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General Mills Saves Over $27,400 by Reducing
Water and Sewer Costs
Decreasing SAC by Evaluating Water Uses
throughout Plant
| Company |
General Mills Bakery
plant
Chanhassen, Minnesota |
| Results |
Reduced
water and sewer costs by $5,400 a year and a one-time
SAC by $22,000 through repairs and modifying process
equipment. Cost $700. Water softening system changes
expected to save another $3,000 annually plus $12,000
in SAC savings. Cost $6,000. |
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The General Mills, Inc. Chanhassen
plant makes food products like cookies, cakes, rolls and muffins
sold to cafeterias and restaurants. Products are either baked
and sold ready-to-eat or are ready-to-bake at the point of
use. All products leave the Chanhassen plant frozen. In 2000,
the plant's total average water use was 100,000 gallons a
day.
| Water Use |
(estimated
percent) |
 |
| Product ingredient |
10 % |
| Domestic purposes |
15 |
| Cooling towers or boilers |
22 |
| Production-floor cleaning
tasks |
53 |
|
Incentives for Change
Water purchases and sewer charges totaled about $140,000 in
2000. Of that, $12,000 was from water use above the previous
service availability charge (SAC) baseline. As part of its
sewer discharge permit renewal, the plant was assessed a one-time
SAC of $135,000 for an increase in sewer use of 123 SAC units*
over its existing SAC baseline. The plant was given one year
to reduce water use in order to decrease the SAC assessment.
The plant already had made significant efforts to reduce water and sewer costs by scraping equipment and sweeping floors before washing the surfaces to keep dough and food solids out of the drains. With the assistance of a consultant, the plant:
- installed a VRTX water conditioning unit on one cooling tower, nearly eliminating blowdown for purging dissolved solids and treatment chemicals;
- optimized the operation of three pan and bucket washers to reduce water use;
- reduced effluent strength charges; and
- was credited with "deducts" for water not sewered.
The consultant estimated these efforts reduced
water use by 41 percent. At the same time, increased concern
about the effect of food allergens on sensitive individuals,
and resulting U.S. Food and Drug Administration (FDA) rules,
led to more frequent line and equipment cleaning.
Average flow is used to set a SAC baseline,
but peak flow is used when recalculating SAC after reductions.
Because of the bakery's day-to-day variability in water use,
its peak flows made further reduction necessary to decrease
the SAC assessment. General Mills requested a MnTAP intern
to help reduce water use, hoping to lower or eliminate the
SAC charge.
Sink Moderators
The production floor has 32 sinks, making hand washing and
utensil cleaning convenient for over 700 production workers.
Each sink's faucet had about a two gallon-per-minute (gpm)
flow when open. Aerators, common conservation devices, were
not used because they inject air, and possibly bacterial contamination,
upstream. The intern identified moderators as an option. Moderators
are flow restrictors that are screwed on faucet openings and
make the stream of water appear larger, like aerators, but
without aerating.
Initially, 0.5 gpm moderators were installed
on all 32 production sinks and all 20 rest room sinks, reducing
water use by an estimated 4,200 gallons per day (gpd). After
several months, experience showed that higher flows were needed
for some cleaning tasks; all but one of the production sinks
were refitted with moderators ranging from 1.0 to 1.5 gpm.
Even with higher flow moderators, water was still reduced
by at least 2,100 gpd, with one-time SAC savings of at least
$9,200 and annual savings of $2,100.
Freezer Belt Washer
In the freezers, belt washers were used for one or two line
cleanings during the week and a more extensive cleanup on
the weekend. When operating, the belt washers consumed 40
gpm from the plant's 180°F water circuit. Belt washers
were the highest single-use of this water. Nearby flows of
hot water were adversely affected when the belt washers were
run. One of the plant's three belt washers was studied and
modified.
Initially flows were decreased to 17 gpm
with good cleaning results. Over the next two months cleaning
effectiveness declined; flow was increased to 25 gpm. Cleaning
effectiveness again declined over time. Investigation led
staff to believe that the diaphragm pump was at fault. After
replacing it with a piston pump providing eight gpm flow,
cleaning was consistent and effective. Savings were roughly
$800 a year in water and sewer costs and $3,000 in one-time
SAC savings. Energy savings were not estimated.
