Europaisches Patentamt 0 320 085 J) European Patent Office 6v Publication number: A1 Office europeen des brevets EUROPEAN PATENT APPLICATION © Application number: 88306710.0 © int. CIA C02F 5/12 , C23F 11/14 @ Date of filing: 21.07.88 © Priority: 11.12.87 US 131754 © Applicant: DuBois CHEMICALS, INC. 1100 DuBois Tower @ Date of publication of application: Cincinnati Ohio 45202(US) 14.06.89 Bulletin 89/24 © Inventor: Christensen, Ronald J. © Designated Contracting States: 8747 Tanagerwoods Drive AT BE CH DE ES FR GB GR IT LI LU NL SE Montgomery Ohio(US) Inventor: Steimel, Llye H. 1117 Imprint Forest Park Ohio(US) © Representative: Allen, Oliver John Richard et al Lloyd Wise, Tregear & Co. Norman House 105-109 Strand London, WC2R OAE(GB) © Oxygen scavenger for boiler water and method of use. © An oxygen scavenger for boiler water includes ascorbic acid neutralized with diethylaminoethanol. The diethylaminoethanol provides condensate treat- ment for the long and short steam lines and im- proves the scavenging of the ascorbic acid. IT) 00 a. UJ Xerox Copy Centre EP 0 320 085 A1 OXYGEN SCAVENGER FOR BOILER WATER AND METHOD OF USE dissolved solid concentrations in boiler water. A recirculating boiler requires an extremely Hydrazine is an effective scavenger at very low high purity of water in order to avoid a plurality of levels of application. Unfortunately, since it is vola- different problems. Unfortunately the quality of the tile itself, it is susceptible to thermal decomposition water available for most boilers is such that the 5 to ammonium and nitrogen. The evolution of am- water employed would rapidly cause a deterioration monium moreover may restrict hydrazine applica- of the boiler eventually requiring a shut down of the tion to avoid corrosion. boiler and potential replacement of various portions In addition to oxygen pitting, there is a corro- of the boiler. sion problem in the after boiler. Water invariably Currently there are a variety of different prob- 70 contains carbon dioxide and ammonia. The ammo- lems treated separately by a variety of different nia may be present in such trace levels that it is compositions. Two very major problems are scale insufficient to either cause problems by overcon- formation and corrosion of the surface of the boiler. centration or to help combat the interaction of CO2 These two problems are interrelated in that corro- with steam which forms carbonic acid in the con- sion of the surface is avoided by maintaining an 75 densate. Accordingly, volatile neutralizing amines alkaline pH. Scale formation is a problem which such as cyclohexylamine, morpholine, exists at alkaline pH's. Boilers generally operate diethanolamine and diethylaminoethanoi are com- under alkaline pH conditions and address the scale monly used to combat corrosion in industrial after formation problem by the use of various scale boiler sections by neutralizing condensate pH. inhibitors and descalants. 20 These amines are present only for this purpose Even under alkaline conditions, there is a cor- and do not have any reported oxygen scavenging rosion problem or pitting attributed to the presence effects. of oxygen in the water. The key to solving this In accordance with the present invention an problem is to remove the oxygen. To avoid this oxygen scavenging system comprises the com- problem, the make up water in a boiler is phys- 25 bination of ascorbic acid and a neutralizing amine ically treated to deaerate the make up water. Oxy- and specifically diethylaminoethanoi. The oxygen gen scavenging chemicals are then added to fur- scavenging effect of the ascorbic acid in combina- ther reduce the possibility of pitting. Chemicals tion with the diethylaminoethanoi (DEAE) is greater commonly used for this purpose are sodium sul- than the oxygen scavenging effect of the ascorbic phite, catalyzed sodium sulphite, hydrazine and 30 acid neutralized with sodium hydroxide. When ad- catalyzed hydrazine. Also, as disclosed in U.S. ded to boiler water in effective amounts, this com- Patent No.4,41 9,327 amine neutralized erythorbic position provides both oxygen scavenging and con- acid can be used to scavenge oxygen. Ammonia is densate treatment as well as metal passivation. In the preferred amine disclosed in this patent. Al- addition, the DEAE has an intermediate distribution though other amines disclosed in this patent appar- 35 ratio which provides condensate treatment for both ently have some catalytic effect on the erythorbic long and short steam lines. This makes this com- acid, ihis is not disclosed. Further the use of DEAE bination particularly versatile. is not discussed in this patent. Ascorbic acid has Ascorbic acid is combined with also been discussed as an oxygen scavenger. It is diethylaminoethanoi to provide an oxygen scaven- structurally very similar to erythorbic acid, but has 40 ging solution which