CA2091097A1 - Boiler double buffers - Google Patents
Boiler double buffersInfo
- Publication number
- CA2091097A1 CA2091097A1 CA 2091097 CA2091097A CA2091097A1 CA 2091097 A1 CA2091097 A1 CA 2091097A1 CA 2091097 CA2091097 CA 2091097 CA 2091097 A CA2091097 A CA 2091097A CA 2091097 A1 CA2091097 A1 CA 2091097A1
- Authority
- CA
- Canada
- Prior art keywords
- steam
- diamine
- oxygen containing
- boiler
- steam generating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000000872 buffer Substances 0.000 title description 8
- 230000007797 corrosion Effects 0.000 claims abstract description 16
- 238000005260 corrosion Methods 0.000 claims abstract description 16
- 238000000034 method Methods 0.000 claims abstract description 15
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 14
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 14
- 239000001301 oxygen Substances 0.000 claims abstract description 14
- 150000004985 diamines Chemical class 0.000 claims abstract description 12
- 239000008346 aqueous phase Substances 0.000 claims abstract description 3
- 125000004432 carbon atom Chemical group C* 0.000 claims abstract 3
- 230000002401 inhibitory effect Effects 0.000 claims abstract 2
- KWYHDKDOAIKMQN-UHFFFAOYSA-N N,N,N',N'-tetramethylethylenediamine Chemical compound CN(C)CCN(C)C KWYHDKDOAIKMQN-UHFFFAOYSA-N 0.000 claims description 6
- KVKFRMCSXWQSNT-UHFFFAOYSA-N n,n'-dimethylethane-1,2-diamine Chemical compound CNCCNC KVKFRMCSXWQSNT-UHFFFAOYSA-N 0.000 claims description 6
- 125000000217 alkyl group Chemical group 0.000 claims description 5
- 239000007791 liquid phase Substances 0.000 claims description 5
- JUXXCHAGQCBNTI-UHFFFAOYSA-N 1-n,1-n,2-n,2-n-tetramethylpropane-1,2-diamine Chemical compound CN(C)C(C)CN(C)C JUXXCHAGQCBNTI-UHFFFAOYSA-N 0.000 claims description 3
- 239000012808 vapor phase Substances 0.000 claims 2
- 239000003795 chemical substances by application Substances 0.000 description 25
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 20
- 150000001412 amines Chemical class 0.000 description 19
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 12
- 229910021529 ammonia Inorganic materials 0.000 description 10
- SZVJSHCCFOBDDC-UHFFFAOYSA-N iron(II,III) oxide Inorganic materials O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 10
- 238000012360 testing method Methods 0.000 description 7
- 239000001569 carbon dioxide Substances 0.000 description 6
- 229910002092 carbon dioxide Inorganic materials 0.000 description 6
- 229910052742 iron Inorganic materials 0.000 description 6
- 239000007788 liquid Substances 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000012071 phase Substances 0.000 description 6
- 230000001276 controlling effect Effects 0.000 description 5
- ROSDSFDQCJNGOL-UHFFFAOYSA-N Dimethylamine Chemical compound CNC ROSDSFDQCJNGOL-UHFFFAOYSA-N 0.000 description 4
- QIGBRXMKCJKVMJ-UHFFFAOYSA-N Hydroquinone Chemical compound OC1=CC=C(O)C=C1 QIGBRXMKCJKVMJ-UHFFFAOYSA-N 0.000 description 4
- YNAVUWVOSKDBBP-UHFFFAOYSA-N Morpholine Chemical compound C1COCCN1 YNAVUWVOSKDBBP-UHFFFAOYSA-N 0.000 description 4
- 239000002253 acid Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000006386 neutralization reaction Methods 0.000 description 4
- 238000011160 research Methods 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 3
- 239000000654 additive Substances 0.000 description 3
- 230000004888 barrier function Effects 0.000 description 3
- 230000003139 buffering effect Effects 0.000 description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 3
- 239000000356 contaminant Substances 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 239000010949 copper Substances 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- KFYRJJBUHYILSO-YFKPBYRVSA-N (2s)-2-amino-3-dimethylarsanylsulfanyl-3-methylbutanoic acid Chemical compound C[As](C)SC(C)(C)[C@@H](N)C(O)=O KFYRJJBUHYILSO-YFKPBYRVSA-N 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 2
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 2
