AmeriChem Systems Inc. (ASI) is a custom process equipment fabricator for select multinational corporations and engineering, procurement and construction firms around the globe. Based in Aurora, Illinois, ASI specializes in developing customized chemical feed systems, boiler feed water systems and cooling tower water treatment packages for some of the largest nuclear power plants and oil and gas refineries around the globe.
The chemical feed systems that ASI builds include the tanks, pumps, piping infrastructure, valves, flow meters and control systems needed to run large-scale industrial water treatment applications. An examination of chemical feed water treatment systems that ASI has delivered to various nuclear power plants in the U.S., as well as one of the largest oil and gas refineries in the Middle East, highlights the factors behind picking the right pumping technology for these sites.
Nuclear Power Plants
ASI’s water treatment applications in nuclear power plants throughout the U.S. feature rotary gear pumps that provide the chemical-dosing capabilities needed for both circulating water systems and service water systems.
The purpose of a circulating water system is to provide cooling water for the power plant’s main condenser using a large heat exchanger that removes heat from the condensing steam exiting the plant’s main turbine. Nuclear power plants typically pump more than 500,000 gallons of water per minute (gpm) through the heat exchangers in circulating water systems, which is why most power plants are near an abundant water source, such as a river, lake or ocean.
Nuclear power plants also have service water systems that provide cooling to smaller, but critical, systems such as air compressors, lube oil systems and systems related to the safe shutdown of the reactor. Once water has entered the circulating system, it must cleaned with chemicals such as sulfuric acid and sodium hypochlorite solutions. These solutions are metered through rotary gear pumps at high dosing rates and low pressures.
The chemical feed process manages micro-bio organisms, as it prevents scaling, corrosion and foulants from hindering the condenser’s efficiency. Clean condenser heat transfer surfaces directly impact a plant’s operating efficiency. Failing to prevent micro-bio fouling can cause expensive plant derates and unplanned outages.
After it is used, the cooling water is discharged back into the environment. Before being discharged, the water is often treated with a dechlorination chemical, such as sodium metabisulfite. When high dosing rates are required, the dechlorination system is another application for rotary gear pumps.
The power industry uses traditional demineralizer systems to purify water for the steam generating loop. These systems are designed to remove contaminants that can negatively affect the steam generator’s performance. Large ion exchange resin beds remove contaminants by substituting H+ (hydron) ions and OH- (hydroxide) ions for dissolved salts in the source water. The resultant water is pure and essentially free of dissolved salts. When exhausted, the resins are regenerated by using sulfuric acid and sodium hydroxide. This regeneration requires large dosing rates at relatively low pressures.
For many years, hydraulically balanced diaphragm metering pumps were frequently used for these applications. Today, some power plants are replacing larger diaphragm pumps with smaller rotary gear pumps.
Picking the Pump
The requirements of exceedingly high-flow volumes and uniform, pulse-free dosing under low pressures prompted ASI’s distributor and authorized service center—Addison, Illinois-based Enpro (Engineered Products)—to recommend a specific type of rotary gear pump.
Enpro’s John Nelson identified five primary benefits to using a rotary gear pump for these types of water treatment applications: