally, because the resin reverse osmosis unit to the new EDI system the MK-2 required would beads don’t require backwashing or units. no longer be needed to regenerate fluidized beds, they do not need to To meet the power plant’s need the resins. That means a technician be installed in the large pressurized for 120 gallons of water per minute would no longer need to engage in tanks. And because EDIs require less (GPM), MPW’s engineers, working in the weekly task of filling the system resin for a given flow, the equip- conjunction with their counterparts with salt water at a concentration ment size is smaller. This means EDI from General Electric, determined appropriate for the feed water the systems require less space. that two rows of nine EDI units, plant treats. Another source of efficiency in one above the other, would meet In addition, the concentrate the latest EDI technology is count- requirements. EDI systems in power recirculation loop that continuously er-current flow. The dilute resin plants typically treat water between pumped water in the MK-2 would bed gets the highest concentration 40 and 700 gpm, though some no longer be needed because the of divalent ions at the entry point. facilities use the technology to treat MK-3 can start up with only feed However, the concentrate flow water as high as 2,000 gpm. water pressure. Eliminating the starts at the opposite end of the Removal of the brine injection recirculation pump is a significant resin bed. This means the highest system and recirculation pump as contributor to the nearly 50 percent concentration of divalent “scaling” well as installation of the new EDI reduction in power consumption for ions are transferred to the outlet units required two days. Another the latest generation of EDIs, which part of the concentrate chamber two days were required to program might seem minor to a plant gen- instead of inlet. This method the system, largely because the erating as much as 500 megawatts provides a two-to-four times power plant wanted to continue annually but nonetheless impacts reduction in scaling potential than using its 1980s era programmable the plant’s bottom line. the co-current method, helping to logic controller (PLC) to operate In fact, the reduction in operating save chemicals with less frequent the water purification process. costs has been a significant driver cleanings. Recognizing this requirement during in growing use of EDI, which is a To ensure the EDI system fulfilled the planning stages, MPW obtained function of how the technology plant management’s expectations an older model laptop so it could works. EDI is based on the same for efficiency, MPW deployed two communicate with the PLC. principles as traditional ion mechanical and one computer As a result, MPW completed exchange. Resin beads exchange technician to the facility for the the replacement and upgrading salts in cation and anion form for installation and reconfiguration of of the plant’s EDI system one day hydrogen and hydroxide. However, its water purification system. The early, avoiding any delay in the the regeneration of the resin is very plant supplied one worker and a generation of electricity due to the different. EDI regenerates the resin forklift truck to assist MPW. system upgrade while providing beads continuously using electricity. Eliminating the brine injection and the capability for the continuous Splitting water at the surface of the recirculation systems was relatively supply of deionized water. And for resin beads creates hydrogen and simple. Connecting the new EDI plant management, the planning hydroxyl ions, which continuously system with pretreated water was and preparation for the installation regenerate the ion-exchange resins. a different story. The EDI system and retrofit made the switch to As a result, this eliminates the needed to be connected to the the new EDI system seem no more need for chemicals to regenerate plant’s reverse osmosis unit, which complicated than the changing of a the resins. Furthermore, this is one of two pretreatment steps light bulb or the resetting of a circuit eliminates the batch process that for the well water that supplies breaker.

9711 Lancaster Rd. SE • Hebron, OH 43025 www.mpwservices.com 24/7 Customer Support: 800.842.4355