Chemistry: analytical and immunological testing – Metal or metal containing – Li – na – k – rb – cs – fr – be – mg – ca – sr – ba – ra
Reexamination Certificate
2002-07-31
2004-09-14
Snay, Jeffrey R. (Department: 1743)
Chemistry: analytical and immunological testing
Metal or metal containing
Li, na, k, rb, cs, fr, be, mg, ca, sr, ba, ra
C436S172000
Reexamination Certificate
active
06790666
ABSTRACT:
FIELD OF INVENTION
This invention is in the field of industrial water systems. Specifically, this invention is in the field of monitoring and controlling soluble hardness in water in industrial water systems. This invention also is in the field of determining whether Total Hardness is due to the presence of calcium or magnesium or some combination of calcium and magnesium.
BACKGROUND OF THE INVENTION
“Total Hardness” is a term that refers to the amount of calcium and magnesium cations present in water and is usually expressed as ppm CaCO
3
equivalents. “Soluble hardness” refers to soluble Ca
+2
and Mg
+2
cations present in water. “Particulate hardness” or “colloidal hardness” refers to hardness that is insoluble (or “non-soluble”). Insoluble hardness can usually be converted to soluble hardness by treating the water with acid and heat. Soluble hardness concentrations in the water of most industrial water systems can range from less than about 1 ppm to about several thousand ppm.
The presence of soluble hardness in industrial waters typically leads to precipitation of those cations as scale on heat transfer surfaces of industrial process equipment. The presence of scale is detrimental to many individual units of industrial process equipment as well as to the industrial water system itself. Systems affected negatively by scale deposits include boilers, multi-stage evaporators, cooling water heat exchangers, cooling towers, hot water heaters, continuous casters, heat recovery steam generators, pipe surfaces and any other heat transfer surfaces of equipment present in industrial water systems.
Scale deposits are undesirable because deposited scale can cause impedance of flow, loss of cooling and reduced heat transfer capability, and “under deposit” corrosion problems. Under deposit corrosion problems are caused when chemical species which lead to corrosion (such as hydroxyl ions) concentrate to a point significantly higher than that found in the boiler bulk water. These high concentrations are more corrosive and can lead to tube failure.
Scale deposits are also undesirable because they can provide an environment that allows microbiological attachment and growth leading to microbiological induced corrosion problems. These undesirable situations can ultimately result in equipment failure such as boiler tube ruptures and heat exchanger failures, and unscheduled outages where it is not possible to operate the equipment. All of these undesirable situations can lead to a loss of capital equipment with resultant loss of production time and money.
The process by which soluble species precipitate from the water in a boiler onto a surface is usually referred to as “scaling”. The process by which insoluble species suspended in water are ‘left behind’ and adhere to surfaces is usually referred to as “deposition” and the insoluble species that adhere to surfaces are typically referred to as a “deposit”. In a boiler, this is of most concern at the areas where a wet/dry interface is present. This wet/dry interface is where the steam bubble is initiated, grows, and then detaches from the surface. Insoluble matter can collect and adhere at the interface of the bubble to the surface as it grows. With detachment of the steam bubble, the insoluble matter may adhere to the surface forming a deposit. These deposits are unwanted as their presence disrupts the heat transfer from the surface to the water.
It is common to monitor the soluble hardness in the water of an industrial water system and to treat industrial water systems such that soluble hardness does not scale and insoluble hardness does not deposit. The treatment products used to treat water are many and varied. “Scale inhibitors” are typically defined as chemical treatments that are added to water which reduce or eliminate the scaling process. “Dispersants” are typically defined as chemical treatments that are added to water to reduce or eliminate the accumulation of insoluble species as deposits on surfaces. When the insoluble matter is dispersed, it typically is not able to deposit. If the insoluble matter remains dispersed then it can be “carried away” in the natural flow patterns of the industrial water system.
Treatment products for industrial waters to remove, inhibit or control the detrimental effects of scale and deposits caused by the presence of soluble and insoluble hardness present in said waters are well known. Chemical treatment methods useful to treat water for undesirable hardness, based on soluble hardness, include such methods as coagulation, flocculation, precipitation, chelation, sequestration, complexation, dispersion and crystal modification. Treatment products for use in these chemical treatment methods include
a) anionic polymer that can effectively complex with magnesium; these anionic polymers include polyacrylates, polymethacrylates and acrylate styrene sulfonate copolymers;
b) chelants such as ethylenediaminetetraacetic acid, nitrilotriacetic acid, 1-hydroxyethylidene-1,1-diphosphonic acid and hexamethylenediaminetetra methylene phosphonic acid;
c) inorganic phosphates and organic phosphates such as hexametaphosphate, tripolyphosphate and ortho phosphate;
d) polyphosphonates;
e) natural and synthetic cationic polymers such as lignins, lignosulfonates, tannins, poly peptides, polyamines, quaternary amines, celluloses, starches, polymaleic anhydrides and polyvinyl sulfonates;
f) inorganic carbonates and organic carbonates;
g) surfactants; and
h) mixtures thereof, and
i) known salts thereof.
There are industry standards for hardness in the water of industrial water systems. The American Society of Mechanical Engineers (ASME) has published a consensus on operating practices for the control of boiler feedwater and boiler water chemistry in modern industrial boilers. The ASME along with other organizations such as the Electric Power Research Institute (“EPRI”), British Boiler Manufacturers, Japanese Boiler Manufactures, German (VGB) boiler feedwater and boiler water guidelines for boiler systems, specify the acceptable maximum amount of hardness in feedwater to minimize the potential for hardness scale deposit problems that can lead to boiler failures.
The amount of soluble hardness present in industrial waters can change rapidly. If this change in soluble hardness goes unnoticed and the amount of treatment product for soluble hardness is unchanged in the water, the change in soluble hardness will result in under dosing or overdosing of the treatment products that are used to control, inhibit or eliminate the detrimental scaling of soluble hardness and depositing of insoluble hardness.
There are a number of known methods to measure and monitor soluble hardness in industrial waters. Some of these known methods include using sophisticated, time-consuming and expensive instrumentation such as Atomic Absorption Spectrophotometers and Inductively Coupled Argon Plasma Emission Spectrophotometers. Colorimetric methods include visual as well as instrumentation methods. Colorimetric methods that do not require expensive instrumentation include titration techniques that use indicator dyes sensitive to hardness which change color to the naked eye in the presence (or with some dyes, in the absence) of hardness. The majority of these known methods are subject to interferences, are known to be time consuming and the visual calorimetric methods can be very subjective based on subtle-to-the-eye distinctions in color changes.
It would be desirable to have a relatively inexpensive, reliable, non-colorimetric method for determining the level of soluble hardness in the water of an industrial water system. It would also be desirable to have a method to determine what part of the soluble hardness is attributed to calcium and what part of the soluble hardness is attributed to magnesium.
SUMMARY OF THE INVENTION
The first aspect of the instant claimed invention is a method of determining the amount of soluble hardness in the water of an industrial water system comprising the steps of:
1) providing an industrial water system;
2) pro
Dang Xiaojun
Grattan David A.
Link Linda M.
Breininger Thomas M.
Brumm Margaret
Nalco Company
Snay Jeffrey R.
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