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It takes much more than paper and ink to efficiently print
paper currency. Banknote printing plants use large quantities
of caustic solutions to clean the printing presses. These
chemicals are expensive to purchase, and disposing of the
used, inky solution is difficult and costly.
The Beijing Banknote Printing Plant, also known as the Beijing
Mint, is a branch of China’s Banknote Printing and Minting
Corp. (CBPMC). It has been an innovative leader in China in
addressing business expenses and the environmental impact
resulting from the use of caustic cleaning solutions. With
a state-of-the-art membrane filtration system employing membranes
from Koch Membrane Systems, the Beijing Mint is now reusing
90% of the caustic cleaning solutions, and dramatically reducing
chemical consumption and waste-disposal expenses.
The Challenge
The success of the Beijing Mint filtration program comes after
a decade of incremental improvements. Prior to the mid-1990s,
each of the CBPMC mints used a conventional chemical treatment
method to dispose of caustic cleaning solution. Unfortunately,
the process required a high quantity of expensive and hazardous
chemicals, such as acids, coagulants, and flocculants. Moreover,
the process produced inconsistent results because ink is very
difficult to settle.
The conventional process began by first neutralizing the
caustic solution with acid, and then adding chemicals and
polymers in a coagulation and flocculation process to settle
the ink from the solution. The settled ink was run through
a filter press and transported from the plant by truck. The
wastewater from the settling tank was then sent to a wastewater
treatment facility inside the plant.
During the mid-1990s, in an effort to improve this expensive
and hazardous process, the plant began recycling caustic cleaning
solution by implementing a hollow-fiber ultrafiltration (UF)
membrane system. The new membrane filtration system recovered
about 40% to 50% of the caustic solution, thereby cutting
in half the purchase cost of caustic. Additionally, the system
decreased the load on the conventional filtration system,
allowing for a 50% reduction in the consumption of acids,
coagulants, and flocculants.
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| SelRO tubular membranes, capable
of operating in a pH range of 0 to 14.0, are installed
in the caustic recovery system shown here. |
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| Two trains containing a total
of 84 SelRO model MPT-U20 tubular membranes having been
in operation at the Beijing mint since last August. |
Although the filtration system was a considerable improvement
over what CBPMC had before, the membranes were not able to
tolerate the high pH of the caustic solution (pH 13.5–14.0),
and the average life of the membranes proved to be less than
one year.
“The initial membrane filtration system recovered some
of the caustic solution and reduced the load on our conventional
treatment system, but we wanted a more cost-efficient and
environmentally friendly solution,” says Zhao Yanhong,
chief of the technical center at the Beijing Mint.
In 2003, executives at the plant invited several competing
membrane vendors to participate in a side-by-side, 6-month
pilot study to evaluate and compare pH tolerance and membrane
longevity. Analysis from the study found that one membrane
far out-performed all of the other participants.
The SelRO tubular UF (model MPT-U20) from Koch Membrane Systems
Inc. (KMS) recovered 90% of the caustic solution and produced
one-fifth the amount of waste compared to Beijing Mint’s
existing membranes, which recovered just 50% of the caustic
solution and produced five times more waste.
Additionally, the performance of the KMS SelRO membranes
was stable throughout the pilot study, whereas the inky waste
stream caused a significant reduction in flux with the existing
hollow fiber membranes. “High tangential flow across
the SelRO tubular membrane surface helps limit membrane fouling,
reduces cleaning requirements, and maintains high performance,”
says Imran Jaferey, global business manager for industrial
water and wastewater at Koch Membrane Systems.
Other products that participated in the side-by-side study
were more expensive, required higher energy consumption, or
demonstrated inferior performance when compared to the SelRO
product.
Almost immediately after the study results were released,
executives at the Beijing Mint selected the system with KMS
SelRO to replace the plant’s existing filtration system.
“Not only did the SelRO membranes prove to perform most
consistently, they were also the only membranes capable of
withstanding the pH extremes,” says Yanhong.
The new system, using KMS SelRO membranes, was commissioned
in August 2004. Built by local contractor Nanjing Kaimi Technology
Co. Ltd in May using 84 12-foot-long KMS tubular modules,
the new system became operational a few months later and went
online at a flow rate of 15 m-3/hr.
The Results
Since the startup of the new SelRO system, the Beijing Mint
plant has increased recovery by 40% and, more importantly,
has been able to entirely eliminate the conventional chemical
treatment process, including the expensive and messy chemicals
that it required.
The new system allows the permeate that passes through the
SelRO membrane to be purified for reuse while the retentate
is concentrated ink that is treated by a filter press and
sold as fuel.
Executives at the Beijing Mint were particularly impressed
with the SelRO membranes’ unique ability to increase
the efficiency of their operations while still protecting
the environment.
“Now our operators rarely have to supplement the recovered
solution, and the cost of caustic cleaning chemicals is no
longer a significant expense for our plant,” says Yanhong.
Another benefit was the reduced maintenance requirements and
energy consumption. “The new system is much easier to
maintain and clean and it consumes only half of the energy
used by any other tubular membrane system we have tested.”
The general manager of Nanjing Kaimi Technology Co., Wang
Hualin, who has had experience working with hollow-fiber and
ceramic membrane for many years, is also pleased with the
results. Wang has said that the reason he selected KMS SelRO
product for the pilot was that he had come to realize that
SelRO tubular membranes are much more stable, easier to maintain,
last longer, and provide more energy savings than other products.
Since the implementation of tubular membranes at the Beijing
Mint, the Shanghai Mint is close to installing SelRO membranes
in its new plant, and the three other CBPMC mints are considering
KMS membranes as well.
RUMING PANG is with Koch Membrane Systems
in Shanghai, China.
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- November/December 2005
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