Repairs
Pan Washer. While trying to resolve a discrepancy between
the manufacturer’s specified water use and the actual
volume measured on one of two pan washers in the plant, the
intern discovered a bent, leaking rinse header. Replacing
the header reduced water use by 1.5 gpm (2,100 gpd). This
saved $8,800 in one-time SAC fees and $2,200 in water and
sewer fees. Six months later cleaning quality in the other
pan washer declined. Based on the intern’s previous discovery,
maintenance quickly traced the problem to a damaged rinse
header and fixed it.
Faucet Leak. Repairing a dripping
faucet reduced water use by 100 gpd, saving $400 in SAC fees
and $150 in annual water and sewer charges.
Boiler Purge Cooling. In an attempt
to comply with a sewer discharge rule that prohibits discharge
of water above 150°F, the small, continuous purge of the
surface water in the boiler was mixed with fresh, cold water.
When measured, the temperature of the purge was 138°F
before cold water was added—already below the discharge
limit. Even if the temperature at the floor drain exceeded
the limit, the purge volume was relatively miniscule and its
heat would dissipate in the overall plant discharge before
entering the city sewer lines. Eliminating this cold water
mixing saved $400 in SAC fees and $150 in annual water and
sewer charges.
Softened Water
Split streaming. Softening facility water is generally
all or nothing—city water is used directly with a hardness
that reflects the water source, or all water is softened.
But with split streaming a portion of the water supply is
softened and then mixed with hard city water in constant proportion
so the water has a consistent, known hardness to meet facility
needs.
In order to decrease variability in product
quality, General Mills set a corporate water hardness specification
at 100 to 300 parts per million (ppm) (5.8-17.5 grains hardness).
Split streaming to achieve a target hardness of 150 ppm will
decrease the frequency of softener regeneration by nearly
40 percent, reducing water demand by about 2,500 gpd, and
saving $3,000 a year in water and sewer cost, and possibly
$12,000 in SAC. Installation is expected to cost about $6,000.
The facility's maintenance staff expect
split streaming to decrease plumbing maintenance costs. Controlling
the hardness of the water will create a balance between pipe
corrosion from water that is too soft and scale buildup from
water that is too hard. The Chanhassen plant plans to install
split streaming controls when it is completely shut down,
allowing for the switch over.
Softener regenerating. Regenerating
the softener resin consumed about five percent of the plant's
process and domestic water. The intern identified four steps
in the regenerating process that could be adjusted depending
on facility requirements. At the General Mills plant, the
final fast rinse intended to pack to the resin bed used 15
percent of regeneration water and appeared to be a candidate
for reduction. Split streaming cut the volume of softened
water, reducing the need to consider this option. Companies
that use large volumes of softened water, 100,000 gpd or larger,
may want to investigate ways to optimize the softener's regeneration
cycle.
Application to Other
Companies
Crucial to the success of this MnTAP intern project was identifying,
quantifying and understanding the individual uses of water
in the plant and critically evaluating the volumes used and
procedures to see if they matched the production, quality
and safety requirements.
Additional Reduction:
VRTX Cooling Tower Water Conditioners
The Chanhassen General Mills plant installed a VRTX water
conditioner on a trial basis in July 2000 on a cooling tower
with 1,270 tons of cooling capacity, as an alternative to
chemical water treatment. A second VRTX unit was installed
on a 1,550 ton cooling tower in August 2001.
The installed cost of both units was about
$130,000. No chemical additions have been made to the two
cooling towers since their VRTX units were installed. Blowndown
to control the buildup of dissolved solids decreased from
about 30 percent of the makeup water volume to about three
percent.
De-mister plates have been freer of scale and microbial fouling,
resulting in lower electrical and maintenance costs. Total
annual savings were estimated at more than $108,000 a year
plus a one time SAC savings of about $35,000. Based on the
experience at the Chanhassen plant, 19 additional VRTX units
were installed at General Mills production plants around the
country as of September 2002.
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 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.
This project was conducted
in 2001 by MnTAP intern, Nancy Mahagnoul a chemical engineering
junior at the University of Minnesota.
* SAC unit = 274 gallons of sewered
water per day.
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