can be added in minor greater thermal stability. amounts to the make up water of a boiler to chemi- Each of these have various problems. Sodium cally scavenge oxygen. In a preferred composition sulphite reacts with oxygen to form sodium sul- the combination of ascorbic acid and DEAE is phate. To scavenge oxygen effectively, eight parts formed by dissolving the ascorbic acid in water and of sodium sulphite are required for each part of 45 subsequently adding the DEAE to the ascorbic acid dissolved oxygen. Sodium sulphite provides effi- solution. As purchased, the ascorbic acid is a cient scavenging in medium and low pressure boil- 100% solid dry powder. Alternately, it can be in ers with no harmful by-products. Its use, however, liquid form and can be neutralized sodium ascor- is precluded in boilers operating at or above 1800 bate. psig where the high pressures cause the formation 50 The ratio by weight of ascorbic acid relative to of SO2 and H2S by thermal decomposition of the DEAE can vary substantially and will range from chemical. about 1/1 to about 1/15 ascorbic acid to DEAE. The Hydrazine reacts with equal parts of oxygen to DEAE is preferably present in sufficient amount to form inert nitrogen and water. Since the products adjust the pH of the ascorbic acid solution to at are neutral, this treatment does not increase the least about 7. Further, since the DEAE is also EP 0 320 085 A1 providing condensate treatment, it is preferable to acid/DEAE solution was 33% more effective than add excess DEAE relative to the ascorbic acid NaOH neutralized ascorbic acid and more than 100 raising the pH to at least about 7.5-8.5 in the times more effective than hydrazine under the condensate. Therefore the pH of the product same conditions. (concentrate) should be about 1 1 . The DEAE once 5 The present invention provides oxygen scaven- added to the ascorbic acid solution is mixed thor- ging and condensate treatment. Further.the con- oughly and provides a stable solution of ascorbate densate treatment, the DEAE, improves the effi- and diethylaminoethanol. ciency of the oxygen scavengers. No further treatment of the solution is neces- sary. However, if the DEAE added does not in- w crease the pH to about 10 added base may be Claims needed to prevent bacterial growth. The concentrated solution of ascorbic acid and 1. An oxygen scavenging solution comprising DEAE should be from about 1% to 25% ascorbic ascorbic acid neutralized with diethylaminoethanol. acid and 1% to 50% DEAE. Practicality sets the 75 2. A solution as claimed in claim 1 wherein the lower limit. A solution with an extremely low con- ratio of ascorbic acid to diethylaminoethanol is centration will require that a large amount be ad- from 1/1 to about 1/15. ded. This would be expensive because of shipping 3. A solution as claimed in claim 1 or 2 having and storage costs. a pH of at least about 10. Advantageously, this solution is compatible 20 4. A method of removing dissolved oxygen with many different components of a boiler water from boiler feedwater comprising adding to the treatment system including sulphite, hydrazine.low boiler feedwater an oxygen scavenging amount of molecular weight anionic polymers such as poly- a solution of ascorbic acid neutralized with maleic anhydride, polymethacrylate, polyacrylate diethylaminoethanol. and phosphonates as well as soda ash and sodium 25 5. A method as claimed in claim 4 wherein the glucoheptonate. These again would simply be ad- solution is added to the feedwater in an amount ded to the solution and mixed in. sufficient to establish a concentration of at least 1 The oxygen scavenging solution of the present ppm ascorbic acid. invention is added to the boiler water at basically 6. A method as claimed in claim 4 or 5 wherein acid any point along the circulating water system of the 30 the solution has a ratio of ascorbic to boiler. Preferably, however, it is added to the diethylaminoethanol of from 1/1 to about 1/15 on a deaerator storage sections. molar basis. Sufficient oxygen scavenging solution is added 7. A method as claimed in claim 5 wherein to establish or maintain the concentration of the sufficient solution is added to establish a con- about 10 oxygen scavenging solution within the boiler water 35 centration of ascorbic acid at at least at a desired and effective oxygen scavenging con- ppm. centration. Basically, the concentration of the 8. A method as claimed in claim 7 wherein the ascorbic acid in the solution must be from about 1 concentration in the feed water of to about 40 parts per million with 10-20 ppm pre- diethylaminoethanol is established at least about 1 ferred. Ascorbic acid is consumed in use. There- 40 ppm. fore the amount added is greater than the amount in the boiler. From about 1 to about 200 parts per million of DEAE should be present, preferably no more than 15 ppm in the steam.