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Pollution Prevention and Control Technologies for Plating Operations


Section 3 - Chemical Recovery

3.4 ION EXCHANGE

3.4.5 Costs

3.4.5.1 Capital Costs

Capital costs for modular and integrated ion exchange systems for metal recovery and water recycle (anion and cation columns) are presented in Exhibit 3-29. The modular ion exchange system costs are based on two responses to the Vendors Survey . The graphs show the costs for one and two modules of 2 cu. ft. and 3 cu. ft. capacities each. A single regeneration station is included in the cost for both the one and two module cases. Typically, one regeneration station can serve up to ten modules. Therefore, capital costs would be expected to increase in the step-wise manner shown in Exhibit 3-29 up to 20 cu. ft./30 cu. ft. resin capacities. The installed costs were estimated based on the projected costs for electrical and piping, including two components of electrical costs (service module and regeneration station) and three components of the piping costs (service module, regeneration module and service/regeneration module interface). The Vendor 1 system is hard piped to the regeneration station and the Vendor 2 system is transported (e.g., hand truck) to the regeneration station. Therefore, the vendor 2 installed cost includes only the first two piping components.

The integrated system capital costs include automated and semi-automated systems. The fundamental difference between the two types is that the regeneration cycle of the automated system is automatically initiated and the unit goes back into service automatically, whereas the semi-automatic system requires an operator to initiate regeneration and to put it back into service. Both systems operate automatically after regeneration or service is initiated. The installed cost for each system is the same, based on estimates for electrical and piping costs.

For small, manual applications, capacity is usually expressed in terms of resin volume, to which capital costs are directly related. Larger system capacities are more often expressed in terms of flow rate, but direct vendor-to-vendor pricing comparisons based only on capacity units such as gallons-per-minute can be quite misleading. Based only on flow rate specifications of four vendors, Exhibit 3-29 does not account for several cost factors including the amount of customization, the precise level of automation (which can vary considerably within the categories of "automatic" and "semi-automatic"), the type and quality of metering and monitoring instrumentation, and the general design strategies and criteria pursued by the manufacturer. These factors, in part, explain the wide range of prices quoted for similar flow rates.

Manual systems are often sized to provide an acceptable service period. Larger columns offer the benefit of fewer regenerations or replacements, less downtime and less labor expense. Automatic systems, on the other hand, are sized to handle the expected flow rate. While still a major design consideration, the service period has less impact on the user in terms of planning and labor. Thus, for highly automated systems, more frequent regenerations of smaller columns is a viable design strategy. An extreme example of this strategy is the reciprocation flow ion exchange, described in Section 3.4.4.3.

Water recycling systems are, in general, more expensive than metal-scavenging units. These systems require both anion and cation columns, which alone roughly doubles the regenerations required, and the cation resin must remove all cations, including non-regulated common cations such as calcium, sodium and potassium. In most cases, these factors make automation highly desirable or an outright requirement.

Installation expenses are site-specific but can be significant typically 5 to 40 percent or more of basic equipment costs). Shops currently employing trenches may require extensive plumbing to segregate the ion exchange stream from other wastewater. On the other hand, modular systems with off-site regeneration may incur no significant installation costs at all. In general, water-recycle systems that service several sources will require the largest installation outlay.

3.4.5.2 Operating Costs

Labor, regeneration chemistry, resin replacement, and energy are the major operating cost categories. Exhibit 3-30 presents operating costs for various operating modes of the ion exchange technology. This operating cost graph is based on a water-recycle application handling copper sulfate rinse water and is not necessarily representative of a wide range of applications.

 

Exhibit 3-30. Operating and Maintenance Costs for Ion Exchange Systems

Labor costs are significantly affected by the automation level of the system and automation capital costs are often quickly returned. Undersized or mis-applied equipment can greatly impact labor and other costs (see section 3.4.7).

Resin life is usually measured in years, but can be shortened by misuse and improper application. Resin fouling, mentioned by several respondents (see section 3.4.7), is usually a result of a marginal application, misuse, or insufficient upstream filtration or pre-treatment. Instrumentation designed to halt ion exchange system operation when harmful levels of chemistries enter the feed stream can be cost-effective where spills and accidental dumps are possible.

The operating costs estimates are based on the following assumptions:

Feed Characteristics (rinse water)/Resin Capacity

  • Copper sulfate plating process generating rinse water containing 50 mg/l Cu++.
  • Resin capacity of 38 eq. Cu++/cu. ft. (=12,900 gal between regenerations for 2 cu. ft. column).
  • Assume two anion regenerations for each cation regeneration (=1.79 days between regenerations for 2 cu. ft. column).

Energy

  • 1 hp-hr/300 gal
  • $.10/kWh (= $0.25/1,000 gal)

Regeneration Chemicals

  • Assume 4 bed volumes for cocurrent (Vendor 1-Modular) and 2 bed volumes for counterflow (all others).
  • H2SO4 (Modular 1): 12 gal (conc.) @ $2/gal per 12,900 gal flow (= $1.9/1,000 gal)
  • NaOH (Modular 1): 24 gal (conc.) @ $2/gal per 12,900 gal flow (= $3.8/1,000 gal)

Resin Replacement

  • Assume 5 year life with 3% mechanical loss per year.
  • Cation: $200/cu. ft. (= $0.03/1,000 gal)
  • Anion: $400/cu. ft. (= $0.06/1,000 gal)

Labor

  • $25.00/hr
  • Modular 1: 1.0 hr/day (= $2.71/1,000 gal)
  • Modular 2: 2.0 hr/day (requires transport) (= $5.43/1,000 gal)
  • Semi-automatic: 1.0 hr/day (= $2.71/1,000 gal)
  • Automatic: 0.5 hr/day (= $1.36/1,000 gal)

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