March 2008
A PPI Special Report
Modern technology and revered tradition co-exist in the small city of Bhadrachalam (population 45,000) in India's southern state of Andhra Pradesh. The rural community is home to one of the country's most important Hindu pilgrimage shrines, the abode of Lord Rama, situated at the bank of the holy Godavari River.
Not far away, the Paperboards & Specialty Papers Division (PSPD) of ITC Ltd. operates India's largest paperboard mill. The plant produces packaging and graphic paperboard, specialty board (including with polycoated barriers), and paper for the tobacco industry, fine printing, and decoration. The facility has earned a reputation for technological innovation and environmental stewardship. The ISO-14001 certified mill is 98% power self-sufficient through cogeneration, and it recently commissioned India's only elemental chlorine-free pulp mill (PPI, August 2006).
The Bhadrachalam business unit is 100% carbon positive through CO2 sequestration of plant emissions and extensive farm forestry programs. These forestry programs have rejuvenated wastelands and alleviated poverty for tens of thousands of local farming families.
With a capacity of 300,000 tonnes/yr of standard paperboard, ITC Bhadrachalam holds a 30% share of the domestic market, expected to grow to 40% this year. The company's market share in value-added paperboard products is 90%.
A problem with silica
The Bhadrachalam mill generates 250 tonnes/hr of high-pressure (62 bar) steam to satisfy its power and process requirements. Engineers at the plant found that the silica impurities in the boiler water were high, necessitating frequent blowdown operations that consumed large volumes of water and wasted heat energy. Further investigation determined that the source of the problem was colloidal silica in the form of fine mud in the boiler feed water.
"We determined that membrane ultrafiltration (UF) was the best method for solving our problem," says ITC Bhadrachalam general manager, V. Srinivasan. "We visited several operating plants in India where UF has effectively removed the colloidal silica in feed water used for similar boiler applications. In addition, we also found that ultrafiltration will filter the organic matter in the water to protect the ion exchange resins from organic fouling." As a result, in 2004, ITC Bhadrachalam commissioned a UF system employing 44 TARGA-10 hollow fiber membrane cartridges from US-based Koch Membrane Systems, Inc. (KMS), of Wilmington, Mass. The TARGA-10 cartridges are 10.75-inches (273 mm) in diameter and 72-inches (1,829 mm) in length. The ultrafiltration system was designed and constructed by Driplex Water Engineering of New Delhi.
"We analyzed membranes from three vendors and we selected the KMS membranes because our analysis determined that their ultrafiltration membranes were especially effective at handling the colloidal silica in boiler feed water," explains Srinivasan.
The TARGA cartridges are composed of thousands of hollow fibers made from a proprietary polymer, and the pore size is 10,000 Daltons. The TARGA membranes have the advantage of being pH tolerant and chlorine resistant up to 200 ppm at 10.5 pH. The internal diameter of the hollow fibers is 0.035inch (0.9 mm). The membranes operate from the inside to the outside during filtration. The feed water (retentate) flows through the center of the hollow fiber and the filtered water (permeate) passes through the fiber wall to the outside of the membrane fiber. The tangential flow of the retentate continually acts to limit membrane fouling.
Economic and environmental benefits
"The KMS ultrafiltration membranes have successfully addressed our problem," says Srinivasan. "The blowdown from the boiler has been reduced to less than 1%, from the previous level of 3%, and the total silica level in the boiler feed water has dropped from 35 to 15 parts per billion." The improved water quality results in significantly increased heat transfer efficiency and lower fuel consumption, less carbon emission and a more than 66% reduction in the volume of treated boiler water that is wasted during the blowdown process. It has also reduced resin fouling in the demineralization system. Prior to the installation of the UF system, fouling of the cation and anion exchange resin beds continually diminished performance and necessitated monthly cleaning, which resulted in the costly shutdown of the demineralization process and the entire boiler operation.
The installation of the ultrafiltration process upstream of the demineralization system has dramatically reduced resin fouling, which has improved resin performance and completely eliminated the need for resin cleaning and the associated downtime. The reduced fouling should also significantly extend resin life.
"Ultrafiltration of our boiler feed water is a sensible solution, with economic and environmental benefits," believes Srinivasan. "And the membranes have proven durable and easy to clean. We operate the system according to the manufacturer's guidelines, and we expect that membrane life will be as long as eight years. It has been a good investment, and we have plans to work with KMS during our future expansion of the plant."
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