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Technical Plating Saves Over $45,000
by Reducing Water and Sewer Costs
Decreasing a SAC Fee
| Company |
Technical
Plating
Brooklyn Park, Minnesota |
| Results |
Improved
flow control on one
plating line and effluent reuse
reduced water demand by
2,625,000 gallons per year, saving
$7,100 a year plus $44,100 in one-time SAC fees. |
|
Technical Plating
is a small metal finisher that specializes in applying tin,
tin-lead and electroless nickel coatings on parts as a service
to electronics, medical and general manufacturing industries.
The plating processes generally involve degreasing, etching
or otherwise activating the metal surface, electroplating,
and rinsing between each step to remove any contaminants or
chemicals remaining on part surfaces. Typically, the parts
are plated to change the functional characteristics of the
surface, such as improving corrosion resistance, solderability
or conductivity.
Much of Technical Plating's work is small
parts in large volumes. The company processes most parts in
plating barrels, but it also does rack plating and reel-to-reel
plating.
Incentives for Change
Between 1998 and 2001, water use at Technical Plating increased
from 40,500 to 54,000 gallons per day (gpd). The local sewer
authority, Metropolitan Council Environmental Services (MCES),
proposed a one-time sewer access charge (SAC) of $56,000 for
this increased water use. SAC fees help defray future capital
costs to accommodate and treat these higher flows. MCES gave
Technical Plating one year to review practices and reduce
flows.
Technical Plating requested a MnTAP intern
to help reduce water use, hoping to lower or eliminate the
SAC. The intern helped the company explore how to reuse treated
effluent for some plating rinses and devised and evaluated
an internal rinse system for barrel plating.
Effluent Reuse
Wastewater from rinses and from batch dumps of exhausted chemical
baths was treated to remove metals and adjust pH to levels
specified by MCES. Technical Plating speculated that this
treated water was clean enough for reuse. The intern tested
reuse of the effluent on the matte-tin and bright-tin lines
because they can tolerate wider operating parameters. The
effluent was cloudy and had a brown tint. Using only the treated
effluent as rinse water, parts from the matte-tin trials met
all specifications for adhesion, solderability and appearance.
Parts in the bright-tin trials met adhesion and solderability
specifications but had a cloudy appearance. Using a 50/50
effluent/fresh water rinse improved appearance to equal a
100 percent fresh water rinse.
Further work showed that filtering effluent
to 0.5 micron would eliminate total suspended solids (TSS)
but, as expected, did little to reduce total dissolved solids
(TDS) levels measured by conductivity. By modeling concentrations
under various reuse conditions, the intern investigated the
affects of effluent reuse on the levels of sulfate, chloride
and TDS that might build up over time. Simulations showed
that contaminants would increase to about five times the concentration
in city water. Because the maximum concentration would be
reached
quickly, adverse affects would show up without delay.
To reuse the effluent, Technical Plating
installed a sand filter and two holding tanks. One tank was
used to recirculate water through the sand filter for one
to two hours, and the second tank held the filtered effluent
until it was needed on the line. Effluent was reused on one
line with no measurable decrease in the quality of parts produced.
The system cost $5,200 to install and costs
$800 a year to operate. It saved $3,800 a year in fresh water
purchase and sewer fees by eliminating 5,500 gpd [1,375,000
gallons per year (gpy)] of water use. The system also reduced
one-time SAC fees by $23,100.
Improving Rinse Efficiency
To start research on internal barrel rinsing, the intern
wanted to determine water use baselines on the rinses in order
to estimate the impact of reduction efforts. After measuring
many of the rinses' flow rates, the intern saw that the flows
varied between plating lines and different days on the same
line—with some flows being three times higher than others.
Part volumes and quality specifications did not explain this
variability.
The intern noticed that for most of the
company's two-stage, cascaded rinses, the conductivity of
the second rinse dropped to the freshwater level very early
in the cycle instead of gradually—indicating water overuse.
Ball valves. The variability was
due in part to the use of ball valves to control flow. Although
commonly used, ball valves do not regulate flow well and are
best used as on/off controls. Operators set flow rates by
adjusting the position of the ball valve handle, without measuring
or seeing the actual flow. Water entered the rinse tanks near
the bottom where the flow was not visible. Optimal flows had
not been set for the rinse operations and operators lacked
incentive to avoid overuse.
Flow meters. Technical Plating installed
three flow meters on one line's rinses at a cost of $450.
After management gave instructions to limit flows, water use
decreased by 5,000 gpd (1,250,000 gpy), saving $4,100 in sewer
and water costs and $21,000 in one-time SAC fees.
Optimal flow rates. The intern investigated
the method of Pinkerton and Graham1 for calculating rinse
flow rates based on dragout concentration and volume, the
time between plating cycles and acceptable contaminant concentration
in the rinse. The method appeared to be a good starting place
for setting flow rates for rinses.