- 239000005751 Copper oxide Substances 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 229940123973 Oxygen scavenger Drugs 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 229910000431 copper oxide Inorganic materials 0.000 description 2
- PAFZNILMFXTMIY-UHFFFAOYSA-N cyclohexylamine Chemical compound NC1CCCCC1 PAFZNILMFXTMIY-UHFFFAOYSA-N 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 238000005272 metallurgy Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- -1 octadecylamine Chemical class 0.000 description 2
- 230000001681 protective effect Effects 0.000 description 2
- FAXDZWQIWUSWJH-UHFFFAOYSA-N 3-methoxypropan-1-amine Chemical compound COCCCN FAXDZWQIWUSWJH-UHFFFAOYSA-N 0.000 description 1
- CMGDVUCDZOBDNL-UHFFFAOYSA-N 4-methyl-2h-benzotriazole Chemical compound CC1=CC=CC2=NNN=C12 CMGDVUCDZOBDNL-UHFFFAOYSA-N 0.000 description 1
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 description 1
- REYJJPSVUYRZGE-UHFFFAOYSA-N Octadecylamine Chemical compound CCCCCCCCCCCCCCCCCCN REYJJPSVUYRZGE-UHFFFAOYSA-N 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 239000003929 acidic solution Substances 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000003190 augmentative effect Effects 0.000 description 1
- 150000003851 azoles Chemical class 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000008139 complexing agent Substances 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000009867 copper metallurgy Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000009472 formulation Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 229910021506 iron(II) hydroxide Inorganic materials 0.000 description 1
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 230000003472 neutralizing effect Effects 0.000 description 1
- 230000009972 noncorrosive effect Effects 0.000 description 1
- 239000006259 organic additive Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 239000003039 volatile agent Substances 0.000 description 1
- 239000003643 water by type Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
- C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids
- C23F11/10—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids using organic inhibitors
- C23F11/14—Nitrogen-containing compounds
- C23F11/141—Amines; Quaternary ammonium compounds
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Preventing Corrosion Or Incrustation Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method of inhibiting corrosion of metallic surfaces in a steam generating system is disclosed which comprises the step of adding to the aqueous phase of the system a non-oxygen containing alkylated diamine having at least two carbon atoms between the diamine nitrogen atoms.
A method of inhibiting corrosion of metallic surfaces in a steam generating system is disclosed which comprises the step of adding to the aqueous phase of the system a non-oxygen containing alkylated diamine having at least two carbon atoms between the diamine nitrogen atoms.
Description
2~9~ ~97 BOILER DOUBLE BUFFERS
FIELD OF THE INVENTION
The present invention relates to methods for controlling metal loss in boiler/condensate steam systems. More particularly, the present invention relates to methods of controlling pH by feeding a single control agent to inhibit corrosion in both the liquid and steam phases of a boiler system.
BACKGROUND OF THE INVENTION
Corrosion in steam generating systems, especially of iron and copper, results in damage to piping and equipment as well as the loss of high quality ~ater and energy. The corrosion products and process chemicals if returned to the boiler can contribute to the formation of damaging boiler deposits thereby reducing the overall system reliability and increasing operating and maintenance costs.
2~9~97 As water temperatures rise, ferrous hydroxide is converted to magnetite (Fe304) in the absence of oxygen to form a protective film barrier. In actual boiler systems the presence of contaminants such as dissolved oxygen and carbon dioxide promote corrosion reactions.
