While power plants in the U.S. require trillions of gallons of water each year, various substances in significantly more precise measurements are needed to transform the liquid into ultra-pure water for boilers that help generate electricity. These compounds commonly include ferric sulfate, which is a crystalline salt that is soluble in water and used as a coagulant, and sulfuric acid, which is a highly corrosive and toxic mineral acid that is soluble in water at all concentrations. In power plants, ferric sulfate helps remove solid particulates from water, and sulfuric acid is used to control the pH, or alkalinity, of the water used in boilers.
Ensuring that proper doses and flow rates of ferric sulfate and sulfuric acid are reliably achieved is important for power plant operators. To ensure the proper concentration and flow of ferric sulfate and sulfuric acid, hydraulically actuated diaphragm metering pumps may be an ideal solution. They can help guarantee that water used in power generation meets the high levels of purity required.
The purification of water needed for power generation occurs through a number of specific operational stages. The first involves the water's passage through a clarifier, where any large, solid impurities are removed. Next, the water travels through a filter, where any dissolved solids—not visible to the naked eye—are removed. These initial pretreatment stages are critical because, from there, the water moves through a demineralizer that cannot handle water containing solids
When water is demineralized, most of the positive and negative ions are removed, creating, by definition, an ion-free solution. This is another critical stage in the power generation process because only demineralized water can be heated in the boilers to create the steam that generates power.
Ferric sulfate is used in the clarifying and filtering stages of power generation. Because it is a coagulant, it interacts with solid particles in the water and causes them to clump together, making it easier for the particulates to be removed. The sulfuric acid is used in the demineralization process to balance the water's pH level and achieve the required neutral state before it can be heated. Users of sulfuric acid must also be cognizant of the substance's harmful effects, such as blindness that can result if it is splashed into eyes or possible severe chemical burns if there is contact with skin. As a result, sulfuric acid must be properly and fully contained during its handling, transfer and use.
Though thousands of gallons of water pass through the clarifiers, filters and demineralizers on an hourly basis, the amount of ferric sulfate and sulfuric acid introduced in the process must be precisely controlled. In other words, the amounts must be exact.
For these critical dosing applications, most power plant operations feature skids with chemical-feed pumps that have electronic stroke controllers following a 4-20 milliamp (mA) signal—allowing automatic adjustment of the pump capacity—for feeding the chemicals. The challenge for the power plant operator is to identify and deploy the best pumping technology for the operation, specifically one that can reliably and repeatedly inject the precise amount of ferric sulfate and sulfuric acid without leakage or spillage.
Hydraulically actuated diaphragm metering pumps possess the operational capabilities and reliability to perform these crucial operations in a power plant. For instance, metering pumps can handle these applications because they can be dialed in to meet specific flow and dosage parameters, which are the lifeblood of a power plant's water purification process.
Some metering pump designs also offer specialized stroke-adjustment capabilities that can allow better valve performance than competitive variable-linkage designs. Designs may also give the valve checks extra time to seat since they are idle during the bypass portion of the suction and discharge strokes. Operators can also find their desired flow rates in some of these pumps using a micrometer dial that can be calibrated to 1 percent increments. Some models have repeatable accuracy of +/- 1 percent of full scale over the range of 10 to 100 percent of capacity.