Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Maintaining environment nondestructive to metal
Reexamination Certificate
2000-09-15
2002-04-09
Warden, Sr., Robert J. (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Maintaining environment nondestructive to metal
C422S014000, C422S028000, C422S030000, C149S046000, C149S060000
Reexamination Certificate
active
06368552
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a water treating agent which has a high safety and is to be used for preventing corrosion and scale formation in the make-up water supply system and steam generation system and for preventing corrosion in the steam condensate system in various plants and in steam generating apparatuses, such as boilers and steam generators. The invention also relates to a water treating method using such water treating agent.
BACKGROUND OF THE INVENTION
In apparatuses and plants where steam is generated, such as boilers and steam generators (in the following, referred to sometimes as steam generating units), occurrence of corrosion in the steam condensate system where steam and the condensate contact with metal surfaces of the condensate system may often be seen, since oxygen and carbon dioxide contained in the feed water and carbon dioxide formed by thermal decomposition of carbonates and bicarbonates included in the feed water are transferred to the steam system. In boiler water internal treatment in recent years, cases not employing any deoxidizing treatment come to be found frequently, in which almost all the dissolved oxygen in the feed water is transferred to the steam condensate system and the corrosion in the steam condensate system becomes more facilitated. As a result, there occurs possibilities of increase in the energy loss due to possible steam leakage and of increase in the cost and time for maintenance in the pipe lines, heat exchangers and so on.
For preventing such corrosion problems, a countermeasure has been employed, in which a neutralizing amine having functions of corrosion prevention and volatility or a long chain aliphatic amine is introduced into the feed water or into the steam condensate line. In particular, an intense request becomes posed on the innoxiousness of steam in recent years and, therefore, a special regard has to be paid on a high safety of the chemicals to be employed. Thus, cyclohexylamine, diethylethanolamine and morpholine for the neutralizing amine and octadecylamine for the long chain aliphatic amine have found wide use as additives to be incorporated in corrosion prevention in boilers, which have been accepted in the FDA standard in the USA and in the FDBCS standard in Canada. The neutralizing amine functions to prevent corrosion by neutralizing carbon dioxide in the steam condensate system, whereas the long chain aliphatic amine reveals its corrosion preventive function by forming a water-repellent anticorrosive film on the internal surface of steam condensate lines. Also, there is a technique of using a composite anticorrosive agent exhibiting both of these functions, in which a neutralizing amine and film-forming amine are incorporated in a single liquid medium.
However, in the case of an internal treatment of boiler water without deoxydizing treatment and with the corresponding presence of a large amount of dissolved oxygen in the steam condensate lines transferred from the boiler, any sufficient corrosion preventive effect is not attained by neutralizing the dissolved carbon dioxide with a neutralizing amine, since the corrosion in the steam condensate line proceeds with a rate-determining step by oxygen migration. For achieving a sufficient corrosion preventive effect using only a neutralizing amine, it is necessary to employ an amount of a neutralizing amine as to reach a pH of 9 or higher. However, the least tolerable concentration of neutralizing amine in steam is prescribed by the FDA standard in the USA and this prescription is applied also in Japan. In the case of using a raw water or a softened water as the feed water, carbon dioxide formed by thermal decomposition of a carbonate and bicarbonate in the feed water is brought into the steam and requires so much of the neutralizing amine to be neutralized that the amount permitted by the FDA standard may be insufficient to reach a high enough pH value, whereby a sufficient corrosion preventive effect is not attained. When a neutralizing amine is used in an amount greater than that prescribed by the FDA standard, a high concentration of carbonate salt of the amine will be formed in the steam condensate system, which may cause a problem of clogging of dead-stop lines, such as a pressure gauge line and drain trap line, by being accumulated therein at high concentration.
When a long chain aliphatic amine is used, this will be adsorbed on the internal surfaces of the steam condensate lines to form a protective film to effect corrosion prevention. Here, a considerable dilatoriness has to be endured for sufficient building-up of the protective film on peripheral or terminal parts of the condensate lines. In particular, in a plant installing a steam condensate system having greater internal surface areas of the lines or operating with smaller amounts of steam to be generated, some three months or more may occasionally be required for establishing a sufficient protective anticorrosive film, permitting some corrosion to proceed before the anticorrosive film is established. In the case of an internal boiler water treatment without deoxidation and, thus, having a large amount of dissolved oxygen brought into the condensate system, more retardation may be caused due to the occurrence of considerable corrosion in the condensate lines, before establishment of such an anticorrosive film, bringing about a possible problem of an insufficient corrosion preventive effect even after the establishment of the anticorrosive film due to incomplete suppression of oxygen cell corrosion. Moreover, a long chain aliphatic amine is present at normal temperatures as a solid matter and is difficultly soluble in water and, therefore, it is brought into practical use in the form of an emulsion. While such an emulsion itself is, in general, considerably stable, separation and deposition of the emulsion may sometimes occur after a prolonged standstill, especially, when the emulsion is diluted at a high dilution ratio, which may occasionally cause deposition and aggregation of the amine after introduction of the emulsion into the feed line, resulting in a possible clogging of a strainer or the like in the feed line. Even in a condensate line in which steam is completely condensed into the liquid phase, deposition of the long chain aliphatic amine may occur and similar problems of clogging of the line due to aggregate of the amine may be brought about.
On the other hand, as a water treating agent of high safety for boiler feed water, one in which an aldonic acid of a heptose or hexose, a salt thereof or a deltalactone is incorporated together with an aliphatic carboxylic acid is proposed (See Japanese Patent Kokai Hei 10-130874). Here, it is not able to attain sufficient corrosion preventive effect by a sole use of the aldonic acid of a heptose or hexose, its salt or the deltalactone, in addition to a lower tendency of being transferred to the steam phase, so that it was not able to be used as an anticorrosive agent for steam condensate lines.
An object of the present invention is to provide a water treating agent which is highly safe and can be used as an alternative for the neutralizing amine and long chain aliphatic amine of the prior art and which is capable of being brought into the steam phase and into the condensate due to its high volatility and exhibits a high corrosion preventive effect even for a feed water containing carbonates and biocarbonates, without causing accumulation in the system to be treated, and to provide a water treating method using this water treating agent.
Another object of the present invention is to provide a water treating agent which can prevent the occurrence of corrosion and scale formation in the feed water system and the steam generating system as well as prevent the occurrence of corrosion in the steam condensate system, wherein the water treating agent is highly safe and can be brought into the steam phase and into the steam condensate due to its high volatility and which exhibits a high corrosion preventive effect, even for a feed
Shimura Yukimasa
Taya Shiro
Flynn ,Thiel, Boutell & Tanis, P.C.
Kurita Water Industries Ltd.
Soubra Imad
Warden, Sr. Robert J.
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