In addition to iron corrosion in water which is augmented by the presence of oxygen, corrosion of copper by oxygen may also occur. If copper complexing agents such as ammonia are present, a protective copper oxide film cannot become permanently estab-lished. High concentrations of carbon dioxide in the condensatesystem, at lower pH values (less than 8), have an effect similar to ammonia in dissolving a copper oxide film.
Due to the aqueous solubility of carbon dioxide when water is heated in steam generating systems, the concentration of carbon dioxide in the water decreases and the gas enters the produced steam. ~pon condensation, carbon dioxide again dissolves in the water to form carbonic acid. Since the condensate contains rela-tively few dissolved solids and thus little buffering capacity, the carbonic acid can drastically lower the condensate pH. In turn, when acidic condensate mixes with makeup water, the steam generator feedwater pH can also decrease.
Waters containing carbonic acid cause acidic or general corrosion of the iron and copper metallurgies found in condensate and feedwater systems. This type of corrosion is evidenced by a 2~91~9~
general wastage or by grooving of the metal surface. If untreated, - corrosion can cause failure of condensate return lines, feedwater piping, and other equipment (condensate receivers, pumps, heaters, etc.) associated with steam generating and hot water heating systems.
Several methods have been devised to control acid-induced corrosion in these systems. Materials can be added that adsorb to the metal surface to form a thin barrier between the metal and the acidic solution. Examples of effective barrier forming materials that are routinely used are long chain amines, such as octadecylamine, and azoles such as tolyltriazole.
A second, more often utilized method of controlling carbonate caused corrosion is the addition of volatile amines to neutralize the carbonate and thereby increase the aqueous pH.
Many different volatile amines are utilized, but some commonly used materials include cyclohexylamine, morpholine, and methoxy-propylamine. On an equal weight basis, the most effective amines are those that possess high basicity and low molecular weight.
The high basicity allows attainment of high pH after acid neutralization, and low molecular weight allows a greater molar concentration (and thus more neutralization). The addition of volatile amines neutralizes the acid (H+) generated by the solution of carbon dioxide in condensate. The amines hydrolyze in water to generate the hydroxide ions required for neutralization.
2~91097 By regulating the neutralizing amine feedrate, the condensate pH
can be elevated to within a desired range (e.g. 8.5 to 9.5).
Numerous amines can be used for condensate pH neutralization and elevation. The selection of the appropriate amine is currently controlled by the basicity, stability and distribution ratio characteristics of the particular amine.
Steam generating systems are operated under several dif-ferent control programs, but the general purpose of all boiler control programs is to minimize corrosion of the metal surfaces.
This is accomplished by maintaining the pH within a specific window of operation, a window determined experimentally to fit the particular metallurgy, chemistry, and pressure of the system.
In high pressure systems, the feedwater is very pure with little hardness and iron, and little to no organic contaminants. The boiler control methodology is designed to maintain a passive magnetite layer on the iron metallurgy and prevent adverse corrosion reactions at metal surfaces.
The solubility of magnetite is very pH dependent, with the minimum in a specific pH range. Boiler corrosion control is designed to operate in this pH window of magnetite solubility and to prevent excessive deposition while maintaining a thin magnetite layer for passivity. This control scheme is designed to maximize the efficiency of heat transfer across the boiler and condensate surfaces. Maintaining a passive magnetite is critical on both the liquid and steam side of steam generating systems.
209~097 Con~rol agents, either a single component or a mixture of addi-tives, must be able to maintain the pH of both aqueous phases near the magnetite pH minimum. High pressure ~above 1500 psig) steam generating equipment control agents can be categorized into two groups; inorganic and organic. Inorganic agents are typically phosphate or borate-based, while the organic systems are usually amine-based with varying physical properties.
