Scale Control in Sea Water Distillation Equipment - Contact Stabilization

Langelier, W. F.; Caldwell, Donald H.; Lawrence, W. B.; Spaulding, Charles H.

doi:10.1021/ie50481a034

Cited by 59 publications

(31 citation statements)

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“…Langelier in 1950 [24] proposed that the first step in the formation of alkaline scale is the bimolecular thermal decomposition of hydrogen carbonate ion to produce carbonate ion (Re. 23.5).…”

Section: Langelier Mechanismmentioning

confidence: 99%

“…Temperature and the amount of carbon dioxide present are the most important factors controlling the position of the equilibria discussed above, and in practice, Mg(OH) 2 rapidly becomes important above 80 C and with increasing carbon dioxide outgassing, while most scale-retarding additives have been more effective at lower temperatures [24]. It is probable that the mechanism of alkaline scale involves competitive equilibria between the unimolecular and bimolecular decomposition of hydrogen carbonate.…”

Section: Dooly and Glater Mechanismmentioning

confidence: 99%

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Thermal Desalination

Fellows

Al-Hamzah²

2015

Mineral Scales and Deposits

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Section: Langelier Mechanismmentioning

confidence: 99%

Section: Dooly and Glater Mechanismmentioning

confidence: 99%

Thermal Desalination

Fellows

Al-Hamzah²

2015

Mineral Scales and Deposits

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“…Langelier (8) has given a limited amount of data on tbe bemihydrate (CaS04.1/2 H 2 0 ) in sea water, but little is known about the solubilities of the various forms of calcium sulfate in sea water and sea water concentrates. Langelier (8) has given a limited amount of data on tbe bemihydrate (CaS04.1/2 H 2 0 ) in sea water, but little is known about the solubilities of the various forms of calcium sulfate in sea water and sea water concentrates.…”

Section: Existing Datamentioning

confidence: 99%

“…The volumetric behavior of methane has been reported in several studies (2, 3, 6,8,9). Matthews and Hurd (8) and Canjar (2) have evaluated the thermodynamic properties of methane from pressure, volume, temperature data.…”

Section: Vapormentioning

confidence: 99%

Solubility of gypsum in sea water and sea water concentrates at temperatures from ambient to 65.degree.

Shaffer¹

1967

J. Chem. Eng. Data

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When strong brines derived from decarbonated sea water ore evaporated at temperatures from 35' to 6O0C., gypsum, CoS04.2Hn0, forms in the bulk of the liquid. In sea water of normal concentration, the solubility product of this substance is nearly independent of temperature; in the interval 20' to 60' C., the average value is 1.57 x (mole)'/( kg. solvent)'. In strong brines, six times normal concentration, the solubility product is much greater; it increases from 3.58 X (mole)*/(kg. solvent)' at 20'C. to 4.41 X (mole)'/(kg. solvent)' at 6OOC. THE FURTHER CONCENTRATION of the brines discharged from conventional evaporator cycles has been studied as part of a continuing program to lower the cost of desalinated water. Tests conducted in 1961 showed that low temperature evaporation would permit the concentration of sea water from a total dissolved solids of 31,000 p.p.m. to over 300,000 p.p.m. without scale formation on the evaporator heat transfer surfaces. These findings have been reported by Fisher and Gilbert ( 3 ) , who also described the triple-effect superconcentrator that was used for further engineering evaluation of the concentration process.The triple-effect flash evaporator was designed to operate using either sea water or the blowdown from a conventional evaporator as feed. When the evaporator was operated under conditions such that the minimum concentration of the brine circulating in the system was never less than five times sea water, and the maximum temperature was below 65"C., a nonfouling precipitate formed in the brine. This type of operation is achieved through the use of a feed and bleed system in each effect.The precipitate appeared to be a form of calcium sulfate, and the author thought that the ability to prepare this salt reproducibly would be useful in terms of scale control cycles and by-product recovery schemes. Therefore, the nature of this precipitate has been determined, and the conditions under which it formed have been investigated. EXISTING DATABecause of the technological importance of calcium sulfate, a considerable number of papers on this substance have appeared. To put our program in perspective, it is useful to mention briefly some of the more important reviews and sources of data. Posnjak reviewed the material published prior to 1938 (10) and, in 1941, Kelly, Southard, and Anderson (7) published a comprehensive review dealing with gypsum (CaS04. 2H20) and its dehydration products..By way of orientation, we have prepared Figure 1, which summarizes the relationships among the various forms of calcium sulfate. Only three-gypsum (CaS04. 2H20), calcium sulfate hemihydrate (a-hemihydrate) , and anhydrite (CaS04)-can coexist with aqueous systems. The equilibrium temperatures shown for the interconversions between these phases are based on thermodynamic analyses-that is, on the crossing points of the solubility or vapor pressure curves of the various solids; they do not necessarily imply that the transition will occur at the stated temperature. These thermodynamic transition temperatu...

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“…Acid will neutralize the alkalinity and by pH control prevent the alkaline scales from forming (2,3,7,8). Contact stabilization has been used to minimize alkaline scale formation (4,6).…”

Section: Scale Formationmentioning

confidence: 99%

Minimizing Scale Formation in Saline Water Evaporators

McIlhenny

1963

Advances in Chemistry

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Temperatures and concentrations of saline water evaporators are now limited by the potential calcium sulfate scale. Partial ion exchange softening has been demonstrated to be effective in minimizing scale formation. Sea water was softened in a novel fluidized bed, and the ion exchange resin regenerated by the concentrated evaporator blowdown brine. No additional regenerant was required. The rate of scaling during a 1000-hour pilot plant test on softened sea water was less than one thirteenth that found when raw sea water was fed. The ion exchange equilibria in the Ca+ 2 -Mg+ 2 -Na+ system are presented and a method of calculation for the ternary system is indicated.T he formation of scale has always been a problem in the production of fresh water from sea water. As water is removed, the dissolved salts concentrate in the brine until the limit of solubility is reached for some compounds. These precipitate and form scale, especially on any heat transfer surfaces, rapidly causing a loss in thermal efficiency, and if they are not removed, eventually result in deterioration of the equipment.No entirely satisfactory method has been proved for the control of all scales. CaC03 and Mg(OH)2 may be controlled by addition of acid, or by a sludge recycle. CaS04 scale limits the design of virtually all sea water conversion equipment as well as equipment designed for many other saline or brackish waters. The only proved method has been to halt the concentration before CaS04 becomes insoluble.When magnesium and calcium are removed from sea water, a softer sea water is produced. When used as a feed to a sea water evaporator in place of ordinary raw sea water, this can be evaporated at higher temperatures to greater concentrations. Evaporator thermal efficiency and on-stream time can be increased and evaporation capital can be reduced.The incoming raw sea water can be softened by a cation resin, and the concentrated evaporator blowdown liquor can be used as the sole regenerant for the ion exchange resin. No additional regenerant is ordinarily required. 40Downloaded by UNIV OF IOWA on June 22, 2016 |

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Scale Control in Sea Water Distillation Equipment - Contact Stabilization

Cited by 59 publications

References 1 publication

Thermal Desalination

Thermal Desalination

Solubility of gypsum in sea water and sea water concentrates at temperatures from ambient to 65.degree.

Minimizing Scale Formation in Saline Water Evaporators

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