Effective/Efficient Rinsing in Metal Finishing

Transcription

1 Effective/Efficient Rinsing in Metal Finishing Les Zenack, P.E., MWRA Consultant LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 1

2 Outline O Definition of Rinsing O Effective Rinsing - How Rinsed is Rinsed? O Efficient Rinsing LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 2

3 Outline (continued) Types of Rinses» Static»Flowing» Countercurrent» Spray (Fog)» Reactive LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 3

4 Outline (continued) O Achieving Efficient Rinsing» by type of rinse» by rinse tank design» by applying controls O Impacts of Water Conservation» on waste water quality» on waste water treatment LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 4

5 Outline (continued) O Optimizing Rinse Water Quality O Example Rinsing Station Initial Configuration O Example Rinsing Station Revised Configuration O Using Rinscalc or Perfect Rinsing LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 5

6 Definition of Rinsing Removal ( dilution ) of a clinging film of process solution from the surface of a workpiece by substituting a film of water. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 6

7 Effective Rinsing How Rinsed is Rinsed? O Effective rinsing is reaching a specific dilution of the clinging film of process solution. O The specific dilution is chosen to limit contamination of a subsequent process to manageable levels. O The specific dilution should be measurable as a Quality Control Standard. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 7

8 Effective Rinsing How Rinsed is Rinsed? PERMISSIBLE CONTAMINATION CRITERIA* Type of Rinse Adequate Rinsing (mg/l) Following Cleaner / Acid Pickle 400 to 1,000 Following Functional Plating 100 to 700 Following Bright Plating 5 to 40 * from Pollution Prevention and Control Technology Manual LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 8

9 Efficient Rinsing O Measured by the amount of water used to meet the rinsing Quality Control Standard. O Increasing water/sewer charges and wastewater treatment system capital and operating costs provide incentives to improve rinsing efficiency. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 9

10 Static Rinse Dragin Rinse Tank Rinse water contaminants increase until the rinse water is replaced. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 10

11 Flowing Rinse Dragin Rinse Water Makeup Rinse Tank Waste Water For steady dragin rate, makeup flow sets the rinse water quality: SALT IN = SALT OUT LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 11

12 Countercurrent Rinse Rinse Water Makeup Dragin Dragover Rinse Tank Rinse Tank Waste Water LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 12

13 Spray (Fog) Rinse Evaporation Spray (fog) rinse nozzle Dragout Process / Dragout Tank For steady state, spray rinse flow equals tank evaporation rate. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 13

14 Reactive Rinse Dragout Dragin Dragout Dragin Dragin Dragout Rinse Water Makeup Dragin Process Tank (Alkaline Cleaner) Rinse Tank Process Tank (Acid Pickle) Rinse Tank Waste Water ( high ph ) Waste Water ( low ph ) LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 14

15 Achieving Efficient Rinsing RELATIVE FLOW RATES Rinsing System Rinse Flow (gpm) Single Rinse 10.0 (arbitrary) Two Series Rinses 0.6 (1.2 total) Three Series Rinses 0.3 (0.9 total) Two Counterflow Rinses 0.3 Three Counterflow Rinses 0.1 LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 15

16 Achieving Efficient Rinsing (continued) Optimal Rinse Tank Design O Use minimum rinse tank size O Locate rinse water inlet and outlet at opposite tank positions O Use flow distributor / sprayer O Use air agitation or mechanical mixing O Use warm rinsing LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 16

17 Achieving Efficient Rinsing (continued) Rinse Water Controls O Manually turn off rinse water O Use conductivity or ph rinse controllers O Use timer rinse controls O Use flow restrictors O Use flow meters/totalizers LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 17

18 Impacts of Efficient Rinsing O With all other parameters constant, more efficient rinsing will INCREASE waste water concentrations. O Increased concentrations may affect compliance status because discharge standards are often concentrationbased. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 18

19 Impacts of Efficient Rinsing (continued) O Increased waste water concentrations from more efficient rinsing may IMPROVE waste water treatment performance. O Decreased waste water flow from more efficient rinsing should DECREASE the capital and operating costs of waste treatment. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 19

20 Optimizing Rinse Water Quality O As in countercurrent rinsing, the cleanest rinse water is usually needed only in final rinses. O In closed loop situations, high purity (deionized) water may be needed to avoid contaminant buildup in process baths. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 20

21 Example Rinsing Station Initial Configuration Rinse Water Makeup Rinse Water Makeup Dragin 1 vol. Dragover 1 vol. Process Tank Rinse Tank Rinse Tank Conc = 100 % Conc = 3.16 % Conc = 0.1 % Waste Water 30.6 vol. Waste Water 30.6 vol. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 21

22 Example Rinsing Station Revised Configuration Rinse Water Makeup Dragin 1 vol. Dragover 1 vol. Process Tank Rinse Tank Rinse Tank Conc = 100 % Conc = 3.21 % Conc = 0.1 % Waste Water 31.1 vol. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 22

23 Using Rinscalc or Perfect Rinsing O Software that can calculate rinse water use, chemical loss, and evaporation loss. O Inputs are dragout rate, chemical concentration, temperature, process tank dimensions and volume, and target concentration in the final rinse. LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 23

24 Where to get more information O - American Electroplaters and Surface Finishers Society. O - a search engine for P2 and environmental compliance. O - searchable database for P2 information. O - National Metal Finishing Resource Center. O (the feds, with links to other sites) LDZ - May 27, 1999 EPA Region I Strategic Goals Program Page 24