Inorganic control agents preserve the boiler water chemistry in a non-corrosive state and are very effective at preventing problems on the water side of a steam generating system. However, they are of limited effectiveness on the steam side. Typical inorganic control agents must be used in combination with a volatile additive in order to provide pH
control in the steam phase. Also, inorganic control agents often form insoluble salts with hardness and iron contaminants resulting in increased deposition. Thus, inorganic control agents are not typically employed on the steam side because of solubility and/or deposition problems.
Typical organic control agents can usually be classified as highly volatile or less volatile. The highly volatile agents have very short residence times in steam generators and will tend to maintain the pH of the steam phase only. The less volatile amines tend to maintain the p~ of the liquid phase with limited activity in the steam phase. In addition, organic additives tend to thermally decompose and form potentially corrosive species 2 ~ 7 such as ammonia and or low molecular weight`organic acids. Such decomposition can be caused by high temperatures.
In the current use of organic boiler control agents, amine blends are employed to minimize these problems by providing a formulation which provides both high and low volat;lities.
Such mixtures, while effective control agents may have undesir-able properties such as low flash points, incompatibility with - other additives, etc.
SUMMARY OF THE INVENTION
The present invention relates to methods of controlling the pH of a steam generating system in which a single amine pH
control treatment agent is employed. The amine control agents of the present invention are "double buffers" which help to maintain the pH of both the liquid and steam phases within the system in a preferred range, typically ~.5 to 9.5. The control agents of the present invention also exhibit a strong buffering capacity and do not significantly break down into ammonia within a steam generating system.
The control agents of the present invention maintain both liquid and steam pH's in a steam generating system by the addition of a single "double buffer" amine. The control agents of the present invention are non-oxygen containing alkylated ~1097 diamines with at least two-carbons between the diamine nitrogens of the general formula:
R R
N - [ CH2 ] - N
/ x Rl Rl wherein R is H or alkyl, Rl is H or alkyl, R and Rl are not both H and x equals 2 or more and preferably 2 to 6. The control agents of the present invention exhibit very little decomposition to ammonia in either the steam or liquid phases while maintaining both steam and liquid phase pH above a threshold level. The control agents are effective when added at relatively low concentrations.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The inventors discovered a specific class of amines which act as "double buffers" in the treatment of a boiler system. By "double buffer" is meant that the control agents will effectively control pH in both the liquid and steam phases. The control agents were found to provide ef~ective pH buffering to maintain a desir-able magnetite layer throughout a boiler system at relatively low treatment concentrations. The control agents maintain a desirable magnetite layer by controlling pH to the range of about 8.5 to 9.S. The buffers of the present invention show a resistance to degradation into ammonia.
2~910~7 The buffers of the present invention are non-oxygen.
containing alkylated diamines having at least two carbons between the diamine nitrogens of the general formula:
R \ R
N [ CH2 ] N
x Rl Rl wherein R and Rl are hydrogen or alkyl (preferrably Cl - C6 alkyl), R and Rl are not both hydrogen and x is 2 or more preferrably 2 to 6. Exemplary diamines include:
N,N,N',N'-tetramethylethylenediamine, N, N'-dimethylethylene-diamine, and N,N',N'-tetramethylpropylenediamine.
The effectiveness of representative non-oxygen containing alkylated diamines of the present invention was evaluated in testing perfor~ed in research scale boilers. The research boilers employed in the following example are D-shaped electrically heated stainless steel assembl;es with 4000 watt electrical immersion heaters that produce 19.8 pounds per hour of steam at a maximum operating pressure of 1,500 psig. Operation o~ the research boilers is described in U.S. Patent No. 4,288,327 incorporated herein by reference.
The tests were run at 1,45~ psig at 50 cycles for 44 hours with no condensate return. Daily inalyses were made of the steam and blowdown (liquid) products. The feedwater for the boilers was supplied by a demineralizer train and treated with the control agent alkylated diamine. Hydroquinone at a treatment rate of 0.3 ppm was added to each feedwater tank as an oxygen scavenger.
