Sea water Desalination Chemical Packages
Seawater Reverse Osmosis (SWRO)
Scaling species typically found in seawater evaporators (CaCO3, Mg(OH)2, and CaSO4), all exhibit inverse solubility.
This means they become less soluble at a higher temperatures.
Scaffix SI series, which is a low molecular weight organic co-polymer designed to prevent deposition of hard scale in seawater desalination plants.
It has excellent control of CaCO3 and Mg (OH)2 scale deposition. Scaffix SI series functions as a crystal inhibitor effectively increasing the solubility of dissolved salts, while the temperature increase.
Scaffix SI series should be fed continuously against the feedwater line, upstream of the heat recovery section with the following dosages 2 – 5 ppm in proportion to the makeup flow rate.
MECHANISM OF ACTION
SCAFFIX series polymer inhibits scale buildup on surfaces through at least three mechanisms:
· Solubility enhancement or threshold effect, which reduces precipitation of low solubility inorganic salts.
· Crystal modification, which deforms the growing inorganic salt crystals to give small, irregular, readily fractured crystals that
do not adhere well to surfaces.
· Dispersing activity, which prevents precipitated crystals or other inorganic particles from agglomerating and depositing on
Foaming occurring in the evaporator can lead to a deterioration of the distillate quality. This cause of a solid carryover problem cannot be economically corrected through adjustment of water balance or the installation of additional external treatment equipment. The use of antifoam chemical is mandatory.
The recommended chemical as antifoam is Melasil EO-125, containing block co-polymer like other poly-glycols which weaken the walls of foam bubbles, causing them burst quickly at the water surface. This prevents the formation of high volume stable foam, which can carryover with vapor in the MSF evaporators, leading to increase solids in the distillate.
Melasil EO-125 should be fed continuously against feedwater line, upstream of the heat recovery section with the dosage: 0.1 - 1.0ppm in proportion to the makeup flow rate.
MACROFOULING AGENT / CLAM CONTROL
Vanicide NX-550 is derived from amine chemistry in which field Harvest Chemical has set the industrial standard. The active ingredient is decylisononyldimethylammonium chloride and functions as a highly efficient, low-cost biocide and surfactant.
Laboratory studies have shown Vanicide NX-550 to provide excellent control of such macrofoulants, as Zebra mussels and Asiatic clams. One hundred percent mortality in Asiatic clams was achieved at levels below 5 ppm active. Excellent Zebra mussel control has been demonstrated with a 96 hour LC50 of only 0.7 ppm active and an LT50 (lethal time for 50% mortality) of less than 2 hours at 10 ppm active level.
As a low foaming quat,Vanicide NX-550 eliminates unsightly foam buildup. This can improve system aesthetics and make product spraying feasible in certain applications. Foam heights of less than 1 cm at 15 ppm active are generated in shake tests, and equilibrium foam heights in recirculation tests are only 2 cm.
The ability to control macro-fouling using only short exposure provides a number of environmental, performance, and cost advantages over chlorine and other oxidizers. These include:
· Less chemical released to the environment
· Completely biodegradable
· Safe to handle
· Capital cost on the dosing systems is insignificant compared to chlorine gas dosing systems.
· These non-oxidizers are powerful cationic surfactants in cleaning of bio-slime.
· Product concentrations can be monitored and verified during the entire application.
· Reduced risk of under-deposit corrosion and pitting attack on yellow metal metallurgy since
Vanicide NX-550 does not induce corrosion.
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