Internal Rinse Barrels
Standard barrel plating requires significantly larger volumes
of rinse water than other types of plating because of the
difficulty of getting rinse water inside the barrel.
The intern designed and developed a system
for internal rinsing. The final design modified an existing
barrel by installing large hubs on each end of the barrel
cylinder. The hubs remain stationary as the barrel rotates.
The new hubs had a diameter large enough to accommodate holes
for danglers bringing an electrical charge to the parts in
the barrel, and also for a permanently mounted pipe along
the central axis of the barrel. The pipe had holes drilled
to spray water on the parts evenly down the length of the
barrel, and a quick connect fitting outside the barrel to
help move the barrel between plating tanks.
Tests were done comparing internal barrel
rinsing to two-tank, counterflow rinsing. The internal rinse
barrels each require 30 seconds more rinse time than the counterflow
immersion rinses. Substituting internal rinse barrels in place
of the rinse tanks on one line should reduce water consumption
by 1,400 gpd (350,000 gpy) and save about $3,800 year. Operating
the line would require three modified barrels, costing $300
each. Because the rinse steps are not the production bottleneck,
line capacity and labor costs would not be affected.
Expanding the use of internal rinse barrels
to four additional lines would require modifying 12 more barrels
at a cost of $1,200. They should reduce water use by 21,700
gpd (5,400,000 gpy) and save a total of $22,300 a year.
Counterflow internal rinsing. The
intern also simulated counterflow rinsing in the internal
rinse barrel and found this could reduce water consumption
by another 60 percent. This could save an additional $3,500
if implemented on the five barrel plating lines.
Patents. Patents cover some types
of internal barrel rinsing. While they appear to cover counterflow
internal rinsing, it is less clear if they cover internal
rinsing with single pass, fresh water. The intern looked at
the economics of purchasing commercial internal rinsing equipment
and found paybacks of five to 10 years at Technical Plating
while retrofitted barrels using single pass water could payback
in one to four months.
Overall Results
With the help of a MnTAP intern, Technical Plating reduced
water demand by 2,625,000 gpy, saving $7,100 a year plus $44,100
in one-time SAC fees.
Technical Plating had started working on
maximizing its water use to minimize its SAC fee. But with
the assistance of a MnTAP intern, the company was able to
accelerate its development and testing. MnTAP was able to
offer Technical Plating a staff person dedicated to its water
conservation problem.
| Results |
 |
| Effluent
reuse |
Improved
flow control |
|
| Reduced water use (gpy) |
1,375,000 |
|
1,250,000 |
| Savings per year |
$3,000 |
|
$4,100 |
| SAC savings |
$23,100 |
|
$21,000 |
| Cost |
$5,200 |
|
$450 |
| First year savings |
$20,900 |
|
$24,650 |
|
| Total
first year savings |
$45,550 |
|
|
Application to Other
Facilities
MCES starts its SAC review one year prior to any new assessments.
This gives companies the opportunity to reduce water use/discharge
in lieu of new SAC fees. If your company receives notice of
an impending SAC increase, the earlier you start working on
water conservation the more likely you are to find opportunities
to cut water use and lower the SAC fee.
Deciding to reuse treated plating effluent
for plating rinses is a case-by-case situation. Facilities
should consider rinse reuse for processes that are resilient
or have less stringent water quality needs. Reuse opportunities
may be better if clean wastewater, like high-purity rinses
or non-contact cooling water, can be segregated from other
wastewater streams.
To begin improving rinse efficiency, a first step is knowing the flow rates of specific operations and the variability of these flows. In many situations controlling flows may be beneficial. Areas for reducing water use include:
- processes where the water use volume is unknown
- processes where flow is not visible and offers no feedback to the operator
- flows controlled by ball valves, especially if flows are not visible
- flows that are clean, either visibly or measurably (e.g., low conductivity)
- cooling flows that are still cool when going to drain
Internal rinse barrels have the potential
to reduce rinse consumption wherever large volumes of small
parts are cleaned. Carried to the concept’s maximum extent,
a single internal rinse barrel would be used with a single
tank. During set cycles, process chemicals would be delivered
from reservoirs to the barrel and chemical would be reclaimed
from the tank after each step. This would reduce floor space
and labor by bringing chemicals to the finishing barrel rather
than bringing the barrel to the tanks.
More Information
MnTAP has a variety of technical assistance services available to help Minnesota businesses implement industry-tailored solutions that maximize resource efficiency, prevent pollution, increase energy efficiency, and reduce costs.Our information resources are available online. Or,
call MnTAP at 612.624.1300 or 800.247.0015 from greater Minnesota
for personal assistance or more information about MnTAP’s
Intern Program.
References
- Electroplating Engineering Handbook, Third Edition.
Van Nostrand Reinhold Company, New York, 1971.
This project was conducted in 2002 by MnTAP
intern, Eric Tsai a chemical engineering junior at the University
of Minnesota.
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