Hydroquinone was selected as the oxygen scavenger due to the need for quantitative testing for ammonia. The control agent being tested was fed at a concentration of 10 ppm in the feedwater tank.
The boilers were run for 44 hours to establish equilibrium between the test chemistry and the research boiler. After 44 hours samples were analyzed for ammonia and pH.
A control agent was deemed successful if it produced the following results for this test methodology:
(1) steam pH above 8.5 (2) blowdown pH above 8.5 (3) difference between steam and blowdown pH not greater than 1.5 pH units (4) ammonia levels in the steam and blowdown not to exceed 0.4 ppm Table 1 summarizes the results of such testing on a variety of amines and shows the unique effectiveness of the class of amines of the present invention.
~91~97 .
- Test Run Results All concentrations in ppm Control Agent 5 (10 ppm in DH Ammonia Feedwater~ _ BD Stm BD Stmlest Results TMEDA 9.66 9.10 < 0.05 0.09 Pos DMEDA 9.40 9.25 0.21 0.26 Pos TMPDA 9.26 8.66 0.27 0.22 Pos 10 Morpholine 8.73 8.30 0.12 0.16 Neg DMAPA 9.48 9.02 0.33 0.75 Neg DMA 7.32 9.76 < 0.3 0.3 Neg . NOTES: BD = Blowdown Stm = Steam TMEDA = N,N,N'-tetramethylethylenediamine DMEDA = N,N'-dimethylethylenediamine TMPDA = N,N,N',N'-tetramethylpropylenediamine DMAPA = Dimethyleaminopropylamine DMA = Dimethylamine While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The claims and this invention generally should be construed to cover all such obvious forms and modifi-cations which are within the true spirit and scope of the present invention.
FIELD OF THE INVENTION
The present invention relates to methods for controlling metal loss in boiler/condensate steam systems. More particularly, the present invention relates to methods of controlling pH by feeding a single control agent to inhibit corrosion in both the liquid and steam phases of a boiler system.
BACKGROUND OF THE INVENTION
Corrosion in steam generating systems, especially of iron and copper, results in damage to piping and equipment as well as the loss of high quality ~ater and energy. The corrosion products and process chemicals if returned to the boiler can contribute to the formation of damaging boiler deposits thereby reducing the overall system reliability and increasing operating and maintenance costs.
2~9~97 As water temperatures rise, ferrous hydroxide is converted to magnetite (Fe304) in the absence of oxygen to form a protective film barrier. In actual boiler systems the presence of contaminants such as dissolved oxygen and carbon dioxide promote corrosion reactions.
In addition to iron corrosion in water which is augmented by the presence of oxygen, corrosion of copper by oxygen may also occur. If copper complexing agents such as ammonia are present, a protective copper oxide film cannot become permanently estab-lished. High concentrations of carbon dioxide in the condensatesystem, at lower pH values (less than 8), have an effect similar to ammonia in dissolving a copper oxide film.
Due to the aqueous solubility of carbon dioxide when water is heated in steam generating systems, the concentration of carbon dioxide in the water decreases and the gas enters the produced steam. ~pon condensation, carbon dioxide again dissolves in the water to form carbonic acid. Since the condensate contains rela-tively few dissolved solids and thus little buffering capacity, the carbonic acid can drastically lower the condensate pH. In turn, when acidic condensate mixes with makeup water, the steam generator feedwater pH can also decrease.
Waters containing carbonic acid cause acidic or general corrosion of the iron and copper metallurgies found in condensate and feedwater systems. This type of corrosion is evidenced by a 2~91~9~
general wastage or by grooving of the metal surface. If untreated, - corrosion can cause failure of condensate return lines, feedwater piping, and other equipment (condensate receivers, pumps, heaters, etc.) associated with steam generating and hot water heating systems.
