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The following are some issues surrounding the operation of portable exchange deionization (PEDI), beginning with an explanation of what PEDI is through plant logistics and maintenance considerations.
What is PEDI, and What are PEDI Plants?
PEDI (a.k.a. service deionization) is a service business whereby tanks known as two bed and/or mixed bed regenerated bottles of resin are placed in service to produce a desired water quality at a customer location and when exhausted are exchanged (replaced) with fresh regenerated bottles. The exhausted bottles are returned to the portable exchange plant for regeneration. Then the cycles of service flow, resin exhaustion and resin regeneration begins again. PEDI plants are processing plants that accept spent (exhausted) resins for reconditioning (regeneration) to allow repeated re-use. This type of service offers many advantages.
Customer benefits include
Dealer Benefits include
Types of Plants
There are two basic types, commonly referred to as batch and funnel. Each offers two-bed, mixed bed or a combination of each.
Batch plants are multifunctional and designed to regenerate large quantities of resin within one cycle. These are available in several sizes. Common sizes are 10 ft3, 20 ft3 and 40 ft3 plants. This style plant dependent on size accepts many of the small PE tanks previously exhausted by customers for regeneration.
Two-bed batch DI plants permit the resins to be taken directly from the exchange bottle and loaded into the respective cation or anion regeneration vessel. The resin is regenerated, quality tested and loaded down into numerous smaller portable bottles.
Mixed-bed batch plants permit the resin to be loaded directly from the exchange bottles into a separation vessel. Once separated the resins are moved into the respective cation and anion regeneration vessels. The resin is regenerated, quality tested and moved into a re-mix vessel. The resin is mixed and placed back into exchange bottles with a final quality test.
Two-bed batch plants include separate cation and anion regeneration vessels with either pumped or educted chemical systems and a test station. Associated controls, waste neutralization and other related accessories.
Mixed-bed batch plants include a two-bed plant and a separation, ,re-mix or single unit designed for both separation and re-mix. Figure 1 provides an illustration of a two-bed DI and a mixed-bed DI batch-style plant.
In comparison a funnel plant as the name implies is designed around the use of a large clear funnel. This plant type regenerates several small batches of resin at a given time. Common sizes are of single-, three- and five-station plants. With a base design each station regenerates a single cation and anion bottle.
When regenerating two-bed DI trains, this type of plant works on the basis of using the funnel for the purpose of resin backwash. The resin is backwashed out of the bottle into the funnel. When backwash is complete the resin is dropped back into the bottle. The bottle is moved to a regeneration station and regenerated.
Mixed-bed bottles use the funnel for backwash, separation and re-mix. Bottles are brought to the funnel where resins are lifted from the spent bottle into the funnel where the resins are backwashed and separated. Once separated, the resins are downloaded from the funnel into separate cation and anion bottles, which are moved to a regeneration station, regenerated and quality tested. The bottles are moved back to and lifted into the funnel. The cation resin and anion resin is mixed together and loaded back into PE tanks as mixed beds and tested.
Funnel plants in addition to the funnel include cation and anion regeneration stations with either pumped or educted chemical systems, a test station and waste neutralization. Usually one backwash funnel is provided for each regeneration station. The funnels and components are usually sized to handle 9-, 12- and 14-inch diameter bottles. Figure 2 provides a simple illustration of funnel-style plants.
Advantages of Batch Plant.
Advantages of Funnel Plant.
The resin is segregated to each bottle allowing assurance that each customer receives the same resin time and again.
Disadvantage of Batch Plant.
All resins are mixed together. Resin/customer segregation requires the individual customer to have a resin demand equal to the size of one regenerated batch.
Disadvantage of Funnel Plant.
Determining Plant Size
A study of the local market is necessary to determine the amount of available business within your area. The distributor or service provider should perform this study to accomplish two major goals: the amount and the type of expected DI business.
The amount of business begins to identify the daily quantity requirements for regenerated resin. The type of business defines through customer water quality needs the type of needed bottles. This being either two-bed and/or mixed-bed units. Customer types and customer requirements should be defined.
This study also should include an in-depth look at area waters. The quality of the feed water determines the level of pretreatment needed to enable the IX resins to produce water qualities. It also serves as an indicator of whether resin fouling will occur. Customer feed water quality and required treated quality ultimately determines cost and charges.
There are three basic bottle setups of which two belong to the two-bed family and the third is a mixed bed. These setups are described as
PEDI Plant Requirements
Regardless of the type of plant used, each requires additional treatment equipment. The equipment ensures proper resin regeneration, handling of the waste regenerate chemicals and treatment of the waste regenerate waters. Additional equipment needs include
Other important ingredients are water, pressure, gas and electric. These utilities are the lifline of the system. (See Table 2 for more details.)
Regenerate and Other Chemicals
About the Author
Nevin Rudie is senior application engineer at Ecodyne Water Treatment, Inc. in Naperville, Ill. He has been in water treatment since 1976, having been involved in the design and operation of PEDI plants for 16 years. He can be reached by phone at 630-637-2116; e-mail [email protected]