limestone contactors- steady state design relationships
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This paper presents a steady-state model for the design of limestone contactors. The model relates key design parameters like the depth of limestone required, influent and effluent water chemistry, limestone properties, and operating conditions. As acidic water passes through a packed bed of crushed limestone, calcium carbonate dissolves, increasing the pH, calcium concentration, and alkalinity of the water. The rate of limestone dissolution depends on the transport of calcium ions away from the limestone surface. When the pH at the surface drops below 9.5, the dissolution rate is controlled solely by ion transport away from the interface.
limestone contactors- steady state design relationships
- 1. Journal of Environmental Engineering <Previous Article Volume 117, Issue 3 (May 1991) Next Article > Letterman, R., Hadad, M., and Driscoll, C. (1991). Limestone Contactors: SteadyState Design Relationships. J. Environ. Eng.,117(3), 339358. TECHNICAL PAPERS Limestone Contactors: SteadyState Design Relationships Article History Published: 01 May 1991 Publication Data ISSN (print): 0733-9372 ISSN (online): 1943-7870 Publisher: American Society of Civil Engineers Raymond D. Letterman, Member, ASCE1 ; Marwan Hadad2 ; and Charles T. Driscoll3 1 Prof., Dept. of Civ. and Envir. Engrg., Syracuse Univ., Syracuse, NY 13244 2 Prof., Dept. of Civ. Engrg., AnNajah Univ., Nablus, West Bank, Israel 3 Prof., Dept. of Civ. and Envir. Engrg., Syracuse Univ., Syracuse, NY Abstract: Limestone contactors can mitigate corrosion in small watersupply systems that use dilute, acidic water. As water is transported through a packed bed of crushed limestone, CaCO3dissolves and the pH, calciumion concentration, and alkalinity increase. Operation of a contactor can be effectively modeled by considering the rate of dissolution and interfacial transport of calcium ions. The steadystate model developed and tested in this study relates the depth of limestone required in the contactor to the desired effluent water chemistry, influent water chemistry, limestoneparticle size and shape, bed porosity, water temperature, and superficial velocity. The magnitude of the rate constant that describes the release of calcium ions from the calcite surface varies with the pH at the particle surface. When this pH is less than about 9.5, the rate constant for the surface reaction becomes large, and the rate of dissolution tends to be controlled solely by the transport of calcium ions away from the interface.