Several methods have been devised to control acid-induced corrosion in these systems. Materials can be added that adsorb to the metal surface to form a thin barrier between the metal and the acidic solution. Examples of effective barrier forming materials that are routinely used are long chain amines, such as octadecylamine, and azoles such as tolyltriazole.
A second, more often utilized method of controlling carbonate caused corrosion is the addition of volatile amines to neutralize the carbonate and thereby increase the aqueous pH.
Many different volatile amines are utilized, but some commonly used materials include cyclohexylamine, morpholine, and methoxy-propylamine. On an equal weight basis, the most effective amines are those that possess high basicity and low molecular weight.
The high basicity allows attainment of high pH after acid neutralization, and low molecular weight allows a greater molar concentration (and thus more neutralization). The addition of volatile amines neutralizes the acid (H+) generated by the solution of carbon dioxide in condensate. The amines hydrolyze in water to generate the hydroxide ions required for neutralization.
2~91097 By regulating the neutralizing amine feedrate, the condensate pH
can be elevated to within a desired range (e.g. 8.5 to 9.5).
Numerous amines can be used for condensate pH neutralization and elevation. The selection of the appropriate amine is currently controlled by the basicity, stability and distribution ratio characteristics of the particular amine.
Steam generating systems are operated under several dif-ferent control programs, but the general purpose of all boiler control programs is to minimize corrosion of the metal surfaces.
This is accomplished by maintaining the pH within a specific window of operation, a window determined experimentally to fit the particular metallurgy, chemistry, and pressure of the system.
In high pressure systems, the feedwater is very pure with little hardness and iron, and little to no organic contaminants. The boiler control methodology is designed to maintain a passive magnetite layer on the iron metallurgy and prevent adverse corrosion reactions at metal surfaces.
The solubility of magnetite is very pH dependent, with the minimum in a specific pH range. Boiler corrosion control is designed to operate in this pH window of magnetite solubility and to prevent excessive deposition while maintaining a thin magnetite layer for passivity. This control scheme is designed to maximize the efficiency of heat transfer across the boiler and condensate surfaces. Maintaining a passive magnetite is critical on both the liquid and steam side of steam generating systems.
209~097 Con~rol agents, either a single component or a mixture of addi-tives, must be able to maintain the pH of both aqueous phases near the magnetite pH minimum. High pressure ~above 1500 psig) steam generating equipment control agents can be categorized into two groups; inorganic and organic. Inorganic agents are typically phosphate or borate-based, while the organic systems are usually amine-based with varying physical properties.
Inorganic control agents preserve the boiler water chemistry in a non-corrosive state and are very effective at preventing problems on the water side of a steam generating system. However, they are of limited effectiveness on the steam side. Typical inorganic control agents must be used in combination with a volatile additive in order to provide pH
control in the steam phase. Also, inorganic control agents often form insoluble salts with hardness and iron contaminants resulting in increased deposition. Thus, inorganic control agents are not typically employed on the steam side because of solubility and/or deposition problems.
Typical organic control agents can usually be classified as highly volatile or less volatile. The highly volatile agents have very short residence times in steam generators and will tend to maintain the pH of the steam phase only. The less volatile amines tend to maintain the p~ of the liquid phase with limited activity in the steam phase. In addition, organic additives tend to thermally decompose and form potentially corrosive species 2 ~ 7 such as ammonia and or low molecular weight`organic acids. Such decomposition can be caused by high temperatures.
In the current use of organic boiler control agents, amine blends are employed to minimize these problems by providing a formulation which provides both high and low volat;lities.
Such mixtures, while effective control agents may have undesir-able properties such as low flash points, incompatibility with - other additives, etc.
SUMMARY OF THE INVENTION
The present invention relates to methods of controlling the pH of a steam generating system in which a single amine pH
control treatment agent is employed. The amine control agents of the present invention are "double buffers" which help to maintain the pH of both the liquid and steam phases within the system in a preferred range, typically ~.5 to 9.5. The control agents of the present invention also exhibit a strong buffering capacity and do not significantly break down into ammonia within a steam generating system.
