India’s ITC Paperboards has found an alternative solution to frequent blowdown operations to remedy colloidal silica in wastewater
By Samir Chaubal
Modern technology and revered tradition coexist 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 manufacturing plant. The plant produces packaging and graphic paperboards, specialty boards including boards with polycoated barriers, and paper for cigarette tissue, 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.
The Bhadrachalam business unit is 100% carbon positive through CO2 sequestration of plant emissions and extensive farm forestry programs. These forestry programs have rejuvenated area wastelands and alleviated poverty for tens of thousands of local farm families.
With a capacity to produce 300,000 tonnes per year of standard paperboard PSPD-Bhadrachalam holds a 30% domestic market share, growing to 40% by 2007-2008, and a full 90% market share in value-added paperboard products.
The plant generates 250 tonnes per hour of high-pressure steam at 62 bars to satisfy the mill’s 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.
UF Removes Silica
“We determined that membrane ultrafiltration (UF) was the best method for solving our problem,” said Mr. V. Srinivasan, general manager of PSPD-Bhadrachalam. “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, PSPD-Bhadrachalam commissioned a UF system employing 44 TARGA®-10 hollow fiber membrane cartridges from U.S.-based Koch Membrane Systems Inc. (KMS), of Wilmington, Massachussetts. The cartridges are 10.75-inches (273 mm) in diameter and 72-inches (1,829 mm) in length. The system was designed and constructed by Driplex Water Engineering of New Delhi.
“We analyzed membranes from three vendors and selected the KMS membranes because our analysis determined that their ultrafiltration membranes were especially effective at handling the colloidal silica in boiler feed water,” Mr. Srinivasan said.
The TARGA cartridges are composed of thousands of hollow fibers made from a proprietary polymer, and the pore size is 10,000 Daltons. The membranes have the advantage of being pH tolerant and chlorine resistant up to 200 ppm at 10.5 pH. Internal diameter of the hollow fibers is 0.035 inches (0.9 mm). During filtration, feed water (retentate) flows through the center of the hollow fiber and filtered water (permeate) passes through the fiber wall to the outside of the membrane fiber. Tangential flow of the retentate continually acts to limit membrane fouling.
Economic & Environmental Benefits
“The KMS ultrafiltration membranes successfully addressed our problem,” said Mr. Srinivasan. “Blowdown from the boiler has been reduced to less than 1%, from 3%, and the total silica level in the boiler feed water has dropped from 35 to 15 parts per billion.”
