PRACTICAL, AVAILABLE TECHNOLOGY
Preventing scale in lime slurry systems Hercules’ product solves the scale-forming problem commonly encountered in water and wastewater treatment Lime, the environment’s large tonnage chemical, is a basic chemical that has been used for centuries. This year, nearly two million tons will be used for wastewater treatment, water softening, sludge stabilization and stack-gas scrubbing. By 1985, the use of lime in environmental cleanup could triple. Environmental concerns account for 30-40% of all the lime commercially used. The main environmental uses are water softening and wastewater treatment. Other smaller uses include stack-gas desulfurization, stabilization of sludge and absorption of fluorine gas effluent. In any area where lime is fed as a slurry, the potential for scaling and scale build up exists. When a lime slurry is fed, the lime (CaO) reacts with the natural alkalinity in the dilution water and calcium carbonate precipitates. This precipitate builds up on pipes, tanks, valves, and pumps. Depending on the severity of the scale up, the equipment may have to be cleaned from once every several months to as frequently as weekly. There are three general approaches to a solution of the scale up but all are time consuming and costly. They are: rodding out the lines cleaning the lines with acid replacing the lines. But scaling no longer need be a problem causing downtime or expensive maintenance. Answer from technology Water Management Chemicals, a Division of Hercules, Inc. (Wilmington, Del.) has a product that prevents the scale from forming initially. Its product, SP-944, interferes with crystal formation and prevents the calcium carbonate from forming a 380
Envlronmental Science & Technology
scale but allows lime to perform its neutralization function at the same time. This product, which has been on the market for six years, has been used for the past four years at the Blue Plains Waste Treatment Facility (Washington, D.C.) (ES&i,October 1974, p 892). Mr. 0. W. Taylor, Engineering Technician in Solids Processing, explains that the product is used in a vacuum filter operation. At Blue Plains the lime is slurried and fed to the sludge line. The sludge then goes into the filter box and is filtered. In this type of operation, where lime is used to aid in vacuum filtration, it is normal for the feed lines, the filter grids, and the drain lines to become plugged with scale. Taylor says, “In the four years that SP-944 has been in use at Blue Plains, none of this cleaning has been required.” Eastern Stainless Steel (Baltimore,
Md.) uses a lime slurry for acid waste neutralization. Here, the lime is made up to a 10% slurry. This slurry is pumped to a waste acid area where it neutralizes the waste acid. Pollution control engineer Tony Bonaccorsi said, “Before Eastern Stainless Steel started using SP-944 several years ago, the lime slurry feed system was cleaned once a week. This cleanup required three workers from 8-16 hours each, or about $30 000 per year on maintenance.” Bonaccorsi explains that the steel company now spends less than $1000 per year on SP-944; the only maintenance now required is a routine yearly cleanup. In any area where lime is fed as a slurry the potential for scale exists. But it no longer needs to be a problem causing downtime or expensive maintenance. SP-944 can keep the lines clean and functioning.
Checking. Hercules’ J i m Haag ( l e f t )discusses use with Taylor at Blue Plains