The control agents of the present invention maintain both liquid and steam pH's in a steam generating system by the addition of a single "double buffer" amine. The control agents of the present invention are non-oxygen containing alkylated ~1097 diamines with at least two-carbons between the diamine nitrogens of the general formula:
R R
N - [ CH2 ] - N
/ x Rl Rl wherein R is H or alkyl, Rl is H or alkyl, R and Rl are not both H and x equals 2 or more and preferably 2 to 6. The control agents of the present invention exhibit very little decomposition to ammonia in either the steam or liquid phases while maintaining both steam and liquid phase pH above a threshold level. The control agents are effective when added at relatively low concentrations.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The inventors discovered a specific class of amines which act as "double buffers" in the treatment of a boiler system. By "double buffer" is meant that the control agents will effectively control pH in both the liquid and steam phases. The control agents were found to provide ef~ective pH buffering to maintain a desir-able magnetite layer throughout a boiler system at relatively low treatment concentrations. The control agents maintain a desirable magnetite layer by controlling pH to the range of about 8.5 to 9.S. The buffers of the present invention show a resistance to degradation into ammonia.
2~910~7 The buffers of the present invention are non-oxygen.
containing alkylated diamines having at least two carbons between the diamine nitrogens of the general formula:
R \ R
N [ CH2 ] N
x Rl Rl wherein R and Rl are hydrogen or alkyl (preferrably Cl - C6 alkyl), R and Rl are not both hydrogen and x is 2 or more preferrably 2 to 6. Exemplary diamines include:
N,N,N',N'-tetramethylethylenediamine, N, N'-dimethylethylene-diamine, and N,N',N'-tetramethylpropylenediamine.
The effectiveness of representative non-oxygen containing alkylated diamines of the present invention was evaluated in testing perfor~ed in research scale boilers. The research boilers employed in the following example are D-shaped electrically heated stainless steel assembl;es with 4000 watt electrical immersion heaters that produce 19.8 pounds per hour of steam at a maximum operating pressure of 1,500 psig. Operation o~ the research boilers is described in U.S. Patent No. 4,288,327 incorporated herein by reference.
The tests were run at 1,45~ psig at 50 cycles for 44 hours with no condensate return. Daily inalyses were made of the steam and blowdown (liquid) products. The feedwater for the boilers was supplied by a demineralizer train and treated with the control agent alkylated diamine. Hydroquinone at a treatment rate of 0.3 ppm was added to each feedwater tank as an oxygen scavenger.
Hydroquinone was selected as the oxygen scavenger due to the need for quantitative testing for ammonia. The control agent being tested was fed at a concentration of 10 ppm in the feedwater tank.
The boilers were run for 44 hours to establish equilibrium between the test chemistry and the research boiler. After 44 hours samples were analyzed for ammonia and pH.
A control agent was deemed successful if it produced the following results for this test methodology:
(1) steam pH above 8.5 (2) blowdown pH above 8.5 (3) difference between steam and blowdown pH not greater than 1.5 pH units (4) ammonia levels in the steam and blowdown not to exceed 0.4 ppm Table 1 summarizes the results of such testing on a variety of amines and shows the unique effectiveness of the class of amines of the present invention.
~91~97 .
- Test Run Results All concentrations in ppm Control Agent 5 (10 ppm in DH Ammonia Feedwater~ _ BD Stm BD Stmlest Results TMEDA 9.66 9.10 < 0.05 0.09 Pos DMEDA 9.40 9.25 0.21 0.26 Pos TMPDA 9.26 8.66 0.27 0.22 Pos 10 Morpholine 8.73 8.30 0.12 0.16 Neg DMAPA 9.48 9.02 0.33 0.75 Neg DMA 7.32 9.76 < 0.3 0.3 Neg . NOTES: BD = Blowdown Stm = Steam TMEDA = N,N,N'-tetramethylethylenediamine DMEDA = N,N'-dimethylethylenediamine TMPDA = N,N,N',N'-tetramethylpropylenediamine DMAPA = Dimethyleaminopropylamine DMA = Dimethylamine While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The claims and this invention generally should be construed to cover all such obvious forms and modifi-cations which are within the true spirit and scope of the present invention.
Claims (6)
1. A method of inhibiting corrosion of metallic surfaces in both the liquid and vapor phases of a steam generating system which comprises adding to the aqueous phase of a steam generating system an amount sufficient for the purpose of a non-oxygen containing alkylated diamine having at least two carbon atoms between the diamine nitrogen atoms.
2. The method of claim 1 wherein said non-oxygen containing alkylated diamine has the general formula wherein R and R1 are H or alkyl, R and R1 are not both H, and x is two or more.
3. The method of claim 1 wherein said non-oxygen containing alkylated diamine is selected from the group consisting of N,N,N', N'-tetramethylethylenediamine, N,N'-dimethyl-ethylenediamine, and N,N,N', N'-tetramethylpropylenediamine.
4. A method of maintaining the pH of the liquid and vapor phases of a steam generating system within the range of 8.5 to 9.5 which comprises adding a sufficient amount for the purpose of maintaining pH of a non-oxygen containing alkylated diamine having at least two carbon atoms between the diamine nitrogen atoms.
5. The method of claim 4 wherein said non-oxygen containing alkylated diamine has the general formula:
wherein R and R1 are H or alkyl, R and R1 are not both H, and x as two or more.
wherein R and R1 are H or alkyl, R and R1 are not both H, and x as two or more.
6. The method of claim 4 wherein said oxygen containing alkylated diamine is selected from the group consisting of N,N,N', N'-tetramethylethylenediamine, N,N'-dimethyl-ethylenediamine, and N,N,N', N'-tetramethylpropylenediamine.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86541992A | 1992-04-08 | 1992-04-08 | |
| US07/865,419 | 1992-04-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2091097A1 true CA2091097A1 (en) | 1993-10-09 |
Family
ID=25345471
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2091097 Abandoned CA2091097A1 (en) | 1992-04-08 | 1993-03-05 | Boiler double buffers |
Country Status (2)
| Country | Link |
|---|---|
| EP (1) | EP0565371A2 (en) |
| CA (1) | CA2091097A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10203329A1 (en) * | 2002-01-29 | 2003-08-14 | Bayer Ag | Corrosion protection agent for the protection of metallic materials in a strongly alkaline medium |
| CN102910689A (en) * | 2012-11-09 | 2013-02-06 | 青海电力科学试验研究院 | Chemicals feeding method used for preventing water supply system from being corroded |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2659693A (en) * | 1952-05-10 | 1953-11-17 | Standard Oil Dev Co | Process for preventing corrosion of ferrous metals |
| GB742342A (en) * | 1952-10-23 | 1955-12-21 | Rohm & Haas | Improvements in or relating to isomerization of diaminobutynes |
| US3432527A (en) * | 1964-11-05 | 1969-03-11 | Armour Ind Chem Co | Corrosion inhibitor composition and method |
| CA1339761C (en) * | 1988-07-11 | 1998-03-24 | Anthony M. Rossi | Corrosion control composition and method for boiler/condensate stem system |
| US5091108A (en) * | 1991-02-21 | 1992-02-25 | Nalco Chemical Company | Method of retarding corrosion of metal surfaces in contact with boiler water systems which corrosion is caused by dissolved oxygen |
-
1993
- 1993-03-05 CA CA 2091097 patent/CA2091097A1/en not_active Abandoned
- 1993-04-07 EP EP93302761A patent/EP0565371A2/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP0565371A2 (en) | 1993-10-13 |
| EP0565371A3 (en) | 1994-